Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Studies related to the synthesis of bisindole alkaloids of the Indole-Indoline type Treasurywala, Adi Minoo 1974

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1974_A1 T74.pdf [ 7.79MB ]
Metadata
JSON: 831-1.0061077.json
JSON-LD: 831-1.0061077-ld.json
RDF/XML (Pretty): 831-1.0061077-rdf.xml
RDF/JSON: 831-1.0061077-rdf.json
Turtle: 831-1.0061077-turtle.txt
N-Triples: 831-1.0061077-rdf-ntriples.txt
Original Record: 831-1.0061077-source.json
Full Text
831-1.0061077-fulltext.txt
Citation
831-1.0061077.ris

Full Text

c ( STUDIES RELATED TO THE SYNTHESIS OF BISINDOLE ALKALOIDS OF THE INDOLE-INDOLINE TYPE BY ADI MINOO TREASURYWALA B.Sc. Honours, University of Toronto, 1970 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Chemistry We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA December, 1973 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r equ i r emen t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s tudy . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y pu rposes may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d that c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l owed w i thout my w r i t t e n p e r m i s s i o n . Depa rtment The U n i v e r s i t y o f B r i t i s h Co lumbia Vancouver 8, Canada Date - i i -ABSTRACT The f i r s t part of t h i s thesis describes the synthesis of 3,4~ fu n c t i o n a l i z e d cleavamine templates bearing a C. „- carbomethoxy group. Io Thus hydroboration of 188-carbomethoxycleavamine (29) produced two epimeric alcohols; 18a- and 183-carbomethoxydihydrocleavamin -3 - o l (56 and 57). These compounds could be interconverted by using boron t r i f l u o r i d e etherate i n benzene. One of these compounds (56) could be oxidized to the corresponding C^ ketone which i s a key intermediate f o r future work. The second part describes the research i n the area of the s o - c a l l e d dimerization r e a c t i o n . The gen e r a l i t y of a procedure which had been used before was tested. When the chloroindolenine of 4(3-dihydrocleavamine and 18-carbomethoxy-43-dihydrocleavamine were each treated with vi n d o l i n e i n 1.5% methanolic hydrogen chloride,good y i e l d s of dimeric i products were obtained. These materials have been shown by X-ray to be epimeric at C Q , to the nat u r a l dimers v i n c r i s t i n e (VCR) and Io v i n b l a s t i n e (VLB). When these conditions were applied to the chloro-indolenines of 183-carbomethoxycleavamine arid the 18a- and 18$-carbomethoxy-cleavaminols (56 and 57),good y i e l d s of dimers did not r e s u l t . A d e t a i l e d study, which has illum i n a t e d the mechanism of t h i s r e a c t i o n , was thus undertaken. As a r e s u l t of t h i s study, an improved procedure for the dimerization of such s e n s i t i v e cleavamine templates was discovered. The i n s i g h t gained from t h i s study has permitted changes i n the reac t i o n conditions which have resulted i n the i s o l a t i o n of two dimeric products from a s i n g l e dimerization r e a c t i o n . Previously, only one dimer had resulted from such reactions s t e r e o s e l e c t i v e l y . - i i i -Several new and exciting other approaches to the coupling of the indole and dihydroindole portions have been explored. Some of these have uncovered novel and useful avenues for eventually achieving the synthesis of the natural dimers such as VLB, VCR leurosine and leurosidine. - i v -TABLE OF CONTENTS Page T I T L E PAGE . • i ABSTRACT . i i TABLE OF CONTENTS . . . . . i v L I S T OF FIGURES v L I S T OF TABLES v i i ACKNOWLEDGEMENTS v i i i INTRODUCTION 1 DISCUSSION • 2 5 PART I 2 6 PART I I . 5 2 EXPERIMENTAL 1 5 3 BIBLIOGRAPHY 1 9 3 - v -LIST OF FIGURES Figure Page 1 Structural modifications vs. activity 2 Kutney's total synthesis of the Aspidosperma skeleton 18 3 Kutney's total synthesis of the Iboga skeleton 20 4 Kutney's total synthesis of Catharanthine 22 5 Mass spectrum of 183 alcohol (56) 37 6 Mass spectrum of 18a alcohol (57) 37 7 Nmr spectrum of 183 alcohol (56) 41 8 Nmr spectrum of 18a alcohol (57) 42 9 Proposed uses of hydroboration products 56 and 57 .. 48 10 Dolby's mechanism for the formation of the 2-acyl-indole (74) 55 11 Proposed path for the formation of 80 from 79 56 12 Pathways of reaction of chloroindolenines , 59 13 Buchi's partial synthesis of dimeric Voacanga alkaloids 62 14 Nmr spectrum of dimer (99) 73 15 Nmr spectrum of vinblastine (VLB) (15) 74 16 Nmr spectrum of dimer (94) 75 17 Nmr spectrum of vindoline (10) 76 18 Nmr spectrum of dimer (102) 78 19 Proof of the structure of compound 99 79 20 Nmr spectrum of dimer (106) 85 21 Mass spectrum of dimer (106) 86 22 Uv comparison of VLB (15) with dimer (94) 90 23 Nmr comparison of various monomers and dimers 92 - v i -Figure Page 24 Proposed mechanism of the standard dimerization .... 107 25 Nmr spectrum of the vi c i n a l alcohol-ether (111) .... 109 26 Mass spectrum of the vic i n a l alcohol-ether (111) ... H O 27 Proposed details of the coupling step H3 28 X-ray structure of dimer (95) 1 2 3 29 A mechanism for the epimerization of dimer (96) .... 124 30 X-ray structure of dimer (97) I 2 6 31 Nmr spectrum of 15-bromovindoline (114) 129 32 Mass spectrum of 15-bromovindoline (114) 130 H O 1 o o 33 Mass spectral fragmentation scheme for vindoline. - L J Z 112 n o 34 Gilman's synthesis of compound 116 1 J J 35 Approaches to the synthesis of the acylindole (117). 138 36 Reactions of the chloroindolenine of compound 118 under acidic conditions 1^ 37 Nmr spectrum of aldehyde (121) 1^ 1 38 General approach to the biomimetic dimerization .... 14^ 39 Nmr spectrum of dimer (127) 1^ 40 Mass spectrum of dimer (127) 15C 41 Proposed mechanism for the formation of dimer (127). 151 - v i i -LIST OF TABLES T a b l e Page I C h e m i c a l s h i f t s o f c l e a v a m i n e - t y p e compounds „ 39 I I E f f e c t o f d i f f e r e n t c h l o r i n a t o r s on t h e y i e l d and s t e r e o c h e m i s t r y o f dimers p r o d u c e d ^ I I I Temperature o f c h l o r i n a t i o n v s . y i e l d and t y p e o f dimer 1 0 1 IV E f f e c t o f the temper a t u r e o f t h e c o u p l i n g s t e p on the y i e l d and s t e r e o c h e m i s t r y o f dimer ............. 103 V E f f e c t o f s o l v e n t s and Lewis a c i d s on the d i m e r i z a -t i o n r e a c t i o n .... 1 1 6 VI E f f e c t o f a c i d c o n c e n t r a t i o n on t h e c o u p l i n g r e a c t i o n - v i i i -ACKNOWLEDGEMENTS I wish to express my sincere thanks to a l l of my teachers for having made this experience as richly educative as i t has been; but particularly to Professor J.P. Kutney for his guidance throughout the course of this research. I am very grateful to my wife without whose encouragement and patience this endeavour would never have been possible. I am grateful to the National Research Council of Canada and the National Institutes of Health of the U.S.A. for the financial support provided. i INTRODUCTION Throughout the history of man, he has been inquisitive about his surroundings. In most cases, this curiousity has led to some form of "progress". Perhaps the oldest preoccupation has dealt with the examination of the chemistry of natural products. The ancient Egyptian discoveries of dyestuffs from plant sources were, surely, one of the earliest fruits of primitive natural products chemistry. Tribal medicine represents another form of these early investigations, and has led to an accumulation of observations about the pharmacological effects of various natural products. In recent times, one of the main goals of the so-called natural products chemist i s the discovery of compounds that are of some interest to man either i n the curing of ailments or the control of pests or in some other area. Tribal folk remedies are often starting points of such searches. However, today crude plant preparations have been largely replaced by pure compounds (or a set of pure compounds) to which a l l , or most, of the activity of the old remedy may be ascribed. Once such a pure active ingredient has been isolated, i t s structure must be proved before i t s action may be f u l l y understood. This i s often an exacting task requiring detailed spectral studies of the compound and several of i t s derivatives using, for example, infrared, - 2 -ultraviolet, and nuclear magnetic resonance spectroscopy. A tool that has provided great impetus i n this area in very recent times i s X-ray crystallography. Once a structure has been unambiguously assigned, a synthesis of the compound may be undertaken. The latter operation may be essential for several reasons. In a case where a c l i n i c a l l y useful compound i s present i n only a minute amount i n nature, a synthesis from readily available starting materials may compete favourably as a source of the drug. Usually a synthetic scheme i s designed so that a whole family of structurally analogous drugs may be synthesized. In this case It is possible that a derivative, unavailable from the natural source, may have higher activity, with relatively fewer side effects, than the parent compound. Finally, the compound may be of sufficient structural and stereochemical uniqueness to provide an academic challenge to the synthetic chemist. Amongst the various classes of compounds isolated from nature that are of some pharmacological interest to man, compounds which contain nitrogen atoms as part of the molecule appear to predominate. These basic, nitrogen containing compounds are cla s s i f i e d as alkaloids. As a class of compounds, they d i f f e r widely i n structure as well as pharmacological activity. A few examples are such well-known compounds as tetracycline (1), quinine (2), ephedrine (3), nicotine (4), strychnine (5), and lysergic acid (6). - 3 -(7) - 4 -These indole alkaloids are postulated to arise from the amino-acid tryptophan (8) and a "non-tryptophan" unit which in the case of some recent studies, turns out to be a monoterpenoid compound; loganin (9) or i t s derivatives. The alkaloids which have these two structural units incorporated into them are C 2 Q or compounds most of which may be clas s i f i e d as belonging to the Corynanthe, Strychnos, Aspidosperma or Iboga families. Examples of the latter three are strychnine (5), vindoline (10) and catharanthine (11), respectively. One of the newer groups of indole alkaloids i s the bisindole alkaloid family, or the "dimeric" indole alkaloids, as they are sometimes called. More than eighty such compounds are presently known. Structural elucidations of most of these, however, awaited the development of efficient separation techniques and as a result^" date back only some twelve years. These bisindole alkaloids may easily be - 5 -divided into two categories. The f i r s t i s composed of alkaloids with identical or very closely related components in which the same centres act as linkage points. This group contains the Calycanthaceous and Calabash-curare alkaloids. An example of this family i s folicanthine ( 1 2 ) . The second group of bisindoles consists of those where the alkaloid components are of different structural types, or i n which two similar types are linked through different centres. Examples of these are geisospermine ( 1 3 ) and villalstonine ( 1 4 ) . Recently another such type of bisindole alkaloid has been discovered. This i s the so-called "vinblastine" type. The most interesting members of this family are vinblastine (vincaleukoblastine, - 6 -VLB) (15), vincristine (leurocristine, VCR) (16), leurosidine (17), and leurosine (18). These four compounds, amongst others, have been R l " R2 R3 R4 (15) C02CH3 CH3 OH H (16) C02CH3 CHO OH H (17) C02CH3 CH3 H OH (18) C02CH3 CH3 — o - - — " isolated i n minute amounts from the common periwinkle plant - Vinca  rosea Linn or Catharanthus roseus G. Don - and show marked anti-cancer activity. The story of the isolation and characterization of these compounds, particularly vinblastine (VLB) and vincristine (VCR) dates back to 2 an observation by W.R.N. Drew et a l . in 1929 that the administration of Vinca rosea leaf extracts to rabbits lowered their blood sugar content. Further attempts to study this effect later by two 3 4 5 independent groups ' met with varied success. In 1955 Noble and Beer, in an attempt to study this reported hypoglycemic activity discovered - 7 -that the plant extracts exhibited marked anti-neoplastic effects. This observation immediately catalyzed a great deal of interest in the constituents of this plant and in 1958 the isolation of the f i r s t bisindole alkaloid of the vinblastine type from V. rosea was reported. The compound was leurosidine (17).^ There followed a rapid succession of reports about the isolation of other members of this category and their c l i n i c a l a ctivity. The elucidation of the structures of VLB and VCR was quite stimulating and much was learned about the chemistry of these "dimeric" compounds at the same time. The alkaloids were each found to possess two individual chromophores; an indole and a 6-methoxyindoline in the case of VLB; and an indole and an N-formyl-6-methoxyindoline in the case of VCR. An important landmark in the elucidation of the structure of VLB^ was the discovery that the infrared spectrum of this alkaloid closely resembled that of an equimolar mixture of vindoline (10) and catharanthine (11); two co-occurring monomeric alkaloids. The structures of these two compounds were, at that time, largely unknown but they were quickly determined by chemical correlations to known compounds and 8 9 from a study of their mass spectral fragmentation patterns. 8 Reduction of VLB and VCR with lithium aluminum hydride gave the same pentahydroxy derivative thus correlating the two alkaloids with each other.^ It was possible to elucidate the constitution shown (15) for 9 VLB on the basis of chemical and spectroscopic data alone. The relative and absolute configuration had to be determined, however, from 11 12 an X-ray analysis of VCR monomethiodide. ' Owing to the earlier determination of an incorrect molecular formula (2 hydrogens less) for - 8 -VLB and VCR i t had been assumed that the indole portion of these "dimers" represents a dihydro-dihydroxy-catharanthine.^ Establishment of the correct molecular formula, however, made this postulate 13 untenable. Reductive cleavage (in concentrated hydrochloric acid containing stannous chloride and tin) of the "dimers" VLB and VCR led to one and the same indolic base, velbanamine (19), and a different indoline i n each case: deacetylvindoline from VLB and des-N^-methyldeacetylvindoline from VCR. The constitution of 19 available by this reductive acid cleavage of VLB; and in particular, the location of the hydroxyl group was assigned on the basis of the mass spectral fragmentation peak at m/e = 154 which could be shown to arise from the fragment (20) below. The complete structure of velbanamine was 8 (19) (20) ^n2 established by correlating i t with the compound cleavamine (21) whose structure had been independently proved by X-ray analysis of the . ... 14,15 methiodide. (21) - 9 -2 Reductive cleavage of VLB i n a deuterating medium led to [ H,]-o velbanamine in which four deuterium atoms were attached to the aromatic ring and the remaining two to the C position or else one 18 each to the C and C positions. 8 18 Acid catalyzed cleavage in the absence of reducing agents led to the amino acid (22) which could be converted to the ester (23) which, in turn, upon treatment with stannous chloride i n DCl-^O again gave 2 [ Hg]-velbanamine which was identical i n every respect to that obtained previously. This excluded C as a possible point of deutefation during cleavage and therefore as a possible site of linkage of the two monomers. This l e f t C as the only choice for 18 such a linkage.^ 22;- R - H 23; R = CH3 While the structures of these new "dimeric" compounds were being pursued, research was also simultaneously under way to investigate their interesting biological a c t i v i t y . After Beer and Noble were able to demonstrate that vinblastine 5 16—18 was capable of producing severe leukopenia in rats, * a team from the E l i L i l l y Laboratories began exploring the possibility that the periwinkles contained other interesting alkaloids of the VLB type. A systematic search resulted in the isolation of a total of seventy-two - 10 -alkaloids from this source by a variety of methods. Of these twenty-four were shown to have "dimeric" structures. Only four of this latter group, however, were of any c l i n i c a l interest i n the area of cancer control (structures 15-18 above). A great deal of effort was expended 19-34 in developing procedures for isolating these compounds and 35-39 detecting them in minute amounts. The mode of action of these drugs i s largely unknown even today despite considerable effort by several groups to learn something about i t . On the basis of several observations made during these researches, a working hypothesis for their mode of action has arisen and is widely 40 41 accepted although not yet conclusively established. ' It appears that these compounds may be classified with other structurally diverse drugs such as colchicine (24) as "mitotic poisons". The primary effect of these compounds seems to be the inhibition of -fc-RNA synthesis thus causing in turn a decrease in the protein synthesis. The alkaloids enter the c e l l only between praphase and metaphase and thus intracellular protein synthesis i s blocked at the very time when i t is most needed to spread the fibres of the spindle apparatus apart and support them in a fanned out position. Spindle fibres in cells affected by these alkaloids appear tangled and - 11 -disarrayed. The migration of the chromosomes under such conditions is blocked and inhibition of DNA synthesis as a result of this metaphase arrest i s observed. The exact metabolic path of these drugs in vivo is not known and some attempts to elucidate this path by the administration of radio-actively labelled alkaloids to laboratory animals has been undertaken 42-47 in the past. In this area, several important questions remain to be answered. For example, the possibility that i t may be a metabolite of the drug which exerts the antitumor effect, has not yet been excluded. Much research i s currently i n progress to answer such questions. Some studies have been possible by chemical modifications of VLB i t s e l f to yield new drugs. Some of these were shown to have an even better therapeutic index than the parent compound. For example, W.W. 48 Hargrove observed that i n i n i t i a l tests deacetyl VLB was less active and more toxic than VLB. This prompted some speculation that the acetyl group in VLB was important for i t s activity. This fact, coupled with the observation that deacetyl VLB was relatively easily available, by the hydrolytic action of anhydrous methanol saturated at 0°C with hydrogen chloride, led him to study a series of compounds made by attaching other acyl groups to deacetyl VLB. Chloroacetyl VLB so produced, for example, caused a 127% prolongation of l i f e in mice infected with P-1534 leukemia as opposed to a 25-30% prolongation under similar conditions by the parent compound (VLB) i t s e l f . This was indeed a significant finding and several other acyl substituents were 49-53 examined. As i s obvious from the number of patents arising out - 12 -of this work, the technique was thoroughly exploited for the development of new and potentially more useful drugs than were directly available from nature. Some other structural modifications were attempted and these are 54 summarized in Figure 1 below. A detailed and systematic study, of the relationship between the structure and activity of these alkaloids must await a general synthetic entry into this skeletal system. 1. 2. 3. 4. 5. 6. Reaction Hydrogenation Hydrogenation LiAlH. Reduction 4 Acid Hydrolysis Derivative Dihydro-VLB Hexahydro-VLB VLB-carbinol Desformyl-VCR Activity Relative Toxicity Relative to VLB to VLB Acetylation (Ketene) Triacetoxy-VLB Acetylation (AC2O) Diacetoxy-VLB 1/3 none 11 11 less none 11 tt Figure 1. Structural modifications vs. activity. - 13 -Changes other than in the functional groups on the molecule, however, are less simple to achieve. Two p o s s i b i l i t i e s for the solution of this problem present themselves: (a) Partial degradation of one of the more readily available bisindole alkaloids (probably VLB) followed by structural modification and resynthesis, or (b) synthesis of analogous compounds by appropriate "dimerizations" of preformed Iboga and Aspidosperma type units. The observed l a b i l i t y of the to C^, bond in these alkaloids would suggest that approach (a) is somewhat unfavourable. This l a b i l i t y i s to be expected on the basis that the Aspidosperma unit i s , after a l l , a meta-methoxy anilino compound. This renders i t nucleophilic at the C ^ position by virtue of the mesomeric electron donating effect of both the methoxy as well as the nitrogen substituents. Thus i t would be expected to be protonated under acidic conditions at this site. Cleavage of the C ^ to C^gt bond then simply neutralizes the positive charge so generated. This same mesomeric donation which makes the bond cleavage so facile also renders the C ^ position i n the monomeric Aspidosperma unit nucleophilic and a "dimerization" reaction simply involves finding the appropriate conditions by which the above process may be "reversed". Because Kutney and coworkers had developed a general scheme for the synthesis of both the Aspidosperma and Iboga alkaloid types, the approach of affecting a suitable "dimerization" between such templates became attractive. A key step i n the synthesis of these monomeric entities was the transannular cyclization step. This had already been postulated in - 14 -1962 by Wenkert"^ in a biosynthetic scheme proposed for these compounds. The relevant part of his postulate is shown below. C0 2Me 0 (25) C 0 2 C H 3 (26) Aspidospenna (27) - (28) Iboga Dihydrocleavamine (31) could be obtained from catharanthine (11) via the scheme shown below~^ in moderate yield. . Compound 31 provided C0 2CH 3 (11) (29) H H (31) H CC^CHjl (30) - 15 -a good model with which to test Wenkert's hypothesis above. It i s well-known that the treatment of many tertiary amines with mercuric acetate converts them to the corresponding iminium species. Treatment of dihydrocleavamine (31) with mercuric acetate in acetic acid yielded the corresponding iminium species which underwent cyclization, when heated, in the manner shown below to yield, upon reductive workup, the Aspidosperma skeleton.^ When the analogous reaction was carried out - 16 -on 1 8 - c a r b o m e t h o x y d i h y d r o c l e a v a m i n e ( 3 0 ) , p s e u d o v i n c a d l f f o r m i n e ( 3 2 ) , d i h y d r o c a t h a r a n t h i n e (33) and I t s 4 - e t h y l e p i m e r c o r o n a r l d i n e (34) 58 w e r e a l l i s o l a t e d . Clearly the Aspidosperma skeleton so synthesized is aberrant in that i t is an ethyl isomer of the natural compounds. The natural skeleton embodied in the structure of aspidospermidine (36) was synthesized however by the same transannular cyclization of quebrachamine (35). This cyclization i s of great interest because i t has been shown _5». (35) (36) 59 to be completely stereospecific by both chemical and X-ray studies. Thus the proper choice of stereochemistry of the lone asymmetric centre i n the starting material makes available either of the two known stereochemical series of the Aspidosperma skeleton. The u t i l i t y of this approach to the synthesis of Iboga and Aspido-sperma systems rested on the a v a i l a b i l i t y of the appropriate nine-membered ring compounds. The synthesis of intermediate-sized rings has been known, for some time, to be fraught with d i f f i c u l t i e s . However in this particular case, these d i f f i c u l t i e s were overcome by the s k i l l f u l use of the nitrogen atom present in the ring system. The key intermediate for this synthetic approach was the quaternary salt (37) (Figure 2). Ring opening of this intermediate was shown to occur readily under reducing conditions (sodium in liquid ammonia) to give dl-quebrachamine (35). The appropriate ethyl isomer of (37) under similar conditions could be made to yield dl-dihydrocleavamine - 18 -H H CO CH CH v l n c a m l n o r l n e ; H CO2CH3 j{ J 3 3 H CO-CH, C H3 vincaninoridlne Figure 2. Kutney's t o t a l synthesis of the Aspidosperma skeleton. - 19 -(31)."" The introduction of a carbomethoxy group was achieved by finding conditions to achieve the ring opening of compound 37 by the nucleophilic attack of cyanide ion followed by hydrolysis and esterification. The resulting intermediate when transannularly cyclized yielded the Aspidosperma skeleton bearing a carbomethoxy group at the appropriate position. A similar approach was possible with an ethyl isomer,as shown i n Figure 3, to yie l d an entry into the Iboga skeleton. Here the decarbomethoxy compounds were synthesized f i r s t followed by the introduction of cyanide on the appropriate chloroindolenines. This approach was f i r s t discovered by Buchi and 63 coworkers and was reported i n his synthesis of voacangine. It i s an important reaction that has been greatly ut i l i z e d in the course of subsequent work and w i l l be described in detail in a subsequent section of this thesis. Hydrolysis and esterification of the resulting n i t r i l e afforded carbomethoxydihydrocleavamine (30) which could be cyclized, as mentioned before, to coronaridine (34) and dihydrocatharanthine (33). Since catharanthine i s a readily available alkaloid, and since i t bears the required functionality for further elaboration towards the cleavamine-type part of the VLB-type "dimers", i t s use as a relay compound became attractive. In order to achieve this goal two c r i t e r i a needed to be satisfied: (1) A total synthesis of catharanthine needed to be achieved, and (2) Some means of converting the r i g i d pentacyclic Iboga skeleton of catharanthine to the tetracyclic cleavamine system was necessary. - 20 -1) Bg(0Ac)2 2) NaEH CN (31) MeOH/HCX R - H . R' - Et (33) R • E t , R' • H (34) Figure 3. Kutney's t o t a l synthesis of the Iboga skeleton. - 21 -The former of these two objectives was achived by an interesting 64 sequence. This sequence also made available several previously inaccessible functionalized cleavamine systems such as isovelbanamine (47) and velbanamine (19). These were obviously very closely similar to the materials required to make the naturally occurring dimeric alkaloids. The starting material was dihydrocatharanthine (33) available in racemic form by the total synthesis described above or in optically active form from the hydrogenation of catharanthine ( 1 1 ) . T h e latter was reduced with lithium aluminum hydride to the alcohol (40)„ Treat-ment of the tosylate of this compound (41) with triethylamine resulted in an interesting fragmentation (shown in Figure 4) to give the secodiene (42) in 62% overall yield. This compound could be converted to the t r i o l (44) by standard methods, and the latter could in turn be converted to the ketol (45) by cleavage of the v i c i n a l diol with sodium perlodate. The ketol could be part i a l l y reduced to the di o l (46) or else the "benzylic" hydroxyl group could be removed to yie l d isovelbanamine (47) Isomeric at the position with the cleavage product of VLB; velbanamine (19) to which i t could be easily converted by treatment with aqueous sulfuric acid. Treatment of compound 47 on the other hand with concentrated sulfuric acid led to the expected dehydration of the tertiary alcohol to cleavamine (21). Introduction of the carbomethoxy group by the previously described method resulted in 183-carbomethoxycleavamine (29) which could be transanularly cyclized to catharanthine thus completing the total synthesis of this compound.^ It should be mentioned that the synthesis of velbanamine - 22 -Figure 4 . Kutney's total synthesis of Catharanthine, - 23 -and catharanthine using a totally different approach was reported 67 68 almost simultaneously by Buchi and coworkers. ' There only remained, the development of a high yielding ring opening reaction that would convert catharanthine into carbomethoxy-cleavamine. This reaction had been reported using zinc in acetic acid but the yield and stereochemical purity of the resulting carbomethoxy-cleavamine was not good enough to render i t synthetically useful. The discovery that the treatment of catharanthine hydrochloride i n refluxing g l a c i a l acetic acid with an excess of sodium borohydride under carefully controlled conditions resulted in a 65% overall conver-sion to 183-carbomethoxycleavamine was thus a discovery of singular importance. In summary then, methods for the development and elaboration of both "halves" of the natural VLB type dimers had been developed in our laboratories. The remaining requirements could be summarized as follows: (1) To find a mild and general method of coupling both these monomeric units together at the appropriate centres so as to yield a junction which was stereochemically equivalent at the C , position 18 to the stereochemistry found in a l l naturally occurring oncolytic dimers (namely in the C Q, carbomethoxy dimers - the C ,-R stereo-l o 18 chemistry). (2) To elaborate the previously described scheme so as to obtain the exact functionality at the C^ , and/or C^ , positions of the carbomethoxycleavamine skeleton so that dimerization would produce compounds which were either the natural products themselves or else - 24 -C , epimers of them, l o (3) To obtain a total synthesis of vindoline. The description of the progress towards the goals (1) and (2) is the subject of this thesis. Goal (3) is an exacting one and i s currently under study by several workers in our laboratories. - 25 -DISCUSSION The research embodied in this section may be conveniently divided into two major categories: (1) Some work was required to modify the monomeric species available from previous work in these and other laboratories i n order to obtain monomeric indole moieties which closely resembled the appropriate parts of the natural oncolytic alkaloids. The work towards this goal i s treated together for purposes of convenience and i s contained in Part I of this discussion. (2) There remained, in the area of the so-called "dimerization reaction", three major questions which were largely unanswered. These were: (a) What i s the stereochemistry at C 1 Q, of the bisindole alkaloid resulting from the "dimerization reaction" conditions so far e m p l o y e d ? ^ (b) What can be said of the mechanism of this dimerization reaction? And f i n a l l y , (c) once enough i s known about the mechanism of this dimerization reaction, what modifications and/or new approaches may be attempted in order to ensure that a stereochemistry about C^g, similar to that of the natural compounds is obtained? The efforts to shed some light on these questions represent a major portion of this thesis and are embodied in Part II. - 26 -Part I The four known oncolytic dimers (15-18) a l l contain some oxygen functionality at C^, and/or C^,. The synthesis of any of these indolic templates therefore required a compound with some suitable "handle" at one or both of these positions which could easily be transformed into the appropriate oxygen functionality. The presence of a double bond at precisely this position in 18-carbomethoxycleavamine and i t s ready a v a i l a b i l i t y from the reduction of catharanthine with sodium borohydride i n acetic acid, as mentioned earlier, made i t a prime candidate. This observation together with the numerous methods available in the literature for converting olefins to the appropriate oxygen functionality suggested that this approach may be a rewarding one. An attempt was thus made to explore the conditions of direct "hydration" of the double bond of 18-carbomethoxycleavamine. If this could be achieved i n the Markovnikoff sense then 18-carbomethoxy-isovelbanamine or -velbanamine would become available and the possible epimerization of the former, i f i t formed, could be investigated. Velbanamine i t s e l f had already been synthesized; i n our laboratory by 64 the epimerization of synthetic isovelbanamine, and i n the laboratory 68 of G. Buchi by the reaction of ethyl magnesium bromide on the corresponding ketone. These reactions indicated that the stereo-chemistry of the alcohol i n velbanamine was the more stable one. Indeed an examination of the molecular model of velbanamine and the X-ray structure of VCR monomethiodide showed that when the piperidine ring was in the most stable chair conformation, the ethyl group was equatorial in velbanamine (and VCR) and axial in isovelbanamine. - 27 -These results thus supported the view that 18-carbomethoxyisovelban-amine should in principle be epimerizable to 18-carbomethoxyvelbanamine. It was obvious that conditions which would yield directly the velbanamine type of stereochemistry at C^. needed to be investigated f i r s t . If such reaction conditions were successful they would circumvent an epimerization at this centre altogether. The addition 72 of acylhypoiodites to olefins i s indeed a well documented reaction, and in some cases the trans-diaxial halohydrin ester may be obtained. Since the reaction conditions required for such a reaction are usually mild in terms of time and temperature, i t was resolved to attempt to use them here. The accepted mechanism for this reaction requires attack of a "positive iodine" species upon the ir-system of a double bond from the less hindered side to yield a cyclic iodonium ion. In our case, i t was thus expected that attack would occur from the side closest to N, (vide infra). Finally this cyclic iodonium ion b could be attacked in a concerted manner by the acyl species to provide the trans-diaxial halohydrin ester. Some cases had been reported where this intermediate could be isolated and transformed to the halohydrin which could then be closed to the appropriate epoxide by treatment with a base. Following through this anticipated reaction pathway, would result in the (3-epoxide (48), as shown below. In a majority of cases, however, the trans-diaxial diester resulted. This could easily be converted to the corresponding d i o l . Such a product in the case in point would result in a trans d i o l in which one alcohol was secondary and the other tertiary. Conversion of the secondary alcohol to a suitable leaving group followed by displacement by the - 2 8 -adjacent a l c o h o l i c oxygen would again r e s u l t i n compound 48. RCO Ag-RCO I R = CH 3 or CF 3 H C0 2CH 3' ( 2 9 ) H CO CH 0 ^ * J R' R' =SCR II 0 R' = H H C0 2CH 3 ^ i f 0 C 0 2CH 3- o H H C 0 2 C H 3 Compound 48 would be an extremely valuable one because i t i s exactly the indole template required f o r the synthesis of one of the n a t u r a l dimers - leurosine (18). Furthermore, i t could be converted by appropriate manipulation to 18-carbomethoxyvelbanamine (49) as we l l as the corresponding secondary a l c o h o l (50), each of - 29 -H C0 2CH 3 : (50) Several attempts to induce this reaction to proceed as desired were made. Temperatures between 0° and 40°C (refluxing methylene chloride) were investigated together with changes in reaction times from 0.5 hours to overnight. The efforts were a l l uniformly useless. In each case unchanged starting material was recovered to the extent of 94% of the i n i t i a l weight. This was proved to be the case by the comparison of the i r and nmr spectra of the reaction product with starting material. One possible explanation of the inertness of this molecule to these reaction conditions i s that the incoming iodonium ion i s too bulky to attach i t s e l f to the 7r-system of the 3,4 double bond. An alternative and somewhat preferable explanation i s that the - 30 -displacement of the intermediate cyclic iodonium ion at the position would be an energetically highly unfavourable step requiring attack by the carboxylate anion from the side which would be anticipated to be quite st e r i c a l l y hindered. If the reason for the failure of this reaction involves steric crowding on the B-face of the double bond then the hope of directly obtaining a C^ B alcohol could not be realized. Thus attention was turned to an investigation of the possible synthesis of a C^a alcohol which could then be epimerized to the 73 5 desired one at some later stage. Previously, Kutney and coworkers ' had investigated in detail, the effect of mercuric acetate on indole moieties (vide supra). They had established that the primary effect of mercuric acetate on cleavamine-type molecules lacking a 3,4 double bond, in acetic acid, was the oxidation of in the molecule to the corresponding iminium species. It remained to investigate this reaction under the conditions of oxymercuration usually employed for the hydration of double bonds.^ ^ The reaction of would be reversed upon treatment with sodium borohydride in aqueous alcohol. The oxymercuration reaction required just such a workup i n order to break the carbon-mercury bond formed during the reaction. It was thus f e l t that this reactivity of N, towards mercuric acetate constituted b no problem in this reaction and may indeed have the added advantage of protecting this centre from any other side reactions. As a model, catharanthine was treated in aqueous tetrahydrofuran (1:1) with two equivalents of mercuric acetate - under reflux for 2.5 hours. Workup by reduction with sodium borohydride resulted in a - 31 -precipitation of mercury which was f i l t e r e d off. Only one half of the material could be recovered. However, the examination of this reaction mixture showed that roughly half of i t had been converted to another more polar compound. This may have been the desired alcohol on the basis of i t s infrared spectrum which showed a shoulder at 3300 cm ^ on the usual indole N-H absorption at 3440 cm ^. On the basis of this result, several attempts to duplicate this employing 18-carbomethoxycleavamine were made. This compound was treated with two equivalents of mercuric acetate i n aqueous tetrahydro-furan under reflux. The crude reaction mixture, after borohydride reduction, contained only one major spot. An nmr investigation of this reaction mixture showed that this compound was starting material. In particular, no exchangeable protons were encountered in the nmr upon shaking with deuterium oxide. No change in this reaction mixture could be detected when i t was attempted to acetylate i t using acetic anhydride and pyridine. These facts ruled out the p o s s i b i l i t y that even any minor constituents of the mixture were alcohols. Finally, purification of the major compound was possible using thin layer chromatography on alumina. An infrared comparison of this product with authentic 188-carbomethoxycleavamine rapidly established that i t was unchanged starting material. Several other attempts to induce this reaction to proceed as desired also failed. Formation of N^-C^ iminium species i n the flexible tetracyclic cleavamine system results in the formation of a dihydropyridinium ion. This delocalized system deactivates the 3,4 double bond towards electrophilic attack. Thus the formation of the intermediate acetoxy-- 32 -mercurium ion may not be f a c i l e . In other words, the positive charge in the iminium system i s delocalized over the entire diene system of the dihydropyridinium ring thus depleting the electron density of the 3,4 double bond and of course correspondingly reducing i t s reactivity towards electrophiles. The relative apparent "success" i n the r i g i d pentacyclic system of catharanthine, on the other hand may result from the failure of i t to form an iminium ion because of the strain associated with the formation of such an intermediate under these particular 73 reaction conditions. Kutney and coworkers have studied the rearrangement of catharanthine i n concentrated acid to cleavamine and decarbomethoxycatharanthine. In this study they implicated a similar iminium species to the one required here i n the tetracyclic case (51). An equivalent one in the pentacyclic case has, however, never been ceported. The formation of the analogous iminium (52) i n the r i g i d system would clearly violate Bredt's Rule and would thus be much more d i f f i c u l t to form. (51) (52) Under the conditions of the reaction the primary reaction of carbomethoxycleavamine then, i s the formation of the dihydropyridinium species. This reverts to starting material when treated with sodium borohydride. On the other hand this reaction i s suppressed or eliminated in the more rigi d system and so the more normal oxymercuration results. - 33 -It was thus clear that the Markovnikoff hydration of the 3,4 double bond could not be readily achieved, and attention was turned to the possible factors affecting any form of electrophilic hydration of the 3,4 double bond. Several factors needed to be considered. Fi r s t of a l l , the double bond to be functionalized i s i n a s t e r i c a l l y crowded environment thus mitigating against the approach by large electrophilic groups of relatively low reactivity. Molecular models revealed, furthermore, that i f an electrophile i s to approach the ol e f i n i n a plane perpendicular to the plane of the double bond so as to maximize overlap with the Tt-system; i t may only enter from the side closest to the atom. Indeed this had been previously corroborated in our laboratory.^ The catalytic hydrogenation of 18-carbomethoxycleavamine with Adamfe catalyst at atmospheric pressure and room temperature i n ethyl acetate yielded only 18-carbomethoxy-43-dihydrocleavamine. Thus i t was established that hydrogenation had occurred from the side closest to N, . Functionalization of the 3,4 double bond should D therefore be expected to yield compounds where the oxygen functionality i s epimeric to that obtained i n the natural dimers. Secondly, the presence of a basic nitrogen atom may be expected to complicate matters somewhat by i t s own i n t r i n s i c reactivity towards some electrophilic reagents. The reactivity of such basic nitrogen atoms to peracids to yield N-oxides is well documented.^ This reactivity i s u t i l i z e d later in this thesis and w i l l be discussed at that point. Suffice i t to say, here, that one would expect to obtain a reaction between any sufficiently reactive electrophile and the lone pair of electrons present on this nitrogen. - 34 -F i n a l l y , the r e a c t i v i t y o f the . i n d o l e s to e l e c t r o p h i l e s i s w e l l known. F o r example, t h e s e compounds r e a c t r e a d i l y w i t h s o u r c e s o f " p o s i t i v e h a l o g e n " such as N-bromosuccinimide, N - c h l o r o a c e t a m i d e , and 7 8 — 8 3 t - b u t y l h y p o c h l o r i t e t o i n c o r p o r a t e h a l o g e n atoms i n t o t h e p o s i t i o n o f the i n d o l e n u c l e u s w i t h the f o r m a t i o n o f i n d o l e n i n e s . T h i s r e a c t i o n has been mentioned p r e v i o u s l y i n t h i s t h e s i s and forms the b a s i s o f most o f the work i n P a r t I I o f the d i s c u s s i o n . X H Thus, i n summary, the d i r e c t f u n c t i o n a l i z a t i o n o f 18-carbomethoxy-c l e a v a m i n e (29) t o t h e n e c e s s a r y i n d o l e t e m p l a t e s f o r the s y n t h e s i s o f the n a t u r a l l y o c c u r r i n g d i m e r s , w i t h o u t the i n t e r m e d i a c y o f an e p i m e r i z a t i o n o f t h e oxygen f u n c t i o n a l i t y i n t r o d u c e d , w a s u n l i k e l y . F u r t h e r m o r e the i n t r o d u c t i o n o f oxygen f u n c t i o n a l i t y must be performed i n such a way t h a t the o t h e r f u n c t i o n a l i t i e s i n t h e m o l e c u l e a r e e i t h e r u n a f f e c t e d o r e l s e a r e c o n v e r t e d i n s i t u t o a d e r i v a t i v e from w h i c h the p a r e n t f u n c t i o n a l i t y may be e a s i l y r e g e n e r a t e d . I t i s known t h a t o l e f i n s r e a c t w i t h d i b o r a n e i n s o l u t i o n to form s t a b l e b o r o n a d d u c t s where boron has a t t a c h e d i t s e l f to the l e s s -s u b s t i t u t e d t e r m i n u s o f the d o u b l e bond. Oxygen may t h e n be r e a d i l y s u b s t i t u t e d f o r the b o r o n by the use o f a l k a l i n e hydrogen p e r o x i d e to g i v e the s o - c a l l e d l e a s t s u b s t i t u t e d a l c o h o l . S i n c e the a t t a c k by b o r o n i s r a p i d and s i n c e the s t e r i c r e q u i r e m e n t s o f t h i s r e a c t i o n a r e - 35 -minimal, i t was decided to attempt to hydroborate 18-carbomethoxy-cleavamine. Treatment of 186-carbomethoxycleavamine with an excess of diborane i n tetrahydrofuran under rigourously anhydrous conditions at 0°C followed by slow warming to room temperature resulted i n a good yield of the boron adducts. This material could be treated with an aqueous alkaline solution of hydrogen peroxide to yield, after workup, a greater than 75% yield of two alcohol amine-boranes. These amine-boranes had resulted from the attachment of the electrophilic boron atom to the basic N, atom. Absorptions in the infrared spectra of b such amine-boranes at 2375 cm 1 (v B-H) and 1170 cm 1 with 2260 cm 1 overtone (6 B-H) f a c i l i t a t e s their detection in a reaction mixture. This was not an unexpected result and had been encountered previously during the hydroboration of similar alkaloids. Indeed other workers i n our laboratory had perfected a method for the removal of such amine-boranes by refluxing a mixture of the 84 substrate and triethylamine i n tetrahydrofuran for 2.5 hours. Such treatment of the crude reaction mixture resulted in an overall total yield of two alcohols of roughly 70%. These were available in a ratio of approximately 1:1 and were readily separable by column chromatography on deactivated alumina. An examination of their infrared spectra showed that they both possessed an absorption at approximately 3600 cm 1 distinct from the indole N-H absorption at about 3440 cm \ They were thus both alcohols. Furthermore a comparison of these spectra showed that they were indeed closely related. The ease with which both were acetylated established their identity as secondary alcohols; and their ultraviolet spectra were typically indolic in both cases, eliminating any poss i b i l i t y that the indole chromophore had been somehow modified during the reaction. The best evidence in favour of their assigned structures was however available from their mass spectral fragmentation patterns. These were entirely in accord with that expected on the basis of previous work in this area^^ and confirmed the presence of an alcohol moiety in the piperidine ring system by the presence of an intense peak at m/e = 154 attributable to the fragment 53 shown below. OH (53) The reasons for the isolation of two alcohols instead of one was not immediately obvious. The starting material was optically pure, being obtained in one stereospecific step from a known natural alkaloid. Since two new optical centres were created during the hydroboration sequence at and the possibility of diastereomers 85 needed consideration. However, i t i s well established that the addition of boron and hydrogen to adjacent carbon atoms of an olefin occurs from the same side. Thus the stereochemistry at the two new centres was fixed i n a relative sense. Furthermore, replacement of boron by oxygen is also known to be entirely stereospecific resulting in the overall retention of configuration at that centre. In other words, mechanistic arguments required the alcohol at and the ethyl group at Ct to be trans. Two possible compounds could be drawn with this - 38 -to rule out compound 55 as a possible one on the basis that i t would require approach of the reagent from the more hindered side (see above). Thus i t was necessary to conclude that one of the asymmetric centres already present in the molecule had been epimerized during the course of the reaction. Since two products had appeared after treatment with diborane, and before any further treatment, i t was necessary to assume that diborane i t s e l f was responsible for the isomerization. Indeed treatment of either alcohol or either amine-borane separately with aqueous alkaline hydrogen peroxide or with t r i -ethylamine under reflux failed to yield a mixture of the two corresponding products. As part of an attempted total synthesis of indole and dihydroindole alkaloids, Kutney and coworkers had cleaved catharanthine to four isomeric 18-carbomethoxydihydrocleavamines. It was possible at this time to assign the stereochemistry at the C^g and positions to each of these compounds chiefly on the basis of nmr, in particular, the chemical shifts of the signal attributable to the C^g proton and the ethyl group. It was shown that the series of 183-carbomethoxy-dihydrocleavamines exhibited a one proton multiplet in the region - 39 -x 4.5-5.0 attributable to the C. Q proton. In contrast, in the 18a-l o carbomethoxydihydrocleavamines this C. 0 proton appeared as a multiplet i o in the region T 6.0-6.2. The seemingly anomalous values i n the 188 series, were explained by the argument that i n this case the C-_ J.O proton is in close proximity to the atom and may be deshielded by i t s lone pair. This argument had been used previously by Mokry and Kompis to assign the stereochemistry of some other related Vinca 86 alkaloids. It could be noticed furthermore that within each series of C-0 isomers the C.a compound exhibited a three proton t r i p l e t , attributable to the methyl group of the ethyl, at slightly lower frequency than the corresponding compound. (See Table I). Finally, the absorptions of the ethyl-methyl of both epimers were at higher frequency in the C. _a series than the corresponding ones in l o the C. „3 series. Thus by a simple examination of the nmr spectra of l o Table I. Chemical shifts of cleavamine-type compounds C-4 ethyl C-18 carbomethoxy 0. Name a ethyl ethyl T = 9.09; 4.53 T = 9.12; 4.98 18-carbomethoxy-dihydrocleavamine x 9.08; 5.00 18-carbomethoxy-dihydrocleavaminol x = 9.33; 6.13 x = 9.45; 6.12 18-carbomethoxy-dihydrocleavamine T = 9.44; 6.00 18-carbomethoxy-a dihydrocleavaminol - 40 -cleavamine-type compounds one could assign the stereochemistry at both C. „ and C positions. The generality of this approach had been lo 4 proved by i t s use i n the corresponding 18-cyano- and 18-methoxy-dihydro-87 cleavamines and Indeed, was u t i l i z e d in the structure elucidation of three dimeric compounds, deoxy VLB-'A', deoxy VLB-'B' and deoxy VLB-'C' A similar examination of the nmr spectra of the two alcohols available from the hydroboration above (see Figures 7 and 8), readily revealed them to be epimeric at C. _ and not at C. and/or C.. In fact l o J 4 by analogy i t appeared that both compounds bore a C^ 3 ethyl group, indicating that attack had been from the side closest to the atom i n support of the previous steric arguments. Acetylation of both alcohols independently, showed that the previous assignments of signals to the C. Q proton were indeed correct by virtue of the fact that they were unchanged by such treatment. Both compounds were independently decarboxylated using aqueous concentrated hydrochloric acid and were shown to be identical to one another by superimposible infrared, nmr, and elemental analysis together with melting point of the corres-ponding acetates. Furthermore, each was independently also shown to be completely identical to an authentic sample of 4g-dihydrocleavaminol 84 acetate prepared by the hydroboration of cleavamine i t s e l f . Finally, the interconversion of these two alcohols to a mixture of both compounds by the use of boron trifluoride-etherate in benzene under reflux put this assignment on firm ground. This method of epimerization of the C._ carbomethoxy group had been used previously in the inter-lo 69 conversion of 18a- and 183-carbomethoxydihydrocleavamines. It i s tempting to speculate that the mechanism of this known - 41 -- 42 -- 43 -epimerization of the carbomethoxy group is analogous to that occurring during hydroboration. In each case an electron-deficient boron-containing molecule attaches i t s e l f to the electron-rich carbonyl oxygen of the carbomethoxy group, thus forcing the loss of a proton from the C^g position reversibly. This deprotonation-reprotonation mechanism f i n a l l y results in a thermodynamically controlled mixture of epimers. Thus compounds 56 and 57 could be obtained in one step from 18B-carbomethoxycleavamine. This constituted, then, a direct functionalization of the 3,4 double bond i n the 18-carbomethoxycleavamine series and i s the f i r s t and only one reported thus far. - 44 -(57) (56) 18a-carbomethoxy-48-ethyl- 18B-carbomethoxy-4g-ethyl-dihydrocleavamin-3a-ol dihydrocleavamin-3a-ol These compounds were of central importance for two reasons. F i r s t of a l l , the natural oncolytic dimer, leurosidlne (17) had been postulated to have an indole portion,18-carbomethoxyvinrosamine with 88 exactly such a secondary alcohol functionality. During the structure elucidation of leurosidine, however, the stereochemistry at C^, and C^, could not be definitively established. However, on the basis of analogy with the structures of VLB (15) and VCR (16) the structure of vinrosamine (58), available from the cleavage of leurosidine (17), was assigned as shown below. There existed now for the f i r s t time a real possibility to correlate the products of the hydroboration above with the compound available from the cleavage of leurosidine and thus prove the stereo-- 45 -chemistry at and of the naturally derived compound. Towards this end, i t would be necessary to obtain a l l four possible compounds with differing stereochemistry at and C A. These are shown below. H (60) (58) (59) H (61) Compound 61 i s available from the direct hydroboration of cleavamine""' or, alternatively, by decarboxylation of either alcohol available from the above hydroboration. Oxidation of this secondary alcohol to the corresponding ketone provided the key intermediate for the synthesis of compounds 58, 59 and 60 stereoselectively. Thus epimerization of the adjacent C^ position using strong base or Lewis acids such as boron t r i f luoride-etherate should yield an entry into the C^ct-ethyl series. The epimerization of the other adjacent position at i s impossible since the necessary enol or enolate double bond violates Bredt's rule. - 46 -Subsequent reduction with a suitable hydride source should result in the delivery of hydride from the less hindered side, namely that closest to N, , and should thus yield the CLB alcohols. By combining b J the epimerization at with this reduction at C^, compounds 58 and 60 should be secured. Perhaps the isomerization of the ethyl group may sufficiently alter the conformation of the piperidine ring so as to allow reduction, at least partially, from the face furthest away from and so permit the isolation of compound 59 as well. If not, other means of arriving at that compound could be devised. Although significant, this was not the only use that compounds 56 and 57 furnished in the overall synthetic aim. The oxidation of the secondary alcohol in these compounds would provide a compound of the most central and v i t a l importance to the entire project. This 3-keto-carbomethoxycleavamine compound should be u t i l i z a b l e ; as outlined above in the decarbomethoxy case; in the production of four isomeric templates bearing a carbomethoxy group at C 1 Q. These, when coupled with vindoline, should provide the f i r s t synthetic dimers bearing oxygen functionality at C^i• In fact one of these compounds would necessarily be identical to leurosidine at least at the C^, and C^, positions and should represent the closest analogue of the natural compounds so far synthesized. Secondly, this 3-keto compound should activate the adjacent position and allow placement of a suitable precursor of an epoxide and eventually the tertiary alcohol; thus allowing an entry into the functionalized templates required for the synthesis of the other natural dimers. In short, this 3-keto-carbomethoxycleavamine would in principle - 47 -make available a l l the templates necessary to synthesize not only a l l the known natural dimers but also other closely related analogues previously unavailable from nature. Finally, decarboxylation of this ketone should yield another direct entry into the compounds mentioned above. A l l these steps are summarized in Figure 9. The oxidation of the alcohols 56 and 57 to the compound 62 proved to be remarkably d i f f i c u l t . 89 Albright and Goldman had reported that the use of mixtures of acid anhydrides and dimethyl sulfoxide (DMSO) proved to be a mild and effective method for the conversion of alcohols to ketones i n various indole containing compounds. For example yohimbine (67) could be transformed to yohimbinone (68) i n 80% yield i n twelve hours at room temperature using a twenty-fold excess of acetic anhydride i n DMSO. The use of benzoic anhydride afforded an even greater yield under the same conditions. H H OH (67) (68) - 48 -• I OH (49) Figure 9. Proposed uses of hydroboration products 56 and 57. - 49 -These authors claimed this to be the method of choice for the oxidation of alcohols in sensitive indole alkaloids. However, they were quick to caution against the use of these reagents i n cases where 8 "alcohols are rapidly esterified under the conditions of the reaction..." The compound 56 was treated with a five-fold molar excess of acetic anhydride i n DMSO for a period of eighteen hours at room temperature. Workup afforded two major compounds which proved to be the unreacted starting material and the corresponding acetate, both of which could be readily identified by spectral comparisons with the authentic materials. On this basis i t was f e l t that the competing esterification could be blocked by the use of benzoic anhydride and so these conditions were attempted. Treatment of compound 56 with an excess of benzoic anhydride in dimethyl sulfoxide for twenty-three hours at room temperature followed by workup afforded an 80% recovery of the corresponding benzoate ester. The identity of this compound could easily be deduced by inspection of the aromatic portion of i t s nmr spectrum. Several attempts were made to find conditions which would yield the desired ketone via this reaction but i t appeared that under conditions mild enough to suppress esterification, no reaction occurred at a l l and the starting material was recovered unchanged. An oxidizing agent of roughly the same mildness and without the concomitant problem of esterification i s the complex of sulfur trioxide and pyridine in DMSO as solvent. This reagent was f i r s t described by 90 von Doering. Reaction of the sulfur trioxide-pyridine complex in DMSO with compound 56 at room temperature for periods ranging from twenty-four hours to six days resulted in a near quantitative recovery - 50 -of starting material together with traces of decomposition products which were polar. The latter lacked the normal indole absorptions in their uv spectra. Several other attempts at accomplishing this apparently simple conversion resulted uniformly i n failure. Another worker in our 91 laboratory, for example, investigated the various chromium based oxidation techniques such as Collins and Jones oxidations and met with the same result. Finally, after several conditions had been attempted, 92 and rejected, the Moffat conditions using dicyclohexylcarbodiimide, phosphoric acid and dimethyl sulfoxide were attempted. It had been reported i n passing that leurosidine i t s e l f could be oxidized under 88 these conditions to the corresponding ketone. Submission of both compounds 56 and 57 to this oxidation under very carefully controlled conditions resulted i n an interesting discovery. Under identical conditions compound 56 could be oxidized i n an optimal y i e l d of 50% to the desired ketone (62) whereas compound 57 was recovered unchanged. A satisfying explanation of this observation is as yet unavailable. This does not, however, constitute any serious limitation on this method because as mentioned earlier compound 57 can be epimerized to 56. Thus, the overall conversion of the products of the hydroboration to 62 in reasonable yield had now been achieved. As mentioned previously this compound provides an opportunity for the study of several aspects of i t s chemistry which are of pivotal importance to the overall synthetic scheme. Work in our laboratories is currently under way to extend this finding as outlined in Figure 9. - 51 -Preliminary studies have indicated that 188-carbomethoxy-48-cleavamin-3-one (62) cannot easily be converted to a compound of the type 63. Upon treatment with one equivalent of base, i t yields the corresponding anion resulting from removal of the indolic N-H proton as the major, and i n many cases the only product. This, of course, enhances the reactivity of the indole-3-position towards electrophiles. In fact attempts to add two equivalents of base followed by electrophiles such as bromine or sources of "positive" halogen have resulted primarily in the destruction of the indole chromophore as evidenced by ultraviolet spectroscopy. Attempts to trap any enolate that may form by the formation of enol acetates under similar basic conditions have also met with l i t t l e success. Reactions under acidic conditions such as the use of isopropenyl acetate with a catalytic amount of p-toluenesulfonic acid and bromine in acetic acid have resulted i n 93 destruction of the indole chromophore as well. It was found, however, that treatment of the ketone (62) with sodium hydride in 1,2-dimethoxy-ethane followed by quenching with deuterium oxide resulted in', the formation of mono- and di-deuterio compounds. This conclusion was arrived at by a systematic mass spectral study. It was found that, in accordance with the expected mass spectral fragmentation^"''^'''""* for cleavamine-like compounds, the most intense peak in the mass spectrum of compound 62 was at m/e=152 which could be assigned to the fragment shown below. 0 m/e = 152 - 52 -In the monodeuterated compound this peak was expected to appear at 153 provided that this material had been deuterated in the piperidine portion. A measurement of the relative intensities of the peaks at m/e = 152 and 153 of the crude reaction mixture from the above deuteration experiment compared to the relative intensities of these peaks in the undeuterated starting material showed that i t was 63% undeuterated in the piperidine portion and 37% monodeuterated in the piperidine ring. Thus, i t was established that the desired enolate had indeed formed under these conditions. Efforts to u t i l i z e these reaction conditions to introduce some useful functionality at have so far not succeeded. From the above discussion then,the apparently straightforward "direct" functionalization of the carbomethoxycleavamine system at C^, has not borne f r u i t yet. The more demanding and laborious task of systematically protecting a l l of the sensitive and reactive functionality in the molecule prior to functionalization, and then deprotection again after this step, appears necessary. Others workers in our labora-tory are currently investigating this area. - 53 -Part II In this part, the developments in the area of the so-called dimerization reaction w i l l be discussed. Several different approaches have been investigated and an attempt w i l l be made to present them in a concise and logical sequence. As is the nature of research of any kind at this level, several other new and exciting approaches remain to be explored and, at the end of this section, these w i l l be summarized and their relative merits and disadvantages discussed. Some of the earlier chemistry in the area of indole alkaloids bears strongly on the complexion of this work. Thus i t may be useful to discuss i t here. 81 In 1956 W.O. Godtfredsen and S. Vangedal reported that treatment of yohimbine (67) and related alkaloids with tertiary butyl hypochlorite led cleanly to a compound having the following properties: (1) It had no indole-N-H absorption i n i t s infrared spectrum (around 3440 cm ^ ) . (2) It had none of the usual oxidizing properties of an N-chloro-compound. (3) Hydrogenation over platinum in ethylene glycol monomethyl ether regenerated the parent compound. 95 It was some time before Finch and Taylor assigned the structure of the chloroindolenine (69) to this compound and were able to show that i t rearranged upon treatment with aqueous acid or base, followed by hydrolysis of the intermediate, to the oxindole (70). This was shown to be a general reaction for most indole containing compounds. With this observation the chloroindolenine chemistry of indoles was (70) born and i t has grown to be one of the more important and synthetically useful reactions in this f i e l d . It was also shown that other 96 indolenines such as the hydroxyindolenines could be formed; and that they reacted in an exactly analogous way to chloroindolenines when treated with acids or bases-The chloroindolenine formation reaction has found application i n 97 the synthesis of 2-acylindoles. Dolby and coworkers converted the tetracyclic amine (71) to the corresponding chloroindolenine (72) by standard methods. A mixture of separable epimers about the carbon-chlorine bond was obtained. These compounds were converted to the quaternary methiodide salts (73) and each in turn was treated with sodium acetate in aqueous ethanol. Hydrolysis of the product resulted, in each case, in the isolation of two compounds (74) and (75), which were shown not to be interconvertible. A "reasonable mechanistic scheme" to rationalize the formation of these compounds was presented and i t i s summarized in Figure 10. - 55 -(74) Figure 10. Dolby's mechanism for the formation of the 2-acylindole (74). - 56 -It was pointed out that this proposal was in agreement with the 79 general mechanistic scheme of Taylor. Further, i t was stated that intermediate 77 was an attractive one because the alternative pathway of concerted S^' displacement on compound 78 must involve nucleophilic attack on a tertiary centre. A l l y l i c rearrangement of this compound via the carbonium ion intermediate was unlikely i n this case because the carbonium ion would be a doubly charged species with adjacent positive charges in one of the possible resonance contributors. The ion 77 is an interesting one since similar ions have been postulated by several workers in this area. 9 Another application of this reaction was made by Buchi and Manning. 96 Following the report of Patrick and Witkop that 11-hydroxytetrahydro-carbazolenine (79) was converted to the dimer (80) by treatment with an acid they reasoned that this conversion had probably occurred via the intermediate imine (81) as shown in Figure 11. OH (79) (79) (81) OH (80) Figure 11. Proposed path for the formation of 80 from 79. - 57 -Application of this type of reaction to ibogaine (82) allowed them to introduce such functionalities as hydroxyl, methoxyl and n i t r i l e into the C^g position. Thus treatment of the parent base (82) with _t-butyl hypochlorite in solution resulted in the formation of the chloroindolenine in excellent yield. Exposure of the chloroindolenine to a solution of potassium cyanide in methanol resulted in a good overall conversion to the corresponding 18-cyano-ibogaine. Hydrolysis and esterification of this last compound led to the synthesis of voacangine (compound 82 bearing a carbomethoxy group at C 1 D ) : a natural product. Similarly, treatment of the chloroindolenine with methanolic (82) hydrogen chloride resulted i n a conversion to 18-methoxy-ibogaine whereas treatment with dilute aqueous hydrochloric acid resulted in the corresponding 18-hydroxy-compound. The latter could be converted to the methoxy compound by treatment with acidic methanol and the conversion of the methoxy- to the hydroxy-compound was achieved when the former was exposed to aqueous mineral acid. These interconversionswere a l l considered to proceed via the ubiquitous imine (83), analogous to compounds 77 and 81 above, or i t s conjugate acid. In the pentacyclic iboga skeleton this ion has much b u i l t - i n strain, and so the alternative delocalized ion (84) was also proposed here as an intermediate. T h i s a p p r o a c h was l a t e r u t i l i z e d b y B u c h i e t a l " ° t o i n t r o d u c e a n e s t e r f u n c t i o n a t t h e C p o s i t i o n d u r i n g a t o t a l s y n t h e s i s o f l o c a t h a r a n t h i n e ( 1 1 ) . I n o u r l a b o r a t o r i e s , t h i s a p p r o a c h h a s b e e n i m p r o v e d and e x t e n d e d t o p r o v i d e a n e n t r y i n t o t h e c l e a v a m i n e s k e l e t o n 6 1 , 8 7 b e a r i n g a c a r b o m e t h o x y g r o u p a t C Q . T h u s f o r m a t i o n o f t h e l o c h l o r o i n d o l e n i n e o f 4 B - d i h y d r o c l e a v a m i n e ( 3 1 ) i n t h e u s u a l w a y , f o l l o w e d b y i n t r o d u c t i o n o f a n i t r i l e r e s u l t e d i n 1 8 - c y a n o - 4 8 - d i h y d r o c l e a v a m i n e w h i c h c o u l d be h y d r o l y z e d a n d e s t e r i f i e d t o 1 8 - c a r b o m e t h o x y - 4 8 - d i h y d r o -c l e a v a m i n e s (33) a n d ( 3 4 ) ; ( s e e F i g u r e 3 ) . A n a n a l o g o u s s e q u e n c e i n 64 t h e c l e a v a m i n e s e r i e s l e d t o a t o t a l s y n t h e s i s o f 1 8 8 - c a r b o m e t h o x y -c l e a v a m i n e , a n d i n t u r n , c o m p l e t e d t h e t o t a l s y n t h e s i s o f c a t h a r a n t h i n e (11) ( s e e F i g u r e 4 ) . I n summary, t h e i n d o l e s c a n be s m o o t h l y c o n v e r t e d t o i n d o l e n i n e s w h i c h c a n r e a c t f u r t h e r i n one o f two w a y s when e x p o s e d t o h y d r o x y l i c s o l v e n t s u n d e r a c i d i c c o n d i t i o n s . T h e s e a r e shown i n F i g u r e 1 2 . The p r o d u c t s a r e t h o s e o f s u b s t i t u t i o n o n one h a n d a n d r e a r r a n g e m e n t o n 98 t h e o t h e r . I t h a s b e e n p r o p o s e d t h a t p a t h w a y A i s p r e f e r r e d when i t i s s t e r i c a l l y p o s s i b l e t o accommodate t h e l e a v i n g c h l o r i d e a n d t h e i n c o m i n g n u c l e o p h i l e c i s t o one a n o t h e r , s i n c e t h i s i s t h e n e c e s s a r y - 59 -Figure 12. Pathways of r e a c t i o n of indolenines. - 60 -condition for the concerted, stereospecific rearrangement postulated. Indeed i n several cases where this rearrangement occurs, i t has been shown to be completely concerted and stereospecific. Whenever the above condition cannot be met, a stepwise elimination of HC1 followed by a nucleophilic substitution occurs as shown in path B. Turning our attention now to another aspect of the "dimerization reaction", i t had been reported^ that the natural dimers could be cleaved into their corresponding monomeric templates by treatment with acids in the presence of reducing agents such as stannous chloride and t i n . Indeed this cleavage reaction has played an important role 10,13,88 70 i n the structural elucidations of natural as well as synthetic dimers. The mechanism for this cleavage reaction was not f u l l y understood. Part of the work i n this section of the thesis provides some c l a r i f i c a t i o n of the cleavage reaction and has important mechanistic overtones for the so-called dimerization reaction. These 100 are discussed at a later stage. Buchi and coworkers reasoned that a dimerization between two halves simply involved a formal reversal of the above cleavage reaction. Previously, Plant and coworkers"^1 had reported that the dimerization of compound 85 to the dimer (80) under acidic conditions occurred with ease. The mechanism of this reaction was believed to be closely p a r a l l e l to that shown i n Figure 11 and indeed the same intermediate (81) was viewed as being responsible for this conversion in both cases. Along these lines, Buchi and coworkers treated dregamine (86) with sodium borohydride and obtained dregaminol (87) stereoselectively i n 80% yield. This compound is analogous to compound 85 above and i t was f e l t that i t could be dimerized with voacangine (88) under acidic conditions by creating a - 61 -(80) s i m i l a r i o n . I n d e e d t r e a t m e n t o f d r e g a m i n o l (87) i n m e t h a n o l c o n t a i n i n g 1% h y d r o g e n c h l o r i d e w i t h one e q u i v a l e n t o f v o a c a n g i n e (88) r e s u l t e d 102 i n a 50% y i e l d o f d i h y d r o v o a c a m i n e ( 8 9 ) , i d e n t i c a l w i t h a u t h e n t i c m a t e r i a l o b t a i n e d f r o m t h e h y d r o g e n a t i o n o f n a t u r a l l y a v a i l a b l e v o a c a m i n e ( 9 0 ) . The o n l y o t h e r r e p o r t e d d i m e r i c p r o d u c t f r o m t h i s r e a c t i o n was a p o s i t i o n a l i s o m e r o f d i h y d r o v o a c a m i n e , n a m e l y d i h y d r o v o a c a m i d i n e ( 9 1 ) . T h i s s e q u e n c e i s s u m m a r i z e d b e l o w i n F i g u r e 1 3 . The r e a c t i o n was e x t e n d e d t o t h e s y n t h e s i s o f o t h e r members o f t h i s f a m i l y o f d i m e r i c i n d o l e a l k a l o i d s by t h e u s e o f s u i t a b l y f u n c t i o n a l i z e d t e m p l a t e s w i t h t h e same s k e l e t a l f e a t u r e s . I n e a c h c a s e , i n a g r e e m e n t w i t h t h e a b o v e s c h e m e , o n l y one e p i m e r o f t h e j u n c t i o n and one e p i m e r o f t h e j u n c t i o n was i s o l a b l e . The s t e r e o s e l e c t i v i t y o f t h e s e r e a c t i o n s , and t h a t o f t h e b o r o h y d r i d e r e d u c t i o n s t e p , may h a v e b e e n due t o t h e s e v e r e s t e r i c s t r a i n a s s o c i a t e d w i t h t h e a p p r o a c h o f a n u c l e o p h i l e f r o m t h e same s i d e a s t h e c a r b o m e t h o x y g r o u p - b e a r i n g b r i d g e . F i g u r e 1 3 . B u c h i ' s p a r t i a l s y n t h e s i s o f d i m e r i c V o a c a n g a a l k a l o i d s . - 6 3 -I n a n a n a l o g o u s s t u d y H a r l e y - M a s o n and Rahman r e p o r t e d t h e s y n t h e s i s o f two e p i m e r i c 1 8 - h y d r o x y - d i h y d r o c l e a v a m i n e s (92 a n d 9 3 ) , e p i m e r i c a b o u t t h e C . p o s i t i o n o n l y . When t h e m i x t u r e o f t h e s e two e p i m e r s was t r e a t e d w i t h one e q u i v a l e n t o f v i n d o l i n e (10) i n m e t h a n o l c o n t a i n i n g 1% h y d r o g e n c h l o r i d e ; two s e p a r a b l e d i m e r s c o u l d be i s o l a t e d . Had t h e d i m e r i z a t i o n n o t b e e n s t e r e o s e l e c t i v e , e a c h C . , i s o m e r w o u l d h a v e y i e l d e d two C 1 Q , e p i m e r s 4 l o and t h u s f o u r d i a s t e r e o m e r i c compounds w o u l d be e x p e c t e d . The c o m p l e t e s t e r e o s e l e c t i v i t y i s more d i f f i c u l t t o e x p l a i n i n t h i s c a s e t h a n i n t h e p r e v i o u s c a s e o f v o a c a m i n e ( 9 0 ) . I n d e e d a p l a n a r , l o n g - l i v e d c a r b o n i u m i o n a p p e a r s q u i t e u n l i k e l y i n b o t h c a s e s . I n 1 9 6 8 , i n a n a t t e m p t t o e l u c i d a t e t h e s t r u c t u r e s o f two n a t u r a l l y d e r i v e d compounds d e s i g n a t e d d e o x y V L B ' A ' and d e o x y V L B ' B ' , t h e L i l l y g r o u p c a r r i e d o u t a n i n t e r e s t i n g s e r i e s o f t r a n s f o r m a t i o n s . ^ F i r s t , d e o x y V L B ' A ' , u p o n c l e a v a g e w i t h c o n c e n t r a t e d h y d r o c h l o r i c a c i d u s i n g s t a n n o u s c h l o r i d e a n d t i n , y i e l d e d d e a c e t y l v i n d o l i n e and 4 a - d i h y d r o -c l e a v a m i n e . L e u r o s i n e (18) ( C „ , . , e p o x y d i m e r ) c o u l d be t r e a t e d w i t h - 64 -Raney nickel in ethanol under reflux to yield an isomer - deoxy VLB'B' -which could be shown by an analogous cleavage reaction to contain the 43-dihydrocleavamine moiety. Deoxy VLB'A' and 'B' were thus designated as C^, ethyl epimers of each other. In an attempted partial synthesis of deoxy VLB'B', these workers transformed 43-dihydrocleavamine to i t s chloroindolenine by standard methods. Treatment of this compound with vindoline in 1.5% methanolic hydrogen chloride resulted in the isolation of a single dimeric compound. This product was a third compound - deoxy VLB'C'. The conversion of a l l three compounds to their decarbomethoxy -deacetyl hydrazides showed that decarbomethoxy-deacetyl-deoxy VLB'A' and 'B' hydrazides were not isomeric about C.Q, because their nmr spectra lo clearly showed the same chemical shift for the new C Q, proton at about l o T 6.5. On the other hand, decarbomethoxy-deacetyl-deoxy VLB'C' hydrazide was isomeric at C. o l to both these compounds as evidenced by a displace-lo ment of i t s C. O I proton by about 1 T unit downfield to T 5.5. Further, lo an attempted isomerization of any of these compounds i n 1% methanolic hydrogen chloride i n the deoxy VLB hydrazide series f a i l e d . The treatment of decarbomethoxy-deacetyl-VLB hydrazide i t s e l f , however, with 1.5% methanolic hydrogen chloride achieved epimerization to the corres-ponding C 1 Q, epimer. These conclusions were a l l based solely on the lo chemical shift of the C 1 0 f proton introduced during the hydrazide l o formation. It was thus impossible to decide which one of a pair of epimeric dimers possessed a stereochemistry at the c r i t i c a l C 1 Q, centre l o which was similar to that obtained in the natural dimers (this w i l l henceforth be called the natural stereochemistry at C 1 0, and the corres-l o ponding epimer w i l l be designated as the unnatural stereochemistry). - 65 -JLUt A r e c e n t X - r a y s t u d y , k i n d l y p e r f o r m e d b y P r o f e s s o r J . C . C l a r d y i n c o l l a b o r a t i o n w i t h o u r l a b o r a t o r y , h a s b e e n i m m e n s e l y u s e f u l i n t h i s a n d o t h e r a r e a s . I t w i l l be d i s c u s s e d a t a l a t e r s t a g e . I n o u r l a b o r a t o r i e s i t was d i s c o v e r e d t h a t t h e t r e a t m e n t o f c h l o r o i n d o l e n i n e s o f c l e a v a m i n e - t y p e m o l e c u l e s w i t h v i n d o l i n e i n 1.5% m e t h a n o l i c h y d r o g e n c h l o r i d e r e s u l t e d i n a good o v e r a l l c o n v e r s i o n t o d i m e r i c m a t e r i a l . ^ T h i s r e a c t i o n has come t o be c a l l e d " t h e d i m e r i z a t i o n r e a c t i o n " . A t t h e t i m e t h i s r e s e a r c h was i n i t i a t e d , w h a t h a s b e e n d e s c r i b e d a b o v e i s a l l t h a t was known r e g a r d i n g t h i s d i m e r i z a t i o n r e a c t i o n . S e v e r a l i m p o r t a n t q u e s t i o n s a b o u t t h e d e t a i l s o f t h i s r e a c t i o n r e m a i n e d u n a n s w e r e d . A s h a s b e e n m e n t i o n e d p r e v i o u s l y , i n two s e r i e s ( v o a c a n g a a n d V L B -t y p e ) t h e d i m e r i z a t i o n r e a c t i o n i n v o l v i n g , p o s s i b l y , a n i m i n e o f t h e t y p e d e p i c t e d i n compounds 7 7 , 8 1 o r 8 3 , h a d y i e l d e d , s t e r e o s e l e c t i v e l y o n l y one p r o d u c t i n t h e h a n d s o f s e v e r a l w o r k e r s . The c o u p l i n g o f 1 8 - c a r b o m e t h o x y - 4 B - d i h y d r o c l e a v a m i n e and 4 6 - d i h y d r o c l e a v a m i n e w i t h v i n d o l i n e i n o u r own l a b o r a t o r y v i a t h e i r r e s p e c t i v e c h l o r o i n d o l e n i n e s h a d y i e l d e d i n e a c h c a s e a s i n g l e d i m e r i c compound 94 a n d 96 r e s p e c t i v e l y . CH 3 - 66 -B e f o r e any o t h e r i n v e s t i g a t i o n s c o u l d be p e r f o r m e d , i t was i m p e r a t i v e t o d e t e r m i n e i f a n e p i m e r i c d i m e r was p r e s e n t a t a l l i n t h e s e r e a c t i o n m i x t u r e s . A n e x h a u s t i v e s e a r c h o f t h e r e a c t i o n m i x t u r e s f r o m t h e a b o v e d i m e r i z a t i o n s was c a r r i e d o u t . One h u n d r e d p e r c e n t b y w e i g h t o f t h e r e a c t i o n m i x t u r e was a c c o u n t e d f o r . A l l p r o d u c t s , o t h e r t h a n t h e d i m e r s a c t u a l l y i s o l a t e d p r e v i o u s l y and m e n t i o n e d a b o v e , w e r e f o u n d t o be m o n o m e r i c and c o u l d be c l a s s i f i e d a s i n d o l e o r d i h y d r o i n d o l e o n t h e b a s i s o f t h e i r u l t r a v i o l e t s p e c t r a . T h u s , t h e s t e r e o s e l e c t i v i t y o f t h i s r e a c t i o n was e s t a b l i s h e d t o b e 100% i n b o t h c a s e s , and t h e p o s s i b i l i t y t h a t t h e d e s i r e d d i m e r s w e r e b e i n g f o r m e d i n e i t h e r c a s e , e v e n i n m i n u t e a m o u n t s , was r u l e d o u t . A t t e n t i o n was now t u r n e d t o a n i n v e s t i g a t i o n o f t h e g e n e r a l i t y o f t h e d i m e r i z a t i o n r e a c t i o n . I n o r d e r t o a c h i e v e a s y n t h e s i s o f t h e n a t u r a l compounds i t was c l e a r t h a t a t some s t a g e , t h e d i m e r i z a t i o n o f 3 , 4 -f u n c t i o n a l i z e d c l e a v a m i n e t e m p l a t e s w o u l d be n e c e s s a r y . S i n c e s u c h t e m p l a t e s w e r e a l r e a d y a v a i l a b l e f r o m t h e w o r k d e s c r i b e d i n P a r t I o f t h i s D i s c u s s i o n , i t seemed l o g i c a l t o u s e them i n a n a t t e m p t t o t e s t t h e g e n e r a l i t y o f t h e d i m e r i z a t i o n c o n d i t i o n s . The p r o d u c t s w o u l d p r o v i d e , f o r t h e f i r s t t i m e , s y n t h e t i c d i m e r s b e a r i n g f u n c t i o n a l i t y a t t h e same p o s i t i o n a s t h e n a t u r a l c o m p o u n d s . A s s u c h t h e y s h o u l d be u s e f u l i n t h e o v e r a l l s t u d y o f s t r u c t u r e - a c t i v i t y r e l a t i o n s i n t h i s s e r i e s o f d r u g s . I n v i e w o f t h e w o r k r e p o r t e d i n P a r t I , t h e l o g i c a l c h o i c e s o f i n d o l e t e m p l a t e s f o r t h i s i n v e s t i g a t i o n w e r e 1 8 3 - c a r b o m e t h o x y c l e a v a m i n e (29) and t h e 1 8 - c a r b o m e t h o x y - 4 3 - d i h y d r o c l e a v a m i n - 3 a - o l s (56 and 5 7 ) . These compounds w e r e now r e a d i l y a v a i l a b l e v i a t h e r o u t e a l r e a d y d e s c r i b e d a n d w o u l d s e r v e w e l l f o r a t e s t o f t h e g e n e r a l i t y o f t h e s o - c a l l e d - 67 -d i m e r i z a t i o n r e a c t i o n . I n o u r l a b o r a t o r i e s , i n t h e p a s t , s e v e r a l d i f f e r e n t c h l o r o i n d o l e n i n e s h a d b e e n p r e p a r e d f r o m c l e a v a m i n e - t y p e c o m p o u n d s . I n e a c h c a s e , t h e s e m a t e r i a l s c o u l d be i d e n t i f i e d by t h e f o l l o w i n g p r o p e r t i e s : (a) I n t h e i n f r a r e d s p e c t r a o f t h e s e compounds t h e s h a r p a b s o r p t i o n a t a b o u t 3440 cm ^ a t t r i b u t a b l e t o t h e i n d o l e N - H s t r e t c h o f t h e p a r e n t compound h a d d i s a p p e a r e d . (b ) The u l t r a v i o l e t s p e c t r a o f t h e s e compounds showed a c h a n g e f r o m t h e n o r m a l i n d o l e a b s o r p t i o n s a t 2 9 3 , 2 8 5 , 278 a n d 226 nm ( l o g e 3 . 8 , 3 . 9 , 3 . 8 and 4 . 5 r e s p e c t i v e l y ) t o 2 2 7 , 260 and 303 nm ( l o g e 4 . 3 , 3 . 5 a n d 3 . 4 r e s p e c t i v e l y ) when t h e s e s p e c t r a w e r e m e a s u r e d i n i s o o c t a n e s o l u t i o n . T h e s e c h a n g e s w e r e r a t h e r s u b t l e , a n d c o u l d o n l y be o b s e r v e d when t h e s p e c t r a w e r e r u n i n i s o o c t a n e . ( c ) When d e v e l o p e d o n a n a l u m i n a t i c p l a t e u s i n g t h e s o l v e n t s y s t e m a m e n a b l e t o t h e d e t e c t i o n o f t h e p a r e n t c o m p o u n d , t h e y a p p e a r e d a l w a y s a s s l i g h t l y more p o l a r s p o t s . These compounds gave a r e m a r k a b l y b r i g h t p i n k c o l o r when s p r a y e d w i t h e e r i e s u l f a t e w h e r e a s t h e p a r e n t compounds w e r e a l i g h t , a l m o s t i n v i s i b l e b l u e . Upon s p r a y i n g a n o t h e r s i m i l a r l y d e v e l o p e d p l a t e w i t h a n t i m o n y p e n t a c h l o r i d e i n c a r b o n t e t r a c h l o r i d e t h e p a r e n t b a s e a p p e a r e d a s a n i n t e n s e b r o w n o r g r e e n s p o t w h e r e a s t h e c h l o r o i n d o l e n i n e was u n d e v e l o p e d . These t h r e e m e t h o d s , w e r e s e n s i t i v e a n d p r o v i d e d a c o n v e n i e n t method f o r m o n i t o r i n g t h e p r o g r e s s o f a c h l o r o i n d o l e n i n e - f o r m i n g r e a c t i o n . P r o c e e d i n g , i n a l o g i c a l f a s h i o n t h e n , t h e c h l o r o i n d o l e n i n e o f 1 8 8 -c a r b o m e t h o x y c l e a v a m i n e (98) was p r e p a r e d . The r e a c t i o n was p e r f o r m e d I n t h e u s u a l way by r e a c t i n g a d i l u t e s o l u t i o n o f _ t - b u t y l h y p o c h l o r i t e 68 -i n c a r b o n t e t r a c h l o r i d e a t l o w t e m p e r a t u r e , s l o w l y , w i t h a s o l u t i o n o f 1 8 8 - c a r b o m e t h o x y c l e a v a m i n e (29) i n m e t h y l e n e c h l o r i d e . The r e a c t i o n p r o c e e d e d a l m o s t as a t i t r a t i o n a n d upon c h e c k i n g t h e r e a c t i o n m i x t u r e by t h e t i c t e c h n i q u e d e s c r i b e d a b o v e , i t was e s t i m a t e d t o h a v e p r o c e e d e d i n g r e a t e r t h a n 95% y i e l d . The m a t e r i a l c o u l d be p u r i f i e d t o y i e l d a n a n a l y t i c a l s a m p l e b y c o l u m n c h r o m a t o g r a p h y on a l u m i n a . T h i s m a t e r i a l c o u l d be shown t o h a v e a l l t h e s p e c t r a l and p h y s i c a l p r o p e r t i e s i n a c c o r d w i t h i t s p o s t u l a t e d s t r u c t u r e a s t h e c h l o r o i n d o l e n i n e o f 1 8 6 -c a r b o m e t h o x y c l e a v a m i n e ( 9 8 ) . T h i s p u r i f i c a t i o n o f t h e c h l o r o i n d o l e n i n e h o w e v e r , p r o v e d t o b e a c o s t l y o n e . O n l y a 30% r e c o v e r y o f t h e p u r e c h l o r o i n d o l e n i n e c o u l d be r e a l i z e d t o g e t h e r w i t h a l a r g e amount o f o t h e r new d e c o m p o s i t i o n p r o d u c t s i n s u b s e q u e n t f r a c t i o n s . T h u s , a f t e r t h e i n i t i a l c h a r a c t e r i z a t i o n i t was r e s o l v e d t o r e a c t t h e " c r u d e " ( b u t u s u a l l y g r e a t e r t h a n 90% p u r e ) c h l o r o i n d o l e n i n e d i r e c t l y i n t h e n e x t s t e p . The a b o v e r e s u l t was n o t e n t i r e l y a n e x p e c t e d o n e . _ t - B u t y l h y p o c h l o r i t e i s a p o w e r f u l s o u r c e o f " p o s i t i v e " h a l o g e n and a s s u c h , i s a s t r o n g e l e c t r o p h i l e . T h u s , i t may h a v e r e a c t e d w i t h t h e 3 , 4 d o u b l e b o n d i n s t e a d o f , o r a s w e l l a s , t h e i n d o l e m o i e t y . The c o m p l e t e and i n s t a n t a n e o u s r e a c t i o n a t t h e i n d o l e , t o f o r m t h e c h l o r o i n d o l e n i n e , i s a t e s t i m o n i a l o f t h e e x t r e m e r e a c t i v i t y o f t h i s c h r o m o p h o r e t o w a r d s s u c h (29) (98) - 69 -r e a g e n t s . The a c h i e v e m e n t o f c h l o r i n a t i o n o f 1 8 - c a r b o m e t h o x y c l e a v a m i n e , was e n c o u r a g i n g and a n e x p l o r a t i o n o f w h e t h e r d i m e r i z a t i o n w o u l d a l s o o c c u r u n d e r t h e u s u a l c o n d i t i o n s was u n d e r t a k e n . The c h l o r o i n d o l e n i n e (98) was p r e p a r e d as a b o v e . T h i s t i m e h o w e v e r , when t h e r e a c t i o n was deemed t o be c o m p l e t e , by t h e v a r i o u s c r i t e r i a d e s c r i b e d a b o v e , i t was w o r k e d up by s i m p l y e v a p o r a t i n g t h e s o l v e n t s a t 0°C u n d e r h i g h vacuum t o y i e l d a f o a m . To t h i s f o a m , one e q u i v a l e n t o f v i n d o l i n e was a d d e d f o l l o w e d b y a s o l u t i o n o f 1.5% h y d r o g e n c h l o r i d e i n m e t h a n o l . The r e a c t i o n m i x t u r e was t h e n r e f l u x e d f o r t h r e e h o u r s . H o w e v e r , w o r k u p , f o l l o w e d by a c h e c k o f t h e c r u d e r e a c t i o n m i x t u r e by t i c , a f f o r d e d t h e r a t h e r d i s a p p o i n t i n g e v i d e n c e t h a t t h e r e was no d e t e c t a b l e d i m e r i c m a t e r i a l . S t a r t i n g m a t e r i a l s o f b o t h h a l v e s w e r e e a s i l y i d e n t i f i e d by t h e i r v a l u e s a n d c h a r a c t e r i s t i c c o l o r - r e a c t i o n s . D e a c e t y l v i n d o l i n e a n d v i n d o l i n e a c c o u n t e d f o r v i r t u a l l y a l l o f t h e d i h y d r o i n d o l e t y p e m a t e r i a l . The o n l y new compound i n t h e r e a c t i o n m i x t u r e h a d a c h a r a c t e r i s t i c b l u e c o l o r - r e a c t i o n o n t i c t o a n t i m o n y p e n t a c h l o r i d e i n c a r b o n t e t r a c h l o r i d e . T h i s m a t e r i a l was p u r i f i e d and e x a m i n e d s p e c t r o s c o p i c a l l y . Though i t s s t r u c t u r e i s a s y e t u n k n o w n , no s i n g l e p i e c e o f e v i d e n c e s u p p o r t e d t h e v i e w t h a t i t was d i m e r i c . Thus t h e u l t r a v i o l e t s p e c t r u m o f t h i s compound was t h a t o f a d i h y d r o i n d o l e . S i n c e v i n d o l i n e a n d d e a c e t y l v i n d o l i n e a l r e a d y a c c o u n t e d f o r a l l o f t h e A s p i d o s p e r m a p o r t i o n i t was c l e a r t h a t t h i s s u b s t a n c e was d e r i v e d f r o m t h e c h l o r o i n d o l e n i n e . The nmr s p e c t r u m o f t h i s compound was a l s o r e m i n i s c e n t o f a C^, . s u b s t i t u t e d A s p i d o s p e r m a - t y p e s k e l e t o n . However t h e mass s p e c t r u m l a c k e d a l l o f t h e c h a r a c t e r i s t i c f r a g m e n t a t i o n o f t h e A s p i d o s p e r m a a l k a l o i d s a n d showed a m o l e c u l a r i o n p e a k a t m/e = 3 7 0 . I n d e e d , t r e a t m e n t o f t h e - 70 -c h l o r o i n d o l e n i n e (98) i n a b s o l u t e m e t h a n o l w i t h o n l y a t r a c e o f a c i d as c a t a l y s t r e s u l t e d i n a c o n v e r s i o n t o t h i s compound t o g e t h e r w i t h o t h e r d e c o m p o s i t i o n p r o d u c t s . T r e a t m e n t o f v i n d o l i n e , on t h e o t h e r h a n d , i n m e t h a n o l i c h y d r o g e n c h l o r i d e , r e s u l t e d o n l y i n a c o n v e r s i o n t o a m i x t u r e o f v i n d o l i n e and d e a c e t y l v i n d o l i n e . The s t r u c t u r e o f t h e l a t t e r c o u l d be p r o v e d by c o m p a r i n g i t w i t h a n a u t h e n t i c s a m p l e as w e l l a s b y a c e t y l a t i n g i t u n d e r t h e u s u a l c o n d i t i o n s ( a c e t i c a n h y d r i d e a n d p y r i d i n e a t room t e m p e r a t u r e ) t o y i e l d a g a i n , v i n d o l i n e . Thus t h e o r i g i n o f t h i s b l u e s p o t was e s t a b l i s h e d . Though s e v e r a l schemes may be w r i t t e n f o r t h e d e r i v a t i o n o f t h e r e q u i s i t e s k e l e t o n f r o m t h e c h l o r o i n d o l e n i n e none o f t h e s e was c o m p a t i b l e w i t h a l l t h e a v a i l a b l e e v i d e n c e . B e c a u s e o f i t s n o n - d i m e r i c n a t u r e , t h i s p a r t i c u l a r compound was n o t s t u d i e d i n d e t a i l . I n s p i t e o f t h i s r a t h e r d i s c o u r a g i n g i n i t i a l r e s u l t , i t was f e l t t h a t t h e d i m e r i z a t i o n s h o u l d p r o c e e d , a t l e a s t i n p a r t , and t h u s a n o t h e r r e a c t i o n was p e r f o r m e d . T h i s t i m e , i n s t e a d o f t h e u s u a l p u r i f i c a t i o n by c o l u m n c h r o m a t o g r a p h y o n a l u m i n a , a s e p a r a t i o n o n t h e b a s i s o f m o l e c u l a r s i z e was a t t e m p t e d u s i n g g e l p e r m e a t i o n c h r o m a t o g r a p h y o n Sephadex L H - 2 0 . S e v e r a l a d v a n t a g e s w e r e a n t i c i p a t e d b y t h i s d e v i a t i o n f r o m t h e n o r m a l w o r k u p p r o c e d u r e s . F i r s t , t h e p a c k i n g m a t e r i a l was c o m p l e t e l y i n e r t , i n t h e s e n s e t h a t no c h e m i c a l r e a c t i o n b e t w e e n t h e s u b s t r a t e and t h e p a c k i n g m a t e r i a l c o u l d be v i s u a l i z e d . S e c o n d l y , a s t e a d y e l u t i o n w i t h o n l y one s o l v e n t was r e q u i r e d so t h a t t h i s s o l v e n t c o u l d be p u r i f i e d t h o r o u g h l y b e f o r e b e g i n n i n g t h e c h r o m a t o g r a p h y so as t o r i d i t o f any d e t r i m e n t a l i m p u r i t i e s . T h i r d , t h e c o l u m n was e s s e n t i a l l y i n d e f i n i t e l y r e u s a b l e . I f a n a d e q u a t e l y e f f i c i e n t c o l u m n and s o l v e n t w e r e f o u n d , i t c o u l d be r e p e a t e d l y u s e d f o r t h e r o u t i n e - 71 -s e p a r a t i o n o f a l l d i m e r i z a t i o n r e a c t i o n m i x t u r e s . F i n a l l y , s i n c e t h e l a r g e r m o l e c u l e s w e r e e x p e c t e d t o be d i s p l a c e d t h r o u g h t h e g e l f i r s t , t h e d i m e r s w o u l d be q u i c k l y removed f r o m c o n t a c t w i t h t h e c o l u m n ; t h u s c o r r e s p o n d i n g l y d i m i n i s h i n g t h e c h a n c e o f d e c o m p o s i t i o n on t h e c o l u m n . By t h i s t e c h n i q u e , f r o m a r e a c t i o n m i x t u r e o f 800 mg a s a m p l e o f 60 mg o f t h e d i m e r (99) o f 1 8 - c a r b o m e t h o x y c l e a v a m i n e and v i n d o l i n e c o u l d be i s o l a t e d p u r e (10% y i e l d ) . T h i s p r o v e d t o be t h e o p t i m a l y i e l d t h a t c o u l d be r e a l i z e d a n d v a r i o u s o t h e r a t t e m p t e d i m p r o v e m e n t s f a i l e d t o i n c r e a s e t h e amount o f t h i s compound f o r m e d i n any d i m e r i z a t i o n r e a c t i o n (99) - 72 -u s i n g t h e s e c o n d i t i o n s . The u l t r a v i o l e t s p e c t r u m o f t h i s compound was a n e x a c t s u m m a t i o n o f i n d o l e and d i h y d r o i n d o l e a b s o r p t i o n s and was a l m o s t c o m p l e t e l y s u p e r i m p o s a b l e on t h a t o f compounds 94 a n d 96 a s w e l l as t h e known n a t u r a l d i m e r s , VLB and V C R . T h u s , t h e u l t r a v i o l e t s p e c t r u m a l o n e p r o v i d e d a s t r o n g s u p p o r t f o r t h e s t r u c t u r e o f 9 9 . The nmr s p e c t r u m ( F i g u r e 14) o f t h i s compound s i m i l a r l y was e x a c t l y a s e x p e c t e d o n t h e b a s i s o f p r e v i o u s e x p e r i e n c e ( see F i g u r e 15 f o r t h e nmr s p e c t r u m o f VLB and F i g u r e 16 f o r t h a t o f compound 9 4 ) . The p o s i t i o n o f d i m e r i z a t i o n was e s t a b l i s h e d a s b e i n g b e t w e e n C . ^ o n v i n d o l i n e and C Q 15 l o o n 1 8 - c a r b o m e t h o x y c l e a v a m i n e b y , (a) t h e d i s a p p e a r a n c e o f t h e s i g n a l a t t r i b u t a b l e t o t h e C . D p r o t o n i n t h e s t a r t i n g m a t e r i a l a t T 5 . 6 2 a n d lei (b) t h e d i s a p p e a r a n c e o f t h e d o u b l e t o f d o u b l e t s c o r r e s p o n d i n g t o t h e C . ^ p r o t o n o f v i n d o l i n e a t T 3 . 7 0 ( J = 2 . 5 and 8 c p s ) ( s e e F i g u r e 17) and t h e a c c o m p a n y i n g c o l l a p s e o f t h e s i g n a l s a t t r i b u t a b l e t o t h e p r o t o n s a t C ^ ^ a n d C ^ t o s i n g l e t s due t o a l a c k o f o r t h o - and m e t a - c o u p l i n g r e s p e c t i v e l y . The c o m p l e t e d e t a i l s o f t h e s t r u c t u r e o f t h i s compound w e r e p r o v e d p r i m a r i l y i n two w a y s . F i r s t , a s a m p l e o f compound 99 was c l e a v e d u s i n g 7% m e t h a n o l i c h y d r o g e n c h l o r i d e c o n t a i n i n g s t a n n o u s c h l o r i d e a n d t i n . The p r o d u c t s w e r e c o m p a r e d o n t h e b a s i s o f t h i n l a y e r c h r o m a t o g r a p h y and i n f r a r e d s p e c t r o s c o p y a f t e r i s o l a t i o n o f e a c h c o m p o n e n t . C l e a v a m i n e ( 2 1 ) , v i n d o l i n e ( 1 0 ) , d e a c e t y l v i n d o l i n e , and s t a r t i n g d i m e r (99) w e r e t h e o n l y compounds i s o l a t e d . T h u s , t h e r e h a d b e e n no u n e x p e c t e d r e a r r a n g e m e n t s d u r i n g d i m e r i z a t i o n , and compound 99 i n d e e d d i d h a v e t h e s t r u c t u r e s h o w n . I t was now n e c e s s a r y t o e s t a b l i s h t h e s t e r e o c h e m i c a l r e l a t i o n s h i p a t C 1 Q t i n t h i s compound t o t h a t i n compound 9 4 . To t h i s l o 6,26 T 1 1 1 1 1 1 1 1 r F i g u r e 1 5 . Nmr s p e c t r u m o f v i n b l a s t i n e (VLB) ( 1 5 ) . - 75 -F i g u r e 1 7 . Nmr s p e c t r u m o f v i n d o l i n e ( 1 0 ) . - 77 -e n d , a s e r i e s o f r e a c t i o n s c u l m i n a t i n g i n a d i r e c t c o r r e l a t i o n o f compounds 94 and 99 was e x e c u t e d . V i n d o l i n e (10) was h y d r o g e n a t e d by s t a n d a r d methods t o y i e l d d i h y d r o v i n d o l i n e ( 1 0 0 ) . Compound 100 was t r e a t e d w i t h t h e c h l o r o i n d o l e n i n e (101) p r e p a r e d f r o m 1 8 - c a r b o m e t h o x y - 4 g - d i h y d r o c l e a v a m i n e ( 3 0 ) , u n d e r t h e u s u a l d i m e r i z a t i o n c o n d i t i o n s t o y i e l d ( i n a p p r o x i m a t e l y 70% y i e l d ) t h e t e t r a h y d r o a n a l o g u e (102) o f compound 9 9 . T h i s compound was f u l l y c h a r a c t e r i z e d b y p h y s i c a l and s p e c t r o s c o p i c m e t h o d s , a l l o f w h i c h w e r e e n t i r e l y i n a c c o r d a n c e w i t h t h e p o s t u l a t e d s t r u c t u r e . Of p a r t i c u l a r v a l u e , i n t h i s c a s e , was t h e nmr s p e c t r u m w h i c h i s shown i n F i g u r e 1 8 . Now compound 94 was h y d r o g e n a t e d i n e t h a n o l o v e r A d a m ' s c a t a l y s t o n a q u a n t i t a t i v e b a s i s . The u p t a k e o f one m o l e o f h y d r o g e n was n o t e d a n d , u p o n w o r k u p , a d i m e r was i s o l a t e d w h i c h was i d e n t i c a l i n e v e r y r e s p e c t ; i n c l u d i n g s u p e r i m p o s a b l e n m r , i r , a n d mass s p e c t r a l f r a g m e n t a t i o n a s w e l l a s u n d e p r e s s e d m i x e d m e l t i n g p o i n t ; w i t h compound 102 o b t a i n e d a b o v e . The s t e r e o c h e m i s t r y a b o u t t h e C 1 0 , p o s i t i o n f o r compound 102 was t h u s u n a m b i g u o u s l y e s t a b l i s h e d as b e i n g t h e same as t h a t i n compound 9 4 . S i m i l a r t r e a t m e n t o f compound 99 y i e l d e d , a g a i n , a compound w h i c h was i d e n t i c a l i n e v e r y r e s p e c t t o compound 102 o b t a i n e d b y b o t h o f t h e a b o v e r o u t e s . T h i s s e q u e n c e i s s u m m a r i z e d i n F i g u r e 19 b e l o w and c o n c l u s i v e l y e s t a b l i s h e s t h e s t r u c t u r e o f compound 99 a n d 102 i n e v e r y d e t a i l i n c l u d i n g t h e r e l a t i v e s t e r e o c h e m i s t r y a b o u t C , O I . The ' l o l a t t e r was a g a i n shown t o be t h e same a s i n compound 94 i n b o t h c a s e s . F i g u r e 1 9 . P r o o f o f t h e s t r u c t u r e o f compound 9 9 . - 80 -I t s h o u l d be p o i n t e d o u t t h a t t h e c o n d i t i o n s o f h y d r o g e n a t i o n u s e d , n a m e l y u s i n g t h e f r e e b a s e s and a b s o l u t e e t h a n o l , c a u s e d s e v e r e l o s s e s o f m a t e r i a l r e s u l t i n g i n a p o o r r e c o v e r y o f t h e p r o d u c t o f any g i v e n d i m e r h y d r o g e n a t i o n . T h i s was u n d o u b t e d l y due t o t h e a t t a c h m e n t o f t h e amine p o r t i o n o f t h e s e d i m e r s t o t h e p l a t i n u m c a t a l y s t . The p o i s o n i n g o f c a t a l y s t s by a m i n e s i s i n f a c t a w e l l - k n o w n phenomenon. O t h e r g r o u p s o f w o r k e r s ' ^ " ' ' ^ " ^ h a v e c i r c u m v e n t e d t h i s p r o b l e m b y p e r f o r m i n g t h e h y d r o g e n a t i o n o f VLB i n e t h a n o l c o n t a i n i n g some h y d r o g e n c h l o r i d e . The f o r m a t i o n o f t h e h y d r o c h l o r i d e s a l t s b l o c k s a n y p o s s i b l e i n t e r a c t i o n b e t w e e n t h e a m i n e a n d t h e c a t a l y s t and makes t h e r e a c t i o n s y n t h e t i c a l l y u s e f u l . The l o w y i e l d o f compound 99 o b t a i n e d by t h e u s u a l d i m e r i z a t i o n r e a c t i o n s e q u e n c e p r o m p t e d a s t u d y o f some o t h e r m o d i f i c a t i o n s o f t h i s p r o c e d u r e w i t h t h e a i m o f i n c r e a s i n g t h i s y i e l d . The f i r s t a r e a t o be i n v e s t i g a t e d was t h e c h l o r o i n d o l e n i n e f o r m a t i o n . The u s e o f 1 - c h l o r o b e n z o t r i a z o l e (103) as a m i l d and s e l e c t i v e c h l o r i n a t i n g a g e n t f o r v a r i o u s i n d o l e s h a d b e e n r e p o r t e d " * " ^ and i t was r e s o l v e d t o s e e i f t h i s a g e n t c o u l d a f f e c t t h e y i e l d o f t h e d i m e r f o r m e d i n t h e s u b s e q u e n t s t e p . The c h l o r o i n d o l e n i n e was p r e p a r e d i n t h e p r e s c r i b e d manner u s i n g t h i s r e a g e n t , and a f t e r w o r k u p , was s u b j e c t e d t o t h e u s u a l d i m e r i z a t i o n i n 1.5% m e t h a n o l i c h y d r o g e n c h l o r i d e . The y i e l d o f CI (103) - 81 -i s o l a t e d d i m e r was 8 .0%. T h u s , on t h e b a s i s o f t h e p u r i t y o f t h e r e s u l t i n g c h l o r o i n d o l e n i n e as w e l l a s t h e y i e l d o f t h e d i m e r f o r m e d , t h e r e was n o t h i n g t o be g a i n e d i n t h i s c a s e by u s i n g t h e newer r e a g e n t . S i n c e t h e p r o b l e m o f l o w y i e l d seemed t o c e n t r e o n t h e d i m e r i z a t i o n r e a c t i o n i t s e l f , i t was d e c i d e d t o a t t e m p t , e m p i r i c a l l y , t o f i n d t h e o p t i m u m c o n d i t i o n s f o r t h e f o r m a t i o n o f t h e d e s i r e d d i m e r i n t h i s c a s e . V a r i a t i o n s o f r e a c t i o n t e m p e r a t u r e and t i m e o f r e a c t i o n r e s u l t e d i n some i m p r o v e m e n t s i n t h e y i e l d o f t h e d e s i r e d m a t e r i a l . The o p t i m u m c o n d i t i o n s w e r e r e a l i z e d when a 1.5% m e t h a n o l i c h y d r o g e n c h l o r i d e s o l u t i o n o f t h e r e a c t a n t s was s t i r r e d a t room t e m p e r a t u r e f o r t e n d a y s . The r e s u l t i n g c r u d e r e a c t i o n m i x t u r e c o u l d t h e n be p u r i f i e d t o a f f o r d a 20% y i e l d o f d i m e r 9 9 . The s o - c a l l e d b l u e s p o t was c o r r e s p o n d i n g l y d i m i n i s h e d i n amount i n t h i s c a s e . A p a r a l l e l s t a n d a r d d i m e r i z a t i o n r e a c t i o n p e r f o r m e d on t h e same s a m p l e o f c h l o r o i n d o l e n i n e a f f o r d e d a n 8% y i e l d o f t h e d i m e r and p r o v e d t h a t t h i s m o d i f i c a t i o n h a d i n d e e d r e s u l t e d i n a g e n u i n e i m p r o v e m e n t o f t h e o v e r a l l y i e l d o f d e s i r e d 108 m a t e r i a l . I t s h o u l d be p o i n t e d o u t t h a t Rahman h a s r e c e n t l y i n d e p e n d e n t l y r e p o r t e d t h e s y n t h e s i s o f compound 99 by s t a n d a r d m e t h o d s . No y i e l d s a r e q u o t e d and no a t t e m p t s t o o p t i m i z e r e a c t i o n c o n d i t i o n s w e r e r e p o r t e d . The p r e s e n c e o f a c i d c a t a l y s t s may i n t e r f e r e w i t h t h e c o u r s e o f t h e d i m e r i z a t i o n r e a c t i o n when t h e i n d o l e t e m p l a t e b e a r s some f u n c t i o n a l i t y a t t h e 3 , 4 p o s i t i o n s , by p r o m o t i n g e l i m i n a t i o n o f o x y g e n f u n c t i o n a l i t i e s f o r e x a m p l e , o r r e a r r a n g e m e n t s i n t h e c a r b o n s k e l e t o n i t s e l f . I n d e e d , s u c h r e a r r a n g e m e n t s must be i n v o l v e d i n t h e f o r m a t i o n o f t h e s o - c a l l e d b l u e s p o t m a t e r i a l m e n t i o n e d a b o v e . I f t h e a c i d c a t a l y s t c o u l d be r e p l a c e d by some o t h e r a g e n t t h a t w o u l d f u n c t i o n s i m i l a r l y , t h e n a - 82 -s u b s t a n t i a l i n c r e a s e i n t h e o v e r a l l y i e l d o f d i m e r s i n s u c h c a s e s must r e s u l t . By a n a l o g y t o t h e r e a s o n i n g o f o t h e r w o r k e r s m e n t i o n e d p r e v i o u s l y , i t was f e l t t h a t t h e h y d r o g e n c h l o r i d e f u n c t i o n s t o p r o t o n a t e t h e c h l o r i n e atom o f t h e c h l o r o i n d o l e n i n e , t h u s i n i t i a t i n g t h e f o r m a t i o n o f i o n 104 w h i c h b e a r s a s t r o n g r e s e m b l a n c e t o i o n s 7 7 , 81 and 8 3 . I f some o t h e r , n o n - a c i d i c m a t e r i a l c o u l d be u s e d t o a c h i e v e CI (98) ( 1 0 4 ) t h i s g o a l t h e n t h e d i m e r i z a t i o n c o u l d e s s e n t i a l l y be p e r f o r m e d u n d e r n e u t r a l c o n d i t i o n s . The s i l v e r ( I ) i o n i s j u s t s u c h a m a t e r i a l s i n c e i t i s e x p e c t e d t o r e a c t i r r e v e r s i b l y w i t h c h l o r i d e t o p r e c i p i t a t e s i l v e r c h l o r i d e . S i l v e r n i t r a t e i s a good s o u r c e o f s i l v e r ( I ) i o n s and t h e a n i o n i c s p e c i e s l e f t i n s o l u t i o n (NO^ ) i s n o t e x p e c t e d t o be s t r o n g l y n u c l e o p h i l i c i n c o m p a r i s o n t o v i n d o l i n e i t s e l f . S i l v e r n i t r a t e , h o w e v e r , p r o v e d t o be i n s o l u b l e i n most o r g a n i c s o l v e n t s . E t h y l e t h e r was f o u n d t o d i s s o l v e s i g n i f i c a n t amounts o f t h e r e a c t a n t s a s w e l l a s s i l v e r n i t r a t e and t h e i n i t i a l r e a c t i o n was p e r f o r m e d i n t h i s s o l v e n t . U n f o r t u n a t e l y , e v e n a f t e r s e v e r a l h o u r s o f r e f l u x , no d i m e r i c m a t e r i a l c o u l d be d e t e c t e d . S e v e r a l o t h e r a t t e m p t s t o i n d u c e t h i s r e a c t i o n t o p r o c e e d by u s i n g v a r i o u s c o - s o l v e n t s s u c h as d i m e t h y l s u l f o x i d e and t r i e t h y l a m i n e a l s o f a i l e d . I t a p p e a r s t h a t t h e a b i l i t y o f t h e s i l v e r i o n t o c o m b i n e w i t h t h e c h l o r i n e a tom b o u n d t o c a r b o n , and f o r c e c l e a v a g e - 83 -o f t h e c a r b o n - c h l o r i n e bond i s e x t r e m e l y l i m i t e d . T h i s may be due t o t h e s t e r i c b u l k o f t h e s i l v e r ( I ) i o n . I n d e e d , t h e g e n e r a l c o n c e p t o f t h i s a p p r o a c h may s t i l l p r o v e t o be a v a l i d o n e . H o w e v e r , f o r t h e t i m e b e i n g i t was a b a n d o n e d . The a t t a i n m e n t o f a l o w o v e r a l l y i e l d o f t h e d e s i r e d d i m e r i n t h e 3 4 A ' compound c o u l d , a t t h i s s t a g e , be i n t e r p r e t e d i n one o f two w a y s . E i t h e r i t was t h e r e s u l t o f some i n t e r a c t i o n s p e c u l i a r t o t h i s compound a l o n e and as s u c h c o m p l e t e l y i r r e l e v a n t t o t h e g e n e r a l s c h e m e ; o r i t was t h e f i r s t i n d i c a t i o n t h a t 3 , 4 f u n c t i o n a l i z e d i n d o l e t e m p l a t e s may u n d e r g o d i f f e r e n t s i d e r e a c t i o n s u n d e r t h e d i m e r i z a t i o n c o n d i t i o n s . I n o r d e r t o c a s t some l i g h t o n w h i c h one o f t h e s e two a l t e r n a t i v e s was c o r r e c t , a d i m e r i z a t i o n o f t h e a l c o h o l s (56 a n d 57) was i m p e r a t i v e . 1 8 8 - C a r b o m e t h o x y - 4 B - d i h y d r o c l e a v a m i n - 3 c x - o l (56) was t r e a t e d i n t h e u s u a l way w i t h _ t - b u t y l h y p o c h l o r i t e a n d t h e f o r m a t i o n o f t h e c h l o r o -i n d o l e n i n e was a g a i n m o n i t o r e d b y t h e t i c t e c h n i q u e m e n t i o n e d a b o v e . Compound 56 showed t h e e x p e c t e d r e a c t i v i t y t o t h i s r e a g e n t and t h e c h l o r o i n d o l e n i n e (105) was f o r m e d a l m o s t as s o o n a s t h e r e a g e n t h a d b e e n a d d e d . T h i s c r u d e c h l o r o i n d o l e n i n e , w h i c h was g r e a t e r t h a n 80% p u r e , was n o t p u r i f i e d f u r t h e r b u t i n s t e a d , was t r e a t e d w i t h one e q u i v a l e n t o f v i n d o l i n e w h i c h h a d b e e n d i s s o l v e d i n m e t h a n o l c o n t a i n i n g 1.5% h y d r o g e n c h l o r i d e . The r e s u l t i n g m i x t u r e was r e f l u x e d f o r t h r e e h o u r s a n d t h e n w o r k e d up and c h r o m a t o g r a p h e d o n d e a c t i v a t e d a l u m i n a t o y i e l d t h e d e s i r e d d i m e r (106) i n a n o v e r a l l y i e l d o f 8%. A s i m i l a r r e a c t i o n r u n s i m u l t a n e o u s l y was p u r i f i e d by g e l f i l t r a t i o n u s i n g t h e same Sephadex L H - 2 0 c o l u m n m e n t i o n e d a b o v e w i t h m e t h a n o l as e l u e n t . I n t h i s c a s e , a n 18% o v e r a l l y i e l d o f t h e same d i m e r (106) c o u l d be r e a l i z e d . T h i s d e m o n s t r a t e d t h a t , i n c a s e s w h e r e t h e o v e r a l l y i e l d o f d i m e r i c - 84 -m a t e r i a l was n o t h i g h , s e p h a d e x c h r o m a t o g r a p h y d i d i n d e e d p o s s e s s t h e a n t i c i p a t e d a d v a n t a g e s o v e r t h e more commonly u s e d a d s o r b e n t . A s e c o n d , and p e r h a p s more i m p o r t a n t , d e d u c t i o n c o u l d be made f r o m t h e a b o v e e x p e r i m e n t s . I n a l l t h e 3 , 4 f u n c t i o n a l i z e d c l e a v a m i n e t e m p l a t e s so f a r i n v e s t i g a t e d , t h e y i e l d o f d i m e r s , r e s u l t i n g f r o m t h e c o n v e n t i o n a l r e a c t i o n c o n d i t i o n s , was d r a m a t i c a l l y l o w e r t h a n i n t h e 3 , 4 d i h y d r o c a s e s w h e r e t h e y i e l d was u s u a l l y a p p r o x i m a t e l y 50-70%. I t c o u l d be s h o w n , b y a n e x a c t l y a n a l o g o u s r e a c t i o n s e q u e n c e t h a t t h e 18cx-carbomethoxy a l c o h o l (57) c o u l d a l s o be d i m e r i z e d i n t h e same w a v t o a f f o r d a g a i n , a n o v e r a l l y i e l d o f 15-20% o f d i m e r 1 0 6 . The i d e n t i t y o f t h i s d i m e r was p r o v e d by i t s u v and nmr s p e c t r a ( F i g u r e 20) i n a n a n a l o g o u s way t o t h e d i m e r 99 i n t h e 1 8 - c a r b o m e t h o x y c l e a v a m i n e c a s e . Mass s p e c t r a l d a t a o b t a i n e d w e r e a l s o e n t i r e l y i n a c c o r d w i t h t h i s s t r u c t u r e and c o n f i r m e d i t s d i m e r i c n a t u r e ( F i g u r e 2 1 ) . C l e a v a g e o f compound 106 u n d e r t h e u s u a l c o n d i t i o n s r e s u l t e d i n t h e i s o l a t i o n o f d i h y d r o c l e a v a m i n o l , v i n d o l i n e , a n d d e a c e t y l v i n d o l i n e w h i c h w e r e i d e n t i f i e d b y t i c and i r c o m p a r i s o n s w i t h t h e a u t h e n t i c m a t e r i a l s , t o g e t h e r w i t h t r a c e s o f t h e s t a r t i n g 1 8 - c a r b o m e t h o x y d i h y d r o c l e a v a m i n o l s (56 and 57) w h i c h w e r e i d e n t i f i e d b y t i c c o m p a r i s o n s a l o n e b e c a u s e o f t h e s m a l l amounts o f t h e s e m a t e r i a l s p r e s e n t . A n a t t e m p t e d d i m e r i z a t i o n o f b o t h t h e 1 8 - c a r b o m e t h o x y a l c o h o l s as t h e i r a c e t a t e s i n two s e p a r a t e r e a c t i o n s f a i l e d t o y i e l d any d e t e c t a b l e d i m e r i c m a t e r i a l a t a l l . T h e r e a p p e a r s t o be no t r u l y s a t i s f a c t o r y e x p l a n a t i o n o f t h i s o b s e r v a t i o n a l t h o u g h some e x p l a n a t i o n s i n v o l v i n g s t e r i c o r c o n f o r m a t i o n a l a r g u m e n t s may be o f f e r e d . I n summary, i t h a d b e e n e s t a b l i s h e d t h a t (a) i n e v e r y c a s e so f a r e x a m i n e d , t h e s t e r e o c h e m i c a l outcome o f t h e c o n v e n t i o n a l d i m e r i z a t i o n - 87 -r e a c t i o n was s u c h t h a t o n l y one e p i m e r a t C , was p r o d u c e d e n t i r e l y l o s t e r e o s e l e c t i v e l y and (b) t h e 3 , 4 f u n c t i o n a l i t y o f t h e t y p e e x a m i n e d so f a r r e s u l t e d i n some c o m p l i c a t i o n i n t h e n o r m a l r e a c t i o n s e q u e n c e s o t h a t t h e y i e l d o f d i m e r was d r a m a t i c a l l y r e d u c e d . I t was r e s o l v e d t o i n v e s t i g a t e c l o s e l y t h e s o - c a l l e d " c o n v e n t i o n a l " d i m e r i z a t i o n t e c h n i q u e i n o r d e r t o l e a r n s o m e t h i n g a b o u t t h e d e t a i l s o f t h e r e a c t i o n i t s e l f a s w e l l a s t o i n v e s t i g a t e t h e c o n d i t i o n s o f o p t i m u m r e a c t i o n i n much g r e a t e r d e t a i l t h a n p r e v i o u s l y . I t was f e l t t h a t p e r h a p s a s t u d y o f t h e m e c h a n i s m o f t h i s d i m e r i z a t i o n r e a c t i o n c o m b i n e d w i t h a t h o r o u g h u n d e r -s t a n d i n g o f t h e e f f e c t s o f v a r i o u s f a c t o r s s u c h as t e m p e r a t u r e , s o l v e n t s , e t c . may be c r i t i c a l i n t h e d e v e l o p m e n t o f any new and b e t t e r a p p r o a c h e s t o d i m e r i z a t i o n . The s t u d y o f t h e s y n t h e t i c d i m e r s o f s e v e r a l t y p e s h a d , f u r t h e r m o r e , p o i n t e d t o a n u n n a t u r a l s t e r e o c h e m i s t r y a t C 1 Q , i n t h e s e c o m p o u n d s . The d e t a i l e d a n d t h o r o u g h s t u d y m e n t i o n e d a b o v e l o may l e a d t o a n u n d e r s t a n d i n g o f why t h i s was t h e c a s e and w h a t c o u l d be done t o c h a n g e t h i s s i t u a t i o n . D i m e r s w i t h a n u n n a t u r a l s t e r e o c h e m i s t r y a b o u t C ^ g , w e r e n o t e n t i r e l y u n d e s i r a b l e s i n c e s u c h compounds w o u l d p r o v e u s e f u l f o r t h e o v e r a l l s t u d y o f s t r u c t u r e - a c t i v i t y r e l a t i o n s h i p s . I n d e e d d i m e r 9 6 , f o r e x a m p l e , h a s b e e n r e c e n t l y f o u n d t o p o s s e s s a 109 t h e r a p e u t i c i n d e x a t l e a s t a s good a s , i f n o t b e t t e r t h a n VCR ( 1 6 ) . T h i s compound may s o o n compete s u c c e s s f u l l y w i t h t h e r a r e a n d e x p e n s i v e n a t u r a l l y d e r i v e d d r u g a s a c l i n i c a l a n t i - c a n c e r a g e n t . T h i s s t u d y was v i s u a l i z e d as s e r v i n g a d u a l p u r p o s e : (a) I f a m e t h o d o f d i m e r i z i n g s e n s i t i v e c l e a v a m i n e t e m p l a t e s u n d e r m i l d c o n d i t i o n s i n h i g h y i e l d c o u l d be f o u n d , t h e s e compounds w o u l d become a v a i l a b l e f o r t h e f i r s t t i m e f o r c l i n i c a l e v a l u a t i o n as s y n t h e t i c a n a l o g s o f t h e n a t u r a l d r u g s . As s u c h t h e y w o u l d be e x p e c t e d t o c o n t r i b u t e t o t h e - 88 -u n d e r s t a n d i n g o f t h e s t r u c t u r e - a c t i v i t y r e l a t i o n s h i p s i n t h i s s e r i e s , (b) I f t h e m e c h a n i s m o f t h i s r e a c t i o n c o u l d be s u f f i c i e n t l y u n d e r s t o o d t o e n a b l e c h a n g e s i n t h e o v e r a l l s t e r e o s e l e c t i v i t y o f t h e d i m e r i z a t i o n s t e p so a s t o y i e l d d i m e r s w i t h t h e a l t e r n a t i v e s t e r e o c h e m i s t r y a t C Q , t h e n a m a j o r b r e a k t h r o u g h w o u l d s u r e l y h a v e b e e n a c h i e v e d . 18B - C a r b o m e t h o x y-4B - d i h y d r o c l e a v a m i n e (107) was c h o s e n as t h e s u b s t r a t e f o r t h i s s t u d y f o r s e v e r a l r e a s o n s . F i r s t , i t was a compound b e a r i n g t h e C . 0 c a r b o m e t h o x y g r o u p r e q u i r e d f o r t h e e v e n t u a l s y n t h e s i s l o o f n a t u r a l d i m e r s . I t c o u l d t h u s be u s e d as a n e f f e c t i v e m o d e l f o r a n y s t u d y o f t h e y i e l d o r s t e r e o c h e m i c a l e f f e c t s o f a n y c h a n g e i n r e a c t i o n c o n d i t i o n s b e c a u s e i t w o u l d p o s s e s s a l l t h e f u n c t i o n a l i t y n e c e s s a r y a t t h e c r i t i c a l c e n t r e ( C 1 0 , ) . S e c o n d , i t l a c k e d a n y c o m p l i c a t i o n i n t h e s e n s e t h a t i t p o s s e s s e d no 3,4 f u n c t i o n a l i t y . By u s i n g compound 107, f o r t h e t i m e b e i n g one c o u l d c o n c e n t r a t e o n i m p r o v i n g t h e r e a c t i o n c o n d i t i o n s i n a c a s e w h e r e t h e i s o l a t i o n o f t h e d i m e r i c p r o d u c t w o u l d n o t be u n d u l y l a b o r i o u s . F i n a l l y , a n d p e r h a p s most i m p o r t a n t o f a l l , a d i r e c t X - r a y s t r u c t u r e was a v a i l a b l e f o r t h e p r o d u c t o f t h e c o n v e n t i o n a l d i m e r i z a t i o n i n t h i s s e r i e s ( v i d e i n f r a ) so t h a t c o r r e l a t i o n s b e t w e e n i t and any new p r o d u c t o r p r o d u c t s , t h a t may r e s u l t , w o u l d be o n a s o u n d b a s i s . S i n c e one o f t h e g o a l s o f t h i s s t u d y was t o a t t e m p t t o r e d u c e , a s f a r a s p o s s i b l e , t h e s t e r e o s e l e c t i v i t y o f t h e d i m e r i z a t i o n s t e p , i t was n e c e s s a r y t o a n t i c i p a t e i n a d v a n c e t h e c h a n g e s w h i c h w o u l d be i n d u c e d i n t h e v a r i o u s s p e c t r a o f a d i m e r by a change i n i t s . s t e r e o -c h e m i s t r y a t C 1 0 , i n t h e C 1 o I c a r b o m e t h o x y d i m e r s e r i e s . A c o m p a r i s o n l o l o 84 o f t h e i r , n m r , and uv s p e c t r a o f compound 94 w i t h VLB (15) ( s e e - 89 -Figure 16 and 15 f o r these nmr spectra and Figure 22 for a uv comparison) showed that the degree of p o t e n t i a l usefulness of any of these techniques for d i s t i n g u i s h i n g between possible epimers at C 1 Q, was, i n ascending l o order: uv < i r < nmr. In other words, the u l t r a v i o l e t spectra of these two compounds were v i r t u a l l y superimposable with only a s l i g h t s h i f t of the absorptions of one compound r e l a t i v e to those of the other. This s h i f t could conceivably be diagnostic of a change i n stereochemistry at C^g, but i t could j u s t as e a s i l y be due to some other d i f f e r e n c e between these molecules. The i n f r a r e d spectra s i m i l a r l y , were not informative with regard to t h i s point because, as expected, the change i n stereochemistry could not s u b s t a n t i a l l y a l t e r the absorptions of so large and complex a molecule except i n the f i n g e r p r i n t region (1430-910 cm - 1). In contrast, the nmr s p e c t r a l comparison showed small but d e f i n i t e d i f f e r e n c e s p a r t i c u l a r l y i n the p o s i t i o n of the aromatic and protons of v i n d o l i n e which could only be r a t i o n a l i z e d i n terms of the stereochemical d i f f e r e n c e about C-0, between these two compounds. This l o was coupled with s l i g h t s h i f t s i n the p o s i t i o n of the C., methoxyl l b group of v i n d o l i n e which would also be expected to be af f e c t e d by changes at the C^ g, p o s i t i o n . Furthermore, the ethyl-methyl of the v i n d o l i n e C,. p o s i t i o n provided yet another d i f f e r e n c e between the two spectra. The protons mentioned above are a l l on the v i n d o l i n e p o r t i o n and since t h i s p o r t i o n i s completely unchanged i n both the compounds being compared these d i f f e r e n c e s must represent a c e r t a i n s e n s i t i v i t y of these protons to the stereochemistry at C1Q,. The protons of the indole l o template were s i n g u l a r l y uninformative. For example, the C^ , ethyl-methyl remained remarkably constant throughout t h i s s e r i e s appearing at T 9.13 - 90 -- 91 -i n d i h y d r o c l e a v a m i n e , a t T 9 . 1 7 i n t h e c o r r e s p o n d i n g d i m e r ( 9 6 ) , a t T 9 . 0 9 i n compound 94 and s t i l l u n s h i f t e d a t T 9 . 1 2 when t h e C ^ , p o s i t i o n h a d a t e r t i a r y a l c o h o l a t t a c h e d t o i t as i n V L B . These s i m i l a r i t i e s and d i f f e r e n c e s i n t h e nmr d a t a o f t h e p e r t i n e n t c e n t r e s o f a s e r i e s o f compounds a r e s u m m a r i z e d i n F i g u r e 2 3 . Some r e m a r k a b l e f a c t s emerge f r o m t h e d a t a p r e s e n t e d . F i r s t , i t w o u l d a p p e a r , t h a t t h e s y n t h e t i c d i m e r s a r e c l o s e r t h a n VLB (15 ) t o t h e c o r r e s p o n d i n g monomers w i t h r e g a r d t o t h e c h e m i c a l s h i f t s o f a l l t h e p r o t o n s l i s t e d . Thus t h e w h o l e c h a r t may be v i e w e d as a s e t o f s e l f - c o n s i s t e n t numbers t o w h i c h VLB i s a n e x c e p t i o n . S i n c e VLB may d i f f e r f r o m t h e a b o v e d i m e r s i n i t s s t e r e o c h e m i s t r y a t C 1 Q , i t i s lo t e m p t i n g t o c o n s i d e r t h e d i f f e r e n c e s as b e i n g due t o t h i s c h a n g e . A d e t a i l e d s t u d y o f t h e s e c h e m i c a l s h i f t s i s o f some v a l u e . The most d r a m a t i c s h i f t i s t h a t o f t h e C,. e t h y l - m e t h y l o f t h e v i n d o l i n e p a r t . I n t h e s y n t h e t i c d i m e r s i t a p p e a r s i n t h e r e g i o n o f T 9 . 4 - 9 . 5 . H o w e v e r , i n VLB i t i s s h i f t e d t o T 9 . 1 2 . T h i s i s n o t r e a d i l y e x p l i c a b l e b u t may be v i e w e d i n t e r m s o f some i n t e r a c t i o n t h r o u g h s p a c e b e t w e e n t h i s e t h y l g r o u p a n d t h e i n d o l e t e m p l a t e i n t h e n a t u r a l d i m e r w h i c h i s l o s t when t h e C , e p i m e r i c d i m e r s a r e s y n t h e s i z e d . The p r o t o n o n C . . i s lo 14 t h e c l o s e s t one o n t h e v i n d o l i n e u n i t t o t h e c r i t i c a l j u n c t i o n and w o u l d be e x p e c t e d o n t h i s b a s i s t o be t h e one most s e n s i t i v e t o c h a n g e s i n t h e s t e r e o c h e m i s t r y a t C 1 Q | . I n d e e d , i t d e m o n s t r a t e s a d r a m a t i c l o s h i f t f r o m x 3 . 1 2 i n v i n d o l i n e t o T 3 . 4 2 i n V L B ( 1 5 ) . S u r p r i s i n g l y , t h e c h a n g e b e t w e e n i t s c h e m i c a l s h i f t i n VLB and t h a t i n t h e s y n t h e t i c d i m e r s i s n o t so g r e a t , a l t h o u g h i t i s c o n s i s t e n t l y l o w e r (T 3 . 3 2 t o x 3 . 0 2 ) and i n some c a s e s i s e v e n s h i f t e d i n t h e o p p o s i t e s e n s e f r o m Figure 23. Nmr comparison of various monomers and dimers. 3 C0 2CH 3 Compounds No. '17 '14 -CH2CH3 H H '4 H C 1 8, and C 3 -C02CH3 "16 -OMe N l -Me -CH2CH3 R..H: R =R =R =H,R =Et 1 3 D O H R^H: R3=C02CH3(g), R^=Rg=H,R^=Et R1H: R4=Et,R3=C02CH3(6),R5;R6= = R^H: R3=C02CH;J(6),Ri=EtsR5=H,R6=OH R2H: RnR_: R„ =R_ =R, =H,R. = Et 1 2 3 5 6 4 R 1 R 2 : R 3 = C 0 2 C H 3 ' R 5 = R 6 = H ' R 4 = E t R 1 R 2 : R 3 = C 0 2 C H 3 ' R 5 , R 6 = = ' R 4 = E t RXR2: R3=C02CH3,R5=H,R6=OH,R4=Et 31 9.13 107 6.25 9.12 29 6.42 8.96 56 6.31 9.06 10 9.55 3.98 3.12 4.58 6.26 6.26 7.38 96 9.39 3.92 3.32 4.66 6.14 6.28 6.36 7.35 9.17 94 9.34 4.05 3.05 4.67 6.29 6.29 6.16 7.40 9.09 99 9.40 4.00 3.02 4.64 6.27 6.27 6.14 7.39 9.00 106 9.40 4.00 3.11 4.63 6.25 6.25 6.14 7.39 9.02 Figure 23 (continued) Compounds No. -CH2CH3 '17 H 14 H '4 H C 1 8, and C 3 -C02CH3 "16 -OMe N l -Me C4' -CH2CH3 R 1 R 2 : R 3 = H » R 4 = E t » R 5 = = ° H , R 6 = H R 1 R 2 : R 3 = C 0 2 C H 3 ' R 4 = 0 H » R 5 = E t » R 6 = H 9.49 3.97 3.30 4.68 6.19 6.27 6.27 7.39 9.24 !5 9.12 3.94 3.42 4.56 6.26 6.26 6.43 7.33 9.12 i vO CO I - 94 -v i n d o l i n e to the corresponding s h i f t from v i n d o l i n e to VLB. The proton a l s o shows a s l i g h t but d i s t i n c t s h i f t from x 3.94 i n VLB to higher f i e l d i n the s y n t h e t i c dimers. This s h i f t i s thus i n the opposite sense to that observed f o r the proton. The adjacent methoxyl a l s o shows a d i s t i n c t and c o n s i s t e n t s h i f t from x 6.43 i n VLB to lower f i e l d and more towards i t s p o s i t i o n i n v i n d o l i n e at x 6.26. S i m i l a r l y the N methyl i s s h i f t e d to higher f i e l d i n the s y n t h e t i c SL dimers from x 7.33 i n VLB towards i t s p o s i t i o n i n v i n d o l i n e at T 7.38. F i n a l l y , a s l i g h t s h i f t i s a l s o observed i n the proton between the s y n t h e t i c and n a t u r a l dimers. In summary, the f o l l o w i n g groups were p o t e n t i a l d i a g n o s t i c t o o l s f o r the determination of stereochemistry about C. o l: (a) the C, e t h y l - m e t h y l , (b) the C.n and C.. aromatic l o D 1/ l q protons, (c) the C , methoxyl and the N methyl and perhaps, (d) the proton. A l l of these s i g n a l s were c l o s e r to the monomers i n the s y n t h e t i c dimers analyzed than i n VLB. To g a i n any i n s i g h t i n t o the many f a c e t s of the c o n v e n t i o n a l d i m e r i z a t i o n r e a c t i o n , i t was necessary to set up a r i g i d sequence of steps which would represent the standard or norm. This sequence would have to be followed e x a c t l y to determine the y i e l d and type of d i m e r i c m a t e r i a l obtained. I t would have to be s u f f i c i e n t l y r e f i n e d and r e p r o d u c i b l e so as to y i e l d r e l i a b l e r e s u l t s , and f i n a l l y , i t would have to be quick and convenient i n order to f a c i l i t a t e the r a p i d a n a l y s i s of any given r e a c t i o n mixture. The s e r i e s of experiments described below used, as a b a s i s , the standard d i m e r i z a t i o n r e a c t i o n c o n d i t i o n s . Each experiment was repeated twice to check i t s r e p r o d u c i b i l i t y . In every case, the o v e r a l l y i e l d of dimer obtained i n these d u p l i c a t e runs agreed w i t h i n + 5%. In those cases where no d i m e r i c m a t e r i a l - 95 -was i s o l a t e d , r e p r o d u c i b l y , t h e s t a n d a r d c o n d i t i o n s w e r e r e p e a t e d u s i n g t h e same r e a g e n t s and t h e y i e l d o f t h i s r e a c t i o n was u s e d as a means t o d e t e r m i n e t h e v a l i d i t y o f s u c h r e s u l t s . The r e a c t i o n s w e r e a l l p e r f o r m e d o n t h e same s c a l e (50 mg o f e a c h monomer) . S i n c e t h e s t a n d a r d c o n d i t i o n s p l a y s u c h a p i v o t a l r o l e i n t h i s s t u d y i t i s p e r h a p s a p p r o p r i a t e t o d e s c r i b e them i n some d e t a i l h e r e . The c o n v e n t i o n a l r e a c t i o n may be d i v i d e d i n t o two p a r t s (a) c h l o r o -i n d o l e n i n e f o r m a t i o n and (b) c o u p l i n g r e a c t i o n . (a) C h l o r o i n d o l e n i n e s w e r e f o r m e d by d i s s o l v i n g 1 8 3 - c a r b o m e t h o x y - 4 $ -d i h y d r o c l e a v a m i n e (107) i n a f i x e d v o l u m e o f d r y m e t h y l e n e c h l o r i d e c o n t a i n i n g one e q u i v a l e n t o f t r i e t h y l a m i n e , c o o l i n g i t t o 0°C and a d d i n g one e q u i v a l e n t o f a n i c e - c o l d s o l u t i o n o f 0 . 0 5 M t - b u t y l h y p o c h l o r i t e i n c a r b o n t e t r a c h l o r i d e o v e r a p e r i o d o f t w e n t y m i n u t e s . A f t e r t h i s t i m e t h e t i c c h e c k , d e s c r i b e d p r e v i o u s l y , was a p p l i e d a n d t h e r e a c t i o n was r o u t i n e l y f o u n d t o h a v e p r o c e e d e d t o c o m p l e t i o n . E v a p o r a t i o n o f t h e s o l v e n t a t 0 °C u n d e r h i g h vacuum u s u a l l y r e s u l t e d i n a f o a m . (b) To t h i s foam was a d d e d a n e q u a l w e i g h t o f v i n d o l i n e f o l l o w e d by a s o l u t i o n o f 1.5% h y d r o g e n c h l o r i d e i n m e t h a n o l u n d e r a s t r e a m o f n i t r o g e n , a n d t h e w h o l e was p l u n g e d i n t o a p r e h e a t e d o i l b a t h a t 7 0 ° C , (107) - 96 -a n d a l l o w e d t o r e f l u x f o r t h r e e h o u r s . W o r k u p , f o l l o w e d by c o l u m n c h r o m a t o g r a p h y o f t h e r e a c t i o n m i x t u r e a c c o r d i n g t o a r i g i d l y s t a n d a r d i z e d p r o c e d u r e r e s u l t e d i n t h e i s o l a t i o n o f d i m e r 94 i n 65% y i e l d . The nmr s p e c t r u m o f t h i s compound was t a k e n t o be t h e s t a n d a r d s p e c t r u m t o w h i c h a l l s u b s e q u e n t e x p e r i m e n t a l r e s u l t s w e r e c o m p a r e d . The f i r s t q u e s t i o n t h a t n e e d e d t o b e c l a r i f i e d i n t h i s s t u d y c o n c e r n e d i t s e l f w i t h w h e t h e r t h e d i m e r i z a t i o n r e a c t i o n was s t e r e o -s p e c i f i c o r s t e r e o s e l e c t i v e w i t h r e g a r d t o t h e s t e r e o c h e m i s t r y a t C 1 Q l o i n t h e c l e a v a m i n e t e m p l a t e . T h e r e h a d a l r e a d y b e e n some i n d i c a t i o n s t h a t t h e s t e r e o c h e m i s t r y a t t h e C . _ p o s i t i o n d i d n o t p l a y any r o l e i n l o t h e s t e r e o c h e m i s t r y o f t h e r e s u l t i n g d i m e r s . Work i n t h e d e c a r b o m e t h o x y s e r i e s w h e r e t h i s s t e r e o c h e m i s t r y i s n o n - e x i s t e n t , f o r e x a m p l e , h a d y i e l d e d o n l y one d i m e r ( 9 6 ) , a n d f u r t h e r m o r e , t h e a t t e m p t e d d i m e r i z a t i o n o f t h e C . _ e p i m e r i c a l c o h o l s (56 and 57) h a d r e s u l t e d i n one and t h e l o same d i m e r f r o m e i t h e r s t a r t i n g a l c o h o l . I n o r d e r t o p r o v e t h i s i n t h e 3 , 4 d i h y d r o s e r i e s , 1 8 a - c a r b o m e t h o x y - 4 B - d i h y d r o c l e a v a m i n e was d i m e r i z e d i n t h e s t a n d a r d way t o a f f o r d a 45% y i e l d o f i s o l a t e d d i m e r w h i c h was. p r o v e d t o be i d e n t i c a l , b y n m r , t o compound 9 4 . T h u s , i t c o u l d be c o n c l u d e d t h a t , i n a l l t h e c a s e s a n a l y z e d so f a r , t h e r e a c t i o n p r o c e e d e d s t e r e o s e l e c t i v e l y w i t h r e g a r d t o t h e C . Q p o s i t i o n t o y i e l d a t t a c k b y l o v i n d o l i n e f r o m o n l y one s i d e o f t h e c l e a v a m i n e t e m p l a t e . The y i e l d o f d i m e r i c m a t e r i a l i s o l a t e d was s l i g h t l y b u t d i s t i n c t l y l o w e r when t h e s t a r t i n g m a t e r i a l p o s s e s s e d a n 1 8 c t - c a r b o m e t h o x y g r o u p t h a n when i t p o s s e s s e d a n 1 8 g - o n e . The p r e v i o u s r e p o r t s o f c h l o r o i n d o l e n i n e - f o r m i n g r e a c t i o n s i n t h e 97 l i t e r a t u r e r e q u i r e d t h e a d d i t i o n o f one e q u i v a l e n t o f t r i e t h y l a m i n e . The f u n c t i o n o f t h i s r e a g e n t i n t h e r e a c t i o n had n e v e r b e e n e x p l o r e d . - 97 -Thus, an entirely parallel dimerization experiment to the above was performed on compound 107 without the addition of triethylamine at the chlorination step. The resulting dimer was unchanged in stereo-chemistry and overall yield (65%). There was, in fact, an added advantage that the solvents were much easier to remove at the end of the chlorination step in this case. Although i t had been shown that the dimerization step proceeded stereoselectively with respect to the C 1 Q stereochemistry, i t was possible that the reaction was concerted and thus stereospecific with regard to the stereochemistry of the carbon-chlorine bond of the 84 chloroindolenine. One mechanism that had been proposed to account for this was as shown below. . virti u n r a t y r a l s t e r e o c h e m i s t r y a b o u t C ^ g , It had been pointed out that, based on this mechanism, a mixture of two dimers could be visualized in two ways: (a) The chlorination could occur ji p r i o r i from either face of the molecule to yield two isomeric chloroindolenines which, upon concerted displacement would yield two dimers or (b) the tautomerization of the indolenine double bond could lead to cis and trans isomers about the C^g centre. Concerted displace-ment would then produce two dimers again. The isolation of only one dimer in a l l the cases studied implied one of several alternatives. - 98 -I t was p o s s i b l e under the c o n d i t i o n s o f c h l o r i n a t i o n , t h a t the s t e r i c b u l k o f the c h l o r i n a t i n g agent caused p r o h i b i t i v e i n t e r a c t i o n s on the a - f a c e o f the m o l e c u l e so t h a t the c h l o r o i n d o l e n i n e was i t s e l f formed s t e r e o s e l e c t i v e l y . T h i s s i t u a t i o n then governed the s t e r e o -c h e m i s t r y of the dimer formed a c c o r d i n g to the c o n c e r t e d mechanism shown above. There was some s u p p o r t f o r t h i s h y p o t h e s i s from the f a c t t h a t t h e s e c h l o r o i n d o l e n i n e s appeared to behave as s i n g l e compounds on s e v e r a l t i c systems. S p e c t r o s c o p i c t e c h n i q u e s as w e l l , had n e v e r s u g g e s t e d the p r e s e n c e o f two i s o m e r i c m a t e r i a l s . F u r t h e r m o r e , by examining t h e m o l e c u l a r model o f the s t a r t i n g m a t e r i a l i t was p o s s i b l e to see t h a t the B-face was s l i g h t l y more a c c e s s i b l e than the c o r r e s p o n d i n g a - f a c e . The f o r m a t i o n o f o n l y a s i n g l e dimer, however, n e c e s s i t a t e d more than mere s t e r e o s e l e c t i v i t y o f the c h l o r i n a t i o n s t e p . I t was n e c e s s a r y to assume, f u r t h e r , t h a t none o f the c i s - t r a n s i s o m e r i z a t i o n mentioned above o c c u r r e d p r i o r t o the d i m e r i z a t i o n under the r e a c t i o n c o n d i t i o n s . T h i s a s s u m p t i o n c o u l d a l s o be j u s t i f i e d by an e x a m i n a t i o n o f the s t e r i c f a c t o r s a s s o c i a t e d w i t h p l a c i n g a t r a n s d o u b l e bond i n a nine-membered r i n g . I t c o u l d be shown t h a t the most f a v o u r a b l e c a r b o n - c h l o r i n e s t e r e o c h e m i s t r y when c o u p l e d w i t h the d o u b l e bond s t e r e o c h e m i s t r y which would y i e l d the p r e f e r r e d c i s d o u b l e bond i n the nine-membered r i n g , was such t h a t c o n c e r t e d a t t a c k by v i n d o l i n e o c c u r r e d from the B-face to g i v e e x c l u s i v e l y the u n n a t u r a l s t e r e o c h e m i s t r y a t C o i i n a c c o r d a n c e w i t h l o the e x p e r i m e n t a l r e s u l t s . I f t h i s mechanism was o p e r a t i n g , and dimer f o r m a t i o n was i n d e e d a c o n c e r t e d and s t e r e o s p e c i f i c r e a c t i o n , then the problem o f o b t a i n i n g - 99 -two e p i m e r i c d i m e r s f r o m any g i v e n r e a c t i o n c o u l d be r e p h r a s e d s i m p l y as a p r o b l e m o f r e d u c i n g t h e s t e r e o s e l e c t i v i t y o f t h e c h l o r i n a t i o n s t e p . Two p o s s i b l e s t r a t e g i e s f o r t h e a c h i e v e m e n t o f t h i s g o a l c o u l d be p r e s e n t e d . The u s e o f s m a l l e r , l e s s s t e r e o s e l e c t i v e , a n d p e r h a p s more r e a c t i v e c h l o r i n a t i n g a g e n t s a p p e a r e d t o be a l o g i c a l d i r e c t i o n i n w h i c h t o p r o c e e d . T o g e t h e r w i t h t h i s , a c h a n g e i n r e a c t i o n t e m p e r a t u r e s u p w a r d s f r o m 0°C was a p p r o p r i a t e . T h i s l a t t e r a p p r o a c h was a n t i c i p a t e d t o c a u s e a g r e a t e r m o b i l i t y i n t h e n i n e - m e m b e r e d r i n g o f t h e t e t r a c y c l i c s u b s t r a t e s o t h a t , p e r h a p s , t h e a - f a c e c o u l d become as a c c e s s i b l e as t h e B - f a c e and c h l o r i n a t i o n w o u l d o c c u r l e s s s e l e c t i v e l y . The s t a n d a r d d i m e r i z a t i o n c o n d i t i o n s w e r e u s e d o n s e v e r a l c h l o r o -i n d o l e n i n e r e a c t i o n m i x t u r e s p r e p a r e d by t h e u s e o f d i f f e r e n t c h l o r i n a t i n g a g e n t s . The m o s t i m p o r t a n t r e s u l t s a r e s u m m a r i z e d i n T a b l e I I . I t i s c l e a r f r o m t h i s t a b l e t h a t t h e u s e o f e v e n t h e s m a l l e s t and l e a s t T a b l e I I : E f f e c t o f d i f f e r e n t c h l o r i n a t o r s o n t h e y i e l d and s t e r e o -c h e m i s t r y o f d i m e r s p r o d u c e d . R e a g e n t S o l v e n t T ime t o T e m p e r a - Y i e l d o f Type o f c o m p l e t i o n t u r e °C d i m e r ( % ) d i m e r ( m i n ) 1 - c h l o r o b e n z o - b e n z e n e 20 20 60 " u n n a t u r a l " t r i a z o l e ti m e t h y l e n e 20 0 60 " u n n a t u r a l " c h l o r i d e 0 . 05 M t - B u O C l 11 15 49 50 " u n n a t u r a l " i n CCI4 N - C h l o r o s u c c i n - 11 20 25 50 " u n n a t u r a l " i m i d e N - C h l o r o a c e t a m i d e " 20 25 50 " u n n a t u r a l " Na0Cl (H 20) it 60 25 30 " u n n a t u r a l " ( h o u s e h o l d ( two p h a s e ) b l e a c h ) - 100 -d i s c r i m i n a t o r y c h l o r i n a t i n g a g e n t s f a i l e d t o p r o d u c e e v e n t h e f a i n t e s t t r a c e o f a n y new d i m e r when t h e p r o d u c t s w e r e c o u p l e d i n t h e s t a n d a r d way w i t h v i n d o l i n e . T h i s p o i n t e d t o t h e f a c t t h a t p e r h a p s t h e s t e r e o -c h e m i s t r y o f t h e c a r b o n - c h l o r i n e b o n d d i d n o t g o v e r n t h e o u t c o m e o f t h e d i m e r i z a t i o n r e a c t i o n . F u r t h e r s u p p o r t f o r t h i s h y p o t h e s i s was o b t a i n e d when t h e u s e o f t _ - b u t y l h y p o c h l o r i t e a s a c h l o r i n a t i n g a g e n t was e x a m i n e d i n g r e a t e r d e t a i l . I n i t i a l l y , t h i s r e a g e n t h a d b e e n u s e d as a d i l u t e s o l u t i o n , w h e r e t h e r a t e a n d s t e r e o s e l e c t i v i t y w o u l d be e x p e c t e d t o be d i f f u s i o n c o n t r o l l e d . T h u s , i n o r d e r t o p r o d u c e t h e o p p o s i t e e f f e c t , t h e u s e o f n e a t t - b u t y l h y p o c h l o r i t e i n t h i s r e a c t i o n was e x a m i n e d . One e q u i v a l e n t o f t h i s c o m p o u n d , n e a t , was i n j e c t e d , d i r e c t l y i n t o a s o l u t i o n o f compound 107 i n m e t h y l e n e c h l o r i d e a t 0°C u s i n g a m i c r o s y r i n g e . The y i e l d o f c h l o r o i n d o l e n i n e f o r m e d was n o t s e r i o u s l y a l t e r e d b y t h i s p r o c e d u r e b u t i t was f o u n d t h a t a s l o w a d d i t i o n o f t h e d i l u t e s o l u t i o n o f t h e r e a g e n t was s l i g h t l y p r e f e r a b l e . The y i e l d o f d i m e r o b t a i n e d u p o n s u b s e q u e n t s t a n d a r d d i m e r i z a t i o n was 55%, and t h e s t e r e o c h e m i s t r y a b o u t C^g» was a g a i n u n a l t e r e d . The t e m p e r a t u r e o f t h i s r e a c t i o n was t h e f i n a l v a r i a b l e l e f t t o b e e x a m i n e d . R e a c t i o n t e m p e r a t u r e s b e t w e e n 0°C and 77°C w e r e u s e d b y r e f l u x i n g t h e s u b s t r a t e i n t h e a p p r o p r i a t e m i x t u r e o f m e t h y l e n e c h l o r i d e i and c a r b o n t e t r a c h l o r i d e , f o l l o w e d b y t h e a d d i t i o n o f n e a t t - b u t y l h y p o c h l o r i t e . T h i s d a t a i s s u m m a r i z e d i n T a b l e I I I . I t i s o b v i o u s f r o m t h i s t a b l e t h a t t h e y i e l d o f d i m e r r e s u l t i n g f r o m c o u p l i n g c h l o r o -i n d o l e n i n e s so d e r i v e d w i t h v i n d o l i n e i s s e n s i t i v e t o t h e t e m p e r a t u r e o f t h e c h l o r i n a t i o n s t e p b u t t h a t t h e s t e r e o c h e m i c a l o u t c o m e i s c o m p l e t e l y u n a l t e r e d b y c h a n g e s i n t h e t e m p e r a t u r e a t w h i c h t h e c h l o r i n a t i o n i s p e r f o r m e d . - 101 -T a b l e I I I . T e m p e r a t u r e o f c h l o r i n a t i o n v s . y i e l d and t y p e o f d i m e r . S o l v e n t T e m p e r a - Y i e l d o f Type o f M e t h y l e n e c h l o r i d e : c a r b o n t e t . t u r e °C d i m e r (%) d i m e r 1 1 0 65 " u n n a t u r a l " 1 0 50 45 " u n n a t u r a l " 3 2 50 10 " u n n a t u r a l " 1 1 55 5 " u n n a t u r a l " 0 1 77 No d i m e r 1 4 72 No d i m e r Two p o s s i b l e e x p l a n a t i o n s f o r t h i s phenomenon may be o f f e r e d . I t was p o s s i b l e , a l t h o u g h q u i t e i m p r o b a b l e , t h a t t h e s t e r i c f a c t o r s g o v e r n i n g t h e s t e r e o s e l e c t i v i t y o f t h i s r e a c t i o n w e r e s u c h t h a t a l l t h e a b o v e e f f o r t s t o o b t a i n two e p i m e r i c c h l o r o i n d o l e n i n e s h a d f a i l e d . T h i s p o s s i b i l i t y c o u l d o n l y be c o n c l u s i v e l y r u l e d o u t b y t h e i s o l a t i o n a n d s e p a r a t i o n o f two s u c h e p i m e r i c c o m p o u n d s , b o t h o f w h i c h c o u l d t h e n be d i m e r i z e d i n d e p e n d e n t l y . T h i s o b j e c t i v e h a s n o t b e e n a c h i e v e d y e t . I f t h e f o r m a t i o n o f two e p i m e r i c c h l o r o i n d o l e n i n e s had o c c u r r e d a t l e a s t t o some e x t e n t i n a minimum o f one o f t h e a b o v e c o n d i t i o n s , t h e n i t was n e c e s s a r y t o c o n c l u d e f r o m t h e a b o v e d a t a t h a t t h e s t e r e o -c h e m i s t r y o f t h e c a r b o n - c h l o r i n e b o n d was i r r e l e v a n t t o t h e o u t c o m e o f t h e r e a c t i o n . T h i s was l a t e r p r o v e d by t h e i s o l a t i o n and d i m e r i z a t i o n o f a n i n t e r m e d i a t e l a c k i n g a c a r b o n - c h l o r i n e b o n d ( v i d e i n f r a ) . The p r e v i o u s l y p r o p o s e d c o n c e r t e d m e c h a n i s m was t h u s u n t e n a b l e . T h i s d e d u c t i o n had a n i m p o r t a n t b e a r i n g on t h e d i r e c t i o n o f f u r t h e r e f f o r t s . - 102 -It meant that these e f f o r t s to change e i t h e r the stereochemistry or the y i e l d of the dimerization r e a c t i o n must concentrate on the area of the coupling reaction i t s e l f and not on the chloroindolenine-forming step. Attention was thus turned to t h i s part of the dimerization r e a c t i o n . Several factors were involved at t h i s stage. In order to reach a cle a r understanding about the r o l e that they played, a systematic study of each of these f a c t o r s was necessary. The temperature of the coupling re a c t i o n was the f i r s t v a r i a b l e to be examined. I t was conceivable that, regardless of the exact nature of the t r a n s i t i o n state, the stereo-s e l e c t i v i t y of t h i s coupling step was a r e f l e c t i o n of the s t e r i c i n t e r a c t i o n s experienced by v i n d o l i n e when i t approached the a-face of the molecule i n order to lead to the n a t u r a l stereochemistry at C Q'. If these were considerably greater than those on the g-face, then at lower temperatures when conformational m o b i l i t y was diminished i n the intermediate, attack would occur e x c l u s i v e l y on the less hindered B-face to produce only the unnatural stereochemistry at C If t h i s l o l i n e of reasoning was co r r e c t , the attack upon the a-face of the molecule may be favoured by increasing the temperature of t h i s step so as to supply greater conformational m o b i l i t y to the system. One disadvantage of t h i s approach was that the chloroindolenine could be expected, on the basis of the work mentioned above, to be heat-s e n s i t i v e . Thus, the y i e l d of dimeric material r e s u l t i n g from dimeriza-tions at higher temperatures may be expected to be s u b s t a n t i a l l y diminished. Coupling reactions were performed at several temperatures ranging from room temperature to 140°C. These reactions were monitored - 103 -by t i c u n t i l " a maximum amount of dimer had been formed and then worked up i n the usual way. This time of optimum rea c t i o n provided a measure of the r e l a t i v e rate of the reactio n . In the case of the higher temperatures, t h i s was s l i g h t l y more inconvenient and necessitated several runs. When the optimum time had been deduced another r e a c t i o n was run, i t s product i s o l a t e d , and the y i e l d determined. The pertinent data derived from t h i s sequence of experiments i s summarized i n Table IV. I t can be seen that the "r a t e " of t h i s r e a c t i o n increased as the Table IV. E f f e c t of the temperature of the coupling step on the y i e l d and stereochemistry of dimer. Temperature Time Y i e l d Stereochemistry (°C) (hr) (%) 0 30 "unnatural" 65 "unnatural" 75 "unnatural" 140 100 68 25 0.5 0.25 2.5 18 temperature was increased. The y i e l d , as had been expected, was inve r s e l y correlated with the temperature, being optimal at the r e l a t i v e l y lower temperatures. Unfortunately, the stereochemistry at C 1 Q , of the l o r e s u l t i n g product was completely independent of the temperature of the coupling step. Thus, again the hope of a l t e r i n g the stereochemical outcome of th i s r e a ction, based on the above arguments, had been f r u s t r a t e d . - 104 -The r e a c t i o n mixture r e s u l t i n g from the re a c t i o n at room temperature, however, was remarkably simple i n nature c o n s i s t i n g of v i n d o l i n e , deacetyl v i n d o l i n e , and baseline material as the minor components of the r e a c t i o n and the dimer (94) as the only major component. As mentioned previously, these r e a c t i o n conditions had been discovered to be 3 4 preferable to the conventional ones i n the A ' case as w e l l . They thus represent a genuine improvement upon the standard r e a c t i o n . Some progress i n one of the two goals of the study had thus been achieved. Vindoline i t s e l f had previously demonstrated a remarkable inertness to 1.5% methanolic hydrogen chloride (vide supra). The fate of the chloroindolenine during the coupling step may have been c r i t i c a l i n determining the o v e r a l l y i e l d of dimeric material i s o l a t e d . I t was possible that when t h i s compound was mixed with v i n d o l i n e and then treated with the a c i d i c methanol, the chloroindolenine decomposed p a r t i a l l y before i t had an opportunity to dimerize. Vindoline was dissolve d i n a small amount of the solvent i n a separate f l a s k and added slowly to the chloroindolenine. When t h i s a d d i t i o n was complete at room temperature, the remaining amount of the solvent was added and the normal dimerization was performed. A s l i g h t improvement i n the o v e r a l l y i e l d of dimer 94 was r e a l i z e d by t h i s approach (70%) but i t was not s u f f i c i e n t l y s i g n i f i c a n t to be c l a s s i f i e d as a r e a l advance p a r t i c u l a r l y i n view of the added inconvenience associated with t h i s m o dification. An i n t e r e s t i n g discovery was made, however, upon i n v e r t i n g the d i r e c t i o n of t h i s a d d i t i o n . When the chloroindolenine was mixed with 1.5% methanolic hydrogen chloride and then added to s o l i d v i n d o l i n e , the y i e l d - 105 -o f d i m e r i s o l a t e d a f t e r t h e s t a n d a r d d i m e r i z a t i o n a p p e a r e d t o be r e m a r k a b l y d e p e n d e n t u p o n t h e l e n g t h o f t i m e f o r w h i c h t h e c h l o r o i n d o l e n i n e h a d r e m a i n e d i n t h i s s o l u t i o n p r i o r t o t h e a d d i t i o n , and t h e t e m p e r a t u r e a t w h i c h t h i s s o l u t i o n h a d b e e n m a i n t a i n e d . I n f a c t , i f t h e c h l o r o -i n d o l e n i n e s o l u t i o n was a l l o w e d t o r e f l u x f o r f i v e m i n u t e s , o r s t a n d a t room t e m p e r a t u r e f o r an h o u r , o r a t 0°C o v e r n i g h t , t h e y i e l d o f d i m e r i c m a t e r i a l i s o l a t e d a f t e r t h e s t a n d a r d c o u p l i n g s t e p was r e d u c e d t o z e r o . S u c h e x p e r i m e n t s w i t h t h e c h l o r o i n d o l e n i n e u n d e r t h e a b o v e c o n d i t i o n s r e v e a l e d b y t i c t h a t i t had c o m p l e t e l y d i s a p p e a r e d and had b e e n r e p l a c e d by a p o l a r , s a l t - l i k e m a t e r i a l w h i c h h a d t h e c h a r a c t e r i s t i c uv a b s o r p t i o n s o f a n i n d o l e . On t h e b a s i s o f s i m i l a r w o r k i n o u r l a b o r a t o r i e s , " ' " " ' ' ' ' ' t h e s t r u c t u r e 108 b e l o w was t e n t a t i v e l y a s s i g n e d t o t h i s compound o n t h e b a s i s o f i t s nmr and uv s p e c t r a . A l l a t t e m p t s t o d i m e r i z e t h i s s o - c a l l e d q u a t e r n a r y s a l t i n a s e p a r a t e s t e p f a i l e d c o m p l e t e l y u n d e r t h e s t a n d a r d c o n d i t i o n s . I t s h o u l d be p o i n t e d o u t t h a t t h e c h l o r o i n d o l e n i n e was q u i t e u n r e a c t i v e i n t h e a b s e n c e o f a c i d i c o r b a s i c c a t a l y s t s , and c o u l d be r e c o v e r e d u n c h a n g e d when r e f l u x e d i n d r y , d i s t i l l e d a c e t o n e o r r i g o r o u s l y a n h y d r o u s m e t h a n o l ( d i s t i l l e d f i r s t f r o m m a g n e s i u m and t h e n f r o m a s m a l l amount o f s o d i u m ) f o r p e r i o d s i n e x c e s s o f s i x h o u r s . C 0 2 C H 3 ^ (108) - 106 -C l e a r l y t h e n , t h e a c i d c a t a l y s t s r e a c t e d w i t h t h e c h l o r o i n d o l e n i n e t o p r o d u c e a n i n t e r m e d i a t e w h i c h was q u i t e r e a c t i v e and w h i c h t h e n r e a c t e d w i t h v i n d o l i n e o r any o t h e r n u c l e o p h i l e t h a t may be p r e s e n t o r e l s e f o r c e d t h e i n t r a m o l e c u l a r c o n d e n s a t i o n w i t h N, t o y i e l d b compound 108 a b o v e . The w o r k d e s c r i b e d a t t h e b e g i n n i n g o f t h i s p a r t o f t h e d i s c u s s i o n s u g g e s t e d t h e n a t u r e o f t h i s i n t e r m e d i a t e t o be 109 a n d i t was t h u s p o s t u l a t e d t o a r i s e as shown i n F i g u r e 2 4 . I n t e r m e d i a t e 109 i s s t r o n g l y r e m i n i s c e n t o f compounds 7 7 , 81 and 83 p r o p o s e d by o t h e r s i n c l o s e l y a n a l o g o u s c a s e s ( v i d e s u p r a ) . T h i s m e c h a n i s m was s u p p o r t e d by t h e f a c t t h a t t h e C . ~ a l c o h o l s , when s o l v o l y z e d i n t h e p r e s e n c e o f l o v i n d o l i n e , y i e l d e d t h e same p r o d u c t ^ > l u 3 a s C O u l d be o b t a i n e d f r o m t h e c h l o r o i n d o l e n i n e a p p r o a c h i m p l i c a t i n g t h e same i n t e r m e d i a t e i n b o t h c a s e s . O n l y one f u r t h e r e x p e r i m e n t n e e d e d t o be p e r f o r m e d i n o r d e r t o p r o v e t h i s m e c h a n i s m . I t was n e c e s s a r y t o t r a p t h i s r e a c t i v e compound i n some w a y . T h i s t r a p p e d f o r m c o u l d be i s o l a t e d and t h e n u s e d i n a n i n d e p e n d e n t s t e p t o r e g e n e r a t e compound 109 i n t h e p r e s e n c e o f v i n d o l i n e and a l l o w n o r m a l d i m e r i z a t i o n t o p r o c e e d . I f t h e y i e l d a n d s t e r e o -c h e m i c a l outcome o f s u c h a n e x p e r i m e n t w e r e t h e same as t h e s t a n d a r d o n e , t h e n t h i s p o s t u l a t e w o u l d be s t r o n g l y s u p p o r t e d . F o r t u n a t e l y , s u c h a n e x p e r i m e n t was i n d e e d p o s s i b l e . T r e a t m e n t o f t h e c h l o r o i n d o l e n i n e o f compound 107 w i t h 1% m e t h a n o l i c h y d r o g e n c h l o r i d e u n d e r m i l d e r c o n d i t i o n s (0°C f o r t e n m i n u t e s ) y i e l d e d a r a p i d a n d v i s i b l e r e a c t i o n w i t h t h e i n i t i a l l y c l e a r l i g h t y e l l o w s o l u t i o n b e c o m i n g a deep w i n e - r e d c o l o u r . E v a p o r a t i o n o f t h e s o l v e n t u n d e r h i g h vacuum a t 0°C a f f o r d e d a r e d d i s h -b r o w n s o l i d w h i c h was p r o v e d t o be compound 110 shown b e l o w . I t s i d e n t i t y - 1 0 7 -C 0 2 C H 3 ^ (108) Figure 24. Proposed mechanism of the standard dimerization. - 108 -H C I C H 3 0 C 0 2 C H 3 (110) L i A l H ^ THF C H 3 ° C H 2 0 H ^ (111) + H C H 2 O H (112) + (107) c o u l d be i n f e r r e d b y a n e x a m i n a t i o n o f t h e nmr s p e c t r u m o f t h e compound a s t h e f r e e b a s e w h i c h showed t h e e x p e c t e d d i s a p p e a r a n c e o f t h e C ^ g p r o t o n a s w e l l as t h e a p p e a r a n c e o f t h e new t h r e e p r o t o n s i n g l e t due t o t h e C 1 Q m e t h o x y l g r o u p . When c o n v e r t e d t o t h e f r e e b a s e , compound 110 l o was q u i t e u n s t a b l e a n d d e c o m p o s e d , u p o n s t a n d i n g f o r s e v e r a l h o u r s , t o t h e q u a t e r n a r y s a l t ( 1 0 8 ) . I t s s t r u c t u r e c o u l d h o w e v e r be c o n c l u s i v e l y e s t a b l i s h e d by r e d u c i n g i t w i t h l i t h i u m a l u m i n u m h y d r i d e t o t h e s t a b l e v i c i n a l a l c o h o l - e t h e r (111) w h i c h was c o m p l e t e l y c h a r a c t e r i z e d by nmr ( s e e F i g u r e 25) , i r a n d uv a s w e l l a s e l e m e n t a l a n a l y s i s a f t e r c r y s t a l l i z a -t i o n f r o m e t h y l a c e t a t e and h i g h a n d l o w r e s o l u t i o n mass s p e c t r o m e t r y ( see F i g u r e 2 6 ) . The r e d u c t i o n was h o w e v e r somewhat d i f f i c u l t b e c a u s e compound 110 was c h a r a c t e r i s t i c a l l y i n s o l u b l e i n any e t h e r i a l s o l v e n t a s t h e h y d r o c h l o r i d e s a l t . The a d d i t i o n o f l i t h i u m a l u m i n u m h y d r i d e - 109 -- I l l -g e n e r a t e d t h e f r e e b a s e w h i c h t h e n d i s s o l v e d . H o w e v e r , g e n e r a t i o n o f t h e f r e e b a s e a l l o w e d q u a t e r n i z a t i o n t o y i e l d compound 108 t o compete e f f e c t i v e l y i n t h e b a s i c medium w i t h r e d u c t i o n t o a f f o r d compound 1 1 1 . T h i s was f u r t h e r c o m p l i c a t e d by t h e f a c t t h a t a t t a c k by t h e a c t i v e " h y d r i d e " a g e n t c o u l d o c c u r a t t h e C. „ p o s i t i o n d i r e c t l y as w e l l t o y i e l d l o d i h y d r o c l e a v a m i n o l (112) f r o m h y d r o g e n o l y s i s o f t h e m e t h o x y l g r o u p w i t h c o n c o m i t a n t r e d u c t i o n o f t h e e s t e r f u n c t i o n a l i t y . The i s o l a t i o n o f t h e d e s i r e d compound (111) i n o v e r a l l 37% y i e l d f r o m t h i s r e d u c t i o n , h o w e v e r , p r o v e d t h e i d e n t i t y o f t h e p r e v i o u s p r o d u c t ( 1 1 0 ) . I n a p a r a l l e l e x p e r i m e n t , compound 110 was p r o d u c e d e x a c t l y a s a b o v e a n d d i s s o l v e d i n 1.5% m e t h a n o l i c h y d r o g e n c h l o r i d e c o n t a i n i n g v i n d o l i n e . D i m e r i z a t i o n i n t h e s t a n d a r d way a f f o r d e d a 55% y i e l d o f d i m e r i c m a t e r i a l whose s t e r e o c h e m i s t r y was t h e same as t h a t o b t a i n e d i n t h e s t a n d a r d r e a c t i o n . The compound 109 was t h u s most p r o b a b l y a r e a l r e a c t i o n i n t e r m e d i a t e d u r i n g t h e s t a n d a r d d i m e r i z a t i o n r e a c t i o n . The u s e o f t h i s c o n c e p t a l l o w e d t h e e x t e n s i o n o f t h e r e a c t i o n t o p e r m i t t h e i n t r o d u c t i o n o f s e v e r a l C D s u b s t i t u e n t s o t h e r t h a n m e t h o x y l . These l o compounds w i l l be d i s c u s s e d a t a l a t e r s t a g e . T h i s p o s t u l a t e d m e c h a n i s m i s c o n s i s t e n t w i t h a l l t h e f a c t s so f a r o b t a i n e d a b o u t t h e d e p e n d e n c e , f o r e x a m p l e , o f t h e r e a c t i o n o n s u c h f a c t o r s as t h e t e m p e r a t u r e o f t h e c o u p l i n g r e a c t i o n e t c . I t a l s o e x p l a i n s t h e o b s e r v e d l a c k o f c o r r e l a t i o n b e t w e e n t h e s t e r e o c h e m i s t r y a t e i t h e r t h e C^g o r t h e i n d o l e - 3 - p o s i t i o n o f t h e c h l o r o i n d o l e n i n e , and t h e s t e r e o c h e m i s t r y o f the i s o l a t e d d i m e r . F u r t h e r m o r e , t h i s p o s t u l a t e d m e c h a n i s m i s e n t i r e l y c o n s i s t e n t w i t h t h e p r e v i o u s p o s t u l a t e s by o t h e r w o r k e r s ( v i d e s u p r a ) i n c l o s e l y s i m i l a r c a s e s . U s i n g t h e m e c h a n i s t i c - 112 -scheme o f F i g u r e 24 t h e s t e r e o s e l e c t i v i t y o f t h e s t a n d a r d r e a c t i o n c o u l d be v i e w e d i n one o f two e x t r e m e w a y s . I f i t w e r e p o s s i b l e t o d e c i d e w h i c h one o f t h e s e was o p e r a t i n g t h e n s u i t a b l e means f o r r e d u c i n g t h i s s t e r e o s e l e c t i v i t y c o u l d be d e v i s e d . The a t t a c k o f v i n d o l i n e on t h e compound u n d e r t h e c o n d i t i o n s o f t h e r e a c t i o n may be v i e w e d as t h e n o r m a l F r i e d e l - C r a f t s a l k y l a t i o n o f t h e m e t a - m e t h o x y - a n i l i n o s y s t e m o f v i n d o l i n e by t h e r e a c t i v e g r o u p . The d e t a i l s o f s u c h a r e a c t i o n may be d e p i c t e d a s shown i n F i g u r e 2 7 . I f t h i s r e a c t i o n s e q u e n c e i s v i s u a l i z e d as p r o c e e d i n g e s s e n t i a l l y i r r e v e r s i b l y , t h e n t h e s t e r e o c h e m i s t r y o f t h e p r o d u c t must r e f l e c t t h e i n i t i a l s i d e o f a p p r o a c h p r e f e r r e d b y v i n d o l i n e . I t i s r e a s o n a b l e t o assume t h a t v i n d o l i n e e n t e r s t h e r e a c t i o n s i t e o r t h o g o n a l t o t h e e x i s t i n g TT s y s t e m so as t o m a x i m i z e o v e r l a p . A n e x a m i n a t i o n o f a m o l e c u l a r m o d e l o f t h e i n t e r m e d i a t e r e v e a l e d t h a t t h e m o l e c u l e was c o n s i d e r a b l y more c r o w d e d o n i t s c o n c a v e , a - f a c e , t h a n o n t h e c o r r e s p o n d i n g c o n v e x , 8 - f a c e . Thus t h e e x c l u s i v e a t t a c k b y v i n d o l i n e o n t h e B - f a c e o f t h i s m o l e c u l e t o y i e l d d i m e r s o f t h e u n n a t u r a l s t e r e o c h e m i s t r y was u n d e r s t a n d a b l e . T h i s e x p l a n a t i o n i m p l i e d t h a t t h e r e a c t i o n was p r o c e e d i n g e s s e n t i a l l y u n d e r k i n e t i c c o n t r o l and t h e r e f o r e t h a t t h e u s u a l s t e r e o -c h e m i s t r y a b o u t C 1 0 , was t h e k i n e t i c p r o d u c t , l o A t t h e o t h e r e x t r e m e , i t may be a r g u e d t h a t t h e r e a c t i o n may a^  p r i o r i p r o c e e d e n t i r e l y r e v e r s i b l y u n d e r t h e c o n d i t i o n s o f t h e r e a c t i o n t o y i e l d t h e t h e r m o d y n a m i c a l l y most s t a b l e p r o d u c t . C e r t a i n l y , t h e p r o t o n a t i o n o f t h e C^, . p o s i t i o n o f a d i m e r u n d e r h i g h l y a c i d i c c o n d i t i o n s may be v i s u a l i z e d t o y i e l d t h e same i n t e r m e d i a t e (113) shown i n F i g u r e 2 7 . The c l e a v a g e o f t h e C . , - C 1 Q , b o n d , i n s t e a d o f t h e l o s s o f t h i s p r o t o n , - 113 -F i g u r e 2 7 . P r o p o s e d d e t a i l s o f t h e c o u p l i n g s t e p . w o u l d e f f e c t i v e l y r e v e r s e t h e d i m e r i z a t i o n r e a c t i o n t o y i e l d i n t e r m e d i a t e 109 and v i n d o l i n e . The c l e a v a g e r e a c t i o n c a n now be e x p l a i n e d i n t h e l i g h t o f t h e p r o p o s e d m e c h a n i s m i n e x a c t l y t h i s w a y . U n d e r t h e s e c o n d i t i o n s t h e i n t e r m e d i a t e 109 i s i m m e d i a t e l y r e d u c e d b y t h e s t a n n o u s c h l o r i d e and t i n jLn s i t u , and so i t i s t r a p p e d , and t h e e q u i l i b r i u m r e a c t i o n i s t h u s " d r a i n e d " o v e r t o t h e s i d e o f m o n o m e r i c c l e a v a g e p r o d u c t s . - 114 -I t s h o u l d be m e n t i o n e d i n p a s s i n g t h a t t h i s c l e a v a g e r e a c t i o n was p o s s i b l e w i t h o u t t h e u s e o f t h e r e d u c i n g a g e n t o n l y i n t h e c a s e o f VLB ( 1 5 ) . I n t h i s c a s e , t h e C ^ , a l c o h o l p a r t i c i p a t e d t o t r a p t h e monomer ic s p e c i e s a n a l o g o u s t o 109 a s t h e C . - C „ e t h e r 4 l o ( 2 2 ) . I n t h e l i g h t o f t h e p r o p o s e d m e c h a n i s m n o w , t h e a p p a r e n t s i d e r e a c t i o n o f t h e 3 , 4 f u n c t i o n a l i z e d t e m p l a t e s c o u l d be e x p l a i n e d e x a c t l y a n a l o g o u s l y . I t was c o n c e i v a b l e t h a t t h e 3 , 4 f u n c t i o n a l i t y may a c t i n a s i m i l a r way as i n t h e c a s e o f VLB a b o v e , u n d e r t h e d i m e r i z a t i o n c o n d i t i o n s , t o w a r d s a n i n t e r m e d i a t e a n a l o g o u s t o 109 t o t r a p i t i n some way and t h u s b l o c k i t s p a r t i c i p a t i o n i n t h e d i m e r i z a t i o n r e a c t i o n . A l t h o u g h t h e c o n c e n t r a t i o n o f a c i d u s e d i n t h e c l e a v a g e c o n d i t i o n s was o b v i o u s l y h i g h enough t o a l l o w t h e r e a c t i o n t o become r e v e r s i b l e , i t was n o t c l e a r w h e t h e r t h e r e a c t i o n was p r o c e e d i n g a c c o r d i n g t o k i n e t i c o r t h e r m o d y n a m i c c o n t r o l u n d e r t h e s t a n d a r d d i m e r i z a t i o n c o n d i t i o n s . M o l e c u l a r m o d e l s o f t h e two e p i m e r i c d i m e r s w e r e s t u d i e d c l o s e l y , i n a n a t t e m p t t o d i s c o v e r i f t h e s e c o n d a r y i n t e r a c t i o n s e m b o d i e d i n a n y one e p i m e r a b o u t t h e C 1 o ! c e n t r e w e r e d i s t i n c t l y g r e a t e r t h a n t h o s e l o i n t h e o t h e r . A l t h o u g h i t must be a d m i t t e d a t t h e o u t s e t t h a t s u c h s t u d i e s i n a m o l e c u l e o f t h i s s i z e a n d c o m p l e x i t y may be m i s l e a d i n g , i t s h o u l d be m e n t i o n e d t h a t t h e s e m o d e l s f a i l e d t o show a n y g r e a t d i f f e r e n c e s i n t h e s t a b i l i t y o f one e p i m e r o v e r t h e o t h e r . T h u s , i f t h e r e a c t i o n w e r e p r o c e e d i n g u n d e r t h e r m o d y n a m i c c o n t r o l , t h e i s o l a t i o n o f o n l y one d i m e r was n o t r e a d i l y e x p l i c a b l e . I n summary, i t a p p e a r e d t h a t u n d e r t h e r e a c t i o n c o n d i t i o n s e m p l o y e d i n t h e s t a n d a r d d i m e r i z a t i o n , t h e c o u p l i n g o f v i n d o l i n e t o compound 109 p r o c e e d e d u n d e r k i n e t i c c o n t r o l t o y i e l d o n l y t h e k i n e t i c p r o d u c t o f t h e r e a c t i o n . - 115 -Two s t r a t e g i e s f o r m o d i f y i n g t h e r e s u l t o f t h i s r e a c t i o n , o n t h e a s s u m p t i o n t h a t i t was p r o c e e d i n g a c c o r d i n g t o k i n e t i c c o n t r o l , c o u l d be c o n c e i v e d . (a) I f t h e r e a c t i o n m e c h a n i s m was i n d e e d as d e s c r i b e d a b o v e , t h e n a t u r e o f t h e t r a n s i t i o n s t a t e w o u l d a f f e c t t h e n a t u r e o f t h e p r o d u c t . I t was t h u s c o n c e i v a b l e t h a t t h e u s e o f d i f f e r e n t s o l v e n t s and L e w i s a c i d s may s u f f i c i e n t l y a l t e r t h e n a t u r e o f t h i s t r a n s i t i o n s t a t e so a s t o p e r m i t a change i n t h e o v e r a l l s t e r e o c h e m i s t r y o f t h e d i m e r o b t a i n e d . S e v e r a l L e w i s a c i d s a n d s o l v e n t s w e r e i n v e s t i g a t e d . The r e a c t i o n s w e r e r u n a t t h r e e t e m p e r a t u r e s - room t e m p e r a t u r e , 7 0 ° C , and t h e r e f l u x t e m p e r a t u r e o f t h e s o l v e n t e m p l o y e d . I n e a c h c a s e , t h e p r o g r e s s o f t h e r e a c t i o n was m o n i t o r e d by t i c a n d w o r k e d up when o p t i m a l d i m e r i z a t i o n h a d o c c u r r e d . These r e s u l t s a r e s u m m a r i z e d i n T a b l e V . F o r p u r p o s e s o f b r e v i t y , o n l y t h e o p t i m a l t e m p e r a t u r e i n e a c h c a s e i s r e p o r t e d . I t s o o n became c l e a r t h a t t h e change i n t h i s t r a n s i t i o n s t a t e was n o t a s i m p l e m a t t e r a n d a t t e n t i o n was t h u s t u r n e d t o a more s y s t e m a t i c a p p r o a c h . (b) I f t h e r e a c t i o n m e c h a n i s m was a s shown i n F i g u r e 2 7 , t h e d e g r e e o f r e v e r s i b i l i t y o f t h e r e a c t i o n , and t h e r e f o r e t h e e x t e n t o f t h e r m o d y n a m i c c o n t r o l , was d e p e n d e n t o n t h e c o n c e n t r a t i o n o f a c i d p r e s e n t i n t h e r e a c t i o n m e d i u m . I n o t h e r w o r d s , t h e f o r m a t i o n o f t h e i n t e r m e d i a t e 109 u n d e r t h e u s u a l c o n d i t i o n s may be v i e w e d as t h e r a t e l i m i t i n g s t e p . Once t h i s i o n was f o r m e d t h e n e x t s t e p s w o u l d be r a p i d and e s s e n t i a l l y i r r e v e r s i b l e . A n i n c r e a s e i n t h e c o n c e n t r a t i o n o f t h e a c i d p r e s e n t s h o u l d f u n c t i o n t o s l o w down t h e s t e p w h i c h c o n v e r t s i n t e r m e d i a t e 113 t o compound 94 b e c a u s e , i n s i m p l e t e r m s , t h e l o s s o f a p r o t o n i n t o t h e medium ( o r t h e o v e r a l l l o s s o f H - C l ) w o u l d become l e s s - 116 -Table V. Effect of solvents and Lewis acids on the dimerization reaction. Solvent Lewis acid Temp. (°C) Time (hr) Yield (%) Stereochemistry Trifluoroacetic acid - 25 48 5 "unnatural" N,N-Dimethyl-formamide HC1 25 19 60 "unnatural" Tetrahydrofuran HC1 66 2.5 25 "unnatural" Dioxane HC10. 4 25 48 5 "unnatural" Methanol HC1 70 3 65 "unnatural" Methanol HBr 25 48 50 "unnatural" Methanol ZnCl 2 25 48 0 Methanol Si0 2 25 48 0 Benzene A1C13 25 48 0 Benzene BF 3 80 1.75 5 "unnatural" fa c i l e as the concentration of HC1 in the medium was increased. Further-more, this increase of the activation energy for the loss of a proton may eventually become sufficiently great that carbon-carbon bond cleavage was competitive. In such a case, the kinetics may be viewed as a rapid conversion of the chloroindolenine to the intermediate 109 irreversibly, which would then slowly be converted to the intermediate 113 reversibly. Compound 113 would then lose a proton reversibly in the rate determining step to form dimer 94, or i t s epimer at C _,, or else l o a mixture of these compounds. - 117 -A s t u d y o f t h e y i e l d and s t e r e o c h e m i c a l outcome o f t h e c o n v e n t i o n a l d i m e r i z a t i o n r e a c t i o n a s a f u n c t i o n o f a c i d c o n c e n t r a t i o n was t h u s u n d e r t a k e n . C o n c e n t r a t i o n s o f a c i d b e l o w 1.5% w e r e u s e d t o s e e w h e t h e r o r n o t t h e same d i m e r was f o r m e d u n d e r t h e s e c o n d i t i o n s w h i c h b e t t e r f a v o u r e d k i n e t i c c o n t r o l . A t v e r y l o w a c i d c o n c e n t r a t i o n s h o w e v e r , t h e r a t e d e t e r m i n i n g f o r m a t i o n o f i n t e r m e d i a t e 109 was s u f f i c i e n t l y s l o w t o p e r m i t t h e d e c o m p o s i t i o n o f t h e c h l o r o i n d o l e n i n e i r r e v e r s i b l y t o o t h e r p r o d u c t s and t h u s t h e y i e l d o f d i m e r i c m a t e r i a l o b t a i n e d was d r a m a t i c a l l y r e d u c e d . I n t h e l i m i t i n g c a s e , when t h e d i m e r i z a t i o n was a t t e m p t e d i n a b s o l u t e m e t h a n o l i t was f o u n d t h a t t h e c h l o r o i n d o l e n i n e and v i n d o l i n e c o u l d be r e c o v e r e d u n c h a n g e d as v i r t u a l l y t h e o n l y p r o d u c t s a f t e r s e v e r a l h o u r s o f r e f l u x i n g . A t t h e o t h e r end o f t h e s c a l e h o w e v e r , t h e g r a d u a l i n c r e a s e i n t h e a c i d c o n c e n t r a t i o n up t o 5% r e v e a l e d no d e t e c t a b l e c h a n g e i n t h e s t e r e o c h e m i s t r y o f t h e d i m e r i c p r o d u c t . A r e m a r k a b l e d i s c o v e r y was made u p o n p e r f o r m i n g t h e r e a c t i o n a c c o r d i n g t o t h e c l e a v a g e c o n d i t i o n s 84 p r e v i o u s l y r e p o r t e d d u r i n g t h e c h a r a c t e r i z a t i o n o f compound 9 4 . T h i s d i m e r h a d b e e n c o m p l e t e l y c l e a v e d by r e f l u x i n g i t f o r o n l y one h o u r i n a n h y d r o u s 7% m e t h a n o l i c h y d r o g e n c h l o r i d e c o n t a i n i n g s t a n n o u s c h l o r i d e and t i n . When t h e c h l o r o i n d o l e n i n e o f compound 107 and v i n d o l i n e w e r e r e f l u x e d t o g e t h e r f o r 3 . 5 h o u r s i n 7% m e t h a n o l i c h y d r o g e n c h l o r i d e t h e m a j o r p r o d u c t s , i n c o n t r a s t t o t h e a b o v e r e s u l t , w e r e t h e d i m e r 94 a n d i t s d e a c e t y l a n a l o g u e . M i n o r p r o d u c t s i n c l u d e d v i n d o l i n e , d e a c e t y l v i n d o l i n e and b a s e l i n e m a t e r i a l . Upon p u r i f i c a t i o n o f t h e d i m e r i c f r a c t i o n s , i t r a p i d l y became o b v i o u s t h a t t h e y c o n t a i n e d a n o t h e r m a t e r i a l w h i c h was a l m o s t i n s e p a r a b l e - 118 -from the dimer 9 4 . This material had a c h a r a c t e r i s t i c c o l o u r - r e a c t i o n on t i c to antimony pentachloride i n carbon t e t r a c h l o r i d e . A l l of the synthetic dimers so f a r analyzed showed a brown co l o u r - r e a c t i o n to t h i s reagent which was in v a r i a n t with time. This compound, on the other hand, was d i s t i n g u i s h a b l e from compound 94 i n the following way: when i n i t i a l l y sprayed with t h i s reagent both compounds showed up as in d i s t i n g u i s h a b l e brown spots. The new compound gradually turned pink while the spot corresponding to compound 94 did not change. A f t e r much e f f o r t and extensive decomposition, t h i s compound could be p u r i f i e d from dimer 94 by the use of high pressure l i q u i d chromatography on a s p e c i a l l y prepared column of deactivated alumina. Mass s p e c t r a l studies on t h i s p u r i f i e d f r a c t i o n revealed a molecular weight of 794 which was exactly the same as the molecular weight of dimer 9 4 . The F o u r i e r -Transform nmr of t h i s compound was not d i r e c t l y comparable to the normal spectrum of compound 9 4 . This was due to the f a c t that i n the extremely d i l u t e s o l u t i o n of the compound i n deuteriochloroform i t reacted with the r e s i d u a l aci d i n t h i s solvent to p a r t i a l l y form a s a l t . This s a l t thus modified the spectrum observed. The phenomenon was not e n t i r e l y new i n our la b o r a t o r i e s and had been observed by other workers as w e l l . The nmr of a mixture of the new compound with compound 94 p r i o r to separation was concentrated enough that t h i s problem was not serious here. This spectrum was extremely u s e f u l . It showed that the new compound did not lack any of the f u n c t i o n a l i t y present i n dimer 9 4 . The chemical s h i f t s of the protons which were expected to be diagnostic of changes i n stereochemistry about C 1 Q , were a l l exactly l o as expected for the C 1 0, epimer of compound 94. On th i s b a s i s , t h i s - 119 -compound was t e n t a t i v e l y p o s t u l a t e d t o be t h e d e s i r e d n a t u r a l s t e r e o -c h e m i s t r y d i m e r . I t s h o u l d h o w e v e r be e m p h a s i z e d t h a t t h i s a s s i g n m e n t was by no means d e f i n i t e . The c o m p l e t e s t r u c t u r a l a s s i g n m e n t o f t h i s compound must a w a i t i t s i s o l a t i o n i n l a r g e r q u a n t i t i e s t o p e r m i t f u r t h e r a n a l y s e s s u c h a s n o r m a l n m r , c l e a v a g e t o t h e monomers , a n d , p e r h a p s , f i n a l l y e v e n X - r a y c r y s t a l l o g r a p h y . N e v e r t h e l e s s , t h e i s o l a t i o n o f a new d i m e r i c compound u n d e r t h e s e c o n d i t i o n s e v e n i n t r a c e amounts i s a n e x t r e m e l y u s e f u l and g r a t i f y i n g r e s u l t s i n c e i t s u p p o r t s t h e p r e d i c t i o n s o f t h e t h e o r e t i c a l a r g u m e n t s m e n t i o n e d a b o v e . I f t h e s e p r e d i c t i o n s w e r e i n d e e d b e i n g b o r n e o u t i n t h e a b o v e e x p e r i m e n t , i t may be a r g u e d t h a t t h e e p i m e r i z a t i o n o f compound 94 t o a m i x t u r e o f t h e s e compounds must be p o s s i b l e u n d e r t h e r e a c t i o n c o n d i t i o n s . I n d e e d , s u b m i s s i o n o f d i m e r 94 t o i d e n t i c a l c o n d i t i o n s y i e l d e d a r e a c t i o n m i x t u r e w h i c h was e x a c t l y t h e same as t h a t o b t a i n e d a b o v e a n d f r o m w h i c h a s i m i l a r l y l o w (< 10%) y i e l d o f t h e new d i m e r was i s o l a b l e . U n f o r t u n a t e l y , a l l a t t e m p t s t o i m p r o v e t h e y i e l d o f t h i s compound b y i n c r e a s i n g t h e a c i d c o n c e n t r a t i o n b e y o n d 7% f a i l e d . F u r t h e r m o r e t h e o v e r a l l y i e l d o f d i m e r i c m a t e r i a l s l o w l y d e c r e a s e d as t h e a c i d c o n c e n t r a t i o n was i n c r e a s e d b e y o n d 15%. T h e s e r e s u l t s a r e s u m m a r i z e d i n T a b l e V I . C o n d i t i o n s f o r i m p r o v i n g t h i s r e a c t i o n a r e c u r r e n t l y b e i n g s o u g h t i n o u r l a b o r a t o r i e s . - 120 -T a b l e V I . E f f e c t o f a c i d c o n c e n t r a t i o n o n t h e c o u p l i n g r e a c t i o n . % HC1 i n m e t h a n o l Time ( h r ) Y i e l d (%) Type o f d i m e r 1 . 5 3 . 5 30 " u n n a t u r a l " 1 . 6 3 . 5 36 " u n n a t u r a l " 2 . 0 3 . 0 45 " u n n a t u r a l " 5 . 0 2 . 0 56 . " u n n a t u r a l " 7 . 0 3 . 5 50 m i x t u r e 15 3 . 5 40 m i x t u r e 30 3 . 0 30 m i x t u r e 60 3 . 0 25 m i x t u r e The s e c o n d g o a l o f t h i s s t u d y , n a m e l y t o i m p r o v e t h e y i e l d o f t h e d i m e r i z a t i o n u n d e r p o s s i b l y m i l d e r c o n d i t i o n s , was a l s o f o r t u i t o u s l y r e a l i z e d . D u r i n g t h i s s t u d y , t h e m e t h a n o l i c h y d r o g e n c h l o r i d e h a d b e e n p r e p a r e d b y a d d i n g t h e c a l c u l a t e d v o l u m e o f p u r i f i e d a c e t y l c h l o r i d e t o a n h y d r o u s m e t h a n o l w h i c h h a d b e e n c o o l e d t o 0 ° C . These two compounds r e a c t e d i n s t a n t l y t o y i e l d m e t h y l a c e t a t e and h y d r o g e n c h l o r i d e . T h u s , d u r i n g t h e s t u d y o f t h e e f f e c t s o f a c i d c o n c e n t r a t i o n m e n t i o n e d a b o v e , s u c c e s s i v e l y l a r g e r a l i q u o t s o f a c e t y l c h l o r i d e h a d b e e n a d d e d ; F o r t h e s a k e o f c o m p l e t e n e s s , a c o n v e n t i o n a l d i m e r i z a t i o n i n a c e t y l c h l o r i d e as s o l v e n t a t i t s r e f l u x t e m p e r a t u r e ( 5 1 - 5 2 ° C ) was a t t e m p t e d . The c h l o r o i n d o l e n i n e and v i n d o l i n e r e a d i l y d i s s o l v e d i n t h i s s o l v e n t . H o w e v e r , as t h e r e a c t i o n p r o c e e d e d , d i m e r 94 p r e c i p i t a t e d . Workup c o n s i s t e d m e r e l y o f r e m o v i n g t h e s o l v e n t u n d e r vacuum t o l e a v e a - 121 -w h i t i s h p o w d e r . D i s s o l u t i o n i n a n o r g a n i c s o l v e n t , ( m e t h y l e n e c h l o r i d e ) b a s i f i c a t i o n , a n d e x t r a c t i o n r e s u l t e d i n a n e a r q u a n t i t a t i v e y i e l d o f t h e d i m e r 94. I f t h i s r e a c t i o n w e r e r u n a t room t e m p e r a t u r e f o r a l o n g e r p e r i o d o f t i m e i t s h o u l d c o n s t i t u t e a m i l d and much i m p r o v e d s y n t h e s i s o f d i m e r s b e a r i n g s e n s i t i v e i n d o l e t e m p l a t e s . I n d e e d , i n i t i a l r e s u l t s i n t h e 18 - c a r b o m e t h o x y c l e a v a m i n e c a s e t o y i e l d d i m e r 99 h a v e b e e n e n c o u r a g i n g . T h u s , t h e g o a l o f a m i l d e r and h i g h e r y i e l d i n g r e a c t i o n f o r t h e d i m e r i z a t i o n o f s e n s i t i v e i n d o l e t e m p l a t e s h a d a l s o b e e n r e a l i z e d . I n summary, t h i s l a b o r i o u s and p a i n s t a k i n g s t u d y h a s b o r n e f r u i t i n s e v e r a l a r e a s . I t h a s p e r m i t t e d , f o r t h e f i r s t t i m e a p r o p e r and d e t a i l e d u n d e r s t a n d i n g o f t h e o v e r a l l d i m e r i z a t i o n r e a c t i o n . T h i s i n s i g h t h a s a l l o w e d t h e p r e d i c t i o n o f ways and means o f a r r i v i n g a t t h e n a t u r a l s t e r e o c h e m i s t r y . F i n a l l y , a m i l d a n d h i g h y i e l d i n g d i m e r i z a t i o n r e a c t i o n i s i n h a n d . A l l o f t h e s e f i n d i n g s a r e e x p e c t e d t o c o n t r i b u t e i m m e n s e l y t o t h e s y n t h e t i c g o a l s o f t h i s e n d e a v o u r . T h e r e r e m a i n e d , h o w e v e r , one q u e s t i o n o f p i v o t a l i m p o r t a n c e . T h i s d e a l t w i t h t h e c o n c l u s i v e e s t a b l i s h m e n t o f t h e a b s o l u t e s t e r e o c h e m i s t r y o f t h e c r u c i a l C 1 Q , c e n t r e . I t h a d b e e n a p p a r e n t f o r some t i m e t h a t l o a l t h o u g h s p e c u l a t i o n s b a s e d o n v a r i o u s s p e c t r a w e r e p o s s i b l e a n d i n d e e d w e r e p r o b a b l y c o r r e c t , c o n c r e t e p r o o f i n t h i s a r e a c o u l d o n l y be f u r n i s h e d by an X - r a y s t u d y o f one o f t h e s e d i m e r s . R e c e n t l y , P r o f e s s o r J . C . C l a r d y o f Iowa S t a t e U n i v e r s i t y e x p r e s s e d a n i n t e r e s t i n p e r f o r m i n g s u c h a s t u d y . D i m e r 94, w h i c h was t h e m a j o r compound f r o m a l l t h e e x p e r i m e n t s j u s t d e s c r i b e d , was c o n v e r t e d t o i t s c r y s t a l l i n e monometh-i o d i d e . A n X - r a y s t u d y has r e v e a l e d t h a t t h i s compound i s i n d e e d 104 i s o m e r i c t o t h e n a t u r a l d i m e r s a t C 1 Q | . I t s s t r u c t u r e may t h u s be - 122 -more p r o p e r l y r e p r e s e n t e d a s shown i n F i g u r e 28 ( 9 5 ) . Thus t h e p r e v i o u s d e d u c t i o n s , o n t h e b a s i s o f nmr d a t a , a b o u t t h e s t e r e o c h e m i s t r y a t C ^ g , w e r e p r o v e d t o be c o m p l e t e l y c o r r e c t . The s t r u c t u r e o f t h e d i m e r s 102 and 99 w e r e a l s o s e c u r e d by t h i s s t u d y . From t h e e v i d e n c e p r e s e n t e d i n F i g u r e 1 9 , i t was c l e a r t h a t t h e s t e r e o c h e m i s t r y a b o u t t h e C ^ g , c e n t r e i n t h e s e c a s e s was a l s o t h e u n n a t u r a l o n e . On t h i s b a s i s , a s w e l l a s o n t h e b a s i s o f t h e nmr d a t a p r e s e n t e d i n F i g u r e 2 3 , i t may be d e d u c e d t h a t i n d e e d , i n a l l t h e s y n t h e t i c d i m e r s made i n t h e s t a n d a r d w a y , t h e s t e r e o c h e m i s t r y a b o u t C 1 0 , i s u n n a t u r a l . l o T h i s g e n e r a l i z e d s t a t e m e n t was s u p p o r t e d b y a s e c o n d X - r a y s t u d y p e r f o r m e d o n d i m e r 96 - t h e compound l a c k i n g t h e C 1 Q , c a r b o m e t h o x y g r o u p l o b u t o t h e r w i s e i d e n t i c a l i n e v e r y r e s p e c t ; t o compound 94 a b o v e . D i m e r 96 h a s r e c e n t l y s t i m u l a t e d a g r e a t d e a l o f i n t e r e s t . Upon t e s t i n g i t 109 f o r a n t i n e o p l a s t i c a c t i v i t y , t h i s compound d e m o n s t r a t e d a c t i v i t y a g a i n s t P O O Q l y m p h o c y t i c l e u k e m i a i n m i c e a t d o s e l e v e l s c o m p a r a b l e t o J o o v i n c r i t i n e ( V C R ) . I n f a c t , m o s t r e c e n t e v i d e n c e a p p e a r s t o s u g g e s t t h a t i t may p o s s e s s a s u f f i c i e n t l y good t h e r a p e u t i c i n d e x t o w a r r a n t i t s c o n s i d e r a t i o n as a c l i n i c a l l y u s e f u l d r u g f o r man. I f d i m e r 96 i s a s u s e f u l a n a n t i c a n c e r a g e n t a s i n i t i a l t e s t s h a v e i n d i c a t e d , i t s h o u l d compete s u c c e s s f u l l y w i t h t h e e x t r e m e l y e x p e n s i v e n a t u r a l d r u g , V C R , t o become t h e f i r s t c l i n i c a l l y i m p o r t a n t s y n t h e t i c d i m e r e v e r t o be r e p o r t e d i n t h i s s e r i e s . T h i s a c t i v i t y c o u l d be e x p l a i n e d i n t h r e e ways a_ p r i o r i (a) I t c o u l d be a n i n d i c a t i o n t h a t t h e C 1 Q , c a r b o m e t h o x y g r o u p i s o f no l o c o n s e q u e n c e as f a r as s t r u c t u r e - a c t i v i t y r e l a t i o n s a r e c o n c e r n e d . (b) A somewhat more i n t r i g u i n g p o s s i b i l i t y was t h a t , i n t h e c a s e o f t h e - 123 -o COOMe (95) F i g u r e 2 8 . X - r a y s t r u c t u r e o f d i m e r ( 9 5 ) . - 124 -C Q , h y d r o g e n d i m e r s , t h e s t e r e o c h e m i s t r y a t t h i s c e n t r e was i n v e r t e d l o r e l a t i v e t o compound 94 i n t h e s y n t h e t i c m a t e r i a l . ( c ) F i n a l l y , i t i s p o s s i b l e t h a t t h e b i o l o g i c a l s y s t e m o f t h e h o s t mouse i s a b l e t o p e r f o r m t h i s i n v e r s i o n t o a n a t u r a l s t e r e o c h e m i s t r y d i m e r e v e n i f t h e s t e r e o -c h e m i s t r y i s i n i t i a l l y u n n a t u r a l . A m e c h a n i s m f o r t h i s i n v e r s i o n may be a s shown i n F i g u r e 2 9 . The C 1 Q , p r o t o n i s b e n z y l i c w i t h r e s p e c t l o CH 0 3 CH30 CH 3 C02CH3 3" C02CH3 F i g u r e 2 9 . A m e c h a n i s m f o r t h e e p i m e r i z a t i o n o f d i m e r ( 9 6 ) , t o t h e v i n d o l i n e p o r t i o n a n d " a l l y l i c " w i t h r e g a r d t o t h e i n d o l e p o r t i o n . The l o s s o f t h i s p r o t o n s h o u l d t h u s g e n e r a t e a r a t h e r s t a b l e c e n t r e a t C 1 Q , and r e p r o t o n a t i o n f r o m t h e l e s s h i n d e r e d B - f a c e w o u l d l e a d l o t o t h e e p i m e r i c d i m e r . S i n c e t h i s m e c h a n i s m c o u l d , i n p r i n c i p l e , o c c u r i n v i v o , o r i n v i t r o u n d e r t h e r e a c t i o n c o n d i t i o n s i t was n e c e s s a r y t o p r o v e t h e s t r u c t u r e o f compound 96 by X - r a y c r y s t a l l o g r a p h y . To t h i s e n d , compound 96 was t r a n s f o r m e d i n t o i t s c r y s t a l l i n e m o n o h y d r o -b r o m i d e a n d t h e n s u b j e c t e d t o X - r a y a n a l y s i s . The r e s u l t s c o n f i r m e d t h a t t h e s t e r e o c h e m i s t r y was i n d e e d t h e u n n a t u r a l one as shown i n - 125 -Figure 30. This compound is now more properly represented as structure 97. The possibility that this epimerization may have occurred under the reaction conditions was thus ruled out. This X-ray analysis also provided some concrete evidence for earlier work in other laboratories. As mentioned previously, the L i l l y group had elucidated the structures of three dimeric compounds: deoxy VLB-'A', -'B' and -'C1. They had shown that 'A' and 'B' were not C l g, epimers of each other but that both were epimeric to deoxy VLB-'C' at this centre. This claim was based on an nmr comparison of their decarbo-methoxydeacetoxy hydrazides. However, at that time they were unable to assign the stereochemistry at this centre as either natural or unnatural with any degree of certainty. Since deoxy VLB-'C' and compound 97 are in fact the same compound, this X-ray study enables one to assign the unnatural stereochemistry to this compound about C-^ g? and, therefore, the natural stereochemistry to the compounds in the deoxy VLB-'A' and -'B' series. Both these X-ray studies have thus provided v i t a l information in this area of chemistry and have replaced speculation by a concrete framework upon which much more rational discussions may be based. It i s possible that the carbomethoxy group at C. o l is unimportant l o to the overall activity of any dimer or even that of a hydrogen at this centre i s necessary for biological activity. It would seem logical to synthesize the decarbomethoxy (at C. ,) analogs of dimers 99, 102, and l o 106 at some future date and to examine their anticancer activity. This would enable a more thorough evaluation of the importance of the above finding and may also simultaneously provide other drugs with - 1 2 6 -F i g u r e 3 0 . X - r a y s t r u c t u r e o f d i m e r ( 9 7 ) . - 127 -perhaps a d i f f e r e n t spectrum of a c t i v i t y . While the study j u s t described was under way, other avenues of approach that might y i e l d the natural stereochemistry dimers by a mild and possibly h i g h - y i e l d i n g step, were simultaneously being considered and explored. Some of these studies have shown great promise and are currently under a c t i v e s c r u t i n y by other workers i n our l a b o r a t o r i e s . It i s useful at t h i s stage to describe these concepts and the general pattern of thought behind them as w e l l as to mention the i n i t i a l experiments that have been performed. The l i n k i n g of two carbon atoms, i n t e r - or intra- m o l e c u l a r l y , may, i n p r i n c i p l e be v i s u a l i z e d as occurring i n one of three p o s s i b l e ways: (a) Carbon atom A may function as the nucleophile and may attack atom B which has been s u i t a b l y a c t i v a t e d as an e l e c t r o p h i l i c centre. (b) Carbon atom B may function as the nucleophile and attack atom A or, (c) The two centres may come together by a free r a d i c a l coupling r e a c t i o n . A l l of the work thus f a r described i n t h i s thesis and indeed, a l l of the work reported i n t h i s s e r i e s of a l k a l o i d s i n the l i t e r a t u r e , has concentrated on v a r i a t i o n s of the f i r s t approach i n which the C ^ p o s i t i o n of vi n d o l i n e functions as the nucleophile. This was, i n many respects, the l o g i c a l choice from the point of view of a synthetic plan because t h i s p o s i t i o n i s ele c t r o n r i c h . Furthermore, the a c t i v a t i o n of the C^g p o s i t i o n of the indole template as an e l e c t r o p h i l e i s f a c i l e . Some other avenues of approach which also u t i l i z e v i n d o l i n e as the nucleophile were attempted i n our laboratory. The work mentioned above - 128 -c o n c e n t r a t e d a l m o s t e x c l u s i v e l y on c o n d i t i o n s , f o r t h e c o u p l i n g r e a c t i o n , t h a t w e r e e s s e n t i a l l y a c i d i c . S u c h c o n d i t i o n s w o u l d o f c o u r s e f a v o u r t h e n o n - c o n c e r t e d m e c h a n i s m v i a i n t e r m e d i a t e 109 as o u t l i n e d i n F i g u r e s 24 a n d 2 7 . The s t e r e o c h e m i c a l outcome o f s u c h a m e c h a n i s m h a s a l r e a d y b e e n a m p l y d e m o n s t r a t e d . What w o u l d be t h e s t e r e o c h e m i c a l o u t c o m e , h o w e v e r , u n d e r c o n d i t i o n s t h a t w e r e n e u t r a l o r b a s i c a n d w h i c h d i d n o t f a v o u r t h e f o r m a t i o n o f s u c h a n i n t e r m e d i a t e ? The n o r m a l F r i e d e l -C r a f t s a l k y l a t i o n o f a r o m a t i c s y s t e m s u n d e r s u c h c o n d i t i o n s i s d i f f i c u l t i f n o t i m p o s s i b l e . Some m o d i f i c a t i o n s w e r e n e c e s s a r y i n o r d e r t o f u r n i s h a n a n s w e r t o t h e above q u e s t i o n . I t was f o u n d t h a t v i n d o l i n e r e a c t e d s p o n t a n e o u s l y w i t h s o u r c e s o f " p o s i t i v e " h a l o g e n i n s o l u t i o n . The c a r e f u l l y c o n t r o l l e d a d d i t i o n o f 1 . 0 0 m o l e e q u i v a l e n t s o f N - b r o m o s u c c i n i m i d e t o a s o l u t i o n o f v i n d o l i n e i n m e t h y l e n e c h l o r i d e a t 0°C r e s u l t e d i n t h e i s o l a t i o n o f 1 5 - b r o m o -v i n d o l i n e (114) as t h e o n l y p r o d u c t . I t c o u l d be c o m p l e t e l y c h a r a c t e r i z e d b y i t s i r , n m r , and uv s p e c t r a t o g e t h e r w i t h e l e m e n t a l a n a l y s i s and mass s p e c t r o s c o p y . The m o s t i n f o r m a t i v e s p e c t r a i n t h i s c a s e w e r e t h e nmr ( F i g u r e 31) and t h e mass s p e c t r a ( F i g u r e 3 2 ) . The f o r m e r showed t h a t a l l t h e f u n c t i o n a l i t y o f t h e v i n d o l i n e m o i e t y was i n t a c t a n d t h a t t h e d o u b l e t o f d o u b l e t s a t T 4 . 2 a t t r i b u t a b l e t o t h e C^, . p r o t o n o f v i n d o l i n e h a d d i s a p p e a r e d . F u r t h e r m o r e , t h e and p r o t o n s i g n a l s h a d c o l l a p s e d t o s i n g l e t s , and had s h i f t e d s l i g h t l y f r o m t h e i r p o s i t i o n s i n v i n d o l i n e a t T 3 . 1 2 and 3 . 9 8 r e s p e c t i v e l y t o T 2 . 8 6 and 3 . 8 7 r e s p e c t i v e l y a s w o u l d be e x p e c t e d by t h e i n t r o d u c t i o n o f b r o m i n e a t t h e C^, . p o s i t i o n . The mass s p e c t r u m showed t h e e x p e c t e d i s o t o p e r a t i o o f 1 : 1 f o r t h e m o l e c u l a r i o n p e a k a t t r i b u t a b l e t o t h e i s o t o p i c r a t i o o f t h e two i s o t o p e s o f - 129 -- 131 -b r o m i n e , t h u s c o n f i r m i n g t h e i d e n t i t y o f t h i s c o m p o u n d . I n a d d i t i o n , t h e f r a g m e n t a t i o n o f v i n d o l i n e h a s b e e n c a r e f u l l y s t u d i e d and t h e e s t a b l i s h e d f r a g m e n t a t i o n scheme i s a s shown i n F i g u r e 3 3 . T h i s f r a g m e n t a t i o n p a t t e r n was v i r t u a l l y c o m p l e t e l y s u p p o r t e d by t h e mass s p e c t r u m o f t h e 1 5 - b r o m o v i n d o l i n e . A l l t h e f r a g m e n t s c o n t a i n i n g t h e a r o m a t i c p o r t i o n a p p e a r e d a s two p e a k s i n a 1 : 1 r a t i o a t 79 a n d 81 u n i t s h i g h e r t h a n t h e c o r r e s p o n d i n g p e a k s i n v i n d o l i n e . The p e a k s c o r r e s p o n d i n g t o t h e f r a g m e n t s n o t c o n t a i n i n g t h e a r o m a t i c r i n g w e r e u n s h i f t e d r e l a t i v e t o v i n d o l i n e . T h u s , t h e c o m p l e t e s t r u c t u r e o f t h i s compound c o u l d , i n t h e o r y , be d e d u c e d f r o m e i t h e r t h e nmr o r mass s p e c t r u m a l o n e . 113 H . G i l m a n and c o w o r k e r s h a d p r e v i o u s l y t r e a t e d r e l a t e d a r o m a t i c h a l i d e s , p a r t i c u l a r l y b r o m i d e s , w i t h r i - b u t y l l i t h i u m u n d e r c o n t r o l l e d c o n d i t i o n s a n d h a d o b t a i n e d h i g h y i e l d s o f t h e c o r r e s p o n d i n g a r o m a t i c o r g a n o l i t h i u m c o m p o u n d s . F o r e x a m p l e , t r e a t m e n t o f d i b r o m o c a r b a z o l e (115) a c c o r d i n g t o t h e scheme shown i n F i g u r e 34 a f f o r d e d a h i g h y i e l d o f t h e c o r r e s p o n d i n g d i a c i d b y t h i s a p p r o a c h . I f i t w e r e p o s s i b l e t o make t h e c o r r e s p o n d i n g a n i o n f r o m 1 5 - b r o m o v i n d o l i n e , t h i s p o s i t i o n w o u l d be f u r t h e r a c t i v a t e d t o w a r d s d i m e r i z a t i o n as w e l l as m a k i n g i t p o s s i b l e f o r t h e r e a c t i o n t o be p e r f o r m e d u n d e r b a s i c c o n d i t i o n s w h e r e t h e m e c h a n i s m may be d i f f e r e n t f r o m t h e one p o r t r a y e d b e f o r e . V i n d o l i n e i s a l a r g e a n d c o m p l e x m o l e c u l e b e a r i n g s e v e r a l f u n c t i o n a l i t i e s s u c h as c a r b o m e t h o x y and a c e t o x y g r o u p s w h i c h a r e t h e m s e l v e s s u s c e p t i b l e t o a t t a c k by o r g a n o l i t h i u m c o m p o u n d s . I f t h e a n i o n c o u l d be made w i t h a s t o i c h i o m e t r i c amount o f j n - b u t y l l i t h i u m u n d e r r e l a t i v e l y m i l d c o n d i t i o n s , h o w e v e r , t h e most r e a c t i v e c e n t r e s h o u l d r e a c t f i r s t . A c c o r d i n g t o - 132 -F i g u r e 3 3 . Mass s p e c t r a l f r a g m e n t a t i o n scheme f o r v i n d o l i n e . - 133 -S t a r t i n g m a t e r i a l Time Temp. P r o d u c t Y i e l d 2 - b r o m o c a r b a z o l e 60 m i n r e f l u x 2 - l i t h i o c a r b a z o l e 5 7 . 8 5 - e t h y l - 2 - b r o m o c a r b a z o l e 70 m i n r e f l u x 5 - e t h y l - 2 - l i t h i o - 7 1 . 1 c a r b a z o l e 5 - e t h y l - 2 - i o d o c a r b a z o l e 20 h r r e f l u x 5 - e t h y l - 2 - l i t h i o - 6 7 . 0 c a r b a z o l e 5 - e t h y l - 2 , 8 - d i i o d o c a r b a z o l e 75 m i n r e f l u x 5 - e t h y l - 2 , 8 - d i - 7 9 . 0 l i t h i o c a r b a z o l e F i g u r e 3 4 . G i l m a n ' s s y n t h e s i s o f compound 1 1 6 . - 134 -p r e v i o u s w o r k i n t h e l i t e r a t u r e , t h i s was e x p e c t e d t o be t h e C^, . b r o m i n e a t o m . Once h a l o g e n - m e t a l i n t e r c o n v e r s i o n h a d o c c u r r e d , t h e a n i o n o f v i n d o l i n e w o u l d be t o o b u l k y t o p a r t i c i p a t e i n i n t e r m o l e c u l a r c o n d e n s a t i o n s a t t h e c a r b o m e t h o x y o r a c e t o x y g r o u p s o f a n o t h e r v i n d o l i n e m o l e c u l e . M o l e c u l a r m o d e l s r e v e a l e d t h a t b o t h t h e s e g r o u p s w e r e i n a r a t h e r s t e r i c a l l y c r o w d e d e n v i r o n m e n t . One f u r t h e r f a c t o r f a v o u r e d s u c h a n a p p r o a c h . U n d e r a p p r o p r i a t e c o n d i t i o n s , n - b u t y l l i t h i u m h a s b e e n u s e d t o a c t a s a s t r o n g b a s e r a t h e r t h a n a n u c l e o p h i l e t o p r o d u c e , f o r e x a m p l e , t h e e n o l a t e a n i o n s o f c a r b o n y l g r o u p s . T h u s , i t was f e l t t h a t u n d e r t h e r e a c t i o n c o n d i t i o n s c h o s e n f o r t h e h a l o g e n -m e t a l i n t e r c h a n g e p e r h a p s a n u c l e o p h i l i c c o n d e n s a t i o n by t h e n - b u t y l a n i o n o n t o t h e c a r b o m e t h o x y o r a c e t o x y g r o u p s c o u l d a l s o be r u l e d o u t . S i n c e t h e v i n d o l i n e m o i e t y has a n a c t i v e h y d r o g e n i n t h e a l c o h o l f u n c t i o n a l i t y , h o w e v e r , a n e x t r a m o l e e q u i v a l e n t o f t h e b a s e w o u l d be r e q u i r e d i n o r d e r t o f o r m t h e l i t h i u m a l k o x i d e a t t h i s p o s i t i o n a n d consume t h i s a c i d i c h y d r o g e n . The i n i t i a l r e a c t i o n p e r f o r m e d e x c e e d e d a l l e x p e c t a t i o n s . The a n i o n was p r o d u c e d i n t e t r a h y d r o f u r a n , by t h e g r a d u a l a d d i t i o n o f two m o l e e q u i v a l e n t s o f a 2 . 0 M s o l u t i o n o f n - b u t y l l i t h i u m i n h e x a n e a t - 7 8 ° C . Warming t o 20°C f o l l o w e d b y q u e n c h i n g t h e r e a c t i o n w i t h w a t e r p r o v i d e d a c r u d e p r o d u c t w h i c h by nmr a n d t i c c o n s i s t e d m a i n l y o f v i n d o l i n e and d e a c e t y l v i n d o l i n e a s j u d g e d b y t h e c h a n g e s i n t h e s i g n a l s a t t r i b u t a b l e t o t h e and p o s i t i o n s a s w e l l a s t h e a p p e a r a n c e o f a new q u a r t e t . I n p a r t i c u l a r , t h e C^, . bromo compound h a d c o m p l e t e l y d i s a p p e a r e d . The d e a c e t y l a t i o n r e a c t i o n may h a v e o c c u r r e d e i t h e r d u r i n g t h e r e a c t i o n o r d u r i n g t h e w o r k u p when l i t h i u m h y d r o x i d e was g e n e r a t e d . When t h e - 135 -a n i o n was f o r m e d as a b o v e and q u e n c h e d w i t h a c e t y l c h l o r i d e , t h e a c y l g r o u p was i n c o r p o r a t e d and l i t h i u m c h l o r i d e p r e c i p i t a t e d . To p r o v i d e c o n c r e t e p r o o f t h a t b o t h t h e s e r e a c t i o n s d i d n o t , f o r e x a m p l e , p r o c e e d v i a a b e n z y n e i n t e r m e d i a t e , i t was n e c e s s a r y t o o b t a i n a c o n d e n s a t i o n o f t h i s a n i o n o n t o a k e t o n e . A n o n - e n o l i z a b l e k e t o n e was n e c e s s a r y b e c a u s e t h e a n i o n may f u n c t i o n s i m p l y as a s t r o n g b a s e t o f o r m t h e e n o l a t e a n d t h u s no a p p a r e n t r e a c t i o n w o u l d o c c u r . B e n z o p h e n o n e was c h o s e n s i n c e i t h a d b e e n e m p l o y e d b e f o r e as a t e s t f o r s u c h a n i o n s . The c o n d e n s a t i o n o f t h i s compound o n t o v i n d o l i n e , h o w e v e r , p r o v e d t o be a n e x t r e m e l y c a p r i c i o u s r e a c t i o n and a p p e a r e d t o w o r k o n l y when t h e e n t i r e r e a c t i o n was c a r r i e d o u t i n one f l a s k i n a b e n z e n e s o l u t i o n a t room t e m p e r a t u r e . U n d e r t h e s e c o n d i t i o n s , a r e a c t i o n m i x t u r e c o u l d be i s o l a t e d f r o m w h i c h t h e m a j o r compounds c o u l d be i d e n t i f i e d a s d e a c e t y l v i n d o l i n e and a p r o d u c t t h a t m i g h t h a v e b e e n t h e d i p h e n y l -d e a c e t y l v i n d o l i n e - c a r b i n o l o n t h e b a s i s o f i t s nmr s p e c t r u m . F i r m e v i d e n c e f o r t h e f o r m a t i o n o f t h i s compound, h o w e v e r , i s as y e t l a c k i n g . I n any e v e n t , i t was d e c i d e d t o a t t e m p t t o r e a c t t h i s compound w i t h t h e c h l o r o i n d o l e n i n e o f compound 1 0 7 . I t was p o s s i b l e t h a t u n d e r t h e c o n d i t i o n s e m p l o y e d , a c o n c e r t e d r e a c t i o n may o c c u r a n d t h i s may be r e f l e c t e d i n t h e f i n a l s t e r e o c h e m i s t r y o f t h e d i m e r i c p r o d u c t . The c h l o r o i n d o l e n i n e was f o r m e d i n t h e u s u a l way and t h e n r e a c t e d w i t h a t w o -f o l d e x c e s s o f t h e a n i o n o f v i n d o l i n e w h i c h h a d b e e n made , a s d e s c r i b e d a b o v e , i n t e t r a h y d r o f u r a n . Workup f o l l o w e d by p u r i f i c a t i o n a f f o r d e d a 10% o v e r a l l y i e l d , b a s e d o n t h e c h l o r o i n d o l e n i n e , o f t h e d i m e r 94 a s t h e o n l y i s o l a b l e d i m e r i c p r o d u c t . C l e a r l y , t h e s m a l l amount o f f r e e l i t h i u m i o n s p r e s e n t i n s o l u t i o n h a d c a t a l y z e d a n o n - c o n c e r t e d l o s s o f t h e c h l o r i d e as l i t h i u m c h l o r i d e t o g e n e r a t e t h e same i n t e r m e d i a t e (109) - 136 -as i n t h e c a s e o f t h e a c i d c a t a l y z e d r e a c t i o n s . The s u b s e q u e n t d i m e r i z a t i o n o f t h i s w i t h t h e v i n d o l i n e g e n e r a t e d b y t h e a b s t r a c t i o n o f t h e C . Q p r o t o n o f t h e c h l o r o i n d o l e n i n e by t h e v i n d o l i n e a n i o n w o u l d l o a c c o u n t f o r t h e d i m e r i c p r o d u c t . R e c e n t l y , F . G . B o r d w e l l a n d T . G . 114 M e c c a h a v e p r e s e n t e d a s t r o n g c a s e a g a i n s t t h e e x i s t e n c e i n v i t r o o f S N ^ ' r e a c t i o n s p e r s e . C e r t a i n l y , t h e r e s u l t s d e s c r i b e d a b o v e c a n n o t be u s e d t o d i s c o u n t t h e c l a i m s o f t h e s e w o r k e r s , and may i n d e e d c o n f i r m a n d s u p p o r t t h e m . S e v e r a l o t h e r m o d i f i c a t i o n s w e r e a t t e m p t e d . F o r e x a m p l e , t h e p o s s i b i l i t y o f a n o n - c o n c e r t e d l o s s o f c h l o r i d e may be c i r c u m v e n t e d by u s i n g t h e r e a c t i o n d e s c r i b e d e a r l i e r t o i n t r o d u c e a C s u b s t i t u e n t l o s u c h as m e t h o x y l o r a c e t o x y l i n a s e p a r a t e s t e p . T h i s c o u l d t h e n be d i s p l a c e d i n a c o n c e r t e d SN^ r e a c t i o n by t h e v i n d o l i n e a n i o n . The c e n t r e a t w h i c h d i s p l a c e m e n t was t o o c c u r h o w e v e r , was a t e r t i a r y o n e . A l t h o u g h i n some c a s e s , c o n c e r t e d d i s p l a c e m e n t s : a d j a c e n t t o a n e s t e r g r o u p w e r e known t o o c c u r e v e n a t s u c h c e n t r e s , some d i f f i c u l t i e s w e r e a n t i c i p a t e d h e r e p r i m a r i l y b e c a u s e o f t h e b u l k o f t h e i n c o m i n g n u c l e o p h i l e . N o n e t h e l e s s , t h i s e x p e r i m e n t was p e r f o r m e d w i t h 1 8 - m e t h o x y - a n d 1 8 -a c e t o x y - c a r b o m e t h o x y - 4 8 - d i h y d r o c l e a v a m i n e s p r o d u c e d by r e a c t i n g t h e c h l o r o i n d o l e n i n e o f compound 107 w i t h a 1.5% s o l u t i o n o f h y d r o g e n c h l o r i d e i n m e t h a n o l a n d a c e t i c a c i d r e s p e c t i v e l y . I n b o t h c a s e s , t h e f o r m a t i o n o f t h e C^g s u b s t i t u t e d m a t e r i a l was r a p i d and o c c u r r e d i n h i g h y i e l d . T h e s e compounds f a i l e d t o r e a c t i n t h e d e s i r e d w a y , h o w e v e r , w i t h t h e a n i o n o f v i n d o l i n e u n d e r a w i d e v a r i e t y o f c o n d i t i o n s . F i n a l l y , i n a n a t t e m p t t o s e e w h e t h e r t h e s e compounds w o u l d r e a c t a t a l l w i t h o r g a n o -l i t h i u m r e a g e n t s , t h e C , H a c e t o x y compound was r e a c t e d w i t h an e x c e s s o f - 137 -m e t h y l l i t h i u m . The r e a c t i o n m i x t u r e was f o u n d t o be e x t r e m e l y c o m p l e x . The l a b o r i o u s s e p a r a t i o n and i d e n t i f i c a t i o n o f t h e m a j o r p r o d u c t s a f f o r d e d t h e r a t h e r d i s a p p o i n t i n g r e s u l t t h a t none o f t h e d e s i r e d C^g m e t h y l compound had b e e n f o r m e d . On t h e b a s i s o f t h i s d i s c o u r a g i n g e v i d e n c e , t h i s p a r t i c u l a r a p p r o a c h was a b a n d o n e d . I t was f e l t , h o w e v e r , t h a t t h e p r e s e n c e o f a c a r b o n y l a t C 0 may l o f a c i l i t a t e a t t a c k by t h e a n i o n o n t o t h i s p o s i t i o n and may y i e l d two e p i m e r i c C-^gi h y d r o x y d i m e r s . T h e s e compounds w o u l d n o t o n l y be i n t e r e s t i n g i n t h e m s e l v e s i n a c l i n i c a l s e n s e b u t c o u l d e a s i l y be c o n v e r t e d , by h y d r o g e n o l y s i s o f t h e C 1 Q , a l c o h o l , t o a C . o t h y d r o g e n l o l o d i m e r e p i m e r i c a t C , t o d i m e r 97 f o r w h i c h X - r a y e v i d e n c e was now l o a v a i l a b l e . F u r t h e r m o r e i t m i g h t be p o s s i b l e t o r e p l a c e t h e h y d r o x y l f u n c t i o n a l i t y w i t h a c a r b o n - c a r b o n l i n k a g e w h i c h may be c o n v e r t e d t o t h e C o l c a r b o m e t h o x y g r o u p . T h i s c o u l d , f o r e x a m p l e , be a n i t r i l e g r o u p , l o I f t h i s r e a c t i o n w e r e p e r f o r m e d i n a n o n - c o n c e r t e d S N ^ m a n n e r , t h e i n t e r m e d i a t e w o u l d be s i m i l a r t o 109 a b o v e . I f i t i s assumed t h a t t h e same s t e r e o s e l e c t i v i t y o p e r a t e s i n t h i s i n t e r m e d i a t e as o p e r a t e d d u r i n g t h e c o n v e n t i o n a l d i m e r i z a t i o n r e a c t i o n , t h e n t h e i n c o m i n g n i t r i l e must a t t a c k t h e 6 - f a c e o f t h e m o l e c u l e t o p r o d u c e t h e n a t u r a l s t e r e o c h e m i s t r y a b o u t C ^ g , i n t h e r e s u l t i n g n i t r i l e d i m e r . The a p p r o a c h e s e n v i s i o n e d f o r t h e s y n t h e s i s o f t h e r e q u i r e d a c y l i n d o l e a r e o u t l i n e d i n F i g u r e 3 5 . E a c h one o f t h e s e a p p r o a c h e s h a s c e r t a i n d i f f i c u l t i e s a s s o c i a t e d w i t h i t a n d p r e l i m i n a r y e x p e r i m e n t s h a v e r e v e a l e d some o f t h e s e d i f f i c u l t i e s i n e a c h c a s e . A p p r o a c h A a p p e a r e d t o i n v o l v e t h e most d i r e c t e x t e n s i o n o f known c h e m i s t r y . I n d e e d t h i s w h o l e s e q u e n c e had been c a r r i e d o u t (R = OAc) f r o m compound 107 t o - 138 F i g u r e 3 5 . A p p r o a c h e s t o t h e s y n t h e s i s o f t h e a c y l i n d o l e ( 1 1 7 ) . - 139 -117 as p a r t o f t h e p r o o f o f t h e s t r u c t u r e o f t h e C _ a c e t o x y c o m p o u n d . As m e n t i o n e d p r e v i o u s l y i n t h e d e s c r i p t i o n o f a s i m i l a r r e a c t i o n i n t h e C 1 D m e t h o x y s e r i e s ( v i d e s u p r a ) t h e h y d r i d e r e d u c t i o n o f t h e C „ l o l o s u b s t i t u t e d compound p r o c e e d e d i n l o w o v e r a l l y i e l d t o g i v e a r a t h e r c o m p l e x r e a c t i o n m i x t u r e . I n a g r e e m e n t w i t h t h i s o b s e r v a t i o n , t h e o v e r a l l y i e l d o f compound 117 i s o l a t e d by r o u t e A f r o m compound 107 was r o u g h l y 10%. B o t h p a t h w a y s B a n d C r e p r e s e n t a t t e m p t s t o c i r c u m v e n t t h i s l o w y i e l d i n g r e d u c t i o n s t e p . I n p a t h w a y B t h i s was a c c o m p l i s h e d by r e d u c i n g t h e e s t e r p r i o r t o a n y C . Q f u n c t i o n a l i z a t i o n . Though t h e l o r e d u c t i o n p r o c e e d e d i n n e a r l y q u a n t i t a t i v e y i e l d i n t h i s c a s e t o a f f o r d compound 1 1 8 , i t was f o u n d t h a t any t r e a t m e n t o f t h e c o r r e s p o n d i n g c h l o r o i n d o l e n i n e o f t h i s compound u n d e r a c i d i c c o n d i t i o n s r e s u l t e d i n t h e f o r m a t i o n o f t h e C . Q a l d e h y d e (121) a s t h e m a j o r p r o d u c t (70%) l o t o g e t h e r w i t h t h e d e s i r e d d i o l as a m i n o r p r o d u c t (30%). The m e c h a n i s m f o r t h i s r e a c t i o n i s t h o u g h t t o be as shown i n F i g u r e 3 6 . T h i s phenomenon h a d b e e n n o t e d i n a s i m i l a r c a s e i n o u r l a b o r a t o r i e s . The a l d e h y d e was e a s i l y i d e n t i f i e d o n t h e b a s i s o f i t s nmr s p e c t r u m ( F i g u r e 37) as w e l l a s t h e c a r b o n y l a b s o r p t i o n i n i t s i r s p e c t r u m . I t c o u l d be r e d u c e d w i t h s o d i u m b o r o h y d r i d e i n e t h a n o l t o t h e s t a r t i n g p r i m a r y a l c o h o l ( 1 1 8 ) , t h u s p r o v i n g i t s s t r u c t u r e t o be as a s s i g n e d . A t t e m p t s t o b l o c k s u c h a r e a c t i o n b y s u i t a b l y m a s k i n g t h e p r i m a r y a l c o h o l f u n c t i o n a l i t y a r e c u r r e n t l y i n p r o g r e s s i n o u r g r o u p . P a t h w a y C e f f e c t i v e l y removes t h e p r o b l e m a t i c c e n t r e i n p a t h w a y A and B e n t i r e l y . T h u s , i n t h e o r y , i t s h o u l d be d e v o i d o f any o f t h e t e c h n i c a l p r o b l e m s o f t h e o t h e r two s c h e m e s . One p r o b l e m t h a t may be a n t i c i p a t e d h e r e i n v o l v e s t h e f i n a l o x i d a t i o n s t e p . Though o n t h e s u r f a c e - 140 -C I CHO (121) F i g u r e 3 6 . R e a c t i o n s o f t h e c h l o r o i n d o l e n i n e o f compound 118 u n d e r a c i d i c c o n d i t i o n s . - 141 -- 142 -i t may a p p e a r t o be t h e t r i v i a l l y s i m p l e o x i d a t i o n o f a n " a l l y l i c " s e c o n d a r y a l c o h o l ( 1 2 0 ) ; p a s t e x p e r i e n c e s w i t h i n d o l e a l k a l o i d s i n o u r l a b o r a t o r i e s (some o f w h i c h a r e m e n t i o n e d i n P a r t 1 o f t h i s d i s c u s s i o n ) w o u l d s u g g e s t t h a t t h e i n d o l e c h r o m o p h o r e i s r e m a r k a b l y s u s c e p t i b l e t o o x i d a t i o n i t s e l f . One method o f a c h i e v i n g t h i s o x i d a t i o n w o u l d be t o u t i l i z e t h i s r e a c t i v i t y o f t h e i n d o l e by f o r m i n g t h e c h l o r o i n d o l e n i n e o f compound 120 a g a i n . T h i s may be s o l v o l y z e d i n a n o n - h y d r o x y l i c s o l v e n t s u c h a s c h l o r o f o r m o r d i c h l o r o m e t h a n e . S u c h c o n d i t i o n s w o u l d f o r c e i n t r a m o l e c u l a r p a r t i c i p a t i o n by t h e l o n e p a i r o f e l e c t r o n s o n t h e C , Q a l c o h o l o x y g e n t o r e g e n e r a t e a r o m a t i c i t y a n d p r o d u c e t h e d e s i r e d l o 2 - a c y l i n d o l e i n one s t e p . E v e n t h e u s e o f h y d r o x y l i c s o l v e n t s s u c h a s m e t h a n o l i c h y d r o g e n c h l o r i d e w o u l d r e s u l t i n e i t h e r t h e f o r m a t i o n o f t h e a c y l i n d o l e d i r e c t l y v i a t h e i n t r a m o l e c u l a r r e a c t i o n m e n t i o n e d a b o v e o r e l s e w o u l d r e s u l t i n t h e f o r m a t i o n o f a h e m i k e t a l s t r u c t u r e v i a s o l v e n t p a r t i c i p a t i o n w h i c h w o u l d be c o n v e r t e d i n s i t u , o r u p o n w o r k u p , t o compound 1 1 7 . A n o t h e r p r o m i s i n g a n d u s e f u l s e q u e n c e , t h a t h a s b e e n d e v e l o p e d by o t h e r w o r k e r s i n o u r g r o u p i n v o l v e s e s s e n t i a l l y a c y a n y l a t i o n o f t h e p r e f o r m e d d i m e r 9 7 . T h i s a p p r o a c h i s p a r t i c u l a r l y a p p e a l i n g b e c a u s e i t t u r n s t h e p r e v i o u s l y u n d e s i r a b l e s t e r e o s e l e c t i v i t y o f t h e c o u p l i n g r e a c t i o n t o a d v a n t a g e by a l l o w i n g t h e same s t e r e o s e l e c t i v i t y t o g u i d e t h e a p p r o a c h o f c y a n i d e o n t o t h e m o l e c u l e . T h u s , i f t h e c h l o r o i n d o l e n i n e o f t h e d i m e r 97 i s t r e a t e d u n d e r m i l d l y a c i d i c o r n e u t r a l c o n d i t i o n s w i t h a s o u r c e o f c y a n i d e , t h i s n u c l e o p h i l e must a t t a c k t h e r e s u l t i n g i n t e r m e d i a t e f r o m t h e 3 - f a c e , e x c l u s i v e l y , t o f o r m a C 1 Q , c y a n o d i m e r l o w h i c h b e a r s t h e n a t u r a l s t e r e o c h e m i s t r y a b o u t C 1 R l . T h u s , i n e f f e c t , - 143 -t h e o r d e r o f i n t r o d u c t i o n o f t h e c a r b o m e t h o x y g r o u p and t h e v i n d o l i n e m o i e t y o n t o t h e c l e a v a m i n e t e m p l a t e h a s b e e n r e v e r s e d by t h i s a p p r o a c h r e l a t i v e t o t h e d i m e r i z a t i o n o f compound 107 w i t h v i n d o l i n e . U n t i l r e c e n t l y , t h i s a p p r o a c h was p l a g u e d b y two m a j o r d r a w b a c k s : (a ) a r e a c t i o n t o f o r m t h e C O I c y a n o d i m e r i n r e a s o n a b l y h i g h y i e l d l o was u n a v a i l a b l e a n d (b) when t h i s d i m e r was p r o d u c e d i n s m a l l amounts and i s o l a t e d , i t was f o u n d t o be r e m a r k a b l y s e n s i t i v e t o a c i d i c c o n d i t i o n s . Thus t h e c o n d i t i o n s r e q u i r e d f o r t h e c o n v e r s i o n o f t h e n i t r i l e t o t h e c o r r e s p o n d i n g c a r b o m e t h o x y g r o u p w e r e s u c h t h a t c l e a v a g e and d e c o m p o s i t i o n o f t h i s d i m e r m i g h t be a n t i c i p a t e d . R e c e n t l y , t h e f i r s t p r o b l e m has b e e n e l i m i n a t e d by t h e s k i l l f u l u s e o f t e t r a - n - b u t y l a m m o n i u m c y a n i d e as a s o u r c e o f c y a n i d e w h i c h i s r e a d i l y s o l u b l e i n o r g a n i c s o l v e n t s . When t h e c h l o r o i n d o l e n i n e o f d i m e r 97 and t h e a b o v e r e a g e n t w e r e r e f l u x e d i n 1 , 2 - d i c h l o r o e t h a n e , t h e y r e a c t e d s m o o t h l y t o p r o d u c e t h e d e s i r e d c y a n o d i m e r a p p a r e n t l y i n r e a s o n a b l e y i e l d . The s e c o n d p r o b l e m may be o v e r c o m e b y u s i n g t h e a b o v e a p p r o a c h t o i n t r o d u c e , n o t a n i t r i l e b u t , f o r e x a m p l e , a n a l d e h y d e masked a s t h e t e t r a - j i - b u t y l a m m o n i u m s a l t o f 1 , 3 - d i t h i a n e . T h i s c o u l d be e a s i l y c o n v e r t e d t o t h e a l d e h y d e and t h e n c e t o t h e C , D , c a r b o m e t h o x y l o g r o u p . T h i s s t r a t e g y h o l d s g r e a t p r o m i s e f o r t h e f u t u r e . A r a t h e r d i f f e r e n t a p p r o a c h t o d i m e r i z a t i o n has e v o l v e d d u r i n g t h e c o u r s e o f t h e s e s t u d i e s w h i c h i s t r u l y a t t r a c t i v e f r o m a n a e s t h e t i c and a c a d e m i c p o i n t o f v i e w a s w e l l a s f r o m t h e p u r e l y p r a c t i c a l a n d p r a g m a t i c o n e . V . r o s e a i s p r o b a b l y one o f t h e most s t u d i e d p l a n t s y s t e m s . A s m e n t i o n e d i n t h e i n t r o d u c t i o n o f t h i s t h e s i s , e x t e n s i v e e f f o r t s h a v e b e e n made t o i s o l a t e , c h a r a c t e r i z e and t e s t a l l o f i t s - 144 -a l k a l o i d s . D e s p i t e t h i s f a c t , and a f t e r t h e i s o l a t i o n and c h a r a c t e r i z a t i o n o f r o u g h l y 120 a l k a l o i d s , t h e r e h a s n e v e r b e e n any r e p o r t o f t h e i s o l a t i o n o f a m o n o m e r i c t e t r a c y c l i c i n d o l e t e m p l a t e r e s e m b l i n g c l e a v a m i n e . I f t h e p l a n t s y n t h e s i z e d a n d c o u p l e d s u c h monomers i n two s e p a r a t e s t e p s , t h e i r i s o l a t i o n f r o m N a t u r e , a t l e a s t i n s m a l l a m o u n t s , s h o u l d be p o s s i b l e . On t h e o t h e r h a n d , t h e r i g i d p e n t a c y c l i c I b o g a s k e l e t o n e p i t o m i z e d b y c a t h a r a n t h i n e (11) i s q u i t e a b u n d a n t i n t h e p l a n t s y s t e m . The i n v i v o d i m e r i z a t i o n may t h u s be v i e w e d as a f o r m a l r i n g o p e n i n g o f c a t h a r a n t h i n e by a n u c l e o p h i l e - v i n d o l i n e t o g e n e r a t e a d i m e r b e a r i n g t h e c l e a v a m i n e s k e l e t o n i n a s i n g l e s t e p . F u n c t i o n a l i z a t i o n o f t h e 3 , 4 d o u b l e bond w o u l d t h e n c o m p l e t e t h e s y n t h e s i s o f t h e n a t u r a l d i m e r s . I n f a c t s u c h f u n c t i o n a l i z a t i o n may a c t i v a t e t h e c a t h a r a n t h i n e s k e l e t o n a n d i n i t i a t e t h e d i m e r i z a t i o n . I n t h e l a b o r a t o r y , t h e c o n v e r s i o n o f c a t h a r a n t h i n e t o 1 8 - c a r b o m e t h o x y c l e a v a m i n e i s a c c o m p l i s h e d w i t h s o d i u m b o r o h y d r i d e i n g l a c i a l a c e t i c a c i d . The c l e a v a m i n e t e m p l a t e i s t h e n a c t i v a t e d , t h r o u g h t h e i n d o l e p o r t i o n , t o w a r d s n u c l e o p h i l i c a t t a c k b y v i n d o l i n e a t t h e C . Q p o s i t i o n . The two s t e p s - r i n g o p e n i n g a n d c o u p l i n g -l o a r e s e p a r a t e d j i n v i t r o . What w o u l d be t h e s t e r e o c h e m i c a l o u t c o m e , h o w e v e r , i f a r e a c t i o n c o u l d be d e v i s e d w h e r e t h e s e s t e p s w e r e r e u n i t e d a s i n N a t u r e ? A n i n s p e c t i o n o f m o l e c u l a r m o d e l s r e v e a l e d t h a t i f v i n d o l i n e c o u l d i be u s e d t o d i s p l a c e t h e C - C b o n d i n a t r a n s - c o p l a n a r f a s h i o n , t h e 1 8 J r e s u l t i n g d i m e r w o u l d p o s s e s s t h e n a t u r a l s t e r e o c h e m i s t r y a b o u t C . l o T h i s was i n d e e d a n e x c i t i n g p o s t u l a t e f o r two r e a s o n s . F r o m a p u r e l y a c a d e m i c s t a n d p o i n t i t meant t h a t t h e a c h i e v e m e n t o f an i n v i t r o f r a g m e n t a -t i o n o f t h e k i n d e n v i s a g e d w o u l d be t a n t a m o u n t t o a b i o m i m e t i c d i m e r i z a t i o n . - 145 -E v e n more i m p o r t a n t , h o w e v e r , was t h e f a c t t h a t d i m e r s c o u l d be o b t a i n e d by s u c h a r e a c t i o n d i r e c t l y f r o m t h e two m o s t a b u n d a n t a l k a l o i d s o f t h e p l a n t - c a t h a r a n t h i n e (11) and v i n d o l i n e ( 1 0 ) . A t t e n t i o n was t h u s t u r n e d t o w a r d s a c h i e v i n g t h i s g o a l . I t was o b v i o u s , f r o m t h e o u t s e t , t h a t a s u i t a b l e l e a v i n g g r o u p was n e c e s s a r y a t C ^ , and t h a t a p a r t i c u l a r s t e r e o c h e m i s t r y o f t h i s l e a v i n g g r o u p was a b s o l u t e l y m a n d a t o r y i n o r d e r t o make a c o n c e r t e d f r a g m e n t a t i o n p o s s i b l e . The g e n e r a l scheme i s o u t l i n e d i n F i g u r e 3 8 , t o g e t h e r w i t h some o f t h e a n t i c i p a t e d s i d e r e a c t i o n s . The p r o p e r c h o i c e o f a method o f p l a c i n g s u c h a l e a v i n g g r o u p o n t h e p o s i t i o n may a l s o p e r m i t t h e s i m u l t a n e o u s f u n c t i o n a l i z a t i o n o f t h e p o s i t i o n t h u s p e r m i t t i n g t h e s y n t h e s i s o f a 3 , 4 f u n c t i o n a l i z e d d i m e r o f t h e c o r r e c t s t e r e o c h e m i s t r y a t C 1 Q , . The s t e r e o c h e m i s t r y o f l o t h e f u n c t i o n a l i t y w o u l d a l m o s t c e r t a i n l y be a o n t h e b a s i s o f a l l t h e p r e v i o u s w o r k d e s c r i b e d i n P a r t I . T h i s was f o r t u n a t e l y e x a c t l y t h e r e q u i r e d one t o p e r m i t t h e d e s i r e d d i m e r i z a t i o n r e a c t i o n . The f i r s t c h o i c e o f a n a c t i v a t i n g g r o u p a t t h e 3 , 4 p o s i t i o n was t h e d i o l r e s u l t i n g f r o m t h e o s m y l a t i o n o f c a t h a r a n t h i n e . C l e a r l y i f t h i s d i o l c o u l d be p r o d u c e d , t h e t e r t i a r y C^ a l c o h o l c o u l d be s o l v o l y z e d u n d e r a c i d i c c o n d i t i o n s t o y i e l d e x a c t l y t h e c a r b o n i u m i o n o f t h e t y p e shown i n compound 1 2 3 , and t h u s p e r m i t t h e d e s i r e d f r a g m e n t a t i o n t o o c c u r . The a d v a n t a g e o f t h i s a p p r o a c h was t h a t i t w o u l d y i e l d a d i m e r b e a r i n g an o x y g e n f u n c t i o n a l i t y a t t h e C ^ , p o s i t i o n i n t h e same s t e r e o c h e m i s t r y as was a l r e a d y a v a i l a b l e i n d i m e r 106 d e r i v e d f r o m t h e h y d r o b o r a t i o n p r o d u c t s (56 and 57) o f 1 8 - c a r b o m e t h o x y c l e a v a m i n e . Thus any d i f f e r e n c e s b e t w e e n t h e d i m e r g e n e r a t e d by t h i s a p p r o a c h and d i m e r 1 0 6 , may be - 146 -F i g u r e 3 8 . G e n e r a l a p p r o a c h t o t h e b i o m i m e t i c d i m e r i z a t i o n . - 147 -i n t e r p r e t e d as b e i n g i n d i c a t i v e o f some change i n s t e r e o c h e m i s t r y a b o u t t h e C 1 Q , p o s i t i o n , l o S e v e r a l a t t e m p t s t o o s m y l a t e t h i s s t e r i c a l l y h i n d e r e d d o u b l e bond u n d e r a v a r i e t y o f c o n d i t i o n s , r e s u l t e d i n no r e a c t i o n u n d e r m i l d e r c o n d i t i o n s , and d e s t r u c t i o n o f t h e i n d o l e c h r o m o p h o r e u n d e r more s t r i n g e n t c o n d i t i o n s . A t t e n t i o n was t u r n e d t o o t h e r means o f a c h i e v i n g t h e same g o a l . E p o x i d a t i o n was t h e n e x t c h o i c e . I t r a p i d l y became c l e a r t h a t t h e t r e a t m e n t o f c a t h a r a n t h i n e , a s t h e f r e e b a s e , w i t h 1 . 0 e q u i v a l e n t o f m - c h l o r o p e r b e n z o i c a c i d y i e l d e d , a l m o s t e x c l u s i v e l y , t h e N - o x i d e o f c a t h a r a n t h i n e . The s t r u c t u r e o f t h i s compound was n o t a t a l l a s i m p l e m a t t e r t o p r o v e . Upon a t t e m p t e d p u r i f i c a t i o n b y c o l u m n c h r o m a t o g r a p h y o r e v e n by r e c r y s t a l l i z a t i o n f r o m n e u t r a l o r g a n i c s o l v e n t s , i t r e a r r a n g e d c l e a n l y t o a n o t h e r c o m p o u n d . The s t r u c t u r e o f t h e r e a r r a n g e -ment p r o d u c t i s n o t known w i t h c e r t a i n t y b e y o n d t h e f a c t t h a t i t p o s s e s s e s a n e x c h a n g e a b l e p r o t o n i n t h e nmr s p e c t r u m , o t h e r t h a n t h e i n d o l i c N - H , i n d i c a t i n g t h a t i t may be a n a l c o h o l . T h i s i s c o r r o b o r a t e d by t h e i r s p e c t r u m . H o w e v e r , u p o n p r o d u c i n g c a t h a r a n t h i n e N - o x i d e and h y d r o g e n a t i n g i t i m m e d i a t e l y , w i t h o u t p u r i f i c a t i o n , t h e N - o x i d e g r o u p i n g c o u l d be h y d r o g e n o l y z e d t o g e n e r a t e d i h y d r o c a t h a r a n t h i n e w h i c h was i d e n t i c a l i n e v e r y way t o t h e a u t h e n t i c m a t e r i a l p r e p a r e d by t h e d i r e c t h y d r o g e n a t i o n o f c a t h a r a n t h i n e i t s e l f . T h e r e f o r e , i t was n e c e s s a r y t o p r o t e c t t h e b a s i c N ^ a tom p r i o r t o any a t t e m p t t o e p o x i d i z e t h e 3 , 4 d o u b l e b o n d o f c a t h a r a n t h i n e . When c a t h a r a n t h i n e h y d r o c h l o r i d e i n d r y m e t h y l e n e c h l o r i d e was t r e a t e d w i t h an e x c e s s o f m - c h l o r o p e r b e n z o i c a c i d , t h e m a j o r p r o d u c t i n t h e r e a c t i o n m i x t u r e was n o t t h e N - o x i d e n o r t h e s t a r t i n g m a t e r i a l . T h i s p r o d u c t - 148 -was purified and treated with vindoline in a biomimetic reaction using 1.0 N hydrochloric acid at room temperature for ten days. It yielded a reaction mixture from which a dimeric compound could be isolated in 30% yield. Nmr (Figure 39) and mass spectral (Figure 40) studies were rather confusing however. They indicated that the 3,4 double bond was intact and that another benzylic or o l e f i n i c proton had been generated. In fact, i t appeared that dimerization may not have occurred at C 1 0, but rather at C c as shown below (Figure 41). In a separate experiment, i t could be shown that the reagent had attacked the indole portion of the compound to produce fragmentation to a tetracyclic inter-mediate which had subsequently undergone dimerization. Reaction of the chloroindolenine of catharanthine^^ under the same conditions also produced the same dimer in similar yield; thus demonstrating the above postulate. Furthermore, the treatment of dihydrocatharanthine hydrochloride with m-chloroperbenzoic acid followed by dimerization with vindoline i n 1.0 N hydrochloric acid also produced a similar dimer lacking the 3',4' double bond but otherwise quite analogous to the previous dimer. The same sequence repeated on the chloroindolenine of dihydrocatharanthine confirmed and supported the above claim. In summary, i t was clear from these results that the order of reactivity within the catharanthine moiety towards electrophilic reagents 3 4 is N, > N > A ' and at present the fragmentation approach, though D cL fascinating and potentially useful, must await another study currently under way in our laboratories to block the other two reactive centres, epoxidize the 3,4 double bond, and then systematically deprotect both centres. This study is visualized as serving a dual purpose: (a) In the - 149 -- 150 -- 151 -(127) F i g u r e 4 1 . P r o p o s e d m e c h a n i s m f o r t h e f o r m a t i o n o f d i m e r ( 1 2 7 ) . - 152 -t e t r a c y c l i c c l e a v a m i n e t e m p l a t e , i f a method o f e p o x i d i z i n g t h e 3 , 4 d o u b l e b o n d , a f t e r b l o c k i n g a l l p o s s i b l e s i d e r e a c t i o n s , i s f o u n d t h e n a c r i t i c a l i n t e r m e d i a t e f o r t h e s y n t h e s i s o f t h e i n d o l e p o r t i o n o f t h e v a r i o u s n a t u r a l d i m e r s w o u l d h a v e b e e n s y n t h e s i z e d . (b) I f a n e p o x i d e c a n be i n t r o d u c e d i n t o t h e 3 , 4 p o s i t i o n o f t h e r i g i d c a t h a r a n t h i n e s k e l e t o n , t h e n t h e f i r s t o p p o r t u n i t y f o r t e s t i n g t h i s i n t e r e s t i n g f r a g m e n t a t i o n scheme w o u l d become a v a i l a b l e . I n c o n c l u s i o n , when t h i s w o r k was i n i t i a t e d , t h r e e v i t a l q u e s t i o n s r e m a i n e d u n a n s w e r e d . As a r e s u l t o f t h e e f f o r t s o f t h i s r e s e a r c h a l l o f t h e s e q u e s t i o n s h a v e b e e n a n s w e r e d . The q u e s t i o n s d e a l t w i t h t h e s t e r e o c h e m i c a l outcome o f t h e c o n v e n t i o n a l d i m e r i z a t i o n , t h e m e c h a n i s m o f t h i s r e a c t i o n a n d t h e d e v e l o p m e n t o f new methods f o r p e r f o r m i n g t h i s s t e p . The q u e s t i o n o f s t e r e o c h e m i s t r y i n t h e c o n v e n t i o n a l r e a c t i o n has b e e n c o n c l u s i v e l y e s t a b l i s h e d i n s e v e r a l c a s e s as a r e s u l t o f t h e X - r a y s t u d i e s m e n t i o n e d . The d e t a i l s o f t h e m e c h a n i s m o f t h i s r e a c t i o n h a v e b e e n e l u c i d a t e d by t h e s t u d y o f t h e d i m e r i z a t i o n o f 1 8 8 -c a r b o m e t h o x y - 4 8 - d i h y d r o c l e a v a m i n e ( 1 0 7 ) . F i n a l l y , new methods and c o n c e p t s h a v e b e e n e x p l o r e d w h i c h may l e a d t o a n i m p r o v e m e n t i n t h e y i e l d o r a n i n v e r s i o n o f t h e s t e r e o c h e m i s t r y o f t h e s y n t h e t i c d i m e r s . These r e s u l t s h a v e b e e n o b t a i n e d by s l o w a n d p a i n s t a k i n g s t u d y r a t h e r t h a n by a s e r i e s o f f o r t u i t o u s d i s c o v e r i e s . H o w e v e r , i f a s i n g l e one o f t h e s e a v e n u e s b e a r s f r u i t a t some f u t u r e d a t e i n t e r m s o f p r o v i d i n g a s y n t h e s i s o f t h e t a r g e t m o l e c u l e , t h i s w i l l be a s u f f i c i e n t r e w a r d f o r any e f f o r t s t h a t may h a v e b e e n , o r may n e e d t o b e , s p e n t . - 153 -EXPERIMENTAL Melting points were determined on a Kofler block and are uncorrected. The ultraviolet spectra (uv) were recorded on a Cary 11 spectrophotometer using ethanol as solvent unless otherwise specified. Infrared spectra (ir) were recorded on a Perkin-Elmer Model 21 and Model 137 spectro-photometers. Nuclear magnetic resonance (nmr) spectra were recorded in deuteriochloroform at 100 MHz on Varian HA-100 and XL-100 instruments o and the chemical shifts are given in Tiers T scale with reference to tetramethylsilane as the internal standard. Mass spectra were recorded on an Atlas CH-AB or an AE-MS-902 mass spectrometer. Analyses were carried out by Mr. P. Borda of the microanalytical laboratory, The University of Bri t i s h Columbia. Woelm neutral alumina (acc. to Stahl) containing 1% by weight of General Electric Retina p-1 type 188-2-7 electronic phosphor were used for analytical thin-layer chromatography ( t i c ) . Chromatoplates were developed using 1:1 carbon tetrachloride antimony pentachloride solution and aqueous eerie sulfate solution as stated. Woelm neutral alumina (activity III) was used for column chromatography (unless otherwise indicated). - 154 -18-Carbomethoxy-4g-dihydroclevamin-3ct-ol (56) and (57) To a s o l u t i o n of 188-carbomethoxycleavamine (2.2792 g, 6.44 mmoles) i n anhydrous t e t r a h y d r o f u r a n (THF) (100 ml) contained i n a 250 ml 3-necked round-bottomed f l a s k cooled to 0°C and under a b r i s k stream of dry n i t r o g e n , was added a s o l u t i o n of diborane i n THF (9.6 ml of a 1.5 M s o l u t i o n ) over a p e r i o d of 30 minutes w i t h s t i r r i n g . A f t e r the a d d i t i o n was complete the pale y e l l o w s o l u t i o n was allowed to come to room temperature during a f u r t h e r 1 hour. Removal of the s o l v e n t in. vacuo at not higher than 20°C af f o r d e d a w h i t i s h - y e l l o w gum. This m a t e r i a l was taken up i n a f u r t h e r p o r t i o n of f r e s h l y d i s t i l l e d THF (100 ml) and cooled again to 0°C. Bas i c hydrogen peroxide (4 ml of a s o l u t i o n c o n t a i n i n g 9 ml of 30% hydrogen peroxide and 1 ml of 10% by weight aqueous sodium hydroxide) was added w i t h s t i r r i n g over 10 minutes. Removal of the s o l v e n t r e s u l t e d again, i n a y e l l o w i s h gum which was p a r t i t i o n e d between water and dichloromethane. The aqueous phase was washed w i t h s e v e r a l p o r t i o n s of dichloromethane (4 x 40 ml). The combined organic phase was d r i e d over anhydrous sodium s u l f a t e , f i l t e r e d , and evaporated to dryness under reduced pressure to y i e l d a l i g h t foam (2.2 g ) . This m a t e r i a l was d i s s o l v e d again i n dry THF (100 m l ) , d i s t i l l e d t r i e t h y l a m i n e (4.5 ml) was added and the whole r e f l u x e d f o r 1.5 hours under a p o s i t i v e pressure of dry n i t r o g e n . Evaporation of the so l v e n t i n vacuo r e s u l t e d i n a y e l l o w gum (3.0 g ) . This was immediately chromatographed on alumina (200 g ) . E l u t i o n was begun w i t h benzene, dichloromethane (1:1). E l u t i o n w i t h pure dichloromethane a f f o r d e d 18g-carbomethoxy-48-dihydro-cleavamin-3ct-ol (56) pure and c r y s t a l l i n e (574.5 mg) i n f r a c t i o n s 12 to 22. EtOH This compound was r e c r y s t a l l i z e d from methanol, mp 158-163° dec. X nm: max - 155 -2 9 3 , 2 8 5 , 278 ( s h ) , 226 ( l o g e 3 . 8 , 3 . 9 , 3 . 8 , 4 . 5 r e s p e c t i v e l y ) ; v 3 cm : 3442 , 2 9 2 0 , 1 7 1 8 , 1 4 6 0 , 1 3 3 1 , 1 3 0 5 , 1 2 6 0 , 1 1 5 5 , 1 0 4 0 , 9 0 5 ; max Nmr: T 1 . 1 3 ( b r o a d s i n g l e t , I H , N - H ) , 2 . 4 0 - 3 . 0 0 ( d i f f u s e m u l t i p l e t , 4 H , a r o m a t i c ) , 5 . 0 0 ( t r i p l e t , J - W c p s , I H , C - 0 H ) , 6 . 3 1 ( s i n g l e t , 3 H , lo — C 1 8 ~ C ° 2 C — 3 ^ ' 6 , 3 2 ( < l u a r t e t » J = 10 c p s , I H , C ^ ) , 9 . 0 6 ( t r i p l e t , J = 7 c p s , 3 H , - C ^ C H ^ ) ; mass s p e c t r u m : m a i n p e a k s a t m/e = 3 5 6 , 2 2 6 , 1 5 4 , 1 4 0 , 1 3 8 , 1 2 4 . A n a l . F o u n d : C , 70 .74%; H , 7.99%; N , 7.66%. C a l c d . f o r C o 1 H o o N o 0 _ : C , 70 .76%; H , 7.92%; N , 7.86%. H i g h r e s o l u t i o n mass s p e c t r o m e t r y : F o u n d , 3 5 6 . 2 0 1 7 ; R e q u i r e d f o r c 2 i H 2 8 N 2 ° 3 ' 3 5 6 • 2 0 9 8 • F u r t h e r e l u t i o n w i t h d i c h l o r o m e t h a n e , e t h y l a c e t a t e ( 1 : 1 ) y i e l d e d 1 8 a - c a r b o m e t h o x y - 4 B - d i h y d r o c l e a v a m i n - 3 c t - o l (57) ( 9 2 9 . 2 mg) i n f r a c t i o n 23 and 7 4 . 5 mg o f t h e compound s l i g h t l y c o n t a m i n a t e d w i t h o t h e r m a t e r i a l s i n f r a c t i o n 2 4 , mp 1 1 0 - 1 1 2 ° C . X E t 0 H nm: 2 9 3 , 2 8 5 , 276 ( s h ) , 226 ( l o g e max CHCl _•] 3 . 8 , 3 . 9 , 3 . 8 , 4 . 5 r e s p e c t i v e l y ) ; v 3 cm : 3 4 4 0 , 2 9 2 0 , 1 7 2 0 , 1 4 6 0 , max 1 3 3 0 , 1 1 6 5 , 1 0 1 0 ; Nmr : T 1 . 2 0 ( b r o a d s i n g l e t , I H , N - H ) , 2 . 4 6 - 3 . 0 6 ( d i f f u s e m u l t i p l e t , 4 H , a r o m a t i c ) , 5 . 9 9 ( m u l t i p l e t , I H , C . _ H ) , 6 . 3 2 ( s i n g l e t , lo 3 H , C 1 0 - C 0 - C H „ ) , 9 . 4 3 ( t r i p l e t , J = 7 c p s , 3 H , - C H 0 C H J ; mass s p e c t r u m : l o L —J 2. —3 m a i n p e a k s a t m/e = 3 5 6 , 3 2 7 , 2 2 6 , 1 5 4 , 1 4 0 , 1 3 8 , 1 2 4 . A n a l . H i g h r e s o l u t i o n mass s p e c t r o m e t r y : F o u n d , 3 5 6 . 2 1 2 9 ; R e q u i r e d f o r c 2 i H 2 8 N 2 ° 3 ^ M + ^ ' 3 5 6 • 2 0 9 8 • T h e t o t a l y i e l d o f a l c o h o l s was 6 9 . 5 % . E p i m e r i z a t i o n o f 1 8 a - and 1 8 g - C a r b o m e t h o x y - 4 B - d i h y d r o c l e a v a m i n - 3 a - o l t o  an E q u i l i b r i u m M i x t u r e To a s o l u t i o n o f 1 8 B - c a r b o m e t h o x y - 4 B - d i h y d r o c l e a v a m i n - 3 a - o l (56) (150 mg) i n b e n z e n e (10 m l ) was a d d e d b o r o n t r i f l u o r i d e e t h e r a t e (1 m l ) - 156 -a n d t h e w h o l e s y s t e m m a i n t a i n e d a t r e f l u x u n d e r a p o s i t i v e p r e s s u r e o f n i t r o g e n f o r 6 h o u r s . A t t h e end o f t h i s t i m e t h e r e a c t i o n m i x t u r e was c o o l e d t o room t e m p e r a t u r e and t h e n p o u r e d i n t o a n a q u e o u s s o l u t i o n o f 10% s o d i u m b i c a r b o n a t e a t 0 ° C . The two p h a s e s w e r e s e p a r a t e d and t h e a q u e o u s p h a s e was a g a i n w a s h e d w i t h d i c h l o r o m e t h a n e (2 x 50 m l ) . The c o m b i n e d o r g a n i c p h a s e was d r i e d o v e r s o d i u m s u l f a t e , f i l t e r e d , a n d e v a p o r a t e d u n d e r r e d u c e d p r e s s u r e t o y i e l d a w h i t i s h foam (151 m g ) . T h i s m a t e r i a l was c h r o m a t o g r a p h e d on a l u m i n a ( n e u t r a l Woelm I I I ) . E l u t i o n w i t h m e t h y l e n e c h l o r i d e a f f o r d e d 70 mg o f t h e s t a r t i n g compound (56) . G r a d u a l i n c r e a s e s i n t h e s o l v e n t p o l a r i t y t o a m i x t u r e o f m e t h y l e n e c h l o r i d e a n d e t h y l a c e t a t e ( 1 : 1 ) a f f o r d e d t h e C n 0 e p i m e r i c a l c o h o l l o (57) (77 mg) t o g e t h e r w i t h some m i n o r f r a c t i o n s c o n t a i n i n g m i x t u r e s o f t h e s e two c o m p o u n d s . These compounds c o u l d be i d e n t i f i e d by c o m p a r i s o n w i t h a u t h e n t i c m a t e r i a l s . 1 8 8 - C a r b o m e t h o x y - 4 g - d i h y d r o c l e a v a m i n - 3 c i - a c e t a t e 1 8 $ - C a r b o m e t h o x y - 4 3 - d i h y d r o c l e a v a m i n - 3 a - o l (56) (150 mg) was d i s s o l v e d i n a 1 : 1 m i x t u r e (15 m l ) o f a c e t i c a n h y d r i d e a n d p y r i d i n e . The r e a c t i o n m i x t u r e was a l l o w e d t o s t i r a t room t e m p e r a t u r e o v e r n i g h t . I t was t h e n p o u r e d o n t o i c e c o l d 10% s o d i u m b i c a r b o n a t e and e x t r a c t e d w i t h m e t h y l e n e c h l o r i d e . The aqueous l a y e r was f u r t h e r e x t r a c t e d o n c e w i t h m e t h y l e n e c h l o r i d e . The c o m b i n e d o r g a n i c p h a s e s w e r e d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e and f i l t e r e d . R e m o v a l o f t h e s o l v e n t i n v a c u o f o l l o w e d by e v a c u a t i o n u n d e r h i g h vacuum f o r s e v e r a l h o u r s y i e l d e d 1 8 8 -c a r b o m e t h o x y - 4 8 - d i h y d r o c l e a v a m i n - 3 a - a c e t a t e (147 mg) w h i c h c o u l d be CHC1 —1 p u r i f i e d by r e c r y s t a l l i z a t i o n f r o m e t h y l a c e t a t e . v 3 cm : 3 4 4 0 , J max 2 9 4 0 , 1 7 2 0 , 1460 , 1370 , 1 3 3 0 , 1 3 0 0 , 1020 ( b r o a d ) ; Nmr: T 1 . 3 5 ( b r o a d - 157 -singlet, IH, N-H), 2.46-3.04 (diffuse multiplet, 4H, aromatic), 4.90 (multiplet, 2H, C. QH and C,H) , 6.33 (singlet, 3H, C -CO.CHJ, 7.97 l o — j — lo z —J (singlet, 3H, C3-0Ac), 9.13 (tr i p l e t , J = 7 cps, 3H, -CH2CH_3). 18q-Carbomethoxy-4g-dihydrocleavamin-3a-acetate 18a-Carbomethoxy-4g-dihydrocleavamin-3a-ol (57) (150 mg) was dissolved in a mixture (1:1) of acetic anhydride and pyridine. The reaction mixture was allowed to s t i r overnight at room temperature. It was then poured onto ice cold 10% sodium bicarbonate and extracted with methylene chloride. The aqueous layer was further extracted once with methylene chloride. The combined organic phase was dried over anhydrous sodium sulfate and f i l t e r e d . Removal of the solvent in vacuo followed by evacuation under high vacuum for several hours yielded 152 mg of a reaction mixture consisting mainly of 18a-carbomethoxy-4g-dihydro-cleavamin-3a-acetate. This compound was purified by column chromatography CHC1 —1 over deactivated alumina (grade III). v 3 cm : 3440, 2920, 1720, max 1460, 1365, 1250 (broad), 1160, 1005; Nmr: T 1.26 (broad singlet, IH, N-H), 2.42-3.02 (diffuse multiplet, 4H, aromatic), 5.51 (broad multiplet, IH, C3-H), 6.04 (tr i p l e t , J ^ 5 cps, IH, C^-H), 6.32 (singlet, 3H, C 1 Q-C0„CH_), 8.01 (singlet, 3H, C -OAc), 9.42 ( t r i p l e t , J % 7 cps, 3H, l o <£ — j j -CH2CH3). 4g-Dihydrocleavaminol Acetate from 18a- and 18g-Carbomethoxy-4g-dihydro- cleavamin-3a-ols (56 and 57) 18a-Carbomethoxy-4g-dihydrocleavamin-3a-ol (24.8 mg) and 188-carbomethoxy-4g-dihydrocleavamin-3a-ol (23.6 mg) were taken separately in two identical flasks and were treated with 3 ml each of 5 N HC1. These - 158 -fla s k s were then placed under a p o s i t i v e pressure of dry nitrogen and immersed into an o i l bath at 90°C with s t i r r i n g . After 7 hours the darkly coloured reaction mixtures were cooled to room temperature and poured into i c e cold 10% sodium carbonate. Extraction with several aliquots of methylene chloride followed by drying of the combined organic phase (i n each case separately) over anhydrous sodium s u l f a t e and f i l t r a t i o n and evaporation of the solvent i n vacuo yi e l d e d 26.8 mg of crude 48-dihydrocleavamin-3a-ol from the 18a se r i e s and 23.1 mg of 48-dihydro-cleavamin-3a-ol from the 188 s e r i e s . These were immediately acetylated i n the usual way to y i e l d a f t e r p u r i f i c a t i o n pure c r y s t a l l i n e 48-dihydrocleavamin-3a-acetate (6.5 mg) from the 18a s e r i e s and 48-dihydrocleavamin-3a-acetate (6.4 mg) from the 188 s e r i e s . Both these compounds were i d e n t i c a l to one another as judged by mixed melting points which were undepressed as we l l as completely superimposable i n f r a r e d spectra both as chloroform solutions as we l l as nu j o l mulls. In the l a t t e r case, both spectra were shown to be super-imposable independently with a n u j o l spectrum of authentic 48-dihydrocleavamin-3a-acetate obtained from the hydroboration of cleavamine and the a c e t y l a t i o n of the product of t h i s r e a c t i o n . Samples from the MeOH decarboxylation reactions: X nm: 292, 286, 278, 226 (log E roughly max C H C I — i 3.8, 3.9, 3.8, 4.5 r e s p e c t i v e l y ) ; v 3 cm : 3470, 2920, 1725, 1460, J max 1370, 1250 (broad), 1020 (broad); v ™ ^ 0 1 cm"1: 3400, 2920, 2850, 1725, 1460, 1378; Nmr: x 2.16 (broad s i n g l e t , IH, N-H), 2.4-3 (broad m u l t i p l e t , 4H, aromatic), 4.90 (multiplet, IH, C„-H), 6.40 (multiplet, IH, C 1 Q-H), j — l o — 7.97 ( s i n g l e t , 3H, CyOAc), 9.17 ( t r i p l e t , 3H, C 4-CH 2CH 3); mp 136-139°C. Authentic material: v n ^ 0 1 cm"1: 3400, 2920, 2850, 1725, 1460, 1378 max (ac t u a l l y completely superimposable i n every d e t a i l when run at the same - 159 -t i m e a s t h e a b o v e s a m p l e s . ) Nmr: x ( r e p o r t e d ) 2 . 0 8 ( b r o a d s i n g l e t , I H , N - H ) , 2 . 5 - 3 . 0 ( d i f f u s e , 4 H , a r o m a t i c ) , 4 . 9 0 ( d o u b l e t o f d o u b l e t s , J = 6 , 1 0 H z ; I H , C . - H ) , 6 . 4 ( c o m p l e x m u l t i p l e t , I H , C . 0 - H ) , 9 . 1 7 ( t r i p l e t , J l o — 3 H , - C H 2 C H 3 ) . 1 8 g - C a r b o m e t h o x y - 4 g - d i h y d r o c l e a v a m i n e - 3 - o n e (62) D i c y c l o h e x y l c a r b o d i i m i d e ( 4 . 4 1 4 g , 2 1 . 6 mmoles) was d i s s o l v e d i n d r y d i m e t h y l s u l f o x i d e (35 m l , r e f l x u e d o v e r b a r i u m o x i d e and t h e n d i s t i l l e d a n d s t o r e d o v e r t y p e 4A m o l e c u l a r s i e v e s ) and 10 m l o f a n h y d r o u s p h o s p h o r i c a c i d ( s t a n d i n g o v e r p h o s p h o r o u s p e n t o x i d e ) was a d d e d . Compound 56 ( 2 . 0 4 0 g , 5 . 7 2 mmoles) was d i s s o l v e d i n d r y d i m e t h y l s u l f o x i d e (25 m l ) a n d a d d e d t o t h e a b o v e m i x t u r e s l o w l y w i t h s t i r r i n g u n d e r a s t r e a m o f d r y n i t r o g e n . A f t e r a l l o w i n g t h e r e a c t i o n t o p r o c e e d f o r 26 h o u r s a t room t e m p e r a t u r e i t was w o r k e d up a s f o l l o w s . The c r u d e r e a c t i o n m i x t u r e was p o u r e d i n t o w a t e r (160 m l ) , e t h e r (80 m l ) and 1 M p h o s p h o r i c a c i d (4 m l ) w i t h c o o l i n g i n a n i c e b a t h and s t i r r i n g . The r e s u l t i n g s u s p e n s i o n o f d i c y c l o h e x y l u r e a was f i l t e r e d a n d w a s h e d w i t h w a t e r a n d e t h e r . T h i s a c i d i c s o l u t i o n was e x t r a c t e d w i t h e t h e r (5 x 125 m l ) . E v a p o r a t i o n o f t h e s o l v e n t i n v a c u o y i e l d e d a y e l l o w s o l i d ( 1 . 4 g) w h i c h c o u l d be i d e n t i f i e d a s a m i x t u r e o f t h e d e s i r e d k e t o n e ( r o u g h l y 55%) and d i c y c l o h e x y l u r e a . B a s i f i c a t i o n and r e - e x t r a c t i o n o f t h e a q u e o u s p h a s e w i t h m e t h y l e n e c h l o r i d e y i e l d e d t h e u n r e a c t e d s t a r t i n g m a t e r i a l h e a v i l y c o n t a m i n a t e d w i t h d i c y c l o h e x y l u r e a . P r e p a r a t i v e t h i n l a y e r c h r o m a t o g r a p h y o f t h e i m p u r e k e t o n e on a l u m i n a ( m e t h y l e n e c h l o r i d e e l u t i o n ) y i e l d e d a n a n a l y t i c a l s a m p l e o f 1 8 g - c a r b o -m e t h o x y - 4 g - d i h y d r o c l e a v a m i n - 3 - o n e ( 6 2 ) . x E t 0 H n m : 2 9 2 , 2 8 4 , 277 ( s h ) , 160 -2 2 6 , a n d a s m a l l p e a k a t 332 ( l o g e 3 . 8 , 3 . 9 , 3 . 8 , 4 . 5 , 1 r e s p e c t i v e l y ) ; CHC1 —1 v 3 cm : 3 4 5 0 , 3 0 0 0 , 1 7 2 5 , 1 5 2 0 , 1 4 6 0 , 1 4 2 5 , 1 3 4 0 , 1 3 2 0 , 9 2 0 ; Nmr: max x 1 . 3 0 ( b r o a d s i n g l e t , I H , N - H ) , 2 . 5 0 - 3 . 0 0 ( m u l t i p l e t , 4 H , a r o m a t i c ) , 5 . 3 8 ( d o u b l e t , J ^ 10 c p s , I H , C , Q - H ) , 6 . 3 2 ( s i n g l e t , 3 H , C . o - C 0 o C H _ ) , l o — l o Z —O 9 . 1 0 ( t r i p l e t , J ^ 8 c p s , 3 H , C ^ - C H ^ C H ^ ) ; mass s p e c t r u m : m a i n p e a k s a t m/e = 354 , 2 9 5 , 2 5 7 , 2 2 4 , 2 1 5 , 1 8 2 , 1 6 9 , 1 5 2 , 1 5 1 , 1 4 0 . C h l o r o i n d o l e n i n e o f 1 8 g - c a r b o m e t h o x y c l e a v a m i n e (98) To a s o l u t i o n o f 1 8 g - c a r b o m e t h o x y c l e a v a m i n e (102 mg) i n a b s o l u t e b e n z e n e (2 m l ) was a d d e d , a t room t e m p e r a t u r e , w i t h s t i r r i n g 1 - c h l o r o -b e n z o t r i a z o l e ( 9 4 . 6 mg) i n b e n z e n e (2 m l ) o v e r a p e r i o d o f 20 m i n u t e s . A f t e r t h i s a d d i t i o n was c o m p l e t e t h e r e m a i n i n g 1 - c h l o r o b e n z o t r i a z o l e was r i n s e d i n w i t h a f u r t h e r p o r t i o n o f b e n z e n e ( 0 . 5 m l ) o v e r a p e r i o d o f 5 m i n u t e s . The r e a c t i o n m i x t u r e was t h e n p a r t i t i o n e d b e t w e e n b e n z e n e and i c e c o l d w a t e r (10 m l o f e a c h ) . The b e n z e n e l a y e r was s e p a r a t e d , d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e , f i l t e r e d a n d e v a p o r a t e d u n d e r r e d u c e d p r e s s u r e t o y i e l d a y e l l o w i s h - b r o w n foam (115 m g ) . T h i s m a t e r i a l was q u i c k l y c o l u m n e d t h r o u g h a p l u g o f a l u m i n a ( n e u t r a l Woelm I I I ) w i t h b e n z e n e e l u t i o n f o l l o w e d b y d i c h l o r o m e t h a n e a n d t h e n f i n a l l y m e t h a n o l . The p u r e c h l o r o i n d o l e n i n e was e l u t e d f i r s t f r o m t h e c o l u m n (29 mg, -v 30%). A E t 0 H nm: 335 ( s h ) , 291 ( s h ) , 2 8 5 , 260 ( s h ) , 2 2 2 ; max c n - i v 4 cm : 2 9 9 0 , 1 7 9 0 ( s h ) , 1 7 4 9 , 1 6 7 5 , 1 6 2 0 , 1 5 7 5 , 1 4 5 5 , 1 4 2 5 ; N m r : max T 2 . 3 5 - 3 . 4 0 ( m u l t i p l e t , 4 H , a r o m a t i c ) , 4 . 6 ( b r o a d d o u b l e t , J ^ 8 c p s , I H , C - o l e f i n i c ) , 5 . 6 5 ( b r o a d d o u b l e t , J % 10 c p s , I H , C 1 Q - H ) , 6 . 3 8 J lo ( s i n g l e t , 3 H , C 0 o C H _ ) . The r e m a i n d e r o f t h e m a t e r i a l was u n i d e n t i f i a b l e and c o r r e s p o n d e d t o d e c o m p o s i t i o n on t h e c o l u m n . P r i o r t o c h r o m a t o g r a p h y a t i c c h e c k o f t h e r e a c t i o n m i x t u r e r e v e a l e d t h a t i t c o n t a i n e d >90% o f - 161 -t h e d e s i r e d m a t e r i a l . D i m e r 99 V i n d o l i n e (400 mg) was d i s s o l v e d i n a n h y d r o u s 1.5% m e t h a n o l i c h y d r o g e n c h l o r i d e (75 m l ) p r e p a r e d by t h e a d d i t i o n o f p u r i f i e d a c e t y l c h l o r i d e ( 9 . 2 5 m l ) t o a n h y d r o u s m e t h a n o l (400 m l ) . T h i s s o l u t i o n was a d d e d q u i c k l y , u n d e r a s t r e a m o f n i t r o g e n , t o t h e c h l o r o i n d o l e n i n e o f 1 8 8 - c a r b o m e t h o x y c l e a v a m i n e (98) (400 m g ) . The r e a c t i o n m i x t u r e r a p i d l y t u r n e d t o a deep w i n e - r e d c o l o u r when r e f l u x e d f o r 2 . 5 h o u r s u n d e r a p o s i t i v e p r e s s u r e o f n i t r o g e n . A f t e r t h i s t i m e i t was c o o l e d t o room t e m p e r a t u r e , d i l u t e d w i t h w a t e r and c a u t i o u s l y b a s i f i e d w i t h p o t a s s i u m b i c a r b o n a t e . When i t was w e a k l y b a s i c , i t was e x t r a c t e d (4 x 40 m l ) w i t h d i c h l o r o m e t h a n e a n d t h e c o m b i n e d o r g a n i c l a y e r was d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e and f i l t e r e d . E v a p o r a t i o n o f t h e s o l v e n t u n d e r r e d u c e d p r e s s u r e a f f o r d e d a b r o w n foam (800 m g ) . T h i s m a t e r i a l was i n t r o d u c e d o n t o a c o l u m n o f Sephadex L H - 2 0 p r e p a r e d i n t h e f o l l o w i n g w a y . The g e l - b e a d s w e r e a l l o w e d t o s w e l l by s t i r r i n g them i n a b e a k e r c o n t a i n i n g m e t h a n o l f o r 4 h o u r s a t room t e m p e c a t u r e . The r e s u l t i n g s l u r r y was p a c k e d i n t o a c o l u m n 3 6 " x 1 " d i a m e t e r . T h i s c o l u m n was a l l o w e d t o s e t t l e f o r 1 h o u r a n d t h e n s t a b l i z e d u n d e r r u n c o n d i t i o n s o v e r n i g h t . The f l o w r a t e a t t h i s s t a g e was 2 m l / m i n u t e . S e v e r a l 10 m l f r a c t i o n s w e r e c o l l e c t e d a f t e r t h e s a m p l e was i n t r o d u c e d o n t o t h e c o l u m n . F r a c t i o n s 7 t o 10 EtOH i n c l u s i v e c o n t a i n e d t h e d e s i r e d d i m e r (99) (60 m g ) . A nm: 3 1 0 ( s h ) , max v ' ' 2 9 2 , 2 8 6 ( s h ) , 2 5 9 , 2 2 1 ( s b ) , 212 ( l o g e 3 . 8 , 3 . 9 , 3 . 9 , 3 . 9 , 4 . 4 , 4 . 5 r e s p e c t i v e l y ) ; Nmr: x 0 . 7 0 ( b r o a d s i n g l e t , I H , N - H ) , 0 . 9 1 ( b r o a d s i n g l e t , I H , O H ) , 2 . 5 5 - 3 . 0 0 ( m u l t i p l e t , 4 H , a r o m a t i c ) , 3 . 0 2 ( s i n g l e t , I H , C A ~ H ) , - 162 -\ A.00 ( s i n g l e t , IH, C ^ - H ) , A.10 ( d o u b l e t o f d o u b l e t s , J ^ 10, A cps, IH, C ? - H ) , A.50 ( m u l t i p l e t , IH, C ,-H), A.6A ( s i n g l e t , IH, C^-H), A.70 ( d o u b l e t , J = 10 c p s , IH, C 6 - H ) , 6.14 ( s i n g l e t , 3H, C^-OMe), 6.27 ( s i n g l 6H, C 1 o , - C 0 o C H . and C -C0_CH_), 7.39 ( s i n g l e t , 3H, N.-CH-), 7.95 ( s i n g l e t l o z —:i 3 2. ~J 1 J 3H, C^-OAc), 9.00 ( t r i p l e t , J ^ 8 cps, 3H, C^.-CH^CH ), 9.AO ( t r i p l e t , J ^ 8 c p s , 3H, C^-C^CH^) ; mass spectrum: main peaks a t m/e = 106, 107, 108, 121, 122, 135, 136, 1A9, 188, 282, 339, 335, 669, 791, 792. A n a l . H i g h r e s o l u t i o n mass s p e c t r o m e t r y : Found, 792.A103; R e q u i r e d f o r C ^ H^OgN^, 792.A098. F u r t h e r f r a c t i o n s c o n t a i n e d t h i s same dimer c o n t a m i n a t e d w i t h s m a l l amounts o f b l u e s p o t (25 mg). T o t a l y i e l d o f dimer c o u l d be e s t i m a t e d a t 10% from t h i s r e a c t i o n . The major new p r o d u c t o f the r e a c t i o n was the s o - c a l l e d b l u e s p o t ( o b t a i n e d i n f r a c t i o n 12-20). Bl u e s p o t : A ^ ° H nm: 307, 295(sh), 257, 212 ( l o g e 3.8, 3.8, A.0, A.3 CHC1 —1 r e s p e c t i v e l y ) ; v 3 cm : 3000, 2960, 28A0, 17A0, 1620, 1500, 1468, max 1440, 1380, 1260, 1150(broad), 900, 880; Nmr: T 2.00-3.10 ( m u l t i p l e t , AH), 3.27 ( s i n g l e t , I H ) , 3.99 ( s i n g l e t , I H ) , A.20 ( d i f f u s e m u l t i p l e t , 2H), A.59 ( s i n g l e t , I H ) , A.80 ( d i f f u s e m u l t i p l e t , 2H), 6.28 ( s i n g l e t , 7H), 7.A2 ( s i n g l e t , 3H), 8.02 ( s i n g l e t , 3H), 9.72 ( t r i p l e t , J = 8 c p s , 3H); mass spectrum: main peaks a t m/e = 370, 356, 355, 290, 289, 69, 57, 55, 50, AA, A3, A l . A n a l . C. 66.16%; H, 7.05%; N, 6.31%. Dimer 99 by M o d i f i e d C o n d i t i o n s The c h l o r o i n d o l e n i n e (98) o f 188-carbomethoxycleavamine was made by i n j e c t i n g n eat t - b u t y l h y p o c h l o r i t e (0.07 ml) i n t o a s o l u t i o n o f 188-- 163 -c a r b o m e t h o x y c l e a v a m i n e (200 mg) i n r e f l u x i n g d i c h l o r o m e t h a n e ( 6 . 5 m l ) c o n t a i n i n g t r i e t h y l a m i n e ( 0 . 1 m l ) . The r e s u l t i n g y e l l o w i s h - o r a n g e s o l u t i o n was s t i r r e d f o r 30 m i n u t e s a t r e f l u x , t h e n c o o l e d t o room t e m p e r a t u r e and e v a p o r a t e d t o d r y n e s s u n d e r r e d u c e d p r e s s u r e t o y i e l d a l i g h t b r o w n f o a m . T h i s compound was d i s s o l v e d i n d i c h l o r o m e t h a n e and d i v i d e d i n t o two e q u a l p o r t i o n s w h i c h w e r e a g a i n t a k e n t o d r y n e s s . To e a c h o f t h e s e p o r t i o n s was a d d e d a s o l u t i o n o f v i n d o l i n e (100 mg) i n 1.5% m e t h a n o l i c h y d r o g e n c h l o r i d e (20 m l ) . One p o r t i o n was h e a t e d t o r e f l u x f o r 3 . 5 h o u r s . A f t e r t h i s p e r i o d i t was c o o l e d t o room t e m p e r a t u r e and c a u t i o u s l y a d d e d t o a n i c e c o l d aqueous s o l u t i o n o f s o d i u m b i c a r b o n a t e (10%, 50 m l ) , and e x t r a c t e d w i t h d i c h l o r o m e t h a n e (3 x 25 m l ) . The c o m b i n e d o r g a n i c p h a s e was d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e f i l t e r e d and e v a p o r a t e d t o d r y n e s s t o y i e l d a b r o w n foam (200 mg) f r o m w h i c h d i m e r 99 ( 1 6 . 4 mg) was p u r i f y a b l e by c o l u m n c h r o m a t o g r a p h y o n a l u m i n a ( n e u t r a l Woelm I I I ) by e l u t i o n w i t h b e n z e n e c o n t a i n i n g 15% e t h y l a c e t a t e (8% y i e l d ) . The o t h e r p o r t i o n was a l l o w e d t o s t i r a t room t e m p e r a t u r e f o r 10 d a y s . A f t e r t h i s p e r i o d , t h e s o l v e n t was removed u n d e r r e d u c e d p r e s s u r e t o y i e l d a g r e e n gum w h i c h was t a k e n up i n 0 . 1 M c i t r i c a c i d (25 m l , r e s u l t i n g pH = 1 . 8 ) and e x t r a c t e d w i t h b e n z e n e (25 m l ) . The b e n z e n e l a y e r was i s o l a t e d and e v a p o r a t e d t o d r y n e s s t o y i e l d 27 mg o f m o n o m e r i c m a t e r i a l s i d e n t i f i e d by t i c a n d u v . T h e n , t h e pH was a d j u s t e d s t e p w i s e t o 1 0 . 7 a n d a b e n z e n e e x t r a c t i o n p e r f o r m e d a t e a c h s t e p . The d i m e r 99 e n r i c h e d f r a c t i o n s w e r e f o u n d t o be b e t w e e n pH v a l u e s o f 4 . 5 and 5 . 4 (74 m g ) . T o t a l w e i g h t r e c o v e r y was 1 9 2 . 3 mg f r o m 200 mg o r 96 .5%. The d i m e r e n r i c h e d f r a c t i o n s w e r e c o m b i n e d and p u r i f i e d by p r e p a r a t i v e t i c - 164 -o n a l u m i n a ( e t h y l a c e t a t e ) t o y i e l d p u r e d i m e r 99 (40 mg) i d e n t i c a l i n e v e r y r e s p e c t t o t h a t o b t a i n e d p r e v i o u s l y (20% y i e l d ) . D i m e r 102 f r o m 1 8 - 0 a r b o m e t h o x y d i h y d r o c l e a v a m i n e and D i h y d r o v i n d o l i n e 1 8 B - C a r b o m e t h o x y - 4 3 - d i h y d r o c l e a v a m i n e ( 3 5 3 . 7 mg) was d i s s o l v e d i n d r y b e n z e n e (20 m l ) a n d a s o l u t i o n o f 1 - c h l o r o b e n z o t r i a z o l e ( 2 0 0 . 4 mg) i n b e n z e n e (10 m l ) was a d d e d o v e r 10 m i n u t e s w i t h s t i r r i n g a t room t e m p e r a t u r e , and t h e n r i n s e d i n w i t h a f u r t h e r p o r t i o n o f b e n z e n e (10 m l ) a d d e d o v e r 5 m i n u t e s . The s o l v e n t was removed i n v a c u o a f t e r t h i s p e r i o d t o y i e l d t h e c h l o r o i n d o l e n i n e as a y e l l o w i s h f o a m . T h i s m a t e r i a l was d i s s o l v e d i n b e n z e n e (4 m l ) and a d d e d s l o w l y t o a s o l u t i o n o f d i h y d r o v i n d o l i n e (372 mg) i n 1.5% m e t h a n o l i c h y d r o g e n c h l o r i d e (6 m l ) m a i n t a i n e d a t 5 0 ° C u n d e r a s t r e a m o f n i t r o g e n . The c h l o r o i n d o l e n i n e was r i n s e d i n w i t h a f u r t h e r p r o t i o n o f b e n z e n e (2 m l ) . The r e a c t i o n m i x t u r e i m m e d i a t e l y c h a n g e d f r o m a l i g h t b l u e c o l o u r t o a b r o w n i s h - r e d . A f t e r 2 . 5 h o u r s t h e r e a c t i o n was c o o l e d t o room t e m p e r a t u r e p o u r e d c a u t i o u s l y o n t o a n i c e c o l d s o l u t i o n o f 10% a q u e o u s s o d i u m b i c a r b o n a t e (50 m l ) and e x t r a c t e d w i t h d i c h l o r o m e t h a n e (3 x 30 m l ) . The c o m b i n e d o r g a n i c p h a s e was d r i e d o v e r s o d i u m s u l f a t e , f i l t e r e d and t a k e n t o d r y n e s s u n d e r r e d u c e d p r e s s u r e t o y i e l d a b r o w n i s h foam (726 m g ) . T h i s m a t e r i a l was c h r o m a t o g r a p h e d o n 75 g o f a l u m i n a ( n e u t r a l Woelm I I I ) . B e n z e n e c o n t a i n i n g 20% e t h y l a c e t a t e e l u t e d t h e d e s i r e d t e t r a h y d r o -d i m e r (102) i n f r a c t i o n s 6 t h r o u g h 14 ( 4 4 3 . 6 mg, 61% y i e l d ) p u r e , t o g e t h e r w i t h s e v e r a l s u b s e q u e n t f r a c t i o n s c o n t a i n i n g t h i s m a t e r i a l i n i m p u r e f o r m . X E t 0 H nm: 3 1 0 , 2 9 5 , 2 8 7 , 2 6 0 , 216 ( l o g e 3 . 8 , 3 . 9 , 3 . 9 , 4 . 0 , 4 . 5 max r e s p e c t i v e l y ) ; v C H C 1 3 c m " 1 : 3460 ( b r o a d ) , 2 9 6 0 , 1 7 4 0 , 1 6 2 0 , 1 5 0 0 , 1 4 6 5 , max 1 4 3 5 , 1 3 7 5 , 1 1 6 0 , 1 0 4 0 , 1 1 1 0 ; Nmr : T 0 . 9 1 ( s i n g l e t , I H , N - H ) , 2 . 5 0 - 2 . 9 2 - 165 -( m u l t i p l e t , 4 H , a r o m a t i c ) , 2 . 9 5 ( s i n g l e t , I H , C ^ - H ) , 3 . 9 7 ( s i n g l e t , I H , C - H ) , 4 . 3 6 ( s i n g l e t , I H , C . - H ) , 6 . 1 4 ( s i n g l e t , 3 H , C 1 £ - 0 M e ) , 6 . 2 0 1 / — H — l b — ( s i n g l e t , 3 H , C 0 2 C H _ 3 ) , 6 . 2 4 ( s i n g l e t , 3 H , C0 2 CH_ 3 ) , 7 . 4 2 ( s i n g l e t , 3 H , IS^-C H _ 3 ) , 7 . 9 0 ( s i n g l e t , 3 H , C ^ - O A c ) , 9 . 0 1 ( t r i p l e t , J ^7 c p s , 3 H , - C H 2 C H 3 ) , 9 . 4 4 ( t r i p l e t , J 6 c p s , 3 H , - C H 2 C H _ 3 ) ; mass s p e c t r u m : m a i n p e a k s a t m/e = 8 2 4 , 8 1 0 , 796 , 7 9 4 , 7 6 8 , 7 5 3 , 7 3 9 , 5 9 4 , 5 7 8 , 4 7 1 , 4 2 9 , 3 9 8 , 3 8 4 , 3 8 2 , 3 7 0 , 3 6 8 , 3 6 7 , 3 5 5 , 354 , 3 5 2 , 3 4 2 , 3 4 0 , 3 3 9 , 3 3 8 , 3 3 6 , 3 2 6 , 3 1 2 , 3 1 0 , 2 9 8 , 2 9 7 , 2 9 5 , 2 9 4 , 2 9 1 , 2 8 4 , 2 8 1 , 2 6 8 , 2 1 0 , 2 0 9 , 1 9 4 , 1 8 2 , 1 8 0 , 1 7 0 , 1 6 9 , 1 6 8 , 1 6 7 , 1 5 6 , 1 5 4 , 1 4 4 , 1 4 3 , 1 3 8 , 1 3 6 , 1 3 3 , 1 2 5 , 1 2 4 , 1 1 0 , 1 0 5 . Mp 2 2 1 - 2 2 4 ° C d e c . A n a l . H i g h r e s o l u t i o n mass s p e c t r o m e t r y : F o u n d , 7 9 6 . 4 4 1 9 6 1 ; R e q u i r e d f o r C ^ H ^ O g N ^ 7 9 6 . 4 4 1 0 8 8 . C l e a v a g e o f D i m e r 99 D i m e r 99 (9.0 mg) was d i s s o l v e d i n a n h y d r o u s 7% m e t h a n o l i c h y d r o g e n c h l o r i d e (4 m l ) and t i n (39 mg) and s t a n n o u s c h l o r i d e (36 mg) w e r e a d d e d . The r e a c t i o n m i x t u r e was r e f l u x e d f o r 2 h o u r s , and t h e n c o o l e d , d i l u t e d w i t h w a t e r , and b a s i f i e d w i t h ammonium h y d r o x i d e . T h i s b a s i c s o l u t i o n was e x t r a c t e d w i t h d i c h l o r o m e t h a n e (4 x 20 m l ) . D r y i n g o f t h e c o m b i n e d o r g a n i c p h a s e o v e r a n h y d r o u s s o d i u m s u l f a t e , f i l t r a t i o n , a n d e v a p o r a t i o n o f t h e s o l v e n t u n d e r r e d u c e d p r e s s u r e a f f o r d e d a b r o w n f o a m . T h i s m a t e r i a l c o u l d be s e p a r a t e d by p r e p a r a t i v e t i c on a l u m i n a u s i n g c h l o r o f o r m a s t h e d e v e l o p e r t o y i e l d c l e a v a m i n e (3 m g ) , v i n d o l i n e (3 m g ) , d e a c e t y l v i n d o l i n e (1 mg) and s t a r t i n g d i m e r ( 1 . 1 mg) as t h e o n l y i s o l a b l e m a t e r i a l s . These c o u l d a l l be i d e n t i f i e d by i n f r a r e d and m e l t i n g p o i n t c o m p a r i s o n s w i t h t h e a u t h e n t i c m a t e r i a l s . - 166 -D i m e r 106 \ To a s o l u t i o n o f 1 8 8 - c a r b o m e t h o x y - 4 ( 3 - d i h y d r o c l e a v a m i n - 3 a - o l (56) (250 mg) i n d i c h l o r o m e t h a n e (25 m l ) c o n t a i n i n g t r i e t h y l a m i n e (1 m l ) was a d d e d a s o l u t i o n o f t - b u t y l h y p o c h l o r i t e (40 m l o f a 0 . 0 2 M s o l u t i o n ) i n c a r b o n t e t r a c h l o r i d e a t 0°C w i t h s t i r r i n g o v e r 1 . 5 h o u r s . E v a p o r a t i o n o f t h e s o l v e n t a t 0°C u n d e r h i g h vacuum a f f o r d e d a r e d d i s h -b r o w n f o a m . V i n d o l i n e (150 mg) was d i s s o l v e d i n 1.5% m e t h a n o l i c h y d r o g e n c h l o r i d e (50 m l ) a n d a d d e d , u n d e r a s t r e a m o f n i t r o g e n , t o t h e c h l o r o i n d o l -e n i n e a b o v e , a n d t h e w h o l e r e f l u x e d f o r 2 . 5 h o u r s . A f t e r t h i s t i m e i t was c o o l e d t o room t e m p e r a t u r e , d i l u t e d w i t h w a t e r , b a s i f i e d w i t h s o l i d p o t a s s i u m b i c a r b o n a t e a n d e x t r a c t e d w i t h d i c h l o r o m e t h a n e (4 x 25 m l ) . The c o m b i n e d o r g a n i c p h a s e was d r i e d o v e r s o d i u m s u l f a t e , f i l t e r e d a n d e v a p o r a t e d t o d r y n e s s u n d e r r e d u c e d p r e s s u r e t o y i e l d a foam (402 m g ) . T h i s m a t e r i a l was c h r o m a t o g r a p h e d o n a l u m i n a ( n e u t r a l Woelm I I I ) t o y i e l d , u p o n e l u t i o n w i t h b e n z e n e c o n t a i n i n g 25% e t h y l a c e t a t e , t h e EtOH d e s i r e d d i m e r (106) a s a w h i t i s h g l a s s (40 mg, 8% y i e l d ) . * m a x n m : 3 ^ 5 , 2 9 5 , 2 8 6 , 2 6 2 , 2 2 5 ( s h ) , 216 ( l o g e 3 . 8 , 3 . 9 , 3 . 9 , 3 . 9 , 4 . 4 , 4 . 5 r e s p e c t i v e l y ) ; N m r : T 0 . 5 8 ( b r o a d s i n g l e t , I H , N ' - H ) , 1 . 0 2 ( s i n g l e t , I H , C - O H ) , 2 . 5 0 -3 . 0 0 ( m u l t i p l e t , 4 H , a r o m a t i c ) , 3 . 1 1 ( s i n g l e t , I H , C ^ - H ) , 4 . 0 0 ( s i n g l e t , I H , C ^ - H ) , 4 . 1 0 ( m u l t i p l e t , I H , C - H ) , 4 . 6 3 ( s i n g l e t , I H , C , - H ) , 4 . 6 0 1/ — / — 4 — ( m u l t i p l e t , I H , C 6 ~ H ) , 6 . 1 4 ( s i n g l e t , 3 H , C 1 6 - 0 C H _ 3 ) , 6 . 2 5 ( s i n g l e t , 6 H , 2 x C 0 2 C H 3 ) , 7 . 3 9 ( s i n g l e t , 3 H , N - j - C H g ) , 7 . 7 5 ( s i n g l e t , 3 H , C ^ - O A c ) , 9 . 0 2 ( t r i p l e t , J % 7 c p s , 3 H , C H 2 C H _ 3 ) , 9 . 4 0 ( t r i p l e t , J ^ 7 c p s , 3 H , - C H 2 C H 3 ) ; mass s p e c t r u m : m a i n p e a k s a t m/e = 8 1 0 , 7 6 5 , 4 6 9 , 3 5 2 , 3 2 3 , 2 8 2 , 2 0 2 , 2 0 0 , 1 8 8 , 1 5 6 , 1 5 4 , 1 4 4 , 1 3 8 , 1 3 6 , 1 3 5 , 1 2 4 , 1 2 2 , 1 2 1 , 1 0 7 . - 167 -D i m e r 106 by S e p h a d e x C h r o m a t o g r a p h y 1 8 g - C a r b o m e t h o x y - 4 3 - d i h y d r o c l e a v a m i n - 3 a - o l (250 mg) was c o n v e r t e d t o i t s c h l o r o i n d o l e n i n e a c c o r d i n g t o t h e p r o c e d u r e a b o v e a n d d i m e r i z e d w i t h v i n d o l i n e (200 mg) i n 1.5% m e t h a n o l i c h y d r o g e n c h l o r i d e (100 m l ) by r e f l u x i n g t h e r e a c t i o n m i x t u r e f o r 2 . 7 5 h o u r s . A f t e r t h i s t i m e i t was w o r k e d up a s a b o v e t o a f f o r d t h e c r u d e r e a c t i o n m i x t u r e as a l i g h t y e l l o w i s h - b r o w n foam (500 m g ) . T h i s m a t e r i a l was i n t r o d u c e d o n t o t h e same Sephadex L H - 2 0 c o l u m n m e n t i o n e d p r e v i o u s l y . A 2 m l / m i n u t e f l o w r a t e was m a i n t a i n e d a n d 10 m l f r a c t i o n s w e r e c o l l e c t e d . F r a c t i o n s 1 2 , 1 3 and 14 a f f o r d e d t h e d e s i r e d d i m e r (106) s l i g h t l y c o n t a m i n a t e d w i t h b l u e s p o t m a t e r i a l . T h i s c r u d e d i m e r c o u l d be p u r i f i e d by p r e p a r a t i v e t i c t o a f f o r d t h e p u r e d i m e r (106) ( 9 2 . 3 mg, 18.4% y i e l d ) . C l e a v a g e o f D i m e r 106 D i m e r 106 (13 mg) was d i s s o l v e d i n a n h y d r o u s 7% m e t h a n o l i c h y d r o g e n c h l o r i d e a n d t i n (35 mg) a n d s t a n n o u s c h l o r i d e (50 mg) w e r e a d d e d . The r e a c t i o n m i x t u r e was r e f l u x e d f o r 1 . 5 h o u r s and t h e n c o o l e d , d i l u t e d w i t h w a t e r and b a s i f i e d w i t h ammonium h y d r o x i d e . The r e s u l t i n g b a s i c s o l u t i o n was e x t r a c t e d w i t h d i c h l o r o m e t h a n e (4 x 20 m l ) and t h e c o m b i n e d o r g a n i c p h a s e d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e , f i l t e r e d and e v a p o r a t e d t o d r y n e s s u n d e r r e d u c e d p r e s s u r e t o y i e l d a f o a m . From t h i s m a t e r i a l , v i n d o l i n e , d e a c e t y l v i n d o l i n e , 4 B - d i h y d r o c l e a v a m i n o l , and d i m e r 106 c o u l d be i s o l a t e d by p r e p a r a t i v e t i c , and a l c o h o l s 56 a n d 57 c o u l d be i d e n t i f i e d i n t r a c e a m o u n t s . - 168 -18-Methoxy-18-carbomethoxy-4g-dihydrocleavamine hydrochloride (110) To a s o l ution of 18(3—carbomethoxy—4$—dihydrocleavarnine (250 mg) i n dichloromethane (25 ml) i n a 100 ml round-bottomed f l a s k was added, at 0°C with s t i r r i n g , Jt-butyl hypochlorite (200 micro/t.). T i c check (alumina, benzene, eerie s u l f a t e spray, then alumina, benzene, antimony pentachloride i n carbon t e t r a c h l o r i d e spray) revealed that the s t a r t i n g material had been completely replaced by the chloroindolenine. The solvent was removed under reduced pressure at room temperature to y i e l d a whitish foam. To t h i s material was added 1.5% methanolic hydrogen c h l o r i d e (8 ml) at 0°C with s t i r r i n g . The r e a c t i o n mixture was a deep wine-red colour. A f t e r s t i r r i n g f o r 0.5 hours at 0°C a t i c check (alumina, benzene, uv, then eerie s u l f a t e spray) revealed that the chloroindolenine had completely disappeared, and had been replaced by a s l i g h t l y more polar major spot. Evaporation of the solvent under high vacuum at 0°C afforded a reddish-brown powder i d e n t i f i e d as the desired compound (110) c h i e f l y on the basis of i t s nmr: T 2.35-3.00 (multiplet, 4H, aromatic), 4.85 (broad s i n g l e t , IH, N^ +-H), 5.70 ( t r i p l e t , J ^ 7 cps, IH), 6.18 ( s i n g l e t , 3H, C l g-C0 2CH 3), 7.00 ( s i n g l e t , 3H, C -OMe), 9.20 (broad unresolved t r i p l e t , 3H, C^-C^CH^) . This material was quite stable and could be r e c r y s t a l l i z e d from non-hydroxylic solvents such as p u r i f i e d e t h y l acetate. It was however quite unstable as the free base. 18-Methoxy-18-hydroxymethylene-4e-dihydrocleavarnine (111) Compound (110) (255 mg) was dissolved i n f r e s h l y d i s t i l l e d dry tetrahydrofuran (30 ml) and cooled to room temperature. Lithium aluminum - 169 -h y d r i d e (250 mg, 27 m o l e e q u i v a l e n t s ) was a d d e d i n f o u r e q u a l p o r t i o n s w i t h s t i r r i n g . A f t e r 1 . 7 5 h o u r s , t h e e x c e s s l i t h i u m a l u m i n u m h y d r i d e was d e s t r o y e d b y t h e d r o p w i s e a d d i t i o n o f a s a t u r a t e d a q u e o u s s o l u t i o n o f s o d i u m s u l f a t e a t 0°C (an i m p r o v e m e n t i n t h e r e c o v e r y o f m a t e r i a l was r e a l i z e d by u s i n g s o l i d ^ 2 8 0 ^ - 1 0 ^ 0 i n s t e a d ) . When no f u r t h e r e f f e r v e s c e n c e was d e t e c t a b l e u p o n t h e a d d i t i o n o f a d d i t i o n a l d r o p s o f t h e a q u e o u s s o l u t i o n , t h e r e a c t i o n m i x t u r e was f i l t e r e d u n d e r vacuum t h r o u g h a b e d o f c e l i t e . A w h i t e , a l m o s t c r y s t a l l i n e , r e s i d u e was c o l l e c t e d and r e t u r n e d t o t h e f l a s k . Some more t e t r a h y d r o f u r a n was a d d e d a n d t h e w h o l e r e f l u x e d g e n t l y on a s t e a m b a t h and t h e n f i l t e r e d a g a i n . The c o m b i n e d f i l t r a t e was e v a p o r a t e d t o d r y n e s s u n d e r r e d u c e d p r e s s u r e t o a f f o r d a w h i t e foam ( 2 3 2 . 7 m g ) . T h i s m a t e r i a l was c h r o m a t o g r a p h e d o n a l u m i n a ( n e u t r a l Woelm I I I ) . E l u t i o n w i t h g r a d u a l l y i n c r e a s i n g l y p o l a r s o l v e n t c o m b i n a t i o n s y i e l d e d t h e d e s i r e d compound (111) (115 mg) i n s e m i p u r e f o r m by e l u t i n g w i t h e t h y l a c e t a t e . T h i s m a t e r i a l was r e - c h r o m a t o g r a p h e d i n a s i m i l a r manner t o y i e l d compound 111 p u r e ( r e c r y s t a l l i z e d t w i c e f r o m e t h y l E t O H a c e t a t e , 100 m g , 40% y i e l d ) , mp 1 3 9 - 1 4 1 ° C A m a x nm: 2 9 2 , 2 8 5 , 279 £ h ) , 2 2 5 ( l o g e 3 . 8 , 3 . 9 , 3 . 8 , 4 . 5 r e s p e c t i v e l y ) ; v C H C 1 3 c m " 1 : max 3 5 6 0 , 3 4 1 0 , 2 9 2 0 , 1 4 9 0 , 1 4 6 5 , 1 4 4 0 , 1 3 7 5 , 1 3 4 0 , 1 3 0 5 , 1 1 5 5 , 1 1 4 0 , 1 0 8 0 , 1 0 4 0 ; Nmr : T 0 . 1 4 ( b r o a d s i n g l e t , I H , N - H ) , 2 . 4 0 - 3 . 0 0 ( m u l t i p l e t , 4 H , a r o m a t i c ) , 6 . 8 8 ( s i n g l e t , 3 H , C 1 o - 0 M e ) , 9 . 0 8 ( t r i p l e t , J 7 c p s , 3 H , l o C ^ - C H 2 C H 3 ) ; mass s p e c t r u m : m a i n p e a k s a t m/e = 3 4 2 , 3 1 1 , 3 1 0 , 2 7 1 , 185 , 1 8 1 , 1 8 0 , 1 6 8 , 1 5 6 , 1 4 4 , 1 3 9 , 1 3 8 , 1 3 7 , 1 2 6 , 1 2 5 , 1 2 4 , 1 2 2 , 1 1 0 . A n a l . F o u n d : C , 71 .33%; H , 8 . 81%; N , 7.60%. C a l c d . f o r C 2 1 H 3 0 N 2 O 2 ' i / 2 E t O A c : C , 71 .47%; H , 8 .87%; N , 7 .25%. H i g h r e s o l u t i o n - 170 -mass s p e c t r o m e t r y : F o u n d , 3 4 2 . 2 2 8 2 ; R e q u i r e d f o r c 2 i H 3 o N 2 0 2 ' 3 4 2 • 2 3 0 6 5 F o u n d , 3 4 1 . 2 2 0 3 ; R e q u i r e d f o r M + - l , 3 4 1 . 2 2 2 8 ; F o u n d , 3 4 0 . 2 1 2 2 ; R e q u i r e d f o r M + - 2 , 3 4 0 . 2 1 5 0 ; F o u n d , 1 3 8 . 1 2 7 6 ; R e q u i r e d f o r C g H ^ ^ , 1 3 8 . 1 2 8 2 . S t u d y o f t h e M e c h a n i s m o f t h e C o n v e n t i o n a l D i m e r i z a t i o n R e a c t i o n E a c h o f t h e e x p e r i m e n t s b e l o w h a v e b e e n c h e c k e d f o r r e p r o d u c i b i l i t y and w h e r e no d i m e r s c o u l d be o b s e r v e d , t h e q u a l i t y o f t h e r e a g e n t s h a s b e e n t e s t e d b y r e p e t i t i o n o f t h e s t a n d a r d r e a c t i o n w i t h y i e l d o f i s o l a t e d d i m e r o b t a i n e d a s 60% + 5%. E x p e r i m e n t 1 S t a n d a r d D i m e r i z a t i o n To a s o l u t i o n o f 1 8 B - c a r b o m e t h o x y - 4 8 - d i h y d r o c l e a v a m i n e ( 4 0 . 4 mg) i n m e t h y l e n e c h l o r i d e (4 m l ) a n d t r i e t h y l a m i n e ( 0 . 0 2 m l ; one d r o p ) c o o l e d i n a n i c e - w a t e r b a t h , was a d d e d a s o l u t i o n o f _ t - b u t y l h y p o c h l o r i t e i n c a r b o n t e t r a c h l o r i d e (3 m l o f a 0 . 0 5 M s o l u t i o n ) o v e r a p e r i o d o f 45 m i n u t e s . The s o l u t i o n was w a s h e d w i t h i c e - w a t e r (2 x 3 . 0 m l ) d r i e d o v e r a n h y d r o u s N a 2 S 0 4 and t h e s o l v e n t removed i n v a c u o t o g i v e t h e c h l o r o i n d o l e n i n e a s a foam ( 4 4 . 0 m g ) . The c h l o r o i n d o l e n i n e a b o v e and v i n d o l i n e ( 3 1 . 1 mg) w e r e d i s s o l v e d i n a n h y d r o u s m e t h a n o l i c 1.5% h y d r o g e n c h l o r i d e (2 m l ) and t h e r e s u l t i n g s o l u t i o n was s t i r r e d a t room t e m p e r a t u r e u n d e r a n i t r o g e n a t m o s p h e r e and t h e n r e f l u x e d f o r a f u r t h e r 2 h o u r s . The s o l v e n t was removed i r i v a c u o and t h e r e s i d u e p a r t i t i o n e d b e t w e e n m e t h y l e n e c h l o r i d e and aqueous 10% s o d i u m b i c a r b o n a t e s o l u t i o n . - 171 -The a q u e o u s p h a s e was e x t r a c t e d w i t h f u r t h e r p o r t i o n s o f m e t h y l e n e c h l o r i d e (2 x 10 m l ) and t h e c o m b i n e d o r g a n i c e x t r a c t s w e r e d r i e d o v e r s o d i u m s u l f a t e . The s o l v e n t was removed t o g i v e a l i g h t y e l l o w foam (% 70 m g ) . T h i s m a t e r i a l was c h r o m a t o g r a p h e d o n Woelm I I I a l u m i n a (^ 10 g ) . B e n z e n e , e t h y l a c e t a t e ( 4 : 1 ) e l u t i o n gave t h e d e s i r e d d i m e r (94) i n 65% y i e l d ( 4 5 . 0 m g ) . T h i s m a t e r i a l was a n a l y z e d by T - 6 0 n m r . E x p e r i m e n t 2 S t a n d a r d D i m e r i z a t i o n o f P u r e 1 8 q - C a r b o m e t h o x y - 4 g - d i h y d r o c l e a v a m i n e To a s o l u t i o n o f 1 8 a - c a r b o m e t h o x y - 4 g - d i h y d r o c l e a v a m i n e ( 3 8 . 6 rag) i n m e t h y l e n e c h l o r i d e (4 m l ) and t r i e t h y l a m i n e (one d r o p ) c o o l e d i n a n i c e - w a t e r b a t h was a d d e d a s o l u t i o n o f _ t - b u t y l h y p o c h l o r i t e i n c a r b o n t e t r a c h l o r i d e ( 2 . 5 m l o f a 0 . 0 5 M s o l u t i o n ) o v e r a p e r i o d o f 1 h o u r . The s o l u t i o n was w a s h e d w i t h i c e - w a t e r ( 2 x 3 m l ) d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e a n d t h e s o l v e n t removed i n v a c u o t o g i v e t h e c h l o r o -i n d o l e n i n e a s a w h i t i s h foam ( 4 0 . 0 m g ) . The a b o v e c h l o r o i n d o l e n i n e and v i n d o l i n e ( 3 1 . 2 mg) w e r e d i s s o l v e d i n a n h y d r o u s m e t h a n o l i c 1.5% h y d r o g e n c h l o r i d e (2 m l ) a n d t h e r e s u l t i n g s o l u t i o n was s t i r r e d a t room t e m p e r a t u r e f o r 30 m i n u t e s u n d e r a n i t r o g e n a t m o s p h e r e and t h e n r e f l u x e d f o r a f u r t h e r 2 . 5 h o u r s . The s o l v e n t was removed i n v a c u o and t h e r e s i d u e p a r t i t i o n e d b e t w e e n m e t h y l e n e c h l o r i d e and a q u e o u s 10% s o d i u m b i c a r b o n a t e s o l u t i o n . The a q u e o u s p h a s e was e x t r a c t e d w i t h f u r t h e r p o r t i o n s o f m e t h y l e n e c h l o r i d e (3 x 10 m l ) and t h e c o m b i n e d e x t r a c t s w e r e d r i e d o v e r s o d i u m s u l f a t e . The s o l v e n t was removed i i i v a c u o t o g i v e a l i g h t b r o w n i s h foam (*\/ 70 m g ) . T h i s m a t e r i a l was c h r o m a t o g r a p h e d o n Woelm I I I a l u m i n a - 172 -(y 10 g ) . B e n z e n e , e t h y l a c e t a t e ( 4 : 1 ) e l u t i o n a f f o r d e d d i m e r i c m a t e r i a l i n 45% y i e l d . T h i s m a t e r i a l was f o u n d t o be i d e n t i c a l t o d i m e r 94 by n m r . E x p e r i m e n t 3 D i m e r i z a t i o n w i t h t h e C h l o r o i n d o l e n i n e F o r m a t i o n i n R e f l u x i n g  M e t h y l e n e C h l o r i d e To a s o l u t i o n o f 1 8 B - c a r b o m e t h o x y - 4 B - d i h y d r o c l e a v a m i n e ( 4 3 . 5 mg) i n d i c h l o r o m e t h a n e (5 m l ) m a i n t a i n e d a t r e f l u x t e m p e r a t u r e by i m m e r s i o n i n a n o i l b a t h k e p t a t 5 0 ° C , was a d d e d n e a t J ^ - b u t y l h y p o c h l o r i t e ( 1 6 . 8 mg) w i t h a m i c r o s y r i n g e a l l a t once u n d e r a n i t r o g e n a t m o s p h e r e . The y e l l o w c o l o u r e d s o l u t i o n was r e f l u x e d f o r a f u r t h e r 5 m i n u t e s , t h e n c o o l e d t o room t e m p e r a t u r e w a s h e d w i t h i c e - w a t e r (2 x 15 m l ) d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e and t h e s o l v e n t removed i n v a c u o t o y i e l d a f o a m . The a b o v e c h l o r o i n d o l e n i n e and v i n d o l i n e ( 3 3 . 0 mg) w e r e d i s s o l v e d i n a n h y d r o u s m e t h a n o l i c 1.5% h y d r o g e n c h l o r i d e ( 2 . 3 m l ) a n d t h e r e s u l t i n g s o l u t i o n was s t i r r e d a t room t e m p e r a t u r e f o r 30 m i n u t e s u n d e r a n i t r o g e n a t m o s p h e r e and t h e n r e f l u x e d f o r a f u r t h e r 2 h o u r s . The s o l v e n t was removed i n v a c u o a n d t h e r e s i d u e p a r t i t i o n e d b e t w e e n m e t h y l e n e c h l o r i d e and a q u e o u s 10% s o d i u m b i c a r b o n a t e . The a q u e o u s p h a s e was t h e n f u r t h e r e x t r a c t e d w i t h p o r t i o n s o f m e t h y l e n e c h l o r i d e (2 x 10 m l ) . The c o m b i n e d o r g a n i c p h a s e was d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e and t h e s o l v e n t removed u n d e r r e d u c e d p r e s s u r e t o y i e l d a foam (64 m g ) . T h i s m a t e r i a l was c h r o m a t o g r a p h e d on 8 g o f Woelm I I I a l u m i n a . B e n z e n e , e t h y l a c e t a t e ( 4 : 1 ) e l u t i o n gave d i m e r i c m a t e r i a l i n - 173 -r o u g h l y 35% y i e l d . T h i s was f o u n d t o be i d e n t i c a l t o d i m e r 94 by n m r . E x p e r i m e n t 4 E x p e r i m e n t 3 w i t h T r i e t h y l a m i n e A s o l u t i o n o f 1 8 g - c a r b o m e t h o x y - 4 g - d i h y d r o c l e a v a m i n e ( 4 0 . 8 mg) i n m e t h y l e n e c h l o r i d e ( 4 . 5 m l ) c o n t a i n i n g t r i e t h y l a m i n e (one d r o p ) was m a i n t a i n e d a t r e f l u x t e m p e r a t u r e by i m m e r s i o n i n a n o i l b a t h k e p t a t 5 0 ° C . To t h i s s o l u t i o n was a d d e d _ t - b u t y l h y p o c h l o r i t e ( 1 4 . 0 mg) a l l a t o n c e u n d e r a n i t r o g e n a t m o s p h e r e and t h e r e f l u x c o n t i n u e d f o r a f u r t h e r 5 m i n u t e s . The y e l l o w s o l u t i o n was t h e n c o o l e d , w a s h e d w i t h i c e - w a t e r (2 x 15 m l ) d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e and t h e s o l v e n t removed i n v a c u o t o y i e l d a l i g h t b r o w n foam ( 7 1 . 6 m g ) . T h i s m a t e r i a l was c o l u m n e d on 9 . 5 g o f Woelm I I I a l u m i n a i n t h e u s u a l way t o y i e l d ^ 40% d i m e r i c m a t e r i a l . T h i s was i d e n t i f i e d by nmr as d i m e r 94 . E x p e r i m e n t 5 E x p e r i m e n t 4 u s i n g a S o l u t i o n o f C h l o r i n a t i n g A g e n t i n C a r b o n  T e t r a c h l o r i d e To a s o l u t i o n o f 1 8 6 - c a r b o m e t h o x y - 4 B - d i h y d r o c l e a v a m i n e (40 mg) i n m e t h y l e n e c h l o r i d e (4 m l ) c o n t a i n i n g t r i e t h y l a m i n e (one d r o p ) h e a t e d t o r e f l u x i n an o i l b a t h , was added a s o l u t i o n o f t _ - b u t y l h y p o c h l o r i t e i n c a r b o n t e t r a c h l o r i d e (3 m l o f a 0 . 0 5 M s o l u t i o n ; b a t h t e m p e r a t u r e 4 9 ° C ) u n d e r n i t r o g e n o v e r a p e r i o d o f 15 m i n u t e s . The r e a c t i o n m i x t u r e was c o o l e d , washed w i t h i c e - w a t e r ( 3 x 2 m l ) d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e and t h e s o l v e n t removed i n v a c u o t o y i e l d a l i g h t f o a m . - 174 -The s t a n d a r d d i m e r i z a t i o n w i t h 32 mg o f v i n d o l i n e and 2 m l o f a n h y d r o u s m e t h a n o l i c 1.5% h y d r o g e n c h l o r i d e f o l l o w e d by t h e u s u a l c o l u m n r e s u l t e d i n a n i s o l a t i o n o f a 50% y i e l d o f d i m e r w h i c h was i d e n t i f i e d b y nmr t o be d i m e r 9 4 . E x p e r i m e n t 6 E x p e r i m e n t 3 u s i n g a M i x t u r e o f M e t h y l e n e C h l o r i d e , C a r b o n  T e t r a c h l o r i d e ( 1 : 4 ) as S o l v e n t To a s o l u t i o n o f 1 8 B - c a r b o m e t h o x y - 4 8 - d i h y d r o c l e a v a m i n e ( 2 0 . 7 mg) i n 3 . 5 m l o f c a r b o n t e t r a c h l o r i d e and 1 m l o f m e t h y l e n e c h l o r i d e h e a t e d t o r e f l u x i n a n o i l b a t h a t 7 2 ° C , was a d d e d t - b u t y l h y p o c h l o r i t e (20 mg) a l l a t o n c e u n d e r a n i t r o g e n a t m o s p h e r e . A f t e r 5 m i n u t e s t h e r e a c t i o n m i x t u r e was c o o l e d t o room t e m p e r a t u r e and w a s h e d (2 x 10 m l ) w i t h i c e w a t e r . The o r g a n i c p h a s e was d r i e d o v e r s o d i u m s u l f a t e , f i l t e r e d and t h e s o l v e n t e v a p o r a t e d t o y i e l d a g r e e n i s h - b r o w n f o a m . The a b o v e c h l o r o i n d o l e n i n e and v i n d o l i n e (15 mg) w e r e d i s s o l v e d i n 1 m l o f a n h y d r o u s m e t h a n o l i c 1.5% h y d r o g e n c h l o r i d e a n d d i m e r i z e d i n t h e u s u a l w a y . No d i m e r c o u l d be i s o l a t e d by s u b s e q u e n t c o l u m n c h r o m a t o -g r a p h y . T h i s e x p e r i m e n t was c h e c k e d i n t h e u s u a l way f o r r e p r o d u c i b i l i t y a n d t h e n t h e s t a n d a r d d i m e r i z a t i o n was r e p e a t e d t o y i e l d d i m e r 94 i n 60% y i e l d . E x p e r i m e n t 7 E x p e r i m e n t 6 w i t h 1 : 1 M i x t u r e o f M e t h y l e n e C h l o r i d e , C a r b o n  T e t r a c h l o r i d e To a s o l u t i o n o f 1 8 - c a r b o m e t h o x y - 4 B - d i h y d r o c l e a v a m i n e (y 30% 1 8 a , 70% 186) (41 mg) i n m e t h y l e n e c h l o r i d e , c a r b o n t e t r a c h l o r i d e ( 1 : 1 ) - 175 -(7 m l ) m a i n t a i n e d a t a r e f l u x t e m p e r a t u r e o f 5 3 ° b y i m m e r s i o n i n a n o i l b a t h a t 5 5 ° C was a d d e d _ t - b u t y l h y p o c h l o r i t e (20 mg) a l l a t o n c e u n d e r n i t r o g e n . The r e f l u x was a l l o w e d t o c o n t i n u e f o r a f u r t h e r 5 m i n u t e s . The r e a c t i o n m i x t u r e was t h e n c o o l e d t o room t e m p e r a t u r e w a s h e d w i t h i c e - w a t e r (2 x 10 m l ) d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e a n d t h e s o l v e n t removed i n v a c u o t o y i e l d a g o l d e n c o l o u r e d f o a m . T h i s m a t e r i a l was d i m e r i z e d u n d e r s t a n d a r d c o n d i t i o n s w i t h v i n d o l i n e ( 2 8 . 7 mg) i n m e t h a n o l i c 1.5% h y d r o g e n c h l o r i d e t o y i e l d a n e s t i m a t e d 0.5% o f d i m e r i c m a t e r i a l ( i . e . n o t v i s i b l e e i t h e r u n d e r uv l i g h t o r u p o n s p r a y i n g w i t h a n t i m o n y p e n t a c h l o r i d e o n a n a l u m i n a p l a t e ) . E x p e r i m e n t 8 E x p e r i m e n t 7 w i t h 2 : 1 M i x t u r e o f M e t h y l e n e C h l o r i d e t o C a r b o n  T e t r a c h l o r i d e E x p e r i m e n t 7 a b o v e was r e p e a t e d e x a c t l y u s i n g 4 3 . 4 mg o f 1 8 - c a r b o -m e t h o x y - 4 8 - d i h y d r o c l e a v a m i n e and 7 m l o f m e t h y l e n e c h l o r i d e , c a r b o n t e t r a c h l o r i d e ( 2 : 1 ) . R e f l u x t e m p e r a t u r e h e r e was 5 0 ° C . The d i m e r i z a t i o n was p e r f o r m e d u n d e r s t a n d a r d c o n d i t i o n s u s i n g 2 9 . 0 mg o f v i n d o l i n e and 2 . 0 m l o f m e t h a n o l i c 1.5% h y d r o g e n c h l o r i d e . The y i e l d o f d i m e r was e s t i m a t e d a s a b o v e t o be 1 0 . 0 % . E x p e r i m e n t 9 S t a n d a r d D i m e r i z a t i o n w i t h P r i o r R e a c t i o n o f t h e C h l o r o i n d o l e n i n e  w i t h M e t h a n o l To a s o l u t i o n o f 1 8 - c a r b o m e t h o x y - 4 8 - d i h y d r o c l e a v a m i n e ( 4 1 . 9 mg) i n m e t h y l e n e c h l o r i d e (4 m l ) c o o l e d i n a n i c e - w a t e r b a t h , was a d d e d a - 176 -s o l u t i o n o f _ t - b u t y l h y p o c h l o r i t e i n c a r b o n t e t r a c h l o r i d e ( 2 . 6 m l o f a 0 . 0 5 M s o l u t i o n ) o v e r a p e r i o d o f 30 m i n u t e s . The s o l u t i o n was w a s h e d w i t h i c e c o l d s a t u r a t e d b r i n e (2 x 20 m l ) , d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e and t h e s o l v e n t removed in_ v a c u o t o y i e l d a l i g h t f o a m . T h i s was t r e a t e d w i t h c h l o r o f o r m and m e t h a n o l a t 0°C f o l l o w e d by e v a p o r a t i o n o f t h e s o l v e n t a t room t e m p e r a t u r e . No r e a c t i o n was a p p a r e n t b y t i c . D i m e r i z a t i o n i n m e t h a n o l i c 1.5% h y d r o g e n c h l o r i d e (2 m l ) w i t h 2 6 . 5 mg o f v i n d o l i n e r e s u l t e d i n a 75% y i e l d o f d i m e r i s o l a t e d a f t e r c o l u m n c h r o m a t o g r a p h y i n t h e u s u a l way o n 10 g o f Woelm I I I a l u m i n a ( i s o l a t e d 4 9 . 8 mg f r o m 6 6 . 5 mg o f c r u d e p r o d u c t ) . T h i s m a t e r i a l was f o u n d t o be i d e n t i c a l t o d i m e r 94 by n m r . E x p e r i m e n t 10 S t a n d a r d D i m e r i z a t i o n w i t h P r i o r R e a c t i o n o f t h e C h l o r o i n d o l e n i n e  w i t h 1.5% M e t h a n o l i c H y d r o g e n C h l o r i d e To a s o l u t i o n o f 1 8 - c a r b o m e t h o x y - 4 B - d i h y d r o c l e a v a m i n e ( 4 2 . 2 mg) i n m e t h y l e n e c h l o r i d e (4 m l ) c o o l e d i n a n i c e - w a t e r b a t h , was a d d e d a s o l u t i o n o f t _ - b u t y l h y p o c h l o r i t e i n c a r b o n t e t r a c h l o r i d e (2 m l o f a 0 . 0 5 M s o l u t i o n ) o v e r a p e r i o d o f 30 m i n u t e s . The u s u a l w o r k u p a s a b o v e y i e l d e d a l i g h t y e l l o w f o a m . To t h i s foam was a d d e d , a t room t e m p e r a t u r e , m e t h a n o l i c 1.5% h y d r o g e n c h l o r i d e and t h e r e s u l t i n g s o l u t i o n s t i r r e d f o r 15 m i n u t e s . A c h e c k by t i c a t t h i s p o i n t r e v e a l e d t h e c o m p l e t e d i s a p p e a r a n c e o f s t a r t i n g c h l o r o i n d o l e n i n e and t h e a p p e a r a n c e o f new more p o l a r s p o t s , one o f w h i c h was c l e a r l y t h e m a j o r one and c o u l d be a s c r i b e d t o a n 18-0Me compound by c o r r e l a t i o n w i t h some o t h e r w o r k ( v i d e s u p r a ) . - 177 -A t t h i s p o i n t s o l i d v i n d o l i n e was a d d e d ( 3 2 . 1 mg) and t h e s o l u t i o n s t i r r e d a t room t e m p e r a t u r e f o r a f u r t h e r 15 m i n u t e s and t h e n p l u n g e d i n t o a p r e h e a t e d o i l b a t h a t 6 5 ° C . W i t h i n 30 m i n u t e s o f h e a t i n g , t h e r e a c t i o n was c o m p l e t e and n o r m a l w o r k u p and c o l u m n c h r o m a t o g r a p h y y i e l d e d 55% ( 3 2 . 8 mg f r o m 7 2 . 8 mg c r u d e p r o d u c t ) o f a d i m e r i c compound w h i c h was i d e n t i f i e d by nmr as d i m e r 9 4 . E x p e r i m e n t 11 E x p e r i m e n t 10 w i t h a n NMR o f t h e C r u d e I n t e r m e d i a t e a f t e r M e t h a n o l i c HC1 R e a c t i o n o n t h e C h l o r o i n d o l e n i n e E x p e r i m e n t 10 was r e p e a t e d e x a c t l y as a b o v e w i t h t h e s i n g l e e x c e p t i o n t h a t t h e r e a c t i o n p r o d u c t f r o m t h e r e a c t i o n o f t h e c h l o r o -i n d o l e n i n e w i t h m e t h a n o l i c h y d r o g e n c h l o r i d e was i s o l a t e d by b a s i f i c a t i o n w i t h d i l u t e ammonium h y d r o x i d e a n d e x t r a c t i o n w i t h m e t h y l e n e c h l o r i d e . The r e s u l t i n g o r g a n i c p h a s e was d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e and t h e s o l v e n t r e m o v e d i n v a c u o t o y i e l d a g l a s s (82 mg f r o m 87 mg o f s t a r t i n g c h l o r o i n d o l e n i n e ) . T h i s m a t e r i a l was a n a l y z e d b y nmr and showed a c l e a r i n c o r p o r a t i o n o f a m e t h o x y l g r o u p i n t o t h e m o l e c u l e . S u b s e q u e n t s t a n d a r d d i m e r i z a t i o n f o l l o w e d by i s o l a t i o n o f t h e d i m e r i c m a t e r i a l y i e l d e d 40 .5% y i e l d (34 mg f r o m 84 mg o f c r u d e r e a c t i o n m i x t u r e o b t a i n e d f r o m 44 mg o f t h e a b o v e OMe c o n t a i n i n g compound w i t h 40 mg o f v i n d o l i n e ) o f d i m e r i d e n t i f i e d by nmr a s d i m e r 9 4 . E x p e r i m e n t 12 D i m e r i z a t i o n a t 1 4 0 ° C To a s o l u t i o n o f 1 8 8 - c a r b o m e t h o x y - 4 8 - d i h y d r o c l e a v a m i n e (55 mg) i n m e t h y l e n e c h l o r i d e ( 4 . 5 m l ) c o o l e d i n an i c e w a t e r b a t h , was a d d e d a - 178 -s o l u t i o n o f _ t - b u t y l h y p o c h l o r i t e i n c a r b o n t e t r a c h l o r i d e (2.5 m l o f a 0.05 M s o l u t i o n ) o v e r 30 m i n u t e s . E v a p o r a t i o n o f t h e s o l v e n t i n v a c u o y i e l d e d t h e d e s i r e d c h l o r o i n d o l e n i n e (60 mg)as a l i g h t b r o w n f o a m . The a b o v e m a t e r i a l was c o m b i n e d w i t h v i n d o l i n e (110 mg) i n m e t h y l e n e c h l o r i d e (1 m l ) and t h e r e s u l t i n g r e d d i s h o i l y s o l u t i o n was t r a n s f e r r e d t o a t u b e w h i c h was t h e n e v a c u a t e d t o y i e l d a w h i t e f o a m . The t u b e was f l u s h e d w i t h d r y n i t r o g e n a n d m e t h a n o l i c 1.5% h y d r o g e n c h l o r i d e (30 m l ) was a d d e d a t 0°C. The t u b e was s e a l e d a n d p l u n g e d i n a n o i l b a t h w h i c h h a d b e e n p r e h e a t e d t o 140°C. A f t e r 30 m i n u t e s t h e r e a c t i o n m i x t u r e was c o o l e d t o room t e m p e r a t u r e and w o r k e d up i n t h e u s u a l way t o y i e l d no d i m e r a t a l l . E x p e r i m e n t 13 E x p e r i m e n t 12 a t 100°C The c h l o r o i n d o l e n i n e o f 18B - c a r b o m e t h o x y-4B - d i h y d r o c h l e a v a m i n e (160 mg) was made as a b o v e i n e x p e r i m e n t 12. T h i s m a t e r i a l was c o m b i n e d w i t h 200 mg o f v i n d o l i n e i n m e t h y l e n e c h l o r i d e (1 m l ) and t r a n s f e r r e d t o a t u b e w h i c h was t h e n e v a c u a t e d t o y i e l d a w h i t e f o a m . To t h i s was a d d e d , a t 0°C, m e t h a n o l i c 1.5% h y d r o g e n c h l o r i d e (2 m l ) . The t u b e was s e a l e d and i m m e r s e d i n a n o i l b a t h w h i c h h a d b e e n p r e h e a t e d t o 100°C. A f t e r 15 m i n u t e s t h e r e a c t i o n m i x t u r e was c o o l e d t o room t e m p e r a t u r e a n d w o r k e d up i n t h e u s u a l way t o y i e l d d i m e r i c p r o d u c t w h i c h was i d e n t i f i e d by nmr as d i m e r 94 (^  30% y i e l d ) . - 179 -E x p e r i m e n t 14 D i m e r i z a t i o n u s i n g B e n z e n e as t h e S o l v e n t a n d BF^ E t h e r a t e as t h e  C a t a l y s t The c h l o r o i n d o l e n i n e o f 1 8 B - c a r b o m e t h o x y - 4 B - d i h y d r o c l e a v a m i n e ( 3 1 . 2 mg) was made as i n e x p e r i m e n t 13 a b o v e . T h i s m a t e r i a l was c o m b i n e d w i t h v i n d o l i n e ( 3 2 . 5 mg) i n b e n z e n e (4 m l ) and t h e s o l u t i o n was t r e a t e d w i t h B F ^ e t h e r a t e ( f i v e d r o p s ) . The m i x t u r e was s t i r r e d a t room t e m p e r a t u r e o v e r n i g h t and t h e n w o r k e d up i n t h e u s u a l way t o y i e l d no d i m e r i c m a t e r i a l a t a l l . E x p e r i m e n t 15 D i m e r i z a t i o n i n N , N - D i m e t h y l f o r m a m i d e w i t h HC1 C a t a l y s t To a s o l u t i o n o f 1 8 8 - c a r b o m e t h o x y - 4 3 - d i h y d r o c l e a v a m i n e ( 4 7 . 5 mg) i n m e t h y l e n e c h l o r i d e (5 m l ) c o o l e d i n a n i c e - w a t e r b a t h , was a d d e d a s o l u t i o n o f _ t - b u t y l h y p o c h l o r i t e i n c a r b o n t e t r a c h l o r i d e ( 2 . 5 m l o f a 0 . 0 5 M s o l u t i o n ) o v e r 30 m i n u t e s . E v a p o r a t i o n o f t h e s o l v e n t i n v a c u o r e s u l t e d i n a l i g h t y e l l o w f o a m . To t h i s foam was a d d e d v i n d o l i n e ( 1 0 3 . 2 mg) and m e t h y l e n e c h l o r i d e (1 m l ) . The r e s u l t i n g s o l u t i o n was e v a p o r a t e d t o y i e l d a n i n t i m a t e m i x t u r e o f v i n d o l i n e and t h e c h l o r o i n d o l e n i n e as a c r i s p w h i t e f o a m . T h i s m a t e r i a l was d i s s o l v e d i n 3 m l o f N , N - d i m e t h y l f o r m a m i d e and d r y HC1 gas was b u b b l e d i n f o r 15 s e c o n d s a t a b r i s k r a t e , c a r e b e i n g t a k e n t o e n s u r e t h a t t h e r e a c t i o n v e s s e l r e m a i n e d a t room t e m p e r a t u r e . A f t e r s t i r r i n g f o r 19 h o u r s u n d e r n i t r o g e n a t room t e m p e r a t u r e t h e r e a c t i o n m i x t u r e was p o u r e d o n t o i c e - c o l d a q u e o u s 10% s o d i u m b i c a r b o n a t e and e x t r a c t e d s e v e r a l t i m e s w i t h m e t h y l e n e c h l o r i d e (3 x 25 m l ) . The c o m b i n e d r e d d i s h - b r o w n o r g a n i c p h a s e was d r i e d o v e r a n h y d r o u s s o d i u m - 180 -s u l f a t e a n d t h e s o l v e n t was e v a p o r a t e d t o y i e l d a r e d d i s h o i l w h i c h c o u l d be c o n v e r t e d t o a foam by e x t e n d e d e v a c u a t i o n . The c r u d e r e a c t i o n m i x t u r e 150 mg) was s u b j e c t e d t o c o l u m n c h r o m a t o g r a p h y o n 30 g o f Woelm I I I a l u m i n a and y i e l d e d 60 mg o f d i m e r i c m a t e r i a l 60% b a s e d o n t h e f a c t t h a t o n l y 50 mg o f v i n d o l i n e a r e e x p e c t e d t o r e a c t ) w h i c h was i d e n t i f i e d b y nmr a s d i m e r 9 4 . E x p e r i m e n t 16 D i m e r i z a t i o n i n T e t r a h y d r o f u r a n (THF) w i t h HC1 C a t a l y s t The c h l o r o i n d o l e n i n e o f 1 8 B - c a r b o m e t h o x y - 4 3 _ d i h y d r o c l e a v a m i n e ( 5 0 . 0 mg) was f o r m e d u n d e r s t a n d a r d c o n d i t i o n s . T h i s m a t e r i a l was d i s s o l v e d w i t h v i n d o l i n e (50 mg) i n a n h y d r o u s THF c o n t a i n i n g 1.5% h y d r o g e n c h l o r i d e . The r e s u l t i n g s o l u t i o n was r e f l u x e d f o r 3 h o u r s u n d e r n i t r o g e n . The s o l v e n t was r e m o v e d u n d e r r e d u c e d p r e s s u r e a n d t h e r e s i d u e p a r t i t i o n e d b e t w e e n m e t h y l e n e c h l o r i d e a n d a q u e o u s 10% s o d i u m b i c a r b o n a t e . The a q u e o u s p h a s e was washed w i t h f u r t h e r p o r t i o n s o f m e t h y l e n e c h l o r i d e and t h e c o m b i n e d o r g a n i c p h a s e was d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e . E v a p o r a t i o n o f t h e s o l v e n t i n v a c u o r e s u l t e d i n a gum (102 mg) w h i c h u p o n c h r o m a t o g r a p h y y i e l d e d d i m e r i c m a t e r i a l (26 mg o r r o u g h l y 25%) w h i c h was i d e n t i f i e d by nmr t o be d i m e r 9 4 . E x p e r i m e n t 17 D i m e r i z a t i o n i n M e t h a n o l i c 1.5% H y d r o g e n C h l o r i d e P r e p a r e d f r o m  Wet M e t h a n o l To a s o l u t i o n o f 1 8 8 - c a r b o m e t h o x y - 4 B - d i h y d r o c l e a v a m i n e (50 mg) i n m e t h y l e n e c h l o r i d e (5 m l ) was a d d e d j t - b u t y l h y p o c h l o r i t e ( 2 . 5 m l o f a 0 . 0 5 M s o l u t i o n ) o v e r 30 m i n u t e s a t 0 ° C . E v a p o r a t i o n o f t h e s o l v e n t - 181 -in vacuo resulted in a light brown foam (52 mg). Reagent grade methanol (400 ml) was cooled in an ice bath and treated dropwise with dry acetyl chloride (9.25 ml). This solution (3 ml) was used to.dissolve the above chloroindolenine and vindoline (100 mg) together. The resulting solution was stirred at room tempera-ture for 4 hours and then bri e f l y heated (45 minutes) at reflux. The usual workup procedure yielded crude material (171.9 mg) as a foam. This was chromatographed on Woelm III alumina (20 g) to yield dimeric material i n roughly 30% yield which was identified by nmr to be dimer 94. Experiment 18 Standard Dimerization with Acetic Acid Added as a Cocatalyst To a solution of 188-carbomethoxy-4(3-dihydrocleavamine (40 mg) in methylene chloride (4 ml) was added _t-butyl hypochlorite (2 ml of a 0.05 M solution in carbon tetrachloride) at 0°C over 30 minutes. Evaporation of the solvent in vacuo yielded a brownish foam (43 mg). To a solution of the above chloroindolenine and vindoline (40 mg) in methanolic 1.5% hydrogen chloride (5 ml) was added glacial acetic acid (2 ml). The whole solution was refluxed under nitrogen for 3 hours and then worked up in the usual way to yield some small quantity of dimeric material (less than 5%). The reaction was repeated two more times with the quantity of acetic acid being 3.0 and 4.0 m i l l i l i t r e s respectively. It was found that the yield of dimeric material decreased sharply being just detectable - 182 -i n t h e f o r m e r and c o m p l e t e l y a b s e n t i n t h e l a t t e r c a s e . The c o m b i n e d d i m e r i c f r a c t i o n s f r o m t h e f i r s t two a t t e m p t s w e r e a n a l y z e d by nmr a n d f o u n d t o be d i m e r 9 4 . E x p e r i m e n t 19 D i m e r i z a t i o n i n T r i f l u o r o a c e t i c A c i d a s S o l v e n t and C a t a l y s t To a s o l u t i o n o f 1 8 3 - c a r b o m e t h o x y - 4 8 - d i h y d r o c l e a v a m i n e (50 mg) i n b e n z e n e (10 m l ) was a d d e d a s o l u t i o n o f 1 - c h l o r o b e n z o t r i a z o l e ( 3 1 . 2 mg) i n b e n z e n e (10 m l ) a t room t e m p e r a t u r e o v e r 30 m i n u t e s . A f t e r a n a d d i t i o n a l 30 m i n u t e s t h e s o l v e n t was removed i n v a c u o and t h e r e s u l t i n g m a t e r i a l p a r t i t i o n e d b e t w e e n i c e c o l d b r i n e and m e t h y l e n e c h l o r i d e . The a q u e o u s p h a s e was w a s h e d w i t h f u r t h e r p o r t i o n s o f m e t h y l e n e c h l o r i d e (2 x 10 m l ) and t h e c o m b i n e d o r g a n i c p h a s e was d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e . F i l t r a t i o n and r e m o v a l o f t h e s o l v e n t i n v a c u o y i e l d e d a l i g h t b r o w n f o a m . A s o l u t i o n o f t h e a b o v e m a t e r i a l a n d v i n d o l i n e (10 mg) i n t r i f l u o r o -a c e t i c a c i d (10 m l ) was s t i r r e d a t room t e m p e r a t u r e f o r 50 h o u r s a n d t h e n w o r k e d up as f o l l o w s . The c o n t e n t s o f t h e r e a c t i o n f l a s k was p o u r e d g r a d u a l l y o n t o i c e c o l d ammonium h y d r o x i d e ( d i l u t e ) and t h e r e s u l t i n g m i l k y s u s p e n s i o n was e x t r a c t e d w i t h m e t h y l e n e c h l o r i d e (3 x 50 m l ) . The c o m b i n e d o r g a n i c p h a s e was d r i e d o v e r s o d i u m s u l f a t e a n d f i l t e r e d . E v a p o r a t i o n o f t h e s o l v e n t i n v a c u o y i e l d e d c r u d e m a t e r i a l (110 mg) f r o m w h i c h d i m e r i c m a t e r i a l c o u l d be i s o l a t e d i n m i n u t e q u a n t i t i e s b y c o l u m n c h r o m a t o g r a p h y o n Woelm I I I a l u m i n a . T h i s d i m e r i c m a t e r i a l was a n a l y z e d by F o u r i e r T r a n s f o r m nmr s p e c t r o s c o p y and f o u n d t o be d i m e r 9 4 . - 183 -E x p e r i m e n t 20 D i m e r i z a t i o n i n D i o x a n e w i t h P e r c h l o r i c A c i d as C a t a l y s t The c h l o r o i n d o l e n i n e o f 1 8 B - c a r b o m e t h o x y - 4 8 - d i h y d r o c l e a v a m i n e ( 5 0 . 0 mg) was f o r m e d u n d e r s t a n d a r d c o n d i t i o n s . T h i s m a t e r i a l was d i s s o l v e d w i t h v i n d o l i n e (50 mg) i n d i o x a n e (10 m l ) and a f e w d r o p s ( f i v e d r o p s ) o f p e r c h l o r i c a c i d w e r e a d d e d . The r e s u l t i n g b l u i s h s o l u t i o n was s t i r r e d u n d e r n i t r o g e n a t room t e m p e r a t u r e f o r 48 h o u r s . A t t h e end o f t h i s p e r i o d , i t was p o u r e d i n t o a n a q u e o u s s o l u t i o n o f 10% s o d i u m b i c a r b o n a t e and e x t r a c t e d s e v e r a l t i m e s w i t h e t h y l a c e t a t e (4 x 30 m l ) . The c o m b i n e d o r g a n i c p h a s e was d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e , f i l t e r e d , a n d t h e s o l v e n t r e m o v e d u n d e r r e d u c e d p r e s s u r e t o y i e l d a b r o w n i s h - r e d f o a m . C o l u m n c h r o m a t o g r a p h y y i e l d e d d i m e r 94 (5 mg) w h i c h c o u l d be i d e n t i f i e d as s u c h by nmr s p e c t r o s c o p y . E x p e r i m e n t 21 D i m e r i z a t i o n i n M e t h a n o l C o n t a i n i n g HBr as C a t a l y s t The c h l o r o i n d o l e n i n e o f 1 8 6 - c a r b o m e t h o x y - 4 S - d i h y d r o c l e a v a m i n e ( 5 0 . 0 mg) was f o r m e d i n t h e s t a n d a r d w a y . To t h i s m a t e r i a l , v i n d o l i n e ( 5 0 . 0 mg) was a d d e d a n d t h e w h o l e was d i s s o l v e d i n m e t h a n o l (10 m l ) w h i c h h a d b e e n f r e s h l y d i s t i l l e d f r o m m a g n e s i u m t u r n i n g s i n t o t h e r e a c t i o n f l a s k . H y d r o g e n b r o m i d e was b u b b l e d i n t o t h i s r e a c t i o n m i x t u r e , a f t e r p a s s a g e t h r o u g h a d r y i n g t o w e r , f o r a s h o r t p e r i o d (15 s e c o n d s ) . A f t e r t h i s t h e r e a c t i o n v e s s e l was c o n n e c t e d t o a p o s i t i v e p r e s s u r e o f n i t r o g e n a n d s t i r r e d a t room t e m p e r a t u r e f o r 48 h o u r s . Workup and c h r o m a t o g r a p h y i n t h e u s u a l way a f f o r d e d d i m e r 94 as t h e o n l y d i m e r i c p r o d u c t (50 mg, 50% y i e l d ) . - 184 -E x p e r i m e n t 22 A n I n v e s t i g a t i o n o f t h e E f f e c t o f H y d r o g e n C h l o r i d e C o n c e n t r a t i o n  o n t h e D i m e r i z a t i o n R e a c t i o n The c h l o r o i n d o l e n i n e o f 1 8 8 - c a r b o m e t h o x y - 4 8 - d i h y d r o c l e a v a m i n e (200 mg) was made i n t h e s t a n d a r d way and was t h e n d i v i d e d i n t o 4 e q u a l p a r t s and t r e a t e d as f o l l o w s : A . 50 mg o f v i n d o l i n e w i t h 5 m l o f m e t h a n o l i c 1.5% HC1 B . 50 mg o f v i n d o l i n e w i t h 5 m l o f m e t h a n o l i c 1.6% HC1 C . 50 mg o f v i n d o l i n e w i t h 5 m l o f m e t h a n o l i c 2.0% HC1 D . 50 mg o f v i n d o l i n e w i t h 5 m l o f m e t h a n o l i c 5.0% HC1 T h e s e w e r e a l l s i m u l t a n e o u s l y l o w e r e d i n t o a p r e h e a t e d o i l b a t h a t 6 0 ° C . R e a c t i o n r a t e s a s e v i d e n c e d by c o l o u r c h a n g e s a n d t i c m o n i t o r i n g c o u l d be c l e a r l y c o m p a r e d a n d w e r e f o u n d t o r o u g h l y v a r y i n l i n e a r f a s h i o n w i t h a c i d c o n c e n t r a t i o n . The r e a c t i o n s w e r e a l l w o r k e d up i n 2 h o u r s a n d a f t e r c o l u m n c h r o m a t o g r a p h y t h e f o l l o w i n g r e s u l t s w e r e o b t a i n e d by nmr a n a l y s i s . A . 30 mg d i m e r 94 30% y i e l d B . 3 6 . 4 mg d i m e r 94 36% y i e l d C . 4 5 . 0 mg d i m e r 94 45% y i e l d D . 5 6 . 4 mg d i m e r 94 56% y i e l d . No nmr was t a k e n i n c a s e A s i n c e t h i s was t h e s t a n d a r d d i m e r i z a t i o n w h i c h has y i e l d e d c o n s i s t e n t l y o n l y d i m e r 9 4 . - 185 -E x p e r i m e n t 23 A n I n v e s t i g a t i o n i n t o t h e E f f e c t s o f HC1 C o n c e n t r a t i o n a t H i g h e r  C o n c e n t r a t i o n s o f A c i d The c h l o r o i n d o l e n i n e o f 1 8 B - c a r b o m e t h o x y - 4 3 - d i h y d r o c l e a v a m i n e (200 mg) was made i n t h e s t a n d a r d way and was t h e n d i v i d e d i n t o 4 e q u a l p a r t s a n d t r e a t e d as f o l l o w s : A . 50 mg o f v i n d o l i n e w i t h 5 m l o f m e t h a n o l i c 15% HC1 B. 50 mg o f v i n d o l i n e w i t h 5 m l o f m e t h a n o l i c 30% HC1 C . 50 mg o f v i n d o l i n e w i t h 5 m l o f m e t h a n o l i c 60% HC1 D . 50 mg o f v i n d o l i n e w i t h 5 m l o f a c e t y l c h l o r i d e . T h e s e w e r e a l l s i m u l t a n e o u s l y l o w e r e d i n t o a p r e h e a t e d o i l b a t h a t 6 7 ° C . A f t e r 3 . 0 h o u r s t h e s e w e r e a l l w o r k e d u p . C o l u m n c h r o m a t o g r a p h y o f e a c h r e a c t i o n m i x t u r e i n t h e u s u a l way a f f o r d e d t h e f o l l o w i n g r e s u l t s by nmr a n a l y s i s . A . 40 mg o f d i m e r i c m a t e r i a l (94) c o n t a i n i n g a t r a c e o f some o f t h e o t h e r m a t e r i a l . Y i e l d 40%. B. 2 6 . 8 mg o f d i m e r i c m a t e r i a l c o n t a i n i n g m o s t l y d i m e r 9 4 . Y i e l d 27%. C . 25 mg o f d i m e r i c m a t e r i a l c o n t a i n i n g m o s t l y d i m e r 9 4 . Y i e l d 25%. D . 97 mg o f d i m e r 9 4 . Y i e l d 97%. E x p e r i m e n t 24 D i m e r i z a t i o n u n d e r " C l e a v a g e " C o n d i t i o n s The c h l o r o i n d o l e n i n e o f 1 8 3 - c a r b o m e t h o x y - 4 6 - d i h y d r o c l e a v a m i n e (50 mg) was p r e p a r e d i n t h e u s u a l way and t h e n s o l i d v i n d o l i n e (50 mg) was a d d e d t o i t . T h i s m i x t u r e was d i s s o l v e d i n 10 m l o f f r e s h l y p r e p a r e d 7% m e t h a n o l i c h y d r o g e n c h l o r i d e u n d e r a p o s i t i v e p r e s s u r e o f - 186 -d r y n i t r o g e n . The r e s u l t i n g r e d d i s h - p u r p l e s o l u t i o n was r e f l u x e d f o r 3 . 5 h o u r s . A f t e r t h i s p e r i o d i t was c o o l e d t o room t e m p e r a t u r e a n d w o r k e d up i n t h e u s u a l w a y . Column c h r o m a t o g r a p h y y i e l d e d t h e d i m e r 94 (47 mg) u p o n e l u t i o n w i t h b e n z e n e c o n t a i n i n g 20% e t h y l a c e t a t e . G r a d u a l i n c r e a s e s i n t h e p o l a r i t y o f t h e s o l v e n t t o p u r e e t h y l a c e t a t e a f f o r d e d a m i x t u r e o f d i m e r 94 a n d a n o t h e r d i m e r ('v 10 mg) . T h i s m i x t u r e was r e s o l v e d by h i g h p r e s s u r e l i q u i d c h r o m a t o g r a p h y o n d e a c t i v a t e d a l u m i n a w i t h e t h y l a c e t a t e c o n t a i n i n g 2.5% m e t h a n o l a s s o l v e n t . New compound p u r e : A E t ^ ' max nm: 3 0 5 , 2 9 5 , 2 8 5 , 2 6 4 , 2 2 6 ( s h ) , 215 ( l o g e 3 . 8 , 3 . 9 , 3 . 8 , 3 . 9 , 4 . 5 , 4 . 5 , r e s p e c t i v e l y ) ; v 3 cm : 3 6 8 0 , 3 6 2 0 , 3 4 5 0 , 2 9 4 0 , 1 7 3 0 , 1 6 2 0 , in 3.x 1 4 7 0 , 1380 ; mass s p e c t r u m : p e a k s a t m/e = 8 2 2 , 8 0 8 , 7 9 4 ( M + ) . 1 5 - B r o m o v i n d o l i n e (114) -3 To a s o l u t i o n o f v i n d o l i n e ( 1 . 0 2 4 9 g , 2 . 1 8 x 10 m o l e s ) i n d i c h l o r o m e t h a n e (10 m l ) c o n t a i n e d i n a 100 m l r o u n d - b o t t o m e d f l a s k was a d d e d 1 . 0 m o l e e q u i v a l e n t s ( 3 9 0 . 6 2 mg) o f N - b r o m o s u c c i n i m i d e d i s s o l v e d i n d i c h l o r o m e t h a n e (15 m l ) a t room t e m p e r a t u r e o v e r a p e r i o d o f 15 m i n u t e s . The r e a c t i o n m i x t u r e was s t i r r e d f o r a f u r t h e r 15 m i n u t e s . A f t e r t h i s p e r i o d i t was p o u r e d i n t o i c e - c o l d w a t e r a n d t h e l o w e r o r g a n i c p h a s e was s e p a r a t e d and w a s h e d w i t h 10% s o d i u m b i c a r b o n a t e (3 x 50 m l ) , b r i n e (1 x 50 m l ) and f i n a l l y , w a t e r . The c o m b i n e d o r g a n i c p h a s e was d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e , f i l t e r e d and s o l v e n t removed u n d e r r e d u c e d p r e s s u r e t o a f f o r d a w h i t e powder c o n s i s t i n g s o l e l y o f t h e d e s i r e d p r o d u c t ( 1 . 2 3 5 0 g o r 97% y i e l d ) . T h i s m a t e r i a l was one s p o t o n a l u m i n a t i c d e v e l o p e d i n c h l o r o f o r m , c h l o r o f o r m - b e n z e n e - 187 -( 1 : 1 ) o r b e n z e n e . I t c o u l d be r e c r y s t a l l i z e d f r o m e t h a n o l , mp 2 6 7 - 2 6 9 ° C . X E t ° H nm: 3 1 2 , 2 5 5 , 212 ( l o g e 3 . 7 , 3 . 9 , 4 . 5 r e s p e c t i v e l y ) ; v C H C 1 3 c m " 1 : nicix TOcix 2 9 9 5 , 2 9 5 0 , 2 8 7 0 , 1 7 3 5 , 1 6 0 0 , 1 4 9 0 , 1 4 2 9 , 1 3 7 0 , 1 0 4 0 ; Nmr : T 0 . 5 - 0 . 9 ( b r o a d d i f f u s e s i n g l e t , I H , C^OR), 2 . 8 6 ( s i n g l e t , I H , C ^ - H ) , 3 . 8 7 ( s i n g l e t , I H , C ^ - H ) , 4 . 1 0 ( d o u b l e t o f d o u b l e t s o f d o u b l e t s , J = 1 1 , 6 , 2 c p s , I H , C 7 ~ J I ) , 4 . 5 4 ( s i n g l e t , C ^ - H ) , 4 . 7 4 ( b r o a d d o u b l e t , J ^ 11 c p s , I H , C , - H ) , 6 . 1 1 ( s i n g l e t , 3 H , C . , - 0 M e ) , 6 . 2 0 ( s i n g l e t , 4 H , C - C 0 „ C H o , o — l b — 3 z —3 a n d C 2 - H ) , 6 . 4 8 ( m u l t i p l e t , 2 H , C g - C H ^ ) , 7 . 3 0 ( s i n g l e t , 3 H , N - j - C H ^ , 7 . 9 3 ( s i n g l e t , 3 H , C ^ O A c ) , 9 . 4 7 ( t r i p l e t , J c p s , 3 H , C 5 - C H 2 C H _ 3 ) ; mass s p e c t r u m : m a i n p e a k s a t m/e = 5 3 7 , 5 3 5 , 4 7 8 , 4 7 6 , 3 7 7 , 3 7 6 , 3 7 5 , 3 7 4 , 2 8 2 , 2 6 9 , 2 6 8 , 2 6 7 , 2 6 6 , 2 5 5 , 2 5 4 , 2 5 3 , 2 5 2 , 2 4 1 , 2 4 0 , 2 3 9 , 2 2 2 , 1 8 8 , 1 8 7 , 1 7 2 , 1 3 6 , 1 3 5 , 1 2 2 , 1 2 1 , 1 0 7 . A n a l . F o u n d : C , 5 6 . 0 5 % ; H , 5 .92%; N , 5 .26%; B r , 1 4 . 7 1 % ; C a l c d . f o r C 2 5 H 3 1 N 2 0 6 B r : C , 56 .10%; H , 5 .80%; N , 5 .25%; B r , 1 4 . 7 1 % . A n i o n o f V i n d o l i n e b y H a l o g e n - M e t a l I n t e r c h a n g e B r o m o v i n d o l i n e (50 mg) was d i s s o l v e d i n f r e s h l y d i s t i l l e d a n h y d r o u s t e t r a h y d r o f u r a n (20 m l ) and c o o l e d t o - 7 8 ° C b y i m m e r s i o n i n t o a d r y i c e - a c e t o n e b a t h . E x a c t l y 2 . 0 m o l e e q u i v a l e n t s o f a 2 . 0 2 M s o l u t i o n o f n - b u t y l l i t h i u m i n h e x a n e was a d d e d s l o w l y (20 m i n u t e s ) w i t h s t i r r i n g u n d e r a n i n e r t a t m o s p h e r e o f a n h y d r o u s n i t r o g e n . The s o l u t i o n became c l e a r and t u r n e d t o a l i g h t y e l l o w c o l o u r . A f t e r t h e a d d i t i o n was c o m p l e t e , t h e r e a c t i o n m i x t u r e was s l o w l y warmed t o room t e m p e r a t u r e a f t e r 0 . 5 h o u r s ; and q u e n c h e d b y t h e i n j e c t i o n o f w a t e r i n t o t h e s y s t e m . Nmr s p e c t r o s c o p y t o g e t h e r w i t h t i c c o m p a r i s o n s ( a l u m i n a , b e n z e n e as d e v e l o p e r ) w i t h a u t h e n t i c m a t e r i a l showed t h a t t h e c r u d e - 188 -product contained less than 5 to 10% of unreacted bromovindoline and consisted almost entirely of vindoline and deacetyl vindoline together with a small amount of unidentifiable baseline material. Dimer 94 from the Reaction of the Anion of Vindoline on the Appropriate  Chloroindolenine The chloroindolenine of 188-carbomethoxy-4B-dihydrocleavamine (250 mg) was dissolved in anhydrous, d i s t i l l e d , tetrahydrofuran and added slowly (45 minutes) to the anion of vindoline (400 mg in 40 ml of tetra-hydrofuran) prepared as above, at -78°C. After 4 hours, the reaction was allowed to come to room temperature and then poured into saturated aqueous ammonium chloride. The organic phase was collected and the reddish aqueous phase was washed (2 x 25 ml) with ethyl acetate. The combined organic extract was dried (anhydrous sodium sulfate), f i l t e r e d and taken to dryness in vacuo to yield a light brown foam (712.2 mg). This material was submitted to two sequential counter current distributions over 72 tubes at a pH gradient of 2.3 to 3.95 and 3.5 to 3.75 respectively ( c i t r i c acid/ammonium hydroxide buffer as the stationary lower phase and benzene as the moving upper phase). The earliest tubes (1-16) afforded dimer 94 (22.1 mg) and deacetyl dimer 94 (8.5 mg) as the only dimeric products. The identity of the former was deduced on the basis of nmr and i r being superimposable with those of authentic material. Catharanthine N-Oxide Catharanthine (250 mg) as the free base, was dissolved in dichloro-methane (35 ml). To this clear colorless solution was added, at room - 189 -t e m p e r a t u r e , 1 . 1 m o l e e q u i v a l e n t s o f m - c h l o r o p e r b e n z o i c a c i d (150 mg) i n s o l i d f o r m . A f t e r s t i r r i n g f o r 1 h o u r a t room t e m p e r a t u r e , t h e r e a c t i o n was w o r k e d u p . The c l e a r c o l o r l e s s s o l u t i o n was s h a k e n w i t h a n i c e c o l d a q u e o u s 10% s o d i u m b i c a r b o n a t e s o l u t i o n (25 m l ) . The o r g a n i c p h a s e was s e p a r a t e d , d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e , f i l t e r e d a n d t a k e n t o d r y n e s s u n d e r vacuum t o y i e l d a w h i t e g l a s s (262 m g ) . T h i s m a t e r i a l was q u i c k l y c h r o m a t o g r a p h e d o n d e a c t i v a t e d a l u m i n a ( n e u t r a l Woelm I I I , 20 g) by e l u t i o n w i t h d i c h l o r o m e t h a n e (300 m l , 2 f r a c t i o n s ) and m e t h a n o l (300 m l , 1 f r a c t i o n ) . The f i r s t two f r a c t i o n s c o n t a i n e d a r e a r r a n g e m e n t p r o d u c t o f c a t h a r a n t h i n e N - o x i d e (35 m g ) . A E t ° H nm: 2 9 3 , 2 8 5 , 2 7 6 ( s h ) , 2 2 6 , ( l o g E 3 . 8 , 3 . 9 , 3 . 8 , 4 . 5 max PHn —1 r e s p e c t i v e l y ) ; v 3 cm : 3 4 5 0 , 2 9 5 0 , 2 9 2 0 , 1 7 2 5 , 1 4 6 5 , 1 4 3 5 , max 1 3 4 0 , 1 2 6 5 , 1 1 6 0 , 1 1 2 0 , 1 0 5 5 , 1 0 3 0 , 1 0 1 5 , 9 1 5 , 9 0 5 ( s h ) , 8 9 0 ; N m r : T 1 . 2 0 ( b r o a d s i n g l e t , I H ) , 2 . 3 0 - 3 . 0 0 ( m u l t i p l e t , 4 H , a r o m a t i c ) , 3 . 7 5 ( s i n g l e t , I H ) , 5 . 4 2 ( b r o a d d o u b l e t , J ^ 9 c p s , I H ) , 6 . 2 1 ( s i n g l e t , 3 H , C 0 2 C H 3 ) , 8 . 8 0 ( t r i p l e t , J ^ 7 c p s , 3 H , C H ^ C H ^ ) ; mass s p e c t r u m : m a i n p e a k s a t m/e = 352 ( M + ) , 2 5 4 , 2 4 8 , 2 2 2 , 2 0 4 , 1 3 5 , 1 2 1 , 1 1 9 . The m a j o r compound i s o l a t e d w a s , h o w e v e r , t h e d e s i r e d c a t h a r a n t h i n e N - o x i d e ; A E t 0 H nm: 2 9 1 , 2 8 3 , 2 7 5 ( s h ) , 224 ( l o g e 3 . 8 , 3 . 9 , 3 . 8 , 4 . 5 1113. X CHCl —1 r e s p e c t i v e l y ) ; v 3 cm : 3 4 6 0 , 2 9 6 0 , 1 7 3 0 , 1 7 4 0 , 1 4 6 5 , 1 4 4 0 , 1 3 0 5 , 1 2 7 0 , 1 1 8 5 , 1 1 0 0 , 9 2 5 ; Nmr: T 1 . 3 9 ( b r o a d s i n g l e t , I H , N - H ) , 2 . 2 8 -3 . 0 0 ( m u l t i p l e t , 4 H , a r o m a t i c ) , .3 .84 ( b r o a d d o u b l e t , J % 6 c p s , I H , C ^ -o l e f i n i c ) , 5 . 2 4 ( b r o a d s i n g l e t , I H , C _ - H ) , 6 . 2 6 ( s i n g l e t , 3 H , C 1 Q - C 0 o C H _ ) , -> l o L j 8 . 8 3 ( t r i p l e t , J 'v 7 c p s , - C H ^ C H ^ ) ; mass s p e c t r u m : m a i n p e a k s a t m/e = 336 ( M + - 1 6 ) , 3 3 4 , 1 3 5 , 1 2 2 , 1 2 1 , 1 0 7 . The s t r u c t u r e o f t h e l a t t e r compound was p r o v e d by s u b m i t t i n g i t i m m e d i a t e l y t o h y d r o g e n a t i o n - 190 -in ethanol over Adam's catalyst. The sole product was identified by i r and mass spectroscopy as dihydrocatharanthine. The N-oxide underwent rearrangement even when dried to a white powder and stored in an evacuated dessicator, for 48 hours, to yield a 1:1 mixture of the starting N-oxide and the rearrangement product mentioned above. The latter compound once formed was stable to chromatography. Reaction of Catharanthine Hydrochloride with m-Ghloroperbenzoic Acid Catharanthine hydrochloride (62.2 mg) was dissolved in dichloro-methane (7 ml). m-Chloroperbenzoic acid (34.4 mg, 1.1 mole equivalent) was added in solution in dichloromethane (5 ml) over 15 minutes with s t i r r i n g and then washed in with a further portion of solvent (2 ml) and the reaction mixture was allowed to s t i r at room temperature for 32 hours. After this time the clear colourless solution was washed with an aqueous 10% solution of sodium bicarbonate (2 x 10 ml) and the organic phase was dried over anhydrous sodium sulfate, f i l t e r e d and evaporated to yield the crude reaction mixture as a white foam (64.4 mg). This material was purified by preparative t i c on alumina (2 plates 20 cm x 20 cm, 0.3 cm thickness) using chloroform, methanol (20:1) as the developer. The major compound was catharanthine (36.9 mg) identical by nmr, i r , uv, and mass spectroscopy to authentic material. Minor products included catharanthine N-oxide (9.9 mg) and baseline material (4.6 mg). The total weight recovery was 83.5%. - 191 -" B i o m e m e t i c " D i m e r i z a t i o n R e a c t i o n C a t h a r a n t h i n e h y d r o c h l o r i d e (710 mg) was d i s s o l v e d i n d i c h l o r o -methane (30 m l ) a n d c o o l e d t o 0 ° C . A s o l u t i o n o f e x c e s s m - c h l o r o -p e r b e n z o i c a c i d ( 2 . 2 g) i n d i c h l o r o m e t h a n e (30 m l ) was a d d e d d r o p w i s e o v e r 40 m i n u t e s . The r e a c t i o n m i x t u r e was warmed t o room t e m p e r a t u r e and s t i r r e d f o r 3 9 . 5 h o u r s . A f t e r t h i s p e r i o d , s o l i d s o d i u m s u l f i t e was a d d e d and t h e r e s u l t i n g s u s p e n s i o n was s t i r r e d f o r a f u r t h e r 10 m i n u t e s , a f t e r w h i c h i t was p a r t i t i o n e d b e t w e e n i c e - c o l d w a t e r a n d d i c h l o r o m e t h a n e . The o r g a n i c p h a s e was w a s h e d w i t h 10% a q u e o u s s o d i u m b i c a r b o n a t e (2 x 25 m l ) a n d t h e n c o l l e c t e d , d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e , f i l t e r e d and t h e s o l v e n t removed u n d e r r e d u c e d p r e s s u r e t o y i e l d a w h i t i s h - y e l l o w foam (702 m g ) . T h i s m a t e r i a l was c h r o m a t o g r a p h e d o n a l u m i n a ( n e u t r a l Woelm I I I , 100 g ) . B e n z e n e e l u t i o n f u r n i s h e d a compound (31 mg) i n f r a c t i o n s 4 , 5 , and 6 w h i c h was d i f f e r e n t f r o m t h e s t a r t i n g m a t e r i a l o r i t s N - o x i d e . Nmr ( T - 6 0 ) : T 2 . 2 - 3 . 0 ( m u l t i p l e t , 4 H , a r o m a t i c ) , 4 . 0 ( b r o a d u n r e s o l v e d d o u b l e t , . I H , o l e f i n i c ) , 5 . 2 2 ( b r o a d s i n g l e t , I H , C 5 ~ H ) , 6 . 3 8 ( s i n g l e t , 3 H , C O ^ H ^ ) , 8 . 9 7 ( t r i p l e t , J ^ 8 c p s , 3 H , C H 2 C H 3 ) . T h i s m a t e r i a l was d i s s o l v e d i n m e t h a n o l (5 m l ) c o n t a i n i n g v i n d o l i n e (35 mg) a n d 1 M h y d r o c h l o r i c a c i d (7 m l ) was a d d e d . The r e a c t i o n f l a s k was s e a l e d u n d e r a n i t r o g e n a t m o s p h e r e a n d s t i r r e d a t room t e m p e r a t u r e f o r 10 d a y s . D u r i n g t h i s t i m e i t c h a n g e d f r o m a l i g h t y e l l o w c o l o u r t o a d e e p , a l m o s t o p a q u e , e m e r a l d g r e e n . A f t e r t h i s t i m e t h e r e a c t i o n m i x t u r e was p o u r e d i n t o a b e a k e r c o n t a i n i n g w a t e r (10 m l ) and d i c h l o r o -methane (30 m l ) w i t h s t i r r i n g . A l l o f t h e m a t e r i a l r e m a i n e d i n t h e a q u e o u s p h a s e . The a d d i t i o n o f s m a l l amounts o f s o d i u m b o r o h y d r i d e - 192 -(0.5 g i n s m a l l p o r t i o n s over 20 minutes) w i t h r a p i d blending of the two phases r e s u l t e d i n the sudden l o s s of c o l o u r and concomitant e x t r a c t i o n i n t o the organic phase. The organic phase was separated and the aqueous phase washed w i t h f u r t h e r p o r t i o n s (2 x 25 ml) of dichloromethane. The combined organic phase was d r i e d over anhydrous sodium s u l f a t e , f i l t e r e d , and the s o l v e n t removed under reduced pressure to y i e l d a y e l l o w i s h g l a s s - l i k e m a t e r i a l (60 mg) which f l u o r e s c e d e i t h e r i n s o l u t i o n (methanol) or as a s o l i d when exposed to uv l i g h t . Column chromatography on alumina ( n e u t r a l Woelm I I I , 20 g) y i e l d e d , upon e l u t i o n w i t h benzene, e t h y l acetate (4:1) a dimeric m a t e r i a l i n f r a c t i o n 7 to 10 which proved to be the f l u o r e s c e n t p r i n c i p l e i n the r e a c t i o n mixture (20 mg, ^ 30% y i e l d ) . x E t 0 H nm: 296, 285, 265, 215 ( l o g e 3.8, 3.9, 4.0, 4.5 max r e s p e c t i v e l y ) ; Nmr: T 2.0 (broad s i n g l e t , IH), 2.30-3.00 ( m u l t i p l e t , 5H, aromatic + C^-H), 3.94 ( s i n g l e t , IH, C^-H), 4.00 (broad doublet, J -W cps, IH), 4.18 (doublet of d o u b l e t s , JvL0,4 cps, IH, C ?-H), 4.52 ( s i n g l e t , IH, C 4~H), 4.78 (doublet, J ^ 10 cps, IH, Cg-H), 5.24 (broad s i n g l e t , IH), 5.72 ( m u l t i p l e t , IH), 6.20 ( s i n g l e t , 3H, -C02CH_3) , 6.24 ( s i n g l e t , 3H, -C0 2CH_ 3), 6.42 ( s i n g l e t , 3H, C 1 6-0CH_ 3), 7.35 ( s i n g l e t , 3H, N-CH_3), 7.95 ( s i n g l e t , 3H, C^-OAc), 8.79 ( t r i p l e t , J 'W cps, 3H, -CH 2CH 3), 9.29 ( t r i p l e t , J ^ 7 cps, 3H, -CH 2QH 3); mass spectrum: main peaks at m/e = 792, 791, 683, 624, 617, 521, 523, 469, 457, 415, 309, 296, 282, 266, 222, 188, 174, 158, 136, 135, 122, 121. Anal. High r e s o l u t i o n mass spectrometry: Found, 792.4118; Required f o r C^H^O^, , 792.4098. - 193 -BIBLIOGRAPHY 1 . A . A . G o r m a n , M . H e s s e , H . S c h m i d , P . G . Waser and W . H . H o p f f , " B i s i n d o l e A l k a l o i d s " , i n The A l k a l o i d s , V o l . I , S p e c i a l i s t P e r i o d i c a l R e p o r t s , o f The C h e m i c a l S o c i e t y , 1 9 7 1 . 2 . D . H . K . L e e a n d W . R . M . D r e w , M e d . J . A u s t r a l i a , 1, 699 ( 1 9 2 9 ) . 3 . R . A . P a r i s and H . M o y s e - M i g n o n , Compt . R e n d . , 2 3 6 , 1993 ( 1 9 5 3 ) . 4 . A . Q u e v a u v i l l e r , J . L e Men and M . M . J a n o t , A n n . P h a r m . F r a n c , 1 2 , 799 ( 1 9 5 4 ) . 5 . C . T . B e e r , B r i t i s h E m p i r e C a n c e r C a m p a i g n , 3 3 r d . A n n u a l R e p o r t , 487 ( 1 9 5 5 ) . 6 . G . H . S v o b o d a , J . Am. P h a r m . A s s o c . , 4_7, 834 ( 1 9 5 8 ) . 7 . M . G o r m a n , N . N e u s s and G . H . S v o b o d a , J . A m e r . Chem. S o c , 81_, 4745 ( 1 9 5 9 ) . 8 . N . N e u s s a n d M . Gorman, T e t r a h e d r o n L e t t e r s , 206 ( 1 9 6 1 ) . 9 . M . G o r m a n , N . N e u s s and K . B i e m a n n , J . A m e r . Chem. S o c , 8 4 , 1058 ( 1 9 6 2 ) . 1 0 . N . N e u s s , M . G o r m a n , H . E . B o a z a n d N . J . C o n e , J . A m e r . Chem. S o c , 8 4 , 1509 ( 1 9 6 2 ) . 1 1 . J . W . M o n c r i e f and W i l l i a m N . L i p s c o m b , A c t a C r y s t . , 2 1 , 322 ( 1 9 6 6 ) . 1 2 . J . W . M o n c r i e f and W . N . L i p s c o m b , J . A m e r . Chem. S o c , 8 7 , 4963 ( 1 9 6 5 ) . 1 3 . N . N e u s s , M . G o r m a n , W. H a r g r o v e , N . J . C o n e , K . B i e m a n n , G . B u c h i , and R . M a n n i n g , J . A m e r . Chem. S o c , 86_, 1440 ( 1 9 6 4 ) . 1 4 . J . P . K u t n e y , J . T r o t t e r , T . T a b a t a , A . K e r i g a n and N . Camerman, Chem. a n d I n d . , 648 ( 1 9 6 3 ) . 1 5 . N . Camerman and J . T r o t t e r , A c t a C r y s t . , 1_7, 384 ( 1 9 6 4 ) . - 194 -1 6 . J . H . C u t t s , C . T . B e e r a n d R . L . N o b l e , R e v . C a n a d . B i o l . , 1 6 , 476 ( 1 9 5 7 ) . 1 7 . R . L . N o b l e , C . T . B e e r a n d J . H . C u t t s , A n n . N . Y . A c a d . . S c i . , 76.» 882 (1958) and B i o c h e m . P h a r m a c o l . , 1, 347 ( 1 9 5 8 ) . 1 8 . J . H . C u t t s , C . T . B e e r a n d R . L . N o b l e , C a n c e r R e s . , 2 0 , 1023 ( 1 9 6 0 ) . 1 9 . N . N e u s s , M . G o r m a n , G . H . S v o b o d a , G . M a c i a k and C . T . B e e r , J . A m e r . Chem. S o c , 8 1 , 4754 ( 1 9 5 9 ) . 2 0 . G . H . S v o b o d a , M . G o r m a n , N . N e u s s and A . J . B a r n e s , J r . , J . P h a r m , S c i . , 5 0 , 409 ( 1 9 6 1 ) . 2 1 . G . H . S v o b o d a , L l o y d i a , 2 4 , 173 ( 1 9 6 1 ) . 2 2 . G . H . S v o b o d a , M . G o r m a n , A . J . B a r n e s , J r . , a n d A . T . O l i v e r , J . P h a r m . S c i . , 5 1 , 518 ( 1 9 6 2 ) . 2 3 . G . H . S v o b o d a , I . S . J o h n s o n , M . Gorman a n d N . N e u s s , J . P h a r m . S c i . , 5 1 , 707 ( 1 9 6 2 ) . 2 4 . G . H . S v o b o d a , L l o y d i a , 2 5 , 334 ( 1 9 6 2 ) . 2 5 . G . H . S v o b o d a , A . T . O l i v e r a n d D . R . B e d w e l l , L l o y d i a , 26^, 141 ( 1 9 6 3 ) . 2 6 . K . J o v a n o v i c s , G . M a r k , L . Horompo a n d K . S z a s z , A c t a P h a r m . H u n g . , 3 4 , 36 ( 1 9 6 4 ) . 2 7 . G . H . S v o b o d a a n d A . J . B a r n e s , J r . , J . P h a r m . S c i . , 5 3 , 1227 ( 1 9 6 4 ) . 2 8 . G . H . S v o b o d a , L l o y d i a , 2]_, 299 ( 1 9 6 4 ) . 2 9 . N . R . F a r n s w o r t h a n d I . M . H i l i n s k i , J . C h r o m a t o g . , 1 8 , 184 ( 1 9 6 5 ) . 3 0 . H . P . G r e g o r , G . K . H o e s c h e l e , J . P o t e n z a , A . G . T s u k , R . F e i n l a n d , M . S h i d a and P h . T e y s s i e , J . A m e r . Chem. S o c , 8 7 , 5525 ( 1 9 6 5 ) . 3 1 . A . G . T s u k and H . P . G r e g o r , J . A m e r . Chem. S o c , 87_, 5534 ( 1 9 6 5 ) . 3 2 . A . G . T s u k and H . P . G r e g o r , J . A m e r . Chem. S o c , 87^, 5538 ( 1 9 6 5 ) . 3 3 . J . W a l d e n a n d H . P . G r e g o r , P r i n c i p l e s A p p l . : W a t e r C h e m . , P r o c . R u d o l f s R e s . C o n f . , 4 t h , R u t g e r s , S t a t e U n i v . , 491 ( 1 9 6 5 ) , ( P u b l i s h e d 1967! - 195 -3 4 . H . P . G r e g o r , P r e p a r a t i o n o f an o l e o p h i l i c i o n - e x c h a n g e r e s i n : a p p l i c a t i o n i n b i o l o g i c a l s e p a r a t i o n s , I o n E x c h . P r o c e s s I n d . , P a p . C o n f . (1969) ( p u b l i s h e d 1 9 7 0 ) . 3 5 . I . M . J a k o v l j e v i c , J . P h a r m . S c i . , 5 1 , 187 ( 1 9 6 2 ) . 3 6 . N . J . C o n e , R . M i l l e r a n d N . N e u s s , J . P h a r m . S c i . , 5_2, 688 ( 1 9 6 3 ) . 3 7 . D . G r o e g e r a n d K . S t o l l e , A r c h . P h a r m . , 2 9 8 , 246 ( 1 9 6 5 ) . 3 8 . L . N . P r i s t a , M . A . F e r r e i r a and A . S . R o q u e , G a r c i a O r t a , 12_, 277 ( 1 9 6 4 ) , 3 9 . A . N . M o s o u d , N . R . F a r n s w o r t h , L . A . S c i u c h e t t i , R . N . B l o m s t e r a n d W.A. M e e r , L l o y d i a , 3 1 , 202 ( 1 9 6 8 ) . 4 0 . A . C . S a r t o r e l l i and W.A. C r e a s y , A . R e v . P h a r m a c , 9_, 51 ( 1 9 6 9 ) . 4 1 . " S y m p o s i u m o n v i n c r i s t i n e " , C a n c e r C h e m o t h e r . R e p . , 5_2, 453 ( 1 9 6 8 ) . 4 2 . R . E . McMahon, E x p e r i e n t i a , 1 9 ( 8 ) , 434 ( 1 9 6 3 ) . 4 3 . R . J . O w e l l e n a n d D.W. D o n i g i a n , J . M e d . C h e m . , 1 5 , 894 ( 1 9 7 2 ) . 4 4 . H . F . H e b d e n , J . R . H a d f i e l d and C . T . B e e r , C a n c e r R e s . , 3 0 , 1417 (1970) 4 5 . H . F . G r e e n i u s , R.W. M c l n t y r e and C . T . B e e r , J . M e d . C h e m . , 1 1 , 254 ( 1 9 6 8 ) . 4 6 . G . E . C a l f , J . L . G a r n e t t and W .A. S o l l i c h - B a u m g a r t n e r , A d v a n . T r a c e r M e t h o d o l . , h, 11 ( 1 9 6 8 ) . 4 7 . G . E . C a l f and J . L . G a r n e t t , Chem. Comm., 373 ( 1 9 6 9 ) . 4 8 . W.W. H a r g r o v e , L l o y d i a , 2 7 , 340 ( 1 9 6 4 ) . 4 9 . D e a c e t y l a t e d p o l y n u c l e a r i n d o l e s . E l i L i l l y & C o . , (By W.W. H a r g r o v e ) . B e l g . 6 6 0 , 8 4 3 , S e p t . 9 , 1 9 6 5 , U . S . A p p l . M a r c h 9 , 1 9 6 4 . 5 0 . P o l y n u c l e a r d e a c e t y l i n d o l e s . E l i L i l l y & C o . , B e l g . 6 5 9 , 1 1 2 , A u g . 2 , 1 9 6 5 , A p p l . F e b . 1 , 1 9 6 5 . - 196 -5 1 . I n d o l e a l k a l o i d s . E l i L i l l y & C o . N e t h . A p p l . 6 , 5 0 1 , 1 2 1 ( C I . C 0 7 d ) , J u l y 2 9 , 1 9 6 6 , A p p l . J a n . 2 8 , 1 9 6 5 . 5 2 . V i n c a l e u k o b l a s t i n e p o l y n u c l e a r i n d o l e d e r i v a t i v e s . E l i L i l l y & C o . (by W.W. H a r g r o v e ) . B r i t . 1 , 0 3 7 , 3 7 9 ( C I . C 0 7 d ) , J u l y 2 7 , 1 9 6 6 , A p p l . J a n . 1 1 , 1 9 6 5 . 5 3 . N o v e l a m i n o a c y l e s t e r s o f d e a c e t y l v i n c a l e u k o b l a s t i n e . W.W. H a r g r o v e . ( E l i L i l l y & C o . ) . U . S . 3 , 3 8 7 , 0 0 1 ( C I . 2 6 0 - 2 8 7 ) , 4 J u n . 1 9 6 8 , A p p l . 19 O c t . 1 9 6 4 . 5 4 . G . H . S v o b o d a , " P r o c e e d i n g s o f t h e F i r s t Symposium o f t h e E u r o p e a n C a n c e r C h e m o t h e r a p y G r o u p " , E x c e r p t a M e d i c a F o u n d a t i o n , New Y o r k , 1 9 6 6 , p . 9 -27 a n d r e f e r e n c e s t h e r e i n . 5 5 . E . W e n k e r t , J . A m e r . Chem. S o c , 84_, 98 ( 1 9 6 2 ) . 5 6 . M . G o r m a n , N . N e u s s a n d N . J . C o n e , J . A m e r . Chem. S o c , 8 7 , 93 ( 1 9 6 5 ) , 5 7 . J . P . K u t n e y a n d E . P i e r s , J . A m e r . Chem. S o c , 8 6 , 953 ( 1 9 6 4 ) . 5 8 . J . P . K u t n e y , R . T . B r o w n and E . P i e r s , J . A m e r . Chem. S o c , 8 6 , 2286 ( 1 9 6 4 ) . 5 9 . A . Camerman, N . Camerman, J . P . K u t n e y , E . P i e r s and J . T r o t t e r , T e t r a h e d r o n L e t t e r s , 637 ( 1 9 6 5 ) . 6 0 . J . P . K u t n e y , N . A b d u r a h m a n , P . Le Q u e s n e , E . P i e r s and I . V l a t t a s , J . A m e r . Chem. S o c , 8 8 , 3656 ( 1 9 6 6 ) . 6 1 . J . P . K u t n e y , W . J . C r e t n e y , P . Le Q u e s n e , B . McKague and E . P i e r s , J . A m e r . Chem. S o c , 8 8 , 4756 ( 1 9 6 6 ) . 6 2 . J . P . K u t n e y , K . K . C h a n , A . F a i l l i , J . M . F r o m s o n , C . G l e t s o s and V . R . N e l s o n , J . A m e r . Chem. S o c , 9 0 , 3891 ( 1 9 6 8 ) . 6 3 . G . B u c h i and R . E . M a n n i n g , J . A m e r . Chem. S o c , 88_, 2532 ( 1 9 6 6 ) . 6 4 . J . P . K u t n e y and F . B y l s m a , J . A m e r . Chem. S o c , 9 2 , 6090 ( 1 9 7 0 ) . - 197 -65. M. Gorman, N. Neuss and N.J. Cone, J. Amer. Chem. Soc, 8_7, 93 (1965). 66. J.P. Kutney, R.T. Brown, E. Piers and J.R. Hadfield, J. Amer. Chem. Soc, 92, 1708 (1970). 67. G. Buchi, P. Kulsa and R.L. Rosati, J. Amer. Chem. Soc, 90, 2448 (1968). 68. G. Buchi, P. Kulsa, K. Ogasawara and R.L. Rosati, J. Amer. Chem. Soc, 92, 999 (1970). 69. J.P. Kutney, W.J. Cretney, J.R. Hadfield, E.S. Hall and V.R. Nelson, J. Amer. Chem. Soc, 92, 1704 (1970). 70. J.P. Kutney, J. Beck, F. Bylsma and W.J. Cretney, J. Amer. Chem. Soc, 90, 4504 (1968). 71. N. Neuss, M. Gorman, N.J. Cone and L.L. Huckstep, Tetrahedron Letters, 783 (1968). 72. H.O. House, Modern Synthetic Reactions, Benjamin, Menlo Park, California, 2nd Edition, 1972, p. 438. 73. J.P. Kutney, R.T. Brown and E. Piers, Can. J. Chem., 43, 1545 (1965). 74. P.S. Ellington, D.G. Hey and G.D. Meakins, J. Chem. Soc. (C), 1327 (1966). 75. J. Chatt, Chem. Rev., 48, 7 (1951). 76. D.G. Hey, G.D. Meakins and M.W. Pemberton, J. Chem. Soc. (C), 1331 (1966). 77. L. Merlini, G. Nasini and J.D. Phillipson, Tetrahedron, 28, 5971 (1972). 78. A. Patchornik, W.B. Lawson and B. Witkop, J. Amer. Chem. Soc, 80, 4747 (1958). 79. W.I. Taylor, Proc. Chem. Soc, 247 (1962). 80. J.C. Powers, J. Org. Chem., 31, 2627 (1966). 81. W.O. Godtfredson and S. Vangedal, Acta Chim Scand., 10, 1414 (1956). - 1 9 8 -8 2 . P . G . G a s s m a n , G . A . C a m p b e l l and G . M e h t a , T e t r a h e d r o n , 28_, 2749 ( 1 9 7 2 ) . 8 3 . S . A . M o n t i and R . R . S c h m i d t , T e t r a h e d r o n , 27_, 3331 ( 1 9 7 1 ) . 8 4 . F . B y l s m a , P h . D . T h e s i s , U n i v e r s i t y o f B r i t i s h C o l u m b i a ( 1 9 7 0 ) . 8 5 . H . C . B r o w n , H y d r o b o r a t i o n , B e n j a m i n , New Y o r k , N . Y . , 1 9 6 2 . 8 6 . J . M o k r y a n d I . K o m p i s , L l o y d i a , 2 7 , 428 ( 1 9 6 4 ) . 8 7 . J . P . K u t n e y , W . J . C r e t n e y , P . L e Q u e s n e , B . McKague and E . P i e r s , J . A m e r . Chem. S o c , 92_, 1712 ( 1 9 7 0 ) . 8 8 . N . N e u s s , L . L . H u c k s t e p a n d N . J . C o n e , T e t r a h e d r o n L e t t e r s , 811 ( 1 9 6 7 ) . 8 9 . J . D . A l b r i g h t a n d L . G o l d m a n , J . A m e r . Chem. S o c , 8 9 , 2416 ( 1 9 6 7 ) . 9 0 . J . R . P a r i k h a n d W. v o n E . D o e r i n g , J . A m e r . Chem. S o c , 89_, 5505 ( 1 9 6 7 ) . 9 1 . T . J . B r o c k s o m , U n i v e r s i t y o f B r i t i s h C o l u m b i a ( 1 9 7 1 - 1 9 7 2 ) . 9 2 . K . E . P f i t z n e r a n d J . G . M o f f a t t , J . A m e r . Chem. S o c , 8 7 , 5661 ( 1 9 6 5 ) . 9 3 . I . I t o h , U n i v e r s i t y o f B r i t i s h C o l u m b i a ( 1 9 7 2 - ) . 9 4 . P . Bommer, W. M c M u r r a y a n d K . B i e m a n n , J . A m e r . Chem. S o c , 8 6 , 1439 ( 1 9 6 4 ) . 9 5 . N . F i n c h a n d W . I . T a y l o r , J . A m e r . Chem. S o c , 8 4 , 3871 ( 1 9 6 2 ) . 9 6 . J . B . P a t r i c k a n d B . W i t k o p , J . A m e r . Chem. S o c , 7_2_, 633 ( 1 9 5 0 ) . 9 7 . L . S . D o l b y a n d G . W . G r i b b l e , J . O r g . C h e m . , 3 2 , 1391 ( 1 9 6 7 ) . 9 8 . G . B u c h i and R . E . M a n n i n g , J . A m e r . Chem. S o c , 8 8 , 2532 ( 1 9 6 6 ) . 9 9 . W. W i n k l e r , N a t u r w i s s , 4 8 , 694 ( 1 9 6 1 ) . 1 0 0 . G . B u c h i , R . E . M a n n i n g and S . A . M o n t i , J . A m e r . Chem. S o c , 8_6, 4631 ( 1 9 6 4 ) . 1 0 1 . S . G . P . P l a n t , R . R o b i n s o n a n d M . T o m l i n s o n , N a t u r e , 1 6 5 , 928 ( 1 9 5 0 ) . 102 . G . B u c h i , R . E . M a n n i n g and S . A . M o n t i , J . A m e r . Chem. S o c , 8 5 , 1893 (1963) - 199 -1 0 3 . J . H a r l e y - M a s o n and A . Rahman, Chem. Comm., 1048 ( 1 9 6 7 ) . 1 0 4 . We a r e I n d e b t e d t o P r o f . J . C . C l a r d y , Iowa S t a t e U n i v e r s i t y f o r t h e s e X - r a y s t u d i e s . 1 0 5 . D i h y d r o v i n b l a s t i n e . E l i L i l l y & C o . (By M . Gorman and N . N e u s s ) . B e l g . 6 6 1 , 9 4 8 , O c t . 1 , 1 9 6 5 , U . S . A p p l . A p r i l 1 , 1 9 6 4 . 1 0 6 . R . L . N o b l e , C . T . B e e r and R . W . M c l n t y r e , C a n c e r , 20, 885 ( 1 9 6 7 ) . 1 0 7 . K . V . L i c h m a n , J . Chem. S o c . ( C ) , 2539 ( 1 9 7 1 ) . 1 0 8 . A . Rahman, P a k i s t a n . J . S c i . I n d . R e s . , 1 4 , 487 ( 1 9 7 1 ) . 1 0 9 . We a r e i n d e b t e d t o D r s . H . B . Wood and R . R . E n g l e o f t h e N a t i o n a l I n s t i t u t e s o f H e a l t h f o r t h e b i o l o g i c a l t e s t i n g o f t h e s e a n d o t h e r s a m p l e s . 1 1 0 . B . K . M o z a , J . T r o j a n e k , V. Hanus and L . D o l e j s , C o l l e c t i o n C z e c h o s l o v . Chem. Commun. , 29_, 1913 ( 1 9 6 4 ) . 1 1 1 . W . J . C r e t n e y , P h . D . T h e s i s , U n i v e r s i t y o f B r i t i s h C o l u m b i a ( 1 9 6 8 ) . 1 1 2 . H . G i l m a n and S . M . S p a t z , J . A m e r . Chem. S o c , 6 3 , 1553 ( 1 9 4 1 ) . 1 1 3 . R . G . J o n e s and H . G i l m a n , " T h e H a l o g e n - M e t a l I n t e r c o n v e r s i o n R e a c t i o n w i t h O r g a n o l i t h i u m C o m p o u n d s " , i n O r g a n i c R e a c t i o n s , V o l . V I , J o h n W i l e y & S o n s , New Y o r k , 1 9 5 1 . 1 1 4 . F . G . B o r d w e l l a n d T . G . M e c c a , J . A m e r . Chem. S o c , 9 4 , 5829 ( 1 9 7 2 ) . 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0061077/manifest

Comment

Related Items