Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Studies related to the synthesis of monomeric and dimeric vinca alkaloids Bylsma, Feike 1970

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

Notice for Google Chrome users:
If you are having trouble viewing or searching the PDF with Google Chrome, please download it here instead.

Item Metadata

Download

Media
831-UBC_1970_A1 B94.pdf [ 6.72MB ]
Metadata
JSON: 831-1.0059980.json
JSON-LD: 831-1.0059980-ld.json
RDF/XML (Pretty): 831-1.0059980-rdf.xml
RDF/JSON: 831-1.0059980-rdf.json
Turtle: 831-1.0059980-turtle.txt
N-Triples: 831-1.0059980-rdf-ntriples.txt
Original Record: 831-1.0059980-source.json
Full Text
831-1.0059980-fulltext.txt
Citation
831-1.0059980.ris

Full Text

STUDIES RELATED TO THE SYNTHESIS OF MONOMERIC AND DIMERIC VINCA ALKALOIDS by FEIKE BYLSMA B.Sc. Honours, McMaster U n i v e r s i t y , 1966 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE"REQUIREMENTS FOR THE DEGREE OF , DOCTOR OF PHILOSOPHY i n the Department of Chemistry We accept t h i s t h e s i s as conforming, to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1970 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 e q u i r e m e n 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 a g r e e t h a t 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 t u d y . I f u r t h e r agree tha 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 p u r p o s e s 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 t h a t 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 o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f The U n i v e r s i t y o f B r i t i s h Co lumbia V a n c o u v e r 8, Canada - i i -ABSTRACT The f i r s t p a r t o f t h i s t h e s i s describes a sequence which provides a t o t a l s y n t h e s i s of cleavamine (23) and catharanthine (12). Dihydro-c a t h a r a n t h i n o l (76) obtained by l i t h i u m aluminum hydride r e d u c t i o n of dihydrocatharanthine (34) was converted to i t s t o s y l a t e d e r i v a t i v e . The l a t t e r i ntermediate upon hea t i n g i n benzene c o n t a i n i n g two equiva l e n t s of t r i e t h y l a m i n e underwent an i n t e r e s t i n g fragmentation r e a c t i o n to provide a seco-diene (78) c o n t a i n i n g the cleavamine r i n g system. Reaction of t h i s diene w i t h osmium t e t r o x i d e provided a t e t r o l (96) which could be converted to cleavamine on the one hand and the C . - f u n c t i o n a l i z e d cleavamine d e r i v a t i v e s on the other. Thus 4 treatment of the t e t r o l with sodium borohydride allowed the hydrogenolysis of the c a r b i n o l amine f u n c t i o n and provided a t r i o l (97). The v i c i n a l d i o l present i n 97 was cleaved by means of pe r i o d a t e and the r e s u l t a n t 2- a c y l i n d o l e chromophore was f u r t h e r converted by borohydride to a 4,18-dihydroxy dihydrocleavamine d e r i v a t i v e (99). Reductive removal of the C^g hydroxyl f u n c t i o n by means of l i t h i u m aluminum hydride provided isovelbanamine (100). A c i d c a t a l y z e d dehydration of the l a t t e r y i e l d e d cleavamine (23) while i s o m e r i z a t i o n under aqueous a c i d i c c o n d i t i o n s provided velbanamine (22). To complete the t o t a l s y n t h e s i s of catharanthine (12), cleavamine was reacted w i t h t - b u t y l h y p o c h l o r i t e and the r e s u l t a n t c h l o r o i n d o l e n i n e was then subjected to n u c l e o p h i l i c attack by cyanide i o n to provide 183-cyanocleavamine. Basic h y d r o l y s i s of the n i t r i l e f u n c t i o n f o l l o w e d by e s t e r i f i c a t i o n provided 18g-carbomethoxycleavamine (60). This compound upon r e a c t i o n w i t h mercuric acetate was c y c l i z e d to catharanthine. - i i i -The second part of this thesis establishes the u t i l i t y of both the chloroindolenine and the C.--hydroxy analogues of the cleavamine systems to the synthesis of dimeric compounds s t r u c t u r a l l y similar to the natural dimeric alkaloids. Treatment of either of these analogues with vindoline under mild acidic conditions yielded the appropriate dirners containing the indole and dihydroindole units present i n vinca-leukoblastine. The dimerization reaction was shown to be stereospecific and led i n each case to the same stereochemistry at C^g, of the res u l t i n g dirners. - iv -TABLE OF CONTENTS Page T i t l e page Abstract Table of Contents L i s t of Figures ., L i s t of Tables ... Acknowledgements 11 i v V l l v m Introduction Discussion .. Part I . Part II Experimental Bibliography 1 24 24 87 124 159 - V -LIST OF FIGURES Figure Page 1. Summary of the pathway from mevalonate to i n d o l e a l k a l o i d s of tryptamine + ^ type .5 2. Kutney's t o t a l s y n t h e s i s of dl-dihydrocleavamine (29) . 20 3. T o t a l s y n t h e s i s of some Aspidosperma a l k a l o i d s .... 22 4. Mechanism proposed f o r the a c i d c a t a l y z e d rearrange-ment of catharanthine 28 5. A c i d c a t a l y z e d i s o m e r i s a t i o n of dihydrocatharanthine (34) to c o r o n a r i d i n e (35) 30 6. Reduction of catharanthine to the epimeric carbo-methoxydihydrocleavamine and 18g-carbomethoxy-cleavamine 31 7. Proposed dehydrogenation-reduction sequence us i n g the r i n g opened catharanthine intermediate (54).... 33 8. P a r t i a l scheme of the degradation of ajmaline (68). 36 9. Fragmentation of v o a c a g i n o l - O - t o s y l a t e (71a) and conopharyngol-O-tosylate (71b) 37 10. Proposed scheme, f o r r i n g opening of catharanthine to the 5,18-seco-diene system (78) 39 11. Synthesis of cleavamine (23) from the seco-diene (83) v i a osmium t e t r o x i d e o x i d a t i o n 54 12. Mass spectrum of the t e t r o l (96) 56 13. Mass spectrum of the t r i o l (97) 56 14. Nmr spectrum of the t e t r o l (96) 57' - v i -Figure Page 15. Nmr spectrum of the t r i o l (97) 59 16. P a r t i a l nmr spectrum i l l u s t r a t i n g the p e r t i n e n t s i g n a l p a t t e r n s corresponding to the 183-hydroxy-methyl f u n c t i o n 61 17. Mass spectrum of k e t o l (98) 63 i 18. Mass spectrum of d i o l (99) 1 63 19. Nmr spectrum of the d i o l (99) ^ 65 20. Nmr of isovelbanamine (100) 68 21. Mass spectrum of isovelbanamine (100) 70 22. Mass spectrum of 3a-hydroxy-43-dihydrocleavamine... 70 23. Conversion of cleavamine (23) to catharanthine .... 72 24. Taylor's r e a c t i o n scheme f o r f u n c t i o n a l i z a t i o n u s i n g i n d o l e n i n e intermediates 72 25. Nmr spectrum of 18g-cyanocleavamine (109) 75 26. Nmr spectrum of 3a-acetoxy-43-dihydrocleavamine.... 81 27. Mass spectrum o f dimer (118) 90 28. Nmr spectrum of dimer (118) 92 29. Nmr spectrum of v i n d o l i n e (11) 93 30. Nmr spectrum of 4g-dihydrocleavamine 94 31. Mass spectrum of dimer (119) 97 32. Nmr spectrum of dimer (119) 98 33. Uv spectrum of dimer (119) and v i n b l a s t i n e (16).... 102 34. Nmr spectrum of v i n b l a s t i n e (16) 103 35. Nmr. spectrum of dimer (142) H 4 36. Nmr spectrum o f dimer (146) 121 • J - v i i -LIST OF TABLES Table Page I S t r u c t u r e - a c t i v i t y s t u d i e s on v i n b l a s t i n e by H a r g r o v e ^ 11 I I The major d i f f e r e n c e s observed between the nmr s p e c t r a of v i n b l a s t i n e and dimer (119)| 104 - V l l l -ACKNOWLEDGEMENTS I wish t o express my thanks to Pr o f e s s o r J.P. Kutney f o r h i s e x c e l l e n t guidance throughout the course of t h i s research. His encouragement and unbounded optimism were o f t e n evoked and provided much of the stimulus f o r t h i s work. I am very g r a t e f u l to my wif e f o r her support and encouragement throughout t h i s study and a l s o f o r her help i n the p r e p a r a t i o n of t h i s manuscript. I am g r a t e f u l to the N a t i o n a l Research C o u n c i l of Canada and the N a t i o n a l Cancer I n s t i t u t e of Canada f o r the f i n a n c i a l support provided. INTRODUCTION The constant and c o n t i n u i n g quest f o r new t h e r a p e u t i c agents and t h e i r development has been and remains to be one of the main o b j e c t i v e s of the n a t u r a l product chemist. P r i m a r i l y h i s job i n t h i s regard has been the s t r u c t u r a l e l u c i d a t i o n and s y n t h e s i s of compounds of known t h e r a p e u t i c v a l u e . Knowledge of the s t r u c t u r a l d e t a i l s i s of course e s s e n t i a l to the understanding of the mode of a c t i o n of these drugs. T h i s , coupled w i t h the s y n t h e t i c c a p a b i l i t i e s o f the chemist has l e d t o the use of many s y n t h e t i c analogues of the n a t u r a l l y o c c u r r i n g compounds i n modern medicine. I t has been estimated that some f i f t e e n percent or more of a l l v a s c u l a r p l a n t s c o n t a i n a l k a l o i d s . A very l a r g e number of d i f f e r e n t p l a n t species have been i n v e s t i g a t e d w i t h i n the past two decades f o r a l k a l o i d a l c o n s t i t u e n t s . Much of t h i s work has been done by l a r g e pharmaceutical f i r m s who. are i n v o l v e d i n a systematic screening of p l a n t s f o r s p e c i f i c pharmacological a c t i v i t y . 1 A more d i r e c t but l i m i t e d approach has been the study o f g a l e n i c a l s p r e s c r i b e d by f o l k l o r e and p r i m i t i v e medicine. Although most a l k a l o i d s possess some degree of pharmacological a c t i v i t y , many are not m e d i c i n a l l y u s e f u l e i t h e r because t h e i r a c t i v i t y i s too f e e b l e or because t h e i r t o x i c i t y i s too marked. Thus only a r e l a t i v e l y small number among a l l the known - 2 a l k a l o i d s are c u r r e n t l y of importance from the th e r a p e u t i c p o i n t of view. A" d i v e r s i t y of s t r u c t u r e i s e x h i b i t e d by these compounds. The simp l e s t are perhaps those of the phenethylamine group. The Ephedra a l k a l o i d ephedrine (1) resembles the animal hormone epinephrine (2) both s t r u c t u r a l l y and i n i t s adrenergic p r o p e r t i e s . The Peyote a l k a l o i d mescaline (3) i s an h a l l u c i n o g e n i c agent used to 'produce "model psychoses" i n man f o r experimental purposes. OH OCH, OH (1) CH-OH I CH-CH, I 3 NH-CH (2) OCH. In p a r t , the e a r l y b i o s y n t h e t i c p o s t u l a t e s of Robinson and many 3 subsequent experiments d e a l t w i t h the formation o f the s l i g h t l y more complex tropane a l k a l o i d s . Important members of t h i s f a m i l y are the c h o l i n e r g i c b l o c k i n g agent a t r o p i n e (hyoscyamine) (4) and the l o c a l a n a e s t h e t i c cocaine (5). . Morphine (6) and codeine (7) both depressants of the c e n t r a l nervous system are even more complex and have been the objec t o f 4 5 intense s t r u c t u r a l , s y n t h e t i c and b i o s y n t h e t i c i n v e s t i g a t i o n . A very l a r g e group o f a l k a l o i d s numbering about 600, have as t h e i r b a s i c s t r u c t u r a l u n i t , the i n d o l e moiety. The complexity o f t h e i r structures range i n a manner s i m i l a r to those c i t e d above, from the very simple, for example, the neurohormone serotonin (8) to the very complex such as the poison, strychnine ( 9 ) , and the hypotensive agent, reserpine (10). The synthesis of compounds of i n t r i c a t e structure 6 7 such as the l a t t e r two ' represent major achievements i n the f i e l d of synthetic organic chemistry. Most of the indole a l k a l o i d s can be c l a s s i f i e d according to t h e i r - 4 -| (10) s t r u c t u r a l type i n t o f o u r groups; these are Corynanthe, Aspidosperma, Iboga and Strychnos. Examples of each of these r e s p e c t i v e l y are r e s e r p i n e (10), v i n d o l i n e (11), catharanthine (12), and s t r y c h n i n e (9). (11) (12) I t has been e s t a b l i s h e d that b i o s y n t h e t i c a l l y these seemingly u n r e l a t e d s t r u c t u r e s are i n f a c t d e r i v e d from a common inte r m e d i a t e . 8 This i n t e r m e d i a t e , v i n c o s i d e (13), r e s u l t s from a condensation between tryptamine and a monoterpene u n i t , secologanin (15), d e r i v e d from mevalonate through l o g a n i n (14) as shown i n f i g u r e 1. The e l u c i d a t i o n Corynanthe Iboga Aspidosperma Figure 1. Summary of the pathway from mevalonate t o i n d o l e a l k a l o i d s of tryptamine + C n .. n type of the mechanism by which v i n c o s i d e (13) i s converted i n t o each of the s t r u c t u r a l types remains an a c t i v e area of research at present. - 6 -i I The b a s i c s t r u c t u r a l u n i t of the a l k a l o i d s r e s u l t i n g from the above process, i s made up of nineteen or twenty carbon atoms and two n i t r o g e n atoms. However, a number of i n d o l e a l k a l o i d s have been i s o l a t e d over the l a s t f i f t e e n years which possess a molecular formula made up of approximately two such u n i t s . These "dimeric a l k a l o i d s " , i n p a r t i c u l a r , those i s o l a t e d from Catharanthus roseus G. Don, have provided a tremendous stimulus to a l l aspects o f the f i e l d of i n d o l e a l k a l o i d chemistry because of t h e i r proven o n c o l y t i c . a c t i v i t y . The s t u d i e s i n our l a b o r a t o r y l e a d i n g to the sy n t h e s i s of these complex systems i s the subject of t h i s t h e s i s . Catharanthus roseus G. Don, a l s o r e f e r r e d to as Vinca rosea L i n n , i s a t r o p i c a l member of the genus of p l a n t s commonly known as the p e r i w i n k l e s . The use of t h i s species of p l a n t throughout the h i s t o r y of f o l k - m e d i c i n e has been v a r i e d , g a l e n i c a l s prepared from i t have been used as an a b o r t i v e agent, a n t i - d i a b e t i c anti-galactogogue, menstrual 9 r e g u l a t o r , p u r g a t i v e and a number of other uses. A r e c e n t l y p u b l i s h e d a r t i c l e e n t i t l e d " P l a n t s used against Cancer - A Survey" 1^, i s a l i t e r a t u r e survey embracing the recorded h i s t o r y of medicine, pharmacology, materia medica, medical botany, ethnobotany and f o l k l o r e t o 2800 B.C. I t i s i n t e r e s t i n g to note .that of the more than 3000 d i f f e r e n t p l a n t species reported to have been used against growths and tumors, no mentioned i s made of C_. roseus G. Don. I n t e r e s t i n t h i s species arose from i t s reported hypoglycemic a c t i v i t y . Noble and Beer could not s u b s t a n t i a t e t h i s a c t i v i t y but observed i n s t e a d p e r i p h e r a l granulocytopenia and bone marrow depression - 7 -i i i i n r a t s . This l e d to the i s o l a t i o n of v i n b l a s t i n e ( v i n c a l e u k o b l a s t i n e , X 2 V L B ) (16) which was found to produce severe leukopenia i n r a t s . I s o l a t i o n o f v i n b l a s t i n e and l e u r o s i n e (17) and t h e i r a c t i v i t y against 13 P-1534 leukemia i n mice was reported s h o r t l y t h e r e a f t e r by Svoboda. I These p r e l i m i n a r y i n v e s t i g a t i o n s marked the beginning of a very a c t i v e p e r i o d of research i n the Vinca a l k a l o i d s . A t o t a l o f 61 a l k a l o i d s have been obtained from C. Roseus G. Don, 26 of them are dimeric but only 6 of these have o n c o l y t i c a c t i v i t y . These a c t i v e compounds are a l l dimers of the i n d o l e - i n d o l i n e type. The s t r u c t u r e s of f o u r of them, v i n b l a s t i n e ( 1 6 ) , 1 4 l e u r o s i n e ( 1 7 ) , 1 5 l e u r o s i d i n e ( 1 8 ) ^ 14 and v i n c r i s t i n e ( l e u r o c r i s t i n e , VCR) (19), have been e s t a b l i s h e d . R l R 2 R 3 R4 (16) C0 2CH 3 CH 3 OH H (17) C0 2CH 3 C H 3 • 0 (18) C0 2CH 3 C H 3 H OH (19) C0 2CH 3 CHO OH H - 8 -| V i n b l a s t i n e and v i n c r i s t i n e are the most a c t i v e and f o r t h i s reason have been s t u d i e d more e x t e n s i v e l y i n t h e i r c l i n i c a l use than the other a l k a l o i d s . Both have been shown to be e f f e c t i v e i n the treatment of 17 lymphomas and v a r i o u s carcinomas . V i n c r i s t i n e i s a l s o e f f e c t i v e i n the treatment of acute leukemia p a r t i c u l a r l y i n c h i l d r e n . T h e i r usefulness i s l i m i t e d , however, by t h e i r t o x i c i t y ; v i n b l a s t i n e produces leukopenia w h i l e v i n c r i s t i n e e x h i b i t s neuromuscular t o x i c i t y . The mode of a c t i o n of these drugs i s not p r o p e r l y understood. A 18 recent review of t h i s subject makes i t c l e a r that although the many experiments conducted so f a r have pointed out a number of p h y s i o l o g i c a l changes observed i n a v a r i e t y of tumor systems s t u d i e d both i n v i t r o and i n v i v o when subjected to these drugs, i t has been d i f f i c u l t to c o r r e l a t e these r e s u l t s , and the biochemical mechanism of t h e i r a c t i o n remains to be determined. I t does appear t h a t the Vinca a l k a l o i d s have a s i m i l a r i f not i d e n t i c a l mechanism of a c t i o n to t h a t of the other m i t o t i c poisons such as c o l c h i c i n e (20) and p o d o p h y l l o t o x i n (21). - 9 -The f o l l o w i n g working hypothesis i n c o r p o r a t i n g the observed phenomena has been presented by Armstrong at the 'conclusion of a recent 19 symposium on v i n c r i t i n e . The primary i n t r a c e l l u l a r metabolic e f f e c t of the Vinca a l k a l o i d s seems to be the i n h i b i t i o n of t r a n s f e r RNA s y n t h e s i s . Because the f u n c t i o n of t r a n s f e r RNA i s to c a r r y amino acids from the cytoplasm i n t o the ribosomes where p r o t e i n s are formed, i t i s thus the decrease i n t r a n s f e r RNA syn t h e s i s which causes a decrease i n p r o t e i n s y n t h e s i s . The Vinca a l k a l o i d s are permitted t o enter the c e l l s only between prophase and metaphase and thus i n t r a -c e l l u l a r p r o t e i n p r o d u c t i o n becomes decreased at the very time when p r o t e i n should appear between the f i b e r s of the s p i n d l e apparatus to spread them apart and support them i n the fanned out p o s i t i o n they normally adopt during metaphase. In the absence o f t h i s support the s p i n d l e f i b e r s appear c o l l a p s e d and tangled i n c e l l s a r r e s t e d i n meta-phase by the a l k a l o i d . When the s p i n d l e apparatus i s i n such a d i s a r r a y , the chromosomes cannot migrate from the metaphase p o s i t i o n . The i n h i b i t i o n of DNA syn t h e s i s observed, r e s u l t s from metaphase a r r e s t . Such an ex p l a n a t i o n provides an ordered sequence of events to account f o r the expe r i m e n t a l l y observed phenomena but provides no i n s i g h t i n t o the biochemical mode of a c t i o n ; f o r example what i n t e r a c t i o n w i t h the a l k a l o i d s e x i s t s that i n h i b i t s the syn t h e s i s of t r a n s f e r RNA. Having l i t t l e or no knowledge of the a c t u a l r e a c t i o n mechanism a s s o c i a t e d w i t h the pharmacological p r o p e r t i e s e x h i b i t e d by these compounds, the chemist i s i n a poor p o s i t i o n to model a compound with the d e s i r e d t h e r a p e u t i c p r o p e r t i e s and l i t t l e or no t o x i c i t y . He need, of n e c e s s i t y , use a r a t h e r e m p i r i c a l approach, that i s , s t a r t w i t h a compound of known 10 pharmacological p r o p e r t i e s and a l t e r i t stepwise n o t i n g simply the inc r e a s e or decrease i n a c t i v i t y a s s o c i a t e d w i t h each s t r u c t u r a l m o d i f i c a t i o n . In such a way knowledge can be gained of the importance of s t r u c t u r a l u n i t s as r e l a t e d to a c t i v i t y . This method i s fraught with two major d i f f i c u l t i e s . F i r s t , the chemist may have the misfortune of choosing the wrong compound as h i s b a s i s f o r improvement and thereby put h i m s e l f i n the f a r from unique p o s i t i o n of t r y i n g to do the imp o s s i b l e . Second, i f he chooses as we have, a compound with a formula; such as C.,N.0_Hro, ' ^ 46 4 9 58' he i s faced w i t h a near i n f i n i t e number of choices of how best t o modify or a l t e r the s t r u c t u r e . U n f o r t u n a t e l y or f o r t u n a t e l y he i s l i m i t e d i n h i s choice by h i s s y n t h e t i c c a p a b i l i t i e s and the amount o f time a v a i l a b l e . The very s l i g h t s t r u c t u r a l d i f f e r e n c e between v i n b l a s t i n e and v i n c r i s t i n e and the r e l a t i v e l y l a r g e d i f f e r e n c e i n t h e r a p e u t i c p r o p e r t i e s and t o x i c i t y serves to i n d i c a t e t h a t perhaps only a minor change i s necessary to e f f e c t the syn t h e s i s of an improved drug. An attempt to 20 achieve t h i s has been reported by Hargrove. V i n b l a s t i n e was converted d i r e c t l y i n t o a number o f analogues by r e a c t i o n s such as h y d r o l y s i s , hydrogenation and a c e t y l a t i o n . The r e s u l t s are summarized i n t a b l e I . The numbered arrows on the schematic i n d i c a t e the p o s i t i o n a f f e c t e d by the r e a c t i o n . As reference f o r f u r t h e r d i s c u s s i o n , the numbering system commonly used f o r the Iboga and Aspidosperma a l k a l o i d s i s given below. Table I. S t r u c t u r e - a c t i v i t y studies on v i n b l a s t i n e by Hargrove. M o d i f i c a t i o n A c t i v i t y r e l a t i v e to VLB t o x i c i t y 1) reduction of vi n d o l i n e portion | 1/3 less 2) reduction (hexahydro) none --3) ac i d hydrolysis (desacetyl) none 10X 4) L i A l H j reduction none — 5) ac i d hydrolysis of VCR (desformyl) j none --6) a c e t y l a t i o n using ketene ( t r i a c e t a t e ) none --7) a c e t y l a t i o n using Ac 20 (diacetate) none — (6) (7) (4) - 12 -Iboga Aspidosperma More promising r e s u l t s were obtained from the production of 4-acyl analogues r e a d i l y prepared by the r e a c t i o n of d e s a c e t y l VLB w i t h a s e r i e s o f simple a l i p h a t i c a c i d s . The best of these, v i n g l y c i n e ( d e s a c e t y l VLB 4-(N,N-dimethylaminoacetate)) produced from d e s a c e t y l VLB-4-chloroacetate and dimethylamine, equals v i n c r i s t i n e i n i t s a c t i o n a gainst P-1534 leukemia i n mice. This compound proved to be much le s s t o x i c than v i n b l a s t i n e and could thus be t o l e r a t e d at higher dose l e v e l s . Although at t h i s p o i n t VLB has been transformed i n t o an "improved" drug, t h i s was no s o l u t i o n to the problem s i n c e i t s a c t i v i t y seemed to be s i m i l a r to that of v i n c r i s t i n e . Changes other than i n the f u n c t i o n a l groups on the molecule are much more d i f f i c u l t to i n t r o d u c e . Two p o s s i b i l i t i e s present themselves: a) p a r t i a l l y degrade v i n b l a s t i n e and b u i l d i n s t r u c t u r a l m o d i f i c a t i o n s or b) attempt to s y n t h e s i z e analogues u s i n g the a p p r o p r i a t e Iboga and Aspidosperma type u n i t s . Some degradation of v i n b l a s t i n e has been reported and the work i n d i c a t e s that the dimer i s r e a d i l y cleaved i n t o i t s monomeric u n i t s . I t was the i d e n t i f i c a t i o n of these cleavage products which provided much - 13 -of the i n i t i a l evidence f o r the s t r u c t u r e of VLB. When VLB was t r e a t e d under a c i d i c reducing c o n d i t i o n s , the products i s o l a t e d were d e s a c e t y l v i n d o l i n e and velbanamine (22) . Prolonged treatment under the above c o n d i t i o n s a l s o produced some cleavamine (23). (22) (23) Desacetyl v i n d o l i n e was r e a d i l y i d e n t i f i e d by comparison with an 21 a u t h e n t i c sample produced by m i l d h y d r o l y s i s of v i n d o l i n e (11) • The s t r u c t u r e o f velbanamine was e s t a b l i s h e d v i a cleavamine, i t s dehydration product. Cleavamine had been i s o l a t e d from a mixture of products obtained from catharanthine (12) t r e a t e d under c o n d i t i o n s i d e n t i c a l to 22 those used f o r the dimer cleavage. I t s s t r u c t u r e had been c o r r e c t l y 23 assigned based on mass s p e c t r a l data and was l a t e r s u b s t a n t i a t e d by 24 X-ray a n a l y s i s o f cleavamine methiodide. Treatment of v i n b l a s t i n e under non-reducing a c i d i c - c o n d i t i o n s a l s o cleaved i t ; the product of 14 t h i s r e a c t i o n was de s a c e t y l v i n d o l i n e and the ether (24). This ether when subjected t o reducing a c i d i c c o n d i t i o n s y i e l d e d velbanamine. I t i s not s u r p r i s i n g t h a t the bond j o i n i n g these two u n i t s i n the dim e r i c system should be so l a b i l e , p a r t i c u l a r l y under a c i d i c c o n d i t i o n s , The v i n d o l i n e aromatic p o r t i o n i s e s s e n t i a l l y a meta-methoxyaniline - 14 -(24) system which would be expected to undergo f a c i l e e l e c t r o p h i l i c s u b s t i t u t i o n . In t h i s case p r o t o n a t i o n at C^ ,_ would lead to a resonance-s t a b i l i z e d carbonium i o n s i n c e both the ortho-methoxy and p a r a - a n i l i n o n i t r o g e n atom can make co n t r i b u t i o n to i t s s t a b i l i t y . Bond f i s s i o n i s then merely a process which would lead to n e u t r a l i z a t i o n of the p o s i t i v e charge. T h e o r e t i c a l l y , any r e a c t i o n mechanism i s r e v e r s i b l e . Thus the problem i n s y n t h e s i z i n g the dimeric system from i t s two components i s one of making i t e n e r g e t i c a l l y favourable f o r the reverse of the above process t o occur. Because Kutney and coworkers had developed a general s y n t h e t i c route to both the Iboga and Aspidosperma types of a l k a l o i d , the two halves of the dimer, t h i s approach was adopted and i s o u t l i n e d i n t h i s t h e s i s . The key step i n the s y n t h e s i s of the Aspidosperma and Iboga a l k a l o i d s 25 i s a transannular c y c l i z a t i o n which was p o s t u l a t e d i n 1962 by Wenkert i n a b i o s y n t h e t i c scheme lea d i n g to these compounds. The Aspidosperma system was proposed to r e s u l t from the transannular c y c l i z a t i o n of the app r o p r i a t e b i o s y n t h e t i c precursor (25 -»- 26) and the Iboga could a r i s e v i a a s i m i l a r process (27 -*• 28) . - 15 -(27) (28) The f i r s t experimental v e r i f i c a t i o n f o r t h i s scheme was provided 26 2 by Kutney. Dihydrocleavamine (29) a v a i l a b l e from catharanthine (12), provided a convenient model system. O x i d a t i o n w i t h mercuric acetate gave the r e q u i r e d iminium, s a l t (30) which on r i n g c l o s u r e f o l l o w e d by r e d u c t i o n r e s u l t e d i n the Aspidosperma s k e l e t o n (31). When carbomethoxydihydrocleavamine (32) was o x i d i z e d under s i m i l a r 27 c o n d i t i o n s pseudovincadifformine (33) was i s o l a t e d along w i t h dihydro-28 catharanthine (34) and c o r o n a r i d i n e (35). Whereas the c y c l i z a t i o n ' to the Aspidosperma s k e l e t o n i n the dihydrocleavamine case must i n v o l v e - 16 -(29) H H H the e l e c t r o n s inherent i n the i n d o l e system as i n the intermediate (30), i n the carbomethoxydihydrocleavamine case, the d r i v i n g f o r c e comes from the l o s s o f a, hydrogen alpha to the carbomethoxy group i n the intermediate (36) . The presence of both c o r o n a r i d i n e and dihydro-catharanthine i n d i c a t e s that the iminium s a l t (37) i s i n e q u i l i b r i u m w i t h i t s enamine isomer. The Aspidosperma s k e l e t o n as synthesized i n the experiments c i t e d above i s of an unnatural s t r u c t u r e bearing the e t h y l s i d e chain at r a t h e r than at C^. The c o r r e c t s t r u c t u r e was obtained by transannular-c y c l i z a t i o n of quebrachamine (38), which l e d to the syn t h e s i s of aspidospermidine (39). I t i s of i n t e r e s t to note the stereochemical d e t a i l s of t h i s work. The Aspidosperma s k e l e t o n contains four asymmetric centers while the s t a r t i n g cieavamine or quebrachamine systems have only one. I t has been - 17 -(33) (34) R=H, R1=C2H (35) R=C2H5,R1=H - 18 -(38) (39) e s t a b l i s h e d by chemical and X-ray s t u d i e s that the lone asymmetric center i n the s t a r t i n g m a t e r i a l r e s u l t s i n a s t e r e o s p e c i f i c c y c l i z a t i o n 29 and determines the stereochemistry at the other three c e n t e r s . Thus both of the stereochemical s e r i e s known i n the n a t u r a l Aspido-sperma a l k a l o i d s can be obtained by the proper choice of s t a r t i n g m a t e r i a l . Having e s t a b l i s h e d the u t i l i t y of the transannular c y c l i z a t i o n approach to the s y n t h e s i s of both the Aspidosperma and Iboga systems, a general approach to the synt h e s i s o f the appropriate nine membered r i n g intermediate was d e s i r a b l e . The d i f f i c u l t y of s y n t h e s i z i n g i n t e r -mediate s i z e r i n g systems i s w e l l known. In t h i s case the d i f f i c u l t y was obviated by advantageous use of the n i t r o g e n atom present i n the r i n g system. The key intermediate f o r t h i s s y n t h e t i c approach i s the quaternary s a l t (40). Ring opening o f t h i s intermediate i s r e a d i l y achieved under reducing c o n d i t i o n s to give dl-quebrachamine (38) (when R=C2H^ and R^=H) and dl-dihydrocleavamine (29) (when R=H and R^= 30,31,32 The s y n t h e s i s of the intermediate (40) was achieved i n - 19 -a s t r a i g h t forward manner as shown f o r the intermediate (40b) i n 31 30 f i g u r e 2. Intermediate (40a) was obtained i n a s i m i l a r manner. Having obtained dihydrocleavamine, i t was then d e s i r a b l e to extend the s y n t h e t i c sequence to a C -carbomethoxydihydrocleavamine d e r i v a t i v e s i n c e t h i s would then give a t o t a l s y n t h e s i s of d l - d i h y d r o -catharanthine and d l - c o r o n a r i d i n e v i a the t r a n s a n n u l a r c y c l i z a t i o n already mentioned. Use was made of the t e r t - b u t y l h y p o c h l o r i t e o x i d a t i o n of i n d o l e systems to the corresponding c h l o r o i n d o l e n i n e as 33 employed by Buchi i n h i s voacangine s y n t h e s i s . This r e a c t i o n which serves an important r o l e i n the work f o r t h i s t h e s i s , w i l l be discussed i n d e t a i l when th a t work i s presented. The c h l o r o i n d o l e n i n e (41) formed from dihydrocleavamine was reacted with potassium cyanide to i n t r o d u c e the n i t r i l e group at the C l c p o s i t i o n . T h i s , f o l l o w e d by treatment w i t h methanolic h y d r o c h l o r i c a c i d produced the r e q u i r e d 31 18-carbomethoxydihydrocleavamine (32). Subsequent work c a r r i e d out to extend the t o t a l s y n t h e s i s of dl-quebrachamine and aspidospermidine to the more complex members of - 20 -(29) Figure 2. Kutney's t o t a l s y n t h e s i s of dl-dihydrocleavamine (29). - 21 -0C1" (29). (41) (42) (32) the Aspidosperma a l k a l o i d s r e s u l t e d i n the improved sequence as out-32 l i n e d i n f i g u r e 3. Condensation of tryptamine w i t h the aldehyde (43) provided the r e q u i r e d t e t r a c y c l i c intermediate d i r e c t l y thereby e l i m i n a t i n g the low y i e l d i n g o x i d a t i v e step inherent i n the f i r s t approach. This sequence l e d t o the s y n t h e s i s of the quaternary mesylate i n a g r e a t l y improved o v e r - a l l y i e l d . N u c l e o p h i l i c a t t a c k by cyanide on t h i s intermediate e f f e c t e d both the r i n g opening and formation o f the d e s i r e d n i t r i l e i n a s i n g l e step. Conversion of the n i t r i l e to the carbomethoxy group produced d l - v i n c a d i n e and d l - e p i v i n c a d i n e , i s o m e r i c at C 1 C >. This work a l s o provided a t o t a l s y n t h e s i s of d l -vincaminoreine and d l - v i n c a m i n o r i n e , the corresponding i n d o l e N-methyl-analogues. Transannular - c y c l i z a t i o n of the above nine-membered r i n g n a t u r a l products provided t o t a l syntheses of d l - v i n c a d i f f o r m i n e and i t s N-methyl analogue, dl-minovine. An e x t e n t i o n of t h i s sequence to encompass a l k a l o i d s bearing a methoxyl group i n the aromatic r i n g was achieved by the use of 6-methoxytryptamine i n s t e a d o f tryptamine i n the i n t i a l condensation. This has l e d to the t o t a l s y n t h e s i s of the s t r u c t u r e proposed f o r 22 HCO l _ H C0 2Et CH2OBz NH, (43) _ M MeSCLCl OMes 2 N Q_ CH2OBz N ^ \ 2 R R l R 2 R 3 vinc a d i n e H C0 2CH 3 H H ep i v i n c a d i n e H H CH 2C0 3 H vincarainoreine H C0 2CH 3 H C H 3 vincaminorine H H C0 2CH 3 C H 3 vi n c a m i n o r i d i n e C0 2CH 3 H H C0 2CH 3 C H 3 R R 3 v i n c a d i f f o r m i n e H H minovine H Me C02Me Figure 3. T o t a l s y n t h e s i s of some Aspidosperma a l k a l o i d s . 32 - 23 -v i n c a m i n o r i d i n e . Ring c l o s u r e provides a compound which has most of the s t r u c t u r a l features of v i n d o l i n e . From the summary of the experimental work provided, i t i s apparent th a t a general s y n t h e t i c approach to the Aspidosperma and Iboga a l k a l o i d s has been developed. However, w i t h respect to the sy n t h e s i s of the dimer i c systems, a comparison of the s t r u c t u r e s drawn f o r the n a t u r a l dimers and the s t r u c t u r e s drawn i n the s y h t h e t i c schemes, i n d i c a t e t h a t although the c o r r e c t gross s t r u c t u r e s have been s y n t h e s i z e d , the s y n t h e t i c m a t e r i a l s lack some of the r e q u i r e d f u n c t i o n a l i t y . I t was t h e r e f o r e , necessary to develop a means by which the o x i d a t i o n l e v e l of these compounds could be a l t e r e d to th a t found i n the n a t u r a l d i m e r i c systems. Once t h i s had been accomplished, the means to couple the f u n c t i o n a l i z e d Iboga and Aspidosperma u n i t s to form the dimeric compounds would have to be developed. The sy n t h e s i s of the appropriate Aspidosperma u n i t , s p e c i f i c a l l y v i n d o l i n e , i s a demanding problem and i s c u r r e n t l y being s t u d i e d by other workers i n our l a b o r a t o r y . This t h e s i s w i l l deal w i t h the work conducted towards a c h i e v i n g the c o r r e c t o x i d a t i o n l e v e l of the Iboga system and the m o d i f i c a t i o n s necessary to e f f e c t coupling w i t h v i n d o l i n e . DISCUSSION The aim'of t h i s work, as o u t l i n e d i n the i n t r o d u c t i o n , i s the s y n t h e s i s o f a s e r i e s of compounds analogous 'to the n a t u r a l d i m e r i c Vinca a l k a l o i d s . The s t u d i e s c a r r i e d out t o t h i s end can be c l a s s i f i e d under two general headings: 1) the appropriate f u n c t i o n a l i z a t i o n of the nine-membered r i n g present i n the cleavamine-type system so as to make a v a i l a b l e u n i t s s i m i l a r to those found i n the n a t u r a l a l k a l o i d s and 2), the c o u p l i n g of these u n i t s with v i n d o l i n e t o give the a p p r o p r i a t e d i m e r i c molecules c l o s e l y r e l a t e d i n s t r u c t u r e t o the anti-tumor agents. For purposes of c l a r i t y and ease of p r e s e n t a t i o n , these two p a r t s of the work w i l l be d e a l t with s e p a r a t e l y i n t h i s d i s c u s s i o n . Part I The f o u r d i m e r i c Vinca a l k a l o i d s which have shown i n t e r e s t i n g anti-tumor a c t i v i t y possess a cleavamine type u n i t which i s f u n c t i o n -a l i z e d at the C^ and/or C^ p o s i t i o n s . The nature of these f u n c t i o n a l groups, e i t h e r hydroxyl or epoxide, suggest t h a t the corresponding compound having a double bond between C^ and C^ would be a v a l u a b l e intermediate i n a general scheme f o r the s y n t h e s i s of these f u n c t i o n a l i z e d systems. A number of methods could be u t i l i z e d f o r the i n t r o d u c t i o n of the necessary groups once the double bond i s p r o p e r l y placed i n the cleavamine system. At the time t h i s study was i n i t i a t e d , compounds having the - 25 -d e s i r e d degree of u n s a t u r a t i o n such as 18-carbomethoxycleavamine (60) on cleavamine (23) could only be obtained by degradation of the n a t u r a l l y 22 37 o c c u r r i n g a l k a l o i d , catharanthine (12) . ' However, the satura t e d analogues of these compounds, that i s , dihydrocleavamine (29), 18-carbomethoxydihydrocleavamine (32) and dihydrocatharanthine (34) had 27 31 been obtained i n a t o t a l l y s y n t h e t i c manner i n our l a b o r a t o r i e s . ' I t was thus of i n t e r e s t to develop a method by which the r e q u i r e d double bond could be introduced i n t o these compounds and thereby extend the s y n t h e t i c work to encompass these members. From another p o i n t of view i t was a l s o necessary to t o t a l l y s y n t h e s i z e catharanthine (12). I t became d e s i r a b l e i n our s y n t h e t i c s t u d i e s to have a s u i t a b l e r e l a y m a t e r i a l , one that would o b v i a t e the n e c e s s i t y of making l a r g e amounts of m a t e r i a l s , necessary f o r f u r t h e r - 26 -s t u d i e s , v i a a lengthy s y n t h e t i c sequence. Catharanthine, a major a l k a l o i d i s o l a t e d from the leaves of C.roseus, was the compound most s u i t a b l e to our i n t e r e s t and one which was used e x t e n s i v e l y throughout t h i s work. Therefore any s t u d i e s which would achieve the i n t r o d u c t i o n of the double bond i n t o the dihydrocatharanthine system would be h i g h l y d e s i r a b l e . Our approach to t h i s problem was to attempt |to synthesize cleavamine from one of the m a t e r i a l s already a v a i l a b l e v i a the previous s y n t h e t i c s t u d i e s . E a r l i e r i n our l a b o r a t o r y , i t had been shown that dihydrocleavamine could be converted t o 18-carbomethoxydihydrocleavamine and the l a t t e r v i a o x i d a t i o n to an iminium i n t e r m e d i a t e , would undergo 27 31 transannular c y c l i z a t i o n to dihydrocatharanthine. ' I t was c l e a r that t h i s sequence of r e a c t i o n s could be a p p l i e d i n the conversion of cleavamine to catharanthine v i a 18-carbomethoxycleavamine. On t h i s b a s i s a s y n t h e s i s of cleavamine should a l s o c o n s t i t u t e a s y n t h e s i s of the a l k a l o i d , c a t haranthine. Catharanthine can be converted i n t o a number of cleavamine d e r i v a t i v e s by known procedures. These compounds as w e l l as the chemistry i m p l i e d i n the t r a n s f o r m a t i o n of catharanthine to them, have been used throughout t h i s t h e s i s . I t i s i n s t r u c t i v e f o r t h i s reason to summarize b r i e f l y the r e l e v a n t p o r t i o n s of t h i s work. Dihydrocatharanthine, l i k e i t s Iboga r e l a t i v e s , i s r e a d i l y decarboxy-l a t e d under a c i d i c c o n d i t i o n s . In c o n t r a s t , the d e c a r b o x y l a t i o n of catharanthine occurs i n poor y i e l d only under f o r c i n g c o n d i t i o n s , ( r e f l u x i n g concentrated h y d r o c h l o r i c acid) . The accepted d e c a r b o x y l a t i o n - 27 -mechanism f o r the Iboga a l k a l o i d s ' r e q u i r e s the intermediacy of (61). (61) 22 36 The h i g h l y s t r a i n e d nature of t h i s intermediate has been c i t e d ' to account f o r the f a i l u r e o f t h i s r e a c t i o n under normal r e a c t i o n c o n d i t i o n s . I n i t i a l r e p o r t s of t h i s work i n d i c a t e the i s o l a t i o n of cleavamine as 22 w e l l as some descarbomethoxycatharanthine. Subsequent i n v e s t i g a t i o n of t h i s work by Kutney and coworkers showed that 4-g and 4 - c t-dihydro-cleavamine were a l s o products of t h i s r e a c t i o n . These r e s u l t s were r a t i o n a l i z e d on the b a s i s of the mechanism shown i n f i g u r e 4. Ring cleavage u t i l i z i n g the lone p a i r of e l e c t r o n s on would r e s u l t i n the conjugated iminium ion(44). H y d r o l y s i s of the e s t e r f u n c t i o n and d e c a r b o x y l a t i o n of the f l e x i b l e r i n g opened system gives the intermediate (46). Ring c l o s u r e would r e s u l t i n descarbomethoxycatharanthine (47) w h i l e a p r o t o t r o p i c s h i f t to r e s t o r e the i n d o l e system leads to(48). D i r e c t 1,2-reduction of the conjugated iminium s a l t leads to cleavamine (23) w h i l e 1,4-reduction would produce the enamine (49) which could be reduced, v i a the iminium s a l t (50) i n e q u i l i b r i u m w i t h i t , to y i e l d the epimeric 4a (51) and 4g (52) dihydrocleavamines. In the absence of added reducing agents these r e a c t i o n s s t i l l occur but i n lower y i e l d s . Under these c o n d i t i o n s , one merely v i s u a l i z e s an o x i d a t i o n - r e d u c t i o n ' - 28 -- 29 -process i n which the dihydropyridinium intermediate (48) i n i t s r o l e as a reducing agent, i s oxidized to the pyridinium s a l t (53) while converting 48 to the dihydrocleavamines. (53) In g l a c i a l a c e t i c a c i d , decarboxylation i s not observed f o r e i t h e r dihydrocatharanthine or catharanthine. Dihydrocatharanthine (34) treated i n t h i s manner i s recovered along with i t s C^ epimer coronaridine (35). A mechanistic r a t i o n a l e of t h i s i n t e r e s t i n g conversion reveals that the ring-opened species (54) i s i n equilibrium with the pentacyclic 22 compounds v i a i t s enamine tautomer as shown i n f i g u r e 5. Catharanthine i n g l a c i a l a c e t i c a c i d with zinc dust was reported 14 to produce carbomethoxydihydrocleavamine. A careful' study of t h i s r e a c t i o n i n our laboratories showed that four epimeric compounds 37 (epimeric at C^g and C^) were produced i n t h i s r e a c t i o n . These r e s u l t s can be r e a d i l y explained by a r e a c t i o n scheme (figure 6) s i m i l a r to the one outlined i n f i g u r e 4. The intermediate (44) instead of undergoing h y d r o l y s i s and decarboxylation as i n the previous scheme, proceeds to restore the indole system (56) with r e s u l t a n t epimers at C.„. As before, 1,4-reduction followed by tautomerization etc. i n the manner, 56 -»• 59 produces the four carbomethoxydihydrocleavamines (59) . - 30 -(35) Figure 5. A c i d c a t a l y z e d i s o m e r i s a t i o n of dihydrocatharanthine (34) to c o r o n a r i d i n e (35) . 31 -(44) M e 0 2 C Me0oC (60) 2 (23) (56) Me02C 1,2-reduction 1,4-reduction Me02C (59) Figure 6. Reduction of catharanthine to the epimeric carbomethoxy-37 dihydrocleavamines and 183-carbomethoxycleavamine. - 32 -On the other hand, 1,2-reduction of the intermediate (56) would be expected to y i e l d carbomethoxycleavamine. Indeed catharanthine on r e a c t i o n w i t h sodium borohydride i n hot g l a c i a l a c e t i c a c i d gave a good 37 y i e l d o f the p r e v i o u s l y unknown 18g-carbomethoxycleavamine (60). Because t h i s l a t t e r compound can be e a s i l y decarboxylated, t h i s procedure thereby made c l e a vamine (23) and dihydrocleavamine (29) r e a d i l y a v a i l a b l e . Previous t o the work c a r r i e d out f o r t h i s t h e s i s , attempts had been made by other workers i n our l a b o r a t o r y to o b t a i n the unsaturated cleavamine system from one of the t o t a l l y s y n t h e t i c compounds. T h e i r , approach made use of the a c i d c a t a l y z e d r i n g opening of dihydrocatharan-t h i n e (34) ( f i g u r e 5). The r e s u l t i n g intermediate iminium s a l t (62) which may be i n e q u i l i b r i u m w i t h (54) was expected to provide a "handle" f o r subsequent f a c i l e dehydrogenation to an aromatic system. Thus the te t r a h y d r o p y r i d i n i u m system (63) would lead t o the p y r i d i n i u m s a l t (64) as shown i n f i g u r e 7. Sodium borohydride r e d u c t i o n o f such p y r i d i n i u m s a l t s i s known to provide the t e t r a h y d r o p y r i d i n i u m system ( f o r example, 38 65 -»• 66) and i t i s c l e a r t h a t the above conversion could lead to the d e s i r e d carbomethoxycleavamine (60). (66) - 33 -(60) Figure 7. Proposed dehydrogenation-reduction sequence using the ring opened catharanthine intermediate (54). Experimentally, this reaction scheme could not be realized. The acid catalyzed ring opening step could be readily achieved; evidence for this reaction was the presence of coronaridine in the product mixture - 34 -(see f i g u r e 5). The d i f f i c u l t y was encountered i n the dehydrogenation step. Reagents used f o r t h i s purpose were 2,3-dichloro-5,6-dicyano-benzoquinone (DDQ), p a l l a d i u m , mercuric acetate and lead t e t r a c e t a t e . A broad range o f experimental c o n d i t i o n s were t r i e d . Under m i l d c o n d i t i o n s no r e a c t i o n was observed and dihydrocatharanthine was recovered along w i t h some c o r o n a r i d i n e . More f o r c i n g c o n d i t i o n s con-sumed s t a r t i n g m a t e r i a l but gave no i d e n t i f i a b l e ! products. Considera-39 40 ! t i o n o f the mechanism f o r t h i s o x i d a t i o n ' i n d i c a t e s t h a t the iminium s a l t i ntermediate i s incapable o f being o x i d i z e d f u r t h e r without f i r s t undergoing i s o m e r i z a t i o n t o the corresponding enamine. Because the a c i d i c c o n d i t i o n s r e q u i r e d f o r r i n g opening may not favour enamine formati o n , a number o f experiments were a l s o c a r r i e d out i n which the a c i d i c r e a c t i o n mixture c o n t a i n i n g the r i n g opened species was taken t o dryness and then o x i d i z e d i n a b a s i c medium. No f a v o r a b l e r e s u l t s were obtained under these c o n d i t i o n s . Attempts to o b t a i n the enamine o f 4B-dihydrocleavamine (29) and of 183-carbomethoxydihydrocleavamine (32) by i s o m e r i z a t i o n o f the corresponding iminium s a l t s r e s u l t i n g from mercuric acetate o x i d a t i o n u s i n g b a s i c treatment were a l s o u n s u c c e s s f u l . Some of the transannular c y c l i z a t i o n products (29 -»- 31 and 32 -> 33) were obtained i n each case i n d i c a t i n g that o x i d a t i o n was indeed o c c u r r i n g but i s o l a t i o n o f the appropriate enamines ( i f formed) could not be achieved. The approach adopted f o r t h i s t h e s i s i n v o l v e d a fragmentation r e a c t i o n which, i f s u c c e s s f u l , would generate the nine-membered r i n g system inherent i n cleavamine as w e l l as the enamine group. In a general way, t h i s r e a c t i o n can be represented as f o l l o w s : - 35 -\ N — C — C — C — X *• N=C + C=C + X K i V i x x X = halogen, OTs, -OH + etc. The d e s i r e d h e t e r o l y t i c cleavage between the 3 and y carbon atoms would be dependent on the ease w i t h which the -C-X bond i s broken and the s a t i s f a c t i o n of the r e s u l t a n t e l e c t r o n d e f i c i e n c y at the y carbon atom. The l a t t e r c o n d i t i o n i s w e l l accommodated by the b a s i c n i t r o g e n w h i l e good l e a v i n g groups such as t o s y l a t e would s a t i s f y the f i r s t requirement. A number o f competing r e a c t i o n s are p o s s i b l e : 1) s u b s t i t u t i o n ; 2) 1 , 2 - e l i m i n a t i o n and 3) i n t e r - or i n t r a m o l e c u l a r q u a t e r n i z a t i o n of the n i t r o g e n atom (see f o r eq. 74 -> 75). I t i s found, however, that when the i n v o l v e d centres are i n a trans coplanar arrangement as shown i n s t r u c t u r e 67, i t i s favourable f o r the fragmentation to occur and t h i s i s the predominant mode of r e a c t i o n 44 observed. (67) This r e a c t i o n was o r i g i n a l l y employed i n the a l k a l o i d f i e l d i n the 41 degradation of ajmaline (68). The i s o q u i n u c l i d i n e system of the sarpagine (69) d e r i v e d from ajmaline was converted to the corynanthe-type s t r u c t u r e (70) as shown i n f i g u r e 8. - 36 -(70) Figure 8. P a r t i a l scheme of the degradation of ajmaline (68). This same r e a c t i o n scheme was subsequently a p p l i e d by Renner t o 42 the Iboga a l k a l o i d s . Voacanginol-O-tosylate (71a) underwent f i s s i o n t o y i e l d the 5,18-secodiene (72a) which was reduced by sodium borohydride to the dihydro compound (73a). S i m i l a r l y cOnopharyngol-0-t o s y l a t e (71b) was converted to the corresponding fragmentation product (72b) and i t s dihydro d e r i v a t i v e (73b). In c o n t r a s t iboxygaine (74) which does not have the d e s i r e d trans coplanar arrangement o f the 1,3-aminoalcohol grouping f a i l s to undergo r i n g cleavage on t o s y l a t i o n - 37 -MeO CH2OTs (71a), R=H (71b), R=OMe MeO MeO (73a), R=H (73b), R=OMe (72a), R=H (72b), R=OMe Figure 9. Fragmentation of vo a c a g i n o l - O - t o s y l a t e (71a) and conopharyngol-O-tosy.late (71b) . and gives i n s t e a d the quaternary t o s y l a t e s a l t (75) 43 TsO" MeO (74) (75) - 38 -Renner's r e a c t i o n scheme ( f i g u r e 9) seemed p a r t i c u l a r l y r e l e v a n t I to our problem. Catharanthine could be converted t o d i h y d r o c a t h a r a n t h i n o l (76) using known procedures. Fragmentation of the corresponding t o s y l a t e (77) should then give the 5,18-seco-diene (78). Whereas i n • • i the a c i d c a t a l y z e d r i n g opening of dihydrocatharanthine ( f i g u r e 5) i t was necessary t o t r a p the enamine (55) from an e q u i l i b r a t i n g system, i n t h i s case, the enamine would be the r e s u l t of an i r r e v e r s i b l e fragmentation r e a c t i o n . Once t h i s enamine system were a v a i l a b l e , a number of methods might then be employed to e f f e c t a m i g r a t i o n of t h i s double bond to the d e s i r e d cleavamine system. The e x o c y c l i c methylene i n t h i s intermediate would a l s o be u s e f u l i n t h a t t h i s f u n c t i o n would provide a "handle" by which the carbomethoxy group could be r e i n t r o d u c e d . Catharanthine was r e a d i l y converted to dihydrocatharanthine by c a t a l y t i c hydrogenation u s i n g Adam's c a t a l y s t i n ethanol. L i t h i u m aluminum hydride r e d u c t i o n of t h i s product gave d i h y d r o c a t h a r a n t h i n o l 22 (76), the s t a r t i n g m a t e r i a l f o r our sequence. Treatment of dihydro-c a t h a r a n t h i n o l w i t h an excess of t o s y l c h l o r i d e i n dry p y r i d i n e gave the d e s i r e d t o s y l a t e . This m a t e r i a l f a i l e d to c r y s t a l l i z e using the 45 normal work up procedure. E x t r a c t i o n from aqueous medium gave the crude t o s y l a t e i n a p y r i d i n e s o l u t i o n . The p y r i d i n e had to be removed i n vacuo at 0°C s i n c e the presence of t h i s s o l v e n t could not be t o l e r a t e d i n the subsequent displacement step. Rapid decomposition of the t o s y l a t e occurred i f the above op e r a t i o n was conducted at room temperature. The red-brown gum thus obtained could be induced to c r y s t a l l i z e by adding a l i t t l e benzene and l e t t i n g the s o l u t i o n stand at 0°C overnight. The t o s y l a t e obtained as a l i g h t brown c r y s t a l l i n e m a t e r i a l appeared t o be - 39 -CH2OR (76), R=H (77a),R=Tos (77b),R=Mes CH, (79) (78) Figure 10. Proposed scheme f o r r i n g opening o f catharanthine to the 5,18-seco-diene system (78). s t a b l e at room temperature. A l l attempts to r e c r y s t a l l i z e t h i s m a t e r i a l f a i l e d . The i r and uv s p e c t r a of t h i s crude c r y s t a l l i n e m a t e r i a l were in accord wit h the d e s i r e d s t r u c t u r e . The benzene mother l i q u o r s from the above c r y s t a l l i z a t i o n could be fr e e z e d r i e d to give a d d i t i o n a l q u a n t i t i e s o f the t o s y l a t e as a brown amorphous powder. The t o s y l a t e could be used i n the f o l l o w i n g s t ep, however, as the crude gum provided 40 -very l i t t l e p y r i d i n e were present. \ i Displacement of the t o s y l a t e occurred r a p i d l y i n a warm s o l u t i o n l of benzene c o n t a i n i n g some t r i e t h y l a m i n e . The change of chromophore from i n d o l e to a v i n y l - i n d o l e system allowed t h i s r e a c t i o n to be conven i e n t l y monitored by uv spectroscopy. Optimum r e s u l t s were obtained by keeping the s o l u t i o n at 70°C f o r two hours under a dry n i t r o g e n atmosphere. The 5,18-seco-diene was q u i t e unstable i n s o l u t i o n when exposed to the atmosphere. The work up procedure c o n s i s t e d of c o o l i n g the s o l u t i o n under the n i t r o g e n atmosphere, f l u s h i n g i t under p o s i t i v e pressure through a very short column of d e a c t i v a t e d alumina and then s t r i p p i n g o f f the solvent at room temperature under reduced pressure. In t h i s manner, the dark brown r e a c t i o n mixture was converted to a l i g h t y e l l o w s o l u t i o n which c r y s t a l l i z e d r e a d i l y on evaporation of s o l v e n t . This m a t e r i a l (mp 129-135) was almost pure as determined by s p e c t r o s c o p i c means and was obtained i n 62% o v e r a l l y i e l d based on s t a r t i n g d i h y d r o c a t h a r a n t h i n o l . Much of our e a r l i e r work i n t h i s sequence was f r u s t r a t e d by the apparently complex mixtures obtained from t h i s r e a c t i o n as evidenced by t i c (both alumina and s i l i c a ) on the crude product as w e l l as a m u l t i t u d e of products obtained by column chromatography. I t turned out i n f a c t t h a t the 5,18-seco-diene obtained c r y s t a l l i n e and pure by the above procedure a l s o gave an extremely complex mixture on t i c (about eig h t spots on both alumina and s i l i c a ) and i t became obvious at t h i s p o i n t t h a t the m a t e r i a l was very unstable to chromatographic procedures. An a n a l y t i c a l l y pure sample, obtained by s u b l i m a t i o n , mp 136-136.5 was exposed to a d e t a i l e d s p e c t r o s c o p i c a n a l y s i s . High r e s o l u t i o n mass spectrometry gave the c o r r e c t molecular formula, ^20^24^2' ^ o r t^ i e compound. The enamine gave a strong i r ab s o r p t i o n at 1657 cm and the s i n g l e enamine proton of t h i s system appeared at x 4.29 as a broad s i n g l e t i n the nmr spectrum. The e x o c y c l i c o l e f i n was apparent as 47 pa r t of the v i n y l - i n d o l e chromophore i n the uv ( A 306), by the IIT13-X absorptions at 1408 and 880 cm 1 i n the i r , and two s i n g l e t s at T 4.75 and 4.89 i n the nmr. F i n a l l y s p e c t r o s c o p i c comparison w i t h an a u t h e n t i c sample of the 5,18-seco-diene system d e r i v e d from voacanginol-0 - t o s y l a t e ( f i g u r e 8) which d i f f e r s from our compound only i n the presence of the C^-methoxyl> e s t a b l i s h e d w i t h c e r t a i n t y that our 46 m a t e r i a l possessed the d e s i r e d s t r u c t u r e (78). Reduction of t h i s compound w i t h sodium borohydride i n methanol produced the expected e x o c y c l i c o l e f i n (79). The nmr of t h i s m a t e r i a l s t i l l showed the protons a t t r i b u t e d to the e x o c y c l i c o l e f i n i c protons as observed i n the s t a r t i n g m a t e r i a l but the s i n g l e proton s i n g l e t a t t r i b u t e d to the enamine system had disappeared. The u l t r a v i o l e t spectrum a l s o showed the same v i n y l i n d o l e chromophore. The y i e l d of the o v e r a l l sequence from dihydrocatharanthinol to the e x o c y c l i c o l e f i n (79) was optimum (72%) when the intermediate seco-diene (78) was not i s o l a t e d but immediately reduced d i r e c t l y i n the r e a c t i o n mixture. The analogous r e a c t i o n sequence us i n g the mesylate i n s t e a d of t o s y l a t e was a l s o s t u d i e d . The mesylate of dihydrocatharanthinol (77b) formed r e a d i l y by r e a c t i n g the s t a r t i n g m a t e r i a l w i t h methanesulphonyl c h l o r i d e i n p y r i d i n e at 0°C. This m a t e r i a l could be p u r i f i e d by chromatography although with c o n s i d e r a b l e l o s s and thus the best y i e l d s were obtained by the use of the crude m a t e r i a l i n the subsequent displacement r e a c t i o n . Displacement of the mesylate i n t h i s case was - 42 -c a r r i e d out using potassium t e r t - b u t o x i d e i n t e r t - b u t a n o l . The i i intermediate (78) could not be i s o l a t e d from t h i s r e a c t i o n mixture. I Sodium borohydride r e d u c t i o n of t h i s mixture gave the e x o c y c l i c o l e f i n i d e n t i c a l to that from the t o s y l a t e sequence but i n much lower y i e l d s i (20%). The above s t u d i e s had now provided, i n good y i e l d , an enamine grouping i n the nine-membered r i n g cleavamine-type system. I t was now necessary to e f f e c t an i s o m e r i z a t i o n of t h i s double.bond to the C^-C^ p o s i t i o n . Our f i r s t approach to t h i s problem was to attempt to dehydrogenate t h i s t e t r a h y d r o p y r i d i n e system to e i t h e r the d i h y d r o p y r i d i n e or the f u l l y aromatic p y r i d i n i u m s a l t . S e l e c t i v e r e d u c t i o n on e i t h e r of these intermediates i n a manner p a r a l l e l to that attempted on the a c i d c a t a l y z e d r i n g opened species d e r i v e d from dihydrocatharanthine ( c f . f i g u r e 7) c o u l d provide an entry to the cleavamine system bearing a C^-C^ (81) (83) (82) - 43 -I double bond. Although a r o m a t i z a t i o n would be the d r i v i n g f o r c e thereby j f a v o u r i n g the formation of the intermediate p y r i d i n i u m s a l t (82), an examination of the molecular models of t h i s intermediate showed i t to be s e v e r e l y s t r a i n e d and i t was thought that dehydrogenation would not occur t o t h i s extent. However, the d i h y d r o p y r i d i n i u m s a l t (81) 3 which r e t a i n s an sp h y b r i d i z e d carbon at the bridged p o s i t i o n i s not s t r a i n e d and would be expected to form. Reduction of such a system 37 had been accomplished w i t h sodium borohydride and;would lead to the d e s i r e d diene system ( c f . f i g u r e 6, 56 ->• 60). Reaction of the seco-diene (78) w i t h DDQ i n benzene at room temperature l e d to the immediate formation of a dark green p r e c i p i t a t e . T his m a t e r i a l on r e d u c t i o n w i t h sodium borohydride i n methanol l e d to a number of products, a major one being the e x o c y c l i c o l e f i n (79). The remaining products showed i n d o l e a b s o r p t i o n i n the uv s p e c t r a i n s t e a d of the v i n y l - i n d o l e system which was necessary f o r our f u r t h e r s t u d i e s . Dehydrogenation w i t h mercuric acetate l e d to a very complex mixture of products. The uv s p e c t r a of f r a c t i o n s from the chromato-graphy of t h i s mixture a l s o i n d i c a t e d an i n d o l e chromophore. An examination of the model of the d e s i r e d diene product (83) i n d i c a t e d that i t i s more, d i f f i c u l t f o r t h i s s t r u c t u r e than i t i s f o r the o l e f i n (79), to e x i s t i n a conformation which would a l l o w the e x o c y c l i c double bond to be i n the plane of the i n d o l e system and hence i n conjugation w i t h i t . Thus although the o l e f i n (79) e x h i b i t s the c h a r a c t e r i s t i c v i n y l - i n d o l e a b s o r p t i o n , the diene which could conceivab have the e x o c y c l i c double bond i n a plane orthogonal to that of the i n d o l e moiety, might i n such a case e x h i b i t a simple i n d o l e a b s o r p t i o n . The m u l t i t u d e of products obtained from the dehydrogenation r e a c t i o n s - 44 -i | could not t h e r e f o r e be ignored as being undesired m a t e r i a l s j u s t i because they e x h i b i t e d an i n d o l e a b s o r p t i o n i n the uv spectrum. From these i n i t i a l experiments i t became c l e a r that i s o l a t i o n o f the diene (83) i n reasonable y i e l d from t h i s dehydrogenation-reduction approach might be d i f f i c u l t . I t was thought that t h i s task could be s i m p l i f i e d c o n s i d e r a b l y i f t h i s compound were obtained f i r s t v i a a pathway s t a r t i n g with a model substance already c o n t a i n i n g the d e s i r e d double bond. I f the model sequence could provide the diene, i t s s t a b i l i t y , s p e c t r a l p r o p e r t i e s and p a r t i c u l a r l y procedures f o r i t s i s o l a t i o n could be s t u d i e d . I t would then be an e a s i e r matter to determine whether the dehydrogenation-reduction approach was a c t u a l l y capable of producing t h i s compound and i f so, then to set about o p t i m i z i n g the r e a c t i o n c o n d i t i o n s . The model substance which appeared i d e a l f o r t h i s study was the a l k a l o i d , catharanthine. Ring opening of c a t h a r a n t h i n o l - O - t o s y l a t e (85) would give the same intermediate (81) d e s i r e d i n the dehydrogenation r e a c t i o n . Reduction of t h i s compound would then give the diene (83). - 45 -| C a t h a r a n t h i n o l (84) obtained by l i t h i u m aluminum hydride r e d u c t i o n j of catharanthine was t o s y l a t e d i n the usual manner. This compound was subjected to c o n d i t i o n s i d e n t i c a l t o those s u c c e s s f u l l y employed i n the case o f d i h y d r o c a t h a r a n t h i n o l - O - t o s y l a t e . The product obtained j was not i s o l a t e d but subjected immediately to sodium borohydride r e d u c t i o n . A complex mixture of products was obtained. Attempts to i s o l a t e these m a t e r i a l s by chromatography l e d t o an even worse product mixture than had been observed i n the previous s t u d i e s . I t was now c l e a r that t h i s procedure would provide no simple s o l u t i o n to our problem and we turned to an a l t e r n a t i v e method f o r the p r e p a r a t i o n of the d e s i r e d diene (83) . Carbomethoxycleavamine (60) had C02Me CH20R (60) (86), R=H (87) , R=Tosyl (88) , R=Acetyl (89) _, R=3,5-Dinitrobenzoyl (83) - 46 -i ' • ' I i most of the r e q u i r e d s t r u c t u r a l f eatures and a conversion of the carbo-methoxy f u n c t i o n to a methylene group would provide the diene (83). The i carbomethoxy group i n (60) was r e a d i l y reduced by l i t h i u m aluminum hydride to 18-hydroxymethyl ., cleavamine (86). Dehydration using a v a r i e t y of c o n d i t i o n s gave no encouraging r e s u l t s . The corresponding t o s y l a t e (87) decomposed r a p i d l y to give a mixture of products. The acetate (88) was c o n s i d e r a b l y more s t a b l e and treatment w i t h strong base gave mainly unchanged s t a r t i n g m a t e r i a l . P y r o l y s i s , however, gave a product mixture which on t i c showed a continuum of spots. The 3,5-d i n i t r o b e n z o a t e (89) was prepared i n an attempt to achieve an intermediate between the unstable t o s y l a t e and s t a b l e a c e t a t e . Treatment of t h i s d e r i v a t i v e w i t h a number o f bases produced a mixture of the unreacted benzoate, the corresponding a l c o h o l and some very p o l a r m a t e r i a l s which because of t h e i r p o l a r nature could be disregarded as not being the d e s i r e d diene. This c o l l e c t i o n of negative r e s u l t s discouraged f u r t h e r work i n t h i s d i r e c t i o n and thus an a l t e r n a t e study t o e f f e c t the m i g r a t i o n of the double bond i n the seco-diene system (78) was i n i t i a t e d . Enamines are subject t o e l e c t r o p h i l i c s u b s t i t u t i o n and a d d i t i o n r e a c t i o n s ; both the n i t r o g e n and B-carbon are capable of r e a c t i n g w i t h 49 e l e c t r o p h i l e s . In our case the B - p o s i t i o n of the enamine i s a t e r t i a r y carbon and s t e r i c f a c t o r s might i n f a c t favour a t t a c k at the n i t r o g e n . However, i f r e a c t i o n d i d occur at the t e r t i a r y B - p o s i t i o n , the s u b s t i t u e n t thus introduced should be e a s i l y e l i m i n a t e d and thereby r e i n t r o d u c e a double bond i n t o the system. - 47 -j . | The r e a c t i o n of choice i n our case was hydroboration. Hydrobora-t i o n of enamines has been used i n the conversion^ of ketones to alkenes v i a an intermediate enamine. In our system, hydroboration f o l l o w e d by RCOOH o x i d a t i o n would be expected t o introduce an hydroxyl f u n c t i o n at the p o s i t i o n . This i s the same p o s i t i o n which bears the hydroxyl i n the n a t u r a l dirners v i n b l a s t i n e (16) and v i n c r i s t i n e (19) . The a l c o h o l obtained from t h i s r e a c t i o n would t h e r e f o r e be a v a l u a b l e intermediate f o r subsequent d i m e r i z a t i o n r e a c t i o n s . Furthermore t e r t i a r y a l c o h o l s r e a d i l y dehydrate to the corresponding o l e f i n s . I t had already been shown that velbanamine (22), the monomeric u n i t d e r i v e d from the degrada-t i o n of v i n b l a s t i n e , dehydrated to give cleavamine (23) under a c i d i c 21 c o n d i t i o n s . This approach could t h e r e f o r e a l s o be expected to y i e l d the unsaturated compound (86) having the double bond i n the d e s i r e d C_-C. p o s i t i o n . I t was expected that the e x o c y c l i c double bond would 48 a l s o be hydrated i n t h i s process. O x i d a t i o n of the primary a l c o h o l thus formed, f o l l o w e d by e s t e r i f i c a t i o n of the ackd would provide a convenient method f o r i n t r o d u c i n g the carbomethoxy f u n c t i o n . (78) CH o0H 2 (90) CH 20H (86) In the course of t h i s work and i n subsequent hydroboration e x p e r i -ments, i t was found that the t e r t i a r y n i t r o g e n i n these compounds could complex with the diborane.to form amine-borane adducts. These adducts were s t a b l e t o chromatographic s e p a r a t i o n and could be i s o l a t e d i n t h i s manner as c r y s t a l l i n e m a t e r i a l s . As a c l a s s of compounds these amine-borane complexes are e a s i l y i d e n t i f i e d by a medium t o s t r o n g , f a i r l y % -1 broad a b s o r p t i o n bonds i n the i r spectrum i n the r e g i o n 2200-2400 cm u s u a l l y accompanied by a sharp a b s o r p t i o n at about 2300 cm-''' which i s an overtone o f the BH^ asymmetric deformation seen at about 1150 cm~*.^" - 49 -i i A convenient method was found to convert these amine-borane complexes to the f r e e bases. This procedure simply i n v o l v e d exchange of the b o r i n e from one amine base t o a stronger amine base. Thus, the complex when r e f l u x e d i n t e t r a h y d r o f u r a n i n the presence of t r i e t h y l a m i n e , provided the f r e e base and t r i e t h y l a m i n e - b o r a n e . Some of the complexes obtained were found to undergo only p a r t i a l exchange using t h i s procedure; an e q u i l i b r i u m mixture was obtained. In these cases, complete exchange could be achieved by u s i n g t r i e t h y l a m i n e as s o l v e n t at r e f l u x i n g temperature. The hydroboration of the seco-diene system (78) i n t e t r a h y d r o f u r a n using an excess of diborane, l e d t o a mixture of products. One of these was shown t o be the amine-borane complex of the major decomposition product observed p r e v i o u s l y i n other r e a c t i o n s of the enamine system. Three other m a t e r i a l s of i n t e r e s t were obtained. The i r s p e c t r a of these compounds i n d i c a t e d t h a t one was the a l c o h o l and the other two were amine-boranes. Both of these compounds gave on exchange a compound which was i d e n t i c a l w i t h the a l c o h o l obtained d i r e c t l y from the r e a c t i o n mixture. The presence of two amine-boranes which y i e l d on exchange the same compound i n d i c a t e s t h a t these compounds are most l i k e l y epimeric at the n i t r o g e n atom. It. i s w e l l known that amines undergo f a c i l e i n v e r s i o n and i t i s reasonable to expect that each of the i n v e r s i o n epimers formed by t e r t i a r y amines could be trapped by complexing with the lone p a i r of e l e c t r o n s . The a l c o h o l obtained from t h i s hydroboration r e a c t i o n showed i n the i r spectrum, an a b s o r p t i o n at 3300 cm * (v 0-H) and at 1045 cm ^ (v C-0 f o r primary a l c o h o l s ) while the uv gave a t y p i c a l i n d o l e a b s o r p t i o n . - 50 -j Nmr showed a l o s s of both the enamine proton and the two protons of the e x o c y c l i c methylene. Two m u l t i p l e t s of i n t e r e s t appeared, a one proton i q u i n t u p l e t (two overlapping t r i p l e t , J = 9 and 5 Hz) at T 5.81 and a two proton doublet (J = 5 Hz) at T 6.24. In a decoupling experiment, i r r a d i a t i o n at the frequency of the doublet, reduced the q u i n t u p l e t to a broad doublet (J = 9 Hz). These data were i n accord w i t h the h y d r a t i o n of the e x o c y c l i c o l e f i n which would give an hydroxymethyl grouping on a t e r t i a r y carbon. No evidence f o r the h y d r a t i o n of the enamine par t of t h i s molecule was obtained although i t was c l e a r from the i r and nmr, that the enamine was no longer present i n the product. The mass spectrum gave the f i r s t i n d i c a t i o n that t h i s a l c o h o l was not the d e s i r e d d i o l (90) . The molecular i o n was seen at m/e 312 i n s t e a d o f the expected value of 326, and showed a fragmentation p a t t e r n i n d i c a t i n g r e d u c t i o n of the enamine r a t h e r than h y d r a t i o n . A pure sample of the a l c o h o l obtained by s u b l i m a t i o n (mp 146.5-147.5) gave the c o r r e c t a n a l y s i s f o r the reduced enamine a l c o h o l . To e s t a b l i s h the i d e n t i t y of t h i s compound, the o l e f i n (79) was hydroborated. As i n the previous case, two amine-borane complexes were i s o l a t e d along w i t h the f r e e a l c o h o l . Exchange of these complexes w i t h t r i e t h y l a m i n e produced the same f r e e a l c o h o l . This a l c o h o l (92) was i d e n t i c a l w i t h that obtained from the seco-diene as shown by comparison of s p e c t r a l data, t i c , and m e l t i n g p o i n t s . C02Me (32) Reduction of 188-carbomethoxy-48-dihydrocleavamine (93) with l i t h i u m aluminum hydride gave the same a l c o h o l (92) and e s t a b l i s h e d without doubt that the s t r u c t u r e of the a l c o h o l obtained from both the o l e f i n (79) and secodiene (78) by hydroboration was 186-hydroxymethyl-43-dihydrocleavamine. In an attempt to l i m i t the r e d u c t i o n of the enamine system, a number of hydroboration experiments were run using decreasing amounts of diborane. In the above hydroboration of the secodiene system a ten-f o l d excess of diborane had been employed. When t h i s excess decreased to 0.5 moles based on mono-alkylboranes being formed r a t h e r than d i -or t r i - a l k y l b o r a n e s , the o l e f i n (79) and i t s amine-borane were i s o l a t e d from the r e a c t i o n mixture i n a d d i t i o n to the products noted -• 52 -before. Reduction of the enamine system, t h e r e f o r e , was o c c u r r i n g before hydroboration of the e x o c y c l i c double bond. When the excess of diborane was f u r t h e r decreased, carbonyl c o n t a i n i n g products were obtained i n d i c a t i n g h y d o l y s i s of unreacted enamine presumably i n the work up. ' ' These r e s u l t s show that the d e s i r e d h y d r a t i o n of t h i s enamine system could not be achieved by hydroboration and thus an a l t e r n a t e route had to be devised. A number of reagents have been used to 52 oxygenate enamines. The r e a c t i o n g e n e r a l l y gives a g-oxygenated iminium s a l t intermediate which normally i s then hydrolyzed to give the a-oxygenated carbonyl system. In our case h y d r o l y s i s was not p e r m i s s i b l e and the intermediate imminium s a l t would have to be reduced to give the g-oxygenated amine. O x i d a t i o n i n the presence of an i n d o l e moiety, however, g e n e r a l l y presents a problem because 53 the i n d o l e group i s i t s e l f r a p i d l y o x i d i z e d under m i l d c o n d i t i o n s . The use of the conventional reagents f o r enamine o x i d a t i o n s , such as p e r a c i d s , was t h e r e f o r e not s u i t a b l e . Our choice of reagent f o r t h i s r e a c t i o n was osmium t e t r o x i d e . Although there have been no previous r e p o r t s of t h i s reagent having been used f o r the h y d r o x y l a t i o n of enamines, examples of i t s use i n other systems i n d i c a t e d that i t would probably serve w e l l i n c a r r y i n g out the r e q u i r e d t r a n s f o r m a t i o n . For example, g - a l l y l i n d o l e had been o x i d i z e d to 3,3' - i n d o l y l p r o p a n - 1 , 2 - d i o l i n high y i e l d u s i n g osmium 54 t e t r o x i d e at low temperature. Under these c o n d i t i o n s , the i n d o l e system was una f f e c t e d and r e a c t i o n was s p e c i f i c to the double bond. Use of t h i s r e a c t i o n was made subsequently by van Tamelen i n h i s - 53 -i i yohimbine syntheses to achieve hydroxy1ation of the c y c l i c enol (94) to the d i o l ( 9 5 ) . I n both of the above i n s t a n c e s , the double bond which i s o x i d i z e d i s a c t i v a t e d to e l e c t r o p h i l i c a t t a c k . The enamine double bond would a l s o be expected to undergo f a c i l e a t t a c k and i t seemed reasonable t h a t h y d r o x y l a t i o n should occur under these c o n d i t i o n s . The r e a c t i o n scheme envisaged f o r the conversion of the secodiene (78) to cleavamine and/or velbanamine i s presented i n f i g u r e 11. The t e t r o l (96) r e s u l t i n g from the osmylation of 78 would be expected to undergo s e l e c t i v e r e d u c t i o n to the t r i o l (97) and the l a t t e r , v i a pe r i o d a t e cleavage and r e d u c t i o n should provide the d i o l (99). Hydrogenolysis of the " b e n z y l i c " a l c o h o l i n t h i s compound would then give (100) which should be e i t h e r velbanamine (22) or i t s epimer. Dehydration of t h i s compound would give cleavamine (23). The osmylation r e a c t i o n was c a r r i e d out at dry-ice-acetone temperature u s i n g e x a c t l y two eq u i v a l e n t s of osmium t e t r o x i d e i n a t e t r a h y d r o f u r a n - p y r i d i n e solvent system. The major product obtained i n 35-40% y i e l d gave s p e c t r a l i n d i c a t i o n s of being the c o r r e c t t e t r o l . - 54 -CH OH (98) (97) (23) gure 11. Synthesis of cleavamine (23) from the secodiene (83) osmium t e t r o x i d e o x i d a t i o n . - 55 -The uv spectrum showed a t y p i c a l i n d o l e absorption while the i r spectrum confirmed the presence of an a l c o h o l with three broad overlapping bands i n the r e g i o n , 3300-3500 cm *. No molecular i o n could be seen i n the mass spectrum, ( f i g u r e 12) the highest peak appearing at m/e 342 (M-18).: High r e s o l u t i o n mass measurement e s t a b l i s h e d the formula ^20^26^2^3' c o r r e s P o n ( i i n g not unexpectedly, to a l o s s of water from the molecular formula ^20^28^2^4' ^ e n m r s P e c 1 : r u m °f t h i s compound ( f i g u r e 14) was p a r t i c u l a r l y i n s t r u c t i v e . A one-proton s i n g l e t at T 5.42 58 was i n the expected p o s i t i o n f o r a carbinol-amine proton. A somewhat broadened s i n g l e t at x 6.36, i n t e g r a t i n g f o r two protons and which showed a dramatic sharpening on deuterium exchange, could be assigned to the hydroxymethyl f u n c t i o n . Deuterium exchange r e s u l t e d i n the l o s s of at l e a s t three protons, other than the i n d o l e N-H, as shown by comparison of the i n t e g r a l before and a f t e r exchange. Two of these hydroxyl protons appeared as s u r p r i s i n g l y sharp s i n g l e t s at x 6.58 and x 7.51 and t h i s r e s u l t i n d i c a t e s that these protons are probably e x p e r i e n c i n g strong i n t r a m o l e c u l a r hydrogen bonding. The r e l a t i v e l y non-polar nature of t h i s compound as shown on t i c and column chromatography undoubtedly a l s o r e f l e c t s t h i s same phenomenon. I t was expected that the carbinol-amine hydroxyl f u n c t i o n would r e a d i l y undergo hydrogenolysis w i t h a metal hydride reducing agent. The complex normally obtained from the r e a c t i o n of an a l c o h o l i c f u n c t i o n and the hydride would e l i m i n a t e r e a d i l y to form an iminium s a l t i n termediate. This intermediate i n the presence of a d d i t i o n a l metal hydride would r a p i d l y form the s a t u r a t e d amine. The t e t r o l was, t h e r e f o r e , t r e a t e d at room temperature w i t h sodium R E L A T I V E INTENSITY RELATIVE INTENSITY - 9S " - 58 -i i | borohydride i n methanol. The r e s u l t a n t compound formed i n e s s e n t i a l l y q u a n t i t a t i v e y i e l d had a l l the p r o p e r t i e s expected f o r the t r i o l (97). The mass spectrum ( f i g u r e 13) gave a parent i o n at m/e 344 and high r e s o l u t i o n of t h i s peak e s t a b l i s h e d the formula, C20 H28 N2°3' 0 n e of the important f e a t u r e s of t h i s spectrum i s the fragment i o n at m/e 154. By analogy w i t h the mass s p e c t r a l work done on velbanamine, t h i s i o n can be considered to r e s u l t from the fragmentation shown i n s t r u c t u r e 101.* 4 I t t h e r e f o r e presented good evidence f o r the presence CH 20H (101) of an hydroxy1 f u n c t i o n i n the p i p e r i d i n e p o r t i o n of the compound. The i r spectrum showed three broad overlapping absorptions i n the N-H, 0-H s t r e t c h i n g r e g i o n . Comparison of the nmr ( f i g u r e 15) of t h i s compound with t h a t . o f the t e t r o l showed the l o s s of the s i n g l e t a t t r i b u t e d to the c a r b i n o l amine proton. The two-proton s i n g l e t of the hydroxymethyl f u n c t i o n was s t i l l present, appearing now at T 6.22. Deuterium exchange i n d i c a t e d a l o s s of three protons other than the i n d o l e N-H; only one of these hydroxyl protons can be seen as a broad s i n g l e t at x 0.29. Loss of the other two protons i s shown by the i n t e g r a t i o n a f t e r deuterium exchange - 60 -I | Further hydrogenolysis of the t r i o l could be achieved when i t i was t r e a t e d w i t h l i t h i u m aluminum hydride i n r e f l u x i n g t e t r a h y d r o f u r a n . Under these c o n d i t i o n s , the " b e n z y l i c " hydroxyl at C^g (see 102) was l o s t . Although t h i s r e a c t i o n was not on the main s y n t h e t i c pathway, the production of t h i s d i o l (102) was u s e f u l because i t s nmr spectrum proved c o n c l u s i v e l y the osmylation of the e x o c y c l i c o l e f i n p o r t i o n of the s t a r t i n g secodiene. The nmr spectrum of 102 possessed a (97) (102) q u i n t u p l e t at T 5.90 ( J = 5 Hz) and a doublet at T 6.28 ( J = 5 Hz), v i r t u a l l y i d e n t i c a l to the m u l t i p l e t s observed f o r 18g-hydroxymethyl-cleavamine (86) and 183-hydroxymethyldihydrocleavamine (92) ( f i g u r e 16). I t was thus c e r t a i n that the compound obtained from r e d u c t i o n of the t r i o l 97 was represented by 102. For the purpose of completing the cleavamine and f u n c t i o n a l i z e d cleavamine syntheses i t was necessary to remove the C^g-hydroxymethyl f u n c t i o n and reduce t h i s C 1 Q p o s i t i o n to i t s s a t u r a t e d s t a t e . The f i r s t step i n t h i s process was the p e r i o d a t e cleavage of the v i c i n a l g l y c o l p o r t i o n of the t r i o l . The best y i e l d , (about 60% based on t r i o l consumed) was obtained when t h i s r e a c t i o n was c a r r i e d out i n an - 61 -Chemical s h i f t i n x of C. --proton 1 8 A 188-hydroxymethyl-cleavamine 5.74 methylene protons, B 6.32 183-hydroxymethyl-48-dihydrocleavamine 5.84 d i o l (102) 5.90 6.27 6.28 i A B Figure 16. P a r t i a l nmr spectrum i l l u s t r a t i n g the p e r t i n e n t s i g n a l p a t t e r n s corresponding to the 18B-hydroxymethyl f u n c t i o n . acetone-water s o l u t i o n at 0°C. The s p e c t r a l data of the product was^ i n e x c e l l e n t agreement with that expected f o r the k e t o l (98). This molecule has one remaining hydroxyl f u n c t i o n and t h i s f e a t u r e was evident i n the i r spectrum by a broad 0-H s t r e t c h i n g a b s o r p t i o n at 3100 cm * and i n the nmr by a broad one-proton s i n g l e t at x 7.82 which disappeared o n deuterium exchange. The extended conjugation produced by the C^g carbonyl f u n c t i o n a f f e c t s the aromatic absorption i n the uv and the carbonyl ab s o r p t i o n i n the i r r e g i o n s . A t y p i c a l 2-a c y l i n d o l e a b s o r p t i o n 5 6 ( x M e 0 H ( l o g E ) : 317 (4.25), and 238 (4.16)) i s IT13.X 62 observed in the uv and the carbonyl s t r e t c h i n g absorption i n the i r -1 57 i s observed at 1615 cm which i s a l s o normal f o r t h i s system. Further strong evidence f o r t h i s s t r u c t u r e came from the mass spectrum ( f i g u r e 17). High resolution on the parent i o n gave a molecular composition corresponding to the formula of the k e t o l . Examination of the spectrum ( f i g u r e 17) showed a prominent fragment i o n at m/e 154. A fragmentation analogous to the one shown f o r the t r i o l , namely f i s s i o n a and a 1 i n 103 would be expected to provide t h i s i o n . Loss of a 14 mass u n i t s (probably CH^) from t h i s i o n would (103) r e s u l t i n the peak at m/e 140. The other h a l f of the molecule r e s u l t i n g from the f i s s i o n a, a', could provide the i o n at m/e 157. The a l t e r n a t e fragmentations shown as b, a' could account f o r fragments at m/e 143 and 144, while f i s s i o n a, c would produce the i o n observed at m/e 130. Reduction of the k e t o l to the d i o l (99) could be r e a d i l y achieved by the a c t i o n of sodium borohydride i n methanol at room temperature. This r e d u c t i v e process regenerated the i n d o l e system and t h i s was apparent from the uv spectrum. Once again the mass spectrum ( f i g u r e 18) supported the c o r r e c t s t r u c t u r e . The main fragment i o n appeared at m/e 154 and a high r e s o l u t i o n mass measurement on the strong parent peak RELATIVE INTENSITY RELATIVE INTENSITY - £9 " - 64 -| gave the molecular composition corresponding to the formula f o r the d i o l . | On the b a s i s of the nmr spectrum ( f i g u r e 19), the stereochemistry at C 1 C, one of the three asymmetric centres i n t h i s molecule, could be 16 j assigned. In the course of e a r l i e r s t u d i e s i n our l a b o r a t o r y on the 37 a c i d c a t a l y z e d r i n g opening of catharanthine and i n the t o t a l synthes 59 of dihydrocatharanthine a l l u d e d to e a r l i e r , a s e r i e s of dihydro-cleavamine d e r i v a t i v e s possessing a v a r i e t y of s u b s t i t u e n t s (carbo-methoxyl, methoxyl, hydroxyl and n i t r i l e ) at C^g had been obtained. I t was found that these compounds could be c l a s s e d i n t o two groups, those w i t h the C 1 0 - p r o t o n absorbing i n the r e g i o n x 4.5-5.0, and its those absorbing i n the re g i o n x 6.0-6.2. These compounds by v i r t u e of these chemical s h i f t s , could be assigned to the 18g-substituted or 18a-sub s t i t u t e d s e r i e s r e s p e c t i v e l y . The reason f o r t h i s dramatic dependence of the chemical s h i f t of t h i s proton to i t s stereochemistry can be appreciated by c o n s i d e r i n g the conformational s t r u c t u r e s which 37 60 are p o s s i b l e i n these two s e r i e s . ' In the 183-substituted compounds (104) (105) ! - 66 -(104) the C,g-proton i s i n c l o s e p r o x i m i t y to the b a s i c n i t r o g e n atom of the p i p e r i d i n e moiety and i t would be expected to absorb at lower i' frequency. ] Such a s i t u a t i o n does not p r e v a i l f o r the 18a-s u b s t i t u t e d compounds (105) and a more normal resonance frequency would be a n t i c i p a t e d f o r the C 1 D - p r o t o n . The chemical s h i f t observed f o r the C, 0-proton i n the d i o l (99) 1 o i s T 4.28. This i s c l e a r l y i n the r e g i o n f o r the 188-substituted com-pounds although i n t h i s case i t i s s h i f t e d to s l i g h t l y lower f i e l d than i n the above mentioned compounds. This enhanced d e s h i e l d i n g e f f e c t must be a t t r i b u t e d to the a l c o h o l s u b s t i t u e n t s which can be expected to a f f e c t the conformation of the p i p e r i d i n e r i n g and hence, a l t e r the s p a t i a l r e l a t i o n between the n i t r o g e n and C^g-proton. This same e f f e c t can be seen by a comparison of the C^g-proton chemical s h i f t f o r 18B-carbomethoxy-48-dihydrocleavamine and 188-carbomethoxy-46-dihydrocleavamine i n which the e t h y l group would a f f e c t the conformation depending on i t s o r i e n t a t i o n r e l a t i v e to the n i t r o g e n atom. The 4a-compound absorbs at T 4.53 while the 48 absorbs at T 4.98. Hydrogenolysis of the d i o l (99) to the monohydroxy d e r i v a t i v e (100) could be achieved using < the c o n d i t i o n s p r e s c r i b e d by Dolby and coworkers. These workers found that 2 - i n d o l e c a r b i n o l d e r i v a t i v e s were hydrogen-o l y z e d u s i n g l i t h i u m aluminum hydride i n ether s o l v e n t s . When e t h y l ether or t e t r a h y d r o f u r a n was used as s o l v e n t , a mixture of the a l c o h o l and the hydrogenolyzed m a t e r i a l was u s u a l l y obtained. The p r o p o r t i o n of hydrogenolyzed m a t e r i a l could be r a i s e d by c a r r y i n g out the r e a c t i o n i n r e f l u x i n g N-methylmorpholine or i n dioxane. Thus, • - 67 -1-hydroxytetrahydrocarbazole was converted almost q u a n t i t a t i v e l y to t e t r a h y d r o c a r b a z o l e u s i n g b o i l i n g dioxane. N-methyl-l-hydroxytetra-hydrocarbazdle, however, gave only 21% of the hydrogenolyzed product. This i n h i b i t i o n of hydrogep.olysis by methylation of the i n d o l e n i t r o g e n was observed i n a s e r i e s of compounds and suggested t h a t the r e a c t i o n i n v o l v e d an e l i m i n a t i o n - a d d i t i o n sequence i n v o l v i n g an imine i n t e r -mediate such as (106). Such a mechanism i s not p o s s i b l e when the (106) i n d o l e n i t r o g e n i s methylated and i t was suggested that under d r a s t i c c o n d i t i o n s some simple n u c l e o p h i l i c displacement takes p l a c e to . give the low y i e l d of the hydrogenolyzed product observed. In our i n s t a n c e , the d e s i r e d d e r i v a t i v e (100) could be obtained from the d i o l i n 44% y i e l d using l i t h i u m aluminum hydride i n r e f l u x i n g N-methylmorpholine. The nmr spectrum of the_product ( f i g u r e 20) shows tha t the peak assigned to the C^g-proton i n the d i o l has moved con s i d e r a b l y u p f i e l d to x 6.56 and now appears as a complex m u l t i p l e t . This u p f i e l d s h i f t was expected on l o s s of the geminal hydroxyl f u n c t i o n . The remaining 0-H gives a broad, one-proton s i n g l e t at x 8.77 which disappears on deuterium exchange. High r e s o l u t i o n mass' - 69 -a n a l y s i s of the parent i o n i n the mass spectrum e s t a b l i s h e d a molecular composition c o n s i s t e n t with the formula f o r the mono-ol. This compound had to be e i t h e r velbanamine (22), the monomeric degradation product of v i n b l a s t i n e and v i n c r i s t i n e or the epimeric a l c o h o l . Thin l a y e r chromatographic comparison of our compound with an a u t h e n t i c sample of velbanamine obtained by the e s t a b l i s h e d procedure from 21 v i n b l a s t i n e , showed that these compounds were hot the same. The j mass spectrum of our compound which has been named isovelbanamine ( f i g u r e 21) was, however, v i r t u a l l y superimposable with the spectrum obtained f o r velbanamine run under the same c o n d i t i o n s and agrees 6 2 a l s o very w e l l w i t h the p u b l i s h e d mass spectrum f o r velbanamine. This r e s u l t provided strong evidence f o r the f a c t that these compounds were epimeric and t h i s s i t u a t i o n was proved by the next s e r i e s of r e a c t i o n s . I t was known th a t velbanamine undergoes some dehydration to give 2 cleavamine (23) under the a c i d i c c o n d i t i o n used to cleave v i n b l a s t i n e . Because the hydroxyl group e l i m i n a t e d i s that of a t e r t i a r y a l c o h o l , an type e l i m i n a t i o n which need not have a p a r t i c u l a r stereochemical requirement, would be expected. Therefore isovelbanamine should dehydrate under the same .conditions as velbanamine. Treatment of isovelbanamine w i t h concentrated s u l p h u r i c a c i d at 0°C f o r 2 hours gave approximately a 30% y i e l d of cleavamine as i d e n t i f i e d by a comparison w i t h an a u t h e n t i c sample. Apart from e s t a b l i s h i n g the s t r u c t u r e of 100, t h i s r e a c t i o n provided a t o t a l s y n t h e s i s of cleavamine s i n c e the s t a r t i n g m a t e r i a l f o r t h i s sequence dihydrocatharanthine, had already been sy n t h e s i z e d i n our l a b o r a t o r y . 100 8 OH B 601 z LU h-- 4CH u > u 154 •if l* I »illll ..tltl .In H.hll I M 298 Ii llii. uliii iih •• i J i I M il T—"i 1 1 r m / e 100 I r 150 - i . 1 r 200 i • | r 2 5 0 Figure 21. Mass spectrum of isovelbanamine (100). T 1 1 1 — i r 300 --a o 100' 80H >-to 2 Ul 6CH 40H LU > 5 2CH LU 154 'iillll I illlli III lllilll i ihi li ill illl 11 llil llllll|i llii Ii l 298 | 1 1 1 1 T — r 100 -i r 150 ] 1 1 1 1 1 1 I i 1 1 r 300 i i i m / e Q U 200 250 Figure 22. Mass spectrum of 3a-hydroxy-4B-dihydrocleavamine. - 71 -I t was now of i n t e r e s t to extend t h i s sequence f u r t h e r to the syn t h e s i s of catharanthine s i n c e the transannular c y c l i z a t i o n r e a c t i o n discussed p r e v i o u s l y should a l l o w conversion of a carbomethoxy-cleavamine to t h i s a l k a l o i d . The problem of i n t r o d u c i n g a C^g carbomethoxy f u n c t i o n i n t o the cleavamine molecule was now at hand. The f i r s t p a r t of the r e q u i s i t e r e a c t i o n sequence (23 — 1 0 9 , f i g u r e 23) i s a s p e c i a l case of a general type of r e a c t i o n undergone by the i n d o l e system. This was f i r s t recognized by Tay l o r who proposed the scheme shown i n f i g u r e 24 to e x p l a i n a number of t r a n s -63 formations present i n the l i t e r a t u r e . E l e c t r o p h i l i c a t t a c k at the r e a c t i v e B - p o s i t i o n of the i n d o l e system produces the in d o l e n i n e s (111a) and (111b) which are i n e q u i l i b r i u m w i t h each other. The in d o l e n i n e (111b) i s a c t i v a t e d towards n u c l e o p h i l i c a t t a c k at the carbon adjacent to the a - p o s i t i o n of the o r i g i n a l i n d o l e system and such a r e a c t i o n leads to the f u n c t i o n a l i z a t i o n at t h i s carbon. Buchi's 33 conversion of ibogaine (112) to voacangine (113), presented an analogy to the tra n s f o r m a t i o n d e s i r e d i n our sequence. 59 The s t u d i e s i n our l a b o r a t o r y on dihydrocleavamine i n d i c a t e d , however, that the n i t r i l e i n t r o d u c t i o n at the 1 8 - p o s i t i o n u s i n g the c h l o r o i n d o l e n i n e d i r e c t l y was a very poor y i e l d i n g process. A s u b s t a n t i a l improvement was achieved by f i r s t c o n v e r t i n g the c h l o r o i n d o l e n i n e of 4B-dihydrocleavamine (41) to i t s quaternary ammonium s a l t (115) and then t r e a t i n g t h i s s a l t w i t h cyanide-to obtained the n i t r i l e (42). The formation of t h i s s a l t , was r e a d i l y achieved by the r e a c t i o n o f the c h l o r o i n d o l e n i n e w i t h acetate i o n i n g l a c i a l a c e t i c a c i d , g i v i n g the 18-acetoxydihydrocleavamine (114) as (111a) (111b) Figure 24. Ta y l o r ' s r e a c t i o n scheme f o r f u n c t i o n a l i z a t i o n u s i n g i n d o l e n i n e i n t e r m e d i a t e s . - 73 -an i n t e r m e d i a t e . This compound under the c o n d i t i o n s of the r e a c t i o n , undergoes i n t r a m o l e c u l a r displacement of the acetoxy f u n c t i o n r e s u l t i n g i n q u a t e r n i z a t i o n . Thus the unstable c h l o r o i n d o l e n i n e was (41) OAc (114) (115) - 74 -converted to a much more s t a b l e compound, the s a l t (115) . N u c l e o p h i l i c a t t a c k on t h i s s a l t at the 1 8 - p o s i t i o n by the cyanide could be achieved and produced the d e s i r e d n i t r i l e . Because of the experience a v a i l a b l e from the work i n the dihydro-cleavamine s e r i e s , i t was a r e l a t i v e l y simple matter to convert c l e a v -amine to 183-cyanocleavamine. The o x i d a t i o n w i t h t e r t - b u t y l h y p o c h l o r i t e was c a r r i e d out at -15°C to form the c h l o r o i n d o l e n i n e (107). The c h l o r o i n d o l e n i n e s are i n general r e a c t i v e intermediates and no attempt was made to i s o l a t e t h i s m a t e r i a l . Instead, i t was t r e a t e d immediately w i t h fused sodium acetate i n a s o l u t i o n of g l a c i a l a c e t i c a c i d and a c e t i c anhydride to form the quaternary ammonium s a l t (108). Rigorous precautions were taken to prevent the presence of water i n the system during the p r e p a r a t i o n of the s a l t and the subsequent n i t r i l e i n t r o -d u c t i o n . The very p o l a r nature of the quaternary ammonium s a l t made i t d i f f i c u l t to work with t h i s m a t e r i a l and i t was found convenient to immediately t r e a t the s a l t w i t h a large excess of potassium cyanide i n r e f l u x i n g dimethylformamide. The d e s i r e d 18g-cyanocleav-amine (109) was obtained i n 30% y i e l d based on s t a r t i n g cleavamine. This compound e x h i b i t e d the expected s p e c t r a l p r o p e r t i e s , i n p a r t i c u l a r , the c h a r a c t e r i s t i c n i t r i l e s t r e t c h i n g bond was observed i n the i r r e g i o n at 2240 cm High r e s o l u t i o n mass spectrometry e s t a b l i s h e d the c o r r e c t molecular composition f o r the strong parent peak observed. The nmr spectrum of t h i s compound ( f i g u r e 25), showed a one-proton doublet of doublets at T.4.48 ( J = 2 and 10 Hz). This m u l t i p l e t corresponded very c l o s e l y to one observed i n the spectrum of 18g-cyano-4g-dihydro-cleavamine (T 4.55, J = 2 and 10 Hz) and was assigned to the C 1 R-pro'ton. - 76 -On the basis of the chemical s h i f t of t h i s m u l t i p l e t , the stereochemistry i of the Cjg substituent could be assigned as having the 8-configuration. The major d i f f e r e n c e observed between t h i s spectrum and the one observed f o r the dihydro analogue could be explained by the a d d i t i o n a l double i bond i n the molecule. A broad one-proton doublet at T 4.74 was observed f o r the v i n y l proton and the three proton methyl t r i p l e t at x 8.96 was s l i g h t l y deshielded r e l a t i v e to i t s normal p o s i t i o n (x 9.1-9.3) observed i n the saturated analogues possessing the cleavamine skeleton. The hydrolysis of the n i t r i l e could be achieved only under f a i r l y d r a s t i c conditions (20% potassium hydroxide i n diethylene g l y c o l at 150°C f o r nine hours). E s t e r i f i c a t i o n of the acid with diazomethane gave the desired 188-carbomethoxycleavamine (60) i n about 50% y i e l d based on s t a r t i n g n i t r i l e . The product was i d e n t i f i e d by comparison with an authentic sample of 188-carbomethoxycleavamine. The synthetic material had the same melting point, i d e n t i c a l t i c properties and gave an i r spectrum which was superimposable with that of the authentic sample. The transannular c y c l i z a t i o n of 188-carbomethoxycleavamine to 64 catharanthine had already been accomplished i n our laboratory and thus the t o t a l synthesis of 188-carbomethoxycleavamine also completed the t o t a l synthesis of the a l k a l o i d , catharanthine (12). Our f i r s t main objective, the t o t a l synthesis of catharanthine and cleavamine had therefore been achieved. Hence a l l further studies i n t h i s s e r i e s which used compounds derived from catharanthine as s t a r t i n g - 77 -j m a t e r i a l s , could be considered t o t a l l y s y n t h e t i c . Our next considera-t i o n was the i n t r o d u c t i o n of the a p p r o p r i a t e f u n c t i o n a l i t i e s at the and p o s i t i o n s of the cleavamine systems. As explained e a r l i e r , these compounds were important to us as intermediates f o r subsequent d i m e r i z a t i o n work. The r e a c t i o n sequence which was o u t l i n e d above already gave us a s e r i e s of compounds having the hydroxyl f u n c t i o n . The stereochemistry at t h i s centre,as e s t a b l i s h e d i n isovelbanamine (100), d i f f e r s from that at the corresponding centre i n the n a t u r a l dimers. These compounds would be v a l u a b l e i n our d i m e r i z a t i o n work s i n c e they would lead to the s y n t h e s i s of d i m e r i c m a t e r i a l s epimeric at and u l t i m a t e l y a l l o w the e v a l u a t i o n of the importance of the stereochemistry at t h i s centre to b i o l o g i c a l a c t i v i t y . The syntheses of the isomeric a l c o h o l s , that i s , velbanamine (22) and those having the hydroxyl f u n c t i o n at C^, were now d e s i r e d . The l e a s t amount of d i f f i c u l t y was a n t i c i p a t e d w i t h the i n t r o d u c t i o n of the hydroxyl f u n c t i o n at the secondary carbon atom and t h i s became our f i r s t c o n s i d e r a t i o n . Our approach to t h i s was simply to hydroborate cleavamine (23). I t has been w e l l e s t a b l i s h e d that hydroboration i s a s t e r i c a l l y s e n s i t i v e p r o c e s s ^ and i t was expected the secondary a l c o h o l would be obtained e x c l u s i v e l y . I t was d i f f i c u l t to p r e d i c t whether a mono-alkyl or d i - a l k y l b o r a n e would form i n t h i s r e a c t i o n or whether complexing with the b a s i c n i t r o g e n would compete with a t t a c k at the double bond. The q u a n t i t y of diborane needed i n our i n i t i a l e x p e r i -ments could not, t h e r e f o r e , be c a l c u l a t e d and was gauged by the disappearance of the s t a r t i n g m a t e r i a l , cleavamine, as seen by t i c . An experiment conducted i n such a manner l e d to the i s o l a t i o n of a - 78 -i I I c r y s t a l l i n e m a t e r i a l i n about 80% y i e l d . This m a t e r i a l turned out to be an amine-borane which on treatment w i t h t r i e t h y l a m i n e i n t e t r a h y d r o -f u r a n gave back the s t a r t i n g cleavamine. This amine-borane was thus simply the cleavamine N-borane adduct (116) and no hydroboration of the double bond had been achieved. (23) (116) (117) OH An i n t e r e s t i n g experiment was c a r r i e d out w i t h t h i s amine-borane. c I t had been reported that the amine-borane/of simple amines are u s e f u l as hydroborating a g e n t s . 6 5 An e q u i l i b r i u m i s set up between the amine-borane and f r e e amine at high temperatures and the borine thus R 3 N : B H 3 R 3 N + 1 / 2 ( B H 3 ) 2 3RCH=CH2 + 1/2 (BH) »- (RCH CH ) B l i b e r a t e d i s a v a i l a b l e f o r the normal hydroboration r e a c t i o n . In our case, we had i n f a c t a source of b o r i n e b u i l t i n t o our molecule and i t was a n t i c i p a t e d that at e l e v a t e d temperature, an i n t r a or i n t e r m o l e c u l a r t r a n s f e r of borine from the n i t r o g e n to the double bond would take p l a c e . - 79 -The experiment was conducted i n diglyme at r e f l u x i n g temperature and •i was f o l l o w e d by the o x i d a t i v e work up normally employed i n the hydroboration procedure. The main products obtained were s t a r t i n g m a t e r i a l , cleavamine, and dihydrocleavamine (29). Two minor, more p o l a r products were a l s o obtained i n i n s u f f i c i e n t q u a n t i t y f o r c h a r a c t e r i z a t i o n . In subsequent work, however, the secondary a l c o h o l (117) was obtained. A comparison of these minor products w i t h t h i s a l c o h o l showed i n f a c t that one of these had the same t i c p r o p e r t i e s and i r spectrum. The other product had very s i m i l a r t i c p r o p e r t i e s , being very s l i g h t l y l e s s p o l a r and gave a somewhat s i m i l a r i r spectrum. This m a t e r i a l i s p o s s i b l y the epimeric a l c o h o l . No f u r t h e r work was done i n t h i s d i r e c t i o n because of the poor y i e l d s encountered. Instead we turned, back to the normal hydroboration process. The i s o l a t i o n of the cleavamine N-borane i n the previous hydro-b o r a t i o n experiment i n d i c a t e d t h a t an i n s u f f i c i e n t amount of diborane was used i n the r e a c t i o n . When a l a r g e excess of diborane was u t i l i z e d , the d e s i r e d secondary a l c o h o l was obtained i n 77% y i e l d . The s p e c t r a l data f o r t h i s compound were i n complete agreement with the s t r u c t u r e of the a l c o h o l (117) and s u b l i m a t i o n of the compound provided an a n a l y t i c a l sample. A comparison of the mass spectrum of t h i s compound ( f i g u r e 22) w i t h t h a t of velbanamine and isovelbanamine ( f i g u r e 21) showed, as expected, a very c l o s e resemblance between them. The nmr spectrum showed two protons i n the r e g i o n x 6.4. One o f these could be assigned to the C 1 Q - p r o t o n , s i n c e t h i s i s i t s normal p o s i t i o n i n cleavamine-type compounds bearing no s u b s t i t u e n t at C 1 R. - 80 -The other proton with t h i s chemical s h i f t could be assigned to the C^-proton which i s geminal to the hydroxyl f u n c t i o n . The nmr spectrum of the acetate of t h i s a l c o h o l ( f i g u r e 26) showed a s i n g l e proton as a complex m u l t i p l e t at T 6.4, (C, Q-proton) and now showed the C_-proton at lower f i e l d , x 4.90, as a doublet of doublets (J = 6 and 10 Hz.). The stereochemistry of t h i s a l c o h o l (117) at the two asymmetric centres could be assigned by a combination of chemical and nmr evidence. The hydroboration process i s known to r e s u l t i n the c i s h y d r a t i o n of a double bond. That i s , the hydroxyl f u n c t i o n and the proton are introduced at adjacent carbons i n a c i s r e l a t i o n s h i p toward each other and t h i s i s explained m e c h a n i s t i c a l l y by the intermediacy of a c y c l i c t r a n s i t i o n state. 5''' From t h i s i n f o r m a t i o n , the r e l a t i v e stereochemistry between C„ and C. i s e s t a b l i s h e d . 1 3 4 An examination of a model of cleavamine shows c l e a r l y that because of the s t e r i c e f f e c t of the b r i d g e at C_, approach i s very much favoured from the s i d e of the p i p e r i d i n e r i n g opposite t h i s b r i d g e . This i s indeed g e n e r a l l y observed i n other r e a c t i o n s of the cleavamine system. Hydrogenation of cleavamine t h e r e f o r e gives - 82 -e x c l u s i v e l y 48-dihydrocleavamine ( 2 9 ) . The osymlation r e a c t i o n on the enamine (83); reported e a r l i e r i n t h i s work was a l s o s t e r e o s e l e c t i v e , i r e s u l t i n g i r i the eventual formation of isovelbanamine (100). The stereochemistry at of isovelbanamine which has the e t h y l group i n a g - o r i e n t a t i o n shows that a t t a c k i n t h i s case i s a l s o favoured from the s i d e opposite the b r i d g e . Buchi's s y n t h e s i s of v e l b a n a m i n e 6 6 makes use of t h i s s t e r i c approach c o n t r o l . Thus treatment of (150) w i t h ethylmagnesium bromide, f o l l o w e d by l i t h i u m aluminum hydride r e d u c t i o n (150) gave velbanamine ( 2 2 ) . On the b a s i s of these r e s u l t s i t would be expected that the hydroboration of the cleavamine double bond would f o l l o w the same s t e r i c course and lead to the 3a-hydroxy-48-dihydrocleavamine. This suggestion was supported by nmr evidence. The C^-proton i n the acetate of t h i s molecule i s observed as a doublet of doublets J = 6 and 10 Hz. I f a t t a c k i s from the s i d e opposite the b r i d g e , the r e s u l t i n g compound would have the e t h y l and hydroxyl groups i n a t r a n s - d i a x i a l r e l a t i o n s h i p assuming the c h a i r conformation f o r the p i p e r i d i n e r i n g . Because of the conformational m o b i l i t y i n the cleavamine r i n g system i t i s d i f f i c u l t to be e n t i r e l y d e f i n i t i v e about - 83 -the conformational s t r u c t u r e . We can, however, r u l e out the a l t e r n a t e mode of a t t a c k . Attack of the double bond from the same si d e as the bridge at would lead to a compound which has both the e t h y l and hydroxyl groups i n the e q u a t o r i a l p o s i t i o n i n the c h a i r conformation. This s i t u a t i o n represents the most s t a b l e conformation p o s s i b l e . In t h i s case, the d i h e d r a l angles are w e l l d e f i n e d being 180° and 60° between the C^-C^ and ^2~^i protons r e s p e c t i v e l y . From the Karplus 67 r e l a t i o n , these angles should lead to c o u p l i n g constants of about 16 and 2 Hz. This c l e a r l y does not agree w i t h the observed values of 10 and 6 Hz and t h e r e f o r e excludes t h i s course of a t t a c k . Therefore, on the b a s i s of models, chemical precedence and nmr data, the a l c o h o l (117) can be assigned as 3a-hydroxy-43-dihydrocleavamine. I t i s of i n t e r e s t to compare t h i s compound w i t h the monomeric u n i t d e r i v e d from l e u r o s i d i n e (18). Cleavage of t h i s dimer leads to the i s o l a t i o n of a secondary a l c o h o l , vinrosamine, which was assigned the s t r u c t u r e of 3a-hydroxy-4a-dihydrocleavamine.^ A comparison of our data w i t h the p h y s i c a l constants r e p o r t e d f o r vinrosamine and vinrosamine acetate shows d e f i n i t e l y that these compounds are d i f f e r e n t . I t i s reported that vinrosamine e x h i b i t s a mass spectrum i n which the major fragment i o n corresponds to a l o s s of water from the molecular i o n (M + -18), and that the r e s t of the spectrum corresponds to t h a t normally found f o r cleavamine type compounds. Our a l c o h o l , d e s p i t e the f a c t that i t was epimeric to t h i s m a t e r i a l at only one p o s i t i o n (C^) behaved e n t i r e l y d i f f e r e n t l y and gave a spectrum which corresponded c l o s e l y to that of velbanamine and isovelbanamine. This perhaps unexpected d i f f e r e n c e between the mass s p e c t r a of these two secondary -•• - 84 -a l c o h o l s can.be e a s i l y explained by a c o n s i d e r a t i o n of t h e i r s t r u c t u r e s . Vinrosamine i n the c h a i r conformation, has the e t h y l group i n an e q u a t o r i a l p o s i t i o n and the hydroxyl and hydrogen i n a t r a n s -d i a x i a l r e l a t i o n s h i p . This s p a t i a l arrangement between the hydroxyl and adjacent hydrogen i s very f a v o r a b l e f o r e l i m i n a t i o n and the f a c i l e d e h y d r a t i o n : t o cleavamine as observed i n the mass spectrum i s not unexpected. In our a l c o h o l (118), there are no hydrogen atoms which are trans to the hydroxyl group and thus only a c i s e l i m i n a t i o n i s p o s s i b l e . The major fragment i o n i n the mass spectrum of the a l c o h o l (118) i s m/e 154 i n d i c a t i n g that fragmentation at carbon centers adjacent to the i n d o l e aromatic system i s favoured [cf s t r u c t u r e (101)] and the i o n observed corresponds to the hydroxylated p i p e r i d i n e p o r t i o n of the molecule. Having achieved the f u n c t i o n a l i z a t i o n at both and we now turned our a t t e n t i o n to the formation of the epimeric systems. The compounds synth e s i z e d so f a r d i f f e r e d i n stereochemistry at the asymmetric centres and/or C^, from the monomeric u n i t s d e r i v e d from the n a t u r a l dimers and i t was d e s i r a b l e to have a v a i l a b l e as s y n t h e t i c m a t e r i a l s , the compounds having the same stereochemistry at these centers. Of p a r t i c u l a r i n t e r e s t was the s y n t h e s i s of velbanamine (22). I t w i l l become c l e a r i n the second p a r t of the d i s c u s s i o n t h a t the sequence already outlining the t o t a l s y n t h e s i s of isovelbanamine was important i n the s y n t h e s i s of d i m e r i c systems. A means of a l l o w i n g e p i m e r i z a t i o n at the p o s i t i o n of intermediates u t i l i z e d i n the present sequence would give us the s y n t h e t i c c a p a b i l i t y of s y n t h e s i z i n g v i n b l a s t i n e or i s o v i n b l a s t i n e epimeric at only C R . This achievement - 85 -would provide the f i r s t r e a l o p portunity to evaluate the importance of t h i s and other asymmetric centers i n imparting anti-tumor a c t i v i t y l' i n t h i s s e r i e s . The e p i m e r i z a t i o n of the t e r t i a r y C^-hydroxyl f u n c t i o n was a n t i c i p a t e d to be a complex process. From our experience w i t h the dehydration of isovelbanamine to cleavamine, which was r e a d i l y achieved under a c i d i c c o n d i t i o n s , i t seemed l i k e l y t h a t any approach which i n v o l v e d the intermediate carbonium i o n would s u f f e r the undesired l o s s of a proton to give o l e f i n i c products. We thus turned our a t t e n t i o n to S^2 type r e a c t i o n s even though a t e r t i a r y center i s not normally prone t o such s i t u a t i o n s . Our f i r s t experiment i n v o l v e d the use of concentrated sodium hydroxide i n a water-dimethyl sulphoxide s o l u t i o n . Dimethyl sulphoxide was used because i t i s known to g r e a t l y enhance the a c t i v i t y of anions and thus i s an e x c e l l e n t s olvent f o r n u c l e o p h i l i c 69 displacement r e a c t i o n s . The d r i v i n g f o r c e f o r the r e a c t i o n would be the attainment of a more s t a b l e isomer; isovelbanamine has the e t h y l s u b s t i t u e n t i n an a x i a l p o s i t i o n when the p i p e r i d i n e r i n g i s i n a c h a i r conformation, whereas velbanamine has the e t h y l group i n an e q u a t o r i a l p o s i t i o n and a l s o the hydroxyl f u n c t i o n i n the 8 - a x i a l p o s i t i o n i s f a v o r a b l y o r i e n t e d f o r hydrogen bonding w i t h the t e r t i a r y n i t r o g e n . However, the experiment under a v a r i e t y of c o n d i t i o n s , f a i l e d to produce any velbanamine as evidenced by t i c . The f o l l o w i n g approach was based on a known procedure f o r the 70 cleavage of s t e r o i d a l methyl ethers u s i n g boron t r i f l u o r i d e - e t h e r a t e . In these instances the combined r e a c t i o n of BF^-etherate and a c e t i c anhydride i n ether converted secondary methyl ethers to the corresponding - 86 -a c e t a t e s . The product was reported to sometimes c o n s i s t of a mixture of epimeric m a t e r i a l s . I t was f e l t t h a t t h i s r e a c t i o n sequence should i be a p p l i c a b l e to our system. Treatment of isovelbanamine under the p r e s c r i b e d c o n d i t i o n s l e d to the disappearance of s t a r t i n g m a t e r i a l as evidenced by t i c and one major product r e s u l t e d . Treatment of t h i s product w i t h l i t h i u m aluminum hydride gave, however, isovelbanamine as a major product and no velbanamine. Thus isovelbanamine acetate was formed i n d i c a t i n g a t t a c k by the acylium i o n at the hydroxyl oxygen r a t h e r than d i s p l a c e -ment of the hydroxyl by the acetate anion. These experiments confirmed our i n i t i a l s u s p i c i o n s that s t e r i c f a c t o r s were p r o h i b i t i v e to the r e q u i r e d n u c l e o p h i l i c a t t a c k at t h i s c e n ter. We were thus f o r c e d to examine the a l t e r n a t e approach, that i s , r e a c t i o n c o n d i t i o n s which would be expected to generate carbonium i o n i n t e r m e d i a t e s . Under the c o n d i t i o n s f o r the conversion of i s o v e l -banamine to cleavamine (concentrated s u l p h u r i c a c i d at 0°C f o r 2 hours), the carbonium i o n r a p i d l y loses a proton to provide the o l e f i n i c systems. We r e q u i r e d i n t h i s case non-dehydrating c o n d i t i o n s such that the r e a c t i o n at the carbonium i o n would i n s t e a d be n u c l e o p h i l i c a t t a c k . We thus t r e a t e d isovelbanamine with d i l u t e aqueous a c i d at 0°C up to three days and found under these c o n d i t i o n s , the compound underwent no change. A l s o at room temperature no change was observed. However, r e f l u x i n g t h i s same s o l u t i o n , gave a f t e r f o u r hours, the f i r s t i n d i c a t i o n on t i c of the presence of some velbanamine. The p r o p o r t i o n of velbanamine seemed to increase w i t h time and the r e a c t i o n was allowed to continue f o r two days. Work up a f t e r t h i s time gave -87'-both velbanamine and s t a r t i n g isovelbanamine. The velbanamine obtained had the same m e l t i n g p o i n t , i d e n t i c a l t i c p r o p e r t i e s and superimposable i 71 i r spectrum^with that of an a u t h e n t i c sample of velbanamine. The extension of our sequence to the t o t a l s y n t h e s i s of velbanamine s a t i s f i e d one of our main s y n t h e t i c o b j e c t i v e s w i t h respect to the s y n t h e s i s of the n a t u r a l dimeric Vinca a l k a l o i d s and t h e i r c l o s e l y r e l a t e d d i m e r i c analogues. Now that s y n t h e s i s of the i n d o l e (velbanamine) u n i t was i n hand, two problems s t i l l remain to be s o l v e d . These are 1) the completion of the d i h y d r o i n d o l e ( v i n d o l i n e ) u n i t and, 2) the c o u p l i n g of these systems to provide the d i m e r i c a l k a l o i d s . While the v i n d o l i n e s y n t h e s i s i s under study by s e v e r a l other workers i n the group, the i n v e s t i g a t i o n s concerning the d i m e r i z a t i o n r e a c t i o n form Part I I of t h i s t h e s i s . Part I I The d i m e r i c Vinca a l k a l o i d s c o n t a i n a l i n k a g e between the p o s i t i o n of v i n d o l i n e or i t s r e l a t i v e s and C^R of the nine-membered r i n g system c h a r a c t e r i s t i c of the cleavamine f a m i l y . Although i t would be s a t i s f y i n g to complete the t o t a l s y n t h e s i s of the n a t u r a l s e r i e s , i t was of utmost importance to develop, i f p o s s i b l e , a v e r s a t i l e and general c o u p l i n g r e a c t i o n which would provide a new f a m i l y of s y n t h e t i c analogues f o r b i o l o g i c a l e v a l u a t i o n . In t h i s way i n f o r m a t i o n concerning the r e l a t i o n s h i p between chemical s t r u c t u r e and anti-tumor a c t i v i t y , can be obtained. Our approach to t h i s work was to employ a r e a c t i o n w i t h which we p r e v i o u s l y had considerable experience and which seemed a t t r a c t i v e f o r - 88 -t h i s purpose. I t was pointed out e a r l i e r that i n d o l e systems can be converted by o x i d a t i v e procedures to i n d o l e n i n e s which are r e a c t i v e to n u c l e o p h i l i c a t t a c k at centers adjacent to the a - p o s i t i o n of the o r i g i n a l i n d o l e system (see f i g u r e 23). Thus the formation of the c h l o r o i n d o l e n i n e s served as an intermediate step f o r the i n t r o d u c t i o n of n u c l e o p h i l i c s u b s t i t u e n t s at the 18 p o s i t i o n of the Iboga systems ( f o r example see f i g u r e 22). V i n d o l i n e on the other hand i s a c t i v a t e d toward e l e c t r o p h i l i c s u b s t i t u t i o n . The aromatic p o r t i o n of t h i s molecule i s a meta-methoxy-aniline system which because of the combined " e l e c t r o n donating" e f f e c t of the methoxy and a n i l i n o f u n c t i o n s i s a c t i v a t e d at both the 15 and 17 p o s i t i o n s toward e l e c t r o p h i l i c a t t a c k . The 15 p o s i t i o n should i n f a c t be more r e a c t i v e than the 17 p o s i t i o n when s t e r i c f a c t o r s are taken i n t o c o n s i d e r a t i o n . Thus i t was p r e d i c t e d that a r e a c t i o n between the c h l o r o i n d o l e n i n e of the cleavamine type system and v i n d o l i n e , would r e s u l t i n a d i m e r i z a t i o n i n v o l v i n g the c o r r e c t c e n t r e s , C^g, and C^. The numbering system that w i l l be used i n r e f e r r i n g to the dirners, w i l l be that of the corresponding monomeric u n i t s , that i s , Aspido-sperma a l k a l o i d numbering f o r the d i h y d r o i n d o l e u n i t while Iboga numbering f o r the velbanamine moiety. To d i s t i n g u i s h the numbering systems, the numbers of the "Iboga h a l f " w i l l be primed (see 118). Our i n i t i a l experiment was conducted using the l e a s t f u n c t i o n a l i z e d of the cleavamine systems, 48-dihydrocleavamine (29) i n the hope that the p o s s i b i l i t y of s i d e r e a c t i o n s would be minimized. A l s o , the c h l o r o i n d o l e n i n e of t h i s compound had already been synt h e s i z e d as an intermediate i n the conversion of 48-dihydrocleavamine t o 188-carbo-- 89 -methoxy-46-dihydrocleavamine (32). The r a t h e r unstable c h l o r i n d o l e n i n e intermediate (41), formed from t - b u t y l h y p o c h l o r i t e o x i d a t i o n of 29, was reacted w i t h v i n d o l i n e i n an anhydrous methanolic 1% h y d r o c h l o r i c a c i d s o l u t i o n . The r e a c t i o n seemed complete a f t e r two hours at r e f l u x temperature. The major product of t h i s r e a c t i o n e x h i b i t e d a l l the p r o p e r t i e s expected f o r the dimer (118). The uv spectrum appeared as a simple s u p e r i m p o s i t i o n of the i n d o l e and i n d o l i n e a b s o r p t i o n and t h i s agreed q u a l i t a t i v e l y w i t h the spectrum obtained f o r v i n b l a s t i n e . The mass spectrum ( f i g u r e 27) shows a number of fragment ions corresponding t o the fragmentation p a t t e r n e x h i b i t e d by dihydrocleavamine and v i n d o l i n e . The prominent . absorptions at m/e 124, 138 and l e s s i n t e n s e ones at 143, 144, 156, and - 91 -i ^ 22 282 are very c h a r a c t e r i s t i c of dihydrocleavamine. S i m i l a r l y the j strong absorptions at m/e 121, 122, 135, and 149 w i t h l e s s intense i 72 ones at 174 and 188 d e f i n e the v i n d o l i n e p o r t i o n of the molecule. High r e s o l u t i o n mass determination of the parent i o n e s t a b l i s h e d a i molecular formula i n agreement w i t h the s t r u c t u r e of the d e s i r e d compound. From the evidence presented so f a r , there was no doubt that we had a d i m e r i c system composed of a cleavamine and a v i n d o l i n e p o r t i o n . Strong evidence i n f a v o r of the dimer as w e l l as the proof f o r the c o r r e c t j u n c t i o n between the two u n i t s came from the nmr spectrum. In many r e s p e c t s , the nmr spectrum of the dimer ( f i g u r e 28), appeared t o be a combination of the s p e c t r a of the i n d i v i d u a l monomeric u n i t s ( f i g u r e 29,30) but a few important changes were observed. The aromatic protons of v i n d o l i n e appear as three d i s c r e t e m u l t i p l e t s i n the r e g i o n T 6-7; normal c o u p l i n g , ortho and meta with no para c o u p l i n g i s observed. In the dimer, the s i g n a l corresponding to the proton i s absent as expected and the and protons now appear as s i n g l e t s because of the small para c o u p l i n g . The j u n c t i o n i s t h e r e f o r e e s t a b l i s h e d to be at the p o s i t i o n of v i n d o l i n e . The C^g, proton i s observed as the broad doublet c h a r a c t e r i s t i c f o r 1 8 - s u b s t i t u t e d cleavamines. As discussed p r e v i o u s l y , the chemical s h i f t of t h i s proton has been used i n the simple s u b s t i t u t e d cleavamine systems to a s s i g n the stereochemistry at t h i s p o s i t i o n . However, i t was u n l i k e l y that the d i m e r i c system, because of the v a s t l y i n creased s t e r i c bulk of the s u b s t i t u e n t , the v i n d o l i n e moiety, would f i t i n t o t h i s general scheme and no stereochemical assignment f o r t h i s j u n c t i o n could be made at Figure 28. Nmr of dimer 118. - 95 -I | t h i s p o i n t . One f u r t h e r o b s e r v a t i o n could be made from t h i s spectrum. i The two methyl absorptions f o r the carbomethoxy land methoxy s u b s t i t u e n t s i have the same chemical s h i f t i n v i n d o l i n e . However, i n the dimer i t can be seen that one of these methyls i s s h i f t e d to higher f i e l d . j I t i s probable t h a t t h i s s i g n a l represents the methoxyl methyl which, because i t i s adjacent to the j u n c t i o n , i s now put i n c l o s e p r o x i m i t y to the i n d o l e aromatic system and i s thereby a f f e c t e d by the magnetic f i e l d a s s o c i a t e d w i t h t h i s system. : To e s t a b l i s h beyond a doubt that t h i s compound was indeed the dimer (118) and not f o r example a dimer composed of a rearrangement product, a sample of the m a t e r i a l was cleaved. Treatment of t h i s compound under a c i d i c reducing c o n d i t i o n s gave a mixture of products which were separated and i d e n t i f i e d as 48-dihydrocleavamine, v i n d o l i n e , d e s a c e t y l v i n d o l i n e and s t a r t i n g dimer. These i s o l a t e d products accounted f o r 75% of the s t a r t i n g m a t e r i a l . This experiment i n c o n j u n c t i o n w i t h the s p e c t r a l data, presented a r i g o r o u s proof of the s t r u c t u r e of the dimer (118). Our next experiment was designed to t e s t the a p p l i c a b i l i t y of t h i s approach to the s y n t h e s i s of d i m e r i c m a t e r i a l s having a carbo-methoxy f u n c t i o n at C^g,. This f u n c t i o n i s present i n a l l the n a t u r a l dirners of known s t r u c t u r e . I t seemed p r e f e r a b l e t o couple the 18-carbomethoxycleavamine-type system w i t h v i n d o l i n e r a t h e r than to t r y and introduce the carbomethoxy group at a l a t e r stage. For t h i s experiment we t h e r e f o r e s t a r t e d w i t h 18 8-carbomethoxycleavamine (32) which was converted to the c h l o r o i n d o l e n i n e (120) i n the usual f a s h i o n . Reaction of t h i s c h l o r o i n d o l e n i n e w i t h v i n d o l i n e gave one major product - 96 -which e x h i b i t e d the s p e c t r a l p r o p e r t i e s expected f o r the dimer (119). As b e f o r e , the uv spectrum showed the presence of both chromophores and the mass; spectrum ( f i g u r e 31) gave strong evidence f o r the presence of both the i n d o l e and d i h y d r o i n d o l e u n i t s . High r e s o l u t i o n mass measurement on the parent i o n e s t a b l i s h e d the molecular formula expected f o r the product. The nmr spectrum of t h i s compound ( f i g u r e 32) showed many of the fe a t u r e s of the spectrum f o r the previous dimer but with a few important changes. The C^ R I proton seen at T 5.6 f o r dimer (118) was missing i n t h i s spectrum and i t was noted that the s i n g l e t a t t r i b u t e d to the carbomethoxy methyl was enlarged and i n t e g r a t e d f o r two methyl groups. A comparison of the chemical s h i f t s f o r the v i n d o l i n e aromatic protons showed i n t h i s spectrum a s h i e l d i n g e f f e c t f o r the C j ^ proton and a d e s h i e l d i n g e f f e c t f o r the proton r e l a t i v e to that observed i n the descarbomethoxy dimer (118). These s h i f t s could be a t t r i b u t e d to e i t h e r of two f a c t o r s or a combination of them; 1) a d i f f e r e n c e i n the s p a t i a l arrangement of the two halves of the dimer caused by the e x t r a C^ R I s u b s t i t u e n t which could p l a c e these protons i n a d i f f e r e n t p r o x i m i t y to the magnetic f i e l d a s s o c i a t e d w i t h the i n d o l e aromatic system, 2) an a d d i t i o n a l a n i s o t r o p i c e f f e c t caused by the i n t r o d u c t i o n of the carbonyl s u b s t i t u e n t at C^ R I. As with the previous dimer, t h i s compound was subjected to c l e a v i n g c o n d i t i o n s . The products i s o l a t e d were i d e n t i f i e d by t i c and s p e c t r a l comparison w i t h a u t h e n t i c m a t e r i a l s and were found to be: 18a-carbomethoxydihydrocleavamine, 18g-carbomethoxydihydrocleavamine, v i n d o l i n e and d e s a c e t y l v i n d o l i n e . Thus the s t r u c t u r e of the dimer (120) was proved. Figure 32. Nmr spectrum of dimer (119). - 99 -i i In the mass spectrum of both of these dimeric compounds, the i molecular i o n was not the highest molecular weight peak observed i n the spectrum. Instead, M+ +14 and M+ +28 peaks' were present although i n each of the s p e c t r a obtained, they were extremely weak. These i spurious peaks had been p r e v i o u s l y reported i n the mass spectrum of v i n b l a s t i n e 6 ^ and voacamine^ and have been a t t r i b u t e d to an i n t e r -molecular methyl t r a n s f e r from a carbomethoxy group of one molecule to the n i t r o g e n atom of another, f o l l o w e d by a thermal Hofmann-e l i m i n a t i o n . This process can be repeated twice s i n c e two b a s i c n i t r o g e n atoms are a v a i l a b l e f o r r e a c t i o n and thus leads to the M+ +14 and M+ +28 ions observed. When v i n b l a s t i n e was t r e a t e d w i t h hydrazine, the hydrazide (121) obtained possessed no carbomethoxy f u n c t i o n s and indeed, d i d not show these spurious peaks i n i t s mass spectrum. Because i t was a n t i c i p a t e d that mass spectroscopy would p l a y an important r o l e i n the s t r u c t u r a l proof of the s y n t h e t i c d i m e r i c compounds, a p a r a l l e l s e r i e s of d i m e r i z a t i o n experiments were c a r r i e d out by other workers i n our l a b o r a t o r y u s i n g v i n d o l i n e hydrazide i n s t e a d of v i n d o l i n e as reported i n t h i s work. The d i m e r i z a t i o n of 146-dihydrocleavamine w i t h v i n d o l i n e hydrazide gave dimer (122) - 100 -I i 1 possessing no carbomethoxy function. Its mass spectrum had as expected, the highest m/e value as the molecular ion and thus supported the view that we had i n f a c t observed t h i s same transmethyla-t i o n phenomenon i n the spectra of our other dimers and were j u s t i f i e d i n not taking the highest m/e value as our molecular ion. Two other dimerizations were c a r r i e d out, both of these used the chloroindolenine of 18g-carbomethoxy-43-dihydrocleavamine (120). In one case i t was coupled to v i n d o l i n e hydrazide to give the dimer (123) and i n the other case i t was coupled with dihydrovindoline. The d e t a i l s of 76 these three dimerizations, reported i n f u l l elsewhere, were completely consistent with the r e s u l t s presented f o r the dimerizations i n t h i s work. It should also be pointed out, that the synthesis of the dimer of 4g-dihydrochleavamine with v i n d o l i n e hydrazide using the chloroindolenine approach has also been reported recently by another group of workers.^ One f u r t h e r point which has been ignored so f a r , i s the stereo-chemistry at the C^8, end of the junction i n the dimers synthesized using the chloroindolenine as intermediate. In an endeavour to e s t a b l i s h the stereochemistry at t h i s point, we chose to compare dimer (119) with v i n b l a s t i n e i n which the stereochemistry has been established by X-ray a n a l y s i s . Ignoring stereochemical d e t a i l , dimer (119) d i f f e r s from v i n b l a s t i n e i n only one feature, a lack of a hydroxyl function at C^,. This point of d i f f e r e n c e i s f a r removed from the C-^ g, p o s i t i o n and would not be expected to influence the s p e c t r a l properties associated with the stereochemistry at t h i s j u n c t i o n . An inspection of the models of the dimers, indicated that a - 101 -I j d i f f e r e n c e i n stereochemistry at C 1 D, profoundly i n f l u e n c e d the 1 o o v e r a l l shape of the molecule. The s p a t i a l arrangement between the i n d o l e and i n d o l i n e chromophores would be a l t e r e d i f a d i f f e r e n c e i n stereochemistry e x i s t e d between these compounds and although these two chromophoric systems are not i n conjugation w i t h each other, i t was thought that such a change i n s p a t i a l arrangement when these groups are i n c l o s e p r o x i m i t y , would be r e f l e c t e d by a d i f f e r e n c e i n the uv s p e c t r a of these compounds. A comparison of t h e i r uv s p e c t r a , f i g u r e 33, i n d i c a t e s a c o n s i d e r a b l e d i f f e r e n c e i n e x t i n c t i o n c o e f f i c i e n t and a small s h i f t i n the a b s o r p t i o n maxima. These s p e c t r a were recorded u s i n g methanol as s o l v e n t and i t i s p o s s i b l e that the d i f f e r e n c e i n s o l v a t i o n which undoubtedly e x i s t s and i s caused by the h y d r o x y l , can account f o r the d i f f e r e n c e i n e x t i n c t i o n c o e f i c i e n t s . The s h i f t i n the a b s o r p t i o n bands, although they are small could be i n d i c a t i v e of a change i n stereochemistry. A comparison of the nmr s p e c t r a of these compounds, however, showed pronounced changes which could not be explained by the presence or absence of the hydroxyl f u n c t i o n at C^,. The major d i f f e r e n c e s observed between the spectrum of v i n b l a s t i n e ( f i g u r e 34) and that of dimer (119) ( f i g u r e 32) are l i s t e d i n Table I I . I t can be seen from t h i s t a b l e that the s u b s t i t u e n t s on the aromatic p o r t i o n of the v i n d o l i n e h a l f c£ the dimer show a con s i d e r a b l e change i n chemical s h i f t . These protons are very near the j u n c t i o n between the halves of the dimer and the changes i n chemical s h i f t no doubt r e f l e c t s a s u b s t a n t i a l change i n t h e i r environment. These data suggest t h e r e f o r e that the stereochemistry at C^g, d i f f e r s i n the s y n t h e t i c dimer (119) from that of the n a t u r a l s e r i e s . - 102 -Figure 34. Nmr spectrum of vinblastine (16). - 104 -Table I I . The major d i f f e r e n c e s observed between the nmr s p e c t r a of v i n b l a s t i n e and dimer (119) Chemical S h i f t v i n b l a s t i n e dimer (119) H 3.42 3 .05 H 3.94 4 .05 OCH 6.43 6.16 } 9.12 9.34 C.'CH0CH 4 2 — 9.09 Ex p e r i m e n t a l l y , only one isomer has been obtained from each of the d i m e r i z a t i o n r e a c t i o n s . Since the same r e a c t i o n i s i n v o l v e d f o r the sy n t h e s i s of each dimer, i t i s reasonable to assume t h a t these dirners a l l possess the same stereochemistry, and, on the b a s i s of the above comparison, that t h i s stereochemistry d i f f e r s from t h a t of the n a t u r a l s e r i e s . • I t i s d i f f i c u l t to e x p l a i n m e c h a n i s t i c a l l y the 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 . The stereochemistry of the c h l o r o i n d o l e n i n e intermediates have not been e s t a b l i s h e d . From t i c and s p e c t r a l data, i t i s seen that they are s i n g l e m a t e r i a l s r a t h e r than epimeric mixtures. An i n s p e c t i o n of molecular models show th a t the a l i c y c l i c p o r t i o n of the molecule e f f e c t i v e l y b l o c k s one s i d e of the i n d o l e system from a t t a c k and f o r t h i s reason these compounds must be g-chloro-i n d o l e n i n e s . Reaction of t h i s compound w i t h a n u c l e o p h i l e can occur i n - 105 -two ways: 1) a concerted displacement of c h l o r i d e by the n u c l e o p h i l e i n an S^2'-type r e a c t i o n , or 2) i n i t i a l l o s s of c h l o r i d e w i t h subse-quent n u c l e o p h i l i c a t t a c k on the intermediate formed. In the f i r s t case, a t t a c k by the n u c l e o p h i l e i s on the c h l o r o -i n d o l e n i n e . For s t e r i c and e l e c t r o n i c reasons, the d i r e c t i o n of a t t a c k w i l l be from the same s i d e of the molecule as the c h l o r i n e . The c h l o r o i n d o l e n i n e intermediate i s , however, capable of e x i s t i n g i n both the i s o m e r i c forms, i n d i c a t e d by s t r u c t u r e s (124) and (125) and these may be i n e q u i l i b r i u m . This s i t u a t i o n may r e s u l t from the f a c t that a) the c h l o r o i n d o l e n i n e s as shown by s t r u c t u r e s (124) and (125) may be i n e q u i l i b r i u m w i t h the s t r u c t u r e (126), a l l o w i n g (126) - 106 -c o n f o r m a t i o n a l l y very mobile, p a r t i c u l a r l y when i n v e r s i o n of the n i t r o g e n i s allowed. On t h i s b a s i s both double-bond isomers (124) and (125) could e x i s t w i t h no unfavourable i n t e r a c t i o n s . Thus although attack by the n u c l e o p h i l e may occur from one d i r e c t i o n , both epimers could i n f a c t be formed. The second r e a c t i o n mode may i n v o l v e an i n i t i a l l o s s of c h l o r i d e i n a r a t e determining step t o form the intermediate (127). This l a t t e r species may e x i s t i n tautomeric e q u i l i b r i u m w i t h 128 which upon r e a c t i o n w i t h a n u c l e o p h i l e would be expected to y i e l d a mixture of isomers. (127) (128) Although we had expected a mixture of isomers from t h i s r e a c t i o n , the experimental f i n d i n g s were t h a t only one epimer was formed. From the data presented p r e v i o u s l y t h i s dimer appeared to possess the i n c o r r e c t stereochemistry at C, '. I t was d e s i r a b l e , however, to o b t a i n dirners w i t h the stereochemistry as found i n the natural, systems because i t could be seen from molecular models that a change of stereochemistry at t h i s C^g' p o s i t i o n made a s u b s t a n t i a l d i f f e r e n c e to the o v e r a l l shape of the molecule. Since molecular shape o f t e n p l a y s an important r o l e i n determining the b i o l o g i c a l a c t i v i t y , an - 107 -unnatural stereochemistry at t h i s centre may r e v e a l a dramatic a l t e r a t i o n i n the d e s i r e d anti-tumor a c t i o n of these molecules. We t h e r e f o r e turned to an a l t e r n a t e approach f o r the c o u p l i n g of the monomeric u n i t s . The second d i m e r i z a t i o n approach was based on a method developed 74 by Buchi f o r the s y n t h e s i s of voacamine (129). He found that t h i s compound could be synthesized by simply h e a t i n g v o b a s i n o l (130) and voacanginol (131) together i n a s o l u t i o n of methanolic h y d r o c h l o r i c a c i d . This method was subsequently used by Harley-Mason to condense (129) - 108 -18-hydroxydihydrocleavamine (132) w i t h v i n d o l i n e to give the dimer (133). The b r i e f r e p o r t on t h i s work makes no mention of the stereochemical aspects of t h i s r e a c t i o n . The mechanism of t h i s r e a c t i o n would be expected to i n v o l v e a p r o t o n a t i o n of the C 1 0 a l c o h o l f u n c t i o n to form an intermediate oxonium i o n which upon l o s s of water would y i e l d the carbonium i o n (137). Again as i n the mechanism i n v o l v i n g the intermediate 127 and 128, the (137) formation of both epimers at the C. ' p o s i t i o n would be expected. - 109 -In our i n i t i a l i n v e s t i g a t i o n s of t h i s r e a c t i o n , the sequence o u t l i n e d i n Part I of t h i s d i s c u s s i o n ( f i g u r e s 10 and 11) had not been developed. The r e a c t i o n sequence proposed at that time i n v o l v e d the s y n t h e s i s of the e x o c y c l i c o l e f i n (79) from 18-hydroxymethyl-4g-dihydrocleavamine (92). Osmylation of t h i s o l e f i n would give the d i o l (135). This m a t e r i a l could be used f o r d i m e r i z a t i o n and the product would c o n t a i n the hydroxymethyl f u n c t i o n at the |C^R' p o s i t i o n . This f u n c t i o n would provide a convenient handle f o r the eventual p r o d u c t i o n CH20R (92) R=H (138) R=C0Ph (132) (79) dimer (C '-CH.OH) l o 2. dimer (133) dimer (C l g'-C0 2Me) - 110 -of* the C '-carbomethoxy group to give a dimer e i t h e r i d e n t i c a l to dimer (119) or i t s C^g' epimer. An a l t e r n a t e and perhaps more simple route f o r a comparison of the stereochemistry of t h i s d i m e r i z a t i o n w i t h the c h l o r o i n d o l e n i n e approach would be the s y n t h e s i s of dimer (133) v i a the a c y l i n d o l e (136). The l a t t e r intermediate could be r e a d i l y obtained fromthe d i o l (135) by p e r i o d a t e cleavage. In order to evaluate t h i s sequence 183-hydroxymethyl-4B-dihydro-cleavamine (92), r e a d i l y a v a i l a b l e from catharanthine by r i n g opening to 183-carbomethoxycleavamine (see f i g u r e 6 ) , f o l l o w e d by c a t a l y t i c and l i t h i u m aluminum hydride r e d u c t i o n , was considered as a s t a r t i n g m a t e r i a l . The approach equivalent to dehydration i n v o l v e d simply the conversion of the a l c o h o l to a good l e a v i n g group and then e l i m i n a t i o n e i t h e r by use of heat or base. Our f i r s t attempt at t h i s sequence was the p r e p a r a t i o n of the 3,5-dinitrobenzoate. The r e a c t i o n was c a r r i e d out at room temperature i n p y r i d i n e and was f o l l o w e d by a weak aqueous base work up to remove the excess 3 , 5 - d i n i t r o b e n z o y l c h l o r i d e . One product other than s t a r t i n g m a t e r i a l was obtained and t h i s m a t e r i a l gave s p e c t r a l evidence i n d i c a t i n g c l e a r l y that i t was not the 3,5-dinitrobenzoate, C h a r a c t e r i z a t i o n of t h i s m a t e r i a l showed i t to be i n s t e a d , the e l i m i n a t i o n product, o l e f i n (76), obtained i n 40% y i e l d based on s t a r t i n g m a t e r i a l consumed. This m a t e r i a l was shown to be i d e n t i c a l to the o l e f i n obtained subsequently by the r e a c t i o n sequence already discussed (see f i g u r e 10). I t was thought that the y i e l d of o l e f i n could be increased by the p r e p a r a t i o n of a d e r i v a t i v e which was s t a b l e enough to be i s o l a t e d - I l l -and would undergo e l i m i n a t i o n under c o n t r o l l e d c o n d i t i o n s r a t h e r than during the work-up. For t h i s reason, the benzoate (138) was prepared. This m a t e r i a l was s t a b l e and could be p u r i f i e d . Treatment of t h i s compound w i t h base consumed the benzoate but f a i l e d to give the o l e f i n . P y r o l y s i s under high vacuum y i e l d e d benzoic a c i d but the r e s i d u e contained none of the d e s i r e d o l e f i n . A p a r a l l e l s e r i e s of experiments were c a r r i e d out on the acetate of the a l c o h o l and a s i m i l a r set of negative r e s u l t s were obtained. I t was at t h i s time, that the sequence of r e a c t i o n s o u t l i n e d i n f i g u r e 10 were developed and the o l e f i n became a v a i l a b l e i n b e t t e r than 70% y i e l d from d i h y d r o c a t h a r a n t h i n o l . The osmylation, which was the next r e a c t i o n i n our proposed sequence could not be achieved. A v a r i e t y of c o n d i t i o n s were attempted i n c l u d i n g those found to be s u c c e s s f u l f o r the secodiene (78) ( f i g u r e 11). In a l l cases, extremely complicated mixtures of products r e s u l t e d . The subsequent osmylation of the secodiene and ensuing r e a c t i o n s ( f i g u r e 11) l e d to the s y n t h e s i s of two compounds p a r t i c u l a r l y w e l l s u i t e d to t h i s d i m e r i z a t i o n approach, the t r i o l (97) and the d i o l (99). (97) (99) - 112 -Coupling of these compounds w i t h v i n d o l i n e would give dimeric m a t e r i a l s having the hydroxyl f u n c t i o n at C^' as i s found i n the n a t u r a l dirners, although i t was known from the work p r e v i o u s l y d i s c u s s e d , that the stereochemistry at t h i s center was epimeric to that i n the n a t u r a l s e r i e s . The t r i o l d i m e r i z a t i o n should give a dimer with an hydroxy-methyl group at the C ' p o s i t i o n and the conversion of t h i s f u n c t i o n j to the e s t e r would give a dimer possessing a l l the f u n c t i o n a l i t y of v i n b l a s t i n e and d i f f e r i n g only i n the stereochemistry at the C^' and perhaps at the C^g' p o s i t i o n s . The c o u p l i n g of the t r i o l (97) w i t h v i n d o l i n e could, however, not be achieved. The r e a c t i o n l e d to a t o t a l recovery of v i n d o l i n e and lo s s o f a l l the t r i o l . The products obtained showed a t y p i c a l i n d o l e a b s o r p t i o n i n t h e i r uv spectrum and showed a carbonyl s t r e t c h i n g bond i n the i r . That the t r i o l should decompose under a c i d i c c o n d i t i o n s to give carbonyl c o n t a i n i n g compounds i s not e n t i r e l y unexpected. The t e r t i a r y a l c o h o l at C^g could be v i s u a l i z e d to undergo a l o s s of water t o an intermediate such as (139) which would be s u s c e p t i b l e to n u c l e o p h i l i c a t t a c k by v i n d o l i n e . An a l t e r n a t i v e mode CH2OH CHOH CHO (139) (140) (141) - 113 -of dehydration which does not i n v o l v e the l o s s of a r o r a a t i c i t y as e n t a i l e d by s t r u c t u r e (139), gives i n s t e a d the conjugated enol (140). Simple t a u t o m e r i z a t i o n of t h i s intermediate leads to an epimeric mixture of aldehydes (141). The c o u p l i n g o f the d i o l (99) with v i n d o l i n e was achieved under r e f l u x i n g c o n d i t i o n s i n an anhydrous methanolic h y d r o c h l o r i c a c i d (1%) s o l u t i o n . The major product, obtained i n 45% y i e l d , gave s p e c t r a l data c o n s i s t e n t w i t h the s t r u c t u r e of the dimer (142). The dimer i c nature was evident from the su p e r i m p o s i t i o n of the i n d o l e and the i n d o l i n e chromophores i n the uv spectrum. High r e s o l u t i o n mass a n a l y s i s on the molecular i o n i n the mass spectrum gave a molecular composition i n p e r f e c t agreement w i t h that expected f o r the dimer. A comparison of the nmr of t h i s compound ( f i g u r e 35) with that of dimer (118) ( f i g u r e 28) prepared by the c h l o r o i n d o l e n i n e approach confirms the s i m i l a r i t y of (142) Figure 35. Nmr spectrum of dimer (142). - 115 -these two compounds. With respect to f u n c t i o n a l i t y , these compounds d i f f e r only i n that the dimer (142) possesses a hydroxyl at C^1. This leads to minor d i f f e r e n c e s i n the nmr spectrum p a r t i c u l a r l y at higher f i e l d (> T 6.5). At lower f i e l d , however, these s p e c t r a correspond very c l o s e l y to each other. This area of the spectrum contains the protons a s s o c i a t e d w i t h both aromatic systems and, as p o i n t e d out b e f o r e , should be most a f f e c t e d by changes i n s t e r e o -I chemistry at C '. The f a c t that these s p e c t r a j a r e n e a r l y i d e n t i c a l 18 j i n t h i s r e g i o n provides strong evidence f o r the same stereochemistry at t h i s p o s i t i o n i n both these dimers. Cleavage of t h i s dimer under the usual a c i d i c reducing c o n d i t i o n s gave a mixture of v i n d o l i n e , d e s a c e t y l v i n d o l i n e , isovelbanamine, unchanged dimer and the d e s a c e t y l d e r i v a t i v e o f the dimer. This evidence i n a d d i t i o n to the s p e c t r a l data, e s t a b l i s h e d w i t h c e r t a i n t y the s t r u c t u r e of the dimer (142). One other d i m e r i c m a t e r i a l was obtained i n very minor amounts from t h i s d i m e r i z a t i o n r e a c t i o n . An nmr of t h i s compound revealed that i t was the d e s a c e t y l analogue of the dimer (142). This m a t e r i a l probably r e s u l t e d from h y d r o l y s i s during the work up. I t appears from the evidence presented so f a r , that t h i s d i m e r i z a -t i o n approach has the same l i m i t a t i o n s as the d i m e r i z a t i o n v i a the c h l o r o i n d o l e n i n e s , t h a t i s , only one of the two p o s s i b l e isomers at C^g' i s formed and t h i s stereochemistry i s probably not the one found i n the natural.systems. The proof f o r t h i s statement i s not c o n c l u s i v e because i t i s based on comparisons of s p e c t r a l data f o r d i s s i m i l a r compounds. To e s t a b l i s h t h i s w i t h c e r t a i n t y we returned to the problem of s y n t h e s i z i n g e i t h e r o f the dimers (118) or (119), which were - 116 -a v a i l a b l e from the c h l o r o i n d o l e n i n e approach by t h i s second c o u p l i n g procedure. For the s y n t h e s i s of the simplest of these, dimer (118) or i t s epimer, we were r e q u i r e d to s y n t h e s i z e 18-hydroxy-4B-dihydrocleav-amine (132). This compound had been obtained i n e a r l i e r work i n our l a b o r a t o r y from s t u d i e s i n v o l v e d w i t h the i n t r o d u c t i o n of cyanide at the C 1 Q p o s i t i o n i n the c h l o r o i n d o l e n i n e of 48-dihydrocleavamine. l o j As d e s c r i b e d e a r l i e r , i t was advantageous to convert t h i s c h l o r o -i n d o l e n i n e (41) to the quaternary ammonium s a l t (115). The quaternary s a l t r e s u l t e d from an i n t r a m o l e c u l a r displacement of the acetoxy f u n c t i o n at C 1 0 i n the intermediate acetate (114). The 18-acetoxy-4B-dihydrocleavamine (114) could be obtained impure i n low y i e l d but attempts to p u r i f y i t l e d to decomposition and only 18-hydroxy-48-dihydrocleavamine could be i d e n t i f i e d from the products obtained. This m a t e r i a l was obtained from the c h l o r o i n d o l e n i n e i n only 2-3% y i e l d which i s not good enough f o r p r e p a r a t i v e s y n t h e t i c work. An a l t e r n a t e but very s i m i l a r procedure was a v a i l a b l e from p u b l i s h e d work 33 i n the ibogaine s e r i e s . This sequence i n v o l v e d the i n t r o d u c t i o n of an 18-methoxyl s u b s t i t u t u e n t by treatment of the c h l o r o i n d o l e n i n e w i t h methanol and a c i d and then to cleave t h i s methyl ether to give the 18-hydroxy compound. We chose to subject the c h l o r o i n d o l e n i n e of 48-dihydrocleavamine (41) to a s o l u t i o n of aqueous a c e t i c a c i d . E i t h e r of two processes p o s s i b l e i n t h i s system would lead to the d e s i r e d product. I n i t i a l a t t a c k by acetate at the C^g p o s i t i o n would give the 18-acetoxy. compound (114) which in t h i s r e a c t i o n medium would r a p i d l y hydrolyze to - 117 -the 18-hydroxy analogue (132), or the 18-hydroxy compound could be formed d i r e c t l y by n u c l e o p h i l i c a t t a c k of water at the C^g p o s i t i o n . The r e a c t i o n was allowed to proceed at room temperature f o r 24 hours. A f t e r t h i s time one major product was present along w i t h some of the s t a r t i n g c h l o r o i n d o l e n i n e . The product, obtained i n 38% y i e l d based on s t a r t i n g m a t e r i a l consumed, had the same me l t i n g p o i n t , i d e n t i c a l t i c p r o p e r t i e s and gave an i r superimposable w i t h that of an a u t h e n t i c sample of 18B-hydroxy-43-dihydrocleavamine. The d i m e r i z a t i o n of t h i s compound with v i n d o l i n e was r e a d i l y achieved i n r e f l u x i n g anhydrous methanolic 1% h y d r o c h l o r i c a c i d s o l u t i o n . The product of t h i s r e a c t i o n , i s o l a t e d i n 65% y i e l d had i d e n t i c a l t i c p r o p e r t i e s and gave superimposable i r and nmr s p e c t r a compared to the dimer (118) which was prepared us i n g the c h l o r o -i n d o l e n i n e - d i m e r i z a t i o n approach. The only other dimeric m a t e r i a l obtained from t h i s r e a c t i o n was a small amount of the d e s a c e t y l d e r i v a t i v e of dimer (118) present i n about 5% y i e l d . A repeat of t h i s r e a c t i o n at a much lower temperature, 24 hours at -5°C, l e d to a product mixture c o n t a i n i n g much of the s t a r t i n g m a t e r i a l s , some dimer (118) and one other product. The simple i n d o l e chromophore obtained f o r t h i s product i n the uv spectrum excluded the p o s s i b i l i t y of t h i s m a t e r i a l being a dimer. Although a good nmr spectrum was not obtained, the spectrum resembled very c l o s e l y that of 18B-methoxy-4B-dihydrocleavamine and suggested r e a c t i o n of the c h l o r o i n d o l e n i n e w i t h the s o l v e n t . These experiments t h e r e f o r e , confirmed that t h i s d i m e r i z a t i o n - 118 -f o l l o w e d the same stereochemical course as the c h l o r o i n d o l e n i n e dimer-i z a t i o n . Since i t seemed u n l i k e l y at t h i s time that the opposite stereochemistry could be obtained d i r e c t l y i n the c o u p l i n g process, work was i n i t i a t e d to a l t e r the stereochemistry of the dimer once i t was formed. Our approach to t h i s would be to s t a r t w i t h a dimer u n s u b s t i t u t e d at the C^g' p o s i t i o n , such as dimer (118) and to subject t h i s compound to a t e r t - b u t y l h y p o c h l o r i t e o x i d a t i o n i n order to I convert i t to the c h l o r o i n d o l e n i n e . N u c l e o p h i l i c a t t a c k by cyanide would then form the 18'-cyano dimer (143). I f a t t a c k by t h i s n u c l e o p h i l e f o l l o w s the same s t e r i c course as was the case w i t h v i n d o l i n e i n the i n i t i a l formation of the dimer (118), then the o v e r a l l r e s u l t would be an i n v e r s i o n of stereochemistry at the C^g' p o s i t i o n . Conversion of the n i t r i l e to the carbomethoxy f u n c t i o n would then lead to an - 119 -18-carbomethoxy dimer (144) having the opposite stereochemistry at C ' t o th a t of dimer (119). l o Our experience w i t h the formation of 18-cyanocleavamine and 18-cyanodihydrocleavamine by the r e a c t i o n of the corresponding c h l o r o -i n d o l e n i n e s w i t h cyanide, suggested that t h i s conversion i n the dimer i c s e r i e s would be d i f f i c u l t to achieve. To f a c i l i t a t e the i d e n t i f i c a t i o n of the 18-cyano dimer (143), i t was decided to |also s y n t h e s i z e a cyano dimer by the co u p l i n g of 18-cyano-4g-dihydrocleavamine (42) wi t h v i n d o l i n e . The dimer thus obtained should i n f a c t be the epimer of the cyano dimer (143) r e s u l t i n g from the i n v e r s i o n scheme, and would provide a f u r t h e r comparison of two dimers d i f f e r i n g only i n st e r e o -chemistry at C '. 1 o The s y n t h e s i s of 18g-cyano-4B-dihydrocleavamine (42) was 59 developed e a r l i e r i n our l a b o r a t o r y and has already been discussed. Thus 4g-dihydrocleavamine was converted to i t s c h l o r o i n d o l e n i n e (41) and t h i s compound on treatment w i t h sodium acetate i n a c e t i c a c i d gave the quaternary s a l t (115). Treatment of the s a l t w i t h cyanide i n r e f l u x i n g dimethyl formamide provided 18g-cyano-4g-dihydrocleavamine. This compound was then t r e a t e d w i t h t e r t - b u t y l h y p o c h l o r i t e at -15°C to produce the c h l o r o i n d o l e n i n e (145). This m a t e r i a l was found to be unstable and was t h e r e f o r e t r e a t e d immediately w i t h v i n d o l i n e under the usual d i m e r i z i n g c o n d i t i o n s ( r e f l u x i n g i n anhydrous methanolic 1% h y d r o c h l o r i c a c i d s o l u t i o n ) to give the cyano dimer (146). The s p e c t r a l data f o r t h i s compound provided ample proof f o r the s t r u c t u r e (145). Once again the d i m e r i c nature of the m a t e r i a l was evident from both the uv and mass s p e c t r a w h i l e a weak ab s o r p t i o n i n - 120 -i -1 • I the i r at 2250 cm e s t a b l i s h e d the presence of ; the n i t r i l e f u n c t i o n . High r e s o l u t i o n mass measurement provided a molecular composition agreeing w i t h the molecular formula f o r t h i s compound. The nmr spectrum ( f i g u r e 36) can be seen on the b a s i s of our previous experience ! t o be t y p i c a l f o r t h i s c l a s s of dirners. One unusual f e a t u r e was (146) observed i n t h i s spectrum and that i s the chemical s h i f t of the C,.-r 14 proton s i g n a l . In the case of the dirners bearing no s u b s t i t u e n t at C. ' ( c f f i g u r e s 28 and 34) t h i s s i g n a l i s observed at x 3.3. The dimer having a carbomethoxy f u n c t i o n at C 1 Q r shows t h i s proton to be deshielded r e l a t i v e to t h i s and i s observed at x 3.05. In t h i s cyano dimer (146), however, the same proton i s now s t r o n g l y s h i e l d e d and i s observed at x 3.79. This i s not s u r p r i s i n g s i n c e t h i s proton and n i t r i l e f u n c t i o n are q u i t e c l o s e to each other i n one of the two p o s s i b l e rotomers and are arranged s p a t i a l l y such that the axes of t h e i r bonds are p a r a l l e l . Since the s h i e l d i n g cone of the n i t r i l e group - 122 -i s p e r p e n d i c u l a r to the a x i s of the C=N bond, the proton at i s put d i r e c t l y i n t o t h i s f i e l d . The approach to the cyano dimer (143) u s i n g the r e a c t i o n of the c h l o r o i n d o l e n i n e (118) w i t h cyanide i s c u r r e n t l y being i n v e s t i g a t e d by othei*- workers i n our l a b o r a t o r y . I f t h i s r e a c t i o n can be developed, then the d i m e r i z a t i o n approaches u s i n g e i t h e r the c h l o r o i n d o l e n i n e s or the C j 8 - a l c o h o l s w i l l serve as a general s y n t h e t i c scheme f o r both s t e r e o i s o m e r i c s e r i e s of dimers. \ As y e t , no s y n t h e t i c m a t e r i a l s are a v a i l a b l e which possess a l l the f u n c t i o n a l i t y of one of the n a t u r a l dimers. U n t i l such a compound has been sy n t h e s i z e d , the question of whether or not these s y n t h e t i c schemes provide the stereochemistry at C ' corresponding to the l o n a t u r a l systems, w i l l not be p r o p e r l y s e t t l e d . This i s a very important p o i n t and f u r t h e r s t u d i e s i n t h i s d i r e c t i o n are being i n i t i a t e d . For example, the work of t h i s t h e s i s now provides the means of s y n t h e s i z i n g v i n b l a s t i n e or the s t e r e o -isomer at C^g'. 0° the b a s i s of the s u c c e s s f u l i s o m e r i z a t i o n of isovelbanamine to velbanamine and the r e s u l t s obtained from the attempts to dimerize the t r i o l (97), i t i s a n t i c i p a t e d that the t r i o l w i l l be converted to the compound (147) on a c i d treatment. - 123 -This compound now bears the hydroxyl f u n c t i o n at w i t h the c o r r e c t stereochemistry. O x i d a t i o n of the 18-formyl s u b s t i t u e n t f o l l o w e d by e s t e r i f i c a t i o n then gives 18-carbomethoxyvelbanamine (148). D i m e r i z a t i o n w i l l produce e i t h e r v i n b l a s t i n e or i t s C 1 0-epimer and l o e i t h e r r e s u l t w i l l determine w i t h c e r t a i n t y the stereochemical course of the d i m e r i z a t i o n r e a c t i o n . I f the epimeric m a t e r i a l i s obtained the e f f e c t of t h i s stereochemical d i f f e r e n c e on the b i o l o g i c a l a c t i v i t y can then be c l e a r l y a s c e r t a i n e d . Once both these p o i n t s have been s e t t l e d , then a systematic study of the e f f e c t s of f u r t h e r s t r u c t u r a l m o d i f i c a t i o n of the dirners on b i o l o g i c a l a c t i v i t y can being. r ; EXPERIMENTAL M e l t i n g p o i n t s were determined on a K o f l e r block and are uncorrected. The u l t r a v i o l e t s p e c t r a (uv) were recorded on a Cary 11 spectrophoto-meter u s i n g methanol as so l v e n t unless otherwise s p e c i f i e d . I n f r a r e d s p e c t r a ( i r ) were recorded on a Perkin-Elmer Model 21 and Model 137 spectrometers. Nuclear magnetic resonance (nmr) s p e c t r a were recorded i n d e u t e r i o c h l o r o f o r m at 100 Hz on a Va r i a n HA-100 instrument and the chemical s h i f t s are given i n the T i e r s x s c a l e w i t h reference to t e t r a m e t h y l s i l a n e as the i n t e r n a l standard. Mass s p e c t r a were recorded on an A t l a s CH-4 or an AE-MS-9 mass spectrometer. Analyses were c a r r i e d out by Mr. P. Borda of the m i c r o a n a l y t i c a l l a b o r a t o r y , the U n i v e r s i t y of B r i t i s h Columbia. Woelm n e u t r a l alumina and S i l i c a Gel G (acc. to Stahl ) c o n t a i n i n g 1% by weight of General E l e c t r i c R e t i n a p-1 Type 188-2-7 e l e c t r o n i c phosphor were used f o r a n a l y t i c a l t h i n - l a y e r chromatography ( t i c ) . Chromatoplates were developed u s i n g 1:1 carbontetrachloride-antimony p e n t a c h l o r i d e s o l u t i o n . Woelm n e u t r a l alumina ( a c t i v i t y I I I ) was used f o r column chromatography (unless other-wise i n d i c a t e d ) . 22 Dihydrocatharanthine (34) Catharanthine h y d r o c h l o r i d e (20 g) was suspended i n water (400 c c ) , the mixture cooled to 0°C and then b a s i f i e d w i t h i c e - c o l d ammonia. - 125 -The r e s u l t i n g suspension was then e x t r a c t e d w i t h ether, the organic l a y e r d r i e d w i t h anhydrous sodium sulphate and the s o l v e n t removed to give the f r e e base as a white foam. This m a t e r i a l was d i s s o l v e d i n 95% ethanol (1000 c c ) , Adam's c a t a l y s t (800 mg) was added and the mixture s t i r r e d under hydrogen at room temperature f o r 4 days. The c a t a l y s t was f i l t e r e d o f f and the f i l t r a t e taken to dryness to give a white foam of s u b s t a n t i a l l y pure dihydrocatharanthine (17 g). Pure dihydrocatharanthine was obtained by chromatography u s i n g alumina (Woelm n e u t r a l , a c t i v i t y I , 600 g) and e l u t i n g w i t h 5% d i e t h y l ether i n benzene (14.5 g, 80%). C r y s t a l l i z a t i o n from methanol gave p l a t e s 22 mp 68-73° w i t h r e c r y s t a l l i z a t i o n and subsequent mp 145-147° ( l i t . mp i ) 63-65°, i i ) 150° decomp.) 22 D i h y d r o c a t h a r a n t h i n o l (76) L i t h i u m aluminum hydride (5.4 g) was added to a s o l u t i o n of dihydro-catharanthine (11.4 g) i n dry t e t r a h y d r o f u r a n (500 cc) and the r e s u l t i n g mixture r e f l u x e d f o r 5 hours. I t was then cooled i n i c e and water (35 cc) was added dropwise with s t i r r i n g . The grey suspension was heated under r e f l u x f o r 1/2 hour and the r e s u l t i n g white p r e c i p i t a t e f i l t e r e d o f f . The f i l t r a t e was taken to dryness to give a white foam (11.0 g) which was chromatographed on alumina (320 g ) . Pure d i h y d r o c a t h a r a n t h i n o l was e l u t e d w i t h chloroform (10.3 g ) . This m a t e r i a l c r y s t a l l i z e d from c h l o r o f o r m - l i g h t petroleum ether as rhombs mp 142-143° (7.34 g) ( l i t . 2 2 mp 132°). - 126 -D i h y d r o c a t h a r a n t h i n o l O-p-toluenesulfonate (77a) Dih y d r o c a t h a r a n t h i n o l (1.58 g) was d i s s o l v e d i n dry p y r i d i n e (30 cc) and ;p-toluenesulfonyl c h l o r i d e (4.7 g) was added t o t h i s s o l u t i o n . The r e a c t i o n was allowed to proceed f o r 10 hours at room temperature. The r e a c t i o n mixture was then cooled to 0°C, i c e - c o l d methylene c h l o r i d e (50 cc) was added and t h i s s o l u t i o n was washed w i t h 3% sodium bicarbonate s o l u t i o n (3 x 50 c c ) , keeping the s o l u t i o n at 0°C at a l l times. The methylene c h l o r i d e - p y r i d i n e s o l u t i o n was then taken to dryness u s i n g f i r s t waterpump pressure and f i n a l l y h i g h vacuum. Again the s o l u t i o n had to be kept below 0°C throughout t h i s procedure. The r e s u l t i n g red gum s t i l l c o n t a i n i n g t r a c e s of p y r i d i n e , was d i s s o l v e d i n dry benzene (5 cc) and l e f t to c r y s t a l l i z e overnight i n the r e f r i g e r a t o r . The crude t o s y l a t e was f i l t e r e d o f f to give 1.64 g of l i g h t brown c r y s t a l l i n e m a t e r i a l . The mother l i q u o r s were taken up i n benzene (10 cc) and f r e e z e - d r i e d to give a f u r t h e r 0.65 g of s u b s t a n t i a l l y pure t o s y l a t e as a re d d i s h amorphous powder. Attempts to r e c r y s t a l l i z e the c r y s t a l l i n e m a t e r i a l f a i l e d and g e n e r a l l y l e d to l e s s pure t o s y l a t e because of decomposition i n s o l u t i o n . The KBr -1 c r y s t a l l i n e m a t e r i a l gave the f o l l o w i n g data: v m a x 1355 cm (v SCO and 1173 cm - 1 (v SCL); X 292, 285, 276 (sh) . '•as 2 s 2J' max ' ' J 5,18-Seco-diene (78) Dih y d r o c a t h a r a n t h i n o l o - t o s y l a t e (400 mgs; 0.86 mmole) was d i s s o l v e d i n a s o l u t i o n of dry benzene (15 cc) and t r i e t h y l a m i n e (0.24 ml; 1.73 mmole). This s o l u t i o n was s t i r r e d under a n i t r o g e n atmosphere f o r 2 hours at 70°C to e f f e c t the displacement. The s o l u t i o n was then - 127 -cooled to room temperature and was f l u s h e d r a p i d l y through alumina ( b a s i c Woelm:, I I I , 10 g set up as a 1 inch h i g h column) usi n g p o s i t i v e pressure. A; f u r t h e r p o r t i o n of benzene (100 cc) was used to wash the column. The: combined s o l u t i o n s on removal of s o l v e n t under reduced pressure and at room temperature gave a l i g h t y e l l o w gum which c r y s t a l l i z e d on standing to give v i r t u a l l y pure product (155 mg, mp 129-135°C). This m a t e r i a l could be r e c r y s t a l l i z e d from c o l d benzene mp 130-132. Sublimation gave an a n a l y t i c a l l y pure sample mp 136-KRr 1 1 136.5. v 3445 cm ( i n d o l e N-H s t r e t c h ) , 1657 cm (v C=C, max ^ enamine), 1408, 880 ( e x o c y c l i c methylene); A 306, 235 ( s h ) , 340 in 3.x (sh) ( l o g e 4.16, 4.34, 340 r e s p e c t i v e l y ) ; NMR: T 2.05 (broad s i n g l e t , IH, N-H), 2.5-3.0 ( d i f f u s e , 4H, a r o m a t i c ) , 4.29 (broad s i n g l e t , IH, R 3N-CH=CR 2), 4.75 ( s i n g l e t , IH, R2C=CH_2) , 4.89 ( s i n g l e t , IH, R 2C=CH 2), 9.05 ( t r i p l e t , 3H, -CH2CH_3); mass spectrum: main peaks, m/e 292, 185, 168, 135, 122, 121, 107. A n a l . Calcd. f o r C 2 0 N 2 H 2 4 : C, 82.19; H, 8.22; N, 9.59; M.W. 292.194 Found: C, 82.26; H, 8.27; N, 9.72; M.W. 292.191 (high r e s o l u t i o n mass spectrometry). 18-Methylene-4B-dihydrocleavamine (79); concerted sequence from  d i h y d r o c a t h a r a n t h i n o l O-tosylate (77a) D i h y d r o c a t h a r a n t h i n o l O-p-toluenesulfonate (400 mg, 0.86 mmole) was d i s s o l v e d i n a s o l u t i o n of dry benzene (15 cc) and t r i e t h y l a m i n e (0.24 cc, 1.73 mmole). This s o l u t i o n was s t i r r e d under a n i t r o g e n f o r 2 hours at 70°C to e f f e c t the displacement. Solvent was removed, under reduced pressure and the brown res i d u e d i s s o l v e d i n methanol. - 128 -Sodium borohydride (200 mg) was added immediately and the r e a c t i o n mixture s t i r r e d f o r 0.5 hours a f t e r which, the effervescence had ceased. This s o l u t i o n was s t r i p p e d of sol v e n t and the res i d u e was p a r t i t i o n e d between dichloromethane (100 cc) and water (100 c c ) . The aqueous, l a y e r was e x t r a c t e d w i t h a d d i t i o n a l dichloromethane (2 x 50 cc) and the combined organic e x t r a c t was d r i e d over anhydrous sodium s u l f a t e and the s o l v e n t was removed to give a y e l l o w gum. This m a t e r i a l was chromatographed on alumina (100 g). Benzene e l u t i o n gave the d e s i r e d 18-methylene-48-dihydrocleavamine (182 mg); c r y s t a l l i z e d from methanol-water mp 90-94°C. A m a x 306, 315 (sh), 218 (l o g e 3.97, 3.92, 4.16, r e s p e c t i v e l y ) ; NMR: T 1.90 (broad s i n g l e t , IH, N-H), 2.5-3.0 ( d i f f u s e , 4H, arom a t i c ) , 4.79 and 4.93 (two s i n g l e t s , IH each, C^CFLp, 9.13 ( t r i p l e t , 3H, -Q^-CH^) ; Mass spectrum: main peaks, m/e 294, 292, 207, 139, 124. Anal . Calcd. f o r C0-N_H.,: M.W. 294.209. Found: M.W. 294.209. ZU Z ZD D i h y d r o c a t h a r a n t h i n o l O-methanesulfonate (77b) Dih y d r o c a t h a r a n t h i n o l (1.0 g) was d i s s o l v e d i n dry p y r i d i n e (10 cc) and t o t h i s s o l u t i o n cooled to -5°C was added f r e s h l y d i s t i l l e d methanesulfonyl c h l o r i d e (6 c c ) . The r e s u l t i n g red s o l u t i o n was s t i r r e d at 0°C f o r 20 hours. I c e - c o l d chloroform (100 cc) was then added to the r e a c t i o n mixture and the r e s u l t i n g s o l u t i o n e x t r a c t e d w i t h water (3 x 50 c c ) . The c o l d chloroform s o l u t i o n was d r i e d over anhydrous sodium s u l f a t e and concentrated under reduced pressure to a red gum. Rapid p e r c o l a t i o n of t h i s m a t e r i a l using dichloromethane as elu e n t , through alumina (IV, 30 g) removed most of the very p o l a r - 129 -I m a t e r i a l and gave the crude methanesulfonate e s t e r as a y e l l o w o i l . Chromatography on alumina (IV, n e u t r a l , 60 g) y i e l d e d non-polar i m p u r i t i e s (15 mg) i n the benzene f r a c t i o n s f o l l o w e d by the d e s i r e d d i h y d r o c a t h a r a n t h i n o l O-methanesulfonate as a yellow unstable foam. X 276, 283, 292. The methanesulfonate was unstable and was used max immediately' i n the subsequent e l i m i n a t i o n r e a c t i o n . 18-Methylene-4g-dihydrocleavamine (79); from d i h y d r o c a t h a r a n t h i n o l - O-methanesulfonate (77b) A s o l u t i o n of potassium t e r t - b u t o x i d e was prepared by d i s s o l v i n g c l e a n potassium (1.2 g) i n r e f l u x i n g t e r t - b u t a n o l (50 cc, f r e s h l y d i s t i l l e d from sodium). Dihydrocatharanthinol-O-methanesulfonate (350 mg) was d i s s o l v e d i n t h i s s o l u t i o n and the r e s u l t i n g s o l u t i o n r e f l u x e d under a n i t r o g e n atmosphere f o r 50 min. The uv of t h i s s o l u t i o n showed a maximum at 304 my with no i n d o l e a b s o r p t i o n evident. This s o l u t i o n was made j u s t a c i d i c w i t h g l a c i a l a c e t i c a c i d (2 cc) and an excess of sodium borohydride (600 mg) was added. This s o l u t i o n was r e f l u x e d f o r 3 hours. Solvent was removed under reduced pressure, the res i d u e was d i s s o l v e d i n c o l d water (100 cc) and t h i s mixture was e x t r a c t e d w i t h dichloromethane (3 x 50 c c ) . The combined organic e x t r a c t s were d r i e d over anhydrous potassium carbonate and concentrated to give a yel l o w gum (170 mg) which was chromatographed on alumina (IV, n e u t r a l , 6 g) usin g benzene as elu e n t . The e a r l y f r a c t i o n s gave the pure e x o c y c l i c o l e f i n (79) as a c o l o u r l e s s g l a s s (29 mg). This m a t e r i a l had i d e n t i c a l t i c and s p e c t r a l p r o p e r t i e s to the e x o c y c l i c o l e f i n obtained from the r e d u c t i o n of 5,18-seco-diene (78). - 130 -18-Methylene-4g-dihydrocleavamine ( 7 9 ) ; concerted sequence from  d i h y d r o c a t h a r a n t h i n o l v i a methanesulfonate e s t e r D i h y d r b c a t h a r a n t h i n o l (1 g) i n anhydrous p y r i d i n e (9 cc) was t r e a t e d at -r5°C w i t h methanesulfonyl c h l o r i d e (3 cc) . The r e s u l t i n g red s o l u t i o n was kept at 0°C f o r 3 hours. The mixture was poured i n t o i c e - c o l d dichloromethane (75 cc) and e x t r a c t e d w i t h water (2 x 50 c c ) . The organic phase was concentrated to a red c r y s t a l l i n e paste. This m a t e r i a l was p e r c o l a t e d r a p i d l y through alumina (IV, n e u t r a l , 30 g) u s i n g dichloromethane and the s o l u t i o n on removal of s o l v e n t gave a ye l l o w gum. This was d i s s o l v e d i n a s o l u t i o n of potassium t e r t -butoxide i n t e r t - b u t a n o l (3.5 g of potassium i n 200 cc dry butanol) and r e f l u x e d f o r 20 min. Solvent was removed under reduced pressure and the residue p a r t i t i o n e d between ether and water. The ether e x t r a c t was d r i e d over anhydrous sodium s u l f a t e and concentrated. The r e s u l t -i n g y e l l o w o i l was then d i s s o l v e d i n isopropanol (70 cc) and a c e t i c a c i d (1 cc) and excess sodium borohydride (2 g) was added. When the e f f e r v e s -cence had subsided, s o l v e n t was removed, the residue p a r t i t i o n e d between ether and water and the organic layer, a f t e r d r y i n g , concentrated to a y e l l o w gum. This m a t e r i a l was chromatographed on alumina (50 g). The e a r l y benzene f r a c t i o n s gave pure e x o c y c l i c o l e f i n (76) (180 mg) i d e n t i c a l on t i c and nmr w i t h the m a t e r i a l obtained from the r e d u c t i o n of 5,18-seco-diene ( 7 8 ) . 18g-Hydroxymethylcleavamine (86) 18g-Carbomethoxycleavamine (100 mg) was d i s s o l v e d i n dry t e t r a h y d r o f u r a n and l i t h i u m aluminum hydride (50 mg) was added. This - 131 -mixture was r e f l u x e d f o r 2 hours under n i t r o g e n . The r e a c t i o n product was cooled i n an i c e - b a t h and sa t u r a t e d sodium s u l f a t e (10 cc) was added dropwise. Water (50 cc) was then added and the mixture e x t r a c t e d w i t h dichloromethane (4 x 25 c c ) . The combined organic e x t r a c t s were d r i e d over anhydrous sodium s u l f a t e and the so l v e n t CHC1 was removed. The a l c o h o l obtained gave the f o l l o w i n g data; v 3: max 3450 cm"1 (v 0-H), 1030 cm"1 (v C-0); NMR: T 1.50 (broad s i n g l e t , IH, N-H), 2.5-3.0 ( d i f f u s e , 4H, arom a t i c ) , 4.66 (poorly d e f i n e d m u l t i p l e t , IH, C=CH-), 5.74 ( q u i n t u p l e t , IH, C 1 Q - p r o t o n ) , 6.32 (doublet, 2H, — l o CH-CH_20H), 8.98 ( t r i p l e t , 3H, -CH2CH_3). Mass spectrum: main peaks, m/e 310, 187, 136, 135, 124. 186-Hydroxymethylcleavamine acetate (88) 186-Hydroxymethylcleavamine (92 mg) was d i s s o l v e d i n a s o l u t i o n of a c e t i c anhydride i n p y r i d i n e (10% v/v) and the r e s u l t i n g s o l u t i o n s t i r r e d at room temperature f o r 1 day under a n i t r o g e n atmosphere. The r e a c t i o n mixture was cooled t o 0°C and was then poured onto i c e (crushed % 30 g). On s t i r r i n g , the acetate c r y s t a l l i z e d from the KRr 1 -1 mixture (83 mg) mp 123-127°C; v ^ : 1705 cm (v C=0), 1260 cm (v C-0); NMR:T 1.87 (broad s i n g l e t , IH, N-H), 2.5-3.0 ( d i f f u s e , 4H, aro m a t i c ) , 4.75 (broad s i n g l e t , IH, C=CH-), 5.5 (broad t r i p l e t , IH, C 1 0-H), 5.70 and 5.98 (two doublet of doublets, 2H, CH-CHJDAc), 7.98 l o —2. ( s i n g l e t , 3H, -OAc), 8.96 ( t r i p l e t , 3H, -CH^H^) . Mass spectrum: main peaks, m/e 352, 293, 229, 136, 135, 124, 122. - 132 -j 18grHydroxymethylcleavamine 3,5-dinitrobenzoate (89) 183-Hydrpxymethylcleavamine (470 mg) was dissolved i n dry pyr i d i n e (25 c c ) . This s o l u t i o n was cooled to 0°C and 3,5-dinitro-benzoyl ch l o r i d e was added i n portions over a 10 minute i n t e r v a l . The r e s u l t i n g red s o l u t i o n was s t i r r e d f o r 1 hour at 0°C and was then poured onto crushed i c e (^  300 g). On s t i r r i n g a p r e c i p i t a t e formed which was f i l t e r e d o f f to give the crude product (714 mg). Chromato-graphy on alumina (200 g) gave the pure 3,5-dinitrobenzoate (89) (406 mg) with benzene e l u t i o n . The material c r y s t a l l i z e d from methanol KBr as bri g h t orange needles; mp 155-157°C; \ : 293, 285, 228; v : IHcLX IH3.X 3400 cm - 1 ( v N-H), 1710 cm - 1 (v C=0), 1545 cm"1 ( v -NO.), 1340 cm"1 (v s N0 2), 1280 cm - 1 (v C-0); NMR: T 9.09 ( t r i p l e t , IH, benzoate p-proton 1.03 (doublet, 2H, benzoate o-protons), 2.10 (broad s i n g l e t , IH, N-H), 2.5-3.0 ( d i f f u s e , 4H, aromatic), 4.70 (broad doublet, IH, C=CH-), 5.16 ( q u i n t r i p l e t , IH, C^g-H), 5.41 and 5.63 (two doublet of doublets, 2H, CH-CH20R), 8.99 ( t r i p l e t , 3H, -CH2CH_3). 18g-Hydromethyl-4g-dihydrocleavamine (92) from the hydroboration of  the 5,18-seco-diene (78) The 5,18-seco-diene (78), was prepared from dihydrocatharanthinol 0-tosylate (300 mg) and was used as the crude re a c t i o n product. On forming, i t was immediately disso l v e d i n a diborane-tetrahydrofuran s o l u t i o n (diborane produced from sodium borohydride (200 mg) and boron t r i f l u o r i d e - e t h e r a t e (1 cc) i n diglyme (25 cc) and bubled into tetrahydrofuran (25 c c ) ) . This s o l u t i o n was s t i r r e d f o r 1 hour at room temperature. 2 M aqueous potassium hydroxide s o l u t i o n was added - 133 -u n t i l the effervescence had ceased and then hydrogen peroxide (0.5 cc, 30%) was added. The s o l u t i o n was s t i r r e d f o r 10 min.'and was then p a r t i t i o n e d between dichloromethane (100 cc) and water (100 c c ) . Further e x t r a c t i o n w i t h dichloromethane (2 x 50 cc) and removal of s o l v e n t from the combined organic e x t r a c t s gave the crude product as a y e l l o w gum. This m a t e r i a l was chromatographed on alumina (20 g). E l u t i o n w i t h benzene-20% e t h y l acetate gave the l e s s p o l a r decomposi-t i o n products i n the f i r s t three f r a c t i o n s . The f o l l o w i n g ten f r a c t i o n s contained a mixture of the a l c o h o l and the amine boranes of the a l c o h o l . These f r a c t i o n s combined (85 mg) was d i s s o l v e d i n a s o l u t i o n of t e t r a h y d r o f u r a n (25 cc) and t r i e t h y l a m i n e (1 cc) and r e f l u x e d under n i t r o g e n f o r 2 hours. The s o l v e n t was removed under reduced pressure and the crude product chromatographed u s i n g alumina (III, 10 g ) . Benzene-20% e t h y l a c e t a t e e l u t i o n gave 18g-hydroxymethyl-4B-dihydrocleavaraine (47 mg) which c r y s t a l l i z e d from methanol-water. Sublimed sample mp 146.5-147.5°C; X 293, 285, 275(sh), 221 (log e 3.76, 3.84, 3.72, 4.44, r e s p e c t i v e l y ) ; v : 3510 cm ( v N-N), i n 3 . x 3300 cm"1 (v 0-H), 1045 cm"1 (v C-0); NMR: T 1.54 (broad s i n g l e t , IH, NH), 2.5-3.0 ( d i f f u s e , 4H, a r o m a t i c ) , 5.84 ( q u i n t u p l e t , IH, C l g-H), 6.27 (doublet, 2H, CH-CH_20H), 9.16 ( t r i p l e t , 3H, -CH2CH_3) . Mass spectrum: main peak, m/e 312, 207, 138, 124. ~ Anal. C a l c d . f o r C_„H_oN„0: C, 76.91; H, 8.98; N, 8.98; 0, 5.13. Found: C, 77.17; H, 8.88; N, 8.79. - 134 -183-Hydromethyl-43-dihydrocleavamine acetate mp 156-160°C, v KBr max 1700 cm -1 (v C=0), 1265 cm -1 (v C-0); NMR: T 1.92 (broad s i n g l e t , IH, N-H), 2.5-310 ( d i f f u s e , 4H, aromatic), 5.4-6.0 ( d i f f u s e , 3H, -CH^OAc, C l g-H), 7.97 ( s i n g l e t , 3H, OAc), 9.13 ( t r i p l e t , 3H, -CH2CH_3). 18g-Hydroxymethyl-43-dihydrocleavamine (92), from hydroboration of  18-methylene-4g-dihydrocleavamine Dihydrocatharanthinol (200 mg) was converted to 18-methylene-43-dihydrocleavamine (79) using the procedure already o u t l i n e d . The crude product was dissolved i n anhydrous tetrahydrofuran (25 cc) and the s o l u t i o n was cooled to 0°C. Diborane i n tetrahydrofuran (3.0 cc, 2.0 M) was added dropwise over a 1 hour period. The r e a c t i o n mixture was then allowed to come to room temperature and s t i r r e d f o r an a d d i t i o n a l 0.5 hour. The excess diborane and solvent were removed using water-pump pressure. The residue was taken up in tetrahydrofuran (50 c c ) , aqueous sodium hydroxide (10 dp, 3M) was added followed by hydrogen peroxide (0.10 cc, 30%) and the 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 min. The r e a c t i o n mixture was p a r t i t i o n e d between water (150 cc and dichloromethane (100 c c ) . Further e x t r a c t i o n with dichloromethane (2 x 50 cc) and removal of solvent from the combined organic extracts gave the crude product as a yellow gum. This material was chromato-graphed on alumina (70 g) using ethylacetate as e l u t i n g solvent. The main products were; the desired 183-hydroxymethyl-43-dihydrocleav-amine (92) (22 mg), i d e n t i c a l with the material obtained from hydroboration of 5,18-seco-diene; amine-borane, A, (R^ 0.7, alumina t i c , ethylacetate elution) (61 mg) and a second amine-borane, B, - 135 -(R f 0.6, 14 mg). Amine-borane A was d i s s o l v e d i n anhydrous t e t r a h y d r o f u r a n (10 cc) 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 cc) and the s o l u t i o n r e f l u x e d f o r 2 hours under n i t r o g e n . Pure 183-hydroxymethyl-48-dihydrocleavamine was obtained on t a k i n g the r e a c t i o n s o l u t i o n to dryness and c r y s t a l l i z -i n g the r e s i d u e from methano1-water. Amine-borane B, was d i s s o l v e d i n anhydrous t e t r a h y d r o f u r a n (2 cc) c o n t a i n i n g t r i e t h y l a m i n e (0.05 cc) and the s o l u t i o n was r e f l u x e d f o r 2 hours under n i t r o g e n . A mixture of s t a r t i n g amine-borane B and the a l c o h o l was obtained. Separation by p r e p a r a t i v e t i c gave pure 188-hydroxymethy1-48-dihydrocleavamine. 18g-Hydroxymethyl-43-dihydrocleavamine (92) from r e d u c t i o n o f 188- carbomethoxy-48-dihydrocleavamine (52) 188-Carbomethoxy-48-dihydrocleavamine (100 mg) was added to a s o l u t i o n of l i t h i u m aluminum hydride (70 mg) i n t e t r a h y d r o f u r a n (15 cc) and the r e a c t i o n mixture was r e f l u x e d f o r 2 hours. The mixture was cooled i n an i c e bath and sa t u r a t e d aqueous sodium s u l f a t e s o l u t i o n (0.5 cc) was added dropwise. Water (100 cc) was then added and t h i s mixture was e x t r a c t e d w i t h dichloromethane (5 x 25 c c ) . The combined e x t r a c t was d r i e d over anhydrous sodium s u l f a t e and the so l v e n t was removed under reduced pressure. The s l i g h t l y y e l l o w gum could be c r y s t a l l i z e d from methanol-water (64 mg, mp 140-144). Sublimation gave a white c r y s t a l l i n e sample mp 146.5-147.5°C i d e n t i c a l to the m a t e r i a l obtained from the hydroboration of both 5,18-seco-diene and 18-methylene-48-dihydrocleavamine. - 136 -T e t r o l (96) Pure 5,;18-seco-diene (78) (300 mg) was d i s s o l v e d i n a s o l u t i o n o f anhydrous t e t r a h y d r o f u r a n (18 cc) and dry p y r i d i n e (1.8 c c ) . The r e a c t i o n was c a r r i e d out i n a long-necked f l a s k and t h i s f l a s k con-t a i n i n g the s o l u t i o n was immersed i n a dry ice-acetone bath such that 3 or 4 inches of the neck of the f l a s k was a l s o immersed. A s o l u t i o n o f osmium t e t r o x i d e (522 mg) i n anhydrous t e t r a h y d r a f u r a n (5 cc) was then added dropwise over a 1 hour p e r i o d and i n such a manner that i t ran down the cooled neck of the f l a s k . In t h i s way i t was assured t h a t the osmic a c i d s o l u t i o n was cooled to the bath temperature when i t reached the r e a c t i o n mixture. Care was taken to keep the system c l o s e d to the atmosphere w h i l e adding the osmic a c i d s o l u t i o n to prevent condensation of water i n t o the r e a c t i o n s o l u t i o n . The r e a c t i o n mixture was s t i r r e d f o r an a d d i t i o n a l 6 hours and was then allowed to come t o room temperature over a 1/2 hour p e r i o d . I t was then poured i n t o a s o l u t i o n of ethanol-dichloromethane (1:1, 50 cc) and hydrogen s u l f i d e was bubbled through t h i s s o l u t i o n w i t h r a p i d s t i r r i n g f o r 10 min. This mixture was f i l t e r e d through c e l i t e and the black residue was washed w i t h an a d d i t i o n a l amount of ethanol-dichloromethane (1:1, 100 c c ) . The r e s i d u e was then suspended i n t r i e t h y l a m i n e (20 cc) and s t i r r e d f o r about 15 hours. This mixture was f i l t e r e d and washed as before. The combined f i l t r a t e was taken to dryness and chromatographed on alumina (50 g). Dichloromethane-1% methanol s o l u t i o n e l u t e d the d e s i r e d t e t r o l which c r y s t a l l i z e d on t a k i n g the eluent to dryness (187 mg). This m a t e r i a l r e c r y s t a l l i z e d from methanol-water; mp 120-123°C; A 293, 285, 275, 228 ( l o g e 3.85, 3.89, 3.82, 4.52, - 137 -r e s p e c t i v e l y ) ; X n u ; J" 0 1: 3360 cm"1, 3510 cm" 1(sh), 3350 cm"1 (v OH and r / max NH); NMR: T 1.84 (broad s i n g l e t , IH, N-H), 2.4-3.0 ( d i f f u s e , 4H, aro m a t i c ) , 5.42 (broad s i n g l e t , IH, :; N-CHOH), 6.36 (broad s i n g l e t , sharpened on D 20 exchange, 2H, -CH_20H), 8.96 ( t r i p l e t , 3H, -CH2CH_3). Mass spectrum: main peaks, m/e 342, 311, 143, 91, no parent i o n . A n a l : f o r M + - H 20(18). Calcd. f o r C 20 N2°3 H26 : 342.194. Found: 342.192 (high r e s o l u t i o n mass spectrometry). T r i o l (97) The t e t r o l (96) (330 mg) was d i s s o l v e d i n methanol (50 cc) and sodium borohydride (200 mg) was added. The s o l u t i o n was s t i r r e d at room temperature f o r 1 hour. The sol v e n t was removed and the res i d u e was p a r t i t i o n e d between dichloromethane (100 cc) and water (100 c c ) . The aqueous phase was e x t r a c t e d w i t h an a d d i t i o n a l q u a n t i t y of d i c h l o r o -methane (2 x 50 cc) and the combined e x t r a c t s a f t e r d r y i n g over anhydrous sodium s u l f a t e , was s t r i p p e d of s o l v e n t . The res i d u e c r y s t a l l i z e d on t r i t u r a t i o n w i t h methanol to give pure t r i o l (97) (325 mg). This m a t e r i a l could be r e c r y s t a l l i z e d from methanol-water; mp 230-235 (decomp.); X : 293, 285, 277(sh), 227, (log e 3.87, 3.91, 3.87, 4.53, r e s p e c t i v e l y ) ; X n u ^ 0 1 : 3540, 3430 and 3200 cm"1 (v 0-H ' ' r 1 J max ' and N-H); NMR: T 0.29 (broad s i n g l e t , l o s t on deuterium exchange, IH, 0-H), 1.48 (broad s i n g l e t , IH, N-H), 2.5-3.0 ( d i f f u s e , 4H, arom a t i c ) , 6.22 ( s i n g l e t , 2H, -CH_20H), 9.10 ( t r i p l e t , 3H, -CH2CH_3) . Mass spectrum: main peaks, m/e 344, 326, 154, 95, 92, 91. Anal . Calcd. f o r C„ nH„ oN.0_: 344.206. Found: 344.210 (high — - zU zo z J • . r e s o l u t i o n mass spectrometry). - 138 -i K e t o l (98) j The t r i o l (97) (150 mg) was d i s s o l v e d i n acetone (15 cc), and a f t e r d i s s o l u t i o n , water (5 cc) was added. This s o l u t i o n was cooled i n an ice-water bath and to i t was added dropwise an aqueous s o l u t i o n of sodium p e r i o d a t e (90 mg i n 10 c c ) . The s o l u t i o n was s t i r r e d f o r 1.5 hours at 0°C. The r e a c t i o n s o l u t i o n was then poured i n t o ice-water (70 cc) and e x t r a c t e d w i t h dichloromethane (3 x 50 c c ) . The combined e x t r a c t s were d r i e d over anhydrous sodium s u l f a t e and then s t r i p p e d of s o l v e n t to give a y e l l o w gum. This m a t e r i a l was chromatographed on alumina (20 g ) ; dichloromethane-1% methanol e l u t i o n brought down the d e s i r e d k e t o l (98) (75 mg). Further e l u t i o n using dichloromethane-2% methanol gave some of the s t a r t i n g t r i o l (15 mg). The k e t o l could be c r y s t a l l i z e d from methanol-water to give y e l l o w p l a t e s ; mp 105-109 ( d e c ) ; ^ m a x : 317, 238, ( l o g e. 4.25, 4.16, r e s p e c t i v e l y ) ; X ™ j o 1 : 3430 cm"1 (v N-H), 3100 cm"1 (v 0-H), 1615 cm - 1 (v C=0); NMR: x 0.73 (broad s i n g l e t , IH, N-H), 2.4-3.0 ( d i f f u s e , 4H, a r o m a t i c ) , 7.82 (broad s i n g l e t , l o s t on deuterium exchange, IH, 0-H), 9.03 ( t r i p l e t , 3H, -C^CHO . Mass spectrum: main peaks, m/e 312, 154, 144, 143, 140. An a l . Calcd. f o r C 1 9 H 2 4 0 2 N 2 : 312.184. Found: 312.183 (high r e s o l u t i o n mass spectrometry). D i o l (99) The k e t o l (98) (93 mg) was d i s s o l v e d i n methanol (20 cc) and the s o l u t i o n cooled i n an i c e - b a t h . Sodium borohydride (100 mg) was added; the r e a c t i o n mixture was allowed to come t o room temperature and was then s t i r r e d f o r two hours. The s o l u t i o n was taken to dryness and - 139 -p a r t i t i o n e d between dichloromethane (50 cc) and water (50 c c ) . The aqueous phase was f u r t h e r e x t r a c t e d w i t h dichloromethane and then the combined organic e x t r a c t s , a f t e r d r y i n g over anhydrous sodium s u l f a t e , was taken to dryness. The product c r y s t a l l i z e d r e a d i l y from d i c h l o r o -methane to give the pure d i o l (99) (86 mg) mp 195-200°C ( d e c ) ; X : in 3.x 294, 286, 279(sh), 227 ( l o g e 3.83, 3.86, 3.82, 4.50, r e s p e c t i v e l y ) ; n u j o l 3 2 5 0 - 1 a n d 3 3 6 Q c m * l ( s h ) ( v o-H and v N-H); NMR: x 1.62 max v J ^ J ' (broad s i n g l e t , IH, N-H), 2.5-3.0 ( d i f f u s e , 4H, a r o m a t i c ) , 4.28 (doublet of doublets, J=2,10 Hz, IH, C._-H), 9.08 ( t r i p l e t , 3H, -CH_CH_). Mass l o Z —o spectrum: main peaks, m/e 314, 173, 154, 144, 142, 140, 130, 124. An a l . Calcd. f o r CinH-,0-N_:- 314.199. Found: 314.199 (high i y zo z z r e s o l u t i o n mass spectrometry). Isovelbanamine (100) The d i o l (99) (100 mg) was d i s s o l v e d i n anhydrous N-methylmorpholine (20 c c ) , l i t h i u m aluminum hydride (100 mg) was added and the r e s u l t i n g mixture was r e f l u x e d f o r 10 hours. A f t e r t h i s time, i t was cooled i n an i c e - b a t h and a s a t u r a t e d aqueous sodium s u l f a t e s o l u t i o n (0.5 cc) was added dropwise. Water (60 cc) was added to t h i s mixture and t h i s was then e x t r a c t e d w i t h e t h y l acetate (5 x 20 c c ) . The combined e x t r a c t s were taken to dryness and the r e s i d u e chromatographed on alumina (10 g). Dichloromethane e l u t i o n gave isovelbanamine (100) which c r y s t a l l i z e d from t h i s s o l v e n t (42 mg), mp 190-194°; ^ m a x ° . 293, 286, 276(sh), 229 ( l o g e 3.88, 3.90, 3.82, 4.54, r e s p e c t i v e l y ) ; V m a x ° 1 ; 3 2 5 0 c m _ 1 ^ °~ H^' 3 5 0 0 c m _ 1 ^ v N " H ) ; N M R : T 2 - 2 6 ( b r o a d s i n g l e t , IH, N-H), 2.5-3.0 ( d i f f u s e , 4H, a r o m a t i c ) , 6.56 (complex m u l t i p l e t , - 140 -i 1H, C 1 0-H), 8.77 (broad s i n g l e t , disappears on deuterium exchange, IH, l o 0-H), 9.13 ( t r i p l e t , 3H, -CH C H ) . Mass spectrum: main peaks, m/e 298, 154. An a l . C a l c d . f o r CinH_,0N_: 298.205. Found: 298.205 (high i y zo z r e s o l u t i o n mass spectrometry). Cleavamine (23); dehydration of isovelbanamine (100) Concentrated s u l f u r i c a c i d (0.5 cc, 36 N) was cooled i n an i c e -water bath and to t h i s c o l d a c i d was added isovelbanamine (100)(10 mg). The compound d i s s o l v e d s l o w l y and the 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 under a dry n i t r o g e n atmosphere f o r 2 hours. This s o l u t i o n was then added dropwise to an i c e - c o l d ammonium hydroxide s o l u t i o n (10 cc, 2N) and the r e s u l t i n g suspension was e x t r a c t e d w i t h dichloromethane (3 x 5 c c ) . The combined e x t r a c t s were f l u s h e d through alumina (1 g) and the e l u t e d m a t e r i a l concentrated to give a p a l e y e l l o w gum (9 mg). This m a t e r i a l was chromatographed on alumina (1 g) e l u t i n g w i t h benzene to g i ve the d e s i r e d cleavamine contaminated with some s l i g h t l y more p o l a r m a t e r i a l . Rechromatography on alumina (1 g) e l u t i n g w i t h petroleum ether-benzene (1:1) gave pure cleavamine which c r y s t a l l i z e d from methanol (2.6 mg), mp 113-117°C ( L i t 2 2 ' 3 6 mp 117-119°). This m a t e r i a l had t i c p r o p e r t i e s i d e n t i c a l to an a u t h e n t i c sample of cleavamine and the i r spectrum ( n u j o l ) was superimposable to that of the a u t h e n t i c sample. 18g-Cyanocleavamine (109) A s o l u t i o n of cleavamine (250 mg) i n dichloromethane (30 cc) and - 141 -t r i e t h y l a m i n e (0.15 cc) was cooled i n an ice-acetone ,bath and to i t was added dropwise a s o l u t i o n o f t e r t - b u t y l h y p o c h l o r i t e i n carbon l' t e t r a c h l o r i d e (48 cc of 0.38 M), over the p e r i o d of 1 hour. This r e a c t i o n s o l u t i o n was then taken t o dryness and the r e s i d u e d i s s o l v e d i n a s o l u t i o n of fused sodium acetate (250 mg) i n g l a c i a l a c e t i c a c i d (22.5 cc) and a c e t i c anhydride (2.5 c c ) . This s o l u t i o n was s t i r r e d at room temperature f o r 1 hour and then f o r 2 hours at 60°C. The s o l v e n t was removed under vacuum and the r e s i d u e d i s s o l v e d i n ethanol and f l u s h e d through a short column of alumina (20 g as a 1" column). The e l u t e d m a t e r i a l on removal of s o l v e n t gave the crude quaternary ammonium s a l t as a pale y e l l o w foam. This crude m a t e r i a l was d r i e d f o r 3 hours under high vacuum at about 70°C. Potassium cyanide (250 mg) d r i e d i n a s i m i l a r manner was added to t h i s r e s i d u e and dimethyl-formamide (15 cc) was d i s t i l l e d from over barium oxide i n t o the r e a c t i o n f l a s k . This r e a c t i o n mixture was r e f l u x e d under a n i t r o g e n atmosphere f o r 1 3/4 hours. The s o l v e n t was removed under reduced pressure and the r e s i d u e obtained was chromatographed us i n g alumina ( I I I , 15 g). Benzene e l u t i o n gave the d e s i r e d product, 18g-cyano-cleavamine (109), which c r y s t a l l i z e d r e a d i l y from methanol-water (81.3 mg); mp 87-90°; A : 293, 284, 277, 225, ( l o g e 3.89, 3.96, 3.93, 4.57, r e s p e c t i v e l y ) ; v n U ^ Q l : 2240 cm 1 (v C=N); NMR: T 1.60 (broad s i n g l e t , IH, N-H), 2.5-3.0 ( d i f f u s e , 4H, a r o m a t i c ) , 4.48 (doublet of doublets, J = 2 Hz and 10 Hz, IH, C 1 0 - p r o t o n ) , 4.74 (poorly d e f i n e d doublet, IH, CH=C ), 8.96 ( t r i p l e t , 3H, -CH^C^). Mass spectrum: main peaks, m/e 305, 136, 124. - 142 -An a l . Calcd. f o r C^H^y 305.189. Found: 305.187 (high r e s o l u t i o n inass spectrometry). j * 18g-Carbomethoxycleavamine (60), from 18g-cyanocleavamine (109) 18g-Cyanocleavamine (109) (81 mg) was d i s s o l v e d i n d i e t h y l e n e g l y c o l (2.5 cc) and potassium hydroxide (0.5 g) was added. This mixture was kept at 150° f o r 9 hours. The s o l u t i o n was then cooled i n an i c e - b a t h , made s l i g h t l y a c i d i c w i t h a s o l u t i o n of methanol s a t u r a t e d w i t h h y d r o c h l o r i c a c i d . A l a r g e excess of diazomethane i n d i e t h y l e t h e r was added and the r e a c t i o n mixture was s t i r r e d v i g o r o u s l y f o r 0.5 hour. The s o l u t i o n was allowed to come to room temperature and the excess diazomethane was blown o f f u s i n g a stream of n i t r o g e n . Water (150 cc) was then added and the s o l u t i o n was ex t r a c t e d w i t h d i e t h y l e t h e r (4 x 50 c c ) . The combined e x t r a c t s were washed w i t h water (2 x 25 c c ) , d r i e d over anhydrous sodium s u l f a t e and taken to dryness. The res i d u e was chromatographed on alumina (10 g) and pure 18g-carbomethoxycleavamine (45 mg) was obtained on e l u t i o n w i t h petroleum ether-benzene (1:1). This m a t e r i a l c r y s t a l l i z e from methanol, mp 122-126°C ( L i t . mp 122-123°C); i t had i d e n t i c a l p r o p e r t i e s compared with an au t h e n t i c sample of 18g-carbomethoxycleav-amine on t i c , and gave a superimposable i n f r a r e d spectrum. Cleavamine N-borane (116) Cleavamine (50 mg) was d i s s o l v e d i n anhydrous t e t r a h y d r o f u r a n (5 and the s o l u t i o n cooled to 0°C. Diborane produced e x t e r n a l l y (by . the r e a c t i o n of a s o l u t i o n of sodium borohydride (17 mg) i n anhydrous - 1 4 3 ' diglyme (5 cc) with a s o l u t i o n of b o r o n t r i f l u o r i d e - e t h e r a t e (0.07 cc) i n anhydrous'diglyme (2 cc)) was passed i n t o the r e a c t i o n s o l u t i o n over the p e r i o d of 1 hour. The r e a c t i o n mixture was allowed to come to room temperature and s t i r r e d f o r an a d d i t i o n a l 1/2 hour. I t was then p a r t i t i o n e d between dichloromethane (50 cc) and water (50 c c ) ; the aqueous phase was e x t r a c t e d w i t h a d d i t i o n a l dichloromethane (2 x 25 cc) and the combined organic e x t r a c t s taken to dryness. The product c r y s t a l l i z e d r e a d i l y from benzene (43 mg). A : 293, 285, 275(sh); nicLX v C H C 1 3450 cm - 1 (sharp, v N-H), 2375 cm"1 (v B-H), 1170 cm"1 w i t h 2260 max r cm 1 overtone (6 B-H). The amine-borane (25 mg) was d i s s o l v e d i n anhydrous t e t r a h y d r o -fu r a n (1.0 c c ) , t r i e t h y l a m i n e (0.2 cc) was added and t h i s s o l u t i o n was r e f l u x e d f o r 2 hours under a n i t r o g e n atmosphere. The r e a c t i o n mixture was p a r t i t i o n e d between dichloromethane (20 cc) and water (20 cc) and the organic phase was taken to dryness. Chromatography on alumina ( I I I , 10 g) gave on e l u t i o n w i t h petroleum ether-benzene (1:1) pure cleavamine (14 mg), i d e n t i f i e d by t i c and i r . Hydroboration of cleavamine using cleavamine N-borane (116) - Cleavamine N-borane (40 mg) was d i s s o l v e d i n anhydrous diglyme (2 cc) and t h i s s o l u t i o n was r e f l u x e d under a n i t r o g e n atmosphere f o r 1.5 hour. The r e a c t i o n s o l u t i o n was then allowed to come to room temperature, aqueous potassium hydroxide s o l u t i o n (1 dp, 2 M) was added f o l l o w e d by hydrogen peroxide (60 y l , 30%) and the 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 f o r 15 min. The r e a c t i o n mixture was p a r t i t i o n e d between ether (20 cc) and water (20 c c ) , and the organic phase taken - 144 -t o dryness. The product mixture was separated i n t o i t s components by p r e p a r a t i v e t i c . The i n i t i a l s e p a r a t i o n on alumina with benzene-20% e t h y l a c e t a t e e l u t i o n gave the non-polar m a t e r i a l s (18 mg) and two more p o l a r m a t e r i a l s , A w i t h R f 0.2 (2.0 mg) andB with R f 0.15 (2.5 mg). B was i d e n t i c a l i n t i c and i r w i t h 3a-hydroxy-4g-dihydrocleavamine obtained by hydroboration i n subsequent work and A on the b a s i s of s i m i l a r t i c and i r i s probably the epimeric a l c o h o l . A second p r e p a r a t i v e t i c system (alumina, benzene elution 1) was used to separate the l e s s p o l a r m a t e r i a l s . Cleavamine (8 mg) and 4g-dihydrocleavamine (5.5 mg) were obtained and were i d e n t i f i e d by t i c and nmr comparison w i t h a u t h e n t i c samples. 3q-Hydroxy-4g-dihydrocleavamine (117); hydroboration of cleavamine (23) To a s o l u t i o n of cleavamine (23) (450 mg) i n anhydrous t e t r a h y d r o -f u r a n cooled i n an i c e - b a t h , was added to 10 molar excess of diborane (8 cc of 2 M diborane i n tetrahydrofuran) dropwise over a 1 hour p e r i o d . The r e a c t i o n s o l u t i o n was then allowed to come to room temperature and s t i r r e d f o r an a d d i t i o n a l 0.5 hour. The s o l v e n t and excess diborane were removed under water-pump pressure to give a s l i g h t l y y e l l o w gum. This r e s i d u e was d i s s o l v e d i n t e t r a h y d r o f u r a n (50 cc) and aqueous sodium hydroxide (0.5 cc, 3 M) was added f o l l o w e d by hydrogen peroxide s o l u t i o n (0.7 ml, 30%). This s o l u t i o n was s t i r r e d f o r 15 min. at room temperature and r e a c t i o n was then quenched by p a r t i t i o n i n g i t between dichloromethane (100 cc) and water (100 c c ) . The aqueous phase was f u r t h e r e x t r a c t e d w i t h dichloromethane (2 x 50 cc) and the combined e x t r a c t s were taken to dryness to give the crude - 145 -amine-borane (634 mg). This m a t e r i a l was d i s s o l v e d i n t e t r a h y d r o f u r a n (50 c c ) , t r i e t h y l a m i n e (0.7 cc) was added and the s o l u t i o n was r e f l u x e d under a n i t r o g e n atmosphere f o r 2 hours. The so l v e n t was removed and the res i d u e was chromatographed on alumina (200 g). E l u t i o n w i t h dichloromethane gave the d e s i r e d 3a-hydroxy-4B-dihydrocleavamine which c r y s t a l l i z e d on c o n c e n t r a t i o n of the eluent; mp 131-139°C, (342 mg). This m a t e r i a l could be sublimed to give a n ! a n a l y t i c a l sample; mp 140-156°C; X : 293, 286, 277(sh), 229 ( l o g e 3.87, 3.90, 3.85, 4.54, r e s p e c t i v e l y ) ; v C H C 1 3 : 3440 cm - 1 (v N-H), 3250 cm"1 (v 0-H); IH3-X NMR: x 2.14 (broad s i n g l e t , IH, N-H), 2.5-3.0 ( d i f f u s e , 4H, arom a t i c ) , 6.4 (complex m u l t i p l e t , 2H, C^-OH and C l g-H), 8.5 (broad, IH, disappears on deuterium exchange, 0-H), 9.10 ( t r i p l e t , 3H, -C^-CH ) . Mass spectrum: main peaks, m/e 298, 154, 144, 143. . Ana l . Calcd. f o r C 1 9 H 2 6 N 2 0 : C, 76.51; H, 8.72; N, 9.40; M.W. 298.205. Found: C, 76.35; H, 8.57; N, 9.25; M.W., 298.203 (high r e s o l u t i o n mass spectrometry). 3a-Acetoxy-4g-dihydrocleavamine 3ct-Acetoxy-4B-dihydrocleavamine was obtained from 3a-hydroxy-4B-dihydrocleavamine by a normal a c e t i c a nhydride-pyridine a c e t y l a t i o n . The compound c r y s t a l l i z e d from methanol-acetone, mp 212-215°C; vmax°^ : 1720 cm"1 (v C=0), 3370 cm"1 (v N-H); NMR: x 2.08 (broad s i n g l e t , IH, N-H), 2.5-3.0 ( d i f f u s e , 4H, arom a t i c ) , 4.90 (doublet of doublets, J = 6, 10 Hz, IH, C^OAc), 6.4 (complex m u l t i p l e t , IH, C l g-H), 9.17 ( t r i p l e t , 3H, -CH2CH.j) . Mass spectrum: main peaks, m/e 340, 280, 196, 144, 143, 138, 136. - 146 -j A n a l . Calcd. f o r C_.H.oN_0 • 340.215. Found: 340.213 (high — — z l Z o z z , r e s o l u t i o n mass spectrometry). ' . I i -Velbanamine (22) Isovelbanamine (100) (65 mg) was d i s s o l v e d i n an aqueous s u l f u r i c a c i d s o l u t i o n (10 cc, 10% v/v) and t h i s s o l u t i o n was r e f l u x e d under a n i t r o g e n atmosphere f o r 2 days. The s o l u t i o n was then cooled to 0°C and added dropwise to an i c e - c o l d aqueous ammonium hydoxide s o l u t i o n (20 cc, 5 N). The r e s u l t i n g suspension was e x t r a c t e d u s i n g dichloromethane (3 x 25 cc) and the combined organic e x t r a c t was taken to dryness. The r e s i d u e was chromatographed on alumina (20 g). Dichloromethane e l u t i o n gave velbanamine (7.9 mg) i n f r a c t i o n 4 and 5 (15 cc f r a c t i o n s ) and isovelbanamine (21 mg) i n f r a c t i o n s 7 to 10. The velbanamine c r y s t a l l i z e d from methanol-water, mp 144-146° (authentic 71 velbanamine , mp 117-134°, r e c r y s t a l l i z e d from methanol-water, mp 143-146°). The s y n t h e t i c velbanamine e x h i b i t e d i d e n t i c a l t i c p r o p e r t i e s and had an i r spectrum (nu j o l ) superimposable to that of the au t h e n t i c sample. 183-Carbomethoxycleavamine (60) To a 1 l i t r e , three-necked round bottomed'flask, ' f i t t e d w i t h a r e f l u x condenser and mechanical s t i r r e r , was added g l a c i a l a c e t i c a c i d (300 c c ) . The a c i d was heated to 100°C and then catharanthine h y d r o c h l o r i d e (11.0 g) w i t h a f u r t h e r p o r t i o n of a c e t i c a c i d (100 cc) was added with r a p i d s t i r r i n g . Immediately a p o r t i o n of sodium borohydride was added; 42 g were added over about a 1 hour p e r i o d at - 147 -a r a t e which maintained the temperature at 90-105°C, t a k i n g c a u t i o n t o keep the r a t e of hydrogen e v o l u t i o n under c o n t r o l . A f t e r the a d d i t i o n r was complete, the r e a c t i o n mixture was cooled i n an i c e - b a t h and the r e s u l t i n g v i s c o u s mass was poured i n t o aqueous ammonium hydroxide s o l u t i o n (500 cc, 9 N). The r e s u l t i n g suspension was e x t r a c t e d w i t h dichloromethane (3 x 400 cc) and the combined organic e x t r a c t e d a f t e r d r y i n g over anhydrous sodium s u l f a t e , was taken to dryness to give a white foam (10.85 g ) . C r y s t a l l i s a t i o n from methanol gave pure 188-3 carbomethoxycleavamine, f i r s t crop 4.4 g, mp 121-123°C (aut h e n t i c sample mp 122-123°C). 183-Carbomethoxy-48-dihydrocleavamine (32) 188-Carbomethoxycleavamine (4.4 g) was hydrogenated at room temperature and atmospheric pressure over Adam's c a t a l y s t (350 mg) i n e t h y l a c e t a t e (50 c c ) . Hydrogen uptake ceased a f t e r 2 hours. The c a t a l y s t was f i l t e r e d o f f and the sol v e n t removed to give a white foam. This m a t e r i a l c r y s t a l l i z e d from methanol to give pure 48-37 dihydrocleavamine, f i r s t crop 4.1 g, mp 143-145°C (authentic sample mp 146-148°C). 4g-Dihydrocleavamine (29) A s o l u t i o n of 18B-carbomethoxy-4g-dihydrocleavamine (3.0 g) i n aqueous h y d r o c h l o r i c a c i d (190 cc, 5 N) was heated to 90°C under a n i t r o g e n atmosphere and the temperature was maintained f o r 7 hours. The s o l u t i o n was cooled i n an ice-water bath and made j u s t b a s i c by - 148 -the a d d i t i o n ;of ammonium hydroxide (15 N). The suspension was e x t r a c t e d w i t h dichloromethane (3 x 125 c c ) , the organic e x t r a c t s d r i e d f over anhydrous sodium s u l f a t e and the s o l v e n t removed. The r e s i d u e c r y s t a l l i z e d from methanol to give 48-dihydrocleavamine (2.4 g, 37 mp 134-138°); (a u t h e n t i c sample mp 136-138°C). Ch l o r o i n d o l e n i n e of 48-dihydrocleavamine (41) A s o l u t i o n of t e r t - b u t y l h y p o c h l o r i t e i n carbon t e t r a c h l o r i d e (7.1 cc, 0.050 M) was added over a 0.5 hour p e r i o d to a s o l u t i o n of 48-dihydrocleavamine (100 mg) i n dichloromethane (13.3 cc) and t r i e t h y l a m i n e (0.07 cc) which was cooled i n an ice-acetone bath. A f t e r the a d d i t i o n was complete, the s o l u t i o n was s t i r r e d f o r an a d d i t i o n a l 15 min. at the bath temperature. The orange-coloured s o l u t i o n was then d i l u t e d w i t h an equal volume of benzene and r a p i d l y p e r c o l a t e d through a column of alumina (1.5 g ) . Solvent was removed under reduced pressure, the l a s t t r a c e s under high vacuum, to provide X S O O C13.T1e the chloroindolenine as a pale yellow o i l (101 mg); ^ m a x ' 227, CHf" 1 - 1 260, 303 ( l o g e 4.31, 3.55, 3.42 r e s p e c t i v e l y ) ; v 3: 2776 cm max (Bohlman bands), 1600 and 1560 cm - 1 ( i n d o l e n i n e C=N); NMR: T 2.5-3.0 ( d i f f u s e , 4H, a r o m a t i c ) , 8.79 (quar t e t , 2H, -CH_2CH3), 9.14 ( t r i p l e t , 3H, -CH2CH_3); Mass spectrum: main peaks, m7e 316, 281, 138, 124. An a l . Calcd. f o r C ^ H ^ N ^ l : 316.171. Found: 316.172 (high r e s o l u t i o n mass spectrometry). Dimer (118), from c h l o r o i n d o l e n i n e of 48-dihydrocleavamine (41) plus  v i n d o l i n e (11) The c h l o r o i n d o l e n i n e of 48-dihydrocleavamine (557 mg) and v i n d o l i n e - 149 -! 1 | (523 mg) were d i s s o l v e d i n anhydrous methanolic 1.5% h y d r o c h l o r i c I a c i d s o l u t i o n . This s o l u t i o n was r e f l u x e d f o r '2.5 hours under a dry n i t r o g e n atmosphere. The r e a c t i o n mixture was d i l u t e d w i t h water (87 cc) and the r e s u l t i n g s o l u t i o n was made j u s t b a s i c w i t h potassium carbonate. E x t r a c t i o n w i t h dichloromethane (5 x 50 cc) and removal of the s o l v e n t a f t e r d r y i n g the e x t r a c t s over anydrous sodium s u l f a t e gave the crude dimer as a ye l l o w g l a s s - l i k e m a t e r i a l (1.006 g). Chromatography on alumina (100 g) gave the pure dimer (118) on e l u t i o n w i t h benzene-ethylether (1:1) as a c o l o u r l e s s g l a s s (656 mg). CHC1 C r y s t a l l i s a t i o n from methanol gave a sample, mp 205-206°; v m a x 3 : 3430 cm"1 (v N-H), 1733 cm - 1 (v C=0 f o r -OAc, -CO Me), 1630 cm"1 (v C=C f o r v i n d o l i n e ) ; X : 214, 257, 287, 293, 310(sh), ( l o g e 4.63, ni 3.x 4.18, 4.06, 4.07, 3.88 r e s p e c t i v e l y ) ; NMR: T 0.38 (broad s i n g l e t , IH, 0-H), 2.13 (broad s i n g l e t , IH, i n d o l e N-H), 2.5-3.0 ( d i f f u s e , 4H, i n d o l e a r o m a t i c ) , 3.32 ( s i n g l e t , IH, i n d o l i n e , C^-H), 3.92 ( s i n g l e t , IH, i n d o l i n e C^-H), 4.16 (broad doublet of doublets, IH, C =C_HR), I / D I 4.66 ( s i n g l e t , IH, C.HOAc), 4.76 (broad doublet, IH, C_=CAHR), 5.57 (broad doublet, IH, c ' -H), 6.14 ( s i n g l e t , 3H, C.,-0CH,), 6.28 ( s i n g l e t , 0 l o l o —o 3H, -C0CH 3), 6.36 ( s i n g l e t , IH, C 2~H), 7.35 ( s i n g l e t , 3H, N-CH 3), 7.97 ( s i n g l e t , 3H, OAc), 9.17 ( t r i p l e t , 3H, C^CH CH ), 9.93 ( t r i p l e t , 3H, C 5CH 2CH_ 3). Mass spectrum: main peaks, m/e 58, 60, 74, 91, 92, 106, 107, 121, 122, 135, 138, 149. Anal. Calcd. f o r C..H_-0,N.: 736.420. Found: 736.420. Calcd. 44 56 6 4 f o r M + + IH, (C,.H__0,N,); 737.428. Found: 737.425. Calcd. f o r M + - IH 44 57 6 A (C„ .H„ cO,N.); 735.412. Found: 735.408. v 44 55 6 4 J - 150 -Cleavage of dimer (118) The dimer (118) as the hy d r o c h l o r i d e (30 mg) was d i s s o l v e d i n anhydrous methanolic 7% h y d r o c h l o r i c a c i d s o l u t i o n (5 c c ) . To t h i s s o l u t i o n was added t i n (50 mg) and stannous c h l o r i d e (50 mg) and the r e a c t i o n mixture was r e f l u x e d f o r 2 hours under a n i t r o g e n atmosphere. A f t e r t h i s time, a c e t y l c h l o r i d e (1 cc) and an a d d i t i o n a l amount of t i n (50 mg) was added and the mixture r e f l u x e d f o r another 1 hour. This s o l u t i o n was then made b a s i c w i t h ammonium hydroxide s o l u t i o n and e x t r a c t e d w i t h dichloromethane (2 x 25 c c ) . The crude r e a c t i o n product obtained on t a k i n g the organic e x t r a c t to dryness was separated i n t o i t s components u s i n g p r e p a r a t i v e alumina t i c e l u t i n g w i t h e t h y l -a c e tate-chloroform (1:1). The products i s o l a t e d were 48-dihydrocleav-amine (5.9 mg), v i n d o l i n e (2.-3 mg), s t a r t i n g dimer (3.4 mg) and d e s a c e t y l v i n d o l i n e (10.2 mg). Each of these m a t e r i a l s were i d e n t i f i e d by t i c and i r comparison w i t h samples of au t h e n t i c m a t e r i a l . C h l o r o i n d o l e n i n e of 18g-carbomethoxy-4B-dihydrocleavamine (120) To a s o l u t i o n o f 186-carboamethoxy-46-dihydrocleavamine (400 mg) i n dichloromethane (40 cc) and t r i e t h y l a m i n e (0.2 cc) cooled i n an ice-water bath, was added a s o l u t i o n of t e r 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 (25 cc, 0.05 M) over a p e r i o d of 45 min. The s o l u t i o n was washed w i t h ice-water (2 x 30 c c ) , d r i e d over anhydrous sodium s u l f a t e and the sol v e n t was removed under reduced pressure to d 10 X 3-Tl 6 give the c h l o r o i n d o l e n i n e as an amorphous s o l i d (440 mg); ^ m a x : 292, 275, 227 (l o g e 3.44, 3.44, 4.30 r e s p e c t i v e l y ) ; v C H C 1 3 : 2775 cm"' IH3-X (Bohlmann bonds), 1727 cm 1 (v C=0), 1612 and 1575 cm 1 ( i n d o l e n i n e v - 151 -C=N); NMR: T 2.40-2.98 (4H, a r o m a t i c ) , 5.53 (doublet, IH, C g - H ) , 6.41 ( s i n g l e t , 3H', -COOCH_3), 9.14 ( t r i p l e t , 3H, -CH2CH_3). Mass spectrum: main peaks, m/e 376, 374, 138, 124. A n a l . Calcd. f o r C ^ ^ N ^ C l : 374.176. Found: 374.174, (high r e s o l u t i o n mass spectrometry). Dimer (119) The c h l o r o i n d o l e n i n e of 183-carbomethoxy-43-dihydrocleavamine (400 mg) and v i n d o l i n e (336 mg) were d i s s o l v e d i n anhydrous methanolic 1.5% h y d r o c h l o r i c a c i d s o l u t i o n and 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 under a n i t r o g e n atmosphere f o r 3 hours. The s o l v e n t was removed under reduced pressure and the r e s i d u e was p a r t i t i o n e d between dichloromethane (100 cc) and aqueous potassium bicarbonate s o l u t i o n (100 cc, 1%). The aqueous phase was e x t r a c t e d w i t h a f u r t h e r amount of dichloromethane (2 x 30 cc) and the combined e x t r a c t s were d r i e d over anhydrous sodium s u l f a t e . The s o l v e n t was removed to give a y e l l o w g l a s s - l i k e r e s i d u e (823 mg). This m a t e r i a l was chromatographed on alumina (100 g); benzene-diethylether (1:1) e l u t i o n gave the d e s i r e d dimer as a c o l o u r l e s s g l a s s . C r y s t a l l i z a t i o n from methanol gave a sample, mp 221-225°C; X : 217, 265, 287, 296, 313(sh) (l o g e 4.48, 3.93, 3.92, 3.92, 3.78 r e s p e c t i v e l y ) ; v C H C 1 3 : 3430 cm - 1 (v N-H), 1730 cm - 1 (v C=0), 1630 cm"1 (v C=C); NMR: T 0.49 (broad s i n g l e t , IH, OH), 1.00 (broad s i n g l e t , IH, N-H), 2.5-3.0 ( d i f f u s e , 4H, i n d o l e a r o m a t i c ) , 3.05 ( s i n g l e t , IH, C^-H), 4.04 ( s i n g l e t , IH, C^-H), 4.12 (doublet of doublets, IH, C 6=C yHR), 4.67 ( s i n g l e t , IH, C 4~H),. 4.72 (broad doublet, IH, C ?=C 6H), 6.16 ( s i n g l e t , 3H, -OMe), 6.29 ( s i n g l e t , 6H, two-COOMe), 6.36 ( s i n g l e t , IH, C -H), 7.40 ( s i n g l e t , 3H, - 152 -N-Me), 7.96 ( s i n g l e t , 3H, -OAc), 9.09 ( t r i p l e t , 3H, C 4-CH 2CH_ 3), 9.34 ( t r i p l e t , 3Hi C CH CH ). Mass spectrum: main peaks, m/e 58, 74, 91, 106, 107, 121, 122, 135, 138. Anal . C a l c d . f o r M 794.425. Found: 794.419. Cal c d . f o r M + + H, C.JL^OoN,,: ' 46 59 8 4 795.433. Found: 795.428. Cal c d . f o r M + +2H, C.^H^O-N.: 46 60 8 4 Calc d . f o r M + -IH, C,,H_,0oN • ' 46 57 8 4 Calc d . f o r M + -2H, C.-H C £0 oN • ' 46 56 8 4 792.409. 793.417. 796.441. Found: 796.437. Found: 793.410. Found: 792.403 (high r e s o l u t i o n mass spectrometry). Cleavage of dimer (119) The dimer (119) as the hy d r o c h l o r i d e (50 mg) was d i s s o l v e d i n anhydrous methanolic 7% h y d r o c h l o r i c a c i d s o l u t i o n (5 c c ) , and t i n (100 mg) and stannous c h l o r i d e (100 mg) were added. This mixture was r e f l u x e d f o r 1 hour under a n i t r o g e n atmosphere, and was then b a s i f i e d u s i n g ammonium hydroxide s o l u t i o n . To t h i s suspension was added dichloromethane (50 cc) and water (30 cc) and the emulsion formed on shaking was f i l t e r e d under reduced pressure. The aqueous phase was e x t r a c t e d w i t h a f u r t h e r amount of dichloromethane and combined organic e x t r a c t s were d r i e d over anhydrous sodium s u l f a t e and taken to dryness. The crude product (53 mg) was separated i n t o i t s components by p r e p a r a t i v e alumina t i c us i n g e t h y l a c e t a t e - c h l o r o f o r m (1:1) as e l u t i n g s o l v e n t . The products obtained were v i n d o l i n e (12.6 mg), d e s a c e t y l v i n d o l i n e (3.2 mg), 18a-carbomethoxydihydrocleavamine (8.1 mg) and 18g-carbomethoxydihydrocleavamine (8.0 mg). The i d e n t i t y of these products was e s t a b l i s h e d by a comparison w i t h a u t h e n t i c m a t e r i a l s on - 153 -t i c ; superimposable i r s p e c t r a were obtained f o r a l l except 18a-carbo-methoxy-48-dihydrocleavamine. The i d e n t i t y of t h i s compound was e s t a b l i s h e d !by nmr comparison w i t h an a u t h e n t i c sample. 18-Methylene-4g-dihydrocleavamine (79) from 18g-hydroxymethyl-4g- dihydrocleavamine (92) To a s o l u t i o n of 18g-hydroxymethyl-4g-dihydrocleavamine (200 mg) i n dry p y r i d i n e (20 cc) was added f r e s h l y prepared 3 , 5 - d i n i t r o b e n z o y l c h l o r i d e (110 mg). The r e s u l t i n g red s o l u t i o n was s t i r r e d at room temperature f o r 2 days. Dichloromethane (100 cc) was then added to the r e a c t i o n mixture and t h i s s o l u t i o n was then washed b r i e f l y w i t h aqueous sodium carbonate s o l u t i o n (100 cc, 3%), f o l l o w e d by water (100 c c ) . The organic phase was d r i e d over anhydrous sodium s u l f a t e and s t r i p p e d of s o l v e n t to give a red gum. Chromatography on alumina (30 g) gave 18-methylene-4g-dihydrocleavamine (43 mg) w i t h benzene as e l u t i n g s o l v e n t . E l u t i o n w i t h benzene-10% d i e t h y l e t h e r gave s t a r t i n g 18g-hydroxymethyl-4g-dihydrocleavamine (86 mg). The 18-methylene-4g-dihydro-cleavamine was i d e n t i c a l i n a l l respects w i t h a sample obtained from the fragmentation r e a c t i o n of d i h y d r o c a t h a r a n t h i n o l - O - t o s y l a t e . 18-Hydroxymethyl-4g-dihydrocleavamine benzoate (138) 18-Hydromethyl-4g-dihydrocleavamine (200 mg) was d i s s o l v e d i n t r i e t h y l a m i n e (15 cc) and benzoyl c h l o r i d e (0.11 cc) was added. This s o l u t i o n was s t i r r e d at room temperature f o r 12 hours. A f t e r t h i s time, the t r i e t h y l a m i n e was removed under reduced pressure and the r e s i d u e was d i s s o l v e d i n dichloromethane (50 c c ) . This s o l u t i o n was - 154 -washed w i t h aqueous sodium bicarbonate (50 cc, 3%) f o l l o w e d by water (50 cc) and the organic phase was then d r i e d over anhydrous sodium s u l f a t e and s t r i p p e d o f s o l v e n t . The res i d u e was chromatographed on alumina (20 g) u s i n g petroleum ether-benzene (1:1) as eluant to give 183-hydromethyl-48-dihydrocleavamine benzoate (184 mg); X : 227, nicLX pupI _ 1 283, 293, 305(sh), 315 (sh), 335(sh); v 3: 1720 cm (v OO); NMR: m 3.x T 1.32 (broad s i n g l e t , IH, N-H), 1.7-3.0 (complex, 9H, i n d o l e and benzoate a r o m a t i c ) , 5.35 (broad s i n g l e t , 2H, -CH_20C0R), 5.55 ( m u l t i p l e t , I H , c l g - H ) . ; Dimer (142) The d i o l (99) (193 mg) and v i n d o l i n e (226 mg) were d i s s o l v e d i n an anhydrous methanolic h y d r o c h l o r i c a c i d s o l u t i o n (18 cc, 1%) and t h i s s o l u t i o n was r e f l u x e d under a n i t r o g e n atmosphere f o r 4 hours. The r e a c t i o n was then poured i n t o i c e - c o l d aqueous ammonium hydroxide (20 cc, 2N) and the r e s u l t i n g suspension was e x t r a c t e d w i t h d i c h l o r o -methane (3 x 30 c c ) . The combined organic e x t r a c t s were taken to dryness and the res i d u e was chromatographed on alumina (100 g). The dimer (142)(197 mg) was e l u t e d w i t h dichloromethane-1% methanol. Further e l u t i o n w i t h t h i s s o l v e n t gave some d e s a c e t y l dimer (12 mg). The dimer (142) c r y s t a l l i z e d from d i e t h y l - e t h e r ; mp 205-215 (dec); ^ m a x : 213, 257, 286, 293, 312(sh) ( l o g c 4.61, 4.10, 3.95, 3.97, 3.82 resp e c t -i v e l y ) ; v ™ ^ 0 1 : 3400 cm"1 (v N-H, 0-H), 1740 cm"1 (v C=0); NMR: T 0.47 max (broad s i n g l e t , IH, 0-H), 2.24 (broad s i n g l e t , IH, N-H), 2.5-3.1 ( d i f f u s e , 4H, i n d o l e a r o m a t i c ) , 3.30 ( s i n g l e t , IH, C 1 4~H), 3.97 ( s i n g l e t , IH, 0,.,-H), 4.18 (doublet of doublets, IH, C,.=C,HR), 4.68 I / 6 /— ( s i n g l e t , IH, C -H), 4.7 (broad doublet, IH, C =C HR), 5.56 (broad - 155 -doublet, IH, C j g - H ) , 6.19 ( s i n g l e t , 3H, -OMe), 6.27 ( s i n g l e t , 3H, -C0 2Me), 6.36 ( s i n g l e t , IH, C 2~H), 7.39 ( s i n g l e t , 3H, N-Me), 7.99 ( s i n g l e t , 3H, OAc), 9.24 ( t r i p l e t , 3H, C^-CJ^CH ), 9.49 ( t r i p l e t , 3H, CgCH^CH^). Mass spectrum: main peaks, m/e 50, 51, 57, 69, 77, 78, 88, 101, 128, 154, 165, 204. A n a l . Calcd. f o r C..H_£0_N„: 752.415. Found: 752.414 (high 44 56 7 4 • 6 r e s o l u t i o n mass spectroscopy). Cleavage of dimer (142) The dimer (142) (50 mg) was d i s s o l v e d i n an anhydrous methanolic h y d r o c h l o r i c a c i d s o l u t i o n (5 cc, 6%) and t i n (50 mg) and stannous c h l o r i d e (50 mg) were added. This mixture was r e f l u x e d under a n i t r o g e n atmosphere f o r 3 hours. A f t e r t h i s time i t was b a s i f i e d by the a d d i t i o n of ammonium hydroxide s o l u t i o n and e x t r a c t e d w i t h d i c h l o r o -methane (3 x 15 c c ) . The r e s i d u e obtained on t a k i n g the organic e x t r a c t s to dryness was chromatographed on alumina (5 g). E l u t i o n w i t h dichloromethane gave f i r s t v i n d o l i n e (4.0 mg), f o l l o w e d by i s o v e l b a n -amine (3.9 mg). Changing to the dichloromethane-1% methanol as e l u e n t , gave d e s a c e t y l v i n d o l i n e (3.6 mg), s t a r t i n g dimer (18.0 mg) and d e s a c e t y l dimer (8.3 mg). The methanol f l u s h gave a mixture of u n i d e n t i f i e d p o l a r products (6.3 mg). The above m a t e r i a l s were i d e n t i f i e d by comparison on t i c and i r w i t h a u t h e n t i c samples. 188-Hydroxy-4g-dihydrocleavamine (132) 48-Dihydrocleavamine (88 mg) was converted t o the corresponding -c h l o r o i n d o l e n i n e as p r e v i o u s l y described. This m a t e r i a l was d i s s o l v e d - 156 -i n g l a c i a l a c e t i c a c i d (2 cc) and a f t e r d i s s o l u t i o n , water (1 cc) was added. This s o l u t i o n was s t i r r e d at room temperature f o r 24 hours. A f t e r t h i s time i t was poured i n t o aqueous ammonium hydroxide s o l u t i o n (10 c c , 5 N) and the r e s u l t i n g suspension was e x t r a c t e d w i t h d i c h l o r o -methane (3 x 10 c c ) . The combined e x t r a c t was taken to dryness and the resi d u e was chromatographed on alumina (20 g ) . Dichloromethane e l u t i o n . i gave f i r s t some s t a r t i n g c h l o r o i n d o l e n i n e (20 mg) and f u r t h e r e l u t i o n gave the d e s i r e d 18g-hydroxy-4g-dihydrocleavamine (27 mg). This m a t e r i a l c r y s t a l l i z e d from methanol-water, mp 203-205°C. Comparison w i t h an au t h e n t i c sample, mp 202-205°, showed i d e n t i c a l t i c p r o p e r t i e s and superimposable i r s p e c t r a . Dimer (118), from 18g-hydroxy-4g-dihydrocleavamine (132) p l u s v i n d o l i n e 18g-Hydroxy-4g-dihydrocleavamine (132) (106 mg) and v i n d o l i n e (157 mg) were d i s s o l v e d i n an anhydrous methanolic h y d r o c h l o r i c a c i d s o l u t i o n (1%, 10 cc) and the s o l u t i o n was r e f l u x e d under a n i t r o g e n atmosphere f o r 4 hours. The r e a c t i o n mixture was then poured i n t o i c e - c o l d aqueous ammonium hydroxide s o l u t i o n (10 cc, 5 N) and the r e s u l t i n g suspension was e x t r a c t e d w i t h dichloromethane (3 x 30 c c ) . The combined organic e x t r a c t was taken to dryness and the re s i d u e was chromatographed on alumina (100 g). Dichloromethane e l u t i o n gave v i n d o l i n e (10 mg) i n the e a r l y f r a c t i o n and f u r t h e r e l u t i o n gave the dimer (118) (173 mg). Dichloromethane-1% methanol e l u t i o n gave d e s a c e t y l v i n d o l i n e (3 mg) which was fo l l o w e d by d e s a c e t y l dimer (15 mg). The major dime r i c product, dimer (118), had i d e n t i c a l t i c p r o p e r t i e s - a n d gave the same nmr spectrum as that obtained f o r the product from - 157 -the d i m e r i s a t i o n of the c h l o r o i n d o l e n i n e o f 48-dihydrocleavamine (41) w i t h v i n d o l i n e . 18g-Cyano-48-dihydrocleavamine (42) 48-Dihydrocleavamine (1.00 g) was converted to the corresponding c h l o r o i n d o l e n i n e by the procedure already described. This m a t e r i a l I was d i s s o l v e d i n a s o l u t i o n of fused sodium acetate (10 g) i n g l a c i a l a c e t i c a c i d (80 cc) and a c e t i c anhydride (20 c c ) . This s o l u t i o n was warmed to 60°C f o r 2 hours. The s o l v e n t was removed under reduced pressure; high vacuum was used f o r the l a s t t r a c e s . The r e s i d u e was f l u s h e d through a short column of alumina (20 g as a 2" column) us i n g et h a n o l . This s o l v e n t was removed and the r e s i d u e was d r i e d under high vacuum. Potassium cyanide (500 mg) was added and i n t o the r e a c t i o n v e s s e l was d i s t i l l e d dimethylformamide from over barium oxide. This mixture was r e f l u x e d f o r 1 2/3 hour. The s o l v e n t was removed under reduced pressure and the dichloromethane s o l u b l e m a t e r i a l was chromatographed on alumina (200 g ) . Benzene e l u t i o n gave the d e s i r e d 188-cyano-48-dihydrocleavamine (42) (224 mg). This m a t e r i a l c r y s t a l l i z e d from methanol, mp 150-152° and showed i d e n t i c a l t i c p r o p e r t i e s and superimposable i r and nmr spectras compared w i t h an a u t h e n t i c sample, mp 150-152°. Dimer (146), from 18B-cyano-48-dihydrocleavamine 188-Cyano-48-dihydrocleavamine (147 mg) was d i s s o l v e d i n a s o l u t i o n o f dichloromethane (17 cc) and t r i e t h y l a m i n e (0.079 cc) and t h i s s o l u t i o n was cooled to ice-acetone bath temperature. A s o l u t i o n - 158 -of t e r t - b u t y l h y p o c h l o r i t e i n carbon t e t r a c h l o r i d e (12 cc, 0.042 M) was added dropwise to the cooled s o l u t i o n , over a 0.5 hour p e r i o d . The s o l v e n t was removed under reduced pressure and an a l i q u o t of benzene (20 cc) was added to the r e s i d u e and d i s t i l l e d o f f i n order to azeotrope o f f any water which might be present. To t h i s crude c h l o r o -i n d o l e n i n e was added v i n d o l i n e (217 mg) and t h i s mixture was d i s s o l v e d i n an anhydrous methanolic h y d r o c h l o r i c a c i d s o l u t i o n (15 cc, 1%). The s o l u t i o n was r e f l u x e d under a n i t r o g e n atmosphere f o r 2 hours. A f t e r t h i s time, the s o l v e n t was removed, the r e s i d u e was taken up i n water (50 cc) and made s l i g h t l y b a s i c . This mixture was e x t r a c t e d w i t h dichloromethane (3 x 30 cc) and the combined e x t r a c t s taken to dryness. The r e s i d u e was chromatographed on alumina (100 g ) . Benzene-5% e t h y l acetate e l u t i o n gave unconsumed v i n d o l i n e (119 mg) and benzene-10% e t h y l a c e t a t e e l u t i o n gave the dimer (146) (22 mg). This m a t e r i a l c r y s t a l l i z e d from d i e t h y l - e t h e r , mp 204-224°C; * m a x ' 215, 265, 285, 294, 312(sh) ( l o g e 4.68, 4.19, 4.02, 4.01, 3.78, r e s p e c t i v e l y ) ; ^ n u j o l . 3 3 2 0 c m - l ( v N _ H ^ Q _ H ^ 1 7 4 Q c m - l ^ c = 0- ). m R : t Q y ( v e r y broad, IH, 0-H), 1.90 (broad, IH, N-H), 2.5-3.0 ( d i f f u s e , 4H, i n d o l e a r o m a t i c ) , 3.79 ( s i n g l e t , IH, C 1 4-H), 3.94 ( s i n g l e t , IH, C i y-H), 4.20 (doublet of d o u b l e t s , IH, C 6=C ?HR), 4.70 ( s i n g l e t , IH, C 4-H), 4.80 (broad doublet, IH, C ?=C 6HR), 6.12 ( s i n g l e t , 3H, -OCH^, 6.29 ( s i n g l e t , 3H, -C0 2CH_ 3), 6.36 ( s i n g l e t , IH, C 2~H), 7.35 ( s i n g l e t , 3H, N-CH 3), 7.99 ( s i n g l e t , 3H, -OAc), 9.11 ( t r i p l e t , 3H, C 4-CH 2CH_ 3), 9.45 ( t r i p l e t , 3H, Cg-CH2CH_3). Mass spectrum: main peaks, m/e 50, 51, 55, 57, 67, 69, 77, 78, 79, 107, 122, 124, 128, 135, 138. Anal. Calcd. f o r C ^ H ^ O ^ : 761.415. Found: 761.413 (high r e s o l u t i o n mass spectrometry). - 159 -Bi b l i o g r a p h y 1. R.F. Raf f a u f , L l o y d i a , 25, 255 (1962). 2. R. Robinson, J . Chem. S o c , 1079 (1936). 3. E. Leete, "Biogenesis of N a t u r a l Compounds", P. Be r n f e l d (ed), p. 745, Pergamon Press, Oxford and London, 1963. 4. M. Gates, R.B. Woodward, W.F. Newhall and R. K u n z l i , J . Amer. Chem. S o c , 72_, 114 (1950). j 5. D.H.R. Barton, G.W. K i r b y , W. S t e g l i c h and CM. Thomas, J . Chem. S o c , 2423 (1965). A.R. Battersby, T.A. Dobson, and H. Ramuz, i b i d , 2434 and 3323 (1965). 6. R.B. Woodward, M.P. Cava, W.D. O l l i s , A. Hung, H.U. Doeniker and K. Shenker, Tetrahedron 19_, 247 (1963). 7. R.B. Woodward, F.E- Bader, H. B i c k e l , A.J. Frey and R.W. K i e r s t a d , Tetrahedron, 2_> 1 (1968). 8. A.R. Battersby, A.R. Burnett, and P.G. Parsons, Chem. Comm., 1282 (1968), and references c i t e d t h e r e i n . 9. N.R. Farnsworth, L l o y d i a 24_, 105 (1961). 10. J.L. H a r t w e l l , L l o y d i a 30, 379 (1967). 11. C T . Beer, B r i t i s h Empire Cancer Campaign, 33rd Annual Report 487 (1955). 12. R.L. Noble, C T . Beer, and J.H. C u t t s , Ann. N.Y. Acad. S c i . , 76, 882 (1958) and Biochem. Pharmacol., 1_, 347 (1958). 13. C H . Svoboda, J . Amer. Pharm. A s s o c , S c i . Ed., 47, 834 (1958). 14. a) N. Neuss, M. Gorman, W. Hargrove, N.J. Cone, K. Biemann, C Buchi and R. Manning, J . Amer. Chem. S o c , 86, 1440 (1964). b) J.W. Moncrief and W.N. Lipscomb, J . Amer. Chem. S o c , 87, 4963 (1965). 15. a) N. Neuss, M. Gorman, N.J. Cone, and L.L. Huckster, Tetrahedron L e t t e r s , 783 (1968). b) D.J. Abraham, and N.R. Farnsworth, J . Pharm. S c i . , 58, 694 (1969). 16. N. Neuss, L.L. Huckster and N.J. Cone, Tetrahedron L e t t e r s , 811 (1967). 17.. C H . Svoboda, "Proceedings o f the F i r s t Symposium of the European Cancer Chemotherapy Group", Excerpta Medica Foundation, New York, N.Y., 9, 1966. - 160 -18. A.C. S a r t o r e l l i , and W.A. Creasy, A. Rev. Pharmac. 9_, 51 (1969) 19. "Symposium on v i n c r i s t i n e " , Cancer Chemother. Rep., 52, 453 (1968). 20. W.W. Hargrave, L l o y d i a 27, 340 (1964). 21. N. Neuss, M. Gorman, H.E. Boaz and N.J. Cone, J . Amer. Chem. S o c , 84, 1509 (1962). 22. M. Gorman, N. Neuss, and N.J. Cone, J . Amer. Chem. S o c , 87, 93 (1965). 23. K. Biemann and G. S p i t e l l e r , J . Amer. Chem. S o c , 84, 4578 (1962). 24. J.P. Kutney, J . T r o t t e r , T. Tabata, A. Kerigan and N. Camerman, Chem. and Ind., 648 (1963). ' 25. E. Wenkert, J . Amer. Chem. S o c , 84, 98 (1962). 26. J.P. Kutney and E. P i e r s , J . Amer. Chem. S o c , 86^ 953 (1964). 27. J.P. Kutney, R.T. Brown, and E. P i e r s , J . Amer. Chem. S o c , 86, 2286 (1964). 28. J.P. Kutney, R.T. Brown and E. P i e r s , J . Amer. Chem. Soc., 86, 2287 (1964). 29. A. Camerman, N. Camerman, J.P. Kutney, E. P i e r s and J . T r o t t e r , Tetrahedron L e t t e r s , 637 (1965). 30. J.P. Kutney, N. Abdurahman, P. LeQuesne, E. P i e r s and I. V l a t t a s , J . Amer. Chem. S o c , 88_, 3656 (1966). 31. J.P. Kutney, W.J. Cretney, P. LeQuesne, B. McKague and E. P i e r s , J . Amer. Chem. S o c , 88_, 4756 (1966). 32. J.P. Kutney, K.K. Chan, A. F a i l l i , J.M. Fromson, C. G l e t s o s , and V.R. Nelson, J . Amer. Chem. S o c , 90, 3891 (1968). 33. G. Buchi and R.E. Manning, J . Amer. Chem. S o c , 88_, 2532 (1966). 34. U. Renner, D.A. P r i n s , and W.G. S t a l l , Helv. Chim. Act a , 42, 1572 (1959). 35. M.F. B a r t l e t t , D.F. D i c k e l and W.I. T a y l o r , J . Amer. Chem. S o c , 80, 126 (1958). 36. J.P. Kutney, R.T. Brown and E. P i e r s , Can. J . Chem., 43, 1545 (-1965) - 161 -37. J.P. Kutney, W.J. Cretney, J.R. H a d f i e l d , E.S. H a l l and V.R. Nelson, J . Am. Chem. S o c , March (1970). 38. R.C. E l d e r f i e l d , B. F i s h e r and J.M. Lagowski, J . Org. Chem., 22, 1376 (1957). 39. D.G. Lee, "Ox i d a t i o n w i t h T r a n s i t i o n Metal Compounds" i n Ox i d a t i o n , V o l . I , R.L. Augustine ed., Marcel Dekker, Inc., New York, 1969. 40. R. Stewart, O x i d a t i o n Mechanisms, W.A. Benjamin, Inc., New York, 1964. | ! 41 . M.F. B a r t l e t t , R. S k l a r , W.I. T a y l o r , E. S c h l i t t e r , R.L.S. Amai, P. Beak, N.V. B r i n g i and E. Wenkert, J . Amer. Chem. S o c , 84, 622 (1962). 42. U . Renner, K.A. Jaeggi and D.A. P r i n s , Tetrahedron L e t t e r s , 3697 (1965). 43. R. G o u t a r e l , F. Percheron and M.M. Janot, Comp. Rend., 246, 279 (1958). 44. C A . Brob. B u l l . Soc. chim. France, 1360 (1960). 45. L.F. F i e s e r and M. F i e s e r , Reagents f o r Organic S y n t h e s i s , J . Wiley and Sons, Inc., New York (1967). 46. We are indebted to Dr. U. Renner of J.R. Geigy A.G., Basle, f o r a sample of the 5,18-seco-diene d e r i v e d from voacanginol-O-t o s y l a t e . 47. M. Hesse, I n d o l a l k a l o i d e i n T a b e l l e n , Springer V e r l a g , B e r l i n , 1964, J . u l e i n , p. 102. 48. F.E. Z i e g l e r , J.A. Kloek and P.A. Z o r e t i c , J . Amer. Chem. S o c , 91_, 3242 (1969). 49. G.H. A l t , " E l e c t r o p h i l i c S u b s t i t u t i o n s and A d d i t i o n s t o Enamines", i n Enamines, A.G. Cook, ed., Marcel Dekker, New York, 1969. 50. J.W. Lewis and A.A. Pearce, Tetrahedron L e t t e r s , 2039 (1964). 51 . H.C. Brown, Hydroboration, Benjamin, New York (1962). 52. M.E. Kuehne, "Enamines i n Organic S y n t h e s i s " i n Enamines, A.G. Cook, ed., Marcel Dekker, New York, 1969. 53. P.L. J u l i a n , E.W. Meyer, and H.C. P r i n t y , "The Chemistry of Indoles", i n H e t e r o c y c l i c Compounds, R.C. E l d e r f i e l d , Ed., J . Wiley and Son, Inc., New York, (1960), p. 67. - 162 -54. J.B. Brown, H.B. Henbest, and E.R.H. Jones, J . Chem. S o c , 3172 (1952). 55. E.E. van Tamelen, M. Shamma, A.W. Bu r g s t a h l e r , J . Wolinsky, P.Tamm, and P.E. A l d r i c h , J . Amer. Chem. S o c , 80, 5007 (1958). 56. J.A. B a l l a n t i n e , C.B. B a r r e t t , R.J. Beer, R.G. Baggiano, S. Eardby, B.E. Jennings and A. Robertson, J . Chem. S o c , 2227 (1957). 57. L.J. Dolby, and S. Sakai , Tetrahedron 23, 1 (1967). 58. R.M. S i l v e r s t e i n and G.C. B a s s l e r , Spectrometric I d e n t i f i c a t i o n of Organic Compounds, J . Wiley and Son, I n c i , New York, 1964, p. 87. 59. J.P. Kutney, W.J. Cretney, P. LeQuesne, B. McKague and E. P i e r s , J . Amer. Chem. S o c , March (1970). 60. J . Mokry and I . Kompis, L l o y d i a 27_, 428 (1964). 61. L.J. Dolby and D.L. Booth, J . Org. Chem., 30_, 1550 (1965). 62. K. Biemann, L l o y d i a , Z7, 397 (1964). 63. W.I. T a y l o r , Proc. Chem. S o c , 247 (1962). 64. J.P. Kutney, R.T. Brown, E. P i e r s , and J.R. H a d f i e l d , J . Amer. Chem. S o c , March (1970). 65. E.C. Ashby, J . Amer. Chem. S o c , 81_, 4791 (1959). 66. G. Buchi, P. Kulsa, and R.L. R o s a t i , J . Amer. Chem. S o c 90, 2448 (1968). 67. E.L. E l i e l , N.L. A l l i n g e r , S.J. Angyal, and G.A. Morrison, Conformational A n a l y s i s , I n t e r s c i e n c e , New York, 1967, p. 154. 68. N. Neuss, L.L. Huckstep and N.J. Cone, Tetrahedron L e t t e r s , 811 (1967). 69. J . M i l l e r , and A.J. Parker, J . Amer. Chem. S o c , 83, 117 (1961). 70. C R . Narayanan and K.N. I y e r , Tetrahedron L e t t e r s , 759 (1964). 71. We are g r a t e f u l to Dr. N. Neuss, L i l l y Research L a b o r a t o r i e s , f o r a sample of velbanamine. 72. K. Biemann, Mass Spectrometry, McGraw H i l l , New York, 1962, Ch. 8. 73. J.P. Kutney, J . Beck, F. Bylsma, and W.J. Cretney, J . Amer. Chem. S o c , 90, 4504 (1968). - 163 -74. G. Buchi, R.E. Manning, and S.A. Monti, J . Amer. Chem. S o c , 86, 4631 (1964). 75. N. Neuss, M. Gorman, N.J. Cone, L.L. Huckstep, Tetrahedron L e t t e r s , 783 (1968). 76. W.J. Cretney, Ph.D. Th e s i s , U n i v e r s i t y of B r i t i s h Columbia (1968). 77. J . Harley-Mason, and A. Rahman, Chem. Comm., 1048 (1967). 

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}]}"
                            data-media="{[{embed.selectedMedia}]}"
                            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.831.1-0059980/manifest

Comment

Related Items