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Some INDOR and preparative studies of organometallic and carbohydrate derivatives

University of British Columbia

A study involving both the applications of internuclear double resonance (INDOR) spectroscopy and the synthesis of carbohydrates containing organometallic substrates was undertaken. The thesis is divided into two sections to facilitate discussion. The first section involves an evaluation of homonuclear and heteronuclear INDOR as a tool for spectral analysis. Homonuclear INDOR studies of carbohydrate derivatives such as 2-deoxy-a-D-arabino-hexo-pyranose(l), sucrose octaacetate(2) and D-ribose(3) have shown this technique to be extremely effective for analysing multi-line spectra having hidden transitions. Within certain power-level ranges, the resolution of the INDOR responses is comparable to that of the normal proton spectra. Heteronuclear INDOR spectra were obtained indirectly by monitoring specific transitions in the proton spectra while irradiating the appropriate heteronuclear frequency. In this manner, the methoxy-methyl ¹³C INDOR shift of a number of anomeric gluco- and xylo-pyranoside derivatives were measured. The ¹³C shifts of the α anomers were found to be ca. 2 ppm to high field of the β anomer. This difference is more diagnostic than the small 0.1 ppm variation between two methoxy-methyl anomers in the ¹H n.m.r. spectra. Such diagnostic differences were not found for the acetoxy-methyl ¹³C shifts of anomeric sugar acetate derivatives. Other heteronuclear INDOR spectra were readily obtained for organo-metallic compounds such as trimethylphosphite(15), trimethyltin chloride (16), bromosilane(17) and tetramethyl lead(18). The second section of the thesis deals with the synthesis of some phosphorus and organometallic derivatives of monosaccharides. Treatment of various primary O-tosyl sugar derivatives with lithium diphenyl-phosphine reagent ,19, gave, in ca. 70% yields, such products as diphenyl {1,2 :3,5-di-0-methylene-α-D-glucofuranose} 6-C-phosphine oxide(20b), diphenyl {methyl 2,3,4-tri-0-acetyl-α-D-glucopyranoside} 6-C-phosphine oxide(21b) and diphenyl {l,2:3,4-di-0-isopropylidene-α-D-galactopyranose} 6-C-phosphine oxide(22b). The facile preparation of 22b is rather unique because of the known resistance of the O-tosyl group of the sugar reactant toward nucleophilic displacement. Diphenyl {3,6-anhydro-l,2-0-isopropylidene-α-L-idofuranose} 5-C-phosphine oxide(24b) was obtained in 31% yield via nucleophilic displacement of the corresponding 5-0-mesyl derivative using 19_. This typified the much lower yields obtained from secondary sulphonyl displacements. Other secondary sugar diphenyl-phosphine oxide derivatives were prepared in 50-70% yields from the opening of sugar epoxides with 19_. Notably, the scission of the epoxide bond of methyl 2,3-anhydro-3-L-ribopyranoside(29) gave diphenyl ^methyl 2,4-0-acetyl-B-L-xylopyranosidej. 3-C-phosphine oxide(30). The product was found to favour the conformation in which all the major substituents are axial. The ³¹P chemical shifts for all the sugar diphenylphosphine oxide , derivatives were measured using the INDOR technique. These shifts provided confirmation that the products were phosphine oxides. It was further shown by use of ³¹P decoupling that ³JpH ranges of 6.6-11.8 Hz and 22-33 Hz for 60° and 180° dihedral angles respectively, were present in these products. These couplings are similar to those reported for, vicinal P-H couplings in hydroxy phosphonate derivatives. Preliminary experiments, undertaken to evaluate the effectiveness of other organometallics such as lithium triphenyltin(33), lithium tri-phenyllead(34) and lithium triphenylsilane (35) , showed 33 to be an effective reagent for displacing primary O-tosylates and opening epoxides of sugar derivatives. Both 34 and 35 gave poor yields when used to displace the 0-tosylate group of 20b. Generally, organometallic species were shown to provide a viable means of synthesizing novel sugar derivatives.

Text

2011-04-26

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http://hdl.handle.net/2429/33964

Chemistry

University of British Columbia

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