Diastereoselectivity in the synthesis of D -glycero-D -aldoheptoses by 2-trimethylsilylthiazole homologation from hexodialdo-1,5-pyranose derivatives
| Autor: | Gerald O. Aspinall, Ramesh K. Sood, Naveen K. Khare |
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| Rok vydání: | 1994 |
| Předmět: | |
| Zdroj: | Canadian Journal of Chemistry. 72:237-246 |
| ISSN: | 1480-3291 0008-4042 |
| DOI: | 10.1139/v94-036 |
| Popis: | An exploration of the synthesis of D-glycero-D-altro-heptose, a constitutent of O antigen chains in lipopolysaccharides from Campylobacter jejuni serotypes O:23 and O:36 led to a study of the 2-trimethylsilylthiazole homologation procedure for heptose synthesis. In contrast to the diastereoselective formation of a 1,2:3,4-di-O-isopropylidene-D-glycero-α-D-galacto-heptopyranose derivative from 1,2:3,4-di-O-isopropylidene-α-D-galacto-hexodialdo-1,5-pyranose, methyl 2,3,4-tri-O-benzyl-D-hexodialdo-1,5-pyranosides with the gluco and manno configurations showed no preference for the formation of compounds with the D-glycero configuration. Attempts to achieve high diastereoselectivity in the conversion of L-glycero into the D-glycero isomers by oxidation at C-6 followed by reduction with L-selectride were unsuccessful with the thiazole adducts, but the desired products were formed in similar reactions of methyl 2,3,4-tri-O-benzyl-7-O-tert-butyldimethylsilyl-D-heptopyranosides. The approach to homologation in the altro series was thwarted by epimerization at C-5 in the attempted formation of methyl 2,3,4-tri-O-benzyl-α-D-altro-hexodialdo-1,5-pyranoside. The successful synthesis of methyl D-glycero-α-D-altro-heptopyranoside from methyl α-D-glucopyranoside was achieved by homologation followed by configurational alteration from the D-gluco to the D-altro series. |
| Databáze: | OpenAIRE |
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