CHEMICAL SYNTHESIS OF THE PYRUVIC ACETAL-CONTAINING TRISACCHARIDE UNIT OF THE SPECIES-SPECIFIC GLYCOPEPTIDOLIPID FROM MYCOBACTERIUM-AVIUM SEROVARIANT-8

The functionalized, pyruvic acetal-containing haptenic trisaccharide, p-trifluoroacetamidophenyl 6-deoxy-2-O-{3-O-[4,6-O-(S)-(1-methoxycarbonylethylidene)-3-O-methyl-beta-D-glucopyranosyl]-alpha-L-rhamnopyranosyl}-alpha-L-talopyranoside (19), a component of the glycolipid from Mycobacterium avium serovar 8 was synthesized. For the preparation of the terminal pyruvic acetal-containing unit, benzyl 2-O-benzyl-3-O-methyl-beta-D-glucopyranoside (6) was condensed with methyl 2,2-di(ethylthio)propionate (1) in the presence of SO2Cl2-CF3SO3H catalyst to yield benzyl 2-O-benzyl-4,6-O-(S)-(1-methoxycarbonylethylidene)-3-O-methyl-beta-D-glucopyranoside (7S), which was then converted into the suitably substituted glycosyl donor 2-O-acetyl-4,6-O-(S)-(1-methoxycarbonylethylidene)-3-O-methyl-alpha-D-glucopyranosyl trichloroacetimidate (11). The disaccharide glycosyl acceptor p-nitrophenyl endo-3,4-O-benzylidene- 6-deoxy-2-O-(2,4-di-O-benzyl-alpha-L-rhamnopyranosyl)-alpha-L-talopyranoside (15) was glycosylated with 11 in the presence of trimethyl trifluoromethanesulfonate to furnish the protected trisaccharide p-nitrophenyl 2-O-{3-O-[2-O-acetyl-4,6-O-(S)-(1-methoxycarbonylethylidene)-3-O-methyl-beta-D-glucopyranosyl] -2,4-di-O-benzyl-alpha-L-rhamnopyranosyl}-endo-3,4-O-benzylidene-6-deoxy-alpha-L-talopyrano side (16). After deprotection, this gave the spacer-armed unprotected haptenic trisaccharide 19.