Chemical synthesis of the pyruvic acetal-containing trisaccharide unit of the species-specific glycopeptidolipid from Mycobacterium avium serovariant 8

Abstract

The functionalized, pyruvic acetal-containing haptenic trisaccharide, p-trifluoroacetamidophenyl 6-deoxy-2- O-3- O-[4,6- O-( S)-(1-methoxycarbonylethylidene)-3- O-methyl-β- d-glucopyranosyl]-α- l-rhamnopyranosyl-α- 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-β- d-glucopyranoside ( 6) was condensed with methyl 2,2-di(ethylthio)propionate ( 1) in the presence of SO 2Cl 2CF 3SO 3H catalyst to yield benzyl 2- O-benzyl-4,6- O-( S)-(1-methoxycarbonylethylidene)-3- O-methyl-β- 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-α- d-glucopyranosyl trichloroacetimidate ( 11). The disaccharide glycosyl acceptor p-nitrophenyl endo-3,4- O-benzylidene-6-deoxy-2- O-(2,4-di- O-benzyl-α- l-rhamnopyranosyl)-α- 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-β- d-glucopyranosyl]-2,4-di- O-benzyl-α- l-rhamnopyranosyl- endo-3,4- O-benzylidene-6-deoxy-α- l-talopyranoside ( 16). After deprotection, this gave the spacer-armed unprotected haptenic trisaccharide 19.