Synthesis and NMR analysis of 13C-labeled oligosaccharides corresponding to the major glycolipid from Mycobacterium leprae

An improved synthesis of propyl 4-O-(3,6-di-O-methyl-β-d-glucopyranosyl)-2,3-di-O-methyl-α-l-rhamnopyranoside, a disaccharide corresponding to the phenolic glycolipid of Mycobacterium leprae using a trichloroacetimidate as a glycosyl donor is described. The synthetic strategy is also applied to the preparation of three corresponding disaccharide analogues containing 13C-labeled methyl groups. The preparation of the trisaccharide, propyl 2-O-[4-O-(3,6-di-O-methyl-β-d-glucopyranosyl)-2,3-di-O-methyl-α-l-rhamnopyranosyl]-3-O-methyl-α-l-rhamnopyranoside is also reported. The di- and tri-saccharides were characterized by 1H and 13C NMR spectroscopy.