Synthesis of a hexasaccharide acceptor corresponding to the reducing terminus of mycobacterial 3-O-methylmannose polysaccharide (MMP)

The title compound methyl O-(2,6-di-O-benzyl-3-O-methyl-α-d-mannopyranosyl)-[(1 → 4)-O-(2,6-di-O-benzyl-3-O-methyl-α-d- mannopyranosyl)]4-(1 → 4)-2,6-di-O-benzyl-3-O-methyl-α-d-mannopyranoside (2) was synthesized in a blockwise manner, employing trichloroacetimidate (11) and (20) as glycosyl donors. The strategy relies on the single-step preparation of the 3-O-methyl ethers (4) and (12) as starting materials. Since all intermediates contain one or more OCH3 groups, they are easily identified by NMR spectroscopy using the methyl proton signals. Compound 2 corresponds to the reducing terminal hexasaccharide of mycobacterial 3-O-methylmannose polysaccharide (MMP). MMP has the unusual property of stimulating the fatty acid synthetase multienzyme complex. Compound 2 can serve as a suitable glycosyl acceptor for the synthesis of extended fragments of MMP.