Highly stereoselective and iterative synthesis of α-(1→4)-linked polysaccharides composed of 3-O-Methyl-D-mannose

A second-generation synthesis of synthetic 3-O-methyl-D-mannose-containing polysaccharides (sMMPs) is reported. The glycosidation of donor B and acceptor C, prepared from a common precursor A in two and one steps, respectively, is effected by t-butyldimethylsilyl trifluoromethanesulfonate to furnish only the desired alpha-anomer D in high yields. Unlike the first-generation synthesis, this synthesis gives the desired product free from contamination of scrambling products. A three-step protocol is used to deprotect D to furnish sMMPs.