Synthesis of methyl α-glycosides of some higher oligosaccharide fragments of the O-antigen of Vibrio cholerae O1, serotype Inaba and Ogawa

The title oligosaccharides, the tri-through the hexasaccharide in the Inaba series and the penta- and the hexasaccharide in the Ogawa series, have been synthesized using 1-thioglycosides of precursors to 3-O-benzyl-perosamine (4-amino-4,6-dideoxy-d-mannose) as building blocks and N-iodosuccinimide/silver triflate as a promoter. The azido groups in the assembled oligosaccharides were reduced to amino groups, which were then acylated using 2,4-O-benzylidene-3-deoxy-l-glycero-tetronic acid as the derivatizing reagent. Catalytic hydrogenolysis, simultaneously of the benzyl and benzylidene groups, gave the desired products that were characterized by 1H and 13C NMR spectroscopy.