Synthesis of specifically deoxygenated analogues of the methyl α-glycoside of the intracatenary monosaccharide repeating unit of the O-polysaccharide of Vibrio cholerae O:1

Treatment of methyl α-d-perosaminide (1) with γ-butyrolactone gave the 2′-deoxy analogue of methyl 4,6-dideoxy-4-(3-deoxy-L-glycero-tetronamido)-α-d-mannopyranoside (13), the methyl α-glycoside of the intracatenary monosaccharide repeating unit of the O-polysaccharide of Vibrio cholerae O:1. The analogous 4′-deoxy derivative was obtained by hydrogenolysis of a 4′-chlorodeoxy precursor, obtained by chlorination of methyl 2,3-di-O-benzyl-4-(2-O-benzyl-3-deoxy-l-glycero-tetronamido)-4,6-dideoxy-α-d-mannopyranoside with methanesulfonyl chloride in DMF. To obtain the 3-deoxy analogue of 13, methyl 4-amino-2-O-benzyl-4,6-dideoxy-3-O-p-methoxybenzyl-α-d-mannopyranoside was converted into methyl 2-O-benzyl-4,6-dideoxy-4-(2,4-di-O-benzyl-3-deoxy-l-glycero-tetronamido)-α-d-mannopyranoside, which was deoxygenated via the corresponding 3-O-(imidazol-1-ylthiocarbonyl) derivative. Subsequent catalytic debenzylation gave the deoxy compound (24). In an alternative synthesis, which is also generally useful for the preparation of 4-N-acyl-3-deoxy derivatives of 1, methyl 4-azido-4,6-dideoxy-α-d-mannopyranoside was converted through a series of transformations into methyl 4-amino-2-O-benzyl-3,4,6-trideoxy-α-d-mannopyranoside. Subsequent reaction with 2-O-benzyl-3-deoxy-l-glycero-tetronolactone, followed by hydrogenolysis of the formed tetronamido derivative, gave 24.