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

Treatment of methyl alpha-D-perosaminide (1) with gamma-butyrolactone gave the 2'-deoxy analogue of methyl 4,6-dideoxy-4-(3-deoxy-L-glycero-tetronamido)-alpha-D-mannopyranos ide (13), the methyl alpha-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-d ideoxy-alpha- 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-methoxy-benzyl-alpha-D-mannopyranos ide was converted into methyl 2-O-benzyl-4,6-dideoxy-4-(2,4-di-O-benzyl-3-deoxy-L-glycero-tetronami do)- alpha-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-alpha-D-mannopyranoside was converted through a series of transformations into methyl 4-amino-2-O-benzyl-3,4,6-tri-deoxy-alpha-D-mannopyranoside. Subsequent reaction with 2-O-benzyl-3-deoxy-L-glycero-tetronolactone, followed by hydrogenolysis of the formed tetronamido derivative, gave 24.