Treatment of methyl Ot-D-perosaminide (1) with y-butyrolactone gave the 2'-deoxy analogue of methyl 4,6-dideoxy-4-(3-deoxy-L-glycero-tetronamido)-a-D-mannopyranoside (13), the methyl a-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-Lglycero-tetronamido)-4,6-dideoxy-a-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-ot-D-mannopyranoside was converted into methyl 2-O-benzyl-4,6-dideoxy-4-(2,4-di-O-benzyl-3-deoxy-L-glycero-tetronamido)-ct-D-mannopyranoside, which was deoxygenated via the corresponding 3-O-(imidazol-l-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-t~-D-mannopyranoside was converted through a series of transformations into methyl 4-amino-2-O-benzyl-3,4,6-tri-Synthesis of ligands related to the Vibrio cholerae O-specific antigen. Part 4. For Part 3 see Ref. [1].