Synthesis of a tetrasaccharide donor corresponding to the O-specific polysaccharide of Shigella dysenteriae type 1.

O-(2,4-Di-O-benzoyl-3-O-chloroacetyl-alpha-L-rhamnopyranosyl)-(1--> 2)-O-(3,4,6-tri-O-benzoyl-alpha-D-galactopyranosyl)-(1--> 3)-O-(2-acetamido-4,6-di-O-acetyl-2-deoxy-alpha-D-glucopyranosyl)-(1--> 3)-2,4-di-O-benzoyl-alpha-L-rhamnopyranosyl trichloroacetimidate (1) was synthesized in a stepwise manner, using the following monosaccharide units: 2-(trimethylsilyl)ethyl 2,4-di-O-benzoyl-alpha-L-rhamnopyranoside, 2-azido-4,6-O-benzylidene-3-O-chloroacetyl-2-deoxy-beta-D-glucopyranosyl chloride, methyl 3,4,6-tri-O-benzoyl-2-O -(4-methoxybenzyl)-1-thio-beta-D-galactopyranoside, and 2,4-di-O-benzoyl-3-O-chloroacetyl-alpha-L-rhamnopyranosyl chloride. Compound 1 corresponds to a complete tetrasaccharide repeating unit of the O-specific polysaccharide of the lipopolysaccharide of Shigella dysenteriae type 1.