Synthesis of a trisaccharide repeat of the zwitterionic Sp1 capsular polysaccharide utilizing 2-azido-4-benzylamino-4N,3-O-carbonyl-2,4,6-trideoxy-D-galactopyranosyl trichloroacetimidate

2-Azido-4-benzylamino-4N,3-O-carbonyl-2,4,6-trideoxy-D-galactopyranosyl trichloroacetimidate 2 conveniently prepared in six steps from 6-deoxy-D-glucal glycosylated a selectively protected alpha 1,3 linked methyl galabioside to afford the trisaccharide skeleton of a repeating unit of the Sp1 zwitterionic capsular polysaccharide. Lithium hydroxide hydrolysis of the 3,4-cyclic carbamate permitted the creation of a 2-acetamido-4-amino-2,4,6-trideoxygalactose residue. Selective cleavage of p-methoxybenzyl ethers by trifluoroacetic acid gave a selectively deprotected trisaccharide with two hydroxymethyl groups that were oxidized by the TEMPO reagent to afford access to trisaccharide glycoside 1 containing 2-acetamido- 4-amino-2,4,6-trideoxygalactose and two galacturonic acid residues. (C) 2013 Published by Elsevier Ltd.