Synthesis of the conjugation ready, downstream disaccharide fragment of the O-PS of Vibrio cholerae O:139.

The linker-equipped disaccharide, 8-amino-3,6-dioxaoctyl 2,6-dideoxy-2-acetamido-3-O-β-D-galactopyranosyluronate-β-D-glucopyranoside (10), was synthesized in eight steps from acetobromogalactose and ethyl 4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-1-thio-β-D-glucopyranoside. The hydroxyl group present at C-4(II) in the last intermediate, 8-azido-3,6-dioxaoctyl 4-O-benzyl-6-bromo-2,6-dideoxy-2-trichloroacetamido-3-O-(benzyl 2,3-di-O-benzyl-β-D-galactopyranosyluronate)-β-D-glucopyranoside (9), is positioned to allow further build-up of the molecule and, eventually, construction of the complete hexasaccharide. Global deprotection (9→10) was done in one step by catalytic hydrogenolysis over palladium-on-charcoal.