Synthesis of colitose-containing oligosaccharide structures found in polysaccharides from Vibrio cholerae O139 synonym Bengal using thioglycoside donors

The syntheses of the two colitose-containing trisaccharides 8-methoxycarbonyloctyl (3,6-dideoxy-α- l-xylo-hexopyranosyl)-(1 → 2)-β- d-galactopyranosyl-(1 → 3)-2-acetamido-2-deoxy-β- d-glucopyranoside and 8-methoxycarbonyloctyl β- d-galactopyranosyl-(1 → 3)-[(3,6-dideoxy-α- l-xylo-hexopyranosyl)-(1 → 4)]-2-acetamido-2-deoxy-β- d-glucopyranoside, and tetrasaccharide 8-methoxycarbonyloctyl (3,6-dideoxy-α- l-xylo-hexopyranosyl)-(1 → 2)-β- d-galactopyranosyl-(1 → 3)-[(3,6-dideoxy-α- l-xylo-hexopyranosyl)-(1 → 4)]-2-acetamido-2-deoxy-β- d-glucopyranoside are described. The oligosaccharides correspond to structures found in the capsular polysaccharide and the lipopolysaccharide of Vibrio cholerae O139 and also to lipopolysaccharide structures of E. coli O55 and Salmonella greenside. The colitose residues were introduced via dimethyl(methylthio)sulfonium trifluoromethanesulfonate promoted glycosylations using colitose thioglycosides as glycosyl donors. The syntheses of the tetrasaccharide below as well as the two possible monocolitose-containing trisaccharide structures thereof using colitose thioglycoside donors are described. α Colp-(1→2)β- D- Galp-(1→ 3)-[α- Colp-(1→4)]-β- D- Glcp NAc-(1→ OCH 2( CH 2) 7 COOME