Synthesis of a nonasaccharide containing terminal N-acetyl-β-D-lactosaminyl residues, part of the ‘complex-type’ carbohydrate moiety of glycoproteins

Silver trifluoromethanesulphonate-promoted condensation of 3,6-di-O-acetyl-2-deoxy-2-phthalimido-4-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-β-D-glucopyranosyl bromide with benzyl O-(3,6-di-O-benzyl-α-D-mannopyranosyl)-(1 → 3)-O-[3,4,6-tri-O-benzyl-α-D-mannopyranosyl-(1 → 6)]-2,4-di-O-benzyl-α-D-mannopyranoside gave a protected nonasaccharide derivative in 19% yield. The free oligosaccharide was obtained after exchanging the 2-phthalimido-groups for 2-acetamido-groups and deblocking.