Synthesis of three oligosaccharides that form part of the complex type of carbohydrate moiety of glycoproteins.

Silver trifluoromethanesulfonate-promoted condensation of 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl bromide with benzyl 3,6-di-O-benzyl-alpha-D-mannopyranoside and benzyl 3,4-di-O-benzyl-alpha-D-mannopyranoside gave the protected 2,4- and 2,6-linked trisaccharides in yields of 54 and 32%, respectively. After exchanging the 2-deoxy-2-phthalimido groups for 2-acetamido-2-deoxy groups and de-blocking, the trisaccharides 2,4-di-O-(2-deoxy-beta-D-glucopyranosyl)-D-mannose and 2,6-di-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-D-mannose were obtained. Similar condensation of 3,6-di-O-acetyl-2-deoxy-2-phthalimido-4-O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-beta-D-glucopyranosyl bromide with benzyl 3,4-di-O-benzyl-alpha-D-mannopyranoside gave a pentasaccharide derivative in 52% yield. After transformations analogous to those applied to the trisaccharides, 2,6-di-O-[beta-D-galactopyranosyl-(1 leads to 4)-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)]-D-mannose was obtained.