Synthesis of blood-group substances. Part 11. Synthesis of the trisaccharide O-α-D-galactopyranosyl-(1 → 3)-O-β-D-galactopyranosyl-(1 → 4)-2-acetamido-2-deoxy-D-glucopyranose

Abstract

Reaction of 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide with benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-α-D-glucopyranoside in 1,2-dichloroethane in the presence of mercuric bromide and molecular sieves (4 Å) provided after O-deacetylation crystalline benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-4-O-(β-D-galacto pyranosyl)-α-D-glucopyranoside. Acetonation followed by benzylation and mild acid hydrolysis provided crystaline benzyl 2-acetamido-4-O-(2,6-di-O-benzyl-β-D-galactopyranosyl)-3,6-di-O-benzyl-2-deoxy-α-D-glucopyranoside. Reaction of this diol with 1-O-(N-methyl) acetimidyl-2,3,4,6-tetra-O-benzyl-β-D-galactopyranose in nitromethane in the presence of toluene-p-sulphonic acid regiospecifically gave the derivative (15). The title trisaccharide was obtained after catalytic hydrogenolysis. The alcohol benzyl 2-acetamido-4-O-(2,3,6-tri-O-benzyl-β-D-galactopyranosyl)-3,6-di-O-benzyl-2-deoxy-α-D-glucopyranoside was found to be unreactive under the same conditions.