Synthesis of blood-group substances. Part 7. Synthesis of the branched trisaccharide O-α-<scp>L</scp>-fucopyranosyl-(1 → 3)-[O-β-<scp>D</scp>-galactopyranosyl-(1 → 4)]-2-acetamido-2-deoxy-<scp>D</scp>-glucopyranose

Abstract

Reaction of 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide with benzyl 2-acetamido-3-O-allyl-6-O-benzyl-2-deoxy-α-D-glucopyranoside in 1,2-dichloroethane in the presence of mercuric bromide and molecular sieves (4 Å) provided crystalline benzyl 2-acetamido-4-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-3-O-allyl6-O-benzyl-2-deoxy-α-D-glucopyranoside in 77% yield. Deallylation with chloro(tristriphenylphosphine)rhodium(I) followed by condensation with 2,3,4-tri-O-benzyl-α-L-fucopyranosyl bromide provided the derivative (14). The title trisaccharide was obtained after O-deacetylation followed by catalytic hydrogenolysis.