The chemical synthesis of O-α-l-fucopyranosyl-(1→2)-O-β-d-galactopyranosyl-(1→3)-O-[α-l-fucopyranosyl-(1→4)]-2- acetamido-2-deoxy-d-glucopyranose, the lewis b blood-group antigenic determinant

An approach has been developed for the rapid synthesis of benzyl 2-acetamido-2-deoxy-3-O-β-d-galactopyranosyl-β-d-glucopyranoside (5). Disaccharide 5 was per(trimethylsilyl)ated, to provide the fully protected trimethylsilyl (Me₃Si) derivative which, on treatment with pyridine-acetic anhydride-acetic acid for 2 days, gave the disaccharide derivative having O-acetyl groups selectively at the primary positions and Me₃Si groups at the secondary positions. The latter groups were readily cleaved by treatment with aqueous acetic acid in methanol, to afford benzyl 2-acetamido-6-O-acetyl-3-O-(6-O-acetyl-β-d-galactopyranosyl)-2-deoxy-β-d-glucopyranoside, which, on isopropylidenation, gave the desired, key intermediate 9, having two hydroxyl groups free. Condensation of 9 with 2,3,4,-tri-O-benzyl-α-l-fucopyranosyl bromide, under catalysis by halide ion, afforded the tetrasaccharide derivative, from which the title tetrasaccharide was obtained by systematic removal of the protecting groups. The structure of the final product, and of various other intermediates, was established by ¹H- and ¹³C-n.m.r. spectroscopy.