SYNTHESIS OF 0-α-L-FU COPYRANOSYL-(1→2)-0-β-D-GALACTOPYRANOSYL-(1→4) -2-ACETAMIDO-2-DEOXY-D-GLUCOPYRANOSE. THE H BLOOD-GROUP SPECIFIC TRISACCHARIDE^†

Different reaction conditions were investigated for the preparation of benzyl 2-acetamido-3,6-di-0-benzyl-2-deoxy-β-D-glucopyranoside (5). Compound 5 on reaction with 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide afforded the 4-0-substituted 2-acetamido-2-deoxy-β-D-glucopyrano-syl derivative which, on 0-deacetylation, gave benzyl 2-acetamldo-3,6-di-0-benzyl-2-deoxy-4-0-β-D-galactopyranosyl-β-D-glucopyranoside (8). The trimethylsilyl (Me₃Si) derivative of 8, on treatment with pyridine-acetic anhydride-acetic acid for 2 days, gave the disaccharide derivative having an 0-acetyl group selectively introduced at the primary position 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-4-0-(6-0-acetyl-β-D-galactopyranosyl)-3,6-di-0-benzyl-2-deoxy-β-D-glucopyranoside, which on isopropylidenation gave the desired, key intermediate benzyl 2-acetanido-4-0-(6-0-acetyl-3,4-0-isopropylidene-β-D-galactopyranosyl)-3,6-di-0-benzyl-2-deoxy-β-D-glucopyranoside (12). Reaction of 12 with 2,3,4-tri-0-benzyl-α-L-fucopyranosyl bromide under catalysis by bromide ion afforded the trisaccharide derivative from which the title trisaccharide was obtained by systematic removal of the protective groups. The structures of the final trisaccharide and of various intermediates were established by 1_H and ¹³C NMR spectroscopy.