Blood-group li-active oligosaccharides. Synthesis of a tetrasaccharide, a β-(1 → 3) dimer of N-acetyl-lactosamine

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Abstract
Condensation of benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-α-D-glucopyranoside (2) with 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide, followed by de-O-acetylation, acetonation, O-benzylation, and acidic hydrolysis afforded the 3′,4′-diol (5) derived from N-acetyl-lactosamine. This compound was selectively glycosylated at the 3′-position by the oxazoline (7) derived from lactosamine to give the protected tetrasaccharide (8) in 52% yield. Removal of the protecting groups gave the free tetrasaccharide β-D-Galp-(1 → 4)-β-D-GlcpNAc-(1 → 3)-β-D-Galp-(1 → 4)-D-GlcpNAc (9), a β-(1 → 3) dimer of N-acetyl-lactosamine. This structure has been found in various glycolipids isolated from erythrocyte membranes and could be recognized by several anti-iantisera.