Synthesis of a fully protected glycooctaosyl serine isolated from blood group A human ovarian mucin

N-(9-Fluorenylmethoxycarbonyl)-O-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-d-galactopyranosyl)-(1 → 3)-O-[(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)-(1 → 2)]-O-(4,6-di-O-acetyl-β-d-galactopyranosyl)-(1 → 3)-O-(3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1 → 6)]-O-[(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-d-galactopyranosyl)-(1 → 3)-O-[(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)-(1 → 2)-O-(4,6-di-O-acetyl-β-d-galactopyranosyl)-(1 → 3)]-2-acetamido-2-deoxy-α-d-galactopyranosyl)-(1 → 3)-l-serine allyl ester, a protected glycosylserine identified as a blood group A mucin-type determinant, was synthesized for the first time in an efficient and stereocontrolled manner. Ethyl O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-d-galactopyranosyl-(1 → 3)-O-[(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)-(1 → 2)]-O-(4,6-di-O-acetyl-β-d-galactopyranosyl)-(1 → 3)-3,6-di-O-benzyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside and N-(9-fluorenylmethoxycarbonyl)-O-(O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-d-galactopyranosyl)-(1 → 3)-O-[(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)-(1 → 2)]-O-(4,6-di-O-acetyl-β-d-galactopyranosyl)-(1 → 3)-2-acetamido-2-deoxy-α-d-galactopyranosyl)-(1 → 3)-l-serine allyl ester were the key intermediates for the crucial glycosylation to afford the title compound.