Stereoselective synthesis of a blood group A type glycopeptide present in human blood mucin

N,N-Dimethyl-O-(2-acetamido-2-deoxy-α-d-galactopyranosyl)-(1 → 3)-O-[(α-l-fucopyranosyl)-(1 → 2)]-O-(β-d-galactopyranosyl)-(1 → 3)-O-(2-acetamido-2-deoxy-α-d-galactopyranosyl)-(1 → 3)-l-serine, a core I glycotetraosyl peptide structure and a predominant substructure in complex glycan-glycoproteins present in human blood group A ovarian mucin, was synthesized for the first time. The title compound was synthetically accomplished via the following key manoeuvres: regio- and stereo-controlled construction of the α-GalNAc-(1 → 3)-Gal synthon, stereoselective glycosylation generating a α-GalN3-(1 → 3)-Ser glycopeptide synthon and α-selective fucosylation towards an acceptor which was derived from glycosylation of the latter two synthons. An alternative route to that of the latter, to synthesize a fully protected equivalent of the title compound, involving the coupling of a α-GalNAc-(1 → 3)-β-Gal-(1 → 3)-GalN3X synthon to an aglycon serine derivative, is described herein.