Synthesis of T-antigen-containing glycopeptides as potential cancer vaccines

Abstract

In recent years, many tumour-associated carbohydrate antigens have been identified and some of them, including the Tn [GalNAcα(1→O)Ser/Thr] and T [Galβ(1→3)GalNAcα(1→O)Ser/Thr] antigens, are highly expressed in carcinoma-associated mucins. Two novel glycosyl building blocks (3 and 4) containing the T-antigen were synthesised by glycosylation of Fmoc-homoserine and glycolic acid having unprotected carboxy groups with 2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl-(1→3)-2-azido-4,6-O-benzylidene-2-deoxygalactopyranosyl trichloroacetimidate (2) as the glycosyl donor. These building blocks were used directly in the solid-phase synthesis of glycopeptides with varying distances between the peptide and glycan following two different methodologies. In the first strategy, the glycosylated amino acid building block was incorporated into the growing peptide chain using TBTU–NEM activation. The second strategy employed direct, selective, solid-phase acylation of an amino side chain of the relevant amino acid with a suitably protected glycosyl moiety, after the peptide had been completely synthesised. Reduction of the 2-azido group of the galactose moiety and acetylation to the corresponding acetamido function was performed on the solid phase.