Design and Synthesis of Ley-Bearing Glycopeptides that Mimic Cell Surface LeyMucin Glycoprotein Architecture

Abstract

Five Lewisy-based glycopeptide anti-cancer vaccine candidates have been designed and synthesized to target tumor-associated cell-surface glycoprotein antigens and to improve the immunizing performance in comparison to related vaccines. The peptide backbone consisted of two regions, a glycodomain AcNH-SSS- and a nonglycosylated sequence, -AVAV-. The resultant glycopeptide was conjugated, via an additional spacer, to the lipid carrier PamCysSer. In this series of totally synthetic molecular vaccine candidates, one or three of the sequentially arranged serine residues were glycosylated. Furthermore, the Ley tetrasaccharide determinant region was kept constant while the internal glycan core was systematically varied. Glycal assembly was used to prepare the glycosyl donors, and two strategies were applied to provide the serine-O-linked polysaccharide domains. In the first approach, a protected serine derivative was attached directly to the fully elaborated glycan. Following this course, both α- and β-Ser derivatives were accessed. In the second route, a GalNAc-α-Ser was joined with a glycosyl donor to afford exclusively the desired α-serine-linked product. The glycopeptides were assembled using iterative solution phase peptide coupling. Following global deprotection, the lipid carrier was then coupled to the glycopeptide, resulting in the targeted constructs. The synthesis of these molecular vaccine candidates constitutes an important advance that should enable rationalization of carbohydrate-induced immune response as well as identification of optimal Ley-based anti-cancer vaccine leads.