Chemoenzymatic synthesis of sialylated glycopeptides derived from mucins and T-cell stimulating peptides

The Tn, T, sialyl-Tn, and 2,3-sialyl-T antigens are tumor-associated carboh ydrate antigens expressed on mucins in epithelial cancers. such as those af fecting the breast, ovary, stomach, and colon. Glycopeptides carrying these antigens are of interest for development of cancer vaccines and a short, c hemoenzymatic strategy for their synthesis is reported, Building blocks cor responding to the Tn (GalNAc alpha -Scr/Thr) and T [Ga1 beta (1 -->3)GalNAc alpha -Ser/Thr] antigens, which are relatively easy to obtain by chemical synthesis, were prepared and then used in the synthesis of glycopeptides on the solid phase. Introduction of sialic acid to give the sialyl-Tn [Neu5Ac alpha (2-6)GalNAc alpha -Ser/Thr] and 2,3-sialyl-T [Neu5Ac alpha (2 -->3)G al beta (1 -->3)GalNAc alpha -Ser/ Thr] antigens is difficult when performe d chemically at the building block level. Sialylation was therefore carried out with recombinant sialyltransferases in solution after cleavage of the Tn and T glycopeptides from the solid phase. In the same manner, the core 2 trisaccharide [Gal beta1 -->3(GlcNAc beta1 -->6)GalNAc] was incorporated i n glycopeptides containing the T antigen by using a recombinant N-acetylglu cosaminyltransferase. The outlined chemoenzymatic approach was applied to g lycopeptides from the tandem repeat domain of the mucin MUC1, as well as to neoglycosylated derivatives of a T cell stimulating viral peptide.