Efficient synthesis of a sialyl T-antigen-linked glycopeptide by the chemoenzymatic method

A sialyl T-antigen-linked tetrapeptide was prepared by the combined method of chemical synthesis and enzymatic synthesis. The GalNAc-linked peptide wa s first obtained bg using a commercial peptide synthesizer, and then a gala ctose residue was attached with beta-(1 --> 3)-linkage by transglycosylatin g with a recombinant beta-galactosidase from Bacillus circulans. The sialic acid residue was then combined by alpha-(2 --> 3)-linkage with sialytransf erase from rat liver.