Efficient Chemoenzymatic Synthesis of O-Linked Sialyl Oligosaccharides

The tumor associated Tn (GalNAcα(1-1)-Thr/Ser)- and T (Galβ(1-3)-GalNAcα(1-1)Thr/Ser)-antigens and their sialylated derivatives are present on the surface of many cancer cells. Preparative synthesis of these sialylated T- and Tn-structures has been achieved mainly from a chemical synthetic approach due to the lack of the required glycosyltransferases. We demonstrate a flexible and efficient chemoenzymatic approach for using recombinant sialyltransferases including a chicken GalNAcα2,6-sialyltransferase (chST6GalNAc I) and a porcine Galβ(1-3)GalNAcα-2,3-sialyltransferase (pST3Gal I). Using these enzymes, the common O-linked sialosides Neu5Acα(2-6)GalNAcα(1-1)Thr, Galβ(1-3)[Neu5Acα(2-6)]GalNAcα(1-1)Thr, Neu5Acα(2-3)Galβ(1-3)GalNAcα(1-1)Thr, and Neu5Acα(2-3)Galβ(1-3)[Neu5Acα(2-6)]GalNAcα(1-1)Thr were readily prepared at preparative scale. The chST6GalNAc I was found to require at least one amino acid (Thr/Ser) for optimal activity, and is thus an ideal catalyst for synthesis of synthetic glycopeptides and glycoconjugates with O-linked glycans.