Chemoenzymatic Syntheses of Tumor-Associated Carbohydrate Antigen Globo-H and Stage-Specific Embryonic Antigen 4.

Gangliosides have attracted much attention due to their important biological properties. Herein, we report the first chemoenzymatic syntheses of two globo series of ganglioside oligosaccharides, Globo-H 1 and stage-specific embryonic antigen-4 (SSEA-4) 2. The common precursor SSEA-3 pentasaccharide for these two compounds was assembled rapidly using the pre-activation based one-pot glycosylation method. The stereoselectivity in forming the 1,2-cis linkage in SSEA-3 was attributed to a steric buttressing effect of the donor rather than electronic properties of the glycosyl donors. SSEA-3 was then successfully fucosylated by the fucosyltransferase WbsJ and sialylated by sialyltransferases CST-I and PmST1 producing Globo-H and SSEA-4 respectively.