Cyclodextrin-assisted Glycan Chain Extension on a Protected Glycosyl Amino Acid

By the use of cyclodextrins, we have enhanced the solubility of the protected amino acid glycan Fmoc-Thr(GalNAcα1)-OtBu (1b) up to 100-fold. This improvement enabled us to carry out an enzymatic glycosylation employing a β-galactosidase in combination with an α2,3-sialyltransferase without the aid of organic cosolvents. After optimization of the one-pot reaction, the sialylated core 1 structure Fmoc-Thr[Neu5Ac(α2-3)Gal(β1-3)GalNAcα1]-OtBu (3b) could be obtained with 50% yield.