3-Nitro-2-pyridyl glycoside as donor for chemical glycosylation and its application to chemoenzymatic synthesis of oligosaccharide

Article abstract of DOI:10.1016/S0040-4039(99)01280-0

3-Nitro-2-pyridyl (3NPy) glycosides, which act as versatile glycosyl donors in enzymatic transglycosylation, can also be chemically activated. Chemical glycosylation with protected 3NPy glycosides was readily effected at -20°C by using TMSOTf as a catalyst to afford the desired glycosides in good yields. A trisaccharide serine conjugate Gal(β1-3)Gal(β1-4)Xylβ-Ser was synthesized by combined use of enzymatic and chemical glycosylations. The trisaccharide 3NPy glycoside was prepared by stepwise transglycosylation of a Gal-3NPy donor to a Xyl-3NPy acceptor by using a β-galactosidase. After protection of the free hydroxy groups of the trisaccharide by acetylation, the 3NPy glycoside was then subjected to chemical glycosylation of a serine residue to afford the trisaccharide serine conjugate.