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

摘要

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 degrees C by using TMSOTf as a catalyst to afford the desired glycosides in good yields. A trisaccharide serine conjugate Gal(beta 1-3)Gal(beta 1-4)Xyl beta-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 P-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. (C) 1999 Elsevier Science Ltd. All rights reserved. [References: 8]