Chemoenzymatic Approaches for the Preparation of Oligosaccharides and Glycopeptides

Abstract

The sugar chains of glycoproteins are implicated as major roles in protein stability or biological recognition and many efforts have been devoted to clarify the details [1]. However there is one problem in studying the roles and functions of the sugar chains in glycoproteins. It is so-called microheterogeniety in sugar chains on the glycoproteins [2], For the study of the roles and functions of sugar chains in glycoproteins more strictly, the structure of sugar chains should be uniform. If not, the characteristics of proteins may vary from one molecule to another as the sugar chain varies. In order to study further on the details of the roles and functions of sugar chains in glycoproteins, therefore, the glcoproteins having homogeneous sugar chains are needed. Although many efforts have been made for the in vitro synthesis of glycoproteins in homogeneous forms, it is difficult to synthesize glycoproteins that the linkages of the sugar chains are the same structure at least by a present technology. So we changed our target of synthesis from glycoproteins to glycopeptides. Glycopeptides may be used as an alternative substance in some cases for the study of the roles and functions of sugar chains in glycoproteins. For the syntheses of glycopeptides, we report here three types of reactions using various enzymes: 1) step by step elongation method for the synthesis of O-linked glycopeptides, 2) one step transfer method for the synthesis of N-linked glycopeptides using endo β-N-acetylglucosaminidase, 3) one step transfer method for the synthesis of O-linked glycopeptides using endo α-N-acetylgalactosaminidase.