Chemical modification of oligosaccharide chains of N-aspargine-type glycoproteins

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In recent years, oligosaccharide-chains involved in complex glycoconjugates existing on a cell surface have attracted much attention of many researchers in various fields of biochemistry and organic chemistry. Therefore, in order to elucidate roles of oligosaccharide-chains, extensive studies have so far been carried out, and biologically very interesting results have been accumulated.In the present study, carbohydrate-mimicking pseudo-oligosaccharides were designed and synthesized in order to provide chemical tools which may be useful to study roles of glycosidases and glycosyltransferases involved in biosynthesis of such complex oligosaccharide-chanins fo cell-surface glycanes. Several carba-disaccharides and trisaccharides containing carba-sugar residues bonded by way of imino-, ether and sulfide linkages have been newly synthesized and subjected to biological assay. In general, imino-linked carba-oligosaccharides were shown to possess inhibitory action against glycosidases, whereas the carba-oligosaccahrides linked by ether or sulfide-bridge were found to act rather as substrate analogs toward glycosyltransferases. The present results have opened up new opportunity for the design and synthesis of inhibitors for enzymes. Since carba-sugars are chemically very stable cyclitol derivstives but have close similarlity toward three-dimensional structures of true sugars, different kind of chemical modification may be possibly designed for carba-sugar residues.The present studies have been collaborated with biochemistry professors, Drs.Hindsgaul and Palcic (University of Alberta, Canada), and our synthesized carbohydrate mimics of biological interests seem to assist and contribute to their extensive studies on sugar hydrolases and transferases for important oligosaccharide-chains in future.