CHEMOSELECTIVE AND STEREOSELECTIVE GLYCOSYLATION OF HYDROXYLAMINO DERIVATIVES - A VERSATILE APPROACH TO GLYCOCONJUGATES

A general method for the stereoselective coupling of unprotected oligo saccharides with any substrate containing a N,O-disubstituted hydroxyl amine group is described. The cyclic nature of the oligosaccharide red ucing unit is preserved and the substrate glycosylated with high diast ereoselectivity to sugar through an amino (N[OR2]-) or an aminoxy (N[R -1]-O-) linkage. Due to the uniquely high chemical reactivity and spec ificity of disubstituted hydroxylamine toward the sugar reducing end, neither protecting groups nor activation methods are required to perfo rm the reaction in aqueous solution. The characteristic features and t he scope of this new type of glycosylation reaction are exemplified fo r the chemoselective synthesis of model glycopeptides. (C) 1998 Elsevi er Science Ltd. All rights reserved.