Convergent synthesis of higher-order oligosaccharides corresponding to the cell-wall polysaccharide of the β-hemolytic streptococci group A. a branched hexasaccharide hapten

Abstract A convergent synthesis of a hexasaccharide corresponding to the cell-wall polysaccharide of the β-hemolytic Streptococci Group A is described. The strategy relies on the preparation of a key branched trisaccharide unit α- l -Rha p -(1 → 2)[[β- d -Glc p NAc-(1 → 3)]-α- l -Rha p which functions both as a glycosyl acceptor and donor. The hexasaccharide is obtained after only three glycosylation reactions. This fully functionalized unit can serve, in turn, as a glycosyl acceptor or donor for the synthesis of higher-order structures. Deprotection gives a hexasaccharide for use as a hapten in immunochemical studies. The characterization of all compounds by high resolution 1 H- and 13 C-n.m.r. spectroscopy is also described.