CONVERGENT SYNTHESIS OF HIGHER-ORDER OLIGOSACCHARIDES CORRESPONDING TO THE CELL-WALL POLYSACCHARIDE OF THE BETA-HEMOLYTIC STREPTOCOCCI GROUP-A - A BRANCHED HEXASACCHARIDE HAPTEN

A convergent synthesis of a hexasaccharide corresponding to the cell-wall polysaccharide of the beta-hemolytic Streptococci Group A is described. The strategy relies on the preparation of a key branched trisaccharide unit alpha-L-Rhap-(1 --> 2)-[beta-D-GlcpNAc-(1 --> 3)]-alpha-L-Rhap 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 H-1- and C-13-n.m.r. spectroscopy is also described.