CONVERGENT SYNTHESIS OF AN ELUSIVE HEXASACCHARIDE CORRESPONDING TO THE CELL-WALL POLYSACCHARIDE OF THE BETA-HEMOLYTIC STREPTOCOCCUS GROUP-A

A convergent synthesis of a hexasaccharide corresponding to the cell-wall polysaccharide of the beta-hemolytic Streptococcus Group A is described. The strategy relies on the preparation of a key linear trisaccharide unit beta-D-GlcpNAc-(l --> 3)-alpha-L-Rhap-(l --> 2)-alpha-L-Rhap which has previously resisted our efforts. The trisaccharide functions both as a glycosyl acceptor and donor to give an elusive hexasaccharide. This fully functionalized unit can serve, in turn, as a glycosyl acceptor or donor for the synthesis of higher-order structures. Deprotection gives a hitherto unknown hexasaccharide for use as a hapten in immunochemical studies. The characterization of all compounds by high-resolution H-1 and C-13 NMR spectroscopy is also described.