A regular heteropolysaccharide built of tetrasaccharide repeating units is synthesised by means of regio-and stereospecific polycondensation of a tritylated cyanoethylidene derivative. The polysaccharide obtained is identical with the O-antigenic polysaccharides of Shigella flexneri serotypes 3b, 3c, and variant Y. It also represents the basic chain of O- antigenic polysaccharides of all serotypes of this bacterium.
