Efficient, convergent syntheses of oligosaccharide allyl glycosides corresponding to the Streptococcus group A cell-wall polysaccharide

Convergent syntheses of di-, tri, tetra-, penta-, and hexa-saccharide allyl glycosides corresponding to the beta-hemolytic Streptococcus Group A cell-wall polysaccharide are described. The strategy relies on the preparation of related di- and tri-saccharide building blocks: beta-D-Glc pNAc-(1-3)-alpha-L-Rhap and alpha-L-Rhap-(1-2)-[(beta-D-Glc p NAc-(1-3)]-alpha-L-Rhap, which could be used either as glycosyl donors or acceptors in subsequent glycosylation reactions. The protecting groups were chosen to allow the selective removal of the allyl aglycon to access the intermediate glycosyl donors but also to allow their own removal without affecting the allyl group. The allyl group was intended for use in conjugation of the oligosaccharides to soluble protein carriers or solid supports for the preparation of antigens and immunoadsorbents, respectively.