SYSTEMATIC SYNTHESIS OF SIALOGLYCOCONJUGATES GANGLIOSIDES TOWARDS THE ELUCIDATION OF THEIR BIOLOGICAL FUNCTIONS

The facile regio- and stereo-controlled alpha-glycosidations of sialic acid (Neu5Ac) are now well studied by using the thioglycosides of Neu5Ac as glycosyl donors, and suitably protected sugar residues as glycosyl acceptors. High yields of desired products are possible either by using DMTST or NIS/TfOH as thiophilic promoters in acetonitrile. A variety of gangliosides, such as GM4, GM3, GM2, GM1a, GM1b, GD1a, GD1-alpha, GD3, lacto- and neolacto-series gangliosides, and their isomers, have systematically been synthesized by a series of reactions which start from the condensation of sialo-oligosaccharides and 2-azido-sphingosine. Various analogs and derivatives of gangliosides containing thioglycosidic linkage(s) , modified sialic acids and pseudo-ceramides have also been synthesized. Recent advance in the biomedical studies using synthetic gangliosides, especially sialyl Le(X) and its related carbohydrate ligands, is also described.