[Synthetic approaches to tumor-associated glycosphingolipids]

Glycan chains present on cell surfaces carry specific information of biological importance, which is believed to play crucial roles in cell proliferation and cell sociological behavior. In order to provide authentic glycan chains for the purpose of basic as well as applied biological research, several years ago we started our experiments directed toward unambiguous total synthesis of glycoconjugates. To achieve stereo- and regio-controlled synthesis of branched oligosaccharides of glycoconjugates, we developed new technologies and strategies for the regioselective introduction of protective groups into carbohydrates as well as for the stereoselective glycosylations. For example, polyhydroxy systems were efficiently protected after regioselective enhancement of the nucleophilicity of hydroxyl groups through tributylstanylation. Use of the trichloroacetimidate procedure and anomeric fluoride approach developed by Schmidt and Mukaiyama, respectively, notably enhance the efficiency of glycosylations. These new synthetic technologies and strategies were successfully applied to the synthesis of the tumor-associated antigen, lactoganglio-glycotetraosyl-ceramide, as well as I type glycan of glycoconjugates.