48] Synthesis and characterization of metabolically stable sphingolipids

Abstract

Over the past decade, sphingolipids have become candidates of prime interest in phenomena such as cell adhesion and signal transduction, as well as programmed cell death. Studies on the importance of certain sphingolipids as second messenger molecules and receptor modulators have added ceramides, sphingomyelin, and some glycosphingolipids exogenously to cells in culture or laboratory animals. As these compounds are subject to (sometimes rapid) metabolism, it is difficult to know whether the observed effect on cell behavior is elicited by the applied sphingolipid itself or by its metabolic product(s). In addition, for a complete understanding of the role of sphingolipids, information on their intracellular transport would be essential. Thus, it would be desirable to employ metabolically stable sphingolipids or ones with a restricted metabolism in either the catabolic or the anabolic pathway of metabolism. This chapter describes the synthesis of a metabolically stable ceramide analog that proves useful in the study by fluorescence microscopy of its intracellular distribution in cultured fibroblasts and perhaps other cells. This analog carries a stable O-methyl group in place of a primary hydroxyl group and, can neither be glycosylated to glycosphingolipids nor acquire a phosphorylcholine residue to become sphingomyelin. This compound or its radioactive and nonfluorescent homo- log may be valuable for further investigation on the role of ceramide in apoptosis. The synthesis of glycosphingolipid analogs (glucosylceramide and lactosylceramide) that are totally resistant to the action of glycohydrolases is also discussed in this chapter. These compounds feature a thioglycosidic bond that cannot be split in detectable amounts by mammalian glycohydrolases. These analogs of glycosphingolipids are becoming valuable tools in studies on their intracellular transport.