13] Neoglycolipids of 1-deoxy-1-phosphatidylethanolaminolactitol type: Synthesis, structure analysis, and use as probes for characterization of glycosyltransferases

Abstract

Neoglycolipids (NeoGL) of the 1-deoxy- 1-phosphatidylethanolamino-lactitol type (Lac-PtdEtn), synthesized by coupling an oligosaccharide to phosphatidylethanolamine (PtdEtn) by reductive amination, have been used for studies on antigenicity, receptor function, and lectin and toxin binding by carbohydrates. Glycosyl-PtdEtns and especially the N-acetylated derivatives can serve as acceptors for glycosphingolipid (GSL) glycosyltransferases. The NeoGLs are as good acceptors as the authentic GSL analogs, and they are glycosylated by the same enzymes. This chapter describes an improved synthesis of Lac-PtdEtn-type neoglycolipids, their N-acetylation, and their use as acceptors for glycosyl-transferases and for structure elucidation of oligosaccharides by fast atom bombardment-mass spectrometry (FAB-MS). Radiolabeled NeoGL can be useful tools for investigations on glycolipid metabolism in cell culture. For the glycosyl-PtdEtn compounds to serve as substitutes for natural GSL in glycosyltransferase assays, it must be ascertained that neoglycolipids are converted to the analogous products by the same enzymes that act on natural GSL and that they exhibit similar apparent kinetic constants. This chapter illustrates the use of glycosyl-PtdEtns and the N-acetylated derivatives as acceptors for sialyltransferases from rat liver Golgi and discusses the transferase products by FAB-MS. By competition experiments it is demonstrated that the NeoGL and the authentic GSL analog are sialylated by the same respective enzymes.