19] Neoglycolipids: Probes in structure /function assignments to oligosaccharides

Abstract

This chapter reviews the recent structure/function assignments made bythe neoglycolipid technology. Analysis by liquid secondary ion mass spectrometry (LSIMS) of neoglycolipids derived from O-glycosidic oligosaccharides has proved to be a powerful sequencing approach. The chapter discusses the results of the application of the neoglycolipid technology to analyze the core and backbone domains of O-glycosidic oligosaccharides released by alkaline borohydride degradation from mucin-type glycoproteins. As the reduced oligosaccharides contain no reactive aldehydes, mild periodate oxidation conditions are used such that overoxidation does not occur and a reactive aldehyde is generated at the reduced end. The mechanism of oxidative cleavage under the mild periodate conditions used is analyzed by LSIMS. Cleavage occurs specifically at the threo-diol C-4-C-5 bond of the core N-acetylgalactosaminitol, giving rise to two cleavage products with differing molecular masses. Although this cleavage would be a drawback in carbohydrate-recognition systems that require the intact core monosaccharide, it does have the advantage of allowing unambiguous assignment by LSIMS of positions of linkage of oligosaccharide sequences to the core N-acetylgalactosamine.