STRATEGIES FOR CHARACTERIZATION OF GANGLIOSIDE INNER ESTERS .2. GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

Two novel gas chromatography/mass spectrometry (GC/MS) strategies have been developed to assist in characterization of ganglioside inner esters. In the first, lactonized gangliosides which have been ammonolyzed and permethylated (see previous paper) are subjected to methanolysis and acetylation. This produces partially methylated NeuAc derivatives in which previous involvement of the carboxyl group in an ester linkage is indicated by conversion to an N1, N1‐dimethylamide. These can be analyzed by GC/MS using conditions analogous to those used normally in NeuAc methylation analysis, providing glycosidic and ester linkage information in the same procedure. In the second procedure, internally esterified NeuAc hydroxyl groups are located by protection, under neutral conditions, of all free hydroxyl groups of the ganglioside lactone with methoxyethoxymethyl groups, followed by permethylation, methanolysis, and GC/MS analysis of the resulting partially methylated NeuAc methyl ester methyl glycosides as their per‐O‐trimethylsilylates or per‐O‐acetates. This procedure has been used to show unambiguously that in GD3 lactones it is the 9‐hydroxyl group of the internal NeuAc residue which is esterified by the terminal NeuAc carboxyl. Both of these strategies should have general application in characterizing lactones occurring in gangliosides, NeuAc homo‐ and heteropolymers, and oligosaccharides or glycopeptides terminated by polysialosyl chains. Copyright © 1990 John Wiley & Sons, Ltd.