The chemistry and analysis of sphingolipids in natural products

Methods used for the analysis of both synthetic and natural sphingolipids and their components are described. Analytical data is given on ceramides derived from bovine-brain cerebrosides, and on the sphingolipids derived from milk from a predominantly Fresian herd. The major fatty acids in brain sphingolipids are 24:0, h24:0, 22:0, h22:0, 18:0 and h18:0; 24:1 is a less major component in brain cerebrosides, but a major component in brain sphingomyelin. The milk sphingolipids comprise mainly sphingomyelin, ceramide glucoside, and ceramide lactoside. All three sphingolipids contain both non-hydroxy and hydroxy fatty acids, and their compositions are similar; 23:0, 24:0, 22:0 and 16:0 (and the corresponding hydroxy fatty acids) predominate, with 16:0 (or h16:0) and 24:1 (or h24:1) present to a lesser degree. The separation of diastereoisomeric ceramides by TLC on borate-impregnated silica gel, and by GLC, is described. Synthetic ceramides are prepared for this work by direct coupling of long chain base and fatty acid in the presence of a carbodiimide. Side-reaction products produced by this method are analysed, accounting for previously unknown TLC spots present in the crude preparations. Finally the analysis of human serum lipids by spectrodensitometry using phosphomolybdic acid is described. The methods are applied to serums obtained from 68 apparently healthy adults, and quantitative results given for ceramides, monoglycerides, and cholesterol (free and total).