Novel modification of glycosphingolipids by long-chain cyclic acetals: isolation and characterization of plasmalocerebroside from human brain.

A glycosphingolipid component of human brain, having long-chain cyclic acetals, has been isolated and characterized. This compound incorporates a novel type of natural glycan modification, in which a long-chain aliphatic aldehyde is conjugated through a cyclic acetal (plasmal) linkage to the galactosyl moiety of cerebroside. In addition to components normally observed by gas chromatography-mass spectrometry (GC-MS) following methanolysis of cerebroside (fatty acid methyl esters, methyl alpha- and beta-galactosides, sphingosine), this compound produced 16:0, 18:0, and 18:1 fatty aldehydes, unequivocally identified as their enol methyl ether derivatives. Results of positive ion fast atom bombardment mass spectrometry (FAB-MS) of the native compound, and GC-MS of partially methylated hexitol acetates derived from the permethylated derivative, were consistent with structures of galactocerebroside having 3,4- and 4,6-linked cyclic plasmal substituents, as shown. [formula: see text]