Occurrence of 2-O-acyl galactosyl ceramide in whale brain.

Abstract

Four glycolipids (Fr. I, II, III, and IV) were isolated from whale brain and three (Fr. I, II, and III) of them were demonstrated to be galactosyl ceramide combined with fatty acid by ester linkage. Fr. IV was shown to be a monoalkyl monoacyl galactosyl glycerol. For determining the substituted position of the acyl group on the galactose moiety, free hydroxyl groups of ester cerebrosides were protected with dihydropyran, deacylated by mild alkali treatment, and then subjected to permethylation. Finally, the methylated galactitol acetates obtained by hydrolysis and reduction were detected by gas chromatography and identified by gas chromatography-mass spectrometry. By this procedure, Fr. I was shown to be an acyl ester of kerasine, with the ester group at the 6-position of galactose. Fr. II and III were demonstrated to be acyl esters of phrenosine, in which the acyl groups were attached to the 6- and 2-position of the galactose, respectively. While the ester-linked acyl group of Fr. I, II, and III was composed of only normal fatty acids, predominantly palmitic acid, and the amide-linked fatty acids showed a heterogeneous composition of normal and hydroxy fatty acids, C16 to C24.