1-(3'-O-acyl)-beta-glucosyl-N-dihydroxypentatriacontadienoylsphingosine, a major component of the glucosylceramides of pig and human epidermis.

The least polar of four chromatographically distinct glucosylceramides in both pig and human epidermis, was identified from its infrared spectrum and degradation products as O-acylglucosylceramide. Permethylation studies indicated that the acyl group was attached predominantly (80%) to the C-3 of glucose in the pig and only to the C-3 glucose in the human O-acylglucosylceramide. Octadecadienoic acid was the major acid esterified to glucose in both pig and human O-acylglucosylceramides and sphingenine, sphinganine and heptadecasphinganine accounted for most of the long chain bases (87% in pig, 80% in human). Chromatographic and chemical-evidence suggested that a single, unknown unsaturated dihydroxy fatty acid with more than 30 carbon atoms was attached through the amide link to the sphingosines. This was confirmed by mass spectrometry. Precise mass measurements indicated that the acid had a relative molecular mass of 550.496115 (C35H66O4) and was a dihydroxy acid with two double bonds. Other mass spectrometric data suggested that the hydroxyl groups and double bonds were confined to the region between C-16 and C-20. The evidence indicated that the O-acylglucosylceramide in pig epidermis and, by the close similarity of its properties, probably that in human epidermis also was 1-(3'-O-acyl)-beta-glucosyl-N-dihydroxypentatriacontadienoylsphingosine.