Acyl Sphingoids and Related Oxazolines

Abstract

Oxazolines prepared from sphingoids or analogues and imidic esters were obtained as mixtures in which the isomer with heterocyclic oxygen derived from O¹ of the parent sphingoid predominated in the case of erythro sphingoids, and that with original O³ in the case of threo sphingoids. The separated dry oxazolines were stable at 0º but isomerized in alcohol, ether or chloroform solution.Hydrolysis of the oxazolines in acid gave the salts of the expected O-acyl compounds or the free O-acyl compounds at pH 5-6, while N-acyl compounds were formed at pH 8; these transformations occurred without change of configuration except for some inversion of oxazolines containing the original O³ of erythro sphingenine. O-Acyl compounds changed into N-acyl isomers in neutral or alkaline media, but the conversion of N-acyl compounds into O-acyl isomers occurred in traces only. Oxazolines could not be detected as intermediates in the transacylation of O- or N-acyl sphingoids.  Changes of aged ceramide solutions are ascribed to photooxidation rather than transacylation.