Migration during hydrolysis of esters of glycerophosphoric acid. III. Cephalin and glycerylphosphorylethanolamine.

The investigation of the structure of the lecithins and cephalins (phosphatidylethanolamines) from natural sources gave rise to the question, whether the phosphoric acid in these substances is attached to the (Yor P-carbon atom of the glycerol moiety. Since the acid and alkaline hydrolysis of natural lecithins yielded mixtures of CYand p-glycerophosphoric acid (GPA), it was assumed that they existed in the cr as well as the fl form. The subsequent isolation of optically active lecithins was irrefutable proof of the occurrence of the OL form. Doubt of the existence of the p form arose with the growing suspicion that the /3-GPA is an artifact, presumably formed by the migration of phosphoric acid. On examining critically the acid and alkaline hydrolysis of pure synthetic L-or-lecithins (1) and their L-a-glycerylphosphorylcholine (GPC) moiety (a), it was found that the chemical degradation of the lecithins is indeed accompanied by a reversible migration of phosphoric acid. In the case of the L-a-lecithins this reaction gives rise to the formation of DL-a-GPA and ,&GPA, in addition to L-W GPA, the direct product of hydrolysis. Since corresponding hydrolysates of both the synthetic L-a-lecithins and the natural lecithins were found to contain CXand ,&GPA in approximately the same ratios, it was evident that most if not all of the P-GPA in the hydrolysates of the natural lecithins could have been formed by the migration of phosphoric acid and not by the hydrolysis of p-lecithins. The naturally occurring cephalins on acid or alkaline hydrolysis likewise had yielded mixtures of o(and /3-GPA (3-8) and hence were also believed to occur in the o( and fi forms. We noticed, however, that’ the mixtures of a~and p-GPA had pract’ically the same composition as those which we had obtained from synthet’ic L-a-lecithins under comparable conditions of hydrolysis. It seemed reasonable, therefore, to assume that the chemical hydrolysis of the cephalins, like that of the lecithins, is accompanied by a migration of phosphoric acid. We tested this assumption by hydrolyzing