BENZOOLYSIS OF DIACYLGLYCEROPHOSPHOCHOLINES - DEPHOSPHORYLATION AND SEQUENTIAL FORMATION OF ISOMERIC REACTION-PRODUCTS

Benzoolysis experiments are reported in which diacylglycerophosphochol ine is heated at 100 degrees C with benzoic anhydride for variable per iods of time. It is shown that more than 90% of the phospholipid is de phosphorylated after 5 h of heating. Lipid extracts of the reaction mi xture contained 1,2- and 1,3-diacylglycerobenzoate and 1,2- and 1,3-di acylglycerol in nearly constant isomer ratios of about 3:1 and 1:2, re spectively, independent of the heating and extraction time. The total amount of isomeric diacylglycerobenzoates increased more slowly with i ncreasing heating time than corresponded with the dephosphorylation ra te, complete benzoylation being attained only after a 15 h heating per iod. The total amount of isomeric diacylglycerols went through a maxim um after about 4 h and vanished after 15 h of heating. Addition of 4-d imethylaminopyridine subsequent to the heating period resulted in rapi d and complete benzoylation of dephosphorylated phospholipid. However, the ratio of 1,2- to 1,3-diacylglycerobenzoate then found in the lipi d extract depended on heating time, changing from less than 1:1 to abo ut 3:1 upon an increase of heating time from 1 to 15 h. The results ar e interpreted in terms of two consecutive reactions. In a relatively f ast first step, a dephosphorylated intermediate is formed, which, in t he molten benzoic anhydride, is slowly benzoylated. The intermediate y ields diacylglycerols upon extraction in the absence of 4-dimethylamin opyridine and diacylglycerobenzoates upon extraction in the presence o f 4-dimethylaminopyridine.