Breakdown of Phospholipids in Mild Alkaline Hydrolysis.

M i l d alkaline hydrolysis of phospholipids, a method introduced by Dawson ( l ) , is based on the following principle. The carboxyl ester groups of a phospholipid are much more susceptible to nucleophilic attack by hydroxy or alcoholate ions than the phosphate group. Thus, by choosing appropriate concentrations of base, phospholipids can be deacylated (Le., the fatty acid esters can be preferentially hydrolyzed), but the water-soluble phosphate diesters produced are left intact. However, such a clear-cut reaction has not been achieved in practice, there is always some attack on the phosphate group. I n the best known deacylation procedure ( Z ) , there is a 6% breakdown of glyceryl phosphorylcholine and perhaps also some breakdown of glyceryl phosphorylinositol (2, 3). Seemingly milder methods (4, 5 ) , employing lower temperature and shorter reaction time than Dawson’s, have been reported to yield “unidentified compounds” (4, 5 , 6), and it will be shown in the following that the use of chloroform as a solvent in these “mild hydrolysis” procedures is responsible for the formation of several breakdown products from lecithin. Some of the factors governing the breakdown of phosphate esters, as it accompanies and follows the deacylation of phospholipids, have been investigated in this study, with the aim of establishing optimal conditions for deacylation with minimal breakdown of the phosphate esters.