Enzymatic polar head modifications of phospholipids in the presence of ionic liquids

Natural and synthetic phospholipids (PLs) have attracted considerable interest for the multiple scientific and practical applications which follow from their amphiphilic properties. PLs are the focus of biomedical research because of their possible use as pharmaceuticals, food additives, cosmetics, in liposome technology, in gene transfer therapy and in drug delivery systems. However, the investigations and applications rely upon the availability of a great number of purified PLs which can be obtained by semisynthesis from natural sources or from synthetic precursors. The enzymatic modification of the polar heads of natural or synthetic PLs is perhaps the most commonly employed enzymatic modification in the preparation of modified PLs. Phospholipase D (PLD) (E.C. 3.1.4.4) catalyzes the in vivo hydrolysis of PLs to phosphatidic acid (PA). However, in the presence of an alcohol, PLD from Streptomyces PMF catalyzes the in vitro transphosphatidylation of the polar head. This enzyme has been largely used for the transformation of the most abundant natural PL, phosphatidylcholine (PC), into many different PLs. However, the presence of water causes the formation of PA as ubiquitous by-product, thus lowering reaction yields and forcing to further purification steps. Since the purification of this class of compounds is not straightforward, the enhancement of reaction selectivity opens the way to an easier preparation of the target compounds on a relatively large scale. The aim of this work is to investigate innovative reaction media such as ionic liquids for enzymatic PLs transformations in order to obtain a higher selectivity in the enzymatic transphosphatidylation reactions of natural PC catalyzed by PLD from Streptomyces PMF. The opportunity of using ionic liquids (ILs) in PLs chemistry had not been yet investigated. We have tested the stability and the activity of the PLD in various commercial ionic liquids. We illustrate the encouraging preliminary results of the use of ionic liquids as co-solvents in transesterification reactions with different alcohols. This reaction medium seems to be able to drive the reaction towards transphosphatidylation with high depression of competitive hydrolysis.