Direct separation of regio- and enantiomeric isomers of diacylglycerols by a tandem column high-performance liquid chromatography

A novel HPLC-based method for direct separation of the three isomers of mono-acid diacylglycerols (DAGs), i.e., 1,2-DAG, 2,3-DAG and 1,3-DAG, has been established. The method employs a tandem column system, in which two different columns (a conventional silica gel column and a chiral stationary phase column) are connected in series. Two isomeric mixtures of DAGs (i.e., dicapryloylglycerol and dioleoylglycerol) and lipase-catalyzed reaction mixtures were successfully resolved on the tandem column HPLC system without any derivatization prior to the analysis. According to the established analytical method, stereoselectivity of two lipases toward mono-acid triacylglycerols in ethanolysis reaction was investigated. The tested enzymes were immobilized Candida antarctica lipase B (CALB) and Rhizomucor miehei lipase (RML). Analyses of the enantiomeric purity of 1,2-DAG and 2,3-DAG, generated as intermediates during the reaction, revealed that CALB and RML have sn-3 and sn-1 stereopreference, respectively.