Chromatographic resolution of chiral diacylglycerol derivatives: potential in the stereospecific analysis of triacyl-sn-glycerols

Diacylglycerols have been separated as their (S)-(+)-or (R)-(-)-1-(1-naphthyl)ethyl urethanes by high performance liquid chromatography (HPLC) on a column of silica gel with 0.5% 2-propanol in hexane as the mobile phase. The elution order of components derivatized with the (S)-form of the reagent was 1,3-, followed by 1,2-, and finally 2,3-diacyl-sn-glycerols. The elution order of 1,2- and 2,3-diasteromers was reversed when the (R)-form of 1-(1-naphthyl)ethyl isocyanate was used for derivatization. Single-acid 1,2- and 2,3-diastereomers were separated to the baseline with a resolution factor from 5.2-5.7, and the resolution factor between 1,3- and 1,2- or 2,3-diacyl-sn-glycerol derivatives was more than 23. Molecular species of single-acid diacylglycerol derivatives were separated in the sequence 18:1 less than 18:0 less than 18:2 less than 16.0. In order to assess this methodology as part of a procedure for the stereospecific analysis of triacyl-sn-glycerols, we prepared diacyl-rac-glycerols from maize oil, evening primrose oil and egg yolk triacylglycerols by partial hydrolysis with ethyl magnesium bromide. The 1,3-, 1,2- and 2,3-diacyl-sn-glycerols as (S)-(+)-1-(1-naphthyl)ethyl urethanes were isolated and their fatty acid compositions were determined. Although this only permitted an indirect determination of the compositions of positions sn-1, -2 and -3, it was sufficient to indicate the potential of the methodology because results comparable to those published earlier were achieved.