Abstract
A simple method is described for the determination of molecular species of enantiomeric sn-1,2- and sn-2,3-diacylglycerols derived from natural triacylglycerols by Grignard degradation. The method is based on a preparative separation of the enantiomeric diacylglycerols as 3,5-dinitrophenylurethane (DNPU) derivatives by high performance liquid chromatography (HPLC) on a chiral column (25 cm x 4.6 mm ID) containing R-(+)-1-(1-naphthyl)ethylamine as a stationary phase. This is followed by polar capillary gas-liquid chromatography (GLC) of the trimethylsilyl (TMS) ether derivatives of the enantiomeric diacylglycerols derived from the DNPU derivatives using trichlorosilane, which does not cause acyl migration and racemization during the reaction. The cleavage is better than 94% complete. The method was standardized with synthetic sn-1,2- and sn-2,3-dipalmitoyl- and rac-1,2-dioleoylglycerols and was applied to the identification and quantitation of individual molecular species of enantiomeric diacylglycerols generated by Grignard degradation of the triacylglycerols from corn oil, cocoa butter, and lard.
Highlights
A simple method is described for the determination of molecular specie of enantiomeric sn-1,2-and m-2,S-diacylglyceroIs derived from natural triacylglycerols by Grignard degradation
The chiral phase high performance liquid chromatography (HPLC) described by Takagi and Itabashi (1) provides a rapid and complete resolution of enantiomeric sn-1,2- and sn-2,3-diacylglycerols as 3,5-dinitrophenylurethane (DNPU) derivatives containing identical fatty acids, but resolution of enantiomers containingdifferent fattyacids results in arnerlapor intedgitationof many molecular species, and identification of individual sn-1,2and sn-2,3enantiomers becomes difficult or impossible
A mild method of cleaving urethanes with chlorosilanes has been reported (3-5) and we have adopted it for the regeneration of the diacylglycerolmoieties from the DNPU derivatives.The present study reports the conversion of DNPU derivatives into TMS ethersof diacylglycerolsin better than 94% yield by reaction with trichlorosilaneand trimethylchlorosilane at room temperature without affecting the acyl groups
Summary
Sn-1,2-and m-Z,3-dipalmitoylglycerolwsere available in the laboratory from a previous study (6). Cocoa butter, and lard triacylglycerols were isolated from commercial products by silicic acid TLC using hexanediethyl ether 7:3 as developing solvent. The m-1,2(2,3)diacylglycerols were prepared from the triacylglycerols by partial Grignard degradation and were purified by boric acidTLC (7). The DNPU derivativeswere prepared by reacting free diacylglycerolswith 3,5-dinitrophenylisocyanate in the presence of dry pyridine at room temperature; they were purifed by silicic acid TLC (6)
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