Synthesis and characterization of triacylglycerols containing linoleate and linolenate

Triacylglycerols containing linoleate and linolenate found in vegetable oils were synthesized in gram quantities for oxidation studies. Two acylation methods were examined to convert diacylglycerols or monoacylglycerols to the desired triacylglycerols. Acylations with fatty acid and 1,1'-dicyclohexylcarbodiimide in the presence of 4-dimethylaminopyridine were more rapid, gave triacylglycerols of better isomeric purities and generally better overall yields than the acylations with acid chloride in pyridine. The functional and isomeric purity of the synthetic triacylglycerols were investigated by thin-layer and gas-liquid chromatography of the methyl esters, by lipase hydrolysis, and by(13)C NMR. Quantitative(13)C NMR provided a valuable tool to determine isomeric structures of the unsaturated triacylglycerols and complemented the lipase hydrolysis method. The triacylglycerols purified by dry column chromatography were obtained in the following respective percent yields, functional and isomeric purities: LLLn, 92.1, 99.4, 98.1; LLnLn, 91.7, 99.2, 97.4; LLnL, 84.2, 99.7, 98.9; and LnLLn 77.5, 97.8, 99.0 (where L=linoleoyl and Ln=linolenoyl glycerol residues). These synthetic triacylglycerols are valuable models to elucidate the interrelationship of unsaturated fatty acids on the oxidative stability of polyunraturated vegetable oils.