Synthesis and physical properties of symmetrical and non-symmetrical triacylglycerols containing two palmitic fatty acids

A series of symmetrical ABA) and non-symmetrical (AAB) triacylglycerol (TAG) isomers containing "A," palmitic (P; 16: 0) acid, and "B," either oleic (O; 9c-18: 1), elaidic ( E; 9t-18: 1), linoleic (L; 9c, 12c-18:2) or linolenic (Ln; 9c, 12c, 15c-18:3) fatty acids were synthesized by esterification of the thermodynamically more-stable 1,3di- or 1(3)-monoacylglycerols[1,3-DAG or 1(3)-MAG], respectively. 1,3-dipalmitoylglycerol(1,3P-DAG) was esterified with O, L or Ln acid to prepare the symmetrical TAG isomers POP, PLP and PLnP, while the O-E-, L- and Ln-1(3) MAG precursors, synthesized or obtained commercially, were esterified with P acid to prepare the non-symmetrical TAG isomers OPP, EPP, LPP and LnPP, respectively. The drop point( s), solid fat content and melting point values of the synthesized TAG were determined. The 1,3-dipalmitoylglycerol (1,3P-DAG) and 1(3)P-MAG precursors were prepared, in multi-gram quantities, by partial glycerolysis (glycerol/p-toluenesulfonic acid) of tripalmitin. After fractionation by silica gel chromatography, the 1(3)P-MAG and 1,3P-DAG isomers (ca. 80% of total MAG or DAG) were purified (> 98%) by crystallization from acetone [silver ion-HPLC was utilized to determine the structural purities of the DAG (or MAG) precursors, and the synthesized TAG]. Esterification of the appropriate, thermodynamically more-stable MAG or DAG precursors was found to be a very versatile method for synthesis (in 80-90% yields) of multi-gram (3-5 g) quantities of symmetrical and non-symmetrical TAG isomers, in chemical and structural purities of > 96 and 97-99%, respectively.