Synthesis and Physical Properties of Symmetrical and Non‐symmetrical Triacylglycerols Containing Two Palmitic Fatty Acids

Abstract

AbstractA 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 1,3‐di‐ 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.