Synthesis, Purification, and Acyl Migration Kinetics of 2‐Monoricinoleoylglycerol

Abstract

Abstract2‐Monoricinoleoylglycerol (2‐MRG) was synthesized by the Novozym 435 catalyzed alcoholysis of castor oil in excess ethanol (1:70 mol:mol) at ambient temperature. Due to the fatty acid C12‐OH group, conventional liquid–liquid extraction methods developed for less polar, non‐hydroxylated 2‐monoacylglycerols (2‐MAG) proved inadequate for 2‐MRG purification. Alternatively, 2‐MRG was purified by normal‐phase flash chromatography (FC) on silica gel using a binary acetone‐hexane gradient mobile phase. Gram quantities of 2‐MRG were isolated in 63 % yield and contained no residual diacylglycerol (DAG), which fail to separate using liquid–liquid extraction methods. The 2‐MRG was obtained at ~90 mol% relative to 1‐MRG, proving that the FC method did not appreciably catalyze acyl migration. 1H‐NMR spectroscopy was used to monitor the spontaneous acyl migration of isolated 2‐MRG from 20 to 80 °C. The relative energy of activation calculated from the Arrhenius relationship of the 2‐MRG acyl migration rate constants was 82.9 kJ/mol. This was ~two‐fold higher than the theoretical ΔG298.15 calculated from molecular modeling using density functional calculations (B3LYP/6−31 + G*) of 2‐MRG, the ketal ring transition state, and 1‐monoricinoleoylglycerol (1‐MRG). The synthesis and isolation methods reported herein provide a convenient means to access useful intermediates for functionalized structured lipids.