Title: Synthesis, purification, and acyl migration kinetics of 2-Monoricinoleoylglycerol Authors
Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 14, 2013
Publication Date: January 28, 2014
Citation: Compton, D.L., Laszlo, J.A., Appell, M., Vermillion, K., Evans, K.O. 2014. Synthesis, purification, and acyl migration kinetics of 2-Monoricinoleoylglycerol. Journal of the American Oil Chemists' Society. 91(2):271-279. Interpretive Summary: This research describes a method for making and purifying bio-based, eco-friendly chemical intermediates made from hydroxylated vegetable oils. Our mission is to develop new, value added, bio-based chemicals and products that replace those made from petroleum. Hydroxylated (containing –OH groups) fatty acids and vegetable oils play a significant role in the cosmeceutical, pharmacological, and chemical industries and related research. We have developed a method to make and purify a valued vegetable oil intermediate containing a hydroxyl fatty acid. The intermediate has two functional sites where other molecules can be added to form specifically structured vegetable oils. Specifically structured vegetable oils can then be made with unique properties for industry and research in cosmetics and medicine. Our methods of making and purifying the hydroxylated vegetable oil intermediate can be applied to a variety of other vegetable oil intermediates with different functionalities and properties; therefore, our method will be of use to other scientists and researchers trying to design new specifically structured vegetable oils.
Technical Abstract: 2-Monoricinoleoylglycerol (2-MRG) was synthesized by the conventional enzymatic ethanolysis of castor oil. 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 77.7 kJ mol-1. This was ~ two-fold higher than the theoretical 'G298.15 calculated from 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.