Triacylglycerol epoxidation

Recent studies have attempted to improve the efficiency of epoxidation under milder conditions that minimize the formation of byproducts. Chemo-enzymatic epoxidation uses the immobilized lipase from Candida antartica (Novozym 435) (56) to catalyze conversion of fatty acids to peracids with 60% hydrogen peroxide. The fatty acid is then self-epoxidized in an intermolecular reaction. The lipase is remarkably stable under the reaction conditions and can be recovered and reused 15 times without loss of activity. Competitive lipolysis of triacylglycerols is inhibited by small amounts of fatty acid, allowing the reaction to be carried out on intact oils (57). Rapeseed oil with 5% of rapeseed fatty acids was converted to epoxidized rapeseed oil in 91% yield with no hydroxy byproducts. Linseed oil was epoxidized in 80% yield. Methyl esters are also epoxidized without hydrolysis under these conditions. 

G. J. Piazza, T. A. Foglia, One-pot synthesis of fatty acid epoxides from triacylglycerols using enzymes present in oat seeds, /. Am. Oil Chem. Soc. 83 (2006) 1021. 

Sjovall, O. and Kuksis, A. (1997a) Analysis of oxidized triacylglycerols by LC/MS with electrospray ionization. I. Hydroperoxides, hydroxides, and epoxides. Lipids, submitted. 

The ESI technique was applied to the analyses of synthetic isomers of triacylglycerol hydroperoxides of eicosapentaenoic acid, and other oxidation products, including hydroxides, epoxides and triglyceride core aldehydes... 

Giuffrida, F., Destaillats, F., Fabien, R., Skibsted, L.H. and Dionisi, F. Formation and hydrolysis of triacylglycerol and sterol epoxides Role of unsaturated triacylglycerol peroxyl radicals. Free Rad. Biol. Med. 37, 104-114 (2004). 

The hydroperoxide by-products of the reaction of unsaturated triacylglycerol (TAG) (e.g., stearoyl oleoyl stearoyl, palmitoyl palmitoyl oleoyl) with t-butyl hydroperoxide were studied on a Cjg column (ELSD, drift tube 85°C) using a 30-min 80/20 - 20/80 methanol/IPA gradient [426]. Up to 16 peaks.were generated in the product chromatogram. Electrospir MS was used to identify some of the peaks. Common products included TAG hydroperoxide, epoxide, and combined peroxide/epoxide products. 

The triacylglycerol (TAG) autoxidation products of canola oil were studied using two 250 X 4.6 mm Cis columns (ELSD, drift tube T = 140°C, N2 nebulizer gas flow at 2 L/min and a complex 85-min 70/30 - 30/70 acetonitrile/dichloromethane gradient [775]. Along with the triglycerols (e.g., ranging fiom linoliec oleic oleic to stearic oleic stearic), hydropexoxides (e.g., linoleic oleic oleic hydroperoxide) and epoxides (e.g., palmitic oleic oleic epoxide) were identified. 

Fatty acids with polar substituents also retard the migration of triacylglycerols on TLC adsorbents, and those from seed oils that contain epoxy fatty acids can be separated into simpler species that contain from zero to three epoxide residue per mole. For example, silica gel layers and a solvent system of hexane-diethyl ether (3 1, v/v) were used to isolate such fractions from seed oils (Figure 9.1(B)) [192], Similar separations have been achieved with triacylglycerols that contain hydroxyl, estolide and other functional groups in the fatty acids. 

Lipid analysis of the three races of B. braunii indicated, along with large amounts of specific hydrocarbons, the presence of common neutral lipids, such as triacylglycerols, sterols and carotenoids whose distribution will be considered shortly. In addition, extensive analytical investigations on the external lipids of various strains of the A race resulted in the identification of several series of non-classical compounds such as aldehydes, alkenylphenols, epoxides and ether lipids. 

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