Enzymatic preparation of enantiomerically pure sn‐2,3‐diacylglycerols: A stereoselective ethanolysis approach

Abstract

Stereoselective ethanolysis of monoacid TAG by immobilized Rhizomucor miehei lipase (RML) was studied for preparation of optically pure sn-2,3-DAG. Trioctanoylglycerol (TO) was used as a model substrate. The enantiomeric purity of the product, sn-2,3-dioctanoylglycerol (sn-2,3-DO), was very high (percent enantiomeric excess > 99%) when an excess of ethanol was used. The result indicated that RML was highly stereoselective toward the sn-1 position of TO under conditions of excess ethanol. The stereoselectivity of RML depended on the amount of ethanol. The larger the amount of ethanol was, the higher the stereoselectivity became. After optimizing the parameters such as reactant molar ratio, water content, and temperature, (ethanol/TO molar ratio = 31:1 and water content = 7.5 wt% of the reactants at 25°C), optically pure sn-2,3-DO was obtained at 61.1 mol% in the glyceride fraction in 20 min. The above conditions were further applied for ethanolysis of monoacid TAG with different acyl groups such as tridecanoylglycerol (C10:0), tridodecanoylglycerol (C12:0), tritetradecanoylglycerol (C14:0) and trioctadecenoylglycerol [triolein, (C18:1)]. The yields and enantiomeric purities of 1,2(2,3)-DAG were dramatically reduced when TAG with FA longer than decanoic acid were used.Paper no. J11267 in JAOCS 83, 603-607 (July 2006).KEY WORDS: sn-2,3-Diacylglycerols, ethanolysis, monoacid triacylglycerols, Rhizomucor miehei lipase.DAG are widely used as emulsifiers in the food, cosmetics, and pharmaceutical industries. Frequently, mixtures of MAG and DAG are exploited because they are cheap and give appropriate performance (1). At present, DAG are regarded as healthful oils owing to their activity in preventing obesity (2). In addition, pure isomers of DAG have great potential as intermediates for the organic synthesis of phospholipids, glycolipids, prodrugs, and structured lipids (3-6). DAG exist in three isomers: sn-1,3-, sn-1,2-, and sn-2,3-DAG. For monoacid DAG, sn-1,2-and sn-2,3-DAG are enantiomers of each other. Although pure isomers of DAG are difficult to synthesize by traditional chemical synthetic methods, lipase-catalyzed regio-and stereoselective reactions would provide alternative routes. For example, preparation of sn-1,3-DAG at high yield and purity was successfully achieved by direct esterification of glycerol and FFA using 1,3-regiospecific lipase (6-8) and by direct transesterification of glycerol and vinyl esters of medium-chain FA using Candida antarctica lipase B (9).In contrast to the preparation sn-1,3-DAG, chemoenzymatic methods are used for the preparation of optically pure sn-1,2-DAG or sn-2,3-DAG. Some recent publications describe syntheses of enantiomerically pure sn-1,2-DAG by lipase-mediated sequential transesterification of the racemic O-alkyl glycerols (10,11). In another synthetic route, the chiral sn-1,2-DAG are chemically synthesized from (R)-and (S)-enantiomers of O-(4-methoxyphenyl)-glycidol, which are obtained from a onepot reduction of ketone and in situ lipase-mediated resolution (12). Altho...

An insight on acyl migration in solvent-free ethanolysis of model triglycerides using Novozym 435

“…The ethanolysis reactions of triglycerides (TAG) catalyzed by enzymes have been widely studied in the last few years for the production of biodiesel using a short-chain alcohol that can be obtained without resorting to fossil fuels [1][2][3][4][5][6], for the synthesis of acyl glycerides (specific mono-and diglycerides) [7][8][9], or for the synthesis of ethyl esters used in different industrial applications [10].…”

Preparation of Diacylglycerol‐Enriched Oil from Free Fatty Acids Using Lecitase Ultra‐Catalyzed Esterification

“…In the United States, DAG oil has received the status ''Generally Recognized as Safe'' (GRAS) by the US Food and Drug Administration [7]. The application of DAGenriched oil (DEO) is being marketed as a functional cooking oil in Japan and in United States [8].…”

Novel Combi-lipase Systems for Fatty Acid Ethyl Esters Production

“…This seems to reflect their documented complementary catalytic properties in transesterification: TLL is sn-1,3 specific [37], faster processing triglycerides [15] and inhibited by free fatty acids [15,38], while CALB is unspecific [37], faster processing partial glycerides [33] and can esterify free fatty acids [39]. Values of CF that range from 1.0-1.2 were obtained from combinations of TLL and RML: This lower values with regard to those of TLL and CALB were expected, since RML [40] has catalytic properties closer to TLL in transesterification [15].…”