We attempted to synthesize high-purity structured triacylglycerols (TAG) with caprylic acid (CA) at the 1,3-positions and a polyunsaturated fatty acid (PUFA) at the 2-position by a two-step enzymatic method. The first step was synthesis of TAG of PUFA (TriP), and the second step was acidolysis of TriP with CA. Candida antarctica lipase was effective for the first reaction. When a reaction medium of PUFA/glycerol (3:1, mol/mol) and 5% immobilized Candida lipase was mixed for 24 h at 40°C and 15 mm Hg, syntheses of TAG of γ-linolenic, arachidonic, eicosapentaenoic, and docosahexaenoic acids reached 89, 89, 88, and 83%, respectively. In these reactions, the lipase could be used for at least 10 cycles without significant loss of activity. In the second step, the resulting trieicosapentaenoin was acidolyzed at 30°C for 48 h with 15 mol parts CA using 7% of immobilized Rhizopus delemar lipase. The CA content in the acylglycerol fraction reached 40 mol%. To increase the content further, the acylglycerols were extracted from the reaction mixture with n-hexane and were allowed to react again with CA under conditions similar to those of the first acidolysis. After three successive acidolysis reactions, the CA content reached 66 mol%. The content of dicapryloyl-eicosapentaenoyl-glycerol reached 86 wt% of acylglycerols, and the ratio of 1,3-dicapryloyl-2-eicosapentaenoyl-glycerol to 1(3),2-dicapryloyl-3(1)-eicosapentaenoyl-glycerol was 98:2 (w/w). In this reaction, the lipase could be used for at least 20 cycles without significant loss of activity. Repeated acidolysis of the other TriP with CA under similar conditions synthesized 1,3-dicapryloyl-2-γ-linolenoyl-glycerol, 1,3-dicapryloyl-2-arachidonoyl-glycerol, and 1,3-dicapryloyl-2-docosahexaenoyl-glycerol in yields of 58, 87, and 19 wt%, respectively.Paper no. J9783 in JAOCS 78, 611-616 (June 2001).Polyunsaturated fatty acids (PUFA) have various physiological functions. Eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA) play a role in the prevention of a number of human diseases (1-3). The ethyl ester of EPA has been used in the treatment of arteriosclerosis obliterans and hyperlipemia (4), and oil containing 50% DHA has been used as a health food (5). γ-Linolenic acid (18:3n-6; GLA) shows the physiological functions of modulating atopic eczema (6) and rheumatoid arthritis (7), and arachidonic acid (20:4n-6; AA) and DHA are known to be important for preterm infants (8,9). A structured triacylglycerol (TAG) containing mediumchain fatty acids at the 1,3-positions and a long-chain fatty acid at the 2-position (MLM-type) is absorbed into intestinal mucosa more rapidly than natural oils composed of only longchain fatty acids (LLL-type) (10,11). These reports have focused a good deal of attention on the physiological activity of MLM-type structured lipids. To evaluate the nutraceutical effects, the ability to synthesize high-purity MLM-type structured lipid on a laboratory scale is necessary. It was recently reported that 1,3-capryloyl-2-eicosapentaenoy...