Lipase-catalyzed synthesis of chiral triglycerides

Under certain reaction conditions, the acidolysis of tripalmitin with oleic acid using immobilized lipase from Rhizomucor miehei resulted in a higher level of monosubstituted oleoyldipalmitoyl (OPP) triglycerides than had bee n predicted according to kinetic modeling. The reaction products were subje cted to chiral analysis by high-performance liquid chromatography (HPLC), w hich indicated that the enzyme was more active at the sn-1 position of the triglyceride than at the sn-3 position, resulting in synthesis of the chira l triglyceride 1-oleoyl-2,3-dipalmitoyl-sn-glycerol. A kinetic model was de veloped and was correlated with the HPLC method to provide a simple means t o predict the stereoselectivity of lipase-catalyzed reactions. By using the model, the stereoselectivity of immobilized Rhizomucor miehei lipase was f ound to depend strongly on the initial water activity (a(w)) of the reactio n mixture, with greater selectivity occurring at lower a(w). The sn-1 selec tivity was essentially maintained using various solvents, or without solven t, when a, was kept constantly low. Variation in the fatty acid composition of the triglyceride indicated that shorter-chain fatty acids result in gre ater stereoselectivity, while variation of the chainlength of the free fatt y acid indicated an enhancement by the longest chainlength. The stereoselec tivity of this lipase was confirmed using a new C-13 nuclear magnetic reson ance method. By using immobilized R. miehei lipase at low a, approximately 80% of the chiral triglyceride found in the reaction mixture was the sn-1 e nantiomer, at high reaction conversion.