Study On Lipase-catalyzed Resolution Of Vince Lactam In Organic Solvent And Its Ultrasonic Promotion

Drugs with a chiral center are known as chiral drugs. As the importantcompositions of chemically synthetic drugs, the physiological and pharmacologicaleffects of chiral drugs mainly depend on their ability of chiral matching and recognitionwith target molecule in organisms. Therefore, there exists large difference inpharmacological action and toxicity among different isomers of chiral drugs.(1S,4R)-vince lactam is one of the important intermediate raw materials during thesynthesis of peramivir and abacavir. Nowadays,(1S,4R)-vince lactam is mainlysynthesized through chemical resolution whose catalysis is usually toxical. Thus,(1S,4R)-vince lactam with high optical purity was obtained through enzyme-catalyzedresolution in this thesis.Lipase is usually the optimal biocatalysis used in chiral resolution due to its mildreaction conditions, less population as well as high activity and enantioselectivity.Enzymes in organic medium still possess high catalytic ability because theintegrity of their whole conformation and active center was kept. The properties ofenzymes in organic medium are different from those in water because of their rigidstructure in organic medium, like pH-memory, thermodynamic stability, substratespecificity and enantiomeric selectivity. Besides, organic solvents could improve thesolubility of non-polar substrates, strengthen the stability of enzymes and make it easierto recycle the enzyme. Consequently, the synthesized (R, S)-N-hydroxymethyl vincelactam was resolved in organic medium catalyzed by lipase. The ways and factorswhich could affect the activity and enantioselectivity of lipase were also investigated. Itwas proved that optimum conditions were contributed to the improvement of enzemeactivity and enantioselectivity as well as the resolution effect of (R,S)-N-hydroxymethyl vince lactam. The optimum reaction conditions were: lipase(AKL), organic solvent (methyl tert-butyl ether), acyl donor (vinyl acetate), temperature (45℃), Ph (6.5), water activity (αw0.33), content of AKL (20mg) andsubstrate ratio (vinyl ester: N-hydroxymethyl vince lactam=5:1).During recent years, ultrasound, an environment-friendly technology, has beenwidely applied to the enzyme-catalyzed reactions in organic medium. Based on theenzymatic resolution of (R, S)-N-hydroxymethyl vince lactam, ultrasound was adoptedto optimize the AKL-catalyzed esterification of (R, S)-N-hydroxymethyl vince lactam.In addition, the mechanism of ultrasound’s improving the enzymatic reaction was alsoinvestigated. It was found that ultrasound with lower power could improve theenzymatic reaction rate and thus shorten the reaction time, while ultrasound withhigher power could lead to the decrease of enzyme activity and enantioselectivity.Among ultrasound pretreatment, continuous ultrasound and intermittent ultrasound,intermittent ultrasound played the most important role in the transesterification of (R,S)-N-hydroxymethyl vince lactam catalyzed by AKL in methyl tert-butyl ether. Besides,the ultrasound time and more intensive movement of molecule under ultrasound couldalso result in the change of optimum temperature. The screened optimum conditionsduring intermittent ultrasound were: ultrasonic frequency (20KHz), ultrasonic powe r(150W) with ultrasonic time (50s) and interval time (40s), ultrasonic temperature(35℃). Under the optimum reaction conditions, the activity（28.2μmol/gï¹'min） andenantioselectivity (E=25.3) of AKL were dramatically improved.