Asymmetric Reduction Of Carbonyl Compounds Catalyzed By Microbial Cells In Ionic Liquids Media

The biocatalysis and chiral synthesis are attracting more and more attentions nowadays because of the escalating concerns on different pharmacological effects of different optical isomers and the limitations on the registration and application of racemic drugs. Researchers are dedicated to the synthesis methods with high product yield and optical purity, among which. biotransformation is highly interested recently due to its advantages such as mild reaction condition and high selectivity.Ionic liquids (ILs) have been investigated as possible replacement for volatile organic solvents in recent years. This work presents the asymmetric reduction of corresponding carbonyl compounds using microbial cells in aqueous/ ILs biphasic system. It was found that the [bmim][PF6] showed good biocompatibility with Aureobasidium pullulans CGMCC 1244 cells and Saccharoinyces uvarum SW-58 cells, and had little effect on their metabolic activity.The asymmetric reduction of ethyl 4-chloro-oxobutanoate (COBE) to ethyl (S)-4-chloro-3-hydroxybutanoate (CHBE) catalyzed by Aureobasidium pullulans CGMCC 1244 in an aqueous/ILs biphasic system was established. It was shown that the [bmim][PF6] is the most suitable solvent for the biphasic reaction system. The influence of reaction parameters such as shaking rate, volumetric phase ratio, reaction temperature, initial substrate concentration, and pH was tested. The above reaction parameters were found to greatly effect the molar conversion and the initial reaction rate, but have little effect on the optical purity of the product. Under the optimum conditions, the molar conversion, the optical purity and product concentration were 95.6%, 98.5%ee and 47.1 g/L respectively. The results of the reusing of immobilized cells were undesirable compare to that of the free cells. The main reasons could be the inactivation of COBE reductases and dehydrogenase activity after reusing the cells, which lead to difficultlies in regenerating co-enzymes.By investigating of asymmetric reduction of ethyl 4,4,4-trifluor-3-oxobutanoate(TFAAE) to ethyl (R)-4,4,4-trifluoro-3-hydroxybutanoate((R)-TFHBE) in aqueous/ILs biphasic system, the [bmim][PF6] is also identified to be the best solvent for the biphasic system. Under the optimum conditions such as shaking rate, volumetric phase ratio, reaction temperature, initial substrate concentration, and pH, the molar conversion and the optical purity were 85.8% and 89.3%ee. After the re-crystallization, the optical purity of product was enhanced to 95.4%ee .After the aqueous/[bmim][PF6] biphasic system was scaled up for 100 times of asymmetric reduction of TFAAE to (R)-TFHBE, the molar conversion and the optical purity were slightly decreased. In order to further increase the product concentration, batch conversion with substrate feeding was performed. the molar conversion, the optical purity and the product concentration was 65%, 79.4%ee and 32.7 g/L respectively. After the isopropanol extraction, evaporation, and vacuum distillation, the product purity reached 89.7% with a yield of 77.9%. The optical purity of product was increased to reached 97.7%ee after re-crystallization. The recycle of the used ionic liquids in biphasic system was also studied, the recovery rate of 90% was reached using a simple and convenient method.