固定化细胞有机相催化不对称还原β-羰基酯

Asymmetric reduction of ethyl 4-chloro-3-oxobutanoate by immobilized cells in organic solvent

将酵母细胞用海藻酸钙包埋后用于有机相催化不对称还原4-氯乙酰乙酸乙酯制备光学活性的4-氯-3-羟基丁酸乙酯,从中筛选得到具有较高立体选择性和还原能力的菌株假丝酵母SW0401,将此菌株的细胞固定化细胞作为研究对象,系统考察了固定化条件、固定化细胞大小、反应溶剂、初始底物浓度、辅助底物、固定化细胞热处理和抑制剂对还原反应的影响。结果表明,上述因素对反应的摩尔转化率和产物(S)-CHBE光学纯度有显著影响。固定化时所用缓冲液的pH值为7.0时和固定化细胞颗粒平均直径为2.5 mm较合适,以正己烷为反应介质时反应的摩尔转化率和产物光学纯度最优,初始底物浓度以54.7 mmol/L为宜,辅助底物以1-己醇为佳。对固定化细胞的热处理和添加抑制剂烯丙醇均能够明显改善产物的光学纯度,但对提高摩尔转化率有负面影响。

By cultivation and immobilization, several yeast strains were selected to catalyzethe asymmetric reduction of ethyl 4-chloro-3-oxobutanoate （COBE） to optically active ethyl 4-chloro-3-hydroxybutanoate （CHBE） in organic solvent. With higher stereoselectivity and activity, the strain Candida sp. SW 0401 was the desired strain, and was investigated further, such as effects of condition of immobilization, size of immobilized cells, organic solvent, heat treatment, inhibitors, co-substrates and initial concentrations of COBE on the reduction were investigated. The results showed that these factors obviously influenced the molar conversion and the optical purity of the product. The optimal conditions were as follows：pH of the buffer for immobilization being 7.0, the size of immobilized cells 2.5 mm, the reaction solvent hexane, co-substrates 1-hexanol and the initial concentrations of COBE 54.7 mmol/L, respectively. Heat treatment of immobilized cell and addition of inhibitor allyl alcohol could obviously improve the optical purity of （S）-CHBE, but negatively effected the molar conversion.