Enhancement Of Saccharomyces Ellipsoideus Asymmetric Reduction Efficiency For (R)-mandelic Acid Synthesis

Optical mandelic acid is a versatile chiral synthon used for the synthesis of various pharmaceuticals, and the applications of optical mandelic acid have grown markedly in recent years and are likely to expand in the coming years. Preparation of optically pure (R)-MA by biocatalyst has an advantage of mild reaction conditions, high stereoselectivity,high regioselectivity and high chemical selectivity. In this paper, the asymmetric synthesis of (R)-MA catalyzed by Saccharomyces ellipsoideus in aqueous phase was investigated. For the aim of laying a foundation to prepare (R)-MA on industrial scale, the initial reaction substrate concentration, reusing of biocatalyst, extracting and purification of (R)-MA were studied.The fed-batch conversion was optimized through the response surface methodology(RSM). A 3-lebel-3-factor central composite design was employed to evaluate the effects of reaction time, fed-batch number, initial substrate concentration on the yield of (R)-MA. The optimum conditions were as followed: fed-batch number 4, biotransformation time 65 h, initial substrate concentration 5.5 g/L. Under the optimal conditions the yield of product was 10.87 g/L。Combination of in situ adsorption technology and optimal substrate concentration of reaction to increase the reaction substrate concentration were studied. The results showed that by adding NKAⅡadsorbent resin in reaction system, substrate and or product inhibition was mitigated, and the substrate concentration was thus increased. According to adsorption capacity and optimal substrate concentration of reaction, a formula was established about the resin addition amount along with the changing of substrate concentration, according the formula, the PGA concentration in aqueous phase could controlled in best level. Thus, the high substrate concentration and high reaction speed could be achieved. Then 0.6 g NKAⅡadsorbent resin was added to system under an increased substrate concentration of 15 g/L with a preadsorption for 2 h before reaction. When reacting for 84 h under optimized conditions, the optical purity and the yield of (R)-MA reach 100% e.e. and 91.2% respectively.The optimization of temperature, pH, and agitation to reaction system containing resin were studied. The optimum reaction conditions were obtained as 35oC, pH 7.5, shaking speed 150 r/min. Under such conditions, the reaction time shortened by 12 h for 15 g/L substrate concentration. Finally found that combining the two methods are the most effective way and increased substrate concentration from 5 g/L to 20 g/L, 91.6% yield of (R)-mandelic obtained in fed-batch in a added resin system .And reusable capability of cell is very well.The biotransformation at the pilot scale of 5 L was also studied. The substrate amount of 20 g/L, The stirring rotation and aetation were adjusted to 0 vvm and 150 r/min repectively, yield of (R)-mandelic and e.e. are 90% and 100%.