Improvement Of The Whole Cell Catalytic Efficiency Of Asymmetric Production Of (S)-1-phenyl-1,2-ethanediol By In Situ Resin Adsorption

Optically active (S)-1-phenyl-1,2-ethanediol((S)-PED) has special bioactivity and photoelectromagnetism performance, which is a important chiral intermediate in the synthesis of pharmaceuticals, agrochemicals, and fine chemicals. Preparation of optically pure (S)-PED by biocatalyst has an advantage of mild reaction conditions, high stereoselectivity,high regioselectivity and high chemical selectivity. In this paper, the asymmetric synthesis of (S)-PED catalyzed by Candida parapsilosis CCTCCM203011 in aqueous phase was investigated. For the aim of laying a foundation to prepare (S)-PED on industrial scale, the initial reaction substrate concentration, reusing of biocatalyst, extracting and purification of (S)-PED were studied.In situ adsorption technology was used to increase the initial reaction substrate concentration. The results showed that by adding NKAⅡadsorbent resin in reaction system, the initial substrate concentration was increased. A formula was established about the resin addition amount along with the changing of substrate concentration, according to the formula, the PED concentration in aqueous phase could be controlled in best level. Thus, the high substrate concentration and high reaction speed could be achieved. Then 0.74 g NKAⅡadsorbent resin was added to system under an increased substrate concentration of 40 g/L with a preadsorption for 2 h before reaction. After reacting for 108 h, the optical purity and the yield of (S)-enantiomer reach 98.1 %e.e. and 88.5 % respectively. Thus, the (R,S)-PED concentration increased about 166.7 % than ever before.The optimization of temperature, pH, and agitation to reaction system containing resin were studied. The optimum reaction conditions were obtained as 30℃, pH 8.0, shaking speed 120 r/min. Under such conditions, the reaction time was shortened, and the product also had good level when initial (R,S)-PED concentration increased from 40 g/L to 50 g/L. At the same time, the effect of addition of xylose and yeast extract on stability of whole cell was also studied. Xylose and yeast extract could increase catalyzing batch of whole cell. When reaction conditions and addition amount of xylose and yeast extract were optimized, the optical purity and yield of (S)-PED could reach 97.8 % and 80.6 % respectively after reacting for 48 h in second reaction batch, and e.e. reach 95.0 % in the third batch, under the substrate concentration of 30 g/L. Metabolic activity was increased obviously after addition of xylose and yeast extract.The extraction and purification of (S)-1-phenyl-1,2-ethanediol was studied. From 6 kinds of macroporous adsorbent resins, NKAⅡresin was selected to adsorb (S)-PED. The saturated adsorption capacity of NKAⅡresin was 250 mg/(g wet resin) while the time for it to achieve saturation adsorption was 2 h. Besides, the adsorption isotherm data of NKAⅡresin could well fit the Freundlich equation. Ether was selected as a suitable solvent to recrystallization. 1 L solution containing (S)-PED was adsorbed by the resin column with a flow rate of 1.5 BV/h, desorbed by 2 BV ethyl acetate, decolored by 3 %(mass concentration)active carbon by 1 h, recrystallized with about 100 mL ether. When (S)-PED was extracted and purified under this condition, the total yield of (S)-PED was 68.7 %, with mass fraction 98.9 % from 1.4 %, and optical purity 99.0 %.