Microbial Stereoinversion And Preparation Of (S)-1-phenyl-1,2-ethanediol By Candida Parapsilosis

In the research work, (R,S)-PED was deracemized to the corresponding (S)-enantiomer byusing resting whole cell of the Candida parapsilosis CCTCC M203011 as a biocatalytic system.The optimum reaction conditions in 250mL shaking-flask were obtained as cell concentration300g/L, pH 6.3-6.8, 30-32℃, shaking speed 250r/m, reaction time 48hr. Under such conditions,the optical purity of the product was maintained 98.9%e.e. with an increasement of substrateconcentration from 35mol/L to 210mol/L. Moreover, the effects of aeration and agitationcondition on conversion in 5-L bioreactor were investigated. The results showed that conversionof 175mol/L (R,S)-PED to (S)-PED with enantiomeric excess 96% was achieved under theconditions of D.O. above 50% and a agitation speed about 300r/min.To improve the enantioselectivity of Candida parapsilosis, a new process was developed andoptimised by the addition of alcohol substrates during cell cultivation. The results showed thatthere were an increasement of cell mass from 44g/L to 48g/L by addition of 0.1% ethanol.Moreover, the addition of 0.1% etOH in the culture medium influenced the enzyme production,as reflected in the improvement of the oxidation and reduction enzyme activities. Consequently,the higher redox enzyme activities result in the higher conversion ability of the cell. In 5-Lbioreactor, conversion of 210mol/L (R,S)-PED to (S)-PED with enantiomeric excess 100% wasachieved. In the thesis, the effects on cell growth and enzyme production of controlling theaeration during cell culture were also investigated. Under the condition of 0.1L/min aeration in5-L bioreactor, the improvement of cell mass, oxidation and reduction enzyme activity was 10%,40% and 20% respectively.The conversion of (R,S)-PED to (S)-PED by Candida parapsilosis immobilized in calciumalginate was investigated. The best efficiency of immobilization could be obtained under theconditions that the cell concentration was 10% and the concentration of sodium alginate, sodiumchloride and manganese sulphate was 3%, 3% and 1.5% respectively. Compared with the freecell, a wider range of reaction pH value and temperature of immobilized cell were achieved.After research the stability of the immobilized cell, it was found that the thermostability,operation stability and storage stability of immobilized cell were better than the free cell. Therelativity activity of the immobilized cell was about 80% at 60℃ and only 15% of enzymeactivity was lost stored at 4℃ for two months. After six times repeated batch operation, the e.eof produce was also remained above 95%.After purifying the raw product, the pure (S)-PED with the optical purity of 100% e.e andabove 95% chemical purity was obtained. The final yield of this production process was 75%.