光控光合菌生物催化苯乙酮不对称还原的反应机理

Mechanism of Light-Controlled Asymmetric Reduction of Acetophenone by Photosynthetic Bacteria

以苯乙酮作为模型底物,通过制备类球红杆菌(Rhodobacter sphaeroides)的载色体和分离纯化的胞内氧化还原酶混合液,构建了以类球红杆菌全细胞为催化剂、氧化还原酶为催化剂以及载色体与氧化还原酶偶合三种不对称还原反应体系,并通过向反应体系中加入最适氢供体乙酸钠和电子供体硫代硫酸钠提高产物的转化收率.通过检测目标产物的收率、对映体过量(ee)值和光学构型,分析了光控不对称还原的生物催化机理,发现光照可以改变胞内(S)-氧化还原酶和(R)-氧化还原酶的活性,从而产生不同构型的产物,加入电子供体和氢供体后,反应收率和ee值提高的原因是由于分别补充了细菌叶绿素分子Bchl失去的电子和NADPH再生所需的活性氢.

A new kind of asymmetric hydrogenation reaction catalyzed by Rhodobacter sphaeroides and the reaction mechanism have been studied. The advantages are that coenzyme （NADPH） can be regenerated in situ by the photosynthetic electron-transfer reactions of photosynthetic bacteria relying on light energy, and ketone compounds can be chiraly hydrogenated. Acetophenone was selected as the model substrate, and the whole cell catalytic system, the asymmetric reduction system of redox enzymes and the chromatophore coupled with redox enzymes system were built through preparation of chromatophore and isolation and purification of endocellular （ S）-redox enzymes and （R）-redox enzymes of photosynthetic bacteria Rhodobacter sphaeroides. This result in- dicates that these cells have the capacity of capturing light energy to generate NADPH through photosynthetic electron-transfer reactions and the relative enzymatic activities. （S）-redox enzyme and （R）-redox enzyme were largely influenced by the amount of light in the environment. Effect of the electron donors and hydrogen donors on chemical yield in the reaction system was determined. A novel method for stereochemical control of the asym- metric reduction by photosynthetic bacteria was also reported. Enantioselectivity in asymmetric reduction of acetophenone was improved by illumination with fluorescent light. As a result, the yield of asymmetric reduction reaction was largely improved through promoting coenzyme NADPH regeneration.