【作者】 穆晓清；

【导师】 徐岩；

【作者基本信息】 江南大学 ， 发酵工程， 2010， 博士

【摘要】 以外消旋化合物为底物的立体异构反应是手性生物合成中最重要和最具有工业应用前景的制备方法之一。本论文以近平滑假丝酵母(Candida parapsilosis) CCTCC M203011催化立体异构反应制备具有重要工业用途的光学纯苯基乙二醇为模型反应,针对立体异构反应中普遍存在的底物浓度低和反应时间长等制约其工业应用的核心问题,利用动力学和热力学等表征催化特性的研究,在比对获得立体异构反应限制性因子的基础上,以催化特性为导向,在中试规模上对生物催化剂制备和反应过程进行研究,揭示了抑制立体异构反应效率的限制性因素,建立了酶水平的利用辅酶再生进行高效不对称还原制备苯基乙二醇两种光学纯对映体的途径,实现了中试规模下全细胞催化立体异构反应高效制备S-苯基乙二醇的制备。(1)分离纯化获得了催化立体异构反应中立体选择性氧化反应的苯基乙二醇脱氢酶,通过底物专一性和辅酶依赖型的研究发现,该酶只能够催化R-苯基乙二醇选择性氧化为羟基苯乙酮及其逆向不对称还原反应,其氧化反应速率与底物浓度相关,其中高浓度的醇类底物会对立体选择性氧化反应产生明显抑制；通过不同底物浓度下表观动力学参数Km’的变化趋势证实苯基乙二醇脱氢酶催化立体选择性氧化反应属于顺序型双底物反应模型；死巷抑制剂作用下的苯基乙二醇脱氢酶失活动力学研究表明在反应过程中按照苯基乙二醇脱氢酶、辅酶以及醇类底物的顺序进行结合；产物抑制动力学研究及双底物反应动力学方程拟合试验表明立体选择性氧化反应遵循Theorell-Chance Bi Bi机制；基于苯基乙二醇脱氢酶催化不对称还原反应能力的基础,通过与甲酸脱氢酶进行偶联,控制不对称还原反应方向,成功实现了酶法R-苯基乙二醇的制备,在底物浓度为60 mmol·l-1时,10h产率分别达到95.8%,产物光学纯度均接近100%e.e.。(2)分离纯化获得了催化立体异构反应中不对称还原反应的羰基还原酶,通过底物专一性和辅酶依赖型的研究发现,该酶能够催化羟基苯乙酮不对称还原为S-苯基乙二醇,且该反应为不可逆反应,揭示了立体异构反应高转化率和高光学纯度的化学平衡基础,高浓度的底物羟基苯乙酮浓度不会对不对称还原反应速率产生抑制作用,而高浓度辅酶NADPH会对不对称还原反应反应产生明显抑制;通过不同底物浓度下表观动力学参数Km’的变化趋势证实羰基还原酶催化不对称还原反应属于顺序型双底物反应模型;产物抑制动力学研究以及双底物反应动力学方程拟合试验表明立体选择性氧化反应遵循Theorell-Chance Bi Bi机制；建立了羰基还原酶与葡萄糖脱氢酶或6-磷酸葡萄糖脱氢酶偶联辅酶NADPH的反应体系,成功实现了酶法S-苯基乙二醇的制备,在底物浓度为60 mmol·l-1时,10h产率分别达到91.3%和86.8%,产物光学纯度均接近100%e.e.。(3)通过氧化反应和还原反应稳态动力学参数和热力学参数的比较研究发现,无论是在最适作用条件下,还是在中性条件下,羰基还原酶催化不对称还原反应最大速率及催化效率均比苯基乙二醇脱氢酶催化的立体选择性氧化反应速率和催化效率高10倍以上,因此确定氧化反应是立体异构反应的限制性步骤；通过考察温度和pH等重要的环境因子对苯基乙二醇脱氢酶及羰基还原酶催化活性的影响研究,确定苯基乙二醇醇脱氢酶催化立体选择性氧化反应的最佳温度和pH分别为35℃和pH 9.0,羰基还原酶催化不对称还原反应的最佳温度和pH分别为45℃和pH 4.5,结果表明全细胞催化立体异构反应的两个关键蛋白存在不可调和性的矛盾,限制了立体异构反应的效率。(4)通过研究影响近平滑假丝酵母生长的培养基组成和培养条件,分别以发酵生物量和单位细胞具有的催化立体异构反应活性为指标,针对微生物催化活性具有重要影响金属离子,利用Plackett-Burman设计实验和响应面优化确定其最优组成；同时利用正交试验考察了影响生物催化剂发酵的培养条件；研究结果显示微生物的生物量与其具备的生物催化活性的非相关性；在最优发酵培养组成及最适发酵条件下,发酵获得生物量达到33.3 g/L,立体异构反应产物光学纯度达到97.0%e.e.；(5)在7 L发酵罐水平针对溶氧的研究表明通过调节搅拌转速和通气量提高溶氧水平有利于近平滑假丝酵母发酵生物量的提高,同时保持较好的催化活性；而150 L中试规模微生物生长和催化活性的影响研究表明,过高的氧通量有利于微生物生长而不利于细胞催化活性的形成；通过调节搅拌转速和通气量等手段平衡了微生物生长与催化活性之间的矛盾,成功实现了150 L中试规模高效生物催化剂发酵制备,发酵获得生物量达到47 g/L,立体异构反应产物光学纯度达到99.3%e.e.。(6)通过对影响全细胞催化立体异构反应效率的环境因子研究,发现pH、温度、溶氧以及细胞量等环境因子对全细胞催化的立体异构反应影响与酶促反应不尽相同,通过反应条件优化,立体异构反应最适底物浓度达从35 mmol·l-1提高至70 mmol·l-1,产率和产物光学纯度分别达到90%和99%e.e.以上；基于立体异构反应稳态动力学研究中发现的限制性步骤立体选择性氧化反应在高底物浓度下存在的显著抑制作用,利用多种原位分离技术控制反应体系中的底物浓度,其中双水相体系和水-树脂两相反应体系最适底物浓度从70 mmol·l-1提高至220 mmol·l-1,产率和产物光学纯度分别达到90%和99%e.e.以上；并在公斤级中试规模实现了水-树脂两相体系中近平滑假丝酵母全细胞催化立体异构反应,48 h产物光学纯度和产率分别达到99%e.e.和94%以上。更多还原

【Abstract】 Stereoinversion process catalyzed by microorganism whole cell is one of the most important and best industrial application prospect methods in biocatalyst chiral synthesis. The optically phenyl-1,2ethanediol (PED), key intermediates in the synthesis of pharmaceuticals and fine chemicals, is choosed as the model substrate in this thesis. For the common shortcoming of stereoinversion such as long reaction time and low substrate concertration, the studies of reaction mechanism of stereoinversion, fermentation of biocatalyst and optimization of process are carried out to reveal the factors which hinder the improvement of reaction efficiency. Furthermore, the processes for preparation of different isomers of PED by oxidoreductase coupled with the regeneration of coenzyme are established. The stereoinversion process catalyzed by whole cell is succeeded in pilot scale for the production of optically PED with high efficiency.Firstly, the fermentation culture medium, especially the effect of metal ions, was observed by Plackett-Burman design and optimized by response surface analysis while biomass and catalytic ability of cell as the indicator. The cultues conditions including pH, temperature and culture time were also optimized by orthogonal experimental design. At the optimized condition, the biomass and optical purity of product reached 33.3 g/L and 97.0%e.e. respectively.Secondly, the effect dissolved oxygen to the fermentation of biocatalyst was carried out in the 7 L and 150 L fermentor. It was proved that high oxygen throguout was benifitful to the biomass and harmful to the stereoselectity of cell. The biomass and optical purity of product reached 47 g/L and 99.3% e.e. at the controlled dissolved oxygen by adjusting of stirring speed and air volume in 150 L fermentor, respectively.Thirdly, the dehydrogenase, CPADH, which catalyzed the stereoselectly oxidation reaction of stereoinversion, was purified and characteristiced including the substrate specificity and coenzyme independent. CPADH catalyzed the reversible oxidation reaction was inhibited by the high concerntration of substrate. It was indicated that the oxidation reaction followed Theorell-Chance BiBi mechanism by the studies of apparent michaelis constant Km’at different substrate concerntration without product inhibitation, studies of dead-end inhibition and studies of product inhibitation. Based on the ability of catalyzing reduction reaction of CPADH, the asymmetric reduction process for R-PED production coupled with NADH regeneration catalyzed by formate dehydrogenase was estabolished with high yeild and optical purity of 95.8% and 100%e.e. at the substrate concerntration of 60 mmol·l-1, respectively.Forthly, the carbonyl reductase, CPCR, which catalyzed the asymmetric reduction reaction of stereoinversion, was purified and characteristiced including the substrate specificity and coenzyme independent. CPCR catalyzed the irreversible reduction reaction was inhibited by the high concerntration of coenzyme. It was indicated that the reduction reaction also followed Theorell-Chance Bi Bi mechanism by the studies of apparent michaelis constant Km’at different substrate concerntration without product inhibitation and studies of product inhibitation. The asymmetric reduction processes for S-PED production coupled with NADPH regeneration catalyzed by glucose dehydrogenase or glucose-6-phosphate dehydrogenase were established with high yeild of 91.3% and 86.8% and the same optical purity of 100%e.e. at the substrate concerntration of 60 mmol·l-1, respectively.Fifthly, it was suggested that the oxidation reaction was the restrict step of the whole stereoinversion process after the comparasion of kinetic and thermodynamic studies of CPCR and CPADH. The effct of enviromental factors includes optimal reaction temperature and pH value to the kinetic and thermodynamic parameters shown that the great difference between CPCR and CPADH caused the low efficiency of stereoinversion reaction. The optimal eaction temperature and pH value of CPADH was 35℃and 9.0 while it of CPCR was 45℃and 4.5.Sixly, it was found that thefactors including pH value, reaction temperature, dissolved oxygen and biomass to the stereoinversion cataylzed by whole cell was quite different with it in the reaction catalyzed by the purified enzyme. The optimal substrate concerntration was improved from 35 mmol·l-1 to 70 mmol·l-1 with high yeild and optical purity of more than 90% and 99%e.e. Based on the fact that the restrictive step of stereoinversion reaction was inhibited by high concerntration of substrate, in situ product removal (ISPR) techniche was applied to decrease the concerntration of substrate in reaction phase and remove the inhibition of substrate. The substrate concerntration was improved from 70 mmol·l-1 to 220 mmol·l-1 with high yeild and optical purity of more than 90% and 99%e.e. in the bi-aqueous phase system and resin-aqueous phase system. The process of resin-aqueous phase system was succeeding to scale up to 100L reactor with high yeild and optical purity of 94% and 99%e.e. after 48 h.更多还原