双层固定化酵母催化还原4-氯-乙酰乙酸乙酯的研究

以海藻酸钠为内层载体,利用机械强度良好的聚乙烯醇(PVA)改性海藻酸钠混合物作为外层载体,双层固定化高活性酵母,得到固载的生物催化剂,用于由磷酸缓冲溶液和环己烷组成的双相体系,对4-氯-乙酰乙酸乙酯(COBE,ethyl 4-cloro-3-oxobutyrate)进行不对称催化加氢合成(S)-4-氯-3-羟基丁酸乙酯[(S)-CHBE],ethyl[(S)-4-chloro-3-hydro butanoate].在最适条件下,双层固定化酵母的不对称催化还原反应优于游离细胞和单层固定化细胞.在底物COBE的最佳浓度和进料速率分别为170mmol/L,125mL/h的连续操作条件下,最高(S)-CHBE转化率为94.2%,最高对映体过量值为98%.与游离细胞催化COBE相比,反应转化率提高3%,最佳底物浓度比游离细胞增加1倍;与单层固定化细胞催化还原相比,对映体过量值提高8%.连续性实验表明,双层固定化酵母细胞在连续使用5d,其转化率和对映选择性没有明显下降.     

固定化酵母非水相催化羰基不对称还原反应的研究

用海藻酸钙包埋法对增殖培养的酵母细胞进行了固定化,并用于催化有机溶剂中乙酰乙酸乙酯的不对称还原反应。考察了固定化时所用缓冲溶液的pH、催化剂颗粒大小与用量、辅助底物种类、底物浓度、以及重复利用批次等因素对反应产物（S）-3-羟基丁酸乙酯的浓度和光学纯度的影响。结果表明,固定化时应采用pH为7的Tris-HCL缓冲溶液,颗粒的直径以2mm左右为较佳;反应时应以正已烷为溶剂,正已醇为辅助底物,固定化酵母颗粒的最适用量为6g/20ml反应液;底物的初始浓度以100mmol/L为佳,浓度过高对反应有一定的抑制作用;固定化细胞重复利用三次对映选择性基本保持不变。     

不同反应体系中(S)-1-(4-甲氧基)-苯基乙醇的不对称生物合成

在不同反应体系中,研究了固定化红酵母细胞催化对甲氧基苯乙酮不对称还原合成(S)-1-(4-甲氧基)-苯基乙醇的反应.结果表明,在含离子液体的混合反应体系和双相反应体系中,该不对称还原反应的效率得到了不同程度的提高.此外,离子液体中阴阳离子类型对该反应的影响较大,特定阴阳离子间的匹配对同定化红酵母细胞发挥最佳催化效果至关...     

培养基碳源对固定化酵母细胞催化乙酰基三甲基硅烷不对称还原反应的影响

 尽管含芳香基等较大取代基团的底物能被生物转化为高对映体纯手性有机硅醇,但生物催化其他底物还原反应的产物收率及对映体选择性均较低. 作者筛选到一株能高效催化羰基/羟基不对称转化的酵母菌株,探讨了用固定化酵母细胞高效催化乙酰基三甲基硅烷不对称还原制1-三甲基硅乙醇的可能性,系统研究了培养基碳源及其浓度对该反应的影响. 发现在水/正己烷两相体系中,固定化酵母细胞能催化乙酰基三甲基硅烷不对称还原成1-三甲基硅乙醇. 可通过调节培养基碳源的种类及其浓度在一定程度上控制反应的产物收率及对映体选择性. 以最适碳源(3.0%麦芽汁)培养的酵母细胞催化该反应的产物收率和对映体过量值分别为91.3%和72.8%,远高于文献报道值.     

聚甲基丙烯酸羟乙酯载体固定化酵母脂肪酸在有机溶剂中催化酯合成反应的研究

用悬浮聚合法合成了一系列聚甲基丙烯酸羟乙酯载体，考察了它们固定化酵母脂肪酶活力与载体的交联度和致孔剂用量之间的关系。研究了这些固定化酵母脂肪酶在有机溶剂中催化酯合成反应的活性。脂肪酶的固定化使之活力表达更为充分，对亲水性较强的有机溶剂有更强的耐受性，并能为其在有机溶剂中催化酯合成反应提供必需水。考察了ｐＨ值，底物种类对固定化酵母脂肪酶催化酯合成反应的影响。     

新型线粒体氧还酶抑制剂型分子探针: 叠氮水杨酰胺类化合物的合成

以硝基水杨酰胺经还原，重氮化，叠氮化反应合成了五个新的叠氮水杨酰胺类化合物。通过还原反应的研究发现，侧链较短的硝基水杨酰胺用Sn+HCl还原效果较好。侧链较长的硝基水杨酰胺用H~2-Pd/C催化加氢还原效果较好。产品结构经IR，^1H NMR，MS和元素分析确定。合成的新叠氮水杨酰胺类化合物可以作为线粒体呼吸链酶的抑制剂型分子探针。     

聚丙烯酸甲酯载体对柱状假丝酵母脂肪酶固定化的研究（Ⅰ）

合成了一系列不同结构的聚丙烯酸甲酯，考察了它们的固定化酵母脂肪酶催化酯水解反应的效果，得到了载体孔结构对固定化效果影响的一些规律．研究了最佳吸附条件，比较ｐＨ和离子强度对酵母脂肪酶自由酶和固定化酶催化酯水解反应活力的影响．     

聚甲基丙烯酸羟乙酯载体固定化酵母脂肪酶在有机溶剂中催化…

用悬浮聚合法合成了一系列聚甲基丙烯酸羟乙酯载体，考察了它们固定化酵母脂肪酶活力与载体的交联度和致孔剂用量之间的关系。研究了这些固定化酵母脂肪酶在有机溶剂中催化酯合成反应的活性，脂肪酶的固定化使之活力表达更为充分，对亲水性较强的有机溶剂有更强的耐受性，并能为其在有机溶剂中催化酯合成反应提供必需水。考察了ＰＨ值，底物种类对固定化酵母脂肪酶催化酯合成反应的影响。     

水合肼在还原制备苯胺类化合物中的专利技术进展

从专利角度出发,对水合肼作为还原剂,硝基苯类化合物还原制备苯胺类化合物的方法进行综述。对水合肼还原制备硝基苯的专利申请情况、主要申请人的申请情况进行了分析,对镍、钯、铁以及活性炭等催化剂在水合肼还原制备苯胺类化合物中的应用进行归纳和总结,且对活性炭作为催化剂的反应进行了概述,且对其发展趋势进行了展望。     

NaBH4/BiCl3复合体系还原芳香硝基化合物为氧化偶氮苯及其类似物

NaBH4/BiCl3复合体系在甲醇介质中对硝基化合物进行部分还原,可以获得相应的氧化偶氮苯类化合物。实验中发现此反应与反应底物的Hammett常数有着密切的关系。     

Bioreduction of quinone derivatives by immobilized Baker''''s yeast in hexane

Immobilization techniques and biocatalytic transformations performed in organic media are new developing methods for organic reactions. Baker's yeast was immobilized on the alginate supports. This preparation contained about 20% of dry yeast cells. The immobilized Baker's yeast were found to be very effective in the reduction of o-benzoquinone, p-benzoquinones, naphthoquinones, and anthraquinones in hexane.     

Baker's Yeast Mediated Reduction of Optically Active Diketone

Baker's yeast (BY) mediated reduction of synthetic substrate is a useful method for preparing chiral intermediate in synthesis chemistry1,2, because it is readily available and inexpensive. The selectivity is generally predicted by Prelog rule3, that is, a hydride is transferred to the re face of the prochiral ketone.The baker's yeast mediated reduction of bicyclic diketones was previously reported by several groups4-6, but to our knowledge, no application of this reduction to sesquiter-pene-…     

Encapsulation of yeast cells in colloidosomes

Polymeric colloidosomes encapsulating viable Baker's yeast cells were prepared. To make the capsules, an aqueous suspension of 153 nm poly(methyl methacrylate-co-butyl acrylate) latex particles plus yeast cells is emulsified in a continuous phase of sunflower oil. By adding a small amount of ethanol to the oil phase, the latex particles at the surface of the emulsion droplets aggregate, forming the colloidosome shells. The microcapsules have been examined using optical, confocal, and scanning electron microscopies. The viability of the yeast cells was tested using fluorescent molecular probes. The encapsulated Baker's yeast cells were able to metabolize glucose from solution, although at a slower rate compared to nonencapsulated yeast. This demonstrates diffusion limitation through the colloidosome shell. The diffusive resistance could be increased by manufacturing colloidosomes with a double latex shell.     

面包酵母在催化不对称合成中的应用

介绍了当前国内外在以面包酵母为催化剂不对称催化合成手性化合物的研究情况,重点介绍了面包酵母催化各类潜手性羰基的不对称还原、潜手性碳一碳双键的不对称加成和碳一碳键形成的反应情况,讨论了各种提高酵母催化不对称合成反应立体选择性的方法,对酵母催化不对称合成有关生物学方面的研究进行了简单的介绍。     

Highly stereoselective chemoenzymatic synthesis of the 3H-isobenzofuran skeleton. Access to enantiopure 3-methylphthalides

A straightforward synthesis of (S)-3-methylphthalides has been developed, with the key asymmetric step being the bioreduction of 2-acetylbenzonitriles. Enzymatic processes have been found to be highly dependent on the pH value, with acidic conditions being required to avoid undesired side reactions. Baker's yeast was found to be the best biocatalyst acting in a highly stereoselective fashion. The simple treatment of the reaction crudes with aqueous HCl has provided access to enantiopure (S)-3-methylphthalides in moderate to excellent yields.     

Baker's yeast mediated enantiospecific synthesis of anti-(2R,3R)-p-chloro-3-hydroxytyrosine: an α-amino-β-hydroxy acid of vancomycin

Baker's yeast mediated reduction of α-azido-β-keto ester lead to reduction of the carbonyl group with high enantiospecificity and diastereoselectivity at low pH (4.0, e.e. >99%, d.e. 79%). At pH 7, although the enantioselectivity is maintained, the diastereoselectivity is lost.     

Baker''''s yeast mediated reduction of substituted acenaphthenequinones: Regio-and enantioselective preparation of mono-hydroxyacenaphthenones

Baker's yeast mediated reduction of acenaphthenequinone within 4-10 h afforded mono-hydroxyacenaphthenone mainly with low enantioselectivity, the substrate and mono-hydroxyacenaphthenone product almost converted to dihydroxyacenaphthene after 48 h. By control of the reaction time and in the presence of DMF as co-solvent, the reduction of 6-substituted acenaphthenequinones under vigorous agitation afforded the corresponding 2-hydroxyacenaphthenones in 24-84% yields with 10-93% ee.     

Effects of caffeine on stereoselectivities of high cell density biotransformations of cyclic beta-keto esters with Saccharomyces cerevisiae

Caffeine affects the stereoselectivity of microbial high cell density reductions with commercial grade Saccharomyces cerevisiae (Baker's yeast). Cyclic beta-keto esters ethyl 2-oxocyclopentanoate (1) and ethyl 2-oxocyclohexanoate (3) were shown to be reduced with increased diastereoselectivity (1: 90.1 --> 92.1% de, 3: 75.0 --> 90.0% de) after addition of caffeine. Effects on enantioselectivity were less pronounced (1: 97.3 --> 98.5% ee, 3: 90.1 --> 92.1% ee). The observations are ascribed to the action of caffeine on cellular calcium homeostasis. These effects are accompanied by caffeine-induced cell-death, which preferably takes effect on pre-stressed cells which were found to decrease diastereoselectivity.     

Reversible buckling and diffusion properties of silica-coated hydrogel particles

Based on the biomineralization assembly concept, a biomimetic approach has been developed to synthesize high-performance mesoporous TiO(2). The key step of this approach is to apply Baker's yeast cells as biotemplates for deriving the hierarchically ordered mesoporous anatase structure. The mechanism of formation of the yeast-TiO(2) is revealed by characterizing its morphology, microstructure, and chemical composition. The yeast-TiO(2) exhibits outstanding photocatalytic performance. Under visible-light irradiation, the removal efficiency of chemical oxygen demand (COD) and color of the paper industry wastewater has reached 80.3% and nearly 100%, respectively. The approach may open new vistas for fabricating advanced mesoporous materials under ambient condition.     

反-Prelog还原体系、微水相羟氰化酶工作体系的发现 及光学活性化合物的合成

我们从土壤中筛选出一株有自主知识产权的霉菌(白地霉G.38),并发现它有独特的还原性能和优越的反应活性。与啤酒酵母作用相比,催化还原羰基,产物的立体化学上是按anti-Prelog的构型模式进行的。同时我们还开展了羟氰化酶合成光学活性的氰醇化合物的研究,发现和建立了一种适合粗酶作用的微水相工作体系,在工业上有实用前景。并筛选到3个高活性的(R)-氰醇酶源。