氯过氧化物酶在手性有机合成中的应用

氯过氧化物酶(CPO)作为过氧化物酶家族中的一员对多种有机底物表现出了广泛的催化活性.自上世纪60年代被发现以来,CPO在有机合成中的应用一直是一个研究热点.它作为一种生物催化剂能催化广泛的底物合成手性化合物,且有高的产率和高的对映选择率.本文综述了氯过氧化物酶在手性有机合成中的应用,重点关注了卤化、醇氧化、羟基化、环氧化、磺化氧化等反应,并讨论了目前在该领域所面临的问题及今后的发展趋势.     

过氧化物酶在不对称氧化中的应用及氧化反应机理

过氧化物酶尤其是从Caldariomyces fumago中得到的氯过氧化物酶（GPO）能 催化多种底物的氧化和环氧化反应，表现出良好的立体选择性，近年在此领域内的 应用有若干重要的进展。由于CPO与细胞色素P450单加氧酶的相似性，它们的反应 机理与活性部位的研究也十分引人瞩目。     

基于离子液体共溶剂效应的氯过氧化物酶催化氧化邻苯二胺的研究

通过缓冲液-离子液体混合溶剂中氯过氧化物酶(CPO)催化氧化邻苯二胺(OPD)的产物结构和性能的表征,证实此酶促反应的产物为2,3-二氨基吩嗪(DAP);OPD-H2O2-CPO反应体系有望用于荧光酶联免疫分析;酶动力学分析表明以咪唑类离子液体(ILS)为共溶剂时,CPO对底物的亲和力及对底物识别的专一性都得以改善,从而有效提高了产物收率;酶促反应主要受CPO的稳定性及酶的用量等因素控制.在最佳条件下,产率可达81.16%.     

手性环氧氯丙烷的CPO酶催化不对称合成

基于氯过氧化物酶(CPO)对有机底物的手性识别,以CPO催化、叔丁基过氧化氢(TBHP)氧化3-氯丙烯合成手性(R)-环氧氯丙烷,并引入多羟基化合物为添加剂提高了目标产物的产率及对映选择性.反应主要受体系的pH值以及CPO用量等因素控制.UV-vis及CD光谱分析表明,反应体系中引入多羟基化合物(甘油、PEG400、PEG600)时,CPO的血红素辅基暴露程度增加,底物容易接近活性中心,同时CPO的α-螺旋结构得以加强,从而有效提高了产物收率.CPO对底物的手性识别主要基于底物与酶催化中间体([Fe(IV)=O·]+)形成的复合物对酶的稳定性的影响.通过反应条件优化,(R)-环氧氯丙烷产率可达67.3%,对映选择性(ee)97.5%.     

手性苄基甲基亚砜的氯过氧化物酶催化定向合成

基于氯过氧化物酶(CPO)对有机底物的手性识别功能,以CPO催化、叔丁基过氧化氢(TBHP)氧化甲基苄基硫醚合成手性R-苄基甲基亚砜,并在反应体系中引入多羟基化合物及季铵盐提高了目标产物的产率;反应主要受体系的pH值、氧化剂类型、反应时间、氧化剂/底物摩尔比,以及CPO用量等因素控制.引入多羟基化合物(甘油,PEG400,PEG600)时,R-苄基甲基亚砜的产率及ee值可分别达到65.5%和96.3%;而引入季铵盐(TEABr,TPABr,TBABr)时,其产率提高到78.2%～68.5%,ee值为95.4%～94%.UV-vis及荧光光谱分析表明反应体系中引入少量添加剂时CPO活性中心的血红素辅基暴露程度增加,底物容易接近,同时CPO的α-螺旋结构得以加强,从而有效改善了CPO的催化性能.与目前的合成方法相比,CPO酶促氧化制备手性R-苄基甲基亚砜高效、定向,酶用量极少,具有一定的产业化应用潜能.     

咪唑/吡啶离子液体辅助氯过氧化物酶催化氧化环己烯的研究

以氯过氧化物酶(CPO)催化、H2O2氧化实现环己烯的环境友好转化,并通过溶剂工程调控和提高目标产物的产率.研究结果表明缓冲液体系(PBS)中引入咪唑/吡啶类离子液体(ILs)时,含量仅为1.5%(WILS/WPBS)时环己烯转化率即可提高31%.酶促反应动力学参数Km的减小以及Kcat和Kcat的增大表明引入离子液体时CPO对底物的亲和力及对底物识别的专一性得以改善,导致转化数增大,这是底物转化率有效提高的主要原因;此外,紫外,荧光及圆二色谱研究及产物组成分析表明离子液体在反应体系中具有多重功能:相转移催化、诱导酶分子结构优化及调节产物组成.由于反应基本在150 min内结束,酶用量极少,因此具有一定的产业化应用潜能.     

生物催化在非天然寡糖合成中的应用

酶已经成为现代有机合成中一种不可或缺的工具。近年来人们在克隆技术，微生物学以及蛋白纯化方面的研究成果为我们提供了越来越多的生物催化剂，酶最初用于天然产物的合成，而今其在非天然化合物中的应用更引起了生物化学家的广泛关注。酶催化反应可以使不加保护的高官能团化底物进行条件温和，环境友好地转化，得到具有高度化学、区域和立体选择性的产物。本文对近年来糖基转移酶在糖生物学中的应用，特别是其在利用Leloir方法合成非天然寡糖中的应用作一简要回顾。     

氯过氧化物酶修饰电极对一氯二甲酮的催化氯化

通过将氯过氧化物酶溶液(Chloroperoxidase, CPO)与Nafion分散的单壁碳纳米管分散液混合后直接滴涂到玻碳电极表面制得修饰电极. 这个固定了氯过氧化物酶的碳纳米管修饰玻碳电极, 在pH=5.0的磷酸缓冲溶液中测得的循环伏安曲线上有一对准可逆的氧化还原电流峰, 经过与裸电极和没有固定氯过氧化物酶的碳纳米管修饰电极上测得的循环伏安行为对比后确认, 碳纳米管对氯过氧化物酶与电极之间的电子传递反应具有很好的促进作用. 利用该修饰电极能催化一氯二甲酮氯化为二氯二甲酮, 无需添加过氧化氢作为反应启动剂, 紫外光谱的测试结果表明, 每摩尔氯过氧化物酶可催化氯化4.0×105 mol 的一氯二甲酮, 表现出很高的催化效率.     

磁性氧化石墨烯固定化氯过氧化物酶及其在奥酸性蓝45脱色中的应用

以氧化石墨烯和Fe_3O_4为原料制备磁性氧化石墨烯,采用吸附法将氯过氧化物酶固定在磁性氧化石墨烯上,考察了固定化体系缓冲溶液p H值、固定化时间及反应温度对固定效果的影响.以氯过氧化物酶催化氧化奥酸性蓝45染料脱色反应为模型反应,探讨了固定化氯过氧化物酶的操作稳定性.实验结果表明,p H=3.5,反应15 min、反应温度15℃为固定化氯过氧化物酶的最佳催化条件;采用共沉淀法制备载体,加入的NH_4Fe(SO_4)_2·12H_2O与氧化石墨烯(GO)质量比为10.7∶1时,得到的磁性氧化石墨烯(TMGO)的酶固载量大于二者质量比为5.35∶1时得到的磁性氧化石墨烯(FMGO),这可能与FMGO氧化石墨烯表面的Fe_3O_4含量不足有关;与游离酶相比,固定化氯过氧化物酶表现出更好的酸碱稳定性、H_2O_2稳定性、热稳定性和储存稳定性,在35~50℃,聚集或堆积的磁性氧化石墨烯(TMGO)片层打开,导致固定化酶活损失率明显小于游离酶.重复使用5次后,TMGO-氯过氧化物酶(CPO)的相对活性仍然保持在60%以上.     

细胞色素P450酶在生物合成及有机合成中的催化功能及其应用

细胞色素P450酶分布广泛,主要参与生物体外源物质代谢与天然产物生物合成,能以结构多样的有机化合物作为底物催化多种类型的化学反应.P450酶可在温和条件下实现底物分子中C—H键的选择性氧化,因而在精细化学品、化学中间体及药物分子的生产上具有很高的实用价值及多年的应用历史.随着蛋白质工程、氧化还原伴侣工程、底物工程、代谢工程与合成生物学的发展,目前已可初步实现根据反应需求来理性设计或定向进化改造P450酶催化系统来高效催化多种有机反应,拓宽了P450酶在生物合成与有机合成反应中的应用范围.总结了近年来由细胞色素P450酶参与催化的主要反应类型,归纳了拓宽P450酶催化反应类型、提高催化活性和选择性的一些重要策略,并对未来P450酶在生物合成及有机合成反应中的应用发展前景和挑战进行了展望.     

Highly enantioselective oxidation of cis-cyclopropylmethanols to corresponding aldehydes catalyzed by chloroperoxidase.

Chloroperoxidase (CPO) catalyzes the enantioselective oxidation of cyclopropylmethanols, such as 2-methylcyclopropylmethanol, to cyclopropyl aldehydes using tert-butyl hydroperoxide as the terminal oxidant. In all cases, CPO oxidation of cis-cyclopropanes shows much higher enantioselectivity than with the trans isomers, although CPO gives similar catalytic activity on both isomers. This presents the first example for a heme enzyme that catalyzes the enantioselective oxidation of cyclopropylmethanols. This finding enables a novel route to the synthesis of optically active cyclopropane derivatives, which occur widely in natural products and compounds of pharmaceutical interest. In addition, chiral cyclopropane molecules may be useful model substrates to investigate reaction mechanisms of CPO and the related cytochromes P450.     

Catalytic enantioselective synthesis of axially chiral allenes

The conventional procedures for preparing optically active axially chiral allenes generally require stoichiometric chiral sources as either substrates or reagents. On the other hand, examples of catalytic asymmetric synthesis of axially chiral allenes are rare and it is a relatively underdeveloped area in synthetic organic chemistry. In this review article, various methods for preparing enantiomerically enriched axially chiral allenes using substoichiometric chiral sources are surveyed. Some reactions with stoichiometric but recoverable chiral sources are also mentioned. Most of the asymmetric reactions in these categories are transition-metal-catalyzed reactions, and there are a few examples of organocatalytic reactions. In addition, some enzymatic/microbial systems are also known.     

Asymmetric Electrochemical Transformations

The field of electrochemical synthesis has developed rapidly over the last decade and has provided alternative synthetic methods with the absence of stoichiometric amounts of chemical oxidants or reductants. Although sustainable electrosynthetic procedures have been developed, relatively few examples of highly enantioselective catalytic electrosynthesis have been reported to date. The development of general strategies for electrochemical enantiocontrol has thus proven to be a considerable challenge. This Minireview highlights the current knowledge and recent advances in the synthetic utility of electrochemical transformations for asymmetric synthesis. Specifically, three major types of catalytic enantioselective strategy in electrosynthesis are outlined, including electrochemical activation of chiral catalyst‐bound substrates, asymmetric cascade electrochemical processes, and chemically modified chiral electrodes.     

Recent advances in the application of chiral phosphine ligands in Pd-catalysed asymmetric allylic alkylation

One of the most powerful approaches for the formation of simple and complex chiral molecules is the metal-catalysed asymmetric allylic alkylation. This reaction has been broadly studied with a great variety of substrates and nucleophiles under different reaction conditions and it has promoted the synthesis of new chiral ligands to be evaluated as asymmetric inductors. Although the mechanism as well as the active species equilibria are known, the performance of the catalytic system depends on the fine tuning of factors such as type of substrate, nucleophile nature, reaction medium, catalytic precursor and type of ligand used. Particularly interesting are chiral phosphines which have proved to be effective asymmetric inductors in several such reactions. The present review covers the application of phosphine-donor ligands in Pd-catalysed asymmetric allylic alkylation in the last decade.     

Recent Progress in Asymmetric Ion-Pairing Catalysis with Ammonium Salts

Quaternary ammonium salts play an important role in asymmetric catalysis. In this Minireview, how asymmetric ion-pairing catalysis with ammonium ions has been utilized in organic synthesis is explained, particularly in the design of novel catalytic cycles. This includes the use of chiral ammonium-based catalysts for the construction of challenging stereogenic centers. Ammonium-derived electrophilic reagents, typically formed in situ and in the context of phase-transfer catalysis (PTC), have also been utilized in asymmetric bond-forming reactions. Furthermore, ammonium salts have been employed as substrates in several stereocontrolled C−N bond cleavage processes, leading to enantioenriched products by using novel asymmetric induction modes. In addition, merging ammonium ion-pairing catalysis with other catalytic approaches has also emerged as a new platform for achieving previously less straightforward reactions, thereby allowing new synthetic applications.     

Polymer-Supported Chiral Catalysts in Asymmetric Synthesis

By far the best method of synthesis of chiral organic compounds from prochiral substrates is through the use of chiral catalysts or enzymes. This approach has several advantages, the most important of which is that either the enzyme is naturally occurring or the catalyst can be easily generated from a naturally occurring chiral material. If resolution needs to be accomplished, it is carried out with small amounts of catalyst rather than with large quantities of product. Thus from a catalytic amount of chiral material large quantities of one enantiomeric product can be generated.     

手性炔丙醇的不对称催化合成研究进展

手性炔丙醇是一种重要中间体化合物,作为合成多种光学活性化合物的重要合成前体受到学者们广泛关注。目前通过酮的不对称催化反应合成手性炔丙醇的研究开发具有极大发展前景,因此本文围绕酮类化合物的不对称催化反应来进行综述,结合相关反应最新研究进展,全面总结并分类了不对称催化还原、催化不对称加成等反应类型,介绍了合成不同结构手性炔丙醇的新思路,并对酮的不对称催化反应在未来能成为工业化重要生产途径作出展望。     

Synthesis and Catalytic Asymmetric Reaction of Chiral Pyridine Prolinol Derivatives

The enantioselective reduction of prochiral ketones with borane in the presence of a chiral ligand leading to enantiomerically pure secondary alcohols has received considerable attention in recent years. [1] Enantiomerically pure secondary alcohols are important intermediates for the synthesis of various other organic compounds such as halides, esters, ethers, ketones and amines. To the best of our knowledge, the use of pyridine prolinol derivatives in the reduction of ketones has not been reported so far. Thus, it should be of interest to investigate the catalytic a bility of such ligands. We have an ongoing project in the synthesis and application of chiral pyridine derivatives in chiral molecular recognition[2] and we want to evaluate the effect resulting from the introduction of a pyridinyl moiety onto the catalysts. We expect that the cooperation of pyridine unit and chiral prolinol unit in new ligands may result in unique properties for catalytic reaction.     

The Catalytic Asymmetric Aldol Reaction

The construction of C-C bonds with complete control of the stereochemical course of a reaction is of utmost importance for organic synthesis. The aldol reaction-the simple addition of an enolate donor to a carbonyl acceptor-is one of the most powerful reactions available to the synthetic chemist. In general, control of the relative and absolute configuration of the newly formed stereogenic centers has been achieved through the use of chiral starting materials or chiral auxiliaries. In recent years the search for catalytic methods that efficiently and effectively transfer chirality information has become a major effort in synthetic organic chemistry. Two different approaches have been taken toward the catalytic asymmetric aldol reaction: biocatalysis and catalysis with small molecules. Both approaches have specific advantages and limitations, and as a result are complementary to each other. The important efforts toward both approaches are reviewed in this article.