摘要/Abstract
碳氢键选择氧化是合成化学领域的重要课题，其中烷烃选择性羟化反应更是面临着化学选择性、区域选择性和立体选择性等多重挑战.细胞色素P450酶广泛分布于动植物和微生物体内，是公认的多功能生物氧化催化剂.P450酶对惰性C-H键的选择性氧化具有独特优势，在催化烷烃选择性羟化反应方面拥有巨大潜力.本综述简述了P450单加氧酶及其催化烷烃选择性羟化的反应机理，梳理了来自CYP153家族、CYP52家族和其他家族的天然P450酶催化各类烷烃底物的氧化反应和选择性，讨论了理性设计和定向进化策略在开发烷烃羟化P450突变酶过程中的经典案例，介绍了底物工程、诱饵分子、双功能小分子协同催化等几种化学活化P450酶的策略及其在烷烃羟化上的应用，探讨了P450酶在烷烃选择性羟化方面所面临的挑战和解决途径，并展望了其应用前景.
关键词: 烷烃, 酶催化, 羟基化, 细胞色素P450酶, C-H活化, 生物催化, 氧化还原酶, 定向进化
The selective oxyfunctionalization of unactivated C-H bonds is one of long-standing issues and current topics in synthetic chemistry. One of the major synthetic targets for these reactions is the direct and selective hydroxylation of alkanes to alcohols, however, which faces many severe challenges in controlling chemoselectivity, regioselectivity and stereoselectivity. In nature, the oxidative metalloenzymes is capable of selectively catalyzing the insertion of oxygen into inert C-H bonds of alkanes, such as methane monooxygenases (MMO), soluble butane monooxygenases (sBMO), fungal peroxygenases and Cytochrome P450 monooxygenases (P450s). Among them, P450s that catalyze a variety of oxygenation reactions have attracted special attentions because of some intrinsic advantages. P450s are widely distributed in plants, animals and microorganisms and over 41000 sequences of P450 genes have been named from various databases, which enhances the potentials of P450s in developing the oxidative biocatalysts. In addition, compared with MMOs, P450s that have smaller molecule weight (≈45 kDa) are simple and amenable to recombinant expression and engineering. Herein, we reviewed the recent progress of alkanes hydroxylation by P450 enzymes either in its natural forms or engineered variants, as well as chemical activated systems. The related background and the catalytic mechanism of P450s for alkanes hydroxylation were firstly discussed. The representative examples by natural P450s mainly from CYP153, CYP52 and other P450 families were then outlined. The strategies of rational design and directed evolution on P450s engineering were then summarized focusing on the native/non-native alkane substrates. Three unusual strategies, including substrate engineering, decoy molecule, and dual-functional small molecule co-catalysis, were also discussed on their applications for activating P450s to hydroxylate non-native small alkanes. Finally, we perspective the challenges and solutions that faced by P450 enzymes in the development of new biocatalytic systems toward selective hydroxylation of alkanes. In conclusion, cytochrome P450 enzymes in both of their native and modified form are promising biocatalysts for alkanes hydroxylation and need further be investigated to gain the practical industrial applications.
Key words: alkane, enzyme catalysis, hydroxylation, cytochrome P450 enzyme, C-H activation, biocatalysis, oxidoreductases, directed evolution
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