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Methane Generation and Reductive Debromination of Benzylic Position by Reconstituted Myoglobin Containing Nickel Tetradehydrocorrin as a Model of Methyl-coenzyme M Reductase.
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2020-08-14 , DOI: 10.1021/acs.inorgchem.0c00901 Yuta Miyazaki 1 , Koji Oohora 1 , Takashi Hayashi 1
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2020-08-14 , DOI: 10.1021/acs.inorgchem.0c00901 Yuta Miyazaki 1 , Koji Oohora 1 , Takashi Hayashi 1
Affiliation
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Methyl-coenzyme M reductase (MCR), which contains the nickel hydrocorphinoid cofactor F430, is responsible for biological methane generation under anaerobic conditions via a reaction mechanism which has not been completely elucidated. In this work, myoglobin reconstituted with an artificial cofactor, nickel(I) tetradehydrocorrin (NiI(TDHC)), is used as a protein-based functional model for MCR. The reconstituted protein, rMb(NiI(TDHC)), is found to react with methyl donors such as methyl p-toluenesulfonate and trimethylsulfonium iodide with methane evolution observed in aqueous media containing dithionite. Moreover, rMb(NiI(TDHC)) is found to convert benzyl bromide derivatives to reductively debrominated products without homocoupling products. The reactivity increases in the order of primary > secondary > tertiary benzylic carbons, indicating steric effects on the reaction of the nickel center with the benzylic carbon in the initial step. In addition, Hammett plots using a series of para-substituted benzyl bromides exhibit enhancement of the reactivity with introduction of electron-withdrawing substituents, as shown by the positive slope against polar substituent constants. These results suggest a nucleophilic SN2-type reaction of the Ni(I) species with the benzylic carbon to provide an organonickel species as an intermediate. The reaction in D2O buffer at pD 7.0 causes a complete isotope shift of the product by +1 mass unit, supporting our proposal that protonation of the organonickel intermediate occurs during product formation. Although the turnover numbers are limited due to inactivation of the cofactor by side reactions, the present findings will contribute to elucidating the reaction mechanism of MCR-catalyzed methane generation from activated methyl sources and dehalogenation.
中文翻译：
甲烷生成和还原脱溴的苄基四氢脱氢可铁蛋白的肌红蛋白作为甲基辅酶M还原酶的模型。
甲基辅酶M还原酶（MCR）包含镍氢类胡萝卜素辅助因子F430，它通过尚未完全阐明的反应机理在厌氧条件下产生生物甲烷。在这项工作中，将肌红蛋白与人工辅因子四氢氢化镍（I）（Ni I（TDHC））重构，用作MCR的基于蛋白质的功能模型。发现重组蛋白rMb（Ni I（TDHC））与甲基供体（如对甲苯磺酸甲酯和三甲基碘化碘）反应，并在含有连二亚硫酸盐的水介质中观察到甲烷的释放。此外，rMb（Ni I（TDHC））被发现将苄基溴衍生物转化为还原脱溴的产物而没有均偶联产物。反应性按伯>仲>叔苄基碳的顺序增加，表明在初始步骤中对镍中心与苄基碳反应的空间影响。此外，如对极性取代基常数的正斜率所示，使用一系列对位取代的苄基溴的哈米特图显示了引入吸电子取代基后反应性的增强。这些结果表明亲核小号Ñ在Ni（I）物质与所述苄基碳，提供一种有机镍物种作为中间体2型反应。D 2中的反应pD 7.0处的O缓冲液会导致产品的同位素完全移位+1质量单位，这支持了我们提出的在产品形成过程中发生有机镍中间体质子化的提议。尽管由于副反应使辅因子失活而导致周转次数受到限制，但本发现将有助于阐明MCR催化的由活化甲基来源产生甲烷和脱卤的反应机理。
更新日期：2020-09-08
中文翻译：
甲烷生成和还原脱溴的苄基四氢脱氢可铁蛋白的肌红蛋白作为甲基辅酶M还原酶的模型。
甲基辅酶M还原酶（MCR）包含镍氢类胡萝卜素辅助因子F430，它通过尚未完全阐明的反应机理在厌氧条件下产生生物甲烷。在这项工作中，将肌红蛋白与人工辅因子四氢氢化镍（I）（Ni I（TDHC））重构，用作MCR的基于蛋白质的功能模型。发现重组蛋白rMb（Ni I（TDHC））与甲基供体（如对甲苯磺酸甲酯和三甲基碘化碘）反应，并在含有连二亚硫酸盐的水介质中观察到甲烷的释放。此外，rMb（Ni I（TDHC））被发现将苄基溴衍生物转化为还原脱溴的产物而没有均偶联产物。反应性按伯>仲>叔苄基碳的顺序增加，表明在初始步骤中对镍中心与苄基碳反应的空间影响。此外，如对极性取代基常数的正斜率所示，使用一系列对位取代的苄基溴的哈米特图显示了引入吸电子取代基后反应性的增强。这些结果表明亲核小号Ñ在Ni（I）物质与所述苄基碳，提供一种有机镍物种作为中间体2型反应。D 2中的反应pD 7.0处的O缓冲液会导致产品的同位素完全移位+1质量单位，这支持了我们提出的在产品形成过程中发生有机镍中间体质子化的提议。尽管由于副反应使辅因子失活而导致周转次数受到限制，但本发现将有助于阐明MCR催化的由活化甲基来源产生甲烷和脱卤的反应机理。
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