Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Nijenborgh 4, 9726 AG, Groningen, The Netherlands.
Present address: School of Food and Nutritional Science Sciences, University College Cork, College Road, Cork, T12 YN60, Republic of Ireland.
Chembiochem. 2019 Jan 2;20(1):118-125. doi: 10.1002/cbic.201800594. Epub 2018 Dec 17.
Biocatalytic dealkylation of aryl methyl ethers is an attractive reaction for valorization of lignin components, as well as for deprotection of hydroxy functionalities in synthetic chemistry. We explored the demethylation of various aryl methyl ethers by using an oxidative demethylase from Pseudomonas sp. HR199. The Rieske monooxygenase VanA and its partner electron transfer protein VanB were recombinantly coexpressed in Escherichia coli and they constituted at least 25 % of the total protein content. Enzymatic transformations showed that VanB accepts NADH and NADPH as electron donors. The VanA-VanB system demethylates a number of aromatic substrates, the presence of a carboxylic acid moiety is essential, and the catalysis occurs selectively at the meta position to this carboxylic acid in the aromatic ring. The reaction is inhibited by the by-product formaldehyde. Therefore, we tested three different cascade/tandem reactions for cofactor regeneration and formaldehyde elimination; in particular, conversion was improved by addition of formaldehyde dehydrogenase and formate dehydrogenase. Finally, the biocatalyst was applied for the preparation of protocatechuic acid from vanillic acid, giving a 77 % yield of the desired product. The described reaction may find application in the conversion of lignin components into diverse hydroxyaromatic building blocks and generally offers potential for new, mild methods for efficient unmasking of phenols.
芳基甲基醚的生物催化脱甲基反应是一种有吸引力的反应，可用于木质素成分的增值，以及合成化学中羟基官能团的脱保护。我们探索了使用假单胞菌 HR199 的氧化脱甲基酶对各种芳基甲基醚进行脱甲基化。 Rieske 单加氧酶 VanA 及其伴侣电子转移蛋白 VanB 在大肠杆菌中重组共表达，它们至少占总蛋白质含量的 25%。酶促转化表明，VanB 接受 NADH 和 NADPH 作为电子供体。VanA-VanB 系统可对多种芳香族底物进行脱甲基化，存在羧酸部分是必需的，并且催化作用选择性地发生在芳香环中该羧酸的间位。该反应受到副产物甲醛的抑制。因此，我们测试了三种不同的级联/串联反应来进行辅酶再生和甲醛消除；特别是，通过添加甲醛脱氢酶和甲酸脱氢酶，转化率得到了提高。最后，该生物催化剂被用于从香草酸制备原儿茶酸，得到了 77%的所需产物收率。所描述的反应可用于将木质素成分转化为各种羟基芳烃构建块，并且通常为高效去掩蔽酚类的新的温和方法提供了潜力。
