Exploring the Selective Demethylation of Aryl Methyl Ethers with a Pseudomonas Rieske Monooxygenase.
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.
['Lanfranchi|Elisa|E|0000-0002-3964-4925', 'Trajković|Miloš|M|0000-0001-7264-1630', 'Barta|Katalin|K|0000-0002-8046-4248', 'de Vries|Johannes G|JG|0000-0001-5245-7748', 'Janssen|Dick B|DB|0000-0002-0834-2043']
D000445:Aldehyde Oxidoreductases D001426:Bacterial Proteins D055162:Biocatalysis D000073398:Demethylation D004926:Escherichia coli D005557:Formaldehyde D055772:Green Chemistry Technology D008738:Methyl Ethers D006899:Mixed Function Oxygenases D010084:Oxidation-Reduction D010636:Phenols D000075082:Proof of Concept Study D011549:Pseudomonas D011994:Recombinant Proteins D013379:Substrate Specificity
Rieske monooxygenases O-demethylation biocatalysis methoxy groups protein expression