- Exploring the Selective Demethylation of Aryl Methyl Ethers with a Pseudomonas Rieske Monooxygenase
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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,Trajkovi?, Milo?,Barta, Katalin,de Vries, Johannes G.,Janssen, Dick B.
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- Sphingobacterium sp. T2 Manganese Superoxide Dismutase Catalyzes the Oxidative Demethylation of Polymeric Lignin via Generation of Hydroxyl Radical
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Sphingobacterium sp. T2 contains two extracellular manganese superoxide dismutase enzymes which exhibit unprecedented activity for lignin oxidation but via an unknown mechanism. Enzymatic treatment of lignin model compounds gave products whose structures were indicative of aryl-Cα oxidative cleavage and demethylation, as well as alkene dihydroxylation and alcohol oxidation. 18O labeling studies on the SpMnSOD-catalyzed oxidation of lignin model compound guiaiacylglycerol-β-guaiacyl ether indicated that the an oxygen atom inserted by the enzyme is derived from superoxide or peroxide. Analysis of an alkali lignin treated by SpMnSOD1 by quantitative 31P NMR spectroscopy demonstrated 20-40% increases in phenolic and aliphatic OH content, consistent with lignin demethylation and some internal oxidative cleavage reactions. Assay for hydroxyl radical generation using a fluorometric hydroxyphenylfluorescein assay revealed the release of 4.1 molar equivalents of hydroxyl radical by SpMnSOD1. Four amino acid replacements in SpMnSOD1 were investigated, and A31H or Y27H site-directed mutant enzymes were found to show no lignin demethylation activity according to 31P NMR analysis. Structure determination of the A31H and Y27H mutant enzymes reveals the repositioning of an N-terminal protein loop, leading to widening of a solvent channel at the dimer interface, which would provide increased solvent access to the Mn center for hydroxyl radical generation.
- Rashid, Goran M. M.,Zhang, Xiaoyang,Wilkinson, Rachael C.,Fül?p, Vilmos,Cottyn, Betty,Baumberger, Stéphanie,Bugg, Timothy D. H.
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p. 2920 - 2929
(2018/10/20)
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- Regioselective para-Carboxylation of Catechols with a Prenylated Flavin Dependent Decarboxylase
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The utilization of CO2 as a carbon source for organic synthesis meets the urgent demand for more sustainability in the production of chemicals. Herein, we report on the enzyme-catalyzed para-carboxylation of catechols, employing 3,4-dihydroxybenzoic acid decarboxylases (AroY) that belong to the UbiD enzyme family. Crystal structures and accompanying solution data confirmed that AroY utilizes the recently discovered prenylated FMN (prFMN) cofactor, and requires oxidative maturation to form the catalytically competent prFMNiminium species. This study reports on the in vitro reconstitution and activation of a prFMN-dependent enzyme that is capable of directly carboxylating aromatic catechol substrates under ambient conditions. A reaction mechanism for the reversible decarboxylation involving an intermediate with a single covalent bond between a quinoid adduct and cofactor is proposed, which is distinct from the mechanism of prFMN-associated 1,3-dipolar cycloadditions in related enzymes.
- Payer, Stefan E.,Marshall, Stephen A.,B?rland, Natalie,Sheng, Xiang,Reiter, Tamara,Dordic, Andela,Steinkellner, Georg,Wuensch, Christiane,Kaltwasser, Susann,Fisher, Karl,Rigby, Stephen E. J.,Macheroux, Peter,Vonck, Janet,Gruber, Karl,Faber, Kurt,Himo, Fahmi,Leys, David,Pavkov-Keller, Tea,Glueck, Silvia M.
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supporting information
p. 13893 - 13897
(2017/10/09)
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- Synthesis of 3-O-methylgallic acid a powerful antioxidant by electrochemical conversion of syringic acid
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Background A kinetic study of the electrochemical oxidation of syringic acid (3,5-dimethoxy-4-hydroxybenzoic acid) by cyclic voltammetry at treated gold disk was combined with results of electrolyses at Ta/PbO2 anode in order to convert it into potentially high-added-value product. Methods The electrochemical oxidation of syringic acid was carried out in order to convert this compound to 3-O-methylgallic acid. This latter was identified by mass spectrophotometry using LC-MS/MS apparatus. The 3-O-methylgallic acid synthesis was controlled by cyclic volammetry, Ortho-diphenolicdeterminations and DPPH radical-scavenging activity. Results The proposed mechanism is based on the hypothesis of a bielectronic discharge of syringic acid molecule under free and adsorbed form involving two intermediate cation mesomers. Hydrolysis of the more stable of this last one leads to the formation of the 3,4-dihydroxy-5- methoxybenzoic acid (3-O-methylgallic acid) as a major product. The latter aromatic compound was synthesized by anodic oxidation of syringic acid at PbO2 electrode. The cyclic voltammogram of the electrolysis bath of syringic acid shows that the anodic peak potential of 3-O-methylgallic acid was lower (E pa = 128 mV) than that of SA (Epa = 320 mV). And the strongest antiradical activity was detected when the 3-O-methylgallic acid concentration was higher . Conclusion The electrochemical oxidation using PbO2 anode is a rapid, simple and efficient method tool for a conversion of SA into 3-O-methylgallic acid, a potent antioxidant derivative General Significance The electrochemical process consists in a simple transformation of the syringic acid into 3-O-methylgallic acid having a better antioxidant capacity. This result has been justified by cyclic voltametry which shows that anodic peak of 3-O-methylgallic acid is reversible. Furthermore, its potential is lower than that of the irreversible anodic peak of syringic acid to 3-O-methylgallic acid.
- Gargouri, Olfa Dridi,Gargouri, Boutheina,Trabelsi, Souhel Kallel,Bouaziz, Mohamed,Abdelhédi, Ridha
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p. 3643 - 3649
(2013/08/25)
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- DPPH (=2,2-diphenyl-1-picrylhydrazyl) radical-scavenging reaction of protocatechuic acid (=3,4-dihydroxybenzoic acid): Difference in reactivity between acids and their esters
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Prolocatechuic acid (=3,4-dihydroxybenzoic acid; 1) exhibits a significantly slow DPPH (=2,2-diphenyl-1-picrylhydrazyl) radical-scavenging reaction compared to its esters in alcoholic solvents. The present study is aimed at the elucidation of the difference between the radical-scavenging mechanisms of protocatechuic acid and its esters in alcohol. Both protocatechuic acid (1) and its methyl ester 2 rapidly scavenged 2 equiv. of radical and were converted to the corresponding o-quinone structures 1a and 2a, respectively (Scheme). Then, a regeneration of catechol (=benzene-1,2-diol) structures occurred via a nucleophilic addition of a MeOH molecule to the o-quinones to yield alcohol adducts 1f and 2c, respectively, which can scavenge additional 2 equiv. of radical. However, the reaction of protocatechuic acid (1) beyond the formation of the o-quinone was much slower than that of its methyl ester 2. The results suggest that the slower radical-scavenging reaction of 1 compared to its esters is due to a dissociation of the electron-withdrawing carboxylic acid function to the electron-donating carboxylate ion, which decreases the electrophilicity of the o-quinone, leading to a lower susceptibility towards a nucleophilic attack by an alcohol molecule.
- Saito, Shizuka,Kawabata, Jun
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p. 1395 - 1407
(2007/10/03)
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- Gallic acid metabolites are markers of black tea intake in humans
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Gallic acid is one of the main phenolic components of black tea. The objective of this study was to identify urinary gallic acid metabolites with potential for use as markers of black tea intake. In an initial study, nine compounds, assessed by using gas chromatography-mass spectrometry, were found to increase in concentration in urine after 3 cups of black tea over 3 h. A subsequent study employed a controlled crossover design in which 10 subjects consumed 5 cups per day of black tea or water for 4 weeks in random order. Twenty-four hour urine samples were collected at the end of each period. Of the 9 candidate compounds identified in the initial study, only 3 were present at higher concentrations in urine of all 10 subjects during tea- drinking in comparison to water-drinking periods. These compounds were identified as 4-O-methylgallic acid, 3-O-methylgallic acid, and 3,4-O- dimethylgallic acid, all methyl ether derivatives of gallic acid. It is suggested that these compounds have the potential to be used as markers of black tea intake.
- Hodgson, Jonathan M.,Morton, Lincoln W.,Puddey, Ian B.,Beilin, Lawrence J.,Croft, Kevin D.
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p. 2276 - 2280
(2007/10/03)
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- Probing the Role of Polyphenol Oxidation in Mediating Insect-Pathogen Interactions. Galloyl-Derived Electrophilic Traps for the Lymantria dispar Nuclear Polyhedrosis Virus Matrix Protein Polyhedrin
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Galloyl-derived orthoquinone probes have been designed, synthesized, and utilized in an ongoing study of insect-pathogen interactions. A stable galloyl-derived orthoquinone O-methyl ether modified with both acidic and fluorescent appendages was successful in trapping the model nucleophile cysteine, a test protein bearing a single cysteine residue, and the viral occlusion body matrix protein polyhedrin from Lymantria dispar nuclear polyhedrosis virus (LdNPV), a pathogen of the gypsy moth caterpillar (GMc). This latter observation may be related to the molecular mechanism by which gallotannins decrease LdNPV infectivity in GMc's. Sufficient site isolation was not achieved with a polymer-bound reactive galloyl hydroxyorthoquinone electrophile to permit similar nucleophile trapping to compete with oligomerization.
- Feldman, Ken S.,Sambandam, Aruna,Bowers, Katherine E.,Appel, Heidi M.
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p. 5794 - 5803
(2007/10/03)
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- Synthesis and antihepatotoxicity of some Wuweizisu analogues
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A preparation of dimethyl 4,4'-dimethoxy-5,6,5',6'-dimethylenedioxybiphenyl-2,2'-dicarboxylate (VII) was readily achieved. It provided the advantages of specificity, simplicity, and efficiency in reactions. 6-Phenyl-3,9-dimethoxy-1,2-methylenedioxy-10,11-methylenedioxy-6,7- dihydro-5H-dibenz(c, e)azepin (X) was successfully synthesized from VII (DDB) and its liver-protective property proved to be more effective than DDB and silymarin in the in vitro test of carbon tetrachloride-induced damage of primary cultured rat hepatocytes.
- Wu,Chen,Chang,Chen,Lee
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p. 353 - 358
(2007/10/02)
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- The total synthesis of (±)-megaphyllone acetate, a cytotoxic neolignan
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Conversion of 3-methoxy-4,5-methylenedioxybenzaldehyde into (2RS,3SR,4RS)-2-methoxycarbonyl-4-(3-methoxy-4,5-methylenedioxyphenyl)-3-m ethyl-4-butanolide was carried out in seven steps via 1-acetoxy-1-(3-methoxy-4,5-methylenedioxyphenyl)propanone. The butanolide was further converted into (2RS,3SR,3aRS,5RS)-3,3a,4,5-tetrahydro-5-methoxy-2-(3-methoxy-4,5-methylen edioxyphenyl)-3-methyl-3a-(2-propenyl)-6(2H)-benzofuranone (22) in eight steps. Reduction of 22 with lithium aluminium hydride followed by acetylation with acetic anhydride in pyridine afforded (±)-megaphyllone acetate.
- Matsumoto,Imai,Yamaguchi,et al.
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p. 346 - 351
(2007/10/02)
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