Carbon-oxygen bond formation by fungal laccases: cross-coupling of 2,5-dihydroxy-N-(2-hydroxyethyl)-benzamide with the solvents water, methanol, and other alcohols

Abstract

Laccase-catalyzed reactions lead to oxidation of the substrate via a cation radical, which has been described to undergo proton addition to form a quinonoid derivative or nucleophilic attack by itself producing homomolecular dimers. In this study, for the substrate 2,5-dihydroxy-N-(2-hydroxyethyl)-benzamide, we show that, besides the quinonoid form of substrate, all products formed are nonhomomolecular ones. Indeed, without addition of a reaction partner, heteromolecular products are formed from the quinonoid form of the laccase-substrate and the solvents water or methanol present in the incubation assay. Consequently, in laccase catalyzed syntheses performed in aqueous solutions or in the presence of methanol or other alcohols, undesirable heteromolecular coupling reactions between the laccase substrate and solvents must be taken into account. Additionally, it could be shown at the example of methanol and other alcohols that C-O-bound cross-coupling of dihydroxylated aromatic substances with the hydroxyl group of aliphatic alcohols can be catalyzed by fungal laccases.

Comparative analyses of laccase‐catalyzed amination reactions for production of novel β‐lactam antibiotics

“…Together with the redox potential of the T1 site of laccases, which catalyzes the formation of the radical intermediates of the substrates 1a to 1d (Fig. 2, 29), the redox potential difference between the laccase T1 site and the substrate is defined, which in turn determines the reaction velocity. Thus, higher redox potentials of the laccase T1 site and lower redox potentials of the substrate make the redox potential difference larger, resulting in a faster reaction rate 30.…”

Laccase‐Mediated Grafting on Biopolymers and Synthetic Polymers: A Critical Review

“…With laccase from Bacillus SF spores, it was shown that tyramine and syringylglycerol β‐guaiacyl ether (Scheme C) coupled through a C−O bond because the ortho positions, with respect to the phenyl alcohol, were blocked (Scheme , P1 ) . Further transformations included dehydroxylation ( P2 ), oxidation ( P3 ) and nucleophilic attack by either of the solvents water ( P4 ) or methanol ( P5 ); this has been shown to be rather common in laccase‐mediated oxidation …”

“…[39] Further transformations included dehydroxylation (P2), oxidation (P3)a nd nucleophilic attack by either of the solvents water (P4)o rm ethanol (P5); this has been shown to be rathercommon in laccase-mediated oxidation. [40] Apart from grafting phenolics from lignin, Kudanga and coworkers also managed to grafta nd concomitantly hydrophobise beech veneers by using alkylamines. [41] To support their hypothesis that covalent bonding, andn ot mere adsorption,w as responsible for the increase in hydrophobicity,t he authors again reverted back to simple phenolics and lignin model compounds (Scheme 7A,B ).…”

Improvement of the Antifungal Activity Against Botrytis Cinerea of Syringic Acid, a Phenolic Acid From Grape Pomace

“…Numerous authors have reported that the biological activity of phenolic compounds can be improved modifying phenolic molecules by using the enzyme laccase (EC 1.10.3.2) a polyphenol oxidase 8 . Antioxidant, antitumor, and anti-depressive compounds have been synthesized using this enzyme [8][9][10][11] . Additionally, this enzyme has been recently used for the synthesis of antifungal compounds 12 .…”