Chemoselective C-4 Aerobic Oxidation of Catechin Derivatives Catalyzed by the Trametes villosa Laccase/1-Hydroxybenzotriazole System: Synthetic and Mechanistic Aspects

Abstract

Catechin derivatives were oxidized in air in the presence of the Trametes villosa laccase/1-hydroxybenzotriazole (HBT) system in buffered water/1,4-dioxane as reaction medium. The oxidation products, flavan-3,4-diols and the corresponding C-4 ketones, are bioactive compounds and useful intermediates for the hemisynthesis of proanthocyanidins, plant polyphenols which provide beneficial health properties for humans. Determinations of oxidation potentials excluded that catechin derivatives could be directly oxidized by laccase Cu(II), while it resulted in the H-abstraction from benzylic positions being promptly promoted by the enzyme in the presence of the mediator HBT, the parent species producing in situ the reactive intermediate benzotriazole-N-oxyl (BTNO) radical. A remarkable and unexpected result for the laccase/HBT oxidative system has been the chemoselective insertion of the oxygen atom into the C-4-H bond of catechin derivatives. Mechanistic aspects of the oxidation reaction have been investigated in detail for the first time in order to corroborate these results. Since the collected experimental findings could not alone provide information useful to clarify the origin of the observed chemoselectivity, these data were expressly supplemented with information derived by suitable molecular modeling investigations. The integrated evaluation of the dissociation energies of the C-H bonds calculated both by semiempirical and DFT methods and the differential activation energies of the process estimated by a molecular modeling approach suggested that the observed selective oxidation at the C-4 carbon has a kinetic origin.

Removal of pharmaceuticals, steroid hormones, phytoestrogens, UV-filters, industrial chemicals and pesticides by Trametes versicolor: Role of biosorption and biodegradation

“…The laccase-HBT system can also achieve better removal of non-phenolic compounds as the aminoxyl radicals have redox potentials in the order of 1.0-1.1 V (d' Acunzo et al, 2006), which are higher than that of laccase only (0.17V) (Klonowska et al, 2002). For instance, Bernini et al (2011) reported that the laccase-mediator system can effectively trigger the H-abstraction from benzylic carbons of nonphenolic compounds. This can explain the improvement in atrazine, amitriptyline and ametryn removal in the current study in the presence of HBT.…”

Ecofriendly synthesis of halogenated flavonoids and evaluation of their antifungal activity

“…5,7,3 0 ,4 0 -Tetramethoxyflavanone (methylated hesperetin)(15) Yield: 88%; colorless oil; spectroscopic data are according to those reported in the literature 29. 5,7,3 0 ,4 0 -Tetramethoxycatechin(21) Yield: 92%; yellow oil; spectroscopic data are according to those reported in the literature 30. 5,7,3 0 ,4 0 -Tetramethoxyepicatechin(26) Yield: 90%; yellow oil; spectroscopic data are according to those reported in the literature 30.…”

“…Trimethoxyflavanone (methylated naringenin) 12; 5,7,3 0 ,4 0tetramethoxyflavanone (methylated hesperetin) 15; 5,7,3 0 ,4 0tetramethylcatechin 21 and 5,7,3 0 ,4 0 -tetramethylepicatechin 26 were prepared as already reported by us 29,30. 5,7,4 0 -Trimethoxyflavanone (methylated naringenin)(12) Yield: 90%; colorless oil; spectroscopic data are according to those reported in the literature 29.…”

Phytochemical Constituency Profiling and Antimicrobial Activity Screening of Seaweeds Extracts Collected from the Bay of Bengal Sea Coasts

“…Antibiotics, metal ions, and various quaternary ammonium compounds are being used worldwide though these antimicrobial compounds are also being claimed to be associated with antibiotic resistance, complex chemical synthesis, environmental pollution, and high cost [3,4]. However, natural antibacterial agents have been recently identified to overcome these disadvantages [5]. Marine organisms are one of the richest sources of bioactive compounds and chemical diversity [6,7].…”