Tyrosinase and catechol oxidase activity of copper(I) complexes supported by imidazole-based ligands: structure-reactivity correlations.

Four new imidazole-based ligands, 4-((1 H-imidazol-4-yl)methyl)-2-phenyl-4,5-dihydrooxyzole (L 1), 4-((1 H-imidazol-4-yl)methyl)-2-( tert-butyl)-4,5-dihydrooxyzole (L 2), 4-((1 H-imidazol-4-yl)methyl)-2-methyl-4,5-dihydrooxyzole (L 3), and N-(2,2-dimethylpropylidene)-2-(1-trityl-1 H-imidazol-4-yl-)ethyl amine ( L 1), have been synthesized. The corresponding copper(I) complexes [Cu(I)( L 1)(CHCN)]PF (Cu L 1), [Cu(I)( L 2)(CHCN)]PF (Cu L 2), [Cu(I)( L 3)(CHCN)]PF (Cu L 3), [Cu(I)( L 1)(CHCN)]PF (Cu L 1) as well as the Cu(I) complex derived from the known ligand bis(1-methylimidazol-2-yl)methane (BIMZ), [Cu(I)( BIMZ)(CHCN)]PF (Cu BIMZ), are screened as catalysts for the oxidation of 3,5-di- tert-butylcatechol (3,5-DTBC-H) to 3,5-di- tert-butylquinone (3,5-DTBQ). The primary reaction product of these oxidations is 3,5-di- tert-butylsemiquinone (3,5-DTBSQ) which slowly converts to 3,5-DTBQ. Saturation kinetic studies reveal a trend of catalytic activity in the order Cu L 3 ≈ Cu L 1 > Cu BIMZ > Cu L 2 > Cu L 1. Additionally, the catalytic activity of the copper(I) complexes towards the oxygenation of monophenols is investigated. As substrates 2,4-di- tert-butylphenol (2,4-DTBP-H), 3- tert-butylphenol (3-TBP-H), 4-methoxyphenol (4-MeOP-H), N-acetyl- l-tyrosine ethyl ester monohydrate (NATEE) and 8-hydroxyquinoline are employed. The oxygenation products are identified and characterized with the help of UV/Vis and NMR spectroscopy, mass spectrometry, and fluorescence measurements. Whereas the copper complexes with ligands containing combinations of imidazole and imine functions or two imidazole units (Cu L 1 and Cu BIMZ) are found to exhibit catalytic tyrosinase activity, the systems with ligands containing oxazoline just mediate a stoichiometric conversion. Correlations between the structures of the complexes and their reactivities are discussed. [ABSTRACT FROM AUTHOR]

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