title: A dinuclear biomimetic Cu complex derived from l-histidine: synthesis and stereoselective oxidations.
abstract: A dinuclear copper(ii) complex derived from the chiral N6ligand (2S,2'S)-N,N'-(ethane-1,2-diyl)bis(2-((1-methyl-1H-imidazol-4-ylmethyl)-amino)-3-(1-trityl-1H-imidazol-4-yl)propanamide) (EHI) was synthesized and studied as a catalyst in stereoselective oxidation reactions. The ligand contains two sets of tridentate binding units, each of them giving rise to a coordination set consisting of a pair of 5- and 6-membered chelate rings, connected by an ethanediamide linker. Stereoselectivity effects were studied in the oxidations of a series of chiral l/d biogenic catechols and the pair of l/d-tyrosine methyl esters, in this case as their phenolate salts. The oxidation of β-naphthol has also been studied as a model monooxygenase reaction. The catechol oxidation was investigated in a range of substrate concentrations at slightly acidic pH and exhibited a marked dependence on the concentration of the [Cu2EHI]4+complex. This behavior has been interpreted in terms of an equilibrium between a monomeric and a dimeric form of the catalyst. Binding studies of l- and d-tyrosine were performed as a support for the interpretation of the stereoselectivity effects observed in the reactions. In general, [Cu2EHI]4+exhibits a binding preference for the l- rather than the d-enantiomer of the substrates, but it appears that in the catecholase reaction the oxidation of the d-isomer occurs at a faster rate than for the l counterpart. The same type of enantio-discriminating behavior is observed in the oxidation of l-/d-tyrosine methyl esters. In this case the reaction produces a complex mixture of products; the main product consisting of a trimeric compound, likely formed by radical coupling reactions, has been isolated and characterized. The oxidation of β-naphthol yields an additional product of the expected quinone but labeling experiments with 18-O2show no oxygen incorporation into the product, confirming that the oxidation likely proceeds through a radical mechanism.
authors.affiliation: Dipartimento di Chimica, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy. luigi.casella@unipv.it.
authors.forename: Maria L
authors.initials: ML
authors.lastname: Perrone
authors.affiliation: Dipartimento di Chimica, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy. luigi.casella@unipv.it.
authors.forename: Elena
authors.initials: E
authors.lastname: Salvadeo
authors.affiliation: Dipartimento di Chimica, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy. luigi.casella@unipv.it.
authors.forename: Eliana
authors.initials: E
authors.lastname: Lo Presti
authors.affiliation: Dipartimento di Chimica, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy. luigi.casella@unipv.it and Noxamet Srl, Dipartimento di Chimica, Università di Pavia, 27100 Pavia, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Pasotti
authors.affiliation: Dipartimento di Chimica, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy. luigi.casella@unipv.it.
authors.forename: Enrico
authors.initials: E
authors.lastname: Monzani
authors.affiliation: Dipartimento di Chimica, Università di Milano, 20133 Milano, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Santagostini
authors.affiliation: Dipartimento di Chimica, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy. luigi.casella@unipv.it.
authors.forename: Luigi
authors.identifier: http://orcid.org/0000-0002-7671-0506
authors.initials: L
authors.lastname: Casella