Monooxygenation of external phenolic substrates in small-molecule dicopper complexes: implications on the reaction mechanism of tyrosinase

This review describes the reactions of synthetic dicopper complexes with external monophenolic substrates in the presence of O2, generating o-diphenols (catechols) or o-quinones. Such systems are of interest as structural and functional models of the type 3 copper enzyme tyrosinase, which mediates the o-hydroxylation of tyrosine to DOPA and the subsequent two-electron oxidation to dopaquinone. The known dicopper systems mediating the aromatic hydroxylation of monophenolic substrates are described. Systems based on µ-η2 : η2 peroxo, bis-µ-oxo, and trans-µ-1,2-peroxo dicopper cores are considered separately. After reviewing the stoichiometric conversion of phenolic substrates, the available catalytic systems are described. The implications for the reaction pathway of tyrosinase are discussed.