Simplest Monodentate Imidazole Stabilization of the oxy-Tyrosinase Cu2O2 Core: Phenolate Hydroxylation through a CuIII Intermediate

Tyrosinases are ubiquitous binuclear copper enzymes that oxygenate to (Cu2O2)-O-II cores bonded by three histidine N tau-imidazoles per Cu center. Synthetic monodentate imidazole-bonded (Cu2O2)-O-II species self-assemble in a near quantitative manner at -125 degrees C, but N pi-ligation has been required. Herein, we disclose the syntheses and reactivity of three N tau-imidazole bonded (Cu2O2)-O-II species at solution temperatures of -145 degrees C, which was achieved using a eutectic mixture of THF and 2-MeTHF. The addition of anionic phenolates affords a (Cu2O2)-O-III species, where the bonded phenolates hydroxylate to catecholates in high yields. Similar (Cu2O2)-O-III intermediates are not observed using N pi-bonded (Cu2O2)-O-II species, hinting that Nt-imidazole ligation, conserved in all characterized Ty, has functional advantage beyond active-site flexibility. Substrate accessibility to the oxygenated Cu2O2 core and stabilization of a high oxidation state of the copper centers are suggested from these minimalistic models.