Functional Model of Dopamine .beta.-Hydroxylase. Quantitative Ligand Hydroxylation at the Benzylic Position of a Copper Complex by Dioxygen

There has been considerable interest in the modeling of metalloprotein functions and their active site structures in order to understand their catalytic mechanisms and unusual spectroscopic characteristics, which is essential to the development of an efficient catalyst and/or functional material. Among them, copper proteins have long attracted many chemists because of their versatile functions in several living systems. In particular, copper monooxygenases have recently merited much attention owing to their beautiful achievements in Cu/O sub(2) chemistry. Several peroxo dinuclear copper complexes have been prepared, providing valuable information about the binding mode of O sub(2) to the dinuclear copper center of hemocyanin and tyrosinase. The redox chemistry in such Cu sub(2)O sub(2) complexes has also been studied extensively in order to elucidate how O sub(2) is activated in oxygenation reactions. Thus a number of efficient model systems mimicking tyrosinase function (aromatic hydroxylation) have been reported. As far as aliphatic hydroxylation is concerned, however, functional models of dopamine beta -hydroxylase (D beta H) or peptidylglycine alpha -amidating monooxygenase (PAM) are still very rare, and no quantitative aliphatic hydroxylation has so far been achieved. Here we report the first example of quantitative ligand hydroxylation at the benzylic position of a Cu complex by O sub(2), which can be regarded as an efficient functional model of D beta H.