Understanding the copper-phenoxyl radical array in galactose oxidase: contributions from synthetic modeling studies

The two-electron oxidation of primary alcohols with dioxygen to yield aldeh yde and hydrogen peroxide that is catalyzed by galactose oxidase (GAO) occu rs at an intriguing active site comprising of a copper ion ligated by an un usual cysteine-modified tyrosine group. Both the metal ion and the tyrosina te undergo 1-electron redox interconversions during catalysis, the Cu(II)-t yrosyl radical form being a critical species. Due to the novelty of this co upled metal-radical cofactor unit in chemistry and biology and its importan ce within the more general context of radical-enzyme biochemistry, chemists have attempted to prepare model complexes for this and other redox-related states of GAG. The primary goals of such research are to better understand the enzyme active site spectral properties, structural attributes, and rea ctivity. In this review article, progress toward these goals is surveyed, b eginning with a discussion of the synthesis and structural and spectroscopi c characterization of model complexes of the CAO active site and ending wit h a description of more recent discoveries of catalytic reactivity by Cu(II )-phenoxyl radical species that replicate and provide insights into GAO fun ction. (C) 2000 Elsevier Science S.A. All rights reserved.