Unusual substituent effects in the hydroxylation of phenols by a Cu(2+)-ascorbic acid-O2 system, gamma-radiolysis, and microsomes.
Aromatic ring hydroxylation of phenolic compounds proceeded selectively in a Cu(2+)-ascorbic acid-O2 system. In contrast to usual oxidation systems, unusual substituent effects were observed: electron-withdrawing groups accelerate and electron-donating groups retard the hydroxylation. Hydroxyl radicals generated by gamma-radiolysis also converted phenols into catechols and hydroquinones. The close resemblance of these two systems led us to presume that the active intermediate in the Cu(2+)-ascorbic acid-O2 system is hydroxyl radical or an equivalent species. The unusual substituent effects were also observed in the hydroxylation of p-substituted phenol by microsomes, a cytochrome P-450-dependent reaction. These results imply that the Cu(2+)-ascorbic acid-O2 system is an effective biomimetic oxidation system.
Faculty of Pharmaceutical Sciences, University of Tokyo, Japan.
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Y
Urano
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Higuchi
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Hirobe
D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism*; D003300:Copper / Q000378:metabolism*; D005720:Gamma Rays; D006878:Hydroxides; D017665:Hydroxyl Radical; D006900:Hydroxylation; D066298:In Vitro Techniques; D008862:Microsomes, Liver / Q000378:metabolism* / Q000528:radiation effects; D010100:Oxygen / Q000378:metabolism*; D010636:Phenols / Q000378:metabolism*; D051381:Rats
D006878:Hydroxides; D010636:Phenols; D017665:Hydroxyl Radical; D003300:Copper; D001205:Ascorbic Acid; D010100:Oxygen