SUBSTITUENT EFFECT ON SUPEROXIDE ELIMINATION FROM PEROXYL RADICALS OFADENINE AND METHYLATED DERIVATIVES

The hydroxyl radical, generated by UV photolysis of 4-mercaptopyridine -N-oxide, was made to react with adenine and several methylated deriva tives. The formation of the corresponding 8-hydroxy derivatives was ob served in all cases and is the result of the oxidation of the respecti ve 8-hydroxyl adducts. When this oxidation is carried out by molecular oxygen, an intermediate peroxyl radical is formed by addition of O-2 at C(4). Superoxide anion is eliminated from the peroxyl radical, foll owed by deprotonation, resulting in the formation of 8-hydroxyadenines (8-oxo-7,8-dihydroadenines) as the final stable products. The extent of superoxide elimination, as compared to other processes by which per oxyl radicals decay, was found to increase with the number of methyl s ubstituents at either N-6 or N(9). This indicates that positive charge is developed in the transition state, as suggested by the negative rh o value of the Hammett relationship for this reaction. (C) 1998 Elsevi er Science S.A. All rights reserved.