RADICAL OXIDATION OF XANTHINES - A REACTION PATHWAY TO URIC-ACID

The reaction of isocaffeine (1,3,9-trimethylxanthine) with oxidizing r adicals is studied by using pulse radiolysis techniques to study the t ransients and follow their transformation kinetics, and by identifying the corresponding stable final products by HPLC. Isocaffeine reacts w ith OH. to yield an hydroxyl adduct at C(8) that leads, after oxidatio n, to the formation of the corresponding uric acid (1,3,9-trimethpl-8- hydroxyxanthine). Upon reaction with SO4-. the formation of the same u ric acid was also seen, resulting from the hydration of the radical ca tion initially formed, followed by oxidation. This result is in contra st with that observed for purines of the adenine system, where a C(8)- hydroxylated derivative is formed upon oxidation by OH. but not by SO4 -..