5-Hydroxy-6-methyluracil, an Efficient Scavenger of Peroxyl Radical in Water

Abstract

The reactivity of 5-hydroxy-6-methyluracil (HMU) towards peroxyl radicals generated from the aerobic thermal decomposition of 2,2 -azo-bis(2-amidinopropane)dihydrochloride (AAPH) has been investigated. The oxidation product of HMU is dihydro-5,5,6-trihydroxy-6-methylpyrimidin-2,4-dion-e (94%). The relative oxidation rate of HMU vs. quercetin by peroxyl radicals generated from AAPH has been measured as 0.20 ± 0.04 at 54.6°C, hence HMU is the effective scavenger of peroxyl radicals. The overall kinetic parameters and the efficiency of radical generation from AAPH in water solution at pH 7.0 (0.1 M phosphate buffer) have been determined using HMU in temperature range 26° -84°C.

Base-Promoted Reaction of 5-Hydroxyuracil Derivatives with Peroxyl Radicals

“…Indeed its rate constant for reaction with ethylbenzene peroxyl radicals was reported as k = 2.6 × 10 4 M −1 s −1 . A recent investigation has shown that during the thermal decomposition of 2,2′-azo-isobutyronitrile (AIBN) in 2-propanol at 75 °C (in air) HMU prevented the radical-mediated oxidation of the solvent (to form acetone) as efficiently as the well-known antioxidant quercetin, by reacting with initiator-derived peroxyl radicals to yield product 4 . However, the mechanism for such peroxyl-radical-quenching is far from being understood.…”

“…However, the mechanism for such peroxyl-radical-quenching is far from being understood. It was suggested to occur by radical addition to the ring in the 6-position followed by disproportionation, by analogy with the known reactivity of uracil derivatives with hydroxyl radicals (Scheme ) …”