Correlations between the rate constant of singlet oxygen quenching by imidazole derivatives and anti-inflammatory...

The second-order rate constants, k delta, for quenching of molecular singlet oxygen O2 (1 delta g) by nonsteroidal anti-inflammatory imidazole drugs have been determined using time-resolved phosphorescence detection of singlet oxygen. A linear correlation was observed between log k delta (ranging from 7.90 to 8.50) and the anti-inflammatory activity of these compounds (ranging from ED50 = 15 to 300 mg/kg), as measured in rats by Jørgensen and Dyrsting [United States Patent 4,424,229 (1984)]. The correlation between this physico-chemical parameter measured in vitro and a biological activity measured in vivo might be useful in screening other types of candidate anti-inflammatory drugs. The rate constant (k delta) can be considered as a quantitative expression of the electron-donating power of the imidazole drug, as suggested by a correlation of log k deta (ranging from 6.02 to 7.45) with Hammett substituent parameters observed in the case of 2-substituted imidazoles.