Prooxidant activities of quercetin, p-courmaric acid and their derivatives analysed by quantitative structure–activity relationship

In this work, quercetin, p-courmaric acid and their derivatives were chosen to evaluate the prooxidant activity in NADPH/peroxidase/H2O2 and DNA cleavage systems. The balance between antioxidant and prooxidant effect was not apparent. The number of hydroxyl groups, hydrophilicity, steric hindrance, concentration and affinity to peroxidase were critical for the prooxidation behaviour of tested compounds. Ortho-methoxy substitution led to a decreased prooxidant activity for p-courmaric acid. The DNA cleavage activity was in a decreasing order, quercetin = rutin > p-courmaric acid > ferulic acid > quercetin 3-O-glucoside. By calculation of ΔE(LUMO−HOMO) and ΔHOF, the reactivity of forming phenoxyl radicals was quercetin > rutin > quercetin 3-O-glucoside, which was in agreement with their DNA cleavage activities. The prooxidant activity order of p-courmaric acid and ferulic acid was in contrast to their reactivities of forming phenoxyl radical. The logP difference should play a critical role in the prooxidation behaviour.