The role of benzylic-allylic hydrogen atoms on the antiradical activity of prenylated natural chalcones: a thermodynamic and kinetic study.

Prenylated chalcones are a family of natural chalcones that have been reported to exhibit a high antioxidant activity. In this paper, the density functional calculations are carried out to study, systematically, the antiradical properties of four prenylated natural chalcones namely isobavachalcone (I), xanthohumol (II), desmethylxanthohumol (III) and broussochalcone (IV). The radical scavenging ability of all the possible CH and OH bonds of chalcones I-IV were discussed in detail thermodynamically and kinetically. The results reveal that the CH bonds of the prenyl substituent are the most thermodynamically preferred sites for free radical attack and thus play an important role on the antiradical activity of the investigated chalcones. For the OH bonds, it has been found that the B ring is more preferred for attacking free radicals than the A ring. Kinetic investigations have revealed that the CH bond and the OH bonds of the B ring can trap HO•/HOO• radicals. These results are of great significance in better understanding the chemical mechanism of the radical-scavenging action and open new perspectives for the design of new potent antioxidant agents.Communicated by Ramaswamy H. Sarma.