Hydrogen Abstraction of Ketoprofen in the Excited Triplet State with Indole and Methylindoles.

Relaxation of excited states and reactivity of ketoprofen (KP), one of the most popular nonsteroidal anti-inflammatory drugs, with indole and methylindoles have been studied with transient absorption and quantum chemical calculations. KP in the excited triplet state, 3KP*, abstracted a hydrogen atom from indole and methylindoles to afford a ketyl radical and a counter radical. The bimolecular quenching rate constants of 3KP* by indole and methylindoles, kq, and the hydrogen atom abstraction rate constants, kr, were obtained. The kr values for methylindoles were larger than that for indole; in addition, transient spectra at around 350 nm, assigned to the corresponding C-centered radical, was observed. These results indicate that 3KP* abstracts a hydrogen atom of the methyl group as well as that of N-H in the indole frame. These findings give us information on the reactivity of excited KP in the vicinity of tryptophan in a KP-protein complex, which will ultimately cause photosensitization on human skin.