Quinolone and isoquinolone alkaloids: the structural-electronic effects and the antioxidant mechanisms

Abstract

Quinolone and isoquinolone alkaloids, which were found in the plant kingdom, are now potential antioxidants. In this case study, a quantum calculated procedure utilizing the density functional theory (DFT)-B3LYP method coupled with basis set 6–311++G(d,p) was used to investigate free-radical quenching activity of alkaloidal quinolone viridicatol (1) and alkaloidal isoquinolone 5-hydroxy-8-methoxy-4-phenylisoquinolin-1(2H)-one (2). On the basis of thermodynamic perspective and from the findings, the powerful antioxidative potential of these two title compounds in the liquids water, methanol, and especially DMSO was mostly driven by the proton affinity (PA), consistent with the SPLET (sequential proton loss electron transfer) mechanism. The environmental effect has also been investigated, and the antioxidative action caused by O–H bond disruption is easier than that of N–H bond in both the gaseous phase and liquids. In the gaseous phase, the combinations of two studied compounds and •OOH/DPPH radicals are kinetic evidence, including two intermediates and one transition state. From thermodynamic and kinetic viewpoints, compound 2 can be seen as a therapeutically useful agent in antioxidative treatment because of the role of a 5-hydroxy group.