Coumarin sharing the benzene ring with quinoline for quenching radicals and inhibiting DNA oxidation.

Fifteen 8-substituted-phenyl-6-ferrocenyl-4-methyl-2H-pyrano[3,2-g]quinolin-2-ones were synthesized via Povarov three-component reaction, in which the substituted aromatic aldehydes reacted with ferrocenylacetylene and 7-amino-4-methylcoumarin in the presence of Ce(OTf)3 as the catalyst. The obtained coumarin-fused quinolines were applied to quench 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS(+)) and 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH) and to inhibit 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH)-induced oxidation of DNA. It was found that the ferrocenyl group attaching to pyrano[3,2-g]quinolin-2-one scaffold can trap radicals and inhibit DNA oxidation even in the absence of phenolic hydroxyl group. The inhibitory effects on radicals and DNA oxidation can be further enhanced by the electron-donating groups such as p-(N,N-dimethyl amino)phenyl, ferrocenyl, and furan-2-yl group at 8-position. Therefore, ferrocenyl-substituted pyrano[3,2-g]quinolin-2-one skeleton together with electron-donating groups became a novel structural style for antioxidants.