Free Radical Scavenging Activity of Synthetic and Naturally Occurring Polyhydroxy-, Aminohydroxynaphthazarins and Related Compounds

Fifty natural and synthetic hydroxy-, aminohydroxynaphthazarins and related quinones were tested for their antiradical activities using 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) scavenging assay. The main features of structure-antiradical activity relationship of amino- and hydroxyquinones were determined for the first time. It was found that naphthazarins (5,8-dihydroxy-1,4-naphthoquinones) are much more active against ABTS-radical than related 1,4-naphthoquinones and 5-hydroxy-1,4-naphthoquinones. Natural aminonaphthazarins (spinamine E, echinamine A) and polyhydroxylated naphthazarins (spinazarin, echinochrome, spinochrome D and E) revealed high antiradical properties. In most cases, the presence of long chained O-alkoxy substituent in benzenoid part of naphthazarin core enhanced their antiradical activity.