Isolation of isoflavonoids possessing antioxidant activity from the fermentation broth of Streptomyces sp.

Three antioxidant isoflavonoids characterized as 4',7,8-trihydroxyisoflavone (1), 3',4',7-trihydroxyisoflavone (2) and 8-chloro-3',4',5,7-tetrahydroxyisoflavone (3) were isolated from the cultured broth of Streptomyces sp. OH-1049. Among them, 3 is a novel isoflavonoid possessing a chlorine atom in the molecule. In in vitro studies, these antibiotics were found to possess antioxidant activity whereas showed almost no cytocidal activities against HeLa S3 cells.