Rubiginone D2 was isolated from a Streptomyces sp. by Zeeck and co-workers, University of Gottingen, Germany in 2000. Rubiginone D2 is an angucycline, an angular tetracyclic benzanthracene core containing a highly oxygenated A ring. Rubiginone D2 is a potent cytotoxic agent, demonstrating 50% inhibition of growth (GI50) of stomach adenocarcinoma HM02, colon carcinoma Kato III, hepatocellular carcinoma HEPG2 and breast adenocarcinoma MCF7 cell lines at concentrations of 0.1, 0.7, <0.1 and 7.5 µM, respectively.