We now report studies on the chemistry of discorhabdin C together with a further natural product in this series, discorhabdin E (6). Acid-catalyzed rearrangement of discorhabdin C gave another new ring system, with five fused rings including a 2,3-dihydro-lH-azepine. The conformational exchange in these ring systems, as detected in their nuclear magnetic resonance (NMR) spectra, is also discussed. To explore the structural features responsible for the biological activities of the discorhabdins, all the derivatives in this study were tested for toxicity toward leukemia cells and a range of microorganisms. Discorhabdin C and some of these derivatives have also been tested in the U. S. National Cancer Institute (NCI) in vitro primary screen. The comprehensive testing by the NCI has shown that members of the discorhabdin family of compounds exhibit selective cytotoxicity against certain cancer types.