Synthesis and cytotoxic activity of a new series of topoisomerase I inhibitors.

A series of structurally simple analogues of natural topopyrone C were synthesized and tested for cytotoxic and topoisomerase I inhibitory activities. The removal of the hydroxyl groups at the 5 and 9 positions resulted in an increased cytotoxic potency and ability to stabilize topoisomerase-mediated cleavage. In addition, the results suggest that some structural features, such as the pyrone ring and a polar group in position 11, are fundamental for topoisomerase I inhibitory effect. These structural requirements are also consistent with the cytotoxic activity.