The synthesis of 5-substituted camptothecins as potential inhibitors of DNA topoisomerase I

Four new 5-substituted camptothecins (4–7) have been synthesized and evaluated for DNA topoisomerase I inhibition. The results suggested that the pyridone moiety in the D ring of camptothecin plays a crucial role in determining its activity and that the 5 position of the C ring should be unsubstituted for retention of activity.