Optimization of the indenone ring of indenoisoquinoline topoisomerase I inhibitors.

Two series of indenoisoquinoline topoisomerase I inhibitors have been prepared to investigate optimal substituents on the indenone ring at the 9-position. The more exhaustive series was prepared using a nitrated isoquinoline ring that has been previously demonstrated to enhance biological activity. After preliminary biological evaluation, a more focused series of inhibitors was prepared utilizing a 2,3-dimethoxy-substituted isoquinoline ring. The results of the two series indicate the existence of superior functional groups such as methoxy, fluorine, and cyano for the indenoisoquinoline 9-position. Interestingly, these functional groups coincide with established structure-activity relationships for the 11-position of camptothecin.