Synthesis and antitumor activity of pyrano[3,2-i]-fused camptothecin derivatives

A novel series of A-ring modified hexacyclic camptothecin derivatives containing a pyranone ring fused at the 9-positions and 10-positions were designed and synthesized. These new derivatives were screened against four human tumor cell lines and the results showed most of the compounds possessed comparable cytotoxicity to 10-hydroxycamptothecin (HCPT) in vitro. The pyranono-fused derivatives, except for the one with methoxyformyl group at 4′-position (12), displayed similar inhibitory efficiency to saturated dihydropyrano-fused camptothecins (6 and 7) and superior cytotoxic activity compared with topotecan (TPT). These results indicated that the saturated and unsaturated fused-pyran rings would not disrupt the base-stacking between camptothecins and the DNA base pair, as well as the interactions between the compounds and Topoisomerase I.