2,4-Diaryl-5,6-dihydro-1,10-phenanthroline and 2,4-diaryl-5,6-dihydrothieno[2,3-h] quinoline derivatives for topoisomerase I and II inhibitory activity, cytotoxicity, and structure-activity relationship study

► Thirty-two conformationally constrained phenanthrolines and dihydrothienoquinolines were synthesized. ► Prepared compounds were evaluated for topo I and II inhibitors, and cytotoxicity. ► Compounds 33 and 35 displayed significant topo I inhibitory activity. ► Compounds 10, 14, and 18 exhibited strong cytotoxicity. ► SAR exhibited that [2,2′;6′,2″]-terpyridine skeleton is important for cytotoxicity.