Synthesis and biological activities of topoisomerase I inhibitors, 6-N-amino analogues of NB-506

6-N-Amino analogues of NB-506 (3b) were synthesized and tested with respect to topoisomerase inhibition, cytotoxicity and anticancer effects. Among them, a 1,3-dihydroxypropane analogue (J-109,404, 5t) showed more than ten times more potent anticancer activity in MKN-45 human stomach cancer cells implanted in mice than NB-506. Abstract 6-N-Amino analogue of NB-506 [6-N-formylamino-12,13-dihydro-1,11-dihydroxy-13-(β-D-glucopyranosyl)-5H-indolo[2,3-a]pyrrolo[3,4-c]carbazole-5,7(6H)-dione] (3b), J-109,404 (5t), was found to be a more potent anticancer agent in MKN-45 human stomach cancer cells implanted in mice than NB-506.