Definition: Benzo-indoles similar to CARBOLINES which are pyrido-indoles. In plants, carbazoles are derived from indole and form some of the INDOLE ALKALOIDS.
NB 506 [ 6-N-formylamino-12,13-dihydro-1,11-dihydroxy-13-(beta-D-glucopyranosyl)-5H-indolo(2,3-a)pyrrolo(3,4-c)carbazole-5,7(6H)-dione,NB-506 ] an indolocarbazole antitumor agent; structure given in first source; a DNA topoisomerase I inhibitor