The carcinogenicity of two diazadibenzopyrenes.

1,12-Diazadibenzo(a,i)pyrene (I), an isostere of the extremely potent carcinogen dibenzo(a,i)pyrene, also displays carcinogenicity although to a considerably lesser degree than the latter compound. While dibenzo(a,h)pyrene is known to be distinctly less active than dibenzo(a,i)pyrene, surprisingly 4,11-diazadibenzo(a,h)pyrene (II) shows a greater activity than I. Another hexacyclic diaza-hydrocarbon, 4,12-diazadibenzo(g,p)chrysene (III), which is devoid of a meso-phenanthrenic region, proved totally inactive.