Further SAR in the new antitumor 1-amino-substituted gamma-carbolines and 5H-benzo[e]pyrido[4,3-b]indoles series.

Using previously described techniques, various new 1-amino-substituted 5H-pyrido[4,3-b]indoles (gamma-carbolines, gamma-C) and 5H-benzo[e]pyrido[4,3-b]indoles (BPI) have been synthesized and evaluated. For known compounds containing a 1-[(dimethylamino)propyl] group, 1a and 1b in the gamma-C series and 2 in the BPI series are the most active. Studies with newly synthesized derivatives show that: (i) in the gamma-C series, the 4-unsubstituted-8-hydroxy-compound was inactive, whereas the 4-unsubstituted-9-hydroxy-5H-benzo[e]pyrido[4,3-b]indole is active; (ii) the 4-ethyl-8-hydroxy-5H-pyrido[4,3-b]indole derivative retains antitumor properties, but the 1-amino-substituted 4-ethyl-9-hydroxy-5H-benzo[e]pyrido[4,3-b]indole analog is devoid of biological activity; (iii) in the 5H-benzo[e]pyrido[4,3-b]indole series, the displacement of a hydroxyl group from the 9- to 10-position leads to inactive compounds. Based on the structural analogies, these results were unexpected because the same substituents on the 4-position lead to different biological properties in the two series.