Synthesis of 6-substituted beta-carbolines that behave as benzodiazepine receptor antagonists or inverse agonists.

The synthesis of the first beta-carboline, 6-(benzylamino)-beta-carboline (1c), to be devoid of a substituent at the 3-position and that still binds to benzodiazepine receptors with potent affinity is described. Furthermore, 1c proved to be a partial inverse agonist when tested in mice. Addition of the benzylamino group at the 6-position of the beta-carboline nucleus is primarily responsible for the activity of beta-carbolines 1b and 1c. The importance of the Nb-nitrogen atom for binding affinity was also demonstrated since 3-(benzylamino)carbazole (6) exhibited little or no affinity for benzodiazepine receptors in vitro, in contrast to the activity of 1c.