Geometrically constrained analogues of N-benzylindolylglyoxylylamides: [1, 2, 4]triazino[4, 3-a]benzimidazol-4(10H)-one derivatives as potential new ligands at the benzodiazepine receptor.

A series of 3-benzylamino-and 3-arylalkylaminocarbonyl [1, 2, 4]triazino [4, 3-a]benzimidazoles 1-12 were synthesized and biologically assayed as geometrically constrained analogues of N-benzylindolylglyoxylylamides II, which are high affinity ligands at the benzodiazepine receptor (BzR). The intermediate 3-ethoxycarbonyl [1, 2, 4]triazino [4, 3-a]benzimidazol-4(10H)-one 14 and its N(10)-methyl analogue 15 closely related to 3-alkoxycarbonyl-beta-carbolines I were also investigated. The title compounds exhibited a lower affinity compared with the corresponding indolylglyoxylylamide derivatives II. Attempts were made to rationalize these results taking into account the possible tautomeric equilibria involving these ligands.