Synthesis and biological evaluation of pyridazino[4,3-b]indoles and indeno[1,2-c]pyridazines as new ligands of central and peripheral benzodiazepine receptors

A large number of pyridazino[4,3-b]indoles and indeno[1,2-c]pyridazines were synthesised and tested to evaluate their binding affinities at both central (CBR) and peripheral (PBR) benzodiazepine receptors. Relatively good PBR binding affinities were found for ligands belonging to the 3-arylmethyloxy-pyridazinoindole series, whereas only 2-aryl-indenopyridazines 7a, 8a and 10a display a weak binding affinity for CBR. To find out the main structural determinants affecting PBR affinity, a molecular modelling study based on the comparative analysis of the three-dimensional properties of four properly selected derivatives 24a, 3b, 18a and 10d, with those of highly active and selective PBR ligands, taken as reference, was performed.