2-Aryl-2,5-dihydropyridazino[4,3-b]indol-3(3H)-ones: novel rigid planar benzodiazepine receptor ligands

Synthesis, central and peripheral benzodiazepine receptor affinity of pyrazole and pyrazole-containing polycyclic derivatives

A series of new pyrazole-condensed 6,5,5 tricyclic compounds were synthesized and tested to evaluate their binding affinities at both central (CBR) and peripheral (PBR) benzodiazepine receptors. Some 1-aryl-5-phenylpyrazole derivatives were also prepared and tested for comparison with their corresponding rigid tricyclic analogs. Among the newly synthesized 1-aryl-1,4-dihydro-indeno[1,2-c]pyrazoles bearing both an ethoxycarbonyl group at position 3 and a carbonyl function at the position 4, compound 4b emerged as a new potent (IC(50) = 26.4 nM) and selective CBR ligand. The 4-oxo-1-aryl-1,4-dihydro-indeno[1,2-c]pyrazole diethylamide derivative 14a was instead identified as a relatively potent (IC(50) = 124 nM) but highly selective PBR ligand.

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.

Synthesis and antibacterial activity of pyridazino[4,3-b]indole-4-carboxylic acids carrying different substituents at N-2

The synthesis and the in vitro evaluation of antibacterial activity of new pyridazino[4,3-b]indole-4-carboxylic acids 2-4, 6 against some selected representative of Gram-positive and Gram-negative bacteria are reported. The role of the lipophilicity in the modulation of the antibacterial activity of the tested compounds is discussed. All the synthesized compounds appear quite weak against Gram-positive bacteria, whereas have no significant activity against Gram-negative bacteria. Only derivative 2g possesses an interesting activity against Gram-positive bacteria.

High affinity central benzodiazepine receptor ligands. Part 2: quantitative structure-activity relationships and comparative molecular field analysis of pyrazolo[4,3-c]quinolin-3-ones

A large series of 2-aryl(heteroaryl)-2,5-dihydropyrazolo[4,3-c]quinolin-3(3H)-ones (PQ, 106 compounds), carrying appropriate substituents at the quinoline and N2-phenyl rings, were designed, prepared and tested as central benzodiazepine receptor ligands. Compounds with an affinity significantly higher than the parent compound CGS-8216 were obtained, the most active ligand showing a pIC50 = 10.35. Hansch and comparative molecular field analyses gave coherent results suggesting the main structural requirements of high receptor binding affinity. The possible formation of a three-centred hydrogen bond (HB) at the HB donor site H2, as a key interaction for high receptor binding affinity, was assessed by the calculation and comparison of the molecular electrostatic potentials of a series of selected ligands.

Benzodiazepine receptor affinities, behavioral, and anticonvulsant activity of 2-aryl-2,5-dihydropyridazino[4,3-b]indol- 3(3H)-ones in mice

The anticonvulsant properties of 1,4-benzodiazepines (BDZs), pyrazoloquinolones (CGS), 2-aryl-2,5-dihydropyridazino[4, 3-b]indol-3(3H)-ones (PIs) 1 1i 1d 1f 1e 1b 1c 1h, and 1a, the latter being inactive against audiogenic seizures. Some PIs 1 and abecarnil showed anticonvulsant properties against seizures induced by PTZ with a potency lower than that observed in audiogenic seizures. The pharmacological actions of 1d, 1f, and 1i were significantly reduced by a treatment with flumazenil (8.24 micromol/kg IP), suggesting a clear involvement of benzodiazepine mechanisms in the anticonvulsant activity of these compounds or their metabolites. The anticonvulsant activity of 1d, 1f, and 1i was also evaluated against seizures induced by two beta-carbolines namely methyl-beta-carboline-3-carboxylate (beta-CCM) and methyl-6, 7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), in DBA/2 mice: they gave better protection against seizures induced by beta-CCM than the ones by DMCM. The potency of various BDZs and PIs as inhibitors of specific [3H]flumazenil binding to neuronal membranes, was also evaluated. The radioligand binding study, carried out on stable cell lines expressing definite combinations of benzodiazepine receptor subunits, demonstrated that 1b, 1e, 1d, and 1h have preferential interaction with alpha(1), beta(3), gamma(2), receptor subtypes.

Synthesis and structure-affinity relationships at the central benzodiazepine receptor of pyridazino[4,3-b]indoles and indeno[1,2-c]pyridazines

A series of 2-aryl-3-chloro-2H-pyridazino[4,3-b]indoles, 2-aryl-3-methoxy-2H-pyridazino[4,3-b]indoles, and 2-aryl-2,5-dihydroindeno[1,2-c]pyridazino-3(3H)-ones has been prepared and tested for their ability to inhibit the [3H]flunitrazepam binding to the central benzodiazepine receptor. SAR are presented and discussed in comparison with existing pharmacophore models.

Synthesis and antibacterial activity of 2-aryl-2,5-dihydro-3(3H)-oxo-pyridazino[4,3-b]indole-4-carboxylic acids

The in vitro antibacterial and antifungal activities of a series of pyridazinoindolonic acids II against some selected representative of Gram-positive, Gram-negative bacteria and fungi have been investigated. Some interesting observations among the structural features necessary for high antibacterial activity are presented and discussed.

High affinity central benzodiazepine receptor ligands: synthesis and structure-activity relationship studies of a new series of pyrazolo[4,3-c]quinolin-3-ones

A large series of 2-aryl(heteroaryl)-2,5-dihydropyrazolo[4,3-c]quinolin- 3-(3H)-ones, carrying appropriate substituents at the quinoline and N2-phenyl rings, were prepared and tested as central benzodiazepine receptor ligands. Results from structure-affinity relationship studies were in full agreement with previously proposed pharmacophore models and, in addition, quantitative structure-activity analysis gave further significant insight into the main molecular determinants of high benzodiazepine receptor affinity. The intrinsic activity of some active ligands was also determined and preliminary discussed.

Structure-activity relationships of 2-aryl-2,5-dihydropyridazino [4,3-b]indol-3(3H)-ones at the benzodiazepine receptor

A large series of 2-aryl-2,5-dihydropyridazino[4,3-b]indol-3(3H)ones (PIs) carrying properly selected substituents at the indole and N2-phenyl rings was prepared and tested as central benzodiazepine receptor (BZR) ligands and potential (anti)convulsant agents. Stereoelectronic requirements for high receptor affinity were detected by means of 2-D and 3-D QSAR analyses. BZR affinities and pharmacological profiles of the compounds were examined in comparison with some other pyridazinoindolones recently described by us and with pyrazoloquinoline (PQ) analogues. An anticonvulsant activity greater than PQs was generally observed for PIs. Notably, in the test of audiogenically induced seizures, one compound showed a potency comparable to that of diazepam.