D2 dopaminergic and 5-HT1A serotonergic activity of 2-(1-naphthyl)ethyl- and 2-(2-naphthyl)ethyl amines.

Several tertiary 2-phenylethyl, 2-(1-naphthyl)ethyl and 2-(2-naphthyl)ethyl amines were synthesized and their binding affinities for dopamine D(1), D(2) and serotonin 5-HT(1A) receptors evaluated in radioligand binding assays. All compounds were inactive in D(1) dopamine radioligand binding assay. The 2-(1-naphthyl)ethyl analogues expressed a low but significant binding affinity for the D(2) and moderate one for the 5-HT(1A) receptor subtypes. Most of the remaining compounds expressed binding affinity at the 5-HT(1A) receptor subtype but were inactive in D(2) receptor binding assay. Based on these results and considering the chemical characteristics of the compounds synthesized and evaluated for dopaminergic and serotonergic activity throughout the present study it can be concluded that hydrophobic type of interaction (stacking or edge-to-face) plays a significant role in the formation of receptor-ligand complexes of 2-(1-naphthyl)ethyl amines. This structural motive can be applied to design and synthesize new, more potent dopaminergic/serotonergic ligands by slight chemical modifications.

Investigation of mixed D2/5-HT1A activity of N-heteroarylmethyl-N-phenylpiperazines, N-heteroarylethyl-N-phenylpiperazines and N-heteroarylpropyl-N-phenylpiperazines.

Eight novel N-heteroarylalkyl-N-phenylpiperazines have been synthesized, chemically characterized and evaluated for in vitro binding affinity at the dopamine and serotonin receptors. Synaptosomal membranes of fresh bovine caudate nuclei (D1 and D2), the membranes of COS-7 cells (D4.4) and those prepared from fresh bovine hippocampi (5-HT1A) were used as a source of the corresponding receptor subtypes. [3H]SCH 23390 (D1-selective), [3H]spiperone (D2- and D4.4-selective) and [3H]-8-OH-DPAT (5-HT1A-selective) served as radioligands. None of the compounds expressed the affinity for the binding at the D1 subtype receptor. Compounds 7-9 containing a single methylene group serving as a bridge between heteroaryl- and N-phenylpiperazine part of the molecule were inactive [3H]spiperone and [3H]-8-OH-DPAT competitors. Ligands 15-19 (three methylene groups connecting heteroaryl- and N-phenylpiperazine part of the molecule) acted as moderate competitors of [3H]spiperone binding at the D2 receptor subtype, with the exception of 15 (a thione) which expressed a high binding affinity at the D2 receptor subtype. Compounds 15-19 behaved as moderate displacers of 8-OH-[3H]DPAT. Among all eight novel ligands only compound 15 expressed a moderate binding affinity at the D4.4 receptor subtype.

Introduction of a methyl group in alpha- or beta-position of 1-heteroarylethyl-4-phenylpiperazines affects their dopaminergic/serotonergic properties.

1-(2-Heteroarylalkyl)-4-phenylpiperazines containing methyl group in either the alpha- or the beta-position of the side alkyl chain were synthesized as racemic mixtures. They were evaluated for in vitro binding affinity at the D1 and D2 dopamine and 5-HT1A serotonin receptors using synaptosomal membranes of the bovine caudate nucleus and hippocampus, respectively, as a source of the corresponding receptors. Tritiated SCH 23390 (D1 receptor-selective), spiperone (D2 receptor-selective), and 8-OH-DPAT (5-HT1A receptor-selective) were employed as the radioligands. None of the new compounds expressed significant affinity for the D1 receptor. Introduction of the methyl group into the beta-position of the parent molecules increased the affinity for the D2 receptor (10b-13b), and decreased the affinity for the 5-HT1A receptor with the exception of imidazole (11b) which was a rather efficient displacer of 8-OH-DPAT. Most potent of the newly synthesized compounds in [3H]spiperone assay were compounds (+/-)6-[1-methyl-2- (4-phenylpiperazin-1-yl)-ethyl]-1,4-dihydroquinoxaline-2,3-dione (10b), Kd = 6.0 nM and (+/-)5-[1-methyl-2-(4-phenylpiperazin-1-yl)-ethyl]-1,3-dihydrobenzoimidazol- 2-thione (13b), Kd = 5.3 nM. However, compounds containing methyl group in alpha-position (10a-13a) of the parent molecules expressed a decreased affinity for the D2 receptor, while the affinity for the 5-HT1A receptor remained in the same range of concentrations as that of closely related achiral parent compounds (14-17) run in the same binding assays as references.

New substituted 2-methylthiomethyl- and 2-methylsulphinylmethylenebenzimidazoles with D2/5-HT1A activity.

Several 2-methylthiomethylbenzimidazoles (3a-e) and the corresponding sulphinyl derivatives 4a-e were synthesized and evaluated measuring their in vitro binding affinity at the D1 and D2 dopamine (source: synaptosomal membranes of the bovine nucleus caudatus) and 5-HT1A serotonin (source: synaptosomal membranes of the bovine hippocampus) receptors. [3H]SCH 23390, [3H]spiperone, and [3H]-8-OH-DPAT were employed as specific radioligands for the D1, D2 and 5-HT1A receptors, respectively. None of the compounds except for 3b acting as a moderate [3H]SCH 23390, competitor, expressed binding affinity at the D1 receptor. Compounds 4a and 4e were inactive displacers of both [3H]spiperone and [3H]-8-OH-DPAT. Ligands 4b, 3d and 4d acted as weak to moderate [3H]spiperone competitors and 3a was a weak [3H]-8-OH-DPAT displacer. The remaining ligands expressed binding affinity at the corresponding receptors in a nanomolar concentration range. Among them, compound 3b with Ki of 14.2 nM and 8.4 nM in [3H]spiperone and [3H]-8-OH-DPAT binding assay, respectively, was the most potent mixed dopaminergic/serotonergic ligand. Although sterically similar, the two classes of ligands differ with regard to electronic properties of substituents in position 2 of the benzimidazole ring. Oxidation of 2-(methylthiomethyl)benzimidazoles afforded ligands devoid of binding affinity at the 5-HT1A receptor and significantly reduced binding affinity at the D2 receptor. This points to the importance of electronic properties of substituents in position 2 of benzimidazole ring for the D2/5-HT1A affinity ratio of this type of ligands.

Mixed dopaminergic/serotonergic properties of several 2-substituted 4-[2-(5-benzimidazole)ethyl]-1-arylpiperazines.

A series of substituted 4-[2-(5-benzimidazole)ethyl]-arylpiperazines was synthesized by introducing different substituents into position 2 of benzimidazole ring of 4-[2-(N,N-di-n-propyl-amino)ethyl]-1, 2-diaminobenzenes. They were evaluated for in vitro binding affinity at the D1 and D2 dopamine and 5-HT1A serotonin receptors using synaptosomal membranes of the bovine caudate nuclei and hippocampi, respectively. Tritiated SCH 23390 (D1 receptor-selective), spiperone (D2 receptor selective) and 8-OH-DPAT (5-HT1A receptor selective) were employed as the radioligands. Only compound 6 expressed a moderate binding affinity at the dopamine D1 receptor, while the remaining ligands were inefficient or weak competitors of [3H]SCH 23390. Compound 12 was an absolutely inactive competitor of all three radioligands. Also, compound 7 was an inefficient displacer of [3H]-8-OH-DPAT. Compound 19 with a Ki value of 3.5 nM was the most potent competitor of [3H]spiperone and compound 13 (Ki = 3.3 nM) was the most efficient in displacing [3H]-8-OH-DPAT from the 5-HT1A serotonin receptor. Ligands 5,6,8-11, and 13-20 expressed mixed dopaminergic/serotonergic activity in nanomolar range of concentrations with varying affinity ratios which strongly depended on the properties of the substituents introduced into position 2 of benzimidazole ring of the parent compounds.

Synthesis of several substituted phenylpiperazines behaving as mixed D2/5HT1A ligands.

Twenty-two different compounds have been synthesized with the aim of creating new, mixed D2/5HT1A ligands. For this purpose 1-substituted phenylpiperazines attached by the N-4 nitrogen to dopaminergic pharmacophores of the 2-(5-benzimidazole)ethyl-, 2-(5-benztriazole)ethyl-, 2-[5-(benzimidazole-2-thione)]ethyl- and 2-[6-(1,4-dihydroquinoxaline-2,3-dione)]ethyl-type were selected according to known structure-affinity requirements of 1-arylpiperazines. All the new compounds were evaluated for in-vitro binding affinity at the dopamine (D1 and D2) and 5-HT1A receptors. Synaptosomal membranes prepared from fresh bovine caudate nuclei and hippocampi were used as a source of dopamine and 5-hydroxytryptamine receptors, respectively. [3H]SCH 23390 (D1 selective), [3H]spiperone (D2 selective) and 8-OH-[3H]DPAT (5-HT1A selective) were employed as the radio-ligands. None of the compounds expressed affinity for binding at D1 dopamine receptors. Compounds 3b and 4b were inactive 8-OH-[3H]DPAT competitors whereas 1b, 2b and 4b were inactive in the [3H]spiperone-binding assay. The other compounds tested showed fair (1c, 1e, 1f, 2c, 2f, 3b, 3c and 4c) to high (1a, 1d, 2a, 1d, 3a, 3d-3f, 4a, and 4d) affinity in the [3H]spiperone-binding assay, the most potent representative being 4-[2-(5-benzimidazole-2-thione)ethyl]-1-(2-methoxyphenyl)piperazine, 3a (Ki = 1.7 nM). In the 8-OH-[3H]DPAT-displacement assay compounds 1b, 1d, 1f, 2b, 2f and 3f behaved as moderate competitors and 1a, 1c, 1e, 2a, 2c, 2d, 3a, 3c-3e, 4a, 4c, 4d and 4f as rather strong competitors; 4-[2-(5-benztriazole)ethyl]-1-(2-methoxyphenyl)piperazine, 2a had the highest binding affinity at the 5-HT1A receptors (Ki = 2.6 nM). Because many antipsychotic and anxiolytic agents behave as mixed dopaminergic and serotonergic ligands, the high affinity of several of these new ligands for binding at both D2 and 5-HT1A receptors make them promising candidates deserving further pharmacological evaluation as antipsychotic or anxiolytic pharmaceuticals.

Synthesis and dopaminergic properties of 3- and 4-substituted 1-[2-[5-(1H-benzimidazole-2-thione)]ethyl]piperidines and related compounds.

With an aim of creating new, high affinity dopaminergic ligands, six different 3- and 4-substituted 1-[2-[5-(1H-benzimidazole-2-thione)] ethyl]piperidines and nine related heterocyclic congeners were synthesized and evaluated for in vitro binding affinity at D1 and D2 dopamine receptors. Synaptosomal membranes prepared from fresh bovine caudate nuclei were used as a source of the dopamine receptors. Only 4-[bis-(4-fluorophenyl)methylene]-piperidines, compounds 9e, 10d, and 11d, expressed moderate affinity for the D1 receptors, while all other compounds were inactive competitors of [3H]SCH 23390. Compounds 9c, 9d, 10c, 11a, and 11c were inactive in the D2 receptor binding assay, as well. Derivatives of 4-phenylpiperidine (9-11b) and 3-phenylpiperidine (10a) expressed a moderate to low affinity for the D2 receptors. However, racemic (+/-)-1-[2-[5-(1H-benzimidazole-2-thione)] ethyl]-3-phenylpiperidine 9a and its enantiomer (+)-9a behaved as selective, high affinity D2 receptor ligands, the latter being some four times more active than the racemate.