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-HT_1A 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-HAT_1A 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 K_i value of 3.5 nM was the most potent competitor of [³H]spiperone and compound 13 (K_i = 3.3 nM) was the most efficient in displacing [³H]-8-OH-DPAT from the 5-HAT_1A 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.