New substituted 2-methylthiomethyl- and 2-methylsulphinylmethylenebenz- imidazoles with D 2 /5-HT(1A) activity

Abstract

Several 2-methylthiomethylbenzimidazoles (3a-e) and the corresponding sulphinyl derivatives 4a-e were synthesized and evaluated measuring their in vitro binding affinity at the D 1 and D 2 dopamine (source: synaptosomal membranes of the bovine nucleus caudatus) and 5-HT(1A) serotonin (source: synaptosomal membranes of the bovine hippocampus) receptors. [ 3 H]SCH 23390, [ 3 H]spiperone, and [ 3 H]-8-OH-DPAT were employed as specific radioligands for the D 1 , D 2 and 5-HT(1A) receptors, respectively. None of the compounds except for 3b acting as a moderate [ 3 H]SCH 23390, competitor, expressed binding affinity at the D 1 receptor. Compounds 4a and 4e were inactive displacers of both [ 3 H]spiperone and [ 3 H]-8-OH-DPAT. Ligands 4b, 3d and 4d acted as weak to moderate [ 3 H]spiperone competitors and 3a was a weak [ 3 H]- 8-OH-DPAT displacer. The remaining ligands expressed binding affinity at the corresponding receptors in a nanomolar concentration range. Among them, compound 3b with K(i) of 14.2 nM and 8.4 nM in [ 3 H]spiperone and [ 3 H]-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-HT(1A) receptor and significantly reduced binding affinity at the D 2 receptor. This points to the importance of electronic properties of substituents in position 2 of benzimidazole ring for the D 2 /5-HT(1A) affinity ratio of this type of ligands.