Synthesis and Dopaminergic Properties of 3‐ and 4‐Substituted 1‐{2‐[5‐(1H‐Benzimidazole‐2‐thione)]ethyl}piperidines and Related Compounds

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Abstract
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‐phenyl‐piperidine (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.