Synthesis and evaluation of N,N-di-n-propyl-5,6,7,8-tetrahydro-1 H-benz[f]benzimidazol-6-yl-amine and related congeners as dopaminergic ligands.

Four semirigid dopaminergic biosiosteres (N,N-di-n-propyl-5,6,7,8-tetrahydro-1 H-benz[f]benzimidazol-6-yl-amine [sequence: see text] and three related congeners) were synthesized and chemically characterized. The affinity and selectivity of these compounds for D-1 and D-2 classes of the dopamine receptor were determined in competition binding experiments using synaptosomal membranes of the bovine caudate nuclei and [3H]SCH 23390 (D-1 selective) and [3H]spiperone (D-2 selective) as radioligands. None of the four compounds tested expressed significant affinity for D-1 receptors and all of them competed moderately with [3H]spiperone binding to D-2 receptors under conditions that prevented radioligand binding to serotonin 5HT2 receptors. Some aspects of structure affinity relationship for this class of dopaminergic ligands are discussed.