2-[(4-Phenylpiperazin-1-yl)methyl]imidazo(di)azines as Selective D<sub>4</sub>-Ligands. Induction of Penile Erection by 2-[4-(2-Methoxyphenyl)piperazin-1-ylmethyl]imidazo[1,2-<i>a</i>]pyridine (PIP3EA), a Potent and Selective D<sub>4</sub> Partial Agonist
novel 2-[(4-phenylpiperazin-1-yl)methyl]imidazoazines and aza-analogues were prepared and screened at selected dopamine, serotonin, and adrenergic receptor subtypes. 2-Substituted imidazopyridines and pyridazines presented high affinities and selectivities for D4dopamine receptors. Whereas functional experiments indicated neutral antagonists or weak partial agonist effects for most of the target compounds