Synthesis and alpha-adrenergic binding ligand affinities of 2-iminoimidazolidine derivatives

In order to obtain possible veinotonic drugs acting through alpha(2) recept or activation, we prepared clonidine analogues in which the 2-imino-imidazo lidine was attached to various aliphatic or aromatic heterocycles, Among th em, the two benzopyranic derivatives 16 and 22 exhibited interesting affini ties (19 and 95 nM respectively on [H-3]rauwolscine binding, compared to 35 nM for clonidine), Their affinity for alpha(1) receptors was found to be m uch lower: 7570 and 5030 nM for 16 and 22 respectively, suggesting 16 to be 400 times more selective for alpha(2) than for alpha(1)-adrenoceptors.