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

In order to obtain possible veinotonic drugs acting through alpha2 receptor activation, we prepared clonidine analogues in which the 2-imino-imidazolidine was attached to various aliphatic or aromatic heterocycles. Among them, the two benzopyranic derivatives 16 and 22 exhibited interesting affinities (19 and 95 nM respectively on [3H]rauwolscine binding, compared to 35 nM for clonidine). Their affinity for alpha1 receptors was found to be much lower: 7570 and 5030 nM for 16 and 22 respectively, suggesting 16 to be 400 times more selective for alpha2 than for alpha1-adrenoceptors.