α2-Adrenoreceptors Profile Modulation and High Antinociceptive Activity of (S)-(−)-2-[1-(Biphenyl-2-yloxy)ethyl]-4,5-dihydro-1H-imidazole

A number of derivatives structurally related to cirazoline (1) were synthesized and studied with the purpose of modulating α2-adrenoreceptors selectivity versus both α1-adrenoreceptors and I2 imidazoline binding sites. The most potent α2-agonist was 2-[1-(biphenyl-2-yloxy)ethyl]-4,5-dihydro-1H-imidazole (7), whose key pharmacophoric features closely matched those found in the α2-agonist 2-(3-exo-(3-phenylprop-1-yl)-2-exo-norbornyl)amino-2-oxazoline (15). (S)-(−)-7 was the most potent of the two enantiomers, confirming the stereospecificity of the interaction with α2-adrenoreceptors. This eutomer was tested on two algesiometric paradigms and, because of the interaction with α2-adrenoreceptors, showed a potent and long-lasting antinociceptive activity, since it was abolished by the selective α2-antagonist RX821002.