Pharmacology of a new tritiated endomorphin-2 analog containing the proline mimetic cis-2-aminocyclohexanecarboxylic acid

► A new tritiated endomorphin-2 analog was synthesized in which Pro2 is replaced by 2-aminocyclohexanecarboxylic acid. ► It shows high specific radioactivity, μ-opioid receptor affinity, selectivity and enzymatic resistance. ► It is a good tool to envisage the distribution of μ-opioid receptors by using receptor autoradiography. ► It may be more suitable than the parent ligand for receptor-ligand interaction and topographic studies.