A bivalent ligand (KDAN-18) containing δ-antagonist and k-agonist pharmacophores bridges δ2 and k1 opioid receptor phenotypes

To characterize delta- and kappa-opioid receptor phenotypes, bivalent ligands (KDAN series) containing delta-antagonist (naltrindole) and kappa(1)-agonist (ICI-199,441) pharmacophores were synthesized and evaluated by the intrathecal route using the mouse tail-flick assay and binding studies. The data have suggested that KDAN-18 (2) bridges phenotypic delta(2)- and kappa(1)-receptors. A conceptual model is presented to explain the organizational differences between the opioid receptors that give rise to the phenotypes (delta(1), delta(2), kappa(1), kappa(2)).