Pharmacological studies with a nonpeptidic, delta-opioid (−)-(1R,5R,9R)-5,9-dimethyl-2′-hydroxy-2-(6-hydroxyhexyl)-6,7-benzomorphan hydrochloride ((−)-NIH 11082)

In the search for a selective delta-opioid receptor agonist, (−)-(1R,5R,9R)-5,9-dimethyl-2′-hydroxy-2-(6-hydroxyhexyl)-6,7-benzomorphan hydrochloride ((−)-NIH 11082) and the (+)-enantiomer were synthesized and tested. (−)-NIH 11082 displayed antinociceptive activity in the paraphenylquinone test (PPQ test) in male ICR mice [ED50 = 1.9 (0.7–5.3) mg/kg, s.c.] and showed little, if any, activity in the tail-flick and hot-plate assays. The (+)-enantiomer was essentially inactive indicating stereoselectivity. Opioid receptor subtype characterization studies indicated that naltrindole, a delta-opioid receptor antagonist, was potent versus the ED80 of (−)-NIH 11082 in the PPQ test [AD50 = 0.75 (0.26–2.20) mg/kg, s.c]. beta-Funaltrexamine and nor-binaltorphimine, selective mu- and kappa-receptor antagonists, respectively, were inactive versus the ED80 of (−)-NIH 11082. In rats with inflammation-induced pain, (−)-NIH 11082 produced antihyperalgesic effects that were attenuated by naltrindole. In morphine-dependent rhesus monkeys of both sexes, (−)-NIH 11082 neither substituted for morphine nor exacerbated withdrawal signs in the dose range of 4.0 to 32.0 mg/kg, s.c. Neither convulsions nor other overt behavioral signs were observed in any of the species tested. The results indicate that (−)-NIH 11082 has delta-opioid receptor properties.