6N-Cinnamoyl-β-naltrexamine and its p-nitro derivative. High efficacy κ-opioid agonists with weak antagonist actions

6N-cinnamoyl-β-naltrexamine and its p-nitro derivative (7 and 8) are κ-opioid agonists of high potency and exceptional efficacy and are only weakly effective μ opioid antagonists. This contrasts with the p-methyl analogue which has only low efficacy κ-agonism but is a selective irreversible μ-antagonist like β-FNA.