Cyclorphan is an opioid analgesic of the morphinan family that was never marketed. It acts as a μ-opioid receptor (MOR) weak partial agonist or antagonist, κ-opioid receptor (KOR) full agonist, and, to a much lesser extent, δ-opioid receptor (DOR) agonist (75-fold lower affinity relative to the KOR). The drug was first synthesized in 1964 by scientists at Research Corporation.US Patent 3,285,922Varghese V & Hudlicky T. A Short History of the Discovery and Development of Naltrexone and Other Morphine Derivatives. Chapter 6 in Natural Products in Medicinal Chemistry, Volume 60 of Methods and Principles in Medicinal Chemistry. Ed. Stephen Hanessian. John Wiley & Sons, 2013. In clinical trials, it had relatively long duration, good absorption, and provided strong pain relief but produced psychotomimetic effects via KOR activation, so its development was not continued.
See also Butorphanol Levomethorphan Levorphanol Nalbuphine Oxilorphan Proxorphan Xorphanol
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