Cyclorphan


Cyclorphan is an opioid analgesic of the morphinan family that was never marketed. It acts as a μ-opioid receptor weak partial agonist or antagonist, κ-opioid receptor full agonist, and, to a much lesser extent, δ-opioid receptor agonist. The drug was first synthesized in 1964 by scientists at Research Corporation. 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.