Morphinan

Morphinans are a chemical class of organic compounds built on a fused tetracyclic carbon skeleton derived from the morphine framework, including a partially hydrogenated phenanthrene core with a nitrogen-containing ring bridged across it. Members differ by which oxygen-bearing groups sit on the rings, by the presence or absence of an oxygen bridge linking two rings, and by the substituent on the nitrogen. Most morphinans act at opioid receptors, functioning as analgesics, though the exact profile ranges from full agonists to antagonists. The morphine molecule itself, along with codeine and many semi-synthetic opioids, is a variation on this shared rigid scaffold.