Structure–activity relationships of opioid ligands

There are three different types of opioid receptor, namely mu, delta and kappa. Morphine and related clinically useful analgesics exert their actions through the mu opioid receptor. Such compounds represent a huge structural diversity, including both peptides and alkaloids. Nevertheless, there exists a common pharmacophore comprising two critical features, namely an amine nitrogen and an aromatic ring, usually with a hydroxyl substituent; the spatial relationship between them is also vital. [Continues.]