Salvinorin A, a hallucinogenic compound that activates kappa-opioid receptors, also partially inhibits mu-opioid receptor binding through an allosteric mechanism. In cells expressing human mu-opioid receptors, salvinorin A reduced binding of two different radioligands (DAMGO and diprenorphine) in a dose-dependent, nonlinear way, altering both the number of binding sites and their affinity. It also slowed the dissociation of these ligands from the receptor and acted as an uncompetitive inhibitor of receptor signaling. Similar effects were observed in rat brain tissue. Together, these findings indicate that salvinorin A modulates the mu-opioid receptor allosterically, not by binding at the same site as typical opioids.
Salvinorin A, a hallucinogen from the plant Salvia divinorum, is unique as the first non-nitrogenous compound known to bind to opioid receptors. To understand why it selectively targets kappa opioid receptors, researchers systematically altered its structure and tested the effects on receptor binding and activity. This work describes chemical transformations of salvinorin A, including a semisynthesis of salvinicins A and B. It also identifies compound 10a as the first neoclerodane diterpene with delta opioid antagonist activity, providing new tools for studying opioid receptor interactions.