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.
Salvinorin A, the active compound in the hallucinogenic herb Salvia divinorum, does not directly interact with the endocannabinoid system. Although some earlier studies suggested a link, this work shows that salvinorin A does not bind to or activate CB1 cannabinoid receptors. In laboratory tests, it caused reduced movement and pain relief, effects blocked by a kappa-opioid receptor antagonist but not by a CB1 antagonist. Salvinorin A also did not substitute for THC in drug discrimination tests. The results indicate that similarities between salvinorin A and cannabinoid effects stem from its activation of kappa-opioid receptors, and previous findings of CB1 antagonist reversal may be due to that antagonist also dampening kappa-opioid receptor activation.
Removing the C-1 ketone from salvinorin A and its analogue herkinorin changes their activity at opioid receptors. A derivative called 1-deoxo-1,10-dehydrosalvinorin A acts as a moderately potent antagonist at all three opioid receptor subtypes. Herkinorin, a mu opioid agonist, becomes a weak antagonist when its C-1 ketone is removed. These results indicate the C-1 ketone is a key structural feature for mu agonist activity.