Salvinorin A, a compound from the plant Salvia divinorum, binds strongly and selectively to the κ-opioid receptor (KOR). A new series of salvinorin A derivatives with reactive Michael acceptor groups at C-2 was created to explore how the compound interacts with the receptor. Most of these derivatives retained high affinity for KOR, and some also bound to the μ-opioid receptor (MOR). None showed wash-resistant irreversible binding. Using the KOR crystal structure, mutagenesis data, and other methods, the researchers identified possible ways the new compounds interact with both KOR and MOR.
The position of the hydroxyl group on the indole ring of psilocin analogs determines their ability to activate the 5-HT2A receptor and produce psychedelic-like effects. Analogs with the hydroxyl group at the 4th or 5th position (psilocin and bufotenine) show significantly higher agonistic activity and head-twitch responses than those with the group at the 6th or 7th position. Computer simulations reveal that the 4- and 5-position analogs form a crucial hydrogen bond with residue L229 and a stable salt bridge and hydrogen bond with residue D155, guiding them into the binding site. Analogs lacking these interactions fail to reach the orthosteric site and have poor receptor activity.