Structural insights into tryptamine psychedelics: The role of hydroxyl indole ring site in 5-HT2A receptor activation and psychedelic-like activity.

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.

Study at a glance

Abstract

Recent advancements in the study of mushroom-derived tryptamines, particularly psilocybin and its metabolite psilocin, highlight their unique psychedelic properties and potential therapeutic applications, especially for mental health conditions like depression. This study examines how the position of the hydroxyl group on the indole ring affects the 5-HT2A receptor activity and psychedelic-like effects of psilocin analogs. Chemically synthesized psilocin (1) and its analogs bufotenine (2), 6-OH-DMT (3), and 7-OH-DMT (4) were assessed for 5-HT2A receptor agonistic activity using the Gαq-Gγ dissociation bioluminescence resonance energy transfer (BRET) assay and for psychedelic-like effects through the head-twitch response assay. Results show that compounds with hydroxyl group at the 4th and 5th positions exhibit significantly higher 5-HT2A agonistic and psychedelic-like activities than those with hydroxyl group at the 6th and 7th positions. Funnel metadynamics simulations revealed that psilocin (1) and bufotenine (2) have lower binding free energies, correlating with experimental data. Analysis of the simulation trajectories reveals that the formation of a hydrogen bond with residue L229 is crucial for guiding psilocin (1) and bufotenine (2) into the 5-HT2AR binding site. In contrast, analogs 3 and 4, which lack this interaction, fail to be directed into the orthosteric site. Furthermore, psilocin (1) and bufotenine (2) establish a stable salt bridge and hydrogen bond with residue D155. These interactions are more stable compared to those formed by ligands 3 and 4, contributing to the latter's poor 5-HT2AR activities. These findings underscore the critical role of the hydroxyl group position on the indole ring in modulating 5-HT2A receptor activity and the corresponding psychedelic-like effects, offering valuable insights for the development of targeted therapeutics.