Structure-Activity Relationships for Psilocybin, Baeocystin, Aeruginascin, and Related Analogues to Produce Pharmacological Effects in Mice.

4-Phosphoryloxy- N , N -dimethyltryptamine (psilocybin) is a naturally occurring tertiary amine found in many mushroom species. Psilocybin is a prodrug for 4-hydroxy- N , N -dimethyltryptamine (psilocin), which induces psychedelic effects via agonist activity at the serotonin (5-HT) 2A receptor (5-HT _2A ). Several other 4-position ring-substituted tryptamines are present in psilocybin-containing mushrooms, including the secondary amine 4-phosphoryloxy- N -methyltryptamine (baeocystin) and the quaternary ammonium 4-phosphoryloxy- N , N , N -trimethyltryptamine (aeruginascin), but these compounds are not well studied. Here, we investigated the structure-activity relationships for psilocybin, baeocystin, and aeruginascin, as compared to their 4-acetoxy and 4-hydroxy analogues, using in vitro and in vivo methods. Broad receptor screening using radioligand binding assays in transfected cells revealed that secondary and tertiary tryptamines with either 4-acetoxy or 4-hydroxy substitutions display nanomolar affinity for most human 5-HT receptor subtypes tested, including the 5-HT _2A and the serotonin 1A receptor (5-HT _1A ). The same compounds displayed affinity for 5-HT _2A and 5-HT _1A in mouse brain tissue in vitro and exhibited agonist efficacy in assays examining 5-HT _2A -mediated calcium mobilization and β-arrestin 2 recruitment. In mouse experiments, only the tertiary amines psilocin, psilocybin, and 4-acetoxy- N , N -dimethyltryptamine (psilacetin) induced head twitch responses (ED ₅₀ 0.11-0.29 mg/kg) indicative of psychedelic-like activity. Head twitches were blocked by 5-HT _2A antagonist pretreatment, supporting 5-HT _2A involvement. Both secondary and tertiary amines decreased body temperature and locomotor activity at higher doses, the effects of which were blocked by 5-HT _1A antagonist pretreatment. Across all assays, the pharmacological effects of 4-acetoxy and 4-hydroxy compounds were similar, and these compounds were more potent than their 4-phosphoryloxy counterparts. Importantly, psilacetin appears to be a prodrug for psilocin that displays substantial serotonin receptor activities of its own.
Competing Interests: The authors declare the following competing financial interest(s): A.R.C. has an ownership stake in CaaMTech, Inc., which owns patent applications covering new tryptamine compounds, their compositions, formulations, novel crystalline forms, methods of treatment, and methods for synthesis. No other authors report any competing financial interests related to the present work.
(© 2022 American Chemical Society.)