OBJECTIVE: Demand for new antidepressants has resulted in a re-evaluation of the therapeutic potential of psychedelic drugs. Several tryptamines found in psilocybin-containing \"magic\" mushrooms share chemical similarities with psilocybin. Early work suggests they may share biological targets. However, few studies have explored their pharmacological and behavioural effects.
METHODS: We compared baeocystin, norbaeocystin and aeruginascin with psilocybin to determine if they are metabolized by the same enzymes, similarly penetrate the blood-brain barrier, serve as ligands for similar receptors and modulate behaviour in rodents similarly. We also assessed the stability and optimal storage and handling conditions for each compound.
RESULTS: In vitro enzyme kinetics assays found that all compounds had nearly identical rates of dephosphorylation via alkaline phosphatase and metabolism by monoamine oxidase. Further, we found that only the dephosphorylated products of baeocystin and norbaeocystin crossed a blood-brain barrier mimetic to a similar degree as the dephosphorylated form of psilocybin, psilocin. The dephosphorylated form of norbaeocystin was found to activate the 5-HT2A receptor with similar efficacy to psilocin and norpsilocin in in vitro cell imaging assays. Behaviourally, only psilocybin induced head twitch responses in rats, a marker of 5-HT2A-mediated psychedelic effects and hallucinogenic potential. However, like psilocybin, norbaeocystin improved outcomes in the forced swim test. All compounds caused minimal changes to metrics of renal and hepatic health, suggesting innocuous safety profiles.
CONCLUSIONS: Collectively, this work suggests that other naturally occurring tryptamines, especially norbaeocystin, may share overlapping therapeutic potential with psilocybin, but without causing hallucinations.

Primary metabolites of mushroom tryptamines, psilocybin and baeocystin (i.e., psilocin and norpsilocin), exhibit potent agonist activity at the serotonin 2A receptor (5-HT2A) in vitro but differ in their 5-HT2A-mediated effects in vivo. In particular, psilocin produces centrally mediated psychedelic effects in vivo, whereas norpsilocin, differing only by the loss of an N-methyl group, is devoid of psychedelic-like effects. These observations suggest that the secondary methylamine group in norpsilocin impacts its central nervous system (CNS) bioavailability but not its receptor pharmacodynamics. To test this hypothesis, eight norpsilocin derivatives were synthesized with varied secondary alkyl-, allyl-, and benzylamine groups, primarily aiming to increase their lipophilicity and brain permeability. Structure-activity relationships for the norpsilocin analogues were evaluated using the mouse head-twitch response (HTR) as a proxy for CNS-mediated psychedelic-like effects. HTR studies revealed that extending the N-methyl group of norpsilocin by a single methyl group, to give the corresponding secondary N-ethyl analogue (4-HO-NET), was sufficient to produce psilocin-like activity (median effective dose or ED50 = 1.4 mg/kg). Notably, N-allyl, N-propyl, N-isopropyl, and N-benzyl derivatives also induced psilocin-like HTR activity (ED50 = 1.1-3.2 mg/kg), with variable maximum effects (26-77 total HTR events). By contrast, adding bulkier tert-butyl or cyclohexyl groups in the same position did not elicit psilocin-like HTRs. Pharmacological assessments of the tryptamine series in vitro demonstrated interactions with multiple serotonin receptor subtypes, including 5-HT2A, and other CNS signaling proteins (e.g., sigma receptors). Overall, our data highlight key structural requirements for CNS-mediated psychedelic-like effects of norpsilocin analogues.