Psychedelic-like Activity of Norpsilocin Analogues

Psilocin, a metabolite of psilocybin, produces psychedelic effects in vivo, while norpsilocin, which differs by a single N-methyl group, does not. To explore this, eight norpsilocin derivatives with varied secondary amine groups were synthesized to increase lipophilicity and brain permeability. In mouse head-twitch response (HTR) studies, extending norpsilocin's N-methyl group to an N-ethyl group (4-HO-NET) produced psilocin-like activity (ED50 = 1.4 mg/kg). N-allyl, N-propyl, N-isopropyl, and N-benzyl derivatives also induced HTRs (ED50 = 1.1–3.2 mg/kg), with variable maximum effects (26–77 total HTR events). Bulky tert-butyl or cyclohexyl groups did not elicit psilocin-like HTRs. In vitro, these tryptamines interacted with multiple serotonin receptor subtypes and other CNS proteins.

Study at a glance

Abstract

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.