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-HT2A). 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-HT2A and the serotonin 1A receptor (5-HT1A). The same compounds displayed affinity for 5-HT2A and 5-HT1A in mouse brain tissue in vitro and exhibited agonist efficacy in assays examining 5-HT2A-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 (ED50 0.11–0.29 mg/kg) indicative of psychedelic-like activity. Head twitches were blocked by 5-HT2A antagonist pretreatment, supporting 5-HT2A involvement. Both secondary and tertiary amines decreased body temperature and locomotor activity at higher doses, the effects of which were blocked by 5-HT1A 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.

Analogues of 4-phosphoryloxy-N,N-dimethyl­tryptamine (psilocybin) are being sold on recreational drug markets and developed as potential medications for psychedelic-assisted therapies. Many of these tryptamine-based psilocybin analogues produce psychedelic-like effects in rodents and humans primarily by agonist activity at serotonin 2A receptors (5-HT2A). However, the comprehensive pharmacological target profiles for these compounds compared to psilocybin and its active metabolite 4-hydroxy-N,N-dimethyl­tryptamine (psilocin) are unknown. The present study determined the receptor binding profiles of various tryptamine-based psychedelics structurally related to psilocybin across a broad range of potential targets. Specifically, we examined tryptamine psychedelics with different 4-position (hydroxy, acetoxy, propionoxy) and N,N-dialkyl (dimethyl, methyl-ethyl, diethyl, methyl-propyl, ethyl-propyl, diisopropyl, methyl-allyl, diallyl) substitutions. Further, the psilocybin analogue 4-propionoxy-N,N-dimethyl­tryptamine (4-PrO-DMT) was administered to mice in experiments measuring head twitch response (HTR), locomotor activity, and body temperature. Overall, the present pharmacological profile screening data show that the tryptamine psychedelics target multiple serotonin receptors, including serotonin 1A receptors (5-HT1A). 4-Acetoxy and 4-propionoxy analogues of 4-hydroxy compounds displayed somewhat weaker binding affinities but similar target profiles across 5-HT receptors and other identified targets. Additionally, differential binding screen profiles were observed with N,N-dialkyl position variations across several non-5-HT receptor targets (i.e., alpha receptors, dopamine receptors, histamine receptors, and serotonin transporters), which could impact in vivo pharmacological effects of the compounds. In mouse experiments, 4-PrO-DMT displayed dose-related psilocybin-like effects to produce 5-HT2A-mediated HTR (0.3–3 mg/kg s.c.) as well as 5-HT1A-mediated hypothermia and hypolocomotion (3–30 mg/kg s.c.). Lastly, our data support a growing body of evidence that the 5-HT2A-mediated HTR induced by tryptamine psychedelics is attenuated by 5-HT1A receptor agonist activity at high doses in mice.

The title compound, baeocystin or 4-phosphoryloxy-N-methyltryptamine {systematic name: 3-[2-(methylazaniumyl)ethyl]-1H-indol-4-yl hydrogen phosphate}, C11H15N2O4P, has a single zwitterionic molecule in the asymmetric unit. The molecule has an intramolecular N—H...O hydrogen bond between the ammonium cation and the hydrophosphate anion. In the crystal, the molecules are linked by N—H...O and O—H...O hydrogen bonds into a three-dimensional network.

The title compound, 4-hydroxy-N-isopropyltryptamine (4) or 4-HO-NiPT (systematic name: 3-{2-[(propan-2-yl)amino]ethyl}-1H-indol-4-ol), C13H18N2O, was synthesized in three steps from 4-benzyloxyindole (1) (systematic name: 4-phenoxy-1H-indole), C15H13NO. (1) was treated with oxalyl chloride and isopropylamine to produce N-isopropyl-4-benzyloxy-3-indoleglyoxylamide (2) {systematic name: 2-[4-(benzyloxy)-1H-indol-3-yl]-2-oxo-N-(propan-2-yl)acetamide}, C20H20N2O3. (2) was reduced to generate 4-benzyloxy-N-isopropyltryptamine (3) or 4-HO-NiPT, which was characterized as its chloride salt 4-benzyloxy-N-isopropyltryptammonium chloride (3a) (systematic name: {2-[4-(benzyloxy)-1H-indol-3-yl]ethyl}(propan-2-yl)azanium chloride), C20H25N2O·Cl. Finally the benzyl group of (3) was removed via hydrogenation to generate 4-HO-NiPT. The crystal structures of the title compound and all three synthetic precursors are presented.

The solid-state structures of two solvated forms of 4-glutarato-N,N-diisopropyltryptamine were determined by single-crystal X-ray diffraction, namely, 5-[(3-{2-[bis(propan-2-yl)azaniumyl]ethyl}-1H-indol-4-yl)oxy]-5-oxopentanoate methanol monosolvate, C21H30N2O4·CH3OH, and the analogous ethanol monosolvate, C21H30N2O4·C2H6O. In both compounds, the 4-glutarato-N,N-diisopropyltryptamine exists as a zwitterion with a protonated tertiary ammonium and a deprotonated glutarato carboxylate. The tryptamine zwitterions and alcohol solvates in both structures combine to produce near identical hydrogen-bonding networks, with N—H...O and O—H...O hydrogen bonds joining the molecules together in two-dimensional networks parallel to the (100) plane.

The title compound, bis(oxotremorine) fumarate bis(fumaric acid) {systematic name: 1-[4-(2-oxopyrrolidin-1-yl)but-2-ynyl]pyrrolidinium (2E)-but-2-enedioate bis[(2E)-but-2-enedioic acid]}, 2C12H19N2O+·C4H2O4 2−·2C4H4O4, has a single oxotremorine monocation protonated at the pyrrolidine nitrogen, one fumaric acid molecule and half of a fumarate dianion in the asymmetric unit. The ions and fumaric acid molecules are held together by N—H...O and O–H-...O hydrogen bonds in 40-membered rings with graph-set notation R 6 6(40). The fumarate ions join these rings into infinite chains along [001].

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The title compound, serotonin or 5-hydroxytryptamine (5-HT) [systematic name: 3-(2-aminoethyl)-1H-indol-5-ol], C10H12N2O, has one molecule in the asymmetric unit. The conformation of the ethylamino side chain is gauche–gauche [Ca—Ca—Cm—Cm and Ca—Cm—Cm—N (a = aromatic, m = methylene) torsion angles = −64.2 (3) and −61.9 (2)°, respectively]. In the crystal, the molecules are linked into a three-dimensional network by N—H...O and O—H...N hydrogen bonds.