Norpsilocin: freebase and fumarate salt

The solid-state structure of the ‘magic mushroom’ natural product norpsilocin is reported, as well as the synthesis and structure of its fumarate salt.


Chemical context
Psychoactive tryptamines, particularly psilocybin and psilocin, have recently garnered a great deal of interest because of their potential to treat disorders including anxiety, addiction, and depression (Johnson & Griffiths, 2017;Carhart-Harris & Goodwin, 2017). Of note, psilocybin was recently granted the 'breakthrough therapy' designation by the US Food and Drug Administration (Feltman, 2019). To this point, the focus of research on psychedelics in therapy has largely been on psilocybin and psilocin. Despite this focus, there are more than 200 species of 'magic mushrooms' containing many different psychoactive tryptamines and combinations of the same (Stamets, 1996).
The clinical effects observed for extracts of 'magic mushrooms' differ from those observed for pure psilocybin (Zhuk, et al. 2015). This indicates that the minor components of 'magic mushrooms' have psychoactive properties that are important, or that they work in conjunction with psilocybin as part of an entourage effect (Russo, 2011). To have a better understanding of 'magic mushroom' pharmacology, it is necessary to understand the properties of the minor active components. This could lead to formulations that maximize the desired activity while minimizing negative effects, optimizing the clinical experience.
Baeocystin, the monomethyl analog of psilocybin, is the second most abundant naturally occurring tryptamine found in 'magic mushrooms'. It was first isolated from the mushroom Psilocybe baeocystis in 1968 (Leung & Paul, 1968), and subsequently identified in other species, approaching one third of the total tryptamine concentration. Like psilocybin, baeocystin acts as a prodrug when consumed by humans, undergoing rapid hydrolysis of the phosphate ester to afford its active metabolite -the 4-hydroxy analog.
The prodrug psilocybin hydrolyses to the active 4-hydroxy-N,N-dimethyltryptamine (4-HO-DMT), aka psilocin, and the prodrug baeocystin hydrolyses to the active 4-hydroxy-Nmethyltryptamine (4-HO-NMT), aka norpsilocin. Norpsilocin was first identified as a natural product of 'magic mushrooms' in 2017, and isolated as an amorphous, colorless solid (Lenz et al., 2017). In 2020, norpsilocin was synthesized and isolated as a white solid in 98% purity. When tested as an agonist at the human seratonin 2a receptor, synthetic norpsilocin was as potent, if not more so, compared to psilocin (Sherwood et al., 2020).
Despite rapidly growing evidence supporting psilocin/ psilocybin's potential for treating mood disorders, very little work has been done to investigate the properties of other structurally similar compounds found in magic mushrooms, e.g. norpsilocin/baeocystin. Although these compounds have substantial potential as drug candidates, they have undergone limited investigation because of their lack of availability in pure form and the difficulty of their purification. Crystalline solids are the most convenient and reliable chemical forms for studying, handling, and administering pure compounds. There was an unmet need for the structural characterization of norpsilocin, which is important in examining the structureactivity relationship of the psychedelic tryptamine. Herein, we report the first crystal structure of norpsilocin (I), and the first salt of norpsilocin (II) and its solid-state structure.

Structural commentary
The molecular structure of the freebase of norpsilocin, 4-HO-NMT, is shown in Fig. 1. The asymmetric unit contains one full 4-hydroxy-N-methyltryptamine (C 11 H 14 N 2 O) molecule. The ethylamine arm (C9-C10-N2-C11) of the tryptamine is modeled as a two-component disorder with a 0.895 (3) to 0.105 (3) occupancy ratio. The rest of the discussion is restricted to the major component. The indole ring system of the tryptamine is near planar with an r.m.s. deviation from planarity of 0.015 Å . The ethylamine arm of the tryptamine is slightly turned, with a C7-C8-C9-C10 torsion angle of 29.3 (3) . The C10-N2-C11 angle about the amine nitrogen is 113.51 (15) .
The molecular structure of the fumarate salt of norpsilocin is shown in Fig. 2. The asymmetric unit contains one full 4-hydroxy-N-methyltryptammonium (C 11   The molecular structure of 4-hydroxy-N-methyltryptamine, showing the atom labeling. Displacement ellipsoids are drawn at the 50% probability level. Dashed bonds indicate the minor occupancy disordered component in the structure.

Figure 2
The molecular structure of bis(4-hydroxy-N-methyltryptammonium)fumarate, showing the atom labeling. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen bonds are shown as dashed lines. Symmetry code: (i) 1 À x, Ày, 2 À z. tryptamine is near planar with an r.m.s. deviation from planarity of 0.009 Å . Unlike the freebase, the ethyl ammonium arm resides in the same plane as the indole. The planarity of all of the non-hydrogen atoms of the tryptamine is demonstrated with an r.m.s. deviation from planarity of only 0.043 Å . The C10-N2-C11 angle about the ammonium nitrogen is 114.20 (14) . The fumarate itself is also near planar, with an r.m.s. deviation from planarity of 0.050 Å . The carboxylate unit of the fumarate is delocalized, with C-O distances of 1.2488 (18) and 1.2553 (18) Å .

Figure 3
The hydrogen bonding (Table 2) of a fumarate ion in the structure of bis(4-hydroxy-N-methyltryptammonium)fumarate, with hydrogen bonds shown as dashed lines. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms not involved in hydrogen bonding are omitted for clarity. Symmetry codes: (i) 1 À x, Ày, 2 À z; (ii) 2 À x, 1 À y,

Figure 4
The crystal packing of (a) 4-HO-NMT, and of (b) bis(4-HO-NMT) fumarate, both shown along the a axis. The hydrogen bonds (Tables 1 and  2) are shown as dashed lines. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms not involved in hydrogen bonding are omitted for clarity. For (a) only one component of the disorder is shown.

Synthesis and crystallization
Single crystals suitable for X-ray analysis were obtained from the slow evaporation of an acetone solution of a commercial sample of 4-hydroxy-N-methyltryptamine (Angene).
The fumarate salt was synthesized starting with 101 mg of 4-hydroxy-N-methyltryptamine, which was dissolved in 10 mL of methanol. 62 mg of fumaric acid was added to the solution and it was stirred overnight under reflux. Solvent was removed in vacuo to yield a dark-blue powder. The powder was triturated with diethyl ether and then recrystallized in acetone to yield colorless crystals suitable for X-ray analysis. 1

sup-2
Acta Cryst. (2020). E76, 589-593 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.