Quaternary tryptammonium salts: N,N-dimethyl-N-n-propyltryptammonium (DMPT) iodide and N-allyl-N,N-dimethyltryptammonium (DMALT) iodide

The solid-state structures of two quaternary tryptammonium salts, N,N-dimethyl-N-n-propyltryptammonium (DMPT) iodide and N-allyl-N,N-dimethyltryptammonium (DMALT) iodide are reported.


Chemical context
Quaternary tryptammonium salts have been observed in nature going back to 1934 when bufotenidine, the N-trimethyl analogue of serotonin, was discovered in the excretions of toads (Wieland et al., 1934). The unsubstituted N,N,N-trimethyltryptammonium iodide was studied in 1936 and demonstrated nicotine-stimulating action (Lee et al., 1936). In 1987, Gartz first identified a quaternary tryptammonium in 'magic mushrooms' when he isolated aeruginascin, N,N,Ntrimethyl-4-phosphoryloxytryptamine (Gartz, 1987). The tryptamines of 'magic mushrooms' have garnered a great deal of interest of late as their psychotropic activity is being explored for the treatment of mental disorders including depression and anxiety (Johnson & Griffiths, 2017;Daniel & Haberman, 2017). Aeruginascin, in particular, has been featured in popular media for its potential to modulate the activity of psilocybin through an entourage effect (Farah, 2018), as well as its possible involvement in wood-lovers paralysis (Revell, 2020). The recent synthesis of aeruginascin (Sherwood, et al. 2020) and its active metabolite, 4-hydroxy-N,N,N-trimethyltryptamine (Chadeayne, Pham, Reid et al., 2020), as well as the biosynthetic production of both (Milne et al., 2020) further demonstrate the attention that these molecules have received. To this end, we sought to explore new quaternary tryptammonium salts, and the syntheses and structures of N,N-dimethyl-N-n-propyltryptammonium (DMPT) iodide and N-allyl-N,N-dimethyltryptammonium (DMALT) iodide are reported.

Structural commentary
The molecular structure of DMPT iodide is shown on the left of Fig. 1. The asymmetric unit contains one N,N-dimethyl-N-npropyltryptammonium (C 15 H 23 N 2 + ) cation and one iodide anion. The indole ring of the cation is near planar, with a mean deviation from planarity of 0.011 Å . The ethylammonium arm is turned away from the plane with a C7-C8-C9-C10 torsion angle of 89.1 (4) . The molecular structure of DMALT iodide is shown on the right of Fig. 1. The asymmetric unit contains one N-allyl-N,N-dimethyltryptammonium (C 15 H 21 N 2 + ) cation and one iodide anion. The indole ring of the cation is near planar, with a mean deviation from planarity of 0.013 Å . The ethylammonium arm is turned away from the plane with a C7-C8-C9-C10 torsion angle of 101.8 (10) . The allyl group is disordered over two orientations with a 0.30 (4) to 0.70 (4) occupancy ratio for C14, C15 and C14A, C15A, respectively.

Supramolecular features
The DMPT cation and the iodide anion are held together in the asymmetric unit via N1-H1Á Á ÁI1 hydrogen bonds, between the indole nitrogen and the iodide ( Table 1). The packing of DMPT iodide is shown at the left of Fig. 2. The DMALT structure is very similar to that of DMPT, possessing a very similar unit cell with half of the volume. The cation and anion are held together in the asymmetric unit through N1-H1Á Á ÁI1 hydrogen bonds ( Table 2). The packing of DMALT iodide is shown on the right of Fig. 2

Figure 2
The crystal packing of DMPT iodide (left), viewed along the a axis, and the crystal packing of DMALT iodide (right), viewed 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 bonds are omitted for clarity. Only one component of the allyl disorder is shown in the DMALT structure. Table 2 Hydrogen-bond geometry (Å , ) for DMALT.

2-(1H-Indol-3-yl)-N,N-dimethyl-N-propylazanium iodide (DMPT)
Crystal data 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.