Identification of Psychoplastogenic N, N-Dimethylaminoisotryptamine (isoDMT) Analogues through Structure-Activity Relationship Studies

Abstract

Ketamine, N,N-dimethyltryptamine (DMT), and other psychoplastogens possess enormous potential as neurotherapeutics due to their ability to potently promote neuronal growth. Here, we report the first-ever structure-activity relationship study with the explicit goal of identifying novel psychoplastogens. We have discovered several key features of the psychoplastogenic pharmacophore and used this information to develop N,N-dimethylaminoisotryptamine (isoDMT) psychoplastogens that are easier to synthesize, have improved physicochemical properties, and possess reduced hallucinogenic potential as compared to their DMT counterparts.

Figure 1.. Structure of compounds possessing the DMT pharmacophore.

(A) The DMT structure (highlighted in black) is the core scaffold of several known psychoplastogenic compounds. (B) The only difference between the chemical structures of DMT (1) and isoDMT (2) is that the C1 and C3 atoms of the indole are transposed. Predicted chemical properties and calculated MPO scores are shown. clogD = calculated log D; TPSA = total polar surface area; HBD = hydrogen bond donor; MPO = multiparameter optimization score.

Figure 2.. Substrate scope for the N-alkylation of various indoles with 3.

Percent yields following crystallization are indicated. Values in parentheses denote yields based on ¹H NMR spectra obtained after aqueous workup with indole serving as an internal standard. Note: fluoroindole was used as the internal standard when determining the yield of 2. An asterisk indicates that a compound was purified via chromatography.

Figure 3.. Neighboring group participation has a minimal impact on reaction performance.

(A) Hypothesized reactive aziridinium intermediate. (B) Reaction efficiency remains high when using alkylating agents that cannot form a reactive aziridinium intermediate. Percent yields following crystallization are indicated. Values in parentheses denote yields based on ¹H NMR spectra obtained after aqueous workup with 6-fluoroindole serving as an internal standard. An asterisk indicates that a compound was purified via chromatography.

Figure 4.. The indole N–H of tryptamine derivatives is not necessary to promote dendritogenesis.

(A) Representative images of cortical neurons (DIV6) treated with compounds. See Figure S2 for the entire field of view from which these neurons were selected. (B) Sholl analysis demonstrates that 1-Me-DMT (27) and isoDMT (2) increase dendritic arbor complexity to a comparable extent as DMT (1) (n = 46–79 neurons). (C) Maximum number of crossings (N_max) of the Sholl plots in B. Data are represented as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001, as compared to vehicle control following a one-way ANOVA with Dunnett’s post hoc test (F = 9.702; DFn = 4; DFd = 304; p-value < 0.0001). VEH = vehicle, KET = ketamine. Scale bar = 20 μm.

Figure 5.. DMT and isoDMT analogs produce comparable effects on dendritic arbor complexity.

(A) Chemical structures of DMT derivatives and analogous isoDMTs. (B) Maximum number of crossings (N_max) of the Sholl analysis for cortical neurons treated with compounds (n = 82–95 neurons). Data are represented as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001, as compared to vehicle control following a one-way ANOVA with Dunnett’s post hoc test (F = 11.17; DFn = 5; DFd = 524; p-value < 0.0001). VEH = vehicle, KET = ketamine.

Figure 6.. Establishment of the essential psychoplastogen pharmacophore.

(A) Chemical structures of non-basic analogs of of isoDMT 2. (B–C) Maximum number of crossings (N_max) of the Sholl plots for cortical neurons treated with compounds (n = 46–85 neurons). The effects of nitrogen basicity and modifications to the aromatic ring were assessed in B and C, respectively. Data are represented as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001, as compared to vehicle control following a one-way ANOVA with Dunnett’s post hoc test (For B: F = 19.03; DFn = 4; DFd = 273; p-value < 0.0001. For C: F = 6.933; DFn = 8; DFd = 599; p-value < 0.0001). VEH = vehicle, KET = ketamine.

Figure 7.. The impact of indole substitution on the ability of isoDMTs to promote neuronal growth.

Maximum number of crossings (N_max) of the Sholl plots for cortical neurons treated with compounds (n = 39–93 neurons). Data are represented as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001, as compared to vehicle control following a one-way ANOVA with Dunnett’s post hoc test (For R = OMe: F = 13.85; DFn = 5; DFd = 493; p-value < 0.0001. For R = OBn: F = 15.44; DFn = 5; DFd = 372; p-value < 0.0001. For R = F: F = 13.24; DFn = 5; DFd = 506; p-value < 0.0001). VEH = vehicle, KET = ketamine.

Figure 8.. Concentration–response experiments demonstrate that DMTs and isoDMTs have similar psychoplastogenic potencies.

Maximum number of crossings (N_max) of the Sholl plots for cortical neurons treated with compounds at concentrations ranging from 10 μM to 10 pM (n = 66–123 neurons). Data are represented as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001, as compared to vehicle control following a one-way ANOVA with Dunnett’s post hoc test (F = 15.40; DFn = 24; DFd = 2,276; p-value < 0.0001). V = vehicle, K = ketamine.

Figure 9.. The psychoplastogenic effects of isoDMTs are blocked by a 5-HT2A antagonist.

Maximum number of crossings (N_max) of the Sholl plots for cortical neurons treated with compounds (n = 45–63 neurons) in the presence (+) or absence (–) of the 5-HT2A antagonist ketanserin. Data are represented as mean ± SEM. ****p < 0.0001, as compared to vehicle control following a one-way ANOVA with Dunnett’s post hoc test (F = 13.92; DFn = 8; DFd = 461; p-value < 0.0001). V = vehicle, K = ketamine, KTSN = ketanserin.

Figure 10.. Zebrafish behavioral assays demonstrate the similarity between isosteres.

(A) An example motion trace with associated stimuli. Top: Locomotion in wells treated with vehicle (gray) or 5-MeO-DMT (28, 200 μM, red). Individual traces for the 5, 6, and 30 are shown in Figure S3. Bottom: Stimuli applied over time. Colors indicate bright LED light of respective colors. Black traces represent the waveform of acoustic stimuli, and gray vertical lines indicate physical tapping as secondary acoustic stimuli. (B) Concentration–response curves for DMT and isoDMT analogs (n = 21 wells per condition). The y-axis is the mean accuracy of classification against vehicle controls. Gray lines are the mean ± STD under bootstrap. (C) Confusion matrix showing that isosteric pairs produce similar behavioral phenotypes (n = 18 wells per condition). Darkness indicates the percentage of wells classified; the maximum is 50.7% (5-MeO-DMT as itself).

Figure 11.. Mouse HTR assays demonstrate that psychoplastogenic isoDMTs exhibit reduced hallucinogenic potential.

Male and female mice were administered drugs via intraperitoneal injection, and the number of head-twitches were recorded over the next 20 mins (n = 3–8 mice per condition). Data are represented as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001, as compared to vehicle control following a one-way ANOVA with Dunnett’s post hoc test. V = vehicle.