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Synthesis and Characterization of 5‑MeO-DMT Succinate for Clinical
Use
Alexander M. Sherwood,*Romain Claveau, Rafael Lancelotta, Kristi W. Kaylo, and Kelsey Lenoch
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sıSupporting Information
ABSTRACT: To support clinical use, a multigram-scale process
has been developed to provide 5-MeO-DMT, a psychedelic natural
product found in the parotid gland secretions of the toad, Incilius
alvarius. Several synthetic routes were initially explored, and the
selected process featured an optimized Fischer indole reaction to 5-
MeO-DMT freebase in high-yield, from which the 1:1 succinate
salt was produced to provide 136 g of crystalline active
pharmaceutical ingredient (API) with 99.86% peak area by high-
performance liquid chromatography (HPLC) and a net yield of
49%. The report provides in-process monitoring, validated
analytical methods, impurity formation and removal, and solid-
state characterization of the API essential for subsequent clinical
development.
■INTRODUCTION
Recently, interest has increased in understanding the clinical
applications of psychedelic, entactogenic, and dissociative
psychoactive drugs, such as psilocybin (1), DMT (2), LSD
(3), MDMA (4), or ketamine (5) in combination with
psychotherapeutic support to promote improved mental health
conditions (Figure 1).
1,2
In particular, research has indicated
favorable results in treating post-traumatic stress disorder
(PTSD), depression, end of life conditions, and anxiety-related
disorders.
1,3−6
This research shows that while the therapeutic
mechanisms are not fully understood, some factors have been
correlated with improvement in mental health. These factors
include the intensity of mystical experience occasioned by the
psychedelic, the context in which the session was conducted
(known as set and setting), the dose at which the drug is
administered, psychological flexibility, connectedness, emo-
tional breakthrough, and increased neural entropy.
1,7−10
5-MeO-DMT (6) is a tryptamine natural product most
commonly identified as the primary psychoactive component
of the parotid gland secretions of Incilius alvarius, the Sonoran
Desert toad (Figure 2).
11
The alkaloid is also known to be
present in low concentrations in a variety of plants, shrubs, and
Received: October 19, 2020
Accepted: November 16, 2020
Published: December 2, 2020
Figure 1. Structures of clinically explored psychedelic, entactogenic,
and dissociative psychoactive drugs.
Figure 2. (Left) I. alvarius (image courtesy of Holger Krisp, Ulm,
Germany, 2011 under CC BY 3.0) with the parotid gland highlighted.
(Right) Structure of 5-MeO-DMT (6).
Article
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https://dx.doi.org/10.1021/acsomega.0c05099
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This is an open access article published under a Creative Commons Non-Commercial No
Derivative Works (CC-BY-NC-ND) Attribution License, which permits copying and
redistribution of the article, and creation of adaptations, all for non-commercial purposes.
seeds. Human consumption of this material for its psychoactive
properties has been reported in the scientific literature for at
least 100 years.
12−15
Although it has been historically
suggested that 5-MeO-DMT may have been used by
indigenous cultures,
11
there is no known documentation to
support this assertion. Due to the recent discovery of high
concentrations of 5-MeO-DMT in I. alvarius secretions, there
has been a reported increase in its recreational and spiritual
use.
11,16,17
Recent evidence has indicated the presence of 5-
MeO-DMT existing in concentrations between 20 and 30% of
total dry weight or approximately 200−300 mg of 5-MeO-
DMT per dried gram of toad secretion,
17
concentrations much
higher when compared to plant-derived sources of 5-MeO-
DMT.
Anecdotally, and suggested by research over the last 5 years,
5-MeO-DMT has been reported to be helpful in treating
clinical mental health conditions.
8,9,16−18
These data suggest
that 5-MeO-DMT produces mystical experiences with
comparative intensity as seen with psilocybin,
8
has a
significantly shorter duration of effectbetween 10 and 45
min depending on the route of administration used,
19
and
produces increased desired effects when the context of the
experience is carefully curated.
20,21
An extensively supported hypothesis is that commonly
encountered psychedelic effects in humans (e.g., visual
hallucinations, altered sense of self, time, and space, and
atypical thought patterns) are mediated primarily via activation
of the serotonergic 5-HT2A receptor in the central nervous
system (CNS).
22,23
Notably, all currently known psychedelics
are also nonselective, simultaneously interacting with numer-
ous other monoaminergic receptors and transporters in the
CNS, and hence exhibit variable degrees of synergistic
polypharmacology in addition to agonist activity at the 5-
HT2A receptor.
24
5-MeO-DMT has demonstrated sub-micro-
molar binding affinity across most serotonin receptor subtypes
expressed in the CNS, with about 300-fold selectivity for the
human 5-HT1A (3 ±0.2 nM) versus 5-HT2A (907 ±170 nM)
receptor subtypes.
25
Data has suggested that activation of the
5-HT1A receptor may also play a significant role in contributing
to the subjective and behavioral effects elicited by psychedelics
in a synergistic way with 5-HT2A activation.
26−28
In contrast to
5-MeO-DMT, psilocin (the active metabolite of psilocybin) is
about 5-fold more selective for human 5-HT2A receptors (107
nM) versus 5-HT1A (567 nM).
29
In a controlled study in
healthy human volunteers, coadministration of psilocin with
the antianxiety medication buspirone, a selective 5-HT1A
agonist, altered the subjective effects produced by psilocin,
notably reducing the intensity of certain visual hallucinations.
30
Interestingly, anecdotal reports on 5-MeO-DMT consumption
have described a general lack of colorful geometric visual
hallucinations typically associated with other psychedelics.
31
To date, a comprehensive understanding of the correlation
between psychedelics’polypharmacology and the correspond-
ing influence on their subjective effects is not well established.
While a number of potential mechanisms have been
hypothesized to rationalize the therapeutic mode of action of
psychedelics, such as increased structural plasticity in the
prefrontal cortex,
32
still no direct connection has been made
between specific psychedelic pharmacodynamics and positive
therapeutic outcomes.
33
Nevertheless, randomized clinical
trials with the psychedelic psilocybin (1) in the treatment of
serious mental health conditions such as major depressive
disorder (MDD) continue to show promise.
34
To this end, 5-
MeO-DMT appears to be pharmacodynamically unique
compared to previous clinically studied psychedelics and
could provide a useful comparator in contemporary controlled
clinical studies with psychedelics to better understand their
mode of action.
Unlike psilocybin, psychedelic tryptamines such as DMT
(2) and 5-MeO-DMT (6) are subject to rapid first-pass
metabolism by monoamine oxidase and are therefore not orally
active. When consumed parenterally, they produce a
significantly shorter duration of action, typically less than 1
h, compared to the 5−8 h duration of effects produced by
psilocybin. The shorter duration of action may help in
reducing the amount of time a patient would spend in the
clinic. Additionally, compared to DMT, 5-MeO-DMT is
known to be approximately 10−20 times more potent in
humans.
13
With a short duration of action and possibly
significant 5-HT1A receptor selectivity, 5-MeO-DMT possesses
unique pharmacodynamic and pharmacokinetic properties
compared to other clinically studied psychedelics. These
features may correlate with more positive therapeutic out-
comes in controlled human clinical trials. To test this
hypothesis and to better understand the psychotherapeutic
utility of 5-MeO-DMT and enable such clinical trials, the
preparation of active pharmaceutical ingredient (API) is
required with adequate controls to ensure its identity, potency,
purity, and strength. The development of this process is the
topic of this report.
■RESULTS AND DISCUSSION
5-MeO-DMT Dosage and Salt Form Selection. The
most commonly reported route of administration is by
vaporization of the freebase drug, which is generally not a
pharmaceutically acceptable approach compared to other
dosage forms. While other intraperitoneal routes of admin-
istration with 5-MeO-DMT such as dry powder inhalation,
transdermal, or intravenous administration are possible, an
intramuscular injection has been identified as a preferable
compromise for administering this material. In addition to
allowing precise metering of dose, the intramuscular injection
of 5-MeO-DMT in a naturalistic setting has been previously
reported and was claimed to possess an advantageous duration
of action compared to the intense rapid-onset produced by
other intraperitoneal routes.
19
The injectable drug formulated
as a 20 mg/mL solution of API in sterile water with excipients
is capable of delivering a precise dose of API in the range of 2−
15 mg, consistent with the dose range described in previous
anecdotal reports with this material. 5-MeO-DMT freebase has
low water solubility (<10 mg/mL) and the unionized amine
may degrade on exposure to atmospheric oxygen to give the
corresponding N-oxide degradant (vide infra). A water-soluble,
pharmaceutically acceptable salt form of 5-MeO-DMT was
therefore required.
In parallel to the exploration of viable synthetic routes to 5-
MeO-DMT freebase, a range of pharmaceutically acceptable
salt forms were considered from acids with sufficient pKa
difference to fully protonate 6, including the counterions
chloride, sulfate, fumarate, succinate, maleate, lysate, oxalate,
benzoate, tartrate, mesylate, or acetate.
35
Using analytically
pure 5-MeO-DMT freebase, the hydrochloride, sulfate,
fumarate, and succinate salts were initially evaluated. Attempts
at formation of the sulfate salt yielded an intractable gum and
the approach was abandoned. The hydrochloride salt was
readily prepared as an apparent crystalline solid, but the
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material was found to be hygroscopic and was deliquescent
under high-humidity conditions. Both the fumarate and
succinate salts were readily prepared and provided stable,
free-flowing, crystalline materials. The fumarate salts of
structurally analogous tryptamines are commonly reported,
possibly due to their ease of synthesis.
36
DMT (2) fumarate,
for example, has been previously used in clinical studies as an
intravenous injection.
37
Fumaric acid is, however, a known
Michael acceptor and has been shown to form covalent
products with amine-containing APIs under mild condi-
tions.
38,39
Given that terminal sterilization by an autoclave
may be required in the future preparation of sterile solutions of
the 5-MeO-DMT drug product, the potential for this known
reactivity with fumaric acid eliminated it as an acceptable salt
form. Succinic acid is a structurally similar dicarboxylic acid but
lacks the conjugated double bond present in fumaric acid and
would not exhibit similar chemical reactivity.
The succinate salt was therefore explored further as a
potential pharmaceutically acceptable salt form. The material
was prepared and subjected to thorough solid-state character-
ization, including equilibrium water solubility, X-ray powder
diffraction (XRPD), thermogravimetric analysis (TGA), differ-
ential scanning calorimetry (DSC), hyper-DSC, dynamic vapor
sorption (DVS), 1H nuclear magnetic resonance (NMR), and
optical microscopy (see the Supporting Information). Briefly,
5-MeO-DMT succinate (1:1) was not hygroscopic and XRPD
indicated that multiple crystallization conditions resulted in a
common stable crystalline anhydrate (form A) with only a few
conditions that formed unique solvated forms (see the
Supporting Information). The data supported the use of 5-
MeO-DMT succinate (1:1) as a stable and pharmaceutically
acceptable salt form. Given its ease of synthesis and favorable
solid-state properties, this salt form was selected for further
development.
5-MeO-DMT Route Scouting. For clinical development,
the ideal synthetic route to 5-MeO-DMT would utilize
commercially available starting materials, would be scalable
to readily provide the product in the range of 0.1−1 kg, would
not rely on flash silica gel chromatography or fractionation, and
would provide a high-purity final product with no unidentified
individual impurity >0.15% peak area by a validated high-
performance liquid chromatography (HPLC) method. The
literature survey revealed three potentially viable synthetic
routes, and each was explored and evaluated for the ability to
meet the above criteria.
Route 1.A seemingly attractive single-step process
employed a modified Eschweiler−Clarke reaction via reductive
amination between formaldehyde and commercially available
5-methoxy tryptamine (7) with sodium cyanoborohydride as
the reducing agent (Scheme 1).
40
Several small-scale attempts
were initially evaluated with reaction monitoring by liquid
chromatography-mass spectrometry (LCMS). Though product
formation was evident, the reaction was plagued by challenges
that would likely multiply at larger scales. The Pictet−Spengler
reaction to the corresponding tryptoline (8) was difficult to
suppress and removal of this structurally similar and possibly
biologically active byproduct was challenging. Further
optimization to Route 1 may be possible, but ultimately, the
reaction was not recommended for further development. A
related reaction involving N-methylation of tryptamine 7by
methyl iodide has also been suggested; however, this approach
would inevitably lead to difficult-to-control quaternization at
the amine and was therefore also not considered for large-scale
synthesis.
Route 2.The Speeter−Anthony tryptamine synthesis
(Scheme 2) is the most cited general method for preparing
substituted psychedelic tryptamines and has also been used to
prepare 5-MeO-DMT previously.
31,41
Given recent learnings
and optimizations from the large-scale synthesis of psilocin and
psilocybin produced by an analogous process, the route was
considered for the large-scale synthesis of 6from 5-
methoxyindole 9.
42−44
A key consideration in this approach
is performing the final reduction on the ketoamide 10 with
pyrophoric lithium aluminum hydride (LAH) with the
subsequent quench and tedious extraction from solid
aluminum waste salts; the difficulty of this process tends to
increase with scale. Our data has indicated that in most cases
when synthesizing tryptamines, the reduction step will stall at
approximately 90% conversion with 5−10% of an expected β-
hydroxy intermediate, such as 11, remaining (Scheme 2). On
workup, further manipulations of the crude freebase, especially
acidic conditions, can initiate conversion of the β-hydroxy
impurity to a reactive electrophile, such as 12 (Scheme 2), and
give mixtures of isomeric dimerized impurities. Crookes et al.
provided a thorough investigation into the formation of
analogous dimeric byproducts in the LAH reduction to
produce DMT (2) by the mechanism analogous to the
depiction in Scheme 2.
45
Though Route 2 was a viable process,
given the known challenges with scale-up, this route would
require additional process development to ensure that the final
product could reliably meet high-purity specifications without
relying on column chromatography. Therefore, a single-step
procedure based on the Fischer indole reaction was next
explored.
Route 3.Several attributes inherent to the Fischer indole
reaction approach to 6from 4-methoxyphenylhydrazine (13)
and 4,4-diethoxy-N,N-dimethylbutan-1-amine (14), a masked
aldehyde protected as the diethyl acetal derivative (Scheme
3A), were attractive for the development of a scalable process:
the transformation occurs in a single step, it does not rely on
high temperatures, occurs in aqueous solvent, and does not
rely on air-sensitive or pyrophoric reactants such as lithium
aluminum hydride. Additionally, literature precedent exists for
its use specifically in the synthesis of 5-MeO-DMT in addition
to related substituted N,N-dimethyltryptamines,
46
with re-
ported examples for the use of an analogous process in the
commercial manufacture of structurally similar 5-substituted
dimethyltryptamine antimigraine medicines, such as suma-
triptan (15), zolmitriptan (16), and rizatriptan (17)(Scheme
3B).
47
Importantly, the pharmaceutical relevance of trypt-
Scheme 1. Eschweiler−Clarke Reaction to 6 and Mechanism
of Pictet−Spengler Byproduct Formation
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amines 15−17 provided some assurance that the key
butanamine starting material 14 common to all three processes
was well-characterized and would remain commercially
available and inexpensive.
As per the previously published protocol, the reaction was
first conducted in refluxing dilute aqueous sulfuric acid
solution (Table 1, entry 1).
46
Reaction monitoring by LCMS
indicated that the phenylhydrazine limiting reagent 13 was
consumed within 2 h with a crude reaction purity of about 63%
peak area, including several high-molecular-weight impurities
representing the remaining 37% peak area. With the significant
impurity profile, the reaction would have likely required
chromatography to isolate the product of sufficient purity.
Serendipitously, we observed that an aliquoted LCMS sample
removed prior to reflux prepared in acetonitrile instead of
water proceeded to near completion at or below room
temperature and contained almost exclusively 6with few
byproducts. Following this observation, an experiment was
repeated using 1:1 water/acetonitrile as the solvent system at
room temperature overnight to confirm 88% conversion to the
product by LCMS (Table 1,entry2).Basedonthe
encouraging results, the process was repeated, and additional
conditions were explored.
Raising the temperature to 40 °C, the reaction was found to
reach completion within 3 h with acetonitrile cosolvent (Table
1, entry 3). To better understand the role of the cosolvent,
several additional reactions were trialed with different
cosolvents, including methanol, dimethyl sulfoxide (DMSO),
2-methyltetrahydrofuran (2-MeTHF), and dichloromethane
(DCM) (Table 1, entries 4−7) compared to the same volume
of only water under otherwise identical conditions (Table 1,
entry 8). The results indicated that all cosolvents tested were
advantageous in increasing reaction conversion, with water-
miscible polar aprotic DMSO providing results comparable to
that of acetonitrile. Methanol also exhibited a significant
Scheme 2. Speeter−Anthony Tryptamine Synthesis and Byproduct Formation via Reactive Impurity 11
Scheme 3. (A) Fischer Indole Reaction in the preparation of 6 and (B) Approved Antimigraine Medications Prepared by the
Analogous Process
Table 1. Reaction Optimization Conditions
entry equiv 14
(x) cosolvent,
(vol) time
(h) temp.
(°C) conversion
(area %)
a
1 1.2 (0) 2 100 63
2 1.2 MeCN, (10) 19 22 88
3 1.2 MeCN, (10) 3 40 90
4 1.2 MeOH, (10) 3 40 84
5 1.2 DMSO, (10) 3 40 87
6 1.2 MeTHF,
(10) 340 79
7 1.2 DCM, (10) 3 40 77
8 1.2 H2O, (10)
b
340 66
9 1.05 MeCN, (5) 3 35 90
9b 28 35 89
10 1.05 MeCN, (5) 3 35 90 (80)
c
a
UPLC-UV percent area at 269 nm.
b
Total water was 20 vol.
c
Isolated yield.
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enhancing effect on the reaction. The water-immiscible
solvents 2-MeTHF and DCM also moderately improved
reaction conversion. These data indicated that most cosolvents
improved the conversion and purity profile of the reaction, and
the water-miscible polar aprotic cosolvents demonstrated a
significant rate-enhancing effect and minimized side reactions
in the formation of 6. Though both reactants 13 and 14
appeared to be water soluble in the absence of cosolvent, we
hypothesized that the addition of cosolvent possibly assisted in
solubilizing either reactant or prevented the formation of
hydrophobic clusters. The hypothesis is supported by the
observation that in the absence of cosolvent, the major side
reaction impurities formed were indicative of high-molecular-
weight oligomers, which could potentially form from localized
high-concentration clusters of starting reactants. Though
DMSO and acetonitrile performed comparably, acetonitrile
was selected for further development as the high-boiling point
and low volatility of DMSO may have introduced additional
complexity by its eventual removal in the workup.
Further optimization revealed that diethyl acetal 14 could be
reduced to 1.05 equiv relative to limiting reagent 13.
Acetonitrile cosolvent was reduced from 10 to 5 vol, and the
temperature was reduced to 35 °C without measurable impact
on the crude reaction profile or reaction rate (Table 1, entry
9). Further, stressing the same reaction with an extended 28-h
hold time had only a slight impact on the reaction profile with
an overall 1% reduction in a HPLC purity of the crude reaction
mixture (Table 1, entry 9b). The reaction’s indifference to
extended hold times was advantageous and suggested that
reaction time was not a critical process parameter and could
allow for some flexibility with timing when running the process
at scale. Based on the optimizations described, the process was
scaled to 100 mmol (∼35 g) and isolation conditions were
explored to ultimately provide high-purity 6as the succinate
salt in 80% isolated yield (Table 1, entry 9).
Optimization of Workup, Isolation, and Salt For-
mation. Workup. Crude freebase product was initially isolated
by a routine acid/base workup procedure employing dichloro-
methane as both a washing solvent for the acidic crude
reaction mixture and, upon basification, an extraction solvent
for the freebase as well. On larger-scale reactions where
extended hold times of the freebase product in methylene
chloride were required, formation of a heavy insoluble oil
impurity was encountered. Consistent with several literature
reports on the chemical reactivity of DMT and other tertiary
amines with methylene chloride,
48−52
5-MeO-DMT was
suspected to have undergone a similar reaction to form the
quaternary ammonium byproduct 18 (Scheme 4). The crude
heavy oil was analyzed by 1H NMR, which provided a singlet
at 5.69 ppm that integrated to 2H; these data were consistent
with the identity of structure 18 (Scheme 4 and Supporting
Information S14). The apparent reactivity between product 6
and dichloromethane indicated that an alternative solvent
should be used in the workup process, especially at larger
scales where extended hold times may be required.
2-Methyltetrahydrofuran (2-MeTHF) has been previously
suggested as a good substitute for dichloromethane in biphasic
aqueous workups.
53
We found that freebase 6was highly
soluble, and 2-MeTHF formed a clean phase split with the
acidic aqueous crude reaction mixture without the need for
distillation of the acetonitrile cosolvent. Additionally, 2-
MeTHF represented a greener solvent choice for process
chemistry, as it is produced industrially by biorenewable
processes. On smaller scales, the acetonitrile cosolvent was
distilled prior to workup. On larger scales, this distillation was
avoided and the workup proceeded directly into a liquid−
liquid washing step. Subsequent data would indicate that some
product loss occurred in the first washing step by being
extracted into the organic phase, possibly related to increased
partitioning due to the acetonitrile present.
Freebase Purification. Analysis of the crude freebase extract
by LC−UV−high-resolution mass spectrometry (HRMS)
revealed the presence of several isomeric dimer-like products
representing approximately 8% combined peak area for the
crude reaction mixture. HRMS analysis provided m/z
534.3803 with MS/MS fragmentation to m/z316.2383 for
each of the isomers, supporting the putative structure 19
(Scheme 5 and Supporting Information S15), although
different attachment points (denoted by red circles) for the
dimer are also possible. Regardless of connectivity, the HRMS
data supported the identity of a triamine for the isometric
impurities corresponding to m/z534.3803. Though ethanol
was initially identified as a suitable recrystallization solvent for
the succinate salt of 6, the isomeric dimers were found to co-
crystallize with 6at levels that exceeded impurity specifications.
Alternatively, we speculated that a significant differential in
retention would exist between monoamine 6and triamine
isomers of 19 on silica gel, such that a filtration through a small
silica plug would be sufficient to remove the polar impurities
while allowing the product 6to readily elute. Mobile phase
screening experiments with thin-layer chromatography re-
vealed that 10% methanol in acetone provided such separation,
with polar dimer impurities remaining adhered to the baseline
and migration of the product spot for 6with a retention factor
(Rf)ofabout0.3(Supporting Information S16). While
methanol/acetone is an atypical eluent with silica gel,
dichloromethane, which is commonly used in separations
with polar amines, was unacceptable given the reactivity
concerns outlined above. On the preparative scale, filtration
through a 5 wt % silica pad and washing the pad with 100 vol
of 10% methanol in acetone was sufficient to recover 80−90%
mass of the input crude freebase, while the polar dimeric
impurities remained adhered to the baseline and were
effectively removed.
Following the silica filtration step during concentration of
the resulting eluent, a previously unobserved degradant
appeared in up to 3% peak area by HPLC. The degradant
was conclusively identified as oxidation degradant 21, the N-
oxide of 6. The structure was supported by HRMS initially
(Supporting Information S17) and later chemical synthesis
with additional characterization by 1H and 13C NMR (Scheme
6and Supporting Information S18 and S19) conclusively
Scheme 4. Formation of Degradant 18 Annotated With 1H
NMR Shift for the Suspected Dichloromethane Adduct
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characterized 21. Previous in vitro and in vivo metabolism data
has indicated that N-oxide 21 is a metabolite of 6
54
and would
therefore afford some flexibility in the allowable levels of this
degradant in the API.
Succinate Salt Formation. With smaller-scale development
reactions, the succinic acid salt of 6was readily isolated by
adding 1 equiv of succinic acid to a solution of freebase 6in
acetone and collecting the resulting insoluble crystalline
precipitate by filtration. We later found that the inclusion of
a washing step using activated charcoal helped to minimize
slight variability in color observed in the final isolated product.
The color variation was found to be correlated with the use of
different commercial sources of phenylhydrazine 13, even
though all lots were tested upon receipt to >98% purity. The
procedure was modified to form the succinate salt in a solution
of methanol at a volume that did not initially induce
precipitation. The resulting solution was stirred with activated
charcoal, filtered, and then concentrated. The resulting solid
succinate salt was slurried in acetone, filtered, and dried to
provide a crystalline solid consistent with the desired
polymorphic form. The process provided a net yield of 49%
to produce 136 g of isolated succinic acid salt of 6with HPLC
purity of 99.86% peak area. The identified N-oxide degradant
21 was the only detectable impurity at 0.14% peak area.
Though not reported in the larger-scale synthesis, as the
required purity specifications were met, following salt
formation, ethanol was found to perform well as a
recrystallization solvent for further purification of the succinate
salt of 6if necessary.
Future Optimization. The Fischer indole reaction to 6
readily provided API that met all set specifications. Achieving a
high-purity product was the initial focus, and further
optimization could improve the final yield without compro-
mising final product purity. HPLC data indicated that product
conversion was as high as 90%, yet isolated freebase recovery
was 57%. Additionally, in the smaller-scale development
reaction (Table 1, entry 9), an isolated yield of 80% was
achieved. The key difference between the two processes was
the distillation of the cosolvent prior to workup and much of
the yield loss that occurred at the first liquid−liquid washing
step, where approximately 10−20% of the product was
extracted from the acidic aqueous layer in the first wash. In
the future, the washes could potentially be back-extracted to
recover this loss. With further scale-up, the elimination of the
silica pad filtration step would be desirable. Vacuum distillation
of the crude freebase could be an acceptable alternative for the
separation of the freebase product from high-MW dimers such
as 19. Though dimer impurities present in succinate salt were
not readily purged by recrystallization approaches, exploration
of the recrystallization of alternate salt forms prior to
generation of the succinate salt may also circumvent the silica
pad filtration. As an alternative to purification approaches,
additional optimization of reaction conditions could be
explored to further improve the specificity of the reaction
toward formation of 6and minimize side reactions.
■CONCLUSIONS
The first production run has provided sufficient API to meet
current clinical and nonclinical needs to enable first-in-human
clinical trials with 6. The key features of the developed process
were an optimized Fischer indole reaction with advantageous
inclusion of acetonitrile cosolvent to provide crude freebase 6.
The workup featured greener solvent choices with an
intermediate purification via filtration through a silica pad.
The 1:1 succinic acid salt was subsequently prepared from
methanol with an activated charcoal decolorizing step followed
by final purification by acetone slurry. A minor API
degradation product, the corresponding N-oxide 21, was
identified, synthesized, and characterized. The final product
was isolated in 49% overall yield to provide 136 g of API with
99.86% HPLC purity. The controllability and scalability
inherent to the developed process will ensure that current
and future clinical demands for 6are met.
■EXPERIMENTAL SECTION
General Experimental Methods. Reactions were per-
formed using commercially obtained raw materials and
solvents. Unless otherwise stated, all commercially obtained
reagents were identity tested and used as received. Reactions
were conducted in a Borosilicate Glass 3.3 jacketed glass
reactor (5 L) with a Julabo FPW91-SL Ultra-Low Refrigerated-
Heating circulator for temperature control. Distillations (>5 L)
were performed with a Buchi Rotavapor R-220 Pro. Reactions
were monitored by thin-layer chromatography (TLC) using
Scheme 5. Putative Dimer Impurity Structure and MS/MS Fragmentation
a
a
Red circles indicate alternate attachment points.
Scheme 6. Synthesis of N-Oxide 21
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ACS Omega 2020, 5, 32067−32075
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EMD/Merck silica gel 60 F254-precoated plates (0.25 mm).
Flash column chromatography was performed using prepack-
aged RediSepRf columns on a CombiFlash Rf system
(Teledyne ISCO Inc.). 1H and 13C NMR spectra were
recorded on a Bruker Avance 400 (at 400 and 101 MHz,
respectively) and a Bruker Avance 500 (at 500 and 126 MHz,
respectively). Process development and reaction monitoring
was performed with a Waters Acquity I-Class UPLC utilizing a
Waters HSS T3 column (2.5 μm, 2.1 mm ×30 mm) run in
gradient mode with H2O (0.1% formic acid) and acetonitrile
(0.1% formic acid) mobile phases at 0.6 mL/min. Samples
were diluted in acetonitrile or water to approximately 1 mg/
mL and 0.1 μL was injected. Chromatographic peaks were
detected by a diode array detector at 269 nm. High-resolution
mass spectra were acquired in line with UV on a Waters Xevo
G2-XS QTof in ESI-positive mode. Low and high collision
energy mass spectra were acquired using a Waters MSe
experiment.
2-(5-Methoxy-1H-indol-3-yl)-N,N-dimethylethan-
amine (6-freebase). To a clean and dry 5 L reactor was
charged 4-methoxyphenylhydrazine hydrochloride (145.0 g;
0.83 mol, 1.0 equiv, purity >98% confirmed by HPLC)
followed by water (1.45 L, 10 vol) under a nitrogen
atmosphere at 20−25 °C. The contents of the reactor were
then stirred at 30−35 °C and a dark red colored suspension
was observed. To the suspension, concentrated H2SO4(47.7
mL, 0.91 mol, 1.1 equiv) was cautiously added dropwise under
a nitrogen atmosphere over 10 min while maintaining the
temperature below 40 °C. (Note: This addition is slightly
exothermic.) The brown/red solution was heated to 35−40 °C
(with a target temperature of 37 °C) and stirred for an
additional 10 min. A solution of 4,4-diethoxy-N,N-dimethyl-
butan-1-amine (14) (165.0 g, 0.87 mol, 1.05 equiv) was
prepared in acetonitrile (0.58 L, 4.0 vol) and added dropwise
to the reactor under a nitrogen atmosphere over approx-
imatively 60 min while maintaining the temperature between
35 and 40 °C. The addition funnel was rinsed with acetonitrile
(145 mL, 1.0 vol) and added dropwise to the reactor. The
temperature was maintained at 40 °C and the contents were
agitated for an additional 4 h. A sample of the reaction mixture
was aliquoted for HPLC analysis and reaction completion with
a target limit of ≤2% peak area for the limiting reagent.
(Result: 4-Methoxyphenylhydrazine: 1.86% area.) The mixture
was cooled to 20−25 °C and the contents were transferred to a
10 L reactor. The acidic aqueous solution was washed with 2-
MeTHF (2 ×2.03 L, 14.0 vol). After each wash, the layers
were allowed to settle for 15 min. The lower acidic aqueous
layer was collected and the upper 2-MeTHF wash was
discarded. The acidic aqueous layer was recharged to the
reactor and sodium hydroxide solution (4 M, 0.65 L, 4.5 vol)
was added dropwise while maintaining the temperature at 20−
25 °C to bring the pH to 11−12 providing a milky suspension.
The suspension was extracted with 2-MeTHF (3 ×1.45 L,
10.0 vol); following each extraction, the layers were allowed to
settle for 15 min, the lower alkaline water layer was separated
into a drum, and the upper organic layer was collected. The
lower aqueous layer was discarded and the combined 2-
MeTHF organic layers were transferred to a 20 L-flask. The
solution was concentrated in vacuo to an oily amber residue.
Residual water was removed azeotropically by redissolving the
residue with fresh 2-MeTHF (1.45 L, 10 vol) and repeating the
concentration step. This oily residue was dried on the rotatory
evaporator under vacuum (10−20 mbar) for 1 h at 40−45 °C
to provide 117.68 g (64.9% theoretical yield) of crude 5-MeO-
DMT freebase. The crude freebase was dissolved in acetone
(1.45 L, 10.0 vol) and poured through a pad of silica (230−
400 mesh, 725 g, 5 wt). The pad was eluted with acetone/
MeOH (9:1, v-v, 14.5 L, 100.0 vol). The combined filtrates
were concentrated to provide 102.94 g of purified 5-MeO-
DMT freebase (56.8% yield, 98.27% area by HPLC) as a pale
clear orange oil that slowly solidified on standing.
2-(5-Methoxy-1H-indol-3-yl)-N,N-dimethylethan-
amine (6-succinate (1:1)). To the 20 L-flask containing
purified 5-MeO-DMT freebase from the previous step (101.1
g, 0.46 mol, 1.0 equiv) was charged fresh MeOH (1.01 L, 10.0
vol). The flask was attached to a rotary evaporator and rotation
was started without applying vacuum until the material
dissolved. The methanolic solution was then transferred to a
5 L-RBF fitted with an overhead mechanical stirrer. Additional
MeOH (2.02 L, 20.0 vol) was charged to the RBF, under a
nitrogen atmosphere, at 20−25 °C. Succinic acid (57.4 g, 0.48
mol, 1.05 equiv) was added portion wise and the solution was
stirred at 20−25 °C for 48 h under a nitrogen atmosphere.
Charcoal (NORIT SX1, 31.2 g, ∼20% w/w) was charged to
the flask, under a nitrogen atmosphere, at 20−25 °C. The
resulting dark suspension was stirred at 20−25 °C for 2.5 h
under a nitrogen atmosphere and then filtered on a Celite pad.
The Celite pad was rinsed with additional MeOH (3.03 L, 30.0
vol). The collected filtrate (5.05 L) was then concentrated
under reduced pressure. Acetone was charged in portions to
the rotatory evaporator containing the solid 5-MeO-DMT
succinate salt and the solvent concentrated until no more
distillate was observed to ensure that most of the residual
MeOH had been distilled. Fresh acetone (505.5 mL, 5.0 vol)
was added to the flask and the resulting suspension was
slurried at ambient temperature for 1 h. The suspension was
cooled to 0−5°C on an ice bath and was filtered over a
sintered funnel. The filter cake was washed with ice-cold
acetone (2 ×101.1 mL, 1.0 vol) and the solids were pulled dry
on the filter for approximately 30 min. The solid was dried in a
vacuum oven at 40−45 °C to a constant weight to provide
136.0 g (86.0% yield, 48.8% overall yield, 99.86% area) of 5-
MeO-DMT succinate salt (6). TG/DTA Melt onset: 140 °C;
1H NMR (500 MHz, DMSO-d6): δ10.66 (s, 1H), 7.22 (d, J=
9 Hz, 1H), 7.06 (d, J= 2 Hz, 1H), 7.00 (d, J= 2.5 Hz, 1H),
6.72 (dd, J= 9 Hz, 2 Hz, 1H), 3.76 (s, 3H), 2.85 (m, 2H), 2.77
(m, 2H), 2.42 (s, 6H), 2.34 (s, 4H); 13C NMR (126 MHz,
DMSO-d6): δ175.1, 153.5, 131.8, 127.8, 123.9, 112.5, 111.5,
111.2, 100.7, 58.8, 55.8, 44.1, 30.9, 22.2.
2-(5-Methoxy-1H-indol-3-yl)-N,N-dimethylethan-1-
amine oxide (21). Freebase 6(500 mg, 2.3 mmol) was
suspended in 30% w/w H2O2(1.2 mL, 11.5 mmol, 5 equiv)
and stirred. Ethanol (ca. 3 mL) was added dropwise to the
suspension until a homogeneous solution was achieved.
Stirring continued for 48 h whereupon thin-layer chromatog-
raphy (100:10:1; CHCl3/MeOH/NH4OH) indicated com-
plete conversion of the starting material to a new slightly more
polar spot. Without concentration, the reaction mixture was
applied directly to a preparative C18 column (130 g) and
gradient eluted at 85 mL/min with MeOH and H2O, both
containing 1% NH4OH. Collected fractions were combined
and concentrated to provide the target compound as a yellow
deliquescent solid, (470 mg, 88%). HRMS (ESI+): calcd for
[C13H18N2O2] [M+H]+: 235.1441; found: 235.1426. 1H NMR
(400 MHz, DMSO-d6): δ11.29 (s, 1H), 7.24 (d, 1H, J= 8.7
Hz), 7.13 (s, 1H), 7.05 (1H, s), 6.71 (d, 1H, J= 8.7 Hz), 3.75
ACS Omega http://pubs.acs.org/journal/acsodf Article
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ACS Omega 2020, 5, 32067−32075
32073
(s, 3H), 3.45−3.36 (m, 2H), 3.25−3.16 (m, 2H), 3.12 (s, 6H);
13C NMR (101 MHz, DMSO-d6): δ153.0, 131.5, 127.4, 123.6,
112.1, 111.1, 109.9, 100.2, 69.9, 58.5, 55.4, 19.1.
■ASSOCIATED CONTENT
*
sıSupporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acsomega.0c05099.
Certificate of analysis for 5-MeO-DMT succinate salt;
solubility data; characterization data; polymorph screen
summary and results; HPLC methodology and chroma-
tograms; impurity identification and characterization
(PDF)
■AUTHOR INFORMATION
Corresponding Author
Alexander M. Sherwood −Usona Institute, Madison,
Wisconsin 53711, United States; orcid.org/0000-0003-
0895-0791; Email: alex.sherwood@usonainstitute.org
Authors
Romain Claveau −Almac Sciences, Craigavon BT63 5QD,
United Kingdom
Rafael Lancelotta −Habituating to Wholeness, Lakewood,
Colorado 80214, United States
Kristi W. Kaylo −Usona Institute, Madison, Wisconsin
53711, United States
Kelsey Lenoch −Usona Institute, Madison, Wisconsin 53711,
United States
Complete contact information is available at:
https://pubs.acs.org/10.1021/acsomega.0c05099
Author Contributions
The manuscript was written through the contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
■ACKNOWLEDGMENTS
The authors wish to thank William Linton for his vision and
support.
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