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PAPER 935
Synthesis 1999, No. 6, 935–938 ISSN 0039-7881 © Thieme Stuttgart · New York
Improvements to the Synthesis of Psilocybin and a Facile Method for
Preparing the O-Acetyl Prodrug of Psilocin
David E. Nichols,* Stewart Frescas
Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmacal Sciences, Purdue University, West
Lafayette, Indiana 47907, USA
Fax +1(765)4941414; E-mail drdave@pharmacy.purdue.edu
Received 3 December 1998; revised 11 February 1999
Abstract: An improved procedure to accomplish the O-phosphor-
ylation of 4-hydroxy-N,N-dimethyltryptamine (psilocin 5) is report-
ed that utilizes reaction between the O-lithium salt of 5 and tetra-O-
benzylpyrophosphate. The O-benzyl groups were removed by cata-
lytic hydrogenation over palladium on carbon to afford N,N-dime-
thyl-4-phosphoryloxytryptamine (psilocybin, 1). In view of
difficulties encountered in the preparation of 1, it is suggested that
4-acetoxy-N,N-dimethyltryptamine (2) may be a useful alternative
for pharmacological studies. The latter was obtained following cat-
alytic O-debenzylation of 4-benzyloxy-N,N-dimethyltryptamine in
the presence of acetic anhydride and sodium acetate.
Key words: psilocin, psilocybin, tetra-O-benzylpyrophosphate,
phosphorylation
Recently, several laboratories have initiated clinical stud-
ies of hallucinogenic (psychedelic) agents.1–3 This re-
newed interest suggests that there may be some demand
for investigational substances that are suitably pure for
human use that can be prepared in a relatively economical
fashion. Hallucinogens are not commercially available in
large quantities or in purities suitable for human studies,
and research will likely be carried out only with drugs pro-
duced by custom synthesis. Of the various drugs that
might be of interest for this work, most of them, including
mescaline, LSD, DMT, and various substituted amphet-
amines are synthesized relatively easily. Indeed, many
hallucinogens are routinely manufactured in clandestine
laboratories.
By contrast, the synthesis of psilocybin, N,N-dimethyl-4-
phosphoryloxytryptamine (1), is more challenging. Nev-
ertheless, psilocybin has pharmacological features that
make it attractive for clinical research, including a rela-
tively short duration of action. The increasing worldwide
popularity of psilocybin-containing mushrooms as recre-
ational drugs also points to the need for more research
with psilocybin.
We re-examined the synthesis of psilocybin reported by
Hofmann and co-workers.4 Although their approach still
remains useful, there were several weak points that could
be addressed to improve the yields and purities of the final
compound.
The overall synthetic route is shown in Scheme 1. The
most troublesome step is the last, the phosphorylation
of psilocin. In the original synthesis by Hofmann et al.,4
the phosphorylation step was accomplished using O,O-
dibenzylphosphoryl chloride, an unstable reagent that was
used without purification as a solution in carbon tetrachlo-
ride. Furthermore, the final yield of psilocybin was less
than 20%. In view of the overall difficulty in preparing
this material and its precursors, such a low yield in the last
step was deemed unacceptable.
The present synthesis employs a phosphorylation step us-
ing tetrabenzylpyrophosphate, a stable, crystalline re-
agent. The phosphorylation step was complicated by the
previously unreported extremely labile nature of the O,O-
dibenzyl ester of psilocybin. Hydrolytic cleavage of one
of the O-benzyl groups occurred rapidly in the presence of
water, at room temperature, and neutral pH. The purifica-
tion of the resulting zwitterionic material was much more
complicated than for the basic O,O-dibenzyl material.
Illustrated in Scheme 2 is the facile preparation of 4-acet-
oxy-DMT5 2. This O-acetyl prodrug of psilocin is much
more easily prepared than psilocybin, and may offer an
economical alternative for clinicians wishing to study the
psychopharmacology of psilocin. This material is readily
crystallized as the fumarate salt, and is considerably more
stable than psilocin itself. It would seem to be an ideal
prodrug to replace psilocybin in future clinical studies,
since psilocin is the principal metabolite of psilocybin.6
The classical Speeter and Anthony synthesis of
tryptamines from indoles served as the precedent for this
work.7 The key reaction of oxalyl chloride with 4-benz-
yloxyindole was, however, sluggish. Similarly, the reduc-
tion of the 4-substituted glyoxalylamide 3 was much
slower than for indoles without substitution at this posi-
tion. TLC was used to monitor the complete disappear-
ance of starting material and intermediate reduction
products. The O-benzyl group was then readily removed
by catalytic hydrogenolysis to afford 4-hydroxy-N,N-
dimethyltryptamine (psilocin; 5).
936 D. E. Nichols, S. Frescas PAPER
Synthesis 1999, No. 6, 935–938 ISSN 0039-7881 © Thieme Stuttgart ·New York
After experimentation with a variety of phosphorylating
agents, it was finally decided that tetrabenzylpyrophos-
phate (TBPP) was the most suitable reagent.8 This crystal-
line and stable material is commercially available
(Aldrich), but can also be synthesized readily on a multi-
gram scale.
The most convenient base for the phosphorylation step
proved to be butyllithium. Generation of the lithium salt
of psilocin in THF at –70 °C, followed by addition of 1.1
equivalents of TBPP, led to the O,O-dibenzyl ester of
psilocybin, with the generation of one equivalent of lithi-
um O,O-dibenzylphosphate that must ultimately be re-
moved. While ordinarily removal of the lithium salt
would not be problematic, washing the organic reaction
mixture with water led to unexpected and rapid hydrolysis
of one of the O-benzyl groups. Judicious exclusion of
traces of water allowed the isolation of O,O-dibenzyl ester
that was nearly free of 6. The O,O-dibenzyl intermediate
proved to be so sensitive to water, however, that it was
more practical to use an aqueous workup, allow hydro-
lysis to occur, and isolate a product that was largely the
zwitterionic O-monobenzylphosphate 6.
Catalytic hydrogenolysis of the crude O-benzyl ester led
to the formation of psilocybin (1). The procedure was
complicated by small amounts of phosphoric acid gener-
ated from residual dibenzylphosphoric acid carried from
the previous step into the hydrogenolysis reaction. This
highly acidic material leads to discoloration of the product
and prevents satisfactory crystallization. The problem was
solved through the use of anion exchange resin to titrate
the phosphoric acid. The reported pH of a solution of
psilocybin in 50% aqueous ethanol is 5.2.9 Anion ex-
change resin (–OH form) was added in portions, with vig-
orous and extended stirring, to the filtered reaction
solution until the pH of the solution was 5.2. When this
pH was reached, the resin was removed by filtration and
the filtrate was concentrated under vacuum. The crude
product was then recrystallized from a small amount of
methanol, and a large volume of isopropanol, followed by
Scheme 1
Scheme 2
PAPER Improvements to the Synthesis of Psilocybin 937
Synthesis 1999, No. 6, 935–938 ISSN 0039-7881 © Thieme Stuttgart ·New York
storage in the freezer. Psilocybin (1) crystallized as long
colorless needles.
As a potential replacement for 1, 4-Acetoxy-N,N-dimeth-
yltryptamine (2) fumarate was conveniently prepared by
shaking under hydrogen a mixture of 4, acetic anhydride,
and sodium acetate in benzene with Pd/C in a Parr low
pressure hydrogenation apparatus. Following uptake of
the required amount of hydrogen corresponding to O-de-
benzylation, the catalyst and insoluble salts were removed
by filtration. One molar equivalent of fumaric acid was
added to the filtrate, and the solution was concentrated to
dryness under vacuum. The resulting solid was recrystal-
lized to afford white crystals of the desired product. This
material was stable when stored in the cold, but slowly
darkened on storage for several months at ambient tem-
perature.
Mps were determined on a Thomas-Hoover Meltemp melting point
apparatus and are uncorrected except where indicated. 1H NMR
spectra were recorded on a Bruker ARX 300 MHz spectrometer.
Chemical shifts are reported in d values (ppm) relative to an internal
standard of TMS in CDCl3, except where noted. Abbreviations used
in NMR analysis are as follows: s, singlet; d, doublet; t, triplet; m,
multiplet; br s, broad singlet; dd, doublet of doublets, dt, doublet of
triplets. Microanalyses were obtained from the Purdue Microanalyt-
ical Laboratory. A low pressure Parr apparatus was used for all hy-
drogenations. Solvents and reagents were used as purchased, except
as noted. THF was distilled from potassium metal/benzophenone
ketyl. All other compounds were purchased from commercial
sources.
4-Benzyloxyindol-3-yl-N,N-dimethylglyoxylamide (3)
A solution of 4-benzyloxyindole (17.5 g, 0.078 mol) (Biosynth) in
anhyd Et2O (500 mL) was mechanically stirred in a 1 L, 3 necked
flask and cooled in an ice–salt bath to an internal temperature of
0 °C. Oxalyl chloride (20.3 g, 0.16 moles) was added dropwise at a
rate that maintained an internal temperature between 0–5 °C. Stir-
ring was continued for 3 h at a temperature between 5–10 °C with a
gentle argon sparge to remove evolved HCl. The argon sparge was
replaced by a gas inlet tube and a dry ice/acetone condenser. Anhyd
dimethylamine was then bubbled into the reaction with cooling and
vigorous stirring until a pH (determined by moist pH paper) be-
tween 9 and 11 was achieved. At this time, the orange color of the
initial solution had been mostly discharged, and the reaction had the
appearance of a slightly off-white slurry with a few flecks of yellow
unreacted starting material. CH2Cl2 (20 mL) was added to assist sol-
ubilization of the unreacted material and the reaction was stirred for
an additional 6 h to yield finally an off-white slurry. Et2O (150 mL)
was added, and the mixture was cooled to 10 °C. The white solids
were collected by suction filtration on filter paper in a Buchner fun-
nel and then were suspended in distilled H2O (250 mL) and stirred
for 1 h to remove dimethylamine hydrochloride. The slurry was fil-
tered, and the collected solids were washed on the filter with dis-
tilled H2O (3 x 75 mL) and hexane (75 mL) and dried overnight in
a vacuum oven. The dried product weighed 18.3 g. The organic fil-
trates and washes were combined and the solvent was removed by
rotary evaporation. The residue was dissolved in CH2Cl2 (100 mL)
and the organic solution was washed with distilled H2O (2 x 50 mL)
and brine (2 x 50 mL). After drying (MgSO4) the volume was re-
duced by rotary evaporation. The concentrated residual solution
was subjected to flash chromatography over silica gel, first eluting
with CH2Cl2 to recover unreacted indole (1.3 g, 7.4%), followed by
elution with 10% MeOH in CH2Cl2 to recover 3.3 g of 3. The latter
was combined with the initial product to provide a total weight of
21.6 g (85.9%). The crude product was recrystallized from MeOH/
EtOAc to give 19.5 g (77%) of 3 with mp 152–155 °C (Lit.4 mp
146–150 °C).
1H NMR (300 MHz, CDCl3): d = 2.88, 2.92 (2s, 6H, NCH3), 5.21
(s, 2H, CH2), 6.60 (d, 1H, J =7.92 Hz, Ar), 6.86 (d, 1H, J = 8.04 Hz,
Ar), 7.27–7.37 (m, 3H, Ar), 7.50 (m, 3H, Ar), 10.07 (br s, 1H, NH).
4-Benzyloxy-N,N-dimethyltryptamine (4)
A slurry of LiAlH4 (8.90 g, 0.234 mol) in anhyd THF (100 mL) was
prepared in a 2 L, 3-neck flask, previously dried with a heat gun un-
der an argon purge. The flask was fitted with a reflux condenser,
mechanical stirrer, and addition funnel. Anhyd dioxane (200 mL)
was added, and the mixture was heated to 60 °C on an oil bath. 4-
benzyloxyindol-3-yl-N,N-dimethylglyoxylamide (3) (14.5 g, 0.045
moles) was dissolved in a mixture of dioxane (250 mL) and THF
(150 mL) and, with rapid stirring, this solution was added dropwise
over 1 h. The oil bath temperature was held at 70 °C for 4 h, fol-
lowed by vigorous reflux overnight (16 h) at an oil bath temperature
of 95 °C. Thin layer chromatographic analysis (9:1 CH2Cl2/MeOH;
silica plates) showed nearly complete reduction. The reaction was
heated at reflux for an additional 4 h and then cooled to 20 °C. A
solution of distilled H2O (27 mL) in THF (100 mL) was added
dropwise, resulting in a gray flocculent precipitate. Et2O (250 mL)
was added to assist breakup of the complex and improve filtration.
This slurry was stirred for 1 h and the mixture was then filtered with
a Buchner funnel. The filter cake was washed on the filter with
warm Et2O (2 x 250 mL) and was broken up, transferred back into
the reaction flask and vigorously stirred with additional hot Et2O
(500 mL). This slurry was filtered, and the cake was washed on the
filter with Et2O (150 mL) and hexane (2 x 150 mL). All of the or-
ganic filtrates were combined and dried (MgSO4). After the drying
agent was removed by filtration, the filtrate was concentrated under
vacuum at 40 °C and dried under high vacuum at 0.01 mm Hg, lead-
ing to crystallization of the residue as a white waxy solid. Recrys-
tallization from EtOAc yielded 12.57 g, (94.8%) of 4 with mp 124–
126 °C (lit.4 mp 125–126 °C).
1H NMR (300 MHz, CDCl3): d = 2.14 (s, 6H, NCH3), 2.58 (t, 2H, J
= 8.0 Hz, CH2), 3.04 (t, 2H, J = 8.0 Hz, CH2), 5.17 (s, 2H, CH2),
6.52 (d, 1H, J = 7.6 Hz, Ar), 6.87 (s, 1H, Ar), 6.93 (d, 1H, J = 8.0
Hz, Ar), 7.04 (t, 1H, J = 7.9 Hz, Ar), 7.29–7.39 (m, 3H, Ar), 7.49
(br d, 2H, J = 7.0 Hz, Ar), 8.06 (br s, 1H, NH).
4-Hydroxy-N,N-dimethyltryptamine (Psilocin; 5):
A solution of 4 (4.0 g, 0.0135 moles) in 95% EtOH (250 mL) was
added to 1.5 g Pd/C (10% w/w) in a 500 mL Parr low pressure hy-
drogenation bottle. The mixture was shaken under 60 psig of H2
pressure for 2 h. The catalyst was removed by vacuum filtration
through Celite and was washed on the filter with EtOH (3 x 50 mL).
The filtrate was concentrated by rotary evaporation. The clear resid-
ual oil was placed under high vacuum and induced to crystallize by
seeding. The white crystalline powder (2.68 g, 97.0%) was used in
the next step without further purification.
1H NMR (300 MHz, CDCl3): d = 2.36 (s, 6H, NCH3), 2.68 (m, 2H,
CH2),10 2.93 (m, 2H,CH2),10 6.54 (d, 1H, J =7.6, Ar), 6.83 (br d, 2H,
J =12.2 Hz, Ar), 7.03 (t, 1H, J = 7.8 Hz, Ar), 7.86 (br s, 1H, NH),
13.2 (br s, 1H, OH; observed only by integration).
4-O-Monobenzylphosphoryloxy-N,N-dimethyltryptamine (6)
A solution of 0.45 g (2.2 mmol) of psilocin (5) and 0.073 g (0.73
mmol) of diisopropylamine in anhyd THF (50 mL) was magnetical-
ly stirred in a 100 mL 3-necked flask and was cooled to –78 °C in a
dry ice–acetone bath. A 2.5 M solution (1.14 mL, 2.85 mmol) of
BuLi in hexane was added dropwise using a syringe. After complete
addition, the reaction was stirred for 3 min and
tetrabenzylpyrophosphate8 (1.50 g, 2.8 mmol) was added all at
once. The dry ice–acetone bath was replaced by an ice–salt bath,
938 D. E. Nichols, S. Frescas PAPER
Synthesis 1999, No. 6, 935–938 ISSN 0039-7881 © Thieme Stuttgart ·New York
and stirring was continued for 1.5 h. TLC (9:1 CHCl3–MeOH; alu-
mina plates) showed complete disappearance of starting material.
The reaction was quenched by addition of sat. NH4Cl (30 mL). The
biphasic solution was rapidly transferred to a separatory funnel, and
the aqueous layer was separated and washed with EtOAc (2 x 20
mL). The organic layers were combined and washed with brine
(25 mL), followed by drying anhyd (MgSO4). The solution was
then concentrated to a clear residue using rotary evaporation. This
residue (1.12 g) was shown by thin layer chromatography and NMR
analysis to be a mixture of O,O-dibenzylpsilocybin, O-monoben-
zylpsilocybin (6), and a small amount of dibenzyl phosphoric acid.
N,N-Dimethyl-4-phosphoryloxtryptamine (Psilocybin; 1)
In a 250 mL Parr hydrogenation bottle was placed 1.0 g of 10% Pd/
C catalyst followed by anhyd MeOH (50 mL). The dibenzyl/
monobenzylphosphoryloxy-N,N-dimethyltryptamine (1.12 g) pre-
pared in the previous step was added and the mixture was shaken
under 60 psig hydrogen pressure for 3 h, at which time hydrogen up-
take had ceased. The hydrogenation bottle was removed from the
apparatus and the catalyst was removed by filtration through a pad
of Celite 545 on a Buchner funnel. The pH of the clear solution was
measured at 3.7 using a pH meter. Amberlite IRA-400 anion ex-
change resin (–OH form) (0.75g) was added in 3 portions to the
well-stirred methanolic solution to raise the pH to 5.3.9 The resin
was removed by vacuum filtration and the resulting clear filtrate
was concentrated to dryness by rotary evaporation. The residue was
dissolved in a minimum amount of hot MeOH, and hot isopropanol
was added to the cloud point. An additional drop of MeOH pro-
duced a clear solution. Upon storage in a –20 °C freezer the product
slowly crystallized as white needles 0.294 g (46.9%, from psilocin).
This product was dried under high vacuum to produce solvent-free
psilocybin, which had mp 212–213 °C (lit.5 mp 210–212 °C).
1H NMR (300 MHz, D20): d = 2.72 (s, 6H, NCH3), 3.14 (t, 2H, J =
7.3 Hz, CH2), 3.29 (t, 2H, J = 7.5 Hz, CH2), 6.85 (d, 1H, J = 7.6 Hz,
Ar), 6.99 (t, 1H, J = 7.9 Hz, Ar), 7.03 (s, 1H, Ar), 7.09 (d, 1H, J =
8.0 Hz, Ar).
Anal. Calcd for C12H17N2O4P (284.25): C 50.71, H 6.03, N 9.86, P
10.90; found: C 50.37, H 5.91, N 9.68, P 10.75.
4-Acetoxy-N,N-dimethyltryptamine5 fumarate (2)
In a 250 mL Parr hydrogenation bottle was placed 0.25g 10% Pd/C
and anhyd NaOAc (1.50 g, 18 mmol). Benzene (50 mL) was added,
followed by acetic anhydride (5mL, 5.41g, 5.32 mmol), and 4 (0.50g,
1.7 mmol). The mixture was shaken under 60 psig of hydrogen for 4 h.
After the uptake of hydrogen had ceased the hydrogenation bottle
was removed from the apparatus, the mixture was diluted with THF
(25 mL), and the catalyst was removed by filtration through a pad
of Celite 545. The catalyst was washed repeatedly with isopropanol
(3 x 50 mL). The washings and mother liquor were collected sepa-
rately because of unreacted Ac2O in the filtrate. The mother liquor
was concentrated under vacuum to about one half the original vol-
ume, then toluene (50 mL) was added. The solution was again con-
centrated by rotary evaporation. The isopropanol washes were
combined with the residue and also concentrated. The residue was
then dissolved in anhyd MeOH (50 mL). Fumaric acid (0.198 g, 1.7
mmol) was dissolved in MeOH (10 mL) and added to the stirred
methanolic solution of the residue. After stirring for 10 minutes, tol-
uene (50 mL) was added and the solution was concentrated to dry-
ness by rotary evaporation. Absolute EtOH was added to the residue
and a white precipitate of 2 fumarate (0.290 g, 0.8 mmol) formed
and was collected by filtration. The filtrate was evaporated and the
residue was dissolved in a minimum amount of MeOH. EtOAc was
added and clear crystals began to form. After storing the solution in
a freezer at –10 °C, 0.170 g of additional product was collected for
a total yield of 0.460 g (74.8%); mp 172–173 °C.
1NMR (300 MHz, D2O) d = 2.29 (s, 3H, CH3), 2.72 (s, 6H, NCH3),
2.98 (t, 2H, J = 7.1 Hz, CH2), 3.32 (t, 2H, J = 7.1 Hz, CH2), 6.49 (s,
1H, CH), 6.72 (d, 1H, J = 7.7, Ar), 7.08 (t, 1H, J = 8.0, Ar), 7.16 (s,
1H, Ar), 7.29 (d, 1H, J = 8.3, Ar).
Anal. Calcd for C18H22N2O6 (362.38): C 59.66, H 6.12, N 7.73;
found C 59.43, H 6.35, N 7.58.
Acknowledgement
This work was supported in part by grants DA02189 and DA08096
from the National Institute on Drug Abuse.
References and Notes
(1) Strassman, R.J.; Qualls, C.R. Arch. Gen. Psych. 1994, 51, 85.
(2) Strassman, R.J.; Qualls, C.R., Uhlenhuth, E.H.; and Kellner,
R. Arch. Gen. Psych. 1994, 51, 98.
(3) Grob, C.S.; McKenna, D.J.; Callaway, J.C.; Brito, G.S.;
Neves, E.S.; Oberlaender, G.; Saide, O.L.; Labigalini, E.;
Tacla, C.; Miranda, C.T.; Strassman, R.J.; Boone, K.B. J.
Nerv. Ment. Dis. 1996, 184, 86.
(4) Hofmann, A.; Heim, R.; Brack, A.; Kobel, H.; Frey, A.; Ott,
H.; Petrzilka, T.; Troxler, F. Helv. Chim. Acta. 1959, 42, 1557.
(5) U.S patent 3,075,992, Jan 29, 1963.
(6) Hasler, F.; Bourquin, D.; Brenneisen, R.; Bar, T.;
Vollenweider, F.X. Pharm. Acta Helv., 1997, 72, 175.
(7) Speeter, M.E.; Anthony, W.C. J. Am. Chem. Soc. 1954, 76,
6208.
(8) Khorana, H.G.; Todd, A.R. J. Chem. Soc. 1953, 2257.
(9) Reported pH of psilocybin solution, see ref. 4.
(10) Migliaccio, G.P.; Shieh, T.L.N.; Byrn, S.R.; Hathaway, B.A.;
and Nichols, D.E. J. Med. Chem. 1981, 24, 206; this reference
reports a computer simulation for the average coupling
constants between the methylene protons as Jab = 2.7 Hz and
Jab’ = 7.4 Hz.
Article Identifier:
1437-210X,E;1999,0,06,0935,0938,ftx,en;C07398SS.pdf
