Synthesis of a deuterium-labelled standard of bufotenine (5-HO-DMT)

Article abstract of DOI:10.1002/jlcr.1459

The Batcho-Leimgruber strategy was employed to synthesize 3-(2-dimethylamino-[²H₄]-ethyl)-1H-indol-5-ol (bufotenine, 5-HO-DMT) (8) from commercial 3-methyl-4-nitro-phenol (1), benzyl bromide and N,N-dimethylformamide-dimethylacetal. Compound 4 was synthesized from compound 3 using the Batcho-Leimgruber strategy in the presence of Raney nickel and hydrazine hydrate. Compound 4 was treated with oxalyl chloride, dimethylamine and lithium aluminum [²H₄]-hydride to yield [2-(5-benzyloxy-1H-indol-3-yl)-[²H₄]-ethyl] -dimethyl-amine (7). The benzyl ether in compound 7 was cleaved by hydrogenolysis to give bufotenine 8. Copyright

Full text of DOI:10.1002/jlcr.1459

Journal of Labelled Compounds and Radiopharmaceuticals
J Label Compd Radiopharm 2007; 50: 1262–1265.
Published online 1 October 2007 in Wiley InterScience
JLCR
(www.interscience.wiley.com). DOI: 10.1002/jlcr.1459
Research Article
Synthesis of a deuterium-labelled standard of bufotenine
5-HO-DMT)
(
YU-YUN WANG and CHINPIAO CHEN*
Department of Chemistry, National Dong Hwa University, Soufeng, Hualien 974, Taiwan, Republic of China
Received 24 March 2007; Revised 13 August 2007; Accepted 14 August 2007
2
Abstract: The Batcho–Leimgruber strategy was employed to synthesize 3-(2-dimethylamino-[ H ]-ethyl)-1H-indol-5-
4
ol (bufotenine, 5-HO-DMT) (8) from commercial 3-methyl-4-nitro-phenol (1), benzyl bromide and N,N–dimethylfor-
mamide–dimethylacetal. Compound 4 was synthesized from compound 3 using the Batcho–Leimgruber strategy in
the presence of Raney nickel and hydrazine hydrate. Compound 4 was treated with oxalyl chloride, dimethylamine
2
2
4 4
and lithium aluminum [ H ]-hydride to yield [2-(5-benzyloxy-1H-indol-3-yl)-[ H ]-ethyl]-dimethyl-amine (7). The
benzyl ether in compound 7 was cleaved by hydrogenolysis to give bufotenine 8. Copyright # 2007 John Wiley &
Sons, Ltd.
Keywords: bufotenine; deuterium labelled; internal standard
Introduction
Results and discussion
The allegedly psychedelic drug, bufotenine, is an
alkaloid found in frog and toad skins, mushrooms,
high-order plants, and mammals, especially in the
Although bufotenine has been prepared via several
1
9–25
2
synthetic routes,
4
[ H ]-bufotenine has been pre-
1
9
pared using a different method. This study describes
1
,2
2
brain, plasma and urine of schizophrenics.
Bufote-
4
alternative procedures for preparing [ H ]-bufotenine.
nine, commonly known as 5-hydroxy-DMT (5-OH-
DMT), is a tryptamine related to the neurotransmitter
Scheme 1 presents the preparation of 3-(2-dimethyla-
2
mino-[ H ]-ethyl)-1H-indol-5-ol (8). 3-Methyl-4-nitro-
4
3
serotonin.
phenol (1) was treated with benzyl bromide in the
Unknown abused drugs are typically detected and
identified by gas chromatography–mass spectrometry
presence of potassium carbonate to give benzyl-(3-
2
6
methyl-4-nitro-phenyl)-ether (2) in a 99% yield. As in
2
0–25,27–32
(GC–MS) because of the high sensitivity of this method
the Batcho–Leimgruber synthesis of indole,
and its ability to separate complex mixtures of organic
compound 2 was condensed with N,N-dimethylforma-
4
–7
compounds.
Standard samples used for analyzing
mide–dimethyl acetal to yield [2-(5-benzyloxy-2-nitro-
2
7
controlled drugs in Taiwan are very difficult to obtain.
Many studies have been reported for the preparation of
deuterium-labelled control drugs as internal standards
phenyl)-vinyl]-dimethyl-amine (3). Hydrogenolysis of
compound 3 with Raney nickel and hydrazine hydrate
2
6
gave 5-benzyloxy-1H-indole (4) in a 62% yield.
8
–18
33,34
for use as GC–MS analysis.
This work describes
, and presents related
A reaction of compound 4 and oxalyl chloride
and
2
0
synthetic routes to bufotenine-d
4
then dimethyl amine
formed 2-(5-benzyloxy-1H-in-
characteristic analytical data.
dol-3-yl)-N,N-dimethyl-2-oxo-acetamide (6) in a 79%
yield. Reduction of compound 6 with lithium aluminum
2
[
[
H
H
4
]-hydride produced [2-(5-benzyloxy-1H-indol-3-yl)-
2
19
4
]-ethyl]-dimethyl-amine (7) in a 95% crude yield.
Hydrogenolysis of the benzyl ether group in compound
with hydrogen (1 atm.) and Pd/C (10%) gave 3-(2-
7
*
Correspondence to: Chinpiao Chen, Department of Chemistry,
2
National Dong Hwa University, Soufeng, Hualien 974, Taiwan, Republic
of China. E-mail: chinpiao@mail.ndhu.edu.tw
Contract/grant sponsor: National Bureau of Controlled Drugs, Depart-
ment of Health, Taiwan, Republic of China; contract/grant number:
DOH95-NNB-1001
dimethylamino-[ H ]-ethyl)-1H-indol-5-ol (8) in a 99%
4
20
crude yield. In order to purify compounds 7 and 8 by
recrystallization, compound 7 was converted to its
oxalic acid salt which was recrystallized from methanol
Copyright # 2007 John Wiley & Sons, Ltd.

SYNTHESIS OF A DEUTERIUM-LABELLED STANDARD OF BUFOTENINE (5-HO-DMT) 1263
Scheme 1
to give the oxalic acid salt of compound 7 in an 86%
yield. Hydrogenolysis of the benzyl ether group in the
oxalic acid salt of compound 7 gave the oxalic salt of
compound 8 which was recrystallized from methanol/
diethyl ether to give the pure oxalic acid salt of
compound 8 in a 61% yield. The overall yield for the
seven steps is 24%.
All reactions were initially optimized using unlabelled
compounds.
Synthesis of benzyl-(3-methyl-4-nitro-phenyl)-ether
2
6
(2). A mixture of benzyl bromide (1.53 g, 10.0 mmol),
3-methyl-4-nitrophenol (1) (2.22 g, 13.0 mmol) and
potassium carbonate (2.07 g, 15.0 mmol) in dry acetone
(
20 mL) was refluxed for 5 h until compound 1 was
Experimental
General
consumed. Filtration and concentration yielded
a
residue, which was purified by flash column chroma-
tography using silica gel as the stationary phase and
ethyl acetate–hexane (1:19) as the mobile phase to
generate compound 2 (2.40 g, 9.9 mmol). Yield: 99%.
1
H NMR spectra were obtained at 300 or 400 MHz
1
3
35
1
(indicated in each case), and C NMR spectra were
m.p.: 698C (lit. 70–718C). H NMR (300 MHz, CDCl
3
,
obtained at 100.6 MHz using a Bruker NMR spectro-
d): 8.08 (d, J¼ 9:9 Hz, 1H), 7.42–7.35 (m, 5H), 6.89–
1
3
meter. Chemical shifts (d) are reported in ppm relative
6.85 (m, 2H), 5.13 (s, 2H), 2.63 (s, 3H).
C NMR
to CHCl (7.26 and 77.0 ppm). Mass spectra (MS) were
(75 MHz, CDCl , d): 162.2, 142.4, 137.1, 135.7, 128.8,
3
3
obtained using a Micromass Platform II mass spectro-
meter at 70 eV. High-resolution MS (HRMS) were
obtained using a Finnigan/Thermo Quest MAT 95XL
mass spectrometer. Infrared spectra were recorded
using an ATI Mattson spectrometer. All reactions were
performed in anhydrous solvents. Tetrahydrofuran and
diethyl ether were distilled from sodium-benzophenone
under argon. Benzene and N,N-dimethylformamide
were distilled from calcium hydride. All air-sensitive
reactions were performed in dry glassware under
nitrogen using a standard glovebox. Flash column
chromatography was performed using MN silica gel
128.5, 127.6, 127.5, 118.4, 112.6, 70.5, 21.7. IR (KBr,
thin film): 2929, 1588, 1518, 1334, 1252, 1076, 993,
ꢀ
1
þ
837, 761, 702, 655 cm . MS-EI (m/z): 243 (M , 6), 92
(9), 91 (100), 77 (1), 65 (8), 51 (1).
Synthesis of [2-(5-benzyloxy-2-nitro-phenyl)-vinyl]-di-
2
7
methyl-amine (3). A solution of benzyl-(3-methyl-4-
nitro-phenyl)-ether (2) (2.20 g, 9.1 mmol) in N,N-di-
methylformamide–dimethyl acetal (3.6 mL, 27.2 mmol)
and N,N-dimethylformamide (9.0 mL) was heated at
1308C using a reflux condenser for 38 h. The condenser
was replaced with a distillation apparatus to remove
the remaining N,N-dimethylformamide and N,N-di-
methylformamide–dimethyl acetal. The dark brown
6
0 (70–230 mesh) which was purchased from Macher-
ey–Nagel.
Copyright # 2007 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2007; 50: 1262–1265
DOI: 10.1002.jlcr

1
264 Y.-Y. WANG AND C. CHEN
2
residue was used in the subsequent reaction without
further purification.
4
lithium aluminum [ H ]-hydride (0.56 g, 13.3 mmol) in
anhydrous tetrahydrofuran (15 mL) was added, in
small portions, a suspension of 2-(5-benzyloxy-1H-
indol-3-yl)-N,N-dimethyl-2-oxo-acetamide (6) (1.0 g,
3.33 mmol) in tetrahydrofuran (40 mL) and then the
mixture was refluxed for 3.5 h. Following cooling in an
external ice bath, the reaction complex and excess
hydride were decomposed by cautious addition of 2 M
aqueous NaOH. The inorganic solid was removed by
filtration and the filter cake was washed using addi-
tional diethyl ether. The filtrate and washes were
combined and dried over anhydrous magnesium sul-
2
6
Synthesis of 5-benzyloxy-1H-indole (4). To a solution
of crude compound 3 in tetrahydrofuran (9.05 mL),
methanol (9.05 mL) and Raney nickel (ca. 2 g) was
added hydrazine hydrate (0.9 mL, 18.1 mmol) slowly,
and the reaction mixture was stirred at room tempera-
ture. After stirring for 30 min, the Raney nickel was
removed by filtration through a bed of celite. Concen-
tration left a residue, which was purified by flash
column chromatography using silica gel as the sta-
tionary phase and ethyl acetate–hexane (1:9) as the
fate, and the solvents were removed in vacuo, yielding
2
mobile phase to produce compound
4
(1.25 g,
[2-(5-benzyloxy-1H-indol-3-yl)-[ H ]-ethyl]-dimethyl-
4
3
6
5
1
7
5
1
1
2
6
.6 mmol). Yield: 62%. m.p.: 114–1168C (lit.
109–
, d): 8.05 (s, br, 1H),
.53–7.17 (m, 8H), 7.99 (d, J¼ 2:4 Hz, 1H), 6.50 (s, 1H),
amine (7) (0.94 g, 3.2 mmol) in a 95% crude yield. A
solution of oxalic acid (0.35 g, 3.86 mmol) in anhydrous
diethyl ether (30 mL) was added to a solution of
compound 7 (0.82 g, 2.75 mmol) in anhydrous diethyl
ether (20 mL) to form a white precipitate. White
precipitate that formed was filtered and washed with
diethyl ether. The white solid was dissolved in hot
methanol (60 mL); when this saturated solution was
cooled in an ice bath it formed a white powder of the
oxalic acid salt of compound 7 (0.92 g, 2.37 mmol) with
1
118C). H NMR (300 MHz, CDCl
3
1
3
3
.14 (s, 2H). C NMR (75 MHz, CDCl , d): 153.5, 137.8,
31.2, 128.6, 128.3, 127.8, 127.6, 125.0, 113.1,
11.8, 104.0, 102.5, 70.9. IR (thin film): 3313, 3029,
867, 1580, 1481, 1456, 1223, 1149, 996, 728,
ꢀ
1
þ
98 cm . MS-EI (m/z): 223 (M , 75), 132 (73), 104
(32), 91 (100), 77 (12), 65 (12), 51 (8).
Synthesis
methyl-2-oxo-acetamide (6). 5-Benzyloxy-1H-indole
2.90 g, 13.0 mmol) was added in portions to a cool
and well-stirred solution of oxalyl chloride (2.28 mL,
6.1 mmol) in anhydrous diethyl ether (35 mL). The
of
2-(5-benzyloxy-1H-indol-3-yl)-N,N-di-
86% yield. m.p.: 180–1818C. The spectra data of
1
compound 7 are as follows. H NMR (300 MHz, CDCl
3
,
(
d): 7.94 (s, 1H), 7.50–7.32 (m, 5H), 7.22 (s, 1H), 7.13 (d,
J¼ 2:3 Hz, 1H), 6.99 (d, J¼ 2:4 Hz, 1H), 6.94 (m, 1H),
1
3
2
5.12 (s, 2H), 2.33 (s, 6H). C NMR (75 MHz, CDCl , d):
3
mixture was stirred for an additional 30 min. Red solids
that formed were triturated with diethyl ether to give
153.1, 138.1, 132.3, 128.8, 128.5, 128.1, 128.0,
123.3, 113.2, 112.7, 112.4, 102.7, 71.3, 59.5 (m),
45.2, 23.1 (m). IR (KBr, thin film): 3037, 2823, 2200,
3
3,34
compound 5.
Compound 5 in a small amount of
ꢀ
1
anhydrous diethyl ether was added to a solution of
dimethylamine hydrochloride (45.80 g, 0.56 mmol) and
sodium hydroxide (22.40 g, 0.56 mmol) in water
2065, 1586, 1451, 1219, 1051, 937, 789, 732 cm
.
þ
MS-EI (m/z): 298 (M , 41), 238 (5), 160 (5), 147 (8), 133
(2), 119 (5), 91 (24), 65 (3), 60 (100). HRMS-EI (m/z):
2
0
þ
(
54 mL). Stirring was continued for a further 30 min,
[M ] calcd for
298.1981.
C
19
H
18
D
2
N
2
O, 298.1979; found
and the resulting white solid was collected and washed
with diethyl ether to give 2-(5-benzyloxy-1H-indol-3-yl)-
N,N-dimethyl-2-oxo-acetamide (6) (3.31g, 10.3 mmol).
2
Synthesis of 3-(2-dimethylamino-[ H ]-ethyl)-1H-indol-
4
1
9
1
Yield: 79%. m.p.: 178–1798C (lit. 183–1848C). H NMR
300 MHz, CDCl , d): 8.93 (s, 1H), 7.96 (d, J¼ 2:2 Hz,
H), 7.87 (d, J¼ 3:0 Hz, 1H), 7.51–7.29 (m, 6H), 7.02
dd, J ¼ 8:7, 2.2 Hz, 1H), 5.11 (s, 2H), 3.08 (d,
5-ol (8). To a solution of [2-(5-benzyloxy-1H-indol-3-
2
(
3
yl)-[ H
4
]-ethyl]-dimethyl-amine (7) (0.92 g, 3.13 mmol)
1
in anhydrous methanol (10 mL), Pd/C (10%, 92 mg) at
room temperature was added and the reaction mixture
was stirred under a hydrogen atmosphere (1 atm.) for
20.5 h. The catalyst was removed by filtration through
a bed of celite. Concentration left a dark brown solid 8
(0.64 g, 3.1 mmol) in a 99% crude yield. A mixture of
oxalic acid salt of compound 7 (0.90 g, 2.32 mmol) and
Pd/C (10%, 0.09 g) in anhydrous methanol (225 mL)
was stirred under a hydrogen atmosphere (1 atm.) for
24 h. The catalyst was removed by filtration through a
bed of celite. Concentration left a purple solid. The
purple solid was recrystallized from methanol/diethyl
ether to give a purple crystalline of the oxalic acid salt
(
1
3
J¼ 7:3 Hz, 6H) . C NMR (75 MHz, CDCl
3
, d): 186.0,
1
1
3
1
68.3, 155.9, 137.2, 136.0, 131.8, 128.6, 127.9,
27.7, 126.1, 115.1, 114.0, 113.1, 104.7, 70.6, 37.6,
4.4. IR (thin film): 3187, 1641, 1605, 1475, 1434,
ꢀ
1
268, 1081, 789, 743, 643 cm . MS-EI (m/z): 322
þ
(M , 56), 250 (100), 194 (3), 159 (31), 131 (18), 103 (5),
þ
9
1 (44), 72 (10), 65 (4). HRMS-EI (m/z): [M ] calcd for
C
19
H
18
N
2
O
3
, 322.1317; found 322.1321.
2
Synthesis of [2-(5-benzyloxy-1H-indol-3-yl)-[ H
4
]-ethyl]-
1
9
dimethyl-amine (7). To a well-stirred suspension of
Copyright # 2007 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2007; 50: 1262–1265
DOI: 10.1002.jlcr

SYNTHESIS OF A DEUTERIUM-LABELLED STANDARD OF BUFOTENINE (5-HO-DMT) 1265
of compound 8 (0.42 g, 1.41 mmol) in a 61% yield. m.p.:
03–1048C. The spectra data of compound 8 are as
1
1
1
1
1
2
2
5. Springer JB, Colvin OM, Ludeman SM. J Label
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1
1
follows. H NMR (400 MHz, CD
3
OD, d): 7.81 (s, 1H),
7
1
.07 (d, J¼ 8:6 Hz, 1H), 6.90 (s, 1H), 6.82 (d, J¼ 2:3 Hz,
1
3
H), 6.58 (dd, J ¼ 8:6, 2.3 Hz, 1H), 2.27 (s, 6H).
C
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NMR (100.6 MHz, CD OD, d): 149.1, 131.1, 127.3,
3
1
21.9, 110.7, 110.6, 110.3, 101.4, 60.6 (m), 43.2, 22.2
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(
m). IR (KBr, thin film): 3406, 3280, 2956, 2867, 2200,
ꢀ
1
2
2
8
057, 1624, 1583, 1466, 1204, 800 cm . MS-EI (m/z):
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þ
08 (M , 39), 164 (5), 148 (19), 133 (2), 119 (5), 93 (3),
þ
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Acknowledgements
The authors thank Ms Hsu, L. M. at the Instruments
Center, National Chung Hsing University, for their help
in obtaining HRMS. We would also like to thank the
National Bureau of Controlled Drugs, Department of
Health, Taiwan, Republic of China, for financially
supporting this work under Contract DOH95-NNB-
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J Label Compd Radiopharm 2007; 50: 1262–1265
DOI: 10.1002.jlcr