Synthesis of 1-(1-aryl-1H-1,2,3-triazol-4-yl)-β-carboline derivatives

Article abstract of DOI:10.1134/S1070428014020225

Reaction of 5-methyl-1-aryl-1H-1,2,3-triazole-4-carbocylic acid chlorides with tryptamine derivatives afforded substituted 1-aryl-N-[2-(1H-indol-3-yl) ethyl]-5-methyl-1H-1,2,3-triazole-4-carboxamides. At heating these compounds in toluene in the presence of POCl₃ and P₂O₅ Bischler-Napieralski cyclization occurs giving 1-(1-aryl-5-methyl-1H-1,2,3- triazol-4-yl)-4,9-dihydro-3H-β-carbolines that can be transformed into β-carboline and tetrahydro-β-carboline derivatives.

Full text of DOI:10.1134/S1070428014020225

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2014, Vol. 50, No. 2, pp. 275−279. © Pleiades Publishing, Ltd., 2014.
Original English Text © N.T. Pohodylo, V.S. Matiichuk, M.D. Obushak, 2014, published in Zhurnal Organicheskoi Khimii, 2014, Vol. 50, No. 2, pp. 282−286.
Synthesis of 1-(1-Aryl-1H-1,2,3-triazol-4-yl)-β-carboline
Derivatives
N. T. Pohodylo, V. S. Matiichuk, and M. D. Obushak
Ivan Franko Lviv National University, Lviv, 79005 Ukraine
e-mail: obushak@in.lviv.ua
Received September 20, 2013
Abstract—Reaction of 5-methyl-1-aryl-1H-1,2,3-triazole-4-carbocylic acid chlorides with tryptamine derivatives
afforded substituted 1-aryl-N-[2-(1H-indol-3-yl)ethyl]-5-methyl-1H-1,2,3-triazole-4-carboxamides. At heating
these compounds in toluene in the presence of POCl3 and Р2О5 Bischler-Napieralski cyclization occurs giving
1-(1-aryl-5-methyl-1H-1,2,3-triazol-4-yl)-4,9-dihydro-3H-β-carbolines that can be transformed into β-carboline
and tetrahydro-β-carboline derivatives.
DOI: 10.1134/S1070428014020225
Heterocyclic system of β-carboline (9H-pyrido[3,4-b]- The severe conditions may be the reason of complications
indole) is an important structural fragment that is often
occurring in the course of these reactions, especially in
present in alkaloids and their synthetic analogs possess- presence of reactive functional groups. In these cases
ing biological activity [1, 2]. In this connection special softer conditions were developed utilizing in Bischle–Na-
attention is attracted by the methods of isolation and pieralski cyclisation triphosgene [19], also the systems
of oxalyl chloride–(COCl)2–FeCl3 in dichloromethane
[20], triphenylphosphine in boiling CCl4 [21], Tf2O–
DMAP [22] or bromotriphenoxyphosphonium bromide
(PhO)3PBr2 [23].
preparation of either natural or synthetic derivatives of
β-carboline [3–7]. The accesibility of this heterocyclic
system is due, first of all, to the synthetic opportunities
provided by Pictet-Spengler and Bischler–Napieralski re-
actions [8–10]. The last reaction posesses higher diversity
and utilizes more accessible initial reagents. The dihydro-
β-carbolines obtained are easily oxidized to β-carbolines
or reduced to tetrahydro-β-carbolines.
While the cyclization is an electophilic aromatic sub-
stitution, the substrates with electon-donor substituents
give as a rule better results. The compounds that do not
contain electron-donor groups often do not undergo cy-
clization or give final product in small yields.
Bischler–Napieralski reaction is widely used in the
synthetic practice and involves the cyclodehydration
of (het)arylethylamides [9]. Its assumed mechanism in-
volves the formation of intermediate imido chlorides or
nitrilium ions, which is confirmed by some Ritter retro-
reactions [11], and the subsequent intramolecular electro-
philic aromatic substitution. The reaction is applicable to
a wide range of compounds with substituents in aromatic
ring, in α- and β-positions of ethylamine fragment, and
also to various substituted amides [12].
In the present study we investigated the possibility
to obtain by Bischler–Napieralski reaction β-carboline
derivatives with 1,2,3-triazole substituents, using as initial
substances substituted 1,2,3-triazole-4-carbocylic acids.
Considering the results of our previous investigations
[24] we could have expected probable complications con-
nected with the electron-donor effect of the triazole ring
on the reactivity of the carboxy and amide groups, with
the formation of reactive intermediates, and proceeding
of competitive processes. 1,2,3-Triazole-4-carboxylic
acids have never been studied before in such reactions.
In classical version the reaction is carried out in boiling
solvent (e.g., in toluene) with the use of POCl3 or P2O5.
In the syntheses of biologically active compounds by
Bischler–Napieralski reaction POCl3 [13–16], P2O5 [17],
and POCl3 in ionic liquids [18] were used as reagents.
Initial reagents were obtained from commercially
available aromatic amines and diazonium salts on their
basis. Aryl azides IIIа–IIId were obtained by diazotiza-
275

POHODYLO et al.
276
tion of arylamines Іа–Id followed by treating the diazo-
nium salts IIа–IId with potassium azide. The cyclization
of ethyl acetoacetate with aryl azides IIIа–IIId leads to
the formation of 1-aryl-5-methyl-1H-1,2,3-triazole-4-
carboxylic acids that are transformed into acyl chlorides
IVа–IVd [24].All tryptamine derivatives VIа–VIc used
in our investigation were synthesized by Fischer method.
The arylhydrazines Vd–Vf obtained by reduction of
the diazonium salts IId–IIf with SnCl2 were brought
into the reaction with the 4-aminobutanal acetal or with
4-phtalamidobutanal with subsequent removal of the
protection [25–28]. Compounds VIа–VIc smoothly un-
derwent acylation with acid chlorides IVа–IVd, and as
a result amides VIIа–VIIf were obtained that then were
tested in Bischler–Napieralski cyclization.As the experi-
ment demonstrated, the cyclization took place when the
reaction was performed in acetontrile in the presence of
POCl3, but compounds VIIIа–VIIIf were obtained in low
NH2
R1
Iа−If
NaNO2, HCl
N2+Cl_
H
N
N3
SnCl2
NaN3
NH2
R1
R1
O
R1
O
IIа−
IIf
Vd−Vf
IIIа−
IIId
OEt
or
NH2
EtO
O
Cl
N
N
N
OEt
O
R2
O
(1)
Me
C
H2N
(2) SOCl2
N
Me
C
O
N
H
VIа
R1
−
VIc
IVа−
IVd
Et3N
O
N
N
N
R2
N
H
Me
R1
NH
Cl
VIIа−VIIf
N
POCl3, P2O5 Toluene
N
H
N
HN
Me
N
N
N
N
N
Me
N
N
5% Pd/C
HCl
NaBH4
MeOH
R2
N
R1
Cl
N
Me
N
H
N
H
X
IX
Me
VIIIа−VIIIf
I–V, R1 = Н (а), 4-Ме (b), 4-MeО (c), 4-F (d), 4-Cl (e), 3-MeО (f); VI, R2 = 5-F (а), 5-Cl (b), 6-MeО (c); VII, R1 = Н, R2 = 6-MeО
(а), 5-F (b), 5-Cl (c); R1 = 4-F, R2 = 6-MeО (d); R1 = 4-MeО, R2 = 5-F (e); R1 = 4-Ме, R2 = 5-Cl (f); VIII, R1 = Н, R2 = 7-MeО (а),
6-F (b), 6-Cl (c); R1 = 4-F, R2 = 7-MeO (d); R1 =4-MeO, R2 = 6-F (e); R1 = 4-Me, R2 = 6-Cl (f).
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SYNTHESIS OF 1-(1-ARYL-1H-1,2,3-TRIAZOL-4-YL)-Β-CARBOLINE DERIVATIVES
277
89%, mp 169–170°C . 1Н NMR spectrum, δ, ppm: 2.54 s
(3Н, Ме), 2.93 t (2H, СН2, J 6.0 Hz), 3.57 t (2H, СН2,
J 6.0 Hz), 3.76 s (3H, MeO), 6.67 d (1H, indole, J 8.3 Hz),
6.86 s (1H, indole), 7.07 s (1H, indole), 7.49 d (1H, indole,
J 8.3 Hz), 7.60–7.70 br.s (5H, Ph), 8.66 br.s (1H, NH),
10.63 s (1H, NH). Found, %: C 67.26; H 5.42; N 18.56.
C21H21N5O2. Calculated, %: C 67.18; H 5.64; N 18.65.
or medium yields. Rising the temperature of the reaction
to 110°C and bringing P2O5 into the reaction mixture
allowed an essential increase in the yields. Apparently
the P2O5–POCl3 system absorbs water more effectively
and facilitates the formation of ionic nitrilium intermedi-
ates that can promptly react with the aromatic ring. The
reactions should be preferably carried out in toluene or
without solvent.
5-Methyl-1-phenyl-N-[2-(5-fluoro-1H-indol-3-yl)
ethyl]-1H-1,2,3-triazole-4-carboxamide (VIIb). Yield
83%, mp 230–232°C. 1Н NMR spectrum, δ, ppm: 2.55 s
(3Н, Ме), 3.02 t (2H, СН2, J 7.0 Hz), 3.08 t (2H, СН2,
J 7.0 Hz), 6.92 t (1H, indole, J 8.8 Hz), 7.30–7.41 m
(3H, Ar), 7.51–7.71 m (5H, Ar), 8.71 br.s (1H, NH),
11.17 s (1H, NH). Found, %: C 65.93; H 4.81; N 19.14.
C20H18FN5O. Calculated, %: C 66.10; H 4.99; N 19.27.
We have investigated the possibility of reduction of
dihydro-β-carbolines VIII to tetrahydro-β-carbolines
and it is established that the application of NaBH4 as a
reducing agent gives the optimal results. Compound IX
was obtained in 93% yield.
To transform the tetrahydroisoquinolines in the cor-
responding isoquinoline derivatives various reagents are
used, e.g., о-(iodoxy)benzoic acid [29] or sulfur [30]. In
dehydrogenation of compounds VIII the best result was
obtained with palladium on carbon in toluene [31]; the
yield of β-carboline derivative X was 94%.
5-Methyl-1-phenyl-N-[2-(5-chloro-1H-indol-3-yl)-
ethyl]-1H-1,2,3-triazole-4-carboxamide (VIIc). Yield
92%, mp 172–173°C. 1Н NMR spectrum, δ, ppm: 2.50 s
(3Н, Ме), 2.92–3.00 m (2H, СН2), 3.52–3.60 m (2H,
СН2), 7.07 d (1H, indole, J 8.4 Hz), 7.30 s (1H, indole),
7.36 d (1H, indole, J 8.4 Hz), 7.60–7.77 (Ar, 6H), 8.71 s
(1H, NH), 11.07 s (1H, NH). Found, %: C 63.38; H 4.65;
N 18.56. C20H18ClN5O. Calculated, %: C 63.24; H 4.78;
N 18.44.
Thus an approach has been developed to the synthesis
of β-carboline derivatives containing 1,2,3-triazole ring
with various substituents allowing to obtain series of
compounds promising for further testing for biological
activity.
5-Methyl-N-[2-(6-methoxy-1H-indol-3-yl)ethyl]-
1-(4-fluorophenyl)-1H-1,2,3-triazole-4-carboxamide
(VIId). Yield 78%, mp 227–228°C. 1Н NMR spectrum,
δ, ppm: 2.55 s (3Н, Ме), 2.98 t (2H, СН2, J 6.8 Hz),
3.07 t (2H, СН2, J 6.8 Hz), 3.75 s (3H, MeO), 6.64 d (1H,
indole, J 8.5 Hz), 6.87 s (1H, indole), 7.08 s (1H, indole),
7.41 d (1H, indole, J 8.5 Hz), 7.44–7.48 m (2H, С6Н4),
7.62–7.67 m (2H, С6Н4), 8.41 br.s (1H, NH), 10.80 s (1H,
NH). Found, %: C 64.02; H 5.29; N 17.83. C21H20FN5O2.
Calculated, %: C 64.11; H 5.12; N 17.80.
EXPERIMENTAL
1Н NMR spectra of the synthesized compounds were
recorded on a Bruker Avance 500 (500 МHz) spectrom-
eter, solvent DMSO-d6, internal reference TMS.
Aryl azides ІIIа–IIIe were obtained by method [32]
and were described in [24].
1-Aryl-5-methyl-1H-1,2,3-triazole-4-carboxylic acids
and acyl chlorides IVа–IVd were obtained by procedures
[33, 34] and were described in [24].
5-Methyl-1-(4-methoxyphenyl)-N-[2-(5-fluoro-1H-
indol-3-yl)ethyl]-1H-1,2,3-triazole-4-carboxamide
(VIIe). Yield 74%, mp 285–286°C. 1Н NMR spectrum,
δ, ppm: 2.55 s (3Н, Ме), 3.02 br.s (2H, СН2), 3.09 br.s
(2H, СН2), 3.85 s (3H, MeO), 6.91 t (1H, indole,
J 8.8 Hz), 7.13 d (2H, С6Н4, J 7.2 Hz), 7.31–7.39 m (3H,
indole), 7.48 d (2H, С6Н4, J 7.2 Hz), 8.61 br.s (1H, NH),
11.21 br.s (1H, NH). Found, %: C 64.21; H 5.25; N 17.71.
C21H20FN5O2. Calculated, %: C 64.11; H 5.12; N 17.80.
N-[2-(1H-Indol-3-yl)ethyl]-5-methyl-1H-1,2,3-
triazole-4-carboxamides VIIа–VIIf. Aslurry of 5 mmol
of tryptamine hydrochloride VIа–VIc in 30 mL of di-
chlorethane was mixed with 1.38 g (10 mmol) of milled
calcined K2СО3, a solution of 5 mmol of acid chloride
ІVа–IVd in 15 mL of СН2Сl2 was added dropwise at
room temperature. The reaction mixture was stirred at
25°C for 12 h, then washed with water (3 × 20 mL).
The organic layer was dried with MgSO4, filtered, the
solvent was evaporated, the residue was recrystallised
from ethanol.
5-Methyl-1-(4-methylphenyl)-N-[2-(5-fluoro-1H-
indol-3-yl)ethyl]-1H-1,2,3-triazole-4-carboxamide
(VIIf). Yield 91%, mp 188–189°C. 1Н NMR spectrum,
δ, ppm: 2.42 s (3Н, Ме), 2.55 s (3Н, Ме), 2.96 t (2H,
СН2, J 7.2 Hz), 3.56 t (2H, СН2, J 7.2 Hz), 7.07 d (1H,
5-Methyl-N-[2-(6-methoxy-1H-indol-3-yl)ethyl]-1-
phenyl-1H-1,2,3-triazole-4-carboxamide (VIIа). Yield
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POHODYLO et al.
278
indole, J 8.0 Hz), 7.31 s (1H, indole), 7.37 d (1H, indole,
J 8.0 Hz), 7.44 d (2H, С6Н4, J 7.8 Hz), 7.50 d (2H, С6Н4,
J 7.8 Hz), 7.67 s (1H, indole), 8.69 t (1H, NH, J 5.4 Hz),
11.11 br.s (1H, NH). Found, %: C 64.22; H 5.27; N 17.63.
C21H20ClN5O. Calculated, %: C 64.04; H 5.12; N 17.78.
(2H, С6Н4), 11.17 s (1H, NH). Found, %: C 67.27; H 4.74;
N 18.76. C21H18FN5O. Calculated, %: C 67.19; H 4.83;
N 18.66.
1-[5-Methyl-1-(4-metoxyphenyl)-1H-1,2,3-triazol-
4-yl]-6-fluoro-4,9-dihydro-3H-β-carboline (VIIIe).
Yield 75%, mp 182–184°C. 1Н NMR spectrum, δ, ppm:
2.67 s (2H, Me), 2.91 br.s (2H, СН2), 3.26 t (2H, СН2,
J 7.2 Hz), 3.92 s (3H, MeO), 7.01 t (1H, carboline,
J 8.8 Hz), 7.13 d (2H, С6Н4, J 7.4 Hz), 7.52 d (2H, С6Н4,
J 7.4 Hz), 7.54–7.62 m (2H, carboline), 11.33 s (1H,
NH). Found, %: C 67.29; H 4.74; N 18.78. C21H18FN5O.
Calculated, %: C 67.19; H 4.83; N 18.66.
1-(1H-1,2,3-Triazol-4-yl)-4,9-dihydro-3H-β-
carboline derivatives VIIIа–VIIIf. In 25 mL of anhy-
drous toluene was dissolved 0.88 mmol of amide VII
and 1.24 g (8.9 mmol) of Р2О5 was dispersed, 0.83 mL
(8.9 mmol) POCl3 was added dropwise. After adding
POCl3 the reaction mixture was heated for 12 h, the
solvent and POCl3 were distillated in a vacuum, then
cooled and mixed with ~25 g of crushed ice. The resulting
mixture was neutralised with 20% solution of NaOH, the
reaction product was extracted with toluene. The extract
was dried with MgSO4, the solvent was evaporated, the
residue was recrystallised from alcohol.
1-[5-Methyl-1-(4-methylphenyl)-1H-1,2,3-triazol-
4-yl]-6-chloro-4,9-dihydro-3H-β-carboline (VIIIf).
Yield 81%, mp 211–213°C. 1Н NMR spectrum, δ, ppm:
2.46 s (3H, Me), 2.60 s (3H, Me), 2.94 t (2H, СН2,
J 8.2 Hz), 4.01 t (2H, СН2, J 8.2 Hz), 7.24 d (1H, carbo-
line, J 8.7 Hz), 7.49 d (2H, С6Н4, J 8.3 Hz), 7.57 d (2H,
С6Н4, J 8.3 Hz), 7.71 d (1H, carboline, J 8.7 Hz), 7.72 s
(1H, carboline), 11.55 s (1H, NH). Found, %: C 67.01;
H 4.74; N 18.81. C21H18ClN5. Calculated, %: C 67.11;
H 4.83; N 18.63.
1-(5-Methyl-1-phenyl-1H-1,2,3-triazol-4-yl)-7-me-
thoxy-4,9-dihydro-3H-β-carboline (VIIIа). Yield 81%,
mp 190–191°C. 1Н NMR spectrum, δ, ppm: 2.63s (3H,
Ме), 2.89 t (2H, СН2, J 7.6 Hz), 3.79 s (3H, MeO), 4.10 t
(2H, СН2, J 7.6 Hz), 6.79 d (1H, carboline, J 8.4 Hz),
7.21 s (1H, carboline), 7.54 d (1H, carboline, J 8.4 Hz),
7.64–7.73 m (5H, Ph), 11.01 s (1H, NH). Found, %:
C 70.45; H 5.48; N 19.76. C21H19N5O. Calculated, %:
C 70.57; H 5.36; N 19.59.
1-(5-Methyl-1-phenyl-1H-1,2,3-triazol-4-yl)-6-
chloro-2,3,4,9-tetrahydro-1H-β-carboline (IX). To a
solution of 362 mg (1 mmol) of compound VIIIc in 15 mL
of methanol cooled in the ice bath was added 75 mg of
NaBH4. The mixture was stirred at room temperature for
5 min, then boiled for 1 h. Methanol was evaporated, the
residue was dissolved in СН2Cl2 and washed with 10%
NaOH, methylene chloride was evaporated. Yield 91%,
mp 191–192°C. 1Н NMR spectrum, δ, ppm: 2.55 s (3H,
Me), 2.81 m (2H, CH2), 3.62 m (2H, CH2), 4.12 br.s (1H,
СH), 5.45 br.s (1H, NH), 7.14 d (1H, carboline, J 8.4 Hz),
7.53 s (1H, carboline), 7.55–7.69 m (6H,Ar), 11.05 s (1H,
NH). Found, %: C 66.15; H 4.83; N 19.41. C20H18ClN5.
Calculated, %: C 66.02; H 4.99; N 19.25.
1-(5-Methyl-1-phenyl-1H-1,2,3-triazol-4-yl)-6-
fluoro-4,9-dihydro-3H-β-carboline (VIIIb). Yield 74%,
mp 152–153°C. 1Н NMR spectrum, δ, ppm: 2.63 s (2H,
Me), 2.81 t (2H, СН2, J 6.8 Hz), 3.29 t (2H, СН2, J 6.8 Hz),
7.00 t (1H, carboline, J 8.8 Hz), 7.58–7.79 m (7H, Ar),
11.34 s (1H, NH). Found, %: C 69.75; H 4.82; N 20.16.
C20H16FN5. Calculated, %: C 69.55; H 4.67; N 20.28.
1-(5-Methyl-1-phenyl-1H-1,2,3-triazol-4-yl)-6-
chloro-4,9-dihydro-3H-β-carboline (VIIIc). Yield
89%, mp 203–205°C. 1Н NMR spectrum, δ, ppm: 2.65 s
(3H, Me), 2.89 t (2H, СН2, J 7.6 Hz), 4.02 t (2H, СН2,
J 7.6 Hz), 7.21 d (1H, carboline, J 8.4 Hz), 7.57–7.67 m
(6H,Ar), 7.96 s (1H, carboline), 11.36 s (1H, NH). Found,
%: C 66.44; H 4.54; N 19.31. C20H16ClN5. Calculated,
%: C 66.39; H 4.46; N 19.36.
1-[5-Methyl-1-(4-methylphenyl)-6-chloro-1H-
1,2,3-triazol-4-yl]-9H-β-carboline (X). 376 mg
(1 mmol) of the compound VIIIf and 100 mg of 5% Pd/C
were mixed. The mixture was ground to powder-like
condition and heated at 150°C for 30 min. To the reac-
tion mixture 100 mL of СН2Cl2 was added, the mixture
was stirred and filtered. The solvent was distilled off, the
residue was recrystallised from a mixture alcohol-DMF.
1-[5-Methyl-1-(4-phluorophenyl)-1H-1,2,3-triazol-
4-yl]-7-methoxy-4,9-dihydro-3H-β-carboline (VIIId).
Yield 68%, mp 185–186°C. 1Н NMR spectrum, δ, ppm:
2.65 s (3H), 2.87 t (2H, СН2, J 7.2 Hz), 3.26 t (2H, СН2,
J 7.2 Hz), 3.77 s (3H, MeO), 6.74 d (1H, carboline,
J 8.6 Hz), 7.25 s (1H, carboline), 7.48 t (2H, С6Н4,
J 8.6 Hz), 7.59 d (1H, carboline, J 8.6 Hz), 7.62–7.67 m
1
Yield 84%, mp >250°C. Н NMR spectrum, δ, ppm:
2.44 s (3H, Me), 2.65 s (3H, Me), 7.30 d (1H, carboline,
J 8.0 Hz), 7.53 d (2H, С6Н4, J 8.4 Hz), 7.67 d (2H, С6Н4,
J 8.4 Hz), 7.73–7.78 m (2H, carboline), 8.01 d (1H,
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SYNTHESIS OF 1-(1-ARYL-1H-1,2,3-TRIAZOL-4-YL)-Β-CARBOLINE DERIVATIVES
279
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carboline, J 8.0 Hz), 8.54 d (1H, carboline, J 5.1 Hz),
12.05 s (1H, NH). Found, %: C 67.38; H 4.41; N 18.61.
C21H16ClN5. Calculated, %: C 67.47; H 4.31; N 18.73.
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