Synthesis and antiinflammatory activity of heterocyclic indole derivatives

Article abstract of DOI:10.1016/j.ejmech.2003.11.002

Chalcones of indole 1-5 and their corresponding products; pyrazolines 6-10 and azo compounds 11-15 were synthesised and evaluated for their antiinflammatory activity against carrageenan induced oedema in albino rats at a dose of 50 mg kg^-1 oral

Full text of DOI:10.1016/j.ejmech.2003.11.002

European Journal of Medicinal Chemistry 39 (2004) 449–452
www.elsevier.com/locate/ejmech
Short communication
Synthesis and antiinflammatory activity of heterocyclic indole derivatives
Preeti Rani, V.K. Srivastava, Ashok Kumar *
Medicinal Chemistry Division, Department of Pharmacology, L.L.R.M. Medical College, Meerut, U.P.-250004, India
Received 20 March 2003; received and revised form 6 November 2003
Abstract
Chalcones of indole 1–5 and their corresponding products; pyrazolines 6–10 and azo compounds 11–15 were synthesised and evaluated for
their antiinflammatory activity against carrageenan induced oedema in albino rats at a dose of 50 mg kg–1 oral. The structure of compounds
was confirmed by IR, 1H-NMR and mass spectral data.All the compounds of this series showed promising antiinflammatory activity. The most
active compound of this series is 3-[1-acetyl-5-(p-hydroxyphenyl)-2-pyrazolin-3-yl]indole (7) was found to be most potent, which has shown
higher percent of inhibition of oedema, lower ulcerogenic liability and acute toxicity than the standard drug phenylbutazone.
© 2003 Elsevier SAS. All rights reserved.
Keywords: Chalcones; Pyrazolines; Azo derivatives; Synthesis; Albino rates; Antiinflammatory activity; Ulcerogenic activity; Acute toxicity
1. Introduction
sation of compounds 6–10 with aniline yielded 3-[1-acetyl-
5-(substitutedphenyl)-4-phenylazo-2-pyrazolin-3-yl]indoles
i.e. compounds 11–15, respectively.
Indomethacin [1] and tenidap [2] are NSAIDs, and have
been shown to exert its antiinflammatory effects. Indole, the
potent basic pharmacodynamic nucleus has been reported to
possess a wide variety of biological properties viz., antiin-
flammatory [3–5], anticonvulsant [6], cardiovascular [7], an-
tibacterial [8]. Furthermore, substitution of heterocyclic moi-
ety at 3-position markedly influenced the antiinflammatory
activity [9]. Besides these, pyrazoline [10] and azo deriva-
tives [11] have also been reported to possess antiinflamma-
tory activity. Encouraged by these observations we synthe-
sised newer heterocyclic indole derivatives in the hope of
obtaining better antiinflammatory agents.
3. Results
3.1. Antiinflammatory activity
All the newly synthesised compounds (1–15) were evalu-
ated for their antiinflammatory activity against carrageenan
induced rat’s paw oedema at 50 mg kg–1 p.o., which exhib-
ited antiinflammatory activity ranging from 14% to 47%. The
results of all the compounds are depicted in Table 1. Chal-
cones (1–5), the first stage compounds have elicited moder-
ate antiinflammatory activity of varying degree (15–20%).
Cyclisation of these chalcones into pyrazolines (6–10)
showed potent antiinflammatory activity (28–47%). More-
over, the compound 7 exhibited most potent activity (47%
inhibition of oedema at 50 mg kg–1 dose). Being the most
potent compound, it was further studied in detail to establish
a dose–response relationship (25, 50 and 100 mg kg–1 p.o.)
and was also compared with standard drug phenylbutazone
and indomethacin. From the data it was observed that the
potent compound was found to be more potent than phenylb-
utazone and exhibited lower protection than indomethacin.
Fig. 2 showed bar diagram of compound 7 and phenylbuta-
zone at three dose levels. Azo compounds (11–15), third
stage compounds, showed moderate (14–26%) antiinflam-
matory activity.
2. Chemistry
The synthetic route of compounds is outlined in Fig. 1.
The starting compound 3-acetylindole on refluxing with vari-
ous aromatic aldehydes in the presence of 2% NaOH solution
for 10–12 h yielded 3-chalconylindoles 1–5, these chalcones
on cyclisation with hydrazine hydrate in the presence of
glacial acetic acid resulted into corresponding 3-[1-acetyl-5-
(substitutedphenyl)-2-pyrazolin-3-yl]indoles 6–10. Diazoti-
* Corresponding author.
E-mail address: rajput-ak@indiatimes.com (A. Kumar).
© 2003 Elsevier SAS. All rights reserved.
doi:10.1016/j.ejmech.2003.11.002

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P. Rani et al. / European Journal of Medicinal Chemistry 39 (2004) 449–452
the chalcones (1–5) exhibited varying degree of antiinflam-
matory activity (15–20%). Compound 1, in which phenyl
ring was substituted with methoxy at meta and hydroxy at
para position has shown maximum activity (20%), when
phenyl ring was substituted with dimethylamino group at
para position i.e. compound 4 showed lesser degree of inhi-
bition of oedema (15%). The cyclisation of chalcones into
their corresponding pyrazolines 6–10, in general, exhibited
greater degree of inhibition of oedema as compared to their
parent compounds 1–5. The compound 7, which was substi-
tuted with hydroxy group at para position has shown maxi-
mum antiinflammatory activity (47%). On the other hand
when phenyl ring was substituted with dimethylamino group
at para position i.e. 9 showed lower degree of antiinflamma-
tory activity (28%). Hence it may be concluded that all the
five pyrazolines (6–11) possessed more potent antiinflamma-
tory activity than their corresponding chalcones (1–5). Azo
derivatives (11–15) exhibited better activity than chalcones
but found to possess less percentage inhibition of oedema
than the corresponding pyrazolines. Therefore, it may be
concluded by the mentioned data of antiinflammatory activ-
ity that all the five pyrazolines (6–11) possessed more potent
antiinflammatory activity than their corresponding chalcones
(1–5). Azo derivatives (11–15) exhibited better activity than
chalcones but found to possess less % inhibition of oedema
than their corresponding pyrazolines.
5. Experimental protocols
5.1. Chemistry
Melting points were taken in open capillary tubes and are
uncorrected. The purity of the compounds was confirmed by
thin layer chromatography using silica gel-G and spots were
located by iodine. IR spectra were recorded on Perkin Elmer
Fig. 1.
1
881 spectrophotometer in KBr (m;max in cm–1). H-NMR
3.2. Ulcerogenic activity
spectra were recorded on Bruker DPX-300 MHz spectrom-
eter and mass spectra were determined on JEOL-JMS-D-300
spectrometer. Analytical data of C, H, N were within 0.4%
of theoretical values.
Compound 7 was also tested for ulcerogenic activity and
found to be less ulcerogenic liability as compared to phenylb-
utazone (UD50 of compound 7 = 199.9 mg kg–1 i.p. and UD50
of phenylbutazone = 66.6 mg kg–1 i.p.).
5.1.1. 3-Chalconylindoles (1–5)
To a solution of 3-acetylindole (0.01 mol) in methanol
(dry, 50 ml), different aromatic aldehydes (0.01 mol) were
added in the presence of 2% NaOH solution (5 ml). The
reaction mixtures were stirred for 10–12 h at room tempera-
ture. The solvent was distilled off and crude product poured
into ice water. The compound thus obtained was washed with
water and recrystallised from suitable solvents. Physical and
analytical data of compounds 1–5 are given in Table 1.
Compound 2: IR (KBr) (cm–1): 3160 (NH), 3020 (aromatic
3.3. Acute toxicity
All the compounds showed ALD50 > 800 mg kg–1 p.o.,
suggesting a good safety margin. However, the most potent
compound
7
showed approximate lethal dose
(ALD50) > 2000 mg kg–1 p.o. (maximum dose tested).
4. Discussion
C–H), 1710 (C=O), 1630 (–CH=CH–), 1550 (C
C of
1
An insight into the antiinflammatory activity with respect
to chemical structure revealed that compounds having chal-
cone, pyrazoline or azo moiety at 3-position of the indole
nucleus exhibited significant antiinflammatory activity. All
aromatic ring). H-NMR (CDCl3) d; (ppm): 5.82 (1H, d,
–COCH=), 6.86 (1H, d, =CH–Ar), 7.11–7.89 (9H, m, Ar–H),
8.60 (1H, ss, NH of indole, exchangeable with D2O), 9.00
(1H, s, Ar–OH, exchangeable with D2O). MS: [M]+ m/z 263.

P. Rani et al. / European Journal of Medicinal Chemistry 39 (2004) 449–452
451
Table 1
Physical, analytical and biological data of compounds 1–15
Compound
number
R
M.P. Yield Recrystallisation
(°C) (%) solvent
Molecular
formula
Molecular Dose
% Decrease in paw ALD50
UD50
weight a (mg kg–1 p.o.) oedema (anti-
(mg kg–1 p.o.) (mg kg–1 i.p.)
inflammatory
activity)
20 b
1
m-OCH3, 215 75
p-OH
Methanol
C18H15NO3 293
50
>800
–
2
3
4
5
6
p-OH
226 50
172 40
Ethanol/water
Ethanol
C
C
C
C
C
17H13NO2 263
50
50
50
50
50
25
50
100
50
50
50
50
18
>800
>800
>800
>800
>800
–
–
–
–
–
H
17H13NO 247
16
p-N(CH3)2 187 60
p-OCH3 146 55
m-OCH3, 173 50
p-OH
Methanol
19H18N2O 290
18H15NO2 277
20H9N3O3 349
15
Methanol/water
Ethanol/water
18
35
23
7
p-OH
212 35
Ethanol
C
19H17N3O2 319
47 b
72
>2000
199.9
8
9
10
11
H
178 30
Methanol
C19H17N3O 303
C21H22N4O 346
C20H19N3O2 333
C26H23N5O3 453
38 b
28
>800
>800
>800
>800
–
–
–
–
p-N(CH3)2 200 40
p-OCH3 138 25
m-OCH3, 198 40
p-OH
Ethanol/water
DMF/water
Acetone
32
23 b
12
13
14
15
p-OH
224 25
146 30
Ethanol
C25H21N5O2 423
C25H21N5O 407
C27H26N6O 450
C26H23N5O2 437
50
26 b
24
>800
>800
>800
>800
–
–
–
–
H
Ethanol
50
p-N(CH3)2 165 45
p-OCH3 140 20
DMF/water
Methanol
50
14
50
19 b
15
25
Phenylbu-
tazone
–
–
–
–
–
–
–
–
–
–
–
–
50
39 b
66
–
–
66.6
–
100
1.8
3.6
5.4
Indometha-
cin
38
49
63
a C, H, N were found within 0.4%.
b P < 0.001.
5.1.2. 3-[1-Acetyl-5-(substitutedphenyl)-2′-pyrazolin-3-yl]
indoles (6–10)
To a solution of compounds 1–5 (0.01 mol) in absolute
ethanol, hydrazine hydrate (99%, 0.02 mol) and few drops of
glacial acetic acid were added. The reaction mixtures were
refluxed for 6–8 h. The excess of solvent was distilled off and
crude product poured into ice water. The separated solids
were filtered and recrystallised from suitable solvents. Physi-
cal and analytical data of compounds 6–10 are given in
Table 1. Compound 7: IR (KBr) (cm–1): 3150 (NH), 3010
(aromatic C–H), 2930(CH2), 1730 (C=O of acetyl moiety of
pyrazolin ring), 1680 (C=N), 1600 (C–N), 1570 (C
C of
1
aromatic ring), 1510 (N–N). H-NMR (CDCl3) d; (ppm):
2.28 (3H, s, –COCH3), 5.90 (2H, d, –CH2 of pyrazoline ring),
6.55–7.96 (10H, m; 9H, Ar–H + 1H, CHAr), 8.62 (1H, ss,
NH of indole, exchangeable with D2O), 9.02 (1H, s, Ar–OH,
exchangeable with D2O). MS: [M]+ m/z 319.
5.1.3. 3-[1-Acetyl-5-(substitutedphenyl)-4-phenylazo-2-
pyrazolin-3-yl]indoles (11–15)
To a solution of aniline (0.01 mol) in glacial acetic acid
(5 ml) was added conc. HCl (3 ml) at 0–5 °C. A solution of
sodium nitrite (1 g in 5 ml of water) was then added drop-
wise. The diazonium salt solution thus prepared was added to
a solution of compounds 6–10 (0.01 mol) in methanol drop
wise with stirring below 0 °C. The reaction mixtures were
kept at room temperature for 2–3 days and then poured into
cold water (200 ml). The resulting solids were washed with
water and recrystallised from suitable solvents. Physical and
analytical data of compounds 11–15 are given in Table 1.
Compound 12: IR (KBr) (cm–1): 3150 (NH), 3020 (aromatic
Fig. 2. Bar diagram showing mean % antiinflammatory activity of com-
pound 7 and reference drug phenylbutazone at three graded doses.

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P. Rani et al. / European Journal of Medicinal Chemistry 39 (2004) 449–452
C–H), 1710 (C=O), 1680 (C=N), 1600 (C–N), 1560 (C
C
5.2.4. Statistical analysis
All values are expressed as mean S.E.M. Statistical
significance was determined using Student’s ‘t’ test.
of aromatic ring), 1500 (N–N), 1430 (N=N). 1H-NMR
(CDCl3) d; (ppm): 2.17 (3H, ss, –COCH3), 5.92 (1H, d,
–CH-N=N–Ar), 6.25–7.88 (15H, m; 14H, Ar–H + 1H, –CH–
Ar), 8.62 (1H, ss, NH of indole, exchangeable with D2O), 9.0
(1H, s, Ar–OH, exchangeable with D2O). MS: [M]+ m/z 423.
Acknowledgements
We are thankful to CDRI, Lucknow and IIT, Delhi for
elemental and spectral analysis of newly synthesised com-
pounds.
5.2. Pharmacology
5.2.1. Antiinflammatory activity
A freshly prepared suspension of carrageenan (1.0% in
0.9% saline) 0.05 ml, was injected under the planter apo-
neurosis of right paw of the rat by the method of Winter et al.
[12]. The volume of foot was measured by micropipette
method as described by Buttle et al. [13]. The percentage of
antiinflammatory activity was calculated by the following
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5.2.2. Ulcerogenic liability
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5.2.3. Acute toxicity
Approximate lethal dose (ALD50) for all the compounds
was investigated in albino mice by the method of Smith [15].