Synthesis of Some Substituted Pyrazolopyrimidine Derivatives: An Environmentally Benign Approach

Article abstract of DOI:10.1002/jhet.3587

Pyrazolopyrimidines constitute a medicinally important class of heterocyclic compounds. Herein, we report an efficient and environmentally benign method for the synthesis of pyrazolo[3,4-d]pyrimidin-3-ones from 2,4-dinitrophenylhydrazine and diethyl malonate under microwave irradiation in 1,3-dibutylimidazolium bromide ionic liquid. The synthesized compounds were analyzed by elemental analysis and standard spectroscopic techniques. The compounds were screened for their antibacterial and antifungal activities.

Full text of DOI:10.1002/jhet.3587

Month 2019 Synthesis of Some Substituted Pyrazolopyrimidine Derivatives: An Envi-
ronmentally Benign Approach
*
Arpit Kumar Pathak, Sharoni Gupta, Pinki B. Punjabi, Garima Ameta, and Chetna Ameta
Microwave Synthesis Laboratory, Department of Chemistry, University College of Science, M. L. Sukhadia University,
Udaipur 313001, Rajasthan, India
*E-mail: chetna.ameta@yahoo.com
Received September 26, 2018
DOI 10.1002/jhet.3587
Published online 00 Month 2019 in Wiley Online Library (wileyonlinelibrary.com).
Pyrazolopyrimidines constitute a medicinally important class of heterocyclic compounds. Herein, we re-
port an efficient and environmentally benign method for the synthesis of pyrazolo[3,4-d]pyrimidin-3-ones
from 2,4-dinitrophenylhydrazine and diethyl malonate under microwave irradiation in 1,3-
dibutylimidazolium bromide ionic liquid. The synthesized compounds were analyzed by elemental analysis
and standard spectroscopic techniques. The compounds were screened for their antibacterial and antifungal
activities.
J. Heterocyclic Chem., 00, 00 (2019).
INTRODUCTION
and anticancer agents [16]. Furthermore pyrazoles fused
or substituted with other heterocycles constitute the core
of several pharmacological products [17]. Pyrazole
derivatives exhibit remarkable antimicrobial, analgesic,
antipyretic, and anti-inflammatory properties [18–20].
A number of methods for pyrazole-fused pyrimidines
have been reported earlier, but these methods have their
drawbacks such as excessive use of solvents, time-
consuming processes, poor yields, and expensive
experimental set-up. To overcome these drawbacks, an
efficient and eco-friendly method for the synthesis of
pyrazole-fused pyrimidine derivatives under microwave
irradiation in the presence of 1,3-dibutylimidazolium
bromide ionic liquid is reported here.
Synthesis of N-substituted heterocycles using microwave
irradiation has attracted the interest of chemists worldwide
because it is a highly efficient and time-saving process.
Environmentally benign synthesis of N-heterocycles
under microwave irradiation has been reported in literature
[1–6]. The use of ionic liquids in organic synthesis has
further enhanced the efficiency of the entire process of
synthesis, simply owing to their several advantages such
as low melting point, high thermal stability [7,8],
negligible vapor pressure [9], and high ionic conductivity
[10]. Conventionally, the ionic liquids have been
synthesized in stirred tanks using batch or semibatch
processes. But these methods were time and energy
consuming [11]; hence, in recent years, the chemists have
shifted their interest towards clean and efficient techniques
such as microwave irradiation [12,13] and sonochemical
processes [14] for synthesis of ionic liquid.
EXPERIMENTAL SECTION
The reactions were carried out in a microwave
synthesizer (Ragatech, Pune). Thin-layer chromatography
(TLC) was carried out on silica plates precoated with
silica (0.2 mm), and visualization was accomplished by
iodine vapors. NMR spectra were taken on a Bruker
Avance II 400 NMR Spectrometer (Bruker Corp.,
Billerica, MA) in DMSO solvent using tetramethylsilane
Amongst N-substituted heterocycles, pyrimidine is one
of the most important molecules. Pyrimidine skeleton is
involved in biologically important molecules such as
DNA and RNA [15]. Hetero-fused and substituted
pyrimidines are well known as antiviral, antibacterial,
anti-AIDS, anti-inflammatory, antimalarial, antifungal,
© 2019 Wiley Periodicals, Inc.

A. K. Pathak, S. Gupta, P. B. Punjabi, G. Ameta, and C. Ameta
Vol 000
as internal standard, and chemical shifts were expressed in
δ ppm. The Fourier transform infrared spectra were
recorded on Perkin Elmer Spectrum RX-IFTIR
spectrometer. Melting points were measured using
Gallenkamp’s melting point apparatus and are
uncorrected. Solvents and reagents were purchased from
commercial sources and were used without further
purification.
(N–H), 3000 (Ar C–H), 2926 and 2850 (CH2), 1644 (>N–
C═O), 1612 (NH–C═O), 1406 (N–N), 1500, 1350 (–
NO2), 1573, 1488, and 1406 (aromatic ring), and 1060
1
(C–N). H-NMR (δ, ppm, 400 MHz, DMSO), 2.55 (s,
2H, CH2), 8.70 (s, 1H, N–H), and 7.20–7.80 (m, 3H, Ar–H).
Anal. Calcd for C9H6N4O6: C 40.61; H 2.27; N 21.05%.
Found: C 40.21; H 2.05; N 20.90%.
General procedure for microwave-induced synthesis of 4-
(substituted
dione (5a–e).
dinitrophenyl)pyrazolidine-3,5-dione
phenyl)-1-(2,4-dinitrophenyl)pyrazolidine-3,5-
Preparation of ionic liquid 1,3-dibutylimidazolium
bromide [bbim][Br] (1.2). The synthesis of ionic liquid
In an Erlenmeyer flask, 1-(2,4-
(4)
(2.6
g,
was carried out in two steps. The first step involved
synthesis of butyl imidazole (1.1) from the imidazole (1)
(0.68 g, 0.01 mol) using n-butyl lithium as a base and n-
butyl bromide (1.37 g, 0.01 mol) as an alkylating agent
under microwave exposure at 240 W for 10 min. An
equimolar ratio of n-butyl imidazole and butyl bromide
mixture was taken in the second step and heated
intermittently in a microwave synthesizer at 300 W until
a clear monophase was obtained. The resulting ionic
liquid was cooled and washed several times with diethyl
ether to remove the unspent reagent. The product was
0.01 mol), different aromatic aldehydes (0.01 mol), and
NaOH (two to three drops) in 10 mL of ionic liquid
([bbim][Br]) were taken and mixed thoroughly to prepare
chalcones (5a–e). The well-stirred reaction mixture was
irradiated by microwaves for 7 to 8 min at 720 W. The
course of the reaction was monitored by TLC, and the
resultant mass was poured into ice-cold water with
vigorous stirring. The solid product was filtered, washed,
and dried. The purity of compounds was ascertained by
TLC using ethyl acetate:benzene (7:3) as mobile phase.
4-(4-Chlorophenyl)-1-(2,4-dinitrophenyl)pyrazolidine-3,5-
dione (5a). This was obtained in 70% yield; mp 265–
dried under vacuum to obtain
a
viscous 1,3-
dibutylimidazolium bromide ionic liquid (Figure 1).
IR (KBr pellet): ν (cmꢀ1), 3089 (C–H), 2960 (C–H),
2871, 2826 (C–H), 1630 (C═C), 1600 (C═N), and 1085
268°C; IR: (ν, cmꢀ1), 3425 (N–H), 3263 (═C–H), 3050
(Ar C–H), 1635 (>N–C═O), 1609 (NH–C═O), 1550,
1480, and 1450 (aromatic ring), 1500 and 1350 (–NO2),
1416 (N–N), 1073 (C–N), 831 (C–Cl), and 740 and 717
(m-substituent dinitro group). 1H-NMR (δ, ppm,
400 MHz, DMSO), 8.70 (s, 1H, N–H), 7.28–7.80 (m,
7H, Ar–H), and 8.25 (s, 1H, ═C–H). Anal. Calcd for
C16H9ClN4O6: C 49.44; H 2.33; N 14.41%. Found: C
1
(C–N). H-NMR: (δ, ppm, 400 MHz, DMSO-d6), 0.50 (t,
6H, J = 6.9 Hz, CH3), 1.20–1.30 (m, 4H, CH2), 1.75 (m,
4H, CH2), 2.15 (t, 2H, J = 7.4 Hz, CH2), 3.70 (t, 2H,
J = 7.4 Hz, CH2), 6.90 (d, 2H, J = 7.6 Hz, CH), and 9.41
(s, 1H, CH). 13C-NMR: (δ, ppm), 12.5–30.1 (C-2
imidazole), 57.0 (C-10-N butyl), 55.0 (C-1″-N+ butyl),
and 124–133.0 (aromatic imidazole ring carbon).
49.10; H 2.10; N 14.10%.
4-(3-Nitrophenyl)-1-(2,4-dinitrophenyl)pyrazolidine-3,5-
dione (5b). This was obtained in 72% yield; mp 272–
Microwave-induced synthesis of 1-(2,4-dinitrophenyl)
275°C; IR: (ν, cmꢀ1), 3422 (N–H), 3260 (═C–H), 3000
(Ar C–H), 1650 (>N–C═O), 1620 (NH–C═O), 1550,
1440, and 1460 (aromatic ring), 1500 and 1350 (–NO2),
1416 (N–N), 1073 (C–N), and 740 and 717 (m-
pyrazolidine-3,5-dione (4).
A
mixture of 2,4-
dinitrophenyl hydrazine (1.98 g, 0.01 mol) (2) and
diethyl malonate (1.6 g, 0.01 mol) (3) was dissolved in
1,3-dibutylimidazolium bromide ionic liquid (10 mL) in
the presence of acidic medium (acetic acid, 2 mL). The
reaction mixture was irradiated for 6 to 8 min in MW at
300 W. The viscous mass obtained after the completion
of reaction was poured into ice-cold water with vigorous
stirring and left for complete precipitation. The solid
product (4) was filtered, washed, and dried. The purity of
compound was ascertained by TLC using ethyl acetate:
1
substituted dinitro group). H-NMR (δ, ppm, 400 MHz,
DMSO), 8.70 (s, 1H, N–H), 7.25–7.78 (m, 7H, Ar–H),
and 8.00 (s, 1H, ═C–H). Anal. Calcd for C16H9N5O8: C
48.13; H 2.27; N 17.54%. Found: C 48; H 2.20; N 17.40%.
4-(4-Hydroxyphenyl)-1-(2,4-dinitrophenyl)pyrazolidine-3,5-
dione (5c). This was obtained in 65% yield; mp 250–
252°C; IR: (ν, cmꢀ1), 3430 (N–H), 3400 (O–H), 3258
(═C–H), 3000 (Ar C–H), 1652 (>N–C═O), 1625 (NH–
C═O), 1573, 1488, and 1406 (aromatic ring), 1500 and
1340 (–NO2), 1410 (N–N), 1060 (C–N), 1200 (C–O),
benzene (7:3) as mobile phase (Figure 2).
1-(2,4-Dinitrophenyl)pyrazolidine-3,5-dione (4). This was
obtained in 85% yield; mp 160–162°C; IR: (ν, cmꢀ1), 3317
Figure 1. Preparation of ionic liquid 1,3-dibutylimidazolium bromide [bbim][Br].
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2019
Synthesis of Some Substituted Pyrazolopyrimidine Derivatives
Figure 2. Microwave assisted synthesis of pyrazolo[3,4-d]pyrimidin-3-ones.
840 (p-substituent), and 740 and 717 (m-disubstituted nitro
group). 1H-NMR (δ, ppm, 400 MHz, DMSO), 8.70 (s, 1H,
–N–H), 7.25–7.80 (m, 7H, Ar–H), 8.2 (s, 1H, ═C–H), and
10.50 (s, 1H, OH). Anal. Calcd for C16H10N4O7: C 51.90;
H 2.72; N 15.13%. Found: C 51.50; H 2.40; N 15.00%.
(Ar C–H), 1642 (>N–C═O), 1615 (NH–C═O), 1550,
1450, and 1470 (aromatic ring), 1520 and 1360 (–NO2),
1073 (C–N), 1416 (N–N), 835 (p-substituent NO2 group),
1
and 740 and 717 (m-substituted dinitro group). H-NMR
(δ, ppm, 400 MHz, DMSO), 8.70 (s, 1H, N–H), 7.20–
7.78 (m, 7H, Ar–H), and 8.05 (s, 1H, ═C–H). Anal.
Calcd for C16H9N5O8: C 48.13; H 2.27; N 17.54%.
Found: C 47.90; H 2.05; N 17.20%.
The physical data of compounds 4 and 5 (a–e) are given
in Table 1.
4-(2-Chlorophenyl)-1-(2,4-dinitrophenyl)pyrazolidine-3,5-
dione (5d). This was obtained in 75% yield; mp 285–
288°C; IR: (ν, cmꢀ1), 3415 (N–H), 3050 (Ar C–H), 3270
(═C–H), 1650 (>N–C═O), 1625 (NH–C═O), 1570,
1480, and 1450 (aromatic ring C–H bending), 1490 and
1360 (–NO2 coupled vibration), 1073 (C–N), 1410 (N–
N), 830 (C–Cl), and 740 and 717 (m-disubstituted dinitro
General procedure for microwave-induced synthesis of 4-
(substituted phenyl)-1-(2,4-dinitrophenyl)-1,2,4,5-tetrahydro-
1
3aH-pyrazolo[3,4-d]pyrimidine-3,6-dione (6a–e).
The
group). H-NMR (δ, ppm, 400 MHz, DMSO), 8.70 (s,
chalcone (5a) (3.88 g, 0.01) was dissolved in 10 mL of
ionic liquid in an Erlenmeyer flask. Then, urea (0.6 g,
0.01 mol) and NaOH (two to three drops) were added
and mixed thoroughly. The well-stirred mixture was
exposed to microwaves for 5 to 6 min at 720 W. The
completion of the reaction was monitored by TLC. After
1H, –N–H), 7.20–7.80 (m, 7H, Ar–H), and 8.20 (s, 1H,
═C–H). Anal. Calcd for C16H9ClN4O6: C 49.44; H 2.33;
N 14.41%. Found: C 49.10; H 2.15; N 14.10%.
4-(4-Nitrophenyl)-1-(2,4-dinitrophenyl)pyrazolidine-3,5-
dione (5e). This was obtained in 80% yield; mp 300–
302°C; IR: (ν, cmꢀ1), 3425 (N–H), 3275 (═C–H), 3000
Table 1
Physical data of synthesized compounds 4 and 5a–e.
Compound
R
Molecular formula
Molecular weight
mp, °C
Yield, %
Time, min
4
—
C9H6N4O6
266
388
399
370
388
399
160–162
265–268
272–275
250–252
285–288
300–302
85
70
72
65
75
80
7
7
6
9
8
8
5a
5b
5c
5d
5e
4-Cl-C6H4
C16H9ClN4O6
C16H9N5O8
C16H10N4O7
C16H9ClN4O6
C16H9N5O8
3-NO2-C6H4
4-OH-C6H4
2-Cl-C6H4
4-NO2-C6H4
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

A. K. Pathak, S. Gupta, P. B. Punjabi, G. Ameta, and C. Ameta
Vol 000
the reaction mixture was cooled, it was poured into
crushed ice. The obtained solid was filtered, washed with
water, and recrystallized from ethanol. The purity of
compounds was analyzed by TLC using ethyl acetate:
benzene (7:3) as mobile phase. The recovery of ionic
liquid was carried out by evaporation of water and reused
in the next step. The process was repeated with other
chalcones (5b–e).
CH), and 3.65 (d, 1H, J = 3.8 Hz, CH). 13C-NMR: (δ,
ppm), 41.5 (C-3a pyrazolopyrimidine), 44.7 (C-4
pyrazolopyrimidine), 115.0–132.5 (CH aromatic), 133.0
(C-20-NO2 aromatic), 140.5 (C-40-NO2 aromatic), 144.5
(C-10 aromatic), 142.5 (C-3 pyrazolopyrimidine), 147.9
(C-3″-NO2 aromatic), 162.5 (C-7a pyrazolopyrimidine),
160.9 (C-7 pyrazolopyrimidine ring), and 174.0 (C-
3 pyrazolopyrimidine). MS: (m/z, %), 441 [M]˙+, 395
[M–NO2]+., 274 [M-C6H3N2O4]+., 319 [M-C6H4NO2]+..
Anal. Calcd for C17H11N7O8: C 46.27; H 2.51; N 22.22%.
General procedure of microwave-induced synthesis of 4-
(substituted phenyl)-1-(2,4-dinitrophenyl)-6-thioxo-1,2,3a,4,
5,6-hexahydro-3aH-pyrazolo[3,4-d]pyrimidin-3-one (7 a-e
). Chalcone (5a) (3.88 g, 0.01 mol), thiourea (0.76 g,
Found: C 46.15; H 2.35; N 22.05%.
4-(4-Hydroxyphenyl)-1-(2,4-dinitrophenyl)-1,2,4,5-
0.01 mol), and NaOH (two to three drops) in 10 mL of
ionic liquid were taken in an Erlenmeyer flask and mixed
thoroughly. The well-stirred mixture was irradiated in a
microwave oven for 7 to 8 min at 720 W. The
completion of the reaction was monitored by TLC. The
reaction mixture was then cooled at room temperature
and poured into crushed ice. The obtained solid was
filtered, washed with water, and recrystallized from
ethanol. The purity of compounds was analyzed by TLC
using ethyl acetate:benzene (7:3) as mobile phase. The
ionic liquid was recovered by evaporation of water and
reused. The same process was repeated with other
chalcones (5b–e).
tetrahydro-3aH-pyrazolo[3,4-d]pyrimidine-3,6-dione (6c).
This was obtained in 65% yield; mp 90–93°C, IR: (ν,
cmꢀ1), 3405 (OH), 3280 (N–H), 3010 (Ar C–H), 1678
(C═O), 1650 (C═N), 1573, 1480 and 1410 (aromatic
ring), 1560 and 1360 (–NO2 coupled vibration), 1410
(N–N), 1060 (C–N), 835 (p-substituent), and 740 and
717 (m-substituted dinitro group). 1H-NMR (δ, ppm,
400 MHz, DMSO-d6), 8.50 (s, 1H, N–H), 8.15 (s, 1H,
N–H), 7.20–7.75 (m, 7H, Ar–H), 11.44 (s, 1H, OH), 2.90
(d, 1H, J = 4.4 Hz, CH), and 3.65 (d, 1H, J = 3.8 Hz,
CH). 13C-NMR: (δ, ppm), 41.5 (C-3a pyrazolopy-
rimidine), 44.7 (C-4 pyrazolopyrimidine), 113–130.6 (CH
aromatic), 133.0(C-20-NO2 aromatic), 140.0 (C-40-NO2
aromatic), 142.5 (C-1″ aromatic), 144.4 (C-10 aromatic),
154.9 (C-4″-OH aromatic), 160.5 (C-6 pyrazolopy-
rimidine), 162.9 (C-7a pyrazolopyrimidine), and 174.5
(C-3 pyrazolopyrimidine). MS: (m/z, %), 412 [M]˙+, 394
[M-H2O], 319 [M-C6H4OH]+., 245 [M-C6H3N2O4]+..
Anal. Calcd for C17H12N6O7: C 49.52; H 2.93; N
4-(4-Chlorophenyl)-1-(2,4-dinitrophenyl)-1,2,4,5-tetrahydro-
3aH-pyrazolo[3,4-d]pyrimidine-3,6-dione (6a).
This was
obtained in 75% yield; mp 80–82°C; IR: (ν, cmꢀ1), 3285
(N–H), 3010 (C–H, Ar–H), 1677 (C═O), 1650 (C═N),
1409 (N–N), 1510 and 1340 (NO2 coupled vibration),
1550, 1480, and 1450 (aromatic ring), 1155 (C–N), 840
(C–Cl p-substituent), and 700 and 742 (m-substituent).
1H-NMR (δ, ppm, 400 MHz, DMSO), 8.50 (s, 1H, N–H),
8.10 (s, 1H, N–H), 7.20–7.75 (m, 7H, Ar–H), 2.90 (d,
1H, J = 4.4 Hz, CH), and 3.50 (d, 1H, J = 3.6 Hz, CH).
13C-NMR: (δ, ppm), 41.5 (C-3a pyrazolopyrimidine),
44.7 (C-4 pyrazolopyrimidine), 115–130.5 (CH aro-
matic), 132.5 (C4″-Cl aromatic), 133.0 (C-20-NO2
aromatic), 139.0 (C-40-NO2 aromatic), 142.0 (C-1″ aroma
tic), 144.4 (C-10 aromatic), 160.9 (C-7 pyrazolopy-
rimidine), 164.0 (C-7a pyrazolopyrimidine), and 174.5
(C-7 pyrazolopyrimidine). MS: (m/z, %), 430 [M]+., 432
[M + 2]+., 395 [M-Cl]+., 263 [M-C6H3N2O4]+., 319 [M-
C6H4Cl]+.. Anal. Calcd for C17H11ClN6O6: C 47.40; H
2.57; N 19.51%. Found: C 47.26; H 2.40; N 19.35%.
4-(3-Nitrophenyl)-1-(2,4-dinitrophenyl)-1,2,4,5-tetrahydro-
20.38%. Found: C 49.25; H 2.78; N 20.20%.
4-(2-Chlorophenyl)-1-(2,4-dinitrophenyl)-1,2,4,5-tetrahydro-
3aH-pyrazolo[3,4-d]pyrimidine-3,6-dione (6d).
This was
obtained in 80% yield; mp 110–112°C; IR: (ν, cmꢀ1),
3290 (N–H), 3020 (C–H, Ar–H), 1660 (C═O), 1630
(C═N), 1570, 1480, and 1450 (aromatic ring), 1500 and
1340 (–NO2 coupled vibration), 1410 (N–N), 1073 (C–N),
840 (C–Cl), and 740 and 717 (m-disubstituted nitro
1
group). H-NMR (δ, ppm, 400 MHz, DMSO-d6), 8.55 (s,
1H, N–H), 8.10 (s, 1H, N–H), 7.20–7.75 (m, 7H, Ar–H),
3.00 (d, 1H, J = 4.8 Hz, CH), and 3.50 (d, 1H,
J = 3.6 Hz, CH). 13C-NMR: (δ, ppm), 41.5 (C-3a
pyrazolopyrimidine), 44.7 (C-4 pyrazolopyrimidine),
113.5–129.0 (CH aromatic), 132.5 (C-2″-Cl aromatic),
132.9 (C-20-NO2 aromatic), 140.0 (C-40-NO2 aromatic),
142.4 (C-1″ aromatic), 143.7 (C-10 aromatic), 160.0 (C-6
pyrazolopyrimidine), 162.5 (C-7a pyrazolopyrimidine),
and 174.6 (C-3 pyrazolopyrimidine). MS: (m/z, %), 430
3aH-pyrazolo[3,4-d]pyrimidine-3,6-dione (6b).
This was
obtained in 70% yield; mp 50–52°C; IR: (ν, cmꢀ1), 3280
(N–H), 3055 (C–H, Ar–H), 1673 (C═O), 1650 (C═N),
1557, 1440, and 1460 (aromatic ring), 1530 and 1361
(NO2 coupled vibration), 1147 (C–N), and 717 and 730
(m-substituent NO2 bending). 1H-NMR (δ, ppm,
400 MHz, DMSO), 8.50 (s, 1H, N–H), 8.10 (s, 1H, N–
H), 7.20–7.75 (m, 7H, Ar–H), 3.00 (d, 1H, J = 4.6 Hz,
[M]+., 432 [M
+
2]+., 395 [M-Cl]+., 263 [M-
C6H3N2O4]+., 319 [M-C6H4Cl]+.. Anal. Calcd for
C17H11ClN6O6: C 47.40; H 2.57; N 19.51%. Found: C
47.20; H 2.52; N 19.34%.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2019
Synthesis of Some Substituted Pyrazolopyrimidine Derivatives
4-(4-Nitrophenyl)-1-(2,4-dinitrophenyl)-1,2,4,5-tetrahydro-
3aH-pyrazolo[3,4-d]pyrimidine-3,6-dione (6e).
aromatic), 142.1 (C-1″ aromatic), 143.4 (C-10 aromatic),
148.5 (C-3″-NO2 aromatic), 160.5 (C-7a pyrazolopyrimidine),
174.5 (C-3 pyrazolopyrimidine), and 182.0 (C-6
pyrazolopyrimidine). MS: (m/z, %), 457 [M]˙+, 411 [M–
NO2]+., 335 [M-C6H4NO2]+., 290 [M-C6H3N2O4]+.. Anal.
Calcd for C17H11N7O7S: C 44.64; H 2.42; N 21.44%. Found:
This was
obtained in 64% yield; mp 115–118°C; IR: (ν, cmꢀ1),
3290 (N–H), 3022 (C–H, Ar–H), 1690 (C═O), 1630
(C═N), 1500 and 1350 (NO2 coupled vibration), 1570,
1450, and 1470 (aromatic ring), 1400 (N–N), and 740
1
and 717 (m-disubstituted nitro group). H-NMR (δ, ppm,
C 44.50; H 2.25; N 21.25%.
400 MHz, DMSO-d6), 8.55 (s, 1H, N–H), 8.15 (s, 1H,
N–H), 7.20–7.75 (m, 7H, Ar–H), and 3.00 (d, 1H,
J = 4.6 Hz, CH), and 3.90 (d, 1H, J = 4.0 Hz, CH). 13C-
NMR: (δ, ppm), 41.0 (C-3a pyrazolopyrimidine), 44.5(C-
4 pyrazolopyrimidine), 115.0–130.6 (CH aromatic), 132.5
(C-20-NO2 aromatic), 139.5 (C-40-NO2 aromatic), 142.0
(C-1″ aromatic), 144.4 (C-10 aromatic), 146.5 (C-4″-NO2
aromatic), 160.5 (C-6 pyrazolopyrimidine), 165.0 (C-7a
pyrazolopyrimidine), and 174.0 (C-3 pyrazolopy-
rimidine). MS: (m/z, %), 441 [M]˙+, 395 [M–NO2]+., 274
[M-C6H3N2O4]+., 319 [M-C6H4NO2]+.. Anal. Calcd for
C17H11N7O8: C 46.27; H 2.51; N 22.22%. Found: C
4-(4-Hydroxyphenyl)-1-(2,4-dinitrophenyl)-6-thioxo-1,2,3a,
4,5,6-hexahydro-3aH-pyrazolo[3,4-d]pyrimidin-3-one (7c).
This was obtained in 70% yield; mp 252–255°C; IR: (ν,
cmꢀ1), 3290 (N–H), 3400 (OH), 1625 (C═O), 1580
(C═C), 1510 and 1350 (–NO2 coupled vibration), 1060
(C–N), 1410 (N–N), 1270 (C═S), 1573, 1488, and 1406
(aromatic ring), and 740 and 717 (m-disubstituted nitro
group). 1H-NMR spectrum (400 MHz, DMSO-d6), δ,
ppm: 8.50 (s, 1H, N–H), 8.20 (s, 1H, N–H), 7.20–7.70
(m, 7H, Ar–H), 11.38 (s, 1H, OH), 3.05 (d, 1H,
J = 5.4 Hz, CH), and 3.95 (d, 1H, J = 4.8 Hz, CH). 13C-
NMR spectrum, δ, ppm: 41.0 (C-3a pyrazolopyrimidine),
52.0 (C-4 pyrazolopyrimidine), 113.0–130.6 (CH
aromatic), 132.5 (C-20-NO2 aromatic), 140.5 (C-40-NO2
aromatic), 142.5 (C-1″ aromatic), 143.4 (C-10 aromatic),
154.5 (C-4″-OH aromatic), 160.9 (C-7a pyrazolopy-
rimidine), 174.0 (C-3 pyrazolopyrimidine), and 182.5 (C-
6 pyrazolopyrimidine). Mass spectrum, m/z (Irel, %): 428
[M]˙+, 410 [M-H2O]+., 261 [M-C6H3N2O4]+., 335 [M-
C6H4OH]+.. Found, %: C 47.48; H 2.65; N 19.40.
46.15; H 2.35; N 22.05%.
4-(4-Chlorophenyl)-1-(2,4-dinitrophenyl)-6-thioxo-1,2,3a,
4,5,6-hexahydro-3aH-pyrazolo[3,4-d]pyrimidin-3-one (7a).
This was obtained in 77% yield; mp 170–172°C; IR: (ν,
cmꢀ1), 3260 (N–H), 3000 (C–H, Ar–H), 1690 (C═O),
1630 (C═N), 1570, 1480, and 1450 (aromatic ring), 1500
and 1350 (NO2 coupled vibration), 1410 (N–N), 1250
(C═S), 830 (C–Cl p-substituent), and 740 and 717 (m-
1
disubstituted nitro group). H-NMR (δ, ppm, 400 MHz,
C17H12N6O6S. Calculated, %: C 47.66; H 2.82; N 19.62.
4-(2-Chlorophenyl)-1-(2,4-dinitrophenyl)-6-thioxo-1,2,3a,
4,5,6-hexahydro-3aH-pyrazolo[3,4-d]pyrimidin-3-one (7d).
DMSO-d6), 8.55 (s, 1H, N–H), 8.20 (s, 1H, N–H), 7.20–
7.78 (m, 7H aromatic), 3.25 (d, 1H, J = 5.8 Hz, CH), and
3.90 (d, 1H, J = 4.6 Hz, CH). 13C-NMR: (δ, ppm), 41.5
This was obtained in 80% yield; mp 210–212°C; IR: (ν,
cmꢀ1), 3290 (N–H), 3010 (Ar C–H), 1670 (C═O), 1650
(C═N), 1570, 1480, and 1450 (aromatic ring), 1500 and
1350 (NO2 coupled vibration), 1250 (C═S), 1115 (C–N),
832 (C–Cl), and 740 and 717 (m-disubstituted nitro
group). 1H-NMR spectrum (400 MHz, DMSO-d6), δ,
ppm: 8.50 (s, 1H, N–H), 8.20 (s, 1H, N–H), 7.20–7.75
(m, 7H, Ar–H), 3.10 (s, 1H, J = 5.2 Hz, CH), and 3.60
(d, 1H, J = 4.4 Hz, CH). 13C-NMR spectrum, δ, ppm:
(C-3a
pyrazolopyrimidine),
52.7
(C-4
pyrazolopyrimidine), 115.0–128.9 (CH aromatic), 131.0
(C-4″-Cl aromatic), 132.9 (C-20-NO2 aromatic), 139.0 (C-
40-NO2 aromatic), 141.5 (C-1″ aromatic), 144.4 (C-10
aromatic), 160.9 (C-7a pyrazolopyrimidine), 174.8 (C-3
pyrazolopyrimidine), 182.0 (C-6 pyrazolopyrimidine).
MS: (m/z, %), 446 [M]˙+, 448 [M + 2], 411 [M-Cl]+.,335
[M-C6H4Cl]+., 279 [M-C6H3N2O4]+.. Anal. Calcd for
C17H11ClN6O5S: C 45.70; H 2.48; N 18.81%. Found: C
41.0
(C-3a
pyrazolopyrimidine),
52.2
(C-4
pyrazolopyrimidine), 113.5–129.0 (CH aromatic), 132.5
(C-2″-Cl aromatic), 133.0 (C-20-NO2 aromatic), 139.0 (C-
40-NO2 aromatic), 142.8 (C-1″ aromatic), 143.4 (C-10
aromatic), 160.2 (C-7a pyrazolopyrimidine), 174.5 (C-3
pyrazolopyrimidine), and 182.0 (C-6 pyrazolopy-
rimidine). Mass spectrum, m/z (Irel, %): 446 [M]˙+, 448
[M + 2], 411 [M-Cl]+., 335 [M-C6H4Cl]+., 279 [M-
C6H3N2O4]+.. Found, %: C 45.55; H 2.55; N 18.60.
C17H11ClN6O5S. Calculated, %: C 45.70; H 2.48; N 18.81.
4-(4-Nitrophenyl)-1-(2,4-dinitrophenyl)-6-thioxo-1,2,3a,
4,5,6-hexahydro-3aH-pyrazolo[3,4-d]pyrimidin-3-one (7e).
This was obtained in 65% yield; mp 190–192°C; IR: (ν,
cmꢀ1), 3290 (N–H), 1672 (C═O), 1620 (C═N), 1580,
1440, and 1470 (aromatic ring), 1520 and 1361 (–NO2
45.55; H 2.20; N 18.60%.
4-(3-Nitrophenyl)-1-(2,4-dinitrophenyl)-6-thioxo-1,2,3a,
4,5,6-hexahydro-3aH-pyrazolo[3,4-d]pyrimidin-3-one (7b).
This was obtained in 64% yield; mp 160–162°C; IR: (ν,
cmꢀ1), 3250 (N–H), 3010 (C–H, Ar–H), 1670 (C═O),
1650 (C═N), 1550, 1440 and 1460 (aromatic ring), 1515
and 1360 (NO2 coupled vibration), 1230 (C═S), 1115
(C–N), and 740 and 717 (m-disubstituted nitro group).
1H-NMR (δ, ppm, 400 MHz, DMSO-d6), 8.50 (s, 1H, N–H),
8.25 (s, 1H, N–H), 7.20–7.75 (m, 7H, Ar–H), 3.00
(d, 1H, J = 5.0 Hz, CH), and 3.50 (d, 1H, J = 4.2 Hz,
CH). 13C-NMR: (δ, ppm), 41.5 (C-3a pyrazolopy-
rimidine), 52.7 (C-4 pyrazolopyrimidine), 112.5–141.5
(CH aromatic), 132.6 (C-20-NO2 aromatic), 139.6 (C-40-NO2
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

A. K. Pathak, S. Gupta, P. B. Punjabi, G. Ameta, and C. Ameta
Vol 000
coupled vibration), 1409 (N–N), 1270 (C═S), and 1065
(C–N). 1H-NMR spectrum (400 MHz, DMSO-d6), δ,
ppm: 8.55 (s, 1H, N–H), 8.20 (s, 1H, N–H), 7.20–7.80
(m, 7H, Ar–H), 3.00 (s, 1H, J = 5.0 Hz, CH), and 3.90
(d, 1H, J = 4.8 Hz, CH). 13C-NMR spectrum, δ, ppm:
42.0 (C-3a pyrazolopyrimidine), 52.8 (C-4 pyrazolopy-
rimidine), 115.5–130.5 (CH aromatic), 132.5 (C-20-NO2
aromatic), 139.5 (C-40-NO2 aromatic), 142.5 (C-1″
aromatic), 143.4 (C-10 aromatic), 146.0 (C-4″-NO2
aromatic), 160.9 (C-7a pyrazolopyrimidine), 174.8
(C-3 pyrazolopyrimidine), and 182.0 (C-6 pyrazolopy-
rimidine). Mass spectrum, m/z (Irel, %): 457 [M]˙+, 411
[M–NO2]+., 335 [M-C6H4NO2]+., 290 [M-C6H3N2O4]+..
Found, %: C 44.45; H 2.30; N 21.20. C17H11N7O7S.
Calculated, %: C 44.64; H 2.42; N 21.44.
Compounds 5a–e serve as intermediate for the synthesis
of compounds 6a–e and 7a–e. In the first reaction
pathway, treatment of compounds 5a–e with urea in the
presence of NaOH synthesized pyrazolopyrimidine
derivatives (6a–e). The products were confirmed by the
appearance of IR bands at 1650 cmꢀ1 for C═N
stretching, whereas disappearance of NMR signal at
8.2 ppm due to ═C–H proton. In the second reaction
pathway, pyrazolopyrimidine derivatives (7a–e) were
synthesized by treating compounds 5a–e with thiourea in
alkaline medium. The appearance of IR band at
1660 cmꢀ1 for C═N stretching and IR band at
1270 cmꢀ1 due to replacement of C═O band by C═S
bond have confirmed compounds 7a–e. Compounds 7a–e
were further confirmed by disappearance of NMR signal
for ═C–H at 8.2 ppm.
The synthesized compounds were screened in vitro for
their antimicrobial activities against Gram-positive
bacteria Staphylococcus aureus and Streptococcus
pyogenes and Gram-negative bacteria Escherichia coli
and Pseudomonas aeruginosa and three strains of fungi
Aspergillus niger, Candida albicans, and Aspergillus
clavatus (Table 2). Micro broth dilution method was used
to determine minimum growth inhibition concentration.
Ampicillin was used as standard drug for antibacterial
activity, and griseofulvin was used as standard
antifungal drug.
The synthesized compounds 6a, 6e, 7b, and 7d showed
minimum inhibitory concentration (MIC) values similar to
those of the standard drug ampicillin. Further, it was found
that replacing the hydrogen of phenyl ring with hydroxyl
group at p-position in compounds 6c and 7c enhanced
their activity, and they displayed excellent activity against
E. coli. Compounds 6b (3-NO2) and 6d (2-Cl) also
exhibit good activity against E. coli.
RESULTS AND DISCUSSION
Condensation of diethyl malonate (3) with 2,4-
dinitrophenyl hydrazine (2) in the presence of glacial
acetic acid in 1,3-dibutylimidazolium bromide as solvent
afforded compound 4. The presence of IR band at
1644 cmꢀ1 for cyclic C═O and disappearance of band at
3400 cmꢀ1 due to NH2 group confirm the structure of
compound 4. The 1H-NMR signal at 2.55 δ ppm due
active methylene group further characterizes compound
4 as 1-(2,4-dinitrophenyl)pyrazolidine-3,5-dione. Com-
pound 4 on reaction with various substituted aromatic
aldehydes in the presence of NaOH gave 4-(4-substituted
phenyl)-1-(2,4-dinitrophenyl)pyrazolidine-3.5-diones (5a–
e). The disappearance of signal at 2.55 ppm due to CH2
group and appearance of multiplet for five aromatic
protons at 6.4–9.5 ppm and ═C–H stretching frequency at
3200 cmꢀ1 in IR spectra confirm compounds 5a–e.
Table 2
Microbial activity of synthesized compound (minimum inhibition concentration) (μg mLꢀ1).
Bacteria (MIC, μg mLꢀ1 Fungi (MIC, μg mLꢀ1
)
)
Escherichia
coli
Pseudomonas
aeruginosa
Staphylococcus
aureus
Staphylococcus
pyogenes
Aspergillus
niger
Candida
albicans
Aspergillus
clavatus
Compound R
6a 4-Cl-C6H4
6b 3-NO2-C6H4
6c 4-OH-C6H4
6d 2-Cl-C6H4
6e 4-NO2-C6H4
7a 4-Cl-C6H4
7b 3-NO2-C6H4
7c 4-OH-C6H4
7d 2-Cl-C6H4
7e 4-NO2-C6H4
Standard:
100
50
25
62.5
100
50
100
50
125
150
100
200
125
250
200
100
125
200
125
250
62.5
100
200
200
200
125
200
250
100
125
100
200
125
125
100
62.5
200
100
250
500
125
200
500
500
500
100
125
1000
500
500
250
500
1000
500
500
200
500
1000
200
500
200
500
500
1000
1000
100
500
1000
100
125
Ampicillin
100
Not active
250
100
Griseofulvin
100
500
100
Bold values shows excellent activity as compared to standard drug.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2019
Synthesis of Some Substituted Pyrazolopyrimidine Derivatives
All the synthesized compounds showed good activity
when P. aeruginosa strain was used for conducting MIC
test with the ampicillin standard. Ampicillin standard
drug does not show any activity against P. aeruginosa
bacteria. Compound 6c (4-OH) showed excellent activity
against P. aeruginosa strain. Compounds 6a, 6c, and 7c
displayed excellent MIC value than did other compounds
against S. aureus strain. Compounds 7c (4-OH), 7b (3-
NO2), and 7e (4-NO2) showed good activity against
S. pyogenes strain. Owing to high electronegativity
and mesomeric effect of –OH group, the compounds with
–OH group showed more polarity and permeability than
did other compounds. Thus, these compounds easily enter
the cell wall of bacteria and show good activity.
easy recovery, and reusability of ionic liquid. The
biological screenings of prepared derivatives reveal good
antibacterial activities and moderate antifungal activities.
REFERENCES AND NOTES
[1] Mady, M. F.; Saleh, T. S.; El-Kateb, A. A.; El-Rehman, N. M.
A.; El-Moez, S. I. A. Res Chem Intermediat 2016, 42, 753.
[2] Faty, R. M.; Rashed, M. S.; Youssef, M. M. Molecules 2015,
20, 1842.
[3] Tiwari, U.; Ameta, C.; Rawal, M. K.; Ameta, R.; Punjabi, P. B
Indian J Chem Sec B 2013, 52B, 432.
[4] Tiwari, U.; Ameta, C.; Sharma, S.; Sharma, M.; Pathak, A. K.;
Punjabi, P. B. Eur Chem Bull 2013, 242.
[5] Vyas, R.; Swarnkar, N.; Sancheti, A.; Verdia, J.; Punjabi, P. B.
J Indian Chem Soc 2008, 85, 1217.
Compound 7c exhibited activity equivalent to that of
griseofulvin against A. niger. Compounds 6a, 6b, 6d, 7a,
and 7d showed moderate activities against C. albicans.
Excellent activities were shown by compounds 6c and 7c
against C. albicans. When A. clavatus was used as a
strain, compound 7c showed excellent activity. Thus, all
the synthesized compounds showed good antibacterial
activity and moderate to weak antifungal activity.
[6] Sharulatha, V.; Indumathi, U.; Priyadarshini, S. Int J Res Engg
Technol 2014, 3, 1.
[7] Rogers, R. D.; Seddon, K. R. Science 2003, 302, 792.
[8] Sheldon, R. Green Chem 2005, 7, 267.
[9] Earle, M. J.; Esperanc, J. M. S. S.; Gilea, M. A.; Lopes, J. N.
C.; Rebelo, L. P. N.; Magee, J. W.; Seddon, K. R.; Widegren, J. A. Nature
2006, 439, 831.
[10] Sakaebe, H.; Matsumoto, H. Electrochem Commun 2003, 5,
594.
[11] Deetlefs, M.; Seddon, K. R. In Handbook of Green Chemistry,
Green Solvents, Ionic LiquidsWasserscheid, P.; Stark, A. Eds.; Wiley:
Weinheim, 2010; Vol 6, p 1.
[12] Namboodri, V. N.; Varma, R. S. Tetrahedron Lett 2002, 43,
5381.
CONCLUSION
[13] Messali, M.; Ahmed, S. A. Green Sustain Chem 2011, 1, 70.
[14] Ameta, G.; Pathak, A. K.; Ameta, C.; Ameta, R.; Punjabi, P. B.
J Mol Liq 2015, 211, 934.
[15] Basavaiah, D.; Sathyanaryana, T. Tetrahedron Lett 2002, 43,
4301.
[16] Selvam, T. P.; James, C. R.; Dniandev, P. V.; Valzita, S. K.
Res Pharm 2012, 2, 1.
[17] Dastan, A.; Kulkarni, A.; Torok, B. Green Chem 2012, 14, 17.
[18] Matsui, H.; Sakanashi, Y.; Oyama, T. M.; Oyama, Y.; Yokota,
S.; Ishida, S.; Okano, Y.; Oyama, T. B.; Nishimura, Y. Toxicology 2008,
248, 142.
An efficient and environmentally benign method for the
synthesis of pyrazolopyrimidine derivatives under
microwave irradiation in the presence of 1,3-
dibutylimidazolium bromide ionic liquid has been
developed. In the present investigation, imidazolium-
based ionic liquid was prepared under the microwave
irradiation by the N-alkylation method. Thereafter, the
1,3-dibutylimidazolium bromide ionic liquid was used
both as a catalyst and as solvent to synthesize the
pyrazolopyrimidine derivatives. The method offers
several advantages such as rapid synthesis with excellent
yields of products, simple preparation, non-volatility,
[19] Steel, H. C.; Tintinger, G. R.; Anderson, R. Chem Biol Drug
Des 2008, 72, 225.
[20] Karrouchi, K.; Radi, S.; Ramli, Y.; Taoufik, J.; Mabkhot, Y.
N.; Al-aizari, F. A.; Ansar, M. Molecules 2018, 23, 134.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet