Molecular iodine promoted synthesis of new pyrazolo[3,4-d]pyrimidine derivatives as potential antibacterial agents

Article abstract of DOI:10.1016/j.ejmech.2009.10.051

Iodocyclization of 5-amino-1-(2,4-dinitrophenyl)-1H-4-pyrazolcarboxamides with aromatic aldehydes gave a new series of pyrazolo[3,4-d]pyrimidine derivatives in a single step and their antibacterial activity comparable to Streptomycin as reference drug was

Full text of DOI:10.1016/j.ejmech.2009.10.051

European Journal of Medicinal Chemistry 45 (2010) 647–650
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Molecular iodine promoted synthesis of new pyrazolo[3,4-d]pyrimidine
derivatives as potential antibacterial agents
,
b
b
a
a
Mehdi Bakavoli a , Ghodsieh Bagherzadeh , Maryam Vaseghifar , Ali Shiri , Mehdi Pordel ,
*
Mansour Mashreghi c, Parvaneh Pordeli c, Maryam Araghi c
a Department of Chemistry, School of Sciences, Ferdowsi University of Mashhad, Vakilabad Blvd 91775-1436 Mashhad, Iran
b Department of Chemistry, School of Sciences, Birjand University, Birjand, Iran
c Department of Biology, School of Sciences, Ferdowsi University of Mashhad, 91775-1436 Mashhad, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Iodocyclization of 5-amino-1-(2,4-dinitrophenyl)-1H-4-pyrazolcarboxamides with aromatic aldehydes
gave a new series of pyrazolo[3,4-d]pyrimidine derivatives in a single step and their antibacterial activity
comparable to Streptomycin as reference drug was evaluated.
Received 8 April 2009
Received in revised form
21 October 2009
Accepted 30 October 2009
Available online 6 November 2009
Ó 2009 Elsevier Masson SAS. All rights reserved.
Keywords:
Pyrazolo[3,4-d]pyrimidine
Antibacterial agents
Iodine
Heterocyclization
1. Introduction
1H-4-pyrazolcarboxamides with aromatic aldehydes in a single
step with the aim of evaluating their biological activities.
Fused pyrimidinone derivatives have attracted the attention of
numerous researchers over many years due to their important
biological activities. The structural similarity of pyrazolo[3,4-
d]pyrimidines with purines [1] have made them a prime target for
scientific research and in this context several reports dealing with
the synthesis of these fused heterocyclic compounds have
appeared in the literature [1–5,7–15]. An array of biological
activities such as antibacterial, antifungal [2,3], antiphlogistic,
antitumor [4] and herbicidal [5] has been reported to be shown by
various pyrazolopyrimidines. It has been proved that these
heterocyclic compounds are effective as inhibitors of inflammatory
mediators in intact cells [6], anti-M. tuberculosis [7] and human
enterovirus [8]. They also show inhibitory activity towards both
tubulin polymerization and cyclin-dependent kinase [9] and
enzymatic assays on Src and Abl tyrosine kinases [10]. Prompted by
these claims and in continuing our synthetic studies on bioactive
heterocycles [16], we have now synthesized a new series of
pyrazolo[3,4-d]pyrimidine derivatives via molecular iodine
catalyzed oxidative cyclization of 5-amino-1-(2,4-dinitrophenyl)-
2. Results and discussion
2.1. Chemistry
The starting 5-amino-1-(2,4-dinitrophenyl)-1H-4-pyrazolcarbo
nitrile (1) was obtained according to the previously published
method [17]. Concentrated sulfuric acid mediated hydrolysis of this
compound gave the corresponding 5-amino-1-(2,4-dinitrophenyl)-
1H-4-pyrazolcarboxamide (2). Oxidative cyclization of the latter
compound (2) with various substituted aromatic aldehydes in the
presence of equimolar molecular iodine as a mild Lewis acid and
oxidant [18] under neutral conditions in boiling acetonitrile gave
a new series of pyrazolo[3,4-d]pyrimidine derivatives (3a–j) in
good to excellent yields. (Scheme 1).
The structures of these compounds were confirmed from their
spectral and micro analytical data. For example, the 1H NMR
spectrum of compound (3c) did not show the signal at
belonging to NH2 moiety of the precursor but instead showed
a singlet for NH proton at 12.4 ppm which was removed on
d 6.8 ppm
d
deuteration. Furthermore, the spectrum showed an AB quartet
peak at the aromatic region, confirming the presence of an aromatic
ring and the occurrence of heterocyclization. The IR spectrum was
* Corresponding author. Tel.: þ98 511 8797022; fax: þ98 511 8796416.
E-mail address: mbakavoli@yahoo.com (M. Bakavoli).
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.10.051

648
M. Bakavoli et al. / European Journal of Medicinal Chemistry 45 (2010) 647–650
O
O
CN
NH2
NH
NH2
NH2
H+/H2O
N
N
N
N
ArCHO
I2/ CH3CN
X
N
N
N
O2N
O2N
O2N
NO2
NO2
NO2
(3a-j)
(1)
(2)
Ar: 3a: C6H5-; 3b: 4-Me-C6H4-; 3c: 4-MeO-
C6H4-; 3d: 3-MeO-C6H4-; 3e: 4-Br-C6H4-;
3f: 4-Cl-C6H4-; 3g: 4-NO2-C6H4-; 3h: 3-NO2-
C6H4-; 3i: 2-HO-C6H4-; 3j: 3-HO-C6H4-
Scheme 1.
also devoid of the stretching vibration bands resembling the NH2
moiety of the precursor but instead exhibited only one band at
3320 cmꢀ1 for the NH moiety. The molecular ion peak of compound
(3c) was observed at 408 (Mþ) corresponding to the molecular
formula C18H12N6O6.
an incubation period of 24 h at 37 ꢁC. The results of these evalua-
tions are given in Table 1. Streptomycin (binds to the 16SrRNA of the
bacterial ribosome, interfering with the binding of formyl-
methionyl-tRNA to the 30S subunit therefore prevents initiation of
protein synthesis and leads to death of microbial cell) was chosen
as a standard drug at a concentration of 10 m
g mlꢀ1. Streptomycin is
an antibiotic that inhibits both gram-positive and gram-negative
bacteria, and is therefore a useful broad spectrum antibiotic.
As it can be concluded from the data in Table 1, the compounds
bearing 4-Br–C6H4– (3e) and 2-HO–C6H6– (3i) substituents has
shown the highest sensitivity against E. coli and P. aeruginosa,
respectively. Compounds (3h) and (3j) with other substituents of
3-NO2–C6H4– and 3-HO–C6H4– respectively exhibited the best
activity against the S. aureus strains while B. Subtilis has been more
sensitive against compound (3f) with substituent 4-Cl–C6H4–.
Therefore the good activity can be attributed to the presence of
groups 4-bromo, 2 and 3-hydroxy and 4-chloro which are directly
attached to the phenyl ring of the diazine system. All the other
compounds were found to exhibit slight to moderate activities
against the mentioned organisms. These results clearly demon-
strate that hydroxyl or halogen substituted derivatives exhibited
better activity compared to other substituted pyrazolo[3,4-
d]pyrimidines.
2.2. Biological activities
The in vitro antibacterial activity of the newly synthesized
compounds (3a–j) were screened for the antibacterial activity
against several pathogenic representative Gram-positive bacteria
(Staphylococcus aureus PTCC 1074 and Bacillus subtilis PTCC 1365);
Gram-negative bacteria (Escherichia coli HB101 BA 7601C and
Pseudomonas aeruginosa PTCC 1431) using disc diffusion sensitivity
test [19,20]. Mueller–Hinton agar media were sterilized (15 min at
121 ꢁC) and poured into the plates to a uniform depth of 5 mm and
allow it to solidify. The microbial suspension (1.2 ꢂ108 CFU/mL)
(0.5 McFarland Nephelometery Standards) was streaked over the
surface of media using a sterile cotton swab (15 min at 180 ꢁC) to
ensure confluent growth of the organisms. The tested compounds
were dissolved in DMF and diluted with ethanol to get a solution of
100–600 m
g mLꢀ1 concentration. The discs measuring 6.25 mm in
diameter (Whatman no. 1 filter paper) were impregnated with
prepared solution of compounds (3a–j) by 1 mL of the chemical
solution which was added to each bottle contained 12 discs and
placed on Muller-Hinton agar media previously inoculated with
bacterial suspension. The inhibition zones as a criterion for
anti-microbial activity were measured in millimeter at the end of
3. Experimental
Melting points were recorded on an Electrothermal type 9100
melting point apparatus and are not corrected. The 1H NMR
Table 1
Antibacterial data of the synthesized compounds 3a–j.
Compound
Gram-negative bacteria
Gram-positive bacteria
Escherichia coli
Pseudomonas aeruginosa
Staphylococcus aureus
Bacillus subtilis
HB101 BA 7601C
PTCC 1431
PTCC 1074
PTCC 1365
3a
3b
3c
3d
3e
3f
3g
3h
15a (þ)b (400)c
9 (ꢀ) (200)
9.5 (ꢀ) (100)
11.5 (ꢀ) (100)
17 (þþ) (100)
10.5 (ꢀ) (400)
9 (ꢀ) (300)
8 (ꢀ) (400)
7 (ꢀ) (500)
12 (þ) (500)
17
9.5 (ꢀ) (400)
7.5 (ꢀ) (200)
12.5 (þ) (100)
12.5 (þ) (100)
10 (ꢀ) (100)
8 (ꢀ) (400)
13.5 (þ) (300)
9 (ꢀ) (400)
16 (þþ) (500)
9.5 (ꢀ) (500)
10
9 (ꢀ) (400)
13 (þ) (200)
10 (ꢀ) (100)
9 (ꢀ) (100)
9 (ꢀ) (100)
8.5 (ꢀ) (400)
8.5 (ꢀ) (300)
15 (þþ) (400)
9 (ꢀ) (500)
16 (þþ) (500)
15
10 (þ) (400)
9 (ꢀ) (200)
10 (ꢀ) (100)
8 (ꢀ) (100)
9 (ꢀ) (100)
15 (þþ) (400)
9 (ꢀ) (300)
11 (ꢀ) (400)
9 (ꢀ) (500)
12 (þ) (500)
10
3i
3j
Streptomycin (standard)
a
Zones of inhibition in millimeter.
b
(þþ) Highly sensitive; (þ) Moderately sensitive; (ꢀ) Slightly sensitive.
c
concentration in
medium seeded with fresh bacteria separately and the average was reported.
m
g mLꢀ1 and the maximum inhibition zone for each compound has been shown. Disks of each concentration were placed in triplicate in nutrient agar

M. Bakavoli et al. / European Journal of Medicinal Chemistry 45 (2010) 647–650
649
(100 MHz) spectra were recorded on a Bruker AC 100 spectrometer.
Chemical shifts are reported in ppm downfield from TMS as
internal standard; coupling constants J are given in Hertz. The mass
spectra were scanned on a Varian Mat CH-7 at 70 eV. Elemental
J ¼ 8.4 Hz, 1H), 8.75 (d, J ¼ 8.7 Hz, 1H), 8.95 (s, 1H), 12.7 (br s, 1H,
D2O exchangeable); IR spectrum (nmax, cmꢀ1): 3300 (NH), 1650
(C]O); Mass spectrum, m/z 408 (Mþ); Anal. Calcd. for C18H12N6O6
(%): C, 52.95; H, 2.96; N, 20.58; Found: C, 52.55; H, 2.77; N, 20.43.
analysis was performed on
microanalyzer.
Compound (1) was obtained according to the published method
[21]. Other reagents were commercially available.
a Thermo Finnigan Flash EA
3.2.5. 6-(4-Bromophenyl)-1-(2,4-dinitrophenyl)-4,5-dihydro-1H-
pyrazolo[3,4-d]pyrimidin-4-one (3e)
yield ¼ 74%, m.p. ¼ 298–300 ꢁC, 1H NMR spectrum in DMSO-d6
(
d
, ppm): 7.74 (s, 1H), 7.70 (d, J ¼ 7.2 Hz, 2H), 8.21 (d, J ¼ 7.2 Hz, 2H),
3.1. Synthesis of 5-amino-1-(2,4-dinitrophenyl)-1H-4-pyrazol
carboxamide (2)
8.35 (d, J ¼ 8.5 Hz,1H), 8.75 (d, J ¼ 8.8 Hz,1H), 8.95 (s,1H), 12.9 (br s,
1H, D2O exchangeable); IR spectrum (nmax, cmꢀ1): 3330 (NH), 1680
(C]O); Mass spectrum, m/z 457 (Mþ); Anal. Calcd. for C17H9BrN6O5
(%): C, 44.66; H, 1.98; N, 18.38; Found: C, 44.23; H, 1.88; N, 18.03.
5-amino-1-(2,4-dinitrophenyl)-1H-4-pyrazole carbonitrile (1)
was hydrolyzed according to lit. [21]. The resulting solid was
recrystallized from ethanol-water. (Yield ¼ 86%, m.p. ¼ 234 ꢁC, lit.
[22] 234–235 ꢁC).
3.2.6. 6-(4-Chlorophenyl)-1-(2,4-dinitrophenyl)-4,5-dihydro-1H-
pyrazolo[3,4-d]pyrimidin-4-one (3f)
yield ¼ 87%, m.p. ¼ 346–347 ꢁC, 1H NMR spectrum in DMSO-d6
3.2. General procedure for the synthesis of 6-aryl-1-(2,4-
dinitrophenyl)-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidine-4-one
(3a–j)
(d
, ppm): 7.73 (s, 1H), 7.65 (d, J ¼ 8.4 Hz, 2H), 8.15 (d, J ¼ 8.4 Hz, 2H),
8.35 (d, J ¼ 8.4 Hz,1H), 8.75 (d, J ¼ 8.7 Hz,1H), 8.95 (s,1H), 12.7 (br s,
1H, D2O exchangeable); IR spectrum (nmax, cmꢀ1): 3320 (NH), 1680
(C]O); Mass spectrum, m/z 412 (Mþ); Anal. Calcd. for C17H9ClN6O5
(%): C, 49.47; H, 2.20; N, 20.36; Found: C, 49.34; H, 2.13; N, 20.12.
To a mixture of 5-amino-1-(2,4-dinitrophenyl)-1H-4-pyrazol
carboxamide (2) (0.2 mmol, 0.06 g) and various aromatic aldehydes
(0.2 mmol) in dry acetonitrile (5 ml), molecular iodine (0.22 mmol,
0.057 g) was added. Then the mixture was refluxed and the prog-
ress of the reaction was monitored by TLC using chloroform-
methanol (8:2) as eluent. After the reaction was completed, the
mixture was cooled to room temperature. A solution of sodium-
thiosulphate (5%) was added and the resulted solid was filtered off
and washed with water. The crude product was recrystallized from
ethanol.
3.2.7. 1-(2,4-Dinitrophenyl)-6-(4-nitrophenyl)-4,5-dihydro-1H-
pyrazolo[3,4-d]pyrimidin-4-one (3g)
yield ¼ 88%, m.p. ¼ 350 ꢁC, 1H NMR spectrum in DMSO-d6
(d,
ppm): 7.76 (s, 1H), 7.89 (d, J ¼ 9.1 Hz, 2H), 8.35 (d, J ¼ 9.1 Hz, 2H),
8.35 (d, J ¼ 8.5 Hz,1H), 8.75 (d, J ¼ 8.9 Hz,1H), 8.95 (s, 1H),13.3 (br s,
1H, D2O exchangeable); IR spectrum (nmax, cmꢀ1): 3310 (NH), 1670
(C]O); Mass spectrum, m/z 423 (Mþ); Anal. Calcd. for C17H9N7O7
(%): C, 48.24; H, 2.14; N, 23.16; Found: C, 47.98; H, 2.01; N, 22.90.
3.2.1. 1-(2,4-Dinitrophenyl)-6-phenyl-4,5-dihydro-1H-
3.2.8. 1-(2,4-Dinitrophenyl)-6-(3-nitrophenyl)-4,5-dihydro-1H-
pyrazolo[3,4-d]pyrimidin-4-one (3h)
pyrazolo[3,4-d]pyrimidin-4-one (3a)
yield ¼ 78%, m.p. ¼ 260 ꢁC, 1H NMR spectrum in DMSO-d6
(d
,
yield ¼ 81%, m.p. ¼ 338–339 ꢁC, 1H NMR spectrum in DMSO-d6
ppm): 7.52 (m, 5H), 7.73 (s, 1H), 8.35 (d, J ¼ 8.5 Hz, 1H), 8.75 (d,
J ¼ 8.7 Hz, 1H), 8.95 (s, 1H), 12.6 (br s, 1H, D2O exchangeable); IR
spectrum (nmax, cmꢀ1): 3320 (NH),1650 (C ¼ O); Mass spectrum, m/
z: 378 (Mþ); Anal. Calcd. for C17H10N6O5 (%): C, 53.97; H, 2.66; N,
22.22; Found: C, 53.55; H, 2.45; N, 22.01.
(d, ppm): 7.75 (s, 1H), 8.25 (4H, m), 8.35 (d, J ¼ 8.5 Hz, 1H), 8.75 (d,
J ¼ 8.8 Hz, 1H), 8.95 (s, 1H), 13.3 (br s, 1H, D2O exchangeable); IR
spectrum (nmax, cmꢀ1): 3320 (NH),1660 (C]O); Mass spectrum, m/z
423 (Mþ); Anal. Calcd. for C17H9N7O7 (%): C, 48.24; H, 2.14; N, 23.16;
Found: C, 48.04; H, 2.11; N, 22.97.
3.2.2. 1-(2,4-Dinitrophenyl)-6-(4-Methylphenyl)-4,5-dihydro-1H-
pyrazolo[3,4-d]pyrimidin-4-one (3b)
3.2.9. 1-(2,4-Dinitrophenyl)-6-(2-Hydroxyphenyl)-4,5-dihydro-1H-
pyrazolo[3,4-d]pyrimidin-4-one (3i)
yield ¼ 70%, m.p. ¼ 324–325 ꢁC, 1H NMR spectrum in DMSO-d6
yield ¼ 69%, m.p. ¼ 302 ꢁC, 1H NMR spectrum in DMSO-d6
(d,
(d
, ppm): 2.32 (s, 3H, CH3), 7.22 (d, J ¼ 8.0 Hz, 2H), 7.42 (d, J ¼ 8.0 Hz,
ppm): 7.72 (s,1H), 7.12 (4H, m), 8.35 (d, J ¼ 8.3 Hz,1H), 8.75 (d, J ¼ 8.7,
1H), 8.95 (s,1H), 9.54 (br s,1H, OH, D2O exchangeable),13.3 (br s,1H,
NH, D2O exchangeable); IR spectrum (nmax, cmꢀ1): 3300 (NH), 1660
(C]O); Mass spectrum, m/z 394 (Mþ); Anal. Calcd. for C17H10N6O6
(%): C, 51.78; H, 2.56; N, 21.31; Found: C, 51.58; H, 2.44; N, 21.14.
2H), 7.74 (s, 1H), 8.35 (d, J ¼ 8.4 Hz, 1H), 8.75 (d, J ¼ 8.7 Hz, 1H), 8.95
(s, 1H), 12.6 (br s, 1H, D2O exchangeable); IR spectrum (nmax, cmꢀ1):
3330 (NH), 1660 (C]O); Mass spectrum, m/z 392 (Mþ); Anal. Calcd.
for C18H12N6O5 (%): C, 55.11; H, 3.08; N, 21.42; Found: C, 54.95; H,
2.90; N, 21.22.
3.2.10. 1-(2,4-Dinitrophenyl)-6-(3-Hydroxyphenyl)-4,5-dihydro-
3.2.3. 1-(2,4-Dinitrophenyl)-6-(4-Methoxyphenyl)-4,5-dihydro-
1H-pyrazolo[3,4-d]pyrimidin-4-one (3j)
1H-pyrazolo[3,4-d]pyrimidin-4-one (3c)
yield ¼ 68%, m.p. ¼ 316 ꢁC, 1H NMR spectrum in DMSO-d6
(d,
yield ¼ 70%, m.p. ¼ 328 ꢁC, 1H NMR spectrum in DMSO-d6
(d
,
ppm): 7.18 (4H, m), 7.73 (s, 1H), 8.35 (d, J ¼ 8.4 Hz, 1H), 8.75 (d,
J ¼ 8.7 Hz,1H), 8.95 (s,1H), 9.89 (br s,1H, D2O exchangeable),13.3 (br
s,1H, D2O exchangeable); IR spectrum (nmax, cmꢀ1): 3290 (NH),1650
(C]O); Mass spectrum, m/z 394 (Mþ); Anal. Calcd. for C17H10N6O6
(%): C, 51.78; H, 2.56; N, 21.31; Found: C, 51.66; H, 2.43; N, 21.25.
ppm): 3.84 (s, 3H, OCH3), 6.94 (d, J ¼ 9.0 Hz, 2H), 7.22 (d, J ¼ 9.0 Hz,
2H), 7.73 (s, 1H), 8.35 (d, J ¼ 8.5 Hz, 1H), 8.75 (d, J ¼ 8.8 Hz, 1H), 8.95
(s, 1H), 12.4 (br s, 1H, D2O exchangeable); IR spectrum (nmax, cmꢀ1):
3320 (NH), 1650 (C]O); Mass spectrum, m/z 408 (Mþ); Anal. Calcd.
for C18H12N6O6 (%): C, 52.95; H, 2.96; N, 20.58; Found: C, 52.70; H,
2.83; N, 20.29.
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