Synthesis of some new pyrazolo[3,4-d]pyrimidines and thiazolo [4,5-d]pyrimidines and evaluation of their antimicrobial activities

Article abstract of DOI:10.1080/10426500701681581

The desired fused ring system 3-isopropyl-4-aryl-1,4,5,7-tetrahydro- pyrazolo[3,4-d]pyrimidine-6-thiones 4a-d were synthesized by the reaction of 5-isopropyl-2,4-dihydro-3-pyrazolone 1, thiourea and different aromatic aldehydes, while 7-aryl-5-thioxo-4,5,

Full text of DOI:10.1080/10426500701681581

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Synthesis of Some New
Pyrazolo[3,4-d]pyrimidines and
Thiazolo [4,5-d]pyrimidines
and Evaluation of Their
Antimicrobial Activities
J. D. Akbari a , S. D. Tala a , M. F. Dhaduk a , H. S.
Joshi a , K. B. Mehta b & S. J. Pathak b
a Department of Chemistry, Saurashtra University,
Rajkot, India
b Department of Bio-Science, Saurashtra University,
Rajkot, India
Version of record first published: 04 Jun 2008.
To cite this article: J. D. Akbari , S. D. Tala , M. F. Dhaduk , H. S. Joshi , K. B. Mehta
& S. J. Pathak (2008): Synthesis of Some New Pyrazolo[3,4-d]pyrimidines and Thiazolo
[4,5-d]pyrimidines and Evaluation of Their Antimicrobial Activities, Phosphorus,
Sulfur, and Silicon and the Related Elements, 183:6, 1471-1477
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Phosphorus, Sulfur, and Silicon, 183:1471–1477, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701681581
Synthesis of Some New Pyrazolo[3,4-d]pyrimidines and
Thiazolo [4,5-d]pyrimidines and Evaluation of Their
Antimicrobial Activities
J. D. Akbari,1 S. D. Tala,1 M. F. Dhaduk,1 H. S. Joshi,1
K. B. Mehta,2 and S. J. Pathak2
1Department of Chemistry, Saurashtra University, Rajkot, India
2Department of Bio-Science, Saurashtra University,
Rajkot, India
The desired fused ring system 3-isopropyl-4-aryl-1,4,5,7-tetrahydro-pyrazolo[3,4-
d]pyrimidine-6-thiones 4a–d were synthesized by the reaction of 5-isopropyl-2,4-
dihydro-3-pyrazolone 1, thiourea and different aromatic aldehydes, while 7-aryl-
5-thioxo-4,5,6,7-tetrahydro-3H-thiazolo[4,5-d]pyrimidin-2-ones 7a–d were synthe-
sized by using 2,4-thiazolidine 5 instead of 5-isopropyl-2,4-dihydro-3-pyrazolone 1.
The structure of the compounds was assigned on the basis of elemental analysis, IR,
1
H-NMR, and mass spectroscopy. The antibacterial activity of the newly synthesized
compounds were tested against Staphylococcus aureus ATCC 6538, Staphylococcus
epidermidis ATCC 12228, Escherichia coli ATCC 8739, Pseudomonas aeruginosa
ATCC 1539, and their antifungal activity against Candida albicans ATCC 10231
were tested using the disk diffusion method. Compounds 4b, 4c, 4d, 7c and 7d were
found to be active against S. aureus ATCC 6538 (MIC: 185; 78; 156; 78; and 102
μg/Ml, respectively) and compounds 4d and 7d against C. albicans ATCC 10231
(MIC: 312.5 μg/mL) . The minimum inhibitory concentration of these compounds
was determined using the micro dilution method.
Keywords
Antimicrobial activities; pyrazolo[3,4-d]pyrimidines; thiazolo[4,5-
d]pyrimidines
INTRODUCTION
Pyrimidine and their derivatives are well known for their potential
biological activity such as fungiside1, algaecide,2 and as antibiotic.3
Similarly thiazoles have shown wide range of applications,4 in drug
Received 10 July 2007; accepted 3 August 2007.
We thank to Department of Chemistry, Saurashtra University, Rajkot for providing
facilities and Department of Bio-Sciences, for antimicrobial screening. We are also thank-
ful to CIL, RSIC, Chandigarh for providing spectral analysis of compounds.
Address correspondence to H. S. Joshi, Department of Chemistry, Saurashtra Univer-
sity, Rajkot 360005, India. E-mail: drhsjoshi49@gmail.com
1471

1472
J. D. Akbari et al.
development,5 against inflammation,6 bacterial,7 and HIV infection,8
and pyrazolones are also used as starting materials for the synthe-
sis of biologically active compounds,9 as well as for the construction
of condensed heterocyclic systems.10,11 This inspired us to synthe-
size 3-isopropyl-4-aryl-1,4,5,7-tetrahydro-pyrazolo[3,4-d]pyrimidine-6-
thiones 4a–d and 7-aryl-5-thioxo-4,5,6,7-tetrahydro-3H-thiazolo[4,5-
d]pyrimidin-2-ones 7a–d. In the literature it was shown that when
pyrazolone or rhodanine react with different aromatic aldehydes and
thiourea at reflux temperature, new derivatives are formed.12,13 In
this work, in line with literature findings, 5-isopropyl-2,4-dihydro-3-
pyrazolone14,15 or 2,4-thiazolidine16 when react with different aromatic
aldehydes 2 and thiourea afforded desired product. The antibacterial
activity of the new compounds against Staphylococcus aureus ATCC
6538, Staphylococcus epidermidis ATCC 12228, Escherichia coli ATCC
8739, Pseudomonas aeruginosa ATCC 1539, and antifungal activity
against Candida albicans ATCC 10231 were investigated.
RESULTS AND DISCUSSION
Condensation of 5-isopropyl-2,4-dihydro-3-pyrazolone
1
or 2,4-
thiazolidine 5 with different aromatic aldehydes by Knoevenagel
condensation in the presence of piperidine at reflux temperature
to give 4-benzylidene-5-isopropyl-2,4-dihydro-3-pyrazolone 3a–d or
benzylidene-thiazolidine-2,4-dione 6a–d respectively. Which were on
reflux with thiourea in ethanolic HCl to yield 3-isopropyl-4-aryl-1,4,5,7-
tetrahydro-pyrazolo[3,4-d]pyrimidine-6-thiones 4a–d and 7-aryl-5-
thioxo-4,5,6,7-tetrahydro-3H-thiazolo[4,5-d]pyrimidin-2-ones 7a–d re-
spectively (Schemes 1 and 2).
SCHEME 1 Synthesis of substituted pyrazolo[3,4-d]pyrimidine.
The formulas of the compounds were confirmed by the elemental
1
analysis and their structures were determined by IR, H-NMR, and
mass spectral data. The IR spectra of the compounds displayed the
1
characteristic N-H stretching vibration at 3474–3448 cm−1. The H-
NMR spectrums of selected compounds give its characterized peak in

New Pyrazolo and Thiazolo Pyrimidines
1473
SCHEME 2 Synthesis of substituted thiazolo[4,5-d]pyrimidine.
particular region. Mass of all compounds was taken, and it was shown
molecular ion peak (M+) with low intensity.
Experiment were performed to evaluate the antibacterial activity
against Staphylococcus aureus ATCC 6538, Staphylococcus epidermidis
ATCC 12228, Escherichia coli ATCC 8739, Pseudomonas aeruginosa
ATCC 1539, antifungal activity against Candida albicans ATCC 10231
were tested using the disk diffusion method. Compounds 4b, 4c, 4d,
7c and7d were found to be active against S. aureus ATCC 6538 and
compounds 4d and 7d against C. Albicans ATCC 10231. The minimum
inhibitory concentration of these compounds was determined using the
micro dilution method. As a result, four compounds were found to be ac-
tive. The most active compound was compound 4c, which had a methoxy
group on 2nd position of the phenyl ring, while the least active one, 4b.
The compounds 4a, 7a, and 7b did not show any activity. The MIC val-
ues of the compounds 4b, 4c, 4d, 7c, and 7d against S. aureus ATCC
6538 were 185; 78; 156; 78; and 102 μg/mL, respectively, and the com-
pounds 4d and 7p against C. albicans ATCC 10231 were both 312.5
μg/mL (Table I).
TABLE I MIC Values (μg/mL) of
Compounds 4b, 4c, 4d, 7c, and 7d
S. aureus
C. albicans
Compound
ATTC 6535
ATCC 10231
4b
4c
185
78
—
—
4d
7c
156
78
312.5
—
7d
102
1.2
312.5
2.4
Cefuroxim Na

1474
J. D. Akbari et al.
EXPERIMENTAL SECTION
General Procedures
Melting points were estimated in open capillaries and are uncorrected.
Elemental analyses were performed on a Carlo Erba EA 1108 elemen-
tal analyzer. IR spectra were recorded on KBr discs, using FTIR-8400
spectrophotometer. 1H-NMR spectra were taken on a Bruker AVANCE
II 400 (1H: 400 Mz, [d6] DMSO) spectrometer. Mass spectra were deter-
mined on a GCMS-QP2010 mass spectrometer.
General Procedure for the Preparation of 3-Isopropyl-4-aryl-
1,4,5,7-tetrahydro-pyrazolo[3,4-d]pyrimidine-6-thiones (4a–d)
A mixture of 5-isopropyl-2,4-dihydro-3-pyrazolone (0.01 mol) 1 and
aromatic aldehyde 2 (0.01 mol) was taken in round bottom flask (100
mL) containing 10 mL of ethanol, heated under reflux for 30 min and
add pyridine (1 mL) in reaction mixture. Further refluxed it for 5 h;
thus, the solid product was separated, filtered off and washed with cold
mixture of ethanol:water (1:1) to give product 3a–d. The crude prod-
ucts were purified by crystallization from 95% ethanol to afford pure
product.
Product 3a–d (0.01 mol), thiourea (0.011 mol) and ethanolic HCl 10
mL (0.01N) was reflux for 5–6 h and separated solid was isolate from
RBF, washed with ethanol (5mL) and crystallized from ethanol to get
4a–d.
3-Isopropyl-4-phenyl-1,4,5,7-tetrahydro-pyrazolo[3,4-
d]pyrimidine-6-thione (4a)
Yellow crystals (1.03 g, 38%); m.p. 245=248◦C. IR (KBr): v 3447
( NH), 3232 (ArH), 2925 (C H str.), 1439 (C H i.p.def.) cm−1. 1H NMR
(400 MHz, DMSO-d6): δ 1.12 (3H, d, J = 6.92 Hz, CH3), 1.19 (3H, d, J =
6.8 Hz, CH3), 2.95 (1H, m, CH), 6.50–7.42 (6H, m, ArH), 7.84 (1H, s,
NH-pyrazole), 8.58 (1H, s, NH pyrimidine), 8.84 (1H, s, NH pyrimidine).
Mass M+1273. Anal. calcd. for C14H16N4S: C, 61.74; H, 5.92, N, 20.57.
Found: C, 61.22; H, 5.56, N, 20.74.
3-Isopropyl-4-(4-methoxyphenyl)-1,4,5,7-tetrahydro-pyrazolo
[3,4-d]pyrimidine-6-thione (4b)
Yellow powder (1.26 g, 42%); m.p. 221=222◦C. IR (KBr): v 3447 (-
1
NH), 3243 (ArH), 2934 (C H str.), 1436 (C H i.p.def.) cm−1. H NMR
(400 MHz, DMSO-d6): δ 1.14 (3H, d, J = 7 Hz, CH3), 1.23 (3H, d, J =
6.88 Hz, CH3), 2.99 (1H, m, CH), 3.83 (3H, s, OCH3), 6.57=7.35 (5H,
m, ArH), 7.03 (1H, s, NH-pyrazole), 8.55 (1H, s, NH pyrimidine), 8.82

New Pyrazolo and Thiazolo Pyrimidines
1475
(1H, s, NH pyrimidine). Mass M+303. Anal. calcd. for C15H18N4OS: C,
59.58; H, 6.00, N, 18.25. Found: C, 60.89; H, 5.83, N, 18.77.
3-Isopropyl-4-(2-methoxyphenyl)-1,4,5,7-tetrahydro-
pyrazolo[3,4-d]pyrimidine-6-thione (4c)
Light yellow powder (0.96 g, 32%); m.p. 233=235◦C. IR (KBr): v 3420
(-NH), 3309 (ArH), 2925 (C H str.), 1461 (C H i.p.def.) cm−1. 1H NMR
(400 MHz, DMSO-d6): δ 1.12 (3H, d, J = 6.96 Hz, CH3), 1.21 (3H, d, J =
6.88 Hz, CH3), 2.97 (1H, m, CH), 3.82 (3H, s, OCH3), 6.52-7.30 (5H,
m, ArH), 7.44 (1H, s, NH-pyrazole), 8.79 (1H, s, NH pyrimidine), 9.01
(1H, s, NH pyrimidine). Mass M+303. Anal. calcd. for C15H18N4OS: C,
59.58; H, 6.00, N, 18.25. Found: C, 59.31; H, 5.82, N, 18.32.
3-Isopropyl-4-(3,4-dimethoxyphenyl)-1,4,5,7-tetrahydro-
pyrazolo[3,4-d]pyrimidine-6-thione (4d)
Orange crystals (1.56 g, 47%); m.p. 241=242◦C. IR (KBr): v 3421 (-
1
NH), 3276 (ArH), 2932 (C H str.), 1433 (C H i.p.def.) cm−1. H NMR
(400 MHz, DMSO-d6): δ 1.15 (3H, d, J = 6.96 Hz, CH3), 1.23 (3H, d,
J = 6.88 Hz, CH3), 3.00 (1H, m, -CH), 3.83 (3H, s, OCH3), 3.88 (3H, s,
OCH3), 6.53-6.92 (4H, m, ArH), 7.47 (1H, s, NH-pyrazole), 7.82 (1H, s,
NH pyrimidine), 8.01 (1H, s, NH pyrimidine). Mass M+316. Anal. calcd.
for C16H20N4O2S: C, 57.18; H, 6.06, N, 16.85. Found: C, 57.34; H, 5.97,
N, 16.77.
General Procedure for the Preparation of 7-Aryl-5-thioxo-4,5,6,
7-tetrahydro-3H-thiazolo[4,5-d]pyrimidin-2-ones (7a–d)
A mixture of 2,4-thiazolidinone (0.01 mol) 5 and aromatic aldehyde 2
(0.01 mol) was taken in round bottom flask (100 mL) containing 10 mL
of ethanol, heated under reflux for 30 min and add pyridine (1 mL) in
reaction mixture. Further refluxed it for 5 h, thus the solid product was
separated, filtered off and washed with cold mixture of ethanol:water
(1:1) to give product 6a–d. The crude products were purified by crystal-
lization from 95% ethanol to afford pure product.
Product 6a–d (0.01 mol), thiourea (0.011 mol) and ethanolic HCl 10
mL (0.01N) was reflux for 5–6 h and separated solid isolate from RBF,
washed with ethanol (5mL) and crystallized from ethanol to get 7a–d.
7-Phenyl-5-thioxo-4,5,6,7-tetrahydro-3H-thiazolo[4,5-
d]pyrimidin-2-one (7a)
Light yellow crystals (1.08 g, 41%); m.p. 219–220◦C. IR (KBr): v 3474
1
(-NH), 3232 (ArH), 1733 (C O) cm−1. H NMR (400 MHz, DMSO-d6):
6.50–7.90 (6H, m, ArH), 10.03 (1H, s, NH-thiazole), 10.84 (1H, s, NH

1476
J. D. Akbari et al.
pyrimidine), 11.15 (1H, s, NH pyrimidine). Mass M+264. Anal. calcd.
for C11H9N4OS2: C, 50.17; H, 3.44, N, 15.96. Found: C, 49.88; H, 3.32,
N, 15.85.
7-(4-Methoxyphenyl)-5-thioxo-4,5,6,7-tetrahydro-3H-thiazolo
[4,5-d]pyrimidin-2-one (7b)
Orange crystals (1.46 g, 50%); m.p. 215–216◦C. IR (KBr): v 3448 (-
NH), 3232 (ArH), 1742 (C O) cm−1. 1H NMR (400 MHz, DMSO-d6): 3.86
(3H, s, CH3), 698–7.72 (5H, m, ArH), 10.03 (1H, s, NH-thiazole), 11.04
(1H, s, NH pyrimidine), 11.15 (1H, s, NH pyrimidine). Mass M+294.
Anal. calcd. for C12H11N3O2S2: C, 49.13; H, 3.78, N, 14.32. Found: 49.32;
H, 3.88, N, 14.21.
7-(2-Methoxyphenyl)-5-thioxo-4,5,6,7-tetrahydro-3H-thiazolo
[4,5-d]pyrimidin-2-one (7c)
Orange crystals (0.82 g, 28%); m.p. 196–197◦C. IR (KBr): v 3416 (-
1
NH), 3232 (ArH), 1734 (C O) cm−1. H NMR (400 MHz, DMSO-d6):
3.82 (3H, s, CH3), 6.52–7.30 (5H, m, ArH), 10.03 (1H, s, NH-thiazole),
11.22, s, NH pyrimidine), 11.32 (1H, s, NH pyrimidine). Mass M+294.
Anal. calcd. for C12H11N3O2S2: C, 49.13; H, 3.78, N, 14.32. Found: C,
49.21; H, 3.75, N, 14.45.
7-(3,4-Dimethoxyphenyl)-5-thioxo-4,5,6,7-tetrahydro-3H-
thiazolo[4,5-d]pyrimidin-2-one (7d)
Yellow crystals (1.29 g, 40%); m.p. 214–215◦C. IR (KBr): v 3448 (-
NH), 3232 (ArH), 1727 (C O) cm−1. Mass M+324. Anal. calcd. for
C13H13N3O3S2: C, 48.28; H, 4.05, N, 12.99. Found: C, 48.41; H, 4.22,
N, 12.76.
Microbiology
Derivatives 4a–d and 7a–d were tested in vitro for antimicrobial ac-
tivity S. aureus ATCC 6538, S. epidermidis ATCC 12228, E. coli ATCC
8739, P. aeruginosa ATCC 1539, and antifungal activity against C. al-
bicans ATCC 10231 using the disk diffusion method where each disc
contained 200 μg of the tested compound. For this method, Mueller-
Hinto agar (Difco) was melted at 100◦C and after cooing to 56◦C, was
poured into Petri plates of 9 cm diameter in quantities of 20 mL, and
left on a flat surface to solidify and the surface of the medium was
dried at 37◦C. Then, the cultures of each bacteria and yeast strain, af-
ter being kept in Mueller-Hinton broth (Difco) at 37◦C for 18–24 h and
diluted with Mueller-Hinton broth to 105cfu/mL, were pipetted into the
Mueller-Hinton agar plate prepared as described above. The surface of
the medium was allowed to dry. The 10,000 μg/mL (in DMSO) compound

New Pyrazolo and Thiazolo Pyrimidines
1477
impregnated discs were applied to the surface of inoculated plates. The
Petri plates were placed in an incubator at 37◦C. After 10–24 h of incu-
bation, the Petri plates were examined and it was found that compounds
4b, 4c, 4d, 7c, and 7d were active against S. aureus ATCC 6539 and
compounds 4d and 7d against C. albicans ATCC 10231.
The minimum inhibitory concentrations (MIC) of these compounds
were determined by the microbroth dilution technique using Mueller-
Hinton broth. Serial two-fold dilution ranged from 2500 to 2.4 mg/L for
compounds.
The inoculum was prepared in broth, which had been diluted with
Mueller-Hinton broth to give a final concentration of 105cfu/mL in the
test tray. The trays were covered and placed in plastic bags to prevent
drying. After incubation at 37◦C for 18–24 h, the MIC was defi3ed as the
lowest concentration of compound giving complete inhibition of visible
growth. MIC values of the compounds are given in Table I.
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