Organoiodine (III) mediated synthesis of 3-aryl/hetryl-5,7-dimethyl-1,2,4- triazolo[4,3-a]pyrimidines as antibacterial agents

Article abstract of DOI:10.1016/j.ejmech.2004.06.011

Synthesis of some new 3-aryl/hetryl-5,7-dimethyl-1,2,4-triazolo[4,3-a] pyrimidines (3a-k) has been accomplished by the oxidation of 4,6-dimethyl-2-pyrimidinylhydrazones of various aldehydes with iodobenzene diacetate in dichloromethane. Nine new compounds (3b-g and 3i-k) were tested in vitro for their antibacterial activity. Two compounds, namely 3-(4′-pyridyl)-5,7-dimethyl-1,2,4-triazolo[4,3-a]pyrimidine (3k) and 3-(3′,4′-dimethoxyphenyl)-5,7-dimethyl-1,2,4-triazolo[4,3-a] pyrimidine (3f), were associated with substantially higher antibacterial activity than some commercial antibiotics against Bacillus subtilis, Escherichia coli, Staphylococcus aureus and Salmonella typhi at MIC (minimum inhibitory concentration) i.e. 10 μg/ml.

Full text of DOI:10.1016/j.ejmech.2004.06.011

European Journal of Medicinal Chemistry 39 (2004) 1073–1077
www.elsevier.com/locate/ejmech
Preliminary communication
Organoiodine (III) mediated synthesis
of 3-aryl/hetryl-5,7-dimethyl-1,2,4-triazolo[4,3-a]pyrimidines as
antibacterial agents
Om Prakash a,*, Vikas Bhardwaj a, Ravi Kumar a, Parikshit Tyagi b, Kamal R. Aneja b
a Department of Chemistry, Kurukshetra University, Kurukshetra 136119, India
b Department of Microbiology, Kurukshetra University, Kurukshetra 136119, India
Received 4 April 2004; received in revised form 3 June 2004; accepted 9 June 2004
Abstract
Synthesis of some new 3-aryl/hetryl-5,7-dimethyl-1,2,4-triazolo[4,3-a]pyrimidines (3a–k) has been accomplished by the oxidation of
4,6-dimethyl-2-pyrimidinylhydrazones of various aldehydes with iodobenzene diacetate in dichloromethane. Nine new compounds (3b–g and
3i–k) were tested in vitro for their antibacterial activity. Two compounds, namely 3-(4′-pyridyl)-5,7-dimethyl-1,2,4-triazolo[4,3-a]pyrimidine
(3k) and 3-(3′,4′-dimethoxyphenyl)-5,7-dimethyl-1,2,4-triazolo[4,3-a]pyrimidine (3f), were associated with substantially higher antibacterial
activity than some commercial antibiotics against Bacillus subtilis, Escherichia coli, Staphylococcus aureus and Salmonella typhi at MIC
(minimum inhibitory concentration) i.e. 10 µg/ml.
© 2004 Elsevier SAS. All rights reserved.
Keywords: Iodobenzene diacetate; Triazolopyrimidines; Antibacterial activity
1. Introduction
approach for the synthesis of new 1,2,4-triazolo[4,3-
a]pyrimidines (3a–k) by using iodobenzene diacetate as anti-
bacterial agents.
Fused heterocyclic 1,2,4-triazoles have acquired much
importance because of their CNS depressant [1], antiallergy
[2], antimicrobial [3] and anti-inflammatory [4] properties.
The use of organohypervalent iodine compounds as oxidi-
zing reagents has received considerable attention in organic
synthesis [5–13]. Since reactions involving hypervalent io-
dine reagents are mostly carried out under the mild reaction
conditions, these developments have offered superior alter-
native to the reported traditional methods [14]. In a previous
paper [15], we reported the synthesis of fused 1,2,4-
triazolopyridines. Some of the compounds were found to
possess strong antibacterial activity. Encouraged by these
results, we got interested in extending the scope of this
2. Chemistry
The synthetic Scheme 1 used for the synthesis of 3-aryl-
5,7-dimethyl-1,2,4-triazolo[4,3-a]pyrimidines 3 is same as
reported earlier [15,16]. Thus, treatment of substituted pyri-
midinyl hydrazones (2a–k) with 1.1 equivalent of IBD in
dichloromethane (DCM) for about 1 h at room temperature
afforded desired products 3-aryl-5,7-dimethyl-1,2,4-tria-
zolo[4,3-a]pyrimidines 3 in high yields. The hydrazones
(2a–k) were obtained by the condensation of 2-hydrazino-
4,6-dimethylpyrimidine 1 with different aromatic/hetero-
aromatic aldehydes.
Abbreviations: IBD, iodobenzene diacetate; DCM, dichloromethane;
NA, nutrient agar; MIC, minimum inhibitory concentration; B. subtilis,
Bacillus subtilis; S. typhi, Salmonella typhi; S. aureus, Staphylococcus
aureus; E. coli, Escherichia coli.
* Corresponding author.
E-mail address: chem@granth.kuk.ernet.in (O. Prakash).
The structures of all the new triazolopyrimidines 3a–k and
hydrazones 2a–k were elaborated by their spectral data (IR,
1HNMR and MS) and elemental analysis.
Thus, the present study provides an efficient way of syn-
thesising new 11 fused 1,2,4-triazolo[4,3-a]pyrimidines the-
0223-5234/$ - see front matter © 2004 Elsevier SAS. All rights reserved.
doi:10.1016/j.ejmech.2004.06.011

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O. Prakash et al. / European Journal of Medicinal Chemistry 39 (2004) 1073–1077
4.1.1.1. Characterization data of new hydrazones are gi-
ven. 2a: m.p. 84–86 °C, yield 95.93%. IR cm–1 3239.8 N-
Hstr.; 1HNMR.d 2.24 (s, 6H, C4–CH3, C6–CH3), 6.51 (s, 1H,
–N=C–H), 7.31–7.41 (d, 2H, C2′–H, C3′–H), 7.62–7.71 (d,
2H, C5′–H, C6′–H), 8.00 (s, 1H, C5–H).
2b:m.p. 182–184 °C, yield 51.93%. IR cm–1 3215.8 N-
Hstr.; 1HNMR. d 2.33 (s, 6H, C4–CH3, C6–CH3), 6.50 (s, 1H,
–N=C–H), 7.17–7.21 (1H, m, C5′–H), 7.25–7.29 (2H, m,
C4′–H, C6′–H), 8.13–8.16 (1H, dd, J = 1.8, 7.8 Hz, C3′–H).
2c:m.p. 170–172 °C, yield 46.66%. IR cm–1 3257.9 N-
Hstr.; 1HNMR. d 2.24 (s, 6H, C4–CH3, C6–CH3), 2.10 (s, 3H,
C4′–CH3), 6.46 (s, 1H, –N=C–H), 7.10–7.13 (d, 2H, C2′–H,
C3′–H), 7.56–7.59 (d, 2H, C5′–H, C6′–H), 8.00 (s, 1H,
C5–H).
2d: m.p. Ref. [18]; m.p. 166–167/170–172 °C, yield
78.51%.
2e:m.p. 199–201 °C, yield 87.66%. IR cm–1 3185.6 N-
Hstr.; 1HNMR d 2.37 (s, 6H, C4–CH3, C6–CH3), 6.54 (s, 1H,
–N=C–H), 8.45 (s, 1H, C5–H), 7.42–7.43 (1H, m, C5′–H),
7.55–7.57 (m, 1H, C4′–H), 7.94–7.96 (1H, m, C6′–H), 8.28–
8.31 (m, 1H, C3′–H).
Scheme 1
.
reby illustrating the generality of our previous I(III) mediated
approach.
2f:m.p. 180–181 °C, yield 31.46%. IR cm–1 3213.8 N-
Hstr.; 1HNMR. d 2.35 (s, 6H, C4–CH3, C6–CH3), 3.86 (s, 3H,
C4–OCH3), 6.46 (s, 1H, –N=C–H), 3.91(s, 3H, C3′–OCH3),
7.43–7.44 (d, 1H, C5′–H), 6.77–6.80 (d, 1H, C2′–H), 7.17–
7.20 (dd, 1H, C6′–H), 7.6 (s, 1H, C5–H).
3. Biological investigation and results
2g:m.p. 170–172 °C, yield 56.78%. IR cm–1 3565.6 N-
Hstr.; 1HNMR d 2.10 (s, 6H, C4–CH3, C6–CH3), 6.47 (s, 1H,
–N=C–H), 8.5 (s, 1H, C5–H), 3.85 (s, 3H, C4′–OCH3), 3.86
(s, 6H, C3′–OCH3, C5′–OCH3), 7.02 (s, 2H, C2′–H, C6′–H).
2h:m.p. 123–125 °C, yield 54.29%. IR cm–1 3203.7 N-
Hstr.; 1HNMR d 2.10 (s, 6H, C4–CH3, C6–CH3), 6.47 (s, 1H,
–N=C–H), 8.71(s, 1H, C5–H), 7.04–7.07 (m, 1H, C4′–H),
7.27–7.29 (d, 1H, C5′–H, J = 5.1 Hz), 7.35–7.36 (d, 1H,
C3′–H, J = 3.6 Hz).
Compounds 3b–g and 3i–k were tested in vitro for their
antibacterial activity against Bacillus subtilis, Escherichia
coli, Staphylococcus aureus and Salmonella typhi. 3-(4′-
Pyridyl)-5,7-dimethyl-1,2,4-triazolo[4,3-a]pyrimidine (3k)
and 3-(3′,4′-dimethoxyphenyl)-5,7-dimethyl-1,2,4-triazolo-
[4,3-a]pyrimidine (3f) were associated with substantially hi-
gher antibacterial activity than some commercial antibiotics
(Table 1).
2i:m.p. 108–110 °C, yield 45.27%. IR cm–1 3172.8 N-
Hstr.; 1HNMR d 2.10 (s, 6H, C4–CH3, C6–CH3), 6.52 (s, 1H,
–N=C–H), 7.93 (s, 1H, C5–H), 7.25–8.10 (m, 4H, C3′–H,
C4′–H, C5′–H C6′–H).
4. Experimental
4.1. Chemical synthesis
2j:m.p. 152–153 °C, yield 65.60%. IR cm–1 3179.5 N-
Hstr.; 1HNMR d 2.36 (s, 6H, C4–CH3, C6–CH3), 6.51(s, 1H,
–N=C–H), 7.83 (s, 1H, C5–H), 7.23–7.27 (dd, 1H, C5′–H,
J = 4.8, 8.1 Hz), 8.14–8.18 (dd, 1H, C4′–H, J = 2.1, 6.0 Hz),
8.48–8.50 (distorted doublet, 2H, C2′–H, C6′–H).
2k:m.p. 171–172°C, yield 67.40%. IR cm–1 3179.5 N-
Hstr.; 1HNMR d 2.37 (s, 6H, C4–CH3, C6–CH3), 6.54 (s, 1H,
–N=C–H), 7.76 (s, 1H, C5–H), 7.54–7.56 (dd, 2H, C3′–H,
C5′–H, J = 2.1, 5.1 Hz), 8.54–8.56 (dd, 2H, C2′–H, C6′–H,
J = 1.5, 4.5 Hz).
Melting points were determined in open capillaries in
electrical melting point apparatus and are uncorrected. The
IR (KBr) and 1HNMR spectra were recorded on Buck Scien-
tific IR M-500 and Bruker (300 MHz) spectrometers, respec-
tively. All the new compounds gave satisfactory analytical
results (within 0.4 of the theoretical values).
4,6-Dimethyl-2-hydrazinopyrimidine 1 was synthesized
according to the literature procedure commencing with urea
and acetylacetone [17].
4.1.1. Hydrazones 2a–k
4.1.2. 3-Aryl-5,7-dimethyl-1,2,4-triazolo [4,3-a]
The hydrazones 2 required for the oxidative cyclization
were prepared by the condensation of 2-hydrazino-4,6-
dimethylpyrimidine 1 with different aromatic and heteroaro-
matic aldehydes in ethanol with a trace of glacial acetic acid
[18,19].
pyrimidines 3a–k
4.1.2.1. General procedure. To a stirred solution of pyrimi-
dinylhydrazones 2 (0.01 mol) in DCM (25 ml) at room
temperature, IBD (0.01 mol) was added in four to five por-

O. Prakash et al. / European Journal of Medicinal Chemistry 39 (2004) 1073–1077
1075
Table 1
In vitro antibacterial spectrum of chemically synthesized compounds
Compound
Concentration (µg ml–1
)
Inhibition (%)
B. subtilis
Nil
E. coli
Nil
S. aureus
Nil
S. typhi
Nil
3b
500
100
50
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
3c
3d
3e
3f
500
100
50
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
500
100
50
Nil
16.29
Nil
43.67
42.11
33
100
100
92.5
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
98.25
100
100
100
100
100
Nil
Nil
Nil
Nil
500
100
50
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
500
100
50
100
100
100
100
98.24
20
100
100
100
100
Nil
100
100
10
97.5
Nil
3g
3i
500
100
50
Nil
16.67
10
Nil
Nil
Nil
500
100
50
Nil
100
100
100
93.64
45
100
100
100
83.34
100
100
100
100
100
100
100
100
93.85
45.72
92.43
38.58
84.35
31
Nil
Nil
10
Nil
3j
500
100
50
90
86.67
83.34
57
35
15.79
Nil
10
3k
500
100
50
100
100
100
100
100
89.29
48.58
88.47
40
100
100
10
100
Ciprofloxacin
Chloramphenicol
Streptomycin
Ampicillin
500
10
86.96
51.67
94.08
46.67
91.9
36.25
88.22
36
500
10
85.22
Nil
500
10
94.62
36
89.7
Nil
500
10
84.17
Nil
89.53
20
91.18
Nil
1
tions during 5 min. The solvent was evaporated on a steam
bath and the residual mass containing product and iodoben-
zene triturated with petroleum ether to give solid product,
which was recrystallized from methanol to yield pure triazo-
lopyrimidines 3.
3c:m.p. 205–207 °C(decomp.), yield 82.82%. HNMR d
2.21 (s, 3H, C5–CH3), 2.45 (s, 3H, C4–CH3), 2.61 (s, 3H,
C7–CH3), 6.49 (s, 3H, C6–CH3), 7.28–7.30 (d, 2H, C3′–H,
C5′–H, J = 7.8 Hz), 7.41–7.44 (d, 2H, C2′–H, C6′–H,
J = 7.9 Hz). m/z M+ 238.
1
3d:m.p. 247–248 °C, yield 82.70%. HNMR. d 2.27 (s,
4.1.2.2. Characterization data of new triazolopyrimidines
1H, C5–CH3), 2.66 (s, 1H, C7–CH3), 6.54 (s, 1H, C6–H),
7.79–7.82 (d, 2H, C3′–H, C5′–H, J = 8.6 Hz). m/z M+ 269.
3e:m.p. 226–227 °C, yield 92.74%. 1HNMR d 2.15 (s, 3H,
C5–CH3), 2.65 (s, 3H, C7–CH3), 6.56 (s, 1H, C6–H), 7.69–
7.72 (1H, m, C5′–H), 7.80–7.83 (m, 2H, C4′–H,C6′–H),
8.26–8.31 (m, 1H, C3′–H). m/z M+ 269.
3a–k are given. 3a:m.p. 198–199 °C (decomp.), yield
1
40.94%. HNMR d 2.23 (s, 3H, C5–CH3), 2.63 (s, 3H, C7–
CH3), 6.53 (s, 1H, C6–H); 7.51 (s, 4H, C2′–H, C3′–H, C5′–H,
C6′–H). m/z M+ 258.
3b:m.p. 208–209 °C, yield 77.41%. 1HNMR d 2.22 (s, 3H,
C5–CH3), 2.64 (s, 3H, C7–CH3), 6.53 (s, 1H, C6–H), 7.40–
7.46 (1H, m, C5′–H), 7.53–7.55 (2H, m, C4′–H, C6′–H),
7.60–7.63 (1H, dd, J = 1.3, 7.8 Hz, C3′–H). m/z M+ 258.
3f:m.p. 151–153 °C, yield 52.41%. 1HNMR d 2.25 (s, 3H,
C5–CH3), 2.62 (s, 3H, C7–CH3), 3.90 (s, 3H, C4′–OCH3),
3.96 (s, 3H, C3′–OCH3), 6.50 (s, 1H, C6–H), 6.77–6.80 (d,

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O. Prakash et al. / European Journal of Medicinal Chemistry 39 (2004) 1073–1077
1H, C2′–H), 7.39–7.41 (d,1H, C5′–H), 7.15–7.16 (dd, 1H,
C6′–H). m/z M+ 284.
3g:m.p. 160–162 °C, yield 72.78%. 1HNMR d 2.30 (s, 3H,
C5–CH3), 2.66 (s, 3H, C7–CH3), 3.87 (s, 3H, C4′–OCH3),
3.93 (s, 3H, C3′–OCH3, C5′–OCH3), 6.52 (s, 1H, C6–H), 7.09
(s, 2H, C2′–H, C6′–H). m/z M+ 314.
3h:m.p. 90–92 °C, yield 40.48%. 1HNMR d 2.65 (s, 3H,
C5–CH3), 2.80 (s, 3H, C7–CH3), 6.57 (s, 1H, C6–H), 7.14–
7.17 (m, 1H, C4′–H), 7.45–7.46 (d, 1H, C5′–H, J = 5.25 Hz),
7.95–7.96 (d, 1H, C3′–H, J = 3.55 Hz). m/z M+ 230.
3i:m.p. 148–150 °C, yield 80.80%. 1HNMR d 2.53 (s, 3H,
C5–CH3), 2.64 (s, 3H, C7–CH3), 6.61 (s, 1H, C6–H), 7.41–
7.45 (dd, 1H, C5′–H, J = 3.9, 5.4 Hz), 7.86–7.92 (ddd, 1H,
C4′–H, J = 1.5, 7.5, 7.8 Hz), 8.04–8.06 (d, 1H, C3′–H,
J = 7.2 Hz), 8.72–8.74 (d, 1H, C6′–H, J = 5.1 Hz). m/z M+
225.
Fig. 1. In vitro antibacterial assay of test compounds/antibiotics at concen-
tration 10 µg/ml.
Sufficiently, cooled NA medium was poured to the Petri
plates and rotated them to mix the contents. For control,
500 µl of respective dilution of DCM were added in place of
the dilution of test chemical. After solidification, plates were
incubated at 35 °C for 24 h and the colonies observed in the
test and control plates were counted to get percent inhibition
by the test chemical.
3j:m.p. 210–212 °C, yield 75.30%. 1HNMR d 2.25 (s, 3H,
C5–CH3), 2.65 (s, 3H, C7–CH3), 6.57 (s, 1H, C6–H), 7.46–
7.49 (dd, 1H, C5′–H, J = 4.2, 7.2 Hz), 7.95–7.96 (dd, 1H,
C4′–H, J = 1.8, 5.7 Hz), 8.62–8.63 (distorted doublet, 2H,
C2′–H). m/z M+ 225.
3k:m.p. 198–200 °C, yield 84.84%. 1HNMR d 2.30 (s, 3H,
C5–CH3), 2.65 (s, 3H, C7–CH3), 6.60 (s, 1H, C6–H), 7.54–
7.56 (dd, 2H, C3′–H, C5′–H, J = 1.2, 4.8 Hz), 8.0–8.2 (dd, 2H,
C2/–H, C6/–H, J = 1.2, 4.8 Hz). m/z M+ 225.
6. Results and discussion
Nine synthesized compounds 3b–g and 3i–k were tested
in vitro for their antibacterial activity against B. subtilis, E.
coli, S. aureus and S. typhi by the method used by us [15].
Out of the nine compounds tested, 3f and 3k were most active
against all the four test bacteria viz. B. subtilis, E. coli, S.
aureus and S. typhi at all the four concentrations (500, 100,
50 and 10 µg ml–1) showing 100% inhibition. The compound
3i was also found to be inhibitory at all the four concentra-
tions (500, 100, 50 and 10 µg ml–1) for E. coli, S. aureus and
S. typhi but it was completely inactive against B. subtilis. 3j
was also found to be 100% inhibitory against S. aureus and S.
typhi at all the four concentrations, while the activity of the
compound was low against E. coli and B. subtilis at all the
concentrations. The activities of the compounds were also
compared with the four commercial antibiotics (Ciprofloxa-
cin, Chloramphenicol, Streptomycin, Ampicillin) and were
found to be more potent than commercial antibiotics (Table 1
and Fig. 1). Thus, these compounds could be used as lead
structure in pharmaceutical industry if they are nontoxic to
the human system.
5. In vitro antibacterial assays
Antibacterial testing of nine synthesized compounds was
done in vitro by the following method. The stock solution
(1 mg ml–1) of the test chemical was prepared by dissolving
10 mg of the test chemical in 10 ml of DCM. The stock
solution was suitably diluted with sterilized distilled water to
get dilutions of 500, 100 and 50 µg ml–1. Control for each
dilution was prepared by diluting 10 ml of DCM instead of
stock solution with sterilized distilled water.
Four bacteria, namely B. subtilis, S. aureus (Gram +ve,
non-motile), E. coli (Gram –ve, non-motile) and S. typhi
(Gram –ve, motile), were used for the antibacterial assay.
Spread-plate method was used for B. subtilis, E. coli and S.
aureus as they were non-motile. Pour-plate method was used
for S. typhi (as it is motile). For this, 24-h-old broth cultures
were diluted up to 10–3. Fifty microliters of the test chemical
of required dilution and 50 µl of 24-h-old culture broth of
10–3 dilutions were mixed to make a total volume of 0.1 ml.
The mixture was then spread on the surface of nutrient agar
plates with the help of a sterilized spreader. For control, 50 µl
of respective dilution of DCM was added in to the broth
medium. All the plates were incubated at 35 °C for 24 h and
the colonies observed in the test and control plates were
counted.
Acknowledgements
The work reported here has been supported through
DRDO, Extramural Basic Research Grant No. ERIP/ER/
0103294/M/01 and is subjected to sponsor’s disclaimer
whose text can be had from the authors. We are also thankful
to Prof. S.S. Thukral, V.B. Patel Chest Institute, Delhi for
providing us the bacterial cultures used in the experiment.
Twenty-four hour old broth culture of S. typhi was diluted
to 10–3. To the already labelled Petri plates, was added 500 µl
of the test chemical of the required dilution and 500 µl of
culture of 10–3 dilutions to make a total volume of 1 ml.

O. Prakash et al. / European Journal of Medicinal Chemistry 39 (2004) 1073–1077
1077
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