Design, synthesis, and antibacterial studies of potent pyrazolinyltriazoles

Article abstract of DOI:10.1007/s11164-016-2774-6

Abstract: A library of pyrazolinyltriazole hybrids (3a–l, 4a–l) was synthesized via azide–alkyne dipolar (Huisgen) cycloaddition of azidoacetyl pyrazoline and acetylenedicarboxylic esters under solvent-free condition. The in?vitro antibacterial activity of the hybrids was studied against four human pathogens, viz. Escherichia coli (ATCC 25922), Klebsiella pneumonia (ATCC 13883), Proteus mirabilis (ATCC 12453), and Staphylococcus aureus (ATCC 29213), compared with that of ciprofloxacin as standard drug. Six of the 24 compounds synthesised [3d, k, l and 4d, k, l with minimum inhibitory concentration (MIC) of 3.9?μg/mL] were found to be more potent than ciprofloxacin. In fact, the high antibacterial activity of all 24 new compounds against S.?aureus reveals that such compounds with this pyrazolinyltriazole skeleton may emerge as a new class of potential antibacterial agents. Furthermore, the other three pathogens were also effectively inhibited by most of the synthesized compounds (3a, c, d, g, k, l, 4a–e, h–l). Synthesis of the heterocyclic hybrids 3, 4, identification of their core skeleton, and their structure–activity relationship are reported herein. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s11164-016-2774-6

Res Chem Intermed
DOI 10.1007/s11164-016-2774-6
Design, synthesis, and antibacterial studies of potent
pyrazolinyltriazoles
Sivasubramaniyan Archana1 Raja Ranganathan1
•
•
Murugan Dinesh1 Ponnusamy Arul1
•
•
Alagusundaram Ponnuswamy1 Patchaiah Kalaiselvi2
•
•
Subbiah Chellammal2 Gopalan Subramanian2
•
Received: 10 August 2016 / Accepted: 8 October 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract A library of pyrazolinyltriazole hybrids (3a–l, 4a–l) was synthesized via
azide–alkyne dipolar (Huisgen) cycloaddition of azidoacetyl pyrazoline and
acetylenedicarboxylic esters under solvent-free condition. The in vitro antibacterial
activity of the hybrids was studied against four human pathogens, viz. Escherichia coli
(ATCC 25922), Klebsiella pneumonia (ATCC 13883), Proteus mirabilis (ATCC 12453),
and Staphylococcus aureus (ATCC 29213), compared with that of ciprofloxacin as
standard drug. Six of the 24 compounds synthesised [3d, k, l and 4d, k, l with minimum
inhibitory concentration (MIC) of 3.9 lg/mL] were found to be more potent than
ciprofloxacin. In fact, the high antibacterial activity of all 24 new compounds against
S. aureus reveals that such compounds with this pyrazolinyltriazole skeleton may
emerge as a new class of potential antibacterial agents. Furthermore, the other three
pathogens were also effectively inhibited by most of the synthesized compounds (3a, c,
d, g, k, l, 4a–e, h–l). Synthesis of the heterocyclic hybrids 3, 4, identification of their
core skeleton, and their structure–activity relationship are reported herein.
Electronic supplementary material The online version of this article (doi:10.1007/s11164-016-2774-6)
contains supplementary material, which is available to authorized users.
&
Alagusundaram Ponnuswamy
ramradkrish@yahoo.co.in
1
2
Department of Organic Chemistry, School of Chemistry, Madurai Kamaraj University,
Madurai, Tamilnadu 625 021, India
Offshore Platform and Marine Electrochemistry Centre, CSIR - CECRI Unit,
V.O. Chidambaranar Port, Tuticorin 628 004, India
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S. Archana et al.
Graphical Abstract
Keywords 1,2,3-Triazole Á Pyrazoline Á Hybrids Á Solvent-free Á Antibacterial
activity Á Structure–activity relationship
Introduction
A statistical report of the World Health Organization (WHO)1 reveals that
antimicrobial resistance has become a major threat and challenge to human society.
Some of the commonly encountered human pathogens, such as Staphylococcus
aureus, Klebsiella pneumonia, and Escherichia coli, cause diseases such as sepsis,
meningitis, necrotizing fasciitis, pneumonia [1, 2], nosocomial pneumonia [3, 4],
cystic fibrosis, acute leukemia [5], etc. Many antibiotics belonging to the b-lactam,
aminoglycoside, semisynthetic aminoglycoside, etc. classes have been used as drugs
to control infections caused by these pathogens. However, these pathogens have
developed resistance to such drugs by evolving drug-resistant strains. In particular,
Staphylococcus aureus has evolved various drug-resistant strains, such as penicillin-
resistant Staphylococcus aureus (PRSA), methicillin-resistant Staphylococcus
aureus (MRSA), and vancomycin-resistant Staphylococcus aureus (VRSA). Hence,
synthesis of new classes of antibacterial drugs to control such pathogens is urgently
needed in the present scenario.
Pyrazoline is one of the nitrogen-containing five-membered heterocycles,
exhibiting diverse biological activities such as antimicrobial [6], antiinflammatory
[7], analgesic [7], anticancer [8], anticonvulsant [9], anthelmintic [10], and
antioxidant [11] actions.
On the other hand, investigations on the bioactivity of compounds containing the
1,2,3-triazole scaffold have revealed their antiinflammatory [12], antitubercular
[13], anticancer [14], antileishmanial [15], antiviral [16], antimicrobial [17],
antibacterial [18], and antifungal [18] activities.
1
WHO report, March 2012, 10 facts on antimicrobial resistance.
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Design, synthesis, and antibacterial studies of potent…
Recently, hybrid molecules made up of two or more heterocyclic moieties in the
same framework have attracted attention from scientists, as they possess better
qualities as desired by pharmacologists and industrialists. It is pertinent to mention
here that perusal of literature in this regard discloses diversified bioactivities
(Fig. 1) of hybrids containing analogues of the above-mentioned scaffolds.
Our recent research investigations [19, 20] in this regard revealed antibacterial
activity of 1,2,3-triazolyl-2-aminopyrimidine hybrids and 1,2,3-triazolyl dihydropy-
rimidine-2-thione hybrids.
We were therefore prompted to carry out antibacterial studies on hybrid
molecules containing 1,2,3-triazolyl and pyrazoline scaffolds. At the outset, we
planned to design a core skeleton by varying the structural features of the basic
skeleton, viz. N-acetyl-(3,5-diaryl)pyrazoline (I) (Fig. 2). In particular, we envis-
aged that structural variations would be attempted by substituting (1) one of the
acetyl methyl hydrogens and/or (2) one or more of the aryl hydrogens by functional
group/s, or (3) replacing the aryl ring by a heterocyclic moiety. Our findings in this
regard are presented herein.
Results and discussion
Chemistry
Synthesis of N-acetyl- and N-chloroacetylpyrazolines was achieved by direct
acylation of the pyrazoline with corresponding carboxylic acids under reflux
condition in excellent yield, as reported earlier [21]. Subsequently, N-
chloroacetylpyrazoline readily underwent substitution on refluxing with sodium
azide in tetrahydrofuran (THF)/water medium (1:1) for 2 h to afford the
azidoacetylpyrazoline 1 in quantitative yield.
Fig. 1 Some biologically potent 1,2,3-triazole-containing hybrids
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S. Archana et al.
Fig. 2 Basic skeleton
Table 1 Solvent screening for
synthesis of pyrazolinyltriazole
hybrid 3a
Entry
Solvent
Time (h)
Yield (%)a
1
2
3
4
5
6
THF
6
43
50
62
75
80
92
Acetonitrile
Benzene
Toluene
Xylene
4
3
2
1
Solvent free
10 min
a
Isolated yield
Furthermore, optimization of the reaction condition for synthesis of pyrazolinyl-
triazole hybrids 3 was achieved by attempting synthesis of 3a as a representative
compound in various solvents and solvent-free condition (Table 1).
At the outset, the reactions were monitored by refluxing a mixture of N-
(azidoacetyl)-3,5-diphenylpyrazoline (1, 1.0 equiv.) and diethylacetylenedicarboxy-
late (2, 1.0 equiv.) in different organic solvents, viz. THF, CH3CN, benzene,
toluene, and xylene (Scheme 1). It was noted that the yield of the pyrazolinyltri-
azole hybrid 3a in xylene was 80 % in an hour (entry 5), in contrast to other
solvents (entries 1–4), in which the reaction time increased (2–6 h) and the yield
was relatively lower (43–75 %), as summarized in Table 1. To our delight, when the
reaction was carried out at around 90 °C under solvent-free condition (entry 6) on a
boiling water bath, the reaction completed in 10 min, affording 3a in excellent yield
(92 %).
Apparently, the reason for the higher yield and increased reaction rate in xylene
may be attributed to its higher boiling point than the other solvents. On the other
hand, under solvent-free condition, the proximity of the polar reactants might have
enhanced the reaction rate, resulting in very good product yield.
The breadth of scope of the solvent-free method was investigated by synthesis of
a series of pyrazolinyltriazole hybrids (3a–l, 4a–l) from corresponding pyrazolines
in excellent yield and very short reaction time (Table 2).
While synthesized hybrids 3a, c2 are known compounds, the other compounds
(3b, d–l, 4a–l) are hitherto unknown. They were characterized by infrared (IR) and
2
Commercially available with CAS no. 438228-92-3 and 438231-42-6, respectively.
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Design, synthesis, and antibacterial studies of potent…
Scheme 1 Synthesis of pyrazolinyltriazole hybrids
one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance
(NMR) spectral techniques.
Structural assignment
The synthesized pyrazolinyltriazole hybrids 3, 4 were completely characterized by
IR, mass, and (1D and 2D) NMR spectral techniques.
Selected 1H and 13C NMR chemical shift values for 3i
The IR spectrum of 3i shows bands due to ester and amide carbonyl group at
1725 and 1673 cm-1, respectively. The mass spectrum of 3i shows the character-
istic molecular-ion peak at m/z = 521.12 [M ? H]?.
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S. Archana et al.
Table 2 Synthesis of pyrazolinyltriazole hybrids 3a–l, 4a–l
Compound
Ring B
R
Time (min)
Yield (%)a
3a
3b
3c
3d
3e
3f
C6H5–
–C2H5
–CH3
–C2H5
–CH3
–C2H5
–CH3
–C2H5
–CH3
–C2H5
–CH3
–C2H5
–CH3
–C2H5
–CH3
–C2H5
–CH3
–C2H5
–CH3
–C2H5
–CH3
–C2H5
–CH3
–C2H5
–CH3
10
10
10
10
10
10
10
10
10
10
10
5
92
90
93
91
94
92
85
89
93
95
90
91
95
92
91
94
93
90
87
90
91
94
92
90
C6H5–
4-CH3O-C6H4–
4-CH3O-C6H4–
4-Cl-C6H4–
4-Cl-C6H4–
2-Cl-C6H4–
2-Cl-C6H4–
3-NO2-C6H4–
3-NO2-C6H4–
2-Thiophenyl
2-Thiophenyl
C6H5–
3g
3h
3i
3j
3k
3l
4a
4b
4c
4d
4e
4f
5
C6H5–
5
4-CH3O-C6H4–
4-CH3O-C6H4–
4-Cl-C6H4–
4-Cl-C6H4–
2-Cl-C6H4–
2-Cl-C6H4–
3-NO2-C6H4–
3-NO2-C6H4–
2-Thiophenyl
2-Thiophenyl
5
5
5
5
4g
4h
4i
5
5
5
4j
5
4k
4l
5
5
a
Isolated yield
123

Design, synthesis, and antibacterial studies of potent…
1
In the H NMR spectrum of 3i, aromatic protons appear as three multiplets
between 8.17 and 8.13 ppm (two protons), 7.81 and 7.77 ppm (two protons), and
7.63 and 7.48 ppm (five protons). Each of the diastereotopic protons of the
methylene group attached to the carbonyl function appear as separate doublets at
5.95 and 6.08 ppm with J = 18.0 Hz. Similarly, each of the diastereotopic protons
of the methylene group of the pyrazoline ring appears as separate doublet of
doublets at 3.95 ppm (J = 18.0, 12.0 Hz) and 3.28 ppm (J = 18.0, 6.0 Hz). Other
two methylene groups of the diethyl ester moiety give rise to two quartets at 4.42
and 4.27 ppm with J = 6.0 Hz. The two methyl groups show two triplets at 1.39
and 1.25 ppm with J = 6.0 Hz. The methine proton gives rise to a doublet of
doublet at 5.67 ppm (J = 12.0, 6.0 Hz).
In the 13C NMR spectrum of 3i, the signals of two methyl carbons appear at
14.01 and 13.58 ppm, respectively. Four methylene carbons appear at 52.40, 62.42,
61.66, and 42.11 ppm. The methine carbon appears at 59.85 ppm. A further one of
the carbonyls attached to methylene carbon appears at 162.35 ppm, and ester
carbonyl carbons appear at 159.97 and 158.27 ppm. Other carbons show signals at
156.08, 148.42, 142.36, 140.08, 131.99, 131.21, 129.90, 128.83, 126.85, 122.82, and
120.94 ppm.
Pharmacology
Antibacterial studies
The microbiological tests conducted on the reference strains of Gram-positive and
Gram-negative bacteria revealed that many of the newly synthesised pyrazolinyl-
triazole compounds were more potent than the standard drug ciprofloxacin.
Structure–activity relationship
Effect of structural variation in acetyl side chain As a first attempt, one of the
hydrogens of the acetyl methyl group was varied by chloro function, azido group,
and then to 1,2,3-triazolyl ring, and their antibacterial activities compared with that
of standard drug ciprofloxacin. The MIC values obtained in this screen are
summarized in Table 4.
It could be observed that these structural variations had a profound positive
impact on the bioactivity, i.e., increased it, due to such introduction in the order
1,2,3-triazolyl [ azido [ chloro [ hydrogen. Each of these variations resulted in
enhanced antibacterial activity, and finally it is notable that the triazolyl
compound was more potent than ciprofloxacin in inhibiting all four human
pathogens. Thus, introduction of a 1,2,3-triazolyl moiety into the basic pyrazoline
skeleton resulted in a hybrid molecule, viz. N-(1,2,3-triazolylacetyl)-3-phenyl-5-
(4-methoxyphenyl)pyrazoline (3c) (Table 4), with higher bioactivity, being
considered the core skeleton due to its potency equal to that of the standard drug.
Further structural variations were made in the aryl rings A and B of the core
skeleton by introducing electron-withdrawing or electron-releasing groups or
replacing one of the aryl rings by heterocyclic ring and screening for their
123

S. Archana et al.
Fig. 3 Structure–activity relationship
antibacterial activity. The change in antibacterial activity due to such structural
changes are summarized in Fig. 3.
The structure–activity relationship for the 24 structurally varying pyrazolinyl-
triazole hybrids 3a–l, 4a–l reveals the following observations:
Antibacterial activity against Staphylococcus aureus Among the 24 compounds,
22 were potent, with 16 being equally potent to ciprofloxacin and 6 being more
potent.
The compounds with nitro group in aryl ring B showed slightly less antibacterial
activity than ciprofloxacin.
For the rest of the compounds, even with presence of electron-releasing or
electron-withdrawing groups in aryl ring B, the activity was identical to that of
ciprofloxacin.
The six lead compounds which are more potent than the standard drug are either
those which contain methoxy group at the para-position of aryl ring B (3c, 4d) or
those in which aryl ring B is replaced by 2-thiophenyl ring (3k, 3l, 4k, 4l).
Antibacterial activity against Klebsiella pneumonia Among the 24 compounds, 9
were potent, with 8 being equally potent to ciprofloxacin and 1 compound
containing 2-thiophenyl moiety (3k) being more potent than ciprofloxacin.
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Design, synthesis, and antibacterial studies of potent…
Antibacterial activity against Escherichia coli Among the 24 compounds, 21
compounds were potent, with two compounds containing 2-thiophenyl moiety (3l,
4k) being more potent than ciprofloxacin.
Antibacterial activity against Proteus mirabilis Among the 24 compounds, 11
were equally potent to ciprofloxacin.
Hybrid molecules potent against three human pathogens Three of the compounds
(4a, b, l) were equally potent against three pathogens.
Hybrid molecules potent against all four human pathogens It is quite interesting to
note that 6 of the 24 new compounds synthesized (3c, k, l, 4b, e, k) are more potent
against all four human pathogens compared with ciprofloxacin.
Significance of 1,2,3-triazolyl and 2-thiophenyl scaffold in enhancing antibacterial
activity A notable and significant observation of the present study is that the
introduction of triazolyl ring in the acetyl side chain and replacement of aryl ring B
by thiophenyl moiety prominently enhanced the antibacterial activity of the
corresponding hybrid molecules (3k, l, 4k, l). These compounds (MIC of 3.90 lg/
mL) were more potent than the standard drug ciprofloxacin.
Conclusions
We report herein systematic structural variation of the pyrazolinyltriazole base
skeleton for development of potent antibacterial hybrid compounds. While
introduction of aryl or triazolyl group as substituent at position 3 of pyrazoline
had little impact on the bioactivity, structural variation in the acetyl side chain and
introduction of aryl ring at position 5 resulted in significant enhancement of
antibacterial activity (Table 4). In particular, introduction of 1,2,3-triazolyl ring and
thiophenyl ring during structural variation afforded hybrids with greater potency
than the standard drug.
Experimental
Analysis and instruments
All chemicals, reagents, and solvents were of commercial high-purity grade,
purchased from Avra Synthesis Pvt. Ltd. and Merck Ltd. India. Silica gel (60–120
mesh) was used for column chromatographic isolation and purification of
synthesized compounds. Melting points were obtained on an Electrothermal
apparatus and are uncorrected. 1H NMR (300 MHz) and 13C NMR (75 MHz)
spectra were recorded in CDCl3 on Bruker Avance (300 MHz) spectrometer, and
chemical shifts are reported as d values in parts per million (ppm) relative to
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S. Archana et al.
tetramethylsilane, with coupling constant (J) values in hertz. Elemental analyses
were in agreement with calculated values with error within 0.4 %.
General procedure for synthesis of N-(azidoacetyl)-3,5-diarylpyrazolines 1
A
mixture of 2-chloro-1-(3,5-diaryl-4,5-dihydro-1H-pyrazol-1-yl)ethanone
(1.0 mmol) and sodium azide (1.5 mmol) was refluxed for 2 h in THF/water
(5 mL, 1:1 ratio). After reaction completion as monitored by thin-layer chromatog-
raphy (TLC), the reaction mixture was extracted with ethyl acetate and the organic
layer separated then dried over anhydrous sodium sulfate and concentrated under
reduced pressure to afford the corresponding azide (1) in quantitative yield (95 %).
2-Azido-1-(3,5-diphenyl-4,5-dihydro-1H-pyrazol-1-yl)ethanone (1) Pale-yellow
1
solid, yield: 95 %. M.P.: 143–144 °C. IR (KBr): t 2103, 1738 cm-1; H NMR
(300 MHz, CDCl3) d 7.79–7.40 (m, 5H), 7.26–7.18 (m, 5H), 5.92 (dd, J = 12.0,
6.0 Hz, 1H), 4.33 (d, J = 9.0 Hz, 1H), 4.16 (d, J = 9.0 Hz, 1H), 3.87 (dd,
J = 18.0, 12.0 Hz, 1H), 3.09 (dd, J = 18.0, 6.0 Hz, 1H). 13C NMR (75 MHz,
CDCl3) d 165.29, 155.73, 137.54, 131.58, 130.70, 130.42, 130.08, 129.84, 128.97,
128.69, 127.25, 126.68, 57.98, 50.91, 41.17. ESI–MS m/z 306.42 [M ? H]?. Anal.
Calcd. for C17H15N5O: C, 66.87; H, 4.95; N, 22.94. Found: C, 66.92; H, 4.94; N,
22.95.
General procedure for synthesis of pyrazolinyltriazole hybrids 3a–l, 4a–l
A mixture of N-(azidoacetyl)-3,5-diarylpyrazolines (1, 1.0 mmol) and diethy-
lacetylenedicarboxylate/dimethylacetylenedicarboxylate (2, 1.0 mmol) was heated
to 90 °C over a water bath for 5–10 min. The reaction mixture was cooled to room
temperature and washed with diethyl ether to afford the corresponding triazoles 3a–
l, 4a–l in excellent yields (87–95 %).
Diethyl 1-(2-(3,5-diphenyl-4,5-dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-
triazole-4,5-dicarboxylate (3a) (see Footnote 2)
1
White solid, yield: 92 %. M.P.: 135–138 °C. IR (KBr):t 1757, 1677 cm-1; H
NMR (300 MHz, CDCl3) d 7.78 (dd, J = 7.4, 2.0 Hz, 2H), 7.50–7.46 (m, 3H),
7.35–7.23 (m, 5H), 6.03 (d, J = 18.0 Hz, 1H), 5.95 (d, J = 18.0 Hz, 1H), 5.56 (dd,
J = 11.7, 4.8 Hz, 1H), 4.42 (q, J = 7.1 Hz, 2H), 4.22 (q, J = 8.0 Hz, 2H), 3.84
(dd, J = 17.9, 11.8 Hz, 1H), 3.28 (dd, J = 17.9, 4.9 Hz, 1H), 1.39 (t, J = 7.1 Hz,
3H), 1.22 (t, J = 7.1 Hz, 3H). 13C NMR (75 MHz, CDCl3) d 161.83, 160.01,
158.45, 156.19, 140.41, 139.87, 130.88, 130.42, 128.83, 127.88, 126.80, 125.68,
62.41, 61.61, 60.56, 52.42, 42.25, 14.07, 13.60. ESI–MS m/z 498.17 [M ? Na]?.
Anal. Calcd. for C25H25N5O5: C, 63.15; H, 5.30; N, 14.73. Found: C, 63.19; H, 5.32;
N, 14.75.
123

Design, synthesis, and antibacterial studies of potent…
Dimethyl 1-(2-(3,5-diphenyl-4,5-dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-
triazole-4,5-dicarboxylate (3b)
White solid, yield: 90 %. M.P.: 245–248 °C. IR (KBr): t 1728, 1677 cm-1; 1H NMR
(300 MHz, CDCl3) d 7.94–7.11 (m, 10H), 6.05 (d, J = 18.0 Hz, 1H), 5.95 (d,
J = 18.0 Hz, 1H), 5.57 (dd, J = 11.6, 4.8 Hz, 1H), 3.96 (s, 3H), 3.85 (dd, J = 17.9,
11.7 Hz, 1H), 3.76(s, 3H), 3.28 (dd, J = 17.9, 4.8 Hz, 1H). 13C NMR (75 MHz, CDCl3)
d 161.78, 160.33, 158.92, 156.30, 140.37, 139.48, 131.01, 130.41, 128.88, 127.94,
126.83, 125.67, 60.57, 53.04, 52.54, 42.30. ESI–MS m/z 448.28 [M ? H]?. Anal. Calcd.
for C23H21N5O5: C, 61.74; H, 4.73; N, 15.65. Found: C, 61.79; H, 4.75; N, 15.67.
Diethyl 1-(2-(5-(4-methoxyphenyl)-3-phenyl-4,5-dihydro-1H-pyrazol-1-yl)-2-oxoeth
yl)-1H-1,2,3-triazole-4,5-dicarboxylate (3c) (see Footnote 2)
1
White solid, yield: 93 %. M.P.: 145-149 °C. IR (KBr): t 1737, 1669 cm-1; H
NMR (300 MHz, CDCl3) d 7.79 (dd, J = 7.4, 2.1 Hz, 2H), 7.53–7.44 (m, 3H), 7.17
(d, J = 8.7 Hz, 2H), 6.84 (d, J = 8.6 Hz, 2H), 6.00 (d, J = 18.0 Hz, 1H), 5.92 (d,
J = 15.0 Hz, 1H), 5.51 (dd, J = 11.7, 4.8 Hz, 1H), 4.42 (q, J = 7.1 Hz, 2H),
4.26–4.22 (m, 2H), 3.89–3.78 (m, 1H), 3.76 (s, 3H), 3.27 (dd, J = 18.0, 4.9 Hz,
1H), 1.39 (t, J = 7.1 Hz, 3H), 1.23 (t, J = 7.1 Hz, 3H). 13C NMR (75 MHz,
CDCl3) d 161.80, 160.09, 159.30, 158.49, 156.17, 132.70, 130.92, 130.68, 128.84,
127.15, 126.83, 114.25, 62.40, 61.58, 60.21, 55.22, 52.46, 42.20, 14.10, 13.63. ESI–
MS m/z 506.66 [M ? H]?. Anal. Calcd. for C26H27N5O6: C, 61.77; H, 5.38; N,
13.85. Found: C, 61.79; H, 5.39; N, 13.87.
Dimethyl 1-(2-(5-(4-methoxyphenyl)-3-phenyl-4,5-dihydro-1H-pyrazol-1-yl)-2-oxoe
thyl)-1H-1,2,3-triazole-4,5-dicarboxylate (3d)
1
White solid, yield: 91 %. M.P.: 210–213 °C. IR (KBr): t 1732, 1675 cm-1; H
NMR (300 MHz, CDCl3) d 7.79 (d, J = 9.4 Hz, 2H), 7.53–7.43 (m, 3H), 7.17 (d,
J = 8.5 Hz, 2H), 6.85 (d, J = 8.5 Hz, 2H), 6.03 (d, J = 15.0 Hz, 1H), 5.93 (d,
J = 18.0 Hz, 1H), 5.53 (dd, J = 11.9, 5.1 Hz, 1H), 3.96 (s, 3H), 3.85 (dd, J = 17.9,
11.7 Hz, 1H), 3.77 (d, J = 1.7 Hz, 6H) 3.27 (dd, J = 17.9, 4.9 Hz, 1H). 13C NMR
(75 MHz, CDCl3) d 161.85, 160.44, 158.92, 158.83, 156.31, 132.58, 130.99,
128.85, 127.08, 126.83, 114.14, 60.15, 55.24, 53.07, 52.57, 42.24. ESI–MS m/
z 478.12 [M ? H]?. Anal. Calcd. for C24H23N5O6: C, 60.37; H, 4.86; N, 14.67.
Found: C, 60.39; H, 4.85; N, 14.65.
Diethyl 1-(2-(5-(4-chlorophenyl)-3-phenyl-4,5-dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-
1H-1,2,3-triazole-4,5-dicarboxylate (3e)
1
White solid, yield: 94 %. M.P.: 170–172 °C. IR (KBr): t1727, 1681 cm-1; H
NMR (300 MHz, CDCl3) d 7.79–7.76 (m, 2H), 7.51–7.46 (m, 3H), 7.30 (d,
J = 8.5 Hz, 2H), 7.19 (d, J = 8.4 Hz, 2H), 6.02 (d, J = 18.0 Hz, 1H), 5.93 (d,
J = 18.0 Hz, 1H), 5.53 (dd, J = 11.7, 4.9 Hz, 1H), 4.42 (q, J = 7.1 Hz, 2H), 4.24
(q, J = 7.2 Hz, 2H), 3.85 (dd, J = 17.9, 11.8 Hz, 1H), 3.24 (dd, J = 18.0, 5.0 Hz,
123

S. Archana et al.
1H), 1.39 (t, J = 7.1 Hz, 3H), 1.23 (t, J = 7.1 Hz, 3H). 13C NMR (75 MHz,
CDCl3) d 161.79, 159.84, 158.25, 156.08, 139.74, 138.86, 133.40, 130.89, 130.48,
130.07, 128.75, 128.66, 127.23, 126.67, 62.30, 61.46, 59.79, 52.26, 41.95, 13.91,
13.43. ESI–MS m/z 510.24 [M ? H]?. Anal. Calcd. for C25H24ClN5O5: C, 58.88;
H, 4.74; N, 13.73. Found: C, 58.89; H, 4.72; N, 13.75.
Dimethyl 1-(2-(5-(4-chlorophenyl)-3-phenyl-4,5-dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-
1H-1,2,3-triazole-4,5-dicarboxylate (3f)
1
White solid, yield: 92 %. M.P.: 238–242 °C. IR (KBr): t 1726, 1676 cm-1; H
NMR (300 MHz, CDCl3) d 7.79–7.74 (m, 2H), 7.51–7.43 (m, 3H), 7.31 (d,
J = 8.4 Hz, 2H), 7.19 (d, J = 8.4 Hz, 2H), 6.04 (d, J = 17.1 Hz, 1H), 5.93 (d,
J = 17.2 Hz, 1H), 5.54 (dd, J = 11.7, 4.9 Hz, 1H), 3.96 (s, 3H), 3.81 (s, 3H),
3.92–3.84 (m, 1H), 3.24 (dd, J = 18.0, 5.0 Hz, 1H). 13C NMR (75 MHz, CDCl3) d
161.85, 160.35, 158.94, 156.34, 138.61, 133.32, 130.79, 130.03, 128.66, 128.56,
126.96, 126.58, 59.71, 52.74, 52.66, 52.18, 41.91. ESI–MS m/z 482.92 [M ? H]?.
Anal. Calcd. for C23H20ClN5O5: C, 57.33; H, 4.18; N, 14.53. Found: C, 57.39; H,
4.19; N, 14.50.
Diethyl 1-(2-(5-(2-chlorophenyl)-3-phenyl-4,5-dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-
1H-1,2,3-triazole-4,5-dicarboxylate (3g)
1
Viscous liquid, yield: 85 %. IR (KBr): t 1740, 1643 cm-1; H NMR (300 MHz,
CDCl3) d 7.98–7.76 (m, 2H), 7.50–7.43 (m, 3H), 7.38–7.17 (m, 4H), 6.14 (d,
J = 12.0 Hz, 1H), 5.98 (d, J = 12.0 Hz, 1H), 5.90 (dd, J = 12.0, 5.0 Hz, 1H), 4.42
(q, J = 6.0 Hz, 2H), 4.30 (q, J = 6.0 Hz, 2H), 3.93 (dd, J = 18.0, 11.7 Hz, 1H),
3.16 (dd, J = 18.0, 4.7 Hz, 1H). 1.36 (t, J = 7.0 Hz, 3H), 1.28 (t, J = 7.1 Hz, 3H).
13C NMR (75 MHz, CDCl3) d 161.74, 159.70, 158.17, 156.22, 136.83, 136.34,
131.33, 130.72, 130.03, 129.57, 128.74, 128.48, 128.08, 127.52, 126.96, 126.54,
62.19, 62.67, 52.17, 41.10, 13.79, 13.47. ESI–MS m/z 510.97 [M ? H]?. Anal.
Calcd. for C25H24ClN5O5: C, 58.88; H, 4.74; N, 13.73. Found: C, 58.83; H, 4.76; N,
13.75.
Dimethyl 1-(2-(5-(2-chlorophenyl)-3-phenyl-4,5-dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-
1H-1,2,3-triazole-4,5-dicarboxylate (3h)
1
White solid, yield: 89 %. M.P.: 197–202 °C. IR (KBr): t 1727, 1625 cm-1; H
NMR (300 MHz, CDCl3) d 7.77 (d, J = 7.6 Hz, 2H), 7.48–7.38 (m, 3H), 7.29–7.11
(m, 5H), 6.15 (d, J = 15.0 Hz, 1H), 5.99 (d, J = 18.0 Hz, 1H), 5.91 (dd, J = 11.7,
4.8 Hz, 1H), 3.97 (s, 3H), 3.92 (d, J = 11.9 Hz, 1H), 3.86 (s, 3H), 3.17 (dd,
J = 17.9, 5.0 Hz, 1H). 13C NMR (75 MHz, CDCl3) d 161.93, 160.25, 158.94,
156.53, 151.95, 137.17, 136.76, 132.88, 32.68, 131.63, 129.86, 128.96, 128.71,
128.26, 127.79, 127.17, 126.70, 126.15, 58.27, 53.19, 52.94, 52.36, 41.37. ESI–MS
m/z 482.96 [M ? H]?. Anal. Calcd. for C23H20ClN5O5: C, 57.33; H, 4.18; N, 14.53.
Found: C, 57.36; H, 4.16; N, 14.55.
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Design, synthesis, and antibacterial studies of potent…
Diethyl 1-(2-(5-(3-nitrophenyl)-3-phenyl-4,5-dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-
1H-1,2,3-triazole-4,5-dicarboxylate (3i)
Pale-yellow solid, yield: 93 %. M.P.: 143–148 °C. IR (KBr): t 1725, 1673 cm-1
;
1H NMR (300 MHz, CDCl3) d 8.17–8.13 (m, 2H), 7.80–7.78 (m, 2H), 7.65–7.44
(m, 5H), 6.08 (d, J = 18.0 Hz, 1H), 5.95 (d, J = 18.0 Hz, 1H), 5.66 (dd, J = 11.8,
5.4 Hz, 1H), 4.42 (q, J = 9.0 Hz, 2H), 4.27 (q, J = 9.0 Hz, 2H), 3.95 (dd,
J = 18.0, 11.9 Hz, 1H), 3.28 (dd, J = 18.0, 5.4 Hz, 1H), 1.39 (t, J = 7.1 Hz, 3H),
1.25 (t, J = 7.1 Hz, 3H). 13C NMR (75 MHz, CDCl3) d 162.35, 159.97, 158.27,
156.08, 148.42, 142.36, 140.08, 131.99, 131.21, 129.90, 128.83, 126.85, 122.82,
120.94, 62.42, 61.66, 59.85, 52.40, 42.11, 14.01, 13.58. ESI–MS m/z 521.12
[M ? H]?. Anal. Calcd. for C25H24N6O7: C, 57.69; H, 4.65; N, 16.15. Found:
C,57.66; H, 4.66; N, 16.17.
Dimethyl 1-(2-(5-(3-nitrophenyl)-3-phenyl-4,5-dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-
1H-1,2,3-triazole-4,5-dicarboxylate (3j)
Pale-yellow solid, yield: 95 %. M.P.: 190–193 °C. IR (KBr): t 1727, 1681 cm-1
;
1H NMR (300 MHz, CDCl3) d 8.16–8.14 (m, 2H), 7.79 (dd, J = 7.7, 1.8 Hz, 2H),
7.65–7.45 (m, 5H), 6.10 (d, J = 18.0 Hz, 1H), 5.95 (d, J = 18.0 Hz, 1H), 5.67 (dd,
J = 11.9, 5.3 Hz, 1H), 3.96 (s, 3H), 4.00–3.90 (m, 1H), 3.83 (s, 3H), 3.28 (dd,
J = 18.0, 5.3 Hz, 1H). 13C NMR (75 MHz, CDCl3) d 162.23, 160.18, 158.67,
156.18, 148.36, 142.35, 139.69, 131.81, 131.17, 130.33, 129.92, 128.78, 126.82,
122.82, 120.83, 59.79, 52.99, 52.47, 42.08. ESI–MS m/z 493.06 [M ? H]?. Anal.
Calcd. for C23H20N6O7: C, 56.10; H, 4.09; N, 17.07. Found: C, 56.18; H, 4.06; N,
17.09.
Diethyl 1-(2-oxo-2-(3-phenyl-5-(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl)ethyl)-
1H-1,2,3-triazole-4,5-dicarboxylate (3k)
1
Viscous liquid, yield: 90 %. IR (KBr): t 1720, 1679 cm-1; H NMR (300 MHz,
CDCl3) d 7.72 (m, 2H), 7.41 (m, 2H), 7.24–7.12 (m, 1H), 6.97 (s, 1H), 6.88–6.80
(m, 1H), 5.87 (s, 2H), 5.81 (dd, J = 11.3, 4.3 Hz, 1H), 4.36 (q, J = 6.7 Hz, 2H),
4.26 (q, J = 7.1 Hz, 2H), 3.75 (dd, J = 17.8, 11.5 Hz, 1H), 3.37 (dd, J = 17.9,
4.3 Hz, 1H), 1.33 (t, J = 6.3 Hz, 3H), 1.24–1.17 (m, 3H). 13C NMR (75 MHz,
CDCl3) d 161.92, 160.02, 158.35, 156.13, 131.05, 130.91, 128.83, 126.83, 125.69,
125.46, 124.91, 62.43, 61.59, 55.95, 52.41, 42.00, 14.08, 13.63. ESI–MS m/z 482.16
[M ? H]?. Anal. Calcd. for C23H23N5O5S: C, 57.37; H, 4.81; N, 14.54; S, 6.66.
Found: C, 57.39; H, 4.83; N, 14.55; S, 6.68.
Dimethyl 1-(2-oxo-2-(3-phenyl-5-(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl)ethyl)-
1H-1,2,3-triazole-4,5-dicarboxylate (3l)
Pale-yellow solid, yield: 91 %. M.P.: 179–183 °C. IR (KBr): t1731, 1672 cm-1; 1H
NMR (300 MHz, CDCl3) d 7.80 (dd, J = 7.5, 2.1 Hz, 2H), 7.56–7.41 (m, 3H), 7.21
(dd, J = 5.1, 1.2 Hz, 1H), 7.05 (d, J = 3.5 Hz, 1H), 6.92 (dd, J = 5.1, 3.6 Hz, 1H),
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5.97 (d, J = 3.0 Hz, 1H), 5.93 (d, J = 12.0 Hz, 1H), 5.88 (dd, J = 11.9, 5.3 Hz,
1H), 3.97 (s, 3H), 3.88 (dd, J = 17.9, 12.0 Hz, 1H), 3.83 (s, 3H), 3.45 (dd,
J = 17.9, 5.3 Hz, 1H). 13C NMR (75 MHz, CDCl3) d 162.02, 160.18, 158.75,
156.17, 142.46, 131.16, 130.31, 128.90, 126.88, 125.70, 125.54, 125.06, 56.16,
53.13, 52.61, 52.55, 42.08. ESI–MS m/z 454.06 [M ? H]?. Anal. Calcd. for
C21H19N5O5S: C, 55.62; H, 4.22; N, 15.44; S, 7.07. Found: C, 55.69; H, 4.24; N,
15.45; S, 7.09.
Diethyl 1-(2-(3-(1-benzyl-5-methyl-1H-1,2,3-triazol-4-yl)-5-phenyl-4,5-dihydro-1H-
pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-triazole-4,5-dicarboxylate (4a)
1
Viscous liquid, yield: 95 %. IR (KBr): t1727, 1680 cm-1; H NMR (300 MHz,
CDCl3) d 7.92–7.72 (m, 2H), 7.59–7.00 (m, 8H), 5.94 (d, J = 18.0 Hz, 1H), 5.83 (d,
J = 15.0 Hz, 1H), 5.61–5.47 (m, 3H), 4.44 (q, J = 6.0 Hz, 2H), 4.18 (q,
J = 6.0 Hz, 2H), 3.92 (dd, J = 18.0, 6.0 Hz, 1H), 3.72 (dd, J = 17.5, 11.6 Hz,
1H), 2.25 (s, 3H), 1.41 (t, J = 7.5 Hz, 3H), 1.21 (t, J = 7.6 Hz, 3H). 13C NMR
(75 MHz, CDCl3) d 161.34, 159.52, 157.15, 156.56, 151.08, 141.93, 139.64,
134.12, 131.42, 130.42, 130.28, 130.03, 128.32, 128.16, 127.57, 126.73, 126.52,
126.42, 125.23, 61.93, 61.10, 53.20, 51.96, 50.92, 38.67, 13.53, 13.05, 7.40. ESI–
MS m/z 593.07 [M ? Na]?. Anal. Calcd. for C29H30N8O5: C, 61.04; H, 5.30; N,
19.64. Found: C, 61.09; H, 5.32; N, 19.65.
Dimethyl 1-(2-(3-(1-benzyl-5-methyl-1H-1,2,3-triazol-4-yl)-5-phenyl-4,5-dihydro-1H-
pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-triazole-4,5-dicarboxylate (4b)
1
Viscous liquid, yield: 92 %. IR (KBr): t1724, 1681 cm-1; H NMR (300 MHz,
CDCl3) d 7.93–7.07 (m, 10H), 5.89 (d, J = 18.0 Hz, 1H), 5.80 (d, J = 18.0 Hz,
1H). 5.68–5.40 (m, 3H), 3.97 (s, 3H), 3.76 (d, J = 7.3 Hz, 1H), 3.70 (s, 3H),
3.64–3.49 (m, 1H), 2.25 (s, 3H). 13C NMR (75 MHz, CDCl3) d 161.21, 159.76,
157.49, 156.53, 151.38, 141.96, 139.30, 134.13, 131.35, 130.35, 129.97, 128.28,
128.12, 127.54, 126.65, 126.46, 126.38, 125.13, 53.20, 52.87, 52.38, 51.22, 50.82,
38.67, 7.30. ESI–MS m/z 543.14 [M ? H]?. Anal. Calcd. for C27H26N8O5: C,
59.77; H, 4.83; N, 20.65. Found: C, 59.79; H, 4.81; N, 20.66.
Diethyl 1-(2-(3-(1-benzyl-5-methyl-1H-1,2,3-triazol-4-yl)-5-(4-methoxyphenyl)-4,5-
dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-triazole-4,5-dicarboxylate (4c)
1
Viscous liquid, yield: 91 %. IR (KBr): t1732, 1681 cm-1; H NMR (300 MHz,
CDCl3) d 7.42–7.30 (m, 3H), 7.26–7.20 (m, 2H), 7.17 (d, J = 8.7 Hz, 2H), 6.83 (d,
J = 8.7 Hz, 2H), 5.88 (d, J = 15.0 Hz, 1H), 5.80 (d, J = 18.0 Hz, 1H), 5.58 (s,
2H), 5.46 (dd, J = 11.7, 4.8 Hz, 1H), 4.41 (q, J = 6.0 Hz, 2H), 4.24–4.21 (m, 2H),
3.96 (dd, J = 18.8, 11.7 Hz, 1H), 3.76 (s, 3H), 3.55 (dd, J = 18.8, 4.9 Hz, 1H),
2.55 (s, 3H), 1.38 (t, J = 7.1 Hz, 3H), 1.22 (t, J = 7.1 Hz, 3H). 13C NMR
(75 MHz, CDCl3) d 161.21, 159.53, 158.83, 157.89, 156.66, 151.50, 139.36,
137.11, 133.81, 133.32, 132.20, 130.44, 128.61, 128.05, 126.87, 113.66, 62.09,
61.23, 58.70, 54.75, 52.08, 51.41, 42.80, 13.68, 13.37, 9.13. ESI–MS m/z 601.18
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Design, synthesis, and antibacterial studies of potent…
[M ? H]?. Anal. Calcd. for C30H32N8O6: C, 59.99; H, 5.37; N, 18.66. Found: C,
59.95; H, 5.38; N, 18.68.
Dimethyl 1-(2-(3-(1-benzyl-5-methyl-1H-1,2,3-triazol-4-yl)-5-(4-chlorophenyl)-4,5-
dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-triazole-4,5-dicarboxylate (4d)
1
Viscous liquid, yield: 94 %. IR (KBr): t1724, 1681 cm-1; H NMR (300 MHz,
CDCl3) d 7.48–7.23 (m, 3H), 7.27–7.16 (m, 2H), 7.17 (d, J = 8.7 Hz, 2H), 6.85 (d,
J = 8.7 Hz, 2H), 5.89 (d, J = 18.0 Hz, 1H), 5.80 (d, J = 18.0 Hz, 1H), 5.58 (s,
2H), 5.47 (dd, J = 11.6, 4.8 Hz, 1H), 3.97 (dd, J = 18.8, 11.7 Hz, 1H), 3.92 (s,
3H), 3.78 (s, 3H), 3.76 (s, 3H), 3.58 (dd, J = 18.9, 5.0 Hz, 1H), 2.55 (s, 3H). 13C
NMR (75 MHz, CDCl3) d 161.50, 161.27, 160.69, 160.05, 159.02, 151.91, 149.66,
133.82, 133.40, 132.10, 128.81, 128.28, 127.00, 113.88, 58.84, 54.97, 53.29, 52.89,
52.21, 51.73, 42.97, 9.34. ESI–MS m/z 573.22 [M ? H]?. Anal. Calcd. for
C28H28N8O6: C, 58.73; H, 4.93; N, 19.57. Found: C, 58.79; H, 4.91; N, 19.59.
Diethyl 1-(2-(3-(1-benzyl-5-methyl-1H-1,2,3-triazol-4-yl)-5-(4-chlorophenyl)-4,5-
dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-triazole-4,5-dicarboxylate (4e)
1
Viscous liquid, yield: 93 %. IR (KBr): t1721, 1680 cm-1; H NMR (300 MHz,
CDCl3) d 7.51–7.07 (m, 9H), 5.89 (d, J = 15.0 Hz, 1H), 5.81 (d, J = 18.0 Hz, 1H),
5.58 (s, 2H), 5.47 (dd, J = 11.6, 4.7 Hz, 1H), 4.40 (q, J = 9.0 Hz, 1H), 4.22 (q,
J = 9.0 Hz, 1H), 3.99 (dd, J = 18.8, 11.8 Hz, 1H), 3.51 (dd, J = 18.8, 5.0 Hz, 1H),
2.54 (s, 3H), 1.37 (t, J = 7.1 Hz, 3H), 1.22 (t, J = 7.1 Hz, 3H). 13C NMR
(75 MHz, CDCl3) d 161.38, 159.57, 157.92, 151.35, 139.43, 138.53, 136.73,
133.71, 133.42, 132.98, 130.21, 128.55, 128.38, 128.00, 127.01, 126.79, 62.09,
61.24, 58.44, 53.25, 51.33, 42.76, 13.63, 13.18, 9.09. ESI–MS m/z 606.10
[M ? H]?. Anal. Calcd. for C29H29ClN8O5: C, 57.57; H, 4.83; N, 18.52. Found:
C, 57.59; H, 4.84; N, 18.54.
Dimethyl 1-(2-(3-(1-benzyl-5-methyl-1H-1,2,3-triazol-4-yl)-5-(4-chlorophenyl)-4,5-
dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-triazole-4,5-dicarboxylate (4f)
1
Viscous liquid, yield: 90 %. IR (KBr): t1732, 1680 cm-1; H NMR (300 MHz,
CDCl3) d 7.39–7.17 (m, 9H), 5.91 (d, J = 15.0 Hz, 1H), 5.81 (d, J = 15.0 Hz, 1H),
5.58 (s, 2H), 5.48 (dd, J = 11.8, 5.0 Hz, 1H), 4.09–3.99 (m, 1H), 3.95 (s, 3H), 3.79
(s, 3H), 3.52 (dd, J = 18.8, 5.0 Hz, 1H), 2.55 (s, 3H). 13C NMR (75 MHz, CDCl3) d
161.43, 159.97, 158.55, 151.61, 139.31, 138.50, 136.92, 133.76, 133.50, 133.26,
130.44, 128.77, 128.61, 128.24, 127.07, 126.94, 58.60, 52.84, 52.31, 52.14, 51.59,
42.93, 9.28. ESI–MS m/z 577.99 [M ? H]?. Anal. Calcd. for C27H25ClN8O5: C,
56.20; H, 4.37; N, 19.42. Found: C, 56.28; H, 4.39; N, 19.41.
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Diethyl 1-(2-(3-(1-benzyl-5-methyl-1H-1,2,3-triazol-4-yl)-5-(2-chlorophenyl)-4,5-
dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-triazole-4,5-dicarboxylate (4g)
1
Viscous liquid, yield: 87 %, IR (KBr): t1727, 1679 cm-1; H NMR (300 MHz,
CDCl3) d 7.44–7.16 (m, 9H), 6.01 (d, J = 18.0 Hz, 1H), 5.87 (d, J = 18.0 Hz, 1H),
5.64–5.49 (m, 3H), 4.42 (q, J = 6.0 Hz, 2H), 4.29 (q, J = 6.0 Hz, 1H), 4.09 (dd,
J = 18.8, 11.8 Hz, 1H), 3.44 (dd, J = 18.8, 5.2 Hz, 1H), 2.55 (s, 3H), 1.39 (t,
J = 7.1 Hz, 3H), 1.27 (t, J = 7.2 Hz, 3H). 13C NMR (75 MHz, CDCl3) d 161.40,
160.80, 159.55, 157.97, 151.63, 139.48, 136.69, 133.72, 133.38, 131.19, 130.08,
129.37, 128.47, 127.90, 126.76, 125.70, 62.05, 61.21, 56.73, 51.92, 51.26, 42.10,
13.61, 13.25, 9.02. ESI–MS m/z 577.98 [M ? H]?. Anal. Calcd. for C29H29ClN8O5:
C, 57.57; H, 4.83; N, 18.52. Found: C, 57.59; H, 4.81; N, 18.54.
Dimethyl 1-(2-(3-(1-benzyl-5-methyl-1H-1,2,3-triazol-4-yl)-5-(2-chlorophenyl)-4,5-
dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-triazole-4,5-dicarboxylate (4h)
1
Viscous liquid, yield: 90 %. IR (KBr): t1728, 1678 cm-1; H NMR (300 MHz,
CDCl3) d 7.43–7.07 (m, 9H), 6.02 (d, J = 15.0 Hz, 1H), 5.88 (d, J = 9.0 Hz, 1H),
5.55 (m, 3H), 4.18–4.03 (m, 1H), 3.95 (s, 3H), 3.84 (s, 3H), 3.44 (dd, J = 18.8,
5.2 Hz, 1H), 2.55 (s, 3H). 13C NMR (75 MHz, CDCl3) d 161.29, 160.90, 159.72,
158.26, 151.59, 139.06, 136.55, 133.71, 133.37, 131.07, 129.33, 128.39, 127.82,
126.69, 125.62, 56.72, 52.89, 52.65, 51.98, 51.15, 42.02, 8.96. ESI–MS m/z 628.05
[M ? Na]?. Anal. Calcd. for C27H25ClN8O5: C, 56.20; H, 4.37; N, 19.42. Found: C,
56.27; H, 4.38; N, 19.41.
Diethyl 1-(2-(3-(1-benzyl-5-methyl-1H-1,2,3-triazol-4-yl)-5-(3-nitrophenyl)-4,5-
dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-triazole-4,5-dicarboxylate (4i)
1
Viscous liquid, yield: 91 %. IR (KBr): t1719, 1680 cm-1; H NMR (300 MHz,
CDCl3) d 8.14 (d, J = 8.9 Hz, 1H), 7.72–7.11 (m, 8H), 5.95 (d, J = 18.0 Hz, 1H),
5.83 (d, J = 18.0 Hz, 1H), 5.71–5.40 (m, 3H), 4.41 (q, J = 6.0 Hz, 2H), 4.27–4.23
(m, 2H), 4.10 (dd, J = 18.8, 11.9 Hz, 1H), 3.55 (dd, J = 18.8, 5.3 Hz, 1H), 2.57 (s,
3H), 1.35 (t, J = 7.1 Hz, 3H), 1.23 (t, J = 7.1 Hz, 3H). 13C NMR (75 MHz,
CDCl3) d 161.88, 159.67, 158.03, 151.36, 148.08, 142.12, 139.72, 136.67, 133.66,
131.99, 129.91, 129.64, 128.69, 128.16, 126.86, 122.52, 120.61, 62.18, 61.41,
58.50, 52.05, 51.53, 42.92, 13.71, 13.29, 9.22. ESI–MS m/z 638.08 [M ? Na]?.
Anal. Calcd. for C29H29N9O7: C, 56.58; H, 4.75; N, 20.48. Found: C, 56.59; H, 4.77;
N, 20.46.
Dimethyl 1-(2-(3-(1-benzyl-5-methyl-1H-1,2,3-triazol-4-yl)-5-(3-nitrophenyl)-4,5-
dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-triazole-4,5-dicarboxylate (4j)
1
Viscous liquid, yield: 94 %. IR (KBr): t1734, 1680 cm-1; H NMR (300 MHz,
CDCl3) d 8.14 (d, J = 9.8 Hz, 1H), 7.68–7.14 (m, 8H), 5.97 (d, J = 18.0 Hz, 1H),
5.83 (d, J = 15.0 Hz, 1H), 5.63–5.58 (m, 3H), 4.10 (dd, J = 18.9, 12.0 Hz, 1H),
3.95 (s, 3H), 3.80 (s, 3H), 3.55 (dd, J = 18.9, 5.4 Hz, 1H), 2.57 (s, 3H). 13C NMR
123

Design, synthesis, and antibacterial studies of potent…
(75 MHz, CDCl3) d 161.87, 159.94, 158.33, 151.47, 148.04, 142.09, 139.41,
136.65, 133.75, 131.96, 130.00, 129.67, 128.68, 128.15, 126.89, 122.51, 120.56,
58.52, 52.81, 52.29, 51.78, 51.49, 42.97, 9.20. ESI–MS m/z 588.35 [M ? H]?.
Anal. Calcd. for C27H25N9O7: C, 55.19; H, 4.29; N, 21.46. Found: C, 55.16; H, 4.28;
N, 21.48.
Diethyl 1-(2-(3-(1-benzyl-5-methyl-1H-1,2,3-triazol-4-yl)-5-(thiophen-2-yl)-4,5-
dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-triazole-4,5-dicarboxylate (4k)
1
Viscous liquid, yield: 92 %. IR (KBr): t1728, 1680 cm-1; H NMR (300 MHz,
CDCl3) d 7.48–7.15 (m, 6H), 7.05 (d, J = 3.5 Hz, 1H), 6.92 (d, J = 5.0 Hz, 1H),
5.87–5.81(m, 2H), 5.59–5.45 (m, 3H), 4.43 (dd, J = 14.2, 7.1 Hz, 2H), 4.27 (dd,
J = 14.0, 7.0 Hz, 2H), 3.97 (dd, J = 18.7, 11.4 Hz, 1H), 3.75 (dd, J = 18.7,
4.4 Hz, 1H), 2.53 (s, 3H), 1.40 (t, J = 7.1 Hz, 3H), 1.27 (t, J = 6.9 Hz, 3H). 13C
Table 3 In vitro antibacterial
Entry Compound S. aureus K. pneumonia E. coli P.
activity of pyrazolinyltriazole
mirabilis
hybrids (MIC in lg/mL)
1
3a
3b
3c
3d
3e
3f
7.81
7.81
7.81
3.90
7.81
7.81
7.81
7.81
15.62
31.25
3.90
3.90
7.81
7.81
7.81
3.90
7.81
7.81
7.81
7.81
7.81
7.81
3.90
3.90
7
15.62
15.62
7.81
15.62
15.62
7.81
7.81
15.62
15.62
7.81
15.62
62.5
62.5
7.81
3.90
7.81
7.81
7.81
15.62
7.81
31.25
15.62
15.62
15.62
7.81
3.90
7.81
18
7.81
2
15.62
7.81
3
4
15.62
15.62
15.62
15.62
15.62
31.25
62.5
15.62
15.62
15.62
15.62
15.62
62.5
5
6
7
3g
3h
3i
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
3j
62.5
3k
3l
3.90
7.81
7.81
7.81
4a
4b
4c
4d
4e
4f
7.81
15.62
7.81
7.81
7.81
15.62
7.81
7.81
7.81
7.81
15.62
15.62
15.62
15.62
15.62
7.81
15.62
31.25
7.81
4g
4h
4i
7.81
4j
31.25
7.81
4k
4l
15.62
15
7.81
Bold compounds 3a–l, 4a–l are
pyrazolinyltriazole hybrids
Ciprofloxacin
15
123

S. Archana et al.
Table 4 Structural variation in acetyl side chain and in vitro antibacterial activity (MIC in lg/mL)
Entry
1
Compound
S. aureus
K. pneumonia
E. coli
P. mirabilis
31.25
31.25
31.25
31.25
2
26.62
26.62
26.62
26.62
3
4
15.62
7.81
15.62
7.81
15.62
7.81
15.62
7.81
5
6
DMSO
–
7
–
–
–
Ciprofloxacin
15
18
15
– indicates no inhibition
NMR (75 MHz, CDCl3) d 161.40, 159.65, 157.83, 151.47, 142.11, 139.61, 136.87,
133.75, 133.44, 131.69, 130.55, 128.65, 128.09, 126.89, 126.38, 125.21, 124.72,
62.23, 61.32, 54.47, 51.97, 51.48, 42.52, 13.75, 13.33, 9.19. ESI–MS m/z 577.27
[M ? H]?. Anal. Calcd. for C27H28N8O5S: C, 56.24; H, 4.89; N, 19.43; S, 5.56.
Found: C, 56.29; H, 4.87; N, 19.45; S, 5.58.
Dimethyl 1-(2-(3-(1-benzyl-5-methyl-1H-1,2,3-triazol-4-yl)-5-(thiophen-2-yl)-4,5-
dihydro-1H-pyrazol-1-yl)-2-oxoethyl)-1H-1,2,3-triazole-4,5-dicarboxylate (4l)
1
Viscous liquid, yield: 90 %. IR (KBr): t 1720, 1688 cm-1; H NMR (300 MHz,
CDCl3) d 7.45–7.16 (m, 6H), 7.05 (d, J = 3.2 Hz, 1H), 6.92 (d, J = 4.9 Hz, 1H),
5.87–5.76 (m, 2H), 5.63–5.44 (m, 3H), 3.96 (s, 3H), 3.90 (d, J = 10.3 Hz, 1H), 3.82
(s, 3H), 3.73 (dd, J = 18.7, 4.6 Hz, 1H), 2.53 (s, 3H). 13C NMR (75 MHz, CDCl3) d
161.41, 160.00, 158.50, 151.66, 142.18, 139.38, 137.01, 133.54, 130.70, 128.78,
128.22, 126.99, 126.51, 125.29, 124.85, 54.59, 52.90, 52.30, 52.15, 51.61, 42.65,
9.29. ESI–MS m/z 571.28 [M ? Na]?. Anal. Calcd. for C25H24N8O5S: C, 54.74; H,
4.41; N, 20.43; S, 5.85. Found: C, 54.78; H, 4.40; N, 20.44; S, 5.87.
123

Design, synthesis, and antibacterial studies of potent…
In vitro antibacterial studies All synthesized compounds were tested for
antibacterial activity against four human pathogenic bacteria. Bacterial strains,
namely Escherichia coli (ATCC 25922), Klebsiella pneumonia (ATCC 13883),
Proteus mirabilis (ATCC 12453), and Staphylococcus aureus (ATCC 29213), were
collected from Jothi X-RAY, E.C.G. and Clinical Laboratory Thoothukudi. These
strains were maintained in Mu¨ller–Hinton agar (MHA) medium for 24 h at 37 °C.
All strains were identified by standard biochemical methods [22, 23]. Mu¨ller–
Hinton broth (MHB) and Mu¨ller–Hinton agar were used as culture media.
All 24 compounds exhibited different levels of inhibition against the four tested
human pathogenic bacteria (both Gram positive and Gram negative), viz.
Escherichia coli (ATCC 25922), Klebsiella pneumonia (ATCC 13883), Proteus
mirabilis (ATCC 12453), and Staphylococcus aureus (ATCC 29213), and were
compared with that of standard drug ciprofloxacin. Dimethyl sulfoxide (DMSO)
(Merck) was used as negative control. For MIC assays [24], stock solution (1 mg/
mL) of each test compound was prepared in DMSO. Serial dilution of test
compounds was carried out to obtain concentrations ranging from 3 to 400 lg/mL
using DMSO. Test compounds at various concentrations were then added to culture
medium in a test tube, and different strains were inoculated at 108 bacteria/mL
concentration. The tubes were incubated at 37 °C for 24–48 h, then examined for
presence or absence of growth of the tested organism. MIC values were obtained as
the lowest concentration of each test compound where the tube remained clear,
indicating that bacterial growth was completely inhibited at this concentration, as
presented in Table 3.
Acknowledgments The authors thank IRHPA, DST for providing 300 MHz NMR instrument for
recording NMR spectra for the synthesized compounds, and UGC-BSR for giving financial support.
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