Regioselective synthesis and antimicrobial studies of ester linked 1,4-disubstituted 1,2,3-bistriazoles

Article abstract of DOI:10.1016/j.bmcl.2012.05.008

A series of 1,4-disubstituted 1,2,3-bistriazoles was synthesized via click chemistry by cycloaddition of various bisalkynes with benzyl/2-phenylethyl azide. Synthesized triazoles were characterized by IR, ¹H NMR, ¹³C NMR and mass spe

Full text of DOI:10.1016/j.bmcl.2012.05.008

Bioorganic & Medicinal Chemistry Letters 22 (2012) 4353–4357
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Regioselective synthesis and antimicrobial studies of ester linked
1,4-disubstituted 1,2,3-bistriazoles
Kashmiri Lal a, Ashwani Kumar b, M.S. Pavan c, C.P. Kaushik a,
⇑
a Department of Chemistry, Guru Jambheshwar University of Science & Technology, Hisar, Haryana 125001, India
b Department of Pharmaceutical Sciences, Guru Jambheshwar University of Science & Technology, Hisar, Haryana 125001, India
c Solid State and Structural Chemistry Unit, Indian Institute of Sciences, Bangalore 560012, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 1,4-disubstituted 1,2,3-bistriazoles was synthesized via click chemistry by cycloaddition of
various bisalkynes with benzyl/2-phenylethyl azide. Synthesized triazoles were characterized by IR, 1H
NMR, 13C NMR and mass spectral techniques. All the compounds were evaluated for antibacterial/anti-
fungal activities and found to possess moderate to good antimicrobial activities. Further the docking
study for the most active compound against DNA Gyrase was also carried out.
Received 17 March 2012
Revised 21 April 2012
Accepted 2 May 2012
Available online 12 May 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Click chemistry
1,4-Disubstituted 1,2,3-triazoles
Antibacterial activity
Antifungal activity
Docking studies
The 1,2,3-triazole heterocycles have gained significant interest
of synthetic organic chemists for the development of new biologi-
cally active molecules. The basic triazole moiety does not occur in
nature, although it has gained considerable attention as this ring is
a potential pharmacophore. The 1,2,3-triazoles and its derivatives
are reported as anti-HIV,1 antimicrobial,2 antiallergic,3 antifungal,4
antitumor,5 and selective b3 adrenergic receptor agonist.6 Some
substituted 1,2,3-triazoles are also found to be antitubercular
agents7 and cannabinoid CB1 receptor antagonists.8 1,3-dipolar
cycloaddition of azides and terminal alkynes is the most widely
used method for the synthesis of 1,2,3-triazoles. The classical Huis-
gens 1,3-dipolar thermal cycloaddition is relatively slow, occurs at
high temperature resulting into a mixture of 1,4- and 1,5-disubsti-
tuted 1,2,3-triazoles.9 Recently, Meldal and Sharpless indepen-
dently discovered the Cu(I) catalyzed Huisgen 1,3-dipolar
cycloaddition, which has emerged as a novel alternative for the
selective synthesis of 1,4-disubstituted 1,2,3-triazoles with excel-
lent yield.10 Even though this reaction requires only benign reac-
tion conditions, simple workup and purification procedures, still
it can create molecular diversity by joining molecular building
blocks. The better regioselectivity, broad scope and the bio-com-
patibility of the compounds have made it one of the most powerful
click reaction in material, biological and pharmaceutical sciences.11
In addition, the use of click reaction has also been reported for the
synthesis of ionic receptors,12 triazolophanes,13 dendrimers,14
cyclic peptides,15 peptide nanotubes,16 peptidomimetics17 etc.
Herein, we report the synthesis of a series of ester linked 1,4-
disubstituted 1,2,3-bistriazoles (Table 1) from various bisalkynes
and their antibacterial/antifungal activities. To the best of our
knowledge all the prepared compounds are new except 3a.18 The
bisalkynes were prepared by treating acid dichlorides with propar-
gyl alcohol in presence of 4-(Dimethylamino)pyridine (DMAP) in
dichloromethane according to the literature procedure.5 The click
reaction between bisalkynes (except 1e) and the azides (2a, 2b)
was carried out in acetonitrile with Cu(I) as the catalyst and diiso-
propylethylamine (DIPEA) as the base. It afforded the desired prod-
ucts (3a–3h, 3k–3l) in good yield, i.e., 65–85%. However, these
conditions could not be applied for the preparation of compounds
containing pyridine moiety (3i, 3j). These compounds were synthe-
sized by reacting bisalkyne 1e with azides 2a/2b in 1:1 water–THF
mixture containing copper sulfate and sodium ascorbate
(Scheme 1).
All the synthesized bistriazoles were well characterized by IR,
1H NMR, 13C NMR spectroscopy and mass spectrometry. The for-
mation of triazoles was apparent from the absorption band in the
region 3120–3140 cmÀ1 due to @C–H (stretching) of triazole ring
in the IR spectra. The appearance of characteristic singlet in 1H
NMR due to triazolyl protons in the region of d 7.52–7.68 and d
123.60–124.77 in 13C NMR due to C-5 of the triazole ring showed
the formation of triazole ring. To further confirm the structure of
bistriazoles, an X-ray crystallographic study of compound 3j was
also carried out (Fig. 1).19
⇑
Corresponding author. Tel.: +91 1662 263152; fax: +91 1662 276240.
E-mail address: kaushikcp@gmail.com (C.P. Kaushik).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.05.008

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K. Lal et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4353–4357
Table 1
Table 1 (continued)
Synthesis of 1,4 disubstituted 1,2,3-bistriazoles 3a–l
Entry
Alkyne
R
Compound
Entry
Alkyne
R
Compound
O
O
O
O
O
O
O
O
O
O
O
O
2a
N
N
N
N
N N
1a
N N
N N
N N
1
8
1d
2b
3a
3h
O
O
O
O
O
N
O
O
O
O
O
N
N
O
N
O
2
1a
N N
N N
2b
N
N
9
2a
N N
N N
1e
3b
3i
O
O
O
O
O
N
O
O
O
N
N
O
O
O
O
N N
N N
3
4
5
2a
N
N
1b
N N
N N
10
1e
2b
3c
O
O
O
O
3j
N
N
N N
N N
O
O
O
1b
2b
2a
2b
O
O
O
O
O
N
N
N N
N N
11
2b
3d
1f
O
O
O
O
O
O
O
O
N
N
3k
N N
N N
O
O
N
O
O
1c
O
O
O
O
3e
N
N
N
N
N
O
O
12
2b
O
O
1g
N
N
N N
N N
3l
6
1c
3f
Method A
Method B
O
O
O
O
R
N3
O
O
N
O
O
O
O
O
O
O
O
2a-b
N
N
O
O
N
N N
N N
7
2a
1a-g
N N
N N
R
R
1d
3a-l
Scheme 1. Synthesis of 1,4 disubstituted 1,2,3-bistriazoles 3a–3l.22 Reagents and
conditions: Method A: Cu(I), DIPEA, MeCN, rt. Method B: CuSO4Á5H2O, sodium
ascorbate, THF/H2O (1:1), rt.
3g

K. Lal et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4353–4357
4355
Table 2
In vitro antibacterial and antifungal screening studies of the title compounds (MIC,
lmol/mL)
Entry
Compound
B. subtillis
E. coli
A. niger
C. albicans
1
2
3
4
5
6
7
8
9
10
11
12
13
14
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
0.0280
0.0263
0.0271
0.0256
0.0263
0.0249
0.0256
0.0242
0.0123
0.0233
0.0233
0.0233
0.0098
—
0.0280
0.0263
0.0271
0.0128
0.0263
0.0249
0.0128
0.0242
0.0123
0.0233
0.0233
0.0233
0.0098
—
0.0140
0.0263
0.0271
0.0256
0.0263
0.0249
0.0128
0.0242
0.0246
0.0233
0.0233
0.0233
—
0.0140
0.0263
0.0135
0.0128
0.0135
0.0249
0.0128
0.0121
0.0123
0.0233
0.0233
0.0233
—
Norfloxacin
Fluconazole
0.0102
0.0102
of suspension of respective microorganism in sterile saline. Nor-
floxacin was used as standard drug. The inoculated test tubes were
incubated at 37 1 °C for 24 h. Perusal of the activity data shows
that compound 3i is most potent against B. subtilis and E. coli. Fur-
ther the triazoles derived from aromatic alkynes were found to be
more active against both the bacterial strains as compared to that
derived from aliphatic one. The higher activity of compounds 3i–3l
can be due to more rigidity resulting from presence of pyridine and
benzene nucleus. In case of triazoles derived from aliphatic alkynes
compound 3d and 3g are comparatively more active against both
strains. For B. subtilis the activity of compound 3i is comparable
to the Norfloxacin (standard), while in case of E. coli the activities
of compounds 3i, 3d and 3g are nearer to the reference.
Figure 1. X-ray structure of 3j.
The in vitro antifungal activities were evaluated against Candida
albicans (MTCC 183) and Aspergillus niger (MTCC 282) by serial
dilution method using a stock solution of 100 lg/ml concentration.
The synthesized triazoles were screened for their in vitro anti-
bacterial and antifungal activities. The in vitro antibacterial activi-
ties were tested against Gram-positive bacteria Bacillus subtilis
(MTCC 441) and Gram-negative bacteria Escherichia coli (MTCC
7443) by standard serial dilution method20 using a stock solution
Sabouraud dextrose broth was employed as culture media and
dimethylsulphoxide as solvent control. The stock solutions of the
test compounds were serially diluted in test tubes containing
1 ml of sterile medium to get the concentration of 50–3.12
lg/ml
and then inoculated with 100 L of suspension of respective micro-
l
of 100 lg/ml concentration. Double strength nutrient broth was
organism in sterile saline. Fluconazole was used as standard drug.
The inoculated test tubes were incubated at 25 1 °C for 48 h in
case of C. albicans and at 25 1 °C for 120 h in case of A. niger. Anti-
fungal activity was determined by measuring minimum inhibitory
used as culture media and dimethylsulphoxide was used as solvent
control. The stock solutions of the test compounds were serially di-
luted in test tubes containing 1 ml of sterile medium to get the
concentration of 50–3.12 lg/ml and then inoculated with 100 lL
Figure 2. Binding mode of ligand 3i to 1KZN by docking simulation.

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K. Lal et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4353–4357
Figure 3. Sigma–pi interaction of benzene ring of ligand 3i to Asp-45.
hydrogen bond with Arg-76. Both triazole moieties generated
hydrogen bonds with Thr-165 and Asp-79. There is one sigma–pi
interaction between benzene ring of the molecule and carbon
chain of Asp-45 as shown in Figure 3. The surface diagram of the
docked molecule along with co-crystallized ligand is depicted in
Figure 4. Thus these hydrogen bonds, sigma–pi and other vander
waal’s interactions confers good inhibitory activity to the com-
pound under study.
In conclusion, synthesis of some ester linked 1,4-disubstituted
1,2,3-bistriazoles have been reported by Cu(I) catalyzed azide-al-
kyne cycloaddition using different aliphatic/aromatic moieties.
The antimicrobial activity studies revealed that all the compounds
screened showed moderate to good activities. Fitness of most ac-
tive compound 3i against E. coli in Topoisomerase II was studied
using in silico tools.
Acknowledgments
Authors wish to acknowledge SAIF, Panjab University, Chandi-
garh for providing NMR/Mass spectra, Professor T. N. Guru Row, In-
dian Institute of Science, Bangalore for providing the single crystal
X-ray diffraction facility and University Grants Commission, New
Delhi for financial support to carry out above work through Minor
and Major research projects (K.L., C.P.K.).
Figure 4. Surface diagram of the docked molecule (blue color) along with co-
crystallized ligand (yellow color).
concentration. Compounds 3h, 3i, 3d, 3c and 3a are more active
than others against C. albicans, whereas 3g and 3a have more effi-
cacy than other compounds in case of A. niger. Further, compounds
3a and 3g exhibited good activity against both the fungal strains.
The antifungal activity of compounds 3a, 3g and 3a, 3c, 3d, 3e,
3g, 3h, 3i are comparable to standard against A. niger and C. albi-
cans, respectively. No specific activity trend was observed for anti-
fungal studies. The in vitro antibacterial and antifungal activities
data of the tested compounds is depicted in Table 2 as MIC values
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2012.05.
008.
References and notes
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22. General procedure for the synthesis of 1,4-disubstituted 1,2,3 bistriazoles: Method
A:13a The bisalkyne (1 mmol), diisopropylethylamine (2.2 mmol) and azide
(2.2 mmol) were dissolved in dry acetonitrile under Nitrogen atmosphere. To
this solution was added Cu(I) (0.22 mmol) and the reaction mixture was stirred
overnight. The acetonitrile was evaporated, dissolved the residues in ethyl
acetate, filtered, washed the filtrate with 2N H2SO4, water and finally with
saturated aqueous NaHCO3 solution. The organic layer was dried over
anhydrous Na2SO4, filtered and concentrated under vacuum to yield 1, 4-
disubstituted 1,2,3-triazoles. Bis((1-benzyl-1H-1,2,3-triazol-4-yl)methyl) adipate
[3g]: White solid, mp: 121–124 °C, IR(KBr): 3122, 3059, 2943, 1728, 1458,
1448, 1250 cmÀ1 1H NMR (500 MHz, CDCl3): 1.60(br s, 4H), 2.30(br s, 4H),
.
5.18(s, 4H), 5.52(s, 6H), 7.27–7.79(m, 4H), 7.34–7.40(m, 6H), 7.52 (s, 2H). 13C
NMR (100 MHz, CDCl3): 24.1, 33.6, 54.2, 57.6, 123.6, 128.2, 128.9, 129.2, 134.4,
143.3, 173.1. MS m/z: 489.5 [M+H]+, 511.5 [M+Na]+. Method B:
Bisalkyne(1 mmol) and azide (2.2 mmol) were suspended in a 1:1 mixture of
water and THF(3 ml each). To this reaction mixture was added sodium
ascorbate (0.2 mmol) and CuSO4Á5H2O (0.1 mmol). The reaction mixture was
stirred overnight. Upon completion of reaction the reaction mixture was
diluted with cold water (20 ml) and extracted with ethyl acetate
(10 Â 2 ml ml). The combined organic layer was washed with aqueous
solution of NH4Cl:NH3 (9:1) and dried over anhydrous Na2SO4, filtered and
concentrated under vacuum to yield 1, 4-disubstituted 1,2,3-triazoles. Bis((1-
benzyl-1H-1,2,3-triazol-4-yl)methyl) pyridine-2,6-dicarboxylate [3i]: White solid,
mp: 87–89 °C, IR(KBr): 3136, 3092, 1734, 1452, 1252 cmÀ1 1H NMR (400 MHz,
.
CDCl3): 5.52(s, 8H), 7.27–7.38(m, 4H), 7.35–7.38 (m, 6H), 7.68 (s, 2H), 7.97(t,
1H, J = 7.8), 8.24(d, 2H, J = 7.7Hz). 13C NMR (100 MHz, CDCl3): 54.3, 59.1, 124.4,
128.2, 128.3, 128.9, 129.2, 134.3, 138.4, 142.6, 148.0, 1164.1. MS m/z: 510.2
[M+H]+.