Synthesis and biological evaluation of novel 1,2,3-triazole derivatives as anti-tubercular agents

Article abstract of DOI:10.1016/j.bmcl.2017.07.008

A library of seventeen novel 1,2,3-triazole derivatives were efficiently synthesized in excellent yields by the popular ‘click chemistry’ approach and evaluated in vitro for their anti-tubercular activity against Mycobacterium tuberculosis H37Ra (ATCC 25177 strain). Among the series, six compounds exhibited significant activity with minimum inhibitory concentration (MIC) values ranging from 3.12 to 0.78?μg/mL and along with no significant cytotoxicity against MBMDMQs (mouse bone marrow derived macrophages). Molecular docking of the target compounds into the active site of DprE1 (Decaprenylphosphoryl-β-D-ribose-2′-epimerase) enzyme revealed noteworthy information on the plausible binding interactions.

Full text of DOI:10.1016/j.bmcl.2017.07.008

Accepted Manuscript
Synthesis and Biological Evaluation of Novel 1,2,3-Triazole derivatives as Anti-
Tubercular Agents
Abdul Aziz Ali, Dhrubajyoti Gogoi, Amrita K. Chaliha, Alak K. Buragohain,
Priyanka Trivedi, Prakash J. Saikia, Prveen S. Gehlot, Arvind Kumar, Vinita
Chaturvedi, Diganta Sarma
PII:
S0960-894X(17)30701-1
DOI:
http://dx.doi.org/10.1016/j.bmcl.2017.07.008
BMCL 25121
Reference:
Bioorganic & Medicinal Chemistry Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
28 March 2017
9 June 2017
3 July 2017
Please cite this article as: Aziz Ali, A., Gogoi, D., Chaliha, A.K., Buragohain, A.K., Trivedi, P., Saikia, P.J., Gehlot,
P.S., Kumar, A., Chaturvedi, V., Sarma, D., Synthesis and Biological Evaluation of Novel 1,2,3-Triazole derivatives
as Anti-Tubercular Agents, Bioorganic & Medicinal Chemistry Letters (2017), doi: http://dx.doi.org/10.1016/
j.bmcl.2017.07.008
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Synthesis and Biological Evaluation of Novel
1,2,3-Triazole derivatives as Anti-Tubercular
Agents
Abdul Aziz Alia, Dhrubajyoti Gogoib, Amrita K. Chalihab, Alak K. Buragohainb, Priyanka Trivedic, Prakash J.
Saikiad, Prveen S. Gehlote, Arvind Kumare, Vinita Chaturvedic,*, Diganta Sarmaa,*
PDB ID: 4P8C

1
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.els evier.com
Synthesis and Biological Evaluation of Novel 1,2,3-Triazole derivatives as Anti-
Tubercular Agents
Abdul Aziz Alia, Dhrubajyoti Gogoib, Amrita K. Chalihab, Alak K. Buragohainb, Priyanka Trivedic,
Prakash J. Saikiad, Prveen S. Gehlote, Arvind Kumare, Vinita Chaturvedic,*, Diganta Sarmaa,*
aDepartment of Chemistry, Dibrugarh University, Dibrugarh-786004, Assam, India
bDBT-Bioinformatics Infrastructure Facility, Centre for Biotechnology and Bioinformatics, Dibrugarh University, Dibrugarh-786004, Assam, India
cBiochemistry Division, Central Drug Research Institute, CSIR, Lucknow- 226001, India
dAnalytical Chemistry Division, CSIR-North East Institute of Science & Technology, Jorhat-785006, Assam, India
eSalt and Marine Chemicals Division, CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar-364002, India
ARTICLE INFO
ABSTRACT
Article history:
Received
A library of seventeen novel 1,2,3-Triazole derivatives were efficiently synthesized in excellent
yields by the popular ‘click chemistry’ approach and evaluated in vitro for their anti-tubercular
Received in revised form
Accepted
activity against Mycobacterium tuberculosis H37Ra (ATCC 25177 strain). Among the series, six
compounds exhibited significant activity with minimum inhibitory concentration (MIC) values
ranging from 3.12 to 0.78 µg/mL and along with no significant cytotoxicity against MBMDMQs
(mouse bone marrow derived macrophages). Molecular docking of the target compounds into
the active site of DprE1 (Decaprenylphosphoryl-β-D-ribose-2′-epimerase) enzyme revealed
noteworthy information on the plausible binding interactions.
Available online
Keywords:
Tuberculosis
1,2,3-Triazoles
Antimycobacterial activity
Cytotoxicity
2009 Elsevier Ltd. All rights reserved
.
Molecular docking
Tuberculosis (TB), an infectious terrible disease caused by the
acid fast bacillus Mycobacterium tuberculosis remains one of the
most life threatening diseases to public health globally after
human immunodeficiency virus (HIV).1-2 Normally it attacks the
lungs (pulmonary TB) but can attack other organs as well
(extrapulmonary TB) and spreads in the air when patients expel
bacteria by coughing, sneezing, or spit. According to World
Health Organization (WHO) report, 9.6 million new TB cases
were estimated and claiming the lives of 1.5 million people in the
year 2014 despite the great advances in chemotherapy and the
Bacille-Calmette-Guérin (BCG) vaccine.3 The current standard
therapy attributed for TB is a six month regimen, termed DOTS
(Directly Observed Therapy, Short-course) in which the initial 2
months include isoniazid (INH), rifampicin (RIF), pyrazinamide
(PZA), and ethambutol (E), followed by a 4 month continuation
phase of RIF and INH.4 Furthermore, TB attracts numerous
interest of the scientific community due to high weakness of
human immunodeficiency virus (HIV)-infected persons to this
disease and the global emergence of multidrug resistant (MDR)
defined as resistant to the two most efficient TB drugs, rifampin
and isoniazid, and extensively drug-resistant (XDR) strains that
are further resistant to the fluoroquinolones and one of the
second-line injectable drugs (i.e. amikacin, kanamycin, or
capreomycin).5-7 The confines of long-term oral chemotherapy
and scarce compliance to the current treatment regimen, the
discovery of bedaquiline in the end of 2012, build a new hope for
the treatment of TB and especially MDR-TB.8 Nevertheless the
side effects of bedaquiline such as nausea, joint pain and
headache create a risk in clinical use.9-10 Therefore, there is a still
need for the development of new and effective
antimycobacterials with reduced toxicity, synthetically feasible,
stronger efficacy that function by novel mechanisms of action
against emerging MDR and XDR TB bacteria and latent diseases
in shorter treatment duration.
1,2,3-Triazoles are five member N-heterocyclic compounds
and are stable to metabolic degradation. They are also capable of
hydrogen bonding, which can be favorable in the binding of
biomolecular targets and can improve the solubility.11-12
Although absent in nature, the 1,2,3-Triazoles have found a
broad spectrum of biological applications such as anti-
tubercular,13 antibacterial,14 anti-allergic,15 anti-HIV,16 anti-
fungal,17-18 anti-inflammatory,19 anticancer,20-21 and α-glycosidase
inhibitor activities.22 β-lactum antibiotic Tazobactum, anticancer
compound carboxyamidotriazole (CAI), cefatrizine are some
drugs available in the market that possess 1,2,3-triazole moiety.23
Many approaches for the synthesis of 1,2,3-triazoles have been
developed so far, in which a typical click reaction, copper(I)-
catalyzed azide-alkyne cycloaddition (CuAAC) is definitely the
most effective strategies.24 In recent years a wide range of 1,2,3-
triazole derivatives were synthesized and reported to exhibit
potent antitubercular activity (Figure 1), especially benzofuran
salicylic acid derivative (I-A09) is a lead antitubercular agent
*Corresponding authors. E-mail address: dsarma22@gmail.com;
dsarma22@dibru.ac.in (D.Sarma), vinita_chaturvedi@cdri.res.in (V. Chaturvedi)

2
presently in clinical evaluations.25-34 In continuation to our
ongoing study aimed towards the development on 1,2,3-triazole
synthesis35-38 and previous research efforts toward the discovery
of potent anti-TB agents39 herein, we wish to disclose a facile
click synthesis of a series of novel 1,4-disubstituted 1,2,3-
triazole analogues and their antimycobacterial evaluation.
Further, LC mass spectrum showed [M+1] ion peak at m/z
407.9 which is in agreement with the molecular formula
C21H16BrN3O.
Scheme 1. Reagents and conditions: (i) Propargyl bromide, K2CO3, DMF,
90% ; (ii) CuI (1 mol%), DHQD2(PHAL) (1 mol%), H2O/DCM (1:1), rt, 0.5-
2h, 80-96%.
The synthesized compounds were tested for their ability to
inhibit the growth of M. tuberculosis H37Ra (ATCC 25177
strain) by Agar-based proportion Assay as shown in Table 1. The
lowest concentration of a compound up to which there was no
visible growth of bacilli was its minimal inhibitory concentration
(MIC). Out of seventeen compounds screened for their in vitro
anti-tubercular activity against M.tuberculosis H37Ra, six
compounds were found active with MIC in the range of 3.12-0.78
µg/mL (Table 1) and the rest were with MIC >12.5 µg/mL. The
compounds with potent MIC of 3.12 and 1.56 µg/mL were also
tested for their cytotoxicity against MBMDMQs (mouse bone
marrow derived macrophages) and found to be nontoxic on their
selectivity index (SI>10, ratio of CC50 against mammalian cells
and the MIC). Among tested series, compound 4o with fluoro
group at second position on phenyl ring of the triazole derivatives
exhibited excellent antimycobacterial activity with MIC= 0.78
µg/mL as compared to the first-line antitubercular drug
ethambutol (MIC=2.00 µg/mL) whereas compounds 4p and 4q
substituted with -CF3 and –OCHF2 groups at fourth position on
phenyl ring of the triazole moiety exhibited moderate to good
activities with MIC= 3.12 and 1.56 µg/mL, respectively. The
compounds 4k and 4l with 3,4-difluoro and 3-chloro-4-fluoro
group on the phenyl ring displayed considerable
Figure 1. Representative structure of 1,2,3-triazole derivatives that exhibit
anti-tubercular activity
The synthetic strategy was initiated with the preparation of
azides, one of the coupling partners of Cu-catalyzed azide alkyne
cycloaddition reaction. As reported earlier, the benzyl azides
were prepared from the corresponding organic bromides by
stirring the bromide with NaN3 in water/acetone (1:3) at room
temperature to give the desired azide as yellow oil. Similarly
octyl azide was prepared by refluxing1-bromooctane with NaN3
in acetone/water mixture overnight affording the corresponding
azide as colourless oil. Aromatic azides were synthesized by
diazotization of the corresponding aromatic amines with NaNO2
followed by addition of NaN3. Aromatic azides were obtained as
yellow oils with yields ranging from 70% to 95%. The azides
were used directly in the next step without purification and the
chemical structures of the azides were confirmed by analyzing
the crude product using FT-IR spectroscopy. A strong absorption
band at 2090-2100 cm-1, attributed to the stretching vibrations of
the N3 bond of the azido group. The starting alkyne 2 was
prepared by using commercially available 4-phenylphenol, 1 by
simple alkylation with propargyl bromide in the presence of
K2CO3 as a base in N,N-dimethylformamide (DMF) affording the
corresponding alkyne in excellent yield as reported in Scheme 1.
The synthesis of 1,2,3-triazole derivatives were accomplished
through Cu(I) catalyzed Huisgen 1,3-dipolar cycloaddition
reaction between 2 and appropriate azides in presence of CuI as
catalyst and DHQD2(PHAL) as ligand in H2O/DCM for 0.5 to 2h
affording 1,4-disubstituted-1,2,3-triazoles in good to excellent
yields as depicted in Scheme 1 (80-96%). The structures of the
products were characterized by thin layer chromatography
(TLC), 1H NMR, 13C NMR, FT-IR and mass spectrometry. IR
spectrum of 4c showed absorption bands at 2990, 1598 and 1049
cm-1 indicating the presence of -CH2, phenyl and C-N groups.
The 1H NMR spectrum of compound 4c exhibited the presence of
one distinctive singlet signal at around δ 5.32 ppm indicating the
attachment of methylene group to oxygen respectively. In
addition, the appearance of most informative singlet signal
around at δ 8.05 ppm confirms the presence of triazole proton. In
13C NMR, the most prominent carbon signals observed around δ
61.9 ppm accounted for the presence of methylene carbon
attached to the oxygen to the biphenyl ring. In addition, the
characteristic carbon signals appearing around δ 145.2 and 120.6
ppm were assigned to C-4 and C-5 of triazoles ring, while the
various aromatic carbons resonated around δ 145.2-114.9 ppm.
antimycobacterial activity with MIC values of 3.12 and 1.56
µg/mL, respectively. Moreover the compound 4m with ester
group also showed significant activity with MIC=1.56 µg/mL,
corroborating its antimicrobial nature. However, the activity is
not as profound as that of isoniazid (INH), the most active first-
line anti-TB drug.
Molecular docking provides a potent tool to different type of
interactions that govern the binding of a molecule to the
biological receptor. Therefore, with the aim of rationalizing the
observed antitubercular results and to investigate the possible
interactions of the studied compounds (4k-4q), molecular
docking study was performed with the target enzyme,
Decaprenylphosphoryl-β-D-ribose-2′-epimerase, DprE1(PDB ID:
4P8C) of Mycobacterium tuberculosis using CHARMm based
docking software (CDOCKER) available at the BIOVIA
Discovery Studio v4.5 platform. DprE1 is a flavin adenine
dinucleotide (FAD) dependent oxidoreductase; the key enzyme
involved in the biosynthesis of decaprenylphosphoryl-D-
arabinose (DPA), which is the only known donor of D-
arabinofuranosyl residues for the synthesis of arabinogalactan, a
basic precursor for the survival of mycobacteria.40 The binding
interactions of docked compounds with the DprE1 enzyme are
shown in Figure 2. In this study, 3D structure of M. tuberculosis
DprE1 complexed with Y22 (6-(trifluoromethyl)-3-{[4
((trifluoromethyl)benzyl]amino}quinoxaline-2-carboxylic acid)
was selected as target protein and acquired from Protein Data
Bank. The optional binding site was also computed at the Y22
and compounds were docked with the receptor. Docking

3
performance was accessed based on the CDOCKER docking
score.
Table 1. Biological Activity Studies of compounds 4a-4q Using Copper-Catalyzed Click Chemistry
b
Compounds
Structure
C log Pa
4.81
MIC (µg/ml)
CC50
ND
Selectivity Index (SI)
ND
>25.00
N
N
N
N
4a
4b
4c
4d
4e
4f
O
O
NO2
4.55
6.29
6.14
5.57
5.37
5.49
5.09
5.26
6.74
5.70
6.34
3.35
5.14
5.57
6.44
5.93
>25.00
>25.00
>25.00
>25.00
>25.00
>25.00
>25.00
>25.00
>25.00
3.12
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
N
N
N
N
ND
O
N
Br
ND
ND
ND
ND
4g
4h
4i
ND
ND
ND
4j
100.00
100.00
100.00
ND
32.05
64.10
64.10
ND
4k
4l
1.56
1.56
4m
4n
4o
4p
4q
>25.00
0.78
100.00
100.00
100.00
128.20
32.02
32.05
3.12
1.56
Isoniazid
-
-
0.025
2.00
100.00
100.00
4000.00
50.00
Ethambutol
aCLog P calculated using Chemdraw Ultra 12.0 software by Cambridge Soft.bCC50 were evaluated towards Mouse bone marrow macrophages.
ND - not done.

4
(a)
(b)
(c)

5
(d)
(e)
(f)
Figure 2. Binding modes of the compounds 4k (a), 4l (b), 4m (c), 4o (d), 4p (e) and 4q (f) with the active sites of DprE1 from docking
results.

6
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the six molecules and compared with Y22. The Energy scores
were computed in the range of 7.807 kcal/mol to 20.963
kcal/mol, the Y22 was found to have highest energy score of
22.940 kcal/mol indicating the importance of theses six hits as
potential DprE1 inhibitors (Table s1, supporting information).
All the compounds were found to have optimum binding
orientation with the catalytically important amino acids such as
Lys418 and Val365. The compound 4o was found to have
molecular interactions with Pro316, Lys418, Pro116, Val365,
Ser228, Lys134, Phe313 and indicating its novelty as novel M.
tuberculosis DprE1 inhibitor. Compounds 4k, 4l, 4m, 4p and 4q
are also found to be suitable inhibitors for M. tuberculosis
DprE1. The overall computational results of this investigation
well established the novelty of the series of 1,4-disubstituted
1,2,3-triazole derivatives as potential M. tuberculosis DprE1
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reasonably good yields (80−96%) make this synthetic method
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negligible cytotoxicity. Among all the 17 synthesized
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µg/ mL, better or comparable activity to the first line anti-TB
drugs. Moreover molecular docking studies of these derivatives
disclosed a high binding affinity into the active site of DprE1
(Decaprenylphosphoryl-β-D-ribose-2′-epimerase) enzyme. These
findings suggest that the newly designed compounds may be
considered as potential targets for anti-tubarcular drug discovery.
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This work was supported by the Council of Scientific and
Industrial Research (CSIR), New Delhi, India with research grant
No. 02(0154)/13/EMR-II, respectively. A.A.A thanks CSIR, New
Delhi for Senior Research Fellowship. We are grateful to the
Department of Science and Technology for financial assistance
under DST-FIST programme and UGC, New Delhi for Special
Assistance Programme (UGC-SAP) to the Department of
Chemistry, Dibrugarh University.
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Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/
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