Efficient synthesis and in vitro antitubercular activity of 1,2,3-triazoles as inhibitors of Mycobacterium tuberculosis

Article abstract of DOI:10.1016/j.bmcl.2011.10.048

Efficient and rapid synthesis of 1,2,3-triazole derivatives has been achieved via Huisgen's 1,3-dipolar cycloaddition between alkyl/arylazides and diethyl/dimethyl acetylenedicarboxylate in excellent yields under solvent-free conditions. The environmentally friendly solvent-free protocol overcomes the limitations associated with the prevailing time-consuming solution phase protocols and affords the triazoles just in 1-3 min. In vitro antitubercular activity of these triazoles was screened against Mycobacterium tuberculosis H₃₇Rv strain. Four of the compounds showed MIC in the range of 1.56-3.13 μg/mL proving their potential activity.

Full text of DOI:10.1016/j.bmcl.2011.10.048

Bioorganic & Medicinal Chemistry Letters 21 (2011) 7273–7276
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Efficient synthesis and in vitro antitubercular activity of 1,2,3-triazoles
as inhibitors of Mycobacterium tuberculosis
Poovan Shanmugavelan a, Sangaraiah Nagarajan a, Murugan Sathishkumar a,
b
b
Alagusundaram Ponnuswamy a, , Perumal Yogeeswari , Dharmarajan Sriram
⇑
a Department of Organic Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai 625 021, Tamil Nadu, India
b Medicinal Chemistry and Antimycobacterial Research Laboratory, Pharmacy Group, Birla Institute of Technology and Science, Pilani, Hyderabad Campus, Jawahar Nagar,
Hyderabad 500 078, Andhra Pradesh, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Efficient and rapid synthesis of 1,2,3-triazole derivatives has been achieved via Huisgen’s 1,3-dipolar
cycloaddition between alkyl/arylazides and diethyl/dimethyl acetylenedicarboxylate in excellent yields
under solvent-free conditions. The environmentally friendly solvent-free protocol overcomes the limita-
tions associated with the prevailing time-consuming solution phase protocols and affords the triazoles
just in 1–3 min. In vitro antitubercular activity of these triazoles was screened against Mycobacterium
Received 29 April 2011
Revised 6 September 2011
Accepted 14 October 2011
Available online 19 October 2011
tuberculosis H37Rv strain. Four of the compounds showed MIC in the range of 1.56–3.13 lg/mL proving
their potential activity.
Keywords:
1,2,3-Triazoles
1,3-Dipolar cycloaddition
Antituberculosis
Ó 2011 Elsevier Ltd. All rights reserved.
Tuberculosis (TB) is caused by Mycobacterium tuberculosis and
remains as a leading cause of mortality worldwide. Currently,
among the infected individuals approximately eight million
develop active TB, and almost two million die from this disease.
Of the new TB cases reported, 95% occur in developing countries
every year. World Health Organization (WHO) estimates that
about one-third of the world’s population harbors latent infection
of TB and thus declared it as a global emergency.1–3 The mortality
and spread of this disease has been further aggravated by its syn-
ergy with Human Immunodeficiency Virus (HIV).4,5 By destroying
the two most important cells to the containment of tubercle bacilli
(macrophages and CD4-receptor-bearing lymphocytes), HIV
vigorously promotes the progression of recent or remotely
acquired TB infection to active disease.6 The deadly synergy
between TB and HIV has led to a quadrupling of TB cases in several
African and Asian countries. In fact it is estimated that eleven
million adults are now co-infected with HIV and tuberculosis
worldwide.3 Thus both the current HIV pandemic and multidrug-
resistant M. tuberculosis have emerged as major obstacles for treat-
ment and public health control of tuberculosis.1,2
emergence of multiple drug-resistant (MDR) TB revealed the ur-
gent need for new classes of antitubercular drugs.8
Internationally efforts are now being made to develop new
antitubercular agents.3 Several studies have indicated the potential
of analogues of isoniazid9,10 and heterocyclic compounds, such as
BM212,11,12 as tuberculostatic agents. In pursuit of this goal, our
research efforts herein have been directed toward the discovery
of new chemical entities that are effective as antituberculosis
agents.
Organic compounds having triazole nucleus inducing antibacte-
rial,13–15 antifungal,16 antiviral,17 antimicrobial, anti inflammatory
and analgesic18 activity have been explored. Especially,
1,2,3-triazole derivatives are found to inhibit tumor proliferation,
invasion, metastasis19 and anti-HIV activity.20–26 With regard to
the antitubercular activity, 1,2,3-triazole derivatives have been
found to show promising activity profile.27 In the present study
we report an elegant synthesis of hitherto unknown 1,2,3-triazole
derivatives and their antimycobacterial activity against M. tubercu-
losis H37Rv.
Owing to these significant features, a number of protocols for
the synthesis of 1,2,3-triazole compounds have been developed.28
Among them, the most elegant and useful approach is the
Huisgen’s 1,3-dipolar cycloaddition of azides and alkynes.29
From perusal of literature, it is understood that solvent-free
synthesis of triazoles via azide–alkyne cycloaddition is relatively
new. In view of the report of Abu-Orabi et al.30 on the long time-
consuming triazole synthesis, Kenneth Savin et al.31 have accom-
plished a facile, solvent-free cycloaddition of DMADC (dimethyl
Chemotherapy of TB started in the 1940s and since then some
agents have been discovered, including p-aminosalicylic acid
(PAS), isoniazid (INH), pyrazinamide (PZA), cycloserine,
ethionamide, rifampicin, and ethambutol.7 However, the
⇑
Corresponding author. Tel.: +91 9600868323.
E-mail address: ramradkrish@yahoo.co.in (A. Ponnuswamy).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.10.048

7274
P. Shanmugavelan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 7273–7276
Table 1
acetylenedicarboxylate) with benzyl azide in a minute using
microwave irradiation. We, in the present study understand that
there is no need for microwave irradiation in this regard, that is
we have achieved an instantaneous synthesis of triazole deriva-
tives in excellent yields by conventional heating over a hot-plate
(80–120 °C). This substantiates that the increase in the rate of
heating is crucial rather than the source of heating. Thus, in this
paper we describe a facile methodology to synthesize the 1,2,3-tri-
azole derivatives and their screening for in vitro antitubercular
activity against M. tuberculosis H37Rv strain.
At the outset, a mixture of benzylazide (1a) and DEADC (diethyl
aceylenedicarboxylate) in THF at refluxing temperature afford the
triazole (2a) in 80% yield in 7 h (Scheme 1). For further optimiza-
tion, the reaction is performed in different solvents at refluxing
conditions (Table 1, entries 1–4). Solvent screening indicates that
toluene (entry 6) is the right choice giving 88% of 2a in 3 h.
In our next attempt, the reaction is conducted in absence of sol-
vent but with excess of DEADC at 120 °C (entry 5). This results in a
very remarkable observation, that is 96% of 2a is obtained in just
one minute, the pure form of which was obtained after column
chromatographic technique. A modification of the method wherein
1a and DEADC in 1:1 mol equiv (entry 6) at 120 °C for just a minute
gives 2a (96%) as a pure product. Other triazole derivatives (2b–j
and 3a–j) are synthesized by this optimized condition (Scheme
2) with a variety of azides and DEADC/DMADC (Table 2). Except
2a,32 3a,33 3b,34 3i33 and 3j,35 all the other fifteen triazoles are
new compounds.
Optimization of 1,2,3-triazole (2a) synthesis
Entry
Reaction condition
Solvent
Time
Yield (%)
1
2
3
4
5
6
THF
7 h
5 h
4 h
80
80
83
88
96
96
Acetonitrile
Benzene
Toluene
DEADC
—
3 h
1 mina
1 minb
a
Reaction carried out in DEADC in excess in absence of solvent.
Reaction carried out with 1:1 equiv of 1a and DEADC without solvent.
b
N
O
O
N
N
EtOOC
80-120
COOEt
CH2
CH3
°
C, 1-3 min
R
O
O
CH2
CH3
2
R
N3
solvent free
1
O
O
N
N
N
MeOOC
COOMe
°C, 1-3 min
CH3
80-120
R
O
O
CH3
3
The synthesized triazoles (2a–j and 3a–j) are completely char-
acterized by IR and NMR (1D and 2D) spectral techniques.
The 1H NMR spectrum of a representative triazole, 2a shows
two triplets at 1.26 and 1.38 ppm with J = 7.2 Hz for the methyl
protons and two quartets at 4.32 and 4.41 ppm with J = 7.2 Hz
for the methylene protons of the –OCH2CH3 groups. The N-methy-
lene protons show singlet at 5.79 ppm and the five aromatic pro-
tons appeared as multiplet around 7.23–7.34 ppm. In 13C NMR,
the signal of two ester carbonyl groups appeared at 160.0 and
158.4 ppm, two OCH2 carbons at 61.7 and 62.7 ppm, two CH3 car-
bons at 13.6 and 14.0 ppm, one N-methylene carbon at 53.6 ppm,
three quaternary carbons at 140.3, 133.9 and 129.8 ppm, and three
aromatic carbons at 128.7, 128.6 and 127.8 ppm. The IR spectrum
R=
N3
N3
N3
N3
(b)
(a)
(c)
(d)
H3CO
Br
O
O
O
N3
N3
N3
(e)
(i)
Cl
(f)
(g)
h)
O
O
Cl
H3C
N3
O
(j)
N3
O
H3C
N3
O
O
Scheme 2. Synthesis of 1,2,3-triazoles (2a–j and 3a–j).
showed the band due to the carbonyl group at 1732 cmÀ1
.
All the synthesized compounds were screened for their in vitro
antimycobacterial activity against MTB in Middlebrook 7H11 agar
medium supplemented with OADC by agar dilution method similar
to that recommended by the National Committee for Clinical
Laboratory Standards for the determination of MIC in duplicate.36
The MIC is defined as the minimum concentration of compounds
required to completely inhibit the bacterial growth. The MIC values
of the synthesized compounds determined in duplicate at 7.4 pH,
along with that of standard drugs are listed in Table 3.
exhibit antitubercular activity. Among the above mentioned
active compounds, the more potent antitubercular compounds
2b, 2d, 2e and 3d having aromatic ring substitution show MIC
values 3.13, 1.56, 3.13 and 3.13
lg/mL, respectively. The
compounds 2c and 3e having substitution on the aromatic ring
with MIC values 6.25
activity.
lg/mL exhibit reasonable antitubercular
In particular, the compound 2d, with MIC 1.56
endowed with maximum potency, being 2.08 times more active
than the standard drug ethambutol (MIC 3.25 g/mL). However,
lg/mL is
Out of fourteen screened compounds, 2a, 2b, 2c, 2d, 2e, 3b,
3c, 3d and 3e display antitubercular activity with MIC ranging
l
none of the compounds screened in the present work is found
from 1.56 to 12.5
lg/mL against the strain Mycobacterium tuber-
to be more potent than the standard drug isoniazid (MIC
culosis H37Rv (Table 3). The remaining compounds, 2i, 2j, 3i and
0.75 lg/mL). The halogen substitution on aromatic ring generally
3j having alkyl substitution with MIC values >25
l
g/mL do not
leads to the compounds having better activity in comparison to
other compounds with unsubstituted aromatic ring and the com-
pounds with alkyl substitution do not display any significant
activity.
In conclusion, we have developed an efficient and a practical
protocol for the synthesis of 1,2,3-triazoles instantaneously from
the alkyl/aryl azides and alkynes under solvent-free conditions.
The note-worthy features of our method are it is very simple and
gives excellent yields. In vitro antitubercular activity of the tria-
zoles against MTB H37Rv strain has been evaluated. Four of the
O
N
N
N
O
O
N3
EtOOC
COOEt
reaction condition
O
1a
2a
compounds showed MIC in the range of 1.56–3.13
their potential activity.
lg/mL proving
Scheme 1. Synthesis of 1,2,3-triazole (2a).

P. Shanmugavelan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 7273–7276
7275
Table 2
Synthesis of 1,2,3-triazoles (2a–j and 3a–j) from alkyl/arylazides and DEADC/DMADC
Azides (1a–j)
1,2,3-Triazoles (2 and 3)
2a–j
3a–j
Temp. (°C)
2/3
Time (min)
2/3
Yield (%)
2/3
O
O
N
N
O
N
O
N
1a
1b
120/120
80/80
1/1
1/1
96/96
N
N
O
O
O
O
N
O
O
N
N
N
N
N
O
O
O
O
98/98
98/98
O
O
O
O
O
O
N
N
N
N
N
N
O
O
O
O
O
1c
80/80
80/80
1/1
1/1
O
O
O
H3CO
H3CO
O
O
N
N
N
N
N
N
O
O
O
O
O
1d
99/99
O
O
O
O
Br
Cl
Br
Cl
O
O
N
N
N
N
N
N
O
O
O
1e
1f
80/80
80/80
1/1
1/1
99/99
97/97
O
O
O
O
O
O
N
N
N
N
N
N
O
O
O
O
O
O
O
O
Cl
N
Cl
N
N
O
N
O
N
N
O
O
O
O
1g
100/100
3/3
99/99
O
O
O
O
O
O
O
O
O
N
N
N
N
1h
1i
100/100
90/90
3/3
2/2
97/97
96/96
O
N
N
O
O
N
N
N
O
N
O
O
O
O
O
N
N
O
O
O
O
O
O
N
N
O
N
O
N
O
N
1j
90/90
2/2
96/96
O
N
O
O
O
O
O
O

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Acknowledgments
The author wish to acknowledge IRHPA, DST for providing
300 MHz NMR instrument for recording the NMR spectra, UGC
for giving financial support and Medicinal Chemistry and
Antimycobacterial Research Laboratory, Pharmacy Group, Birla
Institute of Technology and Science, Pilani for biological evaluation
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Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2011.10.048.
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