Design and synthesis of 1H-1,2,3-triazoles derived from econazole as antitubercular agents

Article abstract of DOI:10.1016/j.bmcl.2012.09.041

Econazole has been known to be active against Mycobacterium tuberculosis. We have designed and synthesized 1H-1,2,3-triazoles derived from econazole as antitubercular agents. The majority of triazole derivatives have been prepared by microwave-assisted cl

Full text of DOI:10.1016/j.bmcl.2012.09.041

Bioorganic & Medicinal Chemistry Letters 22 (2012) 6844–6847
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design and synthesis of 1H-1,2,3-triazoles derived from econazole
as antitubercular agents
Suhyun Kim a,b, Sang-Nae Cho c, Taegwon Oh c, Pilho Kim a,
⇑
a Cancer & Infectious Diseases Therapeutics Research Group, Korea Research Institute of Chemical Technology, Daejeon, Republic of Korea
b College of Pharmacy, Kyung Hee University, Seoul, Republic of Korea
c Department of Microbiology and Institute for Immunology and Immunological Diseases, Yonsei University College of Medicine, Seoul, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2012
Revised 30 August 2012
Accepted 14 September 2012
Available online 23 September 2012
Econazole has been known to be active against Mycobacterium tuberculosis. We have designed and syn-
thesized 1H-1,2,3-triazoles derived from econazole as antitubercular agents. The majority of triazole
derivatives have been prepared by microwave-assisted click chemistry. It turned out that all of the pre-
pared triazoles had no antifungal activities. However, most of the hydroxy-triazoles (6a and 10) appar-
ently turned out to have antitubercular activities. Overall, hydroxy-triazoles 10 were more active than
their corresponding ether-triazoles 11. While the MIC value of hydroxy-triazole 10d was as good as econ-
Keywords:
Tuberculosis
Econazole
Triazole
azole (16
lg/mL), the MIC value of 10a was two-fold more active than econazole, suggesting that this 1H-
1,2,3-triazole scaffold (3) could be further optimized to develop Mtb specific agents.
Ó 2012 Elsevier Ltd. All rights reserved.
Click chemistry
Microwave-assisted reactions
Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb),
remains one of the most deadly infectious diseases, infecting 8 mil-
lion and killing 2 million people annually.1 In TB drug discovery,
there are two major hurdles to overcome: lengthy regimen and
drug resistance. Although there are first and second line TB drugs
available, current TB chemotherapy requires lengthy treatment
periods: 6–9 months for drug-susceptible patients and 18–
24 months for drug-resistant patients. Since TB patients have to
take TB medications for such a long time, it could have a high
chance to lead to low compliance rates and severe adverse drug ef-
fects.2 Recently, drug-resistant Mtb is getting more prevalent. For
instance, 6–22% of TB patients turned out to be multidrug-resistant
TB (MDR-TB) patients. MDR-TB is defined as Mtb strains resistant
to both isoniazid and rifampin, which are the two most significant
drugs among the first line TB agents. Moreover, extensively
drug-resistant TB (XDR-TB) is becoming more ubiquitous found
in over 50 countries. XDR-TB is defined as Mtb strains resistant
to isoniazid, rifampin, and two series of second line drugs such
It has been shown that antifungal azoles, such as econazole (1)
and miconazole (2), are active against Mtb through interactions
with CYP130 in Mtb (Fig. 1).4 In particular, econazole has encour-
aging activity profiles against wild-type Mtb and MDR-TB.5,6 A re-
cent report demonstrated that antifungal azole analogs could be
modified to discover antibacterial agents.7 Triazoles are also used
very often in the medicinal applications. For instance, a variety of
1H-1,2,3-triazole compounds have been known to have antituber-
cular activity.8–11 Castagnolo et al. reported that enantiomerically
pure 1H-1,2,3-triazole analogs tethered with imidazole were active
against Mtb.12 As our ongoing search for novel antitubercular
agents, we just reported the discovery of econazole-derived mono-
cyclic nitroimidazoles as antitubercular agents.13 Encouraged by
these results and the background information mentioned above,
we launched to explore the feasibility of 1H-1,2,3-triazole
compounds derived from econazole as
a novel scaffold for
antitubercular agents. We envisioned to utilize click chemistry to
as an aminoglycoside and
a fluoroquinolone. For XDR-TB
treatment, currently there are no evident chemotherapy methods
available. However, truly novel antitubercular drugs other than
repurposed drugs have not been developed since the 1960s.3 Thus,
there is an urgent need for discovery of novel drugs, which could
overcome the lengthy regimen and drug resistance.
N
N
R
O
Cl
Cl
Cl
econazole (1, R = H)
miconazole (2, R = Cl)
⇑
Corresponding author.
E-mail address: pkim@krict.re.kr (P. Kim).
Figure 1. Structures of econazole (1) and miconazole (2).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.09.041

S. Kim et al. / Bioorg. Med. Chem. Lett. 22 (2012) 6844–6847
6845
R1
N
prepare 1H-1,2,3-triazoles (3) from azides (4) and alkynes (Fig. 2).
Lately, Ankati et al. demonstrated that this click chemistry would
be feasible by successfully performing a couple of related reactions
to our synthetic design.14
At first, we began our studies to elucidate the replacement
effect of the imidazole on econazole with 1H-1,2,3-triazole or
benzotriazole by constructing triazoles 7a or 7b, respectively
(Scheme 1). Chlorohydrin 5 was treated with 1H-1,2,3-triazole
under microwave conditions to give hydroxy-triazoles 6a (43%)
as a major product in addition to 6b (14%) as a minor product.
N3
R2
N
N
+
R1
R2
Cl
Cl
Cl
Cl
3
4
Figure 2. Design of triazoles (3) derived from econazole.
Cl
OH
Cl
Cl
5
b
a
N
N
N
N
N
N
N
N
N
N
N
N
OH
OH
OH
OH
Cl
Cl
6a
Cl
Cl
6c
Cl
Cl
6b
Cl
Cl
6d
c
c
N
N
O
N
N
N
O
N
Cl
Cl
Cl
Cl
Cl
Cl
7a
7b
Scheme 1. Reagents and conditions: (a) 1H-1,2,3-triazole, CH3CN,
lW, 80 °C, 50 min, 6a (43%), 6b (14%); (b) benzotriazole, CH3CN, lW, 80 °C, 50 min, 6c (25%), 6d (8%); (c) 4-
chlorobenzyl bromide, NaH, TBAI, DMF, À78 °C to rt, 2 h, 7a (77%), 7b (73%).
N3
O
Cl
N3
b
a
OH
OH
Cl
Cl
d
R2
Cl
Cl
Cl
Cl
9
5
8
c
R1
N
R1
N
N
O
N
N
N
OH
Cl
Cl
Cl
Cl
10
R2
11
Scheme 2. Reagents and conditions: (a) NaN3, DMF, reflux, 12 h, 69%; (b) benzyl bromides, NaH, TBAI, DMF, À78 °C to rt, 2–5 h, 90–98%; (c) alkynes, CuI, DIPEA, CH2Cl2,
150 °C, 10 min, 74–94%; (d) alkynes, CuI, DIPEA, CH2Cl2, W, 150 °C, 10 min, 72–94%.
lW,
l

6846
S. Kim et al. / Bioorg. Med. Chem. Lett. 22 (2012) 6844–6847
Table 1
Antitubercular and antifungal activities and cytotoxicity of 1H-1,2,3-triazoles
R1
N
N
N
N
O
N
N
R2
O
R2
Cl
Cl
Cl
Cl
6c 7b
6a, 7a,1 0a-h, 11a-l
,
c
Compound number
R1
R2
MICa Mtb
MICb C. albicans
IC50 vero cell
6a
6c
7a
7b
10a
10b
10c
10d
10e
H
—
H
—
H
256
>256
64
128
8
256
>256
16
>256
>256
>256
>256
>256
>256
NDe
>200
>100
>12.5
>12.5
23.28
274.1
>100
31.94
33.94
4-Cl-Bnd
4-Cl-Bn
4-Cl-Bn
n-Bu
H
H
H
H
H
CH2CH2OH
CH2OH
Cyclohexyl
t-Bu
>256
256
32
H2N
10f
H
32
>256
26.8
NH2
10g
10h
H
H
32
32
>256
ND
33.94
ND
N
11a
11b
11c
11d
11e
11f
11g
11h
11i
n-Bu
n-Bu
n-Bu
CH2CH2OH
CH2CH2OH
CH2CH2OH
CH2OH
Cyclohexyl
t-Bu
4-Cl-Bn
128
>256
>256
>256
>256
>64
>256
>256
>256
>256
10.61
63.38
21.02
24.34
ND
33.68
19.79
>12.5
>25
4-OCF3-Bn
2,4-diF-Bn
4-Cl-Bn
4-OCF3-Bn
2,4-diF-Bn
4-Cl-Bn
>256
>256
>256
>64
128
>256
>256
>256
4-Cl-Bn
4-Cl-Bn
H2N
11j
4-Cl-Bn
>256
>256
>50
NH2
11k
11l
4-Cl-Bn
4-Cl-Bn
256
256
>256
>256
>50
>50
N
1 (econazole)
16
16
rifampicin
0.0625
ND
a
b
c
MIC against M. tuberculosis (H37Rv) (
MIC against C. albicans ( g/mL).
g/mL).
Bn: benzyl.
ND: not determined.
lg/mL).
l
IC50 against VERO cells (
l
d
e
Likewise, compound 5 was reacted with benzotriazole to obtain 6c
(25%) and 6d (8%). Benzylation of 6a and 6C facilitated ether-
triazoles 7a (77%) and 7b (73%) in the presence of NaH and 4-
chlorobenzyl bromide.
In order to construct a variety of 1H-1,2,3-triazoles derived
from econazole, we proposed to use click chemistry.15 Azidation
of commercially available chlorohydrin 5 was carried out under
refluxing NaN3 in DMF to afford azido-alcohol 8 (Scheme 2).
Treatment of 8 with various benzyl bromides and NaH furnished
azido-ethers 9 in over 90% yields. With the azides 8 and 9 in hand,
we have screened many different reaction conditions to optimize
the click chemistry conditions. Among the click chemistry condi-
tions used, a microwave condition with CuI and DIPEA in CH2Cl2
gave the best yield. The click chemistry of 8 or 9 under the micro-
wave conditions gave hydroxy-triazoles 10 or ether-triazoles 11,
respectively.14,16,17
The antitubercular activity of each compound against
Mycobacterium tuberculosis H37Rv was measured by the green

S. Kim et al. / Bioorg. Med. Chem. Lett. 22 (2012) 6844–6847
6847
fluorescent protein reporter assay.18 Briefly, the compound was
initially dissolved in dimethylsulfoxide (DMSO), and two-fold dilu-
tions were made in 7H9 broth in microplates. The initial inoculum
of 2 Â 105 CFU/mL of Mtb H37Rv-GFP, which was grown in Middle-
brook 7H9 media, was exposed to the compounds for 7 days. The
fluorescence was measured in a Fluostar Optima microplate fluo-
rometer (BMG Labtech, Germany), and the MIC was defined as
the lowest concentration of compounds that inhibited fluorescence
by 90%, compared with the fluorescence of bacteria only wells.
We investigated the antitubercular activity of triazole 7a and 7b
32 lg/mL, and investigated the selective indexes (SI). The SI values
were ranged from 1 to 3, indicating that cytotoxicity profile should
be improved further to develop this triazole series as antitubercu-
lar agents.
In summary, replacing the imidazole on econazole with
1H-1,2,3-triazole could be tolerable to maintain antitubercular
activities, based on the activity profiles of the hydroxy-triazoles
(10) prepared. Overall, hydroxy-triazoles (10) tend to be more
active than ether-triazoles (11). While 10d was as active as econa-
zole, 10a was two-fold more active than econazole. Moreover, the
triazole series compounds prepared were not active at all against
C. albicans, suggesting that the mode of action of the triazoles
prepared might be quite different from that of econazole.4,19 Thus,
this 1H-1,2,3-triazole scaffold could be further optimized to
develop Mtb specific agents.
as controls. Triazole 7a gave the MIC value of 64 lg/mL. Although
7a is 4 times less active than econazole, it still maintains the anti-
tubercular activity, indicating that replacing the imidazole on
econazole with 1H-1,2,3-triazole could be tolerated in terms of
the activity (Table 1). However, in case of 7b, the activity was abol-
ished, compared with econazole. While we have tried several dif-
ferent alkynes to prepare ether-triazoles 11, most of them were
not active against Mtb. Moreover, when the benzyl group was re-
placed with 4-trifluoromethoxybenzyl or 2,4-difluorobenzyl sub-
stituents, the activity was not improved. This led us to
investigate the activity of hydroxy-triazoles 10. It turned out that
hydroxy-triazoles 10 appeared to be far more active, compared
with ether-triazoles 11. Some of the hydroxy-triazoles such as
10e, 10f, 10g, and 10h were two-fold less active than econazole.
While 10d (R1 = cyclohexyl) was as active as econazole, 10a
(R1 = n-Bu) was two-fold more active than econazole. However,
their corresponding ether-triazoles 11h and 11a, respectively,
were not active, confirming that hydroxy-triazoles 10 are more ac-
tive than ether-triazoles 11. This trend appears to be applicable in
the case of amine containing triazoles. While the MIC values of
Acknowledgments
This work was supported by Korea Research Institute of
Chemical Technology (KRICT) and by the International Research
& Development Program of the National Research Foundation of
Korea (NRF) funded by the Ministry of Education, Science and
Technology (MEST) of Korea (Grant number: K20501000001-
09E0100-00110, FY 2009)
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.
09.041.
hydroxy-triazoles such as 10f, 10g, and 10h were 32 lg/mL, their
corresponding ether-triazoles (11j, 11k, and 11l, respectively)
were inactive.
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the compound for 48 h, which were made in the same media. The
growth of C. albicans was visualized by Alamar Blue dye (AbD Sero-
tec, UK), and the MIC was defined as the lowest concentration of
compounds that inhibited the color change of the Alamar Blue
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from blue to pink. While econazole gave the MIC value of 16 lg/
mL against C. albicans, all of the triazoles in Table 1 were not active
at all. Surprisingly, substituting the imidazole on econazole with
1H-1,2,3-triazole led to the complete loss of antifungal activities.
These data suggest that the triazole series compounds prepared
could have quite different interaction mode with CYP51 from
C. albicans, compared with that of econazole.19
The cytotoxicity of the compounds was tested in Vero cells by
MTT assay (Promega, USA) in accordance to the manufacturer’s
instruction. The cell suspension, which was in early log phase,
was exposed to serially diluted solution of the compounds for
3 days. Both the cell suspension and the compound dilutions were
made in RPMI 1640 medium. The cytotoxic effect was normalized
by comparing with the effect of DMSO only wells, and the IC50 va-
lue was calculated using Prism software (Graphpad, CA, USA). We
selected the active triazoles with the MIC values lower than
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