Substituted hydrazinecarbothioamide as potent antitubercular agents: Synthesis and quantitative structure-activity relationship (QSAR)

Article abstract of DOI:10.1016/j.bmcl.2010.02.081

A series of novel substituted hydrazinecarbothioamides was synthesized and evaluated for anti-TB activity. Three most active compounds viz. 1, 6 and 12 were found to exhibit minimum inhibitory concentration (MIC) of 0.4 μg/mL, whereas four compounds viz. 3, 5, 10 and 11 showed comparatively lesser activity with MIC value of 0.8 μg/mL against Mycobacterium tuberculosis strain. A highly significant QSAR equation explaining 81.8% variance is described.

Full text of DOI:10.1016/j.bmcl.2010.02.081

Bioorganic & Medicinal Chemistry Letters 20 (2010) 2597–2600
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Substituted hydrazinecarbothioamide as potent antitubercular agents:
Synthesis and quantitative structure–activity relationship (QSAR)
Supriya Singh a, Pintu K. Mandal a, Nagendra Singh a, Anup K. Misra a, Shubhra Singh b, Vinita Chaturvedi b,
Sudhir Sinha b, Anil K. Saxena a,
*
a Medicinal and Process Chemistry Division, Central Drug Research Institute, Lucknow 226 001, India
b Drug Target Discovery and Development Division, Central Drug Research Institute, Lucknow 226 001, 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 novel substituted hydrazinecarbothioamides was synthesized and evaluated for anti-TB activ-
Received 5 September 2009
Revised 13 January 2010
Accepted 19 February 2010
Available online 23 February 2010
ity. Three most active compounds viz. 1, 6 and 12 were found to exhibit minimum inhibitory concentra-
tion (MIC) of 0.4
activity with MIC value of 0.8
equation explaining 81.8% variance is described.
l
g/mL, whereas four compounds viz. 3, 5, 10 and 11 showed comparatively lesser
l
g/mL against Mycobacterium tuberculosis strain. A highly significant QSAR
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Tuberculosis
Hydrazinecarbothioamides
QSAR
Synthesis
Tuberculosis (TB) is one of the respiratory diseases mainly
caused by Mycobacterium tuberculosis (MTb).1 World Health Orga-
nisation estimates that one-third of the world’s population is in-
fected by M. tuberculosis. Annually TB affects 8 million people and
causes 2–3 million deaths around the world. The rising number
of TB affected people is due to the use of immunosuppressive drugs
or substance abuse or HIV/AIDS which is a serious threat to TB
control and prevention.2 The DOTS (Directly Observed Therapy,
Short-course)3 involve a 3 or 4 drug regimen comprising isoniazid,
rifampin, pyrazinamide, and/or ethambutol for a minimum of
6 months. Moreover, the emergence of multi-drug resistant TB
(MDR-TB), and the extensively drug resistant (XDR-TB) strains
has led to the discovery and the development of new potent anti-
TB drugs a global priority.4
MTb produces two series of structurally related peptidic sidero-
phores known as the mycobactins and carboxymycobactins that
vary by the appended lipid residue. Mycobactins have emerged
as attractive targets for the development of anti-TB agent because
of their critical role in the growth and virulence of MTb.5–7 Thus
the development of species resistance against anti-TB drugs in
mycobacterium species are forcing for the development of novel
drugs as anti-TB agents.
hydrazinecarbothioamide using the state of art approaches (sub-
structural approach based on the pattern recognition). These mol-
ecules have been synthesized and screened for their anti-TB
activities. The common structure formula of the synthesized titles
compounds is shown in Figure 1.
The general synthesis of the novel substituted hydra-
zinecarbothioamides is outlined in Scheme 1. The first step in-
volves the reaction of hydrazine hydrate with carbon disulfide in
the presence of KOH at 0–10 °C. The next step involves the drop-
wise addition of methyl iodide to the ice-cooled reaction mixture
over nearly 2 h. During this process, the colour of the reaction
mixture changes from white (colourless) to yellow which indicates
the formation of intermediate I, methyl hydrazinecarbodithionate.9
The third step involves the addition of the substituted aceto-
phenone to the solution of I in 2-propanol to afford the interme-
diate II.10 The last step involves the reaction of the intermediate II
with the substituted/unsubstituted amines to afford the title
compounds.11
Site 1
Site 2
H
N
H
N
N
R'
In view of the above and activity associated with hydra-
zinecarbothioamide,8 we have designed a set of novel substituted
S
R
* Corresponding author. Tel.: +91 522 2612411 18; fax: +91 522 2623405.
E-mail address: anilsak@gmail.com (A.K. Saxena).
Figure 1. The common structural formula of the title compounds with encircled
portions indicate the modification sites viz. site 1 and 2.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.02.081

2598
S. Singh et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2597–2600
a
b
H2N NH2.H2O
HN
C
S
S- K+
C
S
H2N
H2N HN
SCH3
I
O
c
CH3
R
H
N
S
H
N
H
N
R' - NH2
d
N
CH3
N
R'
S
R
II
S
R
Cyclic amine
d
H
Cyclic
N
N
N
S
R
Scheme 1. Synthesis of substituted hydrazinecarbothioamides. Reagents and conditions: (a) CS2 (3 mol), KOH (3 mol), 0–10 °C; (b) CH3I (3 mol), rt; (c) 2-propanol, rt; (d)
ethanol, rt.
The ‘proportion method’, described by McClachy12 was followed
for the determination of anti-TB activity. The synthesized title
compounds exhibited good inhibition of mycobacterium species
with minimum inhibitory concentration (MIC) ranging from 0.4
pMIC
0.380
0.332
BEHm6
ARR
G3u
BEHm6
ARR
G3u
1.000
ꢁ0.383
ꢁ0.070
1.000
0.122
to 25
exhibited MIC value of 0.4
11 were found to be of comparatively lesser activity with MIC
value of 0.8 g/mL. All these compounds were having bromo group
substituted to the phenyl ring (site 1, Fig. 1). The nitro substituted
compounds exhibited MIC value of >3.12 g/mL. The SAR analysis
showed that the bromo substituted compound 12 (R = Br,
MIC = 0.4 g/mL) was about 7 times more potent than the nitro
substituted compound 17 (R = NO2, MIC = 3.12 g/mL). Similarly,
the compound 5 (R = Br, MIC = 0.8 g/mL) was about 15 times
more potent than the compound 21 (R = NO2, MIC >12.5 g/mL).
lg/mL (Table 1). Three most active compounds 1, 6 and 12
ꢁ0.607
1.000
lg/mL. The compounds 3, 5, 10 and
l
This model was of good significance in terms of correlation (r)
and standard error of estimate (SEE). The best model is illustrated
in Eq. (1).
l
l
pMIC ¼ 1:944ðꢀ0:493ÞBEHm6 þ 0:538ðꢀ0:125ÞARR
l
ꢁ 26:977ðꢀ5:701ÞG3u ꢁ 1:940
ð1Þ
l
N = 14; r = 0.904; r2 = 0.818; s = 0.206; F = 14.981; p = 0.0005,where
figures in parentheses denote the standard error of the regression
coefficient, N is the number of compounds, r is the correlation
coefficient, s is the standard deviation of the regression and F is
the value of the Fisher’s test for the overall significance of the equa-
tion. This model with P99% statistical significance (probability
p = 0.0005 explained 81.8% of the variance of the anti-TB activity
of the 14 compounds. The positive correlation of pMIC with BEHm6
(sixth highest eigen value of burden matrix corresponding to atomic
mass) and ARR (fraction of aromatic atoms) descriptors indicates
their conducive effect towards inhibition of mycobacterium species.
The negative correlation of pMIC with G3u (third component sym-
metry directional WHIM index) indicates its negative contribution
towards inhibition of mycobacterium species.
l
Therefore, it can be concluded that the substitution with more
hydrophobic/bulky groups in the site 1 may lead to more active
compounds with lower MIC values.
Among the bromo substituted compounds (R = Br in site 1), the
substitution of more electron withdrawing groups such as halo-
gens, nitro etc. at the ortho position of the aromatic ring (site 2,
Fig. 1) of provided compounds viz. 1, 3, 5, 6, 10, 11 and 12 with
comparatively better antitubercular activity (MIC <0.8 lg/mL).
In order to explore the important physicochemical and structural
parameters responsible for the modulation of the anti-TB activities
of the synthesized compounds, it appeared of interest to develop a
linear regression quantitative-SAR (QSAR) model considering anti-
TB activities (MIC) of a set of 14 compounds and a set of 454 descrip-
tors generated using Dragon13 software. The linear regression meth-
od implemented in the Systat (v12)14 software was used to develop
the quantitative relationship between dependent (pMIC) and the
independent (454 Dragon descriptors) variables. Stepwise multi
parameter regression analysis by forward elimination provided a
set of three independent variables viz. BEHm6,15 ARR16 and G3u17
whose definitions are illustrated in Table 2.
The important descriptors included in the best QSAR equation
along with the observed and predicted pMIC values of 14 com-
pounds are given in Table 3. The 2D scatter plot between the ob-
served and predicted pMIC values of the 14 compounds is shown
in Figure 2.
In order to assess the predictive ability of the developed best
QSAR model (equation 1), the inactive compounds viz. 2, 9, 14,
These three variables were found to be a good correlate for the
pMIC values of the 14 compounds as anti-TB agents. The pearson
correlation matrix is given below.
16, 18, 20–22 with MIC values >12.5
model predicted all of these compounds inactive with MIC values
>33 g/mL. This analysis further proved the robustness of the best
lg/mL were used. The best
l

S. Singh et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2597–2600
2599
Table 1
Table 2
Structures and in vitro activities of the title compounds
Definitions of the best three parameters
Compd
R
R0
MICa
0.4
Mpb
121
SN Variable’s
name
Definition
O2N
1
BEHm6
Sixth highest eigen value of Burden matrix/weighted by
atomic masses
1
Br
2
3
ARR
G3u
Aromatic ratio
Third component symmetry directional WHIM index/
unweighted
2
3
4
5
6
Br
Br
Br
Br
Br
>12.5
0.8
104
128
145
123
123
N
I
Table 3
Dragon descriptors, observed (Obsd) and predicted (Pred.) anti-TB activities of the 14
compounds used in QSAR model development
Cl
3.12
N
N
Compd
Dragon descriptors
Anti-TB activity, pMIC (
Obsd Pred.
0.398
lg/mL)
BEHm6
ARR
G3u
0.8
0.4
OCH3
1
3
4
5
6
3.141
3.141
3.238
3.022
3.205
3.084
2.791
3.141
3.156
3.023
3.037
3.138
2.881
2.961
0.667
0.636
0.483
0.609
0.609
0.583
0.636
0.636
0.467
0.609
0.609
0.625
0.667
0.667
0.162
0.164
0.172
0.174
0.164
0.158
0.164
0.173
0.149
0.159
0.159
0.189
0.174
0.177
0.334
0.280
Cl
Cl
0.097
ꢁ0.494
0.097
ꢁ0.285
ꢁ0.221
0.404
0.398
7
8
ꢁ0.193
ꢁ0.494
0.097
ꢁ0.207
ꢁ0.401
0.037
7
8
Br
Br
1.56
3.12
105
135
HN
F
OCH3
10
11
12
13
15
17
19
0.097
0.176
0.398
0.185
ꢁ0.193
ꢁ0.796
ꢁ0.494
ꢁ0.796
ꢁ0.325
ꢁ0.938
ꢁ0.495
ꢁ0.421
9
Br
Br
>12.5
90
N
10
0.8
0.8
115
Br
N
11
12
Br
Br
125
121
O
N
0.4
H3C
HN
CH3
13
14
Br
Br
1.56
215
ssc
>12.5
NH2
O
15
16
17
Br
6.25
132
178
170
HN
Cl
N
Cl
NO2
NO2
>12.5
Figure 2. 2D scatter plot between the observed and predicted pMIC values of the 14
compounds.
CH3
QSAR model and provided a confidence in its utility in the predic-
tion of the designed compounds prior to their synthesis and biolog-
ical evaluation.
It can be concluded that the hydrazinecarbothioamide repre-
sent a promising bioactive core (substructure). The incorporation
of the important groups at site 1 and site 2 (Fig. 1) has led to potent
3.12
N
18
19
NO2
NO2
>12.5
ss
I
Br
6.25
129
anti-TB compounds viz. 1, 6 and 12 with MIC of 0.4
pounds viz. 3, 5, 10 and 11 have been found to be of comparatively
lesser activity with MIC value of 0.8 g/mL. The above SAR and
QSAR analyses comprising design and synthesis of anti-TB agents
have provided vital informations for potential inhibition of the
Mtb which may be useful in the design of the compounds with
more potent anti-TB activities.
lg/mL. Com-
F
20
21
22
NO2
NO2
NO2
>12.5
158
134
157
l
>12.5
>12.5
OCH3
CH3
Acknowledgements
INH
ETHAMBUTOL
0.02
0.10
The authors are thankful to the CSIR and MOH, New Delhi for
providing fellowship, to Mr. K. K. Roy for valuable suggestions
and to Mr. A. S. Kushwaha for technical assistance.
a
b
c
Minimum inhibitory concentration (
Melting point (°C).
Semi-solid.
lg/mL).

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S. Singh et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2597–2600
additional 2–3 h and kept as such overnight. The separated crystals were
References and notes
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