Synthesis, antitubercular evaluation and 3D-QSAR study of N-phenyl-3-(4-fluorophenyl)-4-substituted pyrazole derivatives

Article abstract of DOI:10.1016/j.bmcl.2011.10.059

As a part of our ongoing research to develop novel antitubercular agents, a series of N-phenyl-3-(4-fluorophenyl)-4-substituted pyrazoles have been synthesized and tested for antimycobacterial activity in vitro against Mycobacterium tuberculosis H37Rv str

Full text of DOI:10.1016/j.bmcl.2011.10.059

Bioorganic & Medicinal Chemistry Letters 22 (2012) 666–678
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis, antitubercular evaluation and 3D-QSAR study of
N-phenyl-3-(4-fluorophenyl)-4-substituted pyrazole derivatives
R.C. Khunt a, V.M. Khedkar b, R.S. Chawda a, N.A. Chauhan a, A.R. Parikh a, E.C. Coutinho b,
⇑
a Department of Chemistry, Saurashtra University, Rajkot, Gujarat, India
b Department of Pharmaceutical Chemistry, Bombay College of Pharmacy, Kalina, Santacruz (E), Mumbai 400 098, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 July 2011
Revised 26 September 2011
Accepted 18 October 2011
Available online 30 October 2011
As a part of our ongoing research to develop novel antitubercular agents, a series of N-phenyl-3-(4-fluo-
rophenyl)-4-substituted pyrazoles have been synthesized and tested for antimycobacterial activity
in vitro against Mycobacterium tuberculosis H37Rv strain using the BACTEC 460 radiometric system. A
3D-QSAR study based on CoMFA and CoMSIA was performed on these pyrazole derivatives to correlate
their chemical structures with the observed activity against M. tuberculosis. The CoMFA model provided
a significant correlation of steric and electrostatic fields with the biological activity while the CoMSIA
model could additionally shed light on the role of hydrogen bonding and hydrophobic features. The
important features identified in the 3D-QSAR models have been used to propose new molecules whose
activities are predicted higher than the existing systems. This study provides valuable directions to our
ongoing endeavor of rationally designing more potent antitubercular agents.
Keywords:
Mycobacterium tuberculosis
Antitubercular agents
CoMFA
CoMSIA
Ó 2011 Elsevier Ltd. All rights reserved.
3D-QSAR
Pyrazole
Tuberculosis (TB) is currently the leading killer of youth,
women and patients suffering from AIDS. The duration of the pres-
ent antitubercular therapy leads to patient non-compliance and
this in turn has contributed to the development of drug resistance.1
In recent years, the pandemic of AIDS poses a major impact on the
worldwide spread of TB. However, since 1980s, the disease has
seen resurgence due to a variety of changes in social, medical
and economic factors. Concomitant with the resurgence of TB, is
the appearance of multidrug-resistant TB which exposes the frail-
ties of the current drug armamentarium.2
Analysis (CoMSIA)17,18 studies were performed. The structure–
activity relationship derived from these analyses was fruitfully
utilized to design a set of novel pyrazole analogs whose activities
are predicted to surpass those in the original set.
4-Formylpyrazole was synthesized by the Vilsmeier reaction
which on Claisen condensation with substituted acetophenones
yielded the chalcones. Further, the chalcones were converted to a
The chemistry of heterocyclic compounds has been an area of
interest for the medicinal chemists working in the field of tubercu-
losis. A literature survey has revealed that pyrazole and their deriv-
atives containing the N–N bond are active against many
mycobacteria.3–6 It has been reported that C6-substituted pyrimi-
dine derivatives display antitubercular activity and pyrazole deriv-
atives possess significant anti-HIV activity. This fact motivated us
to design chemical prototypes bearing these two moieties that
would be active against both drug-resistant strains as well as
against latent bacteria.7–14
In order to study and deduce the correlation between structure
and biological activity of these N-phenyl-3-(4-fluorophenyl)-4-
substituted pyrazole derivatives, Comparative Molecular Field
Analysis (CoMFA)15,16 and Comparative Molecular Similarity
⇑
Corresponding author.
E-mail addresses: drrckhunt12@yahoo.com (R.C. Khunt), evans@bcpindia.org
Figure 1. Atom-fit alignment: Training set aligned on minimum energy conforma-
tion of most active compound 11.
(E.C. Coutinho).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.10.059

R. C. Khunt et al. / Bioorg. Med. Chem. Lett. 22 (2012) 666–678
667
variety of N-phenyl-3-(4-fluorophenyl)pyrazole analogs by reaction
with hydrazine hydrate. It must be noted here that the pyrazoline
ring system has been constructed by nucleophilic cycloaddition of
hydrazine hydrate with chalcones. The chalcones (II) are synthes-
ised by the condensation of N-phenyl-3-(4-fluorophenyl)pyrazole-
4-carboxaldehyde with aromatic ketones. This reaction produces a
cis configuration of the double bond as judged by the coupling con-
stant, J = 8.86 Hz, obtained in the NMR experiment. Due to the for-
mation of cis isomer of chalcones (II), the nucleophilic addition of
hydrazine results in the formation of the R-isomer of the pyrazoline
(III) which was further confirmed by a plane polarised light exper-
iment that showed right angle polarization. Nitroso and benzoyl
groups were introduced at position-1 on the pyrazoline ring by
treatment, respectively, with nitrous acid and benzoyl chloride.
The chalcones (II) on condensation with thiourea and aminoguani-
dine gave 2-thio (V) or 2-amino-4-arylpyrimidines (VI and VII)
(Scheme 1). The yields varied from 76% to 84% in case of chalcones
(II); for the pyrazolines (III) the yields varied from 59% to 71% and
from 51% to 69% for the pyrimidines (VI) and (VII). The structures
of all compounds were confirmed by IR, 1H and 13C NMR and mass
spectroscopy (refer to Supplementary data).
between structure and activity, 3D-QSAR (CoMFA and CoMSIA)
studies were carried out.
The 3D-QSAR studies (CoMFA and CoMSIA) were carried out
with the QSAR module integrated in Sybyl 7.1 (Tripos Inc., USA)20
running on a Pentium IV computer under the Centos WS 4.8 as OS.
The CoMFA model generated with a training set of 33 N-phenyl-
3-(4-fluorophenyl)-pyrazole analogs (carrying different pyrazoline
and pyrimidine substituents at 4th position of pyrazole nucleus) is
a six-component model with a cross-validated (leave-one-out)21,22
correlation coefficient of 0.64 and standard error of 0.10. The non
cross-validated Partial Least Squares (PLS)23 analysis produced a
model with regression coefficient (r2) of 0.98 with F-test value of
175.52, indicating a good linear correlation between the observed
and predicted activities for the molecules in the training set. The
relative contribution of steric and electrostatic fields to the QSAR
equation was found to be 43.3% and 56.7% respectively. External
validation with the test set of 18 molecules yielded a predictive
r2 of 0.60, signifying the ability of the model to predict the activity
of molecules beyond those used in its construction. An r2 value of
0.98 obtained for 100 runs of bootstrap analysis24 further supports
the robustness and the statistical validity of the derived CoMFA
model. The model was also tested for chance correlation by
y-scrambling25 (100 cycles) which yielded a poor r2 of 0.18, there-
by eliminating the possibility of chance correlation. The statistics
of this CoMFA model generated are shown in (Table 2).
Antitubercular activity was determined using the modified
BACTEC 460 system in which stock solutions as test molecules
were prepared in dimethylsulfoxide (DMSO) at 1 mg/ml concentra-
tion and sterilized by passage through 0.22 l
M PFTE filters.19 All
51 compounds were tested for antitubercular activity against M.
tuberculosis H37Rv strain. The concentrations required for 50%
and 90% inhibition are given in Table 1 and these are in the range
The same structural alignment and training/test sets as defined
in the CoMFA studies were used to derive the CoMSIA models
(Fig. 1). Several models were generated considering steric, electro-
static, hydrogen bonding and hydrophobic fields separately or in
various combinations. With steric, electrostatic, H-bond donor
and hydrophobic (SEDH) descriptor fields the CoMSIA model with
5 components produced a non cross-validated r2 of 0.94, q2 of 0.63,
standard error of estimate 0.15, F-test value 190.49. The bootstrap
r2 of 0.97 obtained for 100 runs suggests a good internal consis-
tency within the underlying dataset. Significantly low value of r2,
of 0.47–118.00
pen-1-one at the 4th position of the pyrazole ring produced the
most active molecule (Compound 11) with a IC50 of 0.47 M (Table
lM. Substitution of 1-(p-methoxyphenyl)-2-pro-
l
1). It is interesting to note that for compound 46 with a 4-hydroxy-
phenyl-2-aminopyrimidine at position-4 of the pyrazole ring,
concentrations of 0.88 and 0.47 lM are required for 90% and 50%
inhibition, respectively. Thus, to understand the relationship
O
N
N
+
R
O
40% NaOH
F
F
F
R
R
N
Guanidine
Hydrochloride
Thiourea
N
N
N
N
N
H
N
S
N
N
N
NH2
R
VII
VI
II
F
O
F
R
NH2NH2
F
F
R
N
N
NO
N
N
R
HNO2
N
Benzoyl chloride
N
H
N
N
N
N
N
N
Ph
O
V
III
IV
Scheme 1.

668
R. C. Khunt et al. / Bioorg. Med. Chem. Lett. 22 (2012) 666–678
that is, 0.16 obtained with randomized activity (100 cycles) reveals
that the model is stable and the results are not based on chance
correlation. The relative contributions of the steric, electrostatic,
hydrogen-bond donor and hydrophobic fields to this model are
27.3%, 15.3%, 15.7% and 41.6%, respectively. Further a predictive
r2 of 0.62 obtained for the test set compounds proved the predic-
tive ability of the model. The statistics of this model are summa-
rized in Table 2.
The other combinations viz (i) steric, electrostatic and hydrogen
bond donor (SED), (ii) electrostatic, hydrophobic and hydrogen
Table 1
N-Phenyl-3-(4-fluorophenyl)-4-substituted pyrazole derivatives
Sr. No.
Structure
Melting point (°C)
Yield (%)
IC90
(
l
M)
IC50
(
lM)
pIC90
4.79
pIC50
4.98
F
F
F
F
F
F
F
N
N
N
N
N
N
N
1
139–141
81
16.34
10.08
7.96
10.52
6.39
7.18
33.87
7.14
7.46
N
N
N
N
N
N
N
O
O
O
O
O
O
O
O
2
3
4
5
6
179–181
192–194
209–211
188–190
239–241
78
70
73
86
84
5.00
5.10
4.15
5.09
5.07
5.19
5.14
4.47
5.15
5.13
CH
3
CH
3
Cl
71.34
F
8.09
OH
8.47
7
177–179
74
45.38
26.17
4.34
4.58
HO
F
NO
2
N
8
9
190–192
217–219
82
77
53.48
18.05
12.70
9.77
4.27
4.74
4.90
5.01
N
O
F
N
Br
N
O

R. C. Khunt et al. / Bioorg. Med. Chem. Lett. 22 (2012) 666–678
669
Table 1 (continued)
Sr. No. Structure
Melting point (°C)
Yield (%)
IC90
(l
M)
IC50
(
lM)
pIC90
pIC50
N
F
N
10
173–175
76
13.50
8.08
4.87
5.09
O
S
F
N
11
139–141
59
12.26
0.47
4.91
6.33
N
O
HN
N
CH3
F
N
12
163–165
65
4.08
5.38
5.39
5.27
N
CH3
HN
N
F
N
13
14
141–143
149–151
66
70
68.65
49.76
43.29
31.02
4.16
4.30
4.36
4.51
N
Cl
HN
N
N
N
F
F
N
N
N
N
OH
HN
HN
15
254–256
62
31.72
28.14
4.50
4.55
HO
F
N
N
16
127–129
71
68.74
39.00
4.16
4.41
HN
N
NO2
F
N
17
18
159–161
156–158
64
68
22.85
7.90
4.64
3.90
5.10
4.13
N
Br
HN
N
F
N
126.56
74.40
N
NH2
HN
N
(continued on next page)

670
R. C. Khunt et al. / Bioorg. Med. Chem. Lett. 22 (2012) 666–678
Table 1 (continued)
Sr. No.
Structure
Melting point (°C)
Yield (%)
IC90
(l
M)
IC50
(
lM)
pIC90
pIC50
F
N
O
N
N
N
N
19
219–221
71
86.38
23.77
3.48
50.40
13.82
3.02
4.06
4.30
N
N
N
N
N
N
N
F
N
O
CH3
20
21
22
239–241
225–227
200–202
60
64
53
4.62
5.46
<3.72
4.86
5.52
4.29
O
F
N
O
CH3
F
N
O
>191.94
51.42
Cl
N
F
N
O
N
23
196–198
61
3.22
2.65
5.49
5.58
F
N
N
F
N
O
N
24
270–272
63
>187.42
57.43
<3.73
4.24
NO2
N
N

R. C. Khunt et al. / Bioorg. Med. Chem. Lett. 22 (2012) 666–678
671
Table 1 (continued)
Sr. No. Structure
Melting point (°C)
Yield (%)
IC90
(l
M)
IC50
(
lM)
pIC90
pIC50
F
F
F
F
N
O
N
N
N
25
250–252
67
101.40
75.69
88.74
42.44
37.79
46.92
3.99
4.37
4.42
4.33
N
N
N
N
N
N
NO2
N
O
26
227–229
64
4.12
Br
N
O
27
196–198
69
4.05
S
N
N
N
N
N
N
N
N
28
29
30
233–235
254–256
221–223
58
67
64
>233.96
118.80
25.27
22.49
<3.63
4.39
4.48
3.93
4.60
4.65
N
N
N
N
N
N
N
N
N
HO
F
O
40.51
NO2
N
O
F
33.43
N
NO2
O
F
31
248–250
68
33.71
21.35
4.47
4.67
Br
N
O
(continued on next page)

672
R. C. Khunt et al. / Bioorg. Med. Chem. Lett. 22 (2012) 666–678
Table 1 (continued)
Sr. No.
Structure
Melting point (°C)
Yield (%)
IC90
(
l
M)
IC50
(
lM)
pIC90
4.42
pIC50
4.68
F
F
F
N
N
N
N
N
N
32
254–256
54
37.80
20.89
NH2
N
N
N
O
33
257–259
51
46.26
26.42
4.33
4.58
N
N
S
N
O
CH3
34
35
36
37
38
39
256–258
230–232
223–225
221–223
240–242
198–200
66
55
67
69
66
67
35.46
22.19
10.31
69.24
8.29
4.45
4.74
<3.64
4.95
4.88
4.37
4.65
4.99
4.16
5.08
4.92
4.55
HN
N
S
F
N
Cl
N
18.04
HN
N
S
F
N
OH
N
>227.02
HN
N
S
F
N
N
11.15
HN
HN
HN
N
HO
S
F
N
NO2
N
13.14
12.16
N
S
F
N
N
42.95
27.93
NO2
N
S

R. C. Khunt et al. / Bioorg. Med. Chem. Lett. 22 (2012) 666–678
673
Table 1 (continued)
Sr. No. Structure
Melting point (°C)
Yield (%)
IC90
(
l
M)
IC50
(
l
M)
pIC90
4.42
pIC50
F
N
N
N
N
Br
N
N
N
N
40
177–179
52
38.36
114.19
22.09
22.56
5.94
3.94
4.66
4.65
5.23
4.02
HN
HN
HN
N
N
N
N
N
S
F
NH2
41
42
43
44
215–217
159–161
221–223
230–232
60
65
59
61
>227.53
<3.64
S
F
F
F
F
86.43
4.06
S
S
9.94
5.00
H2N
N
N
N
N
Cl
N
N
N
N
>226.30
95.47
<3.65
N
N
N
N
N
H2N
F
45
46
47
226–228
267–269
244–246
62
61
66
84.27
36.76
4.07
6.05
4.18
4.43
6.33
4.24
N
H2N
F
OH
0.88
0.47
N
H2N
F
65.94
56.96
N
OH
H2N
(continued on next page)

674
R. C. Khunt et al. / Bioorg. Med. Chem. Lett. 22 (2012) 666–678
Table 1 (continued)
Sr. No.
Structure
Melting point (°C)
Yield (%)
IC90
(
l
M)
IC50
(
lM)
pIC90
<3.66
pIC50
4.12
F
N
N
N
N
NO2
N
N
N
N
48
270–272
58
>220.04
>220.04
14.51
75.36
52.92
10.63
13.77
N
N
N
N
H2N
F
49
50
51
233–235
257–259
253–255
51
67
52
<3.66
4.84
4.82
4.28
4.97
4.86
O
N+
O-
N
H2N
F
Br
N
H2N
F
NH2
14.99
N
N
H2N
Table 2
Statistical results of the CoMFA and CoMSIA analyses
CoMFA
CoMSIA (SEDH)
N
33
33
q2
0.64
0.98
0.60
0.63
0.94
0.62
r2
r2pred
r2bs
0.98
0.97
r2 y-scrambling
F
0.18
175.52
0.10
6
0.16
190.49
0.15
5
SE
PLS components
Field contribution
Steric
Electrostatic
H-bond donor
H-bond acceptor
Hydrophobic
0.43
0.57
—
—
—
0.27
0.15
0.16
—
Figure
2. N-Phenyl-3-(p-fluorophenyl)-4-[3-(p-anisyl)-pyrazoline-5-yl]pyrazole
(Compound 11).
0.42
sake of brevity only the CoMFA steric and electrostatic contours
have been discussed. The CoMFA steric contour map (Fig. 3a)
shows large green isopleths around the para position of the phenyl
ring marked as (E) in Fig. 2. The steric contours suggest that bulky
substituents could be added around this position to improve the
potency. This is evident from the fact that molecules 2 (4-methoxy),
3 (4-methyl), 11 (4-methoxy) and 12 (4-methoxy) and 46 (4-hydro-
xy) show higher activity than compounds that lack a substituent at
the para position of the phenyl ring (E). On the other hand, small
yellow contours disfavoring steric bulk are also observed in the
vicinity of the ortho and meta positions of the phenyl ring (E)
suggesting that steric substituents at these positions would be det-
rimental for activity. This is substantiated by the fact that mole-
cules 7 (2-hydroxy), 15 (2-hydroxy), 16 (3-nitro), 28 (2-hydroxy),
bond donor (EHD) and (iii) steric, electrostatic, hydrogen bond do-
nor and acceptor (SEDA) in CoMSIA gave models with relatively
low values for r2 and rp2red
.
The results of the CoMFA and CoMSIA studies can be visualized
as 3D ‘coefficient contour maps’ contoured in terms of contribu-
tion. The most active compound 11 (Fig. 2) has been used to dem-
onstrate the areas where a change in the molecular structure may
affect its activity. The individual contributions of the favored and
disfavored CoMFA/CoMSIA descriptor fields was fixed at 80% and
20%, respectively.
The CoMSIA steric and electrostatic contour maps were found to
be in harmony with that of the CoMFA model and therefore for the

R. C. Khunt et al. / Bioorg. Med. Chem. Lett. 22 (2012) 666–678
675
Figure 3. The CoMFA molecular interaction fields around Compound 11 (a) steric contours—green contours indicate regions where bulky groups increase activity, whereas
yellow contours indicate regions where bulky groups decrease activity (b) electrostatic contours—red contour indicate regions where negative groups increase activity,
whereas blue contours indicate regions where negative charge decreases activity.
30 (3-nitro) and 49 (3-nitro) with substituents around the ortho
and meta positions of the phenyl ring (E) have activity lower than
compounds with a substitution at the para position. There is a bal-
ance as noted by the green (favored) and yellow (disfavored) con-
tours for steric groups (Fig. 3a) over the 4,5-dihydropyrazole (D)
ring. Steric groups are found to be disfavored (yellow contour) over
the nitrogen atoms of ring D. This is justified from the fact that
molecule1s9, 20, 22, 24, 25, 26, 27, 28, 29, 30, 31, 32 and 33 carrying
a substituent on the pyrazoline nitrogen have poor antitubercular
activity. On the other hand, the steric groups, shown in green,
are preferred over the rest of the 4,5-dihydropyrazole (D) ring.
Substituents on molecules 4, 35, 37, 43 and 46 were found to ex-
tend into this green contour.
The electronegative contours are found to influence the 3D-QSAR
model more than the electropositive counterpart (Fig. 3b). No sig-
nificant contribution is observed for electropositive substitution
but both CoMFA as well as CoMSIA models display large red con-
tours on the pyrazole (B) as well as the 4,5-dihydropyrazole (D) ring,
suggesting that electronegative substitutions on these rings could
be beneficial for the activity. An additional red contour favoring
electronegative substitution is observed in the vicinity of the para
position of the phenyl ring (E). Molecules 2, 5, 6, 11, 23 and 46 car-
rying electronegative substituents at these positions were found to
be more active over those lacking substitutions. Only a small blue
contour favoring electropositive substitution is observed around
the 4th and 5th positions of the dihydropyrazole ring (D).
As regards H-bonding, a major cyan isopleth is observed in the
vicinity of the nitrogen atoms of the 4,5-dihydropyrazole (D) ring
suggesting that hydrogen bond donor functionality at these posi-
tions would enhance the activity while purple isopleths disfavor-
ing H-bond donor functionality are observed around the nitrogen
atoms of pyrazole ring (B) (Fig. 4a).
The hydrophobic CoMSIA fields (Fig. 4b) shown in yellow, indi-
cate that the substituents at the para position of phenyl ring (E)
need to be hydrophobic in nature so as to enhance the activity.
Molecules 2, 11, 12 and 46 show higher activities than compounds
that lack a substituent at the para position of the phenyl ring (E).
Another yellow contour was also seen over the phenyl ring C sug-
gesting that this ring is important for the activity. On the other
hand white contours were observed around the nitrogen atoms
of the 4,5-dihydropyrazole (D) ring signifying that the substituents
at these positions need to be hydrophilic.
The structural features identified in the QSAR analysis were
strategically utilized in the design of novel molecules with
improved activity. Modifications were made to the core N-phe-
nyl-3-(p-fluorophenyl)pyrazole structure as recommended by the
CoMFA and CoMSIA isopleths. A few new molecules along with
their predicted activities are given in Table 3. It is noteworthy that
the activities of these new molecules are higher than most of the
molecules in the training set. This indicates that the 3D-QSAR mod-
els presented here are powerful enough to suggest improvement in
the poorly active molecules.
Figure 4. The CoMSIA molecular interaction fields around Compound 11: (a) hydrogen bond donor contours—cyan contours indicate regions where H-bond donor group
increases activity, whereas purple contours indicate regions where H-bond donor group decreases activity. (b) hydrophobic contour plots-yellow contours indicate regions
where hydrophobic groups increases activity, whereas white contours indicate regions where hydrophobic group decreases activity.

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R. C. Khunt et al. / Bioorg. Med. Chem. Lett. 22 (2012) 666–678
InsilicoADMEand toxicityprofileswere builtfor theN-phenyl-3-
(p-fluorophenyl)-4-substituted pyrazole analogs with an objective
to gain an insight into their pharmacokinetic and toxicity attributes.
This was done with the ADME/Tox web-box v3.526,27 tool available
Table 3
Some antitubercular molecules designed with CoMFA and CoMSIA models with their predicted activities
Molecule
Chemical structure
Predicted activity (pIC50)
H2N
N
N
O
NH2
PYR01
6.66
N
N
F
F
H2N
N
N
OH
PYR02
PYR03
PYR04
PYR05
6.15
6.22
6.06
6.64
N
N
F
H2N
N
N
OH
N
N
F
F
H2N
N
N
OH
N
N
OH
HO
H2N
N
N
O
N
N
F

R. C. Khunt et al. / Bioorg. Med. Chem. Lett. 22 (2012) 666–678
677
)
Table 3 (continued)
Molecule
Chemical structure
Predicted activity (pIC50
H2N
N
N
O
PYR06
PYR07
PYR08
6.71
N
N
F
F
H2N
N
N
F
6.15
N
N
F
H2N
N
N
F
6.21
N
N
F
F
online. The ADME and toxicity profiles are given in the Supplemen-
tary data. Most of the molecules have a pKa for the basic group in the
range of 1.0–5.0 indicating that the pyrazole ring is weakly basic; for
theacidic group it is around9.0 suggesting thatthehydroxyl groupis
weakly acidic. The average plasma protein binding for these mole-
cules is around 94–99%. These molecules will predominantly bind
to alpha1-acid glycoprotein and albumin. The molecules also display
fairly good oral bioavailability with very low susceptibility to acid
hydrolysis in the stomach. As ADME/Tox web-box v3.5 does not pre-
dict clearance values, the bioavailability profile may have been de-
rived only from the solubility and permeability of the molecules.
Initial perusal of this data indicates that for most of these molecules
the logD and logP values suggest moderate aqueous solubility. Tox-
icity predictions depict a high oral as well as iv LD50 dose, signifying
that the molecules have a good safety margin. Also, these molecules
show a low potential for genotoxicity as depicted by the low scores
observed for the Ames test, except for molecules
28–33 for which the Ames score is predicted to be higher. Overall,
the predicted pharmacokinetic and toxicity profiles for these mole-
cules appear to be favorable for future lead optimization.
validated our initial proposition that use of a pyrazole and pyrim-
idine substituted pyrazole scaffold would lead to molecules with
potent antitubercular activity. The IC50 values for these compounds
ranged from 0.47 to 118.0 lM. 3D-QSAR analysis was performed to
rationalize the activity data for these pyrazole analogs. The CoMFA
and CoMSIA models developed in this study have good predictive
ability and can be useful in elucidating the relationship between
the structures and their biological activities. The CoMFA and CoM-
SIA models are able to shed light on the role of steric, electrostatic,
and hydrophobic fields around the molecules that can be strategi-
cally altered to modulate the antitubercular activity for these mol-
ecules. The pharmacokinetic and toxicity predictions for these
pyrazole analogs provides additional information on their meta-
bolic stability and safety profile which served as a guide to design
new candidates with higher antitubercular activity.
Acknowledgements
Dr. R.C.K. thanks Saurashtra University for infrastructure facili-
ties and DST, New Delhi for financial support under the Fast Track
Young Scientist Scheme. V.M.K. thanks the Lady Tata Memorial
Trust for the financial support. We also thank Dr. Cecil Kwong,
TAACF, USA, for the antitubercular screening. The computational
facilities were jointly provided by the All India Council of Technical
Education through grant (F. No. 8022/RID/NPROJ/RPS-5/2003-04),
the Department of Science and Technology through their FIST
Conclusion
The synthesis and biological evaluation of a series of N-phenyl-
3-(p-fluorophenyl)-4-substituted pyrazole derivatives as antitu-
bercular agents has been discussed. Most importantly, this work

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R. C. Khunt et al. / Bioorg. Med. Chem. Lett. 22 (2012) 666–678
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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.2011.10.059.
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