Synthesis and in vitro antitubercular activity of some 1-[(4-sub)phenyl]-3- (4-{1-[(pyridine-4-carbonyl)hydrazono]ethyl}phenyl)thiourea

Article abstract of DOI:10.1016/j.bmcl.2005.11.004

Various isonicotinyl hydrazones were prepared by reacting isonicotinyl hydrazide [INH] with 1-(4-acetylphenyl)-3-[(4-sub)phenyl]thiourea and were tested for their antimycobacterial activity in vitro against Mycobacterium tuberculosis H₃₇R_v

Full text of DOI:10.1016/j.bmcl.2005.11.004

Bioorganic & Medicinal Chemistry Letters 16 (2006) 876–878
Synthesis and in vitro antitubercular activity of some
1-[(4-sub)phenyl]-3-(4-{1-[(pyridine-4-carbonyl)
hydrazono]ethyl}phenyl)thiourea
Dharmarajan Sriram,* Perumal Yogeeswari and Kasinathan Madhu
Medicinal Chemistry Research Laboratory, Pharmacy group, Birla Institute of Technology and Science, Pilani 333031, India
Received 8 September 2005; revised 18 October 2005; accepted 2 November 2005
Available online 21 November 2005
Abstract—Various isonicotinyl hydrazones were prepared by reacting isonicotinyl hydrazide [INH] with 1-(4-acetylphenyl)-3-[(4-
sub)phenyl]thiourea and were tested for their antimycobacterial activity in vitro against Mycobacterium tuberculosis H37Rv and
INH-resistant M. tuberculosis using the BACTEC 460 radiometric system. Among the synthesized compounds, 1-(4-fluorophe-
nyl)-3-(4-{1-[(pyridine-4-carbonyl)-hydrazono]ethyl}phenyl)thiourea (4d) was found to be the most potent compound with a min-
imum inhibitory concentration of 0.49 lM against M. tuberculosis H37Rv and INH-resistant M. tuberculosis. When compared to
INH, 4d was found to be 3 and 185 times more active against M. tuberculosis H37Rv and INH-resistant M. tuberculosis, respectively,
with a selectivity index of >300.
ꢀ 2005 Published by Elsevier Ltd.
Tuberculosis (TB) is the most prevalent infectious dis-
ease worldwide and a leading killer caused by a single
infectious agent, that is, Mycobacterium tuberculosis.1,2
According to a World Health Organization (WHO)
tance to INH is related to katG mutations and deletions,
and second to chromosomal mutations in inhA and
kasA.4 Antibacterial resistance to a drug can be counter-
acted by designed new derivatives.7 Further, pharmaco-
kinetic properties and cellular permeability of a drug can
be modulated by derivatization to bioreversible forms of
this drug, namely hydrazones.8,9 On the other hand,
thiourea derivatives were active against many Mycobac-
teria.10 The current work describes the incorporation of
INH in a N,N0-diaryl thiourea moiety and screening for
activity against M. tuberculosis H37Rv and an INH-resis-
tant clinical isolate.
3
report , M. tuberculosis currently infects over 2 billion
people worldwide, with 30 million new cases reported
each year. This intracellular infection accounts for at
least 3 million deaths annually. In most parts of the
world, we are limited to combinations of five drugs to
treat TB effectively, namely rifampicin, isoniazid
(INH), ethambutol, streptomycin, and pyrazinamide.
Problems in the chemotherapy of tuberculosis arise
when patients develop bacterial resistance to any of
these first-line drugs and because second-line drugs, such
as ethionamide, aminosalicylic acid, cycloserine, amika-
cin, kanamycin, and capreomycin, are too toxic and
cannot be employed simultaneously.4 The reemergence
of TB infection is further complicated by an increase
in cases, which are resistant to conventional antitubercu-
lar drug therapy.5 On the other hand, in spite of toxicity
on repeated dosing isoniazid is still considered to be a
first-line drug for chemotherapy of tuberculosis.6
Recently, it was suggested that the mechanism of resis-
Isonicotinyl hydrazones 4a–4f described in this study are
shown in Table 1, and a reaction sequence for the
preparation is outlined in Scheme 1. The starting
compounds (sub)-phenyl isothiocyanates 1a–1f were
prepared according to known procedures11 from appro-
priate anilines. Phenyl isothiocyanates were converted to
thiourea 3a–3f by refluxing with 4-amino acetophenone
2 for 17 h. The reaction between compounds 3a–3f with
isonicotinyl hydrazide in ethanolic solution took place
in the presence of glacial acetic acid. On cooling, the pre-
cipitate was collected, washed with cold ethanol, and
recrystallized from a mixture of DMF and water which
afforded hydrazones 4a–4 f with 50–64% yield. The puri-
ty of compounds was checked by TLC and elemental
analyses. Both analytical and spectral data (1H NMR,
Keywords: Antimycobacterial; Isoniazid; Hydrazones.
*
Corresponding author. Tel.: +91 1596 244684; fax: +91 1596
244183; e-mail: dsriram@bits-pilani.ac.in
0960-894X/$ - see front matter ꢀ 2005 Published by Elsevier Ltd.
doi:10.1016/j.bmcl.2005.11.004

D. Sriram et al. / Bioorg. Med. Chem. Lett. 16 (2006) 876–878
877
Table 1. Physical constants and antimycobacterial activity of the synthesized compounds
Compound
R
Molecular formula
Yield (%)
Mp (ꢁC)
logPa
IC50 (lM)
MICb (lM)
M. tuberculosis INH-resistant
37Rv
H
M. tuberculosis
4a
4b
H
C
21H19N5SO
50
55
51
59
64
50
—
144
234
218
241
223
214
—
3.24
3.18
3.05
3.19
3.27
3.45
0.58
160.47
154.89
133.44
>153.4
>149
4.00
1.93
1.66
0.49
0.47
0.89
1.46
4.00
3.86
1.66
0.49
1.85
1.79
90.94
4-CH3
4-Br
4-F
C22H21N5SO
C21H18N5SOBr
C21H18N5SOF
C22H21N5SO2
C23H23N5SO2
—
4c
4d
4e
4-OCH3
4-OC2H5
—
4f
INH
144.16
>454.7
a logP was calculated using online www.logp.com site.
b MIC = minimum inhibitory concentration.
H2N
COCH3
R
NCS
+
active than INH [MIC: 1.46 lM] against M. tuberculosis
H37Rv. All the compounds were more potent than INH
[MIC: 90.94 lM] against INH-resistant M. tuberculosis
with MICs ranging from 0.49 to 4.0 lM. Compound 4d
was found to be 185 times more active than INH against
this isolate. The order of activity with respect to the sub-
stituents in the 4th position is >F > OCH3 > OC2H5 > Br
> CH3 >H.
1a-f
2
C2H5OH
17h
S
All the compounds were further examined for toxic-
ity (IC50) in a mammalian VERO cell line at con-
centrations of 6.25 and 62.5 lg/mL. After 72 h
exposure, viability was assessed on the basis of cel-
lular conversion of MTT into a formazan product
using the Promega Cell Titer 96 non-radioactive cell
proliferation assay.13 The compounds were non-toxic
as represented in Table 1 and the selectivity index
(IC50/MIC) for the most active compound 4d was
more than 312.
NH C HN
COCH3
R
3a-f
INH
N
S
NNHCO
C CH3
NH C HN
R
The lipophilicity of the synthesized compounds in-
creased remarkably compared with that of the parent
drug, INH. This may render them more capable of pene-
trating various biomembranes,14 consequently improv-
ing their permeation properties through mycobacterial
cell membranes.
4a-f
Scheme 1. Synthetic protocol of isonicotinoyl hydrazones.
13C NMR, and mass spectra) of all the synthesized
compounds were in full agreement with the proposed
structures.12 Lipophilicity of the synthesized derivatives
4a–4f and that of the parent compound, INH, are
expressed in terms of their logP values. These values
were computed with a routine method called calculated
logP (ClogP) using Alchemy software.
Among the newer derivatives, compound 4d showed a
promising activity in vitro. It is conceivable that these
derivatives showing antimycobacterial activity can be
further modified to exhibit better potency than the stan-
dard drugs. These results need to be refined in terms of
degradation kinetic measurements and stability studies
of the synthesized derivatives.
The synthesized compounds 4a–4f were tested for
their antimycobacterial activity in vitro against
M. tuberculosis H37Rv and clinical isolate of INH-resis-
tant M. tuberculosis [obtained from Tuberculosis
Research Center, Chennai, India] using the BACTEC
460 radiometric system. All the compounds were further
examined for toxicity (IC50) in a mammalian cell line,
VERO cells. The results are summarized in Table 1. Rapid
glance at the obtained results revealed that the com-
pounds 4a–4f exhibited very good antimycobacterial
activity. Among the synthesized compounds, compounds
4d and 4e were found to be the most potent compounds
[MIC: 0.49 and 0.47 lM, respectively] and were more
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