Synthesis and antituberculosis activity of new hydrazide derivatives

Article abstract of DOI:10.1002/ardp.200800048

The increasing clinical importance of drug-resistant mycobacterial pathogens, especially Mycobacterium tuberculosis, has lent additional urgency to microbiological research and new antimycobacterial compound development. For this purpose, new hydrazide derivatives of imidazo[1,2-a]pyridine were synthesized and evaluated for antituberculosis activity. The reaction of 2-[(2-carboxyimidazo[1,2-a]pyridine-3-yl)sulfanyl]acetic acid hydrazide with various benzaldehydes gave N-(arylidene)-2-[(2-carboxyimidazo[1,2-a]pyridine-3- yl)sulfanyl]acetic acid hydrazide derivatives. The chemical structures of the compounds were elucidated by IR, ¹H-NMR, FAB-MS spectral data and elemental analysis. Antituberculosis activities of the synthesized compounds were determined by broth microdilution assay, the Microplate Alamar Blue Assay in BACTEC 12B medium. The results were screened in vitro, using the BACTEC 460 Radiometric System against Mycobacterium tuberculosis H37Rv (ATCC 27294) at 6.25 μg/mL; the tested compounds showed significant inhibition.

Full text of DOI:10.1002/ardp.200800048

Arch. Pharm. Chem. Life Sci. 2008, 341, 721–724
Z. A. Kaplancikli et al.
721
Full Paper
Synthesis and Antituberculosis Activity of New Hydrazide
Derivatives
Zafer A. Kaplancikli1, Gulhan Turan-Zitouni1, Ahmet Ozdemir1, Jean-Claude Teulade2
1 Anadolu University, Faculty of Pharmacy, Department of Pharmaceutical Chemistry, Eskisehir, Turkey
2 Univ Clermont 1, UFR Pharmacie, Laboratoire de Chimie Organique, Clermont-Ferrand, France
The increasing clinical importance of drug-resistant mycobacterial pathogens, especially Myco-
bacterium tuberculosis, has lent additional urgency to microbiological research and new antimy-
cobacterial compound development. For this purpose, new hydrazide derivatives of imidazo[1,2-
a]pyridine were synthesized and evaluated for antituberculosis activity. The reaction of 2-[(2-car-
boxyimidazo[1,2-a]pyridine-3-yl)sulfanyl]acetic acid hydrazide with various benzaldehydes gave
N-(arylidene)-2-[(2-carboxyimidazo[1,2-a]pyridine-3-yl)sulfanyl]acetic acid hydrazide derivatives.
The chemical structures of the compounds were elucidated by IR, 1H-NMR, FAB-MS spectral data
and elemental analysis. Antituberculosis activities of the synthesized compounds were deter-
mined by broth microdilution assay, the Microplate Alamar Blue Assay in BACTEC 12B medium.
The results were screened in vitro, using the BACTEC 460 Radiometric System against Mycobacte-
rium tuberculosis H37Rv (ATCC 27294) at 6.25 lg/mL; the tested compounds showed significant
inhibition.
Keywords: Antituberculosis activity / Hydrazide / Imidazo[1,2-a]pyridine /
Received: February 27, 2008; accepted: June 9, 2008
DOI 10.1002/ardp.200800048
which shorten or simplify treatment of TB or provide a
more effective treatment of multidrug-resistant TB; or
improve the treatment of latent TB infection or some
combination of these [7]. As medicinal chemists, we may
handle the problem of obtaining new TB drugs for a fast
and better treatment, in two approaches: (i) synthesis of
analogues, obtained by modifying or derivating existing
chemical structures; (ii) and in case of the multidrug-
resistant TB treatment, building the anti-TB strategy on
the novelty of the chemical structure for the benefical
advantage that the TB organism has not the chance to
develop resistant [7, 8].
The heterocyclic hydrazones constitute an important
class of biologically active drug molecules, which have
attractive attention of medicinal chemists due to their
antituberculosis activities [9–12]. On the other hand, a
lot of studies were carried out on heterocyclic systems
bearing an alkylsulfanyl group as a pharmacophore for
antituberculosis activity. QSAR calculations carried out
on various types of heterocycles proved that the activity
is enhanced with electron-withdrawing substituents. An
alkylsulfanyl group bound to an electron-deficient car-
Introduction
Tuberculosis (TB) has re-emerged both in industrial and
developing countries [1–3]. Further contributing to the
increased morbidity is the emergence of new strains of
Mycobacterium tuberculosis resistant to some or all cur-
rently used antitubercular drugs [4, 5]. Particularly mul-
tidrug-resistant TB (MDR-TB) is alarming. The standard TB
therapy is non-effective in controlling MDR-TB in high
MDR-TB incidence areas [6]. There is great fear that the TB
situation may get even worse with the spread of HIV
worldwide [1] and this is one among other reasons for an
urgent need to develop new TB drugs. The Alliance aims
to get improved TB drugs to those who need them, drugs,
Correspondence: Gulhan Turan-Zitouni, Anadolu University, Faculty of
Pharmacy, Department of Pharmaceutical Chemistry, 26470 Eskisehir,
Turkey.
E-mail: zakaplan@anadolu.edu.tr
Fax: +90 222 335 07 50
Abbreviations: growth index (GI); multidrug-resistant TB (MDR-TB);
(quantitative) structure-activity relationship ((Q)SAR)
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Arch. Pharm. Chem. Life Sci. 2008, 341, 721–724
Table 1. Some characteristics of the compounds.
Compound
R1
R2
R3
Yield (%)
Mp. (8C)
M.W.
Formula
IIIa
IIIb
IIIc
IIId
IIIe
IIIf
IIIg
IIIh
IIIi
H
H
H
H
CH3
CH3
CH3
H
H
H
H
H
H
H
H
CH3
CH3
Cl
75
72
68
75
68
73
70
74
69
192–193
138–140
160–162
186–188
210–212
190–191
226–227
148–150
136–137
388
368
384
399
402
382
413
402
382
C17H13ClN4O3S
C18H16N4O3S
C18H16N4O4S
C17H13N5O5S
C18H15ClN4O3S
C19H18N4O3S
C18H15N5O5S
C18H15ClN4O3S
C19H18N4O3S
CH3
OCH3
NO2
Cl
CH3
NO2
Cl
H
CH3
bon atom in various heterocycles is responsible for anti-
mycobacterial activity [13–16].
In view of these data, we aimed at the synthesis and
antituberculosis evaluations of new N-(benzylidene)-2-[(2-
carboxyimidazo[1,2-a]pyridine-3-yl)sulfanyl]acetic acid
hydrazide derivatives. We have chosen imidazo[1,2-a]pyr-
idines, which have emerged as potentially interesting
drugs, particularly with regard to their antituberculosis
activity [17] among the various heterocycles that have
attracted the attention as potential antitubercular
agents as the basic heterocyclic moiety.
Results and discussion
In this present work, a series of nine new compounds
were synthesized. Scheme 1 illustrates the way used for
the preparation of target compounds. As starting materi-
als, ethyl 3-nitroimidazo[1,2-a]pyridine-2-yl carboxylates
were used to produce ethyl 2-[(2-carboxyimidazo[1,2-
a]pyridine-3-yl)sulfanyl]acetates. The 2-[(2-carboxyimi-
dazo[1,2-a]pyridine-3-yl)sulfanyl]acetic acid hydrazides II
Scheme 1. Synthesis of the N-(arylidene)-2-[(2-carboxyimi-
dazo[1,2-a]pyridine-3-yl)sulfanyl]acetic
derivatives IIIa–i.
acid
hydrazide
were prepared by reacting ethyl 2-[(2-carboxyimidazo[1,2- as a doublet. All the other aromatic and aliphatic protons
a]pyridine-3-yl)sulfanyl]acetates with hydrazine were observed at the expected regions. All compounds
I
hydrate. The condensation of the acid hydrazides with gave satisfactory elemental analyses. Mass spectra (MS
appropriate benzaldehydes resulted in the formation of (FAB)) of the compounds showed a [M+1] peaks in agree-
N-(arylidene)-2-[(2-carboxyimidazo[1,2-a]pyridine-3-yl)sul-
fanyl]acetic acid hydrazide derivatives IIIa–i. Some char-
ment with their molecular weight.
The antituberculosis activities of the synthesized com-
acteristics of the synthesized compounds are shown in pounds were screened in vitro using a BACTEC 460 radio-
Table 1.
metric system against Mycobacterium tuberculosis H37Rv
The structures of the obtained compounds were eluci- (ATCC 27294) at 6.25 lg/mL. Rifampicin was used as the
dated by spectral data. In the IR spectra, some significant test standard. All of the tested compounds showed signif-
stretching bands due the N-H, C=O, C=N and C-O-C were icant antituberculosis activity as can be inferred from
at about 3220–3195 cm– 1, 1670–1645 cm– 1, 1605–
1545 cm– 1 and 1250–1210 cm– 1, respectively.
Table 2. The compounds IIId and IIIg which the 4-nitro-
benzylidene derivatives showed the highest inhibitions
In the 1H-NMR spectra, the signal due to S-CH2 protons with 68%. Other compounds showed varying inhibition
and N=CH proton present in all compounds, appeared at values between 45–53%.
3.75–3.90 ppm and 8.40–8.60 ppm as singlet, respec-
SAR observation showed that 4-nitro substitution on
tively. The NH proton was observed at 12.00–12.40 ppm benzylidene affects the activity.
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Arch. Pharm. Chem. Life Sci. 2008, 341, 721–724
New Hydrazide Derivatives
723
Table 2. Antituberculosis activity of the compounds.
Compound
IIIa
IIIb
IIIc
IIId
IIIe
IIIf
IIIg
IIIh
IIIi
Rifampicin
MIC (lg/mL)
Inhibition (%) 45
A6.25
A6.25
50
A6.25
48
A6.25
68
A6.25
52
A6.25
47
A6.25
68
A6.25
53
A6.25
49
0.25
98
The authors are thankful to the Tuberculosis Antimicrobial Acquisition
and Coordinating Facility (TAACF) in the USA for the in-vitro evalua-
tion of antimycobacterial activity.
1H, aromatic proton), 12.10 (s, 1H, NH). MS (FAB) [M+1]: m/z 389.
Anal. Calc. for C17H13ClN4O3S:C, 52.51; H, 3.37; N, 14.41. Found:
C, 52.53; H, 3.39; N, 14.43.
The authors have declared no conflict of interest.
N-(4-methylbenzylidene)-2-[(2-carboxyimidazo[1,2-
a]pyridine-3-yl)sulfanyl]acetic acid hydrazide IIIb
1H-NMR (250 MHz, DMSO-d6, d ppm): 2.35 (s, 3H, CH3), 3.80 (s, 2H,
S-CH2), 7.10–7.85 (m, 7H, aromatic protons), 8.55 (s, 1H, N=CH),
8.60–8.80 (m, 1H, aromatic proton), 12.00 (s, 1H, NH). MS (FAB)
[M+1]: m/z 369. Anal. Calc. for C18H16N4O3S:C, 58.68; H, 4.38; N,
15.21. Found: C, 58.73; H, 4.39; N, 15.20.
Experimental
Chemistry
All reagents were purchased from commercial suppliers and
were used without further purification. Melting points were
determined by using an Electrothermal 9100 digital melting
point apparatus (Barnstead International, Dubuque, IA, USA)
and were uncorrected. The compounds were checked for purity
by TLC on silica gel 60 F254 (Merck, Darmstadt, Germany). Spectro-
scopic data were recorded on the following instruments: Ele-
mental analyses were performed on a Perkin Elmer EAL 240 ele-
mental analyser (Perkin Elmer, Wellesley, MA, USA), IR (m, cm– 1),
Shimadzu 435 IR spectrophotometer (Shimadzu, Tokyo, Japan);
1H-NMR spectra (d, ppm, Hz) were recorded on a Bruker 250 MHz
spectrometer (Bruker, Billerica, MA, USA) in DMSO-d6 with TMS
as an internal standard. MS-FAB+ was recorded on VG Quattro
mass spectrometer (Agilent Technologies, Santa Clara, CA, USA).
N-(4-methoxybenzylidene)-2-[(2-carboxyimidazo[1,2-
a]pyridine-3-yl)sulfanyl]acetic acid hydrazide IIIc
1H-NMR (250 MHz, DMSO-d6, d ppm): 3.80 (s, 2H, S-CH2), 3.90 (s,
3H, OCH3), 7.05–7.75 (m, 7H, aromatic protons), 8.45 (s, 1H,
N=CH), 8.60–8.70 (m, 1H, aromatic proton), 12.15 (s, 1H, NH). MS
(FAB) [M+1]: m/z 385. Anal. Calc. for C18H16N4O4S:C, 56.24; H, 4.20;
N, 14.57. Found: C, 56.21; H, 4.25; N, 14.60.
N-(4-nitrobenzylidene)-2-[(2-carboxyimidazo[1,2-
a]pyridine-3-yl)sulfanyl]acetic acid hydrazide IIId
1H-NMR (250 MHz, DMSO-d6, d ppm): 3.85 (s, 2H, S-CH2), 7.10–
7.80 (m, 3H, imidazopyridine protons), 8.00 (d, J = 8.76 Hz, 2H,
aromatic protons), 8.35 (d, J = 8.78 Hz, 2H, aromatic protons),
8.70–8.85 (m, 2H, N=CH and imidazopyridine proton), 12.40 (s,
1H, NH). MS (FAB) [M+1]: m/z 400. Anal. Calc. for C17H13N5O5S:C,
51.13; H, 3.28; N, 17.54. Found: C, 51.15; H, 3.34; N, 17.51.
General procedure for synthesis of the compounds Ethyl
2-[(2-carboxyimidazo[1,2-a]pyridine-3-
yl)sulfanyl]acetates I
These compounds were prepared as starting materials in accord-
ance with the method described in the literature [18].
2-[(2-Carboxyimidazo[1,2-a]pyridine-3-yl)sulfanyl]acetic
acid hydrazides II
These compounds were prepared according to the literature, by
reacting ethyl 2-[(2-carboxyimidazo[1,2-a]pyridine-3-yl)sulfanyl]a-
cetates I with hydrazine hydrate [19].
N-(4-chlorobenzylidene)-2-[(2-carboxy-8-
methylimidazo[1,2-a]pyridine-3-yl)sulfanyl]acetic acid
hydrazide IIIe
1H-NMR (250 MHz, DMSO-d6, d ppm): 2.65 (s, 3H, CH3), 3.95 (s, 2H,
S-CH2), 7.05–7.65 (m, 6H, aromatic protons), 8.50 (s, 1H, N=CH),
8.60–8.75 (m, 1H, aromatic proton), 12.00 (s, 1H, NH). MS (FAB)
[M+1]: m/z 403. Anal. Calc. for C18H15ClN4O3S:C, 53.73; H, 3.73; N,
13.93. Found: C, 53.74; H, 3.72; N, 13.95.
N-(arylidene)-2-[(2-carboxyimidazo[1,2-a]pyridine-3-
yl)sulfanyl]acetic acid hydrazides IIIa–i
Equimolar quantities of acid hydrazides II (30 mmol) and appro-
priate benzaldehydes in 25 mL of absolute ethanol were
refluxed for 3-5 h. The resulting solid was filtered and recrystal-
lized from ethanol. IIIa–i: IR (KBr, cm– 1): 3195–3220 (NH),
1645–1670 (CO), 1605–1545 (C=N) and (C=C), 1250–1210 (C-O-
C).
N-(4-methylbenzylidene)-2-[(2-carboxy-8-
methylimidazo[1,2-a]pyridine-3-yl)sulfanyl]acetic acid
hydrazide IIIf
1H-NMR (250 MHz, DMSO-d6, d ppm): 2.35 (s, 3H, phenyl-CH3),
2.60 (s, 3H, CH3), 3.75 (s, 2H, S-CH2), 7.10–7.65 (m, 6H, aromatic
protons), 8.45 (s, 1H, N=CH), 8.50–8.60 (m, 1H, aromatic proton),
12.05 (s, 1H, NH). MS (FAB) [M+1]: m/z 383. Anal. Calc. for
C19H18N4O3S:C, 59.67; H, 4.74; N, 14.65. Found: C, 59.70; H, 4.72;
N, 14.65.
N-(4-chlorobenzylidene)-2-[(2-carboxyimidazo[1,2-
a]pyridine-3-yl)sulfanyl]acetic acid hydrazide IIIa
1H-NMR (250 MHz, DMSO-d6, d ppm): 3.85 (s, 2H, S-CH2), 7.15–
7.80 (m, 7H, aromatic protons), 8.60 (s, 1H, N=CH), 8.70–8.85 (m,
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Z. A. Kaplancikli et al.
Arch. Pharm. Chem. Life Sci. 2008, 341, 721–724
day in the control was compare with that in the drug vial. The
following formula was used to interpret results:
N-(4-nitrobenzylidene)-2-[(2-carboxy-8-
methylimidazo[1,2-a]pyridine-3-yl)sulfanyl]acetic acid
hydrazide IIIg
DGI control A DGI drug = Susceptible
DGI control a DGI drug = Resistant
1H-NMR (250 MHz, DMSO-d6, d ppm): 2.55 (s, 3H, CH3), 3.75 (s, 2H,
S-CH2), 7.00–8.20 (m, 6H, aromatic protons), 8.50–8.65 (m, 2H,
N=CH and imidazopyridine proton), 12.10 (s, 1H, NH). MS (FAB)
[M+1]: m/z 414. Anal. Calc. for C18H15N5O5S:C, 52.30; H, 3.66; N,
16.94. Found: C, 52.34; H, 3.69; N, 16.91.
If a clear susceptibility pattern (the difference of DGI of con-
trol and the drug bottle) was not seen at the time, the control
DGI is 30, the vials were read for one or two additional days to
establish a definite pattern of DGI differences.
N-(4-chlorobenzylidene)-2-[(2-carboxy-5-
methylimidazo[1,2-a]pyridine-3-yl)sulfanyl]acetic acid
hydrazide IIIh
References
1H-NMR (250 MHz, DMSO-d6, d ppm): 2.75 (s, 3H, CH3), 3.90 (s, 2H,
S-CH2), 7.00–7.70 (m, 6H, aromatic protons), 8.45 (s, 1H, N=CH),
8.50–8.70 (m, 1H, aromatic proton), 12.10 (s, 1H, NH). MS (FAB)
[M+1]: m/z 403. Anal. Calc. for C18H15ClN4O3S:C, 53.73; H, 3.73; N,
13.93. Found: C, 53.65; H, 3.69; N, 13.94.
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