Discovery of novel antitubercular 2,10-dihydro-4aH-chromeno[3,2-c]pyridin-3-yl derivatives

Article abstract of DOI:10.1016/j.ejmech.2009.09.033

Twenty two novel 2,10-dihydro-4aH-chromeno[3,2-c]pyridin-3-yl derivatives were synthesized by reacting 3-formyl chromone, (sub)-2-amino pyridines, N1-(prop-2-ynyl)arylamides in the presence of indium triflate. The compounds were evaluated their preliminar

Full text of DOI:10.1016/j.ejmech.2009.09.033

European Journal of Medicinal Chemistry 45 (2010) 120–123
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Discovery of novel antitubercular 2,10-dihydro-4aH-chromeno-
[3,2-c]pyridin-3-yl derivatives
,
a
a
a
Dharmarajan Sriram a , Perumal Yogeeswari , Murugesan Dinakaran , Debjani Banerjee ,
*
Pritesh Bhat a, Sunil Gadhwal b
a Medicinal Chemistry & Antimycobacterial Research Laboratory, Pharmacy Group, Birla Institute of Technology & Science – Pilani, Hyderabad Campus,
Jawahar Nagar, Hyderabad – 500 078, Andhra Pradesh, India
b Syngene International Ltd., C.S. Division, Biocon Park, Bangalore – 560100, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Twenty two novel 2,10-dihydro-4aH-chromeno[3,2-c]pyridin-3-yl derivatives were synthesized by
reacting 3-formyl chromone, (sub)-2-amino pyridines, N1-(prop-2-ynyl)arylamides in the presence of
indium triflate. The compounds were evaluated their preliminary in-vitro and in-vivo activity against
Mycobacterium tuberculosis H37Rv (MTB) and multi-drug resistant M. tuberculosis (MDR-TB). Among
them N-[(4aS)-2-(3-methyl-2-pyridinyl)-10-oxo-2,10-dihydro-4aH-chromeno[3,2-c]pyridin-3-yl]methyl-
4-ethylbenzenecarboxamide 4d was found to be the most active compound in-vitro with MIC’s of 0.22
and 0.07 mg/mL against MTB and MDR-TB respectively. In the in-vivo animal model 4d decreased the
bacterial load in lung and spleen tissues with 1.11 and 2.94-log10 protections respectively at 25 mg/kg
body weight dose.
Received 2 December 2008
Accepted 17 September 2009
Available online 20 September 2009
Keywords:
Antimycobacterial activity
Antitubercular activity
Tuberculosis
Chromenopyridine
Ó 2009 Published by Elsevier Masson SAS.
1. Introduction
multi-drug resistant M. tuberculosis (MDR-TB). We present herein
the preliminary results concerning the synthesis and the in-vitro
Mycobacterium tuberculosis infections are responsible for one in
four avoidable adult deaths in developing countries. While there
are a number of effective drugs available for treating tuberculosis
(TB), current strategies are greatly complicated by the several
months of chemotherapy required to eliminate persistent bacteria.
In addition, widespread non-compliance has contributed to the
emergence of multidrug-resistant (MDR) and (XDR) TB, extensively
drug-resistant strains [1,2]. There is a clear need for fast acting
drugs that are capable of eliminating an infection in just a few
weeks. In an effort to discover new and effective chemotherapeutic
agents for the treatment of tuberculosis, we recently reported the
in-vitro and in-vivo antimycobacterial activity of various thiazolyl
thiourea/thiosemicarbazones [3,4], spiro-piperidin-4-ones [5],
oxobenzothiazolo[3,2-a]quinoline-6-carboxylic acids [6], thia-
zeto[3,2-a]quinoline-3-carboxylic acids [7], 8-naphthyridine-3-
carboxylic acid [8], 5H-thiazolo[3,2-a]quinoline-4-carboxylic acid
[9] and pyrano[3,2-c]pyridine-3-carbonitriles [10]. In the course of
screening to discover new antimycobacterial compounds, we
identified 2,10-dihydro-4aH-chromeno[3,2-c]pyridin-3-yl deriva-
tives which inhibited in-vitro M. tuberculosis H37Rv (MTB) and
and in-vivo antituberculous activity of first representative
compound of this family.
2. Synthesis
Microwave-assisted one-pot synthesis of novel 2,10-dihydro-4aH-
chromeno[3,2-c]pyridin-3-yl derivatives was achieved in two steps
(Scheme 1). Firstly 3-formyl chromone (1) on reaction with 2-amino-
3-methyl pyridine/2-amino-3,5-dibromo pyridine (2a–b) and using
catalytic amount of toluene-p-sulfonic acid [11] under microwave
irradiation (280 w for 1 min) yielded chromone Schiff bases. These
imines were prepared in good yields without the formation of any
side products arising from Michael-type additions onto the carbon–
carbon double bond of the chromone moiety [12]. In the second stage,
cycloaddition reaction was carried out by the addition of a catalytic
amount of indium triflate to chromone Schiff bases and various N1-
(prop-2-ynyl)arylamides (3a–k) in acetonitrile under microwave
irradiation (280 w for 4 min) yielded endo cycloadducts 4–5a–k.
When compared to conventional methods [13] which required 85 ꢀC
for 4 h and gave 42–78% of cycloadducts, microwave irradiation
yielded 68–84% in short reaction time. Compounds N1-(prop-2-
ynyl)arylamides (3a–k) were prepared by reacting equimolar
concentration of corresponding aryl acid chlorides with propargyl
amine in presence of triethylamine in acetonitrile under nitrogen
* Corresponding author. Tel.: þ91 09010534101.
E-mail address: drdsriram@yahoo.com (D. Sriram).
0223-5234/$ – see front matter Ó 2009 Published by Elsevier Masson SAS.
doi:10.1016/j.ejmech.2009.09.033

D. Sriram et al. / European Journal of Medicinal Chemistry 45 (2010) 120–123
121
Table 1
O
O
O
R
Physical constants, in-vitro antimycobacterial activities and cytotoxicity.
R
R1
O
O
H
+
H2N
R1
N
N
N
Ha
2a-b
CH3CN
1
H
N
Indium triflate
R2
H
N
H
R2
O
3a-k
No
R
R1 R2
Yield M.P
(%)
IC50
Vero
(
mM)
MIC (mM)
O
(ꢀC)
MTB MDRTB
7.36 3.68
R
N
R1
4a
CH3
H
Phenyl
78
118–
119
131
126
120–
121
128–
129
118
95
111–
112
123–
125
150
137
127–
129
154–
155
159
>147.59
O
O
5a
4b
5b
Br Br Phenyl
CH3
Br Br 4-Methylphenyl 76
71
NTa
>142.86
NT
11.01 NT
1.78 1.78
5.38 NT
H
4-Methylphenyl 83
N
4c
CH3
H
4-Methoxyphenyl 73
>137.91
1.72 3.44
H
N
R2
5c
4d
5d
Br Br 4-Methoxyphenyl 84
CH3
Br Br 4-Ethylphenyl
NT
>138.42
104.99
10.46 NT
0.22 0.07
2.6 1.30
H
4-Ethylphenyl
80
79
H
4-5a-k
O
4e
CH3
H
3-Chlorophenyl
70
>136.48
1.70 1.70
Scheme 1. Synthetic protocol of the compounds.
5e
4f
5f
Br Br 3-Chlorophenyl
CH3 4-Chlorophenyl
Br Br 4-Chlorophenyl
72
68
69
103.87
136.49
>103.87
5.20 2.60
1.70 3.40
2.95 2.95
H
atmosphere. The structural assignment for the titled compounds as
endo is based on its high-resolution 1H NMR spectra. The diagnostic
signal for the proton Ha in chromone Schiff base, which appeared at
8.65, was absent in the titled compounds, whilst the upfield shift of
this proton from 8.65 to 5.34 showed that cycloaddition had
occurred at the C-2 position of the chromone unit, which clearly ruled
out the possibility of other product and alsothere was no evidence for
the formation of any exo product. The purity of the compounds was
checked by TLC and elemental analyses; and the compounds of this
study were identified by spectral data.
4g
5g
CH3
H
3,4-
Dichlorophenyl
70
67
NT
12.69 NT
9.82 4.91
Br Br 3,4-
Dichlorophenyl
4-Fluorophenyl
Br Br 4-Fluorophenyl
50.69
d
d
4h
5h
CH3
H
73
70
136
121–
122
103–
105
141
149
138–
139
147–
148
110
>141.61
NT
7.09 7.09
10.67 NT
4i
CH3
H
Phenoxymethyl 79
NT
13.78 NT
5i
4j
5j
Br Br Phenoxymethyl 74
CH3
Br Br 2-Naphthyl
NT
141.67
101.24
10.46 NT
0.84 0.42
2.52 5.04
H
2-Naphthyl
84
80
3. Results and discussion
4k
CH3
H
7-Methylnaphth- 76
2-yl
>128.19
0.41 0.13
1.23 0.61
All compounds were screened for their in-vitro antimycobacterial
activity against MTB and MDR-TB by agar dilution method similar to
that recommended by the National Committee for Clinical Labora-
tory Standards [14] for the determination of MIC in duplicate. The
MDR-TB clinical isolate was obtained from Tuberculosis Research
Center, Chennai, India, and was resistant to isoniazid (INH), rifam-
picin, ethambutol and ofloxacin. The minimum inhibitory concen-
tration (MIC) is defined as the minimum concentration of compound
required to give complete inhibition of bacterial growth and MIC’s of
the synthesized compounds along with the standard drugs for
comparison were reported (Table 1). In the first phase of screening
against MTB, all the compounds showed excellent in-vitro activity
5k
Br Br 7-Methylnaphth- 80
2-yl
–
99.00
INH
Rifamp –
Oflox
Etamb
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
>455.8
>75.94
>155.3
>305.90
0.36 45.57
0.12 3.79
2.13 34.59
7.63 122.36
–
–
a
Not tested.
of the compounds were evaluated against MDR-TB, and among the
fifteen compounds screened, all the compounds inhibited MDR-TB
with MIC ranging from 0.07 to 7.09
active than isoniazid (MIC: 45.57 M), ofloxacin (MIC: 34.39
ethambutol (MIC: 122.36 M). Four compounds (4d, 4j, 4k and 5k)
inhibited MDR-TB with MIC of less than 1 M; and compound 4d
endowed with high activity toward MDR-TB. Compound 4d was
found to be the most active compound in-vitro with MIC of 0.07
m
M and were found to be more
m
mM) and
against MTB with MIC less than 15
4k) inhibited MTB with MIC of less than 1
(MIC: 0.22) was more potent than standard isoniazid (MIC: 0.36
When compared to ofloxacin (MIC: 2.13 M), eight compounds (4b,
m
M. Three compounds (4d, 4j and
M and compound 4d
M).
m
m
m
m
m
mM
4c, 4d, 4e, 4f, 4j, 4k and 5k) were found to be more active against
MTB. Fifteen compounds were more potent than ethambutol.
Compound N1-[2-(3-methyl-2-pyridyl)-10-oxo-2,10-dihydro-4aH-
chromeno[3,2-c]pyridin-3-yl]methyl-4-ethylbenzamide (4d) was
found to be the most active compound in-vitro with a low MIC of
against MDR-TB and was 651, 54, 494 and 1748 times more potent
than isoniazid, rifampicin, ofloxacin and ethambutol respectively.
With respect to structure–MTB activity relationship, the results
demonstrated that the antimycobacterial activity was enhanced by
the introduction of electron donating methyl group in the pyridyl
moiety (4a–k), whereas introduction of weakly deactivating electron
withdrawing dibromo groups (5a–k) decreased the activity. Similar
0.22
mM against MTB and was 1.6, 9.6 and 34 times more potent than
isoniazid, ofloxacin and ethambutol respectively. Subsequently some

122
D. Sriram et al. / European Journal of Medicinal Chemistry 45 (2010) 120–123
types of results were found with respect to substitution on the
phenyl ring wherein electron donating methyl, ethyl and methoxy
groups showed good activity. Substitutionwith halogen(s) decreased
the activity considerably. Replacement of phenyl ring with naphthyl
moiety enhanced the activity 4–8 times (4a,5a Vs 4j,5j), and further
introduction of methyl group in naphthyl moiety enhanced the
activity two times (4j,5j Vs 4k,5k). Replacement of phenyl ring with
phenoxymethyl group was detrimental to activity.
uncorrected 1H NMR spectra were scanned on a JEOL Fx 400 MHz
NMR spectrometer using DMSO-d6 as solvent. Chemical shifts are
expressed in
d (ppm) relative to tetramethylsilane. Elemental
analyses (C, H, and N) were performed on Perkin Elmer model 240C
analyzer and the data were within ꢁ0.4% of the theoretical values.
4.1.1. General procedure for the synthesis of 2,10-dihydro-4aH-
chromeno[3,2-c]pyridin-3-yl derivatives (4–5a–k)
Some compounds were further examined for toxicity (IC50) in
a mammalian Vero cell line till 62.5 mg/mL concentrations by serial
double dilution technique [15]. After 72 h of exposure, viability
was assessed on the basis of cellular conversion of MTT into
a formazan product and the results are reported in Table 1. Fifteen
compounds when tested showed IC50 values ranging from 50.69 to
Toluene-p-sulphonic acid (10 mg) was added to a solution of 3-
formyl chromone (1) (1 equival.) and corresponding 2-amino-3-
methyl pyridine/2-amino-3,5-dibromo pyridine (2a–b) (1 equival.)
in acetonitrile and the resulting mixture was kept under micro-
wave irradiation (280 w for 1 min). After that without separation of
compound, Indium triflate (1 equival.) and N1-(prop-2-ynyl)-
arylamides (3a–k) was added and the resulting mixture was kept
under microwave irradiation (280 w for 4 min). After com-
pletion of the reaction (monitored by TLC), the reaction mixture
was concentrated under reduced pressure yielded the products
4–5a–k.
>147.6 mM. A comparison of the substitution pattern at pyridyl
ring demonstrated that 3,5-dibromo-2-pyridyl derivatives were
more cytotoxic than the 3-methyl-2-pyridyl derivatives. These
results are important as the 3,5-dibromo-2-pyridyl substituted
compounds with their increased cytoliability, are much less
attractive in the development of a compound for the treatment of
TB. This is primarily due to the fact that the eradication of TB
requires a lengthy course of treatment, and the need for an agent
with a high margin of safety becomes a primary concern. The
4.1.2. N-[(4aS)-2-(3-methyl-2-pyridinyl)-10-oxo-2,10-dihydro-
4aH-chromeno[3,2-c]pyridin-3-yl]methylbenzenecarboxamide (4a)
Yield: 78%; m.p: 118–119 ꢀC; 1H NMR (DMSO-d6)
d ppm: 2.05 (s,
compound 4d was found to be non-toxic up to 62.5
(>138.42 M) and showed selectivity index (IC50/MIC) of more
than 629 for MTB and 1977 for MDR-TB.
m
g/mL
3H), 4.30 (dd, 2H), 5.10 (m, 1H), 5.7 (d, 1H), 6.2 (s, 1H, D2O
exchangeable), 6.68 (q, 1H), 7.02–8.18 (m, 12H); Anal (C26H21N3O3)
C, H, N.
m
Subsequently, compound 4d was tested for in-vivo efficacy
against MTB at a dose of 25 mg/kg (Table 2) in CD-1 mice [16]. The
mice were infected intravenously with M. tuberculosis ATCC 35801.
Drug treatment by intra-peritoneal route began after 10 days of
inoculation of the animal with microorganism and continued for 10
days. After 35 days post infection the spleens and right lungs were
aseptically removed, and the number of viable organisms was
determined and compared with the counts from negative (vehicle
treated) controls (Mean culture forming units (CFU) in lung:
7.99 ꢁ 0.16 and in spleen: 9.02 ꢁ 0.21). Compound 4d decreased the
bacterial load in lung and spleen tissues with 1.11 and 2.94-log10
protections respectively and was considered to be promising in
reducing bacterial count in lung and spleen tissues. When
compared to isoniazid at the same dose level 4d was found to be
less active in the in-vivo study.
4.1.3. N-[(4aS)-2-(3,5-dibromo-2-pyridinyl)-10-oxo-2,10-dihydro-
4aH-chromeno[3,2-c]pyridin-3-yl]methyl-4-
methylbenzenecarboxamide (5b)
Yield: 76%; m.p: 128–129 ꢀC; 1H NMR (DMSO-d6)
d ppm: 2.32 (s,
3H), 4.30 (dd, 2H), 5.09 (m, 1H), 5.72 (d, 1H), 6.25 (s, 1H, D2O
exchangeable), 6.68 (q,1H), 7.04–8.10 (m,10H); Anal (C26H19Br2N3O3)
C, H, N.
4.1.4. N-[(4aS)-2-(3-methyl-2-pyridinyl)-10-oxo-2,10-dihydro-
4aH-chromeno[3,2-c]pyridin-3-yl]methyl-4-
methoxybenzenecarboxamide (4c)
Yield: 73%; m.p: 120–121 ꢀC; 1H NMR (DMSO-d6)
d ppm: 2.05 (s,
3H), 3.8 (s, 3H), 4.31 (dd, 2H), 5.1 (m,1H), 5.72 (d,1H), 6.25 (s,1H, D2O
exchangeable), 6.64 (q, 1H), 7.02–8.18 (m, 11H); Anal (C27H23N3O4)
C, H, N.
Screening of the antimycobacterial activity of these novel series,
identified 2,10-dihydro-4aH-chromeno[3,2-c]pyridin-3-yl deriva-
tives as a new lead endowed with antitubercular activity, exhibiting
4.1.5. N-[(4aS)-2-(3,5-dibromo-2-pyridinyl)-10-oxo-2,10-dihydro-
4aH-chromeno[3,2-c]pyridin-3-yl]methyl-4-
ethylbenzenecarboxamide (5d)
MIC values between 0.22 and 13.78 mM. In conclusion, it has been
shown that the potency, selectivity, and low cytotoxicity of these
compounds make them valid leads for synthesizing new
compounds that possess better activity. Further structure–activity
and mechanistic studies should prove fruitful.
Yield: 79%; m.p: 111–112 ꢀC; 1H NMR (DMSO-d6)
d ppm: 1.16 (t,
3H), 2.48 (q, 2H), 4.30 (dd, 2H), 5.09 (m,1H), 5.72 (d,1H), 6.25 (s,1H,
D2O exchangeable), 6.68 (q, 1H), 7.02–8.10 (m, 11H); Anal
(C27H21Br2N3O3) C, H, N.
4. Experimental protocols
4.1.6. N-[(4aS)-2-(3-methyl-2-pyridinyl)-10-oxo-2,10-dihydro-
4aH-chromeno[3,2-c]pyridin-3-yl]methyl-3-
chlorobenzenecarboxamide (4e)
4.1. Chemistry
Yield: 70%; m.p: 123–125 ꢀC; 1H NMR (DMSO-d6)
d ppm: 2.05 (s,
Melting points were taken on an electrothermal melting point
apparatus (Buchi BM530) in open capillary tubes and are
3H), 4.30 (dd, 2H), 5.09 (m, 1H), 5.72 (d, 1H), 6.25 (s, 1H, D2O
exchangeable), 6.64 (q,1H), 7.02–8.18 (m,11H); Anal (C26H20ClN3O3)
C, H, N.
Table 2
4.1.7. N-[(4aS)-2-(3,5-dibromo-2-pyridinyl)-10-oxo-2,10-dihydro-
4aH-chromeno[3,2-c]pyridin-3-yl]methyl-4-
chlorobenzenecarboxamide (5f)
In vivo activity of 4d and isoniazid against M. tuberculosis ATCC 35801 in mice.
Compound
Lungs (log CFU ꢁ SEM)
Spleen (log CFU ꢁ SEM)
Yield: 69%; m.p: 127–129 ꢀC; 1H NMR (DMSO-d6)
d ppm: 4.31
Control
Isoniazid (25 mg/kg)
4d (25 mg/kg)
7.99 ꢁ 0.16
5.86 ꢁ 0.23
6.88 ꢁ 0.17
9.02 ꢁ 0.21
4.71 ꢁ 0.10
6.08 ꢁ 0.13
(dd, 2H), 5.12 (m, 1H), 5.72 (d, 1H), 6.25 (s, 1H, D2O exchangeable),
7.02 (q, 1H), 7.42–8.10 (m, 10H); Anal (C25H16Br2ClN3O3) C, H, N.

D. Sriram et al. / European Journal of Medicinal Chemistry 45 (2010) 120–123
123
4.1.8. N-[(4aS)-2-(3-methyl-2-pyridinyl)-10-oxo-2,10-dihydro-
4aH-chromeno[3,2-c]pyridin-3-yl]methyl-2,4-
dichlorobenzenecarboxamide (4g)
conversion of MTT into a formazan product using the Promega Cell
Titer 96 non-radioactive cell proliferation assay.
Yield: 70%; m.p: 154–155 ꢀC; 1H NMR (DMSO-d6)
d ppm: 2.06 (s,
4.4. In-vivo antimycobacterial activity
3H), 4.30 (dd, 2H), 5.09 (m, 1H), 5.72 (d, 1H), 6.25 (s, 1H, D2O
exchangeable), 6.64 (q,1H), 7.02–8.18 (m,10H); Anal (C26H19Cl2N3O3)
C, H, N.
One compound was tested for efficacy against MTB at a dose of
25 mg/kg in six-week-old female CD-1 mice six per group. In this
model, the mice were infected intravenously through caudal vein
approximately 107 viable M. tuberculosis ATCC 35801. Drug treat-
ment by intra peritoneal route began after 10 days of inoculation of
the animal with microorganism and continued for 10 days. After 35
days post infection the spleens and right lungs were aseptically
removed and ground in a tissue homogenizer, the number of viable
organisms was determined by serial 10-fold dilutions and subse-
quent inoculation onto 7H10 agar plates. Cultures were incubated
at 37 ꢀC in ambient air for 4 weeks prior to counting. Bacterial
counts were measured, and compared with the counts from
negative controls (vehicle treated) in lung and in spleen.
4.1.9. N-[(4aS)-2-(3,5-dibromo-2-pyridinyl)-10-oxo-2,10-dihydro-
4aH-chromeno[3,2-c]pyridin-3-yl]methyl-4-
fluorobenzenecarboxamide (5h)
Yield: 70%; m.p: 121–122 ꢀC; 1H NMR (DMSO-d6)
d ppm: 4.30
(dd, 2H), 5.09 (m, 1H), 5.72 (d, 1H), 6.25 (s, 1H, D2O exchangeable),
7.02 (q, 1H), 7.46–8.10 (m, 10H); Anal (C25H16Br2FN3O3) C, H, N.
4.1.10. N-[(4aS)-2-(3-methyl-2-pyridinyl)-10-oxo-2,10-dihydro-
4aH-chromeno[3,2-c]pyridin-3-yl]methyl-2-phenoxyacetamide (4i)
Yield: 79%; m.p: 103–105 ꢀC; 1H NMR (DMSO-d6)
d ppm: 2.06 (s,
3H), 4.30 (dd, 2H), 4.61 (s, 2H), 5.39 (m, 1H), 5.72 (d, 1H), 6.62–6.68
(m, 5H), 7.02–8.19 (m, 9H); Anal (C27H23N3O4) C, H, N.
Acknowledgements
4.1.11. N-[(4aS)-2-(3,5-dibromo-2-pyridinyl)-10-oxo-2,10-dihydro-
The authors are thankful to Dr. Vanaja Kumar, Deputy Director,
Tuberculosis Research Center, Chennai, India for providing bacterial
strains and technical guidance in biological screening. The authors
are also thankful to Department of Biotechnology (BT/01/COE/05/
06/01), Government of India for their financial assistance.
4aH-chromeno[3,2-c]pyridin-3-yl]methyl-2-naphthamide (5j)
Yield: 80%; m.p: 138–139 ꢀC; 1H NMR (DMSO-d6)
d ppm: 4.31
(dd, 2H), 5.1 (m, 1H), 5.72 (d, 1H), 6.25 (s, 1H, D2O exchangeable),
7.02 (q, 1H), 7.2–8.10 (m, 13H); Anal (C29H19Br2N3O3) C, H, N.
4.1.12. N-[(4aS)-2-(3-methyl-2-pyridinyl)-10-oxo-2,10-dihydro-
4aH-chromeno[3,2-c]pyridin-3-yl]methyl-7-methyl-2-
naphthamide (4k)
References
Yield: 76%; m.p: 147–148 ꢀC; 1H NMR (DMSO-d6)
d ppm: 2.06 (s,
[1] M. Zignol, M.S. Hosseini, A. Wright, C.L. Weezenbeek, P. Nunn, C.J. Watt,
B.G. Williams, C. Dye, J. Infect. Dis. 194 (2006) 479–485.
[2] C. Wells, J.P. Cegielski, Emerging Infect. Dis. 13 (2007) 380–387.
[3] D. Sriram, P. Yogeeswari, M. Dinakaran, R. Thirumurugan, J. Antimicrob. Che-
mother. 59 (2007) 1194–1196.
[4] D. Sriram, P. Yogeeswari, R. Thirumurugan, R.K. Pavana, J. Med. Chem. 49
(2006) 3448–3450.
[5] R.R. Kumar, S. Perumal, P. Senthilkumar, P. Yogeeswari, D. Sriram, J. Med.
Chem. 51 (2008) 5731–5735.
3H), 2.37 (s, 3H), 4.30 (dd, 2H), 5.09 (m, 1H), 5.72 (d, 1H), 6.25 (s, 1H,
D2O exchangeable), 6.64 (m, 1H), 7.02 (m, 1H), 7.23–8.37 (m, 12H);
Anal (C31H25N3O3) C, H, N.
4.2. In-vitro antimycobacterial activity
[6] M. Dinakaran, P. Senthilkumar, P. Yogeeswari, A. China, V. Nagaraja, D. Sriram,
Int. J. Antimicrob. Agents 31 (2008) 337–344.
[7] D. Sriram, P. Senthilkumar, M. Dinakaran, P. Yogeeswari, A. China, V. Nagaraja,
J. Med. Chem. 50 (2007) 6232–6239.
[8] R.R. Kumar, S. Perumal, P. Senthilkumar, P. Yogeeswari, D. Sriram, Bioorg. Med.
Chem. Lett. 17 (2007) 6459–6462.
[9] M. Dinakaran, P. Senthilkumar, P. Yogeeswari, A. China, V. Nagaraja, D. Sriram,
Bioorg. Med. Chem. 16 (2008) 3408–3418.
[10] M. Dinakaran, P. Senthilkumar, P. Yogeeswari, A. China, V. Nagaraja, D. Sriram,
Med. Chem. 4 (2008) 482–491.
[11] A.K. Baruah, D. Prajapati, J.S. Sandhu, Tetrahedron 44 (1998) 1241–1244.
[12] A.O. Fitton, J.R. Frost, H. Suschitzky, Tetrahedron Lett. 16 (1975) 2099–2103.
[13] V.Y. Sosnovskikh, R.A. Irgashev, I.A. Khalymbadzha, P.A. Slepukhin, Tetrahe-
dron Lett. 48 (2007) 6297–6299.
All compounds were screened for their in-vitro antimycobacterial
activity against MTB, MDR-TB and MC2 in Middlebrook 7H11agar
medium supplemented with OADC by agar dilution method similar
to that recommended by the National Committee for Clinical Labo-
ratory Standards for the determination of MIC in duplicate. The MDR-
TB clinical isolate was obtained from Tuberculosis Research Center,
Chennai, India, and was resistant to isoniazid, rifampicin, etham-
butol and ofloxacin. The minimum inhibitory concentration (MIC) is
defined as the minimum concentration of compound required to
give complete inhibition of bacterial growth.
[14] National Committee for Clinical Laboratory Standards. 1995. Antimycobacterial
susceptibility testing for Mycobacterium tuberculosis. Proposed standard M24-
T. National Committee for Clinical Laboratory Standards, Villanova, Pa.
[15] L.L. Gundersen, J. Nissen-Meyer, B. Spilsberg, J. Med. Chem. 45 (2002)
1383–1386.
4.3. Cytotoxicity
Some compounds were further examined for toxicity (IC50) in
a mammalian Vero cell line at concentrations of 62.5
72 h of exposure, viability was assessed on the basis of cellular
mg/mL. After
[16] D. Sriram, P. Yogeeswari, S.J. Basha, D.R. Radha, V. Nagaraja, Bioorg. Med.
Chem. 13 (2005) 5774–5778.