Synthesis, antibacterial and antimycobacterial activities of some new 4-aryl/heteroaryl-2,6-dimethyl-3,5-bis-N-(aryl)-carbamoyl-1,4-dihydropyridines

Article abstract of DOI:10.1016/j.ejmech.2011.02.003

A novel class of 4-aryl/heteroaryl-2,6-dimethyl-3,5-bis-N-(phenyl/ substituted phenyl)-carbamoyl-1,4-dihydropyridines has been synthesized by simple, economical and eco-friendly, modified Hantzsch condensation reaction making use of N-arylacetoacetamides, aryl or heteroaryl aldehydes and ammonium acetate. The newly synthesized compounds were characterized by their spectral (IR, ¹H NMR, Mass), elemental analyses data and evaluated for in vitro antitubercular activity against Mycobacterium tuberculosis H ₃₇Rv ATCC 27294 and antibacterial activity against different Gram +ve and Gram -ve bacteria. The preliminary screening results revealed that some of the compounds possess promising antimicrobial activity. Amongst the new series of compounds, 6m containing pyrrolyl and 4-methylphenyl groups and 6r possessing 2-pyridyl and 2-methylphenyl groups were found to exhibit a significant antitubercular activity (MIC = 12.5-25 μg/mL) in comparison with the first line drug pyrazinamide.

Full text of DOI:10.1016/j.ejmech.2011.02.003

European Journal of Medicinal Chemistry 46 (2011) 1564e1571
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis, antibacterial and antimycobacterial activities of some new
4-aryl/heteroaryl-2,6-dimethyl-3,5-bis-N-(aryl)-carbamoyl-1,4-dihydropyridines
*
Kalam Sirisha, Darna Bikshapathi, Garlapati Achaiah , Vanga Malla Reddy
Medicinal Chemistry Research Division, University College of Pharmaceutical Sciences, Kakatiya University, Warangal 506 009, Andhra Pradesh, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel class of 4-aryl/heteroaryl-2,6-dimethyl-3,5-bis-N-(phenyl/substituted phenyl)-carbamoyl-1,4-
dihydropyridines has been synthesized by simple, economical and eco-friendly, modified Hantzsch
condensation reaction making use of N-arylacetoacetamides, aryl or heteroaryl aldehydes and ammo-
nium acetate. The newly synthesized compounds were characterized by their spectral (IR, 1H NMR,
Mass), elemental analyses data and evaluated for in vitro antitubercular activity against Mycobacterium
tuberculosis H37Rv ATCC 27294 and antibacterial activity against different Gram þve and Gram ꢀve
bacteria. The preliminary screening results revealed that some of the compounds possess promising
antimicrobial activity. Amongst the new series of compounds, 6m containing pyrrolyl and 4-methyl-
phenyl groups and 6r possessing 2-pyridyl and 2-methylphenyl groups were found to exhibit a signifi-
Received 22 January 2010
Received in revised form
30 January 2011
Accepted 3 February 2011
Available online 5 March 2011
Keywords:
3,5-Dicarbamoyl-1,4-dihydropyridines
N-Arylacetoacetamides
Antibacterial activity
Antitubercular activity
Antimycobacterial activity
cant antitubercular activity (MIC ¼ 12.5e25
m
g/mL) in comparison with the first line drug pyrazinamide.
Ó 2011 Elsevier Masson SAS. All rights reserved.
1. Introduction
of MDR-TB and XDR-TB, there is an urgent need for the develop-
ment of new chemical entities with novel mechanisms of action [6].
In this regard, it could be noticed that 1,4-dihydropyridines (1,4-
DHPs) are one of the emerging classes of antitubercular agents
[7e9]. Recent studies have shown that the 3,5-dicarbamoyl deriv-
atives of 1,4-DHPs containing lipophilic groups possess consider-
able antitubercular activity against M. tuberculosis H37Rv [10,11].
Such compounds were believed to act as precursors, and after
penetration into the cell wall, convert to their 3,5-carboxylate
anions by enzymatic hydrolysis. It has been reported that the
substitution of ester with N-aryl carbamoyl group at 3- and
5-positions of 1,4-DHPs known for cardiovascular property, results
in a dramatic reduction in the calcium channel antagonistic activity
with an increase in antitubercular activity [12]. Quite recently,
Manvar et al. reported that the presence of a phenyl or substituted
phenyl group at 4-position and as N-substituents at 3- and
5-positions of the 3,5-dicarbamoyl1,4-DHPs resulted in moderate
to good antitubercular activity, in comparison to rifampicin [13]. It
has been also reported that DHPs with an electron-donating eOCH3
group and that too being at ortho- or 2-position of the carbamoyl
phenyl substituent exhibited highest antitubercular activity (93%).
Recently, some new 3,5-bis-N-aryl carbamoyl1,4-DHPs containing
4,5-dichloroimidazole-2-yl moiety at 4-position were reported as
weak to moderate inhibitors of M. tuberculosis (H37Rv) as compared
to rifampicin [14]. Similarly, some new 3,5-dicarbamoyl1,4-DHPs
containing substituted imidazolyl moieties at 4-position and
Tuberculosis (TB), the ‘King of Diseases’ is one of the most
important global infectious diseases known to the mankind. TB is
an ancient enemy and present threat that ranks amongst the
foremost killers of the 21st century. Mycobacterium tuberculosis,
a human pathogen causing TB infects approximately one-third of
the world’s population, kills more than 2 million a year [1]. The
World Health Organization has declared TB to be a ‘global emer-
gency’ and estimates that about 30 million people will be infected
by M. tuberculosis within the next 20 years [2]. The incidence of TB
infection has steadily risen in the last decade. The reemergence of
TB infection has been linked to co-infection with the human
immunodeficiency virus (HIV) [3] and to the emergence of multi-
drug-resistant (MDR) and extensively drug-resistant (XDR)
M. tuberculosis strains which are resistant to the available therapies
[4]. Multidrug-resistant TB and extensively drug-resistant TB are
refractory to treatment with any of the commonly available drugs,
warranting the need for new classes of drugs to counter effectively
the threat posed by these strains [5]. Thus to overcome the menace
* Corresponding author. Tel.: þ91 870 2541334, þ91 9440601054 (mob); fax: þ91
870 2453508.
E-mail address: achaiah_g@yahoo.co.in (G. Achaiah).
0223-5234/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2011.02.003

K. Sirisha et al. / European Journal of Medicinal Chemistry 46 (2011) 1564e1571
1565
various substituted phenyl or pyridyl carboxamide groups at 3- and
5-positions of the 1,4-DHP ring were also reported to exhibit
significant antitubercular activity [15]. It was shown that
a substituted imidazole group is a suitable equivalent for nitro-
phenyl group which was previously reported to be responsible for
the significant antitubercular activity. Literature reveals that some
3,5-dicarbamoyl1,4-DHPs to also possess weak to moderate anti-
bacterial activity against Staphylococcus aureus and Bacillus subtilis
[16]. Gunics et al. [17] have reported that some 4-aryl-3,5-diacetyl-
2,6-dimethyl-1,4-dihydropyridines with phenyl group having
4-chloro or 4-thiomethyl substituents at their 4-position showed
synergistic antibacterial effect with Erythrocin while four more
DHPs exhibited additive effect on MDR clinical isolates of Escher-
ichia coli Recently, the synthesis, antitubercular and antimicrobial
(antibacterial and antifungal) activity of some N-aryl-1,4-dihy-
dropyridine derivatives has been reported by Rokad et al. [18].
Furthermore, it has been reported that the compounds possessing
heterocyclic systems such as pyridine [19], imidazole [20], thio-
phene [21], furan [22], pyrrole [23] or substituted phenyls [24] were
associated with potent bioactivities including antimicrobial [25,26]
and antitubercular activities [27e29]. Thus, in continuation of our
studies on novel 1,4-DHPs [30e32], it was felt worthwhile to
synthesize some new 1,4-DHPs containing the above specified
putative pharmacophoric heterocyclic moieties at 4-position of 1,4-
DHP ring, and evaluate them for their possible antitubercular and
antibacterial activities. In order to derive at a meaningful structure
activity relationship, different substituted phenyl moieties are
chosen on the carbamoyl nitrogens at 3- and 5-positions. Herein,
we present rapid, facile and high yielding syntheses of 24 new
4-aryl/heteroaryl-2,6-dimethyl-3,5-bis-N-(phenyl/substituted
phenyl) carbamoyl-1,4-dihydropyridines (6aex), along with the
data on their antitubercular and antibacterial evaluation.
product in each case, which have been characterized as 4-
substituted-2,6-dimethyl-3,5-bis-N-(phenyl/substituted phenyl)-
carbamoyl-1,4-dihydropyridines (6aex) (Scheme 1), based on their
spectral (IR, 1H NMR, Mass) and elemental analyses data as pre-
sented in Table 2.
The percentage yields of N-arylacetoacetamides (3aec) have
been improved considerably with the presence of potassium tert-
butoxide. Among the four sets of reaction conditions employed for
the synthesis of DHPs, the microwave irradiation solvent-free
method on a solid support of silica gel or acidic alumina and the
microwave heating in a solvent have been found to be almost
identical and offered the advantage of being eco-friendly, simple in
operation with increased reaction rates over the conventional
method. The second in the order has been the barium nitrate-
catalyzed one-pot synthesis. Barium nitrate is safe, commercially
inexpensive reagent and the reaction in absence of organic solvent
makes the process eco-friendly.
2.2. Antibacterial activity in normal and resistant bacteria
The in vitro antibacterial assay of the compounds (6aex) was
performed by the disc-diffusion method [34] in nutrient agar
medium, at three different concentrations, viz., 12.5, 25 and
50
m
g mLꢀ1 using two Gram-positive strains: B. subtilis (NCIM-
2063,ATCC No.6633), S. aureus (NCIM-2079,ATCC No.6538P) and
two Gram-negative strains: E. coli (NCIM-2068,ATCC No.11105),
Proteus vulgaris (NCIM-2027,ATCC No.13315). The compounds with
significant antibacterial activity (6a, 6h, 6j, 6m and 6r) were then
tested against methicillin-resistant S. aureus (MRSA) at a concen-
tration of 1 mg mLꢀ1 (1000 g mLꢀ1). Tetracyclin and streptomycin
m
were used as reference drugs for comparison and the solvent DMSO
as the control. Each compound was assessed in triplicate and an
average of the results for each of the active compounds is presented
in Table 3. The results obtained indicate that most of these
compounds were relatively more active against Gram-negative
bacteria. The compound 6m with 2-pyrrolyl group at 4-position
and 4-methylphenyl group as the N-substituent at 3- and 5-posi-
tions was almost equipotent to streptomycin/tetracyclin against
E. coli. However, the compound 6h with 4-ethylphenyl group at
4-position and phenyl group as N-substituent at 3- and 5- positions
was relatively more potent against B. subtilis. Compounds 6a, 6m
and 6r were also found to show significant inhibition against MRSA
(8e10 mm), at 1 mg/mL concentration.
2. Results and discussion
2.1. Chemistry
The key intermediates, N-arylacetoacetamides (3aec) were
synthesized by the condensation of ethyl acetoacetate (1) with
appropriate aryl amines (2) in the presence of a trace of catalyst,
potassium tert-butoxide in ethanol, adopting the reported proce-
dure [31]. This reaction was also carried out by the microwave
irradiation method to obtain the respective N-arylacetoacetamides,
within 3e5 min. The results are presented in Table 1. Cyclo-
condensation of the N-arylacetoacetamides (3aec) with eight
different aldehydes (4aeh) and ammonium acetate (5) under
different experimental conditions, viz.; conventional heating,
barium nitrate-catalyzed one-pot synthesis [33], microwave irra-
diation in solvent and solvent-free conditions, afforded a single
2.3. Antitubercular activity in sensitive and resistant
Mycobacterium tuberculosis
Five compounds (6a, 6h, 6j, 6m and 6r) which exhibited
significant antibacterial activity (Table 3) and which showed good
Table 1
Physical and analytical data of Intermediates 3aec.
Compound
Substituent R
Mol. formula (Mol. Wt)
m.p (ꢁC)
Conventional
method Yield (%)
(Period/h)
Microwave method
Yield (%) (Period/min)
3a
3b
3c
H
C10H11NO2 (177.20)
C11H13NO2 (191.23)
C11H13NO2 (191.23)
84e86
88e90
108e110
75 (0.5)
80 (1.0)
72 (0.5)
82 (3.0)
85 (5.0)
78 (4.0)
4- CH3
2- CH3

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K. Sirisha et al. / European Journal of Medicinal Chemistry 46 (2011) 1564e1571
Scheme 1. Synthesis of compounds 6aex. Reagents and conditions : (i) EtOH, reflux, 20e30 h (ii) 5 mol% Ba(NO3)2,
alumina, MWI, 4e6min.
6, 30e45 min (iii) MWI, EtOH, 4e6 min (iv) Silica gel or acidic
clog P values amongst the series were tested in vitro against
M. tuberculosis H37Rv (ATCC 27294, susceptible to rifampicin, pyr-
azinamide and isoniazid), at graded concentrations: 6.25, 12.5, 25,
with the reports of Desai et al. [11] to the extent that para-substi-
tution in phenyl group is favorable for better antitubercular potency
since it may influence the enzymatic hydrolysis of carbamoyl
groups to carboxylate ions on their penetration into the mycobac-
terial cell.
50 and 100 m
g mLꢀ1 and also evaluated against a clinical isolate of
multidrug-resistant M. tuberculosis (MDR-T.B, C110/09, resistant to
rifampicin, pyrazinamide and isoniazid) at concentrations: 64, 128
and 256 m
g mLꢀ1 using the LJ proportion method [35]. The activity
4. Experimental
is expressed as minimum inhibitory concentration (MIC), i.e., the
lowest concentration of compound that completely inhibited the
growth on the culture. The results indicated that some of the tested
compounds were promising candidates with uniquely good activity
against both sensitive and resistant strains of M. tuberculosis (H37Rv
and C110/09). The results of three independent determinations are
given in Table 4. The data revealed compound 6m with 2-pyrrolyl
group at 4-position and 4-methylphenyl group as the N-substituent
at 3- and 5- positions as the most potent one amongst the tested
compounds. It was as potent as pyrazinamide against M. tubercu-
losis C110/09 and more potent than pyrazinamide against
M. tuberculosis H37Rv. However, similar compounds with 4-
hydroxyphenyl or2-chlorophenyl substitution at 4-position of DHP
have earlier been reported to exhibit weak antitubercular activity
[13]. Compound 6r with 2-pyridyl group at 4-position and
2-methylphenyl group as the N-substituent at 3- and 5-positions
was also found to exhibit higher antitubercular activity
4.1. Chemistry
Melting points were determined in open capillaries using
Toshniwal electrical melting point apparatus and are uncorrected.
IR spectra were recorded on a Shimadzu FTIR-8700 spectrometer in
KBr discs. 1H NMR spectra were recorded in CDCl3 or DMSO-d6 with
tetramethylsilane (TMS) as an internal standard on a Bruker
80 MHz FT-NMR (300 MHz) spectrometer and the chemical shifts
are reported as
d
(ppm). The 13C NMR spectra of some represen-
tative compounds were recorded in CDCl3 or DMSO on AVANCE
300 MHz NMR spectrometer. Mass spectra were recorded on a GC-
MS QP-1100 Shimadzu instrument (70 eV). Elemental analyses (C,
H, N) of the compounds were obtained from Perkin Elmer 240B
analyzer and were within ꢂ0.4% of theoretical values. The “Little
Chef” domestic microwave oven (LG) was used for microwave
irradiation. The progress of the reactions and purity of the products
were checked by thin-layer chromatography (TLC) on precoated
silica gel 60 F254 aluminum plates (Merck, Germany). Column
chromatography was performed on neutral aluminum oxide 90
(activity I-II, 70e230 mesh. ASTM, Merck).
(MIC
(MIC ¼ 32
¼
25
m
mg
mLꢀ1
)
in comparison to pyrazinamide
g mLꢀ1) against M. tuberculosis H37Rv.
3. Conclusions
The novel synthetic methodologies adopted resulted in new 1,4-
dihydropyridine-3,5-dicarbamoyl derivatives, in high yields. These
new DHPs, based on previous reports were evaluated for their
antibacterial and antitubercular activities. The study indicated that
the replacement of ester groups at 3- and 5- positions with N-aryl
carbamoyl groups in DHPs results in a significant increase in their
antimycobacterial activity. Comparison of the antibacterial and
antitubercular activities of the compounds 6aex showed that two
compounds: 6m and 6r possess potent antibacterial and antitu-
bercular activities. The new DHP 6m having a 2-pyrrolyl substituent
at 4-position and 4-methylphenyl substituent at 3,5-dicarbamoyl
nitrogen has been found to be superior in antitubercular activity in
comparison to others of the series. This particular substitution
pattern, particularly at 3,5-N-phenyl groups, partly is in agreement
4.1.1. General procedure for the synthesis of N-arylacetoacetamides
(3aec)
Conventional method: A mixture of ethyl acetoacetate (1, 1.3 g,
10 mmol), an appropriate amine (2aec, 10 mmol) and a catalytic
amount of potassium tert-butoxide was taken into a 250 mL RB
flask and dissolved in 25 mL of ethanol. The reaction mixture was
heated under reflux for 0.5e1 h. The solvent was removed from the
reaction mixture to a possible extent, under reduced pressure and
the residue was cooled and triturated with dry ether. The product
was filtered and washed with small portions of dry ether. Purifi-
cation was effected by recrystallization from ethanol to obtain
colorless crystalline solid.
Microwave method: A mixture of ethyl acetoacetate (1, 1.3 g,
10 mmol), an appropriate amine (2aec, 10 mmol) and a catalytic

K. Sirisha et al. / European Journal of Medicinal Chemistry 46 (2011) 1564e1571
1567
Table 2
Physical and analytical data of 1,4-DHPs 6aex.
Compd
R
Ar
Mol. formula
(Mol. wt)
m.p (ꢁC)
Conventional methoda
Barium nitrate catalyzed methodb
Microwave methodc
Yield (%)
(Period/h)
Yield (%)
(Period/min)
Method I
Yield
Method II
Yield
Method
I and II
(%)
(%)
(Period/min)
6a
6b
6c
6d
6e
6f
H
2-Furyl
C25H23N3O3
(413.464)
260 (dec)
242e244
246 (dec)
252 (dec)
208e210
292 (dec)
282e284
266 (dec)
176e180
238e240
220 (dec)
262e264
234 (dec)
238 (dec)
240 (dec)
272e274
210e212
258e260
224e226
268e270
218e220
256 (dec)
278e280
238 (dec)
70 (20.0)
60 (25.0)
68 (25.0)
65 (30.0)
72(30.0)
82 (25.0)
74 (30.0)
78 (30.0)
68 (30.0)
75 (30.0)
76 (25.0)
84 (30.0)
76 (30.0)
78 (30.0)
82 (25.0)
73 (30.0)
68 (25.0)
70 (28.0)
62 (29.0)
82 (30.0)
55 (30.0)
72 (25.0)
76 (30.0)
75 (30.0)
78 (35.0)
65 (30.0)
75 (40.0)
68 (40.0)
75(35.0)
85 (40.0)
79 (45.0)
82 (40.0)
72 (40.0)
78 (45.0)
78 (40.0)
86 (40.0)
78 (45.0)
82 (40.0)
85 (40.0)
75 (40.0)
73 (40.0)
72 (40.0)
70 (40.0)
84 (40.0)
58 (45.0)
75 (35.0)
74 (38.0)
78 (30.0)
80
75
80
70
80
85
84
80
70
80
80
88
78
85
84
78
80
75
70
85
68
80
65
82
84
80
82
72
78
85
82
78
72
80
78
86
80
85
80
78
82
72
75
88
65
82
60
82
4.0
H
2-Pyridyl
2-Thienyl
2-Imidazolyl
2-Pyrrolyl
4-ClC6H4
4-FC6H4
C
26H24N4O2
(424.472)
25H23N3O2S
(429.454)
24H23N5O2
(413.444)
25H24N4O2
4.0
4.0
4.0
4.0
4.5
4.5
4.0
4.5
5.0
4.5
4.5
5.0
4.5
4.5
5.5
5.0
4.5
4.5
5.0
6.0
5.0
4.5
4.0
H
C
H
C
H
C
(412.462)
C27H24ClN3O2
(457.982)
C27H24FN3O2
(441.482)
C29H29N3O2
(451.532)
C27H27N3O3
(441.516)
C28H28N3O2
(438.524)
C27H27N3O2S
(457.506)
C26H27N5O2
(440.488)
C27H28N4O2
(440.514)
C29H28ClN3O2
(486.034)
C29H28FN3O2
(469.534)
C31H33N3O2
(479.594)
C27H27N3O3
(441.516)
C28H28N3O2
(438.524)
C27H27N3O2S
(457.506)
C26H27N5O2
(440.488)
H
6g
6h
6i
H
H
4-C2H5C6H4
2-Furyl
4-CH3
4-CH3
4-CH3
4-CH3
4-CH3
4-CH3
4-CH3
4-CH3
2-CH3
2-CH3
2-CH3
2-CH3
2-CH3
2-CH3
2-CH3
2-CH3
6j
2-Pyridyl
2-Thienyl
2-Imidazolyl
2-Pyrrolyl
4-ClC6H4
4-FC6H4
6k
6l
6m
6n
6o
6p
6q
6r
4-C2H5C6H4
2-Furyl
2-Pyridyl
2-Thienyl
2-Imidazolyl
2-Pyrrolyl
4-ClC6H4
4-FC6H4
6s
6t
6u
6v
6w
6x
C27H28N4O2
(440.514)
C29H28ClN3O2
(486.034)
C29H28FN3O2
(469.534)
C31H33N3O2
(479.594)
4-C2H5C6H4
a
Reflux in ethanol for 40e45 h.
Heating in presence of Ba(NO3)2 for 30e45 min.
Microwave irradiation in solvent (method I) and solvent-free (method II).
b
c
amount of potassium tert-butoxide was taken into a 250 mL Pyrex
beaker with an inverted glass funnel and irradiated in a domestic
microwave oven for 3e5 min with 30 s pulses at 480W while
monitoring the progress of the reaction by TLC. On completion of
the reaction, the reaction mixture was cooled and triturated with
ice-cold ether. The product separated was filtered, washed with
small portions of ice-cold ether and dried. Purification by recrys-
tallization from ethanol afforded a colorless crystalline solid.

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K. Sirisha et al. / European Journal of Medicinal Chemistry 46 (2011) 1564e1571
Table 3
Antibacterial activity of some 4-aryl/hetero aryl-3,5-bis-N-(phenyl/substituted phenyl)-carbamoyl-1,4-diydropyridines (6aex)*.
Compounds
clog Pa
Concentration (
m
g mLꢀ1
)
Diameter of zone of inhibition (mm)
Gram positive
Gram negative
B. subtilis
S. aureus
MRSA
E. coli
P. vulgaris
6a
6h
6j
4.399
5.366
4.724
4.827
3.424
12.5
25
50
1000
12.5
25
10
14
16
e
8
e
e
e
10
e
e
e
e
e
e
e
e
e
e
e
10
e
e
e
8
12
15
18
e
8
12
14
e
13
17
e
11
13
21
e
8
10
13
15
e
9
11
16
e
14
16
e
50
1000
12.5
25
9
8
8
9
10
12
e
10
12
e
10
14
e
12
16
e
50
1000
12.5
25
6m
6r
7
9
14
19
22
e
10
14
18
e
11
13
e
11
12
e
50
1000
12.5
25
50
1000
50
1000
50
1000
e
e
14
17
19
e
10
12
16
e
8
10
e
12
15
e
Streptomycin
Tetracyclin
e
e
22
e
21
e
e
18
e
15
23
e
26
e
20
e
22
e
25
e
21
e
MRSA-Methicillin-resistant Staphylococcus aureus.
* The data of the compounds showing significant zones of inhibition at the concentration tested is shown. The rest of molecules are not active at the concentration tested.
a
Calculated by ChemDraw software (6.0 version).
4.1.1.1. N-Phenyl acetoacetamide (3a). IR (KBr) v (cmꢀ1): 3267
(NeH), 2921 (CeH, aromatic),1705 (C]O, amide),1675 (C]O),1585
4.1.2. General procedure for the synthesis of 4-aryl/heteroaryl-2,6-
dimethyl-3,5-bis-N-(aryl)-carbamoyl-1,4-dihydropyridines 6aex
Conventional method: A mixture of N-arylacetoacetamide (3aec,
20 mmol), an appropriate aldehyde (4aeh, 10 mmol) and ammo-
nium acetate (5, 20 mmol) in ethanol (25 mL) was heated under
reflux, on a water-bath for 20e30 h while monitoring the reaction
by TLC. On completion of the reaction, the solvent was removed to
the possible extent by distillation under reduced pressure and the
residue was cooled. The product was filtered, washed with small
portions of ice-cold ethanol and dried. Further purification was
effected by column chromatography using pet.ether-chloroform
(3:1) as eluent.
Barium nitrate-catalyzed one-pot synthesis: A mixture of N-ary-
lacetoacetamide (3aec, 20 mmol), an appropriate aldehyde (4aeh,
1 mmol) and ammonium acetate (5, 20 mmol) in presence of 5 mol
% barium nitrate was heated on a hot water-bath for 30e45 min
while monitoring the reaction by TLC. On completion, the reaction
mixture was poured into ice-cold water (25 mL), while stirring. The
product was filtered, washed with small portions of cold water and
dried. It was purified by column chromatography using pet.ether-
chloroform (3:1) as eluent.
(C]C),1232; 1H NMR (CDCl3)
d (ppm): 2.30 (s, 3H, eCH3), 3.61 (s, 2H,
eCH2), 7.1e7.29 (m, 5H, Ar-H), 9.11 (s, 1H, COeNH); MS m/z (%): 177
(37) [Mþ], 162(19), 134(25), 120(42), 92(53). Anal. Calcd. (%) for
C10H11NO2: C, 67.79; H, 6.21; N, 7.9. Found: C, 67.81; H, 6.19; N, 7.88.
4.1.1.2. N-(4-Methylphenyl)acetoacetamide (3b). IR (KBr) v (cmꢀ1):
3293 (NeH), 1657 (C]O), 1162, 1001, 818, 786; 1H NMR (CDCl3)
d
(ppm): 2.29 (s, 6H, 2x-CH3), 3.54 (s, 2H, eCH2), 7.09e7.40 (m, 4H,
Ar-H), 8.98 (s, 1H, COeNH); MS m/z (%): 191(26) [Mþ], 148(3), 133
(73), 120(10), 107(76), 91(9), 77(53), 65(17). Anal. Calcd. (%) for
C11H13NO2: C, 69.10; H, 6.80; N, 7.32. Found: C, 69.12; H, 6.83; N, 7.35.
4.1.1.3. N-(2-Methylphenyl)acetoacetamide (3c). IR (KBr) v (cmꢀ1):
3286 (NeH str), 3056 (CeH, aromatic), 1762 (C]O, amide), 1600
(C]O); 1H NMR (CDCl3)
d (ppm): 2.32 (s, 3H, Ar-CH3), 3.64 (s, 3H,
COeCH3), 3.98 (s, 2H, eCH2), 6.78e7.12 (m, 4H, Ar-H), 9.25 (s, 1H,
COeNH); MS m/z (%): 191(30) [Mþ], 133(20), 106(42), 77(10), 65(5),
43(40). Anal. Calcd. (%) for C11H13NO2: C, 69.10; H, 6.80; N, 7.32.
Found: C, 69.08; H, 6.79; N, 7.32.
In Solvent Microwave irradiation (Method I): To a mixture of an
N-arylacetoacetamide (3aec, 20 mmol) and an appropriate alde-
hyde (4aeh, 10 mmol) in ethanol (10 mL) taken in a 250 mL Pyrex
beaker, ammonium acetate (5, 20 mmol) was added and irradiated
in the microwave oven at 480W, for 4e6 min with 30 s to 1 min
pulses. After completion of the reaction (TLC), the reaction mixture
was cooled in a refrigerator, and the product obtained was filtered,
washed with ice-cold water and dried. Purification of the product
was effected by recrystallization from ethanol.
Solvent-free microwave irradiation method (Method II): N-aryla-
cetoacetamide (3aec, 20 mmol), an appropriate aldehyde (4aeh,
10 mmol) and ammonium acetate (5, 20 mmol) were mixed thor-
oughly in a mortar with silica gel (w10g). The reaction mixture was
Table 4
Antibacterial activity of compounds 6a, 6h, 6j, 6m and 6r against sensitive and
resistant strains of Mycobacterium tuberculosis.
Compounds
M. tuberculosis
M. tuberculosis
(H37Rv) MIC
(C110/09)
(
m
g mLꢀ1
)
MIC (m )
g mLꢀ1
6a
6h
6j
6m
>25
>25
>25
12.5
25
e
>256
>256
128
256
128
6r
Pyrazinamide (clog P ¼ 0.676)
32

K. Sirisha et al. / European Journal of Medicinal Chemistry 46 (2011) 1564e1571
1569
transferred to a 250 mL Pyrex beaker and irradiated in a microwave
oven at 480W for 3e6 min. The progress of the reaction was
monitored by TLC, the reaction mixture was cooled, on completion
and triturated with dichloromethane (3 ꢃ 50 mL). Silica gel was
removed by filtration, washed with small portions of dichloro-
methane and the washings were added to the filtrate. The
dichloromethane extracts were dried over anhydrous sodium
sulfate, filtered and the solvent was removed under reduced
pressure using a rotary vacuum evaporator to obtain the product
6aex. Further purification was effected by recrystallization from
ethanol.
Anal. Calcd. (%) for C25H24N4O2: C, 72.81; H, 5.82; N,13.59. Found: C,
72.79; H, 5.80; N, 13.56.
4.1.2.6. 4-(4-Chlorophenyl)-2,6-dimethyl-3,5-bis-N-(phenyl)-carbamoyl-
1,4-dihydropyridine (6f). IR (KBr) v (cmꢀ1): 3239 (NeH), 1654 (C]
O), 1554 (NeH bend, amide), 1316 (CeN str), 841, 749; 1H NMR
(CDCl3 þ DMSO)
d (ppm): 2.64 (s, 6H, 2x-CH3), 5.45 (s,1H, H4-DHP),
7.11e7.24 (m, 12H, Ar-H), 7.51e7.63 (m, 2H, Ar-H), 7.87 (s, 1H, NH-
DHP), 10.11 (s, 2H, 2x COeNH); MS m/z (%): 459(8) [Mþ], 366(27),
338(40), 217(12), 116(7), 121(100), 91(15). Anal. Calcd. (%) for
C27H24ClN3O2: C, 70.89; H, 5.25; N, 9.19. Found: C, 70.85; H, 5.23; N,
9.16.
4.1.2.1. 4-(2-Furyl)-2,6-dimethyl-3,5-bis-N-(phenyl)-carbamoyl-1,4-
dihydropyridine (6a). IR (KBr) v (cmꢀ1): 3248 (NeH), 1652 (C]O),
1539 (NeH bend, amide), 1443, 1316 (CeN), 753, 692; 1H NMR
4.1.2.7. 4-(4-Fluorophenyl)-2,6-dimethyl-3,5-bis-N-(phenyl)-carbamoyl-
1,4-dihydropyridine (6g). IR (KBr) v (cmꢀ1): 3257 (NeH), 1662 (C]
O), 1536 (NeH bend, amide), 1336 (CeN), 1229 (CeF), 722; 1H NMR
(CDCl3) d (ppm): 2.45 (s, 6H, 2x-CH3), 5.15 (s, 1H, H4-DHP), 6.34 (d,
J ¼ 3.5 Hz, 1H, H4-furyl), 6.87 (d, J ¼ 3.5 Hz, 1H, H3-furyl), 7.13e7.63
(m, 12H, Ar-H þ H5-furyl þ NH-DHP), 8.81 (s, 2H, 2x COeNH); MS
m/z (%): 412(100) [M-H]þ, 320(4), 226(10), 186(2). Anal. Calcd. (%)
for C25H23N3O3: C, 72.63; H, 5.56; N, 10.16. Found: C, 72.66; H, 5.54;
N, 10.18.
(CDCl3 þ DMSO)
d (ppm): 2.73 (s, 6H, 2x-CH3), 5.53 (s, 1H, H4-DHP),
7.19e7.28 (m, 12H, Ar-H), 7.62e7.68 (m, 2H, Ar-H), 7.92 (s, 1H, NH,
DHP), 10.17 (s, 2H, 2x COeNH); MS m/z (%): 441(15) [Mþ], 349(34),
321(41), 256(52), 239(12), 228(9), 214(66), 209(42), 147(100), 77
(30). Anal. Calcd. (%) for C27H24FN3O2: C, 73.46; H, 5.44; N, 9.52.
Found: C, 73.44; H, 5.41; N, 9.51.
4.1.2.2. 4-(2-Pyridyl)-2,6-dimethyl-3,5-bis-N-(phenyl)-carbamoyl-
1,4-dihydropyridine (6b). IR (KBr) v (cmꢀ1): 3332 (NeH), 1675 (C]
O), 1534 (NeH bend, amide), 1356, 1325 (CeN), 789; 1H NMR
4.1.2.8. 4-(4-Ethylphenyl)-2,6-dimethyl-3,5-bis-N-(phenyl)-carbamoyl-
1,4-dihydropyridine (6h). IR (KBr) v (cmꢀ1): 3240 (NeH), 1647 (C]
O), 1557 (NeH bend, amide), 1319 (CeN), 751; 1H NMR (CDCl3)
(CDCl3)
d (ppm): 2.55 (s, 6H, 2x-CH3), 5.02 (s, 1H, H4-DHP),
6.54e6.67 (m, 3H, H3, H4 and H5-pyridyl), 7.21e7.35 (m, 11H, Ar-
H þ H6-pyridyl), 7.88 (s, 1H, NH-DHP), 8.93 (s, 2H, 2x COeNH); MS
m/z (%): 424(15) [Mþ], 332(23), 304(48), 240(45), 212(12),120(100),
93(33). Anal. Calcd. (%) for C26H24N4O2: C, 73.58; H, 5.66; N, 13.20.
Found: C, 73.55; H, 5.63; N, 13.17.
d (ppm): 1.09 (t, 3H, eCH2eCH3), 2.54e2.56 (q, 2H, eCH2eCH3 ),
2.65 (s, 6H, 2x-CH3), 5.25 (s, 1H, H4-DHP), 7.07e7.30 (m, 15H, Ar-
H þ NH-DHP), 9.95 (s, 2H, 2x COeNH); MS m/z (%): 449(26) [M-
2H]þ, 357(100), 345(2), 264(77), 236(18), 222(11), 208(8), 180(10),
165(6), 139(7), 93(24), 77(19), 65(32). Anal. Calcd. (%) for
C29H29N3O2: C, 77.16; H, 6.43; N, 9.31. Found: C, 77.14; H, 6.41; N,
9.33.
4.1.2.3. 4-(2-Thienyl)-2,6-dimethyl-3,5-bis-N-(phenyl)-carbamoyl-
1,4-dihydropyridine (6c). IR (KBr) v (cmꢀ1): 3276 (NeH),1654 (C]O
str), 1550 (NeH bend, amide), 1444, 1318 (CeN), 756; 1H NMR
4.1.2.9. 4-(2-Furyl)-2,6-dimethyl-3,5-bis-N-(4-methylphenyl)-carbamoyl-
1,4-dihydropyridine (6i). IR (KBr) v (cmꢀ1): 3233 (NeH), 1665 (C]
O), 1542 (NeH bend, amide), 1435, 1336 (CeN), 721; 1H NMR
(CDCl3 þ DMSO)
d (ppm): 2.42 (s, 6H, 2x-CH3), 5.11 (s, 1H, H4-DHP),
6.33e6.45 (m, 2H, H3, H4-thienyl), 6.98 (d, J ¼ 5.5 Hz, 1H, H5-
thienyl), 7.13e7.32 (m, 10H, Ar-H), 7.64 (s, 1H, NH-DHP), 8.66 (s, 2H,
(CDCl3)
d (ppm): 2.25 (s, 6H, Ar-CH3), 2.31(s, 6H, 2x-CH3), 5.03 (s,
2x COeNH); 13C NMR (75 MHz, DMSO)
d
(ppm): 17.43, 104.46,
1H, H4-DHP), 6.13 (d, J ¼ 3.3 Hz, 1H, H4-furyl), 6.56 (d, J ¼ 3.3 Hz,
1H, H3-furyl), 6.97e7.03 (m, 10H, Ar-H þ H5-furyl þ NH-DHP), 8.64
(s, 2H, 2x COeNH); MS m/z (%): 439(43) [M-2H]þ, 373(12), 332(26),
267(42), 240(21), 225(32), 133(5), 120(43), 107(100), 91(27). Anal.
Calcd. (%) for C27H27N3O3: C, 73.46; H, 6.12; N, 9.52. Found: C, 73.48;
H, 6.14; N, 9.54.
114.81, 122.43, 124.47, 126.86, 128.4, 129.2, 134.15, 137.74, 141.88,
146.11, 151.08, 151.58, 167.65; MS m/z (%): 429(13) [Mþ], 346(4), 337
(25), 309(12), 244(45), 216(100), 202(31), 133(16), 93(5), 77(56), 65
(8). Anal. Calcd. (%) for C25H23N3O2S: C, 69.93; H, 5.36; N, 9.79.
Found: C, 69.91; H, 5.33; N, 9.76.
4.1.2.4. 4-(2-Imidazolyl)-2,6-dimethyl-3,5-bis-N-(phenyl)-carbamoyl-
1,4-dihydropyridine (6d). IR (KBr) v (cmꢀ1): 3275 (NeH), 1653 (C]
O), 1542 (NeH bend, amide), 1320 (CeN), 754, 691; 1H NMR (CDCl3)
4.1.2.10. 4-(2-Pyridyl)-2,6-dimethyl-3,5-bis-N-(4-methylphenyl)-
carbamoyl-1,4-dihydro-pyridine (6j). IR (KBr) v (cmꢀ1): 3312 (NeH),
1663 (C]O), 1525 (NeH bend, amide), 1353 (CeN), 701; 1H NMR
d
(ppm): 2.39 (s, 6H, 2x-CH3), 5.12 (s, 1H, H4-DHP), 6.98 (d,
(CDCl3) d (ppm): 2.21 (s, 6H, Ar-CH3), 2.62 (s, 6H, 2x-CH3), 5.21 (s,
J ¼ 2.6 Hz, 2H, H4 and H5-imidazolyl), 7.35e7.47 (m, 10H, Ar-H),
7.53 (s, 1H, NH-DHP, D2O exchangeable), 7.66e7.71 (d, J ¼ 2.3 Hz,
1H, NH-imidazolyl), 8.89 (s, 2H, 2x COeNH, D2O exchangeable); MS
m/z (%): 413(2) [Mþ], 345(61), 320(27), 305(11), 253(100), 226(15),
212(8), 199(36), 186(11), 160(33), 120(21), 106(47), 93(72), 77(63),
65(57). Anal. Calcd. (%) for C24H23N5O2: C, 69.73; H, 5.56; N, 16.94.
Found: C, 69.75; H, 5.53; N, 16.92.
1H, H4-DHP), 6.34e6.47 (m, 3H, H3, H4 and H5-pyridyl), 7.15e7.25
(m, 9H, Ar-H þ H6-pyridyl), 7.65 (s, 1H, NH-DHP), 8.64 (s, 2H, 2x
COeNH); MS m/z (%): 438(5) [Mþ], 360(15), 332(27), 225(100), 204
(45), 197(32), 107(12), 91(33). Anal. Calcd. (%) for C28H28N3O2: C,
76.71; H, 6.39; N, 9.58. Found: C, 76.73; H, 6.41; N, 9.56.
4.1.2.11. 4-(2-Thienyl)-2,6-dimethyl-3,5-bis-N-(4-methylphenyl)-
carbamoyl-1,4-dihydro-pyridine (6k). IR (KBr)
(NeH), 1653 (C]O), 1520 (NeH bend, amide), 1352 (CeN), 735; 1H
NMR (CDCl3) (ppm): 2.18 (s, 6H, Ar-CH3), 2.42 (s, 6H, 2x-CH3), 5.49
v
(cmꢀ1): 3345
4.1.2.5. 4-(2-Pyrrolyl)-2,6-dimethyl-3,5-bis-N-(phenyl)-carbamoyl-
1,4-dihydropyridine (6e). IR (KBr) v (cmꢀ1): 3245 (NeH), 1642 (C]
O), 1511 (NeH bend, amide), 1320 (CeN), 812; 1H NMR (DMSO)
d
(s, 1H, H4-DHP), 6.25e6.32 (m, 2H, H3, H4-thienyl), 6.82 (d,
J ¼ 5.9 Hz, 1H, H5-thienyl), 7.01e7.12 (m, 8H, Ar-H), 7.45 (s, 1H, NH-
DHP), 8.57 (s, 2H, 2x COeNH); MS m/z (%): 457(8) [Mþ], 374(12),
323(5), 351(51), 244(100), 216(15), 202(33), 134(42), 107(12). Anal.
Calcd. (%) for C27H27N3O2S: C, 70.89; H, 5.90; N, 9.19. Found: C,
70.85; H, 5.92; N, 9.18.
d
(ppm): 2.34 (s, 6H, 2x-CH3), 5.23 (s, 1H, H4-DHP), 6.24e6.39 (m,
2H, H3 and H4-pyrrolyl), 6.85 (s, 1H, NH-DHP), 7.12e7.59 (m, 11H,
Ar-H þ H5-pyrrolyl), 7.85 (d, J ¼ 2.2 Hz, 1H, NH-pyrrolyl), 10.12 (s,
2H, 2x COeNH); MS m/z (%): 412(8) [Mþ], 346(21), 320(12), 292
(40), 227(15), 199(51), 185(33), 120(17), 92(24), 77(100), 51(16).

1570
K. Sirisha et al. / European Journal of Medicinal Chemistry 46 (2011) 1564e1571
4.1.2.12. 4-(2-Imidazolyl)-2,6-dimethyl-3,5-bis-N-(4-methylphenyl)-
carbamoyl-1,4-dihydro-pyridine (6l). IR (KBr)
(cmꢀ1): 3362
(NeH), 1652 (C]O), 1576 (NeH bend, amide), 1342 (CeN), 740; 1H
NMR (CDCl3) (ppm): 2.31 (s, 6H, Ar-CH3), 2.58 (s, 6H, 2x-CH3), 5.18
(s, 1H, H4-DHP), 6.82 (m, 2H, H4 and H5-imidazolyl), 7.34e7.41 (m,
9H, Ar-H þ NH-imidazolyl), 7.52 (s, 1H, NH-DHP, D2O exchange-
able), 8.67 (s, 2H, 2x COeNH, D2O exchangeable); MS m/z (%): 441
(6) [Mþ], 374(12), 335(34), 307(100), 200(7), 186(27), 92(48). Anal.
Calcd. (%) for C26H27N5O2: C, 70.74; H, 6.12; N, 15.87. Found: C,
70.76; H, 6.10; N, 15.88.
C27H27N3O3: C, 73.46; H, 6.12; N, 9.52. Found: C, 73.45; H, 6.11; N,
9.50.
v
d
4.1.2.18. 4-(2-Pyridyl)-2,6-dimethyl-3,5-bis-N-(2-methylphenyl)-
carbamoyl-1,4-dihydro-pyridine (6r). IR (KBr)
(NeH), 1689 (C]O), 1575 (NeH bend, amide), 1368 (CeN), 716; 1H
NMR (CDCl3) (ppm): 2.01 (s, 6H, Ar-CH3), 2.24 (s, 6H, 2x-CH3), 5.15
v
(cmꢀ1): 3365
d
(s, 1H, H4-DHP), 6.23e6.37 (m, 3H, H3, H4 and H5-pyridyl), 7.09 (s,
1H, NH-DHP), 7.26e7.34 (m, 9H, Ar-H þ H6-pyridyl), 9.11 (s, 2H, 2x
COeNH); MS m/z (%): 438(15) [Mþ], 360(5), 332(45), 226(100), 204
(38), 197(62), 91(12). Anal. Calcd. (%) for C28H28N3O2: C, 76.71; H,
6.39; N, 9.58. Found: C, 76.69; H, 6.36; N, 9.60.
4.1.2.13. 4-(2-Pyrrolyl)-2,6-dimethyl-3,5-bis-N-(4-methylphenyl)-
carbamoyl-1,4-dihydro-pyridine (6m). IR (KBr)
(NeH), 1645 (C]O), 1547 (NeH bend, amide), 1363 (CeN), 809; 1H
NMR (DMSO) (ppm): 2.17 (s, 6H, Ar-CH3), 2.44 (s, 6H, 2x-CH3,
v
(cmꢀ1): 3356
4.1.2.19. 4-(2-Thienyl)-2,6-dimethyl-3,5-bis-N-(2-methylphenyl)-
carbamoyl-1,4-dihydro-pyridine (6s). IR (KBr) v (cmꢀ1): 3355 (NeH),
1659 (C]O), 1561 (NeH bend, amide), 1325 (CeN), 765; 1H NMR
d
DHP), 5.26 (s, 1H, H4-DHP), 7.15 (m, 2H, H3 and H4-pyrrolyl),
7.22e7.38 (m, 9H, Ar-H þ H5-pyrrolyl), 7.52 (d, J ¼ 2.1 Hz, 1H, NH-
pyrrolyl), 7.91 (s, 1H, NH-DHP), 10.14 (s, 2H, 2x COeNH); MS m/z
(%): 438(5) [M-2H]þ, 373(39), 331(100), 265(41), 237(63), 206(10),
133(15), 91(75). Anal. Calcd. (%) for C27H28N4O2: C, 73.63; H, 6.36; N,
12.72. Found: C, 73.65; H, 6.34; N, 12.73.
(CDCl3) d (ppm): 2.11 (s, 6H, Ar-CH3), 2.38 (s, 6H, 2x-CH3), 5.09 (s, 1H,
H4-DHP), 6.21e6.29 (m, 2H, H3, H4-thienyl), 7.02 (m, 1H, H5-thienyl),
7.21e7.27 (m, 8H, Ar-H), 7.53 (s, 1H, NH-DHP), 8.89 (s, 2H, 2x COeNH);
MS m/z (%): 457(9) [Mþ], 374(41), 323(22), 268(11), 240(100), 216(65),
173(31), 107(17). Anal. Calcd. (%) for C27H27N3O2S: C, 70.89; H, 5.90; N,
9.19. Found: C, 70.91; H, 5.88; N, 9.17.
4.1.2.14. 4.4-(4-Chlorophenyl)-2,6-dimethyl-3,5-bis-N-(4-methylphenyl)-
carbamoyl-1,4-dihydropyridine (6n). IR (KBr) v (cmꢀ1): 3260 (NeH),
1645 (C]O), 1514 (NeH bend, amide), 1317 (CeN), 816; 1H NMR
4.1.2.20. 4-(2-Imidazolyl)-2,6-dimethyl-3,5-bis-N-(2-methylphenyl)-
carbamoyl-1,4-dihydro-pyridine (6t). IR (KBr) v (cmꢀ1): 3349 (NeH),
1661 (C]O), 1545 (NeH bend, amide), 1362 (CeN), 762; 1H NMR
(CDCl3 þ DMSO)
d (ppm): 2.18 (s, 6H, Ar-CH3), 2.55 (s, 6H, 2x-CH3,
DHP), 5.35 (s, 1H, H4-DHP), 6.90e7.49 (m, 12H, Ar-H), 7.78 (s, 1H,
(CDCl3) d (ppm): 2.24 (s, 6H, Ar-CH3), 2.42 (s, 6H, 2x-CH3), 5.05 (s, 1H,
NH-DHP), 9.94 (s, 2H, 2x COeNH); 13C NMR (75 MHz, DMSO)
H4-DHP), 6.67 (d, J ¼ 3 Hz, 2H, H4 and H5-imidazolyl), 7.27e7.31 (m,
8H, Ar-H), 7.45 (s, 1H, NH-DHP, D2O exchangeable), 7.56e7.61 (d,
J ¼ 2.1 Hz, 1H, NH-imidazolyl), 8.45 (s, 2H, 2x COeNH, D2O
exchangeable); MS m/z (%): 441(6) [Mþ], 374(12), 335(34), 307(100),
228(55), 200(7), 185(27), 92(48). Anal. Calcd. (%) for C26H27N5O2: C,
70.74; H, 6.12; N, 15.87. Found: C, 70.72; H, 6.15; N, 15.90.
d
(ppm): 20.43, 22.13, 119.6, 119.78, 127.6, 129.04, 130.32, 130.45,
132.95, 134.45, 135.87, 142.82, 153.45, 165.18; MS m/z (%): 485(20)
[Mþ], 483(50), 379(36), 377(100), 270(59), 244(18),106(98), 91(25),
77(44), 65(12), 51(13). Anal. Calcd. (%) for C29H28ClN3O2: C, 71.60;
H, 5.76; N, 8.64. Found: C, 71.61; H, 5.74; N, 8.66.
4.1.2.15. 4-(4-Fluorophenyl)-2,6-dimethyl-3,5-bis-N-(4-methylphenyl)-
carbamoyl-1,4-dihydropyridine (6o). IR (KBr) v (cmꢀ1): 3264 (NeH),
1657 (C]O),1534 (NeH bend, amide),1356 (CeN),1227 (CeF), 731;
4.1.2.21. 4-(2-Pyrrolyl)-2,6-dimethyl-3,5-bis-N-(2-methylphenyl)-
carbamoyl-1,4-dihydro-pyridine (6u). IR (KBr)
(NeH), 1654 (C]O), 1514 (NeH bend, amide), 1318 (CeN), 816; 1H
NMR (DMSO) (ppm): 2.25 (s, 6H, Ar-CH3), 2.57 (s, 6H, 2x-CH3,
v
(cmꢀ1): 3266
1H NMR (CDCl3 þ DMSO)
d
(ppm): 2.28 (s, 6H, Ar-CH3), 2.65 (s, 6H,
d
2x-CH3), 5.44 (s, 1H, H4-DHP), 7.11e7.23 (m, 10H, Ar-H), 7.45e7.57
(m, 2H, Ar-H), 7.89 (s, 1H, NH, DHP), 10.11 (s, 2H, 2x CO-NH); MS m/z
(%): 441(15) [Mþ], 349(34), 321(41), 256(52), 239(12), 228(9), 214
(66), 209(42), 147(100), 77(30). Anal. Calcd. (%) for C29H28FN3O2: C,
74.20; H, 5.97; N, 8.95. Found: C, 74.23; H, 5.96; N, 8.93.
DHP), 5.15 (s, 1H, H4-DHP), 7.07 (d, 2H, H3 and H4-pyrrolyl),
7.12e7.14 (d, 5H, Ar-H þ NH-pyrrolyl), 7.39e7.45 (t, 1H, H5-pyr-
rolyl), 7.57e7.59 (d, 4H, Ar-H), 7.96 (s, 1H, NH-DHP), 10.29 (s, 2H, 2x
COeNH); MS m/z (%): 438(4) [M-2H]þ, 373(24), 331(17), 312(58),
267(50), 225(68), 206(100), 133(30), 107(85), 91(21), 77(65). Anal.
Calcd. (%) for C27H28N4O2: C, 73.63; H, 6.36; N, 12.72. Found: C,
73.66; H, 6.34; N, 12.74.
4.1.2.16. 4-(4-Ethylphenyl)-2,6-dimethyl-3,5-bis-N-(4-methylphenyl)-
carbamoyl-1,4-dihydro-pyridine (6p). IR (KBr)
(NeH), 1639 (C]O), 1560 (NeH bend, amide), 1315 (CeN), 723; 1H
NMR (CDCl3) (ppm): 1.05 (t, 3H, eCH2eCH3), 2.45e2.47 (q, 2H,
v
(cmꢀ1): 3237
4.1.2.22. 4-(4-Chlorophenyl)-2,6-dimethyl-3,5-bis-N-(2-methylphenyl)-
carbamoyl-1,4-dihydropyridine (6v). IR (KBr) v (cmꢀ1): 3243 (NeH),
1672 (C]O), 1551 (NeH bend, amide), 1335 (CeN), 756; 1H NMR
d
eCH2eCH3 ), 2.26 (s, 6H, Ar-CH3), 2.56 (s, 6H, 2x-CH3), 5.16 (s, 1H,
H4-DHP), 6.97e7.13 (m, 13H, Ar-H þ NH-DHP), 9.77 (s, 2H, 2x
COeNH); MS m/z (%): 449(26) [M-2H]þ, 357(100), 345(2), 264(77),
236(18), 222(11), 208(8), 180(10), 165(6), 139(7), 93(24), 77(19), 65
(32). Anal. Calcd. (%) for C31H33N3O2: C, 77.66; H, 6.88; N, 8.76.
Found: C, 77.64; H, 6.86; N, 8.74.
(CDCl3 þ DMSO)
d (ppm): 2.11 (s, 6H, Ar-CH3), 2.21 (s, 6H, 2x-CH3,
DHP), 5.56 (s, 1H, H4-DHP), 7.12e7.37 (m, 12H, Ar-H), 7.64 (s, 1H,
NH-DHP), 9.14 (s, 2H, 2x COeNH); MS m/z (%): 485(9) [Mþ], 483
(15), 379(28), 377(68), 244(100), 106(65), 91(42), 65(72). Anal.
Calcd. (%) for C29H28ClN3O2: C, 71.60; H, 5.76; N, 8.64. Found: C,
71.58; H, 5.77; N, 8.63.
4.1.2.17. 4-(2-Furyl)-2,6-dimethyl-3,5-bis-N-(2-methylphenyl)-carbamoyl-
1,4-dihydro-pyridine (6q). IR (KBr) v (cmꢀ1): 3270 (NeH), 1694 (C]
O), 1585 (NeH bend, amide), 1375 (CeN), 713; 1H NMR (CDCl3)
4.1.2.23. 4-(4-Fluorophenyl)-2,6-dimethyl-3,5-bis-N-(2-methylphenyl)-
carbamoyl-1,4-dihydropyridine (6w). IR (KBr)
v
(cmꢀ1): 3255
d
(ppm): 1.98 (s, 6H, Ar-CH3), 2.36 (s, 6H, 2x-CH3), 5.70 (s, 1H, H4-
(NeH), 1661 (C]O), 1562 (NeH bend, amide), 1356 (CeN), 1231
DHP), 5.90e5.94 (m, 1H, H4-furyl), 6.12e6.24 (m, 1H, H3-furyl),
6.36 (s, 1H, NH-DHP), 7.08e7.15 (m, 1H, H5-furyl), 7.18e7.56 (m, 8H,
(CeF), 714; 1H NMR (CDCl3 þ DMSO)
d (ppm): 2.27 (s, 6H, Ar-CH3),
2.55 (s, 6H, 2x-CH3), 5.28 (s, 1H, H4-DHP), 7.21e7.35 (m, 10H, Ar-H),
7.42e7.61 (m, 2H, Ar-H), 7.79 (s, 1H, NH, DHP), 10.05 (s, 2H, 2x
COeNH); MS m/z (%): 441(5) [Mþ], 349(36), 321(100), 239(82), 228
(18), 209(55), 147(12), 77(67). Anal. Calcd. (%) for C29H28FN3O2: C,
74.20; H, 5.97; N, 8.95. Found: C, 74.18; H, 5.95; N, 8.97.
Ar-H), 8.71 (s, 2H, 2x COeNH); 13C NMR (CDCl3)
d (ppm): 19.5,
22.69, 104.43, 111.3, 120.9, 127.8, 128.6, 129.4, 130.2, 136.25, 139.6,
141.22, 143.9, 153.5, 158.5, 166.4; MS m/z (%): 439(25) [M-2H]þ, 333
(60), 266(72), 238(15), 174(100), 91(80). Anal. Calcd. (%) for

K. Sirisha et al. / European Journal of Medicinal Chemistry 46 (2011) 1564e1571
1571
4.1.2.24. 4-(4-Ethylphenyl)-2,6-dimethyl-3,5-bis-N-(2-methylphenyl)-
Acknowledgments
carbamoyl-1,4-dihydropyridine (6x). IR (KBr) v (cmꢀ1): 3225 (NeH),
1638 (C]O), 1560 (NeH bend, amide), 1320 (CeN), 725; 1H NMR
(CDCl3) d (ppm): 1.14 (t, 3H, eCH2eCH3), 2.39e2.47 (q, 2H, eCH2eCH3
), 2.52 (s, 6H, Ar-CH3), 2.76 (s, 6H, 2x-CH3), 5.21 (s, 1H, H4-DHP),
7.01e7.13 (m, 13H, Ar-H þ NH-DHP), 9.53 (s, 2H, 2x COeNH); MS m/z
(%): 449(7) [M-2H]þ, 357(48), 345(23), 264(17), 222(75), 208(51), 165
(6), 93(39), 77(25). Anal. Calcd. (%) for C31H33N3O2: C, 77.66; H, 6.88; N,
8.76. Found: C, 77.67; H, 6.89; N, 8.77.
The authors express gratitude to Dr. C.Chitra, Dr. Iravathams
Clinical Laboratory, Hyderabad (AP), India for the facilities and
technical assistance for antimycobacterial screening. One of the
authors (KS) is thankful to the University Grants Commission
(UGC), New Delhi, India for the award of SRF.
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The antitubercular activity was assayed using the conventional
LowensteineJensen (LJ) medium against M. tuberculosis H37Rv
strain ATCC 27294 (susceptible to rifampicin and isoniazid) and
against a clinical isolate of multidrug-resistant strain of M. tuber-
culosis (MDR-TB, C110/09, resistant to rifampicin, pyrazinamide and
isoniazid). The stock solutions of the compounds 6a, 6h, 6j, 6m and
6r were prepared in dimethylsulfoxide (DMSO). Various dilutions
were made from the stock with DMSO, to get the final drug
concentrations: 6.25, 12.5, 25, 50 and 100
Likewise, another set of dilutions were made to get 64, 128 and
256
g mLꢀ1 for C110/09. Sterile LJ medium (4 mL) was poured into
m
g mLꢀ1 for H37Rv.
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drug solutions, tightly capped and kept aside in slanting position,
for overnight. A standard bacterial suspension of either H37Rv or
C110/09 (4 mg mLꢀ1) was inoculated onto LJ medium slants with
a loop of 3 mm internal diameter. All the culture bottles were
incubated at 37 ꢁC. Readings were taken at the end of 4 weeks of
incubation and MIC was determined by counting the colony
forming units and comparing with the culture controls. A negative
control (LJ media alone), a positive control (inoculated LJ medium)
and a solvent control (inoculated LJ medium with DMSO) were
included in the assay to make necessary corrections. Pyrazinamide
was used as reference drug, for comparison.