Synthesis and antibacterial activity of ethyl 2-amino-6-methyl-5-oxo-4- aryl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carboxylate

Article abstract of DOI:10.1016/j.cclet.2013.12.010

The three-component reaction of 4-hydroxy-1-methyl-2(1H)-quinolinone, aromatic aldehydes and ethyl cyanoacetate was carried out in the presence of a catalytic amount of 4-dimethyl aminopyridine (DMAP) in aqueous ethanol. The reactions result in the format

Full text of DOI:10.1016/j.cclet.2013.12.010

Chinese Chemical Letters 25 (2014) 431–434
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
Synthesis and antibacterial activity of ethyl 2-amino-6-methyl-5-oxo-
4-aryl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carboxylate
a
b,c
Sakineh Asghari a,b, , Samaneh Ramezani , Mojtaba Mohseni
*
a Department of Organic Chemistry, Faculty of Chemistry, University of Mazandaran, Babolsar 47416-95447, Iran
b Nano and Biotechnology Research Group, University of Mazandaran, Babolsar 47416-95447, Iran
c Department of Microbiology, Faculty of Sciences, University of Mazandaran, Babolsar 47416-95447, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
The three-component reaction of 4-hydroxy-1-methyl-2(1H)-quinolinone, aromatic aldehydes and
ethyl cyanoacetate was carried out in the presence of a catalytic amount of 4-dimethyl aminopyridine
(DMAP) in aqueous ethanol. The reactions result in the formation of pyranoquinoline derivatives in
excellent yields. Antibacterial activity has been evaluated against Gram positive and Gram negative
bacteria for some of the synthesized compounds. The results indicated that these compounds are
moderately effective against bacterial growth and their effectiveness is highest against Pseudomonas
aeruginosa.
Received 13 August 2013
Received in revised form 19 November 2013
Accepted 26 November 2013
Available online 8 December 2013
Keywords:
Three-component reaction
Pyranoquinoline
ß 2013 Sakineh Asghari. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights
reserved.
4-Dimethyl aminopyridine (DMAP)
Antibacterial activity
1. Introduction
4-dimethyl aminopyridine (DMAP) in H2O/EtOH (1:1) (Scheme 1).
Also, some of the selected products were evaluated for their
Pyranoquinoline derivatives are known to be present in many
natural alkaloids [1–4], and possess various pharmacological and
biological activities such as antimalarial [5], antiseptic [6],
antihypertensive [7], antiviral effect and act as H1-antihistamines
[8,9]. Several quinolone derivatives have been reported as
antimicrobial agents in the treatment of many infections
[10,11]. They are widely used as synthetic precursors for the
construction of many natural polycyclic molecules [12]. Thus,
several methods have been described for the synthesis of
pyranoquinoline derivatives [13–16]. Among available methods,
intramolecular cyclization via multicomponent reaction is an
efficient protocol for constructing these heterocyclic compounds
[17–21]. Moreover, employing appropriate routes to enhance the
efficiency of the reactions is a subject of interest. Besides various
other reaction parameters, the nature of the catalyst and solvent
has significant impact on the reaction [22–25].
antibacterial activity against Gram positive and Gram negative
bacteria.
2. Experimental
Elemental analyses were performed using a Heraeus CHN-O-
Rapid analyzer. NMR spectra were recorded on a BRUCKER DRX-
400 AVANCE spectrometer (at 400.1 for 1H and 100.6 MHz for 13C)
with CDCl3 as solvent. Mass spectra were recorded on a Finnigan-
Matt 8430 mass spectrometer operating at an ionization potential
of 70 eV. IR spectra were recorded on a FT-IR, Brucker, VECTOR 22
spectrometer.
2.1. General procedure for the synthesis of compound 4
(exemplified by 4a)
Thus, in continuation to our studies in the synthesis of new
heterocycles [26–30], we report an efficient synthesis of pyrano-
A mixture of 4-nitrobenzaldehyde (1 mmol) and ethyl cyanoa-
cetate (1 mmol) in H2O/EtOH (1:1) (5 mL) was treated with DMAP
(10 mol%) at room temperature. After the consumption of starting
aldehyde as indicated by TLC analysis (30 min), 4-hydroxy-1-
methyl-2(1H)-quinolinone (1 mmol) was added to the reaction
mixture and the mixture was heated to reflux condition for 2 h.
After the completion of the reaction, the reaction mixture was
brought to room temperature and the solid precipitate was
collected by filtration. The desired product 4a was obtained as a
yellow powder.
quinoline derivatives
4 which are obtained through three-
component reactions of 4-hydroxy-1-methyl-2(1H)-quinolinone
1, aromatic aldehydes 2 and ethyl cyanoacetate 3 catalyzed by
*
Corresponding author at: Department of Organic Chemistry, Faculty of
Chemistry, University of Mazandaran, Babolsar 47416-95447, Iran.
E-mail address: s.asghari@umz.ac.ir (S. Asghari).
1001-8417/$ – see front matter ß 2013 Sakineh Asghari. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2013.12.010

432
S. Asghari et al. / Chinese Chemical Letters 25 (2014) 431–434
NH
2
CO Et
2
OH
CHO
O
CO Et
2
DMAP (10 mol%)
reflux
+
+
H O/EtOH,
CN
2
N
O
N
O
R
CH
R
2
3
CH
3
1
3
4
Scheme 1. Synthesis of pyranoquinoline derivatives 4a–i.
and 4-hydroxy-1-methyl-2(1H)-quinolinone and resulted in pro-
ducts 4b–i in excellent yields (Table 3).
2.2. General procedure for evaluation of antibacterial activity
A plausible rationalization for the reaction mechanism is shown
in Scheme 2. Presumably, compound 5 is formed via Knoevenagel
condensation between aldehyde 2 and ethyl cyanoacetate 3 in the
presence of a catalytic amount of DMAP. Then, the enolate 6, which
is obtained from the reaction between quinolinone 1 and DMAP,
performs the Michael addition to intermediate 5 to generate the
intermediate 7. This intermediate enolizes to produce 8, which
subsequently undergoes an intramolecular cyclization reaction to
form 9. Then, intermediate 9 undergoes a 1,3-proton shift to afford
the product 4 exclusively.
The in vitro biocidal screening, antibacterial activity of
compounds 4a, 4c, 4d, 4f and 4g was assayed using the Kirby–
Bauer disc diffusion method where a filter disc was impregnated
with the compounds and placed on the surface of inoculated agar
plates. The synthesized compounds were dissolved in DMSO to
make a 20 mg mLꢀ1 solution then filtered through a sterilized
0.22
mm Ministart (Sartorius) filter. The antibacterial activity of
the products was investigated against four bacterial species. Test
organisms included Escherichia coli PTCC 1330, Pseudomonas
aeruginosa PTCC 1074, Staphylococcus aureus ATCC 35923 and
Bacillus subtilis PTCC 1023. Late exponential phase of the bacteria
was prepared by inoculating 1% (v/v) of the cultures into a fresh
Muller–Hinton broth (Merck) and incubating on an orbital shaker
at 37 8C and 100 rpm overnight. Before using the cultures, they
were standardized with a final cell density of approximately
108 cfu mLꢀ1. Muller–Hinton agar (Merck) was prepared and
inoculated from the standardized cultures of the test organisms
then spread as uniformly as possible throughout the entire media.
Sterile paper discs (6 mm diameter, Padtan, Iran) were impreg-
The structures of compounds 4a–i were consistent with their
1H NMR, 13C NMR, IR and mass spectra and elemental analysis.
Table 1
The effects of different catalytic amounts of DMAP and HMT on the reaction of 4-
nitrobenzaldehyde, ethyl cyanoacetate and 4-hydroxy-1-methyl-2(1H)-quinoli-
none in H2O/EtOH (1:1) under reflux.
Entry
Catalyst
Mol (%)
Time (h)
Yield of 4a (%)
1
2
3
4
5
6
7
8
DMAP
DMAP
DMAP
DMAP
DMAP
DMAP
HMT
30
20
10
5
2
90
nated with 20
mL of the compound solution then allowed to dry.
2
90
The impregnated disc was introduced on the upper layer of the
seeded agar plate and incubated at 37 8C for 24 h. The antibacterial
activity of the products was compared with known antibiotic
2.5
2.5
2.5
7
87
70
3
60
0
Trace
80
gentamicin (10
m
g/disc) and chloramphenicol (30
mg/disc) as
30
20
2
positive controls and DMSO (20
m
L/disc) as negative control.
HMT
2
75
Antibacterial activity was evaluated by measuring the diameter of
the inhibition zone (mm) on the surface of the plates and the
results were reported as mean ꢁ SD after three repeats.
Table 2
The effects of different solvents on the reaction of 4-nitrobenzaldehyde, ethyl
cyanoacetate and 4-hydroxy-1-methyl-2(1H)-quinolinone using DMAP (10 mol%)
under reflux condition.
3. Results and discussion
3.1. Chemistry
Entry
Solvent
Yield of 4a (%)
1
2
3
4
H2O/EtOH (1:1)
DMF
90
90
85
20
Initially, we investigated different conditions including cata-
lysts and solvents to optimize the reaction. As a model reaction, a
mixture of 4-nitrobenzaldehyde, ethyl cyanoacetate and 4-
hydroxy-1-methyl-2(1H)-quinolinone was treated in the absence
of any catalyst in which trace amount of the product 4a was
obtained. Then, the model reaction was performed in the presence
of various amounts of DMAP and hexamethylenetetramine (HMT).
It was noted that 10 mol% of DMAP provided the best result in
terms of yield and time. Using HMT instead of DMAP, the reaction
proceeded with a decreased yield (Table 1).
Acetone
H2O
Table 3
Synthesis of dihydropyrano[3,2-c]quinoline derivatives catalyzed by DMAP
(10 mol%) in H2O/EtOH (1:1) under reflux condition.
Entry
Product
R
Yield (%)
The model reaction was optimized using various solvents to
obtain the best yield of 4a. Among different solvents, the best
results were obtained using H2O/EtOH (1:1) and DMF. Thus, we
preferred to carry out the reactions using H2O/EtOH (1:1) as an
ecofriendly and safe medium. The results are summarized in
Table 2.
1
2
3
4
5
6
7
8
9
4a
4b
4c
4d
4e
4f
NO2
H
96
88
92
90
87
92
94
70
65
CN
Cl
Br
CH3
OCH3
Furyl
Biphenyl
4g
4h
4i
With the optimal reaction conditions, the reactions of some
other aromatic aldehydes were carried out with ethyl cyanoacetate

S. Asghari et al. / Chinese Chemical Letters 25 (2014) 431–434
433
O
NC
CO Et
2
CO Et
2
N
O
reflux
H O/EtOH,
DMAP,
CO Et
2
2
+
Ar
H
Knoevenagel condensation
CN
3
Ar
-
H
5
2
H O
2
Ar
H
O
H
O
O
OH
N
CH
DMAP
3
7
N
O
N
O
CH
CH
3
1
3
6
Enolization
NH
NH
2
N
O
CO Et
CO Et
2
H
CO Et
2
2
O
O
H
[1,3] H-shift
Cyclization
Ar
Ar
Ar
N
O
O
O
N
N
CH
CH
CH
3
3
3
4
8
9
Scheme 2. Proposed mechanism for the formation of pyranoquinoline derivatives 4a–i.
Table 4
Antibacterial activities of the selected products using Kirby–Bauer disc diffusion method.
Test strain
4a
4c
4d
4f
4g
Gentamicin (10
mg/disc)
Chloramphenicol (30 mg/disc)
Zone of growth inhibition (mm)
E. coli
8.5 ꢁ 0.7
7.5 ꢁ 0.7
NEa
11.0 ꢁ 1.4
11.5 ꢁ 0.7
10.5 ꢁ 0.7
9.5 ꢁ 0.7
10.0 ꢁ 1.4
8.5 ꢁ 0.7
11.5 ꢁ 0.7
11.0 ꢁ 1.4
10.5 ꢁ 0.7
11.0 ꢁ 1.4
10.0 ꢁ 1.4
12.5 ꢁ 0.7
11.5 ꢁ 0.7
9.5 ꢁ 0.7
19.6 ꢁ 1.1
15.6 ꢁ 0.5
20.3 ꢁ 1.5
26.0 ꢁ 1.7
20.7 ꢁ 1.5
NEa
P. aeruginosa
S. aureus
B. subtilis
11.5 ꢁ 0.7
12.0 ꢁ 1.4
21.7 ꢁ 0.6
22.3 ꢁ 1.2
9.5 ꢁ 1.4
a
No effect.
Spectral data of compounds 4a–i are listed in Supporting
information.
ing a three-component reaction of 4-hydroxy-1-methyl-2(1H)-
quinolinone, aromatic aldehydes and ethyl cyano acetate in the
presence of a catalytic amount of DMAP in aqueous ethanol. The
simplicity of the reaction, easy separation procedure, excellent
yields of the products, and short reaction time make it an efficient
rout for synthesizing pyranoquinoline heterocycles. The observed
antibacterial properties suggest that the methoxy derivative of
the synthesized pyranoquinolines exhibited good antibacterial
activity and can be further developed as an effective antimicrobial
agent.
The 1H NMR spectrum of 4a exhibited a triplet for CH3 at
d
1.11,
3.97–4.02 for OCH2, a
4.96, a multiplet for aromatic protons at 7.40–
8.13 and a singlet for NH2 protons at
7.90. The 13C NMR spectrum
a singlet for NCH3 at
singlet for CH at
d 3.55, a multiplet at d
d
d
d
of 4a displayed 20 resonances in agreement with the proposed
structure. Infrared spectral data of 4a displayed four absorption
bands at 3374, 3276, 1696 and 1624 cmꢀ1 indicating the presence
of NH2 and carbonyl groups, respectively. The mass spectrum
displayed a molecular ion peak at m/z 421. The 1H NMR and 13C-
NMR spectra of 4b–i are similar to those of 4a, except for the
signals related to the substituents of the aldehydes.
Acknowledgment
This research was supported by the Research Council of the
University of Mazandaran in Iran.
3.2. Antibacterial activity
The in vitro antibacterial activity of compounds 4a, 4c, 4d, 4f
and 4g was evaluated against Gram positive S. aureus and B. subtilis
and Gram negative E. coli and P. aeruginosa. The inhibition of
microorganism growth was benchmarked against the standard
antibiotics gentamicin and chloramphenicol (Table 4) [31,32]. The
results revealed that the synthesized compounds have moderate to
good bacteriostatic effects against some microorganisms, and
among the bacteria tested, the compounds exhibited the highest
antibacterial activity against P. aeruginosa. The activity of
compound 4g against all test bacteria was good whereas the
compound 4a shows low activity against P. aeruginosa and no effect
against S. aureus (Table 4).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.cclet.2013.12.010.
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