Synthesis and antibacterial activities of some substituted quinolines

Article abstract of DOI:10.14233/ajchem.2015.18323

p-Anisidine (1) on treatment with ethyl acetoacetate in refluxing ethanol for 4 h gave ethyl-3-[(4-methoxyphenyl)imino]butanoate (2) which on thermal cyclization in hot Dowtherm oil at 250 °C gave 4-hydroxy-6-methoxy-2-methylquinoline (3). The latter on h

Full text of DOI:10.14233/ajchem.2015.18323

Asian Journal of Chemistry; Vol. 27, No. 8 (2015), 2947-2950
A
SIAN
J
OURNAL OF HEMISTRY
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http://dx.doi.org/10.14233/ajchem.2015.18323
Synthesis and Antibacterial Activities of Some Substituted Quinolines
1,*
1
2
G. ANUKUMARI , M. ANAND RAO and P.K. DUBEY
1Department of Chemistry, Osmania University, Hyderabad-500 007, India
2Department of Chemistry, J.N.T. University, Kukatpally, Hyderabad-500 085, India
*Corresponding author: E-mail: anukumari.g@gmail.com
Received: 14 June 2014;
Accepted: 26 August 2014;
Published online: 27 April 2015;
AJC-17168
p-Anisidine (1) on treatment with ethyl acetoacetate in refluxing ethanol for 4 h gave ethyl-3-[(4-methoxyphenyl)imino]butanoate (2)
which on thermal cyclization in hot Dowtherm oil at 250 °C gave 4-hydroxy-6-methoxy-2-methylquinoline (3). The latter on heating with
POCl3 gave 4-chloro-6-methoxy-2-methylquinoline (4) which on treatment with aromatic aldehydes (5a-e) gave the corresponding
4-chloro-6-methoxy-2-styrylquinolines (6a-e). 4-Hydroxy-6-methoxy-2-methylquinoline (3) on treatment with ethyl acetoacetate gave
the coumarin substituted quinoline, i.e. 9-methoxy-4,5-dimethyl-2H-pyrano[3,2-C]quinolin-2-one (7). The products thus obtained have
been characterized based on their spectral data and have been evaluated for their antibacterial activities.
Keywords: Styrylquinolines, Aromatic aldehydes, Coumarins.
Preparation of ethyl-3-[(4-methoxyphenyl)imino]-
butanoate (2): A mixture of p-anisidine (1) (12.3 g, 100
mmol), ethyl acetoacetate (13 g, 100 mmol) and ethanol (150
mL) was refluxed on a hot water bath for 4 h. At the end of
this period, the mixture was distilled to half its volume. The
residual mixture was cooled in ice-water at 0-5 °C when a
crystalline solid separated out from the reaction mixture. The
mixture was filtered and the insoluble solid was washed with
cold ethanol (2 × 20 mL) and dried. The crude product was
recrysrallized from methanol11.Yield 25 g (75 %), m.p.: 35 °C
(Lit11 m.p.: 38 °C).
Preparation of 4-hydroxy-6-methoxy-2-methylquino-
line (3): Compound 2 (17 g, 80 mmol) was added slowly to
preheated Dowtherm oil at 250 °C in small lots. After comp-
letion of addition, the reaction mixture was cooled to room
temperature and diluted with hexane (10 mL). The separated
solid was filtered, washed with hexane (2 × 5 mL) and dried.
The solid obtained was dissolved in 10 % NaOH (100 mL),
filtered and neutralized with dil. HCl (20 %, 20 mL). The
separated, off white, solid was filtered, washed with water (2
× 10 mL) and dried11. Yield 10 g (72 %) m.p.: 284 °C (Lit11
m.p.: 267-269 °C).
INTRODUCTION
Quinoline ring system is prevalent in a variety of pharma-
cologically active compounds as well as in natural products1.
A number of biological activities have been associated with
quinoline-containing compounds such as anti-inflammatory,
antiallergic2, antimalarial3, antibacterial4, antiproliferative5,
anticancer6,7 etc. Beside these, quinoline ring also occupies a
unique position in the design and synthesis of novel biolo-
gically active compounds8. Halogen-containing quinolines are
of particular interest, because the halogen atom can play a crucial
role in the compound's bioactivity and provides an avenue for
further structure elaboration9,10. In view of these considerations
it was considered worthwhile to synthesize new quinoline
derivatives and evaluate them for their antibacterial activities.
EXPERIMENTAL
Melting points were determined on a Buchi melting-point
apparatus and are uncorrected. The IR spectra (in KBr pellets)
were recorded on a Shimadzu FTIR 157 spectrometer. All
1H and 13C NMR spectra were recorded on a Bruker instrument,
using TMS as an internal standard at 400 and 100 MHz, respec-
tively. The mass spectra were recorded either on Single Quad-
rupole Mass or XCT Ion trap Spectrometers. Completion of
the reaction was monitored by TLC, plates being visualized
by UV light and/or iodine vapours. p-anisidine and ethyl-
acetoacetate were obtained from commercials supplier and
used as such.
Preparation of 4-chloro-6-methoxy-2-methylquinoline
(4): A mixture of compound 3 (14.15 g, 75 mmol) and POCl3
(8 mL, 80 mmol) in 1:3 ratio (w/v) was heated on a water bath
at 100 °C for 1 h. The reaction mixture was cooled to room
temperature, diluted with ice-cold water (30 mL) and neutra-
lized with saturated NaHCO3 (20 mL) solution. The separated

2948 Anukumari et al.
Asian J. Chem.
solid was filtered, washed with water (2 × 20 mL) and
dried12. Yield 10 g (64.5 %), m.p.: 91-93 °C (Lit12 . m.p.: 92-
95 °C).
Compound 7e:Yield 0.42 g (54.9 %); m.p. 172-175 °C;
IR (KBr, νmax, cm-1): 2878 (C-H), 1498 (C-H); 1H NMR (400
MHz, DMSO-d6): δ ppm 3.21 (s, 4H, NH2), 6.96-7.95 (m,
11H, nine aromatic + two styryl protons); LC/MS; m/z 274
(M+ + 1).
Preparation of 9-methoxy-4,5-dimethyl-2H-pyrano-
[3,2-c]quinoline-2-one (8):A mixture ofcompound 3 (0.45 g,
2.38 mmol), ethyl acetoacetate (0.5 mL, 3 mmol) and conc.
H2SO4 (5 mL) was stirred at room temperature for 2 h. After
completion of the reaction, the mixture was cooled in ice-water
at 0-5 °C and neutralized with aqueous NaOH (25 %, 40 mL).
The separated solid was filtered, washed with water (2 × 20
Synthesis of 4-chloro-6-methoxy-2-styrylquinolines
(6): A mixture of compound 4 (0.52 g, 2.5 mmol) and the
respective benzaldehyde (7.5 mmol), in 1:3 ratio (w/v), was
heated in an oil-bath is at 175-180 °C when water elimination
was observed by water drops appearing on the flask neck.After
0.5 h of heating, the mixture was cooled to room temperature
and washed with hexane (3 × 15 mL) to remove excess benzal-
dehyde. The residue was recrystallized from methanol to obtain
compound 6.
Compound 6a:Yield 0.42 g (56.7 %); m.p. 123-125 °C.
Compound 6b:Yield 0.52 g (66.1 %); m.p. 133-135 °C;
IR (KBr, νmax, cm-1): 2878 (C-H), 1498 (C-H), 1H NMR (400
MHz, DMSO-d6): δ ppm 3.81 (s, 3H, OCH3), 7.01-7.95 (m,
10H, eight aromatic + two styryl protons); LC/MS; m/z 314
(M+ + 1) and 316 (M+ + 3).
Compound 6c:Yield 0.57 g; (68.7 %); m.p. 142-145 °C;
IR (KBr, νmax, cm-1): 2878 (C-H), 1498 (C-H), 1H NMR (400
MHz, CDCl3/TMS): δ ppm 3.81 (s, 3H, OCH3), 6.94-7.95 (m,
10H, eight aromatic + two styryl protons); LC/MS; m/z 331
(M+ + 1) and 333 (M+ + 3).
Compound 6d: Yield 0.44 g (51.5%); m.p. 148-150 °C;
IR (KBr, νmax, cm-1): 2878 (C-H), 1498 (C-H), 1H NMR (400
MHz,CDCl3/TMS): δ ppm 3.81 (s, 3H, OCH3), 7.01-8.32 (m,
10H, eight aromatic + two styryl protons); LC/MS; m/z 341
(M+ + 1) and 343 (M+ + 3).
Compound 6e:Yield 0.42 g (51.33 %); m.p. 153-155 °C;
IR (KBr, νmax, cm-1): 2878 (C-H), 1498 (C-H), 1H NMR (400
MHz, CDCl3/TMS): δ ppm 3.81 (s, 3H, OCH3), 4.1 (s, 3H,
OCH3), 6.96-7.95 (m, 11H, nine aromatic + two styryl protons);
LC/MS; m/z 326 (M+ + 1) and 328 (M+ + 3).
Preparation of 9-methoxy-4,5-dimethyl-2H-pyrano-
[3,2-C]quinolin-2-one (7): A mixture of compound 6 (2.5
mmol) and ammonium acetate (12.5 mmol) in 1:6 ratio (w/w)
was heated at 130-140 °C. The reaction was cooled to room
temperature and diluted with water (20 mL). The separated
solid was filtered, washed with water (2 × 10 mL) and dried.
The solid thus obtained was dissolved in acetic acid (15 mL)
and neutralized with ammonia solution (25 mL). The separated
brown coloured solid was filtered, washed with water (2 × 15
mL) and dried to obtain compound 7.
Compound 7a: Yield 0.22 g (33.8 %); m.p. 163-165 °C.
Compound 7b: Yield 0.42 g (60 %); m.p. 173-175 °C;
IR (KBr, νmax, cm-1): 2878 (C-H), 3000 (-NH); 1H NMR (400
MHz, DMSO-d6): δ ppm 3.21 (s, 4H, NH2), 7.01-7.95 (m,
10H, eight aromatic + two styryl protons); LC/MS m/z 280
(M+ + 1).
Compound 7c:Yield 0.35 g (50.7 %); m.p. 183-184 °C;
IR (KBr, νmax, cm-1): 2878 (C-H), 1498 (C-H); 1H NMR (400
MHz, DMSO-d6): δ ppm 3.21 (s, 4H, NH2), 6.94-7.95 (m,
10H, eight aromatic + two styryl protons); LC/MS m/z 262
(M+ + 1).
Compound 7d:Yield 0.45 g (58.8 %); m.p. 153-155 °C;
IR (KBr, νmax, cm-1): 2878 (C-H), 1498 (C-H); 1H NMR (400
MHz, DMSO-d6): δ ppm 3.21 (s, 4H, NH2), 7.01-8.32 (m,
10H, eight aromatic + two styryl protons); LC/MS; m/z 282
(M+ + 1).
mL) and dried. Yield 0.4 g (66 %); m.p.: 180 °C; IR (KBr,
ν
DMSO-d6): δ ppm 2.56 (s,3H, CH3), 2.67 (s, 3H, CH3), 3.81
(s, 3H, OCH3), 5.96-7.44 (m, 4H, aromatic protons); LC/MS;
m/z 256 (M+ + 1).
1
max, cm-1): 2878 (C-H), 1498 (C-H); H NMR (400 MHz,
Preparation of 4,6-dimethoxy-2-methylquinoline (9):
A mixture of compound 3(14.15 g, 75 mmol), dimethyl sulphate
(8 mL, 80 mmol) and toluene (60 mL) was refluxed on an oil
bath at 115 °C for 1 h. Then, the reaction mixture was cooled
to room temperature, dissolved in conc. HCl (30 mL) and
filtered. The filtrate was neutralized with 10 % NaOH (50 mL)
solution. The separated solid was filtered, washed with water
(2 × 10 mL) and dried to afford compound 3 as a pale pink
solid13. Yield 10 g (65.7 %), 91-93 °C, (Lit13 m.p.: 92-95 °C).
Preparation of 4,6-diamino-2-methylquinoline (10):A
mixture of compound 9 (1.015 g, 5 mmol) and ammonium
acetate (2.31 g, 30 mmol) in 1:6 ratio (w/w) was heated at
130-140 °C. The reaction was cooled to room temperature
and diluted with water (20 mL). The separated solid was
filtered, washed with water (2 × 10 mL) and dried. The solid
thus obtained was dissolved in acetic acid (15 mL) and neutra-
lized with ammonia solution (25 mL). The separated brown
solid was filtered, washed with water (2 × 15 mL) and dried to
obtain compound 10.Yield 0.62 g (70 %), m.p.: 135 °C (Lit14.
m.p.: 138 °C).
Synthesis of compound 11: A mixture of compound 10
(0.44 g, 2.5 mmol) and the respective benzaldehyde (0.75
mmol), in 1:3 ratio (w/v), was heated in an oil bath is at 175-
180 °C when water elimination was observed by water drops
appearing on the flask neck.After 0.5 h of heating, the mixture
was cooled to room temperature and washed with hexane (3 ×
15 mL) to remove excess benzaldehyde. The residue was
recrystallized from methanol.
Compound 11a: Yield 0.22 g (38 %); m.p. 163-165 °C.
Antibacterial studies: The newly synthesized final
compounds were evaluated for their antibacterial activity
against Escherichia coli (ATTC-25922) Staphylococcus aureus
(ATTC-25923), strains by serial plate dilution method15. Serial
dilutions of the drug in Muller-Hinton broth were taken in
tubes. Their pH was adjusted to 5 using phosphate buffer. A
standardized suspension of the test bacterium was inoculated
and incubated for 16-18 h at 37 °C. The minimum inhibitory
concentration (MIC) was noted by observing the lowest
concentration of the drug at which there was no visible growth.
A number of antimicrobial discs are placed on the agar for the
sole purpose of producing zones of inhibition in the bacterial
lawn. Twenty milliliters of agar media was poured into each

Vol. 27, No. 8 (2015)
Synthesis and Antibacterial Activities of Some Substituted Quinolines 2949
Petri dish. Excess of suspension was decanted and plates were
dried by placing in an incubator at 37 °C for 1 h. Using an
agar punch, wells were made on these seeded agar plates and
minimum inhibitory concentrations of the test compounds in
dimethyl sulfoxide (DMSO) were added into each labeled well.
A control was also prepared for the plates in the same way
using solvent DMSO. The Petri dishes were prepared in
triplicate and maintained at 37 °C for 3 to 4 days.Antibacterial
activity was determined by measuring the diameter of inhibi-
tion zone. Activity of each compound was compared with
ampicillin as standard. MIC (mg/mL) and zone of inhibition
(mm) were determined for 6a to 6e and the corresponding
results are summarized in Table-1.
RESULTS AND DISCUSSION
p-Anisidine (1) was condensed with ethyl acetoacetate in
refluxing ethanol to obtain the previously reported11 ethyl-
3-[(4-methoxyphenyl)imino]butanoate (2). The latter was
thermally cyclized by heating at 250 °C in hot dowtherm oil
for 0.5 h to obtain 4-hydroxy-6-methoxy-2-methylquinoline
(3), which is also known in literature11. Compound 3 on treat-
ment with POCl3 followed by aq. NaHCO3 treatment gave
4-chloro-6-methoxy-2-methylquinoline (4), which is also
reported12 in literature. Also, 4 could be reconverted to 3 by
treatment with hot aqueous NaOH. When 4 was treated with
benzaldehyde (5a) in 1:3 ratio (w/v) at 180 °C followed by
simple processing, 4-chloro-6-methoxy-2-styrylquinoline (6a)
was obtained as product whose structure was assigned based
on its spectral characteristics. Thus, its IR in KBr phase showed
no diagnostic absorption assignable to a functional group in
the regions 3500-3000 and 1800-1600 cm-1. Its 1H NMR (400
MHz, CDCl3) spectrum showed signals at δ 3.81 (s, 3H, OCH3),
6.69-8.05 (m, 11H, nine aromatic + two styryl protons); LC/
MS (ESI-MS) showed m/z 295 (M+ + 1) and 297 (M+ + 3) as
twin peaks corresponding to molecular masses of 294 and 296
when recorded in the Q + 1 mode.
TABLE-1
SCREENING OF 2-STYRYLQUINOLINE DERIVATIVES
FOR ANTIBACTERIAL ACTIVITY
Zone of inhibition
Compound and
Entry
Bacterial strains
standard
S. aureus
E. coli
1
2
3
4
5
6
Ampicillin
9
3.5
5
6
6
10
5
5.5
5
5.5
6.5
6a
6b
6c
6d
6e
The above reaction of 4 with 5a has been extended to
other aldehydes (5b-5e) and the products obtained have all
been assigned structures 6b-6e, respectively.
8
Compounds concentration-1 mg/mL; Ac-active
Cl
OH
O
O
c
O
O
O
O
b
a
N
N
g
NH
2
N
4
3
H
2
1
e
h
d
Cl
N
OCH
3
O
O
O
O
N
9
O
R
1
6(a-e)
N
8
f
f
R
1
R
1
NH
2
NH
N
2
N
H N
2
e
X
H N
2
N
N
N
R
1
10
7(a-e)
11(a-e)
Scheme-I:(a) Ethylacetoacetate, ethanol, reflux, 90 °C, 4 h, (b). Dowtherm oil, 250 °C, 0.5 h, (c). POCl3/reflux/1 h, (d). EAA, H2SO4, RT, 3 h e). Aromatic
aldehydes (5a-e), 175-180 °C, 2 h, f). CH3COONH4, g). 5 % NaOH, 100 °C, 0.5 h. h). Dimethylsulphate/toluene, 115 °C, 1 h. i). Aromatic
aldehydes (5a-e)/DMF/reflux, 4 h

2950 Anukumari et al.
Asian J. Chem.
Compound 6a on heating with ammonium acetate in 1:6
ratio (w/w) at 130 °C gave 4,6-diamino-2-styrylquinoline (7a),
whose structure was assigned based on its spectral data. Thus,
its IR in KBr phase showed a broad absorption at 3000 cm-1
which may be due to a combination of -NH- stretching vibra-
tions. No other diagnostic absorption assignable to a functional
group could be seen in IR. Its 1H NMR (400 MHz, DMSO-d6)
spectrum showed signals at δ 3.21 (s, 4H, NH2), 6.69-8.85
(m, 11H, nine aromatic + two styryl protons); Its LC/MS (ESI-
MS) showed m/z at 262 (M+ + 1) corresponding to a molecular
mass of 261 when recorded in Q + 1 mode. The above reaction
of ammonium acetate with 7a has been extended to other
styrylquinolines (6b-6e) and the products obtained have all
been assigned structures 7b-7e, respectively.
Compound 3 on treatment with ethyl acetoacetate in conc.
H2SO4 gave the coumarin substituted quinoline i.e. 9-methoxy-
4,5-dimethyl-2H-pyrano[3,2-c]quinoline-2-one (8) whose
structure has been assigned based on its spectral data, its IR in
KBr phase showed no diagnostic absorption in the region 3500-
3000 and showed diagnostic absorption ≈ 1700 cm-1 assignable
to a functional group. Its 1H NMR (400 MHz, DMSO-d6) spectrum
showed signals at δ 2.26 (s, 6H, CH3), δ 3.81 (s, 3H, OCH3),
5.67 (s, 1H, =CH), 5.69-8.05 (m, 3H, aromatic ); Its LC/MS
(ESI-MS) showed m/z 256 (M+ + 1) corresponding to a mole-
cular mass of 255 when recorded in the Q + 1 mode.
Compound 3 on treatment with dimethyl sulphate in
refluxing toluene followed by hydrolysis with aq. NaOH gave
4,6-dimethoxy-2-methylquinoline (9), which is reported in
literature13. Compound 9 on heating with ammonium acetate
in 1:6 ratio (w/w) at 130 °C gave 4,6-diamino-2-methylquino-
line (10) which is also reported in literature14. Compound 10
on heating with benzaldehyde (5a) in 1:2 ratio (w/v) in DMF
gave a Schiff’s base i.e. (N4′,N6′)-N4,N6-dibenzylidene-2-
methylquinoline-4,6-diamine (11a) whose structure was
assigned based on its spectral characteristics. Thus, its IR in
KBr phase showed no diagnostic absorption assignable to a
functional group. Its 1H NMR (400 MHz, DMSO-d6) spectrum
showed signals at δ 2.61 (s, 3H, CH3), 6.69-8.85 (m, 14H,
twelve aromatic + two imine protons); Its LC/MS (ESI-MS)
showed m/z 350 (M+ + 1) corresponding to a molecular mass
of 349 when recorded in the Q + 1 mode. The above reaction
of 10 with 5a has been extended to other aldehydes (5b-5e)
and the products obtained have all been assigned structures
11b-11e, respectively.
Biological results: in vitro preliminary antimicrobial
screening of newly synthesized compounds against antibac-
terial strains exhibited moderate to very good activity at MIC
of 6.25 to 12.5 mg/mL in DMSO. The styryl derivatives 6a to
6e showed comparatively good activity against all the bacterial
strains. The enhanced antibacterial activity can be attributed
to the presence of active styryl moiety in their structures. It was
also observed that chloro, nitro, methoxy, fluoro-substituted
styryl compounds displayed a significant increase in antibacterial
activity.
ACKNOWLEDGEMENTS
The authors are thankful to the authorities of Osmania
University, Hyderabad, India for providing laboratory facilities
and also to the authorities of Jawaharlal Nehru Technological
University, Hyderabad, India for encouragement.
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