Synthesis, characterization and antibacterial study of 7-O-substituted derivatives of chlorinated Coumarin

Article abstract of DOI:10.14233/ajchem.2014.15480

In this research work, a series of 7-O-alkyl/aralkyl/acyl substituted derivatives of chlorinated coumarin was synthesized and screened for their antibacterial activity. The parent compound 6-chloro-7-hydroxy-4-methyl-2H- chromen-2-one (3) was prepared by

Full text of DOI:10.14233/ajchem.2014.15480

Asian Journal of Chemistry; Vol. 26, No. 3 (2014), 690-696
http://dx.doi.org/10.14233/ajchem.2014.15480
Synthesis, Characterization and Antibacterial Study of
7-O-Substituted Derivatives of Chlorinated Coumarin
1
1,*
1
1
SHAHID RASOOL , AZIZ-UR-REHMAN , MUHAMMAD ATHAR ABBASI , KHADIJA NAFEESA ,
1
1
2
2
ASIA SIDDIQA , GHULAM HUSSAIN , IRSHAD AHMAD and SHAFIA ARSHAD
1Department of Chemistry, Government College University, Lahore, Pakistan
2Department of Pharmacy, Faculty of Pharmacy and Alternative Medicine, The Islamia University of Bahawalpur, Bahawalpur, Pakistan
*Corresponding author: Tel: +92 42 111000010, Ext. 450; E-mail: azizryk@yahoo.com
Received: 14 March 2013;
Accepted: 8 May 2013;
Published online: 30 January 2014;
AJC-14616
In this research work, a series of 7-O-alkyl/aralkyl/acyl substituted derivatives of chlorinated coumarin was synthesized and screened for
their antibacterial activity. The parent compound 6-chloro-7-hydroxy-4-methyl-2H-chromen-2-one (3) was prepared by the coupling of
homogeneous mixing of 4-chlororesorcinol (1) and ethylacetoacetate (2) in a conc. H2SO4 medium. Further, the 7-O-substituted derivatives
of coumarins 5a-i and 7a-h were prepared by the reaction of parent compound with different alkyl/aralkyl/acyl halides 4a-i and 6a-h. The
synthesized compounds were supported via spectral data. The prepared compounds were evaluated for inhibition activity against bacterial
strains including Gram-positive and Gram-negative and were observed that some of the compounds exhibited activity to varying degree.
Keywords: 4-Chlororesorcinol, Chlorinated coumarin, Antibacterial activity, 1H NMR, 13C NMR and EI-MS.
the purity. TLC plates were purchased from local supplier and
visualized under UV254 accompanied by ceric sulfate solution.
Infrared spectra was processed via KBr pellet method utilizing
Jasco-320-A spectrophotometer (cm-1). Melting points of the
finalized compounds were entered with the help of Griffin-
George melting point apparatus via open capillary along with
uncorrection. Nuclear magnetic resonance spectra including
1H and 13C were put down in CDCl3 on a Bruker spectrometers
operating at a frequency of 400 and 125 MHz severally. The
δ-values are accounted in ppm with TMS reference and the
J-values are presented in Hertz. EI-MS spectra were put down
on a JMS-HX-110 spectrometer.
INTRODUCTION
Coumarins belong to a huge heterocyclic family and
detected in plants like tonka bean etc. Coumarin heterocyclic
nucleus and their innumerous derivatives possess the potential
biological activity. These are familiar due to various activities
like antiinflammatory, vasodilator etc.1-8. Rutaceae plants exhibit
antimicrobial activity credibly because of coumarins which
are pharmacologically important9. Coumarin derivatives have
remarkable antimicrobial properties and this encouraged us
to synthesize coumarin derivatives as potential agents.
In continuation of our previous work of O-substituted
derivatives10, the synthesis of 7-O-alkyl/aralkyl/acyl substituted
derivatives of chlorinated coumarins was carried out with an
objective to detect the in vitro antibacterial activity against
Gram-positive and Gram-negative bacteria using standard
procedure. The present research effort was a successful attempt
to find out biologically active compounds.
Synthesis of 6-chloro-7-hydroxy-4-methyl-2H-chromen-
2-one (3): 4-Chlororesorcinol (0.035 moles, 5 g, 1) was dissol-
ved in ethylacetoacetate (0.035 mol, 5.0 mL, 2) in a 500 mL
iodine flask. 15 mL of conc. H2SO4 was added drop wise with
continuous shaking keeping in a cool media and the contents
were kept overnight. Precipitates of the product were generated
by the addition of ice cold water to the reaction mixture. Preci-
pitates were filtered off, washed up with excess cold water
and dried up to acquire the required product 3. Purity was
observed by single spot on TLC plate. Recrystallization was
carried out by using methanol.
EXPERIMENTAL
4-Chlororesorcinol, ethylacetoacetate and alkyl/acyl
halides were purchased from Merck and Alfa Aeser through
local suppliers and were processed further as supplied. The
analytical grade solvents were utilized for the research work.
Thin layer chromatography (TLC) with solvent systems of
ethyl acetate and n-hexane was a valuable tool for analyzing
General procedure for the synthesis of 6-chloro-7-
alkoxy/aralkoxy-4-methyl-2H-chromen-2-one (5a-i): The
product 3 (0.2 g, 0.00095 mol) was thoroughly mixed in 5 mL

Vol. 26, No. 3 (2014)
Synthesis and Antibacterial Study of 7-O-Substituted Derivatives of Chlorinated Coumarin 691
of aprotic solvent DMF, followed by addition of a base LiH
(0.006 g, 0.00095 mol) in a 50 mL round bottom flask and
stirred for 20 min. After that the addition of alkyl/aralkyl
halides (4a-i) was processed following the stirring for 3-4 h.
Reaction completion was tracked via TLC. The formation of
precipitates was achieved through the addition of distilled water
and were filtered off, washed up with cold distilled water and
finally dried up to collect the synthesized products, 5a-i.
General procedure for the synthesis of 6-chloro-7-
alkanoyloxy-4-methyl-2H-chromen-2-one (7a-h):The product
3 (1.00 g, 0.005 mol) was taken in a 250 mL round bottom
flask followed by the addition of distilled water. To make it
soluble, solution of 10 % NaOH was added drop wise with
gradual stirring until clear solution was obtained. Then acyl
halides (0.005 mol, 6a-h) were added and the contents were
stirred for 25 min. TLC was used up to check out the reaction
completion. The formed precipitates were filtered off, washed
up with cold distilled water and dried up to get the synthesized
compounds, 7a-h.
(C-9), 125.4 (C-5), 118.7 (C-6), 113.6 (C-10), 112.7 (C-3),
100.3 (C-8), 18.5 (C-11); EIMS: m/z 212 [M + 2]+, 210 [M]+,
193 [M-OH]+, 182 [M-CO]+, 175 [M-Cl]+, 166 [M-CO2]+, 143
[M-CH4ClO]+, 134 [M-C2HClO]+.
6-Chloro-7-methoxy-4-methyl-2H-chromen-2-one
(5a): Light pink amorphous solid; yield: 53 %; m.p. 142-144
ºC; m.f.: C11H9O3Cl; m.w.: 224 g mol-1; IR (KBr, νmax, cm-1):
3057 (C-H aromatic stretching), 1721 (stretching of α,β-
unsaturated C=O), 1627 (C=C stretching of aromatic ring);
1H NMR (400 MHz, CDCl3, ppm): δ 7.56 (s, 1H, H-5), 6.85
(s, 1H, H-8), 6.16 (s, 1H, H-3), 3.95 (s, 3H, CH3-1'), 2.37 (s,
3H, CH3-11);13C NMR (125 MHz, CDCl3, ppm): δ 160.6 (C-
2), 157.6 (C-7), 153.6 (C-4), 151.6 (C-9), 125.3 (C-5), 118.9
(C-6), 113.8 (C-10), 112.9 (C-3), 100.4 (C-8), 56.6 (C-1'),
18.6 (C-11); EIMS: m/z 226 [M + 2]+, 224 [M]+, 209 [M-
CH3]+, 193 [M-OCH3]+, 189 [M-Cl]+, 180 [M-CO2]+, 143 [M-
C2H6ClO]+, 134 [M-C3H3ClO]+.
6-Chloro-7-(propan-1-yloxy)-4-methyl-2H-chromen-
2-one (5b): White amorphous solid; yield: 59 %; m.p. 128-
130 ºC; m.f.: C13H13O3Cl; m.w.: 252 g mol-1; IR (KBr, νmax
,
Antibacterial activity assay: 96-wells microplates were
used for antimicrobial activity assay after sterilization and also
in sterile conditions. The basic principle of increase in number
of cells in a log phase of microbial growth resulting in increment
in absorbance in the broth medium is applied11,12. The bacterial
strains of Gram-positive and Gram-negative bacteria were
taken into account. The bacteria were grown in agar culture
medium. Twenty µg of the samples diluted by suited solvents
were introduced into each well. The fresh maintained culture
was also introduced into each well to make a volume of 200 µL
after suited dilution with fresh nutrient broth. The incubation
of culture having lid on the micro plate was performed at 37 ºC
for 1 day. The absorbance was observed at 540 nm before
(maintained between 0.12-0.19) and after incubation using
micro plate reader. The difference in absorbance was an
indicator of bacterial growth. The differences were compared
with the reference standards i.e. ampicillin and ciprofloxacin.
The percentage inhibition was computed by applying the
formula,
cm-1): 3055 (C-H aromatic stretching), 1719 (stretching of α,β-
unsaturated C=O), 1624 (C=C stretching of aromatic ring);
1H NMR (400 MHz, CDCl3, ppm): δ 7.55 (s, 1H, H-5), 6.82
(s, 1H, H-8), 6.16 (s, 1H, H-3), 3.99 (t, J = 7.2 Hz, 2H, H-1'),
2.36 (s, 3H, CH3-11), 1.86-1.88 (m, 2H, H-2'), 1.07 (t, J = 6.8
Hz, 3H, CH3-3');13C-NMR (125 MHz, CDCl3, ppm): δ 160.7
(C-2), 157.1 (C-7), 153.5 (C-4), 151.7 (C-9), 125.2 (C-5),
119.2 (C-6), 113.7 (C-10), 112.6 (C-3), 101.0 (C-8), 71.01
(C-1'), 22.1 (C-2'), 18.6 (C-11), 10.4 (C-3'); EIMS: m/z 254
[M+2]+, 252 [M]+, 224 [M-CO]+, 217 [M-Cl]+, 210 [M-C3H6]+,
193 [M-OC3H7]+, 188 [M-CO2]+, 143 [M-C4H10ClO]+, 134 [M-
C5H7ClO]+.
6-Chloro-7-(butan-1-yloxy)-4-methyl-2H-chromen-2-
one (5c): White amorphous solid; yield: 65 %; m.p. 130-132 ºC;
m.f.: C14H15O3Cl; m.w.: 266 g mol-1; IR (KBr, νmax, cm-1): 3053
(C-H aromatic stretching), 1718 (stretching of α,β-unsaturated
C=O), 1629 (C=C stretching of aromatic ring); 1H NMR (400
MHz, CDCl3, ppm): δ 7.54 (s, 1H, H-5), 6.82 (s, 1H, H-8),
6.14 (s, 1H, H-3), 4.06 (t, J = 6.4 Hz, 2H, H-1'), 2.36 (s, 3H,
CH3-11), 1.84 (qui, J = 6.8 Hz, 2H, H-2'), 1.48-1.51 (m, 2H,
H-3'), 0.98 (t, J = 7.2 Hz, 3H, CH3-4');13C NMR (125 MHz,
CDCl3, ppm): δ 160.7 (C-2), 157.2 (C-7), 153.6 (C-4), 151.6
(C-9), 125.2 (C-5), 119.2 (C-6), 113.5 (C-10), 112.7 (C-3),
100.0 (C-8), 69.3 (C-1'), 30.7 (C-2'), 19.1 (C-3'), 18.6 (C-11),
13.7 (C-4'); EIMS: m/z 268 [M + 2]+, 266 [M]+, 238 [M-CO]+,
231 [M-Cl]+, 222 [M-CO2]+, 212 [M-C4H6]+, 210 [M-C4H8]+,
193 [M-OC4H9]+, 143 [M-C5H12ClO]+, 134 [M-C6H9ClO]+.
6-Chloro-7-(butan-2-yloxy)-4-methyl-2H-chromen-2-
one (5d): Light brown amorphous solid; yield: 71 %; m.p.
120-122 ºC; m.f.: C14H15O3Cl; m.w.: 266 g mol-1; IR (KBr,
Control − Test
Inhibition (%) =
×100
Control
where Control = Absorbance in control with bacterial culture,
Test = Absorbance in test sample.
Minimum inhibitory concentration (MIC) was calculated
by using different dilutions (ranging 5-30 µg/well) and EZ-
Fit Perrella Scientific Inc. Amherst USA software.
Statistical analysis: The results are written as mean
sem after performance in three-folds and statistical analysis
by Microsoft Excel 2010.
Spectral characterization of the synthesized compounds
ν
max, cm-1): 3060 (C-H aromatic stretching), 1725 (stretching
6-Chloro-7-hydroxy-4-methyl-2H-chromen-2-one (3):
Light brown amorphous solid; yield: 78 %; m.p. 277-279 ºC;
m.f.: C10H7O3Cl; m.w.: 210 g mol-1; IR (KBr, νmax, cm-1): 3056
(C-H aromatic stretching), 1720 (stretching of α,β-unsaturated
C=O), 1625 (C=C stretching of aromatic ring);1H NMR (400
MHz, CDCl3, ppm): δ 7.54 (s, 1H, H-5), 6.98 (s, 1H, H-8),
6.17 (s, 1H, H-3), 2.37 (s, 3H, CH3-11); 13C NMR (125 MHz,
CDCl3, ppm): δ 160.5 (C-2), 157.7 (C-7), 153.4 (C-4), 151.5
of α,β-unsaturated C=O), 1626 (C=C stretching of aromatic
ring); 1H NMR (400 MHz, CDCl3, ppm): δ 7.55 (s, 1H, H-5),
6.82 (s, 1H, H-8), 6.13 (s, 1H, H-3), 4.35-4.40 (m, 1H, H-1'),
2.36 (s, 3H, CH3-11), 1.36 (d, J = 6.0 Hz, 3H, CH3-4'), 1.21-
1.30 (m, 2H, H-2'), 0.98 (t, J = 7.2 Hz, 3H, CH3-3');13C NMR
(125 MHz, CDCl3, ppm): δ 160.5 (C-2), 157.3 (C-7), 153.7
(C-4), 151.5 (C-9), 125.3 (C-5), 119.1 (C-6), 113.3 (C-10),

692 Rasool et al.
Asian J. Chem.
112.6 (C-3), 100.1 (C-8), 70.3 (C-1'), 31.5 (C-2'), 20.3 (C-4'),
18.7 (C-11), 10.7 (C-3'); EIMS: m/z 268 [M + 2]+, 266 [M]+,
238 [M-CO]+, 231 [M-Cl]+, 222 [M-CO2]+, 212 [M-C4H6]+,
210 [M-C4H8]+, 193 [M-OC4H9]+, 143 [M-C5H12ClO]+, 134
[M-C6H9ClO]+.
(stretching of α,β-unsaturated C=O), 1626 (C=C stretching
of aromatic ring); 1H NMR (400 MHz, CDCl3, ppm): δ 7.60
(s, 1H, H-5), 7.57 (brs, 1H, H-3'), 7.55 (brs, 1H, H-6'), 7.34 (t,
J = 7.2 Hz, 1H, H-5'), 7.22 (t, J = 7.2 Hz, 1H, H-4'), 6.90 (s,
1H, H-8), 6.16 (s, 1H, H-3), 5.24 (s, 2H, H-7'), 2.37 (s, 3H,
CH3-11); 13C NMR (125 MHz, CDCl3, ppm): δ 160.5 (C-2),
156.2 (C-7), 153.4 (C-4), 151.5 (C-9), 134.5 (C-1'), 132.7 (C-
3'), 129.6 (C-6'), 128.6 (C-4'), 127.7 (C-5'), 125.5 (C-5), 121.9
(C-6), 119.3 (C-2'), 114.2 (C-10), 113.1 (C-3), 101.8 (C-8),
70.4 (C-7'), 18.6 (C-11); EIMS: m/z 383 [M+4]+, 381 [M+2]+,
379 [M]+, 351 [M-CO]+, 344 [M-Cl]+, 335 [M-CO2]+, 210 [M-
C7H5Br]+, 193 [M-OC7H6Br]+, 155 [C6H4Br]+, 143 [C5H4Br]+,
134 [M-C9H6BrClO]+, 65 [C5H5]+, 51 [C4H3]+.
6-Chloro-7-(pentan-1-yloxy)-4-methyl-2H-chromen-2-
one (5e): Dark brown amorphous solid; yield: 53 %; m.p. 158-
160 ºC; m.f.: C15H17O3Cl; m.w.: 280 g mol-1; IR (KBr, νmax
,
cm-1): 3052 (C-H aromatic stretching), 1724 (stretching of α,β-
unsaturated C=O), 1623 (C=C stretching of aromatic ring);
1H NMR (400 MHz, CDCl3, ppm): δ 7.54 (s, 1H, H-5), 6.82
(s, 1H, H-8), 6.14 (s, 1H, H-3), 4.06 (t, J = 6.8 Hz, 2H, H-1'),
2.36 (s, 3H, CH3-11), 1.86 (qui, J = 6.8 Hz, 2H, H-2'), 1.38-
1.47 (m, 4H, H-3', H-4'), 0.93 (t, J = 7.2 Hz, 3H, CH3-5');13C
NMR (125 MHz, CDCl3, ppm): δ 160.7 (C-2), 157.2 (C-7),
153.6 (C-4), 151.6 (C-9), 125.2 (C-5), 119.2 (C-6), 113.5 (C-
10), 112.7 (C-3), 101.0 (C-8), 69.6 (C-1'), 28.4 (C-2'), 28.0
(C-3'), 22.3 (C-4'), 18.6 (C-11), 13.9 (C-5'); EIMS: m/z 282
[M+2]+, 280 [M]+, 252 [M-CO]+, 245 [M-Cl]+, 236 [M-CO2]+,
226 [M-C4H6]+, 224 [M-C4H8]+, 193 [M-OC5H11]+, 143 [M-
C6H14ClO]+, 134 [M-C7H11ClO]+.
6-Chloro-7-((3-bromophenyl)methoxy)-4-methyl-2H-
chromen-2-one (5i): Dark pink amorphous solid; yield: 56
%; m.p. 124-126 ºC; m.f.: C17H12O3BrCl; m.w.: 379 g mol-1;
IR (KBr, νmax, cm-1): 3048 (C-H aromatic stretching), 1721
(stretching of α,β-unsaturated C=O), 1626 (C=C stretching
of aromatic ring); 1H NMR (400 MHz, CDCl3, ppm): δ 7.60
(s, 1H, H-5), 7.58 (s, 1H, H-2'), 7.46 (d, J = 7.6 Hz, 1H, H-6'),
7.37 (d, J = 7.6 Hz, 1H, H-4'), 7.27 (d, J = 8.0 Hz, 1H, H-5'),
6.85 (s, 1H, H-8), 6.16 (s, 1H, H-3), 5.16 (s, 2H, H-7'), 2.37
(s, 3H, CH3-11); 13C NMR (125 MHz, CDCl3, ppm): δ 160.4
(C-2), 156.1 (C-7), 153.3 (C-4), 151.8 (C-9), 133.5 (C-1'),
132.1 (C-4'), 128.6 (C-5'), 127.9 (C-2'), 126.0 (C-6'), 125.7
(C-5), 122.3 (C-6), 118.2 (C-3'), 115.2 (C-10), 113.5 (C-3),
100.8 (C-8), 68.4 (C-7'), 18.3 (C-11); EIMS: m/z 383 [M+4]+,
381 [M + 2]+, 379 [M]+, 351 [M-CO]+, 344 [M-Cl]+, 335 [M-
CO2]+, 210 [M-C7H5Br]+, 193 [M-OC7H6Br]+, 155 [C6H4Br]+,
143 [C5H4Br]+, 134 [M-C9H6BrClO]+, 65 [C5H5]+, 51 [C4H3]+.
6-Chloro-4-methyl-2-oxo-2H-chromen-7-yl acetate
(7a): Light pink amorphous solid; yield: 79 %; m.p. 164-166
ºC; m.f.: C12H9O4Cl; m.w.: 252 g mol-1; IR (KBr, νmax, cm-1):
3046 (C-H aromatic stretching), 1740 (C=O stretching of
ester), 1725 (stretching of α,β-unsaturated C=O), 1619 (C=C
stretching of aromatic ring);1H NMR (400 MHz, CDCl3, ppm):
δ 7.53 (s, 1H, H-5), 6.97 (s, 1H, H-8), 6.14 (s, 1H, H-3), 2.36
(s, 3H, CH3-11), 2.26 (s, 3H, CH3-1'); 13C NMR (125 MHz,
CDCl3, ppm): δ 163.8 (C-12), 160.3 (C-2), 157.3 (C-4), 153.4
(C-7), 151.8 (C-9), 125.1 (C-5), 118.7 (C-6), 113.5 (C-10),
112.2 (C-3), 100.3 (C-8), 23.0 (C-1'), 18.4 (C-11); EIMS:
m/z 254 [M+2]+, 252 [M]+, 193 [M-C2H3O2]+, 224 [M-CO]+,
217 [M-Cl]+, 208 [M-CO2]+, 143 [M-C3H6ClO2]+, 134 [M-
C4H3ClO2]+.
6-Chloro-7-(heptan-1-yloxy)-4-methyl-2H-chromen-2-
one (5f): Brown amorphous solid; yield: 62 %; m.p. 172-174
ºC; m.f.: C17H21O3Cl; m.w.: 308 g mol-1; IR (KBr, νmax, cm-1):
3051 (C-H aromatic stretching), 1715 (stretching of α,β-
unsaturated C=O), 1621 (C=C stretching of aromatic ring);
1H NMR (400 MHz, CDCl3, ppm): δ 7.54 (s, 1H, H-5), 6.82
(s, 1H, H-8), 6.14 (s, 1H, H-3), 4.05 (t, J = 5.6 Hz, 2H, H-1'),
2.36 (s, 3H, CH3-11), 1.82-1.86 (m, 4H, H-2', H-3'), 1.29-
1.53 (m, 6H, H-4' to H-6'), 0.88 (t, J = 7.2 Hz, 3H, CH3-7');
13C-NMR (125 MHz, CDCl3, ppm): δ 160.6 (C-2), 157.1 (C-
7), 153.7 (C-4), 151.5 (C-9), 125.4 (C-5), 119.3 (C-6), 113.4
(C-10), 112.9 (C-3), 101.3 (C-8), 69.5 (C-1'), 28.3 (C-2'), 28.1
(C-3'), 26.3 (C-4'), 24.1 (C-5'), 21.0 (C-6'), 18.5 (C-11), 12.9
(C-7'); EIMS: m/z 310 [M+2]+, 308 [M]+, 280 [M-CO]+, 273
[M-Cl]+, 264 [M-CO2]+, 254 [M-C4H6]+, 252 [M-C4H8]+, 193
[M-OC5H11]+, 143 [M-C8H18ClO]+, 134 [M-C9H15ClO]+.
6-Chloro-7-((2-methylphenyl)methoxy)-4-methyl-2H-
chromen-2-one (5g): Light brown amorphous solid; yield:
75 %; m.p. 134-136 ºC; m.f.: C18H15O3Cl; m.w.: 314 g mol-1;
IR (KBr, νmax, cm-1): 3056 (C-H aromatic stretching), 1723
(stretching of α,β-unsaturated C=O), 1628 (C=C stretching
of aromatic ring); 1H NMR (400 MHz, CDCl3, ppm): δ 7.57
(s, 1H, H-5), 7.28-7.43 (m, 4H, H-3' to H-6'), 6.92 (s, 1H,
H-8), 6.15 (s, 1H, H-3), 5.16 (s, 2H, H-7'), 2.39 (s, 3H, CH3-
11), 2.37 (s, 3H, CH3-8');13C NMR (125 MHz, CDCl3, ppm):
δ 160.6 (C-2), 156.3 (C-7), 153.3 (C-4), 151.7 (C-9), 134.3
(C-1'), 131.3 (C-2'), 129.3 (C-3'), 128.1 (C-4'), 125.3 (C-5),
123.2 (C-5'), 122.0 (C-6'), 121.9 (C-6), 114.5 (C-10), 113.4
(C-3), 101.2 (C-8), 69.1 (C-7'), 22.7 (C-8'), 18.6 (C-11); EIMS:
m/z 316 [M+2]+, 314 [M]+, 286 [M-CO]+, 279 [M-Cl]+, 270
[M-CO2]+, 209 [M-C8H9]+, 193 [M-OC8H9]+, 143 [M-
C9H12ClO]+, 134 [M-C10H9ClO]+, 91 [C7H7]+, 79 [C6H7]+, 65
[C5H5]+, 51 [C4H3]+.
6-Chloro-4-methyl-2-oxo-2H-chromen-7-yl-2-bromo-
acetate (7b): Light brown amorphous solid; yield: 86 %; m.p.
192-194 ºC; m.f.: C12H8O4BrCl; m.w.: 331 g mol-1; IR (KBr,
ν
max, cm-1): 3049 (C-H aromatic stretching), 1744 (C=O stretch-
ing of ester), 1723 (stretching of α,β-unsaturated C=O), 1621
(C=C stretching of aromatic ring);1H NMR (400 MHz, CDCl3,
ppm): δ 7.52 (s, 1H, H-5), 6.98 (s, 1H, H-8), 6.13 (s, 1H,
H-3), 2.30 (s, 3H, CH3-11), 3.68 (s, 2H, H-1');13C NMR (125
MHz, CDCl3, ppm): δ 160.6 (C-2), 158.9 (C-12), 157.6 (C-4),
153.7 (C-7), 151.1 (C-9), 125.4 (C-5), 118.2 (C-6), 113.1
(C-10), 112.5 (C-3), 101.1 (C-8), 31.2 (C-1'), 18.2 (C-11);
EIMS: m/z 335 [M+4]+, 333 [M+2]+, 331 [M]+, 193 [M-
C2H2BrO2]+, 303 [M-CO]+, 296 [M-Cl]+, 287 [M-CO2]+, 143
[M-C3H5BrClO2]+, 134 [M-C4H2BrClO2]+.
6-Chloro-7-((2-bromophenyl)methoxy)-4-methyl-2H-
chromen-2-one (5h): White amorphous solid; yield: 78 %;
m.p. 110-112 ºC; m.f.: C17H12O3BrCl; m.w.: 379 g mol-1; IR
(KBr, νmax, cm-1): 3050 (C-H aromatic stretching), 1725

Vol. 26, No. 3 (2014)
Synthesis and Antibacterial Study of 7-O-Substituted Derivatives of Chlorinated Coumarin 693
6-Chloro-4-methyl-2-oxo-2H-chromen-7-yl phenyl
carbonate (7c): Dark brown amorphous solid; yield: 81 %;
m.p. 246-248 ºC; m.f.: C17H11O5Cl; m.w.: 330 g mol-1; IR (KBr,
NMR (125 MHz, CDCl3, ppm): δ 160.4 (C-2), 158.2 (C-12),
156.7 (C-4), 153.1 (C-7), 151.9 (C-9), 134.3 (C-4'), 132.5 (C-
2'), 129.3 (C-6'), 128.2 (C-1'), 127.5 (C-5'), 126.2 (C-3'), 125.1
(C-5), 123.6 (C-6), 114.3 (C-10), 113.5 (C-8), 101.2 (C-3),
18.4 (C-11); EIMS: m/z 389 [M+6]+, 387 [M+4]+, 385 [M+2]+,
383 [M]+, 193 [M-C7H3Cl2O2]+, 355 [M-CO]+, 348 [M-Cl]+,
339 [M-CO2]+, 143 [M-C8H6Cl3O2]+, 134 [M-C9H3Cl3O2]+, 77
[C6H5]+.
ν
max, cm-1): 3055 (C-H aromatic stretching), 1750 (C=O stretch-
ing of ester), 1727 (stretching of α,β-unsaturated C=O), 1633
(C=C stretching of aromatic ring);1H NMR (400 MHz, CDCl3,
ppm): δ 7.59 (s, 1H, H-5), 7.44 (t, J = 7.2 Hz, 2H, H-3' and
H-5'), 7.37 (d, J = 7.2 Hz, 2H, H-2' and H-6'), 7.23-7.19 (m,
1H, H-4'), 6.98 (s, 1H, H-8), 6.13 (s, 1H, H-3), 2.30 (s, 3H,
CH3-11); 13C-NMR (125 MHz, CDCl3, ppm): δ 160.8 (C-2),
158.3 (C-7), 156.2 (C-4), 155.1 (C-9), 153.0 (C-1'), 151.4
(C-12), 134.1 (C-3' and C-5'), 132.7 (C-5), 128.5 (C-4'), 127.3
(C-6), 126.4 (C-2' and C-6'), 114.0 (C-10), 113.3 (C-8), 101.4
(C-3), 18.6 (C-11); EIMS: m/z 332 [M+2]+, 330 [M]+, 193
[M-C7H5O3]+, 302 [M-CO]+, 295 [M-Cl]+, 286 [M-CO2]+, 143
[M-C8H8ClO3]+, 134 [M-C9H5ClO3]+, 77 [C6H5]+.
6-Chloro-4-methyl-2-oxo-2H-chromen-7-yl thiophene-
2-carboxylate (7g): Light grey amorphous solid; yield: 78
%; m.p. 266-268 ºC; m.f.: C15H9O4SCl; m.w.: 320 g mol-1; IR
(KBr, νmax, cm-1): 3062 (C-H aromatic stretching), 1751 (C=O
stretching of ester), 1735 (stretching of α,β-unsaturated C=O),
1650 (C=C stretching of aromatic ring);1H-NMR (400 MHz,
CDCl3, ppm): δ 7.69 (dd, J = 7.2, 1.2 Hz, 1H, H-5'), 7.59 (s,
1H, H-5), 7.47 (t, J = 7.6 Hz, 1H, H-4'), 7.35 (dd, J = 7.2, 1.2
Hz, 1H, H-3'), 6.98 (s, 1H, H-8), 6.17 (s, 1H, H-3), 2.38 (s,
3H, CH3-11);13C NMR (125 MHz, CDCl3, ppm): δ 160.3 (C-
2), 158.3 (C-12), 157.7 (C-7), 153.2 (C-4), 151.9 (C-9), 134.0
(C-2'), 131.2 (C-5'), 129.5 (C-3'), 128.1 (C-4'), 125.2 (C-5),
118.5 (C-6), 113.2 (C-10), 112.4 (C-8), 100.3 (C-3), 18.4 (C-
11); EIMS: m/z 322 [M + 2]+, 320 [M]+, 193 [M-C5H3O2S]+,
292 [M-CO]+, 285 [M-Cl]+, 276 [M-CO2]+, 143 [M-
C6H6ClO2S]+, 134 [M-C7H3ClO2S]+.
6-Chloro-4-methyl-2-oxo-2H-chromen-7-yl benzoate
(7d): Light pink amorphous solid; yield: 81 %; m.p. 236-238
ºC; m.f.: C17H11O4Cl; m.w.: 314 g mol-1; IR (KBr, νmax, cm-1):
3041 (C-H aromatic stretching), 1749 (C=O stretching of
ester), 1733 (stretching of α,β-unsaturated C=O), 1631 (C=C
stretching of aromatic ring);1H NMR (400 MHz, CDCl3, ppm):
δ 7.52 (s, 1H, H-5), 7.46 (dd, J = 7.6, 2.0 Hz, 2H, H-2' and H-
6'), 7.39-7.37 (m, 3H, H-3' to H-5'), 6.98 (s, 1H, H-8), 6.13 (s,
1H, H-3), 2.30 (s, 3H, CH3-11); 13C NMR (125 MHz, CDCl3,
ppm): δ 160.6 (C-2), 158.5 (C-12), 156.3 (C-4), 153.4 (C-7),
151.2 (C-9), 134.6 (C-4'), 131.1 (C-2' and C-6'), 128.2 (C-3'
and C-5'), 126.9 (C-1'), 125.1 (C-5), 124.5 (C-6), 114.9 (C-
10), 113.1 (C-8), 103.2 (C-3), 18.4 (C-11); EIMS: m/z 316
[M+2]+, 314 [M]+, 193 [M-C7H5O2]+, 286 [M-CO]+, 279 [M-
Cl]+, 270 [M-CO2]+, 143 [M-C8H8ClO2]+, 134 [M-C9H5ClO2]+,
77 [C6H5]+.
6-Chloro-4-methyl-2-oxo-2H-chromen-7-yl
morpholine-4-carboxylate (7h): Grey amorphous solid;
yield: 84 %; m.p. 232-234 ºC; m.f.: C15H14NO5Cl; m.w.: 323 g
mol-1; IR (KBr, νmax, cm-1): 3054 (C-H aromatic stretching),
1749 (C=O stretching of ester), 1729 (stretching of α,β-un-
saturated C=O), 1632 (C=C stretching of aromatic ring); 1H
NMR (400 MHz, CDCl3, ppm): δ 7.54 (s, 1H, H-5), 6.93 (s,
1H, H-8), 6.15 (s, 1H, H-3), 3.96 (t, J = 4.8 Hz, 4H, H-2' and
H-6'), 2.96 (t, J = 4.8 Hz, 4H, H-3' and H-5'), 2.33 (s, 3H,
CH3-11); 13C NMR (125 MHz, CDCl3, ppm): δ 160.6 (C-2),
157.6 (C-7), 153.6 (C-4), 151.6 (C-9), 149.6 (C-12), 125.3
(C-5), 118.9 (C-6), 113.8 (C-10), 112.9 (C-8), 100.4 (C-3),
69.9 (C-3' and C-5'), 39.2 (C-2' and C-6'), 18.6 (C-11); EIMS:
m/z 325 [M+2]+, 323 [M]+, 193 [M-C5H8NO3]+, 295 [M-CO]+,
288 [M-Cl]+, 279 [M-CO2]+, 143 [M-C6H11ClNO3]+, 134 [M-
C7H8ClNO3]+.
6-Chloro-4-methyl-2-oxo-2H-chromen-7-yl 2-chloro-
benzoate (7e): Light yellow amorphous solid; yield: 73 %;
m.p. 258-260 ºC; m.f.: C17H10O4Cl2; m.w.: 349 g mol-1; IR (KBr,
ν
max, cm-1): 3059 (C-H aromatic stretching), 1743 (C=O stretch-
ing of ester), 1737 (stretching of α,β-unsaturated C=O), 1641
(C=C stretching of aromatic ring);1H NMR (400 MHz, CDCl3,
ppm): δ 7.73 (dd, J = 7.6, 1.6 Hz, 1H, H-3'), 7.59 (s, 1H, H-5),
7.51 (t, J = 7.6 Hz, 1H, H-4'), 7.47 (dd, J = 7.6, 1.6 Hz, 1H, H-
6'), 7.40 (t, J = 7.6 Hz, 1H, H-5'), 6.93 (s, 1H, H-8), 6.14 (s,
1H, H-3), 2.36 (s, 3H, CH3-11); 13C NMR (125 MHz, CDCl3,
ppm): δ 160.3 (C-2), 158.6 (C-12), 156.4 (C-4), 153.7 (C-7),
151.6 (C-9), 134.2 (C-2'), 132.0 (C-4'), 129.9 (C-1'), 128.3
(C-3'), 127.8 (C-5'), 126.5 (C-6'), 125.3 (C-5), 123.5 (C-6),
114.1 (C-10), 113.7 (C-8), 101.3 (C-3), 18.8 (C-11); EIMS:
m/z 353 [M+4]+, 351 [M+2]+, 349 [M]+, 193 [M-C7H4ClO2]+,
321 [M-CO]+, 313 [M-Cl]+, 305 [M-CO2]+, 143 [M-
C8H7Cl2O2]+, 134 [M-C9H4Cl2O2]+, 77 [C6H5]+.
RESULTS AND DISCUSSION
The 7-O-alkyl/aralkyl/acyl substituted derivatives of
chlorinated coumarins, 5a-i and 7a-h were synthesized accor-
ding to the protocol sketched in Scheme-I. The general reaction
conditions and the structure characterization are already
described.
The purpose of the undertaken research work was to
introduce a series of new derivatives of chlorinated coumarin
supported by antibacterial activity. The synthesis was carried
out by the homogeneous intermixing of 4-chlororesorcinol
(1) with ethylacetoacetate (2) in a strong acidic medium of
conc. H2SO4. The homogeneous mixture was kept still for 10-
12 h in the acidic medium. The solid product 3 was collected
through filtration after the addition of ice cold water. Further,
the compound 3 was treated with different alkyl/aralkyl
halides as electrophiles, 4a-j, to afford the products, 5a-j, with
the help of NaH as weak base and aprotic polar solvent DMF.
6-Chloro-4-methyl-2-oxo-2H-chromen-7-yl 2,4-
dichlorobenzoate (7f): White amorphous solid; yield: 81 %;
m.p. 272-274 ºC; m.f.: C17H9O4Cl3; m.w.: 383 g mol-1; IR (KBr,
ν
max, cm-1): 3049 (C-H aromatic stretching), 1745 (C=O stretch-
ing of ester), 1747 (stretching of α,β-unsaturated C=O), 1646
(C=C stretching of aromatic ring);1H NMR (400 MHz, CDCl3,
ppm): δ 7.87 (d, J = 1.6 Hz, 1H, H-3'), 7.63 (s, 1H, H-5), 7.47
(d, J = 7.2 Hz, 1H, H-6'), 7.41 (dd, J = 7.2, 1.6 Hz, 1H, H-5'),
6.91 (s, 1H, H-8), 6.17 (s, 1H, H-3), 2.33 (s, 3H, CH3-11);13C

694 Rasool et al.
Asian J. Chem.
O
O
O
9
NaH, DMF
stirring
1
R
7
3
5
R-X
4a-i
10
Cl
O
HO
Cl
OH
HO
Cl
O
O
O
11
CH3
Conc. H2SO4
CH3
5a-i
C2H5O
O
12
O
O
R
NaOH/H O
2
2
C
3
1
stirring
CH3
O
RCO-X
6a-h
Cl
CH3
7a-h
C. No.
-R
{ EMBED
C. No.
-R
H3C
C. No.
-R
8'
3'
5'
5a
5b
5g
5h
7d
1'
1'
3'
5'
CH3
1'
H2C
7'
1'
ChemDraw.Document.5.0 }
Br
Cl
CH2 CH2 CH3
2'
3'
5'
7e
3'
5'
3'
1'
H2C
1'
7'
Br
Cl
CH2 CH2 CH2 CH3
2' 3'
3'
5'
3'
5c
5i
7f
3'
5'
1'
4'
Cl
1'
H2C
1'
7 '
4'CH3
CH CH2 CH3
2' 3'
CH3
1'
5d
7a
7g
5'
1'
S
O
3'
CH2 CH2 CH2 CH2 CH3
2' 3'
CH2
1'
Br
2'
5e
5f
7b
7c
7h
1'
5'
4'
5'
N
6'
3'
5'
CH2 CH2 CH2 CH2 CH2 CH2 CH3
2' 3'
O
1'
–
–
1'
5'
6'
7'
4'
Scheme-I: Outline for the synthesis of 7-O-alkyl/aralkyl/acyl-substituted derivatives of chlorinated coumarin
The precipitates of the finalized products were afforded by
filtration after the addition of the ice cold distilled water.
Similarly, the compound 3 was reacted with acyl halides in
the presence of basic medium of 10 % NaOH. The reaction
contents were further stirred for 25 min. The precipitates were
obtained through filtration and washing was carried out by
distilled water. The antibacterial activity of the two series having
ether and ester linkage, respectively of synthesized compounds
was processed against certain bacterial strains along with structure
elucidation through spectral data. The compound 3 was synthe-
sized as light brown amorphous solid which showed three 1H
NMR signals at δ 7.54 (s, 1H, H-5), 6.98 (s, 1H, H-8) and
6.17 (s, 1H, H-3) corresponding to three methine protons and
at δ 2.37 (s, 3H, CH3-11) which showed one methyl group
present in the molecules. In the 13C NMR (BB and DEPT)
spectrum, the ten signals were appeared corresponding to six
quaternary, three methine and one methyl carbons. The six
quaternary signals at δC 160.5 (C-2), 157.7 (C-7), 153.4 (C-4),
151.5 (C-9), 118.7 (C-6) and 113.6 (C-10); three methine
signals at δC 125.4 (C-5), 112.7 (C-3) and 100.3 (C-8) and
one methyl signal appeared at δC 18.5 (C-11).
the carbon atoms. The IR spectrum depicted the major
absorption bands at 3050, 1725 and 1626 cm-1 because of
C-H aromatic stretching, stretching of α,β-unsaturated C=O
and stretching of aromatic C=C in the molecule. The mass
spectrum showed two peaks at m/z 210 and 171 related to the
coumarin cation and the 2-bromobenzyl cation fragments of
the molecule, respectively. In 1H NMR spectrum, the signals
were appeared at δ 7.60 (s, 1H, H-5), 6.90 (s, 1H, H-8), 6.16
(s, 1H, H-3) and 2.37 (s, 3H, CH3-11) were attributed to 6-chloro-
7-hydroxy-4-methyl-2H-chromen-2-one (3). The substitution
of 2-bromobenzyl group was corroborated via five signals at
δ 7.57 (brs, 1H, H-3'), 7.55 (brs, 1H, H-6'), 7.34 (t, J = 7.2 Hz,
1H, H-5'), 7.22 (t, J = 7.2 Hz, 1H, H-4') and 5.24 (s, 2H, H-7')
1
in H NMR spectrum assigned to four protons of aromatic
ring and two protons of methylene group attached to oxygen
of chlorinated coumarin. From 13C NMR (BB and DEPT), the
two signals (with single intensities) showing appearance at δC
134.5 and 119.3 were assigned to two quaternary carbons
(C-1' and C-2', respectively); four signals appearing at δC 132.7,
129.6, 128.6 and 127.7 with single intensities were related to
four methine carbons (C-3', C-6', C-4' and C-5', respectively);
and one signal of methylene carbon (C-7') with single intensity
at δC 70.4 confirmed the attachment of aralkyl group. On the
ground of all above accumulative data, the structure of 5h as
confirmed as 6-chloro-7-((2-bromophenyl)methoxy)-4-methyl-
The compound 5h was synthesized as a white amorphous
solidhaving78%yieldandm.p. 110-112ºC.Them.f. C17H12BrClO3
was based on EI-MS with [M]+ ion peak at m/z 379, 1H NMR
spectrum showing the protons and 13C NMR spectrum showing

Vol. 26, No. 3 (2014)
Synthesis and Antibacterial Study of 7-O-Substituted Derivatives of Chlorinated Coumarin 695
O
O
O
Br
Cl
CH3
Br
+
m/z = 378 [M] (2 %)
+
O
O
O
m/z = 380 [M + 2] (3 %)
CH2
O
O
Cl
CH3
Cl
CH3
O
O
O
Br
Br
Cl
CH3
O
m/z = 169 (99 %)
m/z = 171 (100 %
m/z = 210 (2 %)
m/z = 185 (2 %)
m/z = 187 (2 %)
CO
C HBr
2
- HBr
Br
O
O
- HCHO
O
Cl
CH3
m/z = 65 (4 %)
m/z = 90 (65 %
Fig. 1. Mass fragmentation pattern of 6-chloro-7-((2-bromophenyl) methoxy)-4-methyl-2H-chromen-2-one (5h)
TABLE-1
ANTIBACTERIAL ACTIVITY OF THE SYNTHESIZED COMPOUNDS
MIC
Compound
Basillus subtilis
(+)
Staphylococus
aureus (+)
E. coli
(–)
Shigella sonnei
(-)
Salmonella typhi
(–)
P.aureginosa
(–)
8.43 0.42
19.14 0.17
7.52 0.14
13.37 0.27
11.01 0.22
13.06 0.12
5a
8.88 0.24
7.42 0.16
11.05 0.10
13.01 0.18
15.03 0.27
14.18 0.34
5b
–
–
–
–
–
–
5c
10.00 0.41
11.03 0.09
17.91 0.11
18.3 0.05
15.18 0.17
14.42 0.05
5d
–
–
–
–
–
–
5e
–
–
–
–
–
–
5f
–
–
–
–
–
–
5g
7.78 0.11
6.50 0.29
9.61 0.08
13.01 0.11
14.17 0.26
14.27 0.06
5h
8.402 0.18
6.57 0.12
8.84 0.41
14.66 0.22
11.19 0.31
15.30 0.17
5i
–
–
–
–
–
–
7a
–
–
–
–
–
–
7b
–
–
–
–
–
–
7c
–
–
–
–
–
–
7d
–
–
–
–
–
–
7e
–
–
–
–
–
–
7f
7g
–
–
–
–
–
–
–
–
–
–
–
–
7h
Ampicillin
Ciprofloxacin
13.92 0.29
8.96 0.02
11 0.01
8.12 0.21
11.32 0.13
8.22 0.12
13.11 0.11
11.34 0.02
12.78 0.21
8.19 0.01
16.86 0.31
10.03 0.1
Note: MIC values (minimum inhibitory concentration) of compounds were calculated using EZ–Fit Perella Scientific Inc. Amherst, USA.

696 Rasool et al.
Asian J. Chem.
2H-chromen-2-one. The mass fragmentation pattern of 5h was
clearly outlined in Fig. 1.
ACKNOWLEDGEMENTS
The authors are grateful to HEC Pakistan for fiscal aid.
Antibacterial activity: The results of two series of comp-
ounds against certain bacterial strains are tabulated in Table-1.
An overview of the results proved that the alkylated derivatives
of chlorinated coumarin were more active against the clinically
isolated bacteria (Gram-positive and Gram-negative) than the
acylated derivatives. Among the active compounds, 5a, 5b,
5d, 5h and 5i, all showed better activity potential against all
the bacterial strains. Some of them were more active against
the bacteria with respect to the standard ampicilin and
ciprofloxacin. The active five compounds have the small
aliphatic chain in common. The two compounds, 5h and 5i,
have aromatic ring substituted by halogen and showed good
activity. 5b and 5d were less active than the ciprofloxacin but
showed almost same activity relative to Ampicilin against all
the bacterial strains. All the five active compounds showed
relatively less activity than Ciprofloxacin but almost the same
activity relative to ampicilin against the three Gram-negative
bacteria.
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Conclusion
The synthesized compounds were affirmed by spectral
data. From the Table-1, its clear that all the derivatives having
small aliphatic chains were active against all the strains of
gram +ve and gram -ve bacteria.