Synthesis and antibacterial activity of quinolone-based compounds containing a coumarin moiety

Article abstract of DOI:10.1002/ardp.200700090

A new series of quinolone-based compounds containing a coumarin moiety have been synthesized and studied for their antibacterial activity against a panel of gram-positive and gram-negative bacteria, including methicillin-resistant Staphylococcus aureus (M

Full text of DOI:10.1002/ardp.200700090

42
Arch. Pharm. Chem. Life Sci. 2008, 341, 42–48
Full Paper
Synthesis and Antibacterial Activity of Quinolone-Based
Compounds Containing a Coumarin Moiety
Saeed Emami1, Alireza Foroumadi2, Mohammad A. Faramarzi2, and Nasrin Samadi2
1 Department of Medicinal Chemistry, Faculty of Pharmacy, Mazandaran University of Medical Sciences, Sari,
Iran
2 Faculty of Pharmacy and Pharmaceutical Sciences Research Center, Tehran University of Medical
Sciences, Tehran, Iran
A new series of quinolone-based compounds containing a coumarin moiety have been synthe-
sized and studied for their antibacterial activity against a panel of gram-positive and gram-nega-
tive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). The results of the anti-
bacterial evaluation of N-[2-(coumarin-3-yl)ethyl]piperazinyl quinolone derivatives in comparison
with parent quinolones (norfloxacin, ciprofloxacin, and enoxacin) indicated that N-[2-(coumarin-
3-yl)-2-oxoethyl]ciprofloxacin derivative (compound 8b) showed comparable or more potent anti-
bacterial activity with respect to the reference drugs against the test strains. Generally, in both
gram-positive and gram-negative bacteria, better results are obtained with cyclopropyl at the N-1
position of the quinolone ring and 2-oxo- on the ethyl spacer of coumarin and piperazine rings.
Keywords: Antibacterial activity / Coumarin / Quinolones / Synthesis /
Received: April 30, 2007; accepted: September 20, 2007
DOI 10.1002/ardp.200700090
evolved from agents used solely for the treatment of uri-
Introduction
nary tract infections to molecules with potent activity
against a wide spectrum of significant bacterial patho-
gens [2]. The important strategies in quinolone research
during the last few years include improving the pharma-
cokinetic properties, increasing the activity against
gram-positive cocci and anaerobes [3–6].
As targets, the quinolones have two type-II topoisomer-
ases: DNA gyrase and DNA topoisomerase IV, both
required for cell growth and division [7, 8]. The primary
target of the quinolones depends on the bacteria and
seems to be DNA gyrase in most gram-negative microor-
ganisms and topoisomerase IV in Staphylococcus aureus
and Streptococcus pneumoniae [3, 7–10].
The emergence of multidrug-resistant gram-positive bac-
teria, such as methicillin-resistant Staphylococcus aureus
(MRSA) have made treatment of infectious diseases diffi-
cult and have, over the last decades, become a serious
medical problem. As pathogenic bacteria continuously
evolve mechanisms of resistance to currently used anti-
bacterials, so the discovery of novel and potent antibacte-
rial drugs is the best way to overcome bacterial resistance
and develop effective therapies [1].
Since nalidixic acid was discovered in 1962, numerous
quinolone derivatives have been synthesized to improve
their antibacterial activities. Thus, the quinolones have
Besides the quinolones, other naturally occurring bac-
terial DNA gyrase inhibitors, such as the coumarins,
which include novobiocin 1 (Fig. 1) and structurally
related compounds, clorobiocin 2, and RU 79115 3 have
also been known as antibacterial agents [11, 12]. The cou-
marins inhibit ATPase activity of DNA gyrase by compet-
ing with ATP for binding to the B subunit of the enzyme.
However, due to their toxicity in eukaryotes, their poor
water solubility, and their low activity against gram-nega-
Correspondence: Dr. Saeed Emami, Department of Medicinal Chemis-
try, Faculty of Pharmacy, Mazandaran University of Medical Sciences,
P.O.Box 48175-861, Khazarad Road, Sari, Iran.
E-mail: sd_emami@yahoo.com
Fax: +98 151 3543-084
Abbreviations: methicillin-resistant Staphylococcus aureus (MRSA);
minimum inhibitory concentration (MIC)
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Arch. Pharm. Chem. Life Sci. 2008, 341, 42–48
Quinolone-Based Antibacterials Containing Coumarin Moiety
43
Figure 1. Structures of coumarin and quinolone antibacteri-
als (1–3 and 4–7, respectively) and the newly designed qui-
nolone-coumarin analogues 8.
tive bacteria, no pharmaceutically useful drug has, so combine the structural features of our promising anti-
far, been derived from the coumarins [11]. However, bacterial N-(2-arylethyl) piperazinyl quinolones 7 and
renewed interest in coumarin antibiotics came from coumarin antibacterial drug, RU 79115 3. Thus here, we
their potent gram-positive antibacterial activity and, wish to report the synthesis and antibacterial activity of
especially, against methicillin-resistant strains of staphy- N-[2-(coumarin-3-yl)ethyl]piperazinyl
lococci species (MRSA and MRSE) which are currently one (Fig. 1).
of the major concerns in treatment of bacterial infec-
tions [13].
quinolones
8
The structure-activity relationship studies of quino-
lones have been extensively investigated and the sub-
Results and discussion
stituent at the C-7 position has a great impact of modulat- Chemistry
ing potency, spectrum, and pharmacokinetics [3, 14–17]. The synthesis of N-[2-(coumarin-3-yl)ethyl]piperazinyl qui-
Recently, we have synthesized novel N-substituted 7- nolones 8 was achieved through the versatile and effi-
piperazinyl quinolones 7 (Fig. 1) differing from norfloxa- cient synthetic route outlined in Scheme 1. The starting
cin 4, ciprofloxacin 5, or enoxacin 6, solely by the linkage compound 3-acetylcoumarin 9 was converted to 3-(bro-
of various 2-aryl-2-oxoethyl and 2-aryl-2-oxyiminoethyl moacetyl)coumarin 10 by refluxing with Br2 in CHCl3 [22].
groups to the piperazinyl residue at C-7 of the parent Compound 10 was converted to 3-(bromoacetyl)cou-
drug with in-vitro antibacterial activity comparable or marin oxime 11a by stirring with 3 equivalents of
higher than reference drugs [18–21].
hydroxylamine hydrochloride in methanol at 22–258C.
In the current study, in continuation of our work on N- Similarly, the 3-(bromoacetyl)coumarin oxime ethers
substituted piperazinyl quinolone series, we aimed to 11b, c were prepared by reaction of compound 10 with
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S. Emami et al.
Arch. Pharm. Chem. Life Sci. 2008, 341, 42–48
Table 1. Structures and physicochemical data of compounds 8a–l.
Compound
X
Y
R
Mp.
(8C)
Reaction
Time (h)
Yield
(%)
Formula
M. W.
8a
8b
8c
8d
8e
8f
8g
8h
8i
CH
CH
N
CH
CH
N
CH
CH
N
CH
CH
N
O
O
O
Et
c-Pr
Et
Et
c-Pr
Et
Et
c-Pr
Et
Et
c-Pr
Et
212–214
211–213
215–216
151–152
157–158
155–157
211–212
138–140
216–218
227–228
180–181
170–171
12
12
6
54
70
57
96
85
88
73
66
90
93
83
91
C27H24FN3O6
C28H24FN3O6
C26H23FN4O6
C27H25FN4O6
C28H25FN4O6
C26H24FN5O6
C28H27FN4O6
C29H27FN4O6
C27H26FN5O6
C34H31FN4O6
C35H31FN4O6
C33H30FN5O6
505.49
517.51
506.48
520.51
532.52
521.5
534.54
546.55
535.52
610.63
622.64
611.62
NOH
NOH
NOH
NOCH3
NOCH3
NOCH3
NOBn
NOBn
NOBn
12
12
12
72
72
24
72
72
48
8j
8k
8l
Antibacterial activity
The newly synthesized compounds 8a–l were evaluated
for their in-vitro antibacterial activity against Staphylococ-
cus aureus ATCC 6538p, methicillin-resistant Staphylococ-
cus aureus (MRSA I and MRSA II, clinical isolates), Staphylo-
coccus epidermidis ATCC 12228, Bacillus subtilis ATCC 6633,
Escherichia coli ATCC 8739, Klebsiella pneumoniae ATCC
10031, and Pseudomonas aeruginosa ATCC 9027 using con-
ventional agar-dilution method [23]. The MIC (minimum
inhibitory concentration) values were determined by
comparison to norfloxacin 4, ciprofloxacin 5, and enoxa-
cin 6 as reference drugs. The MICs (lg/mL) obtained for
compounds 8a–l are presented in Table 2.
The MIC values of the test derivatives indicate that
most compounds exhibit good activity against gram-posi-
tives including MRSA and gram-negative bacteria.
Antibacterial screening of compounds 8a–l against
staphylococci reveals that compounds 8b and 8h exhibit
the most potent in-vitro antibacterial activity against
staphylococci and comparable activity (MIC = 0.19–
0.39 lg/mL) with respect to the compounds 4–6
(MIC = 0.19–0.78 lg/mL). In addition, the activities of
compounds 8a, 8c, 8e, and 8g against staphylococci were
respectable (MIC = 0.78–1.65 lg/mL). Most tested com-
pounds had appreciable in-vitro activity (MIC a 0.78 lg/
Reagents and conditions: (a) Br2, CHCl3, 22-258C, and then reflux; (b) hydroxyl-
amine hydrochloride, MeOH, 22 – 258C; (c) methoxy amine hydrochloride, MeOH,
22 – 258C; (d) O-benzyl hydroxylamine hydrochloride, MeOH, 22 – 258C; (e) DMF,
NaHCO3, 22 – 258C.
Scheme 1. Synthesis route of compounds 8a–l.
methoxy amine hydrochloride or O-benzylhydroxyl- mL) against B. subtilis, but were less active than com-
amine hydrochloride [18–20]. Reaction of quinolones (4, pounds 4–6. All compounds did not show any improve-
5, or 6) with a-bromoketone 10 or a-bromo oxime deriv- ment of activity against gram-negative bacteria in com-
atives 11a–c in DMF, in the presence of NaHCO3 at 22–
parison to 4–6. However, the most active compound 8b
258C afforded corresponding ketones 8a–c and oxime showed comparable activity against gram-negative bacte-
derivatives 8d–l, respectively (Table 1) [18–20].
ria, with respect to 4–6.
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Arch. Pharm. Chem. Life Sci. 2008, 341, 42–48
Quinolone-Based Antibacterials Containing Coumarin Moiety
45
Table 2. In-vitro antibacterial activities of compounds 8a–l against selected strains (MICs in lg/mL).
Compound
X
Y
R
Gram-positive organisms
Gram-negative
organisms
S. a.a)
MRSA Ib) MRSA IIb) S. e.c)
B. s.d)
E. c.e)
K. p.f)
P. a.g)
8a
8b
8c
8d
8e
8f
8g
8h
8i
8j
8k
8l
CH
CH
N
CH
CH
N
CH
CH
N
CH
CH
N
O
O
O
Et
c-Pr
Et
Et
c-Pr
Et
Et
c-Pr
Et
Et
c-Pr
Et
0.78
0.19
0.78
6.25
0.78
3.13
0.78
0.39
3.13
50
12.5
50
0.39
0.19
0.39
1.56
0.39
0.78
6.25
1.56
3.13
1.56
0.39
3.13
A100
25
1.56
0.39
0.78
6.25
1.56
3.13
1.56
0.39
3.13
A100
25
0.39
0.049
0.39
3.13
0.39
1.56
1.56
0.39
6.25
100
1.56
100
0.049
0.025
0.098
0.39
0.049
0.39
1.56
0.19
0.78
0.39
0.098
0.78
100
0.78
100
0.098
0.025
0.19
0.049
0.013
0.049
0.39
0.049
0.78
1.56
0.39
6.25
100
1.56
100
0.049
0.013
0.098
0.025
0.003
0.049
0.39
0.025
0.39
0.78
0.19
1.56
12.5
0.78
12.5
0.025
0.003
0.049
1.56
0.39
3.13
25
3.13
12.5
50
NOH
NOH
NOH
NOCH3
NOCH3
NOCH3
NOBn
NOBn
NOBn
50
A100
A100
A100
A100
1.56
0.39
1.56
A100
0.78
0.39
0.78
A100
0.78
0.39
0.78
4 Norfloxacin
5 Ciprofloxacin
6 Enoxacin
a)
S. a.: Staphylococcus aureus ATCC 6538p.
b)
c)
d)
e)
f)
MRSA I and II: methicillin-resistant Staphylococcus aureus (clinical isolates I and II).
S. e.: Staphylococcus epidermidis ATCC 12228.
B. s.: Bacillus subtilis ATCC 6633.
E. c.: Escherichia coli ATCC 8739.
K. p.: Klebsiella pneumoniae ATCC 10031.
g)
P. a.: Pseudomonas aeruginosa ATCC 9027
The MIC values of the ketones, oximes, and oxime related to drug-enzyme interactions. Whereas the great
ethers indicate that the most active compounds in each majority of the new quinolones under development or in
series were ciprofloxacin derivatives (R = cyclopropyl, X = clinical use is incorporated with piperazine or pyrroli-
CH), while enoxacin derivatives and norfloxacin deriv- dine bearing small substitution (e. g. methyl), a few of
atives exhibit equal activity against most strains. These the quinolones are substituted at C-7 with bulky substitu-
results reveal the impact of cyclopropyl substituent at N- ent on the cyclic amine. Recently, we identified a series
1 position in all series. Moreover, the alteration of ketone of N-substituted piperazinyl quinolones 7 in which the N-
to an unsubstituted or substituted oxime group could 4 hydrogen of piperazinyl group of norfloxacin 4, cipro-
not improve the overall activity against most strains. floxacin 5, and enoxacin 6 is replaced with various 2-
Generally, in both gram-positive and gram-negative bacte- oxoethyl or 2-oxyiminoethyl moieties and display in-vitro
ria, better results are obtained with cyclopropyl at N-1 antibacterial activity comparable or higher than respec-
and 2-oxo- on the ethyl spacer of coumarin and pipera- tive parent quinolones [18–21]. Therefore, our strategy
zine (compound 8b).
to achieve a better antimicrobial profile has focused on
According to structure-activity relationships for the introducing new functionality on the piperazine ring. In
quinolones, the spectrum of antibacterial coverage and the present study, structure 7 was used as starting point
the overall pharmacokinetics largely depend upon the C- for chemical manipulations. So, twelve new analogs 8a–l
7 substitution [14–18]. On the other hand, Shen et al. were prepared by replacing the aryl with a coumarin
[24, 25] have suggested along with their cooperative ring on 2-oxoethyl or 2-oxyiminoethyl moieties. These
drug-enzyme-DNA-binding model, that the 7-position is molecules 8, (Fig. 1) carry the structural features of 7-
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S. Emami et al.
Arch. Pharm. Chem. Life Sci. 2008, 341, 42–48
analyzer (Heraeus GmbH, Hanau, Germany) for C, H and N, and
the results are within l 0.4% of the theoretical values. Merck
silica gel 60 F254 plates were used for analytical TLC (Merck).
piperazinylquinolones 7 and RU 79115 3, (well known
inhibitor of DNA gyrase by binding of the coumarin moi-
ety to the B subunit of gyrase). The studies of the antibac-
terial activities of these compounds show that for a mole-
cule to exhibit considerable activity against both gram-
positive and gram-negative bacteria, the correct combina-
tion of the substituents in the molecule is very essential.
Amongst the compounds studied here, compound 8b
exhibits promising antibacterial activity. Although these
restricted series of quinolone-coumarin hybrid mole-
cules could not show high synergistic or additive effects
with respect to the parent quinolones, further tuning of
the molecules could be reached by modifying the sub-
stituents at the different positions of the coumarin ring
to improve the activity. However, in the absence of struc-
tural information on the complex of quinolones with
DNA gyrase it is difficult to rationalize these results at
the molecular level. In addition to the target enzymes
other factors such as bacterial penetration and efflux sys-
tems may play an important role in defining the SAR.
In conclusion, some of the new N-[2-(coumarin-3-yl)e-
thyl]piperazinyl quinolones 8 containing a carbonyl-
related functional groups (ketone, oxime, O-methylox-
ime, and O-benzyloxime) on the ethyl spacer showed con-
siderable antibacterial activity and modification of the
position 8 and N-1 substituent on the quinolone ring,
and ethyl spacer functionality produced relatively major
changes in terms of activity. In general, the results of
antibacterial evaluation of the test compounds in com-
parison with the reference drugs indicated that com-
pound 8b showed comparable or more potent antibacte-
rial activity with respect to the reference drugs 4–6
against all tested species.
3-(Bromoacetyl)coumarin oxime 11a
A solution of 10 (267 mg, 1.0 mmol) and hydroxylamine hydro-
chloride (209 mg, 3.0 mmol) in methanol (10 mL) was stirred at
22–258C overnight. Then, water (25 mL) was added and the pre-
cipitate was filtered and washed with water to give compound
11a (240 mg). Yield 85%; mp. 185–1878C; IR (KBr, cm– 1) 1740,
1723, 1610, 1361, 1258, 955, 835, 760; 1H-NMR (500 MHz, DMSO-
d6) 4.55 (s, 2H, CH2-Br), 7.42 (dt, 1H, H-6 coumarin, J = 7.85 and
0.82 Hz), 7.47 (d, 1H, H-8 coumarin, J = 6.94 Hz), 7.69 (dt, 1H, H-7
coumarin, J = 8.66 and 1.55 Hz), 7.88 (dd, 1H, H-5 coumarin, J =
7.66 and 1.39 Hz), 8.29 (s, 1H, H-4 coumarin), 12.41 (s, 1H,
oxime).
3-(Bromoacetyl)coumarin-O-methyloxime 11b
To a stirred solution of 10 (534 mg, 2.0 mmol) in MeOH (16 mL)
at 22–258C, was added 25% solution of O-methylhydroxyl
ammonium chloride in diluted HCl (1002 mg, 3.0 mmol). After
20 h stirring at 22–258C, the precipitated white solid was fil-
tered off, washed with cold methanol, and dried to give 11b
(518 mg). Yield 87%; mp. 152–1538C; IR (KBr, cm– 1) 1723, 1630,
1606, 1572, 1459, 1434, 1363, 1242, 1163, 1094, 1043, 1001, 886,
1
765; H-NMR (500 MHz, DMSO-d6) 4.12 (s, 3H, CH3), 4.64 (s, 2H,
CH2-Br), 7.37 (t, 1H, H-6 coumarin, J = 7.39 Hz), 7.41 (d, 1H, H-8
coumarin, J = 8.67 Hz), 7.60–7.66 (m, 2H, H-5 and H-7 coumarin),
8.05 (s, 1H, H-4 coumarin).
3-(Bromoacetyl)coumarin-O-benzyloxime 11c
A solution of 10 (534 mg, 2.0 mmol) and O-benzyl hydroxyl-
amine hydrochloride (479 mg, 3.0 mmol) in methanol (16 mL)
was stirred at 22–258C overnight. The resulting suspension was
cooled (0–48C) and the precipitated white solid was filtered off,
washed with cold methanol, and dried to give 11c (550 mg).
Yield 74%; mp. 103–1048C; IR (KBr, cm– 1) 1715, 1621, 1607,
1450, 1362, 1239, 1165, 1094, 1051, 881, 765, 734; 1H-NMR
(500 MHz, DMSO-d6) 4.68 (s, 2H, CH2-Br), 5.36 (s, 2H, O-CH2-Ph),
7.35–7.48 (m, 7H, H-6 coumarin, H-8 coumarin and phenyl),
7.58–7.64 (m, 2H, H-5 and H-7 coumarin), 8.00 (s, 1H, H-4 cou-
marin).
This work was supported by a grant from Iran National Science
Foundation (INSF).
The authors have declared no conflict of interest.
General procedure for the synthesis of compounds
8a–l
A mixture of 3-(bromoacetyl)coumarin 10 or 3-(bromoacetyl)cou-
marin oxime derivatives 11a–c (0.55 mmol), quinolone 4–6
(0.5 mmol), and NaHCO3 (0.5 mmol) in DMF (5 mL), was stirred at
22–258C for 6–72 h. After consumption of quinolone, water
(20 mL) was added and the precipitate was filtered, washed with
water, and crystallized from methanol-chloroform (9 : 1) to give
compound 8a–l.
Experimental
Chemical reagents and all solvents used in this study were pur-
chased from Merck AG (Darmstadt, Germany). The starting mate-
rials 4–6 and 9 were purchased from Aldrich Chemical (Stein-
heim, Germany). The 3-(bromoacetyl)coumarin 10 was prepared
according to the literature [22]. Melting points were determined
in open glass capillaries using Bibby Stuart Scientific SMP3 appa-
ratus (Bibby Sterlin Ltd., U.K.) and are uncorrected. The IR spec-
tra were obtained on a Shimadzu 470 spectrophotometer (potas-
Compound 8a
IR (KBr, cm– 1) 3440, 1728, 1628, 1610, 1559, 1480, 1453, 1384,
1
1
sium bromide disks; Shimadzu, Tokyo, Japan). H-NMR spectra
1261, 1190, 966, 762; H-NMR (500 MHz, DMSO-d6) 1.41 (t, 3H,
were recorded using a Bruker 500 spectrometer (Bruker Bio-
science, Billerica, MA, USA), and chemical shifts are expressed as
d (ppm) with tetramethylsilane as internal standard. Elemental
analyses were carried out on a HERAEUS CHN-O rapid elemental
CH3, J = 7.13 Hz), 2.70–2.78 (m, 4H, piperazine), 3.32–3.39 (m,
4H, piperazine), 3.93 (s, 2H, COCH2), 4.59 (q, 2H, CH2-CH3, J =
7.12 Hz), 7.19 (d, 1H, H-8 quinolone, J = 7.27 Hz), 7.41 (t, 1H, H-6
coumarin, J = 7.49 Hz), 7.49 (d, 1H, H-8 coumarin, J = 8.31 Hz),
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Arch. Pharm. Chem. Life Sci. 2008, 341, 42–48
Quinolone-Based Antibacterials Containing Coumarin Moiety
47
7.76 (dt, 1H, H-7 coumarin, J = 6.99 and 1.54 Hz), 7.92 (d, 1H, H-5
quinolone, J = 13.31 Hz), 7.97 (dd, 1H, H-5 coumarin, J = 7.80 and
1.38 Hz), 8.69 (s, 1H, H-4 coumarin), 8.96 (s, 1H, H-2 quinolone),
15.41 (s, 1H, COOH).
13.48 Hz), 8.15 (s, 1H, H-4 coumarin), 8.99 (s, 1H, H-2 quinolone),
11.30 (s, 1H, oxime), 15.32 (s, 1H, COOH).
Compound 8g
IR (KBr, cm– 1) 3453, 1731, 1629, 1517, 1474, 1452, 1384, 1258,
1045, 1011, 888, 768; H-NMR (500 MHz, DMSO-d6) 1.58 (t, 3H,
Compound 8b
1
IR (KBr, cm– 1) 3449, 1731, 1690, 1628, 1610, 1560, 1475, 1261,
CH3, J = 7.25 Hz), 2.69–2.75 (m, 4H, piperazine), 3.15–3.23 (m,
4H, piperazine), 3.92 (s, 2H, C-CH2-N), 4.04 (s, 1H, OCH3), 4.31 (q,
2H, CH2-CH3, J = 7.24 Hz), 6.78 (d, 1H, H-8 quinolone, J = 6.82 Hz),
7.34 (t, 1H, H-6 coumarin, J = 6.90 Hz), 7.39 (d, 1H, H-8 coumarin,
J = 8.60 Hz), 7.55–7.61 (m, 2H, H-5 and H-7 coumarin), 7.94 (s, 1H,
H-4 coumarin), 8.06 (d, 1H, H-5 quinolone, J = 13.06 Hz), 8.69 (s,
1H, H-2 quinolone), 15.12 (s, 1H, COOH).
1
1185, 964, 761; H-NMR (500 MHz, DMSO-d6) 1.16–1.21 (m, 2H,
cyclopropyl), 1.29–1.34 (m, 2H, cyclopropyl), 2.70–2.79 (m, 4H,
piperazine), 3.32–3.38 (m, 4H, piperazine), 3.80–3.88 (m, 1H,
cyclopropyl), 3.95 (s, 2H, COCH2), 7.44 (t, 1H, H-6 coumarin, J =
7.76 Hz), 7.49 (d, 1H, H-8 coumarin, J = 8.35 Hz), 7.57 (d, 1H, H-8
quinolone, J = 7.42 Hz), 7.77 (dt, 1H, H-7 coumarin, J = 7.79 and
1.46 Hz), 7.91 (d, 1H, H-5 quinolone, J = 13.25 Hz), 7.97 (dd, 1H, H-
5 coumarin, J = 6.59 and 1.36 Hz), 8.67 and 8.69 (two s, 2H, H-2
quinolone and H-4 coumarin), 15.20 (s, 1H, COOH).
Compound 8h
IR (KBr, cm– 1) 3454, 1728, 1627, 1608, 1492, 1456, 1337, 1258,
1
Compound 8c
1046, 889, 760; H-NMR (500 MHz, DMSO-d6) 1.17–1.22 (m, 2H,
IR (KBr, cm– 1) 3433, 1735, 1688, 1630, 1610, 1560, 1466, 1444,
1263, 959, 809, 748; 1H-NMR (500 MHz, DMSO-d6) 1.39 (t, 3H, CH3,
J = 7.00 Hz), 2.69–2.77 (m, 4H, piperazine), 3.80–3.87 (m, 4H,
piperazine), 3.93 (s, 2H, COCH2), 4.49 (q, 2H, CH2-CH3, J = 7.06 Hz),
7.44 (t, 1H, H-6 coumarin, J = 7.40 Hz), 7.48 (d, 1H, H-8 coumarin,
J = 8.34 Hz), 7.76 (dt, 1H, H-7 coumarin, J = 7.86 and 1.43 Hz), 7.97
(dd, 1H, H-5 coumarin, J = 7.75 and 1.13 Hz), 8.09 (d, 1H, H-5 qui-
nolone, J = 13.55 Hz), 8.68 (s, 1H, H-4 coumarin), 8.98 (s, 1H, H-2
quinolone), 15.33 (s, 1H, COOH).
cyclopropyl), 1.35–1.42 (m, 2H, cyclopropyl), 2.68–2.76 (m, 4H,
piperazine), 3.17–3.25 (m, 4H, piperazine), 3.47–3.56 (m, 1H,
cyclopropyl), 3.93 (s, 2H, C-CH2-N), 4.04 (s, 3H, O-CH3), 7.29 (d, 1H,
H-8 quinolone), 7.34 (t, 1H, H-6 coumarin, J = 7.52 Hz), 7.39 (d,
1H, H-8 coumarin, J = 8.62 Hz), 7.56–7.62 (m, 2H, H-5 and H-7
coumarin), 7.94 (s, 1H, H-4 coumarin), 8.01 (d, 1H, H-5 quinolone,
J = 13.08 Hz), 8.78 (s, 1H, H-2 quinolone), 15.05 (s, 1H, COOH).
Compound 8i
IR (KBr, cm– 1) 3444, 1739, 1630, 1468, 1262, 1126, 1040, 1006,
885, 806, 747; H-NMR (500 MHz, DMSO-d6) 1.50 (t, 3H, CH3, J =
Compound 8d
1
IR (KBr, cm– 1) 3443, 1719, 1669, 1629, 1484, 1473, 1387, 1258;
1H-NMR (500 MHz, DMSO-d6) 1.39 (t, 3H, CH3, J = 7.07 Hz), 2.62–
2.68 (m, 4H, piperazine), 3.22–3.30 (m, 4H, piperazine), 3.46 (s,
2H, CNOH-CH2), 4.56 (q, 2H, CH2-CH3, J = 7.17 Hz), 7.15 (d, 1H, H-8
quinolone, J = 7.26 Hz), 7.40 (t, 1H, H-6 coumarin, J = 7.75 Hz),
7.45 (d, 1H, H-8 coumarin, J = 8.30 Hz), 7.66 (dt, 1H, H-7 cou-
marin, J = 7.75 and 1.46 Hz), 7.77 (dd, 1H, H-5 coumarin, J = 7.73
and 1.19 Hz), 7.91 (d, 1H, H-5 quinolone, J = 13.28 Hz), 8.15 (s, 1H,
H-4 coumarin), 8.94 (s, 1H, H-2 quinolone), 11.31 (s, 1H, oxime),
15.35 (s, 1H, COOH).
7.18 Hz), 2.63–2.68 (m, 4H, piperazine), 3.72–3.78 (m, 4H, piper-
azine), 3.90 (s, 2H, C-CH2-N), 4.03 (s, 3H, O-CH3), 4.40 (q, 2H, CH2-
CH3, J = 7.19 Hz), 7.35 (dt, 1H, H-6 coumarin, J = 7.71 and
0.86 Hz), 7.40 (d, 1H, H-8 coumarin, J = 8.35 Hz), 7.57–7.63 (m,
2H, H-5 and H-7 coumarin), 7.95 (s, 1H, H-4 coumarin), 8.10 (d,
1H, H-5 quinolone, J = 13.36 Hz), 8.71 (s, 1H, H-2 quinolone),
15.08 (s, 1H, COOH).
Compound 8j
IR (KBr, cm– 1) 3428, 2826, 1727, 1627, 1480, 1361, 1302, 1257,
1131, 1006, 909, 750; H-NMR (500 MHz, DMSO-d6) 1.58 (t, 3H,
Compound 8e
1
IR (KBr, cm– 1) 3428, 1720, 1627, 1455, 1385, 1337, 1261, 760; 1H-
NMR (500 MHz, DMSO-d6) 1.10–1.20 (m, 2H, cyclopropyl), 1.25–
1.35 (m, 2H, cyclopropyl), 2.59–2.70 (m, 4H, piperazine), 3.09–
3.42 (m, 4H, piperazine), 3.74 (s, 2H, CNOH-CH2), 3.76–3.90 (m,
1H, cyclopropyl), 7.00 (d, 1H, H-8 quinolone, J = 8.32 Hz), 7.40 (t,
1H, H-6 coumarin, J = 7.62 Hz), 7.56 (d, 1H, H-8 coumarin, J =
7.34 Hz), 7.66 (dt, 1H, H-7 coumarin, J = 7.33 and 1.26 Hz), 7.77
(d, 1H, H-5 coumarin, J = 7.69 Hz), 7.91 (d, 1H, H-5 quinolone, J =
13.47 Hz), 8.14 (s, 1H, H-4 coumarin), 8.66 (s, 1H, H-2 quinolone),
11.31 (s, 1H, oxime), 15.21 (s, 1H, COOH).
CH3, J = 7.19 Hz), 2.65–2.72 (m, 4H, piperazine), 3.14–3.22 (m,
4H, piperazine), 3.98 (s, 2H, C-CH2-N), 4.30 (q, 2H, CH2-CH3, J =
7.22 Hz), 5.28 (s, 2H, O-CH2-Ph), 6.77 (d, 1H, H-8 quinolone , J =
6.75 Hz), 7.34 (t, 1H, H-6 coumarin, J = 7.59 Hz), 7.35–7.47 (m,
6H, H-8 coumarin and phenyl), 7.54–7.61 (m, 2H, H-5 and H-7
coumarin), 7.89 (s, 1H, H-4 coumarin), 8.06 (d, 1H, H-5 quinolone,
J = 13.04 Hz), 8.68 (s, 1H, H-2 quinolone), 15.11 (s, 1H, COOH).
Compound 8k
IR (KBr, cm– 1) 3433, 1727, 1627, 1496, 1467, 1337, 1257, 1040,
1011, 880, 757, 720; 1H-NMR (500 MHz, DMSO-d6) 1.17–1.22 (m,
2H, cyclopropyl), 1.35–1.41 (m, 2H, cyclopropyl), 2.66–2.74 (m,
4H, piperazine), 3.17–3.23 (m, 4H, piperazine), 3.48–3.54 (m,
1H, cyclopropyl), 3.98 (s, 2H, C-CH2-N), 5.28 (s, 2H, O-CH2-Ph),
7.26–7.47 (m, 8H, H-8 quinolone, H-6 coumarin, H-8 coumarin
and phenyl), 7.54–7.61 (m, 2H, H-5 and H-7 coumarin), 7.90 (s,
1H, H-4 coumarin), 8.02 (d, 1H, H-5 quinolone, J = 13.08 Hz), 8.79
(s, 1H, H-2 quinolone), 15.05 (s, 1H, COOH).
Compound 8f
IR (KBr, cm– 1) 3431, 1716, 1630, 1444, 1372, 1262, 809, 762; 1H-
NMR (500 MHz, DMSO-d6) 1.39 (t, 3H, CH3, J = 7.18 Hz), 2.67–2.73
(m, 4H, piperazine), 3.80–3.89 (m, 4H, piperazine), 3.72 (s, 2H,
CNOH-CH2), 4.51 (q, 2H, CH2-CH3, J = 7.15 Hz), 7.38 (t, 1H, H-6 cou-
marin, J = 7.83 Hz), 7.39 (d, 1H, H-8 coumarin, J = 7.76 Hz), 7.53
(dt, 1H, H-7 coumarin, J = 7.70 and 1.48 Hz), 7.77 (dd, 1H, H-5 cou-
marin, J = 7.70 and 1.17 Hz), 8.11 (d, 1H, H-5 quinolone, J =
i 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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48
S. Emami et al.
Arch. Pharm. Chem. Life Sci. 2008, 341, 42–48
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Compound 8l
IR (KBr, cm– 1) 3440, 1731, 1631, 1608, 1468, 1358, 1259, 1127,
997, 808, 752; 1H-NMR (500 MHz, DMSO-d6) 1.49 (t, 3H, CH3, J =
7.05 Hz), 2.55–2.71 (m, 4H, piperazine), 3.70–3.77 (m, 4H, piper-
azine), 3.95 (s, 2H, C-CH2-N), 4.39 (q, 2H, CH2-CH3, J = 7.08 Hz),
5.26 (s, 2H, O-CH2-Ph), 7.30–7.45 (m, 7H, H-6 coumarin, H-8 cou-
marin and phenyl), 7.54–7.61 (m, 2H, H-5 and H-7 coumarin),
7.90 (s, 1H, H-4 coumarin), 8.09 (d, 1H, H-5 quinolone, J =
13.31 Hz), 8.70 (s, 1H, H-2 quinolone), 15.08 (s, 1H, COOH).
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Antibacterial activity
[11] A. Maxwell, Mol. Microbiol. 1993, 9, 681–689.
Compounds 8a–l were evaluated for their antibacterial activity
using conventional agar-dilution method [23]. Twofold serial
dilutions of the compounds and reference drugs 4–6 were pre-
pared in Mueller–Hinton agar. Drugs (10.0 mg) were dissolved
in DMSO (1 mL) and the solution was diluted with water (9 mL).
Further progressive double dilution with melted Mueller–Hin-
ton agar was performed to obtain the required concentrations
of 100, 50, 25, 12.5, 6.25, 3.13, 1.56, 0.78, 0.39, 0.19, 0.098, 0.049,
0.025, 0.013, 0.006, 0.003, and 0.0015 lg/mL. The bacteria inoc-
ula were prepared by suspending overnight colonies from Muel-
ler–Hinton agar media in 0.85% saline. The inocula were
adjusted photometrically at 600 nm to a cell density equivalent
to approximately 0.5 McFarland standard (1.56108 CFU/mL).
The suspensions were then diluted in 0.85% saline to give
107 CFU/mL. Petri dishes were spot-inoculated with 1 lL of each
prepared bacterial suspension (104 CFU/spot) and incubated at
35–378C for 18 h. The minimum inhibitory concentration (MIC)
was the lowest concentration of the test compound, which
resulted in no visible growth on the plate. To ensure that the sol-
vent had no effect on bacterial growth, a control test was per-
formed with test medium supplemented with DMSO at the same
dilutions as used in the experiment.
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i 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.archpharm.com