Synthesis and antimicrobial activity of new 4-heteroarylamino coumarin derivatives containing nitrogen and sulfur as heteroatoms

Article abstract of DOI:10.3390/molecules15042246

Synthesis, spectral analysis and bioactivity of new coumarin derivatives are described in this paper. Eight new coumarin derivatives were synthesized in moderate to good yields by condensation of 4-chloro-3-nitrocoumarin and the corresponding heteroarylam

Full text of DOI:10.3390/molecules15042246

Molecules 2010, 15, 2246-2256; doi:10.3390/molecules15042246
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis and Antimicrobial Activity of New 4-Heteroarylamino
Coumarin Derivatives Containing Nitrogen and Sulfur as
Heteroatoms
Biljana R. Dekić 1, Niko S. Radulović 2,*, Vidoslav S. Dekić 1, Rastko D. Vukićević 3 and
Radosav M. Palić 2
1
Department of Chemistry, Faculty of Science and Mathematics, University of Priština, Lole Ribara
29, 38220 Kosovska Mitrovica, Serbia; E-Mail: dekic@inbox.com (V.D.)
2
Department of Chemistry, Faculty of Science and Mathematics, University of Niš, Višegradska 33,
18000 Niš, Serbia; E-Mail: radosavpalic@yahoo.com (R.P.)
3
Department of Chemistry, Faculty of Science, University of Kragujevac, R. Domanovića 12, 34000
Kragujevac, Serbia; E-Mail: vuk@kg.ac.yu (R.V.)
* Author to whom correspondence should be addressed; E-Mail: vangelis0703@yahoo.com;
Tel.: +381-18-533-014; Fax: +381-18-533-015.
Received: 17 March 2010; in revised form: 26 March 2010 / Accepted: 29 March 2010 /
Published: 30 March 2010
Abstract: Synthesis, spectral analysis and bioactivity of new coumarin derivatives are
described in this paper. Eight new coumarin derivatives were synthesized in moderate to
good yields by condensation of 4-chloro-3-nitrocoumarin and the corresponding
heteroarylamine. The synthesized compounds were tested for their in vitro antimicrobial
activity, in a standard disk diffusion assay, against thirteen strains of bacteria and three
fungal strains. They have shown a wide range of activity - from one completely inactive
compound to medium active ones.
Keywords: 4-heteroarylaminocoumarins; synthesis; 4-chloro-3-nitrocoumarin; spectral
analysis; antimicrobial activity

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1. Introduction
Coumarin derivatives have been shown to possess a remarkably broad spectrum of biological
activity including antibacterial [1,2], antifungal [3–5], anticoagulant [6], anti-inflammatory [7],
antitumor [8,9] and anti-HIV [10] activity. In addition, these compounds are used as additives in food
and cosmetics [11], dispersed fluorescent brightening agents and as dyes for tuning lasers [12]. Main
representatives of the class are the hydroxyl derivatives, 4- and 7-hydroxycoumarins, also biologically
active and very important for the synthesis of other coumarin derivatives.
On the other hand, the nitrogen and sulfur heterocyclic system families are very interesting due to
their physicochemical properties, especially in the sense of design of new drugs and new materials.
The chemistry and pharmacology of thiazole derivatives has been of great interest to medicinal
chemists lately [13]. The pyrazole ring is a prominent structural moiety found in numerous
pharmacologically active compounds. Pyrazole-based derivatives have been regarded as anxiolytics
[14], GABA receptor antagonists and insecticides [15], potential PET ligands for CB1 receptors [16],
anti-inflammatory, antimicrobial [17], and growth inhibition agents [18].
In continuation of our ongoing interest in synthesis of the new coumarin derivatives [20–24], and
having in mind the above considerations, we have been prompted to synthesize new, possibly more
potent, pharmacologically active compounds. We decided to combine the coumarinic system with the
above named groups of compounds in hope that the resulting novel heterocycles would be biologically
active. Additionally, a recent QSAR study of the antimicrobial activity of some 3-nitrocoumarins has
put forward some new arguments in this direction [19]. In connection with our previous work [20–24],
in the present paper we report on the synthesis of novel 4-heteroarylamino-3-nitrocoumarin derivatives
and the screening of their in vitro antimicrobial activity.
2. Results and Discussion
The investigations have been started by synthesis of 4-chloro-3-nitrocoumarin (3) applying the
known procedure [24], which was, then, submitted to the reaction with the corresponding nucleophiles
4a-h, all being commercially available [4,5-dihydro-1,3-thiazol-2-amine (4a), 5-methyl-1,3-thiazol-2-
amine (4b), 4-methyl-1,3-thiazol-2-amine (4c), 4H-1,2,4-triazol-4-amine (4d), 4-amino-1,5-dimethyl-
2-phenyl-1,2-dihydro-3H-pyrazol-3-one (4e), 5,6-dimethyl-1,3-benzothiazol-2-amine (4f), 1H-benz-
imidazol-2-amine (4g) and 1H-indazol-6-amine (4h)]. The reaction has been performed by refluxing
the substrate 3, the corresponding nucleophile 4a-h and triethylamine in a 1:1:2 ratio (Scheme 1).
Scheme 1. Synthesis of 4-heteroarylamino-3-nitrocoumarin derivatives 5a–h.
OH
OH
NO2
O
HNO3
AcOH
O
O
O
1
2
POCl3 DMF
Cl
Ar
NH
NO2
NO2
O
EtOAc
Et3N
ArNH2
+
O
5a-h
O
O
4a-h
3

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The target 4-heteroarylamino-3-nitrocoumarin derivatives 5a-h were obtained in medium to good
yields (66–89%), as it can be seen in Table 1.
Table 1. Characterization data of 4-heteroarylamino-3-nitrocoumarin derivatives 5a–h.
Compound
5a
Ar
S
Formula
Mp/ oC Colour Yield/ %
C12H9N3O4S 218-220 yellow
75
71
N
H3C
S
5b
C13H9N3O4S 229-232 orange
N
S
5c
C13H9N3O4S 212-215 yellow
72
82
N
H3C
N
N
5d
C11H7N5O4
249-252 yellow
N
CH3
H3C
N
5e
C20H16N4O5 240-242 yellow
89
N
O
H3C
S
N
5f
C18H13N3O4S 240-242 yellow
C16H10N4O4 253-255 yellow
66
76
H3C
H
N
5g
N
H
N
N
5h
C16H10N4O4 255-257 yellow
69
The structures of compounds 5a–h were confirmed using IR and NMR spectroscopy, and HRMS.
The IR spectra of synthesized compounds showed N-H and Ar-H absorptions in the range of 3,040 to
3,391 cm-1 and strong bands at 1,656–1,722 cm-1 corresponding to absorptions of the C=O and/or C=N
bonds. The IR absorptions due to the presence of the 3-NO2 group appeared at 1,319–1,382 and
1
1,523–1,556 cm-1. In H-NMR spectra, aromatic protons of the coumarin moiety resonated at
7.25–8.45 ppm. The H-6 and H-8 protons were more shielded and appeared as multiplets at 7.25–7.60
ppm. In the case of compound 5g, H-8 proton signal overlapped with the H-5’ and H-6’ signals of the
aryl side group. Protons H-5 and H-7 were more downfield and appeared as doublets of doublets at
8.06–8.45 and doublets of triplets at 7.57–7.95 ppm, respectively. In 1H-NMR spectrum of compound

Molecules 2010, 15
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5h, the signal of H-7 overlapped with the resonance of H-4’, while the signal of the proton H-5 in the
spectrum of compound 5f overlapped with the signals of the other aromatic protons of the coumarin
moiety and aryl side group of the molecule.
The synthesized compounds 5a–h were screened for their in vitro antimicrobial activity against
thirteen strains of bacteria and three fungi strains using a disk diffusion assay [20,25]. The compounds
were tested at the dose of 500 μg per disk [50 μL of the samples solutions (10 mg/mL) in DMSO].
Measured susceptibility zones to the nearest mm were the clear zones around the disk inhibiting the
microbial growth. The obtained results are listed in Table 2. As it can be seen, the prepared compounds
possess a wide range of activities – from a completely inactive compound 5e to medium active ones.
The synthesized compounds 5a–h showed no special selectivity towards any particular microorganism,
although the bacterial strains showed greater susceptibility. Also, the activity of the synthesized
compounds was slightly higher against Gram-positive compared to Gram-negative bacteria. The
largest inhibition zones were noted for S. aureus and S. lutea. On the other hand, the most resistant
strain was S. cerevisiae, being almost completely unsusceptible to the tested compounds. Considering
the antimicrobial effect towards the different strains of the same microorganism, in the case of E. coli
ATCC 8739 and E. coli ATCC 25922, the latter was less resistant to all compounds. Two different
strains of P. aeruginosa exhibited similar susceptibility to the tested compounds. The most active
compounds were 5c, 5g and 5h, showing reduction of bacterial and fungal growth comparable with the
one exhibited by the standards used as positive control (tetracycline and nystatine), especially against
medically important pathogens, though in a much larger dose. The lack of susceptibility of all tested
microorganisms toward 5e was probably the consequence of sterically-hindered nitrogen atoms of the
pyrazole ring.
Table 2. The antimicrobial activity - diameters of growth inhibition zones of compounds
5a–h in a disk diffusion assay at a dose of 500 μg per disk.
compound
Microorganism
5a
20
19
18
18
20
20
18
18
14
19
20
5b
17
21
19
19
22
20
16
18
12
16
18
19
17
14
14
na
5c
20
21
22
22
24
27
20
24
14
22
20
21
22
18
15
10
5d
16
17
17
17
18
18
15
18
13
18
17
17
17
14
15
10
5e
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
5f
16
20
20
17
17
19
18
20
14
20
18
18
19
13
14
14
5g
19
20
20
18
23
23
15
18
15
12
18
17
18
15
15
na
5h Tetracycline
Nystatine
B. subtilis
19
20
21
20
22
20
20
20
na
17
20
21
15
na
15
na
27
27
28
31
27
25
27
28
23
26
26
26
25
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
18
19
17
Cl. pyogenes
Enterococcus sp.
M. flavus
S. lutea
S. aureus
E. coli ATCC 8739
E. coli ATCC 25922
K. pneumoniae
S. enteritidis
P. vulgaris
P. aeruginosa ATCC 27857 17
P. aeruginosa ATCC 9027
A. niger
19
12
14
na
C. albicans
nt
S. cerevisiae
nt

Molecules 2010, 15
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In order to make the discussion more easy to follow and the conclusions statistically supported, we
performed agglomerative hierarchical clustering (AHC) on the mentioned samples (Table 2), using the
Excel program plug-in XLSTAT version 2008.6.07. The method was applied utilizing the values of
diameters of growth inhibition zones as original variables without any recalculation. The results of
AHC are presented in Figure 1. AHC was performed using Pearson dissimilarity (as aggregation
criteria simple linkage, unweighted pair-group average and complete linkage were used) and Euclidean
distance (aggregation criterion: weighted pair-group average, unweighted pair-group average and
Ward’s method). The definition of the groups was based on Pearson correlation, using complete
linkage and unweighted pair-group average method. AHC analysis has clearly indicated the existence
of four groups of compounds under study (designations of the compounds were given in Scheme 1).
Figure 1. Dendrogram (AHC analysis) representing antimicrobial activity (variables-
diameters of growth inhibition zones) dissimilarity relationships of the synthesized
compounds (observations) obtained by Euclidian distance dissimilarity (dissimilarity
within the interval [0, 400]), using aggregation criterion-Ward’s method. Four groups of
the compounds were found.
Dendrogram
450
400
350
300
250
200
150
100
50
0
5h
5a
5g
5b
5c
5d
5f
Compound 5e showed no activity at all towards the tested microorganisms, and was not included in
the AHC analysis. A single compound from the first group, 5h, is distinguished from the rest of the
compounds. Structurally speaking, in 5h the indazole substituent was connected to the coumarin
moiety in such a way that the larger distance of the indazole nitrogen atoms from the nitro-group of
coumarin moiety might be responsible for the observed activity. No correlation between the structure
of the compounds and the observed antimicrobial activity can be drawn out for the compounds placed
in the three remaining groups. The marked antimicrobial activity of the synthesized compounds makes
the 4-arylamino-3-nitrocoumarin derivatives, with the nitrogen and sulfur as heteroatoms, interesting

Molecules 2010, 15
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for further investigation and shows that they are a good basis for the synthesis of new, potentially more
physiologically active compounds.
3. Experimental Section
3.1. General
Melting points were determined on a Kofler hot-plate apparatus and are uncorrected. HRMS(EI)
spectra were recorded on a Finnigan-MAT 8230 BE mass spectrometer. The IR measurements (ATR-
attenuated total reflectance) were carried out with a Thermo Nicolet model 6700 FTIR instrument. The
NMR spectra were recorded on a Varian Gemini 200 spectrometer(1H-NMR at 200 MHz, 13C-NMR at
50 MHz), using DMSO-d6 as the solvent. Chemical shifts are expressed in δ (ppm) using TMS (Me4Si)
as the internal standard. For TLC, silica gel plates (Kiesel 60 F254, Merck) were used. Visualization
was affected by spraying the plates with 1:1 aqueous sulfuric acid and then heating. All the reagents
and solvents were obtained from commercial sources (Aldrich, USA; Merck, Germany; Fluka,
Germany) and used as received, except that the solvents were purified by distillation.
3.2. Synthesis of 4-chloro-3-nitrocoumarin 3
According to the previously published procedure [26], 4-hydroxycoumarin (1) was nitrated in
glacial AcOH with 72% HNO3 to afford 4-hydroxy-3-nitrocoumarin (2). Starting compound 3 was
prepared from 4-hydroxy-3-nitrocoumarin (2) following the method of Kaljaj et a l. [27]. The
preparation was carried out in the following manner: N,N-dimethylformamide (DMF, 2 mL, 26 mmol)
was cooled to 10 ºC in an ice bath. With stirring, POCl3 (4 g, 26 mmol) was added dropwise, and the
obtained mixture was stirred for an additional 15 min. Then, the ice bath was removed and the reaction
was left to proceed at room temperature for a further 15 min. Finally, the solution of 4-hydroxy-3-
nitrocoumarin (2, 5.4 g; 26 mmol) in DMF (12.5 mL) was added dropwise. After 15 minutes of
stirring, the reaction was stopped by adding cold water (15 mL). The precipitated solid was collected
by filtration and washed with saturated sodium-bicarbonate solution and water. Recrystallisation from
the mixture of benzene-hexane (1:1 volume ratio) yielded yellow crystals of 3 (5.1 g; 22.6 mmol) in
87% yield, mp 162–163 ºC. The procedure was repeated twice.
3.3. General procedure for the synthesis of 4-heteroarylamino-3-nitrocoumarins 5a–h
A solution of 4-chloro-3-nitrocoumarin (3, 1 g, 4.4 mmol) and the appropriate heteroarylamine 4a–
h (4.4 mmol) in ethyl acetate (10 mL) was refluxed in the presence of triethylamine (1 mL, 7.2 mmol)
for 3–6 h. After cooling, the precipitated solid was filtered off, washed with ethyl acetate and water.
The purity of the synthesized compounds was checked by TLC.
4-(4,5-Dihydro-1,3-thiazol-2-ylamino)-3-nitro-2H-chromen-2-one (5a): IR (neat): 3,350 – 3,083 (N-H
and Ar-H), 2,945, 1,680 (C=O), 1,605 (C=N), 1,560 (C=C), 1,523 and 1,322 (NO2), 1,219, 1,073, 917,
899, 749 cm−1; 1H=NMR (DMSO-d6) δ ppm: 8.29 (dd, 1H, H-5, J = 1.6, 8.3 Hz), 7.75, (dt, 1H, H-7,
J = 1.4, 8.6 Hz), 7.40–7.54 (m, 2H, H-6, H-8), 3.43-3.55 (overlapping signals, 4H; H-4’, H-5’);

Molecules 2010, 15
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13C- NMR (DMSO-d6) δ ppm: 155.4, 151.1, 147.2, 134.3, 124.8, 124.4, 117.8, 116.5, 114.1, 112.8,
44.5, 32.5; HRMS(EI): M+ (C12H9N3O4S), 291.2810; requires 291.2826 (Δ = -1.6 mmu).
4-[(5-Methyl-1,3-thiazol-2-yl)amino]-3-nitro-2H-chromen-2-one (5b): IR (neat): 3,367–3,116 (N-H
and Ar-H), 2,977 (C-H), 1,682 (C=O), 1,648 (C=N), 1,583 (C=C), 1,523 and 1,382 (NO2), 1,204,
1
1,073, 860, 789 cm−1; H-NMR (DMSO-d6) δ ppm: 8.06 (dd, 1H, H-5, J = 1.4, 8.0 Hz), 7.71 (dt, 1H,
H-7, J = 1.7, 8.4 Hz), 7.34–7.43 (m, 2H, H-6, H-8), 7.14 (brs, 1H, H-4’), 2.25 (s, 3H, CH3); 13C-NMR
(DMSO-d6) δ ppm: 155.4, 152.2, 152.1, 134.3 (two C), 126.4, 124.7, 122.7, 122.6, 119.6, 117.8, 117.0,
12.5; HRMS(EI): M+ (C13H9N3O4S), 303.2951; requires 303.2933 (Δ = +1.8 mmu).
4-[(4-Methyl-1,3-thiazol-2-yl)amino]-3-nitro-2H-chromen-2-one (5c): IR (neat): 3,385–3,175 (N-H
and Ar-H), 2,978, 2,945 (C-.H), 1,677 (C=O), 1,599 (C=N), 1,552 (C=C), 1,513 and 1,319 (NO2),
1,273, 1,036, 803, 756 cm−1; 1H-NMR (DMSO-d6) δ ppm: 8.06 (d, 1H, H-5, J = 7.4 Hz), 7.72 (dt, 1H,
13
H-7, J = 1.7, 8.4 Hz), 7.35–7.44 (m, 2H; H-6, H-8), 6.62 (s, 1H, H-5’), 2.17 (s, 3H, CH3); C-NMR
(DMSO-d6) δ ppm: 155.5, 155.4, 152.2, 152.1, 134.3, 126.4, 126.3, 124.7, 119.9, 117.8, 117.0, 103.7,
14.0; HRMS(EI): M+ (C13H9N3O4S) 303.2919; requires 303.2933 (Δ = -1.4 mmu).
3-Nitro-4-(4H-1,2,4-triazol-4-ylamino)-2H-chromen-2-one (5d): IR (neat): 3,391–3,101 (N-H and Ar-
H), 2,942, 1,656 (C=O), 1,612 (C=N), 1,595 (C=C), 1,527 and 1,332 (NO2), 1,292, 1,034, 929, 798
1
cm−1; H-NMR (DMSO-d6) δ ppm: 8.85 (s, 2H, H-3’, H-5’), 8.20 (dd, 1H, H-5, J = 1.8, 8.1 Hz),
7.62 (dt, 1H, H-7, J = 1.5, 8.7 Hz), 7.25-7.38 (m, 2H, H-6, H-8), 2.50 (s, 1H, N-H); 13C-NMR
(DMSO-d6) δ ppm: 155.9, 154.2, 151.2, 140.9 (two C), 132.9, 124.8, 124.1, 118.3, 116.8, 112.4;
HRMS(EI): M+ (C11H7N5O4), 273.2051; requires 273.2044 (Δ = +0.7 mmu).
1,5-Dimethyl-4-[(3-nitro-2-oxo-2H-chromen-4-yl)amino]-2-phenyl-1,2-dihydro-3H-pyrazol-3-one
(5e): IR (neat): 3,205 – 3,065 (N-H and Ar-H), 2,920 (C-H), 1,706 (C=O), 1,650 (C=N), 1,611 (C=C),
1,556 and 1,370 (NO2), 1,284, 1,056, 895, 794 cm−1; 1H-NMR (DMSO-d6) δ ppm: 9.56 (s, 1H, N-H), 8.39
(d, 1H, H-5, J = 8.0 Hz), 7.79 (t, 1H, H-7, J = 8.0 Hz), 7.27–7.60 (m, 7H, H-6, H-8, H-2”, H-3”, H-4”,
H-5”, H-6”), 3.11 (s, 3H, CH3-N-1’), 2.20 (s, 3H, CH3-C-5’); 13C-NMR (DMSO-d6) δ ppm: 161.0,
155.5, 153.1, 151.2, 146.2, 134.8, 134.3, 129.5, 129.4 (two C), 127.3, 125.1, 124.8 (two C), 124.4,
117.7, 113.9, 105.7, 35.5, 10.5; HRMS(EI): M+ (C20H16N4O5), 392.3662; requires 392.3648
(Δ = +1.4 mmu).
4-[(5,6-Dimethyl-1,3-benzothiazol-2-yl)amino]-3-nitro-2H-chromen-2-one
(5f):
IR
(neat):
3,298–3,040 (N-H and Ar-H), 2,935 (C-H), 1,722 (C=O), 1,641 (C=N), 1,600 (C=C), 1,548 and 1,371
1
(NO2), 1,279, 1,061, 869, 755 cm−1; H-NMR (DMSO-d6) δ ppm: 7.95 (dt, 1H, H-7, J = 1.7 Hz, 8.0
Hz), 7.42–7.81 (m, 5H, H-5, H-6, H-8, H-4’, H-7’), 7.36 (s, 1H, N-H), 2.19 (overlapping signals, 6H,
13
2CH3); C- NMR (DMSO-d6) δ ppm: 154.3, 153.3, 152.8, 152.5, 140.6, 137.0, 136.5, 135.2, 134.1,
126.4, 125.5, 124.0, 119.0, 117.6, 114.1, 113.2, 19.6, 19.3; HRMS(EI): M+ (C18H13N3O4S) 367.3779,
requires 367.3785 (Δ = -0.6 mmu).

Molecules 2010, 15
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4-(1H-Benzimidazol-2-ylamino)-3-nitro-2H-chromen-2-one (5g): IR (neat): 3,125–3,042 (N-H and
Ar-H), 2,979, 1,687 (C=O), 1,610 (C=N), 1,573 (C=C), 1,542 and 1,360 (NO2), 1,279, 1,075, 804, 756
1
cm−1; H-NMR (DMSO-d6) δ ppm: 8.33 (dd, 1H, H-5, J = 1.6 Hz, 7.9 Hz), 7.57 (dt, 1H, H-7, J = 1.7
Hz, 8.2 Hz), 7.37 (dt, 1H, H-6, J = 1.2 Hz, 8.5 Hz), 7.15-7.29 (m, 3H, H-8, H-5’, H-6’), 6.81–7.06 (m,
2H, H-4’, H-7’); 13C-NMR (DMSO-d6) δ ppm: 158.5, 153.0, 150.1, 149.7, 131.4, 129.3, 129.1, 125.7,
124.7, 122.3 (two C), 116.1, 114.8 (two C), 105.7, 99.3; HRMS(EI): M+ (C16H10N4O4), 322.2741;
requires 322.2750 (Δ = -0.9 mmu).
4-(1H-Indazol-6-ylamino)-3-nitro-2H-chromen-2-one (5h): IR (neat): 3,373–3,075 (N-H and Ar-H),
1
1,687 (C=O), 1,605 (C=N), 1,590 (C=C), 1,538 and 1,344 (NO2), 1,240, 1,107, 876, 759 cm−1; H-
NMR (DMSO-d6) δ ppm: 13.14 (brs, 1H, N-H), 10.42 (s, 1H, N-H), 8.45 (dd, 1H, H-5, J = 1.5 Hz, 7.3
Hz), 8.08 (s, 1H, H-3’), 7.70–7.84 (m, 2H, H-7, H-4’), 7.44–7.56 (m, 2H, H-6, H-8), 7.36 (d, 1H, H-
13
7’, J = 0.8 Hz), 7.00 (dd, 1H, H-5’, J = 1.7, 8.5 Hz); C-NMR (DMSO-d6) δ ppm: 155.3, 151.7,
146.1, 139.6, 135.8, 134.5, 133.9, 124.8 (two C), 121.5, 121.2, 117.6, 117.1, 114.9, 114.8, 104.3;
HRMS(EI): M+ (C16H10N4O4), 322.2739; requires 322.2750 (Δ = -1.1 mmu).
3.4. Antimicrobial activity
The in vitro antimicrobial activities of compounds 5a–h were tested against a panel of laboratory
control strains belonging to the American Type Culture Collection (Maryland, USA). Antibacterial
activity was evaluated against six Gram-positive and seven Gram-negative bacteria. The Gram-
positive bacteria used were: Bacillus subtilis (ATCC 6633), Clostridium pyogenes (ATCC 19404),
Enterococcus sp. (ATCC 25212), Micrococcus flavus (ATCC 10240), Sarcina lutea (ATCC 9341) and
Staphylococcus aureus (ATCC 6538). The Gram-negative bacteria utilized in the assays were:
Klebsiella pneumoniae (ATCC 10031), Proteus vulgaris (ATCC 8427), Escherichia coli (ATCC
8739), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27857), Pseudomonas
aeruginosa (ATCC 9027) and Salmonella enteritidis (ATCC 13076). The antifungal activity was
tested against three organisms Aspergillus niger (ATCC 16404), Candida albicans (ATCC 10231) and
Saccharomyces cerevisiae (ATCC 9763).
A disk diffusion method, according to the NCCLS [25], was employed for the determination of
antimicrobial activity of compounds 5a–h. The following nutritive media were used: Antibiotic
Medium 1 (Difco Laboratories, Detroit, MI USA) for growing Gram-positive and Gram-negative
bacteria, Tripton soy agar (TSA – Torlak, Belgrade) for C. albicans and A. niger , and Sabouraud
dextrose agar (Torlak, Belgrade) for S. cerevisiae . Nutritive media were prepared according to the
instructions of the manufacturer. All agar plates were prepared in 90 mm Petri dishes with 22 mL of
agar, giving a final depth of 4 mm. One-hundred microliters of a suspension of the tested
microorganisms (108 cells per mL) were spread on the solid media plates. Sterile filter paper disks
(‘‘Antibiotica Test Blattchen”, Schleicher and Schuell, Dassel, Germany, 6 mm in diameter) were
impregnated with 50 μL of the samples solutions (10 mg/mL) in DMSO (all solutions were filter-
sterilized using a 0.45 μm membrane filter), i.e. 500 μg per disk, and placed on inoculated plates.
These plates, after standing at 4 ºC for 2 h, were incubated at 37 ºC for 24 h for bacteria and at 30 ºC
for 48 h for the fungi. Standard disks of tetracycline and nystatine (origin – Institute of Immunology

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and Virology ‘‘Torlak”, 30 μg of the active component, diameter 6 mm) were used individually as
positive controls, while the disks imbued with 50 μL of pure DMSO were used as a negative control.
The diameters of the inhibition zones were measured in millimeters (to the nearest mm) using a
‘‘Fisher-Lilly Antibiotic Zone Reader” (Fisher Scientific Co., USA). Each test was performed in
quintuplicate. In order to evaluate statistically any significant differences among mean values, a one-
way ANOVA test was used. In all tests the significance level at which we evaluated critical values
differences was 5%.
4. Conclusions
In summary, this paper describes the synthesis, spectral characterization and screening of
antimicrobial activity of some new 4-arylamino-3-nitrocoumarin derivatives. 4-Chloro-3-nitro-
coumarin proved to be a good electrophilic substrate in these reactions. The synthesized compounds
showed a wide range of potentially promising antimicrobial activities. The notable antimicrobial effect
of certain compounds confirms that these are a good basis for the production of a number of new,
possibly physiologically active coumarin derivatives.
Acknowledgements
The authors acknowledge the Ministry of Science and Technological Development of Serbia for
financial support.
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Sample Availability: Samples of the compounds 5a–h are available from the authors.
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