Thiazolyl-pyrazole-biscoumarin synthesis and evaluation of their antibacterial and antioxidant activities

Article abstract of DOI:10.1007/s11164-016-2644-2

Abstract: A series of novel 3-(2-oxo-2H-chromen-3-yl)-1-(4-(2-oxo-2H-chromen-3-yl)thiazol-2-yl)-5-aryl-1H-pyrazol-1-ium bromides have been prepared through a one-pot three-component cyclocondensation of various coumarin chalcones, thiosemicarbazide and 2-

Full text of DOI:10.1007/s11164-016-2644-2

Res Chem Intermed
DOI 10.1007/s11164-016-2644-2
Thiazolyl-pyrazole-biscoumarin synthesis
and evaluation of their antibacterial
and antioxidant activities
Nosrat O. Mahmoodi1 Shahryar Ghodsi2
•
Received: 21 May 2016 / Accepted: 5 July 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract A series of novel 3-(2-oxo-2H-chromen-3-yl)-1-(4-(2-oxo-2H-chromen-3-
yl)thiazol-2-yl)-5-aryl-1H-pyrazol-1-ium bromides have been prepared through a one-pot
three-component cyclocondensation of various coumarin chalcones, thiosemicarbazide
and 2-bromocoumarin. The key features of this reaction are the incorporation of four
heterocyclic rings in the structure of target products, using commonly available and
inexpensive catalysts, high yields, and simple reaction conditions. Final salt products were
obtained by self-capturing of a proton by the nitrogen of the pyrazole moiety. The easy
work-up and mild reaction conditions are notable features of this protocol. The antioxidant,
antibacterial, and anti-fungal activities of the synthetic products were examined. Most of
the compounds showed good biological capacity in comparison to references.
Graphical Abstract
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Electronic supplementary material The online version of this article (doi:10.1007/s11164-016-2644-2)
contains supplementary material, which is available to authorized users.
&
Nosrat O. Mahmoodi
mahmoodi@guilan.ac.ir; nosmahmoodi@gmail.com
1
2
Department of Organic Chemistry, Faculty of Sciences, University of Guilan,
PO Box 41335-1914, Rasht, Iran
Faculty of Science, School of Chemistry, University of Tehran, Tehran, Iran
123

N. O. Mahmoodi, S. Ghodsi
Keywords Thiazolo-pyrazolium Á Coumarin Á One-pot reaction Á Antibacterial Á
Antioxidant
Introduction
In recent years, many studies, either by our research group or others, were carried
out on heterocyclic systems bearing thiazole and pyrazoline groups as pharma-
cophores. Compounds possessing pyrazoles and pyrazolines are an interesting class
of heterocycles because of their synthetic flexibility and useful biological activities
[1], serving as antimicrobials [2, 3], antivirals [4], anti-inflammatories [5, 6],
antidepressants [7], antituberculars [8], antiamoebics [9], and analgesics [10].
Similarly, the thiazole moiety is a prevalent scaffold in a number of naturally
occurring and synthetic molecules with remarkable medicinal value due to their
potential chemotherapeutic [11], fungicidal [12], antiviral [13], antibacterial [14],
anti-HIV [15], hypnotic [16], pesticidal [17], anticonvulsant, anti-inflammatory [18]
enzyme inhibition [19] and antitumour activities [20]. They have also found broad
application in the treatment of allergies [21], schizophrenia [22], hypertension [23],
and, more recently, pain [24], as fibrinogen receptor antagonists with antithrombotic
activity [25]. The presence of a toxophoric moiety (S–C=N) is responsible for such
properties, especially the antimicrobial activity, of these molecules [26].
In addition, coumarin and its derivatives are representative of one the most
important classes of heterocyclic compounds, which encompass a wide variety of
biological activities [1] that include antibacterial [27], antifungal [28, 29], antitumor
[30, 31], herbicidal, anti-inflammatory [32], anticancer [33], anti-HIV [33], and
monoamino oxidase (MAO) enzymatic inhibition [33] properties.
On the other hand, coumarin chalcones exhibit versatile pharmacological and
biological activities like antimicrobial, anti-inflammatory, anti-HIV, anticoagulant,
anticancer, antihypertensive, antimalarial, hypoglycemic, and antileshmanial activ-
ities [34]. An important feature of chalcones is their ability to act as an intermediate
for the synthesis of various valuable heterocyclic compounds such as cyclo-
hexenone, isoxazoline, pyrazoline, pyridine and pyrimidine derivatives, and so on
with considerable biological and medicinal properties [35, 36]. Keeping in mind
these interesting pharmacological features, we planned to design of molecular
skeleton by combination of these three valuable pharmacophores: coumarins,
pyrazoles and thiazoles together in a compact structure, and study the biological
activities of the resulting compounds (Fig. 1).
Experimental
Materials and methods
Melting points (uncorrected) were determined by using a Mettler Fp5 apparatus.
The infrared (IR) spectra were recorded on a Shimadzu IR-470 spectrophotometer
using KBr disc method. Proton (1H) and carbon-13 (13C) spectra were recorded on a
123

Thiazolyl-pyrazole-biscoumarin synthesis and evaluation…
Fig. 1 Structure of products 4a–q and defining biological activities of each moiety
Avance III Bruker 400 MHz spectrometer at 25 °C using tetramethylsilane as an
internal standard and deuterated dimethyl sulfoxide (DMSO-d6 ) as the solvent.
Chemical shifts were reported in ppm (d). Splitting patterns were assigned as: s for
singlet, br s for broad singlet, d for doublet, t for triplet, td for triplet of doublets, dd
for doublet of doublets, ddd for doublet of doublet of doublets, and m for multiplet.
Elemental analyses were performed on a Perkin Elmer series II, 2400 CHN analyzer
and experimental data were within 0.4 % of the theoretical values. A microwave
oven (ETHOS 1600, Milestone) with a power of 600 W specially designed for
organic synthesis was used. Sonication was performed by a Fisher sonicator (with a
frequency of 25 kHz and a nominal power 600 W). The X-ray data were obtained
with a Bruker SMART diffractometer (Fig. 2).
General procedure for the synthesis of compounds 4a–q
An EtOH solution of thiosemicarbazide 3 (5.00 mmol) was added to a solution of
the appropriate prepared coumarin chalcone 1a–d (5.00 mmol) in hot EtOH
(10 mL) with stirring. The resulting solution was refluxed for 4–6 h in the presence
of glacial AcOH. Then, an ethanolic solution (30 mL) of 3-(2-bromoacetyl)-
coumarin 2a–d (1.34 g, 5 mmol) was added to the resulting 4,5-dihydropyrazol-1-
thiocarboxamide 3 and the mixture was refluxed on a water bath for 2 h. After
completion of the reaction [monitored by thin layer chromatography (TLC)] and
neutralization with a saturated solution of NaHCO3 , the precipitated solid was
filtered, washed with EtOH, and recrystallized from a mixture of dimethylfor-
mamide (DMF)/H2O to afford the target compounds.
3-(2-Oxo-2H-chromen-3-yl)-1-(4-(2-oxo-2H-chromen-3-yl)thiazol-2-yl)-5-phenyl-
1H-pyrazol-1-ium (4a) Dark cream-colored solid (2.296 g, 77 %); Mp
287–290 °C; FT-IR (KBr; m max/cm-1): 3419 (stretch N–H), 3118 (stretch C–H
Ar), 1722, 1676 (stretch O–C=O), 1612 (stretch C=N), 1562, 1455 (stretch C=C),
1419 (bending C–H), 1278, 1204, 1089, 1111 (stretch C–O, bending C–N, C–S),
123

N. O. Mahmoodi, S. Ghodsi
Fig. 2 X-ray single crystal structure of compounds 4a, 4d, 4i and 4n
1
934, 861, 756, 700 (OOP C–H); H nuclear magnetic resonance (NMR; 400 MHz,
DMSO-d6): d = 11.23 (br s, 1H, NH, Hr), 8.62 (s, 1H, He), 8.52 (d, J = 5.2 Hz, 1H,
Hd), 8.42 (dd, J1 = 7.6, J2 = 1.6 Hz, 1H, Hb), 8.24–8.25 (m, 2H, Hc, Ha), 8.1 (s,
1H, Hm), 7.917 (s, 1H, Hl), 7.61–7.88 (m, 10H, Hf, Hg, Hh, Hi, Hj, Hk, Hn, Ho, Hp,
Hq) ppm; 13C NMR (100 MHz, DMSO-d6): d; 165.2 (C=O), 162.4, 159.8, 153.9,
150.8, 143.6, 141.9, 135.3, 132.6, 130.9, 128.5, 126.7, 125.3, 124.9, 123.7, 119.2,
118.2, 117.8, 116.7, 116, 112.8, 106; MS (EI) m/z: 516.10 (M)?; Anal. calcd. for
C30H18N3O4S?: C, 69.76; H, 3.51; N, 8.13. Found: C, 69.89; H, 3.61; N, 8.19 %.
1-(4-(8-Methoxy-2-oxo-2H-chromen-3-yl)thiazol-2-yl)-3-(2-oxo-2H-chromen-3-yl)-
5-phenyl-1H-pyrazol-1-ium (4b) Lemon-yellow solid (2.505 g, 80 %); Mp
275–278 °C; FT-IR (KBr; m max/cm-1): 3428 (stretch N–H), 3136 (stretch C–H
123

Thiazolyl-pyrazole-biscoumarin synthesis and evaluation…
Ar), 1721, 1676 (stretch O–C=O), 1611(stretch C=N), 1565, 1458 (stretch C=C),
1366 (bending C–H), 1276, 1203, 1108, 1033 (stretch C–O, bending C–N, C–S),
1
933, 860, 759, 699 (OOP C–H); H NMR (400 MHz, DMSO-d6): d = 11.23 (br s,
1H, NH, Hr), 8.61 (s, 1H, He), 8.42 (d, J = 8 Hz, 1H, Hd), 8.24 (s, 1H, Hm), 7.87 (d,
J = 7.6 Hz, 1H, Hn), 7.71 (t, J = 7.8 Hz, 2H, Hc and Ho), 7.63 (t, J = 7.2 Hz, 2H,
Hh and Hj), 7.43–7.53 (m, 8H, Ha, Hb, Hf, Hg, Hi, Hk, Hl, Hp), 3.93 (s, 3H, OCH3);
MS (EI) m/z: 546.11 (M)?; Anal. calcd. for C31H20N3O5S?: C, 68.12; H, 3.69; N,
7.69. Found: C, 68.20; H, 3.80; N, 6.76 %.
1-(4-(7-Methoxy-2-oxo-2H-chromen-3-yl)thiazol-2-yl)-3-(2-oxo-2H-chromen-3-yl)-
5-phenyl-1H-pyrazol-1-ium (4c) Brown solid (2.505 g, 80 %); Mp 233–237 °C;
FT-IR (KBr; m max/cm-1): 3433 (stretch N–H), 3136 (stretch C–H Ar), 1720, 1681
(stretch O–C=O), 1611 (stretch C=N), 1557, 1456 (stretch C=C), 1368 (bending C–
H), 1279, 1220, 1152, 1024 (stretch C–O, bending C–N, C–S), 933, 845, 761, 702
1
(OOP C–H); H NMR (400 MHz, DMSO-d6): d = 11.23 (br s, 1H, NH, Hr), 8.61
(s, 1H, He), 8.41 (d, J = 8 Hz, 1H, Hd), 8.24 (s, 1H, Hm), 7.87 (d, J = 7.8 Hz, 1H,
Hb), 7.85 (d, J = 7.8 Hz, 1H, Ha), 7.71 (t, J = 7.8 Hz, 1H, Hc), 7.63 (t, J = 7.8 Hz,
2H, Hh, Hj), 7.43–7.53 (m, 8H, Hf, Hg, Hj, Hk, Hl, Hn, Ho, Hq); MS (EI) m/z: 546.11
(M)?; Anal. calcd. for C31H20N3O5S: C, 68.12; H, 3.69; N, 7.69. Found: C, 68.24;
H, 3.75; N, 6.71 %.
5-(4-Chlorophenyl)-3-(2-oxo-2H-chromen-3-yl)-1-(4-(2-oxo-2H-chromen-3-yl)thia-
zol-2-yl)-1H-pyrazol-1-ium (4d) Brick-red solid (2.428 g, 77 %); Mp
283–287 °C; FT-IR (KBr; m max/cm-1): 3413 (stretch N–H), 3116 (stretch C–H
Ar), 1722, 1674 (stretch O–C=O), 1611 (stretch C=N), 1561, 1454 (stretch C=C),
1366, 1322 (bending C–H), 1276, 1203,1088, 1024 (stretch C–O, bending C–N, C–
S), 930, 860, 753, 698 (OOP C–H); 1H NMR (400 MHz, DMSO-d6): d = 11.24 (br
s, 1H, NH, Hr), 8.63 (s, 1H, He), 8.43 (d, J = 7.2 Hz, 1H, Hd), 8.26 (s, 1H, Hm),
7.87 (d, J = 7.6 Hz, 2H, Ha, Hq), 7.72 (t, J = 7.8 Hz, 2H, Hh, Hj), 7.65 (t,
J = 8.3 Hz, 2H, Hg, Hk), 7.40–7.55 (m, 7H, Hb, Hc, Hf, Hl, Hn, Ho, Hp); 13C NMR
(100 MHz, DMSO-d6): d; 169 (C=O), 161.3, 153.8, 150.8, 144, 143.5, 139.8, 138.9,
135.4, 133.16, 131.67, 129.66, 128.84, 125.36, 124.7, 123.56, 122.3, 120.8, 119.68,
118.37, 117.92, 116.63, 116.55, 113.52. MS (EI) m/z: 550.06 (M)?. Anal. calcd. for
C30H17ClN3O4S?: C, 65.40; H, 3.11; N, 7.63. Found: C, 65.31; H, 3.06; N, 7.58 %.
5-(4-Chlorophenyl)-1-(4-(8-methoxy-2-oxo-4a,8a-dihydro-2H-chromen-3-yl)thiazol-2-yl)-
3-(2-oxo-2H-chromen-3-yl)-1H-pyrazol-1-ium (4e) Golden solid (2.643 g, 80 %); Mp
296–299 °C; FT-IR (KBr; m max/cm-1): 3427 (stretch N–H), 3132 (stretch C–H
Ar), 1721, 1676 (stretch O–C=O), 1612 (stretch C=N), 1564, 1456 (stretch C=C),
1367, 1321 (bending C–H), 1277, 1204, 1091, 1033 (stretch C–O, bending C–N, C–
S), 936, 861, 758, 700 (OOP C–H); 1H NMR (400 MHz, DMSO-d6): d = 11.23 (br
s, 1H, NH, Hr), 8.61 (s, 1H, He), 8.41 (d, J = 7.2 Hz, 1H, Hd), 8.24 (s, 1H, Hm),
7.85 (d, J = 7.6 Hz, 1H, Ha), 7.71 (t, J = 7.8 Hz, 2H, Hh,Hj), 7.63 (t, J = 7.8 Hz,
2H, Hg,Hk), 7.43–7.53 (m, 7H, Hb, Hc, Hf, Hl, Hn, Ho, Hp), 3.93 (s, 3H, OCH3); MS
(EI) m/z: 580.07 (M)?; Anal. calcd. for C31H19ClN3O5S?: C, 64.08; H, 3.30; N,
7.23. Found: C, 64.20; H, 3.44; N, 7.41 %.
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N. O. Mahmoodi, S. Ghodsi
5-(2-Chlorophenyl)-3-(2-oxo-2H-chromen-3-yl)-1-(4-(2-oxo-2H-chromen-3-yl)thia-
zol-2-yl)-1H-pyrazol-1-ium (4f) Lemon-yellow solid (2.523 g, 80 %); Mp
292–296 °C; FT-IR (KBr; m max/cm-1): 3418 (stretch N–H), 3118 (stretch C–H
Ar), 1722, 1675 (stretch O–C=O), 1611 (stretch C=N), 1561, 1454 (stretch C=C),
1372 (bending C–H), 1277, 1204, 1103, 1028 (stretch C–O, bending C–N, C–S),
1
935, 862, 756, 699 (OOP C–H); H NMR (400 MHz, DMSO-d6): d = 11.22 (br s,
1H, NH, Hr), 8.61 (s, 1H, He), 8.41 (d, J = 8 Hz, 1H, Hd), 8.23 (s, 1H, Hm), 7.85 (d,
J = 7.6 Hz, 2H, Ha, Hq), 7.71 (t, J = 7.8 Hz, 2H, Hb, Hp), 7.63 (t, J = 7.4 Hz, 2H,
Hc, Ho), 7.43–7.53 (m, 7H, Hf, Hg, Hh, Hi, Hj, Hk, Hl); MS (EI) m/z: 550.06 (M)?;
Anal. calcd. for C30H17ClN3O4S?: C, 65.40; H, 3.11; N, 7.63. Found: C, 65.51; H,
3.16; N, 7.75 %.
5-(2-Chlorophenyl)-1-(4-(8-methoxy-2-oxo-2H-chromen-3-yl)thiazol-2-yl)-3-(2-oxo-2H-
chromen-3-yl)-1H-pyrazol-1-ium (4g) Light cream-colored solid (2.610 g, 79 %);
Mp 298–300 °C; FT-IR (KBr; m max/cm-1): 3420 (stretch N–H), 3122,2931 (stretch
C–H Ar), 1722, 1675 (stretch O–C=O), 1611 (stretch C=N), 1563, 1455 (stretch
C=C), 1380 (bending C–H), 1277, 1203, 1110, 1089 (stretch C–O, bending C–N, C–
S), 934, 861, 756, 699 (OOP C–H); 1H NMR (400 MHz, DMSO-d6): d = 11.23 (br
s, 1H, NH, Hr), 8.62 (s, 1H, He), 8.5 (dd, J1 = 15.4, J2 = 1.2 Hz, 1H, Hd), 8.4 (s,
1H, Hm), 8.22 (dd, J1 = 17.4, J2 = 1.2 Hz, 1H, Hb), 7.89–7.95 (m, 1H, Hc), 7.86 (s,
1H, Hl), 7.25–7.69 (m, 9H, Ha, Hf, Hh, Hi, Hj, Hn, Ho, Hp, Hk), 3.94 (s, 3H, OCH3)
ppm; 13C NMR (100 MHz, DMSO-d6): d; 168.5, 161.3, 153.8, 150.8, 146.8, 146.6,
144, 143.5, 135.4, 133.1, 131.7, 129.6, 128.8, 128.4, 126.8, 125.9, 125.4, 124.7,
121.2, 119.7, 119.3, 119, 118.7, 117.8, 116.5, 113.5, 111.3, 100.8, 89.65, 56.6; MS
(EI) m/z: 580.07 (M)?; Anal. calcd. for C31H19ClN3O5S?: C, 64.08; H, 3.30; N,
7.23. Found: C, 64.16; H, 3.37; N, 7.24 %.
5-(4-Methoxyphenyl)-3-(2-oxo-2H-chromen-3-yl)-1-(4-(2-oxo-2H-chromen-3-yl)thiazol-
2-yl)-1H-pyrazol-1-ium (4h) Cream-colored solid (2.505 g, 80 %); Mp
295–298 °C; FT-IR (KBr; m max/cm-1): 3417 (stretch N–H), 3115 (stretch C–H
Ar), 1719, 1672 (stretch O–C=O), 1610 (stretch C=N), 1560, 1457 (stretch C=C),
1369 (bending C–H), 1272, 1202, 1088 (stretch C–O, bending C–N), 931, 858, 755,
1
699 (OOP C–H); H NMR (400 MHz, DMSO-d6): d = 11.23 (br s, 1H, NH, Hr),
8.62 (s, 1H, He), 8.43 (dd, J1 = 7.4, J2 = 1.2 Hz, 1H, Hd), 8.26 (d, J = 1.2, 1H,
Hm), 7.87 (dd, J1 = 7.8, J2 = 1.2 Hz, 2H, Ha, Hq), 7.72 (dt, J1 = 7.9, J2 = 1.6 Hz,
2H, Hb, Hp), 7.65 (dt, J1 = 7.6, J2 = 1.2 Hz, 2H, Hc, Ho), 7.47–7.56 (m, 7H, Hf, Hg,
Hh, Hj, Hk, Hl, Hn) ppm; 13C NMR (100 MHz, DMSO-d6): d; 161.32, 159.7, 153.8,
150.8, 144, 143.5, 135.4, 135, 133.2, 132.5, 131.7, 129.6, 129.1, 125.8, 125.3,
124.7, 121.9, 119.7, 118.4, 117.9, 116.6, 116.5, 113.5, 106.18, 80.65; MS (EI) m/z:
546.11 (M)?; Anal. calcd. for C31H20N3O5S?: C, 68.12; H, 3.69; N, 7.69. Found: C,
68.15; H, 3.79; N, 7.78 %.
1-(4-(8-Methoxy-2-oxo-2H-chromen-3-yl)thiazol-2-yl)-5-(4-methoxyphenyl)-3-(2-oxo-
2H-chromen-3-yl)-1H-pyrazol-1-ium (4i) Cream-colored solid (2.626 g, 80 %); Mp
292–296 °C; FT-IR (KBr; m max/cm-1) : 3422 (stretch N–H), 3117 (stretch C–H
Ar), 1722, 1675 (stretch O–C=O), 1611 (stretch C=N), 1562, 1455 (stretch C=C),
1380, 1323 (bending C–H), 1276, 1203, 1089, 1028 (stretch C–O, bending C–N, C–
123

Thiazolyl-pyrazole-biscoumarin synthesis and evaluation…
S), 931, 860, 753, 698 (OOP C–H); 1H NMR (400 MHz, DMSO-d6): d = 11.22 (br
s, 1H, NH, Hr), 8.60 (s, 1H, He), 8.40 (d, J = 8 Hz, 1H, Hd), 8.22 (s, 1H, Hm), 7.85
(d, J = 7.6 Hz, 2H, Hg, Hk),7.70 (t, J = 7.8 Hz, 2H, Hb, Hp), 7.63 (t, J = 7.8 Hz,
2H, Hc, Ho), 7.43–7.53 (m, 6H, Ha, Hg, Hh, Hj, Hk, Hl), 3.932 (s, 6H, 2OCH3) ppm;
13C NMR (100 MHz, DMSO-d6): d; 179.59, 164.6, 161.37, 159.69, 153.8, 150.8,
143.98, 143.48, 142.87, 139.56, 136.3, 135.34, 134.35, 133.16, 131.66, 129.66,
128.46, 127.72, 127.19, 125.83, 125.35, 124.66, 122.23, 120.45, 118.36, 117.91,
116.61, 116.54, 113.49, 56.6, 56.9; MS (EI) m/z: 576.12 (M)?; Anal. calcd. for
C32H22N3O6S?: C, 66.66; H, 3.85; N, 7.29. Found: C, 66.54; H, 3.73; N, 7.18 %.
5-(4-Nitrophenyl)-3-(2-oxo-2H-chromen-3-yl)-1-(4-(2-oxo-2H-chromen-3-yl)thiazol-2-yl)-
1H-pyrazol-1-ium (4j) Orange solid (2.405 g, 75 %); Mp 235–238 °C; FT-IR (KBr;
m max/cm-1): 3404 (stretch N–H), 3161 (stretch C–H Ar), 1724, 1679 (stretch O–
C=O), 1607 (stretch C=N), 1504, 1462 (stretch C=C), 1334 (bending C–H), 1239,
1
1107 (stretch C–O, bending C–N), 1000, 954, 845, 752, 698, 588 (OOP C–H); H
NMR (400 MHz, DMSO-d6): d = 11.23 (br s, 1H, NH, Hr), 8.62 (s, 1H, He), 8.51
(d, J = 19.6, 1H, Hd), 8.44 (s, 1H, Hm), 8.32 (d, J = 8.8, 1H, Hn), 7.99 (t,
J = 10.2 Hz, 2H, Hb, Hp), 7.72 (dt, J1 = 7.8, J2 = 1.6 Hz, 2H, Hc, Ho), 7.49–7.56
(m, 8H, Ha, Hf, Hl, Hg, Hh, Hj, Hk, Hq); MS (EI) m/z: 561.09 (M)?; Anal. calcd. for
C30H17N4O6S?: C, 64.17; H, 3.05; N, 9.98. Found: C, 64.04; H, 3.02; N, 9.90 %.
3-(2-Oxo-2H-chromen-3-yl)-1-(4-(2-oxo-2H-chromen-3-yl)thiazol-2-yl)-5-(thiophen-2-yl)-
1H-pyrazol-1-ium (4k) Cream-colored solid (2.409 g, 80 %); Mp 290–292 °C; FT-
IR (KBr; m max/cm-1): 3414 (stretch N–H), 3129 (stretch C–H Ar), 1722, 1675
(stretch O–C=O), 1609 (stretch C=N), 1560, 1456 (stretch C=C), 1372 (bending C–
H), 1276, 1204, 1099, 1028 (stretch C–O, bending C–N, C–S), 935, 860, 756, 699
1
(OOP C–H); H NMR (400 MHz, DMSO-d6): d = 11.22 (br s, 1H, NH, Hr), 8.61
(s, 1H, He), 8.41 (d, J = 8 Hz, 1H, Hi), 8.23 (s, 1H, Hm), 7.85 (d, J = 7.6 Hz, 2H,
Hd, Hn), 7.70 (t, J = 7.6 Hz, 2H, Hb, Hp), 7.63 (t, J = 7.6 Hz, 2H, Hc, Ho),
7.43–7.53 (m, 6H, Ha, Hh, Hi, Hf, Hl, Hq); MS (EI) m/z: 522.06 (M)?; Anal. calcd.
for C28H16N3O4S2?: C, 64.35; H, 3.09; N, 8.04. Found: C, 64.43; H, 3.16; N,
8.15 %.
1-(4-(7-Methoxy-2-oxo-2H-chromen-3-yl)thiazol-2-yl)-3-(2-oxo-2H-chromen-3-yl)-
5-(thiophen-2-yl)-1H-pyrazol-1-ium (4l) Beige solid (2.530 g, 80 %); Mp
272–277 °C; FT-IR (KBr; m max/cm-1): 3360 (stretch N–H), 3131 (stretch C–H
Ar), 1721, 1677 (stretch O–C=O), 1611 (stretch C=N), 1561, 1455 (stretch C=C),
1367 (bending C–H), 1277, 1206, 1088, 1024 (stretch C–O, bending C–N, C–S),
1
968, 931, 853, 754, 699 (OOP C–H); H NMR (400 MHz, DMSO-d6): d = 11.23
(br s, 1H, NH, Hr), 8.61 (s, 1H, He), 8.41 (d, J = 8 Hz, 1H, Hi), 8.23 (s, 1H, Hm),
7.84–7.86 (d, J = 7.8 Hz, 2H, Hd, Hn), 7.71 (t, J = 7.9 Hz, 1H, Hb), 7.63 (t,
J = 7.7 Hz, 2H, Hc, Ho), 7.43–7.53 (m, 6H, Ha, Hh, Hi, Hf, Hl, Hq), 3.89 (s, 3H,
OCH3); MS (EI) m/z: 552.07 (M)?; Anal. calcd. for C29H18N3O5S2?: C, 63.03; H,
3.28; N, 7.60. Found: C, 63.09; H, 3.33; N, 7.66 %.
1-(4-(6-Bromo-2-oxo-2H-chromen-3-yl)thiazol-2-yl)-3-(2-oxo-2H-chromen-3-yl)-5-
(thiophen-2-yl)-1H-pyrazol-1-ium (4m) Golden solid (2.793 g, 82 %); Mp
123

N. O. Mahmoodi, S. Ghodsi
283–287 °C; FT-IR (KBr; m max/cm-1): 3421 (stretch N–H), 3156 (stretch C–H
Ar), 1720, 1675 (stretch O–C=O), 1610 (stretch C=N), 1562, 1458, 1417 (stretch
C=C and N–H bending), 1364 (bending C–H), 1276, 1203, 1086, 1032 (stretch C–
O, bending C–N, C–S), 989, 931, 860, 813, 754, 698 (OOP C–H); 1H NMR
(400 MHz, DMSO-d6): d = 11.23 (br s, 1H, NH, Hr), 8.61 (s, 1H, He), 8.41 (d,
J = 7.6 Hz, 1H, Hd), 8.23 (s, 1H, Hm), 7.85 (d, J = 8 Hz, 2H, Hi, Ha), 7.71 (t,
J = 7.2 Hz, 2H, Hb, Hp), 7.63 (t, J = 7 Hz, 2H, Hc, Hi), 7.43–7.53 (m, 5H, Hh, Hf,
Hl, Hn, Hq); MS (EI) m/z: 599.97 (M)?; Anal. calcd. for C28H15BrN3O4S2?: C,
55.91; H, 2.51; N, 6.99. Found: C, 55.80; H, 2.46; N, 6.94 %.
1-(4-(8-Methoxy-2-oxo-2H-chromen-3-yl)thiazol-2-yl)-3-(2-oxo-2H-chromen-3-yl)-
5-(thiophen-2-yl)-1H-pyrazol-1-ium (4n) Light cream-colored solid (2.403 g,
76 %); Mp 295–297 °C; FT-IR (KBr; m max/cm-1) 3422 (stretch N–H), 3119
(stretch C–H Ar), 1723, 1675 (stretch O–C=O), 1611 (stretch C=N), 1592, 1455
(stretch C=C), 1418 (bending C–H), 1277, 1204, 1110, 1088 (stretch C–O, bending
1
C–N, C–S), 934, 861, 755, 699 (OOP C–H); H NMR (400 MHz, DMSO-d6):
d = 11.23 (br s, 1H, NH, Hr), 8.63 (s, 1H, He), 8.44 (d, J = 6.8 Hz, 1H, Hd), 8.26
(d, J = 1.2, 1H, Ha), 7.88 (dd, J1 = 7.6, J2 = 1.6 Hz, 2H, Hi, Hn), 7.73 (td,
J1 = 7.8, J2 = 1.6 Hz, 1H, Hb), 7.65 (td, J1 = 7.4, J2 = 1.6 Hz, 1H, Hc), 7.31–7.56
(m, 7H, Hh, Hg, Hf, Hl, Hm, Ho, Hp), 3.98 (s, 3H, OCH3) ppm ppm; 13C NMR
(100 MHz, DMSO-d6): d; 171.2, 161.3, 159.7, 153.8, 146.9, 145.7, 143.5, 137.7,
136.3, 135.7, 135.2, 134.1, 133.7, 132.6, 131.6, 130.5, 129.7, 125.8, 125.4, 124.7,
123.8, 121, 120.54, 119.7, 117.9, 116.64, 116.55, 114.09, 113.54, 56.6; MS (EI) m/
z: 552.07 (M)?; Anal. calcd. for C29H18N3O5S2?: C, 63.03; H, 3.28; N, 7.60. Found:
C, 62.84; H, 3.10; N, 7.41 %.
5-(1H-indol-3-yl)-1-(4-(8-methoxy-2-oxo-2H-chromen-3-yl)thiazol-2-yl)-3-(2-oxo-
2H chromen-3-yl)-1H-pyrazol-1-ium (4o) Cream chocolate-colored solid
(2.662 g, 80 %); Mp 217–220 °C; FT-IR (KBr; m max/cm-1): 3427 (stretch N–
H), 3171 (stretch C–H Ar), 1719, 1682 (stretch O–C=O), 1610 (stretch C=N), 1568,
1467 (stretch C=C), 1369 (C–H bending), 1272, 1202, 1098 (stretch C–O, bending
C–N), 934, 858, 820, 765, 719 (OOP C–H); 1H NMR (400 MHz, DMSO-d6):
d = 11.76 (br s, 1H, NH indole), 11.23 (br s, 1H, NH, Hr), 8.62 (s, 1H, He), 8.42 (d,
J = 8 Hz, 1H, Hd), 8.24 (s, 1H, Hm), 7.95 (s, 1H, Hg), 7.87 (t, J = 7.4 Hz, 1H, Hb),
7.71 (t, J = 7.6 Hz, 1H, Hc), 7.64 (t, J = 7.4 Hz, 1H, Hj), 7.28–7.54 (m, 9H, Ha, Hf,
Hh, Hi, Hk, Hl, Hn, Ho, Hp), 3.94 (s, 3H, OCH3) ppm; 13C NMR (100 MHz, DMSO-
d6): d; 177.7, 163.8, 160.6, 158.9, 157.7, 153.1, 150, 146.2, 144.6, 143.2, 142.7,
142.1, 134.6, 132.4, 130.9, 128.9, 125.1, 124.7, 124.6, 123.9, 123.7, 120, 119.7,
118.9, 118.8, 117.6, 117.2, 115.8, 115.6, 114, 112.7, 105.4, 55.9; MS (EI) m/z:
585.12 (M)?; Anal. calcd. for C33H21N4O5S?: C, 67.68; H, 3.61; N, 9.57. Found: C,
67.61; H, 3.49; N, 9.51 %.
5-(1H-indol-3-yl)-1-(4-(7-methoxy-2-oxo-2H-chromen-3-yl)thiazol-2-yl)-3-(2-oxo-
2H-chromen-3-yl)-1H-pyrazol-1-ium (4p) Brick-red solid (2.662 g, 80 %); Mp
292–295 °C; FT-IR (KBr; m max/cm-1): 3415 (stretch N–H), 3117 (stretch C–H
Ar), 1722, 1675 (stretch O–C=O), 1611 (stretch C=N), 1560, 1454, 1419 (stretch
C=C and N–H bending), 1366 (bending C–H), 1277, 1203, 1111, 1088, 1025
123

Thiazolyl-pyrazole-biscoumarin synthesis and evaluation…
(stretch C–O, bending C–N, C–S), 931, 859, 754, 699 (OOP C–H); 1H NMR
(400 MHz, DMSO-d6): d = 11.74 (br s, 1H, NH indole), 11.22 (br s, 1H, NH, Hr),
8.61 (s, 1H, He), 8.41 (d, J = 7.2 Hz, 1H, Hd), 8.23 (s, 1H, Hm), 7.87 (s, 1H, Hg),
7.84 (d, J = 7.8 Hz,1H, Ha), 7.71 (t, J = 7.8 Hz, 1H, Hb), 7.63 (t, J = 7.7 Hz, 2H,
Hc, Hj), 7.43–7.53 (m, 7H, Ha, Hh, Hi, Hl, Hn, Ho, Hq); MS (EI) m/z: 585.12 (M)?;
Anal. calcd. for C33H21N4O5S?: C, 67.68; H, 3.61; N, 9.57. Found: C, 67.73; H,
3.69; N, 9.70 %.
5-(1H-indol-3-yl)-3-(2-oxo-2H-chromen-3-yl)-1-(4-(2-oxo-2H-chromen-3-yl)thiazol-2-yl)-
1H-pyrazol-1-ium (4q) Brick-red solid (2.446 g, 77 %); Mp 223–225 °C; FT-IR
(KBr; m max/cm-1): 3421 (stretch N–H), 3120 (stretch C–H Ar), 1723, 1676 (stretch
O–C=O), 1612 (C=N), 1562, 1455, 1417 (stretch C=C and N–H bending), 1380
(bending C–H), 1273, 1204, 1111, 1088 (stretch C–O, bending C–N, C–S), 935,
1
861, 756, 699 (OOP C–H); H NMR (400 MHz, DMSO-d6): d = 11.76 (br s, 1H,
NH indole), 11.24 (br s, 1H, NH, Hr), 8.63 (s, 1H, He), 8.43 (dd, J1 = 8 Hz,
J2 = 1.2 Hz 1H, Hd), 8.26 (s, 1H, Hm), 7.89 (s, 1H, Hg), 7.87 (dd, J1 = 7.8 Hz,
J2 = 1.2–1.6 Hz, 1H, Hn), 7.72 (td, J1 = 7.8 Hz, J2 = 1.6 Hz, 2H, Hb,Hp), 7.65 (t,
J1 = 7.7 Hz, J2 = 1.6 Hz, 2H, Hc,Ho), 7.46–7.55 (m, 7H, Ha, Hf, Hh, Hi, Hl, Hk,
Hq); MS (EI) m/z: 555.11 (M)?; Anal. calcd. for C32H19N4O4S?: C, 69.18; H, 3.45;
N, 10.08. Found: C, 69.31; H, 3.52; N, 10.17 %.
Biological methods
Antibacterial assay
The antibacterial activities of the synthesized compounds were evaluated by an agar
well diffusion method. First, nutrient agar and nutrient broth cultures were prepared
according to the manufactures’ instructions and incubated at 37 °C. After
incubation for the appropriate time, nutrient agar medium (25 mL) was poured
into each petri plate and the agar plates were swabbed with 40 lL inocula of each
test bacterium and kept for 15 min for adsorption. Using a sterile cork borer of a
5-mm diameter wells were bored into seeded agar plates and these were loaded with
a 30-lL volume. Solutions of the test compounds and standard were prepared in
DMSO at concentrations of 2.0 mg/mL. Dilutions of the compounds (2, 4, 8,
0.5 mg/mL) were inoculated to the corresponding wells. All the plates were
incubated at 37 °C for 18–24 h. Antibacterial activity of the compounds was
evaluated by measuring the zone of growth inhibition compared with gentamycin as
a reference drug. DMSO was used as a negative control.
DPPH radical-scavenging assay
The antioxidant properties of the subject compounds were evaluated quickly and
efficiently using a 2,2-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging
model51 in which the decrease in the strong absorption band at m 517 nm due to the
unpaired electron in DPPH decreased stoichiometrically upon scavenging an
123

N. O. Mahmoodi, S. Ghodsi
electron or hydrogen atom. The DPPH solution was prepared by dissolving an
appropriate amount of DPPH in MeOH to give a concentration of 6.25 9 10-5 M.
Then, 3.9 mL of this solution was added to 0.1 mL of sample solutions of 4a–q in
different concentration (2000, 1000, 500, 250, 125, 62.5 lg/mL in MeOH). The
samples were shaken vigorously and kept in the dark for 30 min The decrease in the
absorbance of the resulting solution was measured at 517 nm and the radical
scavenging activity was expressed as IC50 (half maximal inhibitory concentration)
values, which is the concentration of tested compound required to scavenge 50 % of
the DPPH radical concentration (6.25 9 10-6 M in this case on dilution). All of the
DPPH assays were conducted in triplicate and a synthetic antioxidant, ascorbic acid,
was used as reference standard. MeOH was used as blank and a sample of 3.9 mL
DPPH containing 0.1 mL of MeOH instead of sample was used as control. The
percentage inhibition was calculated for the standard ascorbic acid and other test
compounds and comparison was made. The percentage of inhibition of free radical
DPPH was calculated according to the formula:
ꢀ
ꢁ
Ablank À Asample
Radical scavenging activity % ¼
 100:
Ablank
where Ablank is the absorbance of negative control (containing all reagents except
test compounds) and Asample is the absorbance of the test compounds and all the
reagents. IC50 of the samples was calculated by plotting the radical scavenging
percentage against sample concentration.
Anti-fungal assay
For anti-fungal activity assays, Sabouraud dextrose agar (Merck) media were used
for the cultivation of fungi. Normal saline was used to make a suspension of spores
of the fungal strain. A loopful of a particular fungal strain was transferred to 3 mL
saline to get a suspension of corresponding species. A solution of agar media
(20 mL) was poured into each petri dish. The excess of suspension was decanted
and the plates were dried. After drying, wells were made using an agar punch and
test samples, reference standard and negative control (DMSO) were placed in
labeled wells in each petri plate. The petri plates were incubated at 37 °C for 48 h.
Results and discussion
In a previous study, a series of thiazolyl-coumarin hybrids were designed,
synthesized, and evaluated for their antioxidant properties [37]. It was well known
that the coumarin moiety plays an important role in promoting the antioxidant
properties of molecules. Therefore, inspiring study on the interesting pharmaco-
logical features of coumarin derivatives has encouraged us to synthesize new
thiazolyl-coumarin compounds 4a–q, through a reaction of coumarin chalcones 1a–
g, thiosemicarbazide 3, and 2-bromocoumarin derivatives 2a–d. The general route
followed for the synthesis of coumarin derivatives is illustrated in Scheme 1.
123

Thiazolyl-pyrazole-biscoumarin synthesis and evaluation…
The synthesis of new compounds 4a–q is started from preparation of
(1-phenylprop-1-en-2-yl)-2H-chromen-2-one (coumarin chalcone 1a–g) through
aldolic condensation of 3-acetylcoumarin with various aryl or heteroaryl aldehydes
in the presence of a catalytic amount of piperidine in EtOH by either refluxing or
microwave irradiation in accordance with what is reported in literatures [35, 39]. It
is noteworthy that the reaction which required 5–7 h using conventional methods
was completed efficiently, in 20–30 min with 78–92 % yields, under microwave
conditions (Scheme 1). In the other pot, 3-bromoacetylcoumarins 2a–d were readily
synthesized from 3-acetylcoumarin as reported in literature [40, 41].
In the beginning, coumarin chalcones 1a–g were treated with thiosemicarbazide
3 and allowed to reflux in EtOH in the presence of catalytic amount of HCl for
4–5 h. After in situ formation of pyrazolethioamide (monitored by TLC),
3-bromoacetylcoumarin 2a–d in EtOH was added to the reaction mixture, and
refluxing was continued for an additional 1–2 h. Neutralization with a saturated
solution of NaHCO3, followed by filtration and purification by recrystallization,
gave bromide salts of 4a–q in satisfactory yields (70–80 %; see Table 1; Scheme1).
Addition of thiosemicarbazide to coumarin chalcones is a regioselective reaction
proceeding via addition of the NH2 of thiosemicarbazide to the chalcone carbonyl,
and subsequent intramolecular cycloaddition of N–H to the olefinic bond of the
propenone 6, according to our previously reported work [38].
Formation of in situ-obtained pyrazolethioamide A is followed by the Hantzsch
thiazole synthesis. Initially, nucleophilic substitution of the Br of 3-bromoacetyl-
coumarin 2a–d by the S-atom of thioamide generates the isothiourea, which
subsequently undergoes cyclocondensation and H2O elimination to give the thiazole
ring of 4a–q (Scheme 2). Unexpectedly, in this work the presence of the carbonyl
group of coumarin 5 followed by dehydrogenation of C-5 led to aromatic pyrazole 7
by deprotonation of C-4 of the pyrazoline ring via anchimeric assistance. Proton
capturing by the nitrogen of the pyrazole ring under the reaction conditions gave
target compounds 4a–q (Scheme 2).
Scheme 1 Synthetic protocol of the title compounds (4a–q)
123

N. O. Mahmoodi, S. Ghodsi
Table 1 Reaction products obtained from coumarin chalcones 1, 3-bromoacetylcoumarins 2, and
thiosemicarbazide 3
123

Thiazolyl-pyrazole-biscoumarin synthesis and evaluation…
Scheme 2 Proposed mechanism for production of final thiazolyl-pyrazolium salt
To identify the optimal process, various reaction conditions were studied in
order to synthesize the target coumarin derivatives. For example, a model reaction
was carried out with 3-(2-bromoacetyl)-2Hchromen-2-one 2a–d, thiosemicar-
bazide 3, and coumarin chalcone 1a–g in both EtOH without acidic catalyst and in
EtOH containing a catalytic amount of HCl, both at reflux. In EtOH, after even
12 h reflux, only a 75 % yield of 4a–q was obtained, while in EtOH containing a
catalytic amount of HCl, within 4–6 h, a 90 % yield of products was obtained.
When these reactions are performed under ultrasonic irradiation similar yield
ratios of the products as in previous experiments were obtained within 6 and 3 h,
respectively.
All the synthesized compounds have been characterized on the basis of their
physical data and spectral analysis. Structures of all of the newly synthesized
compounds were established by IR, NMR (1H, 13C) and elemental analyses.
The IR spectra of the compounds 4a–q reveals the presence of a broad band at
3400 cm-1 for the N–H stretching vibration, 1675–1722 cm-1 for the C=O of ester,
which is corroborated by the presence of a lactone C–O at 1276 cm-1. Peaks at
1609–1612 cm-1 are for the C=N group, and peaks in the regions 1355–1375 cm-1
and 1055–1098 cm-1 indicate the presence of C–S and C–N groups. In the 1H NMR
spectra, the C–H peak of the OCH3 group at 3.93 ppm confirms the formation of the
thiazole moiety. Aromatic protons appear in the expected region (7.30–8.63 ppm)
and 11.23 ppm for NH. 13C NMR spectra also confirm structural identities, with
resonances observed at dC of 55.9–56.6 ppm for OCH3, 169.1–170.3 ppm (thiazole
2-C), 159.6–162.6 ppm (C=O), and 153.2–156.3 ppm (C=N). Through single
crystal X-ray diffraction, the adducts of reactions of coumarin chalcones 1a–g with
thiosemicarbazide 3 and 3-bromoacetylcoumarins 2a–d were clearly determined
(Fig. 1).
123

N. O. Mahmoodi, S. Ghodsi
Pharmacology
Antibacterial activity
The new compounds 4a–q were evaluated for their in vitro antibacterial activity
against Escherichia coli (E. coli), Micrococcus luteus (M. luteus), Pseudomonas
aeruginosa (Ps. aeruginosa), and Staphylococcus aureus (S. aureus) by the zone
inhibition method [40]. The results are presented in Table 2. All the tested
compounds possessed moderate to good antibacterial activity against Gram-positive
bacteria (S. aureus and M.luteus) as well as Gram-negative bacteria (E. coli and P.
aeruginosa). On the basis of zone of inhibition against the test bacterium,
compounds 4b, 4c, 4e, 4f, 4k, 4l, 4m, and 4o were found to be most effective
against S. aureus (Gram-positive bacteria), compounds 4n and 4f were found to be
most active against E. coli, and compounds 4j and 4p were effective-against M.
luteus (Gram-positive bacteria), as compared with the standard drug gentamycin.
This may be due to the incorporation of the thiophene ring and the presence of
electron-withdrawing groups like –Cl in comparison to the other compounds. All the
synthesized compounds showed weak antibacterial activity against Ps. aeruginosa
(a Gram-negative bacteria). However, in terms of MIC (minimal inhibitory
concentration), none of the compounds has shown activity.
Table 2 The antibacterial and antifungal activities of the synthesized compounds
Compound
Mean zone of inhibition (mean SD; mm)
M. luteus
S. aureus
E. coli
Ps. aeruginosa
A. niger
A. flavus
4a
–
–
–
8
–
–
8
8
1.52
–
–
–
4b
16 0.70
14 0.57
10 0.70
16 0.70
17 0.70
13 0.57
–
12 0.85
10 0.70
11 0.89
11 0.94
11 0.83
13 0.70
12 0.89
12 0.70
12 0.85
12 0.70
14 0.90
14 0.90
13 0.80
13 0.70
11 0.90
11 0.70
12 0.85
13 0.70
11 0.70
17 0.90
12 0.90
14 0.70
–
4c
9
0.57
–
4d
10 0.57
12 0.57
–
1.52
1.52
11 1.15
4e
11 1.15
4f
12 1.0
–
4g
10 0.57
–
12 0.57
4h
9
9
0.57
0.57
9
9
1.15
0.57
–
–
4i
–
–
4j
15 1.41
10 0.57
15 1.52
15 1.52
15 1.52
13 1.52
15 1.52
–
–
9
0.89
4k
9
9
0.70
0.70
–
11 0.57
14 0.70
4l
11 1.0
–
13 0.70
4m
11 0.57
8
1.0
–
16 0.94
4n
–
13 1.0
–
13 0.83
4o
–
11 0.57
–
13 0.70
4p
13 1.41
9
1.15
11 1.0
–
–
Gentamycina
Floconazola
DMSOb
a
18
–
21
–
20
–
19
–
–
–
25
–
25
–
–
–
–
–
b
Positive control, negative control
123

Thiazolyl-pyrazole-biscoumarin synthesis and evaluation…
Antioxidant activity
Most of the synthesized compounds showed antioxidant activity. According to
Fig. 3, radical scavenging activity was dose-dependent and increased with rise in
concentration of the compounds 4a–q. Compound 4i exhibited the highest DPPH
radical scavenging, while compound 4a had the lowest. The IC50 values were
calculated according to line equations and were reported in Table 3. The IC50 values
were between 0.25 and 6.16 mg/mL. Compound 4i in comparison to ascorbic acid
(0.07 mg/mL) had the lowest IC50 value (0.25 mg/mL). It was worth noting that
compounds 4b, 4c, 4k, 4e, 4m, 4o, and 4p exhibited very high activities against the
DPPH radical (at a concentration of 6.25 9 10-6 M) with IC50 values on the order
of 4.33 9 102 to 1.2 9 104 lM. The antioxidant activity of compounds 4a–q can be
ascribed to the N–H groups of the pyrazole component which can donate a hydrogen
Fig. 3 Evaluation of antioxidant properties by DPPH radical scavenging assay of compounds 4a–q
Table 3 IC50 for DPPH assay
of compounds 1a–q and
comparison to ascorbic acid
Compound
DPPH assay
IC50 (mg/L)
4a
6.16
1.06
2.43
3.69
3.13
1.35
2.1
4b
4k
4m
4e
4o
4p
4c
4.21
0.25
0.07
4i
IC50 half maximal inhibitory
concentration
Ascorbic acid
123

N. O. Mahmoodi, S. Ghodsi
atom to DPPH and then delocalize the resulting unpaired electron through the
conjugated system.
The highest antioxidant capacity of compound 4i in comparison to the other
analogs may be due to the two electron-donating methoxy groups on the aromatic
rings which can better stabilize the radical cation. The proposed radical scavenging
mechanism for compound 4i is depicted in Scheme 3.
Anti-fungal activity
The in vitro anti-fungal activity of compounds 4a–q was also evaluated against
Aspergillus niger and Aspergillus flavus using the drug fluconazole as a reference
standard. Compound 4m indicated promising activity, whereas the antifungal
activity of the other compounds was reasonable or minor. On the basis of obtained
results, the presence of bromine improves the anti-fungal activity.
Scheme 3 Proposed radical scavenging mechanism for 4i
123

Thiazolyl-pyrazole-biscoumarin synthesis and evaluation…
Conclusion
In conclusion, we reported here a three-component cyclo-condensation protocol
synthesis with advantages such as easy an work-up, a fast and regioselective method
for the simultaneous preparation of the target library, together with the use of
inexpensive material and environmentally friendly procedure and providing
antimicrobial and antioxidant properties and so on for the title products. DPPH
assays indicate that most of the synthesized pyrazolium thiazolyl coumarin
derivatives such as 4a, 4b, 4c, 4e, 4i, 4k, 4m, 4o, and 4p had considerable radical
scavenging activity that was comparable to the ascorbic acid. The pyrazole and
thiazole moieties contribute to the free radical scavenging activity. However,
incorporation of the coumarin motif further optimized the radical scavenging
activity and improved the antioxidant activity. Also, some of the compounds
exhibited prominent antimicrobial and anti-fungal properties that may be due to the
incorporation of a thiophene ring and electron-withdrawing groups like –Cl.
Acknowledgments The authors greatly acknowledge the helpful assistance of Prof. Douglas F. Fry and
Dr. Fateme Ghanbari-Pirbasti in processes of this work, and the Research Council of the University of
Guilan for the financial support of this research.
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