Synthesis and biological evaluation of novel conjugated coumarin-thiazole systems

Article abstract of DOI:10.1002/jhet.110

(Chemical Equation Presented) Seven new 2,4-disubstituted thiazoles have been synthesized by Hantzsch condensation and assayed for several biological activities for a preliminary screening. They have been fully characterized by elemental analysis, UV-Vis

Full text of DOI:10.1002/jhet.110

May 2009
Synthesis and Biological Evaluation of Novel Conjugated
Coumarin-Thiazole Systems
575
Franco Chimenti, Simone Carradori,* Daniela Secci, Adriana Bolasco,
Paola Chimenti, Arianna Granese, and Bruna Bizzarri
`
Dipartimento di Chimica e Tecnologie del Farmaco, Universita ‘‘La Sapienza,’’
P.le A. Moro 5, 00185 Roma, Italy
*E-mail: simone.carradori@uniroma1.it
Received August 2, 2008
DOI 10.1002/jhet.110
Published online 5 May 2009 in Wiley InterScience (www.interscience.wiley.com).
Seven new 2,4-disubstituted thiazoles have been synthesized by Hantzsch condensation and assayed
for several biological activities for a preliminary screening. They have been fully characterized by ele-
1
mental analysis, UV–Vis spectroscopy, TG-DTA, IR, and H NMR as well. These structures display dif-
ferent pharmacological (antimicrobic activity, citotoxicity, and hMAO inhibition) and industrial
properties (complete transparency in the region between 465–800 nm and high thermal stability) varying
on their substituents and could be considered as good lead compounds for further developments.
J. Heterocyclic Chem., 46, 575 (2009).
INTRODUCTION
lation of pure products in 86–99% yield was made sim-
ply by filtration under vacuum. All the structures were
fully supported by elemental analysis and spectral data
as reported in the experimental section and in Table 2.
In particular, we obtained compound 3 and 4 as race-
mates, because of the presence of a chiral center in the
structure. Knowing that the stereochemistry could affect
deeply different biological activities and being commer-
cially available the pure (R)-(þ) enantiomer of 3-meth-
ylcyclohexanone, we planned a stereocontrolled synthe-
sis in order to obtain derivative 5 with correlated (R)-
(þ) absolute configuration. The stereochemistry has
been preserved by the stereoconservative synthetic pat-
tern which did not interest the methyl on the cycloali-
phatic moiety. The enantiomeric excess has been deter-
mined by HPLC on the Chiralpak AS-H chiral station-
ary phase (CSP) using the mixture n-hexane-2-propanol
70:30 (v/v) as a mobile phase: ee > 99%; [a]2D0 ¼ ꢀ20
(0.1, EtOH).
In the last few years, researchers have renewed inter-
est in 3-(thiazol-4-yl)coumarins [1–6] for their industrial
applications as fluorescent probes and laser dyes [7], for
their biological activity as pharmaceutical agents [8–10]
and because they could be useful for the construction of
the diazepinone ring [11]. In addition, p-conjugated sys-
tems are known to show interesting electronic, optical,
and electric properties [12]. On the basis of our experi-
ence in the synthesis of thiazole and coumarin [13,14]
derivatives, we were pursued, therefore, to synthesize a
series of novel heterocyclic systems characterized by the
association of a coumarin nucleus with a thiazole ring
linked to a cycloaliphatic group, whose presence and
influence on this kind of molecules have not been
described so far (Table 1).
RESULTS AND DISCUSSION
The compounds, correctly analyzed for their molecu-
lar formula, showed in the IR spectrum strong bands at
1710 and 1600 cmꢀ1 due to the presence of a d-lactone
C¼¼O and C¼¼N group, respectively.
The coumarin-thiazole derivatives (1–7) were pre-
pared by Hantzsch condensation between the appropriate
thiosemicarbazone and 3-a-bromo-acetyl coumarin in 2-
propanol at room temperature according to a protocol
used in our laboratory [15]. In these conditions, the iso-
The UV–visible spectral analysis was carried out in
methanol as solvent and the data are collected in Table
C
V
2009 HeteroCorporation

576
F. Chimenti, S. Carradori, D. Secci, A. Bolasco, P. Chimenti, A. Granese, and B. Bizzarri
Vol 46
Table 1
Structure and CLogP (ChemDraw Ultra 8.0) of compounds 1–7.
Table 3
MIC values (lg/mL) of some derivatives against eight strains
of Candida spp and C ¼ Clotrimazole.
Compound
n
R
CLogP
`
C. albicans C. sake C. parapsilopis C. krusei
1
2
3
4
5
6
7
1
2
2
2
2
2
3
H
H
3.28
3.84
4.36
4.36
4.36
4.36
4.40
Compound (2 strains) (strain)
(strains)
(strains)
2-CH3
3-CH3
(R)-(þ)-3-CH3
4-CH3
H
1
2
7
4
8
32
16
16
8
>128
>128
8–16
8–>128
8
16
8
8
8–16
8
C
2. The absorption spectra of all derivatives are generally
characterized by sharp absorption bands in the region of
230–250 nm and 290–300 nm with the kmax independent
upon the substituent and size of the cycloaliphatic moi-
ety. Accordingly, the coumarin local p-p excitation
appears to be the main type of electronic transition and
complete transparency was observed in the region
between 465–800 nm.
ronidazole resistant strains of Helicobacter pylori and
some Candida albicans strain isolates.
In addition, we evaluated the low citotoxic effect of
the most representative compound (7) against EAhy, a
human cell line obtained from a hybridoma between
HUVEC and epithelial cells from a lung carcinoma. The
viability of cells exposed to test compounds was esti-
mated by the Trypan Blue dye exclusion assay after
24 h of incubation at 37ꢁC. Cells incubated with culture
medium alone represented the control and the cell via-
bility was always greater than 97%. Data represent the
arithmetic mean ꢂ SD of at least three independent
experiments (Table 5).
Further we have also studied the thermal stability of
1–7 using TG-DTA method (heat rate: 10ꢁC/min, Ar
flow: 100 cc/min). All the compounds exhibited a
decomposition temperature (Td) in the range 290–315ꢁC,
a feature which could be significant for NLO applica-
tions because it is superior to that reported (Td
290ꢁC) for the benchmark 4-dimethylamino-40-nitrostil-
bene (DANS) [16].
¼
In the end, all the newly synthesized compounds were
investigated for their ability to inhibit both human MAO
isoforms by measuring their effects on the production of
H2O2 from p-tyramine, using the Amplex Red MAO
assay kit. Microsomial MAO isoforms prepared from
insect cells (BTI-TN-5B1-4) infected with recombinant
baculovirus containing cDNA inserts for hMAO-A
and hMAO–B. Data were calculated as pIC50 for both
isoforms and pSI referred to log selectivity index ¼
pIC50 (MAO-A) ꢀ pIC50 (MAO-B). The data represent mean
values of at least five separate experiments and Clorgy-
line and R-(ꢀ)-deprenyl were used as standard drugs
(Table 6).
From a biological point of view, evaluating the influ-
ence of the bioactive coumarin nucleus on the C4 position
of the thiazole as a modulator of the biological activity
and correlating the results with those obtained in our pre-
vious papers [15,17,18], some of the synthesized com-
pounds (which all show calculated log P values < 5) have
been widely assayed for a preliminary antimicrobic
screening against eight strains of pathogenic fungi (Table
3), several types of routine clinical Gram-positive and
negative isolates (MIC values > 128 lg/mL, data not
shown), and 20 clinical strains of Helycobacter pylori
(Table 4). Clotrimazole and Metronidazole were used as
standard antifungal and antibacterial drug, respectively.
The results showed that all compounds possess an
antibacterial activity targeting selectively towards Met-
Despite their inhibitory activity in the micromolar
range, in examining the influence of the structural varia-
tion, some of them (in particular those which did not
present substituents on the cycloaliphatic moiety) pos-
sessed a moderate A-selectivity. From a qualitative point
Table 2
Table 4
UV–visible absorption of derivatives 1–7 (MeOH).
MIC values (lg/mL) of some derivatives and M ¼ Metronidazole
against 20 H. pylori strains.
Compound
kab (nm)
e ꢃ 104
Metronidazole
sensitive strains
(15 strains)
Metronidazole
resistant strains
(strains)
1
2
3
4
5
6
7
293.74
293.57
291.61
292.03
295.37
298.52
292.30
1.60
1.85
1.29
0.88
0.66
1.23
1.24
Compound
1
2
7
16–32
8–32
8–32
16–32
8–32
8–32
M
0.5–2
64–>128
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

May 2009
Synthesis and Biological Evaluation of Novel Conjugated Coumarin-Thiazole Systems
577
Table 5
tic acid as catalyst. The desired thiosemicarbazone precipitated
from reaction mixture was filtered and crystallized from suita-
ble solvent and dried.
Citotoxicity of derivative 7 expressed as cell survival
fraction ꢂ SD (%).
Typical procedure for the Hantzsch protocol for the
preparation of derivatives 1–7. Equimolar amounts of the
prepared thiosemicarbazones (50 mmol) and 3-a-bromo-acetyl
coumarin [19] (50 mmol), both dissolved in 2-propanol, were
reacted at room temperature under magnetic stirring for 2 h.
The precipitate was filtered, washed with petroleum ether and
diethyl ether, and dried to give compounds 1–7 in 86–99%
yields. All the yields are on isolated basis. The characteriza-
tion data are given in Tables 1 and 2.
3-(2-(2-Cyclopentylidenehydrazynyl)thiazol-4-yl)-2H-
chromen-2-one (1). Yellow crystals, 98% yield, mp 207–
209ꢁC; 1H NMR (CDCl3): d 1.87–1.89 (m, 2H, cyclopentyl),
1.95–1.97 (m, 2H, cyclopentyl), 2.55 (s, 2H, cyclopentyl), 2.64
(s, 2H, cyclopentyl), 7.37–7.39 (m, 1H, C5H-thiaz.), 7.49–7.69
(m, 2H, Ar), 7.81–7.83 (m, 2H, Ar), 8.59 (s, 1H, CH¼¼), 12.20
(br s, 1H, NH, D2O exch.); Anal. Calcd. for C17H15N3O2S: C,
62.75; H, 4.65; N, 12.91. Found: C, 62.77; H, 4.67; N, 12.92.
3-(2-(2-Cyclohexylidenehydrazynyl)thiazol-4-yl)-2H-
chromen-2-one (2). Dark yellow crystals, 98% yield, mp 180–
182ꢁC; 1H NMR (CDCl3): d 1.64–1.71 (m, 4H, cyclohexyl),
1.86 (s, 2H, cyclohexyl), 2.58 (s, 2H, cyclohexyl), 2.69 (s, 2H,
cyclohexyl), 7.36 (s, 1H, C5H-thiaz.), 7.61–7.63 (m, 2H, Ar),
7.80–7.85 (m, 2H, Ar), 8.62 (s, 1H, CH¼¼), 12.39 (s, 1H, NH,
D2O exch.); Anal. Calcd. for C18H17N3O2S: C, 63.70; H, 5.05;
N, 12.38. Found: C, 63.68; H, 5.04; N, 12.39.
Concentration (lg/mL)
Compound
50
5
0.5
0.05
7
52.94 ꢂ 3.8 81.82 ꢂ 5.6 93.75 ꢂ 4.7 97.50 ꢂ 1.8
of view, it must be highlighted the different selective
hMAO inhibition of compound 5 (pure (R)-(þ) enan-
tiomer) in relation to 4 (racemate) bearing the same sub-
stituent in the same position.
CONCLUSION
We reported the synthesis, the spectral characteriza-
tion, and a preliminary biological evaluation of seven
novel heterocyclic systems. According to the biological
results, these compounds exhibited a promising antimi-
crobic activity expecially oriented towards Metronida-
zole resistant strains of Helycobacter pylori and an
interesting anti-Candida spectrum comparable to that of
Clotrimazole. It has been also found a low cytotoxic
effect against EAhy, a human immortalized cell line,
which could justify a safe and therapeutic use of these
derivatives. They further displayed a moderate selective
hMAO-A inhibition which is probably affected by the
steric hindrance of bulky coumarin nucleus inside the
active site. All these results could be useful to evaluate
new substitutions on the coumarin nucleus in order to
enhance biological activities.
3-(2-(2-(2-Methylcyclohexylidenehydrazynyl)thiazol-4-yl)-
2H-chromen-2-one (3). Off white crystals, 86% yield, mp
171–173ꢁC; 1H NMR (CDCl3): d 1.16–1.18 (d, J ¼ 6.3 Hz,
3H, CH3), 1.21–1.23 (m, 2H, cyclohexyl), 1.27–2.04 (m, 5H,
cyclohexyl), 2.50 (s, 1H, cyclohexyl), 3.01 (s, 1H, cyclohexyl),
7.38 (s, 1H, C5H-thiaz.), 7.62–7.64 (m, 2H, Ar), 7.82–7.84 (m,
2H, Ar), 8.60 (s, 1H, CH¼¼), 12.17 (br s, 1H, NH, D2O exch.);
Anal. Calcd. for C19H19N3O2S: C, 64.57; H, 5.42; N, 11.89.
Found: C, 64.59; H, 5.40; N, 11.88.
3-(2-(2-(3-Methylcyclohexylidenehydrazynyl)thiazol-4-yl)-
2H-chromen-2-one (4). Yellow crystals, 99% yield, mp 188–
190ꢁC; 1H NMR (CDCl3): d 1.03–1.05 (d, J ¼ 6.3 Hz, 3H,
CH3), 1.21–1.23 (m, 2H, cyclohexyl), 1.26–2.08 (m, 5H,
cyclohexyl), 2.50 (s, 1H, cyclohexyl), 3.01 (s, 1H, cyclohexyl),
7.38 (s, 1H, C5H-thiaz.), 7.80 (s, 2H, Ar), 7.91 (s, 2H, Ar),
12.20 (br s, 1H, NH, D2O exch.); Anal. Calcd. for
C19H19N3O2S: C, 64.57; H, 5.42; N, 11.89. Found: C, 64.56;
H, 5.43; N, 11.90.
EXPERIMENTAL
The chemicals, solvents for synthesis, and spectral grade
solvents were purchased from Aldrich (Italy) without further
purification. Melting points (uncorrected) were determined
1
automatically on a FP62 apparatus (Mettler-Toledo). H NMR
spectra were recorded at 400 MHz on a Bruker spectrometer.
Chemical shifts are expressed as d units (parts per millions)
relative to the solvent peak. Coupling constants J are valued in
Hertz (Hz). IR spectra were registered on a Perkin-Elmer
FTIR Spectrometer Spectrum 1000 in potassium bromide. Ele-
mental analysis for C, H, and N were recorded on a Perkin-
Elmer 240 B microanalyzer and the analytical results were
within ꢂ0.4% of the theoretical values for all compounds. All
reactions were monitored by TLC on 0.2 mm thick silica gel
plates (60 F254 Merck). UV–vis spectra were recorded on a
Perkin-Elmer UV–vis Spectrometer Lambda 10. Thermal anal-
ysis was performed under an inert gas flux using TGA/DTA
(Pyris Diamond Perkin-Elmer, Waltham, MA).
Table 6
hMAO inhibition and hMAO-A selectivity of derivatives 1–7.
Compound
pIC50 hMAO-A
pIC50 hMAO-B
pSI
1
2
3
4
5
6
7
4.39
5.28
5.04
4.96
5.11
5.15
5.19
8.29
4.17
<4.00
<4.00
5.12
4.97
5.02
>0.39
>1.28
ꢀ0.08
ꢀ0.01
0.09
4.87
0.28
Typical procedure for the thiosemicarbazones synthesis.
The appropriate cycloaliphatic ketone (50 mmol) was dissolved
in 100 mL of 2-propanol and stirred at room temperature with
an equimolar amounts of thiosemicarbazide for 24 h with ace-
<4.00
4.20
7.77
>1.19
ꢀ4.09
3.60
Clorgyline
R-(ꢀ)-deprenyl
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

578
F. Chimenti, S. Carradori, D. Secci, A. Bolasco, P. Chimenti, A. Granese, and B. Bizzarri
Vol 46
REFERENCES AND NOTES
(R)-(1)-3-(2-(2-(Methylcyclohexylidenehydrazynyl)thiazol-
4-yl)-2H-chromen-2-one (5). Yellow crystals, 99% yield, mp
200–201ꢁC; 1H NMR (CDCl3): d 1.02–1.04 (d, J ¼ 6.3 Hz,
3H, CH3), 1.26–1.27 (m, 2H, cyclohexyl), 1.79–1.96 (m, 5H,
cyclohexyl), 2.95–2.99 (m, 2H, cyclohexyl), 7.38 (s, 1H, C5H-
thiaz.), 7.62–7.66 (m, 2H, Ar), 7.80–7.84 (m, 2H, Ar), 8.62 (s,
1H, CH¼¼), 12.18 (br s, 1H, NH, D2O exch.); Anal. Calcd. for
C19H19N3O2S: C, 64.57; H, 5.42; N, 11.89. Found: C, 64.59;
H, 5.44; N, 11.90.
3-(2-(2-(4-Methylcyclohexylidenehydrazynyl)thiazol-4-yl)-
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175–177ꢁC; 1H NMR (CDCl3): d 0.99 (s, 3H, CH3), 1.75 (s,
1H, cyclohexyl), 1.99–2.09 (m, 3H, cyclohexyl), 2.19–2.31 (m,
2H, cyclohexyl), 2.55–2.56 (m, 1H, cyclohexyl), 3.06 (s, 1H,
cyclohexyl), 7.32 (s, 1H, C5H-thiaz.), 7.64 (s, 2H, Ar), 7.84 (s,
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186ꢁC; 1H NMR (CDCl3): d 1.64–1.68 (m, 6H, cycloheptyl),
1.86–1.88 (m, 2H, cycloheptyl), 2.57–2.59 (m, 2H, cyclohep-
tyl), 2.68–2.71 (m, 2H, cycloheptyl), 7.27 (s, 1H, C5H-thiaz.),
7.38–7.40 (m, 2H, Ar), 7.62–7.64 (t, 1H, Ar), 7.81–7.82 (t,
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Found: C, 64.58; H, 5.41; N, 11.89.
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Acknowledgments. This work was supported by grants from
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet