Novel (E)-1-(4-methyl-2-(alkylamino)thiazol-5-yl)-3-arylprop-2-en-1-ones as potent antimicrobial agents

Article abstract of DOI:10.1016/j.bmc.2011.10.059

New (E)-1-(4-methyl-2-(alkylamino)thiazol-5-yl)-3-arylprop-2-en-1-ones, unsubstituted or carrying fluoro, bromo, methoxy, nitro, methyl and chloro groups on the benzene ring, were synthesized and assayed in vitro for their antimicrobial activity against Gram positive and Gram negative bacteria and fungi. The compounds were very potent towards all tested microorganisms and in most cases their activity was better than that of reference drugs.

Full text of DOI:10.1016/j.bmc.2011.10.059

Bioorganic & Medicinal Chemistry 19 (2011) 7349–7356
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Novel (E)-1-(4-methyl-2-(alkylamino)thiazol-5-yl)-3-arylprop-2-en-1-ones
as potent antimicrobial agents
K. Liaras a, A. Geronikaki a, , J. Glamoclija , A. Ciric , M. Sokovic
⇑
b
b
b
´
ˇ
´
´
a Aristotle University, School of Pharmacy, Thessaloniki 54124, Greece
b Institute for biological research ‘S. Stankovi´c’, Mycological laboratory, University of Belgrade, Belgrade 11000, Serbia and Montenegro
a r t i c l e i n f o
a b s t r a c t
Article history:
New (E)-1-(4-methyl-2-(alkylamino)thiazol-5-yl)-3-arylprop-2-en-1-ones, unsubstituted or carrying
fluoro, bromo, methoxy, nitro, methyl and chloro groups on the benzene ring, were synthesized and
assayed in vitro for their antimicrobial activity against Gram positive and Gram negative bacteria and
fungi. The compounds were very potent towards all tested microorganisms and in most cases their
activity was better than that of reference drugs.
Received 18 July 2011
Revised 14 October 2011
Accepted 19 October 2011
Available online 25 October 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Thiazole
Chalcones
Antibacterial
Antifungal
1. Introduction
thiazole-based chalcones (Fig. 1) with significantly improved anti-
bacterial and antifungal activities.
The rapid progress of science in the past decades led to the
significant improvement in the diagnosis and treatment of infec-
tious diseases. Despite these efforts, the emerging resistance of
microorganisms to known antibiotics kept the scientific interest
in developing new classes of antimicrobial compounds.1–5
In addition, the need for effective antimicrobial drugs became
even greater considering the difficulties of dealing with the treat-
ment of infections of hospitalized patients and protection of immu-
nosuppressed and HIV-infected patients.6
Therefore, designing innovating drugs with different mode of ac-
tion could be the choice of preference in order to overcome the prob-
lem of cross resistance to existing therapeuticals. A recent example
of this kind of approach is the introduction of Linezolid, a synthetic
molecule, member of the oxazolidinone class of drugs. Linezolid is
active against most Gram-positive bacteria, including streptococci,
vancomycin-resistant enterococci (VRE), and methicillin-resistant
Staphylococcus aureus (MRSA) and seems to have a unique mecha-
nism of action compared to existing drugs.7–9
N
R'
R
N
H
S
O
R
R΄
4-F
1.
2.
3.
4.
5.
6.
7.
8.
9.
Me
Me
Me
Me
Me
Et
3-F
3-Br
3-Me
2,3-diCl
H
Et
4-NO2
3-NO2
4-Cl
3-Cl
2-Cl
4-F
Et
Et
Taking into account the interesting properties of thiazole deriv-
atives10–19 and chalcones,20–24 as well as our promising findings
regarding, specifically, the antimicrobial activity of thiazole-based
chalcones,25 herein is presented the synthesis of a series of novel
10.
11.
12.
13.
14.
15.
16.
17.
Et
Et
Et
Et
3-F
Et
3-Br
4-OMe
2-OMe
H
Et
Et
⇑
Corresponding author. Address: School of Pharmacy, Department of Pharma-
ceutical Chemistry of Aristotle University of Thessaloniki, Thessaloniki, Greece. Tel.:
+30 2310 997616; fax: +30 2310 998559.
Prop
E-mail address: geronik@pharm.auth.gr (A. Geronikaki).
Figure 1.
0968-0896/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2011.10.059

7350
K. Liaras et al. / Bioorg. Med. Chem. 19 (2011) 7349–7356
Table 1
2. Results and discussion
2.1. Chemistry
Calculated lipophilicity of synthesized compounds
The synthesis of the target chalcones 1–17 was accomplished
by a Claisen–Schmidt condensation (Scheme 1) as described in
our previous publication.25 The reactions proceeded smoothly
and in good yields for the majority of compounds. Structures of
synthesized compounds 1–17 were satisfactorily confirmed by IR,
1H NMR and elemental analysis. In IR spectra were observed
absorptions at 1650–1710 cmꢀ1 (C@O), and sharp bands at
3200 cmꢀ1 (NH). In the 1H NMR spectra, peaks of thiazole-based
chalcones appeared in the region of d 2.50–2.78 (thiazole 4-CH3),
1.17–1.69 (methyl NCH2CH3, compounds 6–16), 2.86–2.94 (NCH3,
compounds 1–5), 3.26–3.41 (NCH2, compounds 6–16), 7.14–7.46
(CO–CH) and 7.46–7.87 (Ar–CH).
N
R'
R
N
H
S
O
Compounds
ClogPa
ALogPsb
AlogPb
ClogPc
1
2
3
4
5
6
7
8
3.11
3.11
3.74
3.48
4.18
3.33
3.27
3.27
3.93
3.93
3.93
3.47
3.47
4.10
3.17
3.17
3.85
3.46
3.46
3.96
3.71
4.05
3.89
3.56
3.61
4.39
4.39
4.40
3.78
3.83
4.48
3.86
3.79
4.30
3.29
3.29
3.83
3.57
4.41
3.43
3.33
3.33
4.09
4.09
4.09
3.64
3.64
4.18
3.41
3.41
3.95
2.99
2.99
3.71
3.35
4.15
3.38
3.12
3.12
4.09
4.09
4.09
3.52
3.52
4.24
3.30
3.30
3.91
The C –Cb double bond in the enone moiety of chalcones can
a
potentially adopt either a Z or an E configuration. The 1H NMR
spectrum of each chalcone exhibited CH@CH protons around
7.14–7.87 ppm, with J >15, and therefore would suggest that the
compounds adopted (E) configuration.26 Theoretical calculations
of lipophilicity as ClogP were performed (Table 1).
9
10
11
12
13
14
15
16
17
2.2. Biological evaluation
a
b
c
Calculated by online program of Chemaxon.
Calculated by online program ALOGPS 2.1.
Calculated by program ClogP 4.0, BioByte Corp.
2.2.1. Antimicrobial activity
The synthesized thiazole-based chalcones were then assayed
in vitro for their antibacterial and antifungal activity against Gram
positive and Gram negative bacteria, and the minimal inhibitory
concentrations that inhibited the growth of the tested microorgan-
isms (MIC) and minimal bactericidal/fungicidal concentrations
were determined. The results of antimicrobial testing are reported
in Table 2, along with those of reference drugs Ampicillin and
Streptomycin.2 All compounds tested could be divided into two
groups, namely methylamino and ethylamino/propylamino
chalcones.
ꢀ2/ml. The antibacterial potential follows the order 3>1>5>2>4.
The best antibacterial effect exhibited compounds 3 and 1 with
inhibitory activity at 1.48–9.93 and 3.26–9.06
respectively and bactericidal effect at 5.93–8.9 and 1.09–
9.06
l
mol ꢁ 10ꢀ2/ml
l
mol ꢁ 10ꢀ2/ml. respectively. The lowest antibacterial activ-
ity observed for compound 4 with MIC of 5.51–11.03
lmol ꢁ 10
ꢀ2/ml and MBC 7.35–11.03
l
mol ꢁ 10ꢀ2/ml. The most sensitive
bacterial species on these compounds are Micrococcus flavus, fol-
lowed by Salmonella typhimurium and Bacillus cereus, while Listeria
monocytogenes is the most resistant species.
The structural modifications to previously synthesized thiazole-
based chalcones25 involve the nature of the substituent R as well as
R0.
As far as the second group is concerned (compounds 6–17),
namely ethylamino and propylamino chalcones results of their anti-
bacterial activity are presented in Table 2. The inhibitory activity for
The results of antibacterial activity of the first group (com-
pounds 1–5) are presented in Table 2. All the compounds showed
very strong antibacterial activity against all the species tested with
mol ꢁ 10ꢀ2/ml and
MIC 1.48–11.03
l
mol ꢁ 10ꢀ2/ml, and MBC 1.09–11.00
lmol ꢁ 10
compounds 6–17 is obtained at 3.0–11.03
l
NH2
NH4OH
NCS
S
N
H
I
II
O
O
NH2
II
N
-HCl
-H2O
R
+
R
N
S
S
N
H
H
O
Cl
III
IV
N
N
R'
R'
NaOH 10%
-H2O
R
R
+
OHC
N
S
N
H
S
H
O
O
IV
V
VI (1-17)
Scheme 1.

K. Liaras et al. / Bioorg. Med. Chem. 19 (2011) 7349–7356
7351
Table 2
Antibacterial activity of substituted/non substituted (E)-1-[4-methyl-2-(alkylamino)thiazol-5-yl)-3-phenylprop-2-en-1-ones (MIC and MBC,
l
mol/ml ꢁ 10ꢀ2
)
N
R'
R
N
H
S
O
Compounds
S. a.
7.25
B. c.
M. f
3.26
L. m.
Ps. aer.
S. typhi
E. coli
En. f.
1
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
3.62
9.06
9.06
9.06
9.06
8.90
7.25
11.09
5.43
7.25
7.42
7.42
7.35
9.19
6.12
9.17
7.35
7.35
4.73
6.31
7.89
7.89
6.53
9.80
6.53
8.17
4.89
6.11
6.89
6.89
6.89
6.89
5.71
7.14
6.62
8.28
8.28
9.93
7.00
9.00
74.40
124.00
17.20
34.40
5.43
7.25
7.25
9.06
5.93
7.42
7.35
9.19
6.12
7.65
3.68
9.19
4.73
6.31
4.73
6.31
4.90
4.90
4.91
6.53
4.89
6.11
5.17
5.17
5.17
5.17
5.71
7.14
4.97
4.97
3.31
8.28
7.00
9.00
24.80
49.20
17.20
34.40
5.43
7.25
5.43
7.25
7.42
7.42
5.51
7.35
4.59
6.12
7.35
11.03
9.46
9.46
6.31
7.89
6.53
9.80
4.91
6.53
4.89
6.11
5.17
6.89
6.89
8.62
5.71
7.14
4.97
6.62
8.28
8.28
7.00
8.80
37.20
49.20
17.20
34.40
5.43
7.25
5.43
7.25
7.42
7.42
5.51
7.35
7.65
7.65
5.51
7.35
4.73
6.31
4.73
6.31
8.17
8.17
4.91
6.53
4.89
6.11
5.17
6.89
5.17
6.89
5.71
7.14
6.62
9.93
8.28
8.28
9.00
9.00
24.80
37.20
4.30
8.60
7.25
7.25
9.06
5.93
7.42
7.35
11.03
6.12
9.17
7.35
11.03
9.46
9.46
9.46
9.46
9.80
9.80
9.80
9.80
8.17
9.81
6.89
6.89
6.89
10.34
5.71
7.14
6.62
9.93
6.62
9.93
9.00
10.50
24.80
37.20
17.20
34.40
5.43
7.25
9.06
9.93
7.42
7.35
9.19
4.59
6.12
7.35
7.35
6.31
9.46
4.73
6.31
8.17
8.17
4.91
6.53
3.27
6.53
8.62
8.62
5.17
6.89
2.86
7.14
6.62
8.28
6.62
8.28
3.50
7.00
24.80
37.20
4.30
8.60
7.25
1.81
7.25
1.48
5.93
7.35
9.19
3.06
9.17
9.19
11.03
9.46
9.46
6.31
9.46
6.53
8.17
3.27
8.17
6.53
9.81
5.17
6.89
3.45
8.62
5.71
8.57
3.13
8.25
3.13
8.28
7.00
10.50
24.80
37.20
8.60
17.20
2
3
8.90
4
11.03
11.03
9.17
5
9.17
6
11.03
11.03
9.46
9.46
9.46
9.46
9.80
9.80
9.80
11.44
9.81
11.43
8.62
10.34
8.62
8.62
8.57
10.00
8.28
9.93
8.28
7
8
9
10
11
12
13
14
15
16
11.59
9.00
17
10.50
37.20
74.40
25.80
51.60
Ampicilin
Streptomycin
S. a.—Staphylococcus aureus (ATCC 6538); B. c.—Bacillus cereus (clinical isolate); M. f.—Micrococcus flavus (ATCC 10240); L. m.—Listeria monocytogenes (NCTC 7973); Ps. aer.—
Pseudomonas aeruginosa (ATCC 27853); S. typhi—Salmonella typhimurium (ATCC 13311); E. coli—Escherichia coli (ATCC 35210); En. f.—Enterococcus faecalis (human isolate).
bactericidal at 5.17–11.59
tial could be presented as following: 12>14>11>13>15>8>7>
l
mol ꢁ 10ꢀ2/ml. The antibacterial poten-
activity than Ampicillin even ten-times lower than compounds in
some cases (against Pseudomonas aeruginosa).
10>9>17>16>6. It can be seen that compound 6 showed the worst
As regards the relationships between the structure and the de-
tected antibacterial activity compounds 1–5 showed a significant
antibacterial activity, greater (5–10 fold) than compounds from
the same series previously synthesized.25 Among the methylamino
derivatives the inhibitory effect appears to be dependent on the
substitution at the benzene ring. Thus the introduction of halogen
substituents led to increase of activity 1.2–5-fold, compared to the
unsubstituted derivative. The best results were observed for flu-
oro- and bromo-derivatives, compared to chloro—ones.25 It should
be mentioned that antibacterial activity is dependent not only on
the nature of substituent but on the position of it in the benzene
ring as well. It seems that position 3 in the benzene ring favored
the antibacterial activity.
antibacterial activity with MIC 3.68–11.03
l
mol ꢁ 10ꢀ2/ml and
MBC 7.35–11.03
l
mol ꢁ 10ꢀ2/ml while compound 12 exhibited
the strongest antibacterial potency at MIC 5.17–8.62
l
mol ꢁ 10ꢀ2
/
ml and MBC at 5.17–10.34
l
mol ꢁ 10ꢀ2/ml.
Streptomycin showed MIC in range of 4.3–25.8
l
mol ꢁ 10ꢀ2/ml
and MBC of 8.6–51.6
l
mol ꢁ 10ꢀ2/ml while Ampicillin showed
inhibitory effect at 24.8–74.4
l
mol ꢁ 10ꢀ2/ml and bactericidal at
37.2–124.0
l
mol ꢁ 10ꢀ2/ml.
Compounds 1–5 showed better antibacterial activity than
streptomycin with exception compounds 1, 2, 3 and 4 against B.
cereus. Compounds8, 10, 11, 17 showed almost the same or slightly
higher inhibitory activity than Streptomycin against B. cereus,
while compound 13 showed slightly lower bactericidal activity
against the same bacterial species. All other compounds are less
potent antibacterial agents than Streptomycin. On the other side,
chalcones from both series (1–17) possessed better antibacterial
As far as regards the second group of compounds with R = Et it
was observed that like in the series of methylamino chalcones the
introduction of halogen substituents as well as methoxy group at
the benzene ring led to increased activity. The introduction of

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K. Liaras et al. / Bioorg. Med. Chem. 19 (2011) 7349–7356
F- and Br-substituents, independently of their position, increase
the antibacterial activity. Position of chloro- and nitro groups in
the benzene ring seems to exert a certain effect. Thus 3-Cl and 2-
Cl derivatives are mostly endowed with higher activity with re-
spect to para substitution on the contrary with methylamino chal-
cones where the best activity was observed for fluoro-substitution.
4-Cl Derivative as well as 4-NO2 exhibited activity equal to unsub-
stituted chalcone, while 3-Cl and 3-NO2 derivatives are slightly
more active than unsubstituted one. Furthemore, it seems that
not only the nature of substituent (R0) in benzene ring but also sub-
stituent R influences much the activity. Thus the introduction in
position 2 of thiazole ring of ethylamino group led to compounds
with increased antibacterial activity (2.8–6 fold).
Comparison of novel ethylamino thiazole-based chalcones
(Table 2) with methylamino ones previously tested25 shows that
insertion of ethyl group led to the production of more potent
compounds. Only in case of 4- and 3-fluoro substitution the anti-
bacterial activity of ethylamino chalcones was lower than in case
of 4-and 3-fluoro methylamino chalcones.
presented in Table 3, in comparison with those of the reference
drugs bifonazole and ketoconazole, respectively. All compounds
showed remarkable antifungal effect with MIC 2.97–7.35
l
mol ꢁ
10–2/ml and MFC 5.93–9.19
l
mol ꢁ 10ꢀ2/ml. The antifungal
potential could be presented as: 3>5>4>2>1. Compound 3 showed
the best antifungal activity among other tested with MIC 2.97–
4.45
l
mol ꢁ 10ꢀ2/ml and MFC with 5.93–7.42
l
mol ꢁ 10ꢀ2/ml,
while compound 1 possessed the lowest antifungal potential with
inhibitory activity at 3.5–7.0 llmol ꢁ 10ꢀ2/ml and fungicidal
activity at 7.0–9.0
l
mol ꢁ 10ꢀ2/ml. The majority of the compounds
showed the best activity against Penicillium funiculosum, while
Candida albicans was the most resistant species.
The ethylamino chalcones as well as propylamino (17) deriva-
tive also showed great antifungal potential with MIC at 3.15–
7.35
l
mol ꢁ 10ꢀ2/ml and MFC at 4.0–9.0
l
mol ꢁ 10ꢀ2/ml. The
antifungal potential is ranged in following order: 14>11>17>13>
12>7>8>10>16>9>15>6. The best antifungal activity was observed
for compound 14 with MIC at 2.89–4.29
l
mol ꢁ 10ꢀ2/ml and MFC
at 4.29–5.72
l
mol ꢁ 10ꢀ2/ml while the worst was obtained for
The results of antifungal activity of methylamino (1–5) and eth-
ylamino/propylamino (6–17) derivatives against eight fungi are
compound 6 with MIC at 3.68–7.35
l
mol ꢁ 10ꢀ2/ml and MFC at
7.35–9.19
l
mol ꢁ 10ꢀ2/ml. The most sensitive fungus to tested
Table 3
Antifungal activity of substituted/non substituted (E)-1-[4-methyl-2-(alkylamino)thiazol-5-yl)-3-phenylprop-2-en-1-ones (MIC and MFC in lmol/ml ꢁ 10ꢀ2
)
N
R'
R
N
H
S
O
Compounds
A. o.
3.62
A. fl.
A. n.
3.62
A. fum.
T. v.
7.25
P. o.
3.62
P. f.
3.62
C. a.
7.25
1
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
MIC
MFC
3.62
3.62
7.25
3.62
7.25
2.97
5.93
3.68
7.35
3.06
6.12
3.68
7.35
4.73
6.31
6.31
7.88
4.90
6.53
3.27
6.53
4.90
6.53
5.17
6.89
3.45
6.89
4.29
5.71
6.62
8.28
4.97
6.62
5.24
7.00
38.00
95.00
48.00
64.00
7.25
3.62
7.25
2.97
5.93
3.68
7.35
3.06
6.12
7.35
9.19
6.31
7.88
6.31
7.88
6.53
8.17
6.53
8.17
3.27
4.90
6.89
8.62
6.89
8.62
2.89
4.29
6.62
8.28
6.62
8.28
3.50
5.24
38.00
95.00
48.00
80.00
9.06
3.62
9.06
2.97
7.42
3.68
9.19
3.06
7.65
7.35
9.19
6.31
7.88
6.31
7.88
6.53
8.17
6.53
8.17
4.90
6.53
6.89
8.62
6.89
8.62
4.29
5.71
6.62
8.28
6.62
8.28
5.24
7.00
285.00
380.00
48.00
64.00
7.25
5.43
7.25
4.45
5.93
3.78
7.35
3.06
6.12
5.51
7.35
4.73
6.31
6.31
7.88
6.53
8.17
6.53
8.17
4.90
6.53
3.45
5.17
3.45
6.89
4.29
5.71
3.31
6.62
4.97
6.62
5.24
7.00
38.00
95.00
48.00
64.00
9.06
3.62
7.25
2.97
5.93
3.68
7.35
3.06
6.12
3.68
7.35
4.73
6.31
4.73
6.31
3.27
6.53
3.27
6.53
3.27
6.53
3.45
6.89
3.45
6.89
2.89
5.72
3.31
6.62
3.31
6.62
2.62
3.50
475.00
570.00
64.00
80.00
7.25
3.62
7.25
2.97
5.93
3.68
7.35
3.06
6.12
3.68
7.35
6.31
7.88
6.31
7.88
6.53
8.17
6.53
8.17
3.27
6.53
6.89
8.62
3.45
6.89
2.89
5.82
6.62
8.28
6.62
8.28
3.50
7.00
380.00
380.00
48.00
64.00
7.25
3.62
7.25
2.97
5.93
3.68
7.35
3.06
6.12
3.68
7.35
3.15
6.31
3.15
6.31
3.27
6.53
3.27
6.53
3.27
6.53
3.45
6.89
3.45
6.89
2.89
4.29
3.31
6.62
3.31
6.62
5.24
7.00
38.00
95.00
64.00
80.00
9.06
5.13
7.25
4.45
5.93
5.51
7.35
4.59
6.12
3.68
7.35
3.15
6.31
3.15
6.31
3.27
6.53
3.27
6.53
3.27
6.53
3.45
6.89
3.45
6.89
2.89
5.72
6.62
8.28
3.31
6.62
3.50
7.00
38.00
95.00
32.20
48.00
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Ketoconazole
Bifonazole
Aspergillus ochraceus (ATCC 12066), Aspergillus fumigatus (human isolate), Aspergillus niger (ATCC 6275), Aspergillus flavus (ATCC 9643), Penicillium funiculosum (ATCC 36839),
Penicillium ochrochloron (ATCC 9112), Trichoderma viride (IAM 5061) and Candida albicans (human isolate).

K. Liaras et al. / Bioorg. Med. Chem. 19 (2011) 7349–7356
7353
compounds was found to be Trichoderma viride, while Aspergillus
flavus is the most resistant one.
All the compounds showed remarkable antimicrobial activity
indicating that the diverse substitutions were well tolerated on
the benzylidene moiety as well as on amino group.
The outstanding properties of this series of novel chalcones and
especially of compound 3 as antimicrobial agents deserve further
investigation in order to clarify the mode of action at molecular le-
vel, responsible for the activity observed.
The commercial antifungal agent, Bifonazole, showed MIC at
38.0–64.0
l
mol ꢁ 10ꢀ2/ml and MFC at 48.0–80.0
l
mol ꢁ 10ꢀ2/ml
while Ketoconazole showed fungistatic activity at 38.0–475.0 lmol
ꢁ 10ꢀ2/ml and fungicidal effect at 95.0–570.0
l
mol ꢁ 10ꢀ2/ml. All
compounds tested exhibited much higher antifungal potential than
bifonazole and ketoconazole, ten-fifty fold higher.
As regards the relationships between the structure and the de-
tected antifungal activity these five methylamino chalcone deriva-
tives exhibited significant antifungal efficacy (5–6 fold), greater
than those of previous published.25 In this case antifungal activity
among methylamino chalcones seems to be dependent on the sub-
stitution at the benzene ring, as it was observed for antibacterial
activity. The introduction of fluoro- and bromo- substituents as
well as methyl group is endowed with better antifungal activity
in respect to unsubstituted chalcone.
Regarding the structure–activity relationship of ethylamino
chalcones it was observed that the introduction of different substit-
uents at the benzene ring has as a result the increase of antifungal
potency. The efficacy depends more on the kind of substituents
than their position at the ring. Thus, chloro- substitution seems in
general to endow antifungal activity which ranged in following or-
der 2-Cl>3-Cl>4-Cl. The same order (2-OMe >4-OMe) was observed
for methoxy derivatives. In case of fluoro- derivatives, m-position is
more favorable compared to p-, while for nitro ones it is the
opposite.
Comparing the results of antifungal effect of methylamino
derivatives (1–5) and ethylamino chalcones (6–16) it can be seen
that the last ones are more potent. It should be mentioned that eth-
ylamino derivatives possess also higher activity compared to
methylamino chalcones with the same substitution in the phenyl
ring.25 Thus, the antifungal potency of such kind of compounds
seems to be dependent not only on the substituent of the phenyl
ring, but also on the elongation of the alkylamino group. It is inter-
esting to point out that in this case the elongation of alkylamino
group leads to higher lipophilicity (Table 1).
4. Experimental
Melting points (°C) were determined with a MELTEMP II capil-
lary apparatus (LAB Devices, Holliston, MA, USA) without correc-
tion. Elemental analyses were performed on a Perkin–Elmer
2400 CHN elemental analyzer and all compounds synthesized
and were within a 0.4% of theoretical values. IR spectra were re-
corded, as Nujol mulls, on a Perkin Elmer Spectrum BX and a
DR-8001 Shimadzu. Wave numbers in the IR spectra are given in
cmꢀ1 1H NMR spectra of the newly synthesized compounds, in
.
DMSO-d6 solutions, were recorded on a Bruker AC 300 instrument
(Bruker, Karlsruhe, Germany) at 298 K. Chemical shifts are re-
ported as d (ppm) relative to TMS as internal standard. Coupling
constants J are expressed in Hertz (Center of Instrumental Analysis
of the University of Thessaloniki). 13C NMR spectra of compounds
in DMSO-d6 were recorded on a Bruker AC 300 instrument or an
INOVA 600 (Varian, USA). Mass spectra were recorded on ESI-MS
(Micromass ZMD Waters) at cone voltage 30 V.
The reactions were monitored by TLC on F254 silica-gel pre-
coated sheets (Merck, Darmstadt, Germany) and each of the puri-
fied compounds showed a single spot.
Solvents, unless otherwise specified were of analytical reagent
grade or of the highest quality commercially available. Synthetic
starting materials, reagents and solvents were purchased from
Aldrich Chemie (Steinheimm, Germany).
4.1. Synthesis of 1-propylthiourea27,28
1-Propyl isothiocyanate (25.29 g, 0.25 mol), was added drop-
wise in NH4OH (29 ml) and the mixture was refluxed until the ex-
cess of NH3 was evaporated (30–45 min). Then the reaction
mixture was treated with activated charcoal (0.5 g) and filtered.
After cooling white crystals of 1-propylthiourea were precipitated.
The product was filtered under vacuum and recrystallized from
petroleum ether/ethanol.
It was observed that the activity of unsubstituted derivatives fol-
lowed the order: methylamino<ethylamino<propylamino (MIC:
19.38–38.8
l
mol ꢁ 10ꢀ2/ml, 3.68–7.35
l
mol ꢁ 10ꢀ2/ml, 2.62–5.24
llmol ꢁ 10ꢀ2/ml and MFC: 38.8–77.52
l
mol ꢁ 10ꢀ2/ml, 7.35–
9.19
l
mol ꢁ 10ꢀ2/ml,
3.50–7.0
l
mol ꢁ 10ꢀ2/ml
respectively)
which are in agreement with the above findings.
It can be noticed that compound 14 exhibited the best anti-
fungal and strong antibacterial activity while compound 1 pos-
sessed the best antibacterial activity but the lowest antifungal
potency. From ethylamino/propylamino derivatives compound 12
showed the best antibacterial but modest antifungal activity.
4.2. General synthesis of 1-(4-methyl-2-(alkylamino)thiazol-
5-yl)ethanones25
1-Alkylthiourea (0.02 mol) was dissolved in 50 ml of acetone. 3-
chloroacetylacetone (2.26 ml, 0.02 mol), diluted in acetone (5 ml)
was added dropwise and mixture was refluxed for 1.5 h. The solid
product was filtered and recrystallized from ethanol.
3. Conclusion
The newly synthesized thiazole-based chalcones 1–17 exhibit a
remarkable inhibition of the growth of a wide spectrum of Gram
positive, Gram negative bacteria and fungi. Almost all our com-
pounds exhibited better antibacterial activity than reference drugs,
with most potent methylamino chalcone 3 and ethylamino 12, fol-
lowed by compound 14. The most sensitive bacterial species on
these compounds is M. flavus, followed by B. cereus, while L. mon-
ocytogenes is the most resistant species.
As far as the fungi are concerned, the tested compounds possess
excellent activity against all the fungal species tested being more
active than ketoconazole and bifonazole. The most promising are
compounds 3 (methylamino group), 14 and 11 (ethylamino). The
most sensitive fungi is P. funiculosum, while C. albicans was the
most resistant species.
4.3. General procedure for the synthesis of unsubstituted/
substituted (E)-1-(4-methyl-2-(alkylamino)thiazol-5-yl)-
3-phenylprop-2-en-1-ones25,29
1-(4-Methyl-2-(alkylamino)thiazol-5-yl)ethanone (1 mol) in
methanol (4.0–4.1 l), was added dropwise to a cooled solution
of corresponding aromatic aldehydes (1 mol) in 10% NaOH
(600–650 ml). The reaction mixture was kept under stirring at
0 °C for 30 min and afterwards at room temperature for several
hours (5–12 h) until solid started separating out. The solid was
filtered under vacuum and recrystallized from dioxane to give
the title chalcones. The yield range after recrystallization of chal-
cones was 18–73%.

7354
K. Liaras et al. / Bioorg. Med. Chem. 19 (2011) 7349–7356
4.3.1. (E)-3-(4-Fluorophenyl)-1-(4-methyl-2-(methylamino)
thiazol-5-yl)prop-2-en-1-one (1)
thiazole 4-CH3), 3.26 (q, J = 7.2 Hz, 2H, N–CH2), 7.29 (d,
J = 15.3 Hz, 1H, CO–CH), 7.43–7.44 (m, 3H, arom. 3, 4 and 5), 7.54
(d, J = 15.3 Hz, 1H, Ar–CH), 7.72–7.74 (m, 2H, arom. 2 and 6),
8.55 (s, 1H, NH). 13C NMR (d ppm, DMSO-d6, 150 MHz): 14.03,
18.99, 39.40, 120.77, 124.87, 128.31, 128.91, 130.13, 134.66,
140.89, 159.15, 170.24, 179.87. MS (m/z) 295 (M+ + Na, 100%)
273 (12%). Anal. Calcd for C15H16N2OS (MW 272): C, 66.15; H,
5.92; N, 10.29. Found: C, 66.12; H, 5.89; N, 10.31.
Yield: 29%, mp: 189–192 °C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 2.78 (s, 3H, thiazole 4-CH3), 2.94 (s, 3H, N–CH3), 7.26
(d, J = 15.6 Hz, 1H, CO–CH), 7.23–7.28 (m, 2H, arom. 3 and 5),
7.53 (d, J = 15.6 Hz, 1H, Ar–CH), 7.56–7.84 (m, 2H, arom. 2 and
6). 13C NMR (d ppm, DMSO-d6, 150 MHz): 19.02, 31.10, 115.92,
120.93, 130.66, 131.37, 139.74, 159.34, 161.90, 164.27, 171.33,
179.78. MS, (ES+) (m/z) 299 (100% M++Na,). (ESꢀ) (m/z) 276 (M+,
16%), 275 (100%), 233 (7%). Anal. Calcd for C14H13FN2OS (MW
276): C, 60.85; H, 4.74; N, 10.14. Found: C, 60.90; H, 4.71; N, 10.10.
4.3.7. (E)-1-(2-(Ethylamino)-4-methylthiazol-5-yl)-3-
(4-nitrophenyl)prop-2-en-1-one (7)
Yield: 58%, mp: 248–249 °C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 1.17 (t, J = 6.9 Hz, 3H, methyl NCH2CH3), 2.55 (s, 3H, thi-
azole 4-CH3), 3.27 (q, J = 7.2 Hz, 2H, N–CH2), 7.46 (d, J = 15.3 Hz,
1H, CO–CH), 7.59 (d, J = 16.6 Hz, 1H, Ar–CH), 8.0 (d, J = 8.7 Hz, 2H,
arom. 2 and 6), 8.23 (d, J = 8.4 Hz, 2H, arom. 3 and 5), 8.70 (s, 1H,
NH). 13C NMR (d ppm, DMSO-d6, 150 MHz): 13.89, 18.97, 39.42
120.75, 123.98, 128.73, 129.30, 138.22, 141.13, 147.76, 160.28,
170.85, 179.52. MS (m/z) 340 (M+ + Na, 100%) 329 (6%), 318 (M+,
5%), 302 (4%), 301 (15%), 239(5%), 229 (8%), 217 (5%), 213 (5%),
207 (11%), 199 (5%), 187 (5%), 185 (9%), 177 (29%), 169 (6%), 167
(14%), 165 (13%), 159 (6%), 155 (9%), 153 (17%), 151 (24%), 149
(15%), 147 (14%), 141 (11%), 137 (12%), 135 (21%), 133 (42%). Anal.
Calcd for C15H15N3O3S (MW 317): C, 56.77; H, 4.76; N, 13.24.
Found: C, 56.73; H, 4.80; N, 13.19.
4.3.2. (E)-3-(3-Fluorophenyl)-1-(4-methyl-2-(methylamino)
thiazol-5-yl)prop-2-en-1-one (2)
Yield: 67%, mp: 191–193 °C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 2.55 (s, 3H, thiazole 4-CH3), 2.87 (s, 3H, N–CH3), 7.25–
7.65 (m, 6H, arom., alkene). 13C NMR (d ppm, DMSO-d6, 75 MHz):
19.10, 32.23, 114.09, 114.38, 117.18, 121.63, 124.42, 130.45,
137.24, 140.96, 160.05, 164.68, 172.80, 180.60. MS (ES+). (m/z)
299 (100%, M++Na). (ESꢀ) (m/z) 276 (20%, M+), 275 (100%). Anal.
Calcd for C14H13FN2OS (MW 276): C, 60.85; H, 4.74; N, 10.14.
Found: C, 60.81; H, 4.68; N, 10.09.
4.3.3. (E)-3-(3-Bromophenyl)-1-(4-methyl-2-(methylamino)
thiazol-5-yl)prop-2-en-1-one (3)
Yield: 73%, mp: 215–217 °C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 2.54 (s, 3H, thiazole 4-CH3), 2.86 (s, 3H, N–CH3), 7.38–
7.58 (m, 3H, arom. 5, alkene), 7.62 (d, J = 8.4 Hz, 1H, arom. 4),
7.74 (d, J = 7.8 Hz, 1H, arom. 6), 7.99 (s, 1H, arom. 2). 13C NMR (d
ppm, DMSO-d6, 150 MHz): 19.05, 31.08, 120.93, 122.35, 126.50,
127.36, 130.72, 132.63, 137.28, 139.25, 159.73, 169.54, 171.55,
179.71. MS (ES+). (m/z) 361 (100%, M+ +Na), 339 (8%), 301 (8%),
193 (8%) MS (ESꢀ) (m/z) 339 (7%), 337 (M+, 93%), 335 (100%). Anal.
Calcd for C14H13BrN2OS (MW 337): C, 49.86; H, 3.89; N, 8.31.
Found: C, 49.80; H, 3.83; N, 8.29.
4.3.8. (E)-1-(2-(Ethylamino)-4-methylthiazol-5-yl)-3-
(3-nitrophenyl)prop-2-en-1-one (8)
Yield: 47%, mp: 246–247 C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 1.17 (t, J = 7.2 Hz, 3H, methyl NCH2CH3), 2.55 (s, 3H, thi-
azole 4-CH3), 3.27 (q, J = 7.2 Hz, 2H, N–CH2), 7.46 (d, J = 15.6 Hz,
1H, CO–CH), 7.63 (d, J = 15.3 Hz, 1H, Ar–CH), 7.70–7.73 (m, 1H,
arom. 5), 8.20–8.23 (m, 2H, arom. 4 and 6), 8.55 (s, 1H, arom. 2),
8.66 (s, 1H, NH). 13C NMR (d ppm, DMSO-d6, 150 MHz): 14.05,
19.08, 39.72, 120.64, 122.81, 124.27, 127.74, 130.38, 134.23,
136.64, 138.40, 148.37, 159.93, 170.59, 179.54. MS (m/z) 340 (M+
+ Na, 100%) 328 (4%), 326 (3%), 318 (M+, 7%), 311 (3%), 301
(12%), 263 (3%), 257 (3%), 245 (4%), 230 (4%), 229 (8%), 217 (6%),
207 (22%), 203 (4%), 191 (6%), 185 (9%), 177 (15%), 167 (7%), 165
(13%), 159 (6%), 153 (19%). Anal. Calcd for C15H15N3O3S (MW
317): C, 56.77; H, 4.76; N, 13.24. Found: C, 56.72; H, 4.79; N, 13.20.
4.3.4. (E)-1-(4-Methyl-2-(methylamino)thiazol-5-yl)-
3-m-tolylprop-2-en-1-one (4)
Yield: 63%, mp: 186–188 °C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 2.35 (s, 3H, Ar–CH3), 2.57 (s, 3H, thiazole 4-CH3), 2.89
(s, 3H, N–CH3), 7.26–7.33 (m, 3H, CO–CH, arom. 2 and 4), 7.49–
7.56 (m, 3H, arom. 5 and 6, Ar–CH). 13C NMR (d ppm, DMSO-d6,
75 MHz): 19.44, 21.78, 32.60, 122.18, 124.86, 125.87, 129.19,
129.31, 131.48, 135.31, 138.97, 143.08, 159.92, 173.08, 181.52.
MS (ES+) (m/z) 295(100%, M++Na). MS (ESꢀ) (m/z) 272 (23%, M+),
271 (100%). Anal. Calcd for C15H16N2OS (MW 272): C, 66.15; H,
5.92; N, 10.29. Found: C, 66.10; H, 5.97; N, 10.32.
4.3.9. (E)-3-(4-Chlorophenyl)-1-(2-(ethylamino)-
4-methylthiazol-5-yl)prop-2-en-1-one (9)
Yield: 67%, mp: 191–293 C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 1.68 (t, J = 6.9 Hz, 3H, methyl NCH2CH3), 2.54 (s, 3H, thi-
azole 4-CH3), 3.26 (q, J = 7.2 Hz, 2H, N–CH2), 7.31 (d, J = 15.3 Hz,
1H, CO–CH), 7.47–7.53 (m, 3H, Ar–CH, arom. 3 and 5), 7.77 (d,
J = 7.8 Hz, 2H, arom. 2 and 6). 13C NMR (d ppm, DMSO-d6,
150 MHz): 14.01, 19.05, 39.44, 120.72, 125.59, 128.92, 130.02,
133.63, 134.57, 139.43, 159.38, 170.34, 179.67. MS (m/z) 329
(M++Na, 100%) 307 (M+, 7%). Anal. Calcd for C15H15ClN2OS (MW
306.5): C, 58.72; H, 4.93; N, 9.13. Found: C, 58.68; H, 4.90; N, 9.11.
4.3.5. (E)-3-(2,3-Dichlorophenyl)-1-(4-methyl-2-
(methylamino)thiazol-5-yl)prop-2-en-1-one (5)
Yield: 42%, mp: 186–188 °C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 2.57 (s, 3H, thiazole 4-CH3), 2.89 (s, 3H, N–CH3), 7.39
(d, J = 15.4 Hz, 1H, CO–CH), 7.46 (d, J = 7.9 Hz, 1H, arom. 6), 7.72
(d, J = 7.9 Hz, 1H, arom. 5), 7.82 (d, J = 15.4 Hz, 1H, Ar–CH), 7.98
(d, J = 7.7 Hz, 1H, arom. 4), 8.65 (s, 1H, NH). 13C NMR (d ppm,
DMSO-d6), 75 MHz): 19.07, 32.23, 121.90, 128.03, 128.2, 128.85,
129.62, 132.53, 132.59, 135.22, 135.55, 160.11, 173.23, 180.37.
MS (m/z) 330 (17%), 329 (13%), 328 (64), 327 (M+ 36%), 326
(92%), 298 (7%), 293 (26%), 291 (67%), 263 (13%), 228 (9%), 209
(10%), 181 (100%), 155 (26%), 136 (22%), 100 (13%). Anal. Calcd
for C14H12Cl2N2OS (MW 327): C, 51.39; H, 3.70; N, 8.56. Found:
C, 51.35; H, 3.68; N, 8.50.
4.3.10. (E)-3-(3-Chlorophenyl)-1-(2-(ethylamino)-4-
methylthiazol-5-yl)prop-2-en-1-one (10)
Yield: 68%, mp: 209–212 C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 1.69 (t, J = 7.2 Hz, 3H, methyl NCH2CH3), 2.54 (s, 3H, thi-
azole 4-CH3), 3.27 (q, J = 7.2 Hz, 2H, N–CH2), 7.35 (d, 1H,
J = 15.6 Hz, CO–CH), 7.43–7.46 (m, 3H, Ar–CH, arom. 4 and 5),
7.68–7.73 (m, 1H, arom. 6), 7.86 (s, 1H, arom. 2). 13C NMR (d
ppm, DMSO-d6, 150 MHz): 14.02, 19.03, 39.89, 120.66, 126.48,
126.94, 127.78, 129.65, 130.65, 133.72, 136.98, 139.17, 159.62,
170.46, 179.62. MS (m/z) 329 (M+ + Na, 38%), 309 (38%), 307
(M++H, 100%), 303 (13%), 185 (12%), 165 (3%), 153 (3%), 143 (6%).
Anal. Calcd for C15H15ClN2OS (MW 306.5): C, 58.72; H, 4.93; N,
9.13. Found: C, 58.70; H, 4.90; N, 9.09.
4.3.6. (E)-1-(2-(Ethylamino)-4-methylthiazol-5-yl)-
3-phenylprop-2-en-1-one (6)
Yield: 32%, mp: 150–152 °C. 1H NMR (d d ppm, DMSO-d6,
300 MHz): 1.18 (t, J = 7.2 Hz, 3H, methyl NCH2CH3), 2.50 (s, 3H,

K. Liaras et al. / Bioorg. Med. Chem. 19 (2011) 7349–7356
7355
4.3.11. (E)-3-(2-Chlorophenyl)-1-(2-(ethylamino)-
4-methylthiazol-5-yl)prop-2-en-1-one (11)
arom. 2 and 6). 13C NMR (d ppm, DMSO-d6, 150 MHz): 14.10,
18.98, 39.43, 55.36, 114.47, 120.85, 122.43, 127.28, 130.20,
141.01, 158.72, 161.06, 170.10, 180.05. MS (m/z) 325 (M++Na,
100%), 305(5%), 303(M+, 10%), 161 (5%), 153 (6%), 143 (5%), 131
(5%), 119 (5%), 117 (8%). Anal. Calcd for C16H18N2O2S (MW 302):
C, 63.55; H, 6.00; N, 9.26. Found: C, 63.50; H, 6.06; N, 9.26.
Yield: 32%, mp: 185–187 C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 1.21 (t, J = 7.2 Hz, 3H, methyl NCH2CH3), 2.63 (s, 3H, thi-
azole 4-CH3), 3.41 (q, J = 7.2 Hz, 2H, N–CH2), 7.37 (d, J = 15.6 Hz,
1H, CO–CH), 7.43–7.57 (m, 3H, arom. 4, 5 and 6), 7.87 (d,
J = 15.3 Hz, 1H, Ar–CH), 7.99–8.02 (m, 1H, arom. 3). 13C NMR (d
ppm, DMSO-d6, 150 MHz): 14.06, 19.07, 39.52, 120.70, 126.52,
126.99, 127.81, 129.70, 130.77, 133.76, 137.02, 139.21, 159.65,
170.49, 179.67. MS (m/z) 329 (M+ + Na, 100%), 327(16%), 326
(12%), 309 (10%), 307 (21%), 276 (16%), 229 (4%), 216 (5%), 201
(4%), 174 (8%), 173 (14%), 153 (9%), 145 (10%), 135 (12%), 131
(24%), 129 (29%), 125 (12%), 123 (20%). Anal. Calcd for
4.3.16. (E)-1-(2-(ethylamino)-4-methylthiazol-5-yl)-3-
(2-methoxyphenyl)prop-2-en-1-one (16)
Yield: 19%, mp: 161–163 C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 1.17 (t, J = 7.2 Hz, 3H, methyl NCH2CH3), 2.55 (s, 3H, thi-
azole 4-CH3), 3.28 (q, J = 6.9 Hz, 2H, N–CH2), 3.89 (s, 3H, OCH3),
6.98–7.12 (m, 2H, arom. 3 and 5), 7.34–7.44 (m, 2H, CO–CH, arom.
4), 7.71–7.80 (m, 2H, Ar–CH, arom. 6), 8.60 (s, 1H, NH). MS (m/z)
303 (M+,100%), 179 (4%), 157 (4%), 155 (6%), 151 (6%). Anal. Calcd
for C16H18N2O2S (MW 302): C, 63.55; H, 6.00; N, 9.26. Found: C,
63.58; H, 6.03; N, 9.23.
C15H15ClN2OS (MW 306.5): C, 58.72; H, 4.93; N, 9.13. Found: C,
58.76; H, 4.95; N, 9.10.
4.3.12. (E)-1-(2-(Ethylamino)-4-methylthiazol-5-yl)-
3-(4-fluorophenyl)prop-2-en-1-one (12)
Yield: 32%, mp: 167–169 C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 1.17 (t, J = 7.2 Hz, 3H, methyl NCH2CH3), 2.55 (s, 3H, thi-
azole 4-CH3), 3.28 (q, J = 6.9 Hz, 2H, N–CH2), 7.24–7.30 (m, 3H, CO–
CH, arom. 3 and 5), 7.54 (d, J = 15.6 Hz, 1H, Ar–CH), 7.81–7.86 (m,
2H, arom. 2 and 6), 8.62 (s, 1H, NH). 13C NMR (d ppm, DMSO-d6,
150 MHz): 14.05, 19.01, 39.91, 115.88, 120.65, 130.62, 131.35,
139.64, 159.20, 162.27, 163.91, 170.22, 179.72. MS (m/z) 313
(M++Na, 100%) 291 (M+, 6.5%), 231 (4%), 229 (9%), 209 (29%), 201
(5%), 199 (10%), 197 (16%), 195 (12%), 187 (5%), 183 (9%), 177
(8%), 167 (5%), 165 (15%), 159 (6%), 155 (9%), 153 (23%), 151
(65%), 149 (8%), 141 (8%), 128 (9%), 127 (31%), 121 (11%). (Anal.
Calcd for C15H15FN2OS (MW 290): C, 62.05; H, 5.21; N, 9.65. Found:
C, 62.07; H, 5.19; N, 9.61.
4.3.17. (E)-1-(4-methyl-2-(propylamino)thiazol-5-yl)-
3-phenylprop-2-en-1-one (17)
Yield: 41%, mp: 150–152 C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 0.93 (t, J = 7.2 Hz, 3H, methyl NCH2CH2CH3), 1.60 (sex-
tet, J = 7.2 Hz, 2H, b-methylene NCH2CH2CH3), 2.55 (s, 3H, thiazole
4-CH3), 3.24 (t, 2H, a-methylene NCH2CH2CH3), 7.28 (d, J = 15.3 Hz,
1H, CO–CH), 7.43–7.44 (m, 3H, arom. 3, 4 and 5), 7.54 (d,
J = 15.6 Hz, 1H, Ar–-CH), 7.71–7.72 (m, 2H, arom. 2 and 6), 8.51
(s, 1H, NH). 13C NMR (d ppm, DMSO-d6, 150 MHz): 11.35, 19.03,
21.73, 46.49, 120.73, 124.91, 128.39, 128.96, 130.17, 134.69,
140.90, 159.23, 170.57, 179.89. MS (ES+) (m/z) 309 (100%,
M++Na), 287 (5%), MS (ESꢀ) (m/z) 286 (M+, 20%), 285 (100%). Anal.
Calcd for C16H18N2OS (MW 286): C, 67.10; H, 6.33; N, 9.78. Found:
C, 67.14; H, 6.30; N, 9.81.
4.3.13. (E)-1-(2-(Ethylamino)-4-methylthiazol-5-yl)-3-
(3-fluorophenyl)prop-2-en-1-one (13)
4.4. Biological evaluation
Yield: 37%, mp: 177–179 C. 1H NMR (d ppm, DMSO-d6, 300 MHz):
1.18 (t, J = 7.2 Hz, 3H, methyl NCH2CH3), 2.55 (s, 3H, thiazole 4-CH3),
3.28 (q, J = 7.2 Hz, 2H, N–CH2), 7.22–7.27 (m, 1H, arom. 2), 7.36 (d,
J = 15.3 Hz, 1H, CO–CH), 7.43–7.51 (m, 2H, Ar–CH, arom. 4), 7.55–
7.59 (m, 1H, arom. 5), 7.67 (d, J = 10.2 Hz, 1H, arom. 6). 13C NMR (d
ppm, DMSO-d6, 150 MHz): 14.05, 19.06, 39.48, 114.45, 116.77,
120.78, 124.77, 126.39, 130.85, 137.31, 139.48, 159.57, 161.29,
163.71, 179.75. MS (m/z) 313 (M+ + Na, 100%) 291 (M+, 2%), 207
(4%), 121 (2%), 117 (4%). Anal. Calcd for C15H15FN2OS (MW 290): C,
62.05; H, 5.21; N, 9.65. Found: C, 62.09; H, 5.19; N, 9.60.
4.4.1. Antibacterial activity
The following Gram-negative bacteria were used: Escherichia
coli (ATCC 35210), Pseudomonas aeruginosa (ATCC 27853),
Salmonella typhimurium (ATCC 13311), Enterococcus faecalis
(human isolate) and the following Gram-positive bacteria: Bacillus
cereus (clinical isolate), Micrococcus flavus (ATCC 10240), Listeria
monocytogenes (NCTC 7973), and Staphylococcus aureus (ATCC
6538). The organisms were obtained from the Mycological
Laboratory, Department of Plant Physiology, Institute for Biological
Research ‘Siniša Stankovic´’, Belgrade, Serbia.
4.3.14. (E)-3-(3-Bromophenyl)-1-(2-(ethylamino)-
4-methylthiazol-5-yl)prop-2-en-1-one (14)
The antibacterial assay was carried out by a microdilution
method34–35 in order to determine the antibacterial activity of
compounds tested against the human pathogenic bacteria.
The bacterial suspensions were adjusted with sterile saline to a
concentration of 1.0 ꢁ 105 CFU/ml. The inocula were prepared dai-
ly and stored at +4 °C until use. Dilutions of the inocula were cul-
tured on solid medium to verify the absence of contamination and
to check the validity of the inoculum.
Yield: 47%, mp: 171–172 C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 1.19 (t, J = 6.9 Hz, 3H, methyl NCH2CH3), 2.55 (s, 3H, thi-
azole 4-CH3), 3.30 (q, J = 7.2 Hz, 2H, N–CH2), 7.33 (d, J = 15.6 Hz,
1H, CO–CH), 7.36–7.41 (m, 1H, arom. 5), 7.49 (d, J = 15.3 Hz, 1H,
Ar–CH), 7.60 (d, J = 8.1 Hz, 2H, arom. 4), 7.73 (d, J = 7.8 Hz, 2H,
arom. 6), 7.96 (s, 1H, arom. 2), 8.51 (s, 1H, NH). 13C NMR (d ppm,
DMSO-d6, 150 MHz): 14.05, 19.05, 39.46, 120.72, 122.35, 126.49,
127.32, 130.71, 130.96, 132.61, 137.27, 139.19, 159.63, 170.51,
179.71. MS (ES+) (m/z) 376 (18%), 375 (100%), 374 (18% M+ + Na),
373 (97%), 353 (8%). Anal. Calcd for C15H15BrN2OS (MW 351): C,
51.29; H, 4.30; N, 7.98. Found: C, 51.25; H, 4.28; N, 7.95.
All experiments were performed in duplicate and repeated
three times.
4.4.2. Microdilution test
The minimum inhibitory and bactericidal concentrations (MICs
and MBCs) were determined using 96-well microtitre plates. The
bacterial suspension was adjusted with sterile saline to a concentra-
tion of 1.0 ꢁ 105 CFU/ml. Compounds to be investigated were dis-
olved in 5% DMSO solution containing 0.1% Tween 80 (v/v) (1 mg/
4.3.15. (E)-1-(2-(ethylamino)-4-methylthiazol-5-yl)-3-(4-
methoxyphenyl)prop-2-en-1-one (15)
Yield: 18%, mp: 175–176 C. 1H NMR (d ppm, DMSO-d6,
300 MHz): 1.18 (t, J = 7.2 Hz, 3H, methyl NCH2CH3), 2.54 (s, 3H, thi-
azole 4-CH3), 3.27 (q, J = 7.2 Hz, 2H, N–CH2), 3.81 (s, 3H, OCH3),
6.99 (d, J = 8.4 Hz, 2H, arom. 3 and 5), 7.14 (d, J = 15.3 Hz, 1H,
CO–CH), 7.51 (d, J = 15.3 Hz, 1H, Ar–CH), 7.69 (d, J = 8.7 Hz, 2H,
ml) and added in broth LB medium (100 ll) with bacterial inoculum
(1.0 ꢁ 104 CFU per well) to achieve the wanted concentrations. The
microplates were incubated at Rotary shaker (160 rpm) for 24 h at
48 °C. The lowest concentrations without visible growth (at the

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K. Liaras et al. / Bioorg. Med. Chem. 19 (2011) 7349–7356
binocular microscope) were defined as concentrations that com-
pletely inhibited bacterial growth (MICs). The MBCs were deter-
negative control, commercial fungicides, bifonazole (Srbolek,
Belgrade, Serbia) and ketoconazole (Zorkapharma, Šabac, Serbia),
mined by serial sub-cultivation of 2
l
l into microtitre plates
were used as positive controls (1–3000
All experiments were performed in duplicate and repeated
three times.
lg/ml).
containing 100 l of broth per well and further incubation for
l
24 h. The lowest concentration with no visible growth was defined
as the MBC, indicating 99.5% killing of the original inoculum. The
optical density of each well was measured at a wavelength of
655 nm by Microplate manager 4.0 (Bio-Rad Laboratories) and com-
pared with a blank and the positive control. Streptomycin (Sigma P
7794)and Ampicillin(Panfarma, Belgrade, Serbia) were used as a po-
sitive control (1 mg/ml in sterile physiological saline). DMSO was
used as a negative control.
References and notes
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4.4.3. Antifungal activity
For the antifungal bioassays, eight fungi were used: Aspergillus
ochraceus (ATCC 12066), Aspergillus fumigatus (human isolate),
Aspergillus niger (ATCC 6275), Aspergillus flavus (ATCC 9643), Peni-
cillium funiculosum (ATCC 36839), Penicillium ochrochloron (ATCC
9112), Trichoderma viride (IAM 5061) and Candida albicans (human
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´
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Minimum inhibitory concentration (MIC) determinations were
performed by a serial dilution technique using 96-well microtiter
plates. The compounds investigated were dissolved in 5% DMSO
solution containing 0.1% Tween 80 (v/v) (1 mg/ml) and added in
broth Malt medium with inoculum. The microplates were incu-
bated at Rotary shaker (160 rpm) for 72 h at 28 °C. The lowest con-
centrations without visible growth (at the binocular microscope)
were defined as MICs.
´
ˇ
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The fungicidal concentrations (MFCs) were determined by serial
subcultivation of a 2
ll of tested compounds disolved in medium
and inoculated for 72 h, into microtiter plates containing 100
l
l
of broth per well and further incubation 72 h at 28 °C. The lowest
concentration with no visible growth was defined as MFC indicat-
ing 99.5% killing of the original inoculum. DMSO was used as a