Synthesis, antibacterial and antifungal activity of some new thiazolylhydrazone derivatives containing 3-substituted cyclobutane ring

Article abstract of DOI:10.1016/j.ejmech.2005.01.013

A series of Schiff bases, combining 2,4-disubstituted thiazole and cyclobutane rings, and hydrazone moieties in the same molecule, was synthesized, characterized and evaluated for screening antibacterial and antifungal activities on microorganisms, respec

Full text of DOI:10.1016/j.ejmech.2005.01.013

European Journal of Medicinal Chemistry 41 (2006) 201–207
http://france.elsevier.com/direct/ejmech
Original article
Synthesis, antibacterial and antifungal activity
of some new thiazolylhydrazone
derivatives containing 3-substituted cyclobutane ring
Alaaddin Cukurovali a,*, İbrahim Yilmaz a, Seher Gur b, Cavit Kazaz c
a
Department of Chemistry, Faculty of Arts and Sciences, Firat University, 23119 Elazig, Turkey
Department of Biology, Faculty of Arts and Sciences, Firat University, 23119 Elazig, Turkey
b
c
Department of Chemistry, Faculty of Arts and Sciences, Atatürk University, 25240 Erzurum, Turkey
Received 28 November 2004; received in revised form 24 January 2005; accepted 27 January 2005
Available online 27 December 2005
Abstract
A series of Schiff bases, combining 2,4-disubstituted thiazole and cyclobutane rings, and hydrazone moieties in the same molecule, was
synthesized, characterized and evaluated for screening antibacterial and antifungal activities on microorganisms, respectively, on four bacteria
1
and Candida tropicalis. The structures of original compounds were confirmed by analytical and spectroscopic (FT-IR, H NMR and 13C NMR)
methods and elemental analysis. Both the antibacterial and antifungal activities and MIC values of compounds were reported. Among the tested
compounds, the most effective compound providing a MIC value of 16 μg ml–1 are 2 against C. tropicalis and Bacillus subtilis and 3 against
B. subtilis only.
© 2005 Elsevier SAS. All rights reserved.
Keywords: Cyclobutane; Thiosemicarbazone; Antibacterial activity; Antifungal activity; MIC
1. Introduction
documented. Simple stable molecules containing the hydroxa-
mic acid [13] functionality as well as methoxy-alkylthiazoles
and 6-hydroxybenzothiazoles [14] were reported as LOs inhi-
bitors.
Prompted by the observed biological activities of the above
mentioned derivatives and in continuation of our ongoing stu-
dies on novel biologically active molecules, we have designed
and synthesized some new hydrazone derivatives, bearing cy-
clobutane, thiazole and azomethine functionality in the same
molecule, as potential antibacterial and antifungal agents.
Since it is a common agreement of multidrug-resistant bac-
teria are the major cause of failure in the treatment of infectious
diseases, the need for the synthesis of novel antibiotics is a
reality. N1-2-(thiazolyl)sulfanilamide (sulfathiazole) which
contains 2-aminothiazole ring and exhibiting herbicidal and
anti-inflammatory [1,2], antimicrobial [3] or antiparasitic activ-
ity [4] is a well-known compound was used as an early anti-
biotic agent since the late 1930s [5,6]. Thiazole itself and its
derivatives are of importance in biological systems as anti-in-
flammatory, analgesic agents and inhibitors on lipoxygenase
activities [7,8]. On the other hand, cyclobutane amino acids
in different structures were described as highly potent l-gluta-
mate, N-methyl-D-aspartate (NMDA) agonist, NMDA antago-
nists and anticonvulsive drugs [9–11]. The effective role of
azomethine linkage in certain biological reactions [12] is well
* Corresponding author.
E-mail address: acukurovali@firat.edu.tr (A. Cukurovali).
0223-5234/$ - see front matter © 2005 Elsevier SAS. All rights reserved.
doi:10.1016/j.ejmech.2005.01.013

202
A. Cukurovali et al. / European Journal of Medicinal Chemistry 41 (2006) 201–207
3. Experimental
Substance
Ar
R1
R2
R3
3.1. Chemistry
1
2
3
4
5
6
7
8
Phenyl (ph)
Phenyl
Phenyl
H
H
H
H
H
H
OCH3
H
H
H
OCH3
H
H
H
H
OH
H
OCH3
H
OH
H
H
OH
H
H
H
H
H
Br
H
H
H
H
H
H
Aldehydes and thiosemicarbazide were purchased from
Merck (pure) and were used without further purification. α-
Chloroketones, 1-phenyl-1-methyl-3-(2-chloro-1-oxoethyl) cy-
clobutane, 1-p-xylyl-1-methyl-3-(2-chloro-1-oxoethyl) cyclo-
butane and 1-mesityl-1-methyl-3-(2-chloro-1-oxoethyl) cyclo-
butane were prepared according to the previously published
procedure in [15]. Solvents were of analytical grade and puri-
fied by standard methods where necessary. Microanalyses were
performed on a LECO CHNSO-932 auto elemental analysis
apparatus. IR spectra were recorded on a Mattson 1000 (Uni-
cam Ltd., Cambridge, UK) Fourier transform-infrared (FT-IR)
Spectrometer using KBr pellets in the range 4000–400 cm−1.
Phenyl
p-Xylyl (p-x)
p-Xylyl
p-Xylyl
Mesityl (Ms)
Mesityl
Mesityl
Mesityl
Mesityl
Mesityl
9
10
11
12
13
14
15
16
Br
H
OCH3
NO2
Cl
Cl
Br
H
H
H
H
Mesityl
Mesityl
Mesityl
Cl
Br
1
The H and 13C NMR spectra were recorded on a Varian-Ge-
mini 200 MHz at 50.34 MHz spectrometer. Melting points
were determined on a Gallenkamp melting point apparatus
and checked by differential scanning calorimetry (DSC) and
are uncorrected.
2. Chemistry
Synthetic process for the synthesis of the target compounds
is outlined in Scheme 1. As known in multi-stage reactions,
such as the synthesis of our compounds, the reaction sequences
are important phenomenon. It is possible that the direct reac-
tion of an α-haloketone with thiosemicarbazide affords several
co-products and the separation of these substances is a tedious
and time consuming process. Instead of this, in the first stage
we have synthesized azomethine compounds (thiosemicarba-
zones), A. Subsequently, they have been converted into their
hydrazone compounds by the reaction of α-haloketones. Such a
modification of literature process produces no co-products and
separations are almost not necessary. The application of the
modified method is given in Section 3.
3.2. Synthesis of the compounds (1–18)
General method: To a solution of thiosemicarbazide
(2.275 g, 25.0 mmol) and 0.05 g of p-toluenesulfonic acid as
catalyst in 50 ml absolute EtOH, a solution of appropriate sal-
icylaldehyde (25.0 mmol) in 20 ml absolute EtOH were added
dropwise at 60–70 °C with continuous stirring. Expected solid
product was formed about half an hour period. The course of
the reaction was monitored by IR spectroscopy. After complet-
ing this reaction, the mixture of appropriate α-chloroketone
(25.0 mmol) and K2CO3 (12.5 mmol) dissolved in anhydrous
ethanol (50 ml) was added and heated at 60–70 °C with con-
tinuous stirring and monitoring the course of the reaction with
IR. Monitoring the visibility of the carbonyl and –CH2–Cl
groups of α-chloroketones is easily done and then it is very
easy to determine when the reaction is complete. At the end
of the reaction period and cooling to the room temperature
the solution neutralized with 5% aqueous ammonia (if neces-
sary), the solid product thus formed was filtered off, washed
with copious water several times, dried in air and crystallized
from aqueous EtOH to give compounds 1–18 [16–19].
The synthesis of the compounds 1–18 was performed in two
steps as shown in Scheme 1. In the first step, desired thiosemi-
carbazones were obtained by heating thiosemicarbazide with
appropriate aldehydes at 50–60 °C with continuous stirring in
the presence of a few drops of p-toluenesulfonic acid as cata-
lyst. In the second step, appropriate thiosemicarbazone was re-
acted with appropriate α-chloroketone to convert into its hydra-
zide derivatives containing 2,4-disubstituted thiazole and
cyclobutane rings in the presence of NaHCO3 or K2CO3 as
neutralizing agent at 60–70 °C for about 5 min. Substances 2,
6, 15 and 16 are fully novel. The structures of the compounds
3.2.1. 2-Hydroxybenzaldehyde [4-(3-methyl-3-
phenylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (1)
1
synthesized here were supported by the spectral data of IR, H
NMR, 13C NMR spectra and elemental analysis results which
are in agreement with the proposed structures. Physical and
spectral data of the compounds are given in Section 3.
Pale yellow crystals. Yield: 64%. M.p.: 194 °C (EtOH). IR
(KBr, υ cm−1): 3182 (–OH), 3131 (–NH–), 1625 (C=N
1
azomethine). H NMR (CDCl3, TMS, δ ppm): 1.47 (s, 3H,
–CH3), 2.47–2.51 (m, 4H, –CH2– in cyclobutane ring), 3.57
(quint, j = 8.9 Hz, 1H, > CH– in cyclobutane ring), 6.06 (s,
1H, = CH–S in thiazole ring), 6.86–7.34 (m, 9H, aromatics),
8.12 (s, 1H, azomethine), 10.0–10.6 (br, 2H, –NH– plus –OH,
D2O exchangeable). 13C NMR (CDCl3, TMS, δ ppm): 171.42,
159.82, 153.64, 153.20, 149.87, 132.97, 132.24, 130.30,
127.53. 126.57, 121.53, 120.05, 118.87, 101.63, 42.02,
Scheme 1. Synthesis and the structures of the compounds.

A. Cukurovali et al. / European Journal of Medicinal Chemistry 41 (2006) 201–207
203
40.97, 32.07, 31.73. Anal. calc. for C21H21N3OS (363.48); C:
69.39, H: 5.82, N: 11.56; found; C: 69.71, H: 6.03, N: 11.34.
2.19 (s, 3H, p-xylyl o-CH3), 2.29 (s, 3H, p-xylyl m-CH3),
2.55 (d, 4H, j = 9.0 Hz, –CH2– in cyclobutane ring), 3.54
(quint, j = 7.0 Hz, 1H, > CH– in cyclobutane), 6.07 (s, 1H,
= CH– in thiazole ring), 6.79–7.28 (m, 6H, aromatics), 8.12
(s, 1H, N=CH–), 10.75–11.45 (br, 2H, –OH plus –NH–, D2O
exchangeable). 13C NMR (CDCl3, δ ppm): 171.02, 159.83,
153.39, 150.82, 149.83, 137.29, 133.26, 133.17, 132.96,
132.26, 129.81, 128.22, 121.51, 120.05, 118.86, 101.73,
43.06, 41.86, 32.14, 29.52, 22.99, 21.49. Anal. calc. for
C23H25N3OS (391.54); C: 70.56, H: 6.44, N: 10.73; found;
C: 70.85, H: 6.05, N: 10.89.
3.2.2. 2,4-Dihydroxybenzaldehyde [4-(3-methyl-3-
phenylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (2)
Orange crystals. Yield: 74%. M.p.: 173 °C (EtOH). IR
(KBr, υ cm−1): 3229 (o-OH), 3452 (p-OH), 3126 (–NH–),
1631 (C=N azomethine). 1H NMR (CDCl3, TMS, δ ppm):
1.47 (s, 3H, –CH3), 2.50 (d, j = 8.7 Hz, 4H, –CH2– in cyclo-
butane ring), 3.53 (quint, j = 8.9 Hz, 1H, > CH– in cyclobutane
ring), 6.03 (s, 1H, = CH–S in thiazole ring), 6.50–7.30 (m, 9H,
aromatics), 7.94 (s, 1H, azomethine), 9.96 (br, 1H, –NH–, D2O
exchangeable), 11.32 (s, 1H, o-OH, D2O exchangeable), 7.43
(s, 1H, p-OH, D2O exchangeable). 13C NMR (CDCl3, TMS, δ
ppm): 173.62, 158.72, 154.24, 153.61, 149.39, 133.07, 132.64,
129.30, 128.63. 127.07, 122.53, 120.45, 119.11, 101.55,
42.12, 41.37, 32.47, 31.64. Anal. calc. for C21H21N3O2S
(379.48); C: 66.47, H: 5.58, N: 11.07, S: 8.45; found; C:
66.03, H: 5.64, N: 10.87, S: 8.18.
3.2.6. 2,4-Dihydroxybenzaldehyde [4-(3-p-xylxl-3-
phenylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (6)
Orange crystals. Yield: 69%. M.p.: 174 °C (EtOH). IR
(KBr, υ cm−1): 3272 (o-OH), 3450 (p-OH), 3121 (–NH–),
1
1631 (C=N azomethine). H NMR (CDCl3, δ ppm): 1.47 (s,
3H, –CH3), 2.18 (s, 3H, o-CH3), 2.25 (s, 3H, m-CH3), 2.52
(d, j = 8.9 Hz, 4H, –CH2– in cyclobutane ring), 3.55 (quint,
j = 8.9 Hz, 1H, > CH– in cyclobutane), 6.04 (s, 1H, = CH– in
thiazole ring), 6.30–7.30 (m, 6H, aromatics), 10.02 (s, 1H, –
NH–, D2O exchangeable), 7.95 (s, 1H, N=CH–), 11.52 (s, 1H,
o-OH, D2O exchangeable), 7.20 (s, 1H, p-OH, D2O
exchangeable). 13C NMR (CDCl3, δ ppm): 166.13, 154.43,
151.77, 141.29, 130.41, 130.34, 127.46, 123.87, 123.70,
123.65, 120.87, 118.32, 110.27, 99.42, 38.77, 38.22, 37.44,
28.78. Anal. calc. for C23H25N3O2S (407.54); C: 67.79, H:
6.18, N: 10.31, S: 7.87; found; C: 67.62, H: 6.15, N: 9.87, S:
8.02.
3.2.3. 5-Bromo-2-hydroxybenzaldehyde [4-(3-methyl-3-
phenylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (3)
Yellow crystals. Yield: 62%. M.p.: 201 °C (EtOH). IR
(KBr, υ cm−1): 3182 (–OH), 3131 (–NH–), 1625 (C=N
1
azomethine). H NMR (CDCl3, δ ppm): 1.50 (s, 3H, –CH3),
2.41–2.62 (m, 4H, –CH2– in cyclobutane ring), 3.54 (quint,
j = 8.9 Hz, 1H, > CH– in cyclobutane), 6.05 (s, 1H, = CH– in
thiazole ring), 6.91–7.27 (m, 8H, aromatics plus –NH–, D2O
exchangeable), 8.0 (s, 1H, N=CH–), 12.4 (s, 1H, –OH, D2O
exchangeable). 13C NMR (CDCl3, δ ppm): 167.10, 155.13,
152.70, 142.20, 131.41, 130.33, 127.06, 124.17, 123.80,
123.63, 119.87, 117.32, 109.87, 99.12, 39.00, 38.02, 37.55,
29.18. Anal. calc. for C21H20N3OSBr (442.38); C: 57.02, H:
4.56, N: 9.50; found; C: 56.69, H: 4.41, N: 9.67.
3.2.7. 2-Hydroxy-3-methoxybenzaldehyde [4-(3-p-xylyl-3-
methylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (7)
Light yellow crystals. Yield: 62%. M.p.: 152 °C (EtOH). IR
(KBr, υ cm−1): 3248 (–OH), 3184 (–NH–), 1574 (C=N
1
azomethine). H NMR (CDCl3, δ ppm): 1.47 (s, 3H, –CH3),
2.17 (s, 3H, p-xylyl o-CH3), 2.25 (s, 3H, p-xylyl m-CH3),
2.51–2.57 (m, 4H, –CH2– in cyclobutane ring), 3.79 (quint,
j = 8.9 Hz, 1H, > CH– in cyclobutane), 3.81 (s, 3H, –OCH3),
6.44 (s, 1H, = CH– in thiazole ring), 6.91–7.28 (m, 6H, aro-
matics), 8.21 (s, 1H, N=CH–), 9.48 (br, 1H, –NH–, D2O ex-
changeable), 11.98 (br, 1H, –OH, D2O exchangeable). 13H
NMR (CDCl3, δ ppm): 169.76, 150.88, 149.73, 147.43,
136.25, 132.70, 132.59, 127.88, 127.73, 122.13, 120.93,
120.73, 120.37, 114.44, 114.37, 101.70, 57.69, 42.82, 32.07,
29.38, 22.55, 22.46, 20.93. Anal. calc. for C24H27N3O2S
(421.57); C: 68.4, H: 6.5, N: 10.0; found; C: 68.5, H: 6.2, N:
9.6.
3.2.4. 2-Hydroxy-3-methoxybenzaldehyde [4-(3-phenyl-3-
methylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (4)
Yellow crystals. Yield: 68%. M.p.: 159 °C (EtOH). IR
(KBr, υ cm−1): 3416 (–OH), 3126 (–NH–), 1580 (C=N
1
azomethine). H NMR (CDCl3, δ ppm): 1.41 (s, 3H, –CH3),
2.46–2.59 (m, 4H, –CH2– in cyclobutane ring), 3.42 (quint,
j = 8.9 Hz, 1H, > CH– in cyclobutane), 3.88 (s, 3H, –OCH3),
5.98 (s, 1H, = CH– in thiazole ring), 6.81–7.37 (m, 8H, aro-
matics), 8.14 (s, 1H, N=CH–), 9.73 (br, 2H, –OH plus –NH–,
D2O exchangeable). 13C NMR (CDCl3, δ ppm): 171.07,
153.64, 149.11, 149.87, 147.16, 136.23, 130.30, 127.53,
126.57, 120.44, 120.37, 113.96, 113.81, 101.63, 57.68,
42.02, 40.97, 32.07, 31.73. Anal. calc. for C22H23N3O2S
(393.50); C: 67.2, H: 5.9, N: 10.7; found; C: 67.0, H: 6.1, N:
10.5.
3.2.8. 2-Hydroxybenzaldehyde [4-(3-mesityl-3-
phenylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (8)
Pale yellow crystals. Yield: 82%. M.p.: 225 °C (EtOH). IR
(KBr, υ cm−1): 3285 (–OH), 3131 (–NH–), 1651 (C=N
azomethine). H NMR (CDCl3, δ ppm): 1.47 (s, 3H, –CH3),
3.2.5. 2,4-Dihydroxybenzaldehyde [4-(3-p-xylyl-3-
phenylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (5)
1
Yellow crystals. Yield: 75%. M.p.: 168 °C (EtOH). IR
2.17 (s, 6H, mesityl o-CH3), 2.41 (s, 3H, mesityl p-CH3),
2.50–2.62 (m, 4H, –CH2– in cyclobutane ring), 3.68 (quint,
j = 8.9 Hz, 1H, > CH– in cyclobutane), 6.06 (s, 1H, = CH– in
(KBr, υ cm−1): 3182 (–OH), 3113 (–NH–), 1619 (C=N
1
azomethine). H NMR (CDCl3, δ ppm): 1.47 (s, 3H, –CH3),

204
A. Cukurovali et al. / European Journal of Medicinal Chemistry 41 (2006) 201–207
thiazole ring), 6.86–7.34 (m, 5H, aromatics), 8.12 (s, 1H,
N=CH–), 10.2 (br, 1H, –NH–, D2O exchangeable), 10.11 (br,
1H, –OH, D2O exchangeable). 13C NMR (CDCl3, δ ppm):
171.42, 159.82, 153.20, 148.38, 145.63, 136.99, 135.38,
132.97, 132.44, 132.24, 121.53, 120.05, 118.87, 101.63,
45.15, 42.88, 32.07, 26.45, 23.38, 22.42. Anal. calc. for
C24H27N3OS (405.57); C: 71.2, H: 6.6, N: 10.4; found; C:
71.1, H: 6.7, N: 10.4.
22.84, 22.76. Anal. calc. for C25H29N3O2S (435.60); C: 68.9,
H: 6.7, N: 9.7; found; C: 69.3, H: 6.6, N: 9.5.
3.2.12. 2-Hydroxy-5-methoxybenzaldehyde [4-(3-mesityl-3-
methylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (12)
Orange crystals. Yield: 94%. M.p.: 231 °C (EtOH). IR
(KBr, υ cm−1): 3310 (–OH), 3125 (–NH–), 1584 (C=N
1
azomethine). H NMR (CDCl3, δ ppm): 1.53 (s, 3H, –CH3),
2.17 (s, 9H, mesityl o-CH3 + mesityl p-CH3), 2.51–2.62 (m,
4H, –CH2– in cyclobutane ring), 3.39 (quint, 1H, j = 7.0 Hz,
> CH– in cyclobutane), 3.71 (s, 3H, –OCH3), 6.42 (s, 1H,
= CH– in thiazole ring), 6.72–7.11 (m, 5H, aromatics), 8.17
(s, 1H, N=CH–), 9.65 (br, 1H, –NH–, D2O exchangeable),
11.12 (br, 1H, –OH, D2O exchangeable). 13C NMR (DMSO-
d6, δ ppm): 167.54, 155.74, 154.02, 151.64, 145.98, 138.43,
135.50, 131.87, 131.45, 121.97, 118.76, 118.64, 112.10,
109.20, 57.15, 42.57, 41.51, 40.06, 26.36, 22.84, 21.85. Anal.
calc. for C25H29N3O2S (435.58); C: 47.99, H: 4.92, N: 18.65;
found; C: 48.11, H: 5.02, N: 18.27.
3.2.9. 2,4-Dihydroxybenzaldehyde [4-(3-mesityl-3-
phenylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (9)
Light brown crystals. Yield: 65%. M.p.: 160 °C (EtOH). IR
(KBr, υ cm−1): 3416 (–OH), 3126 (–NH–), 1631 (C=N
1
azomethine). H NMR (CDCl3, δ ppm): 1.53 (s, 3H, –CH3),
2.16 (s, 6H, mesityl o-CH3), 2.45 (s, 3H, mesityl p-CH3),
2.58–2.66 (m, 4H, –CH2– in cyclobutane ring), 3.32 (quint,
1H, j = 8.9 Hz, > CH– in cyclobutane), 6.31 (s, 1H, = CH– in
thiazole ring), 6.34–7.35 (m, 5H, aromatics), 8.09 (s, 1H,
N=CH–), 9.85 (br, 1H, –NH–, D2O exchangeable), 11.65 (br,
1H, –OH, D2O exchangeable). 13C NMR (CDCl3, δ ppm):
169.58, 161.64, 159.71, 148.38, 145.98, 144.00, 136.43,
136.27, 135.72, 130.92, 109.55, 108.41, 104.28, 44.90,
42.62, 32.23, 26.38, 22.83, 22.70. Anal. calc. for
C24H27N3O2S (421.57); C: 68.5, H: 6.5, N: 9.7; found; C:
68.4, H: 6.5, N: 10.0.
3.2.13. 2-Hydroxy-5-nitrobenzaldehyde [4-(3-mesityl-3-
methylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (13)
Yellow crystals. Yield: 81%. M.p.: 222 °C (EtOH). IR
(KBr, υ cm−1): 3265 (–OH), 3114 (–NH–), 1619 (C=N
1
azomethine). H NMR (CDCl3, δ ppm): 1.52 (s, 3H, –CH3),
2.15 (s, 6H, mesityl o-CH3), 2.18 (s, 3H, mesityl p-CH3),
2.47–2.61 (m, 4H, –CH2– in cyclobutane ring), 3.43 (quint,
1H, j = 8.9 Hz, > CH– in cyclobutane), 6.45 (s, 1H, = CH– in
thiazole ring), 6.71 (s, 2H, aromatics on mesityl), 7.05 (d,
j = 9.0 Hz, 1H aromatics), 8.13 (dd, jo = 9.0 Hz; jm = 2.9 Hz,
1H, aromatics), 8.48 (d, j = 2.9, 1H aromatics), 8.21 (s, 1H,
N=CH–), 12.11 (br, 2H, –OH plus –NH–, D2O exchangeable).
13C NMR (CDCl3, δ ppm): 169.72, 153.09, 145.95, 141.82,
136.43, 136.11, 135.50, 131.88, 131.67, 127.27, 123.27,
123.18, 123.03, 110.41, 44.54, 42.55, 40.04, 28.34, 22.82,
21.84. Anal. calc. for C24H26N4O3S (450.55); C: 64.0, H:
5.8, N: 12.4; found; C: 64.1, H: 5.7, N: 12.5.
3.2.10. 5-Bromo-2-hydroxybenzaldehyde [4-(3-mesityl-3-
phenylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (10)
Pale yellow crystals. Yield: 87%. M.p.: 230 °C (EtOH). IR
(KBr, υ cm−1): 3285 (–OH), 3131 (–NH–), 1600 (C=N
1
azomethine). H NMR (CDCl3, δ ppm): 1.49 (s, 3H, –CH3),
2.14 (s, 6H, mesityl o-CH3), 2.39 (s, 3H, mesityl p-CH3),
2.51–2.59 (m, 4H, –CH2– in cyclobutane ring), 3.31 (quint,
j = 8.9 Hz, 1H, > CH– in cyclobutane), 5.96 (s, 1H, = CH– in
thiazole ring), 6.70–7.37 (m, 5H, aromatics), 8.02 (s, 1H,
N=CH–), 10.10 (br, 1H, –NH–, D2O exchangeable), 10.25
(br, 1H, –OH, D2O exchangeable). 13C NMR (CDCl3, δ
ppm): 171.26, 158.80, 152.37, 148.35, 145.63, 136.99,
136.92, 135.38, 134.19, 132.44, 121.80, 120.73, 113.05,
101.68, 45.15, 42.88, 32.24, 26.45, 23.38, 22.42. Anal. calc.
for C24H26N3OSBr (484.46); C: 59.5, H: 5.4, N: 8.7; found;
C: 59.5, H: 5.2, N: 8.7.
3.2.14. 2-Hydroxy-5-chlorobenzaldehyde [4-(3-mesityl-3-
methylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (14)
Pink crystals. Yield: 83%. M.p.: 240 °C (EtOH). IR (KBr, υ
cm−1): 3283 (–OH), 3115 (–NH–), 1619 (C=N azomethine). 1H
NMR (CDCl3, δ ppm): 1.53 (s, 3H, –CH3), 2.12 (s, 6H, me-
sityl o-CH3), 2.16 (s, 3H, mesityl p-CH3), 2.47–2.87 (m, 4H,
–CH2– in cyclobutane ring), 3.40 (quint, 1H, j = 8.9, > CH– in
cyclobutane), 6.44 (s, 1H, = CH– in thiazole ring), 6.72 (s, 2H,
aromatics on mesityl), 6.89 (d, j = 8.7, 1H, aromatics), 7.21
(dd, jo = 8.7 Hz; jm = 2.7 Hz, 1H aromatics), 7.58 (d,
j = 2.9 Hz, 1H, aromatics), 8.14 (s, 1H, N=CH–), 10.45 (br,
1H, –OH D2O exchangeable), 12.06 (br, 1H, –NH–, D2O
exchangeable). 13C NMR (DMSO-d6, δ ppm): 164.13,
156.40, 123.82, 131.88, 145.86, 144.45, 136.51, 136.17,
135.51, 131.38, 130.63, 124.94, 119.66, 102.69, 42.55,
42.13, 40.45, 26.35, 22.85, 21.86. Anal. calc. for
C24H26ClN3OS (440.0); C: 65.5, H: 6.0, N: 9.6; found; C:
65.6, H: 6.1, N: 9.5.
3.2.11. 2-Hydroxy-3-methoxybenzaldehyde [4-(3-mesityl-3-
methylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (11)
Yellow crystals. Yield: 62%. M.p.: 121 °C (EtOH). IR
(KBr, υ cm−1): 3256 (–OH), 3121 (–NH–), 1612 (C=N
1
azomethine). H NMR (CDCl3, δ ppm): 1.51 (s, 3H, –CH3),
2.17 (s, 6H, mesityl o-CH3), 2.47 (s, 3H, mesityl p-CH3),
2.60–2.70 (m, 4H, –CH2– in cyclobutane ring), 3.33 (quint, j
= 8.9 Hz, 1H, > CH– in cyclobutane), 3.80 (s, 3H, –OCH3),
6.44 (s, 1H, = CH– in thiazole ring), 6.73–7.20 (m, 5H, aro-
matics), 8.21 (s, 1H, N=CH–), 9.51 (br, 1H, –NH–, D2O ex-
changeable), 11.93 (br, 1H, –OH, D2O exchangeable). 13C
NMR (CDCl3, δ ppm): 159.71, 149.66, 147.39, 146.44,
145.99, 135.49, 132.00, 131.68, 131.27, 122.13, 120.94,
120.32, 114.00, 102.77, 57.67, 44.96, 42.64, 32.27, 26.40,

A. Cukurovali et al. / European Journal of Medicinal Chemistry 41 (2006) 201–207
205
3.2.15. 2-Hydroxy-3,5-dichlorobenzaldehyde [4-(3-mesityl-3-
methylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (15)
6.42, N: 9.22, S: 7.04; found; C: 74.12, H: 6.63, N: 9.36, S:
7.07.
Pink crystals. Yield: 83%. M.p.: 228 °C (EtOH). IR (KBr, υ
cm−1): 3280 (–OH), 3115 (–NH–), 1614 (C=N azomethine). 1H
NMR (CDCl3, δ ppm): 1.53 (s, 3H, –CH3), 2.18 (s, 6H, me-
sityl o-CH3), 2.16 (s, 3H, mesityl p-CH3), 2.42–2.59 (m, 4H,
–CH2– in cyclobutane ring), 3.38 (quint, 1H, j = 8.9, > CH– in
cyclobutane), 6.41 (s, 1H, = CH– in thiazole ring), 6.72 (s, 2H,
aromatics mesityl), 7.52 (d, jm = 2.0 Hz, 1H), 7.56 (d, jm = 2.1,
1H) 8.23 (s, 1H, N=CH–), 10.20 (br, 2H, –NH– plus –OH,
D2O exchangeable). Characteristic 13C NMR (CDCl3, TMS, δ
ppm): 123.38 (C1), 145.78 (C2), 114.24 (C3), 128.12 (C4),
117.24 (C5), 125.15 (C6), 135.52 (C7), 152.71 (C8), 103.21
(C9), 136.39 (C10), 40.71 (C11), 41.91 (C12), 44.64 (C13), 26.29
(C14), 131.70 (C15), 128.18 (C16), 124.31 (C17), 130.75 (C18),
21.86 (C19), 22.84 (C20). Anal. calc. for C24H25Cl2N3OS
(474.45); C: 60.76, H: 5.31, N: 8.86, S: 6.76; found; C:
60.51, H: 4.94, N: 9.02, S: 6.89.
3.2.18. (1E)-1-(2-Hydroxy-1-naphthyl)ethanone [4-(3-amino-
3-methylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (18)
Brown crystals. Yield: 81%. M.p.: 169 °C (EtOH). IR (KBr,
υ cm−1): 3429 (–OH), 3129 (–NH–), 1635 (C=N azomethine).
1H NMR (DMSO-d6, δ ppm): 1.51 (s, 3H, –CH3), 2.15 (s, 9H,
mesityl o-CH3 + mesityl p-CH3), 2.40–2.63 (m, 7H, –CH2– in
cyclobutane ring plus –CH3 on azomethine), 3.45 (quint, 1H,
j = 7.0, > CH– on cyclobutane), 6.27 (s, 1H, = CH– in thiazole
ring), 6.71 (s, 2H, aromatics on mesitylene), 7.37–7.86 (m, 6H,
aromatics and D2O exchangeable –NH–), 8.31 (m, 1H aro-
matics), 11.41 (br, 1H, –OH, D2O exchangeable). 13C NMR
(DMSO-d6, δ ppm): 169.87, 157.68, 150.30, 145.81, 136.39,
136.25, 135.71, 131.72, 129.14, 129.01, 127.07, 126.53,
126.42, 124.55, 124.44, 119.68, 114.62, 99.36, 44.26, 41.73,
31.05, 26.18, 22.85, 21.85, 16.03. Anal. calc. for C29H31N3OS
(469.64); C: 74.17, H: 6.65, N: 8.95, S: 7.83; found; C: 74.22,
H: 6.72, N: 9.11, S: 7.63.
3.2.16. 2-Hydroxy-3,5-dibromobenzaldehyde [4-(3-mesityl-3-
methylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (16)
3.3. Microbiology
Light yellow crystals. Yield: 83%. M.p.: 237 °C (EtOH). IR
(KBr, υ cm−1): 3265 (–OH), 3115 (–NH–), 1614 (C=N
1
The compounds were tested against two gram-positive
(Staphylococcus aureus ATCC 6538P, Bacillus subtilis ATCC
6633) and two gram-negative bacteria (Salmonella typhimur-
ium NRRL B 4420, Escherichia coli ATCC 25922). The anti-
fungal activities of compounds were evaluated in vitro against
a yeast-like fungi such as Candida tropicalis ATCC 13803.
The cultures were obtained from Müller–Hinton broth
(Difco) for all the bacterial strains after 24 h of incubation at
37 °C. The yeast was maintained in Sabouraud dextrose broth
(Difco) after incubation for 24 h at 25 °C.
Antibacterial activities of compounds were determined by
using agar dilution method by the National Committee for Clin-
ical Laboratory Standards (NCCLS). Müller–Hinton broth and
Sabouraud dextrose broth were used as medium to prepare mi-
cro dilution. The final inoculum densities were 1–3 × 104 CFUs
ml–1 for bacteria and fungi, respectively. The stock solutions
were prepared in dimethyl formamide (DMF) and DMF had
no effect on the microorganism in the concentrations studied.
The doubling concentrations used for both of them were
1024–4 μg ml–1. Ampicillin (Mustafa Nevzat) and fluconazole
(Pfizer) were used as antibiotic reference powders for bacteria
and fungi, respectively. The antibacterial activity was mea-
sured after 18 h of incubation at 37 °C and after incubation
for 48 h for the antifungal assay.
azomethine). H NMR (CDCl3, δ ppm): 1.47 (s, 3H, –CH3),
2.12 (s, 6H, mesityl o-CH3), 2.21 (s, 3H, mesityl p-CH3),
2.53 (d, j = 8.7 Hz, 4H, –CH2– in cyclobutane ring), 3.26
(quint, 1H, j = 8.9 Hz, > CH– in cyclobutane), 5.93 (s, 1H,
= CH– in thiazole ring), 6.69 (s, 2H, aromatics mesityl), 7.19
(d, jm = 2.3, 1H), 7.63 (d, jm = 2.2 Hz, 1H) 8.03 (s, 1H,
N=CH–), 10.20 (br, 2H, –NH– plus –OH, D2O exchangeable).
Characteristic 13C NMR (CDCl3, TMS, δ ppm): 122.47 (C1),
151.22 (C2), 112.95 (C3), 133.30 (C4), 113.57 (C5), 132.85
(C6), 145.39 (C7), 155.55 (C8), 101.39 (C9), 149.78 (C10),
31.92 (C11), 42.89 (C12), 45.03 (C13), 28.42 (C14), 137.72
(C15), 136.89 (C16), 132.46 (C17), 137.06 (C18), 22.46 (C19),
23.38 (C20). Anal. calc. for C24H25Br2N3OS (563.35); C:
51.17, H: 4.47, N: 7.46, S: 5.69; found; C: 51.40, H: 4.58, N:
7.35, S: 5.53.
3.2.17. 2-Hydroxy-1-naphthaldehyde [4-(3-mesityl-3-
methylcyclobutyl)-1,3-thiazol-2-yl]hydrazone (17)
Yellow crystals. Yield: 94%. M.p.: 221 °C (EtOH). IR
(KBr, υ cm−1): 3430 (–OH), 3151 (–NH–), 1624 (C=N
azomethine). 1H NMR (DMSO-d6, δ ppm): 1.53 (s, 3H,
–CH3), 2.17 (s, 9H, mesityl o-CH3 + mesityl p-CH3), 2.45–
2.66 (m, 4H, –CH2– in cyclobutane ring), 3.45 (quint, 1H,
j = 7.0, > CH– in cyclobutane), 6.42 (s, 1H, = CH– in thiazole
ring), 6.72 (s, 2H, aromatics on mesitylene), 7.20–7.87 (m, 5H,
aromatics), 8.56 (d, 1H aromatics), 8.93 (s, 1H, N=CH–),
11.35 (br, 1H, –OH, D2O exchangeable), 12.02 (br, 1H, –NH–,
D2O exchangeable). 13C NMR (DMSO-d6, δ ppm): 169.64,
158.25, 149.81, 145.88, 138.17, 136.43, 135.53, 133.42,
132.87, 131.71, 130.55, 129.85, 129.30, 125.02, 123.02,
120.13, 111.62, 101.84, 44.79, 41.70, 31.98, 26.31, 22.85,
21.68. Anal. calc. for C28H29N3OS (455.62); C: 73.81, H:
The minimum inhibitory concentration (MIC) was the low-
est concentration of the tested compound and yield no visible
turbidity and growth on the plate.
4. Results and discussion
The structure of all compounds synthesized were identified
1
by H NMR, 13C NMR, FT-IR and elemental analysis.

206
A. Cukurovali et al. / European Journal of Medicinal Chemistry 41 (2006) 201–207
Table 1
The in vitro activities of the compounds and the reference drugs (MIC values in μg ml–1
)
Sample
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
S. aureus
256
32
512
512
512
64
256
256
128
256
256
512
128
256
256
128
256
256
2
B. subtilis
256
16
16
64
S. typhimurium
E. coli
32
32
C. tropicalis
32
16
128
256
256
64
256
256
256
256
256
512
128
256
256
258
256
256
–
128
128
128
64
512
128
256
256
256
256
256
512
64
256
256
128
128
128
2
32
128
256
64
256
64
256
256
128
128
256
256
256
256
512
256
512
128
2
256
256
128
128
128
512
128
256
256
128
128
128
2
16
17
18
Ampicillin
Fluconazole
–
–
–
–
8
most effective compounds with MIC 16 μg ml–1 against
B. subtilis. The compound 2 is also most effective substance
with MIC 16 μg ml–1 against yeast-like fungi, C. tropicalis.
This effectiveness is very close to the effect of fluconazole
against C. tropicalis. First tree substances are very effective
against E. coli providing a MIC value of 32 μg ml–1. The com-
pound 6 has a moderate effect among the other compounds
used against all the bacteria and fungi in comparison to the
reference drugs, but it did not show noteworthy activity against
S. typhimurium. The lowest effective substance is 12 against all
the microorganisms studied. Interestingly, despite all the sub-
stances have very similar structures, their antibacterial and anti-
fungal activities are very different. Most of them demonstrate
weak activity against gram-positive and gram-negative bacteria
and fungi in comparison to the reference drugs. As mentioned
in Section 1, Suzuki et al. [3] and Holla et al. [8] have inves-
tigated the antibacterial and antifungal properties of similar
compounds to that of ours. Their MIC results, especially Holla
et al.’s are in good agreement with our results, since Holla et
al. synthesized and investigated similar thiazolylhydrazone
compounds. The detailed observed data on the antibacterial
and antifungal activities of the compounds and the control
drugs are given in Table 1.
Scheme 2. Intramolecular hydrogen bonding illustration of hydrazones, A.
1
The H NMR spectra of the starting substances A and li-
gands were recorded in DMSO-d6 or CDCl3 solvents and as-
signments are given in Section 3. As expected from the struc-
tures of starting substances A, only aromatic, –NH–, –NH2, –
N=CH– and –OH peaks were observed. These are all singlets
and each one indicates one proton intensity, according to the
integral of the spectra at 200 MHz NMR. This result implies
that the thioamide part of the molecule has a hydrogen bonding
(H···S), shown in Scheme 2. Two of them are broad singlets
supporting our hydrogen bonding interpretation. All of these
protons, except azomethine proton, are D2O exchangeable pro-
tons. –OH group signals for both compounds are broad sing-
lets. This is also a result of the presence of intramolecular hy-
drogen bonding [20]. Phenolic –OH groups of both compounds
exhibit the downfield signals, according to –OH of a free phe-
nol. Since the molecules have electron-attracting groups, this is
an expected result. A more detailed spectral investigation of a
similar cyclobutane compound, synthesized and published by
the same authors, can be found in literature [16].
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respectively. As it can be seen in Table 1, the compounds in-
hibited the bacteria and fungi with MICs between 16 and
512 μg ml–1. Among the tested compounds, 2 and 3 are the
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