Synthesis, antibacterial, antioxidant activity and QSAR studies of novel 2-arylidenehydrazinyl-4-arylthiazole analogues

Article abstract of DOI:10.1248/cpb.c14-00616

A novel series of 2-arylidenehydrazinyl-4-arylthiazole analogues (3a-p) was designed and synthesized in excellent yields using a rapid, simple, efficient methodology. Sixteen novel compounds were screened for in vitro antimicrobial activities against eleven bacteria, namely, Staphylococcus aureus, Listeria monocytogenes, Enterococcus faecalis, Bacillus subtilis, Klebsiella pneumonia, Citrobacter freundii, Cronobacter sakazakii, Salmonella enteritidis, Escherichia coli, Yersinia pestis, and Pseudomonas aeruginosa. All 16 compounds showed significant anti-bacterial activities against both Gram-positive and Gram-negative bacteria. In particular, compound 3g showed potent inhibition of E. coli and K. pneumonia, compound 3i inhibited E. faecalis, compound 3n S. tythi and E. faecalis, and compound 3c E. coli and C. sakazakii. In fact, our results indicate that most of the compounds synthesized exhibit strong antibacterial activity. The qualitative structure-antibacterial activity relationships (QSAR) were studied using the physicochemical and quantum-chemical parameters of the ab initio Hartree-Fock model at the RHF/6-31G level of theory. A good qualitative correlation between predicted physicochemical parameters (log P and polar surface area (PSA)) and antibacterial activity has been found. The synthesized compounds were also evaluated for antioxidant activity. Compounds 3j, 3a and 3i exhibited the greatest antioxidant activity, with IC₅₀ values of 0.66, 0.81, and 1.08 μM, respectively, which were comparable to that of ascorbic acid (IC₅₀ 0.87 μM). The promising antibacterial and antioxidant activities of some of these synthesized 2-arylidenehydrazinyl-4-arylthiazole derivatives, together with the results of quantum-chemical studies, could be helpful for the development of drugs to combat diseases caused by microorganisms and oxidative stress.

Full text of DOI:10.1248/cpb.c14-00616

December 2014
Regular Article
Chem. Pharm. Bull. 62(12) 1259–1268 (2014)
1259
Synthesis, Antibacterial, Antioxidant Activity and QSAR Studies of
Novel 2-Arylidenehydrazinyl-4-arylthiazole Analogues
,a
Mohammad Sayed Alam,a Junaid Uddin Ahmed,b and Dong-Ung Lee*
a Division of Bioscience, Dongguk University; Gyeongju 780–714, Republic of Korea: and b Department of Chemistry,
Jagannath University; Dhaka 1100, Bangladesh.
Received August 28, 2014; accepted September 28, 2014
A novel series of 2-arylidenehydrazinyl-4-arylthiazole analogues (3a–p) was designed and synthesized in
excellent yields using a rapid, simple, efficient methodology. Sixteen novel compounds were screened for in
vitro antimicrobial activities against eleven bacteria, namely, Staphylococcus aureus, Listeria monocytogenes,
Enterococcus faecalis, Bacillus subtilis, Klebsiella pneumonia, Citrobacter freundii, Cronobacter sakazakii,
Salmonella enteritidis, Escherichia coli, Yersinia pestis, and Pseudomonas aeruginosa. All 16 compounds
showed significant anti-bacterial activities against both Gram-positive and Gram-negative bacteria. In par-
ticular, compound 3g showed potent inhibition of E. coli and K. pneumonia, compound 3i inhibited E. faeca-
lis, compound 3n S. tythi and E. faecalis, and compound 3c E. coli and C. sakazakii. In fact, our results indi-
cate that most of the compounds synthesized exhibit strong antibacterial activity. The qualitative structure–
antibacterial activity relationships (QSAR) were studied using the physicochemical and quantum-chemical
parameters of the ab initio Hartree–Fock model at the RHF/6-31G level of theory. A good qualitative correla-
tion between predicted physicochemical parameters (logP and polar surface area (PSA)) and antibacterial
activity has been found. The synthesized compounds were also evaluated for antioxidant activity. Compounds
3j, 3a and 3i exhibited the greatest antioxidant activity, with IC50 values of 0.66, 0.81, and 1.08µM, respec-
tively, which were comparable to that of ascorbic acid (IC50 0.87µM). The promising antibacterial and anti-
oxidant activities of some of these synthesized 2-arylidenehydrazinyl-4-arylthiazole derivatives, together with
the results of quantum-chemical studies, could be helpful for the development of drugs to combat diseases
caused by microorganisms and oxidative stress.
Key words 2-arylidenehydrazinyl-4-arylthiazole; antibacterial; antioxidant; qualitative structure–activity
relationship (QSAR)
Due to the increasing number of multi-drug resistant micro- antihypertensive effects.13) Recently, it was reported that some
bial pathogens, especially Gram-positive bacteria, the treat- new triazolyl-thiazole analogues showed anti-AD activity,14)
ment of infectious disease has become a challenging problem monoamine oxidase (MAO) inhibitory activity of 2-thiazolyl-
in the hospital and community.1) Accordingly, considerable hydrazone derivatives15) and selective acetyl-Co-A carboxylase
efforts are being made to identify antimicrobial agents that are inhibitory activity of phenoxy thiazole derivatives.16) More
effective against pathogenic microorganisms resistant to cur- recently, Netalkar et al.17) reported that some novel transition
rent treatments. In addition, the treatment of immune deficient metal complexes of benzothiazoles showed DNA binding and
individuals, such as, those infected with human immunodefi- cleavage properties and anti-tuberculosis activity, and Turan-
ciency virus (HIV) is becoming increasingly more difficult.2–4) Zitouni et al.18) reported some new (3,4-diaryl-3H-thiazol-2-
Furthermore, oxidative stress produces free radicals, which ylidene)pyrimidin-2-yl amine derivatives had anti-HIV activ-
are highly reactive compounds that cause serious diseases, ity and selective human MAO-B inhibitory activity of novel
such as, Alzheimer’s disease (AD), inflammatory conditions, 1-(4-arylthiazol-2-yl)-2-(3-methylcyclohexylidene)hydrazine
metabolic disorders, cellular aging, reperfusion damage, and derivatives.19)
cancer. Anti-oxidant agents are used to prevent the forma-
In our previous study,20) we observed that 2-arylidenehy-
tion of or neutralize free radicals and repair the cell damage drazinyl-4-arylthiazoles possessing bromine and methoxy
caused.5) Therefore, it is important to find new classes of an- group at the 4-position of benzylidine phenyl ring showed
tibiotics with broad spectrum activity and different modes of significant antibacterial activity. Therefore, in the present
action to combat drug resistant pathogens.
study, we designed and synthesized a series of novel 2-ar-
Thiazoles and their analogues have attracted continuing ylidenehydrazinyl-4-arylthiazole analogues bearing different
interest during the last few decades because of their wide substituents, e.g. OH, OMe, and halogen atoms in various
range biological activities. The thiazole scaffold is an interest- position of phenyl ring and evaluated them as antibacterial
ing component in a variety of natural and synthetic bioactive and antioxidant agents. In vitro antibacterial activities were
compounds used in pharmaceuticals and agrochemicals. A screened against eleven bacterial strains, that is, four Gram-
literature survey revealed that the synthesis of thiazole ana- positive bacteria, Staphylococcus aureus (JMC 2151), Listeria
logues has received research attention for many years due to monocytogenes (ATCC 43256), Enterococcus faecalis (CARS
their wide ranging pharmacological and biological properties, 2011–012), and Bacillus subtilis (IFO 13719) and seven Gram-
which include antitumor,6) anti-inflammatory,7) antimicro- negative bacteria, Klebsiella pneumonia (JCM 1662), Citro-
bial,8,9) antioxidant,10) neuroprotective,11) antidiabetic,12) and bacter freundii (JCM 1657), Cronobacter sakazakii (CARS
2012-J-F), Salmonella enteritidis (ATCC 13076), Escherichia
The authors declare no conflict of interest.
coli (CARS 2011–016), Yersinia pestis (CARS 2013–027), and
© 2014 The Pharmaceutical Society of Japan
*To whom correspondence should be addressed. e-mail: dulee@dongguk.ac.kr

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Vol. 62, No. 12
Pseudomonas aeruginosa (PA01). The qualitative structure– 4-arylthiazoles (3a–p) in good yield (72–95%). The structures
antibacterial activity relationships (QSAR) were studied using of compounds 3a–p were elucidated by IR, 1H-NMR, and
physicochemical and quantum-chemical parameters with the MS. In the IR spectra of compounds 3a–p, the character-
ab initio Hartree–Fock model at the RHF/6-31G level of the- istic O–H and N–H stretching absorption bands appeared
ory using GAMESS interface in the ChemBio3D Pro 12 and at 3400–3475cm−1 and 3150–3275cm−1, respectively. The
molinspiration cheminformatics software. The 1,1-diphenyl- 1H-NMR spectra of compounds 3a–p revealed the presence of
2-picrylhydrazyl (DPPH) free radical scavenging activities of the –CH=N– proton and the =N–NH– proton as two singlets
synthesized compounds were investigated to determine their at 7.93–8.49 and 11.11–12.23ppm, respectively. The thiazole
antioxidant properties.
proton appeared as a multiplet at 7.00–7.81ppm together with
phenyl protons. In addition, the EI-MS or FAB-MS spectra of
3a–p showed molecular ion peaks with intensities of 5–87%.
Antibacterial Activity The newly synthesized 2-aryl-
Results and Discussion
Synthesis The synthesis of the 2-arylidenehydrazinyl-
4-arylthiazoles (3a–p) analogues was carried as we previously idenehydrazinyl-4-arylthiazoles (3a–p) were evaluated for
reported using the Hantzsch method21) from their correspond- their in vitro antibacterial activities against four Gram-pos-
ing arylidenethiosemicarbazones. The synthetic routes to ar- itive bacteria and seven Gram-negative bacteria (as detailed
ylidenethiosemicarbazones (2a–j) and 2-arylidenehydrazinyl- above) using disc diffusion methods. As presented in Table 1,
4-arylthiazoles (3a–p) are outlined in Chart 1. Compounds all tested compounds remarkably resisted the growth of Gram-
2a–j were prepared by the condensation of thiosemicarbazide positive and Gram-negative bacteria at a dose of 300µgdisc−1,
and a substituted benzaldehyde in ethanol in excellent yield and showed activities at this loading comparable to nalidixic
(83–94%) and their structures were determined using IR, acid (positive control) at 50µgdisc−1. It is worth noting that
1H-NMR, and mass spectral data. The syntheses of com- all compounds showed bactericidal activity against L. mono-
pounds 2g–j were reported in our previous study.20) The IR cytogenes, B. subtilis (except 3g and 3p), C. sakazakii, and E.
spectra of the newly synthesized compounds 2a–f showed an coli. In addition, many of the compounds also showed anti-
absorption band around the 3437–3405cm−1 region resulting bacterial activity against S. aureus, E. faecalis, Y. pestis and
from the –OH and –NH2 groups. The stretching absorption P. aeruginosa. Five (3f, 3g, 3j, 3l, and 3m) and eight (3a, 3b,
1
band of –NH– appeared at 3270–3241cm−1. H-NMR spectra 3e, 3f, 3h, 3i, 3l, and 3n) compounds showed activity against
of compounds 2a–f showed singlet protons at 8.08–8.24ppm K. pneumonia and S. enteritidis, respectively. None of the
corresponding to the –CH=N– proton and at 11.18–11.40ppm compounds inhibited the growth of C. frenudii at a concentra-
for the =N–NH– proton. In addition, two amino (–NH2) pro- tion of 300μgdisc−1. In detail, compound 3g showed strong
tons appeared as two singlets at 7.76–7.96 and 7.93–8.02ppm and greatest activity against E. coli and K. pneumonia, and
due to en-thiol tautomerism, which were not observed for produced an inhibition zone similar to that of nalidixic acid.
compounds 3a–p. The electron ionization-mass spectrometry Compounds 3i and 3n also strongly inhibited the growth of
(EI-MS) spectra of 2a–f showed molecular ion peaks with E. faecalis and S. enteritidis, respectively, and showed larger
intensities of 95–100%.
inhibition zones than nalidixic acid. Compound 3c showed
Hantzsch thioazole synthesis21) applied to arylidenethios- moderate activity against C. sakazakii and E. coli, while com-
emicarbazones (2a–j) and 2-bromoacetophenone or 2,4′-di- pound 3b also exhibited moderate activity against C. sakaza-
bromoacetophenone gave the novel 2-arylidenehydrazinyl- kii and E. faecalis. Compounds 3e and 3m also demonstrated
Reagents and conditions: (a) EtOH–H2O, reflux, yield 83–94%; (b) EtOH, reflux, yield 72–95%.
Chart 1. Synthesis of the Novel 2-Arylidenehydrazinyl-4-arylthiazole Analogues 3a–p

December 2014
1261
moderate activity against E. faecalis. All compounds, 3a–p tions favored activity (3g), while the presence of a more polar
(300 μgdisc−1) showed better activity against L. monocyto- group (OH) at the same positions reduced activity (3c) against
genes than nalidixic acid (50μgdisc−1). Compounds 3a, 3b, E. coli. Introduction of a bromine atom (an electron donat-
3e, 3f, 3h, 3i, and 3l–n showed good activity against Y. pestis, ing group) at R5 position greatly reduced antibacterial effi-
whereas nalidixic acid showed no activity at 50 μgdisc−1. cacy (e.g., 3g>3h and 3c>3d). In most compounds substituent
The minimal inhibitory concentrations (MICs) of most active types and positions did not unduly affect antibacterial activity.
compounds were determined against some selected bacterial
strains and the results are summarized in Table 2.
Computational Studies The electronic properties e.g.
frontier molecular orbitals (FMOs) and physicochemical prop-
Structure–antimicrobial activity relationships did not appear erties e.g. lipophilicity play an important role in exerting mo-
to play a significant role as all compounds, with some excep- lecular reactivity in biological response. To explain the quali-
tions (e.g., E. coli), exhibited similar bactericidal effects. This tative structure–antibacterial activity relationships (QSAR) of
result led us to speculate that the mode of action of these com- 2-arylidenehydrazinyl-4-arylthiazole (3a–p), quantum-chem-
pounds is microorganism dependent. However, the presence ical and physicochemical calculations were carried out with
of an electron donating group (OMe) at the R1 and R3 posi- ab initio Hartree–Fock model at the 6–31G basis set using
Table 1. In Vitro Bactericidal Profiles of the Novel 2-Arylidenehydrazinyl-4-arylthiazole Analogues 3a–p in Terms of Zone of Inhibition
Gram-positive
Gram-negative
Compd.
S. a.
L. m.
E. f.
B. s.
K. p.
C. f.
C. s.
S. e.
E. c.
Y. p.
P. a.
3a
3b
3c
3d
3e
3f
10 1.0
10 1.0
—
13 0.5
12 0.5
13 1.0
11 1.0
12 0.5
13 0.5
11 1.0
13 1.0
14 0.5
13 1.0
11 1.0
12 1.0
12 0.5
11 1.0
11 1.0
11 1.0
12 1.0
12 0.5
—
12 1.0
12 1.0
11 1.0
11 1.0
11 1.0
11 1.0
—
—
—
—
—
14 1.0
15 0.5
15 0.5
11 1.0
13 1.0
14 1.0
12 1.0
12 1.0
13 0.5
12 1.0
11 1.0
12 1.0
13 1.0
11 1.0
12 1.0
12 0.5
23 1.0
10 1.0
11 1.0
—
13 1.0
14 0.5
16 0.5
11 1.0
13 1.0
14 0.5
22 1.0
14 1.0
13 1.0
13 1.0
11 1.0
13 1.0
12 1.0
12 1.0
11 1.0
11 1.0
23 1.0
10 1.0
10 1.0
—
12 1.0
11 1.0
—
—
—
—
—
—
—
—
—
—
10 1.0
11 0.5
—
15 0.5
13 1.0
—
—
—
12 1.0
12 1.0
—
10 1.0
10 1.0
—
11 1.0
12 1.0
—
10 1.0
17 1.0
—
—
3g
3h
3i
—
11 1.0
11 1.0
12 0.5
—
12 1.0
17 0.5
13 1.0
—
12 1.0
14 0.5
11 1.0
10 1.0
10 1.0
11 1.0
10 1.0
10 1.0
—
—
12 1.0
12 1.0
—
13 0.5
13 0.5
10 0.5
13 1.0
12 1.0
—
—
—
3j
10 1.0
—
—
9 0.5
3k
3l
—
—
—
11 1.0
11 1.0
12 1.0
—
11 1.0
15 1.0
15 1.0
—
10 0.5
11 1.0
—
—
10 1.0
—
10 1.0
11 1.0
13 1.0
—
12 1.0
11 1.0
11 1.0
10 1.0
—
3m
3n
3o
3p
NA
—
—
16 0.5
—
—
—
—
—
—
—
—
—
25 1.0
9
0.5
15 1.0
22 1.0
20 1.0
17 1.0
14 1.0
—
20 1.0
Inhibitory activities are expressed as observed inhibition zone diameters (in mm). (—), No activity. Results are the means S.D. of at least three experiments. S. a., Staphylo-
coccus aureus (JMC 2151); L. m., Listeria monocytogenes (ATCC 43256); E. f., Enterococcus faecalis (CARS 2011–012); B. s., Bacillus subtilis (IFO 13719); K. p., Klebsiella
pneumonia (JCM 1662); C. f., Citrobacter freundii (JCM 1657); C. s., Cronobacter sakazakii (CARS 2012-J-F); S. e., Salmonella enteritidis (ATCC 13076); E. c., E. coli
(CARS 2011–016); Y. p., Yersinia pestis (CARS 2013–027); P.a., Pseudomonas aeruginosa (PA01). Compounds were loaded at 300µg disc−1, and the positive control (nali-
dixic acid (NA)) was loaded at 50µg disc−1
.
Table 2. MICs of the Novel 2-Arylidenehydrazinyl-4-arylthiazole Analogues 3a–p against Selected Bacterial Strains
Minimum inhibitory concentration (MIC), μg mL−1
Compd.
Gram-positive
Gram-negative
L. m.
E. f.
B. s.
K. p.
C. s.
S. e.
E. c.
Y. p.
3b
3c
3e
3f
150
50
—
—
—
—
—
—
—
—
150
—
—
—
12
—
—
—
—
50
—
—
—
—
—
12
100
100
—
—
—
—
—
—
—
—
12
—
—
200
—
—
50
—
—
—
—
—
12
—
—
—
—
—
50
50
—
—
75
—
150
100
200
100
50
100
—
3g
3h
3i
—
—
50
3j
50
—
3m
3n
NA
100
150
25
50
100
25
50
12
(—), Not measured. NA, nalidixic acid. L. m., Listeria monocytogenes (ATCC 43256); E. f., Enterococcus faecalis (CARS 2011–012); B. s., Bacillus subtilis (IFO 13719);
K. p., Klebsilla pneumonia (JCM 1662); C. s., Cronobacter sakazakii (CARS 2012-J-F); S. t., Salmonella enteritidis (ATCC 13076); E. c., E. coli (CARS 2011–016); Y. p.,
Yersinia pestis (CARS 2013–027).

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Vol. 62, No. 12
ChemBio3D Pro 12 molecular modeling and molinspiration occupied molecular orbital (HOMO) and lowest unoccupied
cheminformatics software, respectively. Quantum-chemical molecular orbital (LUMO) of 3c (6.447eV), 3g (6.577eV), 3i
properties of some selected highly active (3c, 3g, 3i, and 3n) (6.247eV), and 3n (6.752eV) are less than that of 3d (7.022eV)
and low active (3d and 3k) compounds are presented in Table and 3k (6.808eV). It was reported that thiazole peptide class
3. The calculated Hartree–Fock total energy of compounds of antibiotics exerts their bactericidal action using sulfur
3c, 3g, 3i, and 3n are lower than that of 3d and 3k, indicating atom of thiazole ring and amine group to bind to the target
that the highly active compounds are more thermodynami- site which causes cell lysis and membrane disruption as well
cally stable. Moreover, the energy differences between highest as bacterial protein biosynthesis inhibition. Figure 1 shows
Table 3. Quantum-chemical Properties of Selected Highly Active (3c, 3g, 3n, and 3i) and Low Active (3d and 3k) 2-Arylidenehydrazinyl-4-arylthiazole
Analogues
Compd.
EHF (kJ/mol)
EHOMO (eV)
ELUMO (eV)
ΔEHOMO-LUMO (eV)
HF (kcal/mol)
Dipole (Db)
3c
3d
3g
3i
−3456703.9
−1017662.3
−3660418.9
−3652160.1
−2558174.6
−3981173.8
−6.768
−6.643
−6.938
−6.483
−7.026
−6.908
−0.321
0.379
6.447
7.022
6.577
6.247
6.808
6.752
341.10
235.72
250.57
299.06
351.96
391.86
3.21
4.63
3.92
4.82
2.73
4.84
−0.361
−0.236
−0.218
−0.156
3k
3n
EHF—Total energy; ELUMO—Energy of lowest unoccupied molecular orbital; EHOMO—Energy of Highest occupied molecular orbital; ΔEHOMO-LUMO—Energy difference be-
tween HOMO and LUMO; HF—Heat of formation.
Fig. 1. HOMO and LUMO Isosurfaces for 3c (A), 3d (B), 3g (C), 3i (D), 3k (E), and 3n (F)
Different surface colors represent opposite signs of the wave function.

December 2014
1263
Table 4. Physico-chemical Properties of the Novel 2-Arylidenehydrazinyl-4-arylthiazole Analogues 3a–p
Compd.
MW (g/mol)
c LogPa)
TPSAb)
OH–NH interactc)
O–N interactd)
n rot be)
Volume
3a
3b
3c
3d
3e
3f
311.366
390.262
311.366
390.262
339.42
3.198
3.508
3.394
4.203
3.504
4.213
3.999
4.508
3.511
4.355
3.296
4.105
4.187
4.857
5.444
4.868
77.739
77.739
77.739
77.739
55.751
55.751
55.751
55.751
97.967
97.967
66.745
66.745
57.511
57.511
37.283
40.521
3
3
3
3
1
1
1
1
4
4
2
2
2
2
1
1
5
5
5
5
5
5
5
5
6
6
5
5
4
4
3
4
4
4
4
4
6
6
6
6
4
4
5
5
4
4
4
5
265.114
283.0
265.114
283.0
300.17
318.056
300.17
318.056
273.132
291.018
282.642
300.528
274.982
274.982
280.5
418.316
339.42
3g
3h
3i
418.316
327.365
406.261
325.393
404.289
374.263
374.263
392.709
401.333
3j
3k
3l
3m
3n
3o
3p
312.87
a) Calculated octanol–water partition coefficient; b) Molecular polar surface area; c) Number of hydrogen-bond donors; d) Number of hydrogen-bond acceptors; e) Number
of rotatable bond.
Fig. 2. Correlation between Calculated Octanol–Water Partition Coefficient (cLogP) and Inhibitory Potency in Selected 2-Arylidenehydrazinyl-
4-arylthiazole Analogues against: (A) Staphylococcus aureus, (B) Klebsilla pneumonia, (C) Cronobacter sakazakii, (D) Salmonella enteritidis, (E)
Yersinia pestis, and (F) Pseudomonas aeruginosa

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Vol. 62, No. 12
HOMO and LUMO isosurfaces for 3c (A), 3d (B), 3g (C), inhibitory potencies of active 2-arylidenehydrazinyl-4-aryl-
3i (D), 3k (E), and 3n (E). As we observed, electron density thiazole analogues against L. monocytogenes, B. subtilis, Y.
around the sulfur atom are less in low active compounds e.g., pestis, and P. aeruginosa were found to be 0.56 (n=14, 3a–c,
3d and 3k, whereas more in highly active compounds e.g., 3c, 3e–j, and 3l–p), 0.57 (n=12; 3a–f, 3i, and 3k–o), 0.70 (n=7;
3g, 3i, and 3n, indicating this region can act as a potential 3a, 3b, 3h, 3j, and 3l–n) and 0.71 (n=10; 3a, 3b, 3e, 3h–j,
biological nucleophiles. The above results are consistent with and 3l–o), respectively. As shown in Fig. 3, a good correlation
our previous study.21)
was observed in which antibacterial activity increased with
Octanol–water partition coefficient (logP) of a molecule increasing PSA against L. monocytogenes, B. subtilis, and P.
depends on two important factors, i.e. lipophilicity and polar aeruginosa whereas, activity increased with decreasing PSA
surface area (PSA), which help the molecule to cross or ir- against Y. pestis. Correlation trends shown in Figs. 2 and 3,
reversibly damage the cellular membrane. Therefore, logP indicating that the mode of action of 2-arylidenehydrazinyl-
and PSA is recognized as a meaningful parameter in struc- 4-arylthiazole analogues against K. pneumonia, L. monocy-
ture–activity relationship studies. They are the most informa- togenes, B. subtilis, C. sakazakii, and P. aeruginosa might be
tive and successful physicochemical properties in medicinal same, but different from S. aureus, S. enteritidis, and Y. pestis.
chemistry22,23) and are used as a major experimental and As presented in Table 1, all the compounds (3a–p) showed
theoretical tool in drug design. Physiochemical parameters of selective bactericidal activity but did not showed activity
2-arylidenehydrazinyl-4-arylthiazole analogues (3a–p) are list- against all bacterial strains even clogP and PSAs values are
ed in Table 4. It is known that biological activity usually cor- fallen within the range of higher to lower active compounds.
relates with logP and PSA of a molecule.23,24) The correlation Therefore, maps of lipophilicity potential (MLP) and PSA of
coefficients (r2) between the clogP and inhibitory potencies of some selected highly active (3c, 3g, 3i, and 3n) and low ac-
active 2-arylidenehydrazinyl-4-arylthiazole analogues against tive compounds (3d and 3k) were compared with each other,
S. aureus, K. pneumonia, E. faecalis, C. sakazakii, S. enteriti- indicating that the polarity and lipophilicity are different for
dis, Y. pestis, and P. aeruginosa were found to be 0.71 (n=10; all molecules (Fig. 4). The above result led us to speculate that
3a, 3b, 3e, 3f, 3h–j, and 3l–n), 0.56 (n=5; 3f, 3g, 3j, 3l, and the distribution of lipophilic and polar area in the molecular
3m), 0.54 (n=7; 3e, 3f, 3h–j, 3l, and 3m), 0.58 (n=13; 3a–c, surface is also important to exert their biological activity
3e–j, 3l–n, and 3p), 0.66 (n=7; 3a, 3b, 3e, 3f, 3h, 3i, and 3n), together with the total lipophilicity and hydrophilicity of a
0.63 (n=8; 3a, 3b, 3e, 3f, 3h, and 3l–n) and 0.59 (n=9; 3a, molecule.
3f, 3h–j, and 3l–o), respectively. Although a small number of
Antioxidant Activity Compounds 3a–p were evaluated
compounds were used in the present study, a significant cor- for their free radical scavenging activities using DPPH. As
relation was observed in which antibacterial activity decreased shown in Table 5, all compounds exhibited significant DPPH
with increasing clogP against K. pneumonia, C. sakazakii, radical scavenging activity. Of the compounds examined, 3j,
and P. aeruginosa, while activity increased with increasing 3a, and 3i showed greatest activity followed by 3c, 3l, 3e,
clogP against S. aureus, S. enteritidis, and Y. pestis (Fig. 2). 3f, and 3n. The IC50 values of compound 3j (0.66 µM) and
However, the correlation coefficients (r2) between PSAs and 3a (0.81 µM) were lower than that of the standard antioxidant
Fig. 3. Correlation between Polar Surface Area (PSA) and Inhibitory Potency in Selected 2-Arylidenehydrazinyl-4-arylthiazole Analogues against:
(A) Listeria monocytogenes, (B) Bacillus subtilis, (C) Yersinia pestis, and (D) Pseudomonas aeruginosa

December 2014
1265
Table 5. DPPH Radical Scavenging Activities of the Novel 2-Arylidene-
hydrazinyl-4-arylthiazole Analogues 3a–p
Compd. no
IC50 (µM)
Compd. no
IC50 (µM)
3a
0.81
14.47
1.67
3i
3j
1.08
0.66
15.55
1.96
5.48
2.89
6.13
5.70
0.87
3b
3c
3k
3l
3d
15.37
1.98
3e
3m
3n
3o
3p
3f
2.63
3g
6.97
3h
9.81
Ascorbic acid
Conclusion
The present study reports on the synthesis of novel 2-ar-
ylidenehydrazinyl-4-arylthiazole analogues and their anti-
bacterial and antioxidant activities. Using Hantzsch’s method,
16 compounds were prepared from arylidenethiosemicarba-
zones and investigated with respect to their inhibitory effects
on eleven bacteria and their DPPH free radical scavenging
activities. All compounds showed significant bactericidal
effects on Gram-positive and Gram-negative bacteria. Of the
compounds tested, 3g produced the largest inhibition zones
against E. coli and K. pneumonia, 3i against E. faecalis, 3n
against S. tythi and E. faecalis, and 3c against E. coli and C.
sakazakii. Compounds 3a, 3b, 3e, 3f, 3h–i, and 3i–n signifi-
cantly inhibited the growth of Y. pestis, whereas the positive
control antibiotic, nalidixic acid, showed no activity. Quan-
tum-chemical and physicochemical calculations indicate that
antibacterial activity correlates well with calculated logP, PSA
and HOMO–LUMO energy difference of molecules. Further-
more, most of the compounds showed significant DPPH radi-
cal scavenging activity, and compounds 3j and 3a were found
to be more potent than ascorbic acid. In our opinion, QSAR
studies with respect to antibacterial and antioxidant effects
are likely to aid the development of new therapeutic agents for
diseases caused by microorganisms or oxidative stress.
Fig. 4. Molecular Lipophilicity Potential (Left) and Polar Surface Area
(Right) for 3c (A), 3d (B), 3g (C), 3i (D), 3j (E), 3k (F), and 3n (G)
Showing the Most Lipophilic Area (Blue Color), Intermediate Lipophilic
Area (Pink Color), Most Hydrophilic Area (Yellow Color), Intermediate
Hydrophilic Area (Green Color), Nonpolar Area (Gray White Color), and
Polar Area (Red Color)
(Color images were converted into gray scale.)
agent, ascorbic acid (0.87µM). Polyphenols containing more
hydroxyl groups, such as, 3i and 3j, are known to exhibit
Experimental
General The melting points of the synthesized com-
excellent antioxidant activities. Among the non-hydroxylated pounds were determined using a Stuart SMP3 apparatus, and
analogues, 3e and 3f exerted remarkable activity, whereas the results are uncorrected. Fourier transform (FT)-IR spectra
activities of 3g, 3h, 3o, and 3p were relatively weak.
were obtained using a Bruker Tensor 37 spectrometer using
Among the hydroxylated 2-arylidenehydrazinyl-4-arylthia- KBr discs. NMR spectra were recorded using a Bruker
zoles, compounds containing a bromine atom (3b, 3d, 3f, and 400MHz spectrometer in CDCl3 using TMS as an internal
3h) at the R5 position showed less antioxidant activity than standard. EI- and FAB-MS spectra were acquired using a Jeol
their non-brominated analogues (3a, 3c, 3e, and 3g), except JMS-700 mass spectrometer. Elemental analyses (C, H, N)
compounds 3j and 3l. Complete O-methylation of compounds were performed on a PerkineElmer 2400 II CHN elemental
3a and 3c to produce compounds 3e and 3g, respectively, re- analyzer.
sulted in ca. 2.5–4.2 fold decreases in radical scavenging ac-
General Procedures for the Preparation of Thiosemicar-
tivity. Whereas, complete methylation of 3b and 3d (bromine bazone Analogues (2a–j) The thiosemicarbazone analogues
containing analogues) to afford 3f and 3h, respectively, re- were prepared as we previously reported.20) Briefly, to a
sulted in ca. 5.5–1.6 fold increase in activity as compared with stirred solution of thiosemicarbazide (1mmol) in an ethanol-
3b and 3d. The results obtained in the present study led us to water mixture, an ethanolic solution of a substituted benzalde-
speculate that a hydroxyl group at R2 promotes the antioxidant hyde (1mmol) was added slowly and refluxed for 10–20min.
activity of hydroxyl substituted analogues (e.g., 3a>3c). How- After cooling the reaction mixture to ambient temperature, the
ever, an additional OH group at R4 (R1=R3=R4=OH) in 3i or mixture was filtered to provide a solid crude product, which
3j more potently increased activity.
was crystallized from ethanol to furnish pure compounds 2a–j
at yields of 83–94%.
2-(3,4-Dihydroxybenzylidine)hydrazinecarbothioamide (2a)

1266
Vol. 62, No. 12
Yield 83%, mp 237–238°C (brown powder). IR (cm−1): 3432 Found: C, 61.80; H, 4.29; N, 13.61.
1
(OH, NH2), 3259 (NH), 1588 (C=N), 1295 (C=S). H-NMR
2-(3,4-Dihydroxybenzylidine)hydrazinyl-4-(4-bromophenyl)-
(ppm) δ: 6.42 (d, 1H, J=7.2Hz, Ar-H), 6.85 (s, 1H, Ar-H), 7.04 thiazole (3b) Yield 75%, mp 168–169°C (brown powder). IR
(d, 1H, J=7.2Hz, Ar-H), 7.85 and 7.94 (2×s, 2H, NH2), 8.08 (cm−1): 3468 (OH), 3185 (NH), 3050, 1602, 1502 (C=C, C=N).
(s, 1H, =CH), 11.32 (s, 1H, NH). EI-MS m/z (%): 211 (M+, 1H-NMR (ppm) δ: 7.0 (d, 1H, J=8.2Hz, Ar-H), 7.16–7.36 (m,
25), 209 (100), 193 (30), 175 (20), 136 (18).
5H, Ar-H+thiazole-H), 7.8 (d, 2H, J=8.78Hz, Ar-H), 7.97 (s,
2-(2,4-Dihydroxybenzylidine)hydrazinecarbothioamide (2b) 1H, CH=N), 12.01 (s, 1H, NH). FAB-MS m/z (%): 390 (M+,
Yield 85%, mp 234–235°C (yellow powder). IR (cm−1): 3430 5). Anal. Calcd for C16H12BrN3O2S: C, 49.24; H, 3.10; N, 10.77.
(OH, NH2), 3261 (NH), 1590 (C=N), 1299 (C=S). H-NMR Found: C, 49.31; H, 3.19; N, 10.84.
1
(ppm) δ: 6.42–6.54 (m, 2H, Ar-H), 7.60 (d, 1H, J=7.2Hz,
2-(2,4-Dihydroxybenzylidine)hydrazinyl-4-phenylthiazole
Ar-H), 7.76 and 7.92 (2×s, 2H, NH2), 8.24 (s, 1H, =CH), 11.28 (3c) Yield 76.5%, mp 212–213°C (straw powder). IR (cm−1):
(s, 1H, NH). EI-MS m/z (%): 211 (M+, 12), 209 (100), 192 (30), 3400 (OH), 3196 (NH), 3000, 1600, 1550 (C=C, C=N).
136 (15).
1H-NMR (ppm) δ: 6.33–6.35 (m, 2H, Ar-H), 7.25–7.42 (m,
2-(3,4-Dimethoxybenzylidine)hydrazinecarbothioamide (2c) 5H, Ar-H+thiazole-H), 7.84 (d, 2H, J=7.80Hz, Ar-H), 8.21
Yield 92.8%, mp 206–207°C (white powder). IR (cm−1): 3405 (s, 1H, CH=N), 11.16 (s, 1H, NH). EI-MS m/z (%): 311 (M+,
1
(NH2), 3241 (NH), 1590 (C=N), 1300 (C=S). H-NMR (ppm) 87), 294 (20), 176 (100), 162 (18), 134 (52). Anal. Calcd for
δ: 3.79 and 3.81 (2×s, 6H, OCH3), 6.96 (d, 1H, J=8.3Hz, C16H13N3O2S: C, 61.72; H, 4.21; N, 13.50. Found: C, 61.82; H,
Ar-H), 7.5 (s, 1H, Ar-H), 7.14 (d, 1H, J=8.3Hz, Ar-H), 7.96 4.30; N, 13.59.
and 8.02 (2×s, 2H, NH2), 8.16 (s, 1H, =CH), 11.40 (s, 1H,
2-(2,4-Dihydroxybenzylidine)hydrazinyl-4-(4-bromophenyl)-
NH). EI-MS m/z (%): 239 (M+, 100), 222 (30), 149 (15), 114 thiazole (3d) Yield 73%, mp 248–249°C (brown powder). IR
(30).
(cm−1): 3409 (OH), 3150 (NH), 3025, 1600, 1550 (C=C, C=N).
2-(2,4-Dimethoxybenzylidine)hydrazinecarbothioamide (2d) 1H-NMR (ppm) δ: 6.33–6.36 (m, 1H, Ar-H), 7.34–7.80 (m, 7H,
Yield 94%, mp 198–199°C (white crystal). IR (cm−1): 3408 Ar-H+thiazole-H), 8.21 (s, 1H, CH=N), 11.12 (s, 1H, NH).
1
(NH2), 3270 (NH), 1578 (C=N), 1299 (C=S). H-NMR (ppm) EI-MS m/z (%): 392 (M+3, 10), 391 (M+2, 53), 390 (M+1, 11),
δ: 3.80 and 3.82 (2×s, 6H, OCH3), 6.56–6.69 (m, 2H, Ar-H), 389 (M+, 52), 256 (100), 254 (98), 214 (22), 212 (23), 174 (62),
7.20 (s, 1H, Ar-H), 8.24 (s, 1H,=CH), 7.84 and 7.93 (2×s, 2H, 137 (29). Anal. Calcd for C16H12BrN3O2S: C, 49.24; H, 3.10; N,
NH2), 7.4 (d, 1H, J=7.8Hz, Ar-H), 11.42 (s, 1H, NH). EI-MS 10.77. Found: C, 49.33; H, 3.21; N, 10.86.
m/z (%): 239 (M+, 80), 222 (100), 149 (25), 114 (20).
2-(3,4-Dimethoxybenzylidine)hydrazinyl-4-phenylthiazole
2-(2,4,6-Trihydroxybenzylidine)hydrazinecarbothioamide (3e) Yield 77%, mp 235–236°C (white crystal). IR (cm−1):
(2e) Yield 93.6%, mp 239–240°C (red powder). IR (cm−1): 3233 (NH), 3063, 1617, 1534 (C=C, C=N). H-NMR (ppm)
1
3436 (OH, NH2), 3263 (NH), 1581 (C=N), 1289 (C=S). δ: 3.80 (s, 3H, OCH3), 3.82 (s, 3H, OCH3), 7.01–7.44 (m, 7H,
1H-NMR (ppm) δ: 6.48 (s, 2H, Ar-H), 7.86 and 7.96 (2×s, 2H, Ar-H+thiazole-H), 7.85 (d, 2H, J=1.98Hz, Ar-H), 7.98 (s, 1H,
NH2), 8.04 (s, 1H,=CH), 11.18 (s, 1H, NH). EI-MS m/z (%): CH=N), 11.28 (s, 1H, NH). EI-MS m/z (%): 339 (M+, 40),
227 (M+, 100), 224 (38), 193 (30), 152 (15), 138 (45).
177 (10), 176 (100), 134 (29). Anal. Calcd for C18H17N3O2S: C,
2-(3-Methoxy-4-hydroxybenzylidine)hydrazinecarbothio- 63.70; H, 5.05; N, 12.38. Found: C, 63.81; H, 5.12; N, 12.45.
amide (2f) Yield 88.6%, mp 194–195°C (yellow powder). 2-(3,4-Dimethoxybenzylidine)hydrazinyl-4-(4-bromophenyl)-
IR (cm−1): 3437 (OH, NH2), 3265 (NH), 1596 (C=N), 1299 thiazole (3f) Yield 74%, mp 182–183°C (pink powder). IR
1
1
(C=S). H-NMR (ppm) δ: 3.81 (s, 3H, OCH3), 6.69 (d, 1H, (cm−1): 3200 (NH), 3002, 1600, 1517 (C=C, C=N). H-NMR
J=7.2Hz, Ar-H), 7.06 (d, 1H, J=7.2Hz, Ar-H), 7.11 (s, 1H, (ppm) δ: 3.81 (s, 3H, OCH3), 3.79 (s, 3H, OCH3), 7.00–7.36
Ar-H), 7.89 and 7.93 (2×s, 2H, NH2), 8.08 (s, 1H, =CH), (m, 4H, +thiazole-H), 7.59 (d, 2H, J=8.00Hz, Ar-H), 7.80 (d,
11.26 (s, 1H, NH). EI-MS m/z (%): 225 (M+, 100), 224 (30), 2H, J=8.00Hz, Ar-H), 7.97 (s, 1H, CH=N), 12.01 (s, 1H, NH).
165 (30), 150 (20), 136 (65). The spectral data of compounds EI-MS m/z (%): 420 (M+3, 10), 419 (M+2, 39), 418 (M+1, 11),
2g–j was described in our previous study.20)
417 (M+, 38), 256 (100), 254 (98), 174 (36), 97 (58). Anal. Calcd
General Procedure for the Preparation of 1,3-Thiazole for C18H16BrN3O2S: C, 51.68; H, 3.86; N, 10.05. Found: C, 51.77;
Analogues (3a–p) The novel 1,3-thiazole analogues were H, 3.95; N, 10.14.
prepared by the modification of our previous methods.20)
2-(2,4-Dimethoxybenzylidine)hydrazinyl-4-phenylthiazole
Briefly, a mixture of thiosemicarbazone (1mmol) and 2-bro- (3g) Yield 75%, mp 219–220°C (white crystal). IR (cm−1):
moacetophenone or 2,4′-dibromoacetophenone (1mmol) in 3275 (NH), 3010, 1600, 1484 (C=C, C=N). 1H-NMR (ppm)
ethanol was refluxed for 30–60min and then cooled to ambi- δ: 3.80 (s, 3H, OCH3), 3.82 (s, 3H, OCH3), 6.41–6.70 (m,
ent temperature. The resulting precipitate was filtered and 3H, Ar-H), 7.23–7.72 (m, 3H, Ar-H+thiazole-H), 7.79 (d, 2H,
washed with water to give a crude product, which was puri- J=8.78, Ar-H), 8.49 (s, 1H, CH=N), 11.58 (s, 1H, NH). EI-MS
fied by crystallization in a N,N-dimethylformamide (DMF)– m/z (%): 339 (M+, 35), 176 (100), 149 (10), 134 (28). Anal.
EtOH mixture, affording pure 1,3-thiazole derivatives at Calcd for C18H17N3O2S: C, 63.70; H, 5.05; N, 12.38. Found: C,
yields of 72–95%.
63.79; H, 5.14; N, 12.47.
2-(3,4-Dihydroxybenzylidine)hydrazinyl-4-phenylthiazole
2-(2,4-Dimethoxybenzylidine)hydrazinyl-4-(4-bromophenyl)-
(3a) Yield 77%, mp 227–228°C (red crystal). IR (cm−1): 3417 thiazole (3h) Yield 95%, mp 202–203°C (black powder). IR
1
(OH), 3167 (NH), 3001, 1625, 1525 (C=C, C=N). H-NMR (cm−1): 3276 (NH), 3020, 1609, 1542 (C=C, C=N). 1H-NMR
(ppm) δ: 7.00–7.36 (m, 8H, Ar-H+thiazole-H), 7.86 (d, 1H, (ppm) δ: 3.81 (s, 3H, OCH3), 3.85 (s, 3H, OCH3), 6.61–6.63
J=7.80Hz, Ar-H), 7.93 (s, 1H, CH=N), 11.28 (s, 1H, NH). (m, 1H, Ar-H), 7.33–7.71 (m, 4H, Ar-H+thiazole-H), 7.80 (d,
EI-MS m/z (%): 311 (M+, 5), 231 (28), 216 (20), 176 (100), 134 2H, J=7.82Hz, Ar-H), 8.26 (s, 1H, CH=N), 11.78 (s, 1H, NH).
(75). Anal. Calcd for C16H13N3O2S: C, 61.72; H, 4.21; N, 13.50. EI-MS m/z (%): 420 (M+3, 10), 419 (M+2, 33), 418 (M+1,

December 2014
1267
10), 417 (M+, 32), 256 (100), 254 (98), 174 (20), 149 (20). Anal. zole (3o) Yield 76%, mp 217–218°C (gray powder). IR
1
Calcd for: C18H16BrN3O2S: C, 51.68; H, 3.86; N, 10.05. Found: (cm−1): 3174 (NH), 3025, 1600, 1550 (C=C, C=N). H-NMR
C, 51.79; H, 3.94; N, 10.12.
(ppm) δ: 7.41–7.69 (m, 7H, Ar-H+thiazole-H), 7.81 (d, 2H,
2-(2,4,6-Trihydroxybenzylidine)hydrazinyl-4-phenylthiazole J=7.60Hz, Ar-H), 8.03 (s, 1H, CH=N), 12.23 (s, 1H, NH).
(3i) Yield 74%, mp 224–225°C (red powder). IR (cm−1): 3450 EI-MS m/z (%): 394 (M+3, 12), 393 (M+2, 57), 392 (M+1,
1
(OH), 3159 (NH), 3073, 1600, 1550 (C=C, C=N). H-NMR 11), 391 (M+, 43), 256 (100), 254 (99), 174 (91). Anal. Calcd for
(ppm) δ: 5.98 (s, 2H, Ar-H), 7.28–7.43 (m, 4H, Ar-H+thiazole- C16H11BrClN3S: C, 48.94; H, 2.82; N, 10.70. Found: C, 49.06;
H), 7.84 (d, 2H, J=7.80Hz, Ar-H), 8.46 (s, 1H, CH=N), 10.40 H, 2.91; N, 10.81.
(s, 1H, NH). EI-MS m/z (%): 327 (M+, 24), 309 (23), 189 (35),
2-(4-Dimethylaminobenzylidine)hydrazinyl-4-(4-bromo-
176 (100), 134 (60). Anal. Calcd for C16H13N3O3S: C, 58.70; H, phenyl)thiazole (3p) Yield 83%, mp 230–231°C (greenish
4.00; N, 12.84. Found: C, 58.82; H, 4.11; N, 12.91.
gray powder). IR (cm−1): 3184 (NH), 3018, 1358, 1609, 1558
1
2-(2,4,6-Trihydroxybenzylidine)hydrazinyl-4-(4-bromo- (C=C, C=N). H-NMR (ppm) δ: 2.97 (s, 6H, N(CH3)2, 6.74
phenyl)thiazole (3j) Yield 73%, mp 214–215°C (red powder). (m, 2H, Ar-H), 7.32–7.60 (m, 5H, Ar-H+thiazole-H), 7.80 (m,
IR (cm−1): 3467 (OH), 3250 (NH), 3013, 1642, 1642, 1509 2H, Ar-H), 7.92 (s, 1H, CH=N), 11.80 (s, 1H, NH). EI-MS m/z
1
(C=C, C=N). H-NMR (ppm) δ: 5.96 (s, 2H, Ar-H), 7.36–7.80 (%): 403 (M+3, 11), 402 (M+2, 46), 401 (M+1, 10), 400 (M+,
(m, 5H, Ar-H+thiazole-H), 8.46 (s, 1H, CH=N), 11.39 (s, 45), 256 (100), 254 (98), 174 (14), 147 (34). Anal. Calcd for
1H, NH). EI-MS m/z (%): 408 (M+3, 6), 407 (M+2, 16), 406 C18H17BrN4S: C, 53.87; H, 4.27; N, 13.96. Found: C, 53.98; H,
(M+1, 6), 405 (M+, 15), 389 (100), 387 (97), 256 (98), 254 4.36; N, 14.03.
(99), 174 (86), 133 (30). Anal. Calcd for C16H12BrN3O3S: C,
47.30; H, 2.98; N, 10.34. Found: C, 47.42; H, 3.06; N, 10.43.
Antibacterial Screening A previously described filter
paper disc diffusion method20) against all eleven strains was
2-(3-Methoxy-4-hydroxybenzylidine)hydrazinyl-4-phenyl- used to determine the in vitro antibacterial effects of all com-
thiazole (3k) Yield 74%, mp 235–236°C (black powder). IR pounds. Briefly, nutrient agar (NA) media (Difco Laboratories,
(cm−1): 3425 (OH), 3167 (NH), 3030, 1634, 1509 (C=C, C=N). Lawrence, KS, U.S.A.) was used as a basal medium for test
1H-NMR (ppm) δ: 3.82 (s, 3H, OCH3), 6.82 (d, 1H, J=7.80Hz, bacteria. These agar media were inoculated with 0.2mL of
Ar-H), 7.01–7.43 (m, 7H, Ar-H+thiazole-H), 7.84 (d, 1H, 24-h liquid cultures containing the microorganisms. The sam-
J=7.80Hz, Ar-H), 7.95 (s, 1H, CH=N), 11.93 (s, 1H, –NH). ple discs were placed gently on pre-inoculated agar plates and
EI-MS m/z (%): 325 (M+, 35), 231 (43), 216 (35), 176 (100), 134 then incubated aerobically at 37°C for 24h. Discs with only
(83). Anal. Calcd for C17H15N3O2S: C, 62.75; H, 4.65; N, 12.91. dimethyl sulfoxide (DMSO) were used as a control, and na-
Found: C, 62.86; H, 4.72; N, 13.01.
lidixic acid was used as a positive control. Inhibitory activity
2-(3-Methoxy-4-hydroxybenzylidine)hydrazinyl-4-(4-bro- was assessed (in mm) by measuring the diameters of observed
mophenyl)thiazole (3l) Yield 72%, mp 100–101°C (red inhibition zones. These evaluations were performed in tripli-
crystal). IR (cm−1): 3442 (OH), 3200 (NH), 3070, 1634, 1500 cate for each compound at a concentration of 300µg disc−1.
1
(C=C, C=N). H-NMR (ppm) δ: 3.82 (s, 3H, OCH3), 6.82 (d, The minimal inhibitory concentration (MIC, in µgmL−1) of
1H, J=7.80Hz, Ar-H), 7.06–7.35 (m, 3H, Ar-H+thiazole-H), selected compounds was determined against, Listeria mono-
7.59 (d, 2H, J=7.80Hz, Ar-H), 7.80 (d, 2H, J=7.80Hz, Ar-H), cytogenes (ATCC 43256), Enterococcus faecalis (CARS
7.93 (s, 1H, CH=N), 9.39 (s, 1H, OH), 11.93 (s, 1H, NH). 2011–012), Bacillus subtilis (IFO 13719), Klebsilla pneumonia
EI-MS m/z (%): 406 (M+3, 10), 405 (M+2, 40), 404 (M+1, (JCM 1662), Cronobacter sakazakii (CARS 2012-J-F), Sal-
10), 403 (M+, 40), 256 (100), 254 (99), 174 (34), 134 (10). Anal. monella enteritidis (ATCC 13076), E. coli (CARS 2011–016)
Calcd for C17H14BrN3O2S: C, 50.50; H, 3.49; N, 10.39. Found: and Yersinia pestis (CARS 2013–027) using nutrient broth
C, 50.62; H, 3.56; N, 10.48.
medium (DIFCO) and a serial dilution technique.25) MIC was
2-(4-Hydroxybenzylidine)hydrazinyl-4-(4-bromophenyl)- defined as the lowest concentration of the tested compound (in
thiazole (3m) Yield 74%, mp 232–233°C (brown powder). IR DMSO) that inhibited bacterial growth.
(cm−1): 3475 (OH), 3175 (NH), 3063, 1617, 1513 (C=C, C=N).
DPPH Radical Scavenging Activity The free radical-
1H-NMR (ppm) δ: 6.81 (d, 2H, J=8.2Hz, Ar-H), 7.35–7.59 (s, scavenging activities of the synthesized compounds were as-
5H, Ar-H+thiazole-H), 7.79 (d, 2H, J=8.2Hz, Ar-H), 7.94 (s, sayed according to the Blois method with some modification26)
1H, CH=N), 9.81 (s, 1H, OH), 11.90 (s, 1H, NH). EI-MS m/z using DPPH radical. Briefly, to 0.1mL samples of differ-
(%): 376 (M+3, 11), 375 (M+2, 45), 374 (M+1, 12), 373 (M+, ent concentrations (2.5 to 20mg/mL) in ethanol, 4mL of
44), 256 (100), 254 (100), 174 (52), 133 (10). Anal. Calcd for 1.5×10−5 M DPPH solution was added, thoroughly mixed, and
C16H13N3OS: C, 65.06; H, 4.44; N, 14.23. Found: C, 65.17; H, then left to stand at room temperature in a dark place. After
4.52; N, 14.33.
30min of incubation, solution absorbances were measured at
2-(2-Hydroxybenzylidine)hydrazinyl-4-(4-bromophenyl)- 520nm and the activity was calculated using the following
thiazole (3n) Yield 84% mp 243–244°C (yellow crystal). IR equation:
(cm−1): 3442 (OH), 3175 (NH), 3065, 1617, 1492 (C=C, C=N).
DPPH radical-scavenging activity %
1H-NMR (ppm) δ: 6.8–6.9 (m, 2H, Ar-H), 7.21–7.63 (m, 5H,
Ar-H+thiazole-H), 7.80 (d, 2H, J=8.00Hz, Ar-H), 8.32 (s, 1H,
CH=N), 10.06 (s, 1H, OH), 12.11 (s, 1H, NH). EI-MS m/z (%):
376 (M+3, 19), 375 (M+2, 86), 374 (M+1, 20), 373 (M+, 84),
256 (100), 254 (97), 174 (60), 147 (15), 133 (14). Anal. Calcd
for C16H12BrN3OS: C, 51.35; H, 3.23; N, 11.23. Found: C,
51.45; H, 3.31; N, 11.34.
(
)
=[(Absorbance of the control
×Absorbance of the sample)
÷(Absorbance of the control)]×100
Computational Studies The molecular geometries of the
thiazole analogues were built with a standard bond length
2-(4-Chlorobenzylidine)hydrazinyl-4-(4-bromophenyl)thia- and angles using ChemBio3D Pro 12 molecular modeling pro-

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Vol. 62, No. 12
H., Ashour H. M. A., Bioorg. Med. Chem., 17, 882–895 (2009).
gram (Cambridge Soft Corporation, Cambridge, MA, U.S.A.).
The energy was minimized by semi-empirical molecular
orbital PM3 method27) and then by the Hartree–Fock method
at 6–31G basis set with R-Closed-Shell wave function using
GAMESS Interface in the ChemBio3D ultra Ver. 12. Mu-
liken charges and properties of frontier molecular orbitals of
the compounds were analyzed using the results calculated at
RHF/6–31G level. Physicochemical properties were calculated
using molinspiration cheminformatics software (Molinspira-
tion Cheminformatics, SK 90026 Slovensky Grob, SR). The
method for calculation of clogP was developed by Molinspi-
ration (milogP 2.2–2005) based on group contributions and
correction factors by fitting calculated logP with experimental
logP for a training set more than twelve thousand, mostly
drug-like molecules. Molecular polar surface area (PSA) was
calculated based on the methodology published by Ertl et
al.,28) as a sum of fragment contributions. The maps of mo-
lecular lipophilicity potential (MLP) and PSA were viewed in
Molinspiration Galaxy 3D Structure Generator (ver. 2013.02
beta).
8) Bharti S. K., Nath G., Tilak R., Singh S. K., Eur. J. Med. Chem., 45,
651–660 (2010).
9) Ryu C. K., Nho J. H., Jin G., Oh S. Y., Choi S. J., Chem. Pharm.
Bull., 62, 668–674 (2014).
10) Shih M. H., Ke K. F., Bioorg. Med. Chem., 12, 4633–4643 (2004).
11) Zhang W. T., Ruan J. L., Wu P. F., Jiang F. C., Zhang L. N., Fang
W., Chen X. L., Wang Y., Cao B. S., Chen G. Y., Zhu Y. J., Gu J.,
Chen J. G., J. Med. Chem., 52, 718–725 (2009).
12) Iino T., Hashimoto N., Sasaki K., Ohyama S., Yoshimoto R., Ho-
saka H., Hasegawa T., Chiba M., Nagata Y., EiKi J., Nishimura T.,
Bioorg. Med. Chem., 17, 3800–3809 (2009).
13) Dash J., Melillo B., Arseniyadis S., Cossy J., Tetrahedron Lett., 52,
2246–2249 (2011).
14) Shiradkar M. R., Akula K. C., Dasari V., Baru V., Chiningiri B.,
Gandhi S., Kaur R., Bioorg. Med. Chem., 15, 2601–2610 (2007).
15) Chimenti F., Maccioni E., Secci D., Bolasco A., Chimenti P.,
Granese A., Befani O., Turini P., Alcaro S., Ortuso F., Cardia M. C.,
Distinto S., J. Med. Chem., 50, 707–712 (2007).
16) Clark R. F., Zhang T., Wang X., Wang R., Zhang X., Camp H. S.,
Beutel B. A., Sham H. L., Gu Y. J., Bioorg. Med. Chem. Lett., 17,
1961–1965 (2007).
17) Netalkar P. P., Netalkar S. P., Budagumpi S., Revankar V. K., Eur.
J. Med. Chem., 79, 47–56 (2014).
18) Turan-Zitouni G., Özdemir A., Kaplancikli Z. A., Phosphorus Sul-
phur Silicon Relat. Elem., 186, 233–239 (2011).
19) Chimenti F., Secci D., Bolasco A., Chimenti P., Granese A., Car-
radori S., Yáñez M., Orallo F., Sanna M. L., Gallinella B., Cirilli R.,
J. Med. Chem., 53, 6516–6520 (2010).
20) Alam M. S., Liu L., Lee Y. E., Lee D. U., Chem. Pharm. Bull., 59,
568–573 (2011).
21) Hantzsch A., Weber H. J., Ber. Dtsch. Chem. Ges., 20, 3118–3132
(1887).
22) Testa B., Carrupt P. A., Gaillard P., Billois F., Weber P., Pharm.
Res., 13, 335–343 (1996).
23) Alam M. S., Nam Y. J., Lee D. U., Eur. J. Med. Chem., 69, 790–797
(2013).
24) Cubini H., “ Burger’s medicinal chemistry and drug discovery,”
Vol. I, Interscience, New York, 1995.
25) Nishino C., Enoki N., Tawata S., Mori A., Kobayashi K., Fukushima
M., Agric. Biol. Chem., 51, 139–143 (1987).
26) Blois M. S., Nature (London), 181, 1199–1200 (1958).
27) Stewart J. J. P., J. Mol. Model., 10, 155–164 (2004).
28) Ertl P., Rohde B., Selzer P., J. Med. Chem., 43, 3714–3717 (2000).
Acknowledgments This work was supported by the
Dongguk University at Gyeongju, Korea. Dr. Seen Ae Chae
at Korea Basic Science Institute (Daegu) is acknowledged for
the NMR data.
References
1) Vicini P., Geronikaki A., Anastasia K., Incerti M., Zani F., Bioorg.
Med. Chem., 14, 3859–3864 (2006).
2) Tenover F. C., McDonald L. C., Curr. Opin. Infect. Dis., 18, 300–
305 (2005).
3) Ostrosky-Zeichner L., Casadevall A., Galgaini J. N., Odds F. C.,
Rex J. H., Nat. Rev. Drug Discov., 9, 719–727 (2010).
4) Kathiravan M. K., Salake A. B., Chothe A. S., Dudhe P. B., Watode
R. P., Mukta M. S., Gadhwe S., Bioorg. Med. Chem., 20, 5678–5698
(2012).
5) Sun-Waterhouse D., Chen J., Chuah C., Wibisono R., Melton L. D.,
Laing W., Ferguson L. R., Skinner M. A., Int. J. Food Sci. Nutr., 60
(Suppl 7), 251–264 (2009).
6) Gürsoy E., Güzeldemirci N. U., Eur. J. Med. Chem., 42, 320–326
(2007).
7) Rostom S. A. F., El-Ashmawy I. M., Abd El-Razik H. A., Badr M.