Synthesis and monoamine oxidase A/B inhibitory evaluation of new benzothiazole-thiazolylhydrazine derivatives

Article abstract of DOI:10.1080/10426507.2020.1722667

In this study, a novel series of benzothiazole-thiazolylhydrazine (3a–3i) was synthesized and their structures were characterized by ¹H-NMR, ¹³C-NMR spectrometry, and mass spectroscopy. These compounds were evaluated as inhibitors of

Full text of DOI:10.1080/10426507.2020.1722667

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: https://www.tandfonline.com/loi/gpss20
Synthesis and monoamine oxidase A/B
inhibitory evaluation of new benzothiazole-
thiazolylhydrazine derivatives
Gülhan Turan, Derya Osmaniye, Begüm Nurpelin Sağlik, Ulviye Acar Çevik,
Serkan Levent, Betül Kaya Çavuşoğlu, Ümide Demir Özkay, Yusuf Özkay &
Zafer Asım Kaplancikli
To cite this article: Gülhan Turan, Derya Osmaniye, Begüm Nurpelin Sağlik, Ulviye Acar Çevik,
Serkan Levent, Betül Kaya Çavuşoğlu, Ümide Demir Özkay, Yusuf Özkay & Zafer Asım Kaplancikli
(2020): Synthesis and monoamine oxidase A/B inhibitory evaluation of new benzothiazole-
thiazolylhydrazine derivatives, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI:
10.1080/10426507.2020.1722667
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PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
https://doi.org/10.1080/10426507.2020.1722667
Synthesis and monoamine oxidase A/B inhibitory evaluation of new
benzothiazole-thiazolylhydrazine derivatives
a
a,b
Gulhan Turan , Derya Osmaniye , Begum Nurpelin Saglika,b, Ulviye Acar C¸evika,b, Serkan Leventa,b
,
€
€
€
ꢀ
Betul Kaya C¸avus¸oglu , Umide Demir Ozkay , Yusuf Ozkaya,b, and Zafer Asım Kaplanciklia
a,b
c
€
€
€
ꢀ
b
aFaculty of Pharmacy, Department of Pharmaceutical Chemistry, Anadolu University, Eskis¸ehir, Turkey; Faculty of Pharmacy, Doping and
c
Narcotic Compounds Analysis Laboratory, Anadolu University, Eskis¸ehir, Turkey; Faculty of Pharmacy, Department of Pharmacology, Anadolu
University, Eskis¸ehir, Turkey
ABSTRACT
ARTICLE HISTORY
Received 23 August 2019
Accepted 24 January 2020
In this study, a novel series of benzothiazole-thiazolylhydrazine (3a–3i) was synthesized and their
structures were characterized by 1H-NMR, 13C-NMR spectrometry, and mass spectroscopy. These com-
pounds were evaluated as inhibitors of type A and type B monoamine oxidase (MAO) enzymes. The
most active compound 3b (2-((2-(2-(4-(4-Nitrophenyl)thiazol-2-yl)hydrazineylidene)-2-phenylethyl)thio)-
benzothiazole) showed strong inhibitory activity at hMAO-A (IC50 of 0.095 0.004mM). Furthermore,
compound 3i (2-((2-(2-(4-(2,4-dichlorophenyl)thiazol-2-yl)hydrazineylidene)-2-phenylethyl)thio)benzo-
thiazole) showed significant inhibition profile on hMAO-A with the IC50 values 0.141 0.006 mM.
KEYWORDS
Benzothiazole; thiazolylhy-
drazine; mono-
amine oxidase
GRAPHICAL ABSTRACT
Introduction
same at the amino acid sequence level and possess highly
similar active site structures. Among 16 active site residues,
only 6 differ between MAO-A and MAO-B [6, 7]. Despite
the similarities in structure and function of the two iso-
forms, MAO-A and MAO-B have different substrate and
inhibitor specificities. MAO-A inhibitors are associated with
the treatment of depression and anxiety, and MAO-B inhibi-
tors are associated with the treatment of Parkinson’s and
Alzheimer’s disease. It is known that undesirable side effects
occur when using nonselective MAO inhibitors. These side
effects are listed as hepatotoxicity and hypertension, caused
by the consumption of tyramine-rich food, resulting in the
so-called “cheese effect.” Based on these reasons, there cur-
rently exists the need for the development of compounds
that are selective inhibitors of MAO [8–10]. Although some
Monoamine oxidase (MAO; EC 1.4.3.4) is a flavoprotein
found in the outer membrane of mitochondria in neuronal,
glial, and other cells. MAO is copiously located not only in
noradrenergic nerve terminals, but also in various other tis-
sues such as liver, intestinal mucosa, fibroblasts, and plate-
lets [1, 2]. The function of monoamine oxidases (MAOs) in
brain neurochemistry is mainly related to the oxidative
deamination of biogenic amines (BA). Amines such as
adrenaline, noradrenaline, melatonin, and serotonin are
principally metabolized by MAO-A, whereas benzylamine
and phenylethylamine are controlled by MAO-B. Both types
of MAO isoforms have common substrates such as dopa-
mine and tyramine [3–5]. The MAO-A and MAO-B are
products of different genes. The MAOs are almost 70% the MAO-A inhibitors, including phenelzine, isocarboxazid,
CONTACT Derya Osmaniye
dosmaniye@anadolu.edu.tr
Anadolu Universitesi, Faculty of Pharmacy, Anadolu University Faculty of Pharmacy, Eskisehir
26470, Turkey.
Supplemental data for this article is available online at https://doi.org/10.1080/10426507.2020.1722667.
ß 2020 Taylor & Francis Group, LLC

2
G. TURAN ET AL.
tranylcypromine, iproniazid, moclobemide, and toloxatone, structural tuning [28]. Encouraged by these results, in this
have made great contributions to the depressive patients, study, we designed a series of thiazolylhydrazone derivatives,
clinic usage of MAO-A inhibitors showed some limitations in which the phenylethyl-mercaptobenzothiazole moiety on
due to introduction of other classes of drugs. As a result,
the development of new generation of MAO-A inhibitors
attracted significant attention recently, aiming at safer and
better-tolerated therapeutic agents [11–13].
the hydrazonic N1 was retained for all homologs to evaluate
their MAO inhibitor activities.
Results and discussion
Hydrazine–hydrazone moiety (–NH–N[dbond]C–) and
their derivatives are a versatile class of compounds with
interesting biological properties. The most wanted character-
istics of hydrazones include simplicity of preparation,
increased hydrolytic stability relative to imines, and affinity
to crystallinity. These structural fragments are mainly
responsible for the physical and chemical properties of the
hydrazones [10, 14, 15]. The well-known biological property
of hydrazine moiety is MAO inhibitor activity. The classical
period of the MAO inhibitors started with hydrazine deriva-
tives. Developed as tuberculostatic drug, iproniazid is the
first modern antidepressant. Numerous compounds among
the great variety of substituted hydrazines behave as MAO
inhibitors. A common structural feature of substrates and
inhibitors is an amino or imino group that is assumed to
play an essential role in orientation and complex formation
at the active site of the enzyme [16–18]. Literature studies
show that arylalkylhydrazines inhibit both isoenzymes. Only
the mechanism of inhibition differs. For example, the inhib-
ition between arylalkylhydrazines and MAO-B results in
irreversible alkylation at the N5 position of the flavin ring.
Because of the serious side effects of iproniazid with irre-
versible and nonselective properties, a large number of sub-
stituted hydrazines have been studied as hMAO inhibitors
to discover reversible and safer agents [19, 20].
Many thiazolylhydrazines show hMAO inhibitory activity
in the range of micromolar concentration. 3-D-QSAR stud-
ies helped to explain experimental results and to provide
robust structure–activity relationships: (i) the aryl, especially
a phenyl moiety at C4 of the thiazole is responsible for the
correct orientation of the inhibitor inside the active site of
enzyme close to the catalytic flavin adenine dinucleotide
(FAD) (aromatic cage); (ii) the aryl moiety has to be ortho
and/or para substituted with an electron-withdrawing group
for selective MAO-B inhibition and electron donating group
for selective MAO-A inhibition; (iii) 5- or 6-membered
cycloaliphatic and aromatic rings are preferred on the N1 of
the hydrazine to display selective MAO-B and MAO-A
inhibition, respectively [21, 22]. The different aliphatic,
cycloaliphatic, heterocyclic, and bicyclic moieties on the N1
of the hydrazine allowed a better comprehension of the
physicochemical effect on the enzyme–inhibitor interaction.
The above studies clarified some factors responsible for
selectivity against the A and B isoforms, such as the lipophi-
licity of the inhibitor that is important for achieving effect-
ive binding to MAO-B and the presence of electron-rich
aromatic moieties, typical of selective MAO-A inhibitors
[20, 23–27].
Chemistry
The synthetic route to the target compounds 3a–3i are
presented in Scheme 1. 2-(Benzothiazol-2-ylthio)-1-phenyle-
than-1-one (1) was obtained with reaction between 2-
mercaptobenzothiazole and 2-bromo-1-phenylethan-1-one.
Compound 1 was converted to its corresponding thiosemi-
carbazone by reacting 1 with thiosemicarbazide. Finally, tar-
get compounds (3a–3i) were prepared via ring closure
reaction using compound 2 and an appropriately substituted
2-bromoacetophenones.
The final compounds were purified, and their structures
were characterized by spectroscopic methods (1H-NMR,
13C-NMR, and LCMSMS). In the 1H NMR spectra, the
methylene protons were recorded between 4.91 and
4.93 ppm. The protons on the aromatic rings were recorded
between 7.28 and 8.34 ppm. The –NH protons of thiazoylhy-
drazine assigned as a singlet at 12.30–12.37 ppm.
In the 13C-NMR spectra, the signals for aromatic and ali-
phatic regions were seen at estimated areas. The aliphatic
carbons were recorded between 27.74 and 27.84 ppm. The
aromatic carbons were recorded between 105.21 and
172.45 ppm. The second position of the thiazole ring with
the highest ppm gave
a peak between 169.01 and
174.67 ppm. The carbon at the second position of the benzo-
thiazole ring were recorded between 160.89 and 165.18 ppm.
The mass spectra (ESI-MS) of the compounds [M þ 1] peaks
were in an agreement with their calculated molecu-
lar formula.
MAO-A and MAO-B inhibition assay
The synthesized compounds were evaluated for their
hMAO-A and hMAO-B inhibitory activities. In addition,
selegiline and moclobemide were evaluated as reference
compounds. The results, expressed as % inhibition and IC50
values are summarized in supporting information Tables S1
and S2. In the first step, the synthesized compounds were
prepared at concentrations of 10ꢀ3 to 10ꢀ4 M and inhibition
values of MAO A and MAO B were calculated. The com-
pounds showing >50% inhibition were selected for the
second stage according to the first step results. In this
second step, inhibition values and IC50 values of the selected
compounds at concentrations of 10ꢀ5 to 10ꢀ9 M were calcu-
lated. Considering supporting information Table S2, only
compounds 3b and 3i passed the second step hMAO-A
enzyme inhibition assay.
In accordance with the above information previously, we
Generally, the compounds showed higher activity against
designed and synthesized novel thiazolylhydrazone deriva- hMAO-A than hMAO-B. In particular, compounds 3b and
tives with selective MAO-A inhibitory potency for further 3i have a significant activity value against hMAO-A.

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
3
S
C
O
Br
N
S
S
N
H2NHN
NH2
K
2CO3
SH
S
O
Δ
Acetone/
Δ
Buthanol/
(1)
S
NH2
O
HN
Br
N
S
S
R2
R1
N
(2)
Ethanol
Δ
S
S
N
R1
N
HN
N
R2
S
(3a-3j)
Compounds
R1
-H
-H
-H
-H
-H
-H
-H
-F
R2
-H
-NO2
-CN
-Cl
-Br
-CF3
-Phenyl
-F
-Cl
3a
3b
3c
3d
3e
3f
3g
3h
3i
-Cl
Scheme 1. Pathway for the synthesis of target compounds (3a–3i).
Compounds 3b and 3i showed efficient inhibition against that the chlorine substituent placed in position
hMAO-A with IC50 values of 0.095 0.004 and increases activity.
2
0.141 0.006 lM, respectively. Compared to the reference
The N1 of hydrazine moiety is another significant section
drug moclobemide, it is clear that they show significant of the compounds for an intrinsic enzyme inhibition.
activity. These findings revealed that compounds 3b and 3i According to literature, N1 of the hydrazine group has steric
have significant potency to inhibit hMAO-A compared to and electronic influences on enzyme–inhibitor interaction
reference agent moclobemide. On the other hand, none of [20, 21]. And as we mentioned in our previous study [28],
the compounds could show the same potency against the presence of an aromatic structure in this region
hMAO-B compared to reference agent selegeline. It was increases the selectivity on MAO-A enzyme. From this
determined that the synthesized compounds have selective knowledge in this study, we incorporated 4-(3- or 4-methyl-
inhibition potency against hMAO-A.
piperidin-1-yl)benzylidene fragment to N1 of hydrazine. We
In terms of SARs, considering the structural properties of added a benzothiazole ring to this region, which we have
the phenyl group of thiazole in C4; the 4-nitro and 2,4- previously seen as a MAO enzyme inhibitor [29]. Our aim
dichloro substituents of the phenyl group appear to be most was to increase the activity with a benzothiazole ring on the
active derivatives in the series. The absence of activity in the thiazolylhydrazine structure. However, according to the
compound 3d bearing the 4-chlorine substituent suggests activity results, we obtained less active derivatives than our

4
G. TURAN ET AL.
previous studies. This suggests that the steric hindrance
from the aromatic ring reduces the activity value.
Experimental
Chemistry
All chemicals used in the syntheses were purchased either
from Merck Chemicals (Merck KGaA, Darmstadt, Germany)
or Sigma-Aldrich Chemicals (Sigma-Aldrich Corp., St.
Enzyme kinetic studies
The mechanism of hMAO-A inhibition was examined by
enzyme kinetic studies. Lineweaver–Burk graphs were used Louis, MO, USA). The IR spectra of the compounds were
to assessment the type of inhibition. Data were analyzed by recorded using an IRAffinity-1S Fourier transform IR
recording substrate–velocity curves in the various concentra- (FTIR) spectrometer (Shimadzu, Tokyo, Japan). 1H NMR
tions (IC50/2, IC50 and 2 ꢁ IC50) of the most active com- and 13C NMR spectra were recorded by a Bruker 300 MHz
pound, 3b. The velocity measurements were performed by and 75 MHz digital FT-NMR spectrometer (Bruker
using different substrate concentrations (20–0.625 mM). The Bioscience, Billerica, MA) in DMSO-d6, respectively. In the
Ki (intercept on the x-axis) value of compound 3b was
determined from the secondary plot of the 1/V versus vary-
ing concentrations. The graphical analysis of inhibition type
for compound 3b is displayed in supporting information
Figure S39. The Lineweaver–Burk graphics present the
inhibition type as a mixed-type, competitive, uncompetitive,
or noncompetitive. In the mix-typed inhibition, the control
and inhibitor lines cross neither x- nor y-axis at the same
point. Competitive inhibitors possess the same intercept on
y-axis, but there are diverse slopes and intercepts on x-axis
between the two data sets, as seen in supporting information
Figure S37. There are no crosses between the lines in an
uncompetitive-type inhibition. Noncompetitive inhibition
has plots with the same intercept on the x-axis, but there
are different slopes and intercepts on the y-axis. Therefore,
this pattern indicates that the compound 3b is a competitive
inhibitor, namely, have similar inhibition features with the
substrate. The Ki value for compound 3b was calculated as
0.019 mM, for the inhibition of hMAO.
NMR spectra splitting patterns were designated as follows: s:
singlet; d: doublet; t: triplet; m: multiplet. Coupling con-
stants (J) were reported as Hertz. Melting points of the
obtained compounds were measured by MP90 digital melt-
ing point apparatus (Mettler Toledo, OH) and were pre-
sented as uncorrected. LC-MS-MS studies were performed
on
a
Schimadzu, 8040 LCMSMS spectrophotometer
(Shimadzu, Tokyo, Japan). The purities of compounds were
checked by TLC on silica gel 60 F254 (Merck KGaA,
Darmstadt, Germany). Elemental analyses were also per-
formed on a Leco TruSpec Micro CHN/CHNS elemental
analyzer (Leco, St. Joseph, MI). The Supplemental Materials
1
contains sample H and 13C NMR and IR spectra for prod-
ucts 3 (supporting information Figures S1–S36).
Materials and methods
Synthesis of 2-(benzothiazol-2-ylthio)-1-phenylethan-1-
one (1)
To a stirred solution of 2-mercaptobenzothiazole (1.66 g,
0.01 mol) in acetone (20 mL) was added 2-bromo-1-phenyle-
than-1-one (1.97 g, 0.01 mol), followed by potassium carbon-
ate. The resulting mixture was heated to reflux at 70 ꢂC.
After completion of reaction, acetone was evaporated by
means of reduced pressure. The precipitated product was
washed with water, dried, and recrystallized from ethanol.
Conclusion
To develop biologically active derivatives, the presence of a
pharmacophore group in the compounds whose synthesis is
planned is a basic approach in pharmaceutical chemistry.
Based on this approach, benzothiazole and thiazolylhydra-
zine rings in which we reported MAO inhibitor activities in
previous studies were combined at the same molecule. MAO
inhibitor activities and kinetic studies of the obtained com-
pounds were performed. According to the results of the
in vitro MAO enzyme inhibition assay, it was found that the
compounds 3b and 3i were not effective against MAO-B
enzyme while they were found to be the most active deriva-
tives in the series against the MAO-A enzyme. Compound
3i carries a 2,4-dichlorobenzene ring. This information may
suggest that the chlorine substituent contributes to the activ-
ity through its halogen bond. However, compound 3d with
a chlorine substituent at the 4-position does not show the
same level of activity. Therefore, it can be considered that a
chlorine substituent at the 2-position significantly contrib-
utes to activity. The other active derivative (3b) contains a
nitro substituent. The nitro group has been shown to
Synthesis of 2-(2-(benzothiazol-2-ylthio)-1-
phenylethylidene)hydrazine-1-carbothioamide (2)
A mixture of 2-(benzothiazol-2-ylthio)-1-phenylethan-1-one
(2) (2.76 g, 0.0097 mol), thiosemicarbazide (0.88 g,
0.0097 mol), and catalytic quantity of acetic acid
(CH3COOH) was refluxed in butanol (50 mL) for 24 h. After
completion of the reaction, the mixture was cooled, precipi-
tated product was filtered, washed with deionized water,
dried, and recrystallized from ethanol.
General procedure for the synthesis of target
compounds (3a-3j)
increase activity on MAO enzyme in our previous studies. To a stirred solution of 2-(2-(benzothiazol-2-ylthio)-1-phe-
With the results of the study, compounds derived from 3b nylethylidene)hydrazine-1-carbothioamide
(2) (0.297 g,
and 3i can be found to be effective drug candidates for 0.00083 mol) in EtOH (20 mL) was added appropriate 2-
depression and other neurological diseases. bromo-1-(2,4-substitutedphenyl)ethan-1-one derivatives

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
5
(0.00083 mol), refluxed for 10 h. The precipitated product 139.21 (Ar–C), 144.24 (Ar–C), 149.52 (Ar–C), 152.19
was filtered, washed with cold-ethanol, dried, and recrystal-
lized from ethanol.
(Ar–C), 166.76 (Ar–C), 170.01 (Ar–C). ESI-MS
[M þ H]þ: 484.
2-((2-Phenyl-2-(2-(4-phenylthiazol-2-
yl)hydrazineylidene)ethyl)thio)benzothiazole (3a)
2-((2-(2-(4-(4-chlorophenyl)thiazol-2-yl)
hydrazineylidene)-2-phenylethyl)thio)benzothiazole (3d)
Powder, pale yellow. Yield: 83%, M.P.¼174.2–175.5 ꢂC, FTIR
Powder, green. Yield: 78%, M.P.¼180.1–182.9 ꢂC, FTIR
(ATR, cmꢀ1): 2953 (C–H), 1577 (C[dbond]N), 1141 (C–N),
835. 1H-NMR (300 MHz, DMSO-d6, ppm): 4.91 (2 H, s,
–CH2–), 7.35–7.54 (8 H, m, Ar–H), 7.85 (2 H, d, J ¼ 6.5 Hz,
Ar–H), 7.95 (2 H, d, J ¼ 8.3 Hz, Ar–H), 8.02 (1 H, d,
J ¼ 7.5 Hz, Ar–H), 8.16 (1 H, d, J ¼ 7.9 Hz, Ar–H), 12.32
(1 H, s, –NH). 13C-NMR (75 MHz, DMSO-d6, ppm):
d ¼ 27.76 (–CH2–), 106.02 (Ar–C), 112.89 (Ar–C), 121.68
(Ar–C), 122.53 (Ar–C), 124.69 (Ar–C), 125.33 (Ar–C),
126.51 (Ar–C), 126.93 (Ar–C), 127.65 (Ar–C), 129.05
(Ar–C), 129.23 (Ar–C), 129.59 (Ar–C), 132.56 (Ar–C),
(ATR, cmꢀ1): 2916 (C–H), 1585 (C[dbond]N), 1132 (C–N),
1
746, 707. H-NMR (300 MHz, DMSO-d6, ppm) : 4.93 (2 H,
s, –CH2–), 7.32-7.51 (10 H, m, Ar–H), 7.86 (2 H, d,
J ¼ 6.8 Hz, Ar–H), 7.94 (1 H, d, J ¼ 7.1 Hz, Ar–H), 8.04 (1 H,
d, J ¼ 7.4 Hz, Ar–H), 8.18 (1 H, d, J ¼ 7.4 Hz, Ar–H), 12.31
(1 H, s, –NH). 13C-NMR (75 MHz, DMSO-d6, ppm):
d ¼ 27.79 (–CH2–), 105.28 (Ar–C), 112.89 (Ar–C), 121.70
(Ar–C), 122.53 (Ar–C), 125.31 (Ar–C), 125.95 (Ar–C),
126.49 (Ar–C), 126.85 (Ar–C), 127.64 (Ar–C), 128.18
(Ar–C), 129.05 (Ar–C), 129.20 (Ar–C), 129.54 (Ar–C),
135.38 (Ar–C), 136.10 (Ar–C), 152.29 (Ar–C), 153.55
(Ar–C), 160.89 (Ar–C), 170.90 (Ar–C). ESI-MS [M þ H]þ: 133.98 (Ar–C), 135.36 (Ar–C), 136.03 (Ar–C), 148.18
459. HRMS (m/z): [M þ Na]þ calcd for C24H18N4S3:
(Ar–C), 152.19 (Ar–C), 166.86 (Ar–C), 171.98 (Ar–C). ESI-
MS [M þ H]þ: 493.
481.0586; found: 481.0504.
2-((2-(2-(4-(4-Nitrophenyl)thiazol-2-yl)hydrazineylidene)-
2-((2-(2-(4-(4-Bromophenyl)thiazol-2-yl)
2-phenylethyl)thio)benzothiazole (3b)
hydrazineylidene)-2-phenylethyl)thio) benzothiazole (3e)
Powder, yellow. Yield: 85%, M.P.¼216.2–218.6 ꢂC, FTIR
852. 1H-NMR (300 MHz, DMSO-d6, ppm): 4.92 (2 H, s,
Powder, green. Yield: 85%, M.P.¼190.0–192.3 ꢂC, FTIR
(ATR, cmꢀ1): 2953 (C–H), 1577 (C[dbond]N), 1141 (C–N),
(ATR, cmꢀ1): 2949 (C–H), 1583 (C[dbond]N), 1141 (C–N),
823. 1H-NMR (300 MHz, DMSO-d6, ppm): 4.91 (2 H, s,
–CH2–), 7.38-7.52 (6 H, m, Ar–H), 7.82-7.84 (2 H, m,
–CH2–), 7.35–7.53 (7 H, m, Ar–H), 7.65 (2 H, d, J ¼ 8.6 Hz,
Ar–H), 7.85 (2 H, d, J ¼ 8.3 Hz, Ar–H), 7.88 (1 H, d,
J ¼ 8.4 Hz, Ar–H), 8.02 (1 H, d, J ¼ 7.4 Hz, Ar–H), 8.16 (1 H,
d, J ¼ 7.9 Hz, Ar–H), 12.32 (1 H, s, –NH). 13C-NMR
(75 MHz, DMSO-d6, ppm): d ¼ 27.74 (–CH2–), 106.18
(Ar–C), 121.16 (Ar–C), 121.67 (Ar–C), 122.27 (Ar–C),
122.53 (Ar–C), 125.34 (Ar–C), 126.51 (Ar–C), 126.93
(Ar–C), 127.96 (Ar–C), 129.05 (Ar–C), 129.59 (Ar–C),
Ar–H), 8.03 (1 H, d, J ¼ 7.7 Hz, Ar–H), 8.13 (1 H, d,
J ¼ 8.2 Hz, Ar–H), 8.19 (2 H, d, J ¼ 8.7 Hz, Ar–H), 8.34 (2 H,
d, J ¼ 8.9 Hz, Ar–H), 12.37 (1 H, s, –NH). 13C-NMR
(75 MHz, DMSO-d6, ppm): d ¼ 27.83 (–CH2–), 104.67
(Ar–C), 110.23 (Ar–C), 121.65 (Ar–C), 122.26 (Ar–C),
122.53 (Ar–C), 124.72 (Ar–C), 125.35 (Ar–C), 126.58
(Ar–C), 126.78 (Ar–C), 126.99 (Ar–C), 127.62 (Ar–C),
129.06 (Ar–C), 129.66 (Ar–C), 136.04 (Ar–C), 144.29
(Ar–C), 149.24 (Ar–C), 152.44 (Ar–C), 162.40 (Ar–C), 132.13 (Ar–C), 135.36 (Ar–C), 136.02 (Ar–C), 143.93
174.67 (Ar–C). ESI-MS [M þ H]þ: 504. HRMS (m/z):
(Ar–C), 150.87 (Ar–C), 152.22 (Ar–C), 166.78 (Ar–C),
[M þ Na]þ
calcd
found: 526.0345.
for
C24H17N5O2S3:
526.0437;
169.81 (Ar–C). ESI-MS [M þ H]þ: 536.
2-((2-Phenyl-2-(2-(4-(4-(trifluoromethyl)phenyl)thiazol-2-
yl)hydrazineylidene)ethyl)thio)benzothiazole (3f)
4-(2-(2-(2-(Benzothiazol-2-ylthio)-1-phenylethylidene)
hydrazineyl)thiazol-4-yl)benzonitrile (3c)
Powder, cream. Yield: 79%, M.P.¼201.2–202.9 ꢂC, FTIR (ATR,
Powder, yellowish cream. Yield: 81%, M.P.¼205.1–207.1 ꢂC,
FTIR (ATR, cmꢀ1): 2929 (C–H), 2218 (C[tbond]N), 1575
(C[dbond]N), 1163 (C–N), 835. 1H-NMR (300 MHz,
DMSO-d6, ppm): 4.92 (2 H, s, –CH2–), 7.35–7.53 (6 H, m,
Ar–H), 7.75 (1 H, s, Ar–H), 7.85 (2 H, d, J ¼ 6.5 Hz, Ar–H),
7.93 (2 H, d, J ¼ 8.5 Hz, Ar–H), 8.03 (1 H, d, J ¼ 7.3 Hz,
Ar–H), 8.12 (2 H, d, J ¼ 8.6 Hz, Ar–H), 12.37 (1 H, s, –NH).
13C-NMR (75 MHz, DMSO-d6, ppm): d ¼ 27.76 (–CH2–),
109.16 (Ar–C), 110.17 (Ar–C), 119.47 (Ar–C), 121.64
(Ar–C), 122.56 (Ar–C), 125.35 (Ar–C), 126.55 (Ar–C),
126.57 (Ar–C), 126.94 (Ar–C), 129.06 (Ar–C), 129.66
1
cmꢀ1): 2943 (C–H), 1585 (C[dbond]N), 1141 (C–N), 850. H-
NMR (300 MHz, DMSO-d6, ppm): 4.92 (2 H, s, –CH2–),
7.35–7.54 (6 H, m, Ar–H), 7.68 (1 H, s, Ar–H), 7.82–7.87 (4 H,
m, Ar–H), 8.03 (1 H, d, J ¼ 7.4 Hz, Ar–H), 8.15 (1 H, d,
J ¼ 8.1 Hz, Ar–H), 12.36 (1H, s, –NH). 13C-NMR (75 MHz,
DMSO-d6, ppm): d ¼ 27.84 (–CH2–), 108.11 (Ar–C), 121.65
(Ar–C), 122.27 (Ar–C), 122.54 (Ar–C), 125.34 (Ar–C), 126.24
(Ar–C), 126.48 (Ar–C), 126.54 (Ar–C), 126.96 (Ar–C), 129.06
(Ar–C), 129.63 (Ar–C), 135.37 (Ar–C), 136.00 (Ar–C), 138.70
(Ar–C), 144.10 (Ar–C), 149.69 (Ar–C), 152.22 (Ar–C), 166.65
(Ar–C), 133.31 (Ar–C), 135.37 (Ar–C), 135.96 (Ar–C), (Ar–C), 169.99 (Ar–C). ESI-MS [Mþ H]þ: 527.

6
G. TURAN ET AL.
2-((2-(2-(4-([1,1’-biphenyl]-4-yl)thiazol-2-yl)
hydrazineylidene)-2-phenylethyl)thio)benzothiazole (3g)
studies [28–31]. All pipetting procedures in the enzyme
inhibition assay were carried out using a robotic system,
Biotek Precision XS (Winooski, VT). Selegiline and moclo-
bemide were used as reference drugs. The IC50 values were
calculated from a dose–response curve gained by plotting
the percentage inhibition versus the log concentration with
the use of GraphPad PRISM software (version 5.0,
GraphPad Software Inc., La Jolla, CA). The results are
shown as the mean standard deviation (SD).
Powder, light brown. Yield: 80%, M.P.¼172.2–174.1 ꢂC, FTIR
(ATR, cmꢀ1): 2918 (C–H), 1577 (C[dbond]N), 1136 (C–N), 844.
1H-NMR (300 MHz, DMSO-d6, ppm): 4.93 (2 H, s, –CH2–),
7.36–7.55 (10 H, m, Ar–H), 7.75 (2 H, d, J¼ 7.3 Hz, Ar–H), 7.78
(2 H, d, J¼ 8.5 Hz, Ar–H), 7.86 (2 H, d, J¼ 6.7 Hz, Ar–H), 8.03
(2 H, d, J¼ 8.1 Hz, Ar–H), 8.21 (1 H, d, J¼ 7.1 Hz, Ar–H), 12.36
(1 H, s, –NH). 13C-NMR (75 MHz, DMSO-d6, ppm): d ¼ 27.80
(–CH2–), 117.66 (Ar–C), 121.73 (Ar–C), 122.54 (Ar–C), 125.33
(Ar–C), 126.51 (Ar–C), 126.93 (Ar–C), 126.99 (Ar–C), 127.42 Kinetic studies of enzyme inhibition
(Ar–C), 128.01 (Ar–C), 129.06 (Ar–C), 129.45 (Ar–C), 129.56
In order to determine the type of inhibition on hMAO-A,
(Ar–C), 135.37 (Ar–C), 136.09 (Ar–C), 139.66 (Ar–C), 140.05
(Ar–C), 143.95 (Ar–C), 147.90 (Ar–C), 152.39 (Ar–C), 166.86
(Ar–C), 172.45 (Ar–C). ESI-MS [M þ H]þ: 535.
enzyme kinetic studies were carried out for compound 3b.
The enzyme kinetic assay was performed by means of
Ellman’s method, in keeping with the previous studies
reported by our research group [28–31].
2-((2-(2-(4-(2,4-difluorophenyl)thiazol-2-yl)
hydrazineylidene)-2-phenylethyl)thio)benzothiazole (3h)
Funding
Powder, cream. Yield: 77%, M.P.¼187.4–189.9 ꢂC, FTIR
This study was carried out with the support of Anadolu
University BAP Project No: 1805S190.
(ATR, cmꢀ1): 2920 (C–H), 1583 (C[dbond]N), 1136 (C–N),
1
754, 692. H-NMR (300 MHz, DMSO-d6, ppm): 4.92 (2 H, s,
–CH2–), 7.28–7.52 (9 H, m, Ar–H), 7.85 (2 H, d, J ¼ 7.7 Hz,
Ar–H), 8.03 (1 H, d, J ¼ 8.1 Hz, Ar–H), 8.13 (1 H, d,
J ¼ 8.0 Hz, Ar–H), 12.31 (1 H, s, -NH). 13C-NMR (75 MHz,
DMSO-d6, ppm): d ¼ 27.77 (–CH2–), 105.21 (Ar–C), 111.17
(Ar–C), 121.65 (Ar–C), 122.28 (Ar–C), 122.59 (Ar–C),
125.37 (Ar–C), 126.62 (Ar–C), 126.98 (Ar–C), 129.04
(Ar–C), 129.62 (Ar–C), 130.61 (Ar–C), 136.07 (Ar–C),
137.46 (Ar–C), 140.82 (Ar–C), 144.13 (Ar–C), 149.55
(Ar–C), 152.82 (Ar–C), 155.97 (Ar–C), 159.35 (Ar–C),
166.54 (Ar–C), 169.25 (Ar–C). ESI-MS [M þ H]þ: 495.
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