Synthesis of new hydrazone derivatives and evaluation of their monoamine oxidase inhibitory activity

Article abstract of DOI:10.1016/j.bioorg.2021.105038

A novel series of hydrazone derivatives were designed and synthesized. Their structures were characterized by IR, ¹H NMR, ¹³C NMR and HR-MS spectroscopic methods. The newly synthesized compounds were evaluated for their inhibitory ac

Full text of DOI:10.1016/j.bioorg.2021.105038

Bioorganic Chemistry 114 (2021) 105038
Contents lists available at ScienceDirect
Bioorganic Chemistry
journal homepage: www.elsevier.com/locate/bioorg
Synthesis of new hydrazone derivatives and evaluation of their monoamine
oxidase inhibitory activity
a
b
,
c
b,
Fatih Tok , Begüm Nurpelin Saglık , Yusuf Ozkay c, Sinem Ilgınd, Zafer Asım Kaplancıklıb,
¨
˘
a,*
˘
˘
Bedia Koçyigit-Kaymakçıoglu
a Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Marmara University, Istanbul, Turkey
b Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Anadolu University, Eskis¸ehir, Turkey
c Doping and Narcotic Compounds Analysis Laboratory, Faculty of Pharmacy, Anadolu University, Eskis¸ehir, Turkey
d Department of Pharmaceutical Toxicology, Faculty of Pharmacy, Anadolu University, Eskis¸ehir, Turkey
A R T I C L E I N F O
A B S T R A C T
Keywords:
Hydrazone
Urea
A novel series of hydrazone derivatives were designed and synthesized. Their structures were characterized by
IR, 1H NMR, 13C NMR and HR-MS spectroscopic methods. The newly synthesized compounds were evaluated for
their inhibitory activity against monoamine oxidase enzymes (MAO-A and MAO-B). Compounds 2a, 2k, 4a and
4i showed significant inhibitory activity against MAO-A, with IC50 value in the range of 0.084–0.207 µM
compared to reference drug moclobemide (IC50 value = 6.061 µM). These compounds (2a, 2k, 4a and 4i) were
exposed to cytotoxicity tests to establish their preliminary toxicological profiles and were found to be non-
cytotoxic. Moreover, the most effective compound 4i was evaluated using enzyme kinetics and docking
studies to elucidate the plausible mechanisms of inhibition of MAO-A. According to enzyme kinetic studies,
compound 4i was a reversible and competitive inhibitor with similar inhibition features as the substrates. Also, it
was seen that this compound was settled down very properly at the active site of MAO-A enzyme by doing
important interactions owing to the docking studies. Finally, ADME predictions were applied to estimate
pharmacokinetic profiles of synthesized compounds. According to calculated ADME predictions, all parameters
of the compounds were within the standard ranges in terms of “Rule of Five” and “Rule of Three” and it was
detected that the synthesized compounds (2a-4i) have good and promising pharmacokinetic profiles.
MAO
Docking
ADME
1. Introduction
antidepressant drugs but non-selective or irreversible MAO inhibitors
caused serious side-effects such as tachycardia, hepatotoxicity, drug and
Monoamine oxidase catalyzes the oxidative deamination of biogenic
and xenobiotic amines and it has two isoforms MAO-A and MAO-B [1].
Differences between MAO-A and MAO-B include aminoacid sequences,
sensitivity to inhibitors, substrate specificity and intensity of tissue [2].
MAO-A is generally indicated in catecholaminergic neurons of the cortex
while MAO-B is found in serotonergic neurons, in the brain [3]. MAO-A
inhibitors are mostly used in the treatment of depression, whereas MAO-
B inhibitors are mainly used in the treatment of Parkinson’s and Alz-
heimer’s. MAO-A inhibitors also are useful in the treatment of neuro-
psychiatric disorders, including anxiety, autism and attention deficit
hyperactivity disorder [4]. MAO inhibitors are also identified as neu-
roprotective agents because they can decrease the amount of hydrogen
peroxide and aldehyde species that lead to neuronal cell damage [5].
The first-generation irreversible MAO inhibitors were used as
food interactions such as serotonin syndrome, tyramine-induced hy-
pertensive crisis (cheese-effect) (tyramine reaction) [6–8]. However,
MAO inhibitors were proposed as second choice agents after serotonin
reuptake inhibitors by the American Psychiatric Association [9].
Although current MAO inhibitors are known to be useful for neurode-
generative disorders such as Alzheimer’s, Parkinson’s diseases, or
Depression, these drugs are not enough to fight against these diseases
and many of them have only symptomatic effects [10]. Therefore,
considering all these features, involvement of deregulated metabolism
of monoamines in neurodegenerative and neuropsychiatric diseases
[11], the design and development of more effective and more selective
drug candidates are needed for the discovery of useful therapeutic
agents.
Hydrazones consist of a reaction between a carbonyl compound
* Corresponding author at: Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Marmara University, 34854 4/A Istanbul, Turkey.
˘
˘
E-mail address: bkaymakcioglu@marmara.edu.tr (B. Koçyigit-Kaymakçıoglu).
https://doi.org/10.1016/j.bioorg.2021.105038
Received 6 April 2021; Received in revised form 10 May 2021; Accepted 28 May 2021
Available online 1 June 2021
0045-2068/© 2021 Elsevier Inc. All rights reserved.

F. Tok et al.
Bioorganic Chemistry 114 (2021) 105038
(aldehyde or ketone) and a hydrazine molecule by the elimination of
aliphatic protons were detected in the estimated regions. In the 13C NMR
–
–
– – –
water [12]. Hydrazone derivatives, containing the
C
N
NH
spectra of the compounds, C O carbons of amide or urea moieties were
–
–
–
group, plays an important role in discovering new drug molecules [13].
They exhibit a broad spectrum of biological activities, such as antimi-
crobial, antidepressant, anticonvulsant, anti-inflammatory, anticancer.
Hydrazones bear two different connected nitrogen atoms and these
structural cores are generally responsible for the physical and chemical
properties [14]. The carbon atom of hydrazone shows both electrophilic
and nucleophilic character [15]. Therefore hydrazones are used widely
in the design of new molecules having a variety of activities.
recorded at 162.47–166.28 ppm. The C N carbons of the hydrazone
–
group gave a signal at 153.08–154.61 ppm. In the HR-MS spectra of the
compounds, all masses were in accordance with the expected M + H and
Mꢀ H values.
2.2. In vitro MAO-A and MAO-B inhibition
The in vitro fluorometric method declared previously by our research
group [22–26] was used to evaluate the inhibition potency of the syn-
thesized compounds on MAO isoforms. Table 1 represents the first step
of enzyme activity assay; while, Fig. 2 points out the second step. In the
second step, the reference inhibitors and selected compounds that
showed more than 50% inhibitory activity at 10-4 M concentration were
prepared in their further concentrations by serial dilutions (ranging
from 10-5 M to 10-9 M). Therefore, the half maximal inhibitory con-
centration (IC50) values of the selected compounds and reference in-
hibitors could be calculated and these results are given in Fig. 2.
In summary, it was understood from Table 1 that some compounds in
the series displayed remarkable inhibition potency at 10-3 M concen-
tration; however, none of them showed significant inhibitory activity at
10-4 M concentration on MAO-B enzyme. Generally it was claimed that
all synthesized compounds showed selective MAO-A enzyme inhibitory
activity. It was observed that compounds 2a, 2k, 4a and 4i performed
seriously effective inhibition profile at 10-4 M concentration against
MAO-A enzyme and thus, these compounds were included in the second
stage of enzyme activity assay. Compound 4i was found to be the most
effective agent in the series with the IC50 value of 0.084 ± 0.003 µM.
Furthermore, it was noteworthy that this compound performed an in-
hibition profile 72 times more effective than reference drug moclobe-
mide (IC50 value = 6.061 ± 0.262 µM). Besides, compounds 2a, 2k and
4a were identified as the other most active derivatives in the series with
the IC50 values of 0.207 ± 0.010 µM, 0.187 ± 0.008 µM and 0.138 ±
0.005 µM, respectively.
The identification of the crystal structures of the two isoforms of
human MAO and the selective interactions between the enzymes and
their ligands allows the determination of the pharmacophoric groups
required for the rational design of new inhibitors. It is reported that the
substrates and inhibitors of MAOs usually bear imino or amino groups
that can interact with the active site of the enzyme easily [16,17]. In
addition to hydrazone derivatives, urea and amide moiety have long
been known for their important monoamine oxidase inhibitory activity
[18–21]. In this study, we designed and synthesized a new hydrazone
bearing urea/amide moiety. We investigated their inhibitory activity
against MAO-A and MAO-B enzymes. Some electron-withdrawing and
electron donor groups on the aromatic ring in this synthesis were used to
find out the effects of the substituents on monoamine oxidase inhibitory
activity.
2. Results and discussion
2.1. Chemistry
The general pathway of synthesis was given in Fig. 1. Firstly, 4-
aminoacetophenone is treated with different isocyanate in dichloro-
methane and different benzoyl chloride in chloroform to get the corre-
sponding urea and amide derivatives, respectively. Then condensation
reaction takes place between 2,4-dinitrophenyl hydrazine and starting
material on the ketone group in methanol to get target molecules.
All new hydrazone derivatives were confirmed by IR, 1H NMR, 13
C
NMR and HR-MS spectroscopic methods. In the 1H NMR spectra of
2.3. Enzyme kinetics
ꢀ 1
–
compounds, N H stretching vibrations appeared at 3296–3404 cm
.
The strong sharp absorption bands at 1645–1680 cmꢀ 1 were attributed
Enzyme kinetics studies help to determine the type of inhibition of
the compound on the enzyme and also identify the inhibition as irre-
versible or reversible. The linear Lineweaver-Burk graphs are the most
common method for this. For this purpose, compound 4i was included in
the enzyme kinetic assay to evaluate the inhibition type on MAO-A
enzyme. Enzyme kinetic assay was applied in the same way as previ-
ously mentioned [22–26]. The IC50/2, IC50, and 2(IC50) were used as the
concentrations of compound 4i. The velocity curves of the substrates
–
–
to C O stretching vibrations of amide and urea moieties. Also, char-
acteristic bands at 1602–1649 cmꢀ 1 were assigned to C N stretching
–
–
1
–
vibrations. In the H NMR spectra of the compounds, N H protons
belonging to hydrazone and amide moieties resonated at 11.08–11.13
–
ppm, 10.28–10.98 ppm respectively. However, N H protons belonging
–
to urea moieties appeared with aromatic protons. Protons of the CH3
group were observed at 2.35–2.45 ppm as singlets. Aromatic and other
Fig. 1. The synthesis route of all compounds. Reagents: (i) chloroform, reflux; (ii) methanol, reflux; (iii) dichloromethane, 25 ◦C; (iv) methanol, reflux.
2

F. Tok et al.
Bioorganic Chemistry 114 (2021) 105038
Table 1
% Inhibition of the synthesized compounds and reference agents against MAO-A and MAO-B enzymes at concentrations of 10ꢀ 3 and 10ꢀ 4 M.
Compounds
MAO-A Inhibition %
MAO-A IC50 (µM)
MAO-B Inhibition %
MAO-B IC50 (µM)
Selectivity
Selectivity index (SI)
10-3
M
10-4
M
10-3
M
10-4
M
2a
89.624 1.105
61.917 ± 0.965
76.181 ± 0.995
58.685 ± 0.812
55.106 ± 0.633
57.157 ± 1.057
41.057 ± 0.633
60.834 ± 0.899
74.498 ± 1.265
50.753 ± 0.956
88.302 1.289
93.552 1.240
92.562 ± 1.344
90.823 ± 1.185
87.541 ± 1.005
81.627 ± 0.974
76.715 ± 1.028
93.086 ± 1.066
75.105 ± 1.108
93.581 1.281
94.121 ± 2.760
–
84.104 1.248
33.880 ± 0.748
41.969 ± 0.628
32.606 ± 0.718
47.165 ± 0.475
46.566 ± 0.974
28.273 ± 0.512
42.282 ± 0.716
46.871 ± 0.945
37.704 ± 0.882
80.745 1.475
80.106 1.358
41.187 ± 0.891
47.206 ± 0.852
45.658 ± 0.962
46.493 ± 0.965
40.282 ± 0.887
43.771 ± 0.804
42.794 ± 0.875
87.319 1.059
82.143 ± 2.691
–
0.207 ± 0.010
>100
43.387 ± 0.985
36.935 ± 0.801
43.015 ± 0.628
56.613 ± 0.611
26.515 ± 0.529
47.581 ± 0.997
39.516 ± 0.557
56.935 ± 0.475
58.871 ± 1.052
31.452 ± 0.628
38.076 ± 0.629
56.518 ± 0.978
65.052 ± 1.107
67.297 ± 0.926
71.002 ± 1.125
64.992 ± 0.875
69.412 ± 1.066
77.615 ± 0.997
68.744 ± 1.004
87.361 ± 1.249
–
25.314 ± 0.714
30.806 ± 0.722
28.574 ± 0.525
23.065 ± 0.470
20.147 ± 0.708
27.048 ± 0.816
23.519 ± 0.629
28.288 ± 0.715
32.250 ± 0.729
26.388 ± 0.518
28.537 ± 0.375
20.906 ± 0.880
25.358 ± 0.528
29.547 ± 0.511
41.256 ± 0.627
37.297 ± 0.588
33.625 ± 0.748
31.033 ± 0.622
36.638 ± 0.729
42.218 ± 0.748
–
>1000
>1000
>1000
>100
MAO-A
>4830
2b
MAO-A
>10
2c
>100
MAO-A
>10
2d
>100
–
–
2e
>100
>1000
>1000
>1000
>100
MAO-A
>10
2f
>100
MAO-A
>10
2g
>1000
>100
–
–
2h
–
–
2i
>100
>100
–
–
2j
>100
>1000
>1000
>100
MAO-A
>10
2k
0.187 ± 0.008
0.138 ± 0.005
>100
MAO-A
>5347
4a
MAO-A
>724
4b
>100
–
–
4c
>100
>100
–
–
4d
>100
>100
–
–
4e
>100
>100
–
–
4f
>100
>100
–
–
4 g
>100
>100
–
–
4 h
>100
>100
–
–
4i
0.084 ± 0.003
6.061 ± 0.262
–
>100
MAO-A
MAO-A
MAO-B
>1190
Moclobemide
Selegiline
–
–
–
98.258 ± 1.052
96.107 ± 1.165
0.037 ± 0.001
Fig. 2. IC50 curves and values of 2a, 2k, 4a, 4i and moclobemide against MAO-A.
were reported in the absence and presence of compound 4i. In each case,
in the reversible inhibition [22–26]. As seen in the Lineweaver-Burk plot
of compound 4i (Fig. 3), the lines were intersected on the y-axis, and
their slopes and x-intercepts were different. This observation indicated
that compound 4i was a reversible and competitive inhibitor with
similar inhibition features as the substrates. The Ki value of compound 4i
was calculated as 0.020 µM with the help of a secondary plot.
the initial velocity measurements were collected at various concentra-
tions of substrates (tyramine) varying from 20 μM to 0.625 μM. Thus,
linear Lineweaver-Burk graphs could be formed (Fig. 3-A). The sec-
ondary plot of slope (Km / Vmax) versus varying concentrations (0, IC50
/
2, IC50, and 2(IC50)) (Fig. 3-B) was formed to measure the Ki value of this
compound.
According to Lineweaver-Burk plots, reversible and irreversible in-
hibition type constitute two general categories. Mixed-type, uncom-
petitive, competitive, and noncompetitive inhibition types are included
2.4. Cytotoxicity test
Compounds 2a, 2k, 4a and 4i displayed potent MAO-A inhibition
3

F. Tok et al.
Bioorganic Chemistry 114 (2021) 105038
Fig. 3. (A) Lineweaver–Burk plots for the inhibition of
hMAO A by compound 4i. [S], substrate concentration
(µM); V, reaction velocity (nmol/min/mg protein). In-
hibitor concentrations are shown at the left. Km values
from 2 × IC50 to control; 10.230, 5.667, 3.417 and
(A)
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
-0.02
IC50 / 2 (0.042 μM)
1.015 (μM). Vmax value of the competitive inhibition;
IC50 (0.084 M)
2 x IC50 (0.168 μM)
Control
111.110 ± 2.508 (nmol/min/mg protein). (B) Second-
ary plot for the calculation of the steady-state inhibition
constant (Ki) of compound 4i. Ki was calculated as
0.020 µM.
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
1/[S] μM-1
(B)
0.1
0.08
0.06
0.04
0.02
0
-0.1
-0.05
0
0.05
0.1
0.15
0.2
-0.02
Compound 4i (μM)
profile and were further tested for toxicity using the MTT assay in the
NIH/3T3 cell line; the IC50 values of these compounds are shown in
Table 2. Compounds 2a, 2k, 4a and 4i had the IC50 values of 68.208 ±
1.421 µM, 63.960 ± 2.789 µM, 75.225 ± 2.899 µM and 127.660 ± 4.283
µM, respectively, against NIH/3T3 cells. As seen in Table 2, these values
were very higher than their IC50 values on MAO-A enzyme. Conse-
quently, compounds 2a, 2k, 4a and 4i were found to be non-cytotoxic at
their effective concentrations against MAO-A. This result further in-
creases the importance of the related compounds in terms of medicinal
chemistry.
2.5. Prediction of ADME parameters
The absorption, distribution, metabolism and elimination (ADME)
properties explain the ability of compounds to reach the target protein
and be easily eliminated from the body. The computational approach to
drug design greatly helps to reduce the cost and time of subjecting
various compounds to molecular analyzes. For this purpose, the
¨
Schrodinger QikProp [27] program designed by William L. Jorgensen
was used to predict physically important identifiers and pharmaceuti-
cally relevant properties (ADME) of the synthesized compounds. In
addition to predicting molecular properties, this program provides
ranges to compare the properties of a particular molecule with the
properties of 95% of known drugs [28,29]. The predicted parameters
and their recommended values are presented in Table 3.
The “Rule of Five” by Lipinski and the “Rule of Three” by Jorgensen
were used to analyze the drug-likeness features of the compounds
[30–33]. These rules specify the structural features found in a candidate
compound that can be a pharmaceutical product [30–33]. Table 3
showed that all parameters were within the standard ranges and the
compounds did not cause more than one violation in terms of “Rule of
Five” and “Rule of Three”. As a result, based on the findings of the ADME
Table 2
The IC50 value of the compounds 2a, 2k, 4a and 4i against NIH/3T3 cell line.
Compounds
IC50(µM) NIH/3T3 cell line
IC50(µM) MAO-A enzyme
2a
2k
4a
4i
68.208 ± 1.421
63.960 ± 2.789
75.225 ± 2.899
127.660 ± 4.283
0.207 ± 0.010
0.187 ± 0.008
0.138 ± 0.005
0.084 ± 0.003
4

Table 3
Calculated ADME parameters.
Comp.
MW
RB
DM
MV
DHB
AHB
PSA
logP
logS
PCaco
logBB
PMDCK
PM
CNS
%HOA
VRF
VRT
2a
2b
2c
2d
2e
2f
419.396
437.386
453.841
464.393
487.394
433.423
449.422
465.483
503.394
519.454
488.286
434.41
8
8
8
9
8
8
9
9
9
9
8
8
8
8
9
8
8
9
9
8
16.38
1291.918
1308.03
2
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
6.5
6.5
6.5
7.5
6.5
6.5
7.25
7
150.454
150.462
150.459
199.12
3.269
3.502
3.757
2.577
4.234
3.565
3.316
3.886
4.294
4.703
4.239
2.631
2.863
3.116
1.952
3.592
2.924
2.688
3.251
3.673
ꢀ 6.01
40.282
40.274
40.277
4.14
ꢀ 2.732
ꢀ 2.638
ꢀ 2.61
15.369
27.785
37.912
1.314
4
4
4
5
4
5
5
4
5
4
4
5
4
4
5
4
5
5
4
5
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
74.814
76.178
77.67
0
0
0
1
0
0
1
0
2
1
0
1
1
1
1
2
1
1
1
2
1
1
1
2
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
14.136
14.315
5.223
ꢀ 6.371
ꢀ 6.738
ꢀ 6.275
ꢀ 7.417
ꢀ 6.556
ꢀ 6.144
ꢀ 6.941
ꢀ 7.287
ꢀ 7.866
ꢀ 7.265
ꢀ 5.911
ꢀ 6.269
ꢀ 6.635
ꢀ 6.207
ꢀ 7.31
1336.036
1374.318
1388.746
1350.856
1359.698
1409.287
1397.827
1443.472
1375.545
1309.174
1325.218
1353.246
1391.573
1406.011
1368.111
1376.954
1426.543
1398.746
ꢀ 4.091
ꢀ 2.553
ꢀ 2.799
ꢀ 2.837
ꢀ 2.801
ꢀ 2.6
40.12
10.425
14.326
13.427
12.103
11.407
10.058
17.802
16.907
16.972
17.008
11.544
12.666
14.844
13.639
12.729
18.112
150.453
150.453
158.935
150.453
158.92
40.282
40.282
40.282
40.282
40.282
41.415
52.377
23.474
23.475
23.475
2.413
67.333
15.369
15.369
27.557
67.78
80.464
76.548
62.131
78.426
54.898
70.468
82.534
53.92
2g
2h
2i
6.5
6.5
6.5
6
2j
150.453
147.708
159.752
159.754
159.753
208.418
159.752
159.752
168.233
159.752
159.644
ꢀ 2.56
105.335
88.193
10.103
18.268
24.925
0.864
2k
4a
4b
4c
4d
4e
4f
ꢀ 2.393
ꢀ 2.949
ꢀ 2.857
ꢀ 2.831
ꢀ 4.323
ꢀ 2.778
ꢀ 3.021
ꢀ 3.058
ꢀ 3.027
ꢀ 2.564
452.401
468.855
479.408
502.409
448.437
464.437
480.497
503.301
6
55.279
56.765
32.263
46.59
6
7
6
23.474
23.474
23.474
23.474
29.87
44.264
10.103
10.103
18.115
65.59
6
ꢀ 6.451
ꢀ 6.068
ꢀ 6.851
ꢀ 7.035
55.64
4g
4h
4i
6.75
6.5
6
54.256
57.554
48.94
MW: Molecular weight RB: Number of rotatable bonds (recommended value: 0–15) DM: Computed dipole moment (recommended value: 1–12.5) MV: Total solvent-accessible volume (recommended value: 500–2000)
DHB: Estimated number of hydrogen bond donors (recommended value: 0–6) AHB: Estimated number of hydrogen bond acceptors (recommended value: 2–20) PSA: Van der Waals surface area of polar nitrogen and
oxygen atoms and carbonyl carbon atoms (recommended value: 7–200) logP: Predicted octanol/water partition coefficient (recommended value: ꢀ 2–6.5) logS: Predicted aqueous solubility (recommended value:
ꢀ 6.5–0.5) PCaco: Predicted apparent Caco-2 cell permeability (recommended value: <25 poor, >500 great) logBB: Predicted brain/blood partition coefficient (recommended value: ꢀ 3–1.2) PMDCK: Predicted apparent
MDCK cell permeability (recommended value: <25 poor, >500 great) PM: Number of likely metabolic reactions (recommended value: 1–8) CNS: Predicted central nervous system activity (recommended value: –2
(inactive), +2 (active)) %HOA: Predicted human oral absorption percent (recommended value: >80% is high, <25% is poor) VRF: Number of violations of Lipinski’s rule of five. The rules are: MW < 500, logP < 5, DHB ≤
5, AHB ≤ 10, Positive PSA value. VRT: Number of violations of Jorgensen’s rule of three. The three rules are: logS > -5.7, PCaco > 22 nm/s, PM < 7.

F. Tok et al.
Bioorganic Chemistry 114 (2021) 105038
parameter trials, the synthesized compounds (2a-4i) have good and
promising pharmacokinetic profiles and could be appropriate for clin-
ical usage.
separately with the carbonyl of Gly110. Another hydrogen bond is
observed between the carbonyl of the urea group and the amino of
Val210. The main structural difference of compound 4i from other
compounds in the series is that it carries chlorine atoms at the 2nd and
6th positions of phenyl ring as well as urea group. It is clearly sighted in
Fig. 5 that halogen atom at the 2nd position establishes a halogen bond
with a hydrogen of the amino group of Val210. This additional inter-
action ensures that it binds more strongly to the active site. Furthermore,
all these interactions detected explain why compound 4i exhibits a
stronger inhibition profile than other compounds.
2.6. Molecular docking studies
As mentioned in MAO inhibition assay, compounds 2a, 2k, 4a and,
4i were found as the most active derivatives in the series against the
hMAO-A enzyme. Compound 4i, with an IC50 value of 0.084 ± 0.003
µM, was determined to be the most potent agent among these com-
pounds. Therefore, docking studies were carried out to evaluate its in-
hibition capability as in silico. By using the X-ray crystal structure of
hMAO-A (PDB ID: 2Z5X) [34] docking studies have been performed and
binding modes of compound 4i were assigned. The docking poses of this
compound are presented in Figs. 4–7.
In order to analyze the contribution of van der Waals and electro-
static interactions in binding to the enzyme active site, docking studies
have been detailed by using Glide according to Per-Residue Interaction
panel. Figs. 6 and 7 present van der Waals and electrostatic interactions
of compound 4i. It is seen that this compound has favorable van der
Waals interactions with Tyr69, Leu97, Phe108, Ile180, Ile207, Phe208,
Ser209, Val210, Gln315, Ile325, Ile335, Phe352, Tyr407 and Tyr444,
displayed with pink and red colors as described in the user guide of Glide
[35]. Similarly, promising electrostatic contributions of compound 4i
has been determined with Ala111, Asn181, Ile207, Phe208, Ser209,
Val210, Gln215, Ile335 and Thr336 amino acids.
Compound 4i adequately binds to amino acid residues lining the
cavity and is located very near the FAD cofactor. When analyzed docking
poses of this compound, it is seen that there are all types of interactions
such as π-π, cation-π interactions, the formation of hydrogen bonds.
Compound 4i has nitro groups at the 2nd and 4th positions of the phenyl
ring. Among them, the nitrogen atom in the nitro group at the 4th po-
sition of phenyl is in interaction with para-hydroxyphenyl of Tyr407 by
3. Conclusions
cation-
π interaction. Similarly, the phenyl ring located in the middle of
the structure forms a
π-π interaction with phenyl of Phe208. Also, it is
Medicinal chemists aimed to contribute to the development of new
therapeutic agents that have more efficient, selective, less toxicity and
side effects at the treatment of neurodegenerative disorders. Therefore
understood from docking poses that the urea group is very essential for
polar interactions. As known that the urea group has a carbonyl and two
amino moieties. Each of the amino groups creates hydrogen bonds
Fig. 4. The three-dimensional pose of compound 4i in the active region of hMAO-A (PDB ID: 2Z5X). The important residues in the active site and this compound are
presented by tube model and colored with green and orange, respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to
the web version of this article.)
6

F. Tok et al.
Bioorganic Chemistry 114 (2021) 105038
Fig. 5. The three-dimensional interacting mode of compound 4i in the active region of hMAO-A. The inhibitor and the important residues in the active site of the
enzyme are presented by tube model. The FAD molecule is colored dark blue with ball and stick model. (For interpretation of the references to colour in this figure
legend, the reader is referred to the web version of this article.)
Fig. 6. The van der Waals interaction of compound 4i with active region of hMAO-A. The active ligand has a lot of favourable van der Waals interactions (red and
pink). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 7. The electrostatic interaction of compound 4i with active region of hMAO-A. The residues are colored (blue, red, and pink) according to the distance from
ligand by Per-Residue Interaction panel. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
7

F. Tok et al.
Bioorganic Chemistry 114 (2021) 105038
we synthesized new hydrazone derivatives bearing urea/amide moieties
and evaluated their inhibitory activities on monoamine oxidase enzymes
(MAO-A and MAO-B). Compounds 2a and 4a including a nonsubstituted
phenyl ring and compounds 2k and 4i containing 2,6-dichlorophenyl
ring exhibited excellent activity against MAO-A. The toxicological and
ADME studies ensured the good bioavailability and safety of these
compounds. The docking studies represented the binding modes of
compounds to enzyme active site. These findings probably will have a
good impact on medicinal chemists to synthesize similar compounds in
order to discover new agents against depression.
4.2.5. N-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-4-
fluorobenzamide (2b)
Yield: 77%, M.P. = 252–253 ◦C, FTIR (ATR, cmꢀ 1): 3394, 3308
–
–
–
–
–
– –
C H), 2931 (C H), 1670 (C O), 1649 (C N), 1599,
–
(N H), 3091 (
–
1
–
–
–
–
1585 (C C), 1500 (NO asym), 1327 (NO sym), 831 (
C H). H NMR
–
2
2
–
(300 MHz, DMSO‑d6): δ 2.45 (s, 3H, CH3), 7.36–8.90 (m, 11H, Ar H),
10.47 (s, 1H, CO NH), 11.12 (s, 1H, hydrazone NH). 13C NMR (75
–
–
MHz, DMSO‑d6): δ 13.66, 115.72, 116.01, 117.05, 120.34, 123.53,
127.60, 130.09, 130.59, 130.91, 131.04, 131.59, 132.50, 137.63,
141.27, 144.89, 153.36, 162.99, 166.28. HRMS (m/z): [Mꢀ H]- calcd for
C21H16N5O5F: 436.1063; found: 436.1052.
4. Experimental
4.2.6. N-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-4-
4.1. General information
chlorobenzamide (2c)
ꢀ 1
◦
–
Yield: 85%, M.P. = 264–265 C, FTIR (ATR, cm ): 3315 (N H),
–
–
–
–
– –
3101 ( C H), 2974 (C H), 1656 (C O), 1618 (C N), 1591, 1533
– –
Chemicals and solvents used in the study were purchased from Sigma
Aldrich (St. Louis, MO, USA) and Merck (Darmstadt, Germany). Thin
layer chromatography (TLC) applications performed on silica gel (Kie-
selgel 60, F254) were used for monitoring reactions and chemical pu-
rities of the compounds. Melting points of synthesized compounds were
determined by Schmelzpunktbestimmer SMP II and were uncorrected.
Infrared spectra were recorded on a Shimadzu FTIR 8400 S Spectrom-
eter. 1H NMR and 13C NMR spectra were recorded in deuterated DMSO
using Bruker ACP 200 spectrometer (Bruker Bioscience, Billerica, MA,
USA) at 300 MHz and 75 MHz, respectively. It was used tetramethylsi-
lane (TMS) as an internal standard. High-resolution mass spectrometry
was carried out on an LCMS-IT-TOF system (Shimadzu).
1
–
–
–
–
–
(C C), 1516 (NO asym), 1301 (NO sym), 825 (
C H). H NMR (300
2
2
–
MHz, DMSO‑d6): δ 2.45 (s, 3H, CH3), 7.61–8.89 (m, 11H, Ar H), 10.51
(s, 1H, CO NH), 11.12 (s, 1H, hydrazone NH). 13C NMR (75 MHz,
–
–
DMSO‑d6): δ 13.65, 117.05, 120.37, 123.53, 127.61, 128.98, 130.18,
130.60, 132.59, 133.59, 133.85, 137.07, 137.64, 141.16, 144.88,
153.33, 165.05. HRMS (m/z): [Mꢀ H]- calcd for C21H16N5O5Cl:
452.0767; found: 452.0745.
4.2.7. N-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-4-
nitrobenzamide (2d)
Yield: 76%, M.P. = 213–214 ◦C, FTIR (ATR, cmꢀ 1): 3404, 3296
–
–
–
–
–
– –
C H), 2985 (C H), 1680 (C O), 1602 (C N), 1585,
–
(N H), 3088 (
–
1
–
–
–
–
4.2. Chemistry
1573 (C C), 1516 (NO asym), 1300 (NO sym), 829 ( C H). H NMR
–
2 2
–
(300 MHz, DMSO‑d6): δ 2.41 (s, 3H, CH3), 7.63–8.85 (m, 11H, Ar H),
10.72 (s, 1H, CO NH), 11.08 (s, 1H, hydrazone NH). 13C NMR (75
–
–
4.2.1. The general procedure of amide synthesis
1 mmol 4-aminoacetophenone was dissolved in 10 mL chloroform and
added into the round bottom flask. Then, 1 mmol benzoyl chloride de-
rivatives were added into the flask and the solution was stirred and
heated in a water bath for 8–10 h. After completion of the reaction,
amide derivatives precipitated and they were filtered and recrystallized
from methanol [36].
MHz, DMSO‑d6): δ 13.32, 113.72, 116.82, 120.37, 123.46, 124.03,
127.59, 129.34, 130.46, 132.82, 136.92, 137.62, 140.83, 144.81,
149.66, 151.53, 153.08, 154.61, 164.45. HRMS (m/z): [M + H]+ calcd
for C21H16N6O7: 465.1153; found: 465.1154.
4.2.8. N-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-4-
(trifluoromethyl)benzamide (2e)
ꢀ 1
–
◦
–
Yield: 79%, M.P. = 204–205 C, FTIR (ATR, cm ): 3317 (N H),
4.2.2. The general procedure of urea synthesis
–
–
–
–
– –
3057 ( C H), 2980 (C H), 1656 (C O), 1616 (C N), 1599 (C C),
– – –
1 mmol 4-aminoacetophenone was dissolved in 10 mL dichloro-
methane. To a solution of substituted phenyl isocyanate (1 mmol) in
CH2Cl2 was added to reaction liquid. The mixture was stirred at 25 ◦C for
8 h. After evaporation of the solvent, the precipitated product was
filtered and recrystallized from acetone [37].
1
–
–
–
1519 (NO asym), 1301 (NO sym), 825 (
C H). H NMR (300 MHz,
2
2
–
DMSO‑d6): δ 2.44 (s, 3H, CH3), 7.88–8.88 (m, 11H, Ar H), 10.65 (s, 1H,
CO NH), 11.10 (s, 1H, hydrazone NH). 13C NMR (75 MHz, DMSO‑d6): δ
–
–
13.59, 117.03, 120.39, 122.57, 123.49, 125.87, 125.92, 127.61, 129.14,
130.06, 130.58, 131.7, 132.15, 132.75, 137.64, 138.96, 140.98, 144.86,
153.21, 164.99. HRMS (m/z): [M + H]+ calcd for C22H16N5O5F3:
488.1176; found: 488.1154.
4.2.3. The general procedure of hydrazone synthesis
1 mmol N-(4-acetylphenyl)-4-substitutedbenzamide was treated with 2
mmol o,p-dinitrophenyl hydrazine in 10 mL methanol. The mixture was
stirred and heated with dilute sulphuric acid (0.5 mL) under reflux for
10 h. Finally, the reaction was neutralized with water and the precipi-
tated compound was filtered and recrystallized from methanol [38].
4.2.9. N-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-4-
methylbenzamide (2f)
Yield: 88%, M.P. = 183–184 ◦C, FTIR (ATR, cmꢀ 1): 3363, 3311
–
–
–
–
–
– –
C H), 2928 (C H), 1645 (C O), 1614 (C N), 1593,
–
(N H), 3064 (
–
1
–
–
–
–
4.2.4. N-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)benzamide
1573 (C C), 1516 (NO asym), 1301 (NO sym), 825 ( C H). H NMR
–
2
(2a)
(300 MHz, DMSO‑d6): δ 2.39 (s, 3H, CH3)2, 2.42 (s, 3H, CH3), 7.32–8.85
ꢀ 1
◦
–
–
–
–
Yield: 82%, M.P. = 222–223 C, FTIR (ATR, cm ): 3308 (N H),
(m, 11H, Ar H), 10.34 (s, 1H, CO NH), 11.09 (s, 1H, hydrazone NH).
3095 (
13C NMR (75 MHz, DMSO‑d6): δ 13.65, 21.51, 117.04, 120.28, 123.56,
127.58, 128.24, 129.42, 130.05, 130.60, 131.13, 132.26, 137.61,
141.47, 142.30, 144.88, 153.47, 165.96. HRMS (m/z): [Mꢀ H]- calcd for
–
–
–
–
–
– –
C H), 2989 (C H), 1653 (C O), 1620 (C N), 1597, 1573
–
1
–
–
–
–
(C C), 1506 (NO asym), 1300 (NO sym), 825 (
C H). H NMR (300
–
2
2
–
MHz, DMSO‑d6): δ 2.43 (s, 3H, CH3), 7.54–8.87 (m, 12H, Ar H), 10.44
(s, 1H, CO NH), 11.10 (s, 1H, hydrazone NH). 13C NMR (75 MHz,
C22H19N5O5: 432.1313; found: 432.1293.
–
–
DMSO‑d6): δ 13.58, 117.03, 120.25, 123.50, 127.56, 128.19, 128.89,
130.02, 130.57, 132.22, 132.37, 135.18, 137.60, 141.38, 144.86,
153.29, 166.17. HRMS (m/z): [M + H]+ calcd for C21H17N5O5:
420.1302; found: 420.1303.
4.2.10. N-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-4-
methoxybenzamide (2g)
Yield: 79%, M.P. = 146–147 ◦C, FTIR (ATR, cmꢀ 1): 3365, 3311
–
–
–
–
–
– –
C H), 2933 (C H), 1645 (C O), 1616 (C N), 1593,
–
(N H), 3099 (
–
1
–
–
–
–
1556 (C C), 1516 (NO asym), 1303 (NO sym), 831 (
(300 MHz, DMSO‑d6): δ 2.44 (s, 3H, CH3),23.84 (s, 3H, OCH3), 7.06–8.89
C H). H NMR
–
2
8

F. Tok et al.
Bioorganic Chemistry 114 (2021) 105038
–
–
(m, 11H, Ar H), 10.28 (s, 1H, CO NH), 11.12 (s, 1H, hydrazone NH).
4.2.16. 1-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-3-(4-
–
13C NMR (75 MHz, DMSO‑d6): δ 13.61, 55.94, 114.10, 117.04, 120.53,
127.14, 127.55, 130.04, 130.17, 130.58, 132.15, 137.59, 141.60,
144.88, 153.42, 162.50, 165.49. HRMS (m/z): [Mꢀ H]- calcd for
C22H19N5O6: 448.1263; found: 448.1245.
fluorophenyl)urea (4b)
ꢀ 1
◦
–
Yield: 78%, M.P. = 255–256 C, FTIR (ATR, cm ): 3309 (N H),
–
–
–
–
– –
C H), 2954 (C H), 1645 (C O), 1614 (C N), 1593, 1573
–
3078 (
–
1
–
–
–
–
–
(C C), 1506 (NO asym), 1303 (NO sym), 831 (
C H). H NMR (300
2
2
–
MHz, DMSO‑d6): δ 2.43 (s, 3H, CH3), 7.10–8.96 (m, 13H, Ar H and urea
NH), 11.12 (s, 1H, hydrazone NH). 13C NMR (75 MHz, DMSO‑d6): δ
13.67, 115.52, 115.81, 117.02, 118.40, 120.80, 120.90, 123.41, 127.81,
130.22, 130.43, 131.00, 136.27, 137.77, 142.06, 145.04, 152.92,
153.78, 159.70, 162.47. HRMS (m/z): [Mꢀ H]- calcd for C21H17N6O5F:
451.1172; found: 451.1150.
4.2.11. N-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-4-
(methylthio)benzamide (2h)
ꢀ 1
◦
–
Yield: 68%, M.P. = 166–167 C, FTIR (ATR, cm ): 3309 (N H),
–
–
–
–
–
– –
C H), 2922 (C H), 1645 (C O), 1616 (C N), 1591, 1573
–
3095 (
1
–
–
–
–
(C C), 1512 (NO asym), 1301 (NO sym), 825 (
C H). H NMR (300
–
2
2
MHz, DMSO‑d6): δ 2.45 (s, 3H, CH3), 2.54 (s, 3H, SCH3), 7.38–8.89 (m,
11H, Ar H), 10.39 (s, 1H, CO NH), 11.12 (s, 1H, hydrazone NH). 13C
4.2.17. 1-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-3-(4-
–
–
–
NMR (75 MHz, DMSO‑d6): δ 13.63, 14.52, 117.05, 120.31, 123.54,
125.29, 127.59, 130.07, 130.60, 130.93, 132.33, 137.61, 141.42,
143.89, 144.88, 153.40, 165.51. HRMS (m/z): [Mꢀ H]- calcd for
C22H19N5O5S: 464.1034; found: 464.1046.
chlorophenyl)urea (4c)
ꢀ 1
◦
–
Yield: 75%, M.P. = 275–276 C, FTIR (ATR, cm ): 3311 (N H),
–
–
–
–
– –
C H), 2976 (C H), 1645 (C O), 1616 (C N), 1591, 1575
–
3090 (
–
1
–
–
–
–
(C C), 1506 (NO asym), 1301 (NO sym), 829 (
C H). H NMR (300
–
2
2
–
MHz, DMSO‑d6): δ 2.43 (s, 3H, CH3), 7.32–8.99 (m, 13H, Ar H and urea
NH), 11.11 (s, 1H, hydrazone NH). 13C NMR (75 MHz, DMSO‑d6): δ
13.61, 116.95, 118.23, 120.30, 123.56, 126.02, 127.89, 129.12, 129.99,
130.59, 130.80, 137.52, 138.95, 141.87, 144.88, 152.65, 153.59. HRMS
(m/z): [M + H]+ calcd for C21H17N6O5Cl: 469.1022; found: 469.0993.
4.2.12. N-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-4-
(trifluoromethoxy)benzamide (2i)
ꢀ 1
◦
–
Yield: 75%, M.P. = 197–198 C, FTIR (ATR, cm ): 3309 (N H),
–
–
–
–
–
– –
C H), 2920 (C H), 1651 (C O), 1616 (C N), 1593, 1575
–
3095 (
1
–
–
–
–
(C C), 1516 (NO asym), 1303 (NO sym), 823 (
C H). H NMR (300
–
2
2
–
MHz, DMSO‑d6): δ 2.44 (s, 3H, CH3), 7.53–8.88 (m, 11H, Ar H), 10.54
4.2.18. 1-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-3-(4-
nitrophenyl)urea (4d)
(s, 1H, CO NH), 11.11 (s, 1H, hydrazone NH). 13C NMR (75 MHz,
–
–
DMSO‑d6): δ 13.60, 117.03, 120.30, 121.19, 122.15, 123.50, 127.60,
130.06, 130.62, 132.59, 134.30, 137.63, 141.14, 144.86, 151.01,
153.26, 164.95. HRMS (m/z): [M + H]+ calcd for C22H16N5O6F3:
504.1125; found: 504.1123.
Yield: 80%, M.P. = 215–216 ◦C, FTIR (ATR, cmꢀ 1): 3394, 3308
–
–
–
–
–
– –
C H), 2989 (C H), 1670 (C O), 1619 (C N), 1599,
–
(N H), 3091 (
–
1
–
–
–
–
1585 (C C), 1500 (NO asym), 1327 (NO sym), 831 (
C H). H NMR
–
2
2
–
(300 MHz, DMSO‑d6): δ 2.45 (s, 3H, CH3), 7.58–9.33 (m, 13H, Ar
H
and urea NH), 11.07 (s, 1H, hydrazone NH). HRMS (m/z): [Mꢀ H]- calcd
4.2.13. N-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-4-
for C21H17N7O7: 478.1117; found: 478.1098.
(trifluoromethylthio)benzamide (2j)
ꢀ 1
◦
–
Yield: 74%, M.P. = 208–209 C, FTIR (ATR, cm ): 3317 (N H),
4.2.19. 1-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-3-(4-
(trifluoromethyl)phenyl)urea (4e)
–
–
–
–
–
– –
C H), 2968 (C H), 1645 (C O), 1616 (C N), 1595, 1579
–
3102 (
1
(C C), 1512 (NO asym), 1301 (NO sym), 831 (
C H). H NMR (300
Yield: 75%, M.P. = 238–239 ◦C, FTIR (ATR, cmꢀ 1): 3360, 3306
–
–
–
–
–
2
2
–
–
–
–
–
– – –
(N H), 3101 ( C H), 2926 (C H), 1674 (C O), 1614 (C N), 1587,
– –
MHz, DMSO‑d6): δ 2.45 (s, 3H, CH3), 7.88–8.90 (m, 11H, Ar H), 10.64
(s, 1H, CO NH), 11.12 (s, 1H, hydrazone NH). 13C NMR (75 MHz,
1575 (C C), 1504 (NO asym), 1301 (NO sym), 829 (
C H). H NMR
1
–
–
–
–
–
–
–
2
2
–
DMSO‑d6): δ 13.63, 117.04, 120.35, 123.52, 127.18, 127.64, 130.12,
130.59, 132.74, 136.37, 137.66, 137.88, 141.05, 144.88, 153.28,
165.24. HRMS (m/z): [M + H]+ calcd for C22H16N5O5F3S: 520.0897;
found: 520.0907.
(300 MHz, DMSO‑d6): δ 2.35 (s, 3H, CH3), 7.54–8.99 (m, 13H, Ar H
and urea NH), 11.05 (s, 1H, hydrazone NH). 13C NMR (75 MHz,
DMSO‑d6): δ 13.36, 113.96, 117.00, 118.61, 123.37, 123.49, 124.69,
126.46, 127.81, 128.43, 130.19, 130.41, 131.35, 137.80, 141.61,
143.72, 145.00, 152.56, 153.63. HRMS (m/z): [Mꢀ H]- calcd for
4.2.14. 2,6-Dichloro-N-(4-(1-(2-(2,4-dinitrophenyl)hydrazono)ethyl)
C22H17N6O5F3: 501.1140; found: 501.1125.
phenyl)benzamide (2k)
ꢀ 1
◦
–
Yield: 78%, M.P. = 273–274 C, FTIR (ATR, cm ): 3309 (N H),
4.2.20. 1-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-3-(4-
methylphenyl)urea (4f)
–
–
–
–
–
– –
C H), 2918 (C H), 1645 (C O), 1608 (C N), 1587, 1573
–
3090 (
1
(C C), 1504 (NO asym), 1301 (NO sym), 831 (
C H). H NMR (300
Yield: 78%, M.P. = 201–202 ◦C, FTIR (ATR, cmꢀ 1): 3311, 3308
–
–
–
–
–
2
2
–
–
–
–
–
– – –
(N H), 3095 ( C H), 2933 (C H), 1651 (C O), 1620 (C N), 1589,
– –
MHz, DMSO‑d6): δ 2.42 (s, 3H, CH3), 7.49–8.85 (m, 10H, Ar H), 10.98
(s, 1H, CO NH), 11.08 (s, 1H, hydrazone NH). 13C NMR (75 MHz,
1573 (C C), 1504 (NO asym), 1300 (NO sym), 827 (
C H). H NMR
1
–
–
–
–
–
–
–
2
DMSO‑d6): δ 13.57, 116.97, 117.05, 119.62, 123.42, 127.82, 128.75,
(300 MHz, DMSO‑d6): δ 2.24 (s, 3H, CH3)2, 2.43 (s, 3H, CH3), 7.08–8.91
(m, 13H, Ar H and urea NH), 11.12 (s, 1H, hydrazone NH). 13C NMR
–
130.00, 130.53, 131.65, 132.00, 132.94, 136.63, 137.63, 140.59,
144.80, 153.08, 162.68. HRMS (m/z): [M
+
H]+ calcd for
(75 MHz, DMSO‑d6): δ 13.61, 20.84, 116.96, 118.07, 118.87, 123.59,
127.90, 129.68, 130.54, 130.61, 131.37, 136.49, 137.33, 137.50,
142.17, 144.90, 152.78, 153.69. HRMS (m/z): [Mꢀ H]- calcd for
C
21H15N5O5Cl2: 488.0523; found: 488.0501.
4.2.15. 1-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-3-
phenylurea (4a)
C22H20N6O5: 447.1422; found: 447.1405.
ꢀ 1
◦
–
Yield: 86%, M.P. = 235–236 C, FTIR (ATR, cm ): 3311 (N H),
4.2.21. 1-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-3-(4-
methoxyphenyl)urea (4g)
–
–
–
–
–
– –
C H), 2922 (C H), 1651 (C O), 1614 (C N), 1593, 1573
–
3097 (
1
(C C), 1514 (NO asym), 1300 (NO sym), 831 (
C H). H NMR (300
Yield: 81%, M.P. = 192–193 ◦C, FTIR (ATR, cmꢀ 1): 3358, 3298
–
–
–
–
–
2
2
–
–
–
–
–
– – –
(N H), 3051 ( C H), 2916 (C H), 1674 (C O), 1614 (C N), 1589,
– –
MHz, DMSO‑d6): δ 2.44 (s, 3H, CH3), 6.96–8.91 (m, 14H, Ar H and urea
NH), 11.13 (s, 1H, hydrazone NH). 13C NMR (75 MHz, DMSO‑d6): δ
13.64, 117.03, 118.37, 119.05, 122.57, 123.42, 127.84, 129.19, 130.05,
130.45, 130.98, 137.85, 139.97, 142.10, 145.04, 152.83, 153.82. HRMS
(m/z): [Mꢀ H]- calcd for C21H18N6O5: 433.1266; found: 433.1249.
1
–
–
–
–
–
1531 (C C), 1504 (NO asym), 1317 (NO sym), 823 (
C H). H NMR
(300 MHz, DMSO‑d6): δ 2.42 (s, 3H, CH3),23.72 (s, 3H, OCH3), 6.86–8.89
2
(m, 13H, Ar H and urea NH), 11.11 (s, 1H, hydrazone NH). 13C NMR
–
(75 MHz, DMSO‑d6): δ 13.59, 55.62, 114.46, 116.94, 118.00, 120.63,
123.57, 127.87, 129.95, 130.42, 130.59, 132.89, 137.48, 142.28,
144.88, 152.92, 153.67, 155.07. HRMS (m/z): [Mꢀ H]- calcd for
9

F. Tok et al.
Bioorganic Chemistry 114 (2021) 105038
C22H20N6O6: 463.1372; found: 463.1378.
4.7. Molecular docking
4.2.22. 1-(4-(1-(2-(2,4-Dinitrophenyl)hydrazono)ethyl)phenyl)-3-(4-
(methylthio)phenyl)urea (4h)
A structure based in silico procedure was applied to discover the
binding modes of compound 4i to hMAO-A enzyme active site. The
crystal structures of hMAO-A (PDB ID: 2Z5X) [34], which was crystal-
lized with harmine, were retrieved from the Protein Data Bank server
(www.pdb.org). The docking procedure was conducted according to the
published papers priorly by our research community [22–26].
Yield: 72%, M.P. = 211–212 ◦C, FTIR (ATR, cmꢀ 1): 3352, 3296
–
–
–
–
–
– –
C H), 2989 (C H), 1674 (C O), 1614 (C N), 1583,
–
(N H), 3103 (
–
1
–
–
–
–
–
1543 (C C), 1514 (NO asym), 1317 (NO sym), 844 (
C H). H NMR
2
2
(300 MHz, DMSO‑d6): δ 2.43 (s, 3H, SCH3), 2.44 (s, 3H, CH3), 7.21–8.94
(m, 13H, Ar H and urea NH), 11.12 (s, 1H, hydrazone NH). 13C NMR
–
(75 MHz, DMSO‑d6): δ 13.61, 16.38, 112.61, 116.95, 118.13, 119.55,
123.57, 127.88, 128.13, 129.97, 130.59, 130.70, 137.50, 137.60,
142.02, 144.88, 152.69, 153.63. HRMS (m/z): [Mꢀ H]- calcd for
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
C
22H20N6O5S: 479.1143; found: 479.1123.
4.2.23. 1-(2,6-Dichlorophenyl)-3-(4-(1-(2-(2,4-dinitrophenyl)hydrazono)
ethyl)phenyl)urea (4i)
Appendix A. Supplementary material
Yield: 77%, M.P. = 244–245 ◦C, FTIR (ATR, cmꢀ 1): 3356, 3311
–
–
–
–
The FTIR, 1H-NMR, 13C-NMR, and HR-MS spectrums of compounds
2a–2k and 4a-4i are available online.
–
– –
C H), 2901 (C H), 1674 (C O), 1614 (C N), 1585,
–
(N H), 3102 (
–
1
–
–
–
–
1573 (C C), 1514 (NO asym), 1300 (NO sym), 831 (
C H). H NMR
–
2
2
–
(300 MHz, DMSO‑d6): 2.43 (s, 3H, CH3), 7.31–9.27 (m, 12H, Ar H and
urea NH), 11.12 (s, 1H, hydrazone NH). 13C NMR (75 MHz, DMSO‑d6): δ
13.64, 116.99, 118.12, 123.58, 127.88, 128.96, 129.08, 130.01, 130.61,
130.73, 133.57, 134.48, 137.52, 142.11, 144.90, 152.62, 153.64. HRMS
(m/z): [Mꢀ H]- calcd for C21H16N6O5Cl2: 501.0486; found: 501.0465.
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.bioorg.2021.105038.
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