Synthesis, evaluation of antioxidant activity and crystal structure of 2,4-dimethylbenzoylhydrazones

Article abstract of DOI:10.3390/molecules180910912

2,4-Dimethylbenzoylhydrazones 1-30 were synthesized by condensation reactions of 2,4-dimethylbenzoylhydrazide with various aromatic aldehydes and characterized. The assigned structures of compounds 10, 15 and 22 were further supported by single-crystal X-

Full text of DOI:10.3390/molecules180910912

Molecules 2013, 18, 10912-10929; doi:10.3390/molecules180910912
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis, Evaluation of Antioxidant Activity and
Crystal Structure of 2,4-Dimethylbenzoylhydrazones
1
,
2
3
4
Muhammad Taha *, Nor Hadiani Ismail , Waqas Jamil , Sammer Yousuf ,
2
1
3
4
Faridahanim Mohd Jaafar , Muhammad Imran Ali , Syed Muhammad Kashif and Ejaz Hussain
1
Atta-ur-Rahman Institute for Natural Product Discovery, Universiti Teknologi MARA,
Puncak Alam Campus, Bandar Puncak Alam 42300, Selangor, Malaysia;
E-Mail: mia318.iccs@yahoo.com
2
Faculty of Applied Science Universiti Tecknologi MARA, Shah Alam 40450, Selangor, Malaysia;
E-Mails: norhadiani@salam.uitm.edu.my (N.H.I.); mfaridahanim@yahoo.com (F.M.J.)
3
Institute of Advance Research Studies in Chemical Sciences, University of Sindh Jamshoro,
Hyderabad 76080, Pakistan; E-Mails: waqas143kh@yahoo.com (W.J.);
hope_cancer@yahoo.com (S.M.K.)
4
H.E.J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences,
University of Karachi, Karachi 75270, Pakistan; E-Mails: dr.sammer.yousuf@gmail.com (S.Y.);
ejaz.iccbs@gmail.com (E.H.)
*
Author to whom correspondence should be addressed; E-Mail: taha_hej@yahoo.com or
muhamm9000@puncakalam.uitm.edu.my; Tel.: +60-19-309-8141 or +60-33-258-4761.
Received: 14 August 2013; in revised form: 2 September 2013 / Accepted: 4 September 2013 /
Published: 5 September 2013
Abstract: 2,4-Dimethylbenzoylhydrazones 1–30 were synthesized by condensation
reactions of 2,4-dimethylbenzoylhydrazide with various aromatic aldehydes and characterized.
The assigned structures of compounds 10, 15 and 22 were further supported by single-crystal
X-ray diffraction data. The synthesized compounds were evaluated for their in vitro DPPH
radical scavenging activity. They exerted varying degree of scavenging activity toward
DPPH radical with IC values between 25.6–190 µM. Compounds 1, 4, 2, 3, 7, and 6 have
5
0
IC50 values of 25.6, 28.1, 29.3, 29.8, 30.0 and 30.1 µM respectively, showing better activity
than an n-propyl gallate standard (IC50 value = 30.30 µM). For super oxide anion scavenging
activity compounds 1, 2 and 3 with IC50 values of 98.3, 102.6, and 105.6, respectively, also
showed better activity than the n-propyl gallate standard (IC value = 106.34 µM).
5
0

Molecules 2013, 18
10913
Keywords: 2,4-dimethylbenzoylhydrazones; DPPH scavenging; superoxide ion scavenger;
crystal structure
1
. Introduction
Hydrazone Schiff bases are a versatile set of compounds having unique properties. Hydrazones are
the bimolecular condensation product of an aryl or alkyl hydrazine and a carbonyl compound
aldehyde or ketone). Due to their synthetic simplicity and active pharmacophore group, i.e., the C=N
(
moiety, hydrazones are found to display biological and catalytic activities. One of the most prevalent
in vivo biochemical processes involving the formation of a Schiff base is the condensation of lysine
residues with the carbonyl group of methylglyoxal [1]. In this respect the Schiff base derived from
pyrodoxal and amino acids has been thoroughly studied [2]. A broad range of biological activities of
hydrazones such as anticancer [3] antibacterial [4] antifungal, herbicidal [5,6], anti-convalescent [7],
anti-oxidant [8], and diuretic properties [9,10] have been reported. Several hetrocyclic hydrazones have
been found to be potent cytotoxic [11], antimalarial [12], antiproliferative [13], anticancer and antifungal
agents [14]. Hydrazones are also well known for their applications in foods and dyes as well as the
agrochemical industry [15,16]. Among the various hydrazones, hydrazide-hydrazones merit special
attention due to their distinct structural features. They have been reported as antioxidant [17–19]
antifungal [20], anti-depressant [21], vasodilating [22], and anthelmintic agents [23]. Nifuroxazide, a
hydrazide hydrazone has been patented as an intestinal antiseptic. Some of the more effective
anti-tuberculosis drugs like iproniazide and isocarboxazide also contain hydrazide-hydrazone
moieties [24]. A hydrazide hydazone derived from safrole was found to be s potent
antiinflammatory/antinociceptive agent [25], while benzylidene 10H-phenothiazine-1-carbohydrazide
has also been reported as an important anti-platelet agent [26]. The active pharmacophore
(
-CONH-N=CH-) of hydrazide hydrazones is mainly responsible for the significant biological
activities although the attached neighboring groups may also be responsible [27]. Metal complexes of
hydrazide hydrazones are also biologically active, besides having an important role in catalytic
chemistry [28–31]. These metal complexes showed remarkable anti-cancer, antibacterial and
antifungal activities [32].
Free radicals are highly reactive compounds formed in the body during biochemical reactions. They
are oxidized the other metabolites in the body and can causes diseases such as Alzheimer’s disease
(
AD). The main reason for AD is oxidative stress, so it is necessary to inhibit or stop the formation of
free radicals. Anti-oxidant compounds either natural of synthetic can be used to prevent the formation
of free radicals. The major role of anti-oxidant compounds is to inhibit or neutralize the free radicals as
well as repair the damages caused by free radicals [33].
In the view of the above, a series of structurally similar 2,4-dimethylbenzoylhydrazones were
synthesized and evaluated for their antioxidant potential. This study has revealed some potential leads
for possible pharmaceutical applications and further investigation may help in the development of new
anti-oxidative agents for important metabolic functions.

Molecules 2013, 18
. Results and Discussion
Chemistry
10914
2
In the continuation of our work on benzoylhydrazide [34–36], 2,4-dimethylbenzoylhydrazones
1
–30 were synthesized from 2,4-dimethylbenzoylhydrazide, which in turn was synthesized
from methyl 2,4-dimethylbenzoate by refluxing with hydrazine hydrate for 4 h. The
,4-dimethylbenzoylhydrazide obtained was recrystallized from methanol to afford good yields of
product. Next, 2,4-dimethylbenzoylhydrazones were prepared through the condensation reactions of
,4-dimethylbenzoylhydrazide with different aromatic aldehydes in the presence of acetic acid
Scheme 1). The reaction mixture was refluxed in ethanol for 3 to 4 h. The crude products were
2
2
(
recrystallized from methanol to give needle-like crystal in most cases (all yields are reported as
crude product). Compounds 1–3, 7, 12, 14–16, 20, and 29 are new, while compounds 4–6, 8–11, 13, 17,
18, 21, 23–28, and 30 showed only CAS registry number with zero reference. Only compound 19 and 22
reported in the literature.
Scheme 1. Synthesis of 2,4-dimethylbenzoylhydrazones.
The structural confirmation of 2,4-dimethylbenzoylhydrazones 1–30 was accomplished by several
1
spectroscopic techniques, including H-NMR and mass spectroscopic. All compounds have an
E-configuration as recently reported for some similar products [37–42]. We are also reporting three
new crystal structures of compounds 10, 15 and 22.
3
. Antioxidant Activity
3
.1. DPPH Scavenging Activity
2
,4-Dimethylbenzoylhydrazones 1–30 were evaluated for their in vitro DPPH radical scavenging
activity and showed varying degree of activity, with IC50 values between 25.6–190 µM. Compounds
, 4, 2, 3, 7, and 6 have IC50 values of 25.6, 28.1, 29.3, 29.8, 30.0 and 30.1 µM, respectively, showing
better activity than standard n-propyl gallate IC50 value = 30.30 µM. Compound 5 (IC50 = 34.1 µM),
(IC50 = 34.3 µM), 12, (IC50 = 34.2 µM), and 9 (IC50 = 40.1 µM) exhibited good activity comparable
1
8
to the standard. On the other hand, compounds 14 and 11, with IC50 values of 52.2 and 60.1 µM,
respectively, showed only moderate activities. Compounds 20, 29 and 27 were found to be weakly
active. Compounds 10, 13, 15–19, 21–26, 28 and 30, showed less than 50% activity; and thus their
IC50 values were not evaluated (Table 1).
By comparing structural information and antioxidant activity, it was observed that DPPH radical
scavenging antioxidant activity depends on two parameters: the functional groups on aromatic ring,
and the position of functional groups on the ring. It was observed that the active compounds of the
series bear an -OH group on the ring and activity pattern is such that, the more the -OH groups, the

Molecules 2013, 18
10915
activity will be higher. Thus, the tri-OH group-containing derivatives were found to be more active
than di- and mono-OH substituted analogues. Compound 1, which is a 3,4,5-trihydroxy derivative was
the most active compound of this series, while compound 2 which bears a 2,4,6-trihyroxy group
showed only slightly low activity than compound 1. Two factors might thus be involved in this activity
pattern, one is the position of -OH groups and second, the extra resonance stability of compound 1
compared to compound 2 [43].
Table 1. In vitro DDPH Radical Scavenging Activity of Compounds 1–30.
Comp.
No.
Yield
(%)
IC50
Comp.
No.
Yield
(%)
IC50
R
R
a
a
(µM ± SEM )
(µM ± SEM )
1
'
1
'
6
'
2'
OH
6
'
b
1
2
84
82
25.6 ± 0.5
10
11
88
90
NA
HO
3'
OH
5'
4
'
OH
1'
1
'
HO
OH
6
'
2'
29.3 ± 1.0
60.1 ± 2.2
34.2 ± 2.1
5
'
5'
3
'
OH
OCH3
OH
1
'
1
'
OH
6'
2'
6
'
3
4
78
84
29.8 ± 1.1
12
13
87
90
5
'
3'
Br
HO
4'
OH
1
'
1
'
6
'
2'
OH
6
'
b
28.14 ± 0.8
NA
5
'
3
'
OH
H CO
4'
3
OH
1
'
1'
OH
6'
6
'
I
5
6
85
86
34.1 ± 1.0
30.1 ± 1.3
14
15
87
82
52.2 ± 2.8
3'
5
'
5
'
OH
OCH3
OH
1
'
1
'
OH
OH
6'
6
'
b
NA
5
'
3'
5
'
4
'
OH
OCH3
1
'
1
'
6
'
6'
2'
OCH3
2
'
b
7
8
9
81
83
92
30.0 ± 1.2
34.3 ± 1.5
40.0 ± 1.8
16
17
18
82
84
83
NA
H CO
4'
HO
4'
OH
3
1
'
1'
6
'
2'
6'
5'
2'
b
NA
5
'
OCH3
OCH3
OCH3
OH
1
'
1'
2'
6
'
2'
3'
6'
b
NA
5
'
5
'
OH
4'
OCH3

Molecules 2013, 18
10916
Table 1. Cont.
Comp.
R
Yield
(%)
IC50
Comp.
Yield
(%)
IC50
R
a
a
No.
(μM ± SEM )
No.
(μM ± SEM )
1
'
1'
6
'
6
'
N
b
b
1
2
9
0
85
87
NA
25
82
88
NA
5
'
3'
3'
5
'
4
'
4'
1
'
1
'
6
'
2'
S
2'
b
130.0 ± 4.8
26
27
NA
5
'
5'
F
3'
4
'
Br
1'
1'
6'
2'
6
'
2'
b
2
1
3'
OCH3
88
NA
5'
3'
90
190.0 ± 5.1
5'
O
O
1
'
1
'
6
'
2'
6
'
2'
b
b
2
2
2
2
3
4
90
92
90
NA
28
29
30
92
91
84
NA
5'
3'
N
5
'
4'
Cl
O
O
1'
6'
2'
1'
b
6
'
NA
180.0 ± 4.6
5
'
3'
H CO
3
4' OCH
3
1
'
1'
6
'
2'
3'
6'
2'
3'
b
b
NA
NA
5
'
5
'
N
NO2
30.30 ± 0.2
c
Standard drug n-propyl gallate
a
b
c
SEM is the standard error of the mean; NA = Not active; n-propyl gallate standard used for the DDPH
radical scavenging activity assays.
Interesting results are obtained when we compare the dihydroxy derivatives. Five dihydroxy
derivatives showed excellent activity and variation in their activity is mainly due to the stability of the
resulting radical. Compounds 4, 3, 6, and 7 showed excellent activity, better than standard. Interestingly,
compound 5 having a 2,4-dihydroxy group, is the only dihydroxy analogue which has an IC50 value
above the standard, indicating less stability of its radical as compared to other analogues [44,45].
Their activities of monohydroxy compounds 8–15 mainly depends upon the position of the hydroxy
group. Compounds 8, 9 and 12 showed good activity having a 4-hydroxy group and the variation in
their activities is due to the presence of a 3-methoxy as in compound 8 and a bromine in compound 12,
which showed almost the same activity, and may be due to the resonance stabilizing potential of the
methoxy and bromine substituents. On the other hand compounds 11 and 14 have a 3-hydroxy along
with other sustituents but still showed less activity than the para-substituted analogues. It is well

Molecules 2013, 18
10917
established that para-substitution has more stabilizing potential then meta-substitution. Compounds
0, 13 and 15 having 2-hydroxy group are found to be inactive, which may be due to the
1
intramolecular hydrogen bonding. Compounds 20, 27 and 29 have halogen and ester moieties,
respectively, which weakly stabilized the radical and showed weak activity. Compounds 10, 13,
1
5–19, 21–26, 28 and 30, not having any substituent to help stabilize the radical effectively, were
found to be inactive as expected.
3
.2. Superoxide Scavenging Activity
Compounds 1, 2 and 3 showed IC values of 98.3, 102.6 and 105.6 μM, respectively, better than
5
0
the n-propyl gallate standard (106.3 μM). Compounds 4, 5, 6, 7, 8, 9, 12 and 14 showed moderate
activity respectively (145, 170.2, 175.0, 180.1, 190.1, 208.9, 210.1 and 260.3 μM). Compound 20
showed very weak activity (Table 2).
Table 2. In vitro Superoxide Anion Radical Scavenging Activity of Compounds 1–30.
a
a
Comp. No.
IC50 (μM ± SEM )
Comp. No.
IC50 (μM ± SEM )
b
1
2
3
4
5
6
7
8
9
98.3 ± 1.2
102.6 ± 1.5
105.6 ± 1.7
145 ± 2.1
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
NA
b
NA
b
NA
b
NA
170.2 ± 3.2
175.0 ± 3.5
180.1 ± 3.8
190.1 ± 3.9
208.9 ± 5.4
315.1 ± 8.4
b
NA
b
NA
b
NA
b
NA
b
b
1
1
1
1
1
1
0
1
2
3
4
5
NA
NA
b
b
NA
NA
b
210.1 ± 4.4
NA
b
b
NA
NA
b
260.3 ± 6.4
NA
b
b
NA
c
NA
n-propyl gallate
106.34 ± 1.6
a
b
c
SEM is the standard error of the mean, NA = Not active, n-propyl gallate was the standard drug for the
superoxide anion radical scavenging assays.
Compounds 8, 10, 11, 13, 15–19 and 21–30 showed less than 50% inhibition and therefore the IC50
values were not further evaluated. Compounds 1 and 2 have trihydroxy substitution pattern at ring A,
and showed remarkable activity, more active than the standard. Among the five dihydroxy-substituted
analogues only compound 3 showed better activity than the standard, while the rest of the dihydroxy
derivatives were found to be only moderately active towards superoxide. Compound 9 having a
4
-hydroxy at ring A, showed moderate activity. Surprisingly, compound 8 having a 3-methoxy-4-OH
substituted showed better activity than compound 9, while replacement of -OCH with -Br, decreased
3
the activity. The weak activity of compound 14 might be due to combined effect of iodine and
hydroxyl groups. The dihalogenated compound 20 also showed weak activity.

Molecules 2013, 18
10918
4. Experimental
4.1. General
NMR experiments were performed on an Ultra Shield Bruker FT NMR 500 MHz instrument
(Wissembourg Cedex, France). CHN analysis was performed on a Carlo Erba Strumentazion-Mod-1106
(Milan, Italy). Electron impact mass spectra (EI MS) were recorded on a Finnigan MAT-311A unit
(Bremen, Germany). Thin layer chromatography (TLC) was performed on pre-coated silica gel
aluminum plates (Kieselgel 60, 254, E. Merck, Darmstadt, Germany). Chromatograms were visualized
by UV at 254 and 365 nm.
4
.2. X-ray Crystallography Studies
The structures of compounds 10, 15 and 22 were further supported by single crystal X-ray
diffraction analysis. The 10, 15 and 22 were found to be monoclinic system crystals with space groups
P21/c (compounds 10 and 22) and P21/n (compound 15). The ORTEP views of compounds 10 (Figure 1),
1
5 (Figure 2) and 22 (Figure 3), clearly indicated that structures of all compounds were composed of
two planar phenyl rings (C1—C6 and C9—C14) with an E-configuration azomethine double bond.
The hydroxyl functionality of the phenyl ring played an important role in stabilizing the
E-configuration of the azomethine olefin bond in compounds 10 and 15 via intramolecular interaction.
The crystal details of compounds 10, 15 and 22 as well as experimental data are summarized in Table
3. Single crystal X-ray diffraction data was collected on Bruker Smart APEX II, CCD area detector
diffractometer [46] followed by data reduction preformed by SAINT program. The structure was solved
and expanded by direct method and Fourier transformation techniques, respectively. SHELXL97
2
program was used to refine the structure by using full-matrix least-square calculation on F [47]
(
Sheldrick 1997). The ORTEP program was used to plot the Figures 1–3. Figures were plotted
with the aid of ORTEP program [48]. Crystallographic data of compound 10 (CCDC 933686),
5 (CCDC 933687) and 22 (CCDC 933685) can be obtained from Cambridge Crystallographic Data
1
Center without any cost.
Figure 1. ORTEP view of compound 10 with displacement ellipsoids drawn at 30%
probability level. Dashed lines represent the intermolecular interaction; selected bond lengths
[Å]: C7-O1 1.229(2), O2-C10 1.351(2), N1-C7 1.348(2), N1-N2 1.382(19), N2-C8 1.276(2).

Molecules 2013, 18
10919
Figure 2. ORTEP view of compound 15 with displacement ellipsoids drawn at 30%
probability level. Dashed lines represent the intermolecular interaction; selected bond
lengths [Å]: C7-O2 1.226(18), O2-C14 1.349(2), O3-C12 1.357(2), N1-C7 1.352(2),
N1-N2 1.38(19), N2-C8 1.276(2).
Figure 3. ORTEP view of compound 22 with displacement ellipsoids drawn at 30%
probability level; selected bond lengths [Å]: C7-O1 1.228(2), N1-C7 1.351(3), N1-N2
1
.380(2), N2-C8 1.269(3).
Table 3. The crystal and experimental data of compounds 10, 15 and 22.
Compound 10
Compound 15
Compound 22
Empirical formula
C
16
H
16
N
2
O
2
C
17
H
18
N
2
O
3
15 15 1 3
C H N O
Formula weight
268.31
273(2)
298.33
273(2)
253.30
273(2)
Temperature
Wavelength
0.71073 Å
Monoclinic
P21/c
0.71073 Å
Monoclinic
P21/n
0.71073 Å
Monoclinic
P21/c
Crystal system
Space group
A
12.7293(17) Å
13.0700(17) Å
8.8762(12) Å
94.845(3)°
11.1984(9) Å
10.0703(9) Å
13.8665(12) Å
102.535(2)°
14.0960(14) Å
11.8440(12) A
8.2813(8) Å
100.889(2)°
B
C
β
Volume
3
3
3
1,463.2(3) A
1,526.5(2) A
1,357.7(2) A
Z
4
4
4
3
3
3
Calculated density
Absorption coefficient
F(000)
1.218 mg/m
1.298 mg/m
1.239 mg/m
−
1
−1
−1
0.082 mm
568
0.090 mm
0.080 mm
632
536

Molecules 2013, 18
10920
Table 3. Cont.
Compound 10
Compound 15
0.56 × 0.43 × 0.12 mm
2.13 to 25.49°
8849
Compound 22
Crystal size
θ range
Reflections Collected
0.52 × 0.12 × 0.11 mm
2.24 to 25.49°
8546
0.56 × 0.18 × 0.13 mm
1.47 to 25.40°
7827
Reflections Unique
2713
2758
2522
(
R
int
)
0.0275
0.0212
0.0313
R
R
1
with I > 2σ(I)
with I > 2σ(I)
0.0463
0.0438
0.0536
2
0.1124
0.1248
0.1508
R
1
for all data
0.0774
0.0520
0.0702
R
2
for all data
0.1323
0.1337
0.1607
Goodness of fit
1.030
1.057
1.014
−
3
max/min ρ eA˚
0.140 and −0.110
0.232 and −0.018
0.265 and −0.258
4.3. DPPH (1,1-Diphenyl-2-picryl hydrazyl) Free Radical Scavenging Activity
The free radical scavenging activity was measured by 1,1-diphenyl-2-picrylhydrazyl (DPPH) using
literature protocols. The reaction mixture contained test sample (5 μL, 1 mM in DMSO) and DPPH
Sigma, 95 μL, 300 μM) in ethanol. The reaction mixture was taken into a 96-well microtiter plate and
incubated at 37 °C for 30 min. The absorbance was measured at 515 nm using microtiter plate reader
Molecular Devices, Sunnyvale, CA, USA). Percent radical scavenging activity was determined in
(
(
comparison with DMSO containing control (Table 1). IC50 values represent the concentration of
compounds able to scavenge 50% of DPPH radicals. Propyl gallate was used as positive control. All
chemicals used were of analytical grade (Sigma, Ronkonkoma, NY, USA).
4
.4. In Vitro Assay for Superoxide Anion Radical Scavenging Activity
The superoxide producing system was set up by mixing phenazinemethosulfate (PMS), NADH, and
oxygen (air), and the production of superoxide was estimated by the nitroblue tetrazolium method.
Measurement of superoxide radical scavenging activity was carried out on the basis of the method
described by the modified method used by Ferda. In aerobic reaction mixtures containing NADH,
phenazine methosulphate and nitro blue tetrazolium, PMS is reduced by NADH and then gave rise to
−
−
O
2
, which in turn reduced NBT. On the basis of this PMS has frequently been used to mediate O
2
.
The reaction mixture comprised 100 µΜ β-nicotinamide adenine dinucleotide reduced form
(NADH, 40 µL), 80 µM of nitro blue tetrazolium (NBT, 40 µL), 8 µM phenazine methosulphate
(
PMS, 20 µL), 1 mM sample (10 µL), and 0.1 M phosphate buffer (pH 7.4, 90 µL). The reagents were
prepared in buffer and sample in DMSO. The reaction was performed in 96-well microtitre plate at
room temperature and absorbance was measured at 560 nm. The formation of superoxide was
monitored by measuring the formation of water soluble blue formosan dye. A lower absorbance of
reaction mixture indicated a higher scavenging activity of the sample. Percent radical scavenging
activity (% RSA) by samples was determined in comparison with a control using the following equation:
%RSA = 100 − {(OD test compound/OD control) × 100

Molecules 2013, 18
.5. General Procedure for the Synthesis of 2,4-Dimethylbenzohydrazide
10921
4
Methyl 2,4-dimethylbenzoate (40 mmol) was refluxed with hydrazine hydrate (10 mL) in methanol
50 mL) for 6 h. Excess hydrazine and methanol was evaporated to obtain crude product which was
recrystallized from methanol to give pure 2,4-dimethylbenzohydrazide (92% yield).
(
4
.6. General Procedure for the Synthesis of 2,4-Dimethylbenzohydrazones
The 2,4-dimethylbenzohydrazones were synthesized by refluxing in methanol (15mL) for 3 h each
pure 2,4-dimethylbenzohydrazide (2 mmol) and various aryl aldehydes (2 mmol) in the presence of a
catalytical amount of acetic acid. The progress of reaction was monitored by TLC. After completion of
reaction, the solvent was evaporated by vacuum to afford crude products which were further
recrystallized from methanol and got needle like pure product in good to excellent yields.
1
(
E)-N'-(3,4,5-Trihydroxybenzylidene)-2,4-dimethylbenzohydrazide (1). Yield: 0.504 g (84%); H-NMR
(
DMSO-d ): δ 11.34 (s, 1H, NH), 9.07 (br. s, 3H, 3× OH), 8.02 (s, 1H, ArCH=N-R), 7.33 (d, 1H,
6
J
6,5 = 7.5 Hz, H-6), 7.11 (s, 1H, H-3), 7.01 (d, 1H, J5,6 = 7.5 Hz, H-5), 6.66 (s, 2H, H-2', H-6'), 2.37 (s,
−1
3
H, CH
3
), 2.32 (s, 3H, CH
3
); IR (KBr, cm ): 3460 (OH), 3320 (N-H), 1652 (C=O), 1628 (C=N), 1248
, C = 63.99, H = 5.37, N = 9.33, O = 21.31, Found C = 64.01,
H =5.37, N = 9.34, O = 21.32; EI MS m/z (% rel. abund.): 300.
(
16 2 4
C-N); Anal. Calcd for C16H N O
1
(
E)-N'-(2,4,6-Trihydroxybenzylidene)-2,4-dimethylbenzohydrazide (2). Yield: 0.492 g (82%); H-NMR
DMSO-d ): δ 11.10 (s, 1H, NH), 9.46 (br. s, 3H, 3× OH), 8.30 (s, 1H, ArCH=N-R), 7.28 (d, 1H,
6,5 = 8.0 Hz, H-6), 7.09 (s, 1H, H-3), 6.98 (d, 1H, J5,6 = 8.0 Hz, H-5), 6.78 (s, 2H, H-3', H-5'), 2.36 (s,
(
6
J
−1
3
H, CH
C-N); Anal. Calcd for C16
H = 5.35, N = 9.32, O = 21.33; EI MS m/z (% rel. abund.): 300.
3
), 2.30 (s, 3H, CH
3
); IR (KBr, cm ): 3480 (OH), 3370 (N-H), 1658 (C=O), 1632 (C=N), 1253
(
16 2 4
H N O
, C = 63.99, H = 5.37, N = 9.33, O = 21.31, Found C = 64.02,
1
(
E)-N'-(2,5-Dihydroxybenzylidene)-2,4-dimethylbenzohydrazide (3). Yield: 0.443 g (78%); H-NMR
(
DMSO-d ): δ 11.78 (s, 1H, NH), 10.40 (s, 1H, OH), 8.96 (s, 1H, OH), 8.41 (s, 1H, ArCH=N-R), 7.39
6
(
d, 1H, J6,5 = 8.5 Hz, H-6), 7.14 (s, 1H, H-3), 7.10 (d, 1H, J5,6 = 8.5 Hz, H-5), 6.93 (s, 1H, H-6'),
−1
6
.74–6.70 (m, 2H, H-3', H-4'), 2.37 (s, 3H, CH
3
), 2.32 (s, 3H, CH
3
); IR (KBr, cm ): 3410 (OH), 3330
, C = 67.59, H = 5.37,
N = 9.85, O = 16.88, Found C = 67.58, H = 5.68, N = 9.84, O = 16.89; EI MS m/z (% rel. abund.): 284.
16 2 3
(N-H), 1656 (C=O), 1636 (C=N), 1256 (C-N); Anal. Calcd for C16H N O
(
E)-N'-(3,4-Dihydroxybenzylidene)-2,4-dimethylbenzohydrazide (4) [37]. Yield: 0.477 g (84%);
1
H-NMR (DMSO-d
6
): δ 11.20 (s, 1H, NH), 9.10 (s, 2H, 2× OH), 8.10 (s, 1H, ArCH=N-R), 7.33 (d,
H, J6,5 = 7.5 Hz, H-6), 7.21 (s, 1H, H-2') 7.11 (s, 1H, H-3), 7.09 (d, 1H, J5,6 = 7.5 Hz, H-5), 6.09 (d,
H, J5',6' = 8.5 Hz, H-5'), 6.78 (d, 1H, J6',5' = 8.5 Hz, H-6'), 2.35 (s, 3H, CH ), 2.32 (s, 3H, CH ); IR
1
1
3
3
−1
(KBr, cm ): 3405 (OH), 3330 (N-H), 1658 (C=O), 1634 (C=N), 1250 (C-N); Anal. Calcd for
C H N O , C = 67.59, H = 5.37, N = 9.85, O = 16.88, Found C = 67.58, H = 5.68, N = 9.84,
1
6
16
2
3
O = 16.89; EI MS m/z (% rel. abund.): 284.

Molecules 2013, 18
10922
1
(
(
(
E)-N'-(2,4-Dihydroxybenzylidene)-2,4-dimethylbenzohydrazide (5). Yield: 0.482 g (85%); H-NMR
DMSO-d ): δ 11.7 (s, 1H, NH), 11.45 (s, 1H, OH), 9.91 (s, 1H, OH), 8.36 (s, 1H, ArCH=N-R), 7.38
d, 1H, J6,5 = 7.5 Hz, H-6), 7.27 (d, 1H, J6',5' = 6.5 Hz, H-6'), 7.11 (s, 1H, H-3), 7.08 (d, 1H, J5,6 = 7.5
6
Hz, H-5), 6.36 (dd, 1H, J5',3' = 2.0, J5',6' = 6.5 Hz, H-5'), 6.32 (d, 1H, J = 2.0 Hz, H-3'), 2.37 (s, 3H,
3',5'
−1
CH
C-N); Anal. Calcd for C16
H = 5.68, N = 9.84, O = 16.89; EI MS m/z (% rel. abund.): 284.
3
), 2.33 (s, 3H, CH
3
); IR (KBr, cm ): 3445 (OH), 3325 (N-H), 1657 (C=O), 1631 (C=N), 1251
(
16 2 3
H N O
, C = 67.59, H = 5.37, N = 9.85, O = 16.88, Found C = 67.58,
1
(
E)-N'-(2,3-Dihydroxybenzylidene)-2,4-dimethylbenzohydrazide (6). Yield: 0.488 g (86%); H-NMR
(
DMSO-d ): δ 11.2 (s, 1H, NH), 9.60 (s, 2H, 2× OH), 8.45 (s, 1H, ArCH=N-R), 7.41 (d, 1H, J6,5 = 7.5 Hz,
6
H-6), 7.14 (s, 1H, H-3), 7.10 (d, 1H, J5,6 = 7.5 Hz, H-5), 6.94 (d 1H, J6',5' = 6.5 Hz, H-6'), 6.86 (d, 1H,
4',5' = 7.0 Hz, H-4'), 6.36 (dd, 1H, J5',4' = 7.0, J5',6' = 6.5 Hz, H-5') 2.38 (s, 3H, CH ), 2.33 (s, 3H, CH );
J
3
3
−1
IR (KBr, cm ): 3420 (OH), 3335 (N-H), 1657 (C=O), 1632 (C=N), 1254 (C-N); Anal. Calcd for
C H N O , C = 67.59, H = 5.37, N = 9.85, O = 16.88, Found C = 67.58, H = 5.68, N = 9.84,
1
6
16
2
3
O = 16.89; EI MS m/z (% rel. abund.): 284.
1
(
E)-N'-(3,5-Dihydroxybenzylidene)-2,4-dimethylbenzohydrazide (7). Yield: 0.460 g (81%); H-NMR
DMSO-d ): δ 11.30 (s, 1H, NH), 10.50 (s, H, OH), 9.52 (s, H, OH), 8.40 (s, 1H, ArCH=N-R), 7.40 (d,
H, J6,5 = 7.5 Hz, H-6), 7.18 (s, 1H, H-3), 7.12 (d, 1H, J5,6 = 7.5 Hz, H-5), 6.95 (s, 2H, H-2', H-6'),
(
6
1
6
−1
.72 (s, 1H, H-4'), 2.38 (s, 3H, CH
3
), 2.34 (s, 3H, CH
3
); IR (KBr, cm ): 3435 (OH), 3330 (N-H), 1649
, C = 67.59, H = 5.37, N = 9.85,
O = 16.88, Found C = 67.58, H = 5.68, N = 9.84, O = 16.89; EI MS m/z (% rel. abund.): 284.
16 2 3
(C=O), 1627 (C=N), 1254 (C-N); Anal. Calcd for C16H N O
(
1
E)-N'-(4-Hydroxy-3-methoxybenzylidene)-2,4-dimethylbenzohydrazide (8). Yield: 0.494 g (83%);
H-NMR (DMSO-d
6
): δ 11.45 (s, 1H, NH), 9.50 (s, 1H, OH), 8.19 (s, 1H, ArCH=N-R), 7.35 (d, 1H,
J
6,5 = 7.5 Hz, H-6), 7.31 (d, 1H, J2',6' = 2.0 Hz, H-2'), 7.12 (s, 1H, H-3), 7.10 (d, 1H, J5,6 = 7.5 Hz, H-5),
7
.07 (dd, 1H, J6',2' = 2.0, J = 8.0 Hz, H-6'), 6.84 (d 1H, J5',6' = 8.0 Hz, H-5'), 2.36 (s, 3H, CH ), 2.32
6
'
,
5
'
3
−1
(
s, 3H, CH
Calcd for C17
N = 9.40, O = 16.10; EI MS m/z (% rel. abund.): 298.
3
), IR (KBr, cm ): 3405 (OH), 3335 (N-H), 1659 (C=O), 1633 (C=N), 1249 (C-N); Anal.
18 2 3
H N O
, C = 68.45, H = 5.37, N = 9.39, O = 16.09, Found C = 68.46, H = 6.08,
1
(
E)-N'-(4-Hydroxybenzylidene)-2,4-dimethylbenzohydrazide (9). Yield: 0.493 g (92%); H-NMR
DMSO-d ): δ 11.43 (s, 1H, NH), 9.87 (s, 1H, OH), 8.20 (s, 1H, ArCH=N-R), 7.54 (d, 2H,
2',3' = J6',5' = 8.0 Hz, H-2',H-6'), 7.33 (d, 1H, J6,5 = 7.5 Hz, H-6), 7.17 (s, 1H, H-3), 7.11 (d, 1H,
5,6 = 7.5 Hz, H-5), 6.84 (d, 2H, J3',2' = J5',6' = 8.0 Hz, H-3',H-5'), 2.35 (s, 3H, CH ), 2.32 (s, 3H, CH ),
(
6
J
J
3
3
−1
IR (KBr, cm ): 3410 (OH), 3325 (N-H), 1663 (C=O), 1636 (C=N), 1254 (C-N); Anal. Calcd for
, C = 71.62, H = 6.01, N = 10.44, O = 11.93, Found C = 71.61, H = 6.02, N = 10.45,
O = 11.94; EI MS m/z (% rel. abund.): 268.
16 16 2 2
C H N O
1
(
E)-N'-(2-Hydroxybenzylidene)-2,4-dimethylbenzohydrazide (10). Yield: 0.471g (88%); H-NMR
(
DMSO-d ): δ 11.11 (s, 1H, NH), 9.25 (s, 1H, OH), 9.01 (s, 1H, ArCH=N-R), 7.71 (dd, 1H, J3',4' = 6.5,
6
J3',5' = 6.5 Hz, H-3') 7.43–7.39 (m, 2H, H-6',H-6), 7.17 (s, 1H, H-3), 7.11 (d, 1H, J = 7.5 Hz, H-5),
5,6
−1
6
3 3
.99–6.94 (m, 2H, H-4',H-5'), 2.38 (s, 3H, CH ), 2.33 (s, 3H, CH ); IR (KBr, cm ): 3415 (OH), 3330

Molecules 2013, 18
10923
(
N-H), 1663 (C=O), 1638 (C=N), 1258 (C-N); Anal. Calcd for C H N O , C = 71.62, H = 6.01,
1
6
16
2
2
N = 10.44, O = 11.93, Found C = 71.60, H = 6.03, N = 10.44, O = 11.95; EI MS m/z (% rel. abund.): 268.
(
1
E)-N'-(3-Hydroxy-4-methoxybenzylidene)-2,4-dimethylbenzohydrazide (11). Yield: 0.522 g (90%);
H-NMR (DMSO-d
6
): δ 11.45 (s, 1H, NH), 9.26 (s, 1H, OH), 8.15 (s, 1H, ArCH=N-R), 7.34 (d, 1H,
J6,5 = 7.5 Hz, H-6), 7.32 (d, 1H, J2',6' = 2.0 Hz, H-2'), 7.17 (s, 1H, H-3), 7.10 (d, 1H, J5,6 = 7.5 Hz, H-5),
7
3
.08 (dd, 1H, J6',2' = 2.0, J6',5' = 7.0, H-6'), 7.04 (d, 1H, J5',6' = 7.0, H-5'), 2.35 (s, 3H, CH ), 2.32 (s, 3H,
−1
CH ), IR (KBr, cm ): 3950 (OH), 3320 (N-H), 1658 (C=O), 1630 (C=N), 1254 (C-N); Anal. Calcd for
3
C
17
H
18
N
2
O
3
, C = 68.45, H = 5.37, N = 9.39, O = 16.09, Found C = 68.46, H = 6.08, N = 9.40,
O = 16.10; EI MS m/z (% rel. abund.): 298.
(
1
E)-N'-(3-Bromo-4-hydroxybenzylidene)-2,4-dimethylbenzohydrazide (12). Yield: 0.602 g (87%);
H-NMR (DMSO-d ): δ 11.35 (s, 1H, NH), 10.57 (s, 1H, OH), 8.30 (s, 1H, ArCH=N-R), 7.87 (d, 1H,
6
J2',6' = 2.0 Hz, H-2'), 7.58 (dd, 1H, J6',2' = 2.0, J6',5' = 7.0, H-6'), 7.32 (d, 1H, J = 7.5 Hz, H-6), 7.15 (s,
6,5
1
H, H-3), 7.09 (d, 1H, J = 7.5 Hz, H-5), 7.05 (d, 1H, J = 7.0, H-5'), 2.35 (s, 3H, CH ), 2.32 (s, 3H,
5,6 6',5' 3
−1
CH
3
); IR (KBr, cm ): 3954 (OH), 3318 (N-H), 1655 (C=O), 1635 (C=N), 1250 (C-N); Anal. Calcd for
, C = 55.35, H = 4.35, N = 8.07, O = 9.22, Found C = 55.36, H = 4.35, N = 8.08,
O = 9.21; EI MS m/z (% rel. abund.): 346.
16 2 2
C H15BrN O
(
1
E)-N'-(2-Hydroxy-5-methoxybenzylidene)-2,4-dimethylbenzohydrazide (13). Yield: 0.536 g (90%);
H-NMR (DMSO-d
6
): δ 11.88 (s, 1H, NH), 10.66 (s, 1H, OH), 8.48 (s, 1H, ArCH=N-R), 7.40 (d, 1H,
J
J
6,5 = 7.5 Hz, H-6), 7.14–7.09 (m, 1H, H-5, H-3, H-6'), 6.92 (d, 1H, J3',4' = 7.0, H-3'), 6.87 (d, 1H,
−1
4',3' = 7.0, H-4'), 2.38 (s, 3H, CH
3
), 2.33 (s, 3H, CH
3
); IR (KBr, cm ): 3350 (OH), 3310 (N-H), 1650
, C = 68.45, H = 5.37, N = 9.39,
O = 16.09, Found C = 68.46, H = 6.08, N = 9.40, O = 16.10; EI MS m/z (% rel. abund.): 298.
18 2 3
(C=O), 1632 (C=N), 1248 (C-N); Anal. Calcd for C17H N O
(
(
(
E)-N'-(3-Hydroxy-2-iodo-4-methoxybenzylidene)-2,4-dimethylbenzohydrazide (14). Yield: 0.738 g
1
87%); H-NMR (DMSO-d
6
): δ 11.88 (s, 1H, NH), 9.21 (s, 1H, OH), 8.48 (s, 1H, ArCH=N-R), 7.36
d, 1H, J6,5 = 7.5 Hz, H-6), 7.16 (s, 1H, H-3), 7.10 (d, 1H, J5,6 = 7.5 Hz, H-5), 6.85 (d, 1H, J6',5' = 7.0,
), 2.35 (s, 3H, CH ), 2.32 (s, 3H, CH ); IR
KBr, cm ): 3350 (OH), 3310 (N-H), 1650 (C=O), 1632 (C=N), 1248 (C-N); Anal. Calcd for
, C = 48.13, H = 4.04, N = 6.60, O = 11.31, Found C = 48.14, H = 4.05, N = 6.62,
O = 11.33; EI MS m/z (% rel. abund.): 424.
H-6'), 6.68 (d, 1H, J5',6' = 7.0, H-5'), 3.84 (s, 3H, OCH
3
3
3
−1
(
17 2 3
C H17IN O
(
1
E)-N'-(2-Hydroxy-4-methoxybenzylidene)-2,4-dimethylbenzohydrazide (15). Yield: 0.488 g (82%);
H-NMR (DMSO-d
6
): δ 11.78 (s, 1H, NH), 11.60 (s, 1H, OH), 8.41 (s, 1H, ArCH=N-R), 7.40 (d, 1H,
J
6,5 = 7.5 Hz, H-6), 7.38 (d, 1H, J3',5' = 2.0 Hz, H-3'), 7.14 (s, 1H, H-3), 7.11 (d, 1H, J5,6 = 7.5 Hz, H-5),
6
.53 (d, 1H, J5',6' = 7.5 Hz, H-5'), 6.50 (d, 1H, J = 7.5 Hz, H-6'), 2.37 (s, 3H, CH ), 2.33 (s, 3H,
6',5' 3
−1
CH
3
); IR (KBr, cm ): 3390 (OH), 3300 (N-H), 1655 (C=O), 1630 (C=N), 1250 (C-N); Anal. Calcd for
, C = 68.45, H = 5.37, N = 9.39, O = 16.09, Found C = 68.46, H = 6.08, N = 9.40,
O = 16.10; EI MS m/z (% rel. abund.): 298.
17 18 2 3
C H N O

Molecules 2013, 18
10924
1
(
E)-N'-(3,5-Dimethoxybenzylidene)-2,4-dimethylbenzohydrazide (16). Yield: 0.511 g (82%); H-NMR
DMSO-d ): δ 11.67 (s, 1H, NH), 8.23 (s, 1H, ArCH=N-R), 7.36 (d, 1H, J6,5 = 7.5 Hz, H-6), 7.14 (s,
H, H-3), 7.11 (d, 1H, J5,6 = 7.5 Hz, H-5), 6.86 (s, 2H, H-2', H-6'), 6.57 (s, 1H, H-4'), 3.86 (s, 6H, 2×
(
6
1
−1
OCH ), 2.36 (s, 3H, CH ), 2.33 (s, 3H, CH ); IR (KBr, cm ): 3310 (N-H), 1650 (C=O), 1628 (C=N),
3
3
3
1252 (C-N); Anal. Calcd for C18
H N
20 2
O
3
, C = 69.21, H = 6.45, N = 8.97, O = 15.37, Found C = 69.20,
H = 6.44, N = 8.98, O = 15.38; EI MS m/z (% rel. abund.): 312.
1
(
E)-N'-(3,4-Dimethoxybenzylidene)-2,4-dimethylbenzohydrazide (17). Yield: 0.524 g (84%); H-NMR
DMSO-d ): δ 11.40 (s, 1H, NH), 8.20 (s, 1H, ArCH=N-R), 7.35 (d, 1H, J6,5 = 7.5 Hz, H-6), 7.18 (s,
H, H-2′) 7.12 (s, 1H, H-3), 7.10 (d, 1H, J5,6 = 7.5 Hz, H-5), 6.11 (d, 1H, J5',6' = 8.0 Hz, H-5'), 6.81 (d,
H, J6',5' = 8.0 Hz, H-6'), 3.90 (s, 3H, OCH3), 3.85 (s, 3H, OCH3), 2.38 (s, 3H, CH ), 2.34 (s, 3H,
(
6
1
1
3
−1
3
CH ); IR (KBr, cm ): 3340 (N-H), 1653 (C=O), 1634 (C=N), 1256 (C-N); Anal. Calcd for
C H N O , C = 69.21, H = 6.45, N = 8.97, O = 15.37, Found C = 69.20, H = 6.44, N = 8.98,
1
8
20
2
3
O = 15.38; EI MS m/z (% rel. abund.): 312.
1
(
E)-N'-(3-Methoxybenzylidene)-2,4-dimethylbenzohydrazide (18). Yield: 0.468 g (83%); H-NMR
DMSO-d ): δ 11.66 (s, 1H, NH), 8.28 (s, 1H, ArCH=N-R), 7.45-7.38 (m, 4H, H-4', H-5', H-6', H-6),
.13 (s, 1H, H-3), 7.11 (d, 1H, J5,6 = 7.5 Hz, H-5), 7.08 (d, 1H, J2',6' = 2.0 Hz, H-2'), 3.88 (s, 3H,
(
6
7
−1
OCH3), 2.36 (s, 3H, CH
251 (C-N); Anal. Calcd for C17
H = 6.44, N = 9.91, O = 11.34; EI MS m/z (% rel. abund.): 282.
3
), 2.33 (s, 3H, CH
3
); IR (KBr, cm ): 3324 (N-H), 1658 (C=O), 1638 (C=N),
1
18 2 2
H N O
, C = 72.32, H = 6.43, N = 9.92, O = 11.33, Found C = 72.33,
1
(
E)-N'-(2-Methylbenzylidene)-2,4-dimethylbenzohydrazide (19) [40]; Yield: 0.452 g (85%); H-NMR
DMSO-d ): δ 11.66 (s, 1H, NH), 8.28 (s, 1H, ArCH=N-R), 7.35-7.32 (m, 4H, H-3', H-4', H-5', H-6),
.12 (s, 1H, H-3), 7.09 (d, 1H, J5,6 = 7.5 Hz, H-5), 7.01 (d, 1H, J6',5' = 8.0 Hz, H-6'), 2.38 (s, 3H, CH3),
(
6
7
2
−1
3 3
.35 (s, 3H, CH ), 2.32 (s, 3H, CH ); IR (KBr, cm ): 3330 (N-H), 1652 (C=O), 1642 (C=N), 1255
(
C-N); Anal. Calcd for C H N O, C = 76.66, H = 6.81, N = 10.52, O = 6.01, Found C = 76.68,
17 18 2
H = 6.82, N = 10.50, O = 6.02; EI MS m/z (% rel. abund.): 266.
1
(
(
(
(
E)-N'-(4-Bromo-3-florobenzylidene)-2,4-dimethylbenzohydrazide (20). Yield: 0.605 g (87%); H-NMR
DMSO-d ): δ 11.85 (s, 1H, NH), 8.82 (s, 1H, ArCH=N-R), 7.45–7.38 (m, 3H, H-5', H-6', H-6), 7.21
6
d, 1H, J2',6' = 2.0 Hz, H-2'), 7.11 (s, 1H, H-3), 7.08 (d, 1H, J5,6 = 7.5 Hz, H-5), 2.38 (s, 3H, CH
3
), 2.34
); IR (KBr, cm ): 3310 (N-H), 1651 (C=O), 1632 (C=N), 1247 (C-N); Anal. Calcd for
O, C = 55.03, H = 4.04, N = 8.02, O = 4.59, Found C = 55.03, H = 4.03, N = 8.04,
O = 4.59; EI MS m/z (% rel. abund.): 348.
−1
s, 3H, CH
3
16 2
C H14BrFN
1
(
E)-N'-(4-Methoxybenzylidene)-2,4-dimethylbenzohydrazide (21). Yield: 0.496 g (88%); H-NMR
(
DMSO-d ): δ 11.30 (s, 1H, NH), 8.10 (s, 1H, ArCH=N-R), 7.62 (d, 2H, J = J6',5' = 8.0 Hz, H-2',
6
2',3'
H-6'), 7.34 (d, 1H, J6,5 = 7.0 Hz, H-6), 7.11 (s, 1H, H-3), 7.08 (d, 1H, J5,6 = 7.0 Hz, H-5), 6.92 (d, 2H,
3',2' = J5',6' = 8.0 Hz, H-3', H-5'), 3.84 (s, 3H, OCH3), 2.36 (s, 3H, CH ), 2.33 (s, 3H, CH ); IR
KBr, cm ): 3342 (N-H), 1661 (C=O), 1640 (C=N), 1254 (C-N); Anal. Calcd for C17
C = 72.32, H = 6.43, N = 9.92, O = 11.33, Found C = 72.33, H = 6.45, N = 9.92, O = 11.32; EI MS m/z
% rel. abund.): 282.
J
3
3
−1
(
18 2 2
H N O ,
(

Molecules 2013, 18
10925
1
(
E)-2,4-Dimethyl-N'-((pyridin-3-yl)methylene)benzohydrazide (22). Yield: 0.455 g (90%); H-NMR
DMSO-d ): δ 11.82 (s, 1H, NH), 8.84 (s, 1H, ArCH=N-R), 8.61 (s, 1H, H-2'), 8.31 (s, 1H, H-6'), 8.13
d, 1H, J4',5' = 7.0 Hz, H-4'), 7.49 (d, 1H, J5',4' = 7.0 Hz, H-5'), 7.38 (d, 1H, J6,5 = 7.0 Hz, H-6), 7.14 (s,
(
6
(
−
1
1
H, H-3), 7.12 (d, 1H, J5,6 = 7.5 Hz, H-5), 2.37 (s, 3H, CH ), 2.33 (s, 3H, CH ); IR (KBr, cm ): 3360
3
3
(
N-H), 1670 (C=O), 1645 (C=N), 1258 (C-N); Anal. Calcd for C15
H
15
N
3
O, C = 71.13, H = 5.97,
N = 16.59, O = 6.32, Found C = 71.14, H = 5.98, N = 16.61, O = 6.33; EI MS m/z (% rel. abund.): 253.
1
(
E)-N'-(4-Methylbenzylidene)-2,4-dimethylbenzohydrazide (23). Yield: 0.490 g (92%); H-NMR
6
(DMSO-d ): δ 11.58 (s, 1H, NH), 8.27 (s, 1H, ArCH=N-R), 7.61 (d, 2H, J2',3' = J6',5' = 7.5 Hz, H-2',
H-6'), 7.35 (d, 1H, J6,5 = 7.5 Hz, H-6), 7.32 (d, 2H, J3',2' = J5',6' = 7.5 Hz, H-3', H-5'), 7.17 (s, 1H, H-3),
−
1
7
1
.13 (d, 1H, J = 7.5 Hz, H-5), 2.37 (s, 3H, CH ), 2.33 (s, 6H, 2× CH ), IR (KBr, cm ): 3345 (N-H),
5
,6
3
3
658 (C=O), 1632 (C=N), 1250 (C-N); Anal. Calcd for C17
H N
18 2
O, C = 76.66, H = 6.81, N = 10.52,
O = 6.01, Found C = 76.67, H = 6.82, N = 10.50, O = 6.02; EI MS m/z (% rel. abund.): 266.
1
(
E)-2,4-Dimethyl-N'-((pyridin-4-yl)methylene)benzohydrazide (24). Yield: 0.455 g (90%); H-NMR
(
DMSO-d ): δ 11.99 (s, 1H, NH), 8.65 (d, 2H, J2',3' = J6',5' = 6.0 Hz, H-2', H-6'), 8.30 (s, 1H,
6
ArCH=N-R), 7.66 (d, 2H, J3',2' = J5',6' = 6.0 Hz, H-3', H-5'), 7.40 (d, 1H, J6,5 = 7.5 Hz, H-6), 7.15 (s,
−1
1
H, H-3), 7.12 (d, 1H, J5,6 = 7.5 Hz, H-5), 2.38 (s, 3H, CH
3
), 2.32 (s, 3H, CH
3
), IR (KBr, cm ): 3350
15 3
(N-H), 1654 (C=O), 1638 (C=N), 1254 (C-N); Anal. Calcd for C15H N O, C = 71.13, H = 5.97,
N = 16.59, O = 6.32, Found C = 71.13, H = 6.00, N = 16.62, O = 6.32; EI MS m/z (% rel. abund.): 253.
1
(
E)-2,4-Dimethyl-N'-((pyridin-2-yl)methylene)benzohydrazide (25). Yield: 0.414 g (82%); H-NMR
6
(DMSO-d ): δ 11.87 (s, 1H, NH), 8.55 (d, 2H, J6',5' = 6.0 Hz, H-6'), 8.25 (s, 1H, ArCH=N-R), 7.90–7.86
(
m, 2H, H-4', H-5'), 7.38 (d, 1H, J6,5 = 7.0 Hz, H-6), 7.13 (s, 1H, H-3), 7.10 (d, 1H, J5,6 = 7.0 Hz, H-5),
−1
6
1
.95 (d, 2H, J3',4' = 6.5 Hz, H-3'), 2.37 (s, 3H, CH
3
3
), 2.33 (s, 3H, CH ), IR (KBr, cm ): 3342 (N-H),
656 (C=O), 1636 (C=N), 1253 (C-N); Anal. Calcd for C15
15 3
H N
O, C = 71.13, H = 5.97, N = 16.59,
O = 6.32, Found C = 71.15, H = 6.00, N = 16.62, O = 6.32; EI MS m/z (% rel. abund.): 253.
1
(
(
(
(
E)-2,4-Dimethyl-N'-((thiophen-2-yl)methylene)benzohydrazide (26). Yield: 0.454 g (88%); H-NMR
DMSO-d ): δ 11.63 (s, 1H, NH), 8.51 (s, 1H, ArCH=N-R), 7.66 (s, 1H, H-5'), 7.43 (s, 1H, H-2'), 7.35
d, 1H, J = 7.5 Hz, H-6), 7.11–7.08 (m, 3H, H-3, H-5, H-4'), 2.36 (s, 3H, CH ), 2.33 (s, 3H, CH ), IR
6
6
,5
3
3
−1
KBr, cm ): 3350 (N-H), 1654 (C=O), 1638 (C=N), 1254 (C-N); Anal. Calcd for C14
H
14
N
2
OS,
C = 65.09, H = 5.46, N = 10.84, O = 6.19, Found C = 65.08, H = 5.48, N = 10.83, O = 6.18; EI MS m/z
% rel. abund.): 258.
(
1
Methyl 4-((E)-(2,4-dimethylbenzoylimino)methyl)benzoate (27). Yield: 0.558 g (90%); H-NMR
DMSO-d ): δ 11.83 (s, 1H, NH), 8.36 (s, 1H, ArCH=N-R), 8.04 (d, 2H, J2',3' = J6',5' = 7.5 Hz, H-2',
H-6'), 7.86 (d, 2H, J3',2' = J5',6' = 7.5 Hz, H-3', H-5'), 7.38 (d, 1H, J = 7.5 Hz, H-6), 7.14 (s, 1H, H-3),
(
6
6,5
7
.11 (d, 1H, J5,6 = 7.5 Hz, H-5), 3.88 (s, 3H, OCH
3
), 2.36 (s, 3H, CH
3
), 2.33 (s, 3H, CH
3
), IR (KBr,
−1
cm ): 3345 (N-H), 1658 (C=O), 1632 (C=N), 1250 (C-N); Anal. Calcd for C18
18 2 3
H N O
, C = 69.66,
H = 5.85, N = 9.03, O = 15.47, Found C = 69.67, H = 5.86, N = 9.04, O = 15.48; EI MS m/z (% rel.
abund.): 310.

Molecules 2013, 18
10926
1
(
E)-N'-(4-Chlorobenzylidene)-2,4-dimethylbenzohydrazide (28). Yield: 0.526 g (92%); H-NMR
(
DMSO-d ): δ 11.72 (s, 1H, NH), 8.30 (s, 1H, ArCH=N-R), 7.74 (d, 2H, J2',3' = J6',5' = 7.5 Hz, H-2',
6
H-6'), 7.54 (d, 2H, J3',2' = J5',6' = 7.5 Hz, H-3', H-5'), 7.37 (d, 1H, J6,5 = 7.5 Hz, H-6), 7.13 (s, 1H, H-3),
−1
7
.10 (d, 1H, J5,6 = 7.5 Hz, H-5), 2.36 (s, 3H, CH ), 2.33 (s, 3H, CH ), IR (KBr, cm ): 3345 (N-H),
3
3
1
658 (C=O), 1632 (C=N), 1250 (C-N); Anal. Calcd for C16
H15ClN
2
O, C = 67.02, H = 5.27, N = 9.77,
O = 5.58, Found C = 67.03, H = 5.28, N = 9.78, O = 5.57; EI MS m/z (% rel. abund.): 286.
Methyl 2-((E)-(2,4-dimethylbenzoylimino)methyl)-3,5-dimethoxybenzoate (29). Yield: 0.673 g (91%);
1
H-NMR (DMSO-d
6
): δ 11.62 (s, 1H, NH), 8.41 (s, 1H, ArCH=N-R), 7.36 (d, 1H, J6,5 = 7.0 Hz, H-6),
7
6
.11–7.08 (m, 3H, H-3, H-5, H-6'), 6.72 (d, 1H, J4',6' = 2.0 Hz, H-4'), 3.89 (s, 3H, R-COOCH ), 3.81(s,
3
−1
H, 2× OCH ), 2.37 (s, 3H, CH ), 2.34 (s, 3H, CH ), IR (KBr, cm ): 3345 (N-H), 1658 (C=O), 1632
3
3
3
(
C=N), 1250 (C-N); Anal. Calcd for C20
H
22
N
2
O
5
, C = 64.85, H = 5.99, N = 7.56, O = 21.60, Found
C = 64.87, H = 5.97, N = 7.58, O = 21.62; EI MS m/z (% rel. abund.): 370.
1
(
E)-N'-(4-Nitrobenzylidene)-2,4-dimethylbenzohydrazide (30). Yield: 0.499 g (84%); H-NMR
(
DMSO-d ): δ 11.97 (s, 1H, NH), 8.87 (s, 1H, ArCH=N-R), 8.31 (d, 2H, J2',3' = J6',5' = 8.5 Hz, H-2',
6
H-6'), 7.99 (d, 2H, J3',2' = J5',6' = 8.5 Hz, H-3', H-5'), 7.40 (d, 1H, J6,5 = 7.5 Hz, H-6), 7.15 (s, 1H, H-3),
−1
7
.12 (d, 1H, J5,6 = 7.5 Hz, H-5), 2.38 (s, 3H, CH
3
), 2.34 (s, 3H, CH
3
), IR (KBr, cm ): 3345 (N-H),
1658 (C=O), 1632 (C=N), 1250 (C-N); Anal. Calcd for C16
15 3 3
H N O
, C = 64.64, H = 5.09, N = 14.13,
O = 16.14, Found C = 64.65, H = 5.09, N = 14.14, O = 16.15; EI MS m/z (% rel. abund.): 297.
5
. Conclusions
In this study we synthesized thirty (30) 2,4-dimethylbenzoylhydrazones derivatives. Out of thirty
compounds, six (6) compounds showed better activities than the reference compound (n-propyl gallate)
for DPPH activity and three compounds showed better activity than standard toward superoxide anion.
Along with these results we also reported three new crystal structures. We believe that these molecules
merit further study of their antiaging, antioxidant as well as potential anticancer activities.
Acknowledgments
Authors would like to acknowledge Universiti Teknologi MARA for the financial support under
Dana Kecemerlangan Grant Scheme.
Conflicts of Interest
The authors declare no conflict of interest.
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Sample Availability: Contact authors.
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