Design, synthesis, and antimicrobial evaluation of novel pyrazoles and pyrazolyl 1,3,4-thiadiazine derivatives

Article abstract of DOI:10.3390/molecules23092092

A novel series of pyrazolyl 1,3,4-thiadiazines 5a–c, 8a–c, 12, 15a–c, 17a–c, and 20 was prepared from the reaction of pyrazole-1-carbothiohydrazide 1a,b with 2-oxo-N⁰-arylpropanehydrazonoyl chloride, 2-chloro-2-(2-arylhydrazono)acetate, and 3-bromoacetylcoumarin. Moreover, the regioselective reaction of 5-pyrazolone-1- carbothiohydrazide 1a with 4-substituted diazonium salts and 4-(dimethylamino)benzaldehyde gave the corresponding hydrazones 21a–c and 22. The newly prepared compounds were characterized by spectroscopy and elemental analysis. Many new synthesized compounds showed considerable antimicrobial activity against tested microorganisms. Hydrazones 21a–c and 22 showed remarkable antibacterial and antifungal activities. 4-(2-(p-tolyl) hydrazineylidene)-pyrazole-1-carbothiohydrazide 21a displayed the highest antibacterial and antifungal activities with minimum inhibitory concentration (MIC) values lower than standard drugs chloramphenicol and clotrimazole, in the range of 62.5–125 and 2.9–7.8 μg/mL, respectively.

Full text of DOI:10.3390/molecules23092092

molecules
Article
Design, Synthesis, and Antimicrobial Evaluation of
Novel Pyrazoles and Pyrazolyl
1,3,4-Thiadiazine Derivatives
Ibrahim Ali M. Radini
Chemistry Department, Faculty of Science, Jazan University, Jazan 2097, Saudi Arabia; iradini44@gmail.com;
Tel.: +966-566-644-4196
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Received: 24 July 2018; Accepted: 19 August 2018; Published: 21 August 2018
Abstract: A novel series of pyrazolyl 1,3,4-thiadiazines 5a
from the reaction of pyrazole-1-carbothiohydrazide 1a
–
c
,
,
8a
–c, 12, 15a–c, 17a–c, and 20 was prepared
b with 2-oxo-N0-arylpropanehydrazonoyl
chloride, 2-chloro-2-(2-arylhydrazono)acetate, and 3-bromoacetylcoumarin. Moreover, the regioselective
reaction of 5-pyrazolone-1- carbothiohydrazide 1a with 4-substituted diazonium salts and
4-(dimethylamino)benzaldehyde gave the corresponding hydrazones 21a–c and 22. The newly
prepared compounds were characterized by spectroscopy and elemental analysis. Many new
synthesized compounds showed considerable antimicrobial activity against tested microorganisms.
Hydrazones 21a–c and 22 showed remarkable antibacterial and antifungal activities. 4-(2-(p-tolyl)
hydrazineylidene)-pyrazole-1-carbothiohydrazide 21a displayed the highest antibacterial and
antifungal activities with minimum inhibitory concentration (MIC) values lower than standard
drugs chloramphenicol and clotrimazole, in the range of 62.5–125 and 2.9–7.8 µg/mL, respectively.
Keywords: pyrazole-1-carbothiohydrazide; 1,3,4-thiadiazines; hydrazonyl chlorides; antimicrobial
activity; MIC
1. Introduction
Recently, the incidence of microbial infections had been increased dramatically because of
the misuse of antibiotics has caused the pathogens to become resistant to them and which has
led to serious health hazards [1]. The rate of bacterial resistance to antibiotics is higher than
the rate of development of new classes of antibiotics [
2
] so the design and synthesis of new
compounds have potential antimicrobial activity are very important issue. Pyrazole derivatives
have great attention due to their interesting biological and pharmaceutical activities such as
antidepressant [
antiviral [10 11], anticonvulsant [12], and insecticidal activities [13]. In addition, the natural pyrazole
C-glycoside, pyrazofurin (4-hydroxy-3 -D-dribofuranosyl-1H-pyrazole-5-carboxamide) has a broad
3], antioxidant [4], anti-inflammatory [5], anticancer [6], antimicrobial [7–9],
,
β
spectrum of antimicrobial, antiviral, and antitumor activities [14]. It is well known that pyrazoles
possess significant antibacterial activity. There are many antibiotic drugs containing pyrazole moiety
such as Sulfaphenazole and PNU172576 (Figure 1).
Heterocycles containing the thiadiazines moiety have biological and pharmaceutical
importance [15
good antimicrobial activity. Motivated by the preceding information and continuation of my research
program on the synthesis of novel bioactive heterocycles [ 20 23] I designed and synthesized a
–18]. Recently, Khidre et al. [19] reported that 1,3,4-thiadiazine derivatives have a
7, –
novel series of pyrazole and pyrazolyl 1,3,4-thiadiazine derivatives, for antimicrobial evaluation,
starting from pyrazole-1-carbothiohydrazide 1a,b.
Molecules 2018, 23, 2092; doi:10.3390/molecules23092092
www.mdpi.com/journal/molecules

Molecules 2018, 23, 2092
2 of 12
Figure 1. Representative structures having pyrazole moieties as antimicrobial agents.
2. Results
2.1. Chemistry
My strategy to synthesize a new heterocyclic compounds involved the use of pyrazole-1-
carbothiohydrazide 1a that contains a number of chemically distinct functionalities, which can
be reacted with different hydrazonyl chlorides, -haloketones, diazonium salts, and aldehydes
,
b
α
to a library of molecular diverse compounds (Schemes 1–4). As illustrated in Scheme 1,
3-methyl-5-oxo-4,5-dihydro-1H-pyrazole-1-carbothiohydrazide 1a was prepared in a very good yield
by reaction of equimolar amount of ethyl acetoacetate with thiocarbohydrazide in ethanol containing a
catalytic amount of HCl at reflux temperature. Treatment with a mixture of thiocarbohydrazide in (HCl,
0.05 M) with acetyl acetone at RT for 1.5 h afforded 3,5-dimethyl-1H-pyrazole-1-carbothiohydrazide
1b [24]
. The molecular structure of compounds 1a was confirmed by elemental analyses and
spectroscopic methods. The infrared spectrum of 1a showed a characteristic bands at 3292, 3250,
3182, and 1685 cm−1 due to NH, NH2, and C=O functions, respectively. 1H-NMR revealed two
singlet peaks at 2.02 and 3.28 ppm due to the CH3 and CH2, respectively. Also, molecular weight
determination (MS) of 1a showed the molecular ion peaks at m/z 172.
Scheme 1. Synthesis of pyrazole-1-carbothiohydrazides 1a and 1b.
The carbothiohydrazide moiety in 1a
pyrazolyl 1,3,4-thiadiazine derivatives. Pyrazole-1 carbothiohydrazide 1a was reacted with 2-oxo-
N0-arylpropanehydrazonoyl chlorides 2a
in hot ethanol in the presence of Et3N to yield
5-methyl-2-(5-methyl-6-(aryldiazenyl)-4H-1,3,4-thiadiazin-2-yl)-2,4-dihydro-3H-pyrazol-3-ones 5a
in good yields, via intermediates and (Scheme 2). Similarly, 2-(3-methyl-5-oxo- 4,5-dihydro-
1H-pyrazol-1-yl)-6-(phenyldiazenyl)-4H-1,3,4-thiadiazin-5(6H)-ones 8a were synthesized, in high
yields, from the reaction of 1a with ethyl 2-chloro-2- (2-arylhydrazono)acetate derivatives
6a under the same reaction conditions described for the preparation of 5a . 5-methyl-2-
,b was reacted with selected electrophiles to prepare
–c
–c,
3
4
–
c
–
c
–c

Molecules 2018, 23, 2092
3 of 12
(5-(2-oxo-2H-chromen-3-yl)-4H-1,3,4-thiadiazin-2-yl)-2,4-dihydro-3H-pyrazol-3-one 12 is furnished in
a good yield when 1a was refluxed with 3-bromoacetylcoumarin 9 in ethanol (Scheme 2).
The structure of the compounds 5, 8, and 12 was confirmed by elemental analyses and
spectroscopic methods. The IR spectrum of thiadiazinyl pyrazolone 5c, as a representative example,
revealed the lack of an NH2 absorption peak at 3292 and 3250 cm−1 and appearance of an absorption
peak at 3149 cm−1 owing to the NH group. The 1H-NMR spectrum of 5c exhibited new signals at
δ
1.41,
7.33, and 7.37 ppm assigned to methyl and aromatic protons, in addition, the D2O exchangeable signal
at
11.57 ppm due to cyclic NH. Its 13C-NMR spectrum of 5c revealed the lack of C=S signal at 180 ppm
and appearance 12 carbon signals. Moreover, the mass spectra of compounds 5a gave molecular ion
δ
–
c
peaks at m/z 314, 328, and 348, respectively. This clearly indicates the carbothiohydrazide moiety was
involved in cyclization reaction with hydrazonyl chlorides 2a–c to give thiadiazine.
N
N
O
N
N
H
N
N
N
R1
N
N
NH2
OH
N
N
O
Cl
- H2O
O
NH2
O
2a-c
NH
O
S
S
S
EtOH/Et3N
N
N
R1
N
N
R1
N
N
R1
4
5a-c
3
2-5a
b
c
, R1 = C6H5; , 4-MeC6H4; , 4-ClC6H4
OEt
N
N
N
H
O
N
N
R1
N
N
N
NH2
OEt
NH
- EtOH
N
N
O
Cl
6a-c
O
H
S
S
N
O
NH2
EtOH/Et3N
N
O
S
O
N
N
N
1a
R1
R1
8a-c
7
6-8a
b
c
, R1 = C6H5; , 4-MeC6H4; , 4-ClC6H4
O
R2
N
N
N
Br
N
R2
N
N
9
- H2O
N
N
NH2
OH
S
NH2
O
O
N
N
O
EtOH
S
S
O
R2
R2
10
11
12
R2 =
O
O
Scheme 2. Synthesis of compounds 5a–c, 8a–c, and 12.
In a similar way, 6-(aryldiazenyl)-4H-1,3,4-thiadiazines 15a
5(6H)-ones 17a , and 5-aryl-4H-1,3,4-thiadiazines 20 were synthesized in very good yields from the
reaction of pyrazole-1-carbothiohydrazide 1b with hydrazonyl cholrides 2a 6a , and -haloketone
, respectively, under similar reaction condition as described before (Scheme 3). Compound 20
–c, 6-(aryldiazenyl)-4H-1,3,4-thiadiazin-
–c
–
c,
–c
α
9
was previously synthesized from a one pot reaction of 3-(2-bromoacetyl)- 2H-chromen-2-ones,
thiocarbohydrazide, and pentane-2,4-dione [25]. The IR spectrum of 17b revealed the lack of NH2 band
present in the IR spectra of starting pyrazole 1b and the appearance of new absorption bands at 3176
and 1680 cm−1 corresponding to NH and CO functional groups, respectively. Likewise, the 1H-NMR

Molecules 2018, 23, 2092
4 of 12
spectra showed a new singlet signal at
δ
3.11 ppm due to H-6 of thiadiazine, two doublet signals at
δ
7.13, 7.25 ppm integrated for four protons of 4-disubstitued benzene ring, and D2O-exchangeable
signals at 11.23 ppm due to NH. Its 13C-NMR spectrum did not exhibit the C=S signal at 180 ppm
which observed in the starting material, but instead displayed 13 carbon signals. The mass spectra
of 17a
–c showed molecular ion peaks at m/z 314, 328, and 348, respectively, which were in an accord
with the calculated masses (c.f. experimental section).
Scheme 3. Synthesis of compounds 15a–c, 17a–c and 20.
The coupling reaction of 1a with 4-substituted arenediazonium chloride was performed in
◦
ethanol containing sodium acetate at 0–5 C to give the corresponding hydrazones 21a
–
c. Also,
the reaction of 1a with 4-(dimethylamino)benzaldehyde in ethanol containing few drops of HCl gave
0
N -(4-(dimethylamino)benzylidene)-3-methyl-5-oxo-4,5-dihydro-1H-pyrazole-1-carbothiohydrazide 22
(Scheme 4). The 1H-NMR spectra of 21a
–c showed lack the singlet signal due to CH2 (C-4 of pyrazolone)
and showed an aromatic multiplets in the region 7.22–7.84 ppm. In addition, new D2O-exchangeable
signals appeared in the region 11.74–12.24 ppm. These data support the successful coupling C-4 of
pyrazolone with 4-substituted arenediazonium chloride. The IR spectrum of hydrazone 22 did not
show an NH2 band. The 1H-NMR spectrum of 22 showed a new singlet signal at 9.65 ppm due to the
azamethine proton (N=CH) and an aromatic multiplets at 6.80 and 7.91 ppm. Also, the mass spectra of
21a–c and 22 are in an agreement with the calculated masses.

Molecules 2018, 23, 2092
5 of 12
Scheme 4. Synthesis of compounds 21a–c and 22.
2.2. Antimicrobial Activity
In vitro antimicrobial screening of the newly synthesized compounds was carried out by the agar
diffusion method using cultures of two fungal strains (Candida albicans (ATCC 10231) and Aspergillus
niger (ATCC 16404), as well as four bacteria strains, two Gram positive bacteria (Staphylococcus aureus
(ATCC 29213), Bacillus subtilus (ATCC 6051), and two Gram negative bacteria (Klebsiella pneumoniae
(ATCC 700603) and Escherichia coli (ATCC 25922). The standard antibiotic Chloramphenicol and
Antifungal Clotrimazole was used as controls to evaluate the potency of the compounds being studied
under the same conditions.
As shown in Table 1 compounds 5b
,
8a
,
,
12, and 17a were found to be inactive against all
15b 15c 17b 17c, and 20 exhibited low activity
microorganisms while compounds 5a 5c
,
,
8c 15a
,
,
,
,
against some microorganisms only and inactive against others. Compounds 8b showed good activities
against fungi and Gram positive bacteria. Compound 22 displayed good activities against all
microorganisms except Candida albicans did not show any activity. Compounds 21a–c displayed a broad
spectrum activity against all microorganisms. Compound 21c showed the highest activity against
Candida albicans with inhibition zones of 25 mm while compound 21a showed the highest activity
against other strains, e.g., Aspergillus niger, Staphylococcus aureus, Bacillus subtilus, Klebsiella pneumoniae,
and Escherichia coli with inhibition zones 35, 22, 30, 20, and 27 mm, respectively. The variation in the
effectiveness of different compounds against microorganism depends on either the impermeability of
the cells of the microbes or on differences in the ribosomes of microbial cells [26]. It may be concluded
that the antimicrobial activity of the compounds is related to the cell wall structure of the bacterium as
well as the structure of the pyrazole derivatives itself. It is possible because the cell wall is essential
to the survival of bacteria and some antibiotics are able to kill bacteria by inhibiting a step in the
synthesis of peptidoglycan. Gram-positive bacteria possess a thick cell wall containing many layers of
peptidoglycan and teichoic acids, but in contrast, Gram negative bacteria have a relatively thin cell
wall consisting of a few layers of peptidoglycan surround by a second lipid membrane containing
lipopolysaccharides and lipoproteins. These differences in cell wall structure can produce differences in
antibacterial susceptibility and some antibiotics can kill only Gram-positive bacteria and are ineffective
against Gram-negative pathogens [27].
On the other hand, it is obvious that compounds 21a
> 21b > 21c exhibited potent inhibition
activity owing to its characteristic skeleton that containing free carbothiohydrazide moiety that confer
its softness, six donating N atoms, and planar 4-substituted phenyl group compared with the other
pyrazolyl 1,3,4-thiadiazine derivatives.

Molecules 2018, 23, 2092
6 of 12
The compounds which showed greater antibacterial and antifungal activities were further assayed
for minimum inhibitory concentration (MIC), and the values are listed in Table 2. MIC is the
lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism.
Compounds 21a displayed low MIC value on Aspergillus niger, Staphylococcus aureus, B. subtilis,
and Klebsiella pneumoniae than standard drug Clotrimazole and Chloramphenicol and showed MIC
value on Candida albicans and Escherichia coli equal to standard drugs. The MIC value of compound
21b against Aspergillus niger, B. subtilis, and Klebsiella pneumoniae was equal to standard drugs
Clotrimazole and Chloramphenicol. Moreover, Compound 21c showed a MIC value on Aspergillus niger
Staphylococcus aureus, B. subtilis, Klebsiella pneumonia, and Escherichia coli equal to the standard drugs.
The structure–activity relationship revealed that compounds with pyrazole-1-carbothiohydrazide unit
21a
the presence of free carbothiohydrazide moiety increases the activity of 21a
electron donating substituents at the aromatic ring increased the activity of 21a.
,
21b
,
21c, and 22 showed higher activity than compounds have pyrazolyl thiadiazine unit. Further,
–
c
and the presence of
Table 1. In vitro antimicrobial activity of the synthesized compounds a,b
.
Fungi
Aspergillus
Gram Positive Bacteria
Gram Negative Bacteria
Comp. No.
Candida
albicans
Staphylococcus Bacillus
Klebsiella
Escherichia
coli
niger
aureus
subtilus
pneumoniae
5a
5b
15 ± 1
20 ± 1.53
na c
na
na
na
na
na
17 ± 1.00
na
na
na
5c
8a
12 ± 1.53
na
na
na
na
na
na
na
na
11 ± 0.58
na
na
8b
8c
12
20 ± 1.53
15 ± 2.65
13 ± 0.58
18 ± 0.58
15 ± 2.08
na
11 ± 0.58
na
na
na
9 ± 0.58
na
na
na
na
na
na
na
15a
15b
15c
17a
17b
17c
20
21a
na
na
na
na
na
12 ± 0.00
12 ± 0.58
na
na
na
na
na
na
na
na
na
15 ± 0.58
29 ± 1.00
15 ± 1.15
23 ± 1.53
na
na
na
na
na
na
na
na
na
15 ± 0.58
16 ± 0.58
na
30 ± 1.53
25 ± 0.58
23 ± 1.73
20 ± 0.58
30 ± 1.73
-
na
na
na
14 ± 1.00
16 ± 0.58
12 ± 0.58
27 ± 1.15
25 ± 0.58
25 ± 0.58
20 ± 1.53
24 ± 1.00
-
na
na
17 ± 1.15
na
13 ± 0.00
18 ± 3.06
25 ± 3.00
na
35 ± 3.00
32 ± 0.58
29 ± 1.00
26 ± 0.58
-
22 ± 1.15
21 ± 0.58
12 ± 1.53
15 ± 0.00
25 ± 0.58
-
20 ± 0.58
18 ± 2.08
13 ± 0.58
17 ± 0.58
24 ± 1.15
-
21b
21c
22
Chloramphenicol
Clotrimazole
a
-
24 ± 4.51
20 ± 0.58
Antimicrobial activity expressed as inhibition diameter zones in millimeters (mm) of synthesized compounds
b
against the pathological strains based on well diffusion assay. The experiment was carried out in triplicate and the
average zone of inhibition was calculated. na No activity.
c
Table 2. Minimum inhibitory concentration (MIC) in (µg/mL) for compounds 8b, 21a–c, and 22.
Minimum Inhibitory Concentration (MIC)
Candida
albicans
Aspergillus
niger
Staphylococcus Bacillus
Klebsiella
pneumoniae
Escherichia
coli
Comp. No.
aureus
subtilus
8b
21a
21b
21c
22
125 ± 2.52
7.8 ± 0.17
15.6 ± 0.76
11.6 ± 0.30
93.7 ± 0.95
—
187.5 ± 0.50
2.9 ± 0.06
5.8 ± 0.26
5.8 ± 0.65
46.4 ± 0.84
—
375 ± 3.00
125 ± 0.58
250 ± 8.08
187.5 ± 8.23
250 ± 4.36
187.5 ± 0.06
—-
500 ± 3.51
62.5 ± 0.50
125 ± 0.00
125 ± 1.00
250 ± 4.58
125 ± 0.58
—-
500 ± 4.51
62.5 ± 2.00
125 ± 2.65
125 ± 1.53
250 ± 3.21
125 ± 3.51
—-
na
125 ± 2.52
187.5 ± 8.23
125 ± 0.00
500 ± 8.00
125 ± 1.73
—
Chloramphenicol
Clotrimazole
7.8 ± 0.06
5.8 ± 0.06
na: No activity.

Molecules 2018, 23, 2092
7 of 12
3. Experimental Section
3.1. General Information
All melting points were determined on a digital Gallen-Kamp MFB-595 instrument (Gallenkamp,
London, UK) using open capillary tubes and are uncorrected. IR spectra were recorded on a Schimadzu
FTIR 440 spectrometer (Shimadzu, Tokyo, Japan) using KBr pellets. Mass spectra were performed
at 70 eV on an MS-50 Kratos (A.E.I.) spectrometer (Shimadzu, Tokyo, Japan) provided with a
data system. 1H-NMR and 13C-NMR spectra were recorded on a Bruker model (500 MHz) Ultra
Shield NMR spectrometer (Bruker, Coventry, UK) in CDCl3 or DMSO-d6 using tetramethylsilane
(TMS) as an internal standard; chemical shifts are reported as
δ ppm units. Solvents were dried
by standard techniques. The monitoring of the progress of all reactions and homogeneity of the
synthesized compounds was carried out and was run using thin layer chromatography (TLC)
aluminum sheets silica gel 60 F254 (Merck, Darmstadt, Germany). Compound 1b was prepared
previously by Alekseev et al. [24].
3.2. Synthesis
3-Methyl-5-oxo-4,5-dihydro-1H-pyrazole-1-carbothiohydrazide (1a). Thiocarbohydrazide (10.6 g,
0.1 mol) was dissolved in a mixture of ethanol (20 mL) and HCl (1 mL) and ethyl acetoacetate
was added (13 mL, 0.1 mol). The mixture was refluxed for 1 h. After cooling, the white precipitate
was filtered off, washed with ethanol, and dried under reduced pressure. White crystals, yield (92%),
m.p. 135–136 ◦C. IR (KBr)
ν
(cm−1): 3292, 3250, 3182 (NH2 & NH), 1685 (C=O), 1647 (C=N), 1H-NMR
(500 MHz, CDCl3) (ppm): 2.02 (s, 3H, CH3), 3.28 (s, 2H, pyrazole-H4), 8.7 (d, D2O exchangeable,
δ
2H, NH2), 10.18 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, CDCl3) δC (ppm): 15.5 (CH3),
43.0 (CH2, pyrazole-C4), 160.5 (pyrazole-C3), 166 (C=O), 179 (C=S); MS m/z (%): 172 [M]+ (11%),
130 (100); Anal. Calcd. for C5H8N4OS (172.21): C, 34.87; H, 4.68; N, 32.54, Found: C, 34.57; H, 4.50;
N, 32.41%.
3.2.1. General procedure for synthesis compounds 5, 8, 12, 15, 17, and 20
Equimolar amounts of 1a or 1b (1 mmol) and 2-oxo-N-arylpropanehydrazonoyl chloride
2a
(1 mmol) in absolute ethanol (30 mL) (few drops of triethylamine was added in case of 2a
6a ) was heated under reflux for 3–6 h (TLC), then left to cool. The solid was isolated by filtration,
washed with ethanol, dried, and recrystallized from (EtOH).
–c; ethyl 2-chloro-2-(2-arylhydrazineylidene)acetate 6a
–c
or 3-(2-bromoacetyl)-2H-chromen-2-one
8
–c
and
–
c
5-Methyl-2-(5-methyl-6-(phenyldiazenyl)-4H-1,3,4-thiadiazin-2-yl)-2,4-dihydro-3H-pyrazol-3-one (5a). Red crystals,
yield (85%), m.p. 193–194 ◦C (EtOH); IR (νmax, cm−1): 3242 (NH), 1690 (C=O), 1600 (C=N),
1600–1440 (C=C); 1H-NMR (500 MHz, CDCl3) δH (ppm): 1.25 (s, 3H, CH3), 1.44 (s, 3H, CH3), 3.10 (s,
2H, pyrazole-H4), 7.33 (t, 2H, Ar-H), 7.44 (t, 2H, Ar-H), 8.04 (d, 1H, J = 8.5 Hz, Ar-H), 11.52 (s,
D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, CDCl3) δC (ppm): 12.2 (CH3), 16.0 (CH3), 44.0 (CH2,
pyrazole-C4), 95.4, 121.7, 129.7, 148.2, 151.8, 154.6, 160.5, 166.3 (C=O); MS m/z (%): 314 [M]+ (21%),
245(100); Anal. Calcd. for C14H14N6OS (314.37): C, 53.49; H, 4.49; N, 26.73, Found: C, 53.69; H, 4.19;
N, 26.67%.
5-Methyl-2- (5-methyl-6- (p-tolyldiazenyl)- 4H-1,3,4-thiadiazin- 2-yl)- 2,4- dihydro-3H- pyrazol-3-one (5b).
◦
Brown powder, yield (86%), m.p. 219–220 C (EtOH); IR (νmax, cm−1):, 3244 (NH), 1687 (C=O),
1591 (C=N), 1558–1440 (C=C); 1H-NMR (500 MHz, CDCl3) δH (ppm): 1.27 (s, 3H, CH3), 1.48 (s, 3H,
CH3), 1.54 (s, 3H, CH3), 3.11 (s, 2H, pyrazole-H4), 7.37 (dd, 2H, J = 8.5, 2.5 Hz, Ar-H), 7.82 (dd, 2H,
J = 7.6, 2.5 Hz, Ar-H), 11.54 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, CDCl3) δC (ppm):
12.9 (CH3), 16.5 (CH3), 21.5 (CH3), 42.9 (CH2, pyrazole-C4), 94.9, 128.7, 129.9, 138.6, 146.1, 152.4, 155.4,
160.7, 165.7 (C=O); MS m/z (%): 328 [M]+ (31%), 245 (100); Anal. Calcd. for C15H16N6OS (328.39): C,
54.86; H, 4.91; N, 25.59, Found: C, 55.01; H, 4.67; N, 25.51%.

Molecules 2018, 23, 2092
8 of 12
2-(6-((4-Chlorophenyl)diazenyl)-5-methyl-4H-1,3,4-thiadiazin-2-yl)-5-methyl-2,4-dihydro-3H-pyrazol-3-one
5c). Brown powder, yield (87%), m.p. 230–231 ◦C (EtOH); IR (νmax, cm−1): 3149 (NH), 1692 (C=O),
(
1654 (C=N), 1593–1462 (C=C); 1H-NMR (500 MHz, CDCl3) δH (ppm): 1.22 (s, 3H, CH3), 1.41 (s, 3H,
CH3), 2.53 (s, 2H, pyrazole-H4), 7.33 (dd, 2H, J = 9, 2.5 Hz, Ar-H), 7.37 (dd, 2H, J = 7, 2.5 Hz, Ar-H),
11.57 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, CDCl3) δC (ppm): 12.2 (CH3), 15.8 (CH3),
43.4 (CH2, pyrazole-C4), 96.0, 129.7, 131.7, 134.8, 147.0, 151.6, 154.0, 161.4, 165.6 (C=O); MS m/z (%):
348 [M]+ (35%), 350 [M + 2]+ (10), 245(100); Anal. Calcd. for C14H13ClN6OS (348.81): C, 48.21; H, 3.76;
N, 24.09, Found: C, 48.62; H, 3.46; N, 24.14%.
2-(3-Methyl-5- oxo-4,5-dihydro- 1H-pyrazol-1-yl◦)- 6-(phenyldiazenyl)- 4H-1,3,4-thiadiazin- 5(6H)-one (8a).
Yellow crystals, yield (87%), m.p. 220–221 C (EtOH); IR (νmax, cm−1): 3180 (NH), 1695 (C=O),
1681 (C=O), 1633 (C=N), 1598–1496 (C=C); 1H-NMR (500 MHz, CDCl3) δH (ppm): 2.14 (s, 3H, CH3),
2.27 (s, 2H, pyrazole-H4), 3.52 (s, 1H, thiadiazine-H6), 7.31 (t, 2H, Ar-H), 7.45 (t, 2H, Ar-H), 7.64 (d,
1H, J = 8.5 Hz, Ar-H), 10.6 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, CDCl3) δC (ppm):
14.9 (CH3), 42, 81.5, 121.4, 126.5, 129.5, 151.4, 152.9, 159.7, 165 (C=O), 169 (C=O); MS m/z (%): 316 [M]+
(20%), 350 (8), 98 (100); Anal. Calcd. for C13H12N6O2S (316.34): C, 49.36; H, 3.82; N, 26.57, Found: C,
49.06; H, 3.79; N, 26.35%.
2-(3-Methyl-5- oxo-4,5-dihydro- 1H-pyrazol-1-yl◦)-6- (p-tolyldiazenyl)- 4H-1,3,4-thiadiazin- 5(6H)-one (8b).
Yellow crystals, yield (84%), m.p. 238–239 C (EtOH); IR (νmax, cm−1): 3176 (NH), 1699 (C=O),
1695 (C=O), 1621 (C=N), 1593–1506 (C=C); 1H-NMR (500 MHz, CDCl3) δH (ppm): 2.16 (s, 3H, CH3),
2.22 (s, 2H, pyrazole-H4), 3.42 (s, 1H, thiadiazine-H6), 3.45 (s, 3H, CH3), 7.2 (d, 2H, J = 8 Hz, Ar-H),
7.3 (dd, 2H, J = 6.5, 2 Hz, Ar-H), 10.9 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, CDCl3) δC
(ppm): 14.5 (CH3), 21 (CH3), 42 (CH2), 79.5, 123.4, 129.5, 138.4, 148, 151.4, 159.7, 165 (C=O), 169 (C=O);
MS m/z (%): 330 [M]+ (25%), 350 (8), 98 (100); Anal. Calcd. for C14H14N6O2S (330.37): C, 50.90; H, 4.27;
N, 25.44, Found: C, 50.43; H, 4.15; N, 25.27%.
6-((4-Chlorophenyl)diazenyl)-2-(3-methyl-5-oxo-4,5-dihy◦dro-1H-pyrazol-1-yl)-4H-1,3,4-thiadiazin-5(6H)-one
(
8c). Yellow powder, yield (81%), m.p. 260–261 C (EtOH); IR (νmax, cm−1): 3184 (NH), 1693,
1689 (C=O), 1625 (C=N), 1583–1529 (C=C); 1H-NMR (500 MHz, CDMSO-d6) δH (ppm): 2.08 (s, 3H,
CH3), 2.13 (s, 2H, pyrazole-H4), 3.74 (s, 1H, thiadiazinone-H6), 7.24 (dd, 2H, J = 7, 2 Hz, Ar-H),
7.33 (dd, 2H, J = 9, 2 Hz, Ar-H), 10.58 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, CDCl3) δC
(ppm): 14.7 (CH3), 42 (CH2), 78, 123.9, 129.5, 134.4, 148, 153, 159.5, 164 (C=O), 168 (C=O); MS m/z (%):
349.87 [M]+ (2%), 293.77 (100); Anal. Calcd. for C13H11ClN6O2S (350.78): C, 44.51; H, 3.16; N, 23.96,
Found: C, 44.19; H, 3.02; N, 23.62%.
5-Methyl-2- (5-(2-oxo- 2H-chromen- 3-yl)-6H-1,3,4- thiadiazin-2-yl)- 2,4-dihydro- 3H-pyrazol- 3-one (12).
◦
Brown powder, yield (87%), m.p. 220–221 C (EtOH); IR (νmax, cm−1): 1692, 1681 (2C=O), 1606 (C=N),
1558–1452 (C=C); 1H-NMR (500 MHz, CDCl3) δH (ppm): 2.17 (s, 3H, CH3), 3.42 (s, 2H, pyrazole-H4),
4.97 (s, 2H, thiadiazine-H6), 7.45 (dd, 1H, J = 7.5, 3.5Hz, coumarin-H8), 7.66 (dd, 1H, J = 6, 1.5 Hz,
coumarin-H6), 7.81 (dd, 1H, J = 7.5, 1.5 Hz, coumarin-H7), 8.1 (dd, 1H, J = 7.8, 1, coumarin-H5), 8.94 (s,
1H, coumarin-H4); 13C-NMR (125 MHz, CDCl3) δC (ppm): 13.7 (CH3), 41.5 (CH2), 43.4 (CH2), K 116.4,
122.7, 128.6, 130.8, 135.2, 141.9, 144.5, 148.7, 152.7, 154.7, 158.5, 163.6, 190.3; MS m/z (%): 340 [M]+
(13%), 105 (100); Anal. Calcd. for C16H12N4O3S (340.36): C, 56.46; H, 3.55; N, 16.46, Found: C, 56.19; H,
3.29; N, 16.28.
2-(3,5-Dimethyl-1H-pyrazol-1-yl)-5-methyl-6-(phenyldiazenyl)-4H-1,3,4-thiadiazine (15a). Brown powder,
◦
yield (85%), m.p. 180–181 C (EtOH); IR (νmax, cm−1): 3151 (NH), 1657 (C=N), 1598–1489 (C=C);
1H-NMR (500 MHz, CDCl3) δH (ppm): 2.25 (s, 3H, CH3), 2.29 (s, 3H, CH3), 2.57 (s, 3H, CH3), 6.05 (s,
1H, H4 pyrazole), 7.27 (t, 2H, Ar-H), 7.42 (t, 2H, Ar-H), 8.04 (d, 1H, J = 8.5 Hz, Ar-H), 11.54 (s,
D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, CDCl3) δC (ppm): 8.85 (CH3), 14.3 (CH3), 14.9 (CH3),
110, 117.5, 128, 129, 142.0, 148.5, 150.2, 155.0, 160, 189.5; MS m/z (%): 312 [M]+ (10%), 239.9 (100);
Anal. Calcd. for C15H16N6S (312.40): C, 57.67; H, 5.16; N, 26.90, Found: C, 57.39; H, 5.04; N, 26.55%.

Molecules 2018, 23, 2092
9 of 12
2-(3,5-Dimethyl-1H-pyrazol-1-yl)-5-methyl-6-(p-tolyldiazenyl)-4H-1,3,4-thiadiazine (15b). Brown powder,
◦
yield (86%), m.p. 205–206 C (EtOH); IR (νmax, cm−1): 3156 (NH), 1683 (C=N), 1591–1456 (C=C);
1H-NMR (500 MHz, CDCl3) δH (ppm): 2.26 (s, 3H, CH3), 2.32 (s, 3H, CH3), 2.51 (s, 3H, CH3), 2.57 (s,
3H, CH3), 6.04 (s, 1H, pyrazole-H4), 7.32 (dd, 2H, J = 6 Hz, Ar-H), 7.86 (dd, 2H, J = 8.5 Hz, Ar-H),
11.52 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, CDCl3) δC (ppm): 8.54 (CH3), 13.2 (CH3),
18.6 (CH3), 18.6 (CH3), 103.3, 114.9, 121.0, 129.1, 129.3, 129.6, 148.9, 150.6, 159.2, 189.5; MS m/z (%):
326 [M]+ (30%), 299 (100); Anal. Calcd. for C16H18N6S (326.42): C, 58.87; H, 5.56; N, 25.75, Found: C,
58.49; H, 5.27; N, 25.41%.
6-((4- Chlorophenyl) diazenyl)- 2- (3,5- dimethyl◦-1H- pyrazol-1- yl)- 5- methyl- 4H-1,3,4- thiadiazine (15c).
Brown crystals, yield (84%), m.p. 187–188 C (EtOH); IR (νmax, cm−1): 3153 (NH), 1654 (C=N),
1595–1487 (C=C); 1H-NMR (500 MHz, CDCl3) δH (ppm): 2.25 (s, 3H, CH3), 2.29 (s, 3H, CH3), 2.57 (s,
3H, CH3), 6.05 (s, 1H, pyrazole-H4), 7.33 (dd, 2H, J = 9, Ar-H), 7.98 (dd, 2H, J = 9, Ar-H), 11.56 (s,
D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, CDCl3) δC (ppm): 8.58 (CH3), 13.3 (CH3), 14.4 (CH3),
111, 116.4, 126.8, 128.9, 141.0, 149.6, 151.2, 154.0, 159.2, 189.5; MS m/z (%): 348.97 [M + 3]+ (20%),
345.94 [M]+ (10%), 317 (100); Anal. Calcd. for C15H15ClN6S (346.84): C, 51.95; H, 4.36; N, 24.23, Found:
C, 51.60; H, 4.15; N, 24.07%.
2-(3,5-dimethyl-1H-pyrazol-1-yl)-6-(phenyldiazenyl)-4H-1,3,4-thiadiazin-5(6H)-one (17a). Green powder,
yield (85%), m.p. 126–127 ◦C (EtOH); IR (νmax, cm−1): 3178 (NH), 1681 (C=O), 1602 (C=N), 1575–1473
1
(C=C); H-NMR (500 MHz, CDCl3) δH (ppm): 2.12 (s, 3H, CH3), 2.24 (s, 3H, CH3), 3.2 (s, 1H,
H6 thiadiazinone), 6 (s, 1H, pyrazole-H4), 7.33 (t, 2H, Ar-H), 7.44 (t, 2H, Ar-H), 7.65 (d, 1H, J = 8.5 Hz,
Ar-H), 11 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, CDCl3) δC (ppm): 12.7 (CH3),
14.9 (CH3), 85.2, 114, 121.4, 129.5, 135.4, 142.9, 145.7, 148.6, 152.0, 169.1; MS m/z (%):314 [M]+ (45),
350 (8), 86 (100); Anal. Calcd. for C14H14N6OS (314.37): C, 53.49; H, 4.49; N, 26.73, Found: C, 53.17; H,
4.19; N, 26.43%.
2-(3,5-Dimethyl-1H-pyrazol-1-yl)-6-(p-tolyldiazenyl)-4H-1,3,4-thiadiazin-5(6H)-one (17b). Green powder,
yield (80%), m.p. 164–165 ◦C (EtOH); IR (νmax, cm−1): 3176 (NH), 1680 (C=O), 1612 (C=N), 1599–1465
(C=C); 1H-NMR (500 MHz, CDCl3) δH (ppm): 2.13 (s, 3H, CH3), 2.23 (s, 3H, CH3), 2.46 (s, 3H, CH3),
3.11 (s, 1H, thiadiazine-H6), 6.04 (s, 1H, pyrazole-H4), 7.13 (d, 2H, J = 8 Hz, Ar-H), 7.25 (dd, 2H, J = 6.5,
2 Hz, Ar-H), 11.23 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, CDCl3) δC (ppm): 12.4 (CH3),
14.8 (CH3), 21.7 (CH3), 86.0, 113, 125.7, 130.7, 134.8, 144.0, 147.6, 149, 154.0, 169.6; MS m/z (%): 328 [M]+
(3%), 321(20), 148.8 (90), 85.9 (100); Anal. Calcd. for C15H16N6OS (328.39): C, 54.86; H, 4.91; N, 25.59,
Found: C, 54.39; H, 4.69; N, 25.41%.
6-((4- Chlorophenyl) diazenyl)-2- (3,5-dimethyl- 1H-pyrazol- 1-yl) -4H- 1,3,4- thiadiazin-5 (6H)- one (17c).
◦
Brown powder, yield 83%, m.p. 140–141 C (EtOH); IR (νmax, cm−1): 3169 (NH), 1681 (C=O),
1
1614 (C=N), 1599–1541 (C=C); H-NMR (500 MHz, CDCl3) δH (ppm): 2.12 (s, 3H, CH3), 2.24 (s,
3H, CH3), 3.2 (s, 1H, H6 thiadiazinone), 6.05 (s, 1H, H4 pyrazole), 7.17 (d, 2H, J = 8 Hz, Ar-H), 7.30 (dd,
2H, J = 6.5, 2 Hz, Ar-H), 11.17 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, CDCl3) δC (ppm):
12.4 (CH3), 14.8 (CH3), 81.0, 112, 124.2, 131.5, 135.6, 143.0, 146.7, 148.9, 153.0, 168.6; MS m/z (%):
348 [M]+ (25%), 350 (8), 86 (100); Anal. Calcd. for C14H13ClN6OS (348.81): C, 48.21; H, 3.76; N, 24.09,
Found: C, 47.99; H, 3.62; N, 23.89%.
3.2.2. General procedure for synthesis 21a–c
To a stirred solution of compound 1a (0.516 g, 3 mmol) in ethanol (30 mL) sodium acetate
trihydrate (0.39 g, 3 mmol) was added. After stirring for 15 min, the mixture was chilled at 0 ◦C and
treated with a cold solution of the respective aniline (4-chloroaniline (0.381 g, 3 mmol), p-toluidine
(0.310 g, 3 mmol), or 4-aminobenzenesulfonamide (0.516 g, 3 mmol)) in 6 M hydrochloric acid (1.5 mL)
with a sodium nitrite solution (0.21 g, 3 mmol, in 3 mL water). The addition of the diazonium salt
was stirred for an additional 2 h at 0–5 ◦C and then left for 8 h in a refrigerator (4 ◦C). The resulting

Molecules 2018, 23, 2092
10 of 12
solid was collected by filtration, washed thoroughly with water, and dried. The crude product was
crystallized from ethanol to give hydrazones 21a–c.
3- Methyl- 5- oxo- 4- (2- (p-tolyl) hydrazineylidene)- 4,5- dihydro- 1H-pyrazole- 1-carbothiohydrazide (21a).
◦
Brown powder, yield (80%), m.p. 120–121 C (EtOH); IR (νmax, cm−1): 3254–3142 (NH2 & 2NH),
1698 (C=O), 1595 (C=N), 1556–1485 (C=C); 1H-NMR (500 MHz, CDMSO-d6) δH (ppm): 2.31 (s, 3H, CH3),
2.35 (s, 3H, CH3), 6.85 (d, D2O exchangeable, 2H, NH2), 7.46 (m, 4H, Ar-H), 11.31 (s, D2O exchangeable,
1H, NH), 11.74 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, DMSO-d6) δC (ppm): 11.9 (CH3),
21.4 (CH3), 116.4, 127.4, 128.4, 130, 142.1, 147.5, 163.8, 194.0; MS m/z (%): 290 [M]+ (5%), 95 (100);
Anal. Calcd. for C12H14N6OS (290.09): C, 49.64; H, 4.86; N, 28.95, Found: C, 49.41; H, 4.64; N, 28.77%.
4-(2-(4-Chlorophenyl)hydrazineylidene)-3-methyl-5-oxo-4,5-dihydro-1H-pyrazole-1-carbothiohydrazide (21b).
◦
Red crystals, yield (85%), m.p. 117–118 C (EtOH); IR (νmax, cm−1): 3383–3172 (NH2 & 2NH),
1674 (C=O), 1593 (C=N), 1544–1481 (C=C); 1H-NMR (500 MHz, CDMSO-d6) δH (ppm): 2.31 (s, 3H,
CH3), 6.99 (s, D2O exchangeable, 2H, NH2), 7.1 (s, D2O exchangeable, 1H, NH), 7.48 (m, 4H, Ar-H),
11.76 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, DMSO-d6) δC (ppm): 11.9 (CH3), 116.4,
117.4, 118.4, 128, 129.5, 147.1, 163.8 (C=O), 194 (C=S); MS m/z (%): 310 [M]+ (5%), 285.78 (30), 267.95 (90);
Anal. Calcd. for C11H11ClN6OS (310.76): C, 42.52; H, 3.57; N, 27.04, Found: C, 42.36; H, 3.29; N, 26.88%.
4- (2- (1- (Hydrazinecarbonothioyl)- 3- methyl- 5- oxo- 1,5- dihydro- 4H- pyrazol- 4- ylidene) hydrazineyl)
◦
benzenesulfonamide (21c). Brown powder, yield (80%), m.p. 140–141 C (EtOH); IR (νmax, cm−1):
3296–3221 (2NH2 & 2NH), 1693 (C=O), 1595 (C=N), 1543–1489 (C=C); 1H-NMR (500 MHz, CDMSO-d6)
δH (ppm): 2.28 (s, 3H, CH3), 6.98 (s, D2O exchangeable, 2H, NH2), 7.08 (s, D2O exchangeable, 2H,
NH2), 7.18 (s, D2O exchangeable, 2H, NH2), 7.72 (d, 2H, J = 7.5 Hz, Ar-H), 7.84 (d, 2H, J = 8.5 Hz, Ar-H),
11.31 (s, D2O exchangeable, 1H, NH), 12.24 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz,
DMSO-d6) δC (ppm): 11.8 (CH3), 116.6, 126.8, 140.9, 144, 153.8, 160.7, 169 (C =O), 180 (C=S); MS m/z
(%): 354.93 [M]+ (4%), 255.68 (100); Anal. Calcd. for C11H13N7O3S2 (355.39): C, 37.18; H, 3.69; N, 27.59,
Found: C, 36.98; H, 3.56; N, 27.47%.
0
Synthesis of N -(4-(Dimethylamino)benzylidene)-3-methyl-5-oxo-4,5-dihydro-1H-pyrazole-1-carbothiohydrazide
(22). A few drops of HCl were added to a mixture of 1a (0.516 g, 3 mmol), and 4-(dimethylamino)
benzaldehyde (0.447 g, 3 mmol) in EtOH (20 mL), and the reaction mixture was stirred 6 h.
The precipitate formed was collected by filtration, dried, washed with EtOH, and recrystallized from
EtOH. Red powder, yield (89%), m.p. 261–262 ◦C (EtOH); IR (νmax, cm−1): 3269 (NH), 1689 (C=O),
1510 (C=N), 1504–1456 (C=C); 1H-NMR (500 MHz, CDMSO-d6) δH (ppm): 2.68 (s, 3H, CH3), 3 (s, 6H,
N(CH3)2), 3.04 (s, 2H, CH2, pyrazole-4), 6.80 (m, 2H, Ar-H), 7.91 (m, 2H, Ar-H), 9.65 (s, 1H, CH=N),
11.97 (s, D2O exchangeable, 1H, NH); 13C-NMR (125 MHz, DMSO-d6) δC (ppm): 16.6 (CH3), 40 (CH3),
41 (CH2),111.6, 124, 129.5, 131.3, 154.4, 158, 163 (C=O), 190.5 (C=S); MS m/z (%): 290 [M]+ (25%),
Anal. Calcd. for C14H17N5OS (303.38): C, 55.43; H, 5.65; N, 23.08, Found: C, 55.13; H, 5.30; N, 22.97%.
3.3. Antimicrobial Evaluation
The antibacterial activity of the synthesized compounds was tested against a panel of two gram
positive bacteria (Staphylococcus aureus and Bacillus subtilis) and two Gram-negative bacteria (Klebsiella
pneumoniae and Escherichia coli). The antifungal activities of the compounds were tested against
two fungi (Candida albicans and Aspergillus flavus). A solution of each compounds in DMSO with
concentration 1 mg/mL was prepared separately, paper discs of Whatman filter paper were prepared
with standard size (5 cm) were cut and sterilized in an autoclave. The paper discs soaked in the
desired concentration of the compound solution were placed aseptically in the petri dishes containing
nutrient agar media (agar 20 g + beef extract 3 g + peptone 5 g) seeded with Staphylococcus aureus,
Bacillus subtilis, E. coli, Pseudomonas aeuroginosa, Candida albicans, and Aspergillus flavus. The petri
◦
dishes were incubated at 36 C and the inhibition zones were recorded after 24 h of incubation.
Each treatment was replicated three times. The antibacterial activity of a common standard antibiotic

Molecules 2018, 23, 2092
11 of 12
chloramphenicol and antifungal clotrimazole were also recorded using the same procedure as above at
the same concentration and solvents [28].
The MIC was determined using the disc diffusion technique by preparing discs containing
1.9–1000 µg/mL of each compound against gram positive, gram negative, and fungi. Twofold dilutions
of the solution were prepared. The microorganism suspensions at 10 CFU/mL (colony forming
unit/mL) concentrations were inoculated to the corresponding wells. The plates were incubated at
36 ◦C for 24 h for the bacteria. The standard antibiotic chloramphenicol and antifungal clotrimazole
was also recorded using the same procedure as above at the same concentration and solvents. At the
end of the incubation period, the minimum inhibitory concentrations (MIC) values were recorded
as the lowest concentration of the substance that had no visible turbidity. Control experiments with
DMSO and uninoculated media were run parallel to the test compounds under the same condition [28].
4. Conclusions
A novel series of pyrazole and pyrazolone derivatives was synthesized, in good yields, starting
from pyrazole-1-carbothiohydrazide 1a
,b. A number of prepared compounds showed moderate to
good antimicrobial activities. Hydrazones 21a
–c
showed significant antimicrobial activities with MIC
values equal to or lower than standard drugs chloramphenicol and clotrimazole. It is clearly that the
presence of free carbothiohydrazide moiety increases antimicrobial activity.
Funding: This research was funded by the Deanship of Scientific Research, Jazan University, Saudi Arabia for the
financial support via project No: JUP7//00089 (2014–2015).
Acknowledgments: The author is thankful to Yasser Mokhtar A. Ibrahim, Vacsera, Cairo, Egypt; for handling the
antimicrobial properties.
Conflicts of Interest: The author declares no conflict of interest.
References
1.
2.
3.
Kardas, P.; Devine, S.; Golembesky, A.; Roberts, C. A systematic review and meta analysis of misuse of
antibiotic therapies in the community. Int. J. Antimicrob. Agents 2005, 26, 106–113. [CrossRef] [PubMed]
Song, Y.G. The history of antimicrobial drug development and the current situation. Infect. Chemother. 2012
44, 263–268. [CrossRef]
,
Abdel Aziz, M.; Gamal El-Din, A.; Abuo-Rahma, A.H.A. Synthesis of novel pyrazole derivatives and
evaluation of their antidepressant and anticonvulsant activities. Eur. J. Med. Chem. 2005, 44, 3480–3487.
[CrossRef] [PubMed]
4.
5.
Dinesha, V.S.; Priya, B.K.; Pai, K.S.R.; Naveen, S.; Lokanath, N.K.; Nagaraja, G.K. Synthesis and
pharmacological evaluation of some new fluorine containing hydroxypyrazolines as potential anticancer
and antioxidant agents. Eur. J. Med. Chem. 2015, 104, 25–32. [CrossRef] [PubMed]
Bandgar, B.P.; Gawande, S.S.; Bodade, R.G. Synthesis and biological evaluation of a novel series of pyrazole
chalcones as anti-inflammatory, antioxidant and antimicrobial agents. Bioorg. Med. Chem. 2009, 17, 8168–8173.
[CrossRef] [PubMed]
6.
7.
Lv, P.-C.; Li, H.-Q.; Sun, J.; Zhou, Y.; Zhu, H.-L. Synthesis and biological evaluation of pyrazole derivatives
containing thiourea skeleton as anticancer agents. Bioorg. Med. Chem. 2010, 18, 4606–4614. [CrossRef] [PubMed]
Radini, I.A.M.; Khidre, R.E.; El-Telbani, E.M. Synthesis and antimicrobial evaluation of new pyrazoline
and pyrazolinyl thiazole derivatives bearing tetrazolo[1,5-a]quinoline moiety. Lett. Drug Des. Discov. 2016
,
13, 921–931. [CrossRef]
8.
9.
Altıntop, M.D.; Abu Mohsen, U.; Karaca, H.; Canturk, Z.; Ozdemir, A. Synthesis and Evaluation of Bis-pyrazoline
Derivatives as Potential Antimicrobial Agents. Lett. Drug Des. Discov. 2014, 11, 1199–1203. [CrossRef]
Bai, L.S.; Wang, Y.; Liu, X.H.; Zhu, H.L.; Song, B.A. Novel dihydropyrazole derivatives linked with
multi(hetero)aromatic ring: Synthesis and antibacterial activity. Chin. Chem. Lett. 2009, 20, 427–430. [CrossRef]
10. Ouyang, G.P.; Cai, X.J.; Chen, Z.; Song, B.-A.; Bhadury, P.S.; Yang, S.; Jin, L.-H.; Xue, W.; Hu, D.-Y.; Zeng, S.
Synthesis and antiviral activities of pyrazole derivatives containing an oxime moiety. J. Agric. Food Chem.
2008, 56, 10160–10167. [CrossRef] [PubMed]

Molecules 2018, 23, 2092
12 of 12
11. Ouyang, G.P.; Chen, Z.; Cai, X.J.; Song, B.A.; Bhadury, P.S.; Yang, S.; Jin, L.H.; Xue, W.; Hu, D.Y.;
Zeng, S. Synthesis and antiviral activity of novel pyrazole derivatives containing oxime esters group.
Bioorg. Med. Chem. 2008, 16, 9699–9707. [CrossRef] [PubMed]
12. Alagarsamy, V.; Saravanan, G. Synthesis and anticonvulsant activity of novel quinazolin-4(3H)-one derived
pyrazole analogs. Med. Chem. Res. 2013, 22, 1711. [CrossRef]
13. Song, H.J.; Liu, Y.X.; Xiong, L.X.; Li, Y.; Yang, N.; Wang, Q. Design, synthesis, and insecticidal evaluation
of new pyrazole derivatives containing imine, oxime ether, and dihydroisoxazoline groups based on the
inhibitor binding pocket of respiratory complex I. J. Agric. Food Chem. 2013, 61, 8730–8736. [CrossRef]
[PubMed]
14. Comber, R.N.; Gray, R.J.; Secrist, J.A. Acyclic analogues of pyrazofurin: Syntheses and antiviral evaluation.
Carbohydr. Res. 1991, 216, 441–452. [CrossRef]
15. Schroder, J.; Henke, A.; Wenzel, H.; Brandstetter, H.; Stammler, H.G.; Stammler, A.; Pfeiffer, W.D.;
Tschesche, H. Structure-Based Design and Synthesis of Potent Matrix Metalloproteinase Inhibitors Derived
from a 6H-1,3,4-Thiadiazine Scaffold. J. Med. Chem. 2001, 44, 3231–3243. [CrossRef] [PubMed]
16. Sert-Ozgur, S.; Banu, C.T.; Somuncuoglu, E.I.; Kazkayasi, I.; Ertan, M.; Tozkoparan, B. Design and Synthesis
of 1,2,4-Triazolo[3,2-b]-1,3,5-thiadiazine Derivatives as a Novel Template for Analgesic/Anti-Inflammatory
Activity. Arch. Pharm. Chem. Life Sci. 2017, 350, e1700052. [CrossRef] [PubMed]
ˇ
17. Cacˇic´, M.; Pavic´, V.; Molnar, M.; Šarkanj, B.; Has-Schön, E. Design and Synthesis of Some New
1,3,4-Thiadiazines with Coumarin Moieties and Their Antioxidative and Antifungal Activity. Molecules 2014
19, 1163–1177. [CrossRef] [PubMed]
,
18. Khan, I.; Zaib, S.; Ibrar, A.; Rama, N.H.; Simpson, J.; Iqbal, J. Synthesis, crystal structure and biological
evaluation of some novel 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles and 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazines.
Eur. J. Med. Chem. 2014, 78, 176–177. [CrossRef] [PubMed]
19. Khidre, R.E.; Abdel-Wahab, B.F.; Awad, G.E.A. Multi-component one-pot synthesis of novel (1,3,4-thiadiazin-
2-ylamino)isoindoline-1,3-diones as antimicrobial agents. Heterocycles 2017, 94, 314–325. [CrossRef]
20. Radini, I.A.M.; Abdel-Wahab, B.F.; Khidre, R.E. Synthetic Routes to Imidazothiazines. Phosphorus Sulfur
Silicon Relat. Elem. 2016, 191, 844–856. [CrossRef]
21. Khidre, R.E.; Rodini, I.M.; Ibrahim, D.A. Synthesis of a novel heterocyclic scaffold utilizing 2-cyano-N-
(3-cyano-4,6-dimethyl-2-oxopyridin-1-yl)acetamide. ARKIVOC 2016, 301–317. [CrossRef]
22. Khidre, R.E.; Radini, I.A.M.; Abdel-Wahab, B.F. Synthesis of new heterocycles incorporating
3-(N-phthalimidomethyl)-1,2,4-triazole as antimicrobial agents. Egypt. J. Chem. 2016, 59, 731–744.
23. Radini, I.A.M.; Elsheikh, T.M.Y.; El-Telbani, E.M.; Khidre, R.E. New Potential Antimalarial Agents: Design,
Synthesis and Biological Evaluation of Some Novel Quinoline Derivatives as Antimalarial Agents. Molecules
2016, 21, 909. [CrossRef] [PubMed]
24. Alekseev, V.V.; Zelenin, K.N.; Yakimovich, S.I. Synthesis of Pyrazole, 1,2,4,5-Tetrazine, and 1,2,4-Triazole
Derivatives from Thiocarbonohydrazides and
β-Dicarbonyl Compounds. Russ. J. Org. Chem. 1995,
31, 868–873.
25. Pavurala, S.; Vaarla, K.; Vedula, R.R. One-Pot Three-Component Synthesis of Pyrazolyl-thiadiazinyl-
2Hchromen-2-one Derivatives. J. Heterocycl. Chem. 2015, 52, 1503–1505. [CrossRef]
26. Lawrence, P.G.; Harold, P.L.; Francis, O.G. Antibiotic and Chemotherapy; Edinburgh: London, UK, 1980;
Volume 5, p. 1597.
27. Koch, A.L. Bacterial wall as target for attack: Past, present, and future research. Clin. Microbiol. Rev. 2003
16, 673–687. [CrossRef] [PubMed]
,
28. Balouiri, M.; Sadiki, M.; Ibnsouda, S.K. Methods for in vitro evaluating antimicrobial activity: A review.
J. Pharm. Anal. 2016, 6, 71–79. [CrossRef] [PubMed]
Sample Availability: Samples of the compounds 1a, 1b, 5a, 8a, 12, 15c, 17b, 20, 21b, and 22 are available from
the author.
©
2018 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).