Design, synthesis, molecular prediction and biological evaluation of pyrazole-azomethine conjugates as antimicrobial agents

Article abstract of DOI:10.1080/00397911.2021.1894338

A series of Schiff bases linked with heterocyclic moiety (6a–c, 7a–c, 11a–c, 12a–c, and 13a–c) and ferrocenyl Schiff bases (15a–c) were designed, synthesized, and confirmed based on the spectral data. Also, evaluations of their in?vitro antibacterial and

Full text of DOI:10.1080/00397911.2021.1894338

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
Design, synthesis, molecular prediction and
biological evaluation of pyrazole-azomethine
conjugates as antimicrobial agents
Shorouk S. Mukhtar, Ashraf S. Hassan, Nesrin M. Morsy, Taghrid S. Hafez,
Fatma M. Saleh & Hamdi M. Hassaneen
To cite this article: Shorouk S. Mukhtar, Ashraf S. Hassan, Nesrin M. Morsy, Taghrid S. Hafez,
Fatma M. Saleh & Hamdi M. Hassaneen (2021) Design, synthesis, molecular prediction and
biological evaluation of pyrazole-azomethine conjugates as antimicrobial agents, Synthetic
Communications, 51:10, 1564-1580, DOI: 10.1080/00397911.2021.1894338
To link to this article: https://doi.org/10.1080/00397911.2021.1894338
View supplementary material
Published online: 28 Mar 2021.
Submit your article to this journal
Article views: 55
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=lsyc20

R
SYNTHETIC COMMUNICATIONSV
2021, VOL. 51, NO. 10, 1564–1580
https://doi.org/10.1080/00397911.2021.1894338
Design, synthesis, molecular prediction and biological
evaluation of pyrazole-azomethine conjugates as
antimicrobial agents
Shorouk S. Mukhtara, Ashraf S. Hassana , Nesrin M. Morsya, Taghrid S. Hafeza
Fatma M. Salehb , and Hamdi M. Hassaneenb
,
aOrganometallic and Organometalloid Chemistry Department, National Research Centre, Cairo, Dokki,
b
Egypt; Department of Chemistry, Faculty of Science, Cairo University, Giza, Egypt
ABSTRACT
ARTICLE HISTORY
Received 24 December 2020
A series of Schiff bases linked with heterocyclic moiety (6a–c, 7a–c,
11a–c, 12a–c, and 13a–c) and ferrocenyl Schiff bases (15a–c) were
designed, synthesized, and confirmed based on the spectral data. Also,
evaluations of their in vitro antibacterial and antifungal activities were
performed and some Schiff bases (7a, 13a, b, and 15b) show moder-
ate activities. Moreover, the physicochemical, pharmacokinetic, lipophi-
licity properties, druglikeness, ADME prediction, and toxicity properties
of the newly Schiff bases (6a–c, 7a–c, 11a–c, 12a–c, and 13a–c) were
predicted in silico. The results exhibited that some Schiff bases agree
with druglikeness rules, inhibition of some CYP isoenzymes, and pre-
dicted as negative values on the carcinogenicity test. Also, all the Schiff
bases exhibited more than 70% on the human intestinal absorption
test, moderate permeation on the in vitro Caco-2 cell permeability test,
and low permeability on the in vitro MDCK cell permeability test.
KEYWORDS
Antimicrobial activities;
azomethine-pyrazole;
ferrocene-2-carboxaldehyde;
heterocyclic moiety;
molecular prediction
GRAPHICAL ABSTRACT
CONTACT Taghrid S. Hafez
taghridshafez@yahoo.com
Organometallic and Organometalloid Chemistry
Department, National Research Centre, Cairo, Dokki 12622, Egypt
Supplemental data for this article can be accessed on the publisher’s website.
ß 2021 Taylor & Francis Group, LLC

R
SYNTHETIC COMMUNICATIONSV
1565
Introduction
Various infectious diseases are caused by different types of micro-organisms (e.g. bacteria
and fungi) via their interaction with hosts (human and model organisms). The antimicrobial
drug is an agent that kills microorganisms or stops their growth for diseases treatment and
known as antimicrobial chemotherapy. Sometimes, the antimicrobial drug becomes less
effective due to the microbial transformations. Therefore, continuous scientific co-operation
research in the field of organic and pharmaceutical chemistry is in progress for new prepar-
ation of antimicrobials as vaccines or drugs to overcome infectious diseases.
Schiff bases (–CH¼N–) are one of the most important biomolecules in medicinal and
pharmaceutical fields.[1–5] Some examples of bioactive Schiff bases linked with hetero-
cyclic moiety are Schiff base A bearing benzimidazole, furan and thiadiazole moieties
showed
a
potential antibacterial activity against the three bacterial strains
(Staphylococcus aureus, Escherichia coli, and Bacillus pumilus)[6] and Schiff base B bear-
ing 1, 3, 4-thiadiazole with 1, 2, 4-triazol-3-thione showed antituberculosis activity and
acetylcholinesterase inhibition effect.[7] Also, Schiff base C which bearing 1, 3, 4-oxadia-
zole moiety showed inhibitor of a-glucosidase.[8] Moreover, there are some examples of
Schiff bases (bearing furan heterocyclic moiety) as antimicrobial drugs such as
R
R
R
NitrofurazoneV, NitrofurantoinV and FurazolidoneV.[9,10]
On the other hand, many pyrazole compounds display antitubercular, antibacterial,
antimalarial, antiproliferative, and antituberculosis activities.[11–13] Therefore, the litera-
ture survey exhibited increasing in the synthesis of Schiff bases linked with pyrazole
moiety. For example, the two Schiff bases joined with pyrazole moiety (D–E) which
were synthesized by Hassan et al., in 2020, exhibited in vitro antimicrobial and antipro-
liferative activities.[14] Also, in 2013, Vijesh et al., prepared Schiff base-pyrazole conju-
gates F which showed significant analgesic and antimicrobial activities[15] (Figure 1).
From the above-mentioned biological applications of Schiff bases and in continuation
of our research program,[16–36] we aim to report herein (Figure 2):
i. Synthesis of Schiff bases linked with heterocyclic moiety (6a–c, 7a–c, 11a–c,
12a–c, and 13a–c).
ii. Synthesis of ferrocenyl Schiff bases (15a–c).
iii. Evaluation in vitro antibacterial and antifungal applications of the newly Schiff
bases (6a–c, 7a–c, 11a–c, 12a–c, 13a–c, and 15a–c) against two gram-positive,
two gram-negative, and two fungi were performed.
iv. In silico prediction the physicochemical, pharmacokinetic, lipophilicity proper-
ties, druglikeness, ADME prediction, and toxicity properties of the newly Schiff
bases (6a–c, 7a–c, 11a–c, 12a–c, and 13a–c) were done.
Results and discussion
Chemistry
5-Amino-N-aryl-3-(phenylamino)-1H-pyrazole-4-carboxamide 4a–c were used as starting
materials and were synthesized according to the methods described in our work[37] and in
the literature survey[38] (Scheme 1).

1566
S. S. MUKHTAR ET AL.
Figure 1. Bioactivity of Schiff bases and pyrazole derivatives.
Figure 2. The targets Schiff bases and their studies.

R
SYNTHETIC COMMUNICATIONSV
1567
Ph
Ph
O
O
HN
O
HN
Ar
CH3I
KOH/EtOH
Ph-NCS
Ar
N
HN
Ar
SCH3
N
S-K+
H
H
CN
CN
3a-c
CN
1a-c
2a-c
O
Ar
NH2
NH
1-4
N
H
a
; Ar= C6H5
NH2NH2/EtOH
TEA/Reflux 4 h
b; Ar= 4-CH3C6H4
c; Ar= 4-ClC6H4
N
HN
Ph
4a-c
Scheme 1. Synthesis of pyrazole compounds 4a–c.
O
Ar
NH2
NH
N
EtOH/AcOH
H
EtOH/AcOH
CHO
H3C
Reflux
Reflux
H3C
CHO
N
HN
Ph
N
N
H3C
O
N
Cl
4a-c
N
4, 6, 7a
4, 6, 7b
4, 6, 7c
; Ar= C6H5
; Ar= 4-CH3C6H4
; Ar= 4-ClC6H4
5a
5b
Ar
HN
Ar
O
H3C
CH3
HN
O
H3C
H
N
N
N
H
N
N
N
N
Ph
N
Ph
N
NH
N
NH
O
Cl
6a-c
7a-c
Scheme 2. Synthesis of pyrazole-pyrazole Schiff bases 6a–c and 7a–c.
The reaction of pyrazole derivatives 4a–c with each of 4-antipyrinecarboxaldehyde
(5a) and 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde (5b) in absolute etha-
nol in the presence of a catalytic amount of acetic acid furnished pyrazole-pyrazole
Schiff bases 6a–c and 7a–c, respectively (Scheme 2).
The structures of pyrazole-pyrazole Schiff bases (6a–c and 7a–c) were confirmed
based on the spectral data. For example, IR spectrum of the Schiff base 6c exhibited
bands at ꢀ 3312, 3258, and 3208 cmꢀ1 for three NH groups, two bands at ꢀ 1692 and
1646 cmꢀ1 for two carbonyl groups. In addition to, two bands at ꢀ 1591 and 1546 cmꢀ1
1
for C ¼ N and C ¼ C functions, respectively. Its H NMR spectrum shows two signals
for CH3 and NCH3 protons of antipyrine moiety at d 2.57 and 3.36 ppm, respectively.
Azomethine proton was appeared as a signal at d 8.79 ppm. Three signals for three NH
protons at d 8.95, 10.70, and 12.63 ppm. The fourteen aromatic protons were appeared
at d 6.86 (t, 1H), 7.26–7.30 (m, 4H), 7.42 (d, 2H, J ¼ 7.7 Hz), 7.49 (t, 1H), 7.58 (t, 4H),

1568
S. S. MUKHTAR ET AL.
Ar
HN
OHC
N
O
H
N
8
N
N
Ph
EtOH/AcOH/Reflux
N
NH
11a-c
Ar
HN
O
Ar
NH2
OHC
S
O
N
H
H
9
NH
N
N
N
HN
Ph
Ph
S
EtOH/AcOH/Reflux
N
NH
12a-c
4a-c
OHC
Ar
HN
4, 11-13a
4, 11-13b
4, 11-13c
; Ar= C6H5
; Ar= 4-CH3C6H4
; Ar= 4-ClC6H4
O
N
10
H
N
N
Ph
N
EtOH/AcOH/Reflux
N
NH
13a-c
Scheme 3. Synthesis of Schiff bases 11a–c, 12a-c, and 13a–c.
and 7.97 (d, 2H, J ¼ 8.6 Hz). The 13C NMR spectrum of the Schiff base 6c exhibited two
signals at d 10.80 and 34.01 corresponding to CH3 and NCH3 groups. The two carbonyl
groups were appeared at d 161.46 and 163.49 ppm. Also, the 13C NMR spectrum exhib-
ited signals at d 92.51, 102.08, 116.33, 121.19, 126.43, 127.16, 128.47, 128.97, 129.48,
133.59, 134.06, 135.82, 136.60, 137.29, 138.13, 151.96, 153.93, and 154.21 ppm for 24
carbon atoms. The mass spectrum of the Schiff base 6c [C28H24ClN7O2 (525.99)] exhib-
ited two peaks at 527 (4.02%) and 525.17 (10.05%) for M þ 2 and Mþ, respectively. The
base peak (100%) exhibited at 77.03.
Also, a series of pyrazole-azomethine-heterocyclic moiety as Schiff bases 11a–c,
12a–c, and 13a–c were performed via the direct reaction of pyrazole compounds 4a–c
with some heteroaromatic aldehydes f4-(piperidin-1-yl) benzaldehyde (8), thiophene-2-
carbaldehyde (9), or nicotinaldehyde (10), respectivelyg in good yields and pure forms
(Scheme 3).
IR spectrum of the Schiff base 13a was characterized by bands at ꢀ 3300, 3147, 1655,
1594, and 1547 cmꢀ1 for 3NH, C ¼ O, C ¼ N, and C ¼ C groups, respectively. Also, its
1H NMR spectrum was characterized by a signal at d 8.96 ppm for azomethine proton.
Three signals for three NH protons at d 9.11, 9.82, and 12.87 ppm. The aromatic and
pyridine protons were appeared at d 6.92 (s, 1H), 7.08 (t, 1H), 7.30 (t, 2H), 7.36 (t, 2H),
7.48 (s, 2H), 7.64 (t, 1H), 7.67 (d, 2H, J ¼ 8.2 Hz), 8.43 (d, 1H, J ¼ 7.8 Hz), 8.79 (d, 1H,
J ¼ 4.6 Hz), and 9.18 (s, 1H). Its 13C NMR spectrum was exhibited a signal at d
162.55 ppm corresponding to C ¼ O group. In addition to, signals at d 97.14, 116.85,
119.26, 123.40, 124.46, 128.19, 129.00, 129.13, 130.53, 135.53, 138.38, 140.78, 149.10,
150.83, 152.95, 153.14, and 161.34 ppm for 21 carbon atoms. Finally, the mass spectrum

R
SYNTHETIC COMMUNICATIONSV
1569
OCH3
OCH3
O
O
HN
NH2
N
N
N
Fe
Fe
Fe
HO
Antioxidant activity
II
Anti-inf lammatory eff ect
III
Antifungal and antioxidant activities
I
Figure 3. Bioactivity of ferrocenyl Schiff bases.
O
Ar
NH2
NH
CHO
N
Ar
HN
O
H
EtOH/Triethyl amine
Reflux
+
Fe
N
Fe
N
HN
Ph
NH
HN
Ph
N
4, 15; Ar= C6H5
4, 15; Ar= 4-CH3C6H4
4, 15; Ar= 4-ClC6H4
4a-c
14
15a-c
Scheme 4. Synthesis of ferrocenyl Schiff bases 15a–c.
of the Schiff base 13a was exhibited a peak at 382.26 (Mþ, 71.39%) for C22H18N6O and
a peak at 77.03 (100%) for the base peak.
Finally, ferrocene derivatives possesses a broad spectrum of biological applications
especially ferrocenyl Schiff bases.[39–44] Compound I, N-(3,4-dimethoxybenzylidene)-4-
ferrocenyl aniline, showed appreciable antifungal and antioxidant activities.[45]
Compound II, 2-(1-ferrocenylethylideneamino)phenol, exhibited antioxidant activity.[46]
Recently, Altowyan and co-works in 2020 have prepared ferrocene oxamohydrazide III
which exhibited a potent anti-inflammatory effect[47] (Figure 3).
Therefore, these biological applications of ferrocene derivatives prompted us to pre-
pare a series of ferrocenyl Schiff bases 15a–c via the direct reaction of pyrazole com-
pounds 4a–c with ferrocene-2-carboxaldehyde (14) (Scheme 4).
1H NMR spectrum of ferrocenyl Schiff base 15b was characterized by a signal at d
8.66 ppm for azomethine proton, three signals at d 4.32, 4.80, and 5.00 ppm for nine
protons of the two ferrocene rings, and a signal at d 2.23 ppm for methyl protons. The
nine aromatic protons were appeared as 6.76 (t, 1H), 7.08 (d, 2H, J ¼ 8.1 Hz), 7.17 (d,
2H, J ¼ 8.1 Hz), 7.36 (d, 2H, J ¼ 8.1 Hz), and 7.56 (t, 2H). There are three signals at d
8.92, 9.89, and 11.31 ppm for three NH protons. The mass spectrum of the ferrocenyl
Schiff base 15b was exhibited the base peak (100%) at 503.38 (Mþ) for C28H25FeN5O.
Antimicrobial evaluation
In vitro antimicrobial evaluation of Schiff bases (6a–c, 7a–c, 11a–c, 12a–c, 13a–c, and
15a–c) were performed at the Microanalytical Center, Cairo University, Egypt. The anti-
microbial potential of Schiff bases was investigated toward the test bacterial and fungi
species. The antimicrobial activities were expressed as the diameter of the inhibition

1570
S. S. MUKHTAR ET AL.
zones IZ (mm) using the modified Kirby–Bauer disk diffusion method.[34,48] The anti-
microbial evaluation of active Schiff bases (7a, 13a, 13b, and 15b) are written and
shown in Table 1.
The following results were concluded from Table 1:
ꢁ
Schiff base (7a) which is bearing bis-pyrazole moiety showed antibacterial mod-
erate activities against Streptococcus faecalis (Gþ) with inhibition zone
(IZ)¼13 mm, Escherichia coli (G-) (IZ ¼ 11 mm), and Salmonella typhimrium
(G-) (IZ ¼ 9 mm). Also, showed antifungal moderate activity against Aspergillus
flavus (IZ ¼ 10 mm).
ꢁ
Pyrazole Schiff base (13a) which is bearing pyridine moiety showed antibacterial
moderate activities against Bacillus subtilis (Gþ), Streptococcus faecalis (Gþ),
Escherichia coli (G-), and Salmonella typhimrium (G-) with inhibition zone range
(IZ ¼ 9–11 mm).
ꢁ
ꢁ
Pyrazole-pyridine Schiff base (13b) showed antibacterial moderate activities
against one Gram Bacillus subtilis positive (IZ ¼ 10 mm) and one gram
Salmonella typhimrium negative (IZ ¼ 9 mm).
Ferrocenyl-pyrazole Schiff base (15b) showed antibacterial good activities against
Bacillus subtilis with IZ ¼ 16 mm and Streptococcus faecalis (IZ ¼ 17 mm) as
Gram bacterial species positive. Schiff base (15b) showed moderate activities
against Escherichia coli (IZ ¼ 12 mm) and Salmonella typhimrium (IZ ¼ 14 mm)
as Gram bacterial species negative. Also, showed antifungal moderate activity
against Candida albicans (IZ ¼ 12 mm).
From the above results, we can conclude that
The introduction of some groups may be increasing the biological activities as anti-
bacterial and antifungal. Where it is found some Schiff bases such as pyrazole-pyrazole
Schiff base (7a), pyrazole-pyridine Schiff base (13a, b), and ferrocenyl-pyrazole Schiff
base (15b) show antimicrobial activities more than the rest Schiff bases. Therefore, in
the future, we will modify these Schiff bases to found derivatives more active.
In silico molecular properties prediction
Physicochemical, lipophilicity properties, and drug likeness of Schiff bases
The physicochemical, lipophilicity properties, and druglikeness of Schiff bases (6a–c,
7a–c, 11a–c, 12a–c, and 13a–c) were predicted by using the SwissADME web (http://
swissadme.ch/index.php#undefined).[49] The physicochemical, lipophilicity properties,
and druglikeness of Schiff bases are written and shown in Table 2.
The following results were concluded from Table 2:
ꢁ
ꢁ
The three series of Schiff bases (11a–c, 12a–c, and 13a–c) with the two Schiff
bases (6a and 7a) show agreement to the Lipinski’s (Pfizer) rule.
Veber’s (GSK) rule, all the bases pass this rule (Rotatable bonds ꢂ 10 and the
total polar surface area ꢂ 140).

R
SYNTHETIC COMMUNICATIONSV
1571
Table 1. In vitro antimicrobial evaluation of Schiff bases.
Inhibition zone diameter IZ (mm)
Bacterial species
Gþ
Streptococcus
G-
Fungi
Bacillus
subtilis
Escherichia
coli
Salmonella
typhimurium
Aspergillus
flavus
Candida
albicans
Schiff bases
faecalis
7a
13a
13b
15b
DMSO (solvent)
Ampicillin
Amphotericin B
0
11
10
16
0
13
10
0
17
0
11
10
0
12
0
9
9
9
14
0
27
10
0
0
0
0
0
0
0
12
0
0
26
0
27
0
25
0
0
17
0
21
ꢁ
ꢁ
In the case of Egan’s rule, the Schiff bases (6a–c, 11a, 11b, 12a–c, and 13a–c)
agreement with the rule. The bases (7a–c and 11c) not pass Egan’s rule due to
their lipophilicity (WLOGP) more than 5.88.
Muegge’s rule, only the series Schiff bases 13a–c showed agreement with this
rule and the rest Schiff bases (6a–c, 7a–c, 11a–c, and 12a–c) not acceptable due
to their lipophilicity (XLOGP3) more than 5.
Pharmacokinetics properties of Schiff bases
The pharmacokinetics properties of Schiff bases 6a–c, 7a–c, 11a–c, 12a–c, and 13a–c
were predicted by using the SwissADME web (http://swissadme.ch/index.php#unde-
fined).[49] The pharmacokinetics properties prediction are written and shown in
Table 3.
The following results were concluded from Table 3:
ꢁ
ꢁ
The Schiff base derivatives 6a, b, 11a–c, 12a, and 13a–c show high gastrointes-
tinal absorption (GI).
All the series of Schiff bases 6a–c, 7a–c, 11a–c, 12a–c, and 13a–c are not predict-
able for penetration of the blood-brain barrier (BBB) and non-substrates for P-
glycoprotein.
ꢁ
ꢁ
ꢁ
The Schiff base 13a among all the series which is inhibitor and active toward
CYP1A2 enzyme.
In the case of CYP2C19 enzyme, all the Schiff bases (6a–c, 7a–c, 11a–c, 12a–c,
and 13a–c) are inhibitor.
All the newly Schiff bases are inhibitor of CYP2C9 enzyme except the two Schiff
bases 7b and 7c are non-inhibitor.
ꢁ
ꢁ
The two series 11a–c and 13a–c are inhibitor of CYP2D6 enzyme.
The three Schiff bases 11a, 12b, and 12c are inhibitor of CYP3A4 enzyme.
ADME prediction and toxicity properties of Schiff bases
In silico ADME and toxicity properties of Schiff bases 6a–c, 7a–c, 11a–c, 12a–c, and
13a–c were calculated and predicted by using the PreADMET web (https://preadmet.
bmdrc.kr).[50] The ADME and toxicity properties are written and shown in Table 4.

1572
S. S. MUKHTAR ET AL.

R
SYNTHETIC COMMUNICATIONSV
1573

1574
S. S. MUKHTAR ET AL.

R
SYNTHETIC COMMUNICATIONSV
1575
The following results were concluded from Table 4:
ꢁ
All the Schiff bases exhibited more than 70% on the human intestinal absorption
(HIA) test. Therefore, this Schiff bases are good in permeation across
the membrane.
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
On the in vitro Caco-2 cell permeability test, all Schiff bases 6a–c, 7a–c, 11a–c,
12a–c, and 13a–c showed moderate permeation.
All the Schiff bases 6a–c, 7a–c, 11a–c, 12a–c, and 13a–c showed low permeabil-
ity (less than 25) on the in vitro MDCK cell permeability test.
On the in vitro plasma protein binding (PPB) test, all the Schiff bases were pre-
dicted more than 90% except the three Schiff bases 6c, 7b, and 12b.
On the Ames test, all Schiff bases were predicted as mutagen except the deriva-
tive 7c was predicted as non-mutagen.
On the prediction of the carcinogenicity mouse test, the Schiff bases 6a, 6b,
7a–c, and 13a–c were predicted as negative values. While, carcinogenicity rat
predictions test, the Schiff bases 6c, 7a–c, 11c, 12a–c, and 13c were predicted as
negative values.
ꢁ
On the case of hERG inhibition test, the two Schiff bases (12b and 12c) present
high risk; the four Schiff bases (11b, 11c, 13b, and 13c) present medium risk
and the rest Schiff bases are ambiguous risk.
Conclusions
In this study, we have synthesized a new series of pyrazole-azomethine-heterocyclic
moiety (pyrazole, piperidine, thiophene, and pyridine) as Schiff bases (6a–c, 7a–c,
11a–c, 12a–c, and 13a–c) and ferrocenyl Schiff bases (15a–c). All Schiff bases (6a–c,
7a–c, 11a–c, 12a–c, 13a–c, and 15a–c) were confirmed based on the spectral data.
Antimicrobial activities evaluations of Schiff bases were performed. The evaluation
revealed that some Schiff bases (7a, 13a, 13b, and 15b) show moderate activities. Also,
the molecular and toxicity properties with ADME prediction of Schiff bases (6a–c, 7a–c,
11a–c, 12a–c, and 13a–c) were predicted in silico. The results of in silico exhibited that
some series of Schiff bases are in agreement with druglikeness rules, inhibition of some
CYP isoenzymes, and having a negative values on the carcinogenicity test. As well as,
all series of pyrazole-azomethine-heterocyclic moiety as Schiff bases (6a–c, 7a–c, 11a–c,
12a–c, and 13a–c) exhibited more than 70% on the human intestinal absorption test,
moderate permeation, and low permeability.
From the above conclusions, in the future, we will modify developments and design
of a new series of pyrazole-azomethine-heterocyclic moiety as Schiff bases to obtain
promising antimicrobial agents.
Materials and methods
Chemistry
All melting points were measured on a Gallenkamp melting point apparatus and are
uncorrected. The IR spectra were recorded (KBr disk) on a PerkinElmer 1650 FTIR

1576
S. S. MUKHTAR ET AL.
instrument. 1H NMR (500/300 MHz) and 13C NMR (125/75 MHz) spectra were
recorded on a JEOL spectrometer using DMSO-d6 as solvent and tetramethylsilane
(TMS) as an internal standard. Chemical shifts (d-values) are reported in ppm. Mass
spectra were recorded on a Varian MAT 112 spectrometer at 70 eV. Elemental analyses
were performed at the Micro Analytical Center, Cairo University, Egypt.
Progress of the reactions was monitored by thin-layer chromatography (TLC) using
aluminum sheets coated with silica gel F254 (Merck), viewing under a short-wavelength
UV lamp effected detection. All evaporations were performed under reduced pressure
at 40 ꢃC.
Synthesis of 5-amino-N-aryl-3-(phenylamino)-1H-pyrazole-4-carboxamide (4a-c), 5-
chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde (5 b), and 4-(piperidin-1-yl)
benzaldehyde (8)
Were prepared as reported in the literature.[37,38,51,52]
General method for synthesis of Schiff bases linked with heterocyclic moiety (6a–c,
7a–c, 11a–c, 12a–c, and 13a–c)
A mixture of 5-aminopyrazoles 4a–c (0.01 mol) and the appropriate heteroaromatic
aldehydes (0.01 mol) fnamely; 4-antipyrinecarboxaldehyde (5a), 5-chloro-3-methyl-1-
phenyl-1H-pyrazole-4-carbaldehyde (5b), 4-(piperidin-1-yl) benzaldehyde (8), thio-
phene-2-carbaldehyde (9), and nicotinaldehyde (10)g with a catalytic amount of glacial
acetic acid (1 ml) in absolute ethanol (25 ml) was refluxed for one hour and then left to
cool. The solid product was filtered off, dried and finally recrystallized from ethanol to
afford the corresponding Schiff bases (6a–c, 7a–c, 11a–c, 12a–c, and 13a–c).
N-(4-Chlorophenyl)-5-(((1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)me-
thylene)amino)-3-(phenylamino)-1H-pyrazole-4-carboxamide (6c)
Yellow crystals, m.p. 220–221 ꢃC, yield (79%). IR (KBr) ꢀmax/cmꢀ1 3312, 3258, 3208
(3NH), 1692, 1646 (C ¼ O), 1591 (C ¼ N), 1546 (C ¼ C). 1H NMR (DMSO-d6,
500 MHz, d ppm): 2.57 (s, 3H, CH3), 3.36 (s, 3H, NCH3), 6.86 (t, 1H, ArH), 7.26-7.30
(m, 4H, ArH), 7.42 (d, 2H, J ¼ 7.7 Hz, ArH), 7.49 (t, 1H, ArH), 7.58 (t, 4H, ArH), 7.97
(d, 2H, J ¼ 8.6 Hz, ArH), 8.79 (s, 1H, –CH ¼ N–), 8.95 (s, 1H, NH), 10.70 (s, 1H, NH),
12.63 (s, 1H, NH). 13C NMR (DMSO-d6, 125 MHz, d ppm): 10.80 (C, CH3), 34.01 (C,
NCH3), 92.51, 102.08, 116.33, 121.19, 126.43, 127.16, 128.47, 128.97, 129.48, 133.59,
134.06, 135.82, 136.60, 137.29, 138.13, 151.96, 153.93, 154.21 (24C), 161.46, 163.49 (2C,
2C ¼ O). MS (m/z, %): 527 (M þ 2, 4.02), 525.17 (Mþ, 10.05), 127.01 (100). Anal. Calcd.
(%) for C28H24ClN7O2 (525.99): C, 63.94; H, 4.60; N, 18.64. Found: C, 64.00; H, 4.55;
N, 18.70%.
N-Phenyl-3-(phenylamino)-5-(pyridin-3-ylmethyleneamino)-1H-pyrazole-4-carboxa-
mide (13a)
Orange crystals, m.p. 230–234 ꢃC, yield (67%). IR (KBr) ꢀmax/cmꢀ1 3300, 3147 (3NH),
1
1655 (C ¼ O), 1594 (C ¼ N), 1547 (C ¼ C). H NMR (DMSO-d6, 500 MHz, d ppm): 6.92

R
SYNTHETIC COMMUNICATIONSV
1577
(s, 1H, ArH), 7.08 (t, 1H, ArH), 7.30 (t, 2H, ArH), 7.36 (t, 2H, ArH), 7.48 (s, 2H, ArH),
7.64 (t, 1H, ArH), 7.67 (d, 2H, J ¼ 8.2 Hz, ArH), 8.43 (d, 1H, J ¼ 7.9 Hz, ArH), 8.79 (d,
1H, J ¼ 4.6 Hz, ArH), 8.96 (s, 1H, –CH ¼ N–), 9.11 (s, 1H, NH), 9.18 (s, 1H, ArH), 9.82
(s, 1H, NH), 12.87 (s, 1H, NH). 13C NMR (DMSO-d6, 125 MHz, d ppm): 97.14, 116.85,
119.26, 123.40, 124.46, 128.19, 129.00, 129.13, 130.53, 135.53, 138.38, 140.78, 149.10,
150.83, 152.95, 153.14, 161.34 (21C, Ar), 162.55 (C, C ¼ O). MS (m/z, %): 382.26 (Mþ,
71.39), 77.03 (100). Anal. Calcd. (%) for C22H18N6O (382.42): C, 69.10; H, 4.74; N,
21.98. Found: C, 69.05; H, 4.80; N, 22.00%.
Synthesis of ferrocenyl Schiff bases (15a–c)
A mixture of 5-aminopyrazoles 4a–c (0.01 mol) with ferrocene-2-carboxaldehyde (14)
(0.01 mol, 2.14 gm) in absolute ethanol (30 ml) and a catalytic amount of triethylamine
(four drops) were refluxed for three hours. The solvent was concentrated under reduced
pressure and the solid obtained was collected and recrystallized from ethanol to give fer-
rocenyl Schiff bases (15a–c).
3-(Phenylamino)-5-(ferrocen-2-ylmethyleneamino)-N-(4-methylphenyl)-1H-pyrazole-4-
carboxamide (15b)
Reddish brown crystals, m.p. 110–112 ꢃC, yield (62%). IR (KBr) ꢀmax/cmꢀ1 3362, 3235,
1
3120 (3NH), 1648 (C ¼ O), 1593 (C ¼ N), 1546 (C ¼ C). H NMR (DMSO-d6, 300 MHz,
d ppm): 2.23 (s, 3H, CH3), 4.32 (s, 5H, ferrocene ring), 4.80 (s, 2H, ferrocene ring),
5.00 (s, 2H, ferrocene ring), 6.76 (t, 1H, ArH), 7.08 (d, 2H, J ¼ 8.1 Hz, ArH), 7.17 (d,
2H, J ¼ 8.1 Hz, ArH), 7.36 (d, 2H, J ¼ 8.1 Hz, ArH), 7.56 (t, 2H, ArH), 8.66 (s, 1H,
–CH ¼ N–), 8.92 (s, 1H, NH), 9.89 (s, 1H, NH), 11.31 (s, 1H, NH). MS (m/z, %):
503.50 (Mþ, 100). Anal. Calcd. (%) for C28H25FeN5O (503.38): C, 66.81; H, 5.01; N,
13.91. Found: C, 66.75; H, 5.10; N, 14.00%.
Physical and spectroscopic characterization data of all compounds were given in
Supplemental file.
Antimicrobial evaluation
The antimicrobial evaluation of Schiff bases (6a–c, 7a–c, 11a–c, 12a–c 13a–c, and
15a–c) were performed using the modified Kirby–Bauer disk diffusion method.[34,48]
In silico molecular properties prediction
The physicochemical, lipophilicity properties, druglikeness, and pharmacokinetics prop-
erties of Schiff bases (6a–c, 7a–c, 11a–c, 12a–c, and 13a–c) were predicted by using the
SwissADME web (http://swissadme.ch/index.php#undefined).[49] Also, in silico ADME
and toxicity properties were calculated and predicted by using the PreADMET web
(https://preadmet.bmdrc.kr).[50]
Disclosure statement
No potential conflict of interest was reported by the author(s).

1578
S. S. MUKHTAR ET AL.
Acknowledgments
Authors thank National Research Centre for the financial support through scientific project num-
ber 12010103.
ORCID
Ashraf S. Hassan
Taghrid S. Hafez
Fatma M. Saleh
http://orcid.org/0000-0002-4771-716X
http://orcid.org/0000-0002-1958-3520
http://orcid.org/0000-0003-0451-4802
Hamdi M. Hassaneen
http://orcid.org/0000-0003-0963-4192
References
[1] Ignatova, M.; Stoyanova, N.; Manolova, N.; Rashkov, I.; Kukeva, R.; Stoyanova, R.;
Toshkova, R.; Georgieva, A. Mater. Sci. Eng. C. Mater. Biol. Appl. 2020, 116, 111185. DOI:
DOI: 10.1016/j.msec.2020.111185.
[2] Sahoo, J.; Sahoo, C. R.; Sarangi, P. K. N.; Prusty, S. K.; Padhy, R. N.; Paidesetty, S. K. Eur.
J. Med. Chem. 2020, 186, 111911. DOI: 10.1016/j.ejmech.2019.111911.
[3] (a) Sztanke, K.; Maziarka, A.; Osinka, A.; Sztanke, M. . Bioorg. Med. Chem. 2013, 21,
3648–3666. DOI: 10.1016/j.bmc.2013.04.037.(b) Hameed, A.; Al-Rashida, M.; Uroos, M.;
Ali, S. A.; Khan, K. M. Expert Opin. Ther. Pat. 2017, 27, 63–79. DOI: 10.1080/13543776.
2017.1252752.
[4] Ganguly, A.; Chakraborty, P.; Banerjee, K.; Choudhuri, S. K. Eur. J. Pharm. Sci. 2014, 51,
96–109. DOI: 10.1016/j.ejps.2013.09.003.
[5] (a) da Silva, C. M.; da Silva, D. L.; Modolo, L. V.; Alves, R. B.; de Resende, M. A.;
^
ꢀ
€
Martins, C. V. B.; de Fatima, A. J. Adv. Res. 2011, 2, 1–8. DOI: 10.1016/j.jare.2010.05.004.
€
€
(b) Alyar, S.; Ozmen, U. O.; Adem, S¸.; Alyar, H.; Bilen, E.; Kaya, K. J. Mol. Struct. 2021,
1223, 128911. DOI: 10.1016/j.jare.2010.05.004.
[6] Abdel-Motaal, M.; Almohawes, K.; Tantawy, M. A. Bioorg. Chem. 2020, 101, 103972. DOI:
10.1016/j.bioorg.2020.103972.
[7] Cebeci, Y. U.; Bayrak, H.; S¸irin, Y. Bioorg. Chem. 2019, 88, 102928. DOI: 10.1016/j.bioorg.
2019.102928.
[8] Ullah, H.; Rahim, F.; Taha, M.; Hussain, R.; Tabassum, N.; Wadood, A.; Nawaz, M.;
Mosaddik, A.; Imran, S.; Wahab, Z.; et al. Arabian. J. Chem. 2020, 13, 4904–4915. DOI:
10.1016/j.arabjc.2020.01.005.
[9] Hassan, A. S.; Moustafa, G. O.; Morsy, N. M.; Abdou, A. M.; Hafez, T. S. Egypt. J. Chem.
2020, 63, 4469–4481. DOI: 10.21608/ejchem.2020.26158.2525.
[10] Vardanyan, R. S.; Hruby, V. J. Synthesis of Essential Drugs; Elsevier Science, 2006. pp 519.
DOI: 10.1016/B978-0-444-52166-8.X5000-6
[11] Vekariya, M. K.; Vekariya, R. H.; Patel, K. D.; Raval, N. P.; Shah, P. U.; Rajani, D. P.;
Shah, N. K. ChemistrySelect. 2018, 3, 6998–7008. DOI: 10.1002/slct.201801011.
[12] Hu, C.; Gao, Y.; Du, W. Chem. Biol. Drug Des. 2016, 87, 673–679. DOI: 10.1111/cbdd.
12699.
[13] Keri, R. S.; Chand, K.; Ramakrishnappa, T.; Nagaraja, B. M. Arch. Pharm. 2015, 348,
299–314. DOI: 10.1002/ardp.201400452.
[14] Hassan, A. S.; Askar, A. A.; Naglah, A. M.; Almehizia, A. A.; Ragab, A. Molecules. 2020,
25, 2593. DOI: 10.3390/molecules25112593.
[15] Vijesh, A. M.; Isloor, A. M.; Shetty, P.; Sundershan, S.; Fun, H. K. Eur. J. Med. Chem.
2013, 62, 410–415. DOI: 10.1016/j.ejmech.2012.12.057.
[16] Hassan, A. S. Bull. Chem. Soc. Ethiop. 2020, 34, 533–541. DOI: 10.4314/bcse.v34i3.9.
[17] Elsherif, M. A.; Hassan, A. S.; Moustafa, G. O.; Awad, H. M.; Morsy, N. M. J. App.
Pharm. Sci. 2020, 10, 37–43. DOI: 10.7324/JAPS.2020.102006.

R
SYNTHETIC COMMUNICATIONSV
1579
[18] Hassan, A. S.; Askar, A. A.; Nossier, E. S.; Naglah, A. M.; Moustafa, G. O.; Al-Omar,
M. A. Molecules. 2019, 24, 3130. DOI: 10.3390/molecules24173130.
[19] Hassan, A. S.; Moustafa, G. O.; Askar, A. A.; Naglah, A. M.; Al-Omar, M. A. Synth.
Commun. 2018, 48, 2761–2772. DOI: 10.1080/00397911.2018.1524492.
[20] Magd-El-Din, A. A.; Mousa, H. A.; Labib, A. A.; Hassan, A. S.; Abd El-All, A. S.; Ali,
M. M.; El-Rashedy, A. A.; El-Desoky, A. H. Z. Naturforsch. C. J. Biosci. 2018, 73, 465–478.
DOI: 10.1515/znc-2018-0010.
[21] Elgiushy, H. R.; Hammad, S. F.; Hassan, A. S.; Aboutaleb, N.; Abouzid, K. A. M. J. Adv.
Pharm. Res. 2018, 2, 221–237. DOI: 10.21608/aprh.2018.2839.1049.
[22] Hassan, A. S.; Hafez, T. S. J. App. Pharm. Sci. 2018, 8, 156–165. DOI: 10.7324/JAPS.2018.
8522.
[23] El-Naggar, M.; Hassan, A. S.; Awad, H. M.; Mady, M. F. Molecules. 2018, 23, 1249. DOI:
10.3390/molecules23061249.
[24] Hassan, A. S.; Awad, H. M.; Magd-El-Din, A. A.; Hafez, T. S. Med. Chem. Res. 2018, 27,
915–927. DOI: 10.1007/s00044-017-2113-5.
[25] Hassan, A. S.; Moustafa, G. O.; Awad, H. M. Synth. Commun. 2017, 47, 1963–1972. DOI:
10.1080/00397911.2017.1358368.
[26] Hassan, A. S.; Masoud, D. M.; Sroor, F. M.; Askar, A. A. Med. Chem. Res. 2017, 26,
2909–2919. DOI: 10.1007/s00044-017-1990-y.
[27] Hassan, A. S.; Mady, M. F.; Awad, H. M.; Hafez, T. S. Chin. Chem. Lett. 2017, 28,
388–393. DOI: 10.1016/j.cclet.2016.10.022.
[28] Hassan, A. S.; Hafez, T. S.; Ali, M. M.; Khatab, T. K. Res. J. Pharm. Biol. Chem. Sci. 2016,
7, 417–429. DOI: http://www.rjpbcs.com/pdf/2016_7(4)/[60].pdf.
[29] Abd El-All, A. S.; Hassan, A. S.; Osman, S. A.; Yosef, H. A. A.; Abdel-Hady, W. H.; El-
Hashash, M. A.; Atta-Allah, S. R.; Ali, M. M.; El Rashedy, A. A. Acta Pol. Pharm. 2016,
73, 79–92.
[30] Hassan, A. S.; Osman, S. A.; Hafez, T. S. Egypt. J. Chem. 2015, 58, 113–139. DOI: 10.
21608/ejchem.2015.978.
[31] Hassan, A. S.; Hafez, T. S.; Osman, S. A. Sci. Pharm. 2015, 83, 27–39. DOI: 10.3797/sci-
pharm.1409-14.
[32] Osman, S. A.; Mousa, H. A.; Yosef, H. A. A.; Hafez, T. S.; El-Sawy, A. A.; Abdallah,
M. M.; Hassan, A. S. J. Serb. Chem. Soc. 2014, 79, 953–964. DOI: 10.2298/
JSC130813134O.
[33] Hafez, T. S.; Osman, S. A.; Yosef, H. A. A.; Abd El-All, A. S.; Hassan, A. S.; El-Sawy,
A. A.; Abdallah, M. M.; Youns, M. Sci. Pharm. 2013, 81, 339–357. DOI: 10.3797/scipharm.
1211-07.
[34] Osman, S. A.; Yosef, H. A. A.; Hafez, T. S.; El-Sawy, A. A.; Mousa, H. A.; Hassan, A. S.
Aust. J. Basic. Appl. Sci. 2012, 6, 852–863. DOI: http://www.ajbasweb.com/old/ajbas/2012/
March/852-863.pdf
[35] Elgemeie, G. H.; Elsayed, S. H.; Hassan, A. S. Synth. Commun. 2009, 39, 1781–1792. DOI:
10.1080/00397910802590928.
[36] Elgemeie, G. H.; Elsayed, S. H.; Hassan, A. S. Synth. Commun. 2008, 38, 2700–2706. DOI:
10.1080/00397910802222605.
[37] Khatab, T. K.; Hassan, A. S.; Hafez, T. S. Bull. Chem. Soc. Ethiop. 2019, 33, 135–142. DOI:
10.4314/bcse.v33i1.13.
[38] Elgemeie, G. H.; Elghandour, A. H.; Abd Elaziz, G. W. Synth. Commun. 2004, 34,
3281–3291. DOI: 10.1081/SCC-200030549.
[39] Smolyaninov, I. V.; Poddel’sky, A. I.; Baryshnikova, S. V.; Kuzmin, V. V.; Korchagina,
E. O.; Arsenyev, M. V.; Smolyaninova, S. A.; Berberova, N. T. Appl. Organometal. Chem.
2018, 32, e4121. DOI: 10.1002/aoc.4121.
[40] Liu, Y.-T.; Lian, G.-D.; Yin, D.-W.; Su, B.-J. Spectrochim Acta A Mol. Biomol. Spectrosc.
2013, 100, 131–137. DOI: 10.1016/j.saa.2012.03.049.
[41] Mahmoud, W. H.; Deghadi, R. G.; El Desssouky, M. M. I.; Mohamed, G. G. Appl.
Organometal. Chem. 2019, 33, e4556. DOI: 10.1002/aoc.4556.

1580
S. S. MUKHTAR ET AL.
[42] Hassan, A. S.; Hafez, T. S.; Osman, S. A. M.; Ali, M. M. Turk. J. Chem. 2015, 39,
1102–1113. DOI: 10.3906/kim-1504-12.
[43] Mahmoud, W. H.; Deghadi, R. G.; Mohamed, G. G. Arabian. J. Chem. 2020, 13,
5390–5405. DOI: 10.1016/j.arabjc.2020.03.017.
[44] Liu, Y.; Yang, L.; Yin, D.; Dang, Y.; Yang, L.; Zou, Q.; Li, J.; Sun, J. J. Organomet. Chem.
2019, 899, 120903. DOI: 10.1016/j.jorganchem.2019.120903.
[45] Zaheer, M.; Shah, A.; Akhter, Z.; Qureshi, R.; Mirza, B.; Tauseef, M.; Bolte, M. Appl.
Organometal. Chem. 2011, 25, 61–69. DOI: 10.1002/aoc.1690.
[46] Li, Y.-F.; Liu, Z.-Q. Eur. J. Pharm. Sci. 2011, 44, 158–163. DOI: 10.1016/j.ejps.2011.07.001.
[47] Altowyan, M. S.; Ali, M.; Soliman, S. M.; Al-Majid, A. M.; Islam, M. S.; Yousuf, S.;
Choudhary, M. I.; Ghabbour, H. A.; Barakat, A. J. Mol. Struct. 2020, 1202, 127372. DOI:
10.1016/j.molstruc.2019.127372..
[48] Bauer, A. W.; Kirby, W. M.; Sherris, C.; Turck, M. Am. J. Clin. Pathol. 1966, 45, 493–496.
DOI: 10.1093/ajcp/45.4_ts.493.
[49] Al Wasidi, A. S.; Hassan, A. S.; Naglah, A. M. J. App. Pharm. Sci. 2020, 10, 142–148.
DOI: 10.7324/JAPS.2020.104018.
[50] Naglah, A. M.; Askar, A. A.; Hassan, A. S.; Khatab, T. K.; Al-Omar, M. A.; Bhat, M. A. .
Molecules. 2020, 25, 1431. DOI: 10.3390/molecules25061431.
[51] Xu, C. J.; Shi, Y. Q. J. Chem. Crystallogr. 2011, 41, 1816–1819. DOI: 10.1007/s10870-011-
0178-4.
[52] Soliman, D. H.; Eldehna, W. M.; Ghabbour, H. A.; Kabil, M. M.; Abdel-Aziz, M. M.;
Abdel-Aziz, H. A. Biol. Pharm. Bull. 2017, 40, 1883–1893. DOI: 10.1248/bpb.b17-00361.