A facile synthesis, drug-likeness, and in silico molecular docking of certain new azidosulfonamide–chalcones and their in vitro antimicrobial activity

Article abstract of DOI:10.1007/s00706-020-02568-8

Abstract: New azidosulfonamide–chalcone derivatives were designed and synthesized. Their structures were elucidated by ¹H and ¹³C NMR spectral analyses, in addition to elemental analyses. The synthesized derivatives were tested for their antimicrobial activity against a wide variety of Gram-positive, Gram-negative, and fungal strains. Three azidosulfonamide–chalcones showed relatively broad activity against tested strains. Two compounds exhibited eminent antibacterial activity toward S. aureus, M. luteus, and S. marcens (better than ampicillin trihydrate). The synthesized compounds exhibited moderate activity against K. pneumonia and a lower ability to inhibit E. coli growth. Among six tested fungal species, the most potent derivatives demonstrated strong activity toward only two of the fungal strains (T. rubrum and G. candidum). Assessment of drug-likeness, bioavailability, and promiscuity indicated that the compounds are viable drug candidates. In silico molecular docking analysis revealed that the synthesized azidosulfonamide–chalcones successfully occupied pterin-binding site of the dihydropteroate synthase (DHPS), implying that the prepared compounds could exert their activity by the inhibition of the microbial DHPS enzyme. These results provided essential information for the prospective design of more effective antimicrobial compounds. Graphic abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s00706-020-02568-8

Monatshefte für Chemie - Chemical Monthly (2020) 151:417–427
https://doi.org/10.1007/s00706-020-02568-8
ORIGINAL PAPER
A facile synthesis, drug‑likeness, and in silico molecular docking
of certain new azidosulfonamide–chalcones and their in vitro
antimicrobial activity
Muhamad Mustafa1 · Yaser A. Mostafa2
Received: 25 November 2019 / Accepted: 19 February 2020 / Published online: 31 March 2020
© Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract
New azidosulfonamide–chalcone derivatives were designed and synthesized. Their structures were elucidated by 1H and 13C
NMR spectral analyses, in addition to elemental analyses. The synthesized derivatives were tested for their antimicrobial
activity against a wide variety of Gram-positive, Gram-negative, and fungal strains. Three azidosulfonamide–chalcones
showed relatively broad activity against tested strains. Two compounds exhibited eminent antibacterial activity toward S.
aureus, M. luteus, and S. marcens (better than ampicillin trihydrate). The synthesized compounds exhibited moderate activ-
ity against K. pneumonia and a lower ability to inhibit E. coli growth. Among six tested fungal species, the most potent
derivatives demonstrated strong activity toward only two of the fungal strains (T. rubrum and G. candidum). Assessment of
drug-likeness, bioavailability, and promiscuity indicated that the compounds are viable drug candidates. In silico molecular
docking analysis revealed that the synthesized azidosulfonamide–chalcones successfully occupied pterin-binding site of
the dihydropteroate synthase (DHPS), implying that the prepared compounds could exert their activity by the inhibition
of the microbial DHPS enzyme. These results provided essential information for the prospective design of more efective
antimicrobial compounds.
Graphic abstract
Keywords Azidosulfonamide–chalcones · Antimicrobial · ADMET · Promiscuity · Molecular docking
Introduction
Electronic supplementary material The online version of this
Microbial infections and antibiotic resistance are serious
public health threats. Diseases caused by resistant bacteria
such as diarrhea, meningitis, respiratory tract infections,
sexually transmitted infections, and nosocomial infections
are important targets for researchers in the feld of antimi-
crobial agents. In some instances, the misuse of antibiot-
ics leads to uncontrolled bacterial and fungal infections
and also to the development of microbial strains, such
article (https://doi.org/10.1007/s00706-020-02568-8) contains
supplementary material, which is available to authorized users.
* Yaser A. Mostafa
y3abdelh@uwaterloo.ca
1
Medicinal Chemistry Department, Faculty of Pharmacy,
Deraya University, Minia, Egypt
2
Pharmaceutical Organic Chemistry Department, Faculty
of Pharmacy, Assiut University, Assiut 71526, Egypt
Vol.:(0123456789)
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418
M. Mustafa, Y. A. Mostafa
as MRSA bacterial strains, that till this moment are life-
threatening to human beings [1–6]. Compounds contain-
ing the sulfonamide group (sulfa drugs, –SO2NH2–) are
widely approved as pharmaceutical agents; they exhibit a
wide range of biological activities including anticancer,
anti-infammatory, and antimicrobial [7–11]. Sulfonamides
were the frst drugs widely employed and systemically
used broad-spectrum chemotherapeutics against many
bacterial infections. Additionally, it is estimated that sul-
fonamides account for 16–21% of annual antibiotics usage
around the world [11–15]. It is worth mentioning that anti-
microbial activities of sulfonamides depend on the substit-
uents and their position on the benzene ring as seen with
compounds 1–3 (Fig. 1) [16–18]. Additionally, chalcones
(α, β-unsaturated carbonyl moiety) as small molecules
have been successfully used as potent anti-infective agents.
There are several reports about broad-spectrum antimi-
crobial activity of chalcones bearing hydroxy, alkoxy, or
lipophilic groups in their structures (compounds 1 and
4) (Fig. 1) [16, 19]. Also, it has been reported that link-
ing a chalcone with a sulfonamide moiety (compound 1)
enhances the antimicrobial activity of the prepared deriva-
tives (Fig. 1) [12, 14]; moreover, the literature shows that
aryl azides are a common component of bioactive natural
products and are considered as a synthetic target due to
their feasible and promising applications in click chemis-
try [4, 17–19]. Agard et al. [20] revealed the great efect
of using azides as bioorthogonal chemical reporters on
enhancing the biological activity of several molecules
such as antibacterial, antiviral, anticancer, COX-2 inhi-
bition, and other biologically active molecules (2 and
4–6) (Fig. 1) [17, 19, 21, 22]. The antibacterial activity of
sulfonamides is attributed to targeting the dihydropteroate
synthase enzyme (DHPS) which catalyzes the condensa-
tion of 6-(hydroxymethyl)-7,8-dihydropterin-pyrophos-
phate (DHPPP) and p-aminobenzoic acid (PABA) into
dihydropteroate (DHPt). As a result, the biosynthesis of
dihydrofolic acid is inhibited leading to the prevention of
growth and reproduction of microorganisms [23]. Yun
et al. [24] reported the crystal structure of Bacillus anthra-
cis dihydropteroate synthase (BaDHPS) co-crystallized
with sulfathiazole-6-(hydroxymethyl)–7,8-dihydropterin-
pyrophosphate (STZ–DHPP) adduct. This adduct was
found to occupy both pterin and PABA-binding sites of
DHPS. Given these bewildering fndings of chalcones,
sulfonamides, and aryl azides, along with our interests
in developing new potent antimicrobial agents, we herein
report the synthesis of sulfonamide–chalcones linked to
an azide group as a new approach in developing antimi-
crobial agents. Also, a selected variety of substituents
were implemented on the aryl moiety to test the designed
approach of building a hybrid of an azidosulfonamide scaf-
fold and a chalcone scafold. The efect of the electronic
and the lipophilic environments of the selected substitu-
ents was studied and compared to the activity of the syn-
thesized azidosulfonamide–chalcones hybrids. Also, the
most active compounds 10b and 10c were docked into the
dihydropteroate synthase active site to assess their ability
to perform the same interactions as STZ–DHPP.
Fig. 1 Structures of some biologically active molecules with a sulfonamide, chalcone, and/or azido group scafolds
1 3

A facile synthesis, drug-likeness, and in silico molecular docking of certain new…
Results and discussion
419
number of resonances with distinct signals of C=O, =CH,
=C– fragments (supporting information).
Chemistry
Antibacterial activity
The facile synthesis of the target azidosulfonamide–chal-
cones was achieved from the simple and the commercially
available sulfanilic acid (compound 7) according to the
reactions sequence shown in Scheme 1. Sulfanilic acid
was converted to compound 8 which was used in the next
step without further purifcation. The corresponding azido-
sulfonamide intermediate (compound 9) was synthesized
from the reaction of compound 8 with p-aminoacetophe-
none in pyridine overnight at room temperature. The target
azidosulfonamide–chalcones were then synthesized from
compound 9 via its reaction with the appropriate benzal-
dehyde in a basic medium at the room temperature. The
synthesized azidosulfonamide–chalcones 10a–10e were
All the newly synthesized compounds 9 and 10a–10e were
evaluated for their in vitro antibacterial activity against
various bacterial strains, including Gram-positive bacteria
(Staphylococcus aureus, Micrococcus luteus, and Bacillus
cereus), Gram-negative bacteria (Klebsiella pneumonia,
Escherichia coli, and Serratia marcens). Ampicillin trihy-
drate was used as a reference antibacterial agent. The inhibi-
tion zone diameters (IZD) in millimeters and the minimum
inhibitory concentrations (MIC) in μg/cm3 of the target
compounds are summarized in Table 1. Interestingly, the
unsubstituted derivative 10a, the p-Cl derivative 10b, and
the p-Br sulfonamide 10c showed signifcant activity against
S. aureus with higher IZD of 23, 27, and 33 mm, respec-
tively, than the reference ampicillin trihydrate of 21 mm.
It is worth mentioning that 10b and 10c exhibited approxi-
mately two- and threefold better MIC values than the refer-
ence ampicillin trihydrate. The sulfonamide derivative 10a
showed the same MIC value as the reference compound.
Also, 10e and 10d exhibited approximately the same abil-
ity to inhibit bacterial growth as ampicillin trihydrate. On
M. luteus bacteria, compound 10c exhibited highly potent
activity with IZD of 29 mm and MIC of 1.50 μg/cm3, while
ampicillin trihydrate exhibited IZD of 18 mm and MIC of
10.08 μg/cm3. Likewise, 10a and 10b showed potent anti-
bacterial activity which was better than ampicillin trihydrate
with IZD of 20 and 24 mm, respectively, while the MIC
values were 10.10 and 5.47 μg/cm3, respectively. 10d and
1
characterized by H and 13C NMR, in addition to C, H,
N, S elemental analyses (supporting information). The 1H
NMR spectra of all the compounds showed a characteristic
broad singlet signal at δ=10.8–10.9 ppm corresponding to
the sulfonamide group proton. Also, complex multiplets in
the range of 7.0–8.0 ppm were observed corresponding to
the aromatic protons of the three phenyl rings. Moreover,
the α- and β-H correspond to the –CH=CH– group reso-
nating in the aromatic region as doublets (sometimes over-
lapped with aromatic protons) with a coupling constant
of 15.5 Hz which indicated the formation of the target
chalcones with an E geometry from their corresponding
sulfonamide ketones. The 13C NMR showed a requested
Scheme 1
1 3

420
M. Mustafa, Y. A. Mostafa
Table 1 The inhibition
zone diameters (mm) and
the minimum inhibitory
concentrations (μg/cm3) of
bacterial species
Compounds
Gram-positive bacteria
S. aureus M. luteus
Gram −ve bacteria
B. cereus
K. pneumo- E. coli
nia
S. marcens
IZD MIC IZD MIC IZD MIC IZD MIC IZD MIC IZD MIC
9
17
23
27
33
22
20
15.80 15
5.05 20
2.73 24
1.50 29
10.45 18
10.85 17
5.04 18
31.60 13
10.10 17
5.47 20
1.50 22
20.90 21
43.41 18
10.08 30
31.60
8
>50
8
>50 10
40.41 14
10.95 17
6.05 17
20.90 11
21.70 10
1.25 18
>50
20.20
5.47
10a
10b
10c
10d
10e
40.41 13
21.90 17
24.10 19
41.81 11
43.41 10
2.52 20
40.41 11
21.90 18
12.05 20
>50 14
>50 12
10.08 33
6.02
41.81
43.41
5.04
Ampicillin trihydrate 21
IZD inhibition zone diameter, MIC minimal inhibitory concentration
10e showed approximately the same IZD as the reference
compound. However, MIC values showed a drastic increase
in comparison to ampicillin trihydrate. All the synthesized
derivatives showed relatively moderate activity on B. cereus
when compared to the reference compound. On Gram-neg-
ative bacteria, 10c showed approximately the same IZD and
MIC value as that of ampicillin trihydrate on K. pneumonia.
10b and 10c exhibited potent IZD and MIC value on S. mar-
cens bacteria. The reference ampicillin trihydrate was able
to inhibit the growth of E. coli signifcantly more than all
the synthesized sulfonamides. These results indicated that
compounds bearing electron-withdrawing groups showed
better antibacterial activity than the derivatives bearing
electron-donating groups. Also, the MIC of the key inter-
mediate 9 was so much enhanced (four times lower) upon
its conversion to the frst azidosulfonamide–chalcone 10a
which showed better MIC values compared to ampicillin
trihydrate on both S. aureus and M. Luteus.
pathogenic fungi including (Trichophyton rubrum, Candida
albicans, Fusarium oxysporum, Penicillium chrysogenum,
Geotrichum candidum, and Aspergillus niger). The screen-
ing was performed using the twofold serial dilution method
using fuconazole as the reference drug (Table 2). All the
derivatives showed moderate to potent antifungal efciency
except 10b and 10c which showed a signifcantly potent anti-
fungal potency against T. rubrum. The p-Cl derivative 10b
and the p-Br sulfonamide 10c exhibited higher IZD of 25
and 28 mm, respectively, when compared to the reference
fuconazole (24 mm). Favorably, 10a, 10b, and 10c showed
the best MIC values of 10.10, 2.73, and 3.01 μg/cm3, respec-
tively (fuconazole: 15.30 μg/cm3). Regarding C. albicans,
all the derivatives showed mild activities, however, with less
potency when compared to the reference fuconazole. The
chalcone derivative 10c showed a strong ability to inhibit
the growth of G. candidum exhibiting considerable MIC
value (approximately twice that of fuconazole). Similar to
the antibacterial activity, 10a–10e showed better antifungal
activity than their corresponding intermediate compound 9.
Also, derivatives bearing electron-withdrawing groups (10b
and 10c) exhibited higher antifungal potency than deriva-
tives carrying electron-donating functionalities (10d and
Antifungal activity
The synthesized azidosulfonamide–chalcones were tested
for their in vitro antifungal activity against six diferent
Table 2 The inhibition zones
Compounds Tested fungi
(mm) and the minimum
inhibitory concentrations (μg/
T. rubrum
C. albicans
F. oxysporum P. chrysoge- G. candidum A. niger
num
cm3) of fungal species
IZD MIC
IZD MIC
>50
IZD MIC IZD MIC IZD MIC
IZD MIC
9
10
19
25
28
17
12
15.80 10
10.10 13
2.73 15
3.01 18
20.90 12
21.70 11
15.30 28
<2
<2
N.T. <2
N.T. <2
N.T. <2
N.T. <2
N.T. <2
N.T. <2
N.T. 23
N.T.
8
>50
40.40 <2
10.95 <2
<2
N.T.
N.T.
N.T.
N.T.
N.T.
N.T.
N.T.
10a
10b
10c
10d
10e
>50
43.80 <2
48.20 <2
>50
>50
1.91
N.T. 11
N.T. 18
N.T. 20
N.T. 14
N.T. 11
N.T. 22
6.02
20.90 <2
43.41 <2
<2
<2
<2
26
Fluconazole 24
3.83
18
IZD inhibition zone diameter, MIC minimal inhibitory concentration
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A facile synthesis, drug-likeness, and in silico molecular docking of certain new…
421
10e). None of the tested compounds showed any notable
antifungal activity against either F. oxysporum, P. chrys-
ogenum, or A. niger. A Venn diagram was created for all
compounds exhibiting potent activity against Gram-positive,
Gram-negative, and fungi strains [1]. The diagram showed
that compounds 10b and 10c shared a broad-spectrum anti-
microbial activity profle (Fig. 2).
as candidate drugs (Table 3). Prediction of these ADMET
properties helps in predicting the transport properties of the
molecules through the membranes such as blood–brain bar-
rier (BBB) and gastrointestinal tract (GI tract). If the com-
pounds failed to obey two or more of these drug-likeness
parameters, there would be a high possibility of their poor
bioavailability. All the newly synthesized compounds 9 and
10a–10e were characterized by having 6 H-bond accep-
tor atoms and one H-donor (except compound 10e has 7
H-bond acceptors); these centers helped in H-bond forma-
tion and, therefore, enhanced water solubility. Additionally,
compounds 10a–10d displayed seven rotatable bonds while
10e showed eight rotatable bonds. The importance of these
rotatable bonds is to boost the adaptation and the fexibil-
ity of the compound leading to creating more interactions
within the active site. Another important physicochemical
parameter is lipophilicity or partition coefcient (iLogP);
Drug‑likeness
Lipinski parameters [25, 26] (drug-likeness or ADMET
properties) were calculated by Swiss ADME predictor
software (http://www.swissadme.ch/) [27]. These param-
eters include molecular weight (MW), number of rotat-
able bonds (nrotb), hydrogen-bond acceptors (HBA) and
donors (HBD), lipophilicity (ilogP), and topological polar
surface area (TPSA) of the newly synthesized compounds
Fig. 2 Venn diagram of the antimicrobial activity relation of synthesized compounds
Table 3 Calculated drug-
Compound
MW/g mol−1 Lipinski parameters
HBA HBD Nrotb TPSA/Å2 iLogP
Water solubility
Silicos-IT class
likeness parameters
F
9
316.34
404.44
438.89
483.34
418.47
434.47
≤500
6
6
6
6
6
7
≤10
1
1
1
1
1
1
≤5
5
7
7
7
7
8
≤10
121.37
121.37
121.37
121.37
121.37
130.60
≤140
2.11
2.49
2.98
3.09
2.71
2.19
≤5
0.56 Moderately soluble
0.56 Moderately soluble
0.56 Poorly soluble
0.56 Poorly soluble
0.56 Moderately soluble
0.56 Moderately soluble
10a
10b
10c
10d
10e
Drug lead-
like proper-
ties
MW molecular weight, HBA H-bond acceptor, HBD H-bond donor, nrotb no. of rotatable bonds, TPSA
topological polar surface area, iLogP n-octanol/water partition coefcient, F Abbott bioavailability scores
1 3

422
M. Mustafa, Y. A. Mostafa
compounds having values less than − 0.5 will have poor
dissolution in lipids and will not be able to penetrate cell
membranes. The prepared compounds were found to have
iLogP values between 2.19 and 3.09 which indicated the
probability of a good penetration through cell membranes
and hence better bioavailability. Likewise, TPSA and MW
afect the transportation of the molecules through the bio-
logical membranes. Generally, compounds with MW below
500 g/mol and TPSA less than 140 Ǻ2 could transfx through
membranes easily, rapidly and subsequently will have less
undesirable side efects. Moreover, assessment of the bioac-
tivity score (F) of the new compounds using Swiss ADMET
showed their substantial bioavailability (score above zero)
and hence a higher probability of medicinal impact and bio-
logical activities in clinical trials [28]. Fortunately, all these
calculations did not violate any of the Lipinski rules and met
the bioavailability requirements (Table 3).
Promiscuity
Pan assay interference compounds (PAINS) analysis is
used to illustrate how frequent a compound is used in many
biochemical high-throughput drug discovery screens, thus
could be promising start points for further drug develop-
ment. Promiscuity of the prepared compounds was screened
by bioactivity data-associative promiscuity pattern learning
engine (Badapple: http://pasilla.health.unm.edu/tomcat/
badapple/badapple) (Table 4) [29]. PAINS analysis revealed
interesting fndings which are: frst, both the key intermedi-
ate 9 and the fnal compounds 10a–10e shared a common
scafold, compound 11 (Fig. 3) with a moderate pScore
value accompanied with a “True” result inDrug database;
second, another scafold, compound 12 (Fig. 3) embedded
in the fnal compounds was found to have pScore higher
than 300 with a “True” result inDrug database. Both of these
fndings heighten our compound promiscuity and drug-like-
ness probability; Finally, a third scafold, compound 13, was
generated from PAINS engine with a pScore below 100 and
a “False” fnding inDrug database indicating its absence in
the drug database.
Table 4 The pScore and inDrug fndings from Badapple data base
Cpd
Scafold
pScore
inDrug
9 and 10a–10e
10a–e
10a–e
Sulfonamide 11a
Chalcone 12a
257
785
63
True
True
False
Compound 13a
In silico molecular docking analysis
pScore values advisory:<100 (low), means no indication; 100–300
(moderate), means weak indication of promiscuity;>300 (high),
means strong indication of promiscuity; inDrug results: true, means it
was found in the drug data base; false, means not found
To further rationalize the potent antimicrobial activity of the
prepared compounds, molecular docking was performed in
the dihydropteroate synthase binding site. The PDB code
(3TYE) of the published crystal structure was obtained
aStructures of scafolds are shown in Fig. 3
Fig. 3 Scafolds generated from
promiscuity PAINS database
1 3

A facile synthesis, drug-likeness, and in silico molecular docking of certain new…
423
from Protein Data Bank [24]. To assess the docking per-
formance, the co-crystallized ligand STZ–DHPP was self-
docked into the active site showing an acceptable RMSD
value of 0.7920 Å (Fig. 4a). The docked compounds showed
several favorable van der Waals and hydrogen bonding
interactions with several key amino acids inside the active
site (Table 5, Fig. 4). The docking pose of the p-Cl azido-
sulfonamide–chalcone 10b (magenta) showed a hydrogen
bonding interaction between the chlorine atom and Asn120
(−2.09 kJ/mol) (Fig. 4b).
hydrogen bonding interactions with Ser221 and Gly188
(− 2.09 and − 19.24 kJ/mol, respectively). Also, the sul-
fonamide phenyl ring showed H···π interaction with Lys220
with interaction energy of −1.25 kJ/mol interestingly, the
methylene proton of the chalcone moiety showed a hydro-
gen bond with sulfate residues present in the dihydropter-
oate synthase active site. The role of chalcone moiety was
observed again with a hydrogen bond between the carbonyl
oxygen and Arg68. Both of the docked sulfonamides (10b
and 10c) successfully and completely occupied the recep-
tor active site and were oriented almost identical to the co-
crystallized ligand STZ–DHPP (Fig. 4d). Moreover, 10b and
10c showed several hydrophobic interactions with Arg68,
Pro69, Arg254, Lys220, Gly188, Ser221, and Pro193 amino
acids. These interesting interactions of the docked deriva-
tives indicated their substantial ability to occupy the pocket
preventing the substrate STZ–DHPP from binding, leading
to the inhibitory activity of the prepared compounds against
DHPS. All these essential interactions may account for the
potent antimicrobial efects of the prepared derivatives.
The sulfonamide proton showed a hydrogen bond with
Gly188 while the sulfonamide oxygen showed another
hydrogen bond with Ser221 (− 22.59 and − 2.51 kJ/mol,
respectively). Phe189 and Lys220 made H···π with the sul-
fonamide phenyl ring (− 1.67 and − 1.25 kJ/mol, respec-
tively). The p-Br azidosulfonamide–chalcone 10c (cyan)
which exhibited the highest antimicrobial activity showed
several interactions inside the active site (Fig. 4c). Asn120
and Asp184 showed two favorable hydrogen bonds with the
bromine atom. Also, the sulfonamide group showed two
Fig. 4 Presumptive binding modes of the studied compounds. a Self-
docking of STZ–DHPP with BaDHPS active site; b docking pose of
compound 10b (magenta); c docking pose of compound 10c (cyan); d
presumptive binding modes of compound 10b (magenta), compound
10c (cyan), and STZ–DHPP (yellow). All the docked sulfonamides
and STZ–DHPP are in stick representation (PDB code: 3TYE)
1 3

424
M. Mustafa, Y. A. Mostafa
Table 5 Energy scores (kJ/mol) and binding interactions for the co-
crystallized ligand (STZ–DHPP) and the top potent compounds 10b
and 10c, within dihydropteroate synthase active site
Experimental
The experimental methods, reagents, solvents, 1H and 13
C
Compound Energy
score, S/
Ligand–receptor interactions
Residue Type
NMR data and spectra are listed and described in the sup-
porting information, in addition to elemental analyses (C,
H, N, and S) and melting points for all new compounds.
All starting materials and reagents were obtained from
Alpha Aesar Chemical Company® and Sigma-Aldrich
Chemicals Company®. Pyridine was distilled from KOH
pellets, thionyl chloride was freshly distilled under
reduced pressure, and toluene was distilled over CaH
under reduced pressure. Silica gel chromatography was
performed using silica gel obtained from Fluka™. Melt-
ing points were recorded on Electrothermal™ Melting
Length/Ǻ
kJ mol−1
STZ–DHPP −34.22
Asn120 Hydrogen bond 2.74
Asp184 Hydrogen bond 3.02
Lys220 Hydrogen bond 3.31
Ser221 Hydrogen bond 3.04
Lys220 H···π
4.09
Asn120 Hydrogen bond 3.10
Ser221 Hydrogen bond 3.02
Gly188 Hydrogen bond 2.87
10b
10c
−29.37
−30.08
1
point apparatus. H and 13C NMR spectra were recorded
Lys220 H···π
4.12
4.32
Phe189 H···π
in DMSO-d6 on a JEOL ECA-500 II using TMS as inter-
nal standard (chemical shifts in ppm) and chemical shifts
for 13C spectra are relative to the residual solvent peak
(δ = 39.5 ppm, central peak). Microanalyses determined
for C, H, N, and S were within 0.4 of theoretical values.
2−
SO4
Hydrogen bond 2.51
Asn120 Hydrogen bond 3.08
Asp184 Hydrogen bond 3.22
Ser221 Hydrogen bond 3.11
Gly188 Hydrogen bond 2.81
Lys220 H···π
4.28
4‑Azidobenezenesulfonyl chloride (8)
To a solution of 5.8 g sodium carbonate in 200 cm3 H2O,
250 g sulfanilic acid (7) was added portion-wise with
vigorous stirring. To the resultant solution, 8.4 g sodium
nitrite was added and stirring was continued till complete
dissolution of sodium nitrite. This step was followed by
portion-wise addition of a solution of 14 cm3 concentrated
HCl in 30 cm3 H2O with vigorous stirring in an ice bath
to maintain the reaction between 0 and 5 °C. A white pre-
cipitated was obtained, separated by suction, and washed
with about 80 cm3 of cold water. The precipitate solid
was then dispersed in 40 cm3 of cold water, whereupon a
solution of sodium azide (8 g in 20 cm3 water) was added
portion-wise till the evolution of N2 ceased. After that,
30 g NaCl was added to salt out. The resulting precipitate
was fltered of and dried in vacuum to yield a yellowish-
white precipitate. 5 g of the resultant azido derivative was
dissolved in 20 cm3 thionyl chloride and 3 drops of DMF
and heated till boiling for 30 min. After completion of the
reaction, the excess SOCl2 was removed under vacuum and
the residue was extracted with 100 cm3 ether. The etherial
extract was evaporated under vacuum to aford 4-azido-
benzene sulfonyl chloride (8) as a yellowish-white solid.
Yield: 4.1 g (76%); m.p.: 59–61 °C [7].
Conclusion
To summarize, a series of azidosulfonamide–chalcone
derivatives were successfully designed and synthesized.
The antimicrobial screening and the computational analy-
sis were performed on the prepared derivatives. All the
derivatives exhibited moderate to strong antimicrobial
activities against most of the tested microbial strains.
Among the synthesized compounds and the reference
ampicillin trihydrate, the sulfonamide derivatives 10a,
10b, and 10c showed the best antibacterial activity on S.
aureus and M. luteus bacteria. The p-Br derivative 10c
exhibited strong antifungal activity on T. rubrum, which
was better than the reference fuconazole. It is worth notic-
ing that the derivatives carrying electron-withdrawing
groups (10b and 10c) exhibited higher antimicrobial activ-
ity over the derivatives carrying electron-donating groups
(10d and 10e). Moreover, promiscuity analysis revealed
that all the new derivatives 10a–10e in addition to their
key intermediate 9 shared a common scafold with strong
pScore (>300) which was also found to be commonly used
in the drug database. Finally, in silico screening of the new
derivatives showed considerable interactions within the
dihydropteroate synthase binding site. From all these inter-
esting fndings, this new approach seems to be a promising
start point for further investigations, and these compounds
resemble proper candidates as potent antimicrobial agents.
4‑Azido‑N‑(4‑acetylphenyl)benzenesulfonamide (9,
C14H12N4O3S) To a solution of 8 (0.01 mmol), p-aminoace-
tophenone was added (0.01 mmol) in 1 cm3 dry pyridine at
0 °C. After addition, the reaction was stirred for 16 h at room
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A facile synthesis, drug-likeness, and in silico molecular docking of certain new…
425
temperature, and then pyridine was azeotropically removed
with toluene under vacuum. The residue was dissolved in
EtOAc, washed with H2O and brine. The resultant com-
pound was then dried (Na2SO4), fltered, and concentrated
under vacuum. Purifcation was achieved using recrystal-
lization from EtOH which provided 9 as a pink solid (89%).
M.p.: 94-96 °C; 1H NMR (DMSO-d6, 500 MHz): δ=10.87
(s, 1H, SO2NH), 7.84–7.81 (m, 4H, Ar–H), 7.27 (app. d, 2H,
J=6.5 Hz, Ar–H), 7.19 (app. d, J=9 Hz, 2H, Ar–H), 2.45
(s, 3H, COCH3) ppm.
1H NMR (DMSO-d6, 500 MHz): δ = 10.92 (br s, 1H,
SO2NH), 7.88 (d, 2H, J=16 Hz, =CH–), 7.85–7.80 (m, 4H,
4 Ar–H), 7.65–7.62 (m, 3H, 2 Ar–H, =CH), 7.25–7.17 (m,
4H, Ar–H) ppm; 13C NMR (DMSO-d6, 125 MHz): δ=187.3
(C=O), 144.3, 144.3, 142.6, 141.9, 135.5, 134, 132, 131.7,
130.7, 130.5, 129.7, 128.7 (2 CHAr), 122.5 (CHAr), 119.9 (2
CHAr), 118.1 ppm.
N‑[4‑[3‑(4‑Methylphenyl)acryloyl]phenyl]‑4‑azidobenzene‑
sulfonamide (10d, C22H18N4O3S) Purifcation was achieved
using flash chromatography (ethyl acetate/hexane, 1:9)
which provided 10d as a pale yellow solid (69%). M.p.:
General procedure for the synthesis
of sulfonamide–chalcones 10a–10e
1
297–299 °C; H NMR (DMSO-d6, 500 MHz): δ = 10.87
(br s, 1H, SO2NH), 8.03 (app. d, 2H, J=6.5 Hz, 2 Ar–H),
7.84–7.81 (m, 5H, 4 Ar–H, =CH–), 7.64 (d, 1H, J=15.5 Hz,
=CH–), 7.28-7.18 (m, 4H, Ar–H), 2.49 (s, 3H, CH3 overlap-
ping H2O signal) ppm; 13C NMR (DMSO-d6, 125 MHz):
δ = 187.5 (C=O), 144.5, 143.6, 142.1, 135.2, 132, 130.1,
129.8 (2 CHAr), 129.5, 128.8 (2 CHAr), 120.7 (CHAr), 119.9
(2 CHAr), 118.1 (2 CHAr), 26.4 (CH3) ppm.
To a solution of 9 (0.5 mmol) and appropriate benzaldehydes
(0.5 mmol) in 10 cm3 EtOH, aq. NaOH (1 mmol) was added
drop-wise with constant stirring for 30 min during which a
yellow cake was formed. It was then kept overnight at room
temperature. The solid cake so obtained was acidifed with
dilute HCl, and solid obtained was fltered, washed with 2%
NaHCO3, and again with H2O and brine. The resultant com-
pound was then purifed with fash chromatography to get
target compounds 10a–10e.
N‑[4‑[3‑(3‑Methoyphenyl)acryloyl]phenyl]‑4‑azidobenzene‑
sulfonamide (10e, C22H18N4O4S) Purifcation was achieved
using fash chromatography (ethyl acetate/hexane, 1.5:8.5)
which provided 10e as a yellow solid (73%). M.p.:>300 °C;
1H NMR (DMSO-d6, 500 MHz): δ = 10.92 (br s, 1H,
SO2NH), 8.04 (d, 2H, J=9 Hz, 2 Ar–H), 7.87–7.81 (m, 5H,
4 Ar–H, =CH–), 7.63 (d, 1H, J=15.5 Hz, =CH–), 7.38 (d,
J=7.5 Hz, 1H, Ar–H), 7.34 (t, J=8 Hz, 1H, Ar–H), 7.27–
7.22 (m, 5H, Ar–H), 7.00 (dd, J=2.0, 1.5 Hz, 1H, Ar–H),
3.82 (s, 3H, OCH3) ppm; 13C NMR (DMSO-d6, 125 MHz):
δ=187.4 (C=O), 159.6, 144.3, 143.4, 143.2, 136.1, 135.6,
132.3, 130.3 (2 CHAr), 129.8, 128.7 (2 CHAr), 122.1, 121.5,
119.9 (2 CHAr), 118.1 (2 CHAr), 116.6 (CHAr), 113.2 (CHAr),
55.3 (OCH3) ppm.
N‑[4‑(3‑Phenylacryloyl)phenyl]‑4‑azidobenzenesulfonamide
(10a, C21H16N4O3S) Purifcation was achieved using fash
chromatography (ethyl acetate/hexane, 3:7) which provided
1
10a as a bright yellow solid (87%). M.p.: 283–285 °C; H
NMR (DMSO-d6, 500 MHz): δ=10.93 (br s, 1H, SO2NH),
8.05 (d, 2H, J = 9 Hz, Ar–H), 7.98–7.83 (m, 5H, 4 Ar–H,
=CH–), 7.67 (d, J=15 Hz, 1H, =CH–), 7.45–7.43 (m, 3H,
Ar–H), 7.29–7.23 (m, 4H, Ar–H) ppm; 13C NMR (DMSO-
d6, 125 MHz): δ=187.5 (C=O), 144.5, 143.5, 142.6, 135.4,
134.7, 132.5, 130.6 (2 CHAr), 128.9–128.7 (6 CHAr), 121.8
(CHAr), 120 (2 CHAr), 118.1 (2 CHAr) ppm.
N‑[4‑[3‑(4‑Chlorophenyl)acryloyl]phenyl]‑4‑azidobenze‑
nesulfonamide (10b, C21H15ClN4O3S) Purification was
achieved using fash chromatography (ethyl acetate/hexane,
2:8) which provided 10b as a bright yellow solid (77%).
M.p.:>300 °C; 1H NMR (DMSO-d6, 500 MHz): δ=10.92
(br s, 1H, SO2NH), 8.06 (d, 2H, J=9 Hz, Ar–H), 7.87–7.83
(m, 5H, 4 Ar–H, =CH–), 7.65 (d, J= 15 Hz, 1H, =CH–),
7.50 (d, 2H, J=9 Hz, Ar–H), 7.29–7.23 (m, 4H, Ar–H) ppm;
13C NMR (DMSO-d6, 125 MHz): δ=187.4 (C=O), 144.5,
142.3, 142, 135.1, 134.9, 133.6, 132.5, 130.3 (4 CHAr),
128.8 (4 CHAr), 122.5 (CHAr), 119.9 (2 CHAr), 118.1 (2
CHAr) ppm.
Biological activity
Bacterial and fungal cultures were obtained from Assiut uni-
versity microbiology center (AUMC), Assiut University. Six
bacterial strains, three Gram-positive species: Staphylococ-
cus aureus (S. aureus: AUMC, B-54), Micrococcus luteus
(M. luteus: AUMC, B-224), and Bacillus cereus (B. cereus:
AUMC, B-100), three Gram-negative species: Klebsiella
pneumonia (K. pneumonia: AUMC, B-178), Escherichia
coli (E. coli: AUMC, B-221), and Serratia marcens (S. mar-
cens: AUMC, B-89) were used to test antibacterial activity
of synthesized compounds; and six fungal strains: Tricho-
phyton rubrum (T. rubrum: AUMC 1145), Candida albicans
(C. albicans: AUMC 421), Fusarium oxysporum (F. oxyspo-
rum: AUMC 208), Penicillium chrysogenum (P. chrysoge-
num: AUMC 278), Geotrichum candidum (G. candidum:
N‑[4‑[3‑(4‑Bromophenyl)acryloyl]phenyl]‑4‑azidobenzene‑
sulfonamide (10c, C21H15BrN4O3S) Purifcation was achieved
using fash chromatography (ethyl acetate/hexane, 2.5:7.5)
which provided 10c as a yellow solid (83%). M.p.:>300 °C;
1 3

426
M. Mustafa, Y. A. Mostafa
AUMC 228), and Aspergillus niger (A. niger: AUMC 3364)
according to the agar cup difusion method.
la.health.unm.edu/tomcat/badapple/badapple), data are
shown in Table 4 and structures of scafolds are shown in
Fig. 3.
Antibacterial activity
Molecular docking analysis
Cell suspension of test bacterial strains was prepared from
48-h-old cultures previously grown on nutrient agar (NA) in
15-cm-diameter plates, which were seeded using 0.1 cm3 of
diluted organism. 100 mm3 of tested compounds (10a–10e:
100 μg/cm3 of DMSO), negative control (DMSO), and posi-
tive control (ampicillin trihydrate [31]) was added to speci-
fed wells. The seeded plates were incubated at 35 2 °C for
24 h; after that, the inhibition zone diameter was measured
in millimeters (Table 1). Also, minimum inhibitory concen-
trations (MICs) were determined for the most active com-
pounds using twofold dilution method (Table 1).
In silico molecular modeling and visualization processes
were performed using Molecular Operating Environment
(MOE 2014.0901, Chemical Computing Group, Montreal,
QC, Canada). The co-crystal structure was downloaded from
the RCSB Protein Data Bank (PDB code 3TYE). First, the
compounds were prepared with the standard protocol desig-
nated in MOE 2014.09. However, the energy of the docked
structures was minimized using MMF94FX force feld with
gradient RMS of 0.0001 kcal/mol and then the protein struc-
ture was prepared using the MOE LigX protocol. To validate
the docking study at the dihydropteroate synthase active site,
the co-crystallized ligand STZ–DHPP was re-docked into the
binding site using the same set of parameters as described
above. The RMSD of the best docked pose was 0.7920 Å and
the binding score was −34.22 kJ/mol. The ligands were then
docked in the binding site using the alpha triangle place-
ment method. The refnement was carried out using force
feld and was scored using the afnity ΔG scoring system.
The resulting docking poses were visually inspected, and the
poses of the lowest binding free energy value and with the
best hydrophobic, H-bonding, and electrostatic interactions
within the binding pocket of target protein were considered
to fgure out the antibacterial activity (Table 5, Fig. 4) [30].
Antifungal activity
Spore suspension of test fungi were grown on sterile malt
extract broth agar (MEB), Sabouraud agar (SA), and/or
potato dextrose agar (PDA) according to test fungal spe-
cies with fnal spore concentration of (5×104 spores/cm3)
in sterile Petri dishes (9 cm in diameter). Plates were inocu-
lated with 1 cm3 of spore suspension and were shaken gently
to homogenize the inoculum. Test compounds (10a–10e:
100 mm3 of 100 μg/cm3 of DMSO), negative control
(DMSO), and positive control (fuconazole [31]) were added
to specifed wells in triplicate and plates were incubated at
28 2 °C for 1–7 days according to the test fungi used. The
diameter of inhibition zones (in mm) and MICs (μg/cm3)
of most active compounds were determined using twofold
dilution method (Table 2).
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