Synthesis, structural characterization, and molecular docking studies of bioactive bismuth(III) complexes with substituted hydrazones

Article abstract of DOI:10.1016/j.molstruc.2021.129870

Eight new bismuth(III) complexes (1-8) of substituted hydrazones having general formula; [Bi(RCONHNCHC₅H₄N)Cl_x] and [Bi(RCONHNCHC₉H₆N)Cl_x], where R = C₁₀H₇O (1, and 8)

Full text of DOI:10.1016/j.molstruc.2021.129870

Journal of Molecular Structure 1230 (2021) 129870
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Synthesis, structural characterization, and molecular docking studies
of bioactive bismuth(III) complexes with substituted hydrazones
Sumaira Abbasa, Imtiaz-ud-Dina,∗, Mehwish Mehmooda, M. Khawar Raufa,
S. Sikander Azamb, Ihsan-ul Haqc, M. Nawaz Tahird, Nousheen Parvaizb
a Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan
b Computational Biology Lab, National Center for Bioinformatics, Quaid-i-Azam University, Islamabad 45320, Pakistan
c Department of Pharmacy, Faculty of Biological Sciences, Quaid-i-Azam University, Islamabad 45320, Pakistan
d Department of Physics, University of Sargodha, Sargodha 40100, Pakistan
a r t i c l e i n f o
a b s t r a c t
Article history:
Eight new bismuth(III) complexes (1-8) of substituted hydrazones having general formula;
Received 6 October 2020
Revised 26 December 2020
Accepted 31 December 2020
Available online 6 January 2021
[Bi(RCONHNCHC5H4N)Clx] and [Bi(RCONHNCHC9H6N)Clx], where
R
=
C10 H7O (1, and 8), C4H3S (2),
C6H5O (3, and 6), C7H7 (4), C5H4N (5, and 7), 2 or
x
=
3 have been prepared. The substituted
hydrazones (I1-I8) were synthesized by reacting the stoichiometric amounts of the respective hy-
drazides such as p-toluic hydrazide, 4-hydroxybenzhydrazide, thiophene-2-carboxylic acid hydrazide,
3-hydroxy-2-naphthoic acid hydrazide, Isonicotic acid hydrazide and appropriate aromatic aldehydes like
pridine-2-carboxaldehyde and quinoline-2-carboxyaldehyde. These hydrazones (ligands),then complexed
to Bi(III) species to yield the target compounds. They were characterized by FTIR, and NMR spectroscopy
to find out an explicit evidence about their structural motifs. The X-ray data for (1 & I6) further validate
the chemical structures of the synthesized compounds. The molecular geometry for (1) is predominately
distorted pentagonal bipyramidal where hepta-coordinated Bi(III) center is attached to the nitrogens of
pyridine and of azomethine moieties along with the carbonyl oxygen, two chloro and two oxygens of the
(two) DMSO molecules. The bond lengths for Bi(1)-O(1), Bi(1)-N(1) and Bi(1)-N(2) are 2.323(5), 2.539(6),
2.390(5) oA respectively indicating Bi(1)-O(1) as the strongest linkage to the metal center. The H-bonding,
present in (1), contributed an extra stability to the structure. The synthesized compounds were initially
screened for their possible antimicrobial, alpha-amylase, and protein kinase inhibition, some (1,2,6,8)
exhibit significant activity. The experimental results are further endorsed by molecular docking studies
against helicobacter pylori urease (1E9Y), epidermal growth factor receptor tyrosine kinase (1M17) and
human pancreatic alpha amylase (5U3A) inhibition activity. The significant ligand-receptor interactions,
observed at the binding pocket of the selected drug targets, further revealed the enzyme inhibition
potential of the compounds and highlighting their possible roles as therapeutic agents in future drug
discovery processes.
Keywords:
Bismuth(III) hydrazones
X-ray structure
Enzyme inhibition
H. pylori
Molecular docking
© 2021 Elsevier B.V. All rights reserved.
1. Introduction
such as peptic ulcerations, gastritis, mucosa-associated lymphoid
tissue lymphoma and carcinoma [3], besides the use of radioactive
Bismuth and its derivatives are deliberated biologically active
and virtually to minimal toxic compounds [1,2]. The low toxicity of
bismuth based compounds is due to their insolubility in biological
fluids that cause inhibition to pathogenic bacteria like Helicobacter
pylori (H. pylori) which can cause various gastrointestinal disorders
isotopes of Bi in cancer therapy [4]. Few commercially accessible
bismuth based medicines such as bismuth subsalicylate(BSS) and
bismuth sub-citrates (CBS) have been used in clinics to treat in-
fections caused by H. pylori which is an etiological agent of peptic
ulcers, chronic gastritis and even in stomach cancer [5,6]. In ad-
dition to medicinal applications, the bismuth compounds, are also
used in cosmetics [7], semiconductors [8], metallurgical additives
and alloys [9], along with their uses in photochromic devices [10].
Hydrazones are conspicuous class of compounds owing to their
conformational flexibility, versatility in coordination to metals and
pharmacological activity [11]. Hydrazone derivatives possess anti-
Abbreviations: LD50, Lethal dose 50%; XRD, X-ray diffraction; NMR, Nuclear mag-
netic resonance; DMSO, Dimethyl sulfoxide; GOLD, Genetic optimization for ligand
docking; SAR, Structure to activity relationship.
∗
Corresponding author
E-mail address: drimtiazuddin@yahoo.com (Imtiaz-ud-Din).
https://doi.org/10.1016/j.molstruc.2021.129870
0022-2860/© 2021 Elsevier B.V. All rights reserved.

S. Abbas, Imtiaz-ud-Din, M. Mehmood et al.
Journal of Molecular Structure 1230 (2021) 129870
inflammatory, antimicrobial, anti-convulsing and anti-tubercular
activities [12–15]. Some hydrazone analogues have been investi-
gated for the treatment of diseases such as Alzheimer and tha-
lassemia [16,17]. The Bi(III) hydrazones are eminent group of com-
pounds due to their extensive pharmacological effects, and for that
they are actively employed for their antimicrobial studies along
with potent anti-tumor activities against human lung cancer cell
lines [18,19].
Quantities used; thiophene-2-carboxylicacid hydrazide (0.14 g,
1mmol), pyridine-2-carboxaldehyde (0.1 mL, 1mmol). Off white
crystals, Yield: 81%; M.p 188-190 °C. Anal. Calcd (Found %) for
C11 H9N3OS (231.27 g/mol): C = 57.13 (57.12), H = 3.92 (3.91),
N = 18.17 (18.15); FTIR data (KBr, cm−1): ʋ(NH) 3162, ʋ(C=O) 1638,
ʋ(C=N) 1582, ʋ(N–N) 1011; 1H NMR data (300 MHz, DMSO, δ, ppm)
12.10 (1H, s, NH), 8.63(1H, s, CH),7.22-8.61 (7H, m, Ar-H); 13C NMR
=
=
data (75 MHz, DMSO, δ, ppm) 153.4 (C O), 148.1 (N CH), 150.0
=
(N C).
In continuance to our previous research work [20–22] we report
herein the synthesis, characterization and evaluation of biological
potential of eight new bismuth(III) complexes derived from vari-
ous substituted hydrazones. The experimental and computational
biological data were also collated to arrive at fruitful conclusions.
Owing to the importance and clinical efficacy of the metal contain-
ing drugs, the synthesized bismuth(III) complexes of substituted
hydrazones were also investigated for their in-silico binding pat-
tern through molecular docking studies. Binding affinity of bismuth
containing compounds was evaluated against three potential drug
target proteins including helicobacter pylori (H. pylori) urease, epi-
dermal growth factor receptor (EGFR) tyrosine kinase, and human
pancreatic alpha amylase. The molecular docking method was used
to explore and predict the binding conformation of the synthesized
compounds to the appropriate receptor binding sites.
4-Hydroxy(pyridin-2-ylmethylene)benzohydrazide (I3)
Quantities used; 4-hydroxy benzhydrazide (0.15 g, 1mmol),
pyridine-2-carboxaldehyde (0.1 mL, 1mmol). White crystals, Yield:
84%; M.p 248-250 °C. Anal.Calcd (Found %) for C13H11 N3O2
(241.25 g/mol): C = 64.72 (64.70), H = 4.60 (4.59), N = 17.42
(17.41); FTIR data (KBr, cm−1): ʋ(NH) 3055, ʋ(C=O) 1645, ʋ(C=N) 1587,
ʋ(N–N) 1007; 1H NMR data (300 MHz, DMSO, δ, ppm) 15.42(1H,
s, OH) 11.86 (1H, s, NH), 10.19 (1H, s, CH), 6.86-8.61 (10H, m, Ar-
13
=
H); C NMR data (75 MHz, DMSO, δ, ppm) 163.3 (C O), 149.9
=
–
=
(N CH), 161.3 (C OH), 153.9(N C).
4-Methyl(pyridin-2-ylmethylene)benzohydrazide (I4)
Quantities used; p-toulic benzhydrazide (0.15 g, 1mmol),
pyridine-2-carboxaldehyde (0.1 mL, 1mmol). Pale white crystals,
Yield: 85%; M.p 127-132 °C. Anal. Calcd (Found %) for C14 H13N3O
(239.27 g/mol): C = 70.28 (70.21), H = 5.48 (5.47), N = 17.56
(17.55); FTIR data (KBr, cm−1): ʋ(NH) 3395, ʋ(C=O) 1649, ʋ(C=N) 1557,
ʋ(N–N) 1018; 1H NMR data (300 MHz, DMSO, δ, ppm) 2.38(3H, s,
2. Experimental
2.1. Materials and methods
CH3) 11.99 (1H, s, NH), 8.61 (1H, s, CH), 7.33-8.48 (10H, m, Ar-
13
=
H); C NMR data (75 MHz, DMSO, δ, ppm) 163.6 (C O), 142.5
The hydrazides, aldehydes, and anhydrous bismuth(III) chloride
are available commercially and were used as received. The ana-
lytical grade organic and inorganic solvents were used; however,
the analytical grade methanol was dried according to the reported
method prior to use [23]. The melting point was determined by
melting point instrument of model MP-D Mitamura Riken Kogyo
Japan and all are uncorrected. The IR spectrophotometer of model
FTS 3000 MX was used to collect IR data of the compounds as KBr
discs. Bruker Advanced Digital 300 MHz FT-NMR spectrometer was
used to collect 1H and 13C NMR data of the new compounds in
deuterated solvents relative to Me4Si operating at 300 and 75 MHz,
respectively. The Olex2 and refined ShelXT structure solution pro-
grams were used to resolve the X-ray structure.
=
–
=
(N CH), 149.9 (C OH), 153.7(N C).
(Pyridine-2-ylmethylene)-isonicotinohydrazide (I5)
Quantities used; isonicotinic acid hydrazide (0.14 g, 1mmol),
pyridine-2-carboxaldehyde (0.1 mL, 1mmol). off white powder,
Yield: 82%; M.p 196-197 °C. Anal.Calcd (Found %) for C12H10N4O
(226.23 g/mol): C = 63.71 (63.70), H = 4.46 (4.47), N = 24.76
(24.74); FTIR data (KBr, cm−1): ʋ(NH) 3203, ʋ(C=O) 1660, ʋ(C=N) 1552,
ʋ(N–N) 1066; 1H NMR data (300 MHz, DMSO, δ, ppm) 12.27(1H,
s, NH), 8.49 (1H, s, CH), 7.42-8.81 (8H, m, Ar-H); 13C NMR data
=
=
=
(75 MHz, DMSO, δ, ppm) 162.3 (C O), 140.6 (N CH), 153.3(N C).
4-Hydroxy (quinolin-2-ylmethylene)benzohydrazide (I6)
Quantities used; 4-hydroxy benzhydrazide (0.15g, 1mmol),
quinoline-2-carboxaldehyde (0.16 g, 1mmol). light yellow, Yield:
86%; M.p 177-178 °C. Anal.Calcd (Found %) for C17 H13N3O2
(291.3 g/mol): C = 70.09 (70.08), H = 4.50 (4.51), N = 14.42
(14.40); FTIR data (KBr, cm−1): ʋ(NH) 3038, ʋ(C=O) 1652, ʋ(C=N) 1546,
ʋ(N–N) 1103; 1H NMR data (300 MHz, DMSO, δ, ppm) 12.02(1H,
2.2. Synthesis
The synthetic procedure for the compounds is based on two
steps strategy, that is, preparation of the ligands and their com-
plexation with bismuth(III) moiety.
s, OH) 10.23 (1H, s, NH), 8.59 (1H, s, CH), 6.89-8.42 (10H, m, Ar-
13
=
H); C NMR data (75 MHz, DMSO, δ, ppm) 163.5 (C O), 137.16
=
–
=
(N CH), 161.4 (C OH), 154.4(N C).
(Quinolin-2-ylmethylene)isonicotinohydrazide (I7)
2.2.1. Substituted hydrazones
Quantities used; isonicotinic acid hydrazide (0.14g, 1mmol),
quinoline-2-carboxaldehyde (0.16 g, 1mmol). brown powder, Yield:
80%; M.p 154-156 °C. Anal. Calcd (Found %) for C16 H12N4O
(276.29 g/mol): C = 69.55 (69.53), H = 4.38 (4.37), N = 20.28
(20.27); FTIR data (KBr, cm−1): ʋ(NH) 3051, ʋ(C=O) 1659, ʋ(C=N) 1554,
ʋ(N–N) 1141; 1H NMR data (300 MHz, DMSO, δ, ppm) 12.42 (1H,
s, NH), 8.62 (1H, s, CH), 7.62-8.83 (10H, m, Ar-H); 13C NMR data
The substituted hydrazones as ligands (I1-I8) were synthesized
according to a reported methodology [18]. Recrystallization of the
compounds was done in a mixture of solvents such as acetone and
dichloromethane (1:3) to get the pure products. The characterizing
data for these compounds are depicting as follows:
3-Hydroxy-(pyridine-2-ylmethylene)-2-naphthohydrazide (I1)
Quantities used; 3-hydroxy-2-naphthoic acid hydrazide (0.202
g, 1mmol), pyridine-2-carboxaldehyde (0.1 mL, 1mmol). White
powder, Yield: 81%; M.p 233-235 °C. Anal.Calcd (Found %) for
C17 H13N3O2 (291.3 g/mol): C = 70.09 (70.08), H = 4.50 (4.52),
=
=
=
(75 MHz, DMSO, δ, ppm) 162.5 (C O), 147.83 (N CH), 153.9(N C).
3-Hydroxy(quinolin-2-ylmethylene)-2-naphthohydrazide (I8)
Quantities used; 3-hydroxy-2-naphthoic acid hydrazide (0.202
g, 1mmol), quinoline-2-carboxaldehyde (0.16g, 1mmol). light
brown powder, Yield: 78%; M.p 256-257 °C. Anal. Calcd (Found %)
for C21H15N3O2 (341.36 g/mol): C = 73.89 (73.88), H = 4.43 (4.41),
N = 12.31 (12.30); FTIR data (KBr, cm−1): ʋ(NH) 3046, ʋ(C=O) 1646,
ʋ(C=N) 1595, ʋ(N–N) 1071; 1H NMR data (300 MHz, DMSO, δ, ppm)
N = 14.42 (14.41); FTIR data (KBr, cm−1): ʋ
3254, ʋ(NH) 3052,
(OH)
ʋ(C=O) 1684, ʋ(HC=N) 1594, ʋ(N–N) 1011; 1H NMR data (300 MHz,
DMSO, δ, ppm) 12.17(1H, s, OH), 15.57(1H, s, NH), 8.64(1H, s,
CH),7.33-8.63 (10 H, m, Ar-H); 13C NMR data (75 MHz, DMSO, δ,
=
=
–
=
ppm) 164.4 (C O), 148.9 (N CH), 154.2 (C OH), 153.5 (N C).
(Pyridine-2-ylmethylene)-thiophene-2-carbohydrazide (I2)
2

S. Abbas, Imtiaz-ud-Din, M. Mehmood et al.
Journal of Molecular Structure 1230 (2021) 129870
8.85 (8H, m, Ar H); 13C NMR data (75 MHz, DMSO, δ, ppm) 149.9
12.28(1H, s, OH) 11.13 (1H, s, NH), 8.61 (1H, s, CH), 7.35-8.47 (12H,
–
13
=
m, Ar-H); C NMR data (75 MHz, DMSO, δ, ppm) 164.4 (C O),
=
–
(N CH), 126.1, 124.1, 122.8 (Ar C)
[4-Hydroxy(quinolin-2-ylmethylene)benzohydrazide(trichloro)
Bi(III)] (6)
=
–
=
137.3 (N CH), 154.16 (C OH), 148.7(N C).
Quantities
used;
4-hydroxy(quinolin-2-
2.2.2. Target compounds
ylmethylene)benzohydrazide (0.29 g, 1mmol), BiCl3 (0.315 g,
1mmol). yellow powder, Yield: 63%; M.p 309-310 °C. Anal. Calcd
(Found %) for C17 H13BiCl3N3O2 (606.64 g/mol): C = 33.66 (33.65),
H = 2.16 (2.15), N = 6.93 (6.92); FTIR data (KBr, cm−1): ʋ(C=N)
1542, ʋ(Bi–N) 513, ʋ(Bi–O) 425; 1H NMR data (300 MHz, DMSO,
δ, ppm) 15.84 (1H, s, OH), 10.24 (1H, s, CH), 12.01 (1H, s, NH),
6.88-8.81 (10H, m, Ar-H); 13C NMR data (75 MHz, DMSO, δ, ppm)
The bismuth(III) derivatives of substituted hydrazones were pre-
pared by refluxing the solution of anhydrous BiCl3 and the respec-
tive hydrazone in dry methanol for 4-5 h in an inert atmosphere.
Afterward the reaction mixture was cooled, filtered to get the pre-
cipitates of the crude products that were subsequently washed
with suitable solvents and dried. The compounds were recrystal-
lized in a mixture of acetone and dry ethanol (1:3) to get the pure
products, in some cases fine crystals for X-ray analysis are also ob-
tained.
=
=
–
=
161.81 (C O), 139.06 (N CH), 152.8 (C OH), 145.7(N C).
[(Quinolin-2-ylmethylene)isonicotinohydrazide(trichloro)
Bi(III)] (7)
[3-Hydroxy-(pyridine-2-ylmethylene)-2-
Quantities used; (quinolin-2-ylmethylene)isonicotinohydrazide
(0.27 g, 1mmol), BiCl3 (0.315 g, 1mmol). yellow powder, Yield:
58%; M.p 306-308 °C. Anal. Calcd (Found %) for C16 H12BiCl3N4O
(591.63): C = 32.48 (32.47), H = 2.04 (2.03), N = 9.47 (9.46); FTIR
data (KBr, cm−1): ʋ(C=N) 1556, ʋ(Bi–N) 523, ʋ(Bi–O) 418; 1H NMR data
(300 MHz, DMSO, δ, ppm) 8.83 (1H, s, CH), 12.42 (1H, s, NH), 7.68-
naphthohydrazide(dichloro)Bi(III)] (1)
Quantities
used;
3-hydroxy-(pyridine-2-ylmethylene)-2-
naphthohydrazide (0.3 g, 1mmol), BiCl3 (0.315 g, 1mmol). Yellow
powder, Yield: 72%; M.p about 299-300 °C. Anal. Calcd (Found %)
for C17 H12BiCl2N3O2 (570.18 g/mol): C = 35.81 (35.80), H = 2.12
(2.11), N = 7.37 (7.36); FTIR data (KBr, cm−1): ʋ(C–O) 1363, ʋ(C=N)
1536, ʋ(Bi-N) 511, ʋ(Bi-O) 406; 1H NMR data (300 MHz, DMSO, δ,
8.45 (10H, m, Ar H); 13C NMR data (75 MHz, DMSO, δ, ppm) 162.5
–
=
=
=
(C O), 137.4 (N CH), 150.8 (N C).
[3-Hydroxy(quinolin-2-ylmethylene)-2-
naphthohydrazid(trichloro)Bi(III)] (8)
ppm) 12.23 (1H, s, OH), 9.62 (1H, s, CH), 7.33-8.97 (10H, m, Ar-H);
13
=
C NMR data (75 MHz, DMSO, δ, ppm) 149.9 (N CH), 128.78,
–
127.2,126.3, 124.13, 110.91 (Ar C)
Quantities
used;
3-hydroxy(quinolin-2-ylmethylene)-2-
(Pyridine-2-ylmethylene)-thiophene-2-
carbohydrazide(trichloro)Bi(III)] (2)
naphthohydrazide (0.34 g, 1mmol), BiCl3 (0.315 g, 1mmol).
brown powder, Yield: 62%; M.p 336-338 °C. Anal .Calcd (Found %)
for C21H15BiCl3N3O2 (656.75): C = 38.41 (38.40), H = 2.30 (2.27),
N = 6.40 (6.38); FTIR data (KBr, cm−1): ʋ(C=N) 1570, ʋ(Bi–N) 522,
ʋ(Bi–O) 428; 1H NMR data (300 MHz, DMSO, δ, ppm) 9.78 (1H, s,
Quantities
used;
(pyridine-2-ylmethylene)-thiophene-2-
carbohydrazide (0.231 g, 1mmol), BiCl3 (0.315 g, 1mmol). white
powder, Yield: 50%; M.p 262-264 °C. Anal .Calcd (Found %) for
C11 H9BiCl3N3OS (546.61 g/mol): C = 24.17 (24.16), H = 1.66 (1.65),
N = 7.69 (7.68); FTIR data (KBr, cm−1): ʋ(C=N) 1536, ʋ(Bi–N) 517,
ʋ(Bi-O) 412; 1H NMR data (300 MHz, DMSO, δ, ppm) 12.07 (1H,
CH), 12.19 (1H, s, NH), 7.27-8.93 (12H, m, Ar H); 13C NMR data
–
=
=
(75 MHz, DMSO, δ, ppm) 154.18 (C O), 130.8 (N CH).
s, NH), 7.54 (1H, s, CH), 7.23-8.78 (7H, m, Ar H); 13C NMR data
–
2.3. Biological studies
=
=
=
(75 MHz, DMSO, δ, ppm) 187.6 (C O), 137.7 (N CH), 149.7 (N C).
[4-Hydroxy(pyridin-2-ylmethylene)benzohydrazide
(dichloro)Bi(III)] (3)
2.3.1. Antimicrobial activity
The target compounds (1-8) and the ligands (I1-I8) were tested
against the refreshed bacterial cultures of Bacillus subtilis (ATCC-
6633), Staphylococcus aureus (ATCC-6538), Klebsiella pneumoniae
(ATCC-6538) and Escherichia coli (ATCC-25922). The Broth dilution
technique is used to determine the minimum inhibitory concen-
tration (MIC) and the detailed procedure has been given as sup-
plementary files [24].
Quantities
used;
4-hydroxy(pyridin-2-
ylmethylene)benzohydrazide (0.24 g, 1mmol), BiCl3 (0.315 g,
1mmol). Light greenish yellow powder, Yield: 52%; M.p 298-
300 °C. Anal .Calcd (Found %) for C13H10BiCl2N3O2 (520.12 g/mol):
C = 30.02 (30.01), H = 1.94 (1.93), N = 8.08 (8.07); FTIR data
(KBr, cm−1): ʋ(C–O) 1350, ʋ(C=N) 1542, ʋ(Bi–N) 502, ʋ(Bi–O) 422; 1H
NMR data (300 MHz, DMSO, δ, ppm) 12.37 (1H, s, OH), 10.33 (1H,
All these compounds were also explored for their antifungal
activity by using disc diffusion technique. The four fungal strains
A.niger (FCBP-0198), A. fumigatus (FCBP-66), A. flavus (FCBP-0064)
and Mucor species (FCBP-0300) were employed to determine the
MIC and the detailed procedure is given as supplementary files
[25].
s, CH), 6.88-8.81 (8H, m, Ar H); 13C NMR data (75 MHz, DMSO, δ,
–
=
=
–
=
ppm) 147.3 (C O), 163.9 (N CH), 161.1 (C OH), 150.6(N C).
[4-Methyl(pyridin-2-ylmethylene)benzohydrazide
(trihloro)Bi(III)] (4)
Quantities
used;
4-methyl(pyridin-2-
ylmethylene)benzohydrazide (0.24 g, 1mmol), BiCl3 (0.315 g,
1mmol). White powder, Yield: 57%; M.p 266-269 °C. Anal. Calcd
(Found %) for C14 H13BiCl3N3O2 (554.61 g/mol): C = 30.32 (30.31),
H = 2.36 (2.35), N = 7.58 (7.57); FTIR data (KBr, cm−1): ʋ(C=N)
1539, ʋ(Bi–N) 524, ʋ(Bi–O) 411; 1H NMR data (300 MHz, DMSO,
2.3.2. Protein kinase inhibition assay
The Streptomyces 85E bacterial strain was utilized to determine
the protein kinase inhibition assay, using Surfactin and DMSO as
positive and negative controls, respectively. The detailed protocol
is given as supplementary files [26].
δ, ppm) 2.39 (3H, s, CH3), 11.95 (1H, s, CH), 7.35-8.83 (8H, m,
13
–
=
Ar H); C NMR data (75 MHz, DMSO, δ, ppm) 149.6 (C O), 142.8
=
=
(N CH), 138.9 (C-CH3), 151.9 (N C), 21.59 (CH3).
2.3.3. Alpha-amylase inhibition assay
[(Pyridine-2-ylmethylene)-isonicotinohydrazidetrichloro)
Bi(III)] (5)
The antidiabetic potential for all the synthesized compounds
was determined using alpha-amylase inhibition assay. Here DMSO
and Acarbose (250 μM) were used as negative and positive con-
trols, respectively. Absorbance was measured at 540 nm and per-
centage inhibition was calculated using the following equation
[27].
Quantities used; (pyridine-2-ylmethylene)-isonicotinohydrazide
(0.22 g, 1mmol), BiCl3 (0.315 g, 1mmol). Yellow powder, Yield:
65%; dec. 340-342 °C. Anal. Calcd (Found %) for C12H10BiCl3N4O
(541.57 g/mol): C = 26.61 (26.60), H = 1.86 (1.85), N = 10.35
(10.34); FTIR data (KBr, cm−1): ʋ(C=N) 1563, ʋ(Bi–N) 539, ʋ(Bi–O) 408;
1H NMR data (300 MHz, DMSO, δ, ppm) 12.33 (1H, s, CH), 7.58–
% α-amylase inhibition = (Os-On) / (Ob-On) × 100
3

S. Abbas, Imtiaz-ud-Din, M. Mehmood et al.
Journal of Molecular Structure 1230 (2021) 129870
Scheme 1. Synthetic depiction for (1-8).
Where On = Absorbance of negative control, Os = Absorbance of
sample and Ob = Absorbance of blank well. The detailed procedure
has been mentioned as supplementary files
and Human Pancreatic Alpha amylase (PDB ID: 5U3A) were ob-
tained from RCSB Protein Data Bank (PDB). There are certain ev-
idences in literature [30–32] regarding the binding pocket of the
drug target proteins which were considered as input for docking
procedure. During the docking run, the receptors were prepared
by adding all the necessary hydrogen atoms required for proto-
nation. The binding cavity of the receptor was defined by select-
ing the active site residues retrieved from the literature studies.
The chemical structures of the synthesized compounds were opti-
mized using the molecular mechanical MM2 energy minimization
method [33]. The docking results were evaluated using the Gold
fitness function, by whichcompounds exhibiting greater scores, will
have higher binding affinity with the receptor [34].
2.3.4. Brine shrimp lethality assay
The standard protocol for brine shrimp lethality assay was per-
formed with slight modifications [25]. Doxorubicin (4 mg/mL in
DMSO) and DMSO were used as positive and negative control, re-
spectively. The degree of lethality, induced by each compound, was
quantified after 24 h. The table curve 2D vs. 5.01 software was
used to determine the median lethal doses (LD50) of the com-
pounds with ≥ 50 % mortality, and the details have been given as
supplementary files.
3. Results and discussion
2.4. Computational studies
3.1. Chemistry
Genetic Optimization for Ligand Docking (GOLD) program was
utilized to conduct molecular docking studies on the synthesized
bismuth(III) derivatives to investigate their antibacterial, antidia-
betic, and anticancer potential [28,29]. The GOLD practices genetic
algorithm was employed to dock small molecules into the bind-
ing pocket of the receptors. The crystal structure of H. Pylori ure-
ase (PDB ID: 1E9Y), EGFR tyrosine kinase domain (PDB ID: 1M17)
The substituted hydrazones were made to react with the anhy-
drous bismuth salt in dry solvent under inert conditions, as de-
picted in Scheme 1, to yield the target products (1-8). The bis-
muth(III) derivatives are mostly insoluble in ordinary organic sol-
vents but are soluble in a coordinating solvent, DMSO. They are
stable compounds and for more details in terms of their stabil-
4

S. Abbas, Imtiaz-ud-Din, M. Mehmood et al.
Journal of Molecular Structure 1230 (2021) 129870
The 13C NMR data described the characteristic resonance peaks
=
for unique carbons of HC=N- and C O moieties which appeared
at about 142.5 and 164.4 ppm respectively in the spectra of the
compounds. In case of complexes, there is a slight shift of all the
resonances in comparison to the ligands. The aromatic carbons give
their characteristic peaks in their usual region ranging from 110
to 150 ppm and are in consonance to the already reported values
[19,38]. Thus, NMR data fully validate the proposed structure of
the target compounds in solution phase by manifesting their all
the distinct protons and carbons as detailed in the experimental
section
3.4. X-ray crystallography
The solid state structure for compounds (1) and I6 having
molecular formulae, [Bi(2-OHC10H7)CONHNCH(C5H4N)Cl2(DMSO)2]
and [(C9H6N)CHNNHCO(4-OHC6H4)NO3H2O] respectively were de-
termined by single crystal X-ray analyses in order to authenticate
their chemical structures. The molecular structure for (1) is delin-
eated in Fig, 1, whereas the ORTEP diagrams for (1) and I6 are de-
picted in Figs. 2 and 3, respectively.
Fig. 1. Molecular structural for (1).
ity see elsewhere [21] They were characterized by employing var-
ious spectroscopic and single crystal X-ray diffraction techniques,
besides determining their melting point and CHNS analyses.
3.2. FT-IR data
The crystallographic data and the structure refinement details
for the compounds have been displayed in Table 1 whereas the
selected bond angles, bond lengths and hydrogen bonding data
are given as supplementary files. The compound (1) crystallized
out as monoclinic crystal system having space group P21/c, de-
picting crystal lattice of primitive type with 21 linear axis per-
pendicular to c glide plane. The packing diagram illustrate that
four formula units are packed in one-unit cell. The bismuth is
hepta-coordinated bearing the molecular geometry as distorted
pentagonal bipyramidal with one anionic hydrazone moiety at-
tached to the metal center via its three ligating atoms, that is,
nitrogens of pyridine and of the azomethine moiety along with
the carbonyl oxygen. Furthermore the two chloro- and two oxy-
gens from the (two) DMSO molecules, as coordinated solvent,
linked to bismuth center to complete its coordination sphere [39].
The bond lengths between Bi(1)-O(1), Bi(1)-N(1) and Bi(1)-N(2)
are 2.323(5), 2.539(6), 2.390(5) oA respectively, indicating that at-
tachment through carbonyl C(7)-O(1) moiety is the strongest one
among the hydrazone linkages. The bond lengths for Bi(1)-Cl(1)
and Bi(1)-Cl(2) are 2.732(2), 2.620(3) oA respectively, whereas the
bond angles between O(1)-Bi(1)-N(2), O(1)-Bi(1)-N(1) and N(2)-
Bi(1)-N(1) are 66.08(18), 132.37(17) 66.30(18) respectively and the
data are compatible with the reported ones [39]. The bond lengths
around 2.580(5), 2.593(5), 1.509(6), 1.491(7) and 1.529(10) oA cor-
respond to Bi(1)-O(4), Bi(1)-O(3), S(1)-O(3), S(2A)-O(3) and S(2A)-
O(4) respectively that provide strong evidence for the attachment
of DMSO as coordinating solvent (molecules).
The IR absorption band, ascribed to ν
at 3395-3052 cm−1
(N-H)
in free ligands, disappeared in the spectra of 1 and 3, indicating
the enolization and deprotonation at imine nitrogen, and is au-
thenticated by single crystal XRD data, whereas the same absorp-
tion band is present around 3233-3452 cm−1 in the complexes
(2, 4, 5, 6, 7, 8) indicating the presence of keto form of the lig-
ands. The stretching frequency for ν
appeared around 1594-
(HC=N)
1552 cm−1 in the spectra of hydrazones which shifted to lower
frequency around 1536-1563 cm−1 upon complexation, suggesting
its coordination to bismuth center through the nitrogen. The ab-
sorption band for ν
the ligands, disappeared in complexes 1 and 3, indicating its trans-
observed in range 1684-1638 cm−1 in
(C=O),
–
formation to a single C O bond upon coordination with the con-
current appearance of a new band around 1363 cm−1. However,
this absorption band was observed at around 1650-1612 cm−1 in
complexes (2, 4, 5-8) and shifted considerably to lower wave num-
ber, suggesting that here coordination occur through the carbonyl
oxygen. In plane deformation mode for pyridine ring appeared
in range 607-625 cm−1 in the spectra of free hydrazones which
shifted to 620-616 cm−1 for the complexes (1-8) which indicated
the involvement of hetero-atom, nitrogen, in the coordination pro-
cess [35]. The stretching vibrational bands appearing around 406-
422 and 502–537 cm−1 are assignable to ν(Bi–O) and ν(Bi–N), respec-
tively which clearly demonstrate the development of new linkages
of the respective ligand to the bismuth center [19,36].
The most common types of non-covalent interactions like hy-
drogen bonding etc., control various physical properties of the
compounds, like solubility and catalytic activity. Both inter and in-
tramolecular H-bondings are present in complex (1) and are de-
lineated in Fig. 4, the data are provided as supplementary files.
The intra- molecular hydrogen bonding is present between H(2A)
and the covalently bonded O(2) having bond length 0.82 oA and
with N(3) possessing bond distance of 1.93 oA. The intra molecu-
lar hydrogen bond lengths of H(1) and H(4) with O(4) and O(21)
are 2.52 and 2.40 respectively indicating weaker force of attraction
as compared to H(2A) and N(3). Both the H(1) and H(4) are cova-
lently bonded to C(1) and C(4) with equal bond length of 0.93 oA.
The bond angles of O(2)-H(2A)-N(3), C(1)-H(1)-O(4) and C(4)-H(4)-
O(21) are 135.5o, 127.7o and 167.9o respectively. The intermolecular
H- bonding is present between Cl(1)-H(21B) and Cl(2)-H(21C) with
bond lengths 2.76 and 2.68 oA respectively. These intra and inter
molecular bondings provide some additional stability to the syn-
thesized compounds [40].
3.3. NMR data
The structures of the synthesized compounds were further au-
thenticated by NMR spectroscopic data. The 1H NMR spectra of
–
the free ligands revealed the chemical shift value for N H pro-
ton around 15.57-11.42 ppm which disappeared in case of 1 and
3, confirming the enolization and participation of the NH group in
the process of complexation. While in all other metal complexes
the ligands remain in the keto form with slight shift in their NH
chemical shift values.
The proton of -OH functionality resonated at 12.23 and
12.37 ppm for (1 and 3) respectively which demonstrate its non-
involvement in complex formation. The resonance peaks for methyl
protons appear at 2.39 ppm in case of (4). The chemical shifts for
phenyl protons appear in their usual region for both ligands (6.86-
8.83 ppm) and their respective metal complexes (6.88-8.97 ppm)
as earlier reports manifested [37].
5

S. Abbas, Imtiaz-ud-Din, M. Mehmood et al.
Journal of Molecular Structure 1230 (2021) 129870
Fig. 2. ORTEP diagram for (1).
Fig. 3. ORTEP diagram for (I6).
Fig. 4. Hydrogen bonding diagram for (1).
6

S. Abbas, Imtiaz-ud-Din, M. Mehmood et al.
Journal of Molecular Structure 1230 (2021) 129870
Table 1
Crystallographic data and refinement parameter for (1) and (I6).
Identification code
1
C
I6
Empirical formula
CCDC
21H24N3O4S2Cl2Bi
C17H16N4O6
2017727
372.34
296(2)
Monoclinic
P21/c
1975573
Formula weight
Temperature/K
Crystal system
Space group
726.43
296(2)
Monoclinic
P21/c
˚
a/A
9.0170(11)
7.421(3)
17.777(9)
12.639(7)
90
˚
b/A
20.264(3)
˚
c/A
14.902(2)
α/°
β/°
γ/°
90
91.899(6)
100.79(2)
90
90
3
˚
Volume/A
2721.3(7)
1638.0(14)
4
Z
4
ρcalc g/cm3
μ/mm-1
1.773
1.510
6.859
0.117
F(000)
1408.0
776.0
Crystal size/mm3
0.400 × 0.180 × 0.160
MoKα (λ = 0.71073)
4.52 to 56.128
0.36 × 0.20 × 0.16
MoKα (λ = 0.71073)
5.588 to 51
Radiation
2ꢀ range for data collection/°
Index ranges
-11 ≤ h ≤ 11, -26 ≤ k ≤ 25, -19 ≤ l ≤ 19
18259
-8 ≤ h ≤ 8, -21 ≤ k ≤ 20, -12 ≤ l ≤ 15
9428
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indexes [I> = 2σ (I)]
Final R indexes [all data]
6561 [Rint = 0.0552, R
6561/4/309
= 0.0843]
3027 [Rint = 0.0794, R
3027/3/252
= 0.1085]
sigma
sigma
0.952
0.972
R1 = 0.0506, wR2 = 0.1145
R1 = 0.0985, wR2 = 0.1333
1.25/-1.47
R1 = 0.0660, wR2 = 0.1517
R1 = 0.1518, wR2 = 0.1929
0.28/-0.23
−3
˚
Largest diff. peak/hole / e A
The crystal data for (I6) suggest that crystal system is of mono-
clinic type having space group P21/c where four molecules are con-
fined in one-unit cell. The bond distances for C(7)-O(2) and C(8)-
N(2) are 1.198(4) and 1.255(4) ˚A respectively which are in close
agreement with the reported bond length for double bond. The
N(1)-N(2) bond distance is 1.341 0A which is slightly shorter than
ideal bond distance of single bond that is, 1.411(7) showing some
strains The anti-fungal data discerned that compounds (4, 5 )ex-
hibit significant activity having MIC values of 12.5 and 6.25 μg/mL
respectively against A. flavus as compared to the standard drug
The antimicrobial activity of all the synthesized Bi(III) deriva-
tives (1-8) justified that they are more potent as compared to
the hydrazone Schiff bases (I1-I8), that may be ascribed to the
greater lipophilicity of the metal ion containing moiety and its
permeability through the cell membrane. The plausible explana-
tion for the enhanced activity may be described in term of chela-
tion theory [41]. The structure of all the synthesized ligands (I1-
–
double bond character in N N bond. The inter molecular hydro-
gen bonding is present between H(1A) and the covalently bonded
N(1) having bond length 2.07oA and with O(3) of NO3 moiety. The
bond angles for O(2)-C(7)-N(1) and O(2)-C(7)-C(1) are 120.6(4) and
123.6(4) respectively, displaying a planar structure for the molecule
[18].
=
I8), mainly possess C N bond that coordinate to the Bi(III) moiety
which is responsible for the delocalization of π electrons. This in
turn reduced the polarity due to partial sharing of charges between
trivalent Bi(III) and donor hydrazone group. This process intensify
lipophilicity of the target compounds, resultantly they acquired en-
try into the bacterial or fungal cell membrane and enhance their
antimicrobial activity [42].
3.5. Biological studies
The bismuth(III) hydrazones are deemed to be bioactive com-
pounds owing to inherent biocidal nature of their constituent
species. They were preliminary screened for their possible an-
timicrobial, protein kinase and alpha amylase inhibition activities,
along with brine shrimp lethality assay which isused to estimate
their toxicity level.
3.5.2. Alpha-amylase inhibition data
The alpha amylase inhibition assay was carried out to assess
the antidiabetic nature of the compounds by adopting a reported
methodology [43]. All the compounds were preliminary screened
against alpha-amylase inhibition assay and their percentage inhibi-
tion was recorded at concentration of 100 μg/mL using acarbose
and DMSO as the positive and negative controls and the data are
presented in Table 3. Most of the Bi(III) complexes exhibit good
to significant percentage inhibition when compared with the refer-
ence drug. The data showed that compounds (2, 3, 5, 6, 7 and 8)
exhibit percentage inhibition of 51.33, 51.82, 51.66, 64.4, 89.93 and
67.40% respectively. Mostly metal complexes display very good per-
centage inhibition activity, comparable to the standard drug, that
may owe to their structural flexibility as well as nature of the
complexing species. The ligands (I1-I8) were moderately active at
100 μg/mL but upon complexation with Bi(III), their inhibition be-
come enhanced to some extent. The significant percentage inhibi-
tion of 89.93 % is observed for 7, which is even greater than the
acarbose, and served as a lead compound in the present study that
3.5.1. Antimicrobial data
The synthesized compounds were screened in vitro against four
bacterial and four fungal strains using roxithromycin, cefixime, and
clotrimazole as standard drugs for the respective activity, and the
data are tabulated in Table 2, whereas data are interpreted in term
of minimum inhibitory concentration (μg/mL). Two gram-positive
bacterial strains (Bacillus subtilis and Staphylococcus aureus) and
two gram-negative bacteria (Klebsiella pneumoniae and Escherichia
coli) were used to assess the antibacterial activity of (1-8). The
activity profile for (3, 5, 6 and 7) defined their significant activ-
ity against S. aureus with MIC value of 3.125 μg/mL each, whereas
compound 1 displayed MIC value of 3.125 μg/mL against K. pneu-
moniae. The data described that most of the Bi(III) derivatives are
active at their optimum concentrations against various bacterial
7

S. Abbas, Imtiaz-ud-Din, M. Mehmood et al.
Journal of Molecular Structure 1230 (2021) 129870
Fig. 5. Preferred binding mode for (1) in the binding site of H. pylori urease.
Fig. 6. Two-dimensional depiction of docked complex within the binding pocket of urease protein.
may be evaluated further in future drug discovery and develop-
taining to protein kinase inhibition assay are presented in Table
4. The non-toxic nature of DMSO was also verified by the ab-
sence of respective growth inhibition zone among all the synthe-
sized compounds, the significant bald phenotype of 15 mm cor-
responds to compounds (1, 4) and for ligand (I1), which provided
an indication about the cytotoxic (clear zone) and anticancer na-
ture (bald zone) of the compounds. The presence of electron do-
nating group like -OH and -CH3 in the structures (1, 4) are re-
ment processes.
3.5.3. Protein kinase inhibition data
The protein kinase inhibitory potential for all the synthesized
ligands and their complexes were assessed, using Streptomyces 85E
strain at 100 μg disc loading, by employing a known procedure
with slight modifications [44]. Here surfactin and DMSO were used
as positive and negative controls, respectively. and the data per-
8

S. Abbas, Imtiaz-ud-Din, M. Mehmood et al.
Journal of Molecular Structure 1230 (2021) 129870
Table 2
Anti-microbial∗ data for the synthesized compounds (1-8).
Number
of
MIC(μg/mL)
Antibacterial strains
Bacillus SubtilisStaphylococcus aureusKlebsiella pneumoniaeEscherichia coliAspergillus flavusAspergillus nigerAspergillus fumigatusMucor
Antifungal strains
compounds
I1
50
50
25
25
25
25
50
50
NA
25
NA
25
NA
50
NA
50
1.11
50
12.5
3.125
25
50
50
50
50
50
50
50
50
50
50
50
50
50
25
25
12.5
50
50
50
50
50
50
50
50
50
50
50
50
50
12.5
50
50
50
12.5
>50
˃50
˃50
˃50
˃50
>50
˃50
˃50
>50
>50
>50
>50
>50
>50
>50
>50
1
6.25
50
12.5
25
25
I2
50
2
6.25
50
25
25
50
I3
NA
NA
25
25
3
3.125
50
12.5
12.5
6.25
25
50
I4
NA
25
50
4
6.25
6.25
3.125
50
12.5
25
I5
NA
25
5
25
6.25
25
I6
NA
NA
50
6
3.125
6.26
3.125
NA
25
25
I7
NA
NA
25
50
7
50
25
I8
NA
NA
25
>50
50
8
50
50
Cefixime∗
Roxithromycin∗0.334
Clotrimazole∗
0.334
0.334
0.334
0.334
1.11
0.334
10
-
5
-
5
-
2.5
-
DMSO
-
-
-
-
∗
standard drug
- no activity
Table 3
Alpha amylase, Protein kinase inhibition data and cytotoxicity assay.
Alpha amylase
inhibition assay Protein kinase inhibition assay
Brine shrimp lethality assay(Cytotoxicity)
%age Mortality
Number of
compounds
%age inhibition
100 (μg/mL)
Zones at 100 μg/disc
Clear zone
Bald zone
200 (μg/mL)
100 (μg/mL)
50 (μg/mL)
25 (μg/mL)
LD50
I1
12.34
23.44
-3.63
51.33
-30.07
51.82
31.18
-32.92
-30.92
51.66
-1.89
64.4
13
-
15
15
-
100
100
100
100
100
100
100
100
100
100
40
70
50
50
40
30
40
90
40
50
60
100
30
0
40
30
30
30
30
40
40
10
60
50
20
0
41.58
41.88
53.97
79.98
58.29
27.83
55.94
52.48
21.03
25
1
100
70
I2
20
15
12
-
2
12
-
40
I3
60
3
12
8
100
50
I4
-
4
-
15
-
80
I5
9
60
5
-
10
-
100
40
I6
10
15
15
9
9.64
6
-
100
100
100
80
80
96.26
23.90
0.217
50.93
65.54
I7
72.92
89.93
65.83
67.40
69.29
-
100
100
70
100
100
50
50
80
100
30
20
7
-
I8
-
9
8
15
-
90
50
Acarbose∗
Surfactin∗
Doxorubicin∗
DMSO
-
-
30
-
90
-
80
-
60
-
30
-
5.93
-
-
∗
∗
standard drug.
- no activity.
Table 4
Molecular docking results against H. pylori urease for (1-5).
GOLD Fitness
Compound
1
score
Binding Energy H-bonds
Interacting protein residues
41.94
−77.426
Met555-H
Ala603, Glu551, Arg606, Cys559, Asn406, Ala407, Leu556, Met555, Met604, Gln602,
Gly605
2
3
41.40
33.20
-64.78
-77.79
Gly605-H
His512-O,
His374-O,
His486-O
Ser598-Cl
Pro540, Met604, Gly605, Ser601, Val607, Thr385, Gly608, Glu609, Met555, Arg606
His459, Ala603, His376, Asp600, Asp461, Leu556, Asn406, Arg576, Glu460, Phe572
4
5
34.40
38.53
-63.81
-63.89
Ala654, Met765, Ser595, Lys646, Thr538, His589, Phe594, Asp372, Thr373, Ser599,
His374, Phe511, His509, His512, Thr510, Ile533, Met508
Met420, Thr399, Asn416, Pro412, Lys436, Trp462, Ile410, Thr405, Phe377, Gly397,
Gly400, Phe433, Thr411
Gly398-N
9

S. Abbas, Imtiaz-ud-Din, M. Mehmood et al.
Journal of Molecular Structure 1230 (2021) 129870
Fig. 7. Conformational orientation and binding pattern of (2) in the active site of human pancreatic alpha amylase.
Fig. 8. Two-dimensional depiction of docked complex (2) within the active site of human pancreatic alpha amylase protein.
sponsible for their significant protein kinase inhibition activity. The
3.5.4. Brine shrimp lethality data
assay was performed using Streptomyces 85E strain as it resem-
bles the eukaryotic cells. In eukaryotic cells, phosphatases and pro-
tein kinases are involved in multiple signal transduction pathways
responsible for differentiation and proliferation of cells, whereas
unusual phosphorylation may lead to irregular cell division trig-
gering cancer. Consequently, inhibition of kinases is a significant
pharmaceutical tool to combat against various diseases, especially
cancers.
The brine shrimp lethality assay is an efficient and the least ex-
pensive approach to ascertain cytotoxicity of the synthesized com-
plexes, and for that their toxicity assessment was made in com-
parison to standard drug i.e. doxorubicin. The percent mortality
rate for the tested organism (Artemia salina) was determined in
term of LD50 value using 200, 100, 50 and 25 μg/mL dilutions and
data for all the under trialed compounds are delineated in Table 3.
Among all the synthesized bismuth(III) compounds, the least LD50
10

S. Abbas, Imtiaz-ud-Din, M. Mehmood et al.
Journal of Molecular Structure 1230 (2021) 129870
Table 5
Molecular docking results against Tyrosine Kinase for (1-5).
GOLD Fitness
Compound
score
Binding Energy H-bonds
Interacting protein residues
1
52.85
-92.23
Arg146-O,
Asp142-H,
Asp160-O
-
Arg146, Asp160, Cys102, Thr159, Asp105, Leu149, Phe28, Val31, Asp142, Pro182
2
3
36.97
32.34
-62.12
-80.08
Ala48, Thr159, Thr95, Met71, Leu93, Glu67, Val31, Phe28
Ile49, Thr95, Ile94, Leu93, Ala48, Met71, Val31, Lys50, Asp160, Thr159, Asn147, Leu149,
Cys102, Phe28, Gly101, Met98
Ala48-O,
Thr95-O
Asn1470-H
4
5
43.98
37.24
-71.13
-67.99
Arg146, Glu67, Leu52, Asp160, Phe28, Lys50, Val31, Val148, Leu149, Cys102, Thr159,
Arg146
Gly101-H
Leu23, Leu97, Pro99, Met98, Phe100, His110, Glu109, Try106, Asp105, Cys102, Gly101
values were observed for I6, I7 and the target compound (7) as
9.64, 23.90 and 0.217 μg/mL respectively, which correspond to the
highest toxicity level among all the compounds under study. On
contrary, compounds (2 and 6) exhibit highest LD50 value of 79.98
and 96.26 μg/mL respectively, indicating their least toxic nature,
when compared to already reported compounds [39].
of protein involved in receptor-ligand interactions include Cys102,
Thr159, Asp160, Leu149, Asp105, Phe28, Val31, Asp142, Arg146,
Pro182, and Asn147 as indicated in Figure S2 as supplementary
files. Receptor-ligand interactions within the binding pocket show
strong hydrogen bonds between protein residues (Arg146, Asp142,
Asp160) and the oxygen atoms of the ligand (Figure S3) as de-
picted in supplementary files. Moreover, aromatic interactions such
as alkyl and pi-alkyl are also observed which play a crucial role in
stabilizing receptor-ligand complex. The compounds reported here
can be further explored through advanced computational and ex-
perimental studies to determine their efficacy as kinase inhibitors
[46,47].
3.6. Computational studies
Some selected bismuth(III) complexes of substituted hydrazones
were also investigated for their in-silico binding pattern through
molecular docking studies with various enzymes (proteins) to pre-
dict how strongly the two molecular structures fit together. The
discussion pertaining to docking data of synthesized compounds
against H. pylori urease, tyrosine kinase and alpha amylase are as
follows:
3.6.3. Human pancreatic alpha amylase
Alpha amylase inhibitors have been targeted in various research
studies for developing therapeutic interventions against obesity, di-
abetes, and periodontal diseases [48]. Owing to the importance
of alpha amylase inhibition in the treatment of carbohydrate dis-
orders, molecular docking studies were conducted to investigate
the amylase inhibition potential of the reported compounds. Com-
pound (2) has exhibited highest GOLD fitness score of 57.22 which
shows the potential binding affinity of ligand within the recep-
tor binding pocket of the protein (Table 6). In addition to this,
compounds 1, 5, and 4 have also exhibited significant GOLD fit-
ness scores unfolding their potential as possible amylase inhibitors.
The protein residues involved in receptor-ligand interaction include
Phe256, Asn298, Asp300, Glu233, Arg195, Asp197, His299, Trp58,
Trp59, His201, Ala198, Leu162, Thr163, His101, Tyr62, Ala307,
Gly306, Asn301, and ILE235 (Fig. 7). Several alkyl and pi-alkyl in-
teractions of receptor with the benzene ring of the lead compound
have been observed which are participating in holding the ligand
within the active site of the protein. Additionally, a strong hydro-
gen bond interaction has been observed between Asp197 and hy-
drogen atom of the ligand (Fig. 8). In silico binding analysis sug-
gests that the reported compounds might be potent inhibitors of
amylase. Future research studies can further explore and investi-
gate the potential of these compounds as therapeutic agents.
Significant amount of literature evidence highlights the impor-
tance of chemical synthesis of compounds in facilitating the dis-
covery of lead compounds which has opened pathways for devel-
oping therapeutic drugs. The implementation of advanced in sil-
ico tools on the chemically synthesized compounds play an in-
novative role in drug design and discovery aiding the control of
antimicrobial resistance to treat chronic infections. The current
study has therefore explored the antibacterial, antidiabetic, and an-
ticancer potential of the reported compounds. Conformational ori-
entation and binding poses of the small molecules were predicted
within the binding pocket of the receptor using molecular dock-
ing studies [49]. The findings of the docking studies suggest that
the synthesized Bismuth (III) complexes with formyl pyridine and
quinoline-2-carboxyaldehyde substituted hydrazones (1-5) have a
greater binding potential to the active site of the target proteins.
3.6.1. H. pylori urease
Urease is an important drug target, virulent protein in H. py-
lori, plays a vital role in the survival of the pathogen in the acidic
environment. The current study, therefore, focus on urease protein
to evaluate the antibacterial profile of the synthesized compounds.
Docking results have highlighted the increased binding affinity of
(1) against urease protein with GOLD fitness score of 42 in compar-
ison to the other docked compounds (Table 4). The binding pocket
residues of the receptor that interact with (1) include; Arg606,
Gly605, Gln602, Met555, Met604, Leu556, Ala407, Asn406, Cys559,
and Ala603 (Fig. 5). The conformational orientation and binding
interaction of the ligand-receptor complex shows strong hydrogen
bond between the hydrogen atom of the ligand with the Met555
of the receptor. Moreover, various amide-pi stacked, pi-alkyl, and
alkyl have been observed which are significantly contributing in
stabilizing the ligand within the catalytic site of the receptor [45].
Protein residues Ala603 and Cys559 are interacting with the ben-
zene ring of the ligand forming strong aromatic interactions, con-
tributing to increased binding affinity (Fig. 6). The analysis of the
molecular docking results propose that the reported compounds
are potentially active against H. pylori urease and can be further
exploited as potent inhibitors in upcoming medicinal research de-
velopment programs.
3.6.2. Tyrosine kinase
Research studies have reported high activity of certain kinase
proteins in various types of cancer cells, this gives an impetus
to research focussing on the development of tyrosine kinase in-
hibitors, for the effective treatment of cancerous cells [46]. Owing
to that, molecular docking has been carried out to investigate the
efficacy of the reported compounds as kinase inhibitors. The dock-
ing results suggest that compound (1) exhibited higher binding
affinity in the active site of the receptor with GOLD fitness score of
52.85. Furthermore, (4) has also demonstrated significant binding
affinity against kinase enzyme (Table 5). The active site residues
11

S. Abbas, Imtiaz-ud-Din, M. Mehmood et al.
Journal of Molecular Structure 1230 (2021) 129870
Table 6
Molecular docking results against Human pancreatic alpha amylase for (1-5).
GOLD Fitness
Compound
1
score
Binding Energy h-bonds
Interacting protein residues
50.39
-87.17
Arg146-O,
Asp142-H,
Asp160-O
Asp197-H
Asn301, Phe256, Asn298, Glu233, Arg195, His299, Trp58, Trp59, His201, Ala198, Leu192,
Thr163, His101, Tyr62, Ala307, Gly306, Asp300
2
3
57.22
41.24
-73.24
-75.17
Asn301, Ile235, Phe256, Asn298, Asp300, Glu233, Arg195, His299, Asp197, Trp58, Trp59,
His201, Ala198, Leu162, His101, Tyr62, Ala307
Ser3-O,
Ser3, Asn5, Lys227, Pro228, Tyr2, Gly249, Lys208, Leu211, Asn250
Asn5-O,
Lys227-O,
Lys227-Cl
Ser3-N
4
5
44.85
56.33
-80.53
-80.47
Ser3, Leu211, Lys227, Ile230, Pro228, Tyr2, Asn5, Ser226, Gly225
His305, Leu165, His101, Thr163, Ala198, Gly306, Ala307, Asn307, Phe256, Asn298,
Arg195, Asp197, His299, Tyr62, Trp58, Leu162, Thr163
Ala307-N,
Asp300-N
Compounds (1, 2, and 5) have exhibited significant Gold fitness
scores against urease protein of H. pylori. These compounds have
also shown antibacterial potential in experimental studies against
different bacterial pathogens. The amylase inhibition assay and
molecular docking study of human amylase against the synthesized
bismuth complexes exhibit the significant rate of inhibition for (1,
2, and 5) possibly potent lead compounds against diabetes. The
compound 1 also exhibited high binding affinity against tyrosine
kinase in computational studies, moreover tyrosine kinase inhibi-
tion potential in experimental studies has also been reported for
(1). The computational and experimental data of the current study
are in consonance to the previous findings that described the sub-
stantial therapeutic potential of bismuth-based drugs as antibacte-
rial and anticancer agents [5,19,50]. The future research projects
can conduct advanced computational analysis to further explore
the potential of bismuth-based lead compounds and their possi-
ble role as therapeutic agents for treating antibacterial infections,
diabetes, and cancer cell lines.
carboxyaldehyde substituted hydrazones, particularly 1, 2, and 5
have significant potential to act as therapeutic agents and could
be further explored for their possible biological / medicinal char-
acteristics.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
CRediT authorship contribution statement
Sumaira Abbas: Methodology, Data curation, Writing - origi-
nal draft. Imtiaz-ud-Din: Supervision, Conceptualization, Writing
- review & editing. Mehwish Mehmood: Investigation, Writing -
original draft. M. Khawar Rauf: Data curation. S. Sikander Azam:
Formal analysis, Validation. Ihsan-ul Haq: Data curation. M. Nawaz
Tahir: Data curation. Nousheen Parvaiz: Data curation.
4. Conclusions
Acknowledgment
Eight new bioactive bismuth(III) hydrazones were synthesized
using stoichiometric amounts of the respective hydrazone ligand
and anhydrous BiCl3 in dry methanol under inert conditions. All
the synthesized compounds were characterized using analytical
techniques, such as FT-IR, multinuclear (1H, 13C) NMR spectroscopy
and single crystal X-ray diffraction. The central atom, Bi(III), is
hepta coordinated assuming a typical distorted pentagonal bipyra-
midal molecular geometry. The biocidal properties of the com-
pounds were determined to establish a plausible structural activ-
ity relationship (SAR). The data showed good to significant an-
tibacterial and antifungal activity for (3-7) with MIC values ranging
from 50 to 3.125 μg/mL with reference to the respective standard
drug(s), whereas compound (7) exhibit excellent % alpha amylase
inhibition of 89.93 μg/mL at concentration 100 μg/mL. The brine
shrimp lethality data revealed that most of the synthesized com-
pounds are least toxic making them highly promising drug can-
didate in future innovative research projects. Molecular docking
studies were also carried out to explore the binding conformation
of the reported compounds to the appropriate target binding sites
of human pancreatic alpha amylase (5U3A), H. pylori urease (1E9Y),
and EGFR tyrosine kinase (1M17) so as to find their potential as
antidiabetic, antibacterial, and anticancer agents. The findings of
the computational studies demonstrated the inhibition potential of
some compounds against the respective drug target proteins. The
ligand-receptor interactions at the active sites have shown the cru-
cial role of hydrogen bonding and aromatic interactions in holding
the ligands within the binding pockets of the drug targets. The out-
come of the experimental and computational studies suggest that
the bismuth(III) complexes with formyl pyridine and quinoline-2-
Authors are thankful to HEC, Pakistan and Quaid-i-Azam Uni-
versity for providing financial assistance and granting funds for the
project 6182/Federal/NRPU/R&D/HEC/2016.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2021.129870.
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