Synthesis, characterization, cytotoxicity, and molecular docking studies of ampyrone-based transition metal complexes

Article abstract of DOI:10.1007/s11243-020-00422-8

A novel series of mononuclear transition metal complexes, [Cu(L)Cl] 1, [Zn(L)Cl] 2, [Pd(L)Cl] 3, [Cd(L)I] 4, [Pt(L)Cl] 5, and [Hg(L)Cl] 6, was constructed from a pyrazole-derived Schiff ligand, HL, and characterized by physicochemical and spectroscopic methods. Fourier-transform infrared (FT-IR) spectral data showed the studied ligand to be tridentate and coordinated to the metal ions via ONO donor atoms, whereas powder X-ray diffraction (PXRD) analysis revealed the crystalline nature of all the complexes. The in vitro cytotoxicity of the studied ligand and its complexes were tested by the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay against the human colorectal cancer cell lines HCT116 and HT29. The results suggested that the HCT116 cell line is highly sensitive to complex 1 with a half-maximal inhibitory concentration (IC₅₀) of 45.6?μM, while both cell lines tolerated complexes 2 and 4 better in comparison with HL. In addition, complex 1 with significant anticancer activity was analyzed by molecular docking studies to explore its binding efficacy to the cyclin-dependent kinase?2 active site.

Full text of DOI:10.1007/s11243-020-00422-8

Transition Metal Chemistry
https://doi.org/10.1007/s11243-020-00422-8
Synthesis, characterization, cytotoxicity, and molecular docking
studies of ampyrone‑based transition metal complexes
Mohammad Azam1 · Saikh Mohammad Wabaidur1,6 · Mahboob Alam2 · Zahid Khan3 · Ibrahim O. Alanazi4 ·
Saud I. Al‑Resayes1 · Il Soo Moon5 · Rajendra6
Received: 3 June 2020 / Accepted: 20 August 2020
© Springer Nature Switzerland AG 2020
Abstract
A novel series of mononuclear transition metal complexes, [Cu(L)Cl] 1, [Zn(L)Cl] 2, [Pd(L)Cl] 3, [Cd(L)I] 4, [Pt(L)Cl]
5, and [Hg(L)Cl] 6, was constructed from a pyrazole-derived Schif ligand, HL, and characterized by physicochemical
and spectroscopic methods. Fourier-transform infrared (FT-IR) spectral data showed the studied ligand to be tridentate
and coordinated to the metal ions via ONO donor atoms, whereas powder X-ray difraction (PXRD) analysis revealed the
crystalline nature of all the complexes. The in vitro cytotoxicity of the studied ligand and its complexes were tested by
the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay against the
human colorectal cancer cell lines HCT116 and HT29. The results suggested that the HCT116 cell line is highly sensitive
to complex 1 with a half-maximal inhibitory concentration (IC50) of 45.6 μM, while both cell lines tolerated complexes 2
and 4 better in comparison with HL. In addition, complex 1 with signifcant anticancer activity was analyzed by molecular
docking studies to explore its binding efcacy to the cyclin-dependent kinase 2 active site.
Introduction
with reduced side efects and wide-spectrum action against
curable cancers [6–8]. Schif bases, which are versatile
organic blockers, are considered to be the most “privileged
ligands” and have been widely used due to their prepara-
tive accessibility, structural diversity, and solubility in most
common organic solvents [9, 10]. Furthermore, Schif base
ligands coordinate to various metal ions due to their strong
chelating properties and stabilize them in various oxidation
states [11]. Over the past several years, the coordination
chemistry of transition metal Schif base complexes with
heterocyclic compounds containing N, O, and S atoms has
attracted extensive research interest because of their vari-
ous medicinal properties, viz. in diabetes and cancer, as
Cisplatin, a revolutionary drug in anticancer research, has
been successfully applied in the treatment of various tumors,
particularly ovarian, testicular, and neck cancers [1–3]. How-
ever, the use of cisplatin is limited because of its association
with several side efects including nausea, hair loss, kid-
ney toxicity, and nerve damage [4, 5]. These disadvantages
linked to the use of cisplatin have motivated researchers to
develop potential transition metal-based anticancer drugs
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11243-020-00422-8) contains
supplementary material, which is available to authorized users.
3
* Mohammad Azam
Genome Research Chair, Department of Biochemistry,
azam_res@yahoo.com
College of Science, King Saud University, Riyadh,
Kingdom of Saudi Arabia
* Mahboob Alam
4
mahboobchem@gmail.com
The National Center of Biotechnology, King Abdulaziz
City for Science and Technology, P. O. Box 6086, Riyadh,
Kingdom of Saudi Arabia
* Rajendra
krajendra@banasthali.in
5
Department of Anatomy, College of Medicine, Dongguk
1
Department of Chemistry, College of Science, King
University, Gyeongju 38066, Republic of Korea
Saud University, P. O. Box 2455, Riyadh 11451,
Kingdom of Saudi Arabia
6
Department of Chemistry, Banasthali Vidyapith, Banasthali,
Rajasthan 304022, India
2
Division of Chemistry and Biotechnology, Dongguk
University, 123 Dongdae-ro, Gyeongju, Republic of Korea
Vol.:(0123456789)
1 3

Transition Metal Chemistry
antimicrobial drugs, and in several industrial and catalytic
applications [12–15].
In fact, the primary goal of molecular docking analysis is
the bound conformations and binding afnity between the
ligand and receptor [22].
Pyrazole is a heterocycle compound characterized by a
fve-membered heterocyclic ring with doubly unsaturated
bond and two adjacent hard donor nitrogen atoms, with one
being pyrrole-like and the other being pyridine-like [15, 16].
Over the years, the pyrazole ligand and its derivatives have
received growing interest in coordination chemistry because
of their various coordinating modes and diverse applications
[16]. However, the coordination of pyrazole molecule takes
place via the pyridine-type nitrogen, whereas the pyrrole-
type nitrogen is usually involved in hydrogen bond forma-
tion with available hydrogen acceptor or hydrogen donor
sites [17]. A large number of pyrazolato complexes have
been investigated because of their various therapeutic prop-
erties across a wide spectrum of diseases, demonstrating,
e.g., antimicrobial, antiinfammatory, anticonvulsant, anti-
cancer, anti-viral and anti-tubercular properties [18, 19].
Furthermore, many pyrazole-based compounds have been
successfully utilized as nonsteroidal antiinfammatories,
antipyretics, and analgesics in the treatment of osteoarthri-
tis, rheumatoid arthritis, and spondylitis [20].
Experimental
Materials and methods
4-Aminoantipyrine (>98%), 2-hydroxybenzaldehyde (98%),
triethylamine (99%), potassium tetrachloroplatinate(II)
(99.99%), palladium chloride (99%), copper(II) chloride
dihydrate (99.99%), cadmium iodide (99%), and mercury(II)
chloride (≥ 99.5%) were obtained from Sigma-Aldrich,
while zinc chloride hydrate (99.99%) was purchased from
Alfa Aesar. HCT116 and HT29 cell lines were obtained from
the American Type Culture Collection, whereas fetal bovine
serum (FBS) was obtained from Thermo Fisher Scientifc. C,
H, and N were recorded using an Elementar Vario EL ana-
lyzer. FT-IR spectra were obtained in the range from 4000
to 400 cm−1 from KBr pellets using a PerkinElmer 621 spec-
trophotometer. NMR spectra were recorded with a JEOL 400
spectrometer in CDCl3 and d6-dimethyl sulfoxide (DMSO)
using tetramethylsilane (TMS) as internal standard. Thermal
analyses of the complexes were recorded using an SDTQ-
600 (TA) at 0–1000 °C under inert argon atmosphere. Pow-
der X-ray difraction spectra of the complexes were recorded
using a D2 Phaser X-ray difractometer (Bruker, Germany)
with Cu Kα radiation (k=1.5418 Å). Mass spectrometry data
were obtained with a Micromass Quattro Premier tandem
MS ft with an electrospray ionization (ESI) interface and
measured by MassLynx 4.1 software. MS/MS detection was
accomplished in electrospray positive ionization mode.
Therefore, considering the various biological applications
displayed by pyrazole and its derivatives for a wide spectrum
of diseases, we report herein a novel series of complexes of
the type [M(L)X] [M =copper(II), zinc(II), palladium(II),
cadmium(II), platinum(II), and mercury(II); X = Cl, I]
derived from a pyrazole-based Schif base ligand, HL [21].
In literature, the pyrazole-based Schif base ligand HL has
been used in the construction of Ru(II) complexes [21]. The
structural properties of HL and its complexes were studied
by FT-IR, nuclear magnetic resonance (NMR) spectroscopy,
X-ray powder difraction analysis, and thermal studies. The
in vitro anticancer activity of HL and its complexes was
evaluated against HCT116 and HT29 human colorectal
cancer cell lines. In addition, molecular docking analysis
was also carried out to predict the binding modes of mol-
ecules or metal complexes to the active protein site acting
as a receptor to perform screening of the virtual library of
drug-like chemical species for drug development. Further-
more, molecular docking to the receptor can also be applied
to study the conformation of known binding complexes to
determine their binding strength against targets (receptors).
Synthesis of pyrazole‑based Schif base ligand, HL
Ethanoic solution (10 mL) of 2-hydroxybenzaldehyde
(1.23 mmol, 250 mg) was mixed gradually with ampyrone
(150 mg) in ethanol with constant stirring for 8 h. Orange-
colored precipitate was obtained, separated out by fltration,
and dried in anhydrous CaCl2-loaded desiccator (Scheme 1).
HL: Yield, 82%; m.p. 124 °C; Anal. Calc. for
C18H17N3O2 (%), C, 70.34; H, 5.58; N, 13.67; Found: C,
Scheme 1 Synthesis of com-
plexes
1 3

Transition Metal Chemistry
70.28; H, 5.54; N, 13.61%. IR (KBr, cm−1): 1611 ν(CH=N)
,
159.7 (–CH=N); 114.3–134.5 (Ar–C), 35.4 (–N–CH3),
10.1 (–C–CH3).
1
3046 ν(OH), 1307 phenolic ν(C─O), 1601 v(C=O), H-NMR
(CDCl3) (ppm): 9.80 (s, 1H, –CH=N); 6.85–7.49 (m,
9H, Ar–H); 3.15 (–N–CH3), 2.39 (–C–CH3); 13C-NMR
(CDCl3) (ppm): 160.0 (–CH=N); 134.4–116.3 (Ar–C),
35.7 (–N–CH3), 10.3 (–C–CH3).
Synthesis of [Pd(L)Cl] (3)
General procedure for synthesis of [M(L)X]
[M = copper(II), zinc(II), palladium(II), cadmium(II),
platinum(II), and mercury(II); X=Cl, I].
To a small quantity of dichloromethane was added a mix-
ture of HL (100 mg, 0.325 mol) and [Pd(CH3CN)2Cl2]
(84.2 mg) in 1:1 molar ratio under vacuum followed by
stirring of the resulting solution for 30 min; thereafter, the
volume of the reaction mixture was reduced to 1 mL. Yel-
low-colored precipitate was obtained by adding n-hexane
to the reduced reaction mixture, which was fltered and
dried in vacuum to obtain pure compound.
Methanolic solution of HL (100 mg, 0.325 mol) was
mixed with metal salt in 1:1 molar ratio in same solvent,
and the whole reaction mixture was stirred for 10 h in the
presence of equivalent amount of trimethylamine. A colored
product was obtained, which, however, remained insoluble
even on refuxing for additional 5 h. The product was iso-
lated and washed thoroughly with methanol and dried in
vacuum. Several eforts were made to crystallize the prod-
uct. Unfortunately, we could not fnd any crystal suitable for
single-crystal X-ray difraction.
[Pd(L)Cl) 3: Yield 0.16 g (74%); m.p. 225 °C; Anal.
Calc. for C18H16ClN3O2Pd (%): C, 48.23; H, 3.60; N,
9.38; Found, C, 48.19; H, 3.53; N, 9.34. IR (KBr, cm−1):
1607 ν(CH=N), 3437 ν(–OH), 1H-NMR (d6-DMSO) (ppm):
9.64 (s, 1H, –CH=N); 6.85–7.50 (m, 9H, Ar–H), 3.16
(–N–CH3), 2.35 (–C–CH3); 13C-NMR (d6-DMSO) (ppm):
159.9 (–CH=N), 134.6–114.5 (Ar–C), 35.6 (–N–CH3),
10.3 (–C–CH3).
[Cu(L)Cl] 1: Yield 0.15 g (85%); m.p. 281 °C; Color,
brown; Anal. Calc. for C18H16ClN3O2Cu (%): C, 53.34; H,
3.98; N, 10.37; Found, C, 53.29; H, 3.94; N, 10.31. IR (KBr,
cm−1): 1601 ν(CH=N), 3437 ν(–OH); ESI–MS (M+H)+ (m/z),
406.
[Zn(L)Cl] 2: Yield 0.19 g (68%); m.p. 275 °C;
Color, yellow; Anal. Calc. (%) for molecular formula,
C18H16ClN3O2Zn: C, 53.10; H, 3.96; N, 10.32; Found, C,
Cell culture
Human colorectal cancer cell lines HCT116 and HT29 were
grown in Dulbecco’s modifed Eagle medium (DMEM)
(Thermo Fisher Scientifc) supplemented with 10% FBS,
50 unit/ml penicillin, and 50 μg/ml streptomycin. Cells were
grown to confuency of 70–80% in a humidifed incubator
with 5% CO2 at 37 °C before being utilized in experiments.
53.06; H, 3.89; N, 10.27. IR (KBr, cm−1): 1596 ν(CH=N)
,
1
1
3434 ν(–OH), H-NMR (CDCl3) (ppm): 9.81 (s, H,
–CH=N); 6.87–7.49 (m, 9H, Ar–H) 3.15 (–N–CH3), 2.39
(–C–CH3); 13C-NMR (d6-DMSO) (ppm): 159.9 (–CH=N);
114.5–134.6 (Ar–C), 35.6 (–N–CH3), 10.3 (–C–CH3).
Cd(L)I] 4: Yield 0.18 g (78%); m.p. 282 °C; Color, yel-
low; Molecular formula, C18H16IN3O2Cd; Anal. Calc. (%):
C, 47.60; H, 3.55; N, 9.25; Found, C, 47.55; H, 3.49; N,
Cell viability assay
1
9.19. IR (KBr, cm−1): 1608 ν(CH=N), 3445 ν(–OH), H-
NMR (d6-DMSO) (ppm): 9.65 (s, 1H, –CH=N); 6.85–7.51
(Ar–H, 9H); 3.16 (–N–CH3), 2.36 (–C–CH3); 13C-NMR
(d6-DMSO) (ppm): 158.7 (–CH=N); 113.3–133.5 (Ar–C),
34.4 (–N–CH3), 9.1 (–C–CH3).
HCT116 and HT29 human colorectal cancer cells were
plated at density of 6000 cells per well in a 96-well cell
culture plate and allowed to grow in a humidifed 5% CO2
incubator at 37 °C for 24 h. Cells were treated in triplicate
with increasing concentrations of the compounds from 10 to
150 μM for 48 h. Cells treated with DMSO served as con-
trol. Cell viability was determined by colorimetric method
using the CellTiter 96® AQueous Non-Radioactive Cell Pro-
liferation Assay (Promega, Madison, WI). The absorbance
of tissue culture medium-soluble formazan product formed
due to the bio-reduction of tetrazolium compound MTS by
dehydrogenase enzymes found in metabolically active cells
was measured at 490 nm at 3 h after addition of MTS using
an xMark microplate spectrophotometer (Bio-Rad, Hercules,
CA, USA). IC50 values were determined using a publicly
available IC50 calculator online tool from AAT Bioquest
(https://www.aatbio.com/tools/ic50-calculator).
[Pt(L)Cl) 5: Yield 0.20 g (75%); m.p. 252 °C; Color, yel-
low; Anal. Calc. for C18H16ClN3O2Pt (%): C, 40.27; H, 3.00;
N, 7.83; Found, C, 40.21; H, 2.97; N, 7.77. IR (KBr, cm−1):
1610 ν(CH=N), 3449 ν(–OH), 1H-NMR (CDCl3) (ppm): 9.65
(s, 1H, –CH=N); 6.85–7.51 (Ar–H, 9H); 3.16 (–N–CH3),
2.36 (–C–CH3); 13C-NMR (CDCl3) (ppm): 160.8 (–CH=N);
116.8–132.0 (Ar–C), 35.7 (–N–CH3), 10.3 (–C–CH3).
[Hg(L)Cl] 6: Yield 0.17 g (81%); m.p. 242 °C; Color,
yellow; Anal. Calc. for C18H16ClN3O2Hg (%): C, 39.86; H,
2.97; N, 7.75; Found, C, 39.82; H, 2.93; N, 7.71. IR (KBr,
1
cm−1): 1611 ν(CH=N), 3452 ν(–OH), H-NMR (CDCl3)
(ppm): 9.78 (s, 1H, –CH=N); 6.84–7.45 (Ar–H, 9H); 3.1
(–N–CH3), 2.34 (–C–CH3); 13C-NMR (d6-DMSO) (ppm):
1 3

Transition Metal Chemistry
Molecular docking
of the water ligand was observed at 3434–3452 cm−1 in the
spectra of the complexes [17, 27].
1
For molecular docking analysis, the structure of complex 1
was sketched and converted to a three-dimensional structure
using ChemBiodraw Ultra and ChemBiodraw 3D, respec-
tively. The 3D structure of the complex was forced to pos-
sess minimum energy using MM2 and further optimized by
the density functional theory (DFT)/B3LYP method with the
6-31G(d,p) basis set for C, H, N, and O atoms and LanL2DZ
basis set for Cu atom using the GAUSSIAN 09 program [22,
23], then the calculated fle was saved in pdb format for use
in AutoDockTools (ADT) software [22, 23]. The pdb fle of
1 was then converted to pdbqt format by AutoDockTools
1.5.6 using default parameters. Gasteiger charge was added
to the ligand by ADT to generate the docking input fles. The
crystal structure of cyclin-dependent kinase 2, Cdk2 (PDB:
1AQ1), supposed to be the cause of cancer, was downloaded
from the rcsb pdb website as a receptor, and the active sites
of the receptor were identifed from literature [24]. Before
the docking step, a protein (PDB: 1AQ1) was designed in
which the co-crystallized heteroatoms and attached water
molecules were deleted, creating a passage for the incoming
metal complex during the simulation. The best pose confor-
mation with the minimum binding energy was selected from
the docking results to visualize and explain the noncovalent
and ligand map interactions between the complex and recep-
tor using the Discovery Studio visualizer [25].
The H-NMR spectrum of the free ligand HL revealed
a characteristic singlet due to azomethine proton (s, 1H,
–CH=N) at 9.80 ppm, whereas the multiplets due to the
aromatic protons of salicylaldehyde and ampyrone appeared
at 6.85–7.49 ppm (m, 9H, Ar–H) (Supplementary Fig. S8)
[21, 29]. However, a typical singlet due to the phenolic pro-
ton (s, 1H, –OH) was noticed at 13.5 ppm. Furthermore,
additional singlets at 3.15 ppm and 2.39 ppm were attrib-
uted to –N–CH3 and –C–CH3 protons of pyrazole moiety,
respectively. However, the azomethine proton signal showed
a shift in the spectra of the diamagnetic complexes, suggest-
ing the involvement of azomethine nitrogen in coordination
to metal atom. Nevertheless, the absence of the signal due
to the phenolic proton confrmed its deprotonation in the
spectra of the complexes and participation in coordination to
metal atoms. Furthermore, the aromatic ring protons showed
a downfeld shift upon complexation and appeared as a mul-
tiplet at 7.85–7.65 ppm (Supplementary Figs. S10, 12, 14,
16, and 18). The 1H-NMR spectral results were further con-
frmed by the 13C-NMR data to ascertain the structure of the
ligand and its complexes (Supplementary Fig. S9), reveal-
ing carbon signals due to –CH=N–, –C–OH, and Ar–C– at
160.8, 149.9, and 134.4–116.3 ppm, respectively. Further-
more, signals due to N–CH3 and C–CH3 of pyrazole moiety
appeared at 35.7 ppm and 10.3 ppm, respectively. However,
the position of the carbon signals showed a downfeld shift
upon coordination in the spectra of the metal complexes
(Supplementary Information Figs. S11, 13, 15, 17, and 19).
Thermal decomposition of the studied complexes was
recorded in the range from 0 to 1000 °C under an inert
argon atmosphere (Supplementary Fig. S20). All the com-
plexes showed a similar structure. Therefore, we selected
complex 1 for exploring the thermal studies. The thermo-
gram for complex 1 revealed complete release of water
ligand at ca. 300 °C, accounting for ca. 4.2% of the total
weight of the complex, whereas the ampyrone moiety
showed degradation at a temperature of 500 °C, equivalent
to 48.0% of the total weight of the complex. After that, a
straight line was observed, indicating copper oxide (22.6%)
as the end product.
Results and discussion
The FT-IR data for HL and its complexes 1–6 are listed in
the “Experimental” section. The synthesized ligand revealed
a characteristic high-intensity band due to the azomethine
linkage at 1611 cm−1. However, a considerable diference
of ca. 10–15 cm−1 was noticed in the stretching vibration of
the azomethine linkage ν(CH=N) in the spectra of the com-
plexes, suggesting the formation of metal–ligand bond due
to the withdrawal of electron density from the donor nitrogen
atom (Supplementary Figs. S1–7) [26, 27]. Furthermore, a
broad band, assigned to phenolic ν(OH) group at 3046 cm−1
in the free ligand, disappeared in the complexes, while a
band assigned to ν(M–O) vibrations was formed [27, 28]. In
addition, a medium-intensity band at 1307 cm−1 attributed to
phenolic ν(C─O) vibration was observed in HL, which, how-
ever, showed a signifcant increase in wavenumber by ca.
10 cm−1 in the spectra of the complexes, confrming coordi-
nation via the deprotonated phenolic group to form the metal
complexes [27, 28]. The stretching vibration due to v(C=O)
was noticed at 1601 cm−1 in HL, exhibiting a shift in the
spectra of the complexes to appear at 1605–1620 cm−1 [17,
27]. Furthermore, a broad band assigned to ν(–OH) vibration
The powder samples for the complexes were scanned over
the 2θ range from 10° to 70° at wavelength of 1.5406 Å.
The results indicated well-defned sharp crystalline peaks
for all the studied complexes, suggesting them to be crys-
talline phase (Supplementary Figs. S21, 22). Furthermore,
the similarity between the XRD patterns indicates a similar
structure for all the complexes. Therefore, we only present
two XRD patterns, for 3 and 1, showing maximum refection
at 2θ = 24.518° consistent with an interplanar distance of
d=3.6349 Å. Furthermore, the average crystallite size for
the complexes was calculated using Scherrer’s formula [21].
1 3

Transition Metal Chemistry
Table 1 IC50 data for the ligand
Compound IC50 (μM)
HCT116 HT29
and complexes
HL
1
115.0
45.6
149.9
99.2
161.8
87.6
156.4
101.1
171.8
173.9
–
2
3
4
5
99.5
In vitro cytotoxicity
The antineoplastic activity of the compounds was examined
by measuring their efect on the viability of human colo-
rectal cancer cell lines HCT116 and HT29 by MTS assay.
Each compound was tested over a wide range of concentra-
tions from 10 to 150 μM against these two colorectal can-
cer cells. The calculated IC50 values for both cell lines are
presented in Table 1. The HCT116 colorectal cancer cell
line demonstrated higher sensitivity to all the investigated
compounds compared with HT29 cells (Fig. 1 and Table 1).
A gradual increase in antitumorigenic activity was observed
with increasing concentration of 1 in both colorectal can-
cer cell lines (Fig. 1). Among all the compounds tested, 1
showed the strongest efect with an IC50 value of 45.6 μM
for HCT116 (Table 1). Relative to HL, complexes 1, 3, and
5 exhibited higher cytotoxic efect against HCT116, and 1
and 5 against HT29 . Interestingly, both cell lines showed
better tolerance of 2 and 4 compared with HL, while 3 and
HL showed similar efects at the highest concentration of
150 μM against HT29. Furthermore, due to its very modest
efect at all the concentrations, the IC50 values for compound
4 against HT29 cells could not be determined. Addition-
ally, the cell viability at concentrations above 125 μM for
5 decreased drastically to≤3 for both colorectal cancer cell
lines. Overall, these fndings suggest that compounds 1, 3,
and 5 have potential to be developed as chemotherapeutic
agents against colorectal cancers.
Fig. 1 Cell viability analysis after treatment with various compounds.
HCT116 (a) and HT29 (b) colorectal cancer cell lines were treated
with increasing concentrations of diferent compounds as indicated
for 48 h. Cell viability was determined by MTS assay, and percent
cell viability relative to untreated control for each concentration is
plotted from experiments performed in triplicate as mean standard
deviation (SD)
complexes, forming noncovalent interactions (Fig. 2c–f) with
two hydrophobic amino acids that are normally buried inside
the protein, namely ALA277 and ALA116, in the form of alkyl
and pi–alkyl interactions. Some of the polar and charged amino
acids such as SER120, HIS119, THR182, SER181, SER278,
LYS278, and ARG122 of the receptor also take part in interac-
tions with the complex, establishing hydrogen, van der Waals,
alkyl, pi–alkyl, pi–pi T-shaped, and carbon–hydrogen bonds,
leading to proper orientation of the complex inside the recep-
tor with free binding energy of –9.64 kcal/mol. The minimal
binding energy of 1, docked to the active sites of the receptor,
suggests a stable interaction, enabling 1 to bury deep into the
protein cavity during the docking simulation (Fig. 2b). In addi-
tion, threonine amino acid (THR182) forms hydrogen bonds
with the oxygen atoms of 1, which stabilize the docked sys-
tem of the receptor with the metal complex (Fig. 2e, f). Blue
and green colors indicate donor and acceptor hydrogen bonds
in the hydrogen bond surface of the cyclin-dependent kinase
receptor interacting with 1 in Fig. 2e. Furthermore, the experi-
mental fnding of anticancer activity for 1 reveals its potential
against the HCT116 colorectal cancer cell line. In addition, the
Molecular docking analysis
Molecular docking of complex 1 to the receptor (PDB:
1AQ1) (Fig. 2) was carried out to defne the proper confor-
mation of the complex within the receptor and the second-
ary forces occurring between 1 and active amino acids of the
receptor, leading to the development of the design of a new
drug. Noncovalent bonds, pi–pi, and pi–sigma interactions
between the active amino acids of target receptor and the com-
plex were tested based on the minimal binding energy (kcal/
mol). Interactions taken from the X-ray crystal structure of
cyclin-dependent kinase 2 (PDB: 1AQ1) (Fig. 2a) indicated
that 1 (Fig. 2b) exhibited high biological activity among the
1 3

Transition Metal Chemistry
Fig. 2 Docking analysis between receptor (a) and 1 (b), the best
docked pose of 1 at the receptor binding site (c), receptor–ligand
interactions with the active site of cyclin-dependent kinase 2 (PDB:
1AQ1) (d), hydrogen bond surface of receptor with blue and green
colors indicating donor and acceptor hydrogen bonds, respectively
(e), and two-dimensional (2D) representation showing the nature and
interactions of diferent amino acids of the receptor around a complex
(f)
2. Azam M, Hussain Z, Warad I, Al-Resayes SI, Khan MS, Sha-
kir M, Kruszynska AT, Kruszynski R (2012) Dalton Trans
41:10854–10864
nature of 1 as an anticancer drug is also explained in terms of
the secondary interactions followed by the free energy of bind-
ing obtained via the molecular docking calculations.
3. Azam M, Warad I, Al-Resayes S, Shakir M, Ullah MF, Ahmad
A, Sarkar FH (2012) Inorg Chem Commun 20:252–258
4. Lippard SJ, Pil P (1997) Encyclopedia of cancer, cis-platin and
related drugs. Academic, San Diego, pp 392–410
Conclusions
5. van Rijn JA, Gallego PM, Reedijk J, Lutz M, Spek AL, Bouw-
man E (2009) Dalton Trans 48:10727–10730
A novel series of transition metal complexes including a pyra-
zole-derived Schif base ligand was investigated using several
techniques. The in vitro anticancer activity of the ligand and its
derived complexes were evaluated against HCT116 and HT29
human colorectal cancer cell lines. The results suggest that 1,
3, and 5 have potential to be developed as chemotherapeutic
agents against colorectal cancer.
6. Hartinger CG, Dyson PJ (2009) Chem Soc Rev 38:391–401
7. Yan YK, Melchart M, Habtemariam A, Sadler PJ (2005) Chem
Commun 38:4764–4776
8. Clarke MJ, Zhu F, Frasca DR (1999) Chem Rev 99:2511–2534
9. Cozzi PG (2004) Chem Soc Rev 33:410–421
10. Sacconi L (1966) Coord Chem Rev 1:126–132
11. Collinson RS, Fenton DE (1996) Coord Chem Rev 148:19–40
12. Shechter Y, Goldwaser I, Mironchik M, Fridkin M, Gefel D
(2003) Coord Chem Rev 237:3–11
Acknowledgements The authors acknowledge the fnancial support
through Researchers Supporting Project Number (RSP-2020/147),
King Saud University, Riyadh, Saudi Arabia.
13. Takeuchi T, Bottcher A, Quezada CM, Simon MI, Meade TJ,
Gray HB (1998) J Am Chem Soc 120:8555–8556
14. Chohan ZH, Sumrra SH, Youssouf MH, Hadda TB (2010) Eur
J Med Chem 45:2739–2747
Compliance with ethical standards
15. Ozkınalı S, Gür M, Sener N, Alkın S, Çavus MS (2008) J Mol
Struct 1174:74–83
16. Pérez J, Riera L (2009) Eur J Inorg Chem 2009:4913–4925
17. Yongheng X, Yuanhong Z, Yongting XU, Baoli Z, Shuyun NJU,
Fengying B (2006) Chin Sci Bull 51:2189–2196
Conflict of interest There are no conficts of interest to declare.
18. Keter FK, Darkwa J (2012) Biometals 25:9–21
19. Constable EC, Steel PJ (1989) Coord Chem Rev 93:205
20. Ilango K, Valentina P (2007) Textbook of medicinal chemistry,
1st edn. Keerthi, Coimbatore, pp 327–333
References
1. Lian WJ, Wang XT, Xie CZ, Tian H, Song XQ, Pan HT, Qiao X,
Xu JY (2016) Dalton Trans 45:9073–9087
1 3

Transition Metal Chemistry
21. Rajaa G, Butcher RJ, Jayabalakrishnan C (2012) Spectrochim
Acta A 94:210–215
28. Creaven BS, Devereux M, Foltyn A, McClean S, Rosair G, Than-
gella VR, Walsh M (2010) Polyhedron 29:813
22. Trott O, Olson AJ (2009) J Comput Chem 31:455–461
23. Frisch MJ et al (2016) Gaussian 09, Revision D.01. Gaussian Inc,
Wallingford
29. Azam M, Wabaidur SM, Haque MN, Khan Z, Al-Resayes SI,
Al-Foudhily KA, Soo MI, Kruszynska AT, Kruszynski R (2019)
Inorg Chem Acta 490:235–239
24. Li MSZ, Zheng YZQ, Sun C (2005) Bioorg Med Chem Lett
15:2851–2856
Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional afliations.
25. Accelrys Software Inc (2011) Discovery studio modeling environ-
ment, Release 3.1
26. Azam M, Al-Resayes SI, Trzesowska KA, Kruszynski R, Shakeel
F, Soliman SM, Alam M, Khan MR, Wabaidur SMJ (2020) Mol
Struct 1201:127177
27. Nakamoto K (1986) Infrared and Raman spectra of inorganic and
coordination compounds, 4th edn. Wiley, New York
1 3