Synthesis, characterization and anticancer evaluation of transplatin derivatives with heterocyclic thiones

Article abstract of DOI:10.1016/j.poly.2017.12.016

Platinum(II) complexes of heterocyclic thiones (L) based on transplatin having the general formula, trans-[Pt(NH₃)₂(Thione)₂](NO₃)₂ have been synthesized and characterized using elemental analysis, IR, and NMR (¹H & ¹³C) spectroscopy. The crystal structures of two of them, trans-[Pt(NH₃)₂(Imt)₂](NO₃)₂ (1) and trans-[Pt(NH₃)₂(Me₂Imt)₂](NO₃)₂ (3) were determined by X-ray crystallography. The structures of 1 and 3 consist of trans-[Pt(NH₃)₂L₂]²⁺ complex ions and nitrate counter ions. The platinum atom in both the complex ions adopts a distorted square planar geometry. The spectroscopic data indicated the coordination of thione ligands to platinum(II). The in vitro cytotoxicity of these compounds as well as of cisplatin and carboplatin was investigated using MTT assay against three human cancer cell lines, which are; A549 (lung carcinoma), MCF-7 (breast carcinoma) and HTC15 (colon cancer). The in vitro cytotoxicity in several cases is comparable or even higher, than carboplatin and in two cases than cisplatin.

Full text of DOI:10.1016/j.poly.2017.12.016

Accepted Manuscript
Synthesis, characterization and anticancer evaluation of transplatin derivatives
with heterocyclic thiones
Mohammed Y. Jomaa, Muhammad Altaf, Saeed Ahmad, Ali Alhoshani,
Nadeem Baig, Abdel-Nasser Kawde, Gaurav Bhatia, Jatinder Singh,
Anvarhusein A. Isab
PII:
S0277-5387(17)30799-4
https://doi.org/10.1016/j.poly.2017.12.016
POLY 12973
DOI:
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
6 November 2017
13 December 2017
Please cite this article as: M.Y. Jomaa, M. Altaf, S. Ahmad, A. Alhoshani, N. Baig, A-N. Kawde, G. Bhatia, J. Singh,
A.A. Isab, Synthesis, characterization and anticancer evaluation of transplatin derivatives with heterocyclic thiones,
Polyhedron (2017), doi: https://doi.org/10.1016/j.poly.2017.12.016
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Synthesis, characterization and anticancer evaluation of transplatin
derivatives with heterocyclic thiones
a
b
c
d
a
Mohammed Y. Jomaa , Muhammad Altaf , Saeed Ahmad , Ali Alhoshani , Nadeem Baig ,
a
e
e
a
Abdel-Nasser Kawde , Gaurav Bhatia , Jatinder Singh and Anvarhusein A. Isab*
a
Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261,
Saudi Arabia
b
Center of Research Excellence in Nanotechnology, King Fahd University of Petroleum &
Minerals, Dhahran 31261, Saudi Arabia
c
Department of Chemistry, College of Sciences and Humanities, Prince Sattam bin Abdulaziz
University, Al-Kharj 11942, Saudi Arabia
d
Pharmacology and Toxicology Department, College of Pharmacy, King Saud University P.O.
Box No. 2457, Riyadh 11451, Saudi Arabia
e
Department of Molecular, Biology & Biochemistry, Guru Nanak Dev University, Amritsar-
1
43005, India
Abstract
Platinum(II) complexes of heterocyclic thiones (L) based on transplatin having the general
formula, trans-[Pt(NH ) (Thione) ](NO ) have been synthesized and characterized using
3
2
2
3 2
1
13
elemental analysis, IR, and NMR ( H & C) spectroscopy. The crystal structures of two of them,
trans-[Pt(NH ) (Imt) ](NO ) (1) and trans-[Pt(NH ) (Me Imt) ](NO ) (3) were determined by
3
2
2
3 2
3 2
2
2
3 2
2
+
X-ray crystallography. The structures of 1 and 3 consist of trans-[Pt(NH ) L ] complex ions
3
2 2
and nitrate counter ions. The platinum atom in both the complex ions adopts a distorted square
planar geometry. The spectroscopic data indicated the coordination of thione ligands to
platinum(II). The in vitro cytotoxicity of these compounds as well as of cisplatin and carboplatin
was investigated using MTT assay against three human cancer cell lines, which are; A549 (lung
carcinoma), MCF-7 (breast carcinoma) and HTC15 (colon cancer). The in vitro cytotoxicity in
several cases is comparable or even higher than carboplatin and in two cases than cisplatin.
1

Key words: transplatin; cytotoxicity; heterocyclic thiones; anticancer evaluation; X-ray
structure
_
*
___________________________________________
Corresponding author (E.mail: aisab@kfupm.edu.sa)
2

1
. Introduction
The platinum anticancer compounds in clinical use such as, cisplatin, carboplatin and oxaliplatin
generally exist as neutral molecules and contain two fairly labile cis ligands, e.g., the two
chlorido groups in cisplatin. The labile ligands are replaced by water through aquation reactions
and the resulting cations form bifunctional adducts with DNA [1-12]. The platinum(II)
complexes having two labile groups in a trans conformation, for example trans-[Pt(NH ) Cl ]
3
2
2
(transplatin) or monofunctional platinum(II) complexes, such as [PtCl(dien)]Cl (dien =
diethylenetriamine) or [Pt(NH ) Cl]Cl were ineffective [11-13]. But later studies have shown
3
3
that the replacement of one (or both) ammine ligand(s) of transplatin by aliphatic amines or
heterocyclic ligands such as planar pyridine or non-planar piperazine greatly enhances the
cytotoxicity of such species with respect to their corresponding cis isomers and also to cisplatin
particularly, in cisplatin-resistant tumor cell lines [14-20].
Like cis-platinum-ammine complexes, DNA is also considered as the potential cellular
target for the antitumor derivatives of transplatin [11-16]. However, the nature of Pt-DNA
adducts is different for the two types of complexes. Cisplatin and its analogues mainly form 1,2-
intrastrand cross-links [1-12], while transplatin is not able to form 1,2-intrastrand cross-links,
because of the steric hindrance of the two ammine groups in trans position. Instead it mainly
forms 1,3-interstrand cross-links [4,11,21]. Transplatin may form 1,3-intrastrand cross-links
between two G residues, or between a G and a C residue, separated by at least one base [4-
1
4,19,20]. The enhancement of activities in trans complexes was connected mainly to their
enhanced accumulation in tumor cells and efficiency to form in DNA a markedly higher amount
of more distorting cross-links than transplatin that forms preferentially less distorting and
persisting monofunctional adducts [14].
Several structural studies of thione derivatives of transplatin have been reported [22-26],
which describe a square-planar geometry around the metal center and the thione coordination in
terminal S-bonded modes. But, the antitumor properties of these complexes were not reported,
although many other transplatin analogues are known to exhibit anticancer activities [13-18].
Therefore, in the present study we have undertaken the synthesis, spectroscopic investigation and
in vitro anticancer evaluation of a number of trans-platinum(II) complexes of heterocyclic
thiones. Crystal structures of two of the complexes, trans-[Pt(NH ) (Imt) ](NO ) (1) and trans-
3
2
2
3 2
3

[
Pt(NH ) (Me Imt) ](NO ) (3) were also determined. The structures of the thiones used in this
3 2 2 2 3 2
study are given in Scheme 1.
5
6
5
4
5
4
6
4
7
N3
1N
R/
N3
1N
N3
1N
2
2
2
R
H
R
H
H
S
S
S
(a-g)
(h-i)
(j)
/
/
(
a) R = R = H; Imidazolidine-2-thione (Imt), (b) R = H, R = CH ; N-methylimidazolidine-2-
3
/
/
thione (MeImt), (c) R = CH , R = CH ; N,N -dimethylimidazolidine-2-thione (Me Imt), (d)
3
3
2
/
/
/
R = R = C H ; N,N -diethylimidazolidine-2-thione (Et Imt), (e) R = H, R = C H ; N-
2
5
2
3
7
/
propylimidazolidine-2-thione (PrImt), (f) R = H, R = i-C H ; N-(isopropyl)imidazolidine-2-
3
7
/
/
thione (i-PrImt), (g) R = R = i-C H ; N,N -(di-isopropyl)imidazolidine-2-thione (iPr Imt), (h)
3
7
2
R = C H ; N-ethyl-1,3-Diazinane-2-thione (EtDiaz), (i) 1,3-Diazepane-2-thione (Diap).
2
5
Scheme 1. The structures of thiones used in this study
2
2
. Experimental Section
.1 Chemicals
Transplatin (trans-diamminedichloidoplatinum(II)) was obtained from Strem Chemical
Company, USA. Dimethylsulfoxide-d and D O were purchased from Fluka Chemical Co. The
6
2
thione ligands were prepared according to the procedure mentioned in the literature [27, 28]. (3-
4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, a yellow tetrazole) was purchased
(
from Sigma Chemical Co, St. Louis, MO, USA.
General procedure for the synthesis of trans-[Pt(NH ) (Thione) ](NO ) complexes (1 – 9)
3
2
2
3 2
4

All the compounds were prepared by adding (0.17 g, 1.0 mmol) of AgNO to the solutions
3
containing (0.15g, 0.5 mmol) of trans-diamminedichloridoplatinum(II) (transplatin) in 10 mL
water and stirring the mixture for 2 hours in the dark at room temperature. The solution was
filtered to remove silver chloride as solid. Then 1.0 mmol of thione ligand dissolved in 10 mL
methanol were added to the filtrates drop wise. Mixing and stirring of the solutions resulted in a
colored solution. The solution was filtered and kept at room temperature. Solid powder was
obtained on slow evaporation of the solvent. The complexes, trans-[Pt(NH ) (Imt) ](NO )
3
2
2
3 2
andtrans-[Pt(NH ) (Me Imt) ](NO ) were crystallized from a 1:1 mixture of water and
3
2
2
2
3 2
methanol. Purity of the product was assessed through elemental analysis of C, H, N, and S. The
CHNS data, melting/decomposition points, and % yield of the synthesized complexes are
presented below:
trans-[Pt(NH ) (Imt) ](NO ) (1): M. p. 156 - 158 ºC, Yield: 0.256g, 92%. C, H, N, and S%
3
2
2
3 2
[
Calculated C: 12.93%, H: 3.25%, N: 20.10, S: 11.50 %, Found: C: 12.23%, H: 3.28%, N: 20.
9%, S: 11.75%]. IR: νmax = 3310 (s), 1042 (s), 501 (s), 836 (s), 272 (s).
trans-[Pt(NH ) (MeImt) ](NO ) (2): M.p. 140 - 142 ºC, Yield: 0.234g, 80%. C, H, N, and S%
8
3
2
2
3 2
[
Calculated C: 16.41%, H: 3.79%, N: 19.14, S: 10.95 %, Found: C: 16.28%, H: 3.63%, N:
9.52%, S: 10.76%]. IR: νmax = 3528 (s), 1112 (s), 837 (s), 503 (s), 274 (s).
trans-[Pt(NH ) (Me Imt) ](NO ) (3): M.p. 130 - 132 ºC, Yield: 0.248g, 81%. C, H, N, and S%
1
3
2
2
2
3 2
[
Calculated C: 19.57%, H: 4.27%, N: 18.16, S: 10.45 %, Found: C: 19.22%, H: 4.25%, N:
8.87%, S: 10.57%]. IR: νmax = 1118 (s), 825 (s), 491 (s), 265 (s).
trans-[Pt(NH ) (Et Imt) ](NO ) (4): M.p. 124 - 126 ºC, Yield: 0.224g, 67%. C, H, N, and S %.
1
3
2
2
2
3 2
[
Calculated C: 25.11%, H: 5.12%, N: 16.73, S: 9.58 %, Found: C: 25.38%, H: 5.23%, N:
6.75%, S: 9.72%]. IR: νmax = 1065 (s), 826 (s), 502 (s), 284 (s).
trans-[Pt(NH ) (PrImt) ](NO ) (5): M.p. 106 - 108 ºC, Yield: 0.247g, 77%. C, H, N, and S %
1
3
2
2
3 2
[
Calculated C: 22.46%, H: 4.71%, N: 17.48, S: 9.99 %, Found: C: 22.87%, H: 4.83%, N:
7.21%, S: 10.05%]. IR: νmax = 3373 (s), 1033 (s), 824 (s), 503 (s), 282 (s).
trans-[Pt(NH ) (iPrImt) ](NO ) (6): M. p. 83 - 85 ºC, Yield: 0.234g, 73%. C, H, N, and S%
1
3
2
2
3 2
[
calculated C: 22.46%, H: 4.71%, N: 17.48, S: 9.99 %, Found: C: 21.98%, H: 4.49%, N: 17.38%,
S: 9.48%]. IR: νmax = 3566 (s), 1064 (s), 867 (s), 495 (s), 279 (s).
5

trans-[Pt(NH ) (iPr Imt) ](NO ) (7): M. p. 132 – 134 ºC, Yield: 0.210g, 58%. C, H, N, and
3
2
2
2
3 2
S% [Calculated C: 29.79%, H: 5.83%, N: 15.44, S: 8.84 %, Found: C: 29.89%, H: 5.87%, N:
5.27%, S: 8.58%]. IR: νmax = 1106 (s), 856 (s), 497 (s), 283 (s).
trans-[Pt(NH ) (EtDiaz) ](NO ) (8): M. p. 92 - 94 ºC, Yield: 0.227g, 71%. C, H, N, and S%
1
3
2
2
3 2
[
Calculated C: 22.46%, H: 4.71%, N: 17.48, S: 9.99 %, Found: C: 22.25%, H: 4.68%, N:
7.37%, S: 9.78%]. IR: νmax = 3448 (s), 1074 (s), 835 (s), 501 (s), 279 (s).
trans-[Pt(NH ) (Diap) ](NO ) (9): M. p. 164 - 166 ºC, Yield: 0.191g 62%. C, H, N, and S%
1
3
2
2
3 2
[
Calculated C: 19.57%, H: 4.27%, N: 18.26, S: 10.45 %, Found: C: 19.72%, H: 4.32%, N:
1
8.07%, S: 10.33%]. IR: νmax = 3270 (s), 1053 (s), 822 (s), 510 (s), 269 (s).
2
.2 Spectroscopic measurements
Elemental analysis of was performed on Perkin Elmer Series 11 (CHNS/O), Analyzer 2400. The
solid state FTIR spectra of the ligands and their platinum(II) complexes were recorded on a
Perkin Elmer FTIR180 spectrophotometer or NICOLET 6700 FTIR using KBr pellets over the
-1
range 4000-400 cm .
1
13
The H and C NMR spectra in DMSO were carried out on a JEOL JNM-LA 500 NMR
1
3
spectrometer at 500.00 MHz and 125.65 MHz operating frequency respectively. The C NMR
1
spectra were recorded with H broadband decoupling at 297 K. The spectral conditions were; 32
1
K data points, 0.963 s acquisition time, 3.2 s pulse delay and a 5.75 µs pulse width for H NMR,
1
3
and 32 K data points, 0.963 s acquisition time, 2.5 s pulse delay and a 5.12 µs pulse width for C
NMR. The chemical shifts were measured relative to Tetramethylsilane (TMS).
2
.3 X-ray diffraction analysis
The intensity data for 1 and 3 were collected at 173K (-100°C) on a Stoe Mark II-Image Plate
Diffraction System [29]. Equipped with a two-circle goniometer and using MoK graphite
monochromated radiation ( = 0.71073 Å). The structure was solved by direct methods with
SHELXS-97 [30]. The refinement and all further calculations were carried with SHELXL-2014
[
31].
6

The N- and C-bound H-atoms were included in calculated positions and treated as riding
atoms with N–H = 0.91 Å, C–H = 0.99 and 0.98 Å for CH and CH H-atoms, respectively, and
2
3
with U (H) = 1.5U (C) for methyl H atoms and = 1.2U (N or C) for other H atoms. The non–
iso
eq
eq
2
H atoms were refined anisotropically, using weighted full-matrix least-squares on F . A semi-
empirical absorption correction was applied using the MULABS routine in PLATON [32]. A
summary of crystal data and refinement details for complexes 1 and 3 are given in Table 1.
7

Table1. Crystal data and refinement details for crystal structures of complexes 1 and 3.
Parameter
1
3
Formula
C H N PtS ·2(NO )
C H N PtS ·2(NO )
6
18
6
2
3
10 26
6
2
3
Formula weight
Crystal size/mm
Wavelength/Å
Temperature/K
Crystal symmetry
Space group
a/Å
557.49
613.60
0.41 × 0.34 × 0.21
0.71073
0.40 × 0.36 × 0.28
0.71073
173
173
Monoclinic
Monoclinic
P 2 /n
P 2 /n
1
1
5.4002 (4)
23.4438 (15)
6.6485 (5)
105.458 (6)
811.26 (10)
2
7.0160 (5)
18.6235 (10)
8.0794 (6)
107.228 (6)
1008.31 (12)
2
b/Å
c/Å
β/°
3
V/Å
Z
-3
 calc /Mgm
2.282
2.021
-1
μ(Mo-Kα)/mm
F(000)
8.95
7.21
536
600
θ value(°)
θmax = 25.6, θmin = 1.7
θmax = 25.7, θmin = 2.2
No. measured, independent
and observed [I >2σ(I)]
reflections
10466, 1532, 1332
13070, 1900, 1550
Rint
0.087
0.046
2
2
2
R[F > 2σ(F )], wR(F ), S
0.023, 0.050, 1.04
0.297, 1.000
0.99, −1.86
0.015, 0.035, 0.98
0.402, 1.000
0.76, −0.75
T , T
min
max
-3
Largest diff. peak, hole/e Å
8

2
.5
In vitro cytotoxic activity against A549, MCF7 and HTC15 human cancer cell lines
) ](NO ) complexes were evaluated for in vitro cytotoxic activity
The trans-[Pt(NH ) (
3
2
2
3 2
against A549 (human lung cancer), MCF-7 (human breast cancer) and HTC15 (human colon
3
cancer) cell lines. The cells were seeded at 4 x 10 cells/well in 100 μL DMEM containing 10 %
o
FBS in 96-wells tissue culture plate and incubated for 72 h at 37 C, 5 % CO in air and 90 %
2
relative humidity in CO incubator. After incubation, 100 μL of each sample solution (50, 25,
2
1
2.5 and 6.25 μM), prepared in DMEM, were added to cells and the cultures were incubated for
2
4 h. The medium of wells was discarded and 100 μL DMEM containing MTT (3-(4,5-
Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium Bromide) (5 mg/mL) was added to the wells and
o
incubated in CO incubator at 37 C in dark for 4 h. After incubation, purple colored formazan
2
(artificial chromogenic dye, product of the reduction of water insoluble tetrazolium salts e.g.,
MMT by dehydrogenases and reductases) in the cells is produced and appeared as dark crystals
in the bottom of the wells. The resultant crystals were solublized by adding 100 μL of DMSO in
each well. The solution was thoroughly mixed to dissolve the formazan crystals, producing a
purple solution. The absorbance of the 96-wells plate was taken at 570 nm with Labsystems
Multiskan EX-Enzyme-linked immunosorbent assay (EX-ELISA) reader against a reagent blank.
The IC values were calculated from three independent experiments by generating an equation
5
0
of logarithmic trend line of percentage cell viability against concentration of compounds in
Microsoft excel.
3
. Results and discussion
We prepared in the present work nine new analogues of transplatin in which chloride groups are
replaced by heterocyclic thione ligands. The aqua derivatives of transplatin,
[
Pt(NH ) (H O) ](NO ) were first prepared by addition of two equivalents of AgNO to
3 2 2 2 3 2 3
transplatin. The nitrate species were then reacted with thione ligands in a 1:2 molar ratio to
produce the complexes of the general formula, trans-[Pt(NH ) (L) ](NO ) . The purpose of
3
2
2
3 2
preparing the nitrate complexes was to increase the solubility of the resulting compounds
because the poor aqueous solubility is a problem for some platinum anticancer drugs. The
characterization of these complexes was carried out by usual techniques: elemental analysis, IR,
9

1
13
H & C NMR and X-ray crystallography. The elemental analysis data is consistent with the
predicted composition. The compounds obtained are listed in experimental section. The in vitro
cytotoxicity of these platinum compounds was evaluated by MTT colorimetric assay using
A549, MCF-7 and HTC15 cancer cells with cisplatin and carboplatin as positive controls.
3
.1 Crystal Structure Description of complexes 1 and 3
The molecular structures of complexes 1 and 3 are shown in Figures 1 and 2 respectively. The
selected geometrical parameters are given in Table 2. The structure of both complexes consists
2
+
2+
of a complex cation, [Pt(NH ) (Imt) ] (in 1) or [Pt(NH ) (Me Imt) ] (in 2) and two nitrate
3
2
2
3 2
2
2
ions. In the complex ions, Pt(II) atom is bound to two sulfur atoms of thione ligands and two N
atoms of ammonia in a trans fashion. The platinum atom is located on the inversion center and
adopts essentially a square-planar environment lying exactly within the plane defined by the two
S and two N atoms. The cis angles around platinum vary between 87.50 (9)° and 92.50 (9)° in 1,
while in 2 they are 88.52 (7)° and 91.48 (7)°. The trans angles in both are 180°. The Pt–N and
Pt–S bond distances are 2.046 (3) and 2.3260 (9) Ǻ in 1 and, 2.054 (2) and 2.3199 (7) Ǻ in 2.
These bond distance values are very close with the average values reported for similar complexes
[
22-26, 33-36]. The structures of compounds 1 and 3 are very similar to a related complex, trans-
.
[
Pt(NH ) (Diaz) ]Cl 2H O that also crystallizes in the monoclinic space group. However, 1 and
3
2
2
2
2
3
show slightly more distortion from the regular square planar geometry.
2+
The complex cations, trans-[Pt(NH ) (Thione) ] and nitrate anions are associated to
3
2
2
each other through formation of hydrogen bonds. In the crystal packing of complexes, the
molecules are H-bonded via N-H of ammonia or C-H hydrogen of Imt and oxygen atoms of
-
nitrate ion. In 1, N-H hydrogen of Imt and in 3, nitrogen atoms of NO are also involved in
3
hydrogen bonding. The nitrate anion nitrogen shows the weakest contact. The hydrogen bonding
interactions result in the formation of three-dimensional hydrogen bonded network as shown in
Figures 3 and 4 for 1 and 3 respectively. The details of the hydrogen bonds are summarized in
Tables S1 and S2 (Supporting information) for 1 and 3 respectively.
1
0

Table 2. Selected bond distances (Å) and bond angles (˚) for 1 and 3
Bond Distance Bond angles
Complex 1
Pt1—N3
Pt1—S1
2.046(3)
N3—Pt1—S1
92.50 (9)
87.50 (9)
180
i
2.3260(9)
N3 —Pt1—S1
i
N3 —Pt1—N3
i
S1—Pt1—S1
180
Complex 3
Pt1—N3
Pt1—S1
2.054(2)
N3—Pt1—S1
88.52(7)
91.48(7)
180
i
2.3199(7)
N3 —Pt1—S1
i
N3 —Pt1—N3
i
S1—Pt1—S1
180
Symmetry codes: for 1, (i) −x, −y, −z+1; for 3, (i) −x+1, −y, −z+1.
1
1

Figure 1
A view of the molecular structure of 1 with atomic labelling. The displacement
ellipsoids are drawn at the 50% probability level. Atoms not labelled are related by inversion
symmetry
Figure 2
A view of the molecular structure of 3 with atomic labelling. The displacement
ellipsoids are drawn at the 50% probability level. Atoms not labelled are related by inversion
symmetry
1
2

Figure 3
The crystal packing of 1, viewed along the c axis. The N–H…O, N–H…N and C–
H…O hydrogen bonds are shown as dashed lines and lead to the formation of a three-
dimensional structure.
1
3

Figure 4
The crystal packing of 3, viewed along the c axis. The N–H…O, N–H…N and C–
H…O hydrogen bonds are shown as dashed lines and lead to the formation of a three-
dimensional structure.
3
.2 IR spectroscopy
Selected IR frequencies of free thiones and their platinum(II) compounds are given in the
synthesis section and in Table S3 (Supplementary material). The characteristic vibrational bands
in the IR spectra of thione complexes, are usually observed in three frequency regions; (C=S)
-1
−1
vibration around 1200 and 600 cm , the N–H stretching near 3200 cm and M-sulfur stretching
-1
band below 400 cm . The presence of (N–H) and (C=S) bands in all complexes proves that
the thione ligands are coordinated to the metal atom. The spectra of free ligands display a band
−
1
−1
around 600 cm as well as 1200 cm that belongs to ν(C=S) stretching [37-39]. These bands
shifted toward lower wave number upon complexation, while the N–H stretching vibrations
shifted to higher frequency indicating the coordination of thiones through sulfur atom. In order to
investigate the metal-sulfur stretching frequencies of the synthesized complexes, the spectra were
-1
-1
recorded in far-infrared region below 400 cm . This band lies in the range of about 300 cm for
the transition-metal complexes according to the literature [40]. In all complexes, we observed a
1
4

-1
sharp peak around 280 cm that was assigned to platinum- sulfur bond. A sharp band around 825
-1
cm for all trans-[Pt(NH ) (L) ](NO ) complexes and its absence in the free ligand spectra is
3
2
2
3 2
attributed to the presence of non-coordinated nitrate ion [38].
1
13
3
.3 H and C NMR Spectroscopy
1
13
The H and C chemical shifts of the ligands and their platinum(II) complexes in DMSO-d are
6
1
given in Tables 3 and 4 respectively. In H NMR spectra of the complexes, the N–H signal of
thiones became less intense upon coordination and shifted downfield from their positions in free
ligands. The deshielding is related to an increase in  electron density in the C–N bond upon
coordination.
1
3
In C NMR, the C=S resonance of thiones in the complexes is shifted upfield by about
5
.5 – 13.6 ppm as compared to that in free ligands in accordance with the data observed for other
1
0
complexes of d metals with thiones [25,33,34,37,38]. The upfield shift is attributed to the
lowering of C=S bond order upon coordination and a shift of N→C electron density, producing a
partial double bond character in the C–N bond [37, 38]. As the shift difference of the C=S
resonance may be related to the strength of metal-sulfur bond, Table 4 shows that the Me Imt
2
complex would be the most stable among these complexes. A small deshielding effect is
observed in other carbon atoms, which is due to an increase in  character of the C–N bond.
1
5

1
Table 3. H NMR chemical shifts (ppm) of thiones and their Pt(II) complexes in DMSO
Species N–H
H-4
H-5
H-6
H-7/N-C3 N-C1
N-C2
Imt
7.90
9.09
s,4H,3.59 s,4H,3.59
s,4H,3.69 s,4H,3.69
-
-
-
-
-
-
-
-
1
MeImt
7.93
8.47
t,2H,3.63
t,2H,3.71
t,2H,3.43
t,2H,3.56
-
-
-
-
s,3H,2.92
s,3H,2.96
-
-
2
Me Imt
-
-
s,4H,3.48 s, 4H,3.48
s,4H,3.65 s, 4H,3.65
-
-
-
-
s,6H,2.91
s,6H,3.29
-
-
2
3
Et Imt
-
-
s,4H,3.48 s,4H,3.48
s,4H,3.53 s,4H,3.53
-
-
-
-
q,4H,3.37 t,6H,0.97
q,4H,3.48 t,6H,1.12
2
4
PrImt
7.99
8.81
t,2H,3.58
t,2H,3.76
t,2H,3.41
t,2H,3.62
-
-
t,3H,0.73
t,3H,0.79
t,2H,3.31
t,2H,3.35
m,2H,1.45
m,2H,1.55
5
iPrImt
7.96
8.31
t,2H,3.53
t,2H,3.70
t,2H,3.38
t,2H, 3.54
-
-
-
-
m,1H,4.35 d,6H,1.00
m,1H,4.25 d,6H,1.07
6
iPr Imt
-
-
s,4H,3.22 s, 4H,3.22
s,4H,3.49 s, 4H,3.49
-
-
-
-
m,1H,4.48 d,6H,0.99
m,1H,5.10 d,6H,1.05
2
7
EtDiaz
7.89
8.65
t,2H,3.62
t,2H,3.59
m,2H,1.83 t,2H,3.28 -
m,2H,1.84 t,2H,3.33 -
q, 2H,3.12 t, 3H,1.02
q, 2H,3.21 t, 3H,1.09
8
Diap
7.70
8.70
t,4H,1.67
t,4H,1.70
t,4H,3.18 t,4H,3.18 t,4H,1.67
t,4H,3.24 t,4H,3.24 t,4H,1.70
-
-
-
-
9
s: singlet, d: doublet, t: triplet, q: quartet, m: multiplet
1
6

13
Table 4. C NMR chemical shifts (ppm) of the ligands and their Pt(II) complexes in DMSO
Species
C-2
C-4
C-5
C-6
C-7
N-C1 N-C2, N-C3
Imt
182.11 45.38
175.74 45.76
45.38
45.76
-
-
-
-
-
-
-
-
1
MeImt
181.38 42.00
174.90 42.76
51.82
52.65
-
-
-
-
34.35
34.02
-
-
2
Me Imt
180.46 48.77
166.89 50.29
48.77
50.29
-
-
-
-
34.91
36.07
-
-
2
3
Et Imt
178.74 46.13
170.96 47.33
46.13
47.33
-
-
-
-
42.69 11.92
43.79 12.11
2
4
PrImt
180.87 49.14
174.50 50.10
48.86
49.10
42.11 20.65, 11.09
42.82 20.53, 10.95
5
iPrImt
179.70 43.73
174.17 44.65
42.21
42.71
-
-
48.18 19.24
48.78 19.18
6
iPr Imt
174.05 1.52
169.42 42.30
41.52
42.30
-
-
48.25 19.10
49.68 19.26
2
7
EtDiaz
173.26 46.48
167.43 47.32
20.83
20.27
41.04
41.09
49.41 12.33
49.67 12.19
8
Diap
183.99 45.86
176.53 46.35
26.99
26.51
26.99
26.51
45.86
46.35
-
-
-
-
9
3
.4 Antitumor Activity
The cytotoxic activities of the synthesized complexes, cisplatin and carboplatin were evaluated
in vitro against three human cancer lines, which are; A549 (human lung carcinoma), MCF7
(human breast cancer), and HCT15 (human colon adenocarcinoma). The cytotoxic effect was
obtained by the stipulated increase in the concentration of the complexes, cisplatin and
carboplatin against the fixed number of human cancer cells. The exposure of the cells to an
increase in concentration of the complexes resulted in a dose dependent cytotoxic effect. The
survival of the cells (A549, MCF7 and HCT15) as a function of concentration of compounds 1-9
1
7

is explained in Figures 5-7. The IC values obtained from the curves of the concentration of the
5
0
complexes and percentage viability of the cells are given in Table 5. The IC values of the
5
0
complexes for A549 cell line range between 40 to 75 μM. Complexes 2 and 5 have in vitro
cytotoxicity better than cisplatin with IC values 40 and 41 μM respectively, and almost two-
5
0
fold better than that of carboplatin. Complexes 1, 6, 8 and 9 have in vitro cytotoxicity slightly
lower than cisplatin but still higher than carboplatin. Complexes 3 and 7 have the same
cytotoxicity as carboplatin. For MCF7 cell line, the IC values of the complexes are between 45
5
0
and 92 μM (Table 5). Only the complexes 5 and 8 were found to possess cytotoxicity against the
MCF7 cell line between cisplatin and carboplatin. While the others displayed poor
antiproliferative potency as indicated by their higher IC values. Against HCT15 cell line, the
5
0
complexes 2, 5, 8 and 9 have activity comparable to cisplatin with IC values 40, 36, 43, and 41
5
0
µM respectively. The complexes 1 and 7 have almost the same cytotoxicity as carboplatin, while
, 4 and 6 are less potent even than carboplatin. These results are consistent with a significant
3
selective cytotoxicity of the complexes against particular cancer cell lines and its tendency to
undergo ligand exchange with biomolecules like proteins and DNA. When the activity of the
prepared complexes is compared with transplatin analogues of nitrogen donors, it is observed
that the platinum amine complexes in comparison with thione derivatives, exhibit radically
enhanced activity in tumor cell lines [41,42].
1
8

Figure 5 (a & b). Effect of concentration of complexes 1 – 9 on viability of A549 cells.
1
9

Figure 6 (a & b). Effect of concentration of complexes 1 – 9 on viability of MCF7 cells.
2
0

Figure 7 (a & b). Effect of concentration of complexes 1 – 9 on viability of HCT15 cells.
2
1

a
Table 5. IC Values (in µM) of Pt(II) compounds against three human tumor cell lines
5
0
Compounds
Cisplatin
A549
42 ± 2
70 ± 2
MCF7
23 ± 3
63 ± 2
HCT15
32 ± 2
Carboplatin
53 ± 2
1
2
3
4
5
6
7
8
9
52 ± 2
40 ± 1
70 ± 1
75 ± 1
41 ± 2
66 ± 1
69 ± 1
48 ± 1
49 ± 1
80 ± 1
70 ± 2
92 ± 2
89 ± 1
45 ± 1
86 ± 2
87 ± 2
60 ± 2
69 ± 1
50 ± 1
40 ± 2
69 ± 2
63 ± 1
36 ± 1
79 ± 1
53 ± 1
43 ± 1
41 ± 2
a
Errors are standard deviations determined from at least three independent experiments.
4
Conclusion
In this study, transplatin-based complexes (1–9) with the general formulae, trans-
Pt(NH ) (Thione) ](NO ) have been synthesized and characterized using various analytical
[
3
2
2
3 2
methods. The spectroscopic and crystallographic data strongly supported that the thione ligands
coordinated to the Pt(II) center through the sulfur atom. The crystal structures of two complexes
revealed a distorted square planar geometry around platinum. The prepared complexes were
tested for in vitro antitumor activity against the human tumor cell lines. The complexes 2 and 5
exhibited a better cytotoxicity against A549 cancer cell line than cisplatin. This study extends the
existing knowledge on the structure and mechanism of platinum based antitumor complexes
possessing trans geometry.
Supplementary material
CCDC deposit numbers 1545440 and 1545441 have been assigned to the complexes 1 and 3
respectively. Crystallographic data in CIF or other electronic format can be obtained free of
2
2

charge via www.ccdc.cam.ac.uk/data_request/cif, by e-mailing data_request@ccdc.cam.ac.uk, or
by contacting the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1
EZ, UK; fax: +44(0)1223-336033.
Acknowledgment
The authors would like to acknowledge the support by the Deanship of Scientific Research at
King Fahd University of Petroleum & Minerals for funding this work through project No.
IN161005.
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2
5

Graphical Abstract:
Synopsis
Platinum(II) complexes of heterocyclic thiones based on transplatin having the general formula, trans-
[
(
[
Pt(NH ) (Thione) ].2NO have been synthesized and characterized using elemental analysis, IR, and NMR
3
2
2
3
1
13
H & C) spectroscopy. The crystal structures of two of them, trans-[Pt(NH ) (Imt) ].2NO and trans-
3
2
2
3
Pt(NH ) (Me Imt) ].2NO were determined by X-ray crystallography.
3
2
2
2
3
2
6

2
7