Multinuclear magnetic resonance characterization and antiproliferative studies of novel dichlorido platinum(II) complexes containing kinetin riboside and 1-β-D-ribofuranosyl-4-(2-pyridyl)-1H-1,2,3-triazole

Article abstract of DOI:10.1016/j.poly.2020.114428

The chemical reaction between cis-[PtCl₂(dmso)₂] and kinetin riboside (KR) or 1-β-D-ribofuranosyl-4-(2-pyridyl)-1H-1,2,3-triazole (PTR) has resulted in two novel platinum(II) complexes being obtained with different compositions of the coordination sphere: cis-[PtCl₂(PTR)] (1) and cis-[PtCl₂(dmso)(KR)] (2). Based on multinuclear NMR results (¹H, ¹³C, ¹⁵N, ¹⁹⁵Pt), we have demonstrated that the N-donor ligands PTR and KR are able to coordinate to the Pt(II) ion as bidentate via two nitrogen atoms (N(3) and N(7)) or monodentate via only one nitrogen atom (N(7)), respectively. On the other hand, biological studies showed that the novel platinum(II) complexes exhibit different in vitro cytotoxicity towards A549 (lung carcinoma epithelial cells), T24 (urinary bladder cancer cells) and CRL1872 (malignant melanoma cells). The complex cis-[PtCl₂(dmso)(KR)] (2) shows in vitro cytotoxicity against T24 and CRL1872 cell lines (the IC₅₀ parameters amount to 52.2 μM and 21.4 μM, respectively), whereas cis-[PtCl₂(PTR)] (1) is not able to inhibit a proliferation of these cells in the range of tested concentrations.

Full text of DOI:10.1016/j.poly.2020.114428

Journal Pre-proofs
Multinuclear magnetic resonance characterization and antiproliferative studies
of novel dichlorido platinum(II) complexes containing kinetin riboside and 1–
β-D-ribofuranosyl-4-(2-pyridyl)-1H-1,2,3-triazole
Mateusz Jakubowski, Iwona Łakomska, Jerzy Sitkowski, Marta
Pokrywczyńska, Paweł Dąbrowski, Grzegorz Framski, Tomasz Ostrowski
PII:
S0277-5387(20)30085-1
DOI:
https://doi.org/10.1016/j.poly.2020.114428
POLY 114428
Reference:
Polyhedron
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Received Date:
Revised Date:
Accepted Date:
4 November 2019
27 January 2020
28 January 2020
Please cite this article as: M. Jakubowski, I. Łakomska, J. Sitkowski, M. Pokrywczyńska, P. Dąbrowski, G. Framski,
T. Ostrowski, Multinuclear magnetic resonance characterization and antiproliferative studies of novel dichlorido
platinum(II) complexes containing kinetin riboside and 1– β-D-ribofuranosyl-4-(2-pyridyl)-1H-1,2,3-triazole,
Polyhedron (2020), doi: https://doi.org/10.1016/j.poly.2020.114428
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Multinuclear magnetic resonance characterization and antiproliferative
studies of novel dichlorido platinum(II) complexes containing kinetin
riboside and 1-β-D-ribofuranosyl-4-(2-pyridyl)-1H-1,2,3-triazole
Mateusz Jakubowski,a Iwona Łakomska,a Jerzy Sitkowski,b,c Marta Pokrywczyńska,d Paweł
Dąbrowski,d Grzegorz Framski,e Tomasz Ostrowskie
a
Faculty of Chemistry, Nicolaus Copernicus University in Toruń, Gagarina 7, 87-100 Toruń,
Poland
b
National Institute of Medicine, Chełmska 30/34, 00-725 Warszawa, Poland
Institute of Organic Chemistry, Polish Academic of Science, Kasprzaka 44/52, 01-224
c
Warszawa, Poland
d
Chair of Urology, Department of Regenerative Medicine, Cell and Tissue Bank, Ludwik
Rydygier Medical College in Bydgoszcz, Nicolaus Copernicus University in Toruń, Poland
e Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14,
61-704 Poznań, Poland
Abstract
The chemical reaction between cis-[PtCl2(dmso)2] and kinetin riboside (KR) or 1-β-D-
ribofuranosyl-4-(2-pyridyl)-1H-1,2,3-triazole (PTR) has resulted in two novel platinum(II)
complexes being obtained with different compositions of the coordination sphere:
cis-[PtCl2(PTR)] (1) and cis-[PtCl2(dmso)(KR)] (2). Based on multinuclear NMR results (1H,
15
13C, N, 195Pt), we have demonstrated that the N-donor ligands PTR and KR are able to
coordinate to the Pt(II) ion as bidentate via two nitrogen atoms (N(3) and N(7)) or
monodentate via only one nitrogen atom (N(7)), respectively. On the other hand, biological

studies showed that the novel platinum(II) complexes exhibit different in vitro cytotoxicity
towards A549 (lung carcinoma epithelial cells), T24 (urinary bladder cancer cells) and
CRL1872 (malignant melanoma cells). The complex cis-[PtCl2(dmso)(KR)] (2) shows in vitro
cytotoxicity against T24 and CRL1872 cell lines (the IC50 parameters amount to 52.2 μM and
21.4 μM, respectively), whereas cis-[PtCl2(PTR)] (1) is not able to inhibit a proliferation of
these cells in the range of tested concentrations.
Introduction
From a biological as well as a chemical point of view, nucleosides an play important
role in the cells of various organisms. They build genomic blocks and are able to interact
with enzymes, proteins and nucleic acids, which are present in all living cells [1,2]. For that
reason, nucleosides have been considered as model compounds with a wide range of
activities. It has been observed that naturally occurring and synthetic nucleosides can exhibit
antiviral and anti-inflammatory properties [1,3,4,5], and are able to inhibit the metabolic
pathways of various cancer cells by blocking the biosynthesis of nucleic acids [6,7,8]. One of
them is kinetin riboside (KR) which shows satisfactory in vitro cytotoxic activities towards
HOS (bone osteosarcoma), HL-60 (promyelocytic leukemia), CEM (acute lymphoblastic
leukemia), MCF-7 (breast adenocarcinoma) and K-562 (chronic myelogenous leukemia) cell
lines [1,9].
On the other hand, the characterization of the interactions between nucleic acids
components (e.g. nucleosides) and metal ions (e.g. Pt(II)) is the reason why nucleosides have
been considered to be N-donor ligands in platinum(II/IV) complexes [10,11,12]. It is
commonly known that the activity of metal complexes is modified by the application of the
appropriate ligands. Therefore, the coordination of an active ligand to the platinum(II) ion
may enable coordination compounds to be obtained which exhibit therapeutic properties.

Previous studies in this field have demonstrated that Pt(II) monoadducts with different
ribosides present the ability to further interact with DNA and prompt cell death [6,7,13].
These encouraging results have motivated us to search for and obtain novel cisplatin
derivatives with the use of 1-β-D-ribofuranosyl-4-(2-pyridyl)-1H-1,2,3-triazole (PTR) and
kinetin riboside (KR) as N-donor ligands. As a part of our studies in this field, we have
synthesized two novel complexes, i.e. cis-[PtCl2(PTR)] (1) and cis-[PtCl2(dmso)(KR)] (2)
(Fig. 1). Our chemical studies were focused on multinuclear magnetic resonance
measurements of the free ligands and their novel complexes. Moreover, in order to evaluate
preliminary biological properties of these compounds, we have examined their lipophilicity
with the use of the shake-flask method and their in vitro cytotoxicity towards the human
cancer cell lines A549 (lung carcinoma epithelial cells), T24 (urinary bladder cancer cells)
and CRL1872 (malignant melanoma cells), and normal human cell lines, such as CRL2522
(skin fibroblast cells). It was necessary to investigate the impact of KR or PTR insertion in the
Pt(II) ion coordination sphere on the antiproliferative activity of these compounds.
8
11
12
O
9
10
7
15
NH
6
N
6
7
10
5
4
N
1
3
N
13
14
N
11
8
4
9
2
20
2
N
16
HO
N
5
O
N
HO
N
O
3
1
19
18
16
17
15
12
13
14
OH OH
OH OH
PTR
KR
Fig. 1. 1-β-D-ribofuranosyl-4-(2-pyridyl)-1H-1,2,3-triazole (PTR), kinetin riboside (KR) and
their ring-numbering systems.
Experimental
1. Starting materials

1,2,3,5-Tetra-O-acetyl-β-D-ribofuranose was purchased from Carbosynth. K2PtCl4,
thiazolyl blue tetrazolium bromide and other chemical reagents were purchased from Sigma-
Aldrich. The analytical grade solvents were purchased from Avantor Performance Materials
Poland S.A. Anhydrous CH2Cl2 was prepared by distillation with P2O5.
2. Instrumentation
The C, H and N contents were determined with an Elementar Analysensysteme GmbH
Vario MACRO analyser. Analysis by thin layer chromatography (TLC) was carried out on
Merck precoated 60 F254 silica gel plates, while column chromatography used Merck silica gel
60H (40-63 μm).
NMR spectra were recorded at 298 K in DMF-d7 solutions with a Varian INOVA 500
1
spectrometer operating at 499.8, 125.7, 50.6 and 107.4 MHz for H, 13C, 15N and 195Pt,
respectively. The NMR spectra for kinetin riboside (KR) were recorded at 343 K because the
resonance signals for some nitrogen atoms were not observed at 298 K. The reference
1
standards were TMS for H and 13C, CH3NO2 for 15N, and H2PtCl6 for 195Pt. Gradient-
enhanced IMPACT-HMBC 1H-{15N} [14] correlation spectra were optimized for the coupling
constant of 6 Hz under the following experimental conditions: 0.2 s acquisition time, 6000
(F2) and 10,000 (F1) Hz spectral windows, 1 K complex data points, 256 time increments,
30 ms WURST-2 mixing sequence centered within the 60 ms preparation interval (ASAP2)
and the 150° Ernst angle as the excitation pulse [15].
The UV-Vis measurements performed for the lipophilicity determination were
obtained with a HITACHI U-2900 UV-Vis spectrophotometer equipped with 1.0 cm path
length quartz cuvettes (1.5 mL). IC50 values were calculated based on measurement of
absorbance (MTT test) with the use of a Varioskan Lux spectrophotometer (Thermo Fisher
Scientific).

3. Chemical part
3.1. Syntheses of the ligands (KR, PTR) and the starting complex cis-[PtCl2(dmso)2]
Kinetin riboside (KR) was prepared by N6-alkylation of N6-acetyl-2’,3’,5’-tri-O-
acetyladenosine with furfuryl alcohol under Mitsunobu conditions, as previously described
[16]. The cis-[PtCl2(dmso)2] complex was obtained by the reaction of 1 eq. K2PtCl4 and 2 eq.
dmso in aqueous solution [17].
3.1.1. The synthesis of 1-β-D-ribofuranosyl-4-(2-pyridyl)-1H-1,2,3-triazole (PTR)
The
synthesis
of
1-β-D-ribofuranosyl-4-(2-pyridyl)-1H-1,2,3-triazole
(PTR),
accomplished by a 1,3-dipolar cycloaddition between 2,3,5-tri-O-acetyl-β-D-ribofuranosyl
azide (A) and 2-ethynylpyridine, followed by the removal of the acetyl protecting groups, was
based on the reported procedure [18] with modifications (Fig. 2). 2,3,5-Tri-O-acetyl-β-D-
ribofuranosyl azide was prepared from 1,2,3,5-tetra-O-acetyl-β-D-ribofuranose [19].
N
N
N3
N
N
AcO
O
i
ii
N
N
N
N
AcO
HO
O
O
OAc
AcO
3
AcO
HO OH
OAc
2
4
A’
PTR
A
Fig. 2. Synthesis of PTR. Reagents and conditions: (i) 2-ethynylpyridine, CuI, DIEA, AcOH,
anhydrous CH2Cl2, rt; (ii) NH4OH-MeOH-CH2Cl2 1:1:1, rt.
2-Ethynylpyridine (268 mg, 2.60 mmol), copper iodide (826 mg, 4.34 mmol),
diisopropylethylamine (1.4 g, 10.85 mmol) and acetic acid (0.5 mL) were added to a solution
of 2,3,5-tri-O-acetyl-β-D-ribofuranosyl azide [19] (A; 653 mg, 2.17 mmol) in anhydrous
CH2Cl2 (35 mL). The resulting suspension was stirred at room temperature overnight, then
one more portion of 2-ethynylpyridine (45 mg, 0.43 mmol) was added and the reaction was

continued overnight. The mixture was filtered and the insoluble part was washed with CH2Cl2
several times. The filtrate was evaporated and co-evaporated with toluene twice. The residue
was subject to chromatographic separation on a silica gel column with CH2Cl2-MeOH
(100:0→98.5:1.5) to obtain pure the A’ compound as a yellow oil (837 mg, 95% yield) (Fig.
1
2); H NMR (CDCl3) as in the literature [20]. Next, the A’ compound was treated with
NH4OH-MeOH-CH2Cl2 (1:1:1, 60 mL) and stirred at room temperature overnight. The
mixture was evaporated and co-evaporated twice with toluene. Chromatographic separation
was carried out on a silica gel column with CH2Cl2-MeOH (95:5→92:8) to obtain PTR as a
white powder (410 mg, 71% yield); 1H NMR (dmso-d6) as in the literature [21] (Fig. 2).
3.2. Syntheses of the novel platinum(II) complexes cis-[PtCl2(PTR)] (1)
and cis-[PtCl2(dmso)(KR)] (2)
Both novel platinum(II) complexes, cis-[PtCl2(PTR)] (1) and cis-[PtCl2(dmso)(KR)]
(2), with two different ribosides were obtained by the reaction between cis-[PtCl2(dmso)2] and
the corresponding N-donor ligand, i.e. PTR or KR, in 1:1 molar ratios in ethanol. The reaction
mixture was heated to 45 °C and stirred for 5 h. After that period, stirring was continued at r.t.
for 24 h. Slow evaporation of the solvent resulted in the pale yellow cis-[PtCl2(PTR)]
precipitate being obtained, which was freeze-dried. However, the cis-[PtCl2(dmso)(KR)])
precipitate was formed directly in the reaction mixture. The platinum(II) complex was
isolated from the reaction mixture by filtration, washed with ethanol, then diethyl ether and
finally dried under vacuum. An attempt to obtain the complex 1 by the direct reaction
between K2PtCl4 and PTR turned out to be unsuccessful.
1
Cis-[PtCl2(PTR)] (1). Yield: 65%. H NMR (499.8 MHz, 298 K) δ, pm: 7.79 (H9), 8.30
13
(H11), 8.41 (H10), 9.48 (H5), 9.49 (H8); C NMR (125.7 MHz, 298 K) δ, ppm: 61.3 (C16),
70.4 (C14), 76.4 (C13), 87.3 (C15), 95.8 (C12), 122.3 (C11), 124.4 (C5), 126.0 (C9), 140.7

(C10), 148.6 (C4), 148.7 (C8), 149.6 (C6); 15N NMR (50.6 MHz, 298 K) δ, ppm: -175.5 (N7),
-129.6 (N3), -121.9 (N1), -30.8 (N2); 195Pt NMR (107.4 MHz, 298 K) δ, ppm: -2296.
Analysis calc/found for C12Cl2H14N4O4Pt: C, 26.5/26.7; H 2.6/3.0; N, 10.3/9.8%.
1
Cis-[PtCl2(dmso)(KR)] (2). Yield: 60%. H NMR (499.8 MHz, 298 K) δ, ppm: 4.93 (H11),
6.44 (H14), 6.50 (H13), 7.64 (H15), 8.12 (NH10), 8.48 (H2), 9.22 (H8); 13C NMR
(125.7 MHz, 298 K) δ, ppm: 3.50 (DMSO), 37.8 (C11), 61.6 (C20), 70.8 (C18), 75.1 (C17),
86.9 (C19), 89.9 (C16), 107.5 (C13), 110.6 (C14), 116.0 (C5), 142.5 (C8), 142.6 (C15), 148.2
15
(C4), 151.9 (C12), 152.4 (C6), 153.9 (C2); N NMR (50.6 MHz, 298 K) δ, ppm: -289.2
(N10), -224.0 (N7), -203.5 (N9), -155.7 (N3), -145.1 (N1); 195Pt NMR (107.4 MHz, 298 K) δ,
ppm: -3031. Analysis calc/found for C17Cl2H23N5O6PtS: C, 29.5/29.1; H, 3.4/3.4;
N, 10.1/9.8%.
4. Biological part
4.1. Lipophilicity (logP)
The lipophilicities of the new platinum(II) complexes were determined using the standard
shake-flask method, which is common for different types of coordination compounds [22,23].
First, aqueous sodium chloride (0.9% w/v) and organic (n-octanol) phases were saturated for
1 week. Complex 1 was dissolved in the saturated aqueous phase, but complex 2 was
dissolved in n-octanol. Subsequently, based on UV-Vis measurements, the complexes’
stability in the applied solvents was confirmed. All the solutions were at a concentration of
0.30 mg/mL in 4.0 mL. The same volume of the immiscible solvent was added to each
sample. The obtained mixtures were stirred mechanically in plastic tubes for 30 minutes.
The samples were centrifuged (6000 rpm, 15 min). After separation, the phases were analyzed
by UV-Vis spectroscopy to determine the amount of the compound in each phase.
The absorption values at λmax before and after shaking were compared. In the next step, the
partition coefficients in both phases for each compound were calculated according to the

Lambert–Beer Law to determine the logP values. For each complex, the procedure was
repeated three times.
4.2. Cell culture
The cytotoxic activities of tested compounds in vitro were assessed against four human
cell lines: normal fibroblast cells (CRL2522), lung carcinoma epithelial cells (A549), urinary
bladder carcinoma cells (T24) and skin malignant melanoma cells (CRL1872). All the cell
lines were cultured in Dulbecco's Modified Eagle Medium (DMEM)/Ham’s F-12 medium
(Corning, USA) supplemented with 10% fetal bovine serum (FBS; Biowest), 5 μg/mL
amphotericin B, 100 μg/ml streptomycin and 100 U/mL penicillin (Corning). The cells were
grown in 75 cm2 cell culture flasks (Falcon) at 37 °C in a humidified atmosphere with 5%
CO2.
4.3. Preparation of compound dilutions
Stock solutions of the tested compounds (KR, PTR, 1 and 2) at a concentration of 100
μg/ml were prepared by dissolving of 100 μg of each compound in 2 μL of DMSO or ethanol
and adding Dulbecco's Modified Eagle Medium (DMEM)/Ham’s F-12 medium (Corning,
USA). Serial dilutions of the stock solution with DMEM/Ham’s F-12 medium were prepared
to obtain 10, 1 and 0.1 μg/mL solutions of the tested compounds. Culture medium with
solvent was used as a control.
4.4. Cell viability determination by an MTT assay
The cytotoxic activities of the compounds in vitro were evaluated using an MTT assay
with thiazolyl blue tetrazolium bromide. For this purpose, cells were seeded into 24-well
plates at a density of 2 x 104 cells/cm2 and cultured for 24 h. Subsequently, the culture
medium was removed, the tested compounds at their final concentrations (0.1, 1, 10 and
100 μg/mL) were added and incubated for another 24 h. The next day, the tested compound

solutions were removed, the wells were washed with phosphate-buffered saline and filled with
MTT solution (500 μL) at a concentration of 1 mg/mL. After 2 h incubation, the remaining
MTT solution was carefully removed and 1 mL of DMSO was added to the wells. The
absorbance of the resulting solutions was measured at 570 nm wavelength and 655 nm as a
reference in the spectrophotometer. The results were compared to the control (untreated cells)
and expressed as an IC50 value.
Results and discussion
1. NMR spectroscopy
Multinuclear magnetic resonance spectroscopy (1H, 13C, 15N, 195Pt) was applied in
order to determine the central atom environment and the ligand binding mode in the both
platinum(II) complexes (1 and 2). A comparison of the location of the appropriate resonance
signals for each complex (δcomplex) and the free ligands (δligand) allows the calculation of the
coordination shifts (Δcoord. = δcomplex – δligand), which can be used to suggest the structure of the
platinum(II) complexes in solution.
The obtained results, such as chemical shifts characteristics for all the atoms of the N-
donor ligands and their platinum(II) complexes, are summarized in the supplementary
materials (Tab.S1-S2, Fig.S1-S13).
1
The H NMR spectra of 1 and 2 in the aromatic range of chemical shifts exhibit the
strongest resonance signals at δ 7.36-8.89 ppm for PTR and δ 8.20-8.39 ppm for KR (Table
1). The coordination shifts calculated in comparison to the spectra of the free ligands vary
between +0.19 and +0.86 ppm for 1, and -0.08 and +0.83 ppm for 2. Slightly stronger effects
were observed for H(8) which suggests the coordination of PTR by the N(7) atom of the
pyridyl ring and via the N(7) or N(9) atom in the 5-membered purine ring of KR. By
extension, a comparison of the spectra of the free ligands and complexes 1 and 2 clearly
confirms the coordination of the N-donor ligands to the platinum(II) ions. Additionally, the

singlet at δ 3.50 ppm in the 1H NMR spectrum and the resonance signal at δ 42.8 ppm in the
13C NMR spectrum confirm the presence of the S-bonded molecule of dmso in the
coordination sphere of cis-[PtCl2(dmso)(KR)] [24].
Similar changes in the chemical shifts were observed in the 13C NMR spectra. The signals
which belong to the C(4)-C(16) atoms in cis-[PtCl2(PTR)] (1) and to the C(2)-C(20) atoms
in cis-[PtCl2(dmso)(KR)] (2) were found in the ranges δ 61.3-149.6 and 37.8-153.9 ppm,
respectively. The coordination shifts calculated in comparison to the spectra of the free
ligands
vary
between
-1.10
and
+3.6 ppm
for
1
and
between
-4.6 and +2.1 ppm for 2.
Table 1. 1H NMR chemical shifts for the ligands and complexes 1 and 2 in DMF-d7 at 298 K
(coordination shifts in parentheses)
Hydrogen atom
H(5)
PTR
8.89
8.63
7.36
7.93
8.11
KR
cis-[PtCl2(PTR)] (1)
9.48 (+0.59)
H(8)
9.49 (+0.86)
H(9)
7.79 (+0.43)
H(10)
8.41 (+0.48)
H(11)
8.30 (+0.19)
Hydrogen atom
H(2)
cis-[PtCl2(dmso)(KR)] (2)
8.48 (+0.21)
8.27
8.39
8.20
H(8)
9.22 (+0.83)
H(10)
8.12 (-0.08)
Unfortunately, we were unable to indicate expressly which nitrogen atoms are engaged in the
formation of the platinum-nitrogen bond using the shifts values obtained from the 1H and 13C
15
NMR spectra only. In order to solve this problem, heterocorrelation N-1H NMR spectra
were recorded. It was observed that the resonance signals for the N(1) and (N2) atoms in the
PTR spectrum show a relatively small amount of shielding after coordination to the Pt(II) ion
(Δcoord.= -2.4 and -13.6 ppm, respectively) when compared to the shielding characteristic for
the N(3) and N(7) atoms (Δcoord.= -98.4 and -101.7 ppm relatively) (Fig. 3A). A similar

1
dependence was observed for the H-15N NMR experiments for 2. The coordination shifts
calculated for the N(1), N(3), N(9) and N(10) atoms (Δcoord.= +2.3, +0.8, +7.1 and +6.2 ppm
respectively) were definitely smaller that the value characteristic of the N(7) atom
(Δcoord.= 84.1 ppm) (Fig. 3B). It should be noted that the unambiguous assignment of
resonance signals for the N(1) and N(3) atoms in free KR was only possible with the use of
literature data [25]. The above-mentioned dependences verify the fact that the N(3) and N(7)
atoms in PTR and the N(7) atom in KR are the coordination site of these ligands. It confirms
that PTR and KR are bidentate and the monodentate N-donor ligands, respectively.
Additionally, the range of chemical and coordination shifts is in good agreement with these
characteristic parameters of other compounds with similar coordination but other N-donor
ligands [26].
B
A
Fig. 3. 15N chemical shifts for PTR and cis-[PtCl2(PTR)] (1) (A), and for KR and
cis-[PtCl2(dmso)(KR)] (2) (B). The spectra were recorded in DMF-d7 at 298 K for PTR, 1 and
2, and at 343 K for KR.
Additionally, the type of the chromophore system present in the coordination spheres
of 1 and 2 was assayed based on their 195Pt NMR spectra. First, it was observed that resonance
signals of the complexes were definitely shielded in comparison to K2PtCl4 and absolutely

deshielded compared to cis-[PtCl2(dmso)2], both of which were used as substrates in our
synthesis pathways (Fig. 4). Moreover, the 195Pt NMR spectra of 1 and 2 displayed only one
signal at δ -2296 ppm (which can be assigned to a PtCl2N2 complex) and at δ -3031 ppm
(which can be assigned to a PtCl2NS complex), respectively [27,28]. The singlets for both
complexes are in the range typical for dichlorido platinum(II) complexes. Indeed, a change in
the coordination sphere composition, which consists of exchanging the N-donor atom by the
S-donor molecule of dimethyl sulfoxide, causes a distinct shielding of the resonance signal
(Fig. 4).
Fig. 4. 195Pt chemical shifts for different types of platinum(II) complexes in DMF-d7 at 298 K
2. Lipophilicity and in vitro antiproliferative activity of the novel complexes
In the first step of the biological studies we determined the partition coefficients for the
platinum(II) compounds 1 and 2 between aqueous sodium chloride and organic phases. It is
obvious that a drug’s permeability across cell membranes, which has an impact on absorption
efficiency, depends on its lipophilicity [29,30]. The literature data suggest that the best logP
value varies between 0 and 3 [29,31]. Drugs showing a greater lipophilic character are poorly
soluble in water and they are absorbed by the digestive tract to a smaller extent [29,32].

The logP values for cis-[PtCl2(PTR)] and cis-[PtCl2(dmso)(KR)] are -1.33 ± 0.04 and
+1.09 ± 0.05, respectively. Therefore, it is noticeable that our two complexes exhibit
definitely different characters. The positive logP value for complex 2 confirms that it presents
a lipophilic property absolutely higher than that of complex 1. Hence, we can suppose that
lipophilic cis-[PtCl2(dmso)(KR)] (2) is able to be transported and absorbed more efficiently
than cis-[PtCl2(PTR)] (1) [29]. Additionally, the difference between the lipophilicities of these
complexes may result from the different N-donor ligand properties and also the presence of
dimethyl sulfoxide in the coordination sphere of compound 2.
In the next step, the in vitro cytotoxic activities of the PTR and KR ligands, the
platinum(II) compounds (1 and 2) and cisplatin were determined against A549 (non-small cell
lung carcinoma), T24 (urinary bladder cancer), CRL1872 (malignant melanoma) and a normal
human cell line, namely CRL2522 (skin fibroblast cells). Unfortunately, only kinetin riboside
(KR) and the dichlordo platinum(II) complex containing KR (2) were able to inhibit the grow
of these cells in the range of tested concentrations (Fig. 5). It suggests that the lipophilic
complex 2 is more cytotoxic in comparison with hydrophilic complex 1. Obviously, the
inactivity of 1 results from the inactivity of the free ligand PTR.

Fig. 5. In vitro antiproliferative activity of kinetin ryboside (KR) and complex 2
On the other hand, free PTR presents more than 3 times higher in vitro cytotoxicity (IC50
= 17.7 µM) against the non-small cell lung cancer (A549) on comparison with cisplatin (IC50
= 61.0 µM). Moreover, after complexation with the platinum(II) ion, its activity did not
change for A549 and CRL1872 cell lines, but it decreased for the T24 cell (Fig. 5). There are
also differences in the toxicity of the free ligand KR and complex 2 towards the CRL2522
normal cell line. The platinum(II) complex with kinetin riboside is more toxic than the free
kinetin riboside, with IC50 parameters amounting to 24.0 and 41.7 μM, respectively. However,
both are more toxic than cisplatin (IC50 = 71.9 μM) (Fig. 5).
Conclusions
In conclusion, for the first time platinum(II) coordination compounds with ribosides have
been designed and synthesized. During our research, we have successfully obtained and
thoroughly characterized two novel platinum(II) complexes, cis-[PtCl2(PTR)] (1) and
cis-[PtCl2(dmso)(KR)] (2), with the different N-donor ligands kinetin riboside (KR) and 1-β-
D-ribofuranosyl-4-(2-pyridyl)-1H-1,2,3-triazole (PTR).
According to the data gained from multinuclear magnetic resonance spectra (1H, 13C, 15N
and 195Pt), we were able to conclude that KR and PTR are monodentate (via the N(7) atom)
and bidentate (via the N(3) and N(7) atoms) N-donor ligands, respectively. Additionally, it
was observed that the biological properties, including the cytotoxic effect mechanism of the
novel complexes, depend on the type of riboside. Finally, it was possible to suggest that
the lipophilic complex 2 exhibits higher antiproliferative activities towards A549, T24 and
CRL1872 cancer cell lines than complex 1. For the above-mentioned reasons, we can suppose
that the use of KR as the N-donor ligand in platinum(II) complexes is more promising than
PTR insertion into the coordination sphere of the Pt(II) ion.
Acknowledgements

M.J., I. Ł, and M.P. are a members of Center of Excellence “Towards Personalized
Medicine” operating under Excellence Initiative - Research University.
References
Highlights:
 influence of different binding modes and environment around the platinum(II) on
liphophilicity;
 role of N-donor ligands in creation of chemotherapeutic prodrugs;
 influence of type of riboside on lipophilicity, and in vitro activity;
By the reaction between cis-[PtCl2(dmso)2] and kinetin riboside (KR) or 1-β-D-
ribofuranosyl-4-(2-pyridyl)-1H-1,2,3-triazole (PTR) in the M:L molar ratio of 1:1, two novel
platinum(II) complexes with different compositions of the coordination sphere have been
isolated. Biological studies showed that the lipophilic complex cis-[PtCl2(dmso)(KR)] (2)
exhibits higher antiproliferative activity towards A549, T24 and CRL1872 cancer cell lines
than the complex cis-[PtCl2(PTR)] (1).
CRediT author statement
Mateusz Jakubowski: Methodology and Formal analysis (synthesis of platinum(II)
complexes), methodology for structural characterization, lipophilicity study, visualization;
Writing - Original Draft;
Iwona Łakomska: Conceptualization; Formal analysis; management and coordination
responsibility for the research activity planning and execution; Writing- Reviewing and
Editing, supervision.
Jerzy Sitkowski; Methodology and Formal analysis (NMR experiments)
Paweł Dąbrowski & Marta Pokrywczyńska – Methodology and Formal analysis (in vitro
experiments)

Tomasz Ostrowski & Grzegorz Framski – Methodology and Formal analysis (preparation
of ligands (KR and PTR))
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