Pd(II) complexes with N-substituted pyrazoles as ligands. the influence of the R group [OMe versus NMe2] of [1-{R-(CH2) 2-}-3,5-Ph2-(C3HN2)] on their cytotoxic activity on breast cancer cell lines

Article abstract of DOI:10.1016/j.jorganchem.2014.04.034

The study of the reactivity of the novel pyrazole derivative [1-{MeO-(CH₂)₂-}-3,5-Ph₂-(C₃HN ₂)] (1) with Na₂[PdCl₄] or Pd(OAc)₂ under different experimental conditions has allowed us to isolate and characterize the trans-isomers of [Pd{[1-{MeO-(CH₂) ₂-}-3,5-Ph₂-(C₃HN₂)]} ₂(X)₂] [X = Cl (2) or OAc (3)] and the di-μ-ligand bridged cyclopalladated complexes [Pd{κ²,C,N[1-{MeO-(CH ₂)₂-}-3-(C₆H₄),5-Ph-(C ₃HN₂)]}(μ-X)]₂ [X = OAc (4) or Cl (5)]. Further treatment of compounds 4 or 5 with PPh₃ in CH ₂Cl₂ produced the bridge splitting and the formation of [Pd{κ²,C,N[1-{MeO-(CH₂)₂-}-3-(C ₆H₄),5-Ph-(C₃HN₂)]}X(PPh ₃)] [X = OAc (6) or Cl (7)]. The cytotoxic assessment of the free ligand (1) and the Pd(II) complexes on the two breast cancer cell lines MCF7 and MDA-MB231 reveals that: a) compound 1 is less active than its analogue [1-{Me₂N-(CH₂)₂-}-3,5-Ph₂-(C ₃HN₂)] (Ic) and b) palladacycles 4-7 showed a remarkable cytotoxic activity in the MDA-MB231 cell line (with IC₅₀ values in the range 9.1-14.4 μM).

Full text of DOI:10.1016/j.jorganchem.2014.04.034

Accepted Manuscript
Pd(II) complexes with N-substituted pyrazoles as ligands. The influence of the R
group [OMe versus NMe ] of [1-{R-(CH ) -}-3,5-Ph -(C HN )] on their cytotoxic
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activity on breast cancer cell lines
John U. Chukwu , Concepción López , Asensio González , Mercè Font-Bardía , M.
Teresa Calvet , Ramon Messeguer , Carme Calvis
PII:
S0022-328X(14)00216-2
10.1016/j.jorganchem.2014.04.034
JOM 18569
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 25 November 2013
Revised Date: 15 April 2014
Accepted Date: 24 April 2014
Please cite this article as: J.U. Chukwu, C. López, A. González, M. Font-Bardía, M.T. Calvet, R.
Messeguer, C. Calvis, Pd(II) complexes with N-substituted pyrazoles as ligands. The influence of the
R group [OMe versus NMe ] of [1-{R-(CH ) -}-3,5-Ph -(C HN )] on their cytotoxic activity on breast
2
2 2
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3
2
cancer cell lines, Journal of Organometallic Chemistry (2014), doi: 10.1016/j.jorganchem.2014.04.034.
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ACCEPTED MANUSCRIPT
Several types of Pd(II) complexes containing the new pyrazole: [1(OMe-CH2CH2)-3,5Ph-
(C3HN2)] acting as a monodentate (N-donor) or as a [C(phenyl), N(pyrazole)]- bidentate ligand
have been prepared and characterized. Their antiproliferative activity in MCF7 and MDA-
MB231 breast cell lines has also been evaluated and the results revealed that the cytotoxic
activity of some of the cyclopalladated complexes was similar to that of cisplatin in the triple
negative MDA-MB231 breast cancer cell line.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Pd(II) complexes with N-substituted pyrazoles as ligands. The influence of the R
group [OMe versus NMe2] of [1-{R-(CH2)2-}-3,5-Ph2-(C3HN2)] on their cytotoxic
activity on breast cancer cell lines.
John U. Chukwu,a,b Concepción López,a,* Asensio González,c Mercè Font-Bardía,d M.
Teresa Calvet,e Ramon Messeguerf and Carme Calvisf
aDepartament de Química Inorgànica, Facultat de Química, Universitat de Barcelona, Martí i
Franquès 1-11. E-08028-Barcelona, Spain. (C.López: E-mail: conchi.lopez@qi.ub.es).
b Current address: Department of Pure and Industrial Chemistry, University of Port-Hartcourt,
P. M. B. 5323 Choba, Rivers State, Nigeria.
c Laboratori de Química Orgànica, Facultat de Farmàcia, Institut de Biomedicina (IBUB),
Universitat de Barcelona, Av. Joan XIII. s/n, E-08028 Barcelona, Spain.
d Unitat de Difracció de Raigs-X, Centre Científic i Tecnològic de la Universitat de
Barcelona, Solé i Sabarís 1-3, E-08028 Barcelona, Spain.
e Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Facultat de Geologia,
Universitat de Barcelona, Martí i Franquès s/n, E-08028 Barcelona, Spain.
f Biomed Division, Leitat Tecnological Center, Parc Científic de Barcelona, Edifici Hèlix,
C/ Baldiri Reixach, 15–21, E-08028-Barcelona, Spain.
Keywords: palladium(II) complexes/ cyclopalladation/ in vitro studies/ antitumoral activity/
breast cancer
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Abstract.
The study of the reactivity of the novel pyrazole derivative [1-{MeO-(CH2)2-}-3,5-Ph2-
(C3HN2)] (1) with Na2[PdCl4] or Pd(OAc)2 under different experimental conditions has
allowed us to isolate and characterize the trans- isomers of [Pd{[1-{MeO-(CH2)2-}-3,5-
Ph2-(C3HN2)]}2(X)2] [X = Cl (2) or OAc (3)] and the di-µ-ligand bridged cyclopalladated
complexes [Pd{κ2,C,N)[1-{MeO-(CH2)2-}-3-(C6H4),5-Ph-(C3HN2)]}(µ-X)]2 [X = OAc (4)
or Cl (5)]. Further treatment of compounds 4 or 5 with PPh3 in CH2Cl2 produced the bridge
splitting and the formation of [Pd{κ2,C,N)[1-{MeO-(CH2)2-}-3-(C6H4),5-Ph-
(C3HN2)]}X(PPh3)] [X = OAc (6) or Cl (7)]. The cytotoxic assessment of the free ligand
(1) and the Pd(II) complexes on the two breast cancer cell lines MCF7 and MDA-MB231
reveals that: a) compound 1 is less active than its analogue [1-{Me2N-(CH2)2-}-3,5-Ph2-
(C3HN2)] (Ic) and b) palladacycles 4-7 showed a remarkable cytotoxic activity in the
MDA-MB231 cell line (with IC50 values in the range 9.1-14.4 µM).
1. Introduction
Pyrazoles are widely used as core motifs for a large number of compounds of significant
relevancy and they have a variety of applications (i.e. as agrochemicals, dyes, food
additives, catalysts and pharmaceuticals) [1-2]. Moreover, N-substituted derivatives are
particularly attractive in view of their antiproliferative properties against cancer cells [3,4].
Furthermore, this type of heterocycles have a rich and versatile coordination ability with
transition metals that affects their properties [5-6]. This fact, together with the increasing
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interest in the design of novel antitumoral drugs with greater efficiency, lower toxicity and
less undesirable side effects than the current Pt-based drugs [7], have triggered the
development of novel Pd(II) and Pt(II)-pyrazole containing complexes [8-13]. Substituted
pyrazoles in which there is a σ(CꢀH) bond with the proper orientation are valuable
substrates to achieve cyclopallada- or platinated complexes [11-13]. This sort of
metallacycles are relevant due to their chemical, physical or optical properties and their
applications in different areas (i.e. as precursors in organic, organometallic synthesis,
homogeneous catalysis and as building blocks in supramolecular chemistry) [14,15].
On the other hand, Bioorganometallic chemistry is a rapid developing area of increasing
interest and the idea of using organometallic complexes in drug discovery is becoming
more and more popular [16-17]. Antimalarials, antibacterials, neuroprotectors, based on
organometallic compounds have been described [16-17]. Moreover, recent contributions
suggest that cyclopallada- and cycloplatinated compounds are probably amongst the best
candidates for the design of new anticancer drugs [18-20].
Despite the increasing interest in both Pd(II)-pyrazole complexes [21, 22] and
cyclometallated compounds [14,15,18-20], only a few articles on cyclopalladated-pyrazole
derivatives have been published [11, 13]. We have recently reported three N-substituted
pyrazoles of general formulae 1-{Me2N-(CH2)2-}-3,5-R2-(C3HN2) (I) (Figure 1), their
Pd(II) and Pt(II) complexes of general formulae [M{1-[Me2N-(CH2)2-]-3,5-R2-
(C3HN2)}Cl2] [(II) and (III), in Fig. 1) and the cyclometallated derivatives (IV and V)
[11b]. The comparison of their antitumoral activity in three different cell lines (MDA-
MB231, MCF7 and A549) revealed that: a) pyrazoles (I) with R = Ph were more potent
than their analogues with R = H or Me, b) the binding of these ligands to Pd(II) or Pt(II)
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produced an enhancement of their activity, and c) cyclometallated products (IV and V)
were more potent than complexes IIc and IIIc in which the pyrazole Ic acts as a bidentate
(N,N’) ligand.
< Figure 1, here >
In view of these findings and in order to elucidate the effect produced by the functional
group on the pendant arm of the heterocyclic nitrogen, now we report a parallel study on
the novel pyrazole: [1-{MeO-(CH2)2-}-3,5-Ph2-(C3HN2)] (1), that has the OMe group
attached at the end of the -(CH2)2- chain instead of the -NMe2 of Ic.
2. Experimental
2.1. Materials and methods
All the reagents were obtained from commercial sources and used as received. Solvents
were distilled and dried before use [23]. Elemental analyses were carried out at the Serveis
Científico-Tècnics (Universitat Barcelona). Mass spectra (ESI+) were performed at the
Servei d’Espectrometria de Masses (Universitat de Barcelona). Infrared (IR) spectra were
obtained with a Nicolet 400FTIR instrument using KBr pellets. A selection of the most
relevant absorptions observed in the IR spectra are presented in the following sections.
Ultraviolet-visible (UV-vis.) spectra of CH2Cl2 solutions of the free ligand 1 and the Pd(II)
compounds (5-7) were recorded at 298 K with a Cary 100 scan 388 Varian UV
spectrometer. The wavelengths (λ, in nm) and the extinction coefficients (ε, in M-1 cm-1) of
the bands observed in the UV-vis. spectra are specified in the characterization section of the
corresponding product. The retention coefficients (Rf) were obtained using SiO2 (Merck
silica gel 60 F254) plates. High resolution 1H NMR spectra and the two-dimensional [{1H-
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1H} NOESY and COSY and {1H-13C}-heteronuclear single quantum coherence (HSQC),
and heteronuclear multiple bond coherence (HMBC)] experiments were registered with a
13
Varian VRX-500 or a Bruker Avance DMX-500 MHz instruments. C{1H}-NMR spectra
and 31P{1H} spectra of compounds 6 and 7 obtained with a Mercury-400 and a Varian 300
MHz instrument, respectively. NMR studies of 1-3 and 5-7 were carried out at 298 K, using
1
13
CDCl3 (99.9 %) as solvent and SiMe4 [for H and C{1H}-NMR] and P(OMe)3 [δ(31P) =
31
140.17 ppm for P NMR] as references. Due to the low solubility of complex 5 in CDCl3
its NMR studies were performed in DMSO-d6 (99.8%). In all cases, chemical shifts (δ) are
given in ppm and the coupling constants (J) in Hz. In the characterization section of each
product the assignment of signals detected in their NMR spectra refers to the labelling
patterns presented in Scheme 1 (Abreviations for the multiplicities of the signals observed
in the NMR spectra: s = singlet, d = doublet, t = triplet, m = multiplet and br = broad).
2.2. Synthesis
2.2.1. Preparation of 1-{MeO-(CH2)2-}-3,5-Ph2-(C3HN2) (1).
Potassium hydroxide (0.800 g, 14 × 10-3 mol) was treated with 9.0 mL of DMSO and the
resulting mixture was magnetically stirred at room temperature (ca. 298 K) for 30 min.
After this period 3,5-diphenylpyrazole (0.788 g, 3.58 × 10-3 mol) was added and the stirring
was maintained for 30 min at 298 K. Then, 1-chloro 2-methoxyethane (4.0 mL, 45 × 10-3
mol) was gradually added and the reaction mixture was left overnight under stirring at 298
K. After this period, 50 mL of iced cold water was added to eliminate the unreacted KOH;
the organic phase was then extracted with diethylether and washed repeatedly with water,
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dried over Na2SO4 and filtered. Then, the filtrate was concentrated to dryness on a rotary
evaporator. The solid formed was collected and later on dried in vacuum for 3 days. [Yield:
0.880 g, (88 %)]. Characterization data: Anal (%). Calc. for C18H18N2O (MW = 278.35): C,
77.67; H, 6.52; N, 10.06 %; found: C, 77.8; H, 6.6 and N, 10.1. MS (ESI+): m/z = 279.15
{[M] + H}+. IR selected data: 3059-3015 [ν(C-H)] and 2987-2952 [ν(C-H)], 1481(m),
1462(s), 1441(m), 1363(m), 1300(m), 1115(s), 1012(m), 762(s), 691(s) cm-1. UV-vis. data
(c = 5.74 × 10-5 M in CH2Cl2): λ (ε) = 223 (1.5 × 104) and 253 (3.1 × 104). Rf (in CHCl3) =
0.24. 1H NMR data: δ = 3.32 (s, 3H, OMe); 3.91 [t, 3JH,H = 7.2, 2H, (-CH2-d)]; 4.34 [t, 3JH,H
= 7.2, 2H, (-CH2-c)]; 6.65 (s, 1H, H4); 7.35 (t, 3JH,H = 7.7, 1H, H4b); 7.47-7.60 (m, 5H, H3a,
3
3
H4a, H5a, H3b and H5b); 7.70 (d, 2H, JH,H = 7.6, H2b and H6b), 7.92 (d, 2H, JH,H = 7.5, H2a
and H6a). 13C{1H} NMR data: 49.1 (Cd); 58.9 (OMe); 71.4 (Cc); 103.4 (C4); 125.3 (C2b and
C6b); 125.7 (C2a and C6a); 126.0 (C4b); 126.8 (C4a); 128.7 (C3a and C5a); 129.2 (C3b and C5b);
130.7 (C1b); 133.6 (C1a); 145.9 (C5) and 150.9 (C3).
2.2.2. Preparation of trans-[Pd{[1-{MeO-(CH2)2-}-3,5-Ph2-(C3HN2)]2Cl2] (2).
To a solution formed by Na2[PdCl4] (100 mg, 3.4 × 10-4 mol) and methanol (10 mL),
ligand 1 (189 mg, 6.8 × 10-4 mol) was added and the reaction mixture was stirred at 298 K
for 2 h. The yellow solid formed was filtered and dried overnight. Afterwards, it was
dissolved in the minimum amount of CH2Cl2 and passed through a SiO2 (2.0 cm × 8.0 cm)
column. Elution with CH2Cl2 produced a wide yellow band which was collected and
concentrated to dryness on a rotary evaporator and the bright yellow solid formed was
collected and finally dried in vacuum for 2 days. [Yield: 196 mg (78 %)]. Characterization
data: Anal. (%) Calc for C36H36Cl2N4O2Pd: (MW = 734.0): C, 58.91; H, 4.94; N, 7.63;
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Found: C, 59.0; H, 5.0; N, 7.5. MS (ESI+): m/z = 697.16 {[M] - Cl}+. IR selected data:
3047-3015 [ν(C-H)] and 2980-2925 [ν(C-H)], 1483(m), 1461(m), 1448(m), 1124(s), 765(s)
and 700(s) cm-1. UV-vis. data: (c = 8.17 × 10-6 M in CH2Cl2): λ (ε) = 238 (3.8 × 105), broad
1
3
band. Rf (in CHCl3) = 0.19. H NMR data: δ = 3.20 [s, 6 H, 2 (OMe)]; 3.96 [t, JH,H = 6.9,
4H, 2 (–CH2-d)]; 4.89 [t, 3JH,H = 6.9, 4H, 2 (–CH2–c)]; 6.36 [s, 2H, 2 (H4)]; 7.40-7.58 [br. m,
12H, 2(H3a, H4a, H5a , H3b, H4a and H5b)]; 7.62 [d. 3JH,H = 7.6, 4H, 2 (H2b and H6b)] and 8.20
[d, 3JH,H = 7.6, 4H, 2 (H2a and H6a)]. 13C{1H} NMR data: 50.31 (2 Cd); 58.7 (2 OMe); 69.9
(2 Cc); 108.5 (2 C4); 125.5 [2 (C2b and C6b)]; 125.9 (2 C4b); 126.4 (2 C4a); 128.5 [2 (C2a and
C6a)]; 129.4 (2 C1b), 129.8 [2 (C3b and C5b)]; 130.1 [2 (C3a and C5a)]; 132.7 (2 C1a); 149.7 (2
C5) and 154.7 (2 C3).
2.2.3. Preparation of trans-[Pd{[1-{MeO-(CH2)2-}-3,5-Ph2-(C3HN2)]2(OAc)2] (3) and
[Pd{κ2,C,N)[1-{MeO-(CH2)2}-3-(C6H4),5-Ph-(C3HN2)]}(
µ-OAc)]2 (4).
76 mg (3.4 × 10-4 mol) of Pd(OAc)2 was dissolved in 15 mL of toluene at 298 K, then
ligand 1 (95 mg, 3.4 × 10-4 mol) was added. The reaction flask was protected from the light
with aluminium foil and refluxed for 12 h. After this period the black solution was
concentrated to dryness on a rotary evaporator and left overnight in a dessicator. The
residue was then treated with CH2Cl2 (15 mL) and passed through a Celite pad to remove
the metallic palladium. This was repeated until colourless mother liquors were obtained.
The solution was dried with Na2SO4 and the filtrate was concentrated to dryness on a rotary
evaporator. The brownish solid formed consisted on a mixture of compounds 3 and 4 in a
molar ratio (3:4 = 1:10). These products were isolated by SiO2 column chromatography.
Elution with CHCl3 produced a pale yellow band that gave after concentration 11 mg of the
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minor product (3). Afterwards the use of a CHCl3 : MeOH (100:0.4) mixture released
another band that was collected and concentrated to dryness on a rotary evaporator. The
yellowish solid formed (4) was collected, air-dried and dried in vacuum for 2 days (yield:
112 mg). Characterization data for 3: Anal. (%) Calc. for C40H42N4O6Pd (MW = 780.21):
C, 61.59; H, 5.4; N, 7.17; Found: C, 61.4; H, 5.5; N, 7.0. MS (ESI+): m/z = 721.2 {[M]-
(OAc)}+}. IR selected data: 3067-3023 [ν(C-H)] and 2984-2940 [ν(C-H)], 1566
[νas(COO)] and 1386 [νs (COO)] cm-1. UV-vis. data: (c = 1.43 × 10-5 M in CH2Cl2): λ (ε) =
1
234 (4.1 × 105) broad band. Rf (in CHCl3) = 0.21. H NMR data: δ = 1.83 [br.s, 6H, 2
3
(OAc)]; 3.15 (s, 6H, 2 OMe); 3.95 [t, JH,H = 7.1, 4H, 2 (–CH2–d)]; 4.75 [t, 3JH,H = 7.1, 4H,
2 (–CH2–c)]; 6.40 (s, 2H, 2 H4); 7.37-7.58 [m, 16H, 2(H3a, H4a, H5a, H2b, H3b, H4b, H5b and
H6b)] and 8.16 [d, 3JH,H = 7.6, 4H, 2 (H2a and H6a)]. 13C{1H} NMR data: 23.3 [2 Me(OAc)];
50.2 (2 Cd); 58.4 (2 OMe); 70.1 (2 Cc); 108.7 (2 C4); 125.7 [2 (C2b and C6b)]; 126.1 (2 C4b);
126.4 (2 C4a); 128.6 [2 (C2a and C6a)]; 129.5 [2 (C3b and C5b)]; 130.0 [2 (C3a and C5a)];
130.4 (2 C1b); 132.6 (2 C1a); 149.5 (2 C5);154.3 (2 C3) and 180.9 [2 >COO (OAc)]. For 4:
Anal. (%) Calc. for C40H40N4O6Pd2 (MW = 886.1): C, 54.25; H, 4.55; N, 6.32; Found: C,
54.1; H, 4.5; N, 6.0. MS (ESI+): m/z = 425.06 {[M]-2(OAc) + 2(CH3CN)}2+/2. IR selected
data: 3060-3018 [ν(C-H)] and 2984-2940 [ν(C-H)], 1560 [νas(COO)] and 1413 [νs(COO)]
cm-1. UV-vis. data: (c = 1.91 × 10-5 M in CH2Cl2): λ (ε) = 223 (3.2 × 105), 247 (2.5 × 105)
and 341(broad, ≈ 1.9 × 103). Rf (in CHCl3) = 0.14. 1H NMR data: δ = 2.01 [br. s, 6H, 2
(OAc)]; 3.17 [s, 6H, 2 (OMe)]; 3.30-3.40 [(br. m, 4H, 2 (–CH2–d)]; 3.67 [m, 2 H, 2 (one of
the two protons of the –CH2–c unit)]; 3.93 [m, 2 H, 2 (the other proton of the –CH2–c unit)];
6.04 [s, 2H, 2 (H4)]; 6.74 [m, 2H, 2 (H3a)]; 6.81 [m, 2H, 2 (H4a)]; 7.31-7.80 [m, 10H, 2 (H5a,
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13
H6a, H3b, H4b and H5b)] and 8.51 [br., 4H, 2 (H2b and H6b)]. C{1H} NMR data: 23.9 [2
Me(OAc)]; 49.7 (2 Cd); 58.2 (2 OMe); 70.6 (2 Cc); 109.3 (2 C4); 125.5 [2 (C2b and C6b)];
125.9 (2 C4b); 126.3 (2 C4a); 127.6 (2 C5a); 128.3 (2 C6a); 129.0 [2 (C3b and C5b)]; 129.7 (2
C3a); 130.2 (2 C1b); 132.3 (2 C1a); 148.9 (2 C2a), 150.6 (2 C5); 153.9 (2 C3) and 178.9 [2
>COO (OAc)].
2.2.4. Preparation of [Pd{κ2,C,N)[1-{MeO-(CH2)2}-3-(C6H4),5-Ph-(C3HN2)]}(
µ-Cl)]2 (5).
Compound [Pd{κ2,C,N)[1-{MeO-(CH2)2}-3-(C6H4),5-Ph-(C3HN2)]}(µ-OAc)]2 (4) (40
mg, 4.37 × 10-5 mol) was suspended in acetone (20 mL), then LiCl (5 mg, 1.1 × 10-4 mol)
was added. The resulting mixture was stirred overnight at 298 K. The solid formed was
collected by filtration and dried in vacuum for 2 days. [Yield: 32 mg, (81%)].
Characterization data: Anal. (%) Calc. for C36H34Cl2N4O2Pd2 (MW = 838.43): C, 51.7; H,
4.09; N, 6.68; Found: C, 51.6; H, 4.2; N, 6.8. MS (ESI+): m/z = 383.761 {[M]-2Cl}2+/2. IR
selected data: 3055-3022 [ν(C–H)] and 2988-2924 [ν(C–H)]. UV-vis. data: (c = 1.91 × 10-5
M in CH2Cl2): λ (ε) = 240 (br. 2.5 × 105) and 338 (≈ 3.6 × 103). 1H-NMR data (in DMSO-
d6): δ = 3.22 [s, 6H, 2 (OMe)]; 3.30 [br. m, 2H, {one of the protons of the (–CH2–d) unit}],
4.03 [m, 2 H, 2 {one of the protons of the (–CH2–c ) moiety]; the signals due the remaining
protons the (–CH2–)c and d moieties were masked by the broad signal (at δ = 3.50 ppm) of
the residual water present in the DMSO-d6, their chemical shifts [ca. 3.45 (–CH2–d) and
3.85 for that of the –CH2–c unit] were obtained from the HSQC experiment; 6.07 [s, 2H, 2
(H4)]; 6.74 [m, 2H, 2 (H3a)]; 6.81 [m, 2H, 2 (H4a)] and 7.18-8.10 [br.m, 14H, 2 (H5a, H6a,
H2b, H3b, H4b, H5b and H6b)]. 13C{1H} NMR data (in DMSO-d6): 50.1 (2 Cd); 58.0 (2 OMe);
70.3 (2 Cc); 109.1 (2 C4); 125.0 [2 (C2b and C6b)]; 125.7 (2 C4b); 126.0 (2 C4a); 127.9 (2
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C5a); 128.4 (2 C6a); 128.9 [2 (C3b and C5b)]; 129.6 (2 C3a); 130.4 (2 C1b); 131.8 (2 C1a);
151.2 (2 C5); 152.0 (2 C2a) and 153.7 (2 C3)].
2.2.5. Preparation of [Pd{κ2,C,N)[1-{MeO-(CH2)2-}-3-(C6H4),5-Ph-(C3HN2)]}(X)(PPh3)]
{X = OAc (6) or Cl (7)}.
To a mixture containing 3.8 × 10-5 mol of the corresponding dimeric complex 4 (35 mg)
{or 5 (34 mg)} and 20 mL of CH2Cl2, PPh3 (20 mg, 7.6 × 10-5 mol) was added. The
resulting mixture was kept under stirring for 20 min and then filtered. The pale yellowish
filtrate was concentrated to dryness on a rotary evaporator and the solid formed was
collected, air-dried and recrystallized in a CH2Cl2:n-hexane (1:1) mixture. [Yields: 38 mg
(70 %) and 40 mg (77%) for 6 and 7, respectively]. Characterization data for 6: Anal. Calc
for C38H35N2O3PPd (MW= 705.9): C, 64.73; H, 5.00; N, 3.97%; Found: C, 64.6; H, 5.1 and
N, 4.0; MS (ESI+): m/z = 645.14{[M] – (OAc)}+. IR selected data: 3050-3018 [ν(C-H)] and
2985-2925 [ν(C-H)]; 1590 [νas(COO)] and 1381 [νs(COO)] and 1094 (PPh3, X-sensitive),
cm-1. UV-vis. (c = 1.42 × 10-5 M in CH2Cl2): λ (ε) = 229 (4.0 × 10-5), 246 (3.0 ×10-4) and
1
348 (3.5 ×10-3). Rf (in CHCl3) = 0.20. H NMR data: δ =1.85 (s, 3H, OAc); 3.12 (s, 3H,
OMe); 3.67 (t, 3JH,H = 7.3, 2H, –CH2–d); 4.37 (t, 2H, 3JH,H = 7.0, –CH2–c); 6.07 (s, 1H, H4);
6.44 (br. 1H, H3a); 6.96 (m, 1H, H4a); 7.28-7.96 [br.m, 22H, (H5a H6a, H2b-H6b, and aromatic
,
protons of the PPh3 ligand)]. 13C{1H} NMR data: 23.3 [Me(OAc)], 51.4 (Cd); 58.5 (OMe);
70.2 (Cc); 110.2 (C4); 125.3 (C4b); 126.5 (C4a); 127.4 (C2b and C6b); 128.0 (C6a); 128.4
(C5a); 129.1 (C3b and C5b); 129.5 (C3a); 129.8 (C1b); 132.5 (C1a); 150.2 (C5); 151.2 (C2a);
154.7 (C3), 180.4 [>COO (OAc)] and four additional doublets due to four types of carbon-
13 nuclei (ipso, ortho, meta and para) of the PPh3 ligand. 31P{1H} NMR data: δ = 40.3. For
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7: Anal. Calc. for C36H32ClN2OPPd (MW = 680.1): C, 63.45; H, 4.73; N, 4.11%; Found: C,
63.2; H, 4.8; N, 4.1; MS (ESI+): m/z = 645.14 {[M] - Cl}+. IR selected data: 3049-3018
[ν(C–H)] and 2982-2925 [ν(C–H)] and 1094 (X-sensitive of the phosphine ligand) cm-1.
UV-vis. data: (c = 1.8 × 10-5 M in CH2Cl2): λ (ε) = 242(2.0 × 10-5); and 341(3.9 × 10-3). 1H
NMR data: δ = 3.11 (s, 3H, OMe); 3.82 (br., 2H, -CH2-d); 4.50 (br., 2H, –CH2-c); 6.35 (s,
1H, H4); 6.58 (m, 1H, H4a); 6.84 (m, 1H, H3a) and 7.30-8.10 [br.m, 22H, (H5a, H6a, H2b-H6b
and aromatic protons of the PPh3 ligand)]. 13C{1H} NMR data: 51.2 (Cd); 58.4 (OMe); 70.1
(Cc); 110.1 (C4); 125.4 (C4b); 126.3 (C4a); 127.3 (C2b and C6b); 127.8 (C6a); 128.6 (C5a);
129.0 [(C3b and C5b); the {1H-13C}-HSQC spectra showed that the signal due to C3a was
overlapped by this one)]; 129.6 (C1b); 132.8 (C1a); 149.9 (C5); 152.6 (C2a); 153.8 (C3), and
four additional doublets due to the aromatic 13C nuclei of the PPh3. 31P{1H} NMR data: δ =
40.1.
2.3. Crystallography
A plaque-like specimen of compound 2 (dimensions in Table 1), was used for the X-ray
crystallographic analysis. The X-ray intensity data were measured and integration of the
data using a triclinic unit cell yielded a total of 11383 reflections to a maximum θ angle of
28.34° (0.75 Å resolution), of which 4182 were independent (average redundancy 2.722,
completeness = 99.7%, Rint = 2.43 %, Rsig = 2.81 %) and 3912 (93.54 %) were greater than
2σ(F2). The final cell constants (Table 1) are based upon the refinement of the XYZ-
centroids of reflections above 20 σ(I).
< Table 1, here >
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The structure was solved and refined using the Bruker SHELXTL Software Package,
[24] using the space group P-1, with Z = 1 for the formula unit, C36H36Cl2N4O2Pd. The final
anisotropic full-matrix least-squares refinement on F2 with 205 variables converged at R1 =
3.10%, for the observed data and wR2 = 8.03% for all data. The goodness-of-fit was 1.055.
The largest peak in the final difference electron density synthesis was 0.562 e-/Å3 and the
largest hole was -0.269 e-/Å3 with an RMS deviation of 0.065 e-/Å3. Final details
concerning the resolution and refinement of the crystal structure are presented in Table 1.
CCDC 951054 contains the crystallographic information file for compound 2.
2.4. Biological studies.
2.4.1. Cell culture.
Breast cancer MCF7 and MDA-MB231 cells (from European Collection of Cell
Cultures, ECACC) were grown as a monolayer culture in minimum essential medium
(DMEM with L-glutamine, without glucose and without sodium pyruvate) in the presence
of 10 % heat-inactivated fetal calf serum, 10 mM of D-glucose and 0.1%
streptomycin/penicillin in standard culture conditions.
2.4.2. Cell viability assays.
For these studies, compounds were dissolved in 100% DMSO at 50 mM as stock
solution; then, serial dilutions have been done in DMSO (1:1) (in this way DMSO
concentration in cell media was always the same); finally, 1:500 dilutions of the serial
dilutions of compounds on cell media were done. The assay was performed as described by
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Givens et al. [25]. In brief, MDA-MB231 and MCF7 cells were plated at 5000 cells/well or
10000 cells/well respectively, in 100 µL media in tissue culture 96 well plates (Cultek).
After 24 h, media was replaced by 100 µL/well of serial dilution of drugs. Each point
concentration was run in triplicate. Reagent blanks, containing media plus colorimetric
reagent without cells were run on each plate. Blank values were subtracted from test values
and were routinely 5-10 % of uninhibited control values. Plates were incubated for 72 h.
Hexosamidase activity was measured according to the following protocol: the media
containing the cells was removed and cells were washed once with PBS 60 µL of substrate
solution (p-nitrophenol-N-acetyl-β-D-glucosamide 7.5 mM [Sigma N-9376], sodium citrate
0.1 M, pH = 5.0, 0.25 % Triton X-100) was added to each well and incubated at 37 °C for
1-2 hours; after this incubation time, a bright yellow color appeared; then, plates could be
developed by adding 90 µL of developer solution (Glycine 50 mM, pH = 10.4; EDTA 5
mM), and absorbance was recorded at 410 nm.
3. Results and discussion
3.1. Synthesis.
Compound 1-{MeO-(CH2)2-}-3,5-Ph2-(C3HN2) (1) was obtained in a fairly good yield
(88%) by alkylation of 3,5-diphenylpyrazole with a three-fold excess of 1-chloro 2-
methoxyethane [Scheme 1, step i)] [26].
< Scheme 1, here >
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Treatment of 1-{MeO-(CH2)2-}-3,5-Ph2-(C3HN2) (1) with Na2[PdCl4] (in a 1:1 or 2:1
molar ratio) in methanol at 298 K produced a yellow solid that was identified as [Pd{[1-
{MeO-(CH2)2-}-3,5-Ph2-(C3HN2)]}2Cl2] (2) [Scheme 2, step ii)]. Its X- ray crystal structure
(see below) confirmed that it was the trans isomer.
When ligand 1 was reacted with Pd(OAc)2 in toluene under reflux for 12 h a black
solution was obtained. The subsequent chromatography on silica gel gave two products 3
and 4 [Scheme 1, step iii)] in a molar ratio 4:3 =10:1. The minor component (3) was
identified as trans-[Pd{[1-{MeO-(CH2)2-}-3,5-Ph2-(C3HN2)]}2(OAc)2] and characterization
data of the major product (4) were consistent with those expected for the di-µ-acetato-
bridged
cyclopalladated
complex
[Pd{κ2,C,N)[1-{MeO-(CH2)2-}-3-(C6H4),5-Ph-
(C3HN2)]}(µ-OAc)]2 that arises form the activation of the σ(C-H) bond of the phenyl ring
in position 3 of the pyrazole.
The reaction of 4 with an excess of LiCl in acetone at 298 K gave the dinuclear
compound [Pd{κ2,C,N)[1-{MeO-(CH2)2-}-3-(C6H4),5-Ph-(C3HN2)]}(µ-Cl)]2 (5) as a pale
brownish solid [Scheme 1, step iv)]. Further treatment of di-µ-ligand bridged
cyclopalladated products (4 or 5) with PPh3 (in a 1:2 molar ratio) in CH2Cl2 produced the
splitting of the “Pd(µ-X)2Pd” units and the formation of the monomeric derivatives
[Pd{κ2,C,N)[1-{MeO-(CH2)2-}-3-(C6H4),5-Ph-(C3HN2)]}(X)(PPh3)] with X = OAc (6) or
Cl (7) [Scheme 1, step v)] respectively.
3.2. Characterization.
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The new ligand (1) and its palladium(II) derivatives (2-7) were characterized by
elemental analyses, mass spectra and infrared spectroscopy. In all cases the elemental
analyses were consistent with the proposed formulae.
The IR spectra of the complexes 3, 4 and 6 showed the typical bands due to the
symmetric and asymmetric stretchings of the –COO- unit [27] and the separation between
them was consistent with the values reported for related Pd(II)-compounds containing OAc-
ligands acting as monodentate group (in 3 and 6) or as a bridging ligand (in 4) [27]. For
compounds 6 and 7, with the PPh3 ligand, X-sensitive bands were also detected in their IR
spectra.
Compound 2 was also characterized by X-ray difraction. Its molecular structure and the
atom labelling scheme is presented in Figure 2. The crystal contains molecules of [Pd{[1-
{MeO-(CH2)2-}-3,5-Ph2-(C3HN2)]2Cl2] in which, the Pd(II) atom is bound to two nitrogen
atoms of two units of 2 and two chlorido ligands. Bond lengths and angles around the
palladium(II) are similar to those reported for related trans-[Pd(L)2Cl2] complexes (with L
= N-substituted pyrazoles) [28-30].
< Figure 2, here >
The Pd(II) atom is located on a inversion centre and as a consequence of this: a) the two
Cl- ligands are in a trans- arrangement and b) the “(CH2)2OMe” pendant arms are on
opposite sides of the coordination plane. In addition, “PdCl2” moiety is nearly orthogonal to
the heterocycle and the phenyl rings are not coplanar with the pyrazolyl ring (angles
between their main planes = 64.4 and. 36.0°). As a consequence of these arrangements the
distance between the Cl- ligands and one of the protons of the –CH2-O” unit [2.787 Å] is
15

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smaller than the sum or the van der Waals radii of these atoms [31]; thus suggesting an
intramolecular C-H···Cl interaction [32].
In the crystal the molecules are assembled by C-H ··π interactions (Figure 3) involving:
the centroids of the phenyl rings (Cg1 and Cg2) {defined by the sets of atoms [C1-C6] and
[C10-C15], respectively} and one of the hydrogen atoms of the OMe unit (H18C) and the
H5 atom, [distances Cg1···· H18C = 3.440 Å and Cg2··· H5 = 3.477 Å].
< Figure 3, here >
The new products were also characterized in solution by UV-vis. spectroscopy and
NMR. The absorption spectra of the new compounds were registered in CH2Cl2 at 298K.
The UV-vis spectra of the Pd(II) complexes showed a band in the range 320 nm < λ3 < 360
nm {not present in the spectrum of the free ligand (1)} with extinction coefficients between
2.0 ×103 and 4.0 × 103 M-1 cm-1. This band that has also been observed for related Pd(II)
complexes with pyrazole ligands [11] is assigned to a metal-to-ligand charge transfer
(MLCT) transition from the 4d orbitals of the Pd(II), to a π orbital of the ligand. The
remaining bands detected at lower wavelengths (220 nm < λ < 370 nm) are attributed to
metal perturbed intraligand transitions (MPILT).
1
In the H NMR spectra of the Pd(II) complexes (2-7), the chemical shifts of the OMe
protons were very similar to that of the free ligand, thus suggesting that the oxygen of the
methoxy group was not bound to the Pd(II) centre. NMR spectra of 3, 4 and 7 showed the
typical resonances due to the OAc- ligand bound to the Pd(II) atom. The low-field region of
1
these H NMR spectra was complex and the assignment of the signals detected was
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achieved with the aid of 2D NMR experiments [NOESY, COSY, {1H-13C}-HSQC and
HMBC].
For the palladacycles (4-7): a) the signal due to H2a proton was not observed in their 1H-
NMR spectra and b) the resonances of the H3a and H4a nuclei, appeared at higher fields than
for the free ligand (1). Carbon-13 NMR and the 2D {1H-13C}-HMBC spectra showed a
downfield shift of the signal due to the metallated carbon (C2a). All these findings are
consistent with previous NMR studies of cyclopalladated complexes [11a,14b,19b].
The 31P{1H}-NMR spectra of 6 and 7 showed a singlet at around 40 ppm. According to
the bibliography [11], this is indicative of a cis-arrangement of the PPh3 ligand and the
metallated carbon, in good agreement with the transphobia effect [33].
3.3. Study of the antitumor activity of the free ligand and the complexes.
The cytotoxic activity of the new ligand (1) and the palladium(II) complexes (2, 4-7)
against two human breast cancer cell lines (MCF7 and MDA-MB231) was tested using
cisplatin as positive control. The effects of these products on the growth of two cell lines
were assessed after 72 h and the results are displayed in Figure 4. The IC50 values
corresponding to the inhibition of cancer cell growth at 50% level are listed in Table 2. For
comparison purposes the IC50 parameters for the free ligand Ic and the palladacycle [Pd{κ3
C,N,N’)[1-{Me2N-(CH2)2-}-3,5-Ph2-(C3HN2)]2Cl] (V in Figure 1) are also included [11b].
,
< Figure 4, here >
< Table 2, here >
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< Figure 5, here >
The comparison of the in vitro cytotoxic activities of the free ligands (Ic and 1) against
the MCF7 and MDA-MB231 cell lines shows (Table 2 and Figure 4) that the presence of
the NMe2 group on the pendant arm of the two 3,5-diphenyl pyrazole: [1-{R’-(CH2)2-}-3,5-
Ph2-(C3HN2)] produces a greater cytotoxic effect than the OMe. This could be related to
several factors such as their different lipophilicity and their proclivity to protonate in
biological media [18,20].
Complex 2 did not show any significant effect on the MCF7 cell line. This result is
similar to those obtained for compound: [Pd{κ2, N,N’[1-{Me2N-(CH2)2-}-3,5-Ph2-
(C3HN2)]Cl2] (IIc shown in Fig. 1). Except for 6, the remaining cyclopalladated complexes
were more active in the MCF7 cell line than the free ligand (1) and compound 2. Among all
these palladacycles, the di-µ-acetato-bridged complex 4 was the most potent. Its effect was
ca. 1.4 times greater than the palladacycle V (shown in Figure 1) with a (C,N,N’)- pincer
ligand [11b]. Unfortunately, none of these products exhibited IC50 values smaller than
cisplatin.
More encouraging were the results obtained for MDA-MB231 cell line. Compound 2
exhibited a moderate activity and for the remaining products, the IC50 values [in the range:
9.1 µM (for 6) - 14.4 µM (for 5)] were a bit smaller, if significant, than that of V [IC50 =
16.2 ± 4.6 µM] [11b] and closer to that of cisplatin [IC50= 6.5 ± 2.4 µM]. Thus, suggesting
that the new Pd(II) compounds were more effective in the triple negative MDA-MB231
cancer cell line than in the MCF7 line.
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4. Conclusions.
The study of the reactivity of the novel N-substituted pyrazole derivative: [1-{MeO-
(CH2)2-}-3,5-Ph2-(C3HN2)] (1) with Na2[PdCl4] or Pd(OAc)2 has allowed us to isolate and
characterize a family of palladium(II) complexes (2-7). In two of them (2 and 3) the Pd(II)
atom is bound to the heterocyclic nitrogen. The remaining four complexes (4-7) contain one
(in 6 and 7) ot two (in 4 and 5) five-membered palladacycles formed by the binding of the
same nitrogen and the metallation of the phenyl ring on position 3 of the pyrazole. These
findings indicate that ligand 1 may adopt two binding modes [(N) or (C,N)-] in front of the
Pd(II) atom. However, no evidences of the formation of complexes containing 1 as a
(C,N,O)- ligand were detected.
The comparison of the results obtained from in vitro studies of their cytotoxic activity
against the MCF7 cell line and the MDA-MB231 {triple negative (ER, PR and no HER2
over expression)} breast cancer cell line showed that the free ligand (1) was less active than
its analogue Ic (Figure 1) with the NMe2 unit at the end of the pendant arm. We have also
proved that compounds (4-7) exhibit greater cytotoxic activity than the free ligand (1) and
complex 2 (with two units of 1 acting as a monodentate N-donor ligand). The new
cyclopalladated complexes (4-7) have an outstanding antiproliferative effect in the MDA-
MB231 cell line. For all of them the IC50 values (Table 2) are a bit smaller than that
reported for palladacycle V previously reported [11b]; but closer to that of cisplatin (under
identical conditions). These results are especially outstanding because they open up new
possibilities in the design of Pd(II)-pyrazole based complexes as promising alternatives to
cisplatin and related Pt(II) drugs.
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Acknowledgements.
This work was supported by the Ministerio de Ciencia e Innovación, (MICINN) (Grants:
CTQ2009-11501 and TEC2011-29140-C03-02) and the Generalitat de Catalunya (Grant
2009-SGR-1111). Dr. J.U.C is also grateful to the financial support given by the “Coimbra
Group”.
Appendix A. Supplementary material
CCDC 951054 contains the supplementary crystallographic data for this paper. These
data can be obtained free of charge from the Cambridge Crystallographic Data Centre via:
www. ccdc.cam.ac.uk/data_request/cif.
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References
[1] a) J. Elguero, Pyrazoles, in A.R. Katritzy, W. Rees, E.F.V. Scrivens (Eds.),
Comprehensive Heterocyclic Chemistry-II, Pergamon Press, Oxford, 1996, pp. 1ꢀ75
(Chapter 3.01); b) S. Fustero, M. Sánchez-Roselló, P. Barrio, A. Simón-Fuentes,
Chem. Rev. 111 (2011) 6984.
[2] For recent contributions see: a) S.A. Hudson, K.J. McLean, S. Surade, Y.-Q. Yang,
D. Leys, A. Ciulli, A.W. Munro, C. Abell, Angew. Chem. Int. Ed. Engl. 51 (2012),
9311; b) F.K. Keter, J. Darkwa, BioMetals 25 (2012) 9; c) A. Schmidt, A. Dreger,
Curr. Org. Chem. 15 (2011) 1423; d) P.H. Carter, J. Hynes, Expert Opinion on
Therapeutic Patents 20 (2010) 1609; e) R.L. Hudkins, K.A. Josef, Expert Opinion on
Therapeutic Patents 17 (2007) 351; f) E. Arbaciauskiene, K. Kazlauskas, A.
Miasojedovas, S. Jursenas, V. Jankauskas, W. Holzer, V. Getautis, A. Sackus, Synth.
Metals 160 (2010) 490.
[3] a) B.A. Thaher, M. Arnsmann, F. Totzke, J.E. Ehlert, M.H.G. Kubbutat, C.
Schächtele, M.O. Zimmermann, P. Koch, F.M. Boeckler, S.A. Laufer, J. Med. Chem.
55 (2012) 961; b) E. Strocchi, F. Fornari, M. Minguzzi, L. Gramantieri, M. Milazzo,
V. Rebuttini, S. Breviglieri, C.M. Camaggi, E. Locatelli, L. Bolondi, M. Comes-
Franchini, Eur. J. Med. Chem. 48 (2012) 391; c) A. Balbi, M. Anzaldi, C. Maccio, C.
Aiello, M. Mazzei, R. Gangemi, P. Castagnola, M. Miele, C. Rosano, M. Viale, Eur.
J. Med. Chem. 46 (2011) 5293; d) B. Insuasty, A. Tigreros, F. Orozco, J. Quiroga, R.
Abonia, M. Nogueras, A. Sánchez, J. Cobo, Biorg. Med. Chem. 18 (2010) 4965; e)
M.D. Joksovic, G. Bogdanovic, V. Kojic, K.M. Szecsenyi, V.M. Leovac, D. Jakimov,
S. Trifunovic, V. Markovic, L. Joskovic, J. Heterocyclic Chem. 47 (2010) 850.
21

ACCEPTED MANUSCRIPT
[4] a) R. Kalirajan, V. Muralidharan, S. Jubie, B. Gowramma, S. Gomalthy, S. Sankar,
K. Elango, J. Heterocyclic Chem. 49 (2012) 748; b) M.F. Mohamed, M.S. Mohamed,
S.A. Shouman, M.M. Fathi, I.A. Abdelhamid, Appl. Biochem. Biotechn. 168 (2012)
1153; c) S. Xu, S. Li, Y. Tang, J. Zhang, S. Wang, C. Zhou, X. Li, Med. Chem. Res.,
22(2013) 5610; d) Y-R. Liu, J-Z. Luo, P-P. Duan, J. Shao, B-X. Zhao, J-Y. Miao,
Bioorg. Med. Chem 22 (2012) 6882; e) Y. Zheng, M. Zheng, X. Ling, Y. Liu, Y.
Xue, L. An, N. Gu, M. Jin, Bioorg. Med. Chem. 23 (2013) 4471; f) E. Tzanetou, S.
Liekens, K. M. Kasiotis, N. Fokialakis, S.A. Haroutounian, Archiv. Pharm. 345
(2012) 804; g) L.-W. Zheng, J. Zhu, B.-X. Zhao, Y.-H. Huang, J. Ding, J.-Y. Miao,
Eur. J. Med. Chem. 45 (2010) 5887; h) H. A. Abdel-Aziz, H.S.A. El-Zahabi, K. M.
Dawood, Eur. J. Med. Chem. 45 (2010) 2427; i) M. Comes, B. Bonini, C. Camaggi,
D. Gentili, A. Pession, M. Rani, E. Strocchi, Eur. J. Med. Chem. 45 (2010), 2024; j)
B.P. Bandgar, J.V. Totre, S.S. Gawande, C.N. Khobragade, S. C. Warangkar, P.D.
Kadam, BioMedChem. 18 (2010) 6149; k) Z. Ratkovic, Z.D. Juranic, T. Stanojkovic,
D. Manojlovic, R.D. Vukicevic, N. Radulovic, M.D. Joksovic, Bioorg. Chem. 38
(2010) 26.
[5] a) J.A. McCleverty, T.J. Meyer (Eds.), Comprehensive Coordination Chemistry II:
From Biology to Nanotechnology, Elsevier, Amsterdam, (2003); b) C. Pettinari, A.
Tabacaru, I. Boldog, K.V. Domasevith, S. Galli, N. Masciocchi, Inorg. Chem. 51
(2012) 5235; c) S. Konar, A. Jana, K. Das, S. Ray, S. Chatterjee, S. K. Kar,
Polyhedron 47 (2012) 143; d) Y.G. Vlasov, S.S. Levichev, A.A. Kruchinin, Russ. J.
Appl. Chem. 85 (2012) 940; e) C.J. Adams, M.A. Kurawa, A.G. Orpen, Dalton 39
(2010) 6974.
22

ACCEPTED MANUSCRIPT
[6] a) J. Garcia-Anton, R. Bofill, L. Escriche, A. Llobet, X. Sala, Eur. J. Inorg. Chem.
(2012) 4775; b) I. F. Santos, G.P. Guedes, L.A. Mercante, A.M.R. Bernardino, J.
Mol. Struct. 1011 (2012) 99; c) N.V. Kulkarni, A. Kamath, S. Budagumpi, V.K.
Revankar, J. Mol. Struct. 1006 (2011) 580; c) C.-D. Fan, H. Su, J. Zhao, B.-X. Zhao,
S.-L. Zhang, J.-Y. Miao, Eur. J. Med. Chem. 45 (2010) 1438; d) S. Tardito, I.
Bassanetti, C. Biggnardi, L. Elviri, M. Tegoni, C. Mucchino, O. Bussolati, R.
Franchi-Gazzola, L. Marchiò, J. Am. Chem. Soc. 133 (2011) 6235.
[7] a) C.M. Anderson, I.R. Taylor, M.F. Tibbets, J. Philpot, Y. Hu, J.M. Tanski, Inorg.
Chem. 51 (2012) 12917; b) C. Francisco, S. Garna, F. Mendes, F. Marques, I.
Cordeiro dos Santos, A. Paulo, I. Santos, J. Coimbra, E. Gabano, M. Ravera, Dalton
40 (2011) 5781; c) N.J. Wheate, S. Walker, G.E. Craig, R. Oun, Dalton Trans. 39
(2010) 8113; d) M.J. Sullivan, Cancer 115 (2009) 5623; e) B. Köberle, M.T. Tomicic,
S. Usanova, B. Kaina, Biochim. Biophys Acta, Rev. Cancer 1806 (2010) 172.
[8] a) D. Das, B.G. Vats, S. Kannan, D.K. Maity, M.G.B. Drew, Polyhedron 54 (2013)
104; b) S. Muñoz, J. Pons, M. Font-Bardía, C.A. Kilner, M.A. Halcrow, Inorg. Chim.
Acta 373 (2011) 211; c) C. Luque, J. Pons, T. Calvet, M. Font-Bardía, J. García-
Antón, J. Ros, Inorg. Chim. Acta 367 (2011) 35; d) J. Chakraborty, M.K. Saha, P.
Benerjee, Inorg. Chem. Commun. 10 (2007) 671; e) K. Li, M.S. Mohlala, T.V.
Segapelo, P.M. Shumbula, I. A. Guzei, J. Darkwa, Polyhedron 27 (2008) 1017; f) R.
Y. Mawo, D.M. Johnson, J.L. Wood, I.P. Smoliakova, J. Organomet. Chem. 693
(2008) 33; g) I. Ara, L.R. Falvello, J. Forniés, R. Lasheras, A. Martin, O. Oliva, V.
Sicilia, Inorg. Chim. Acta 359 (2006) 4574.
23

ACCEPTED MANUSCRIPT
[9] a) Y. Han, H.V. Huynh, G.K. Tan, Organometallics 26 (2007) 6581; b) I. Ara, J.
Forniés, R. Lasheras, A. Martin, V. Sicilia, Eur. J. Inorg. Chem. (2006) 948; c) F.
Churruca, R. SanMartin, I. Tellitu, E. Domínguez, Synlett. (2005) 3116; d) F. López-
Linares, O. Colmenares, E. Catari, A. Karam, React. Kinet. Catal. Lett. 85 (2005)
139; e) E. Budzisz, U. Krajewska, M. Rozalski, A. Szulawska, M. Czyz, B. Nawrot,
Eur. J. Pharmacol. 502 (2004) 59.
[10] a) J.A. Perez, V. Montoya, J.A. Ayllon, M. Font-Bardía, T. Calvet, J. Pons, Inorg.
Chim. Acta 394 (2013) 21; b) S.Y. Chang, J-L. Chen, Y. Chi, Y-M. Cheng, G-H.
Lee, C-M. Jiang, P. T. Chou, Inorg. Chem. 46 (2007) 11202; c) A. Eisenwiener, M.
Neuburger, T. A. Kaden, Dalton Trans. 36 (2007) 218; d) A.V. Khripun, M. Haukka,
V.Y. Kukushkin, Russ. Chem. Bull. 55 (2006) 247; e) A.V. Khripun, S.I. Selivanov,
V.Y. Kukushkin, M. Haukka, Inorg. Chim. Acta 359 (2006) 320; f) E. Ciesielska, A.
Szulawska, K. Studzian, J. Ochocki, K. Malinowska, K. Kik, L. Szmigiero, J. Inorg.
Biochem. 100 (2006) 1579.
[11] a) C. López, A. González, R. Bosque, P.K. Basu, M. Font-Bardía, T. Calvet, RSC
Adv. 2 (2012) 1986; b) J. Quirante, D. Ruíz, A. González, C. López, M. Cascante, R.
Cortés, R. Messeguer, C. Calvis, L. Baldomà, A. Pascual, Y Guérardel, B. Pradines,
M. Font-Bardía, T. Calvet, C. Biot, J. Inorg. Biochem. 105 (2011) 1720.
[12] a) A.S. Abu-Surrah, K.A. Abu-Safieh, I.-M. Ahmad, M.Y. Abdalla, M.T. Ayoub,
A.K. Qaroush, A.M. Abu-Mahtheieh, Eur. J. Med. Chem. 45 (2010) 471; b) E.
Budzisz, M. Malecka, B.K. Keppler, V.B. Arion, G. Andrijewski, U. Krajewska, M.
Rozalski, Eur. J. Inorg. Chem. (2007) 3728.
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ACCEPTED MANUSCRIPT
[13] a) E. Budzisz, M. Miernicka, I.-P. Lorenz, P. Mayer, E. Balcerczak, U. Krajewska,
M. Rozalski, Eur. J. Med. Chem. 45 (2010) 2613; b) F.K. Keter, S. Kanyanda, S.L.
Lyantagaye, J. Darkwa, D. Jasper, G. Rees, M. Meyer, Cancer Chemother.
Pharmacol. 63 (2008) 127.
[14] a) J. Dupont, M. Pfeffer (Eds.) Palladacycles: Synthesis, Characterization and
Applications, Wiley-VCH, (2008) Weinheim (Germany), Chapter. 13, pages 307-340;
b) K. Godula, D. Sames, Science 312 (2006) 67; c) M. Ghedini, I. Aiello, A. Crispini,
A. Golemme, M. La Deda, D. Pucci, Coord. Chem. Rev. 250 (2006) 1373; d) D.A.
Alonso, C. Najera, Chem. Soc. Rev. 39 (2010) 2891; e) I. Omae, J. Organomet.
Chem. 692 (2007) 2608; f) J. Dupont, C.S. Consorti, J. Spencer, Chem. Rev. 105
(2005) 2527.
[15] For recent advances in pallada- and platinacycles, see: a) J. Albert, R. Bosque, M.
Crespo, J. Granell, J. Rodríguez J. Zafrilla, Organometallics 29 (2010) 4619; b) M.
Crespo, T. Calvet, M. Font-Bardia, Dalton Trans. 39 (2010), 6936; c) M-Y. Yuen,
S.C.F. Kui, K-H. Low, C.-C. Kwok, S.S.-Y. Chui, C.-W. Ma, N. Zhu, C.-M. Che,
Chemistry-A Eur. J. 16 (2010) 14131; d) C. López, S. Pérez, X. Solans, M. Font-
Bardía, A. Roig, E. Molins, P.W.N.M. van Leeuwen G.P.F. van Strijdonck,
Organometallics 26 (2007) 571; e) T-K. Zhang, K. Yuan, X-L. Hou, J. Organomet.
Chem. 692 (2007) 1912; f) P.G. Evans, N.A. Brown, G.J. Clarkson, C.P. Newman,
J.P. Rourke, J. Organomet. Chem. 691 (2006) 1251.
[16] For reviews on Bioorganometallic chemistry: a) R.S. Herrick, C.J. Ziegler, T.C.;
Leeper, J. Organomet. Chem. 751 (2014) 90; b) A. Vessieres, J. Organomet. Chem.
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734 (2013) 3; c) A. Monney, M. Albrecht, Coord. Chem. Rev. 257 (2013) 2420; d)
A.L. Noffke, A. Habtemariam, A.M. Pizarro, P.J. Sadler, Chem. Commun. 48 (2012)
5219; e) C. Biot, D. Dive, Topics in Organomet. Chem. 32 (2010) 155; f) N. Chavain,
C. Biot, Curr. Med. Chem. 17 (2010) 2729; g) R.H. Fish, Richard H. Aust. J. Chem.
63 (2010) 1505; h) S. El Kazzouli, N. El Brahmi, S. Mignani M. Bousmina M.
Zablocka J-P. Majoral Curr. Med. Chem. 19 (2012) 4995; i) E.A. Hillard, G. Jaouen,
Organometallics 30 (2011) 20; j) G. Gasser, I. Ott, N. Metzler-Nolte, J. Med. Chem.
54 (2011) 3.
[17] Recent and relevant contributions: a) F. Dubar, C. Slomianny, J. Khalife, D. Dive, H.
Kalamou, Y. Guerardel, P. Grellier, C. Biot, Angew. Chem. Int. Ed. 52 (2013) 7690;
b) R. Arancibia, C. Biot, G. Delaney, P. Roussel, A. Pascual, B. Pradines, A.H.
Klahn, A. Hugo, J. Organomet. Chem. 723 (2013) 143; c) M.A.L. Blackie, Mini Rev.
Med. Chem. 13 (2013) 597; d) M. Patra, K. Ingram, A. Leonidova, V. Pierroz, S.
Ferrari, M. Robertson, M.H. Todd, K. Keiser, G. Gasser, J. Med. Chem. 56 (2013)
9192.
[18] For review purposes see: A.C.F. Caires, Anti-Cancer Agents in Medicinal Chemistry
7 (2007) 484 and references therein.
[19] For recent contributions on palladacycles with antitumoral activity: a) S. Aliwaini,
A.J. Swarts, A. Blankenberg, S. Mapolie, S. Prince, Biochem. Pharmacol. 86 (2013),
1650; b) J. Albert, S. García, J. Granell, A. Llorca, M.V. Lovelle, V. Moreno, A.
Presa, L. Rodríguez, J. Quirante, C. Calvis, R. Messeguer, J. Badía, L. Baldomà, J.
Organomet. Chem. 724 (2013) 289; c) K. Karami, M.H. Kharat, H. Sadeghi-Aliabadi,
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J. Lipkowski, M. Mirian, Polyhedron 50 (2013) 187; d) M. Carreira, R. Calvo-
Sanjuan, M. Sanau, I. Marzo, M.Contel, Organometallics 31 (2012) 5772; e) J.
Spencer, R.P. Rathnam, M. Motukuri, A.K. Kotha, S.C.W. Richardson, A. Hazrati,
J.A. Hartley, L. Male, M.B. Hursthouse, Dalton Trans. (2009) 4299; f) F.A. Serrano,
A.L. Matsuo, P.T. Montforte, A. Bechara, S.S. Saili, D.P. Santana, T. Rodrigues, F.V.
Pereira, L.S. Silva, J. Machado, E.L. Santos, J.B. Pesquero, R.M. Martins, L.R.
Travassos, A.C.F. Caires, E.G. Rodrigues, BMC Cancer. 11 (2011) 296.
[20] For recent advances on platinacycles with antitumoral activity: a) D. Talancón, C.
López, M. Font-Bardia, T. Calvet, J. Quirante, C. Calvis, R. Messeguer, R. Cortes,
M. Cascante, L. Baldoma, J. Badía, J. Inorg. Biochem. 118 (2013) 1; b) R. Cortés, M.
Crespo, L. Davin, R. Martín, J. Quirante, D. Ruiz, R. Messeguer, C. Calvis, L.
Baldomà, J. Badia, M. Font-Bardía, T. Calvet, M. Cascante, Eur. J. Med. Chem. 54
(2012) 557; c) J. Albert, R. Bosque, M. Crespo, J. Granell, C. López, R. Cortés, A.
González, J. Quirante, C. Calvis, R. Messeguer, L. Baldomà, J. Badia, M. Cascante,
Bioorg. Med. Chem. 21 (2013) 4210; d) R.Cortés, M. Tarrado-Castellarnau, D.
–
Talancón, C. López, W. Link, D. Ruiz, J.J. Centelles, J. Quirante M. Cascante,
Metallomics 6 (2014) 622.
[21] a) G. Xu, Z. Yan, N. Wang, Z. Liu, Eur. J. Med. Chem. 46 (2011) 356; b) L. Ronconi,
P. J. Sadler, Dalton Trans. 40 (2011) 262; c) J. Alemán, V. del Solar, L. Cubo, A.G.
Quiroga C. Navarro-Ranninger, Dalton Trans. 39 (2010) 10601; d) A.P. Neves, G.B.
da Silva, M.D. Vargas, C.B. Pinheiro, L.C. Visentin, J.B.D.M. Filho, A.J. Araujo, L.
V. Costa-Lotufo, C. Pessoa, M.O. de Moraes, Dalton Trans. 39 (2010) 10203; e) G.
Wagner, A. Marchant, J. Sayer, Dalton Trans. 39 (2010) 7747; f) N. Margiotta, N.
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