Isolation of an intermediate in the platination of p-nitroacetophenone 4-methylthiosemicarbazone: Potential application as an antitumor drug

Article abstract of DOI:10.1002/ejic.200800003

The investigation of the formation and reactivity of Pd and Pt thiosemicarbazone complexes has revealed an unstudied intermediate derived from p-nitroacetophenone 4-methylthiosemicabazone (L1H₂). The L1H ₂ ligand leads to a new complex [Pt(L1)(L1H₂)] that supports the postulated mechanism of how cyclometallation reactions take place. All the newly synthesized complexes, [(Pd(L1)₄], [(Pt(L1) ₄], and [Pt(L1)(L1H₂)] (3), have been characterized and tested against MCF7, SF268, and NCI H460 cell lines. The crystal structure of [Pt(L1)(L1H2)]·dmso is reported. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800003

SHORT COMMUNICATION
DOI: 10.1002/ejic.200800003
Isolation of an Intermediate in the Platination of p-Nitroacetophenone
4-Methylthiosemicarbazone: Potential Application as an Antitumor Drug
Adoración G. Quiroga,*[a] Leticia Cubo,[a] Pablo J. Sanz Miguel,[a] Victoria Moneo,[b]
Amancio Carnero,[b] and Carmen Navarro-Ranninger[a]
Keywords: Platinum / Palladium / Thiosemicarbazones / Antitumor drugs / C–M bonds
The investigation of the formation and reactivity of Pd and
Pt thiosemicarbazone complexes has revealed an unstudied
intermediate derived from p-nitroacetophenone 4-methyl-
thiosemicabazone (L1H2). The L1H2 ligand leads to a new
newly synthesized complexes, [(Pd(L1)4], [(Pt(L1)4], and
[Pt(L1)(L1H2)] (3), have been characterized and tested
against MCF7, SF268, and NCI H460 cell lines. The crystal
structure of [Pt(L1)(L1H2)]·dmso is reported.
complex [Pt(L1)(L1H2)] that supports the postulated mecha- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
nism of how cyclometallation reactions take place. All the
Germany, 2008)
published the first orthometallated tetranuclear complexes
of TSCNs with Pd and Pt as metals.[11] The design of these
complexes was inspired by the idea of a synergism between
the TSCNs and the metal ions. We expected that this syner-
gism would result in new metal drugs with higher activity,
and the results obtained were very promising.[11] The pos-
sibility of modulating the cytotoxic activity by changing the
structure of the complex was also proved.[13,14] Moreover,
the variation in the donor atom type and the substituents
in the TSCN structure provided, to these small molecules,
some structure–activity relationships.[6,15] Our studies on a
broad series of benzaldehyde thiosemicarbazones with dif-
ferent substituents as ligands and PdII and PtII as metal
ions resulted in three different kinds of complexes: (i) tetra-
nuclear complexes, where metallation occurred on the ortho
position of the ligand; (ii) dinuclear but not cyclometallated
complexes, in which the thiosemicarbazone acts as a chelat-
ing NS-bidentate donor (this type of dinuclear complex has
been reported as the first step of the cyclometallation pro-
cess); and (iii) mononuclear complexes, with potential leav-
ing groups that could afford active forms and where no or-
thometallation was observed.[6]
For the present study, we have selected p-nitroaceto-
phenone 4-methylthiosemicabazone (L1H2) as ligand be-
cause it is sterically and electronically different, with regard
to the substituents, from the molecules already studied,[6]
and because of its potential for the rapid generation of a
library of compounds for evaluation and structural activity
studies. The investigation of the stability and modular prop-
erties of the complexes will permit an easy comparison with
the complexes already published.[6] Although TSCNs are
usually expected to afford metallation complexes (C–M
bond formation) via the dinuclear chlorido-bridged com-
plexes, we have observed that formation of other intermedi-
Introduction
Structure-based drug design has as its main objective the
identification of appropriate compounds for biological
evaluation.[1] In anticancer research, the study of new po-
tential drugs and the relationship between their structure
and activity has provided an important insight into how to
improve the current clinical drug cisplatin. Nevertheless,
there are still many problems to be addressed in this field,
such as resistance to cisplatin and the important side effects
that it produces.[2] The preparation of innovative chemical
compounds seems to be the most successful approach to
drug design for cancer treatment.[3]
With regard to innovative compounds, thiosemicarb-
azones (TSCNs) have turned out to be versatile molecules
not only because of their broad profile in pharmacological
activity,[4,5] but also because TSCN can act as a ligand in
coordination chemistry in different ways. It has been dem-
onstrated in previous publications that TSCNs afford a di-
verse variety of compounds with different activities.[6,7]
Organometallic complexes have been used as precatalyst
precursors for C–C coupling reactions[8] and have recently
attracted attention as potential anticancer agents.[9] In fact,
some publications have indicated the potential of metall-
acycles as antineoplastic agents,[10] which leads to possible
alternative modes of cytotoxic action.[11,12] Thiosemicarb-
azones are also suitable ligands for C–M bond formation
with metals such as Pd and Pt. In 1998, our research group
[a] Departamento de Química Inorgánica, Universidad Autónoma
de Madrid,
28049 Madrid, Spain
Fax: +34-4974833
E-mail: adoracion.gomez@uam.es
[b] Experimental Therapeutics Programme, CNIO,
28029 Madrid, Spain
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A. G. Quiroga et al.
SHORT COMMUNICATION
ates is also possible with this particular ligand. Here we
present the synthesis and characterization of palladium(II)
and platinum(II) complexes with L1H2. The final com-
plexes were screened for their cytotoxicity against various
cancer cell lines used at the National Cancer Institute (NCI)
for in vitro screens: MCF-7 (adenocarcinoma, from human
mammary gland), NCI-H460 (large cell lung cancer from
human), and SF268 (central nervous system epithelial can-
cer).
Results and Discussion
Chemistry
The reaction between [Pd(AcO)2] and L1H2 resulted in a
tetranuclear complex [Pd(L1)]4, where p-nitroacetophenone
4-methylthiosemicabazone acts as a tridentate CNS ligand
(L1). Orthoplatination was also achieved by reacting L1H2
with the Pt dinuclear allyl complex [Pt(µ-Cl)(η3-C4H7)]2 in
refluxing acetone. However, instead of the expected tetranu-
Figure 1. ORTEP view of complex [Pt(L1)(LIH2)].
clear complex, or the dinuclear intermediate previously re- 92.76(14)° and 101.86(4)°. Both thiosemicarbazone ligands
ported for this type of complexes,[6] the new mononuclear are nearly planar, with a dihedral angle of 43.78°. The
complex [Pt(L1)(L1H2)] was isolated. This complex con- structure also contains a solvent molecule dmso, which is
tains the TSCN ligand coordinated in two different forms: hydrogen bonded to the monodentate ligand: O(1D)···H–
L1 acts as a tridentate ligand (C-, N-, S-coordinated) and N(4L) 2.832(6) Å. Another intermolecular hydrogen bond
orthometallation takes place through this ligand; L1H2 acts that involves two tridentate ligands contributes to the stabi-
as a monodentate ligand that coordinates through the sul- lization of the structure [N(4)–H···N(3) 3.166(6) Å]. One of
fur atom of the thionic form of the ligand to the forth coor- the most relevant aspects of this mononuclear structure is
dination site of the platinum atom (L1H2: S-coordinated).
the strength of the Pt–S bonds, which, as in the case of
In order to isolate the platinum tetranuclear complex the tetranuclear compound,[11] is probably the reason for
with the general formula [Pt(L1)]4, the reaction mentioned preventing its cleavage.
above was also carried out in refluxing acetone, but with a
The mechanism for the formation of the observed mono-
longer reaction time. Whereas the mononuclear intermedi- nuclear species is not completely clear; however, oligomer-
ate is uniformly obtained as the only product in a few ization by the bridging M–S–M unit of TSCN observed by
hours, the formation of the [Pt(L1)]4 complex needs a other authors[16,17] may be the clue to the activation of the
longer reaction time and careful purification by chromatog- second coordinated ligand molecule.
raphy is required to obtain the final compound. Moreover,
the yield of [Pt(L1)]4 is poor.
Since we first published the orthometallation of thio-
semicarbazones, some interesting work has been done in
The three complexes were characterized by the usual this field, especially with respect to the reactivity of the tet-
techniques: NMR and IR spectroscopy, elemental analysis, ranuclear complexes.[18] These polynuclear complexes are
and mass spectrometry. The structure of the complex very stable in solution, and no substitution of the coordi-
[Pt(L1)(L1H2)]·dmso was also determined by X-ray crystal- nated ligands by a classical Lewis base (nitrogen donor) has
lography. Figure 1 shows a view of the complex, where the been observed, such as a nitrogen-DNA base model. By
one TSCN ligand is coordinated to the platinum atom only using phosphane ligands as Lewis bases, mononuclear
through its sulfur atom, while the other TSCN ligand acts complexes have been isolated by cleavage of the M–S bond
as a tridentate ligand. It is clear that activation of the C–H of the tetranuclear complexes.[16] Moreover, we have not
bond takes place, which leads to orthometallation and Pt– been able to find a single example of complexes charac-
C bond formation.
terized by X-ray diffraction in which the TSCN ligand is
Bond lengths between platinum and the atoms of the tri- coordinated in two different manners to the platinum atom,
dentate ligand are: Pt(1)–S(1) 2.3296(11) Å, Pt(1)–N(2) one molecule metallated (CNS-coordinated) and the other
2.006(4) Å, Pt(1)–C(3) 2.021(4) Å. The bond length Pt(1)– molecule available to be metallated (NS-coordinated).
S(1L) [2.2832(12) Å] for the monodentate ligand was found
Only a platinum mononuclear derivative has been found
to be slightly shorter than Pt(1)–S(1) (tridentate ligand). to be in some way similar; the acetylpyridine thiosemicarb-
The angles around the platinum atom deviate from 90° pre- azone ligands are not equivalent in structure, one being tri-
sumably because of the strain induced by the tridentate li- dentate with NNS donation and the other being mono-
gand. The angles that involve the tridentate L1 ligand are dentate with only the sulfur atom as donor.[19] But no cyclo-
81.65(18)° [N(2)–Pt(1)–C(3)] and 83.70(12)° [N2–Pt1–S1]. metallation takes place because the ligand is a pyridine de-
The angles C(3)–Pt(1)–S(1L) and S(1L)–Pt(1)–S(1) are rivative, and the possible oligomerization of this monomer
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p-Nitroacetophenone 4-Methylthiosemicarbazone Platination
has not been reported either, even though it is possible to formed with TSCN ligands,[6] and also with a broad variety
find in the literature tetranuclear complexes in which the of other organic molecules,[11] have shown a notable antitu-
ligand is NNS-coordinated to the palladium ion.[20] With mor activity as well. Surprisingly, the tetranuclear palla-
respect to the biological activity, antibacterial studies have dium complex with the nitro substituent, [Pd(L1)]4, shows
been performed with this complex, and it has been proved no activity at all against the tumor cell lines checked. The
that B. Cereus bacteria was the most sensitive microorga- platinum derivatives [Pt(L1)]4 and [Pt(L1)(L1H2)] seem to
nism to this drug.[21]
be very active against those tumor cell lines screened.
As the values for the platinum derivatives are in the sub-
micromolar range for some tumor cell lines analyzed, nano-
molar concentrations need to be checked in order to find
the most appropriate drug concentration for therapeutic
purposes. We therefore suggest that the toxic concentration
needed with these compounds is probably lower than that
of complexes published before, and these complexes are
therefore more valuable for therapeutic purposes. They de-
serve to be checked in vivo.
The substitution of the nitro group by the isopropyl
group in the TSCN moiety seems to be an important factor
that influences the structures and cytotoxicity. Further in-
vestigations in this field should be conducted to fully com-
prehend the substituents effects; we are in fact proceeding
in this direction.
Biology
To check the anticancer properties of the new series of
complexes, we screened them for their ability to inhibit the
in vitro growth of a panel of cell lines that include examples
of adenocarcinoma from the human mammary gland
(MCF7), large cell lung cancer from a human (NCI-H460),
central nervous system epithelial cancer (SF268). The
tumor cell lines are also used in the NCI to identify novel
potential anticancer drugs.
The new series of complexes were evaluated, and their
results were compared with those of L1H2 (free ligand) and
the structurally related complex [Pt(L2)]4, where L2 is p-
isopropylbenzaldehyde thiosemicarbazone. This last com-
plex was selected as it was the best candidate as a metallo-
drug found from our previous investigations.[6]
Conclusions
The cytotoxic activity was evaluated after 96 h and ex-
pressed as IC50 (drug concentration that reduces the
number of viable cells by 50%). The formation of the metal
complexes with the TSCN selected, L1H2, produced
metallodrugs with antitumor activity, as shown by the IC50
values presented in Table 1. As mentioned before, the syner-
gism between the TSCNs and the metal ions results in a
high antitumor activity. The complexes [Pt(L1)]4 and
[Pt(L1)(L1H2)] gave lower values of IC50 than the free li-
gand L1H2, which, in fact, did not produce cell death at the
concentrations tested (Table 1). The most noteworthy effect
is the high activity of these drugs at sub-micromolar range,
as has already been mentioned specially for the platinum
derivatives. Within this group of platinum complexes scre-
ened, L1 platinum derivatives are more active than the L2
derivative used as the model. The replacement of the iso-
propyl substituent [–CH(CH3)2] in the phenyl group with a
nitro substituent (–NO2) provides an even better potential
as anticancer drug candidates, as can be observed in the
IC50 values from both tetranuclear platinum derivatives
[Pt(L2)]4 and [Pt(L1)]4 (see Table 1).
In summary, polynuclear TSCNs platinum complexes
have been demonstrated, once more, to be good candidates
as antitumor drugs. Although the tetranuclear molecule
does not undergo ligand substitution by a Lewis base,
TSCN oligomerization may be of crucial importance in its
antitumor activity. Some authors have postulated that weak
M···M interactions are possible between d8 metal ions in
polynuclear complexes, with similar distances between the
metal ions as those found for the TSCN tetranuclear com-
plexes, which suggests that binding or interaction of Lewis
acids and/or donor bases to these metal atoms at the axial
position can be modulated by these M···M interactions.[22]
The mononuclear complexes also showed high antitumor
activity, probably because of certain interactions of the
DNA bases with the metal ion, since the breaking of the
Pt–S bond is not expected. Because M···M interactions can-
not be detected in the mononuclear structure, the availabil-
ity of the metal in the mononuclear complex is probably
higher.
Table 1. IC50 values for Pd and Pt TSCN complexes.
Experimental Section
Drug [µ]
MCF7
NCI-H460
SF268
Materials and Methods: 4-Methyl-3-thiosemicarbazide, 4-nitroace-
tophenone, and other reagents and solvents were obtained from
commercial sources and used without prior purification. [Pt(µ-
Cl)(η3-C4H7)]2 was synthesized as described in the literature.[23] All
compounds synthesized were appropriately characterized by the us-
L1H2
[Pt(L1)(L1H2)] 0.28
Ͼ100
Ͼ100
1.88
Ͼ100
0.17
[Pd(L1)]4
[Pt(L1)]4
[Pt(L2)]4
Ͼ100
0.23
1.15
Ͼ100
2.99
12.58
Ͼ100
0.44
0.97
1
ual techniques. H NMR, 13C NMR, and 2D NMR (HMBC and
HMQC)[24] spectra were recorded on
a Bruker AMX-300
(300 MHz) spectrometer in [D6]dmso solution. The spectra were
double-checked over 72 h, and neither coordination of dmso to the
metal nor decomposition of the sample was detected. Elemental
Platinum complexes have been demonstrated to be better
candidates as antitumor agents because of their lower reac-
tivity,[21] although we have noticed that palladacycles analyses were performed on a Perkin–Elmer 2400 series II micro-
Eur. J. Inorg. Chem. 2008, 1183–1187
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1185

A. G. Quiroga et al.
SHORT COMMUNICATION
analyzer. FAB mass spectra (m/z) were obtained with a V.G.
AUTOSPECT high resolution spectrometer. The experimental part
was achieved with the L-SIMS techniques by using m-NBA. The
relative abundance of the peaks is given without taking into ac-
count the matrix peak (m-NBA).
C40H40N16O8Pt4S4 (1780): calcd. C 26.97, H 2.26, N 12.58, S 7.20;
found C 26.62, H 2.51, N 12.89, S 6.94. IR: νmax 3382, 1517, 1564,
˜
749 cm–1. FAB-MS: m/z = 1780.6 (100) [M]+. 1H NMR ([D6]dmso):
δ = 2.07 (s, 3 H, 6-H), 2.89 (br. s, 3 H, 1-NH), 7.84 (dd, 1J = 1.9 Hz,
1
2J = 8.2 Hz, 1 H, 2-H), 8.48 (d, J = 1.9 Hz, 1 H, 2Ј-H), 7.31 (d,
1J = 1.9 Hz, 1 H, 3-H), 7.70 (s, 1 H, 1-NH) ppm. 13C NMR ([D6]-
dmso): δ = 143.65 (C-1), 116.12 (C-2), 123.15 (C-2Ј), 124.97 (C-3),
152.73 (C-3Ј), 152.69 (C-4), 163.58 (C-5), 12.73 (C-6), 161.90 (C-
7), 32.97 (C-8) ppm.
Synthesis
p-Nitroacetophenone 4-Methylthiosemicarbazone (L1H2): L1H2 was
synthesized following a method previously reported[25] with some
modifications. 4-Methyl-3-thiosemicarbazide (1 g) was previously
dissolved in an aqueous solution of 5% glacial AcOH and added
to an EtOH solution of 4-nitroacetophenone (1.5 g) at 40 °C. The
mixture was stirred at this temperature for 24 h. L1H2 was isolated
by filtration as a yellow solid and recrystallized from methanol.
Yield: 1.4 g (60%). C10H12N4O2S (252.06): calcd. C 47.61, H 4.50,
X-ray Diffraction Studies and Crystal Data: The diffraction data
were collected at 100 K on a Bruker SMART 6K CCD dif-
fractometer (Cu-Kα radiation, λ = 1.54178 Å). The structure was
solved by conventional Patterson methods[26] and subsequent Fou-
rier syntheses and refined by full-matrix least-squares for F2 with
the SHELX programs.[27] The positions of all non-hydrogen atoms
were deduced from difference Fourier maps and refined anisotropi-
cally. Hydrogen atoms were included in calculated positions and
refined with isotropic displacement parameters. Crystal data:
[C20H22N8O4PtS2·C2H6OS], M = 775.79, monoclinic, P21/c, a =
15.3137(3), b = 22.0656(4), c = 7.9268(2) Å, β = 91.5350(10)°, V =
2677.55(10) Å3, Z = 4, Dcalcd. = 1.924 gcm–3, R = 0.0311 (wR =
0.077), GOOF = 0.999, number of reflections = 5037. CCDC-
651025 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
N 22.22, S 12.68; found C 47.21, H 4.59, N 22.33, S 12.60. IR:
1
ν
= 3361, 3203, 1546, 855 cm–1. H NMR ([D6]dmso): δ = 8.37
˜
max
(br. s, 4 H, 2-H and 3-H), 2.34 (s, 3 H, 6-H), 3.11 (s, 3 H, 8-H),
10.53 (br. s, 1 H, 1-NH), 8.62 (s, 1 H, 2-NH) ppm. 13C NMR ([D6]-
dmso): δ = 147.49 (C-1), 123.40 (C-2), 127.77 (C-3), 144.09 (C-4),
145.09 (C-5), 14.08 (C-6), 178.97 (C-7), 31.34 (C-8) ppm.
[Pd(L1)]4: L1H2 (169 mg, 0.67 mmol) in glacial AcOH (10 mL) was
added to palladium(II) acetate (150 mg, 0.67 mmol) under argon
whilst stirring; the mixture was then heated (ca. 40 °C) for 48 h.
The resulting bright red solid was filtered off and washed several
times with water, a 5-% aqueous solution of sodium hydrogen
carbonate, water, and acetone. Yield: 763 mg (85%).
C40H40N16O8Pd4S4 (1425.82): calcd. C 33.52, H 3.08, N 14.89, S
Cell Lines and Culture Conditions
8.52; found C 33.54, H 2.73, N 14.93, S 8.45. IR: ν
= 3388,
˜
max
1517, 1564, 749 cm–1. FAB-MS: m/z = 1427.3 (100) [M + 1]+. H
1
Materials: All cell lines were grown in Dulbecco’s modified Eagles
medium (DMEM) supplemented with 10% fetal calf serum (FCS),
fungizone and penicillin/streptomycin.
1
2
NMR ([D6]dmso): δ = 7.83 (dd, J = 2.0 Hz, J = 8.3 Hz, 1 H, 2-
1
2
H), 8.09 (d, J = 2.0 Hz, 1 H, 2Ј-H); 6.90 (d, J = 8.3 Hz, 1 H, 3-
H), 1.60 (s, 3 H, 6-H), 2.83 (s, 3 H, 1-NH), 7.68 (s, 1 H, 2-NH)
ppm. 13C NMR ([D6]dmso): δ = 143.65 (C-1), 116.12 (C-2), 123.15
(C-2Ј), 124.97 (C-3), 152.73 (C-3Ј), 152.69 (C-4), 163.58 (C-5),
12.73 (C-6), 161.90 (C-7), 32.97 (C-8) ppm.
Cytotoxicity Assessment: The compounds were tested in 96-well
trays. Cells growing in a flask were harvested just before they be-
came confluent, counted using a haemocytometer, and diluted with
media thus adjusting the concentration to the required number of
cells per 0.2 mL (volume for each well). Cells were then seeded in
96-well trays at a density between 1000 and 4000 cells/well, de-
pending on the cell size. Cells were left to plate down and grow for
24 h before adding the drugs.
[Pt(L1)(L1H2)]: L1H2 (136 mg, 0.52 mmol) in acetone (4 mL) was
added to [Pt(µ-Cl)(η3-C4H7)]2 (150 mg, 0.26 mmol) and stirred at
high temperature (70 °C) for 6 h. The resulting solution was con-
centrated by rotary evaporation, which led to the precipitation of
a red solid. The red solid was filtered, recrystallized in acetone/
ether (1:1), and finally characterized as the compound
[Pt(L1)(L1H2)]. Yield: 112 mg (62%). C20H22N8O4PtS2 (697.08):
calcd. C 34.43, H 3.17, N 16.06, S 6.19; found C 34.23, H 3.05, N
The drugs were weighed and diluted with dmso to a concentration
of 10 m. A “mother plate” with serial dilutions was prepared from
this at 200 times the final concentration in the culture. The final
concentration of dmso in the tissue culture media did not exceed
0.5%. The appropriate volume of the compound solution (usually
2 µL) was added automatically (Beckman FX 96 tip) to the media
to make up the final concentration for each drug.
16.00, S 6.01. IR: νmax = 3440, 3262, 3082, 1709, 1601, 1578, 1512,
˜
1
818, 778 cm–1. H NMR ([D6]dmso): δ (L1) = 2.39 (s, 3 H, 6-H),
1
2
3.15 (s, 3 H, 1-NH), 7.87 [dd, J = 2.3 Hz, J = 8.5 Hz, 1 H, 2-H],
1
2
8.34 (d, J = 2.3 Hz, 1 H, 2Ј-H), 6.93 (d, J = 8.5 Hz, 1 H, 3-H),
7.34 (s, 1 H, 2-NH) ppm; δ (L1H2) = 2.50 (s, 3 H, 6-H), 2.90 (s, 3
H, 1-NH), 8.19 (br. s, 4 H, 2-H and 3-H), 10.49 (br. s, 1 H, 1-NH),
8.45 (s, 1 H, 2-NH) ppm. 13C NMR ([D6]dmso): δ (L1) = 143.88
(C-1), 119.72 (C-2), 124.57 (C-2Ј), 126.21 (C-3), 150.00 (C-3Ј),
152.69 (C-4), 156.33 (C-5), 13.33 (C-6), 161.90 (C-7), 32. 67 (C-8)
ppm; δ (L1H2) = 147.69 (C-1), 123.17 (C-2), 127.57 (C-3), 144.89
(C-4), 147.29 (C-5), 13.85 (C-6), 178.76 (C-7), 31.09 (C-8) ppm.
The medium was removed from the cells and replaced with 0.2 mL
of medium dosed with the drug. Each concentration was assayed
in triplicate. Two sets of control wells were left on each plate, which
contained either medium without the drug or medium with the
same concentration of dmso. A third control set was used in which
the cells were untreated just before the addition of the drugs (seed-
ing control, number of cells starting the culture).
[Pt(L1)]4: An acetone solution (4 mL) of L1H2 (136 mg,
0.52 mmol) was added to [Pt(µ-Cl)(η3-C4H7)]2 (150 mg, 0.26 mmol)
and stirred at high temperature (70 °C) for 10 d. The solvent was
removed from the filtrate solution by rotary evaporation. The resi-
due was dispersed in Celite and purified by chromatography on a
silica gel column. The products were eluted in the following
order: the starting material first (CH2Cl2) followed by the tetra-
The cells were exposed to the drugs for 96 h and then washed twice
with phosphate-buffered saline solution before being fixed with
10% glutaraldehyde. The cells were washed twice and fixed with
crystal violet (0.5%) for 30 min. They were then washed extensively
and solubilized with 15% acetic acid, and the absorbance was mea-
nuclear complex (CH2Cl2/EtOH, 100:1). Yield: 285 mg (62%). sured at 595 nm.
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p-Nitroacetophenone 4-Methylthiosemicarbazone Platination
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Published Online: February 18, 2008
Eur. J. Inorg. Chem. 2008, 1183–1187
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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