Biologically Active Platinum Complexes Containing 8-Thiotheophylline and 8-(Methylthio)theophylline

Article abstract of DOI:10.1021/ic034868c

Complexes [Pt(μ-N,S-8-TT)(PPh₃)₂]₂ (1), [Pt(μ-S,N-8-TT)(PTA)₂]₂ (2), [Pt(8-TTH)(terpy)]BF ₄ (3), cis-[PtCl(8-MTT)(PPh₃)₂] (4), cis-[Pt(8-MTT)₂(PPh₃)₂] (5), cis-[Pt(8-MTT)(8-TTH)(PPh₃)₂] (6), cis-[PtCl(8-MTT)(PTA)₂] (7), cis-[Pt(8-MTT)₂(PTA) ₂] (8), and trans-[Pt(8-MTT)₂(py)₂] (9) (8-TTH₂ = 8-thiotheophylline; 8-MTTH: = 8-(methylthio)theophylline; PTA = 1,3,5-triaza-7-phosphaadamantane) are presented and studied by IR and multinuclear (¹H, ³¹P{¹H}) NMR spectroscopy. The solid-state structure of 4 and 9 has been authenticated by X-ray crystallography. Growth inhibition of the cancer cells T2 and SKOV3 induced by the above new thiopurine platinum complexes has been investigated. The activity shown by complexes 4 and 9 was comparable with cisplatin on T2. Remarkably, 4 and 9 displayed also a valuable activity on cisplatin-resistant SKOV3 cancer cells.

Full text of DOI:10.1021/ic034868c

Inorg. Chem. 2004, 43, 905−913
Biologically Active Platinum Complexes Containing 8-Thiotheophylline
and 8-(Methylthio)theophylline
,†
,‡
A. Romerosa,* P. Bergamini,* V. Bertolasi,‡ A. Canella,§ M. Cattabriga,‡ R. Gavioli,§ S. Man˜as,†
N. Mantovani,‡ and L. Pellacani‡
AÄ rea de Qu´ımica Inorga´nica, Facultad de Ciencias Experimentales, UniVersidad de Almer´ıa,
04071 Almer´ıa, Spain, Dipartimento di Chimica dell’UniVersita` di Ferrara, Via L. Borsari 46,
44100 Ferrara, Italy, and Dipartimento di Biochimica e Biologia Molecolare dell’UniVersita` di
Ferrara, Via L. Borsari 46, 44100 Ferrara, Italy
Received July 23, 2003
Complexes [Pt(µ-N,S-8-TT)(PPh3)2]2 (1), [Pt(µ-S,N-8-TT)(PTA)2]2 (2), [Pt(8-TTH)(terpy)]BF (3), cis-[PtCl(8-MTT)-
4
(PPh3)2] (4), cis-[Pt(8-MTT)2(PPh3)2] (5), cis-[Pt(8-MTT)(8-TTH)(PPh3)2] (6), cis-[PtCl(8-MTT)(PTA)2] (7), cis-[Pt(8-
MTT)2(PTA)2] (8), and trans-[Pt(8-MTT)2(py)2] (9) (8-TTH ) 8-thiotheophylline; 8-MTTH ) 8-(methylthio)theophylline;
2
PTA ) 1,3,5-triaza-7-phosphaadamantane) are presented and studied by IR and multinuclear (1H, 31P{1H}) NMR
spectroscopy. The solid-state structure of 4 and 9 has been authenticated by X-ray crystallography. Growth inhibition
of the cancer cells T2 and SKOV3 induced by the above new thiopurine platinum complexes has been investigated.
The activity shown by complexes 4 and 9 was comparable with cisplatin on T2. Remarkably, 4 and 9 displayed
also a valuable activity on cisplatin-resistant SKOV3 cancer cells.
Introduction
spectrum of activity and high toxicity; moreover, some cancer
cells develop resistance to the drug. A large number of
modifications of the basic structure cis-[PtX2L2] (X )
halides; L ) nitrogen, sulfur, phosphorus, etc., neutral ligand)
have been made in the attempt to overcome these clinical
limitations.1 These modifications have allowed one to reduce
the toxicity and to alter the modes of delivery, but a very
small number of analogues of cisplatin has been able to
surpass the parent drug in efficacy and convenience.1
The success of cisplatin and related platinum complexes
as anticancer agents has stimulated a diffuse search for other
active transition metal anticancer complexes.1 Cisplatin is a
highly effective antitumor agent used, in particular, to treat
genitourinary and head and neck cancers.1 Despite its
remarkable pharmacological activity, the drug cisplatin
presents heavy disadvantages such as a relatively limited
* To whom correspondence should be addressed. E-mail: romerosa@
ual.es (A.R.).
A few natural purines are building blocks of nucleic acids.
Methylxanthines such as caffeine, theophylline, and theo-
bromine are voluptuary substances with a variety of mild
pharmacological actions (stimulant, cardiotonic, diuretic);
some thiopurines (e.g. mercaptopurine, 6-thioguanine) are
currently exploited in the clinical practice for the treatment
of leukaemia, and more functionalized purines such as
acyclovir, vidarabine, and didanosine are widely used for
their antiviral activity including anti-HIV action.2,3 It is
reasonable to forecast that the binding of platinum to
thiopurines could enhance the pharmacological activity of
† Universidad de Almer´ıa.
‡ Dipartimento di Chimica dell’Universita` di Ferrara.
§ Dipartimento di Biochimica e Biologia Molecolare dell’ Universita` di
Ferrara.
(1) (a) Metal Ions in Biological Systems; Sigel A., Sigel H., Eds.; Marcel
Dekker: New York, 1996; Vol. 32. (b) Cohen, S. M.; Lippard, S. J.
Prog. Nucleic Acid Res. Mol. Biol. 2001, 67, 93. (c) Schneider, A.
G.; Schmalle, H. W.; Arod, F.; Dubler, E. J. Inorg. Biochem. 2002,
89, 227. (d) Colonna, G.; Di Masi, N. G.; Marzilli, L. G.; Natile, G.
Inorg. Chem. 2003, 42, 997. (e) Sullivan, S. T.; Ciccarese, A.; Fanizzi,
F. P.; Marzilli, L. G. Inorg. Chem. 2000, 39, 836. (f) Dubler, E.;
Schmalle, H. W.; Arod, F.; Schneider, A. Acta Crystallogr., Sect. C
2002, 58, m111. (g) Monjardet-Bas, V.; Elizondo-Riojas, M. A.;
Chottard, J. C.; Kozelka, J. Angew. Chem., Int. Ed. 2002, 41, 2998.
(h) Sigel, R. K. O.; Freisinger, E.; Abbate, M.; Lippert, B. Inorg. Chim.
Acta 2002, 339, 355. (i) Roitzsch, M.; Rother, I. B.; Willermann, M.;
Erxleben, A.; Costisella, B.; Lippert, B. Inorg. Chem. 2002, 41, 5946.
(j) Lueth, M. S.; Freisinger, E.; Glahe, F.; Mueller, J.; Lippert, B.
Inorg. Chem. 1998, 37, 3195. (k) Jansen, B. A. J.; Perez, J. M.; Pizarro,
A.; Alonso, C.; Reedijk, J.; Navarro-Ranninger, C. J. Inorg. Biochem.
2001, 85, 229.
(2) Gilman, A.; Hardman, J.; Limbird, L. The Pharmacological Basis of
Therapeutics, 10th ed.; Goodman, A., Gilmans, B., Eds.; McGraw-
Hill Press: New York, 2001.
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Anderson, K. S.; Johnson, K. A. J. Biol. Chem. 2001, 276, 40847.
10.1021/ic034868c CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/13/2004
Inorganic Chemistry, Vol. 43, No. 3, 2004 905

Romerosa et al.
complexes cis-[PtCl2(PPh3)2],8 cis-[PtCl2(PTA)2],9 [PtOH(terpy)]-
BF4,10 and trans-[PtCl2py2]11 have been prepared by following the
procedure described by literature methods. All the other chemicals
and solvents were used as purchased (reagent grade). Elemental
analyses (C, H, N, S) were performed using a Carlo Erba model
EA1110 instrument. FT-IR spectra were recorded on a Nicolet 510P
FT-IR instrument (4000-200 cm-1) using CsI or KBr. NMR spectra
were recorded on a Bruker AM spectrometer 200 MHz for 1H NMR
(TMS internal reference) and 81.15 MHz for 31P{1H} NMR
(H3PO4 85% external reference).
Chart 1
the two species through a synergic action and could affect
the metal distribution in the body exploiting a ligand “carrier
effect”.
The molecular weights were measured by mass spectroscopy
using a Maldi Toff Hewlett-Packard G2025A LD/TOFF mass
spectrometer with R-cyano-4-hydroxycynnamic acid as matrix for
complexes 1 and 2, while that for 3 was determined by a Hewlett-
Packard MS Engine HP 5989 A, equipped with a FAB source, using
3-nitrobenzyl alcohol as matrix.
Another item to consider in the design of new platinum-
based drugs is the solubility both in the body fluids,
constituted essentially by water, and in the cell membrane,
a hydrophobic system. Therefore, the adequate choice of
ligands to be bonded to platinum appears crucial not only
for improving the activity but also for modulating the
solubility to allow both the drug migration through the body
and the reaching of DNA, the drug target, inside the cell
nucleus.
In this paper we present the synthesis and characterization
of new platinum complexes containing thiopurine molecules
together with ligands modulating the solubility of the
complexes in water and in a lipophilic medium. These
complexes constitute a new family of compounds suitable
to undergo citotoxicity tests and to be used as models for
clarifying the interaction between platinum and biomolecules
containing purines.
The selected purine molecules were 8-thiotheophylline (8-
TTH2) and 8-(methylthio)theophylline (8-MTTH) (Chart 1).
For 8-TTH2, both N7H and SH can be deprotonated leading
to the formation of a bianionic bidentate ligand. The 8-MTTH
coordination chemistry is also expected to be rich and
versatile due to the presence of two potentially coordinating
functions: the hard N7 and the soft S-Me site. Moreover
the relative position of these two sites should allow bidentate
coordination in a bridging (M-N-C-S-M) and/or chelat-
ing mode (N-C-S-M). It has also been reported that
palladium complexes with 8-MTTH provide a pathway to
C8 coordination to palladium by elimination of the S-CH3
group.4
We tried to modulate the complexes solubility by choosing
as ancillary ligands the lipophilic phosphane PPh3 or,
alternatively, the water-soluble phosphane PTA (PTA )
1,3,5-triaza-7-phosphaadamantane) both providing a NMR-
active label that allowed us to study the reactions by 31P-
{1H} NMR spectroscopy. Finally, pyridine and terpyridine
were also used to understand how a non-phosphorate ligand
affects the chemical and biological properties of the thio-
purine-platinum complexes.
Synthesis of [Pt(µ-N,S-8-TT)(PPh3)2]2 (1). The ligand 8-TTH2
(0.013 g, 0.06 mmol) was dissolved in 1.2 mL of aqueous NaOH
(0.1 M), and the solution was added to a solution of cis-[PtCl2-
(PPh3)2] (0.05 g, 0.06 mmol) in 10 mL of CH2Cl2. The double-
layered mixture was stirred at room temperature for 1 h, and
afterward the organic phase was separated, washed three times with
water, and dried over Na2SO4. The solvent was removed under
vacuum to leave the complex as a pale yellow powder.
Yield: 0.051 g, 88%. Anal. Found: C, 54.93; H, 3.85; N, 5.60;
S, 3.03. Calcd for C86H72N8O4P4Pt2S2: C, 55.49; H, 3.87; N, 6.02;
S, 3.45. MW by MS Maldi Toff: 1860 Da. IR (KBr, cm-1) selected
data: ν(C6dO) 1686 (s); ν(C2dO) 1643 (s); ν(CdC) + ν(CdN)
1
1531 (s). H NMR (CDCl3; δ (ppm)): 3.0 (s, N1-CH3, 3H), 3.2
(s, N3-CH3, 3H), 6.9-8.2 (m, Ph, 30H). 31P{1H} NMR (CDCl3;
δ (ppm)): 7.9 (d, PA, 2JP P ) 20.7 Hz, 1JPtP ) 3427 Hz), 17.5 (d,
B
A
A
2
1
PB, JP ) 20.7 Hz, JPtP ) 3035 Hz).
APB
B
Synthesis of [Pt(µ-S,N-8-TT)(PTA)2]2 (2). The biphase system
obtained by adding 8-TTH2 (0.017 g, 0.08 mmol), 1.6 mL of NaOH
(0.1 M), cis-[PtCl2(PTA)2] (0.046 g, 0.08 mmol), and 8 mL of CH2-
Cl2 was stirred at room temperature for 1 h. The pale yellow water
solution was separated out and the organic phase evaporated under
vacuum. The solid product was extracted with 15 mL of CHCl3
for 30 min and then the insoluble residue filtered out. The pale
yellow product was obtained by removing the solvent and dried
on P2O5.
Yield: 0.052 g, 90%. Anal. Found: C, 31.02; H, 4.37; N, 18.97;
S, 4.11. Calcd for C38H60N20O4P4Pt2S2: C, 31.71; H, 4.17; N, 19.46;
S, 4.45. MW by MS Maldi Toff: 1438 Da. IR (KBr, cm-1) selected
data: ν(C6dO) 1683 (s); ν(C2dO) 1635 (s); ν(CdC) + ν(CdN)
1530, 1509 (s). 1H NMR (CDCl3; δ (ppm)): 3.0 (s, N1-CH3, 6H),
3.4 (s, N3-CH3, 6H), 4.0-4.5 (m, PTA, 48H). 31P{1H} NMR
2
1
(CDCl3; δ (ppm)): -57.1 (d, PA, JP P ) 22.8 Hz, JPtP ) 2649
B
A
1
A
2
Hz), -72.6 (d, PB, JP ) 22.8 Hz, JPtP ) 3028 Hz).
APB
B
Synthesis of [Pt(8-TTH)(terpy)]BF4 (3). Stirring a suspension
of 8-TTH2 (0.038 g, 0.18 mmol) and [PtOH(terpy)]BF4 (0.096 g,
0.18 mmol) in 40 mL of MeOH at room temperature for 3 h
produced a purple mixture. The purple solid residue was isolated
by filtration and then dried over P2O5.
Experimental Section
(6) Merz, K. W.; Sthal, P. H. Arzneim.-Forsch. 1965, 15, 10.
(7) Daigle, D. J.; Decuir, T. J.; Robertson, J. B.; Darensbourg, D. J. Inorg.
Synth. 1998, 32, 40.
(8) Bailar, J. C.; Itatani, H. Inorg. Chem. 1965, 2, 1618.
(9) Darensbourg, D. J.; Decuir, T. J.; Stafford, N. W.; Robertson, J. B.;
Draper, J. D.; Reibenspies, J. H. Inorg. Chem. 1997, 36, 4218.
(10) Aldrige, T. K.; Stasy, E. M.; McMillin, D. R. Inorg. Chem. 1994, 33,
722.
Ligands 8-thiotheophylline (8-TTH2), 8-(methylthio)theophylline
(8-MTTH),5,6 and 1,3,5-triaza-7-phosphaadamantane (PTA)7 and
(4) Romerosa, A.; Suarez-Varela, J.; Hidalgo, M. A.; Avila-Roso´n, J. C.;
Colacio, E. Inorg. Chem. 1997, 36, 3784.
(5) Romerosa, A.; Lo´pez-Magan˜a, C.; Saoud, M.; Man˜as, S.; Colacio,
E.; Suarez-Varela, J. Inorg. Chim. Acta 2000, 307, 125.
(11) Haake, P.; Mastin, S. H. J. Am. Chem. Soc. 1971, 93, 6823.
906 Inorganic Chemistry, Vol. 43, No. 3, 2004

Biologically ActiWe Platinum Complexes
Yield: 0.113 g, 86%. Anal. Found: C, 36.11; H, 2.34; N, 13.02;
S, 4.25. Calcd for C22H18BF4N7O2PtS: C, 36.34; H, 2.48; N, 13.49;
S, 4.40. IR (KBr, cm-1) selected data: ν(N-H) 2500-3300 3135;
ν(C6dO) 1694 (s); ν(C2dO) 1660 (s); ν(CdC) + ν(CdN) 1602
(m), 1541 (s). 1H NMR (CD3NO2; δ (ppm)): 3.1(s, N1-CH3, 3H),
3.6 (s, N3-CH3, 3H), 8.0-9.0 (m, Ph, 9H), 9.0 (d, H6, 3JPtH ) 41
organic fractions were dried on Na2SO4, and the solvent was
removed under vacuum. The yellow powder obtained was dried
on P2O5.
Yield: 0.093 g, 70%. Anal. Found: C, 30.73; H, 4.33; N, 18.32;
S, 4.08. Calcd for C20H33ClN10O2 P2PtS: C, 31.21; H, 4.29; N,
18.19; S, 4.16. IR (KBr, cm-1) selected data: ν(C6dO) 1684 (s);
3
1
Hz, JHH ) 9 Hz, 2H), 13 (s, N7H, 1H, DMSO-d6). FAB: 639
(m/z).
ν(C2dO) 1653 (s); ν(CdC) + ν(CdN) 1580 (m), 1526 (s). H
NMR (CDCl3; δ (ppm)): 2.7 (s, S-CH3, 3H), 3.4 (s, N1-CH3,
3H), 3.55 (s, N3-CH3, 3H), 3.9-4.6 (m, PTA, 24H). 31P{1H} NMR
Synthesis of cis-[PtCl(8-MTT)(PPh3)2] (4). The ligand 8-MTTH
(0.113 g, 0.5 mmol) was dissolved in 5 mL of aqueous NaOH (0.1
M), and the resulting solution was mixed with 60 mL of CH2Cl2
containing cis-[PtCl2(PPh3)2] (0.394 g, 0.5 mmol). The double-
layered system was refluxed for 4 h, and the yellow organic phase
was separated and dried over Na2SO4. A yellow powder was
obtained by removing the solvent under reduced pressure.
Crystals for X-ray determination of complex 4 were obtained
by recrystallization of the crude product from CHCl3 and Et2O.
Yield: 0.48 g, 97%. Anal. Found: C, 53.76; H, 3.80; N, 5.75;
S, 3.24. Calcd for C44H39ClN4O2P2PtS: C, 53.85; H, 3.98; N, 5.71;
S, 3.26. IR (CsI, cm-1) selected data: ν(C6dO) 1688 (s); ν(C2d
O) 1649 (s); ν(CdC) + ν(CdN) 1584 (m), 1526 (s), ν(PtCl) 311.
1H NMR (CDCl3; δ (ppm)): 2.7 (s, S-CH3, 3H), 3.3 (s, N1-
CH3, 3H), 3.4 (s, N3-CH3, 3H), 7.0-8.0 (m, Ph, 30H). 31P{1H}
NMR (CDCl3; δ (ppm)): 8.1 (d, PA, 2JP P ) 20 Hz, 1JPtP ) 3233
2
1
(CDCl3; δ (ppm)): -69.5 (d, PA, JP P ) 20.5 Hz, JPtP ) 2962
B
A
1
A
2
Hz), -58.4 (d, PB, JP ) 20.5 Hz, JPtP ) 3369 Hz).
APB
B
Synthesis of cis-[Pt(8-MTT)2(PTA)2] (8). The solution obtained
by dissolving 8-MTTH (0.077 g, 0.34 mmol) in 3.4 mL of an
aqueous solution of NaOH (0.1 M) was added to a suspension of
cis-[PtCl2(PTA)2] (0.099 g, 0.17 mmol) in 25 mL of CH2Cl2. After
1 h at refluxing temperature a colorless biphasic system was
obtained. The aqueous phase was separated and reextracted with
CH2Cl2 (3 × 10 mL). The organic fractions were collected and
dried on Na2SO4. Evaporation of the solvent gave a pale yellow
powder which was dried on P2O5.
Yield: 0.132 g, 81%. Anal. Found: C, 34.89; H, 4.97; N, 19.86;
S, 6.93. Calcd for C28H42N14O4P2PtS2: C, 35.05; H, 4.38; N, 20.43;
S, 6.67. IR (KBr, cm-1) selected data: ν(C6dO) 1687 (s); ν(C2d
1
B
A
A
O) 1650 (s); ν(CdC) + ν(CdN) 1586 (m), 1522 (s). H NMR
2
1
Hz), 13.7 (d, PB, JP ) 20 Hz, JPtP ) 3836 Hz).
APB
B
(CDCl3; δ (ppm)): 2.4 (s, S-CH3, 6H), 3.5 (s, N1-CH3, 6H), 3.5
2
Synthesis of cis-[Pt(8-MTT)2(PPh3)2] (5). Into a bilayered
mixture containing 2.5 mL of NaOH (0.1 M) and 15 mL of CH2-
Cl2 was introduced 8-MTTH (0.057 g, 0.25 mmol) and cis-[PtCl2-
(PPh3)2] (0.100 g, 0.125 mmol). After 24 h at refluxing temperature
the organic phase was separated and dried over Na2SO4. Under
vacuum the organic solvent was removed leaving a clear-yellow
powder.
(s, N3-CH3, 6H), 4.1-4.3 (two dd, CHAHB-P, JH
) 15 Hz,
AHB
2JHP ) 2 Hz, 12H), 4.4-4.5 (two broad d, CHAHB-N, JH
)
)
2
AHB
13.5 Hz, 12H). 31P{1H} NMR (CDCl3; δ (ppm)): -68.8 (s, 1JPtP
3066 Hz).
Synthesis of trans-[Pt(8-MTT)2(py)2] (9). Into a light-protected
vessel, AgBF4 (0.17 g, 0.87 mmol) and trans-[PtCl2(Py)2] (0.15 g,
0.35 mmol) in 25 mL of acetone were stirred for 24 h. After AgCl
removing by filtration, a solution of 8-MTTH (0.16 g, 0.70 mmol)
in 7 mL of NaOH (0.1 M) was added producing a white suspension
which was stirred at room temperature for 4 h. The precipitated
product was separated out by centrifugation, washed with H2O
(2 × 3 mL), and dried over P2O5.
Yield: 0.13 g, 89%. Anal. Found: C, 53.07; H, 4.09; N, 9.05;
S, 5.56. Calcd for C52H48N8O4P2PtS2: C, 53.37; H, 4.13; N, 9.57;
S, 5.48. IR (CsI, cm-1) selected data: ν(C6dO) 1690 (s); ν(C2d
1
O) 1648 (s); ν(CdC) + ν(CdN) 1586 (m), 1525 (s). H NMR
(CDCl3; δ (ppm)): 2.2 (s, S-CH3, 3H), 3.25 (s, N1-CH3, 3H),
3.35 (s, N3-CH3, 3H), 6.4-7.9 (m, Ph, 15H). 31P{1H} NMR
Yield: 0.17 g, 60%. Anal. Found: C, 38.20; H, 3.19; N, 17.31;
S, 8.45. Calcd for C26H28N10O4PtS2: C, 38.81; H, 3.48; N, 17.42;
S, 7.96. IR (KBr, cm-1) selected data: ν(C6dO) 1694 (s); ν(C2dO)
1657 (s); ν(CdC) + ν(CdN) 1586 (m), 1526 (s). 1H NMR (CDCl3;
δ (ppm)): 2.6 (s, S-CH3, 6H), 3.4 (s, N1-CH3, 6H), 3.5 (s, N3-
1
(CDCl3; δ (ppm)): -0.75 (s, JPtP ) 3479 Hz).
Synthesis of cis-[Pt(8-MTT)(8-TTH)(PPh3)2] (6). 8-TTH2
(0.022 g, 0.10 mmol) was dissolved in 1 mL of NaOH (0.1 M),
and the solution was added to a solution of 4 (0.1 g, 0.10 mmol)
in 8 mL of CH2Cl2. The mixture was refluxed for 3 days, the organic
layer appearing bright yellow. A further 5 mL of CH2Cl2 was added
to dissolve a small amount of solid product in the interphase; the
organic phase was then separated and dried on Na2SO4. The filtered
organic phase was evaporated to leave the product as a yellow
powder.
3
CH3, 6H), 7.2 (m, 4 H2), 7.6 (t, 2 H3, JH H ) 7.4 Hz), 9.0 (d, 4
2
3
3
3
H1, JH H ) 5.2 Hz; JPtH ) 34 Hz).
2
1
1
X-ray Structure Determinations. Data for compounds 4 and 9
were collected on a Nonius Kappa CCD diffractometer using
graphite-monochromated Mo KR radiation (λ ) 0.7107 Å) at room
temperature (295 K). The data were corrected for Lorentz-
polarization and absorption (SORTAV)12 effects. The crystal
parameters and other experimental details of the data collections
are summarized in Table 1. The structures were solved by direct
methods (SIR92)13 and refined by full-matrix least-squares methods
with all non-hydrogen atoms anisotropic. The carbon atom of the
solvent molecule (CHCl3) for 4 was found to be disordered over
two sites and refined isotropically, each with an occupancy of 0.5.
All hydrogens were included in calculated positions and refined
using a riding model. Selected bond distances and angles are shown
in Table 2. All calculations were performed using SHELXL-9714
and PARST.15
Yield: 0.11 g, 90%. Anal. Found: C, 52.01; H, 4.03; N, 8.84;
S, 5.81. Calcd for C51H46N8O4 P2PtS2: C, 52.93; H, 3.98; N, 9.69;
S, 5.53. IR (KBr, cm-1) selected data: ν(N-H) 3050; ν(C6dO)
1692 (s); ν(C2dO) 1653 (s); ν(CdC) + ν(CdN) 1582 (m), 1531
1
(s). H NMR (CDCl3; δ (ppm)): 2.7 (s, SCH3, 3H), 3.3 (s, N1-
CH3, 8-TT- + 8-MTT-, 6H), 3.4 and 3.5 (2 s, each 3H; 8-TT-
+
8-MTT-, N3-CH3), 7.0-8.0 (m, Ph, 30H), 11.7 (s, N7H, 1H).
2
31P{1H} NMR (CDCl3; δ (ppm)): 18.9 (d, PA, JP P ) 18 Hz,
B
A
1JPtP ) 3127 Hz), 5.1 (d, PB, JP ) 18 Hz, JPtP ) 3250 Hz).
2
1
APB
A
B
Synthesis of cis-[PtCl(8-MTT)(PTA)2] (7). The solution ob-
tained by dissolving 8-MTTH (0.039 g, 0.17 mmol) in 1.7 mL of
NaOH (0.1 M) was added to a suspension of cis-[PtCl2(PTA)2]
(0.099 g, 0.17 mmol) in 15 mL of CH2Cl2. The biphase system
obtained was stirred at room temperature for 1 h. The aqueous phase
was separated and reextracted with CH2Cl2 (3 × 10 mL). The
(12) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33.
(13) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
Inorganic Chemistry, Vol. 43, No. 3, 2004 907

Romerosa et al.
Chart 2
Table 1. Crystallographic Data
4
9
formula
Mr
space group
cryst system
a/Å
PtC44H39ClN4O2P2S‚CHCl3 PtC26H28N10O4S2
1099.70
P21/c
803.782
P21/a
monoclinic
9.5816(1)
27.2650(6)
17.6174(4)
90
monoclinic
8.6483(2)
16.5361(4)
10.8846(3)
90
b/Å
c/Å
R/deg
â/deg
99.512(1)
90
106.781(1)
90
γ/deg
V/Å3
4539.1(2)
4
1490.48(7)
2
Z
Stock solutions (10 mM) of the Pt(II) complexes were made in
DMSO and diluted in AIM-V medium to give final concentration
of 2, 10, and 50 µM.
Dc/g cm-3
F(000)
µ(Mo KR)/cm-1
measd reflcns
unique reflcns
Rint
obsd reflcns [I g 2σ(I)] 8584
θmin-θmax/°
hkl ranges
1.609
2184
34.85
28 728
10 538
0.045
1.791
792
48.99
24 532
4343
Cisplatin was employed as a control for the cisplatin-sensitive
T2 cell line and for the cisplatin-resistant SKOV3. Untreated cells
were placed in every plate as a negative control. The cells were
exposed to the compounds for 72 h, and then 25 µL of a
4,5-(dimethylthiozol-2-yl)-2,5-diphenyltetrazolium bromide solution
(12 mM) was added. After 2 h of incubation, 100 µL of lysing
buffer (50% DMF + 20% SDS, pH 4.7) were added to convert
4,5-(dimethylthiozol-2-yl)-2,5-diphenyltetrazolium bromide into a
brown colored formazane. After an additional 18 h the solution
absorbance, proportional to the number of live cells, was measured
by spectrophotometer and converted in % of growth inhibition.
0.052
3071
3.3-28
3.5-30
-12, 12; -23, 23;
-15, 14
0.0396
0.0895
199
-12, 12; -36, 36;
-23, 22
0.0420
R(F2) (obsd reflcns)
wR(F2) (all reflcns)
no. of variables
0.0941
534
1.084
-1.08, 1.80
goodness of fit
1.182
-1.28, 0.97
F
min, Fmax/e Å-3
Table 2. Selected Bond Distances (Å) and Angles (deg)
4
9
Results and Discussion
Pt1-P1
Pt1-P2
Pt1-N7
Pt1-Cl1
Pt1-N10
N7-C8
N7-C5
2.257(1)
2.272(1)
2.054(4)
2.337(1)
Reactivity of 8-TTH2 with cis-[PtCl2(PPh3)2], cis-[PtCl2-
(PTA)2], and [Pt(OH)(terpy)]BF4. The reaction of 8-TTH2
with 2 equiv of NaOH and 1 equiv of cis-[PtCl2(PPh3)2] in
the biphasic CH2Cl2/H2O system gave the pale yellow
complex [Pt(µ-N,S-8-TT)(PPh3)2]2 (1). The IR spectrum
showed the characteristic absorptions of PPh3 and of the
purine ligands [ν(C6dO) 1686 (s); ν(C2dO) 1643 (s)].
These observations were also supported by 1H NMR
spectroscopy: no resonances for N7-H were observed, while
the signals integrals for PPh3 and purine were consistent with
a 2:1 ratio. The elemental analysis was in agreement with a
1:1:2 Pt/8-TT2-/PPh3 molar ratio. The 31P{1H} NMR pattern
presented two doublets (2JP P ) 20.7 Hz) at 7.9 (PA) and
2.026(4)
2.009(4)
1.336(7)
1.394(6)
1.348(6)
1.374(7)
P1-Pt1-P2
P1-Pt1-N7
P1-Pt1-Cl1
P2-Pt1-N7
P2-Pt1-Cl1
N7-Pt1-Cl1
N7-Pt1-N10
N7-Pt1-N10′
C5-N7-C8
99.1(1)
90.6(1)
174.9(1)
170.4(1)
86.0(5)
84.4(1)
88.9(2)
91.1(2)
104.4(4)
104.0(4)
A
B
17.5 ppm (PB) with satellites due to the coupling with the
Crystallographic data (excluding structure factors) for the
structures in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publications nos.
CCDC 209304 and 209305. Copies of the data can be obtained,
free of charge, on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, U.K. (fax +44 1223 336033 or e-mail deposit@
ccdc.cam.ac.uk).
Growth Inhibition Assays. Cell growth inhibition assays were
carried out using the cisplatin-sensitive T2 human cell line and the
cisplatin-resistant SKOV3 cell line. T2 is a cell hybrid obtained
by the fusion of the human lymphoblastoid line 174 (B lymphocyte
transformed by the Epstein-Barr virus) with the CEM human
cancer line (leukemia T) while SKOV3 is derived from an human
ovarian tumor.
Pt atom. The platinum-phosphorus coupling constants
1
(1JPtP ) 3427 Hz; JPtP ) 3035 Hz) seem to indicate that
A
B
PA is trans to nitrogen and PB is trans to sulfur.16
It can be concluded that in complex 1 platinum must be
coordinated to two magnetically different PPh3 ligands and
one 8-TT2- anion bonded to the metal through both the S
atom and the imidazole N7 atom. This formulation is
consistent with two possible structures (Chart 2): (i) a
mononuclear complex where a 8-TT2- acts as a N7-S
bidentate chelating ligand; (ii) a binuclear complex containing
two 8-TT2- anions bridging to two different Pt atoms by
their N7 and S. Although the first hypothesis seems
disfavored because the four member ring strain would
destabilized the product, it cannot be excluded a priori; in
fact a few complexes containing NCSM rings are known.17
The cells were seeded in triplicate in 96-well trays at a density
of 50 × 103 in 50 µL of AIM-V medium for T2 and 25 × 103 in
50 µL of AIM-V medium for SKOV3.
(14) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refine-
ment; University of Gottingen: Gottingen, Germany, 1997.
(15) Nardelli, M. J. Appl. Crystallogr. 1995, 28, 659.
(16) Appleton, T. G.; Bennett, M. A. Inorg. Chem. 1978, 17, 738.
(17) Wang, S.; Staples, R. J.; Fackler J. R., J. P. Acta Crystallogr. 1994,
C50, 889.
908 Inorganic Chemistry, Vol. 43, No. 3, 2004

Biologically ActiWe Platinum Complexes
Chart 3
Chart 4
To elucidate the right structure, a molecular weight measure-
ment was performed. The data obtained by Maldi Toff MS
(MW ) 1860 Da) confirmed that complex 1 has the binuclear
structure ii.
the N3-CH3 signal moves downfield in the series 1, 2, 3
(1, 3.2 ppm; 2, 3.4 ppm; 3, 3.6 ppm) showing that the
electronic distribution inside the coordinated thiopurine is
affected by the nonpurinic ligand.
Reaction of 8-MTTH with cis-[PtCl2(PPh3)2], cis-[PtCl2-
(PTA)2], and trans-[PtCl2(py)2]. Synthesis and Charac-
terization of the Heteropurine Complex cis-[Pt(8-MTT)(8-
TTH)(PPh3)2] (6). When the ligand 8-MTTH was treated
with NaOH and cis-[PtCl2(PPh3)2] in molar ratios 1:1:1 and
2:2:1, the new complexes cis-[PtCl(8-MTT)(PPh3)2] (4) and
cis-[Pt(8-MTT)2(PPh3)2] (5) were formed, respectively. The
reactions were performed either in a water/CH2Cl2 double-
phase system or in 95% EtOH.
In a similar way, the reaction of 8-TTH2 with NaOH and
cis-[PtCl2(PTA)2] in the biphasic system H2O/CH2Cl2 at room
temperature leads to [Pt(µ-S,N-8-TT)(PTA)2]2 (2), recovered
as a pale yellow powder. This water-soluble complex showed
an elemental analysis consistent with a 1:2:1 Pt/(PTA)/(8-
1
TT2-) molar ratio. The H NMR supported the indications
of the elemental analysis and, in combination with the IR
spectroscopy, suggested that the N7 atom of the purine was
deprotonated. The 31P{1H} NMR displayed two different
doublets (2JPP ) 22.8 Hz) at -57.1 (PA) and -72.6 ppm
(PB) both coupled to platinum (1JPtP ) 2649 Hz and
A
1JPtP ) 3028 Hz, respectively). Also for this complex two
B
The elemental analysis and spectroscopic data were in
agreement with the proposed composition (Chart 4) for 4
and 5. The 31P{1H} NMR of 4 showed two doublets with
satellites at 8.1 (PA) and 13.7 ppm (PB), due to the reciprocal
coupling among the two magnetically different phosphorus
atoms (2JP P ) 20 Hz) and to platinum. The Pt-PA coupling
different structures (Chart 2) are consistent with the data. In
this case we did not succeed in obtaining crystals adequate
for X-ray determination, but a measure of the molecular
weight by Maldi Toff MS (MW ) 1438 Da) allowed us
to unequivocally identify 2 as a binuclear complex
(Chart 2, ii).18
A
B
constant (1JPtP ) 3233 Hz) was smaller than the corre-
A
The reaction of 8-TTH2 with [PtOH(terpy)]BF4 in MeOH
at room temperature gave the yellow product 3, which was
characterized as a mononuclear Pt/8-TTH complex (Chart
sponding for PB (1JPtP ) 3836 Hz), in agreement with a
B
minor trans effect for chloride than for N.
Complex 5 showed a 31P{1H} NMR containing a single
signal at -0.75 ppm with a 1JPtP of 3479 Hz, supporting the
disposition of the PPh3 trans to the thiopurine N7.20
A platinum phosphane complex containing two different
purine ligands could provide important information about
how the presence of a Pt-bonded purine influences the
coordination of a second one.
1
3). The H NMR spectrum indicated the persistence of the
N7 proton in the complex [N7-H ) 13 ppm (DMSO-d6)],
suggesting that the monodeprotonated 8-TTH- acts as a
monodentate anionic ligand through the sulfur atom. The
other key points to define the composition of 3 are (a) the
integrals ratio between the purine N-CH3 and the terpyridine
aromatic signals suggested a 1:1:1 Pt/terpyridine/purine molar
proportion, which was also supported by the elemental
analysis, (b) the monocationic charge of the platinum
complex was indicated by the presence of a single BF4- anion
in the complex composition (elemental analysis), (c) the FAB
analysis showed a signal at 639 m/z, in agreement with the
formula weight of the mononuclear cation, and (d) in the
1H NMR spectrum of the complex the terpyridine protons
showed Pt satellites indicating that terpy is acting as a
terdentate ligand.
The reaction between the 8-MTTH complex 4 and 8-TTH2
in refluxing aqueous NaOH/CH2Cl2 gave cis-[Pt(8-MTT)-
(8-TTH)(PPh3)2] (6) (Chart 5). This complex contains two
different thiopurines bonded to the same platinum nucleus
in two different coordination modes: 8-MTT- and 8-TTH-
coordinated via N7 and S-, respectively. It has been isolated
and fully characterized.
1
The H NMR of 6 showed signals belonging to both
purines. The resonance at 2.7 ppm was easily assigned to
the S-CH3 group of 8-MTT-, but it was not possible to
assign unequivocally the other three signals at 3.3, 3.4, and
3.5 in a 2:1:1 ratio. The highest field peak was tentatively
assigned to the two coincident N1-CH3 of the two purines
on the basis of the chemical shift for that group in other
In the three complexes 1-3, the signals produced by the
purine N-CH3 groups are in the range found for other similar
complexes.19 Nevertheless, it is important to point out that
(18) Colacio, E.; Cuesta, R.; Ghazi, M.; Huertas, M. A.; Moreno, J. M.;
Navarrete, A. Inorg. Chem. 1997, 36, 1652.
(19) Romerosa, A.; Lo´pez-Magan˜a, C.; Saoud, M.; Man˜as-Carpio, S. Eur.
J. Inorg. Chem. 2003, 348.
(20) Pregosin, P. S.; Kunz, R. W. 31P and 13C NMR of Transition Metal
Phosphine Complexes; Springer-Verlag: Berlin, 1979.
Inorganic Chemistry, Vol. 43, No. 3, 2004 909

Romerosa et al.
Chart 5
thiopurine complexes: in fact the N1-CH3 chemical shift
arises in a narrow range, at higher field and is less sensitive
than the N3-CH3 to the purine coordination. The residual
signals at 3.4 and 3.5 were consequently assigned to the two
N3-CH3 groups.4,5 The signal at 11.7 ppm is due to a
residual N7-bonded proton belonging to S-coordinated
8-TTH-, at appreciably higher field than the corresponding
signal in noncoordinated 8-TTH2 (13.36 ppm) or in the gold
complex [Au(8-TTH)PPh3] (12.89 ppm).21
Figure 1. ORTEP view and atom numbering of compound 4 showing
the thermal ellipsoids at 30% probability.
aqueous NaOH (0.1 M). The complex was fully characterized
by spectroscopic techniques (see Experimental Section) and
X-ray diffraction (see further).
The comparative analysis of the thiopurine transitions in
1H NMR for the above 8-MTT- complexes showed that
while there is no evident correlation between the complex
structure and the N1-CH3 and the N3-CH3 chemical shifts,
a trend can be sketched for the S-CH3 chemical shift: this
signal arises at lower field for monopurine complexes (2.7
ppm in 4 and in 7) than for those containing two purine bases
(2.2 in 5; 2.4 in 8, 2.6 ppm in 9).
The 31P{1H} NMR was in agreement with the proposed
structure. Two doublets with satellites were observed at 18.9
(PA) and 5.1 ppm (PB), (2JP P ) 18 Hz). Both signals were
A
B
coupled to platinum with different coupling constants: 3127
Hz for the phosphorus trans to the S thiopurine atom (PA)
and 3250 Hz for the other, trans to the N7 purine atom (PB).
The reaction of 8-MTTH with NaOH and cis-[PtCl2-
(PTA)2] in H2O/CH2Cl2 in 1:1:1 molar proportion gave the
complex cis-[PtCl(8-MTT)(PTA)2] (7) while in 2:2:1 molar
ratio gave cis-[Pt(8-MTT)2(PTA)2] (8) (Chart 6)
Crystal Structure of 4. Crystals of complex 4 were
obtained by recrystallization of the crude product from CHCl3
24
and Et2O. An ORTEP view is displayed in Figure 1; the
Complex 7 and 8 are soluble in H2O (2.6 and 4.1 mM,
respectively) as well as in organic solvents (CH2Cl2 and
CHCl3). The spectroscopic properties and elemental analysis
are in agreement with the proposed composition for both
compounds and are presented in the Experimental Section.
The 31P{1H} NMR spectrum for 7 displayed two doublets
(PA ) -69.5 ppm; PB ) -58.4 ppm; 2JPP ) 20.5 Hz). The
coupling constant between PA and Pt was 2962 Hz, which
is adequate for a P trans to a N, while the corresponding
value for PB (1JPPt ) 3369 Hz) was in agreement with a P
trans to a Cl.20 Complex 8 showed a singlet at -68.8 ppm
with a PtP coupling constant similar in value (3066 Hz) to
PA of complex 7.
Finally, we intended to complete this series of potentially
antiproliferative thiopurine/platinum complexes designing a
comparative complex with no phosphane ligands. Because
the anticancer activity of trans platinum complexes bearing
aromatic flat molecules as neutral ligands has been de-
scribed,22,23 complex trans-[Pt(8-MTT)2(py)2] (9) (Chart 7)
is likely to be active too: it was synthesized by a two-step
reaction from trans-[PtCl2(Py)2], which was treated in
acetone with 2 equiv of AgBF4 and then with 8-MTTH in
crystallographic data are given in Table 1, and a list of
selected bond distances and angles appears in Table 2.
The asymmetric unit contains one CHCl3 molecule and
one cis-[PtCl(8-MTT)(PPh3)2] molecule. In this compound
the platinum(II) atom is coordinated to the phosphorus atoms
of two triphenylphosphane ligands, to a chloride, and to a
8-MTT- anion through the N7 atom. As anticipated by NMR
analysis, the two triphenylphosphane are cis to each other.
The coordination polyhedron of the metal atom adopts a
marked distorted square-planar geometry (P2-Pt-P1 )
99.06(4)°, N7-Pt-Cl ) 84.40(1)°) likely caused by the
steric repulsion between the two triphenylphosphane ligands.
The biggest deviation from the coordination plane of 0.032-
(2) Å corresponds to Cl1 atom [Σ(d/σ)2 ) 459.5 for the
coordination plane]. The Pt1-Cl1 and Pt1- N1 distances
are 2.337(1) and 2.054(4) Å, respectively, as expected when
Cl and N(sp2) are trans to a phosphane group18,25-27 and are
in agreement with other similar thiopurine-metal com-
plexes.4,5,19,21 The purine molecule is roughly planar
(24) Johnson, C. K. ORTEP II. Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976.
(25) Habtemariam, A.; Parkinson, J. A.; Margiotta, N.; Hambley, T. W.;
Parsons, S.; Sadler, P. J. J. Chem. Soc., Dalton Trans. 2001, 362.
(26) Garcia-Sejio, M. I.; Castineiras, A.; Mahieu, B.; Janosi, L.; Berente,
Z.; Kollar, L.; Garcia-Fernandez, M. E. Polyhedron 2001, 20, 855.
(27) Lee, C.; Kang, Y.; Kang, S. O.; Ko, J.; Yoo, J. W.; Cho, M. H. J.
Organomet. Chem. 1999, 587.
(21) Colacio, E.; Romerosa, A.; Ruiz, J.; Roma´n, P.; Gutie´rrez-Zorrilla, J.
M.; Vegas, A.; Mart´ınez-Ripoll, M. Inorg. Chem. 1991, 30, 3743.
(22) Van Beusichem, M.; Farrell, N. Inorg. Chem. 1992, 31, 634.
(23) Kharatishvili, M.; Mathieson, M.; Farrell, N. Inorg. Chim. Acta 1997,
255, 1.
910 Inorganic Chemistry, Vol. 43, No. 3, 2004

Biologically ActiWe Platinum Complexes
Chart 6
[Σ(d/σ)2 ) 101.0] with maximum deviation from the plane
for C8 atom of 0.0305 Å while the exocyclic groups do not
show any significant deviation from the purine plane. The
purine is twisted away from the metal coordination mean
plane. The mean plane of the purine is rotated with respect
to the coordination metal plane by an angle of 88.4(1)° likely
to minimize the steric repulsions between the bulky triphen-
ylphosphane ligands and the thiomethyl group of the purine
ligands.
Finally, the rest of bond distances and angles are similar
to those found in other N(7)-bonded purine complexes4,5,19,21
and there are no significant intra- and intermolecular interac-
tions, less than the sum of the van der Waals radii, between
molecules.
Crystal Structure of 9. Crystals of 9 adequate for X-ray
diffraction determination were obtained from a CHCl3
solution by slow diffusion of Et2O. An ORTEP24 view is
displayed in Figure 2. The crystallographic data are given
in Table 1, and a list of selected bond distances and angles
appears in Table 2.
In complex 9, platinum is bonded to two 8-MTT- ligands
trans to each other by the deprotonated N7 atoms and to
two pyridine molecules. The complex is located on a
crystallographic center of symmetry coincident with the Pt
atom. The angles of the coordination square planar geometry
around the metal are 88.9(2) and 91.1(2)°. The Pt1-N7
distances (2.026(4) Å) are in agreement with those found in
Pt(II) complexes with N(sp2) atoms in mutual trans position
and in particular with the imidazolic N7 purine atoms. Pt
square complexes containing purine derivatives in trans
positions display Pt-N distances in the range 1.996-2.033
Å.18,25-27 The distances of 2.009(4) Å between Pt1 and
pyridine-N5 are in agreement with the values observed in
other similar Pt(II) square planar complexes where the
pyridine, not contained in a strained multidentate ligand, is
in trans position to a N(sp2) atom.28 The square coordination
plane is somewhat regular and perfectly planar for symmetry
reasons. Also the purine molecule is practically planar
Chart 7
Figure 2. ORTEP view and atom numbering of compound 9 showing
the thermal ellipsoids at 30% probability.
Inorganic Chemistry, Vol. 43, No. 3, 2004 911

Romerosa et al.
Table 3. Percentage ((SD) of Growth Inhibition of T2 Cells
Table 4. Percentage ((SD) of Growth Inhibition of SKOV-3 Cells
complex
50 µM
10 µM
5 µM
complex
50 µM
10 µM
5 µM
1
2
3
4
5
6
7
8
68 ( 1.0
16 ( 1.5
20 ( 0.5
92 ( 0.5
76 ( 1.5
71 ( 0.5
16 ( 0.5
20 ( 6.0
92 ( 1.5
90 ( 2.5
32 ( 1.5
5 ( 1.0
15 ( 1.5
2 ( 1.5
5 ( 1.0
53 ( 2.0
20 ( 2.5
2 ( 1.0
1 ( 0.5
10 ( 2.0
10 ( 2.0
62 ( 2.5
1
2
3
4
5
6
7
8
64 ( 2.0
32 ( 2.5
16 ( 1.5
57 ( 3.0
20 ( 3.0
35 ( 3.0
18 ( 1.5
23 ( 1.5
81 ( 2.0
18 ( 1.5
30 ( 1.0
24 ( 1.0
10 ( 2.0
22 ( 3.5
14 ( 1.5
21 ( 5.0
7 ( 2.0
15 ( 2.5
43 ( 2.0
10 ( 2.0
10 ( 1.5
15 ( 2.0
10 ( 2.0
4 ( 1.5
10 ( 1.0
1 ( 0.5
1 ( 0.5
10 ( 3.0
10 ( 2.5
5 ( 1.5
7 ( 1.5
90 ( 0.5
25 ( 3.0
42 ( 1.5
1 ( 0.5
14 ( 4.0
68 ( 2.0
79 ( 1.5
9
9
cis-Pt
cis-Pt
Chart 8. T2 Cell Line Growth Inhibition
Chart 9. SKOV-3 Cell Line Growth Inhibition
[Σ(d/σ)2 ) 11.48], the maximum deviation from the mean
plane being 0.010(6) Å for C5 atom, while the exocyclic
groups do not show any significant deviation from the purine
plane. The ligands mean plane is rotated by an angle of 86.0-
(1)° with respect to the platinum coordination plane. The
pyridine/8-MTTH complex 9 have the ability to induce
inhibition, in contrast to cisplatin. The highest inhibition was
obtained with complex 9. Complexes containing PTA (2, 7,
8) and terpyridine (3) show a low activity, similarly to
cisplatin.
rest of distances and angles are similar to those found in
Although a more exhaustive number of structures and
experiments would be required for defining a complete
structure-activity relationship, some observations can be
attempted:
4,5,19,21
other N(7)-bonded purine complexes
and do not
deserve any additional comments. No significant intra- and
intermolecular short interactions, less than the sum of van
der Waals radii, are present in the crystal.
(a) The most active complexes on the cisplatin-sensitive
T2 human cells are 4 and 9. In the case of 9 it is known that
the parent complex trans-[PtCl2py2] is active29 and therefore
complex 9 could simply act as a prodrug, the active moiety
being the Pt(py)2 group. On the contrary, the precursor of 4,
cis-[PtCl2(PPh3)2], has been reported as nonactive30 and
therefore in this case the thiopurines are not innocent ligands
and may have a role in determining the drug distribution
and its interactions with biomolecules.
Cell Growth Inhibition. Complexes 1-9 have been tested
for their capacity to inhibit the cell growth of two human
cancer cell lines: the cisplatin-sensitive T2 (results reported
in Table 3 and Chart 8) and the cisplatin-resistant SKOV3
(results reported in Table 4 and Chart 9). In both diagrams
the activity of cisplatin was included for comparison. Each
complex was dissolved in DMSO and diluted in AIM-V
medium to obtain final concentrations of 50, 10, and 2 µM
solutions. The chemical stability of the complexes in water/
DMSO solutions was verified by 31P{1H} NMR.
The results clearly show that the activity of complexes
1-9 on cisplatin-sensitive T2 cells is strongly affected by
the nature of the neutral ligands. The complexes containing
PPh3 (1 and 4-6) or pyridine (9) display a significantly better
activity than those containing PTA (2, 7, and 8) or terpyridine
(3).
(b) The most active complexes on the cisplatin-resistant
SKOV3 cells are 1, 4, and 9, this last being the best one.
The three complexes are more active than cisplatin at 50
and 10 µM concentrations. This fact supports the hypothesis
that the complexes containing thiopurines and PPh3 or
pyridine act by a mechanism different from that accepted
for cisplatin.
The tests performed with the cisplatin-sensitive T2 cells
show that 4, 9, and cisplatin complexes have a comparable
inhibitory activity at 50 µM. In particular, complex 4 shows
the highest inhibitory capacity, similar to cisplatin activity.
The tests performed with the cisplatin-resistant SKOV3
cell line show that the 8-TTH2 complex 1 and the 8-MTTH
complex 4, both containing triphenylphosphane, and the trans
(c) Surprisingly very low activity has been found for the
more water soluble PTA complexes. Although a more
detailed investigation is required to correlate the PTA
properties and the biological activity of its Pt complexes,
this observation indicates that the activity is not improved
by a mere increase of hydrophilicity, although the presence
(29) Fontes, A. P. S.; Oskarsson, A.; Lo¨vqvist, K.; Farrell, N. Inorg. Chem.
2001, 40, 1745.
(30) Berners-Price, S. J.; Sadler, P. J. Struct. Bonding 1988, 70, 27.
(28) Deacon, G. B.; Gatehouse, B. M.; Haubrich, S. T.; Ireland, J.; Lawrez,
E. T. Polyhedron 1998, 17, 791.
912 Inorganic Chemistry, Vol. 43, No. 3, 2004

Biologically ActiWe Platinum Complexes
of hydrophilic ligands could be convenient in terms of drug
administration and distribution.
compounds show some inhibitory activity on T2, although
not as strong as cisplatin. Complexes 4 and 9 showed a
appreciable activity also on cisplatin-resistant SKOV3 cells,
which suggests that their activity is produced by a mechanism
different from that consolidated for cisplatin.
Conclusion
We have synthesized and characterized nine new thio-
theophylline platinum complexes containing deprotonated
8-TTH2 and 8-MTTH ligands. The structure of the complexes
cis-[PtCl(8-MTT)(PPh3)2] (4) and trans-[Pt(8-MTT)2(py)2]
(9) have been also characterized by monocrystal X-ray
diffraction.
The cancer cell growth inhibition activity of the above
new platinum complexes have been tested on the cisplatin-
sensitive T2 human cell line and the cisplatin-resistant
SKOV3 cell line, and it has been observed that most of these
Acknowledgment. We thank the “Azione Integrata”
between the Universities of Almeria (Almeria, Spain) and
Ferrara (Ferrara, Italy), the MCYT (Spain) for Project
PPQ2000-1301, and J. And. for Project A29/00 and Con-
sorzio Interuniversitario di Ricerca in Chimica dei Metalli
nei Sistemi Biologici.
IC034868C
Inorganic Chemistry, Vol. 43, No. 3, 2004 913