Bis- and Tris(carboxylato)platinum(IV) Complexes with Mixed Am(m)ine Ligands in the trans Position Exhibiting Exceptionally High Cytotoxicity

Article abstract of DOI:10.1002/ejic.201403226

A series of seven diam(m)inebis(carboxylato)dihydroxidoplatinum(IV) and eleven diam(m)inetris(carboxylato)hydroxidoplatinum(IV) complexes with am(m)ine ligands in the trans position was synthesized and characterized by multinuclear ¹H, ¹³C, ¹⁵N, ¹⁹⁵Pt NMR spectroscopy. IC₅₀ values for all eighteen substances were determined by means of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay for three human cancer cell lines. In cisplatin-sensitive CH1(PA-1) cancer cells, diam(m)inebis(carboxylato)dihydroxidoplatinum(IV) complexes displayed 50 % inhibitory concentrations in the micromolar range, whereas for the most lipophilic compounds of the diam(m)inetris(carboxylato)hydroxidoplatinum(IV) series, promising IC₅₀ values in the nanomolar range were found.

Full text of DOI:10.1002/ejic.201403226

FULL PAPER
DOI:10.1002/ejic.201403226
Bis- and Tris(carboxylato)platinum(IV) Complexes with
Mixed Am(m)ine Ligands in the trans Position Exhibiting
Exceptionally High Cytotoxicity
[
a]
[a]
[a,b]
Björn R. Hoffmeister, Michaela Hejl, Michael A. Jakupec,
[a]
[a,b]
Markus Galanski,* and Bernhard K. Keppler*
Keywords: Platinum / N ligands / Synthesis design / Structure–activity relationships / Cytotoxicity
A series of seven diam(m)inebis(carboxylato)dihydroxido-
platinum(IV) and eleven diam(m)inetris(carboxylato)hydrox-
idoplatinum(IV) complexes with am(m)ine ligands in the
trans position was synthesized and characterized by multi-
bromide (MTT) assay for three human cancer cell lines. In
cisplatin-sensitive CH1(PA-1) cancer cells, diam(m)inebis-
(carboxylato)dihydroxidoplatinum(IV) complexes displayed
50% inhibitory concentrations in the micromolar range,
whereas for the most lipophilic compounds of the diam(m)-
inetris(carboxylato)hydroxidoplatinum(IV) series, promising
IC50 values in the nanomolar range were found.
1
13
15
195
nuclear H, C, N,
all eighteen substances were determined by means of the
-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium
Pt NMR spectroscopy. IC50 values for
3
Introduction
accessible for carboxylation at the axially coordinated
[
9–12]
hydroxido ligands.
By use of a cyclic anhydride for the
Besides cisplatin, whose antiproliferative properties were carboxylation reaction, a free carboxylic acid moiety is ob-
discovered in 1965 by Rosenberg,[1] only two more plati- tained, which can be further derivatized. Following this
num-based agents, namely carboplatin and oxaliplatin (Fig- pathway, series of platinum(IV) complexes have been syn-
ure 1), are in worldwide clinical use.[
2–5]
thesized in recent years by transferring the peripheral carb-
The major drawbacks of these platinum-based drugs are oxylic acid group into esters or amides.[13–22] It was ob-
1) dose-limiting severe systemic toxicity and (2) intrinsic or served that the antiproliferative potency of these plati-
(
acquired resistance of various tumors. A possible way to num(IV) agents was enhanced with increasing lipophilicity,
reduce side effects is the development of kinetically inert and for the most lipophilic compounds 50% inhibitory con-
platinum(IV) complexes, being reduced to the more reactive centrations in the nanomolar range were found.
platinum(II) species (prodrug concept, activation by re-
As enhanced removal of cisplatin-induced DNA adducts
duction), preferentially in the oxygen-deficient milieu of has been reported to play a main role in tumor cell resis-
solid tumors by release of the axial ligands.[6–8] Addition- tance in case of platinum-based drugs,
[23]
the development
ally, octahedrally configured platinum(IV) compounds are of agents that bind differently to DNA is believed to be
Figure 1. Chemical structures of platinum(II) complexes in worldwide clinical use.
[
a] University of Vienna, Institute of Inorganic Chemistry,
Waehringer Strasse 42, 1090 Vienna, Austria
E-mail: markus.galanski@univie.ac.at
a possible strategy to circumvent resistance. One platinum
complex known to possess distinct DNA-binding behavior
is transplatin [SP-4-1-diamminedichloridoplatinum(II)],
which was shown to form mainly 1,3-intrastrand and 1,3-
interstrand cross-links with DNA as opposed to the 1,2-
intrastrand cross-links mainly formed by cisplatin.[
bernhard.keppler@univie.ac.at
http://anorg-chemie.univie.ac.at
[
b] Research Platform “Translational Cancer Therapy Research”,
University of Vienna,
24,25]
Waehringer Strasse 42, A-1090 Vienna, Austria
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While transplatin showed no antiproliferative properties,[26]
Using 1.2–1.5 equiv. of anhydride for the carboxylation
Farrell and co-workers reported that exchange of one leads almost exclusively to the formation of tris(carboxyl-
ammine ligand with a planar amine yielded trans-config- ato) species. The tetrakis(carboxylato) complex, which is
ured platinum(II) complexes exhibiting IC values in the also obtained in a small amount, is soluble in diethyl ether,
5
0
[
27–29]
micromolar range.
Subsequently, platinum(II) com- unlike the main product, and can therefore be easily re-
pounds of trans geometry with different kinds of amines moved. Synthesis of the tetrakis(carboxylato) complexes
(
trans to the ammine) and their dihydroxido platinum(IV) has not been carried out, as (1) the separation is not easy,
[30–32]
analogues have been investigated.
Navarro-Ranninger and, even if the separation were accomplished, (2) the
and co-workers reported on trans-configured platinum(II) tetrakis(carboxylato) products could only be obtained as an
complexes with mixed amines,[ and their corresponding oily residue.
33]
dihydroxido platinum(IV) species, which showed IC50
Bis(carboxylato)dihydroxidoplatinum(IV) complexes 3a–
values in the micromolar range and exhibited high activity 3g and tris(carboxylato)hydroxidoplatinum(IV) complexes
for cisplatin-resistant cell lines.[
34–36]
An advantage of the 4a–4k were characterized by elemental analysis and multi-
1
13
195
dihydroxido platinum(IV) complexes, which showed similar nuclear one- and two-dimensional H, C, and Pt NMR
15
or even higher cytotoxic activity than their platinum(II) spectroscopy; for compounds 4a–4k, N NMR chemical
counterparts, is the higher water solubility they provide. A shifts were detected additionally by 1H, N correlation
strategy to obtain more water soluble trans-configured measurements. Complexes 3a–3c and 3e–3g were dissolved
platinum(II) compounds was introduced by Farrell and co- in [D ]MeOH, complex 3d was dissolved in D O, and com-
15
4
2
[
37,38]
workers, who exchanged chloride ligands with acetato
plexes 4a–4k were dissolved in [D ]DMSO for the spectro-
6
or various carboxylato[
39–41]
ligands, to obtain diam(m)- scopic measurements. Pt NMR chemical signals of com-
complexes showing plexes 3a–3c were observed at δ = 3645 ppm; 3d, which was
promising IC50 values and small resistance factors for cis- dissolved in D O, showed a Pt NMR shift of 3629 ppm,
195
inebis(carboxylato)platinum(II)
195
2
platin-resistant cell lines.[
42]
whereas signals of 3e–3g were observed at δ = 3601 ppm.
The aim of the present work was to combine the possible All these signals are indicative of a PtN O coordination
2
2
advantages of trans-configured complexes featuring carb- sphere. 1 Pt NMR chemical shifts of complexes 4a–4h
oxylato ligands with those of platinum(IV) compounds. (detected between 3790 and 3792 ppm), and those of com-
Here, we report on a series of novel diam(m)inebis- and plexes 4i–4k (observed between 3755 and 3756 ppm) were
diam(m)inetris(carboxylato)platinum(IV) complexes with shifted downfield by around 55 ppm. C=O resonances of
am(m)ine ligands in the trans position. The target com- C-1Ј and C-4Ј in 3a–3g were detected at around 182 (182.4–
pounds were characterized in detail by multinuclear NMR 182.9) and 175 (174.9–176.2) ppm. Chemical shifts of carb-
spectroscopy and elemental analysis and were evaluated re- onyl C-atoms C-1Ј and C-4Ј as well as C-1ЈЈ and C-4ЈЈ in
garding their cytotoxic potential for three human cancer 4a–4k were observed at around 179 (178.6–179.4) and 172
cell lines. Additionally, the rate of reduction of four com- (172.2–172.9) ppm, whereas the C=O chemical shift of the
plexes (two of each kind) in the presence of an excess acetato ligand in 4a and 4f was detected at δ = 177.9 ppm.
95
1
1
15
amount of ascorbic acid was investigated by means of H
NMR spectroscopy.
H, N shift correlation signals for coordinated ammonia
1
were found in the range from 6.11 to 6.14 ( H) and from
–
pentylamine in 4a–4h H, N cross peaks ranging from 6.84
15
43.8 to –43.0 ppm ( N) in 4a–4k. For coordinated cyclo-
1
15
Results and Discussion
to 6.89 and from –8.8 to –8.1 ppm were observed, whereas
1
15
trans-Configured
(SP-4-1)-ammine(dichlorido)(cyclo- coordinated methylamine in 4i–4k showed H, N corre-
pentylamine)platinum(II) (1a) and (SP-4-1)-ammine(di- lation signals between 6.69 and 6.70 and from –34.2 to
chlorido)(methylamine)platinum(II) (1b) were prepared by –34.1 ppm.
reaction of (SP-4-2)-diammine(dichlorido)platinum(II)
The cytotoxicity of complexes 3a–3g and 4a–4k was in-
with cyclopentylamine and methylamine, respectively, vestigated by means of the 3-(4,5-dimethylthiazol-2-yl)-2,5-
followed by heating under reflux of the tetramine inter- diphenyl-2H-tetrazolium bromide (MTT) assay for three
mediate formed with an excess amount of HCl. Subsequent human cancer cell lines representing ovarian terato-
exchange of the chlorido ligands for iodido ligands was carcinoma [CH1(PA-1)], non-small cell lung cancer (A549),
achieved by reaction with potassium iodide in acetone to and colon carcinoma (SW480) (Table 1).
yield precursors (SP-4-1)-ammine(cyclopentylamine)di-
iodidoplatinum(II) (2a) and (SP-4-1)-ammine(diiodido)- complexes 3a–3g in cisplatin-sensitive CH1(PA-1) cells
methylamine)platinum(II) (2b) (Figure 2). By reaction of varied in a wide range from 53 to 0.25 μm, whereas com-
a and 2b with silver 4-alkoxy-4-oxobutanoates and subse- plexes 4a–4k featuring only one hydroxido ligand showed
IC50 values of bis(carboxylato)dihydroxidoplatinum(IV)
(
2
quent oxidation of the bis(carboxylato)platinum(II) inter- even lower half maximal inhibitory concentrations between
mediates with hydrogen peroxide in water, compounds 3a– 6.5 and 0.016 μm. The majority of IC50 values for the
g were obtained. The latter were carboxylated with either intrinsically cisplatin-resistant cell lines A549 and SW480
acetic anhydride or 4-alkoxy-4-oxobutanoic anhydrides, re- were at least an order of magnitude higher; in some cases,
sulting in tris(carboxylato)hydroxidoplatinum(IV) com- cytotoxicity was even decreased by a factor of Ͼ 100 for
plexes 4a–k.
A549 cells compared to that for the CH1(PA-1) cell line.
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Figure 2. Synthesis and chemical structures of the bis- and tris(carboxylato)platinum(IV) complexes with NMR numbering schemes.
1702
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Table 1. 50% inhibitory concentrations of complexes 3a–4k in a cyclopentylamine ligand were more active than their
CH1(PA-1), A549, and SW480 cancer cells.
methylamine analogues. In the same line, an increase in the
IC50 [μm][a]
A549
lipophilicity of the ester moieties in each sub series (3a–3c,
3d–3g, 4b–4e, 4g–4h, and 4i–4k) resulted in decreased IC50
values. Simultaneous variation of both equatorial and axial
ligands (as in series 4i–4k) has an even stronger impact on
cytotoxic potency than changing the equatorial ligands only
Compound
CH1(PA-1)
SW480
a (58)[b]
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
4
3.5Ϯ0.2
1.7Ϯ0.2
0.25Ϯ0.05
53Ϯ7
24Ϯ4
7.3Ϯ1.8
1.9Ϯ0.4
0.087Ϯ0.021
0.15Ϯ0.01
0.046Ϯ0.014
0.026Ϯ0.002
0.016Ϯ0.004
0.030Ϯ0.006
0.034Ϯ0.006
0.016Ϯ0.003
6.5Ϯ0.8
0.69Ϯ0.14
0.051Ϯ0.012
0.077Ϯ0.006
0.18Ϯ0.01
58Ϯ17
61Ϯ19
19Ϯ2
Ͼ 400
Ͼ 400
207Ϯ15
91Ϯ17
5.8Ϯ0.6
13Ϯ5
6.1Ϯ0.8
3.3Ϯ0.2
2.0Ϯ0.1
1.9Ϯ0.6
3.4Ϯ1.1
1.2Ϯ0.4
Ͼ 200
25Ϯ6
18Ϯ2
5.9Ϯ1.0
175Ϯ23
136Ϯ20
45Ϯ8
b
c
[
[
b]
b]
d (55)
(
Figure 3).
e
Consequently, the following conclusions can be drawn on
f
structure–activity relationships: (1) tris(carboxylato)hydro-
xidoplatinum(IV) complexes display a considerably higher
cytotoxicity than their bis(carboxylato)dihydroxidooplatin-
um(IV) counterparts; (2) cyclopentylamine complexes are
more active than analogues featuring a methylamine ligand;
and (3) IC50 values decrease with increasing lipophilicity of
the compounds.
g
21Ϯ5
a
1.4Ϯ0.2
1.8Ϯ0.4
0.87Ϯ0.23
0.56Ϯ0.11
0.39Ϯ0.05
0.42Ϯ0.11
0.69Ϯ0.19
0.23Ϯ0.08
40Ϯ5
4.6Ϯ0.4
0.52Ϯ0.14
3.3Ϯ0.2
0.52Ϯ0.05
b (17)
c
d
e
f
g
h
In order to study the rate of reduction of the novel
platinum(IV) complexes, compounds 3a, 3d, 4b, and 4i were
[
b]
i (13)
j
k
39Ϯ5
incubated with a 25-fold excess amount of ascorbic acid in
4.9Ϯ1.4
6.2Ϯ1.2
4.9Ϯ0.2
[
43]
[
1
Cisplatin
a D O buffered solution (pD = 7.4) and H NMR spectra
2
44]
Oxaliplatin
were recorded until no starting material could be detected
1
[
a] 50% inhibitory concentrations in the MTT assay (96 h expo- anymore (Figure 4). Before addition of ascorbic acid, H
sure). Values are means and Ϯ standard deviations obtained from
at least three independent experiments. [b] Half-lives of reduction
by ascorbic acid in minutes.
NMR spectra were recorded over a period of 24 h in order
to check the stability of the complexes; changes in the
NMR spectra could generally not be seen. Additionally, the
rate of reduction of two platinum(IV) complexes with cis-
Compounds 4e and 4h displayed an exceptionally high anti- configured ammine ligands, (OC-6-44)-acetato(diammine)-
proliferative potential in CH1(PA-1) cells with an IC50 hydroxido(malonato)platinum(IV)
and (OC-6-33)-di-
value of 0.016 μm, being more active than clinically admin- ammine(malonato)bis[(4-methoxy)-4-oxobutanoato]plati-
istered cisplatin (0.077 μm) or oxaliplatin (0.18 μm). num(IV), was determined in the same manner for compari-
Furthermore, both complexes, 4e and 4h, showed a cyto- son.
toxic potency comparable to oxaliplatin for the intrinsically
Complexes 3a and 3d, featuring two hydroxido, two
cisplatin-resistant cell line SW480. Independently from the carboxylato, and two am(m)ine ligands, showed half-lives
chosen cancer cells or the axial ligands, complexes featuring of 58 min and 55 min, respectively. For complexes 4b and
Figure 3. Dependence of IC50 values (means Ϯ standard deviations) in CH1(PA-1) and SW480 cells on the variable ligand residues for
compound series 3a–3c, 3d–3g (left) and 4b–4e, 4i–4k (right). Note the different logarithmic scales.
Eur. J. Inorg. Chem. 2015, 1700–1708
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Experimental Section
All chemicals and solvents were obtained from commercial suppli-
ers and used without further purification. Doubly distilled osmosis
water was used for the synthesis, methanol and ethanol were dried
according to standard procedures, and column chromatography
was carried out with aluminum oxide 90 (Merck). The starting
compound, (SP-4-2)-diammine(dichlorido)platinum(II), was syn-
thesized by Dhara’s method.[
47]
1H, C, 15N, 195Pt, H- H COSY, H- C HSQC, H- N HSQC,
13
1
1
1
13
1
15
1
13
and H- C HMBC NMR spectra were recorded with a Bruker
1
13
Avance III 500 MHz spectrometer at 500.32 ( H), 125.81 ( C),
1
95
15
1
07.55 ( Pt), and 50.70 MHz ( N) at ambient temperature. Pre-
cursors 1a, 1b, 2a, and 2b were dissolved in [D ]acetone, complexes
3a–c and 3e–g in [D ]MeOH, 3d in D O, and 4a–k in [D ]DMSO
for the measurements. For H and C NMR spectroscopy mea-
surements, the solvent residual peaks were used as internal refer-
Figure 4. Time-dependent reduction of complexes 3a, 3d, 4b, and
i (1 mm) in the presence of ascorbic acid (25 mm) at ambient tem-
perature.
6
4
4
2
6
1
13
1
5
195
ence, whereas N and Pt NMR chemical shifts were referenced
relative to external NH Cl or K PtCl . Elemental analyses were
4
2
4
4
i, having only one hydroxido, but three carboxylato, and
carried out by the Microanalytical Laboratory of the University of
Vienna using a Carlo Erba EA 1108 CHNS-O or a Perkin–Elmer
two am(m)ine ligands, half-lives were found to be 17 min
and 13 min, respectively.
2400 CHN elemental analyzer.
These values are not unexpectedly low and are in general
agreement with the reduction rate of the cis-configured
monohydroxido complex (OC-6-44)-acetato(diammine)-
General Procedure for Obtaining the Succinic Acid Monoesters (4-
Alkoxy-4-oxobutanoic Acids): Succinic anhydride was suspended in
an excess amount of an alcohol and stirred at 68 °C under argon
overnight; subsequently, the excess amount of alcohol was evapo-
rated by use of an oil pump to yield the respective succinic acid
monoester, which was used without further purification.
hydroxido(malonato)platinum(IV) with
a
half-life of
27 min. In contrast, the reduction of a cis-configured
tetrakis(carboxylato)
analogue,
(OC-6-33)-diammine-
(
malonato)bis[(4-methoxy)-4-oxobutanoato]platinum(IV),
General Procedure for Preparing the Silver Salts of the Succinic Acid
Monoesters (Silver 4-Alkoxy-4-oxobutanoates): The respective
succinic acid monoester was dissolved in water (in case of the
propyl ester, acetone was added to obtain a clear solution). Silver
is comparably slow; only 50% of the complex was reduced
after 33 h. It seems that the cis- or trans-configuration of
am(m)ine ligands has no significant influence on the re-
duction rate. The fast reduction of the investigated plati- nitrate (1 equiv.) was added, the solution was stirred for a couple
num(IV) complexes featuring one or two hydroxide ligands of minutes, and then ammonium hydroxide (1 equiv.) was added,
is in accord with recent findings.[
45,46]
Gibson and co- upon which a white product precipitated; the silver 4-alkoxy-4-
oxobutanoate was collected by filtration and washed with ethanol
workers showed that tris(carboxylato)monohydroxidoplati-
num(IV) complexes were reduced significantly faster than
and diethyl ether.
the tetracarboxylato species. It is likely that the reduction General Procedure for Synthesizing the Anhydrides of the Succinic
process (transfer of electrons) is easier via coordinated hy- Acid Monoesters (4-Alkoxy-4-oxobutanoic Anhydrides): The respec-
droxide ligands and is hampered by carboxylato ligands. tive succinic acid monoester was heated to reflux with an excess
amount of acetic acid anhydride under argon overnight to obtain
the corresponding succinic acid monoester anhydride; the excess
amount of acetic acid anhydride and the acetic acid formed were
evaporated by use of an oil pump.
This would also explain why a difference between cis- and
trans-configured complexes was not detected.
(
(
SP-4-1)-Ammine(dichlorido)(cyclopentylamine)platinum(II) (1a):
SP-4-2)-Diammine(dichlorido)platinum(II) (2.193 g, 7.31 mmol)
Conclusions
was suspended in H
2
O (20 mL), cyclopentylamine (2.171 mL,
A series of 18 diam(m)inebis(carboxylato)dihydroxido-
platinum(IV) and diam(m)inetris(carboxylato)hydroxido-
platinum(IV) complexes with am(m)ine ligands in the trans
position were synthesized and characterized by one- and
two-dimensional NMR spectroscopy, and elemental analy-
sis. The most lipophilic complexes featuring a cyclo-
pentylamine ligand showed the highest cytotoxic activity in
21.93 mmol) was added, and the suspension was stirred at 40 °C
until a clear, almost colorless solution was obtained. Concentrated
hydrochloric acid (9 mL, in excess) was added, and the reaction
mixture was heated to reflux for 16 h. Upon cooling down, the
yellow product precipitated, which was collected by filtration and
1
washed with H
2
O and diethyl ether. Yield: 1.996 g, 74%. H NMR
(
6
[D ]acetone): δ = 3.99 (br. s, 2 H, NH
2
), 3.50 (m, 1 H, 1-H), 3.39
vitro. IC50 values of complexes 4e and 4h in CH1(PA-1) (br. s, 3 H, NH ), 2.04 (m, 2 H, 2-H/3-H), 1.78 (m, 4 H, 2-H/3-H),
3
5 2 2
cells were markedly lower than those of clinically estab- 1.59 (m, 2 H, 2-H/3-H) ppm. C H14Cl N Pt (368.18): calcd. C
lished agents cisplatin and oxaliplatin, whereas their activity 16.31, H 3.83, N 7.61; found C 16.56, H 3.94, N 7.42.
for the cisplatin-resistant cell line SW480 was comparable
(
SP-4-1)-Ammine(dichlorido)(methylamine)platinum(II) (1b): The
to that of oxaliplatin. Therefore, compounds 4e and 4h are
interesting candidates for further investigations and will be diammine(dichlorido)platinum(II) (1.920 g, 6.4 mmol), methyl-
synthesis was carried out as described for 1a by using (SP-4-2)-
tested for their in vivo behavior in future work.
amine (41% solution in H
2
O, 2.2 mL, 25.4 mmol), and hydro-
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1
3
chloric acid (9 mL, in excess). Yellow solid. Yield: 1.512 g, 75%.
126 mg, 26%. H NMR ([D
4
]MeOH): δ = 4.04 [t( JHH = 6.7 Hz),
1
3
H NMR ([D
H, NH
ppm. CH
C 3.83, H 2.56, N 8.54.
6
]acetone): δ = 4.00 (br. s, 2 H, NH
2
), 3.39 (br. s, 3 4 H, 5Ј-H], 3.44 (m, 1 H, 1-H), 2.67 [t ( JHH = 6.7 Hz), 4 H, 2Ј-
), 2.45 [t(3JHH = 6.4 Hz) + d( JHPt = 32 Hz), 3 H, 1-H] H], 2.58 [t( JHH = 6.7 Hz), 4 H, 3Ј-H], 2.04 (m, 2 H, 2-H), 1.77 (m,
3
3
3
8
Cl Pt (314.08): calcd. C 3.82, H 2.57, N 8.92; found 2 H, 3-H), 1.70 (m, 2 H, 2-H), 1.66 (m, 4 H, 6Ј-H), 1.61 (m, 2 H,
2 2
N
3
13
3-H), 0.95 [t( JHH = 7.4 Hz), 6 H, 7Ј-H] ppm. C NMR ([D
4
]-
MeOH): δ = 182.9 (C-1Ј), 175.0 (C-4Ј), 67.3 (C-5Ј), 56.7 (C-1), 33.8
(
SP-4-1)-Ammine(cyclopentylamine)diiodidoplatinum(II) (2a): (SP-
-1)-Ammine(dichlorido)(cyclopentylamine)platinum(II) (1.613 g,
.38 mmol) was dissolved in acetone (30 mL), and KI (1.819 g,
3
(
(
C-2), 32.0 [s + d( JCPt = 40 Hz), C-2Ј], 30.9 (C-3Ј), 25.1 (C-3), 23.0
4
4
1
1
95
C-6Ј), 10.7 (C-7Ј) ppm. Pt NMR ([D
10Pt (649.61): calcd. C 35.13, H 5.90, N 4.31; found C
5.12, H 5.99, N 4.19.
4
]MeOH): δ = 3645 ppm.
19 38 2
C H N O
3
2
0.96 mmol) was added. After stirring at room temp. for 4 h, H O
(
30 mL) was added, and the acetone was evaporated to yield the
product as an orange solid (suspension in H O), which was col-
lected by filtration and washed with H O. Yield: 2.341 g, 97%. H
NMR ([D ]acetone): δ = 4.00 (br. s, 2 H, NH ), 3.68 (m, 1 H, 1-
H), 3.48 (br. s, 3 H, NH ), 1.96 (m, 2 H, 2-H/3-H), 1.76 (m, 4 H,
-H/3-H), 1.59 (m, 2 H, 2-H/3-H) ppm. C Pt (551.08):
calcd. C 10.90, H 2.56, N 5.08; found C 11.13, H 2.62, N 4.81.
2
(
OC-6-12)-Ammine(dihydroxido)bis[(4-methoxy)-4-oxobutanoato]-
1
2
methylamineplatinum(IV) (3d): The synthesis was carried out as de-
scribed for 3a by using 2b (500 mg, 1.01 mmol) and silver 4-meth-
oxy-4-oxobutanoate (480 mg, 2.01 mmol). The crude product was
6
2
3
2
5 14 2 2
H I N
purified by column chromatography (CH
2
Cl
2
/MeOH, 6:1). Yield:
1
2
84 mg, 52%. H NMR (D O): δ = 3.73 (s, 6 H, 5Ј-H), 2.76 [t
2
3
3
(
SP-4-1)-Ammine(diiodido)(methylamine)platinum(II) (2b): The syn-
( JHH = 6.5 Hz), 4 H, 2Ј-H], 2.67 [t ( JHH = 6.6 Hz), 4 H, 3Ј-H],
3
13
thesis was carried out as described for 2a by using (SP-4-1)- 2.25 [s + d( JHPt = 22.8 Hz), 3 H, 1-H] ppm. C NMR (D
2
O): δ
(1.563 g, = 182.4 (C-1Ј), 176.2 (C-4Ј), 52.3 (C-5Ј), 30.4 [s + d( JCPt = 40 Hz),
3
ammine(dichlorido)(methylamine)platinum(II)
1
95
4
2
3
3
.98 mmol) and KI (2.065 g, 12.44 mmol). Orange solid. Yield: C-2Ј], 29.5 (C-3Ј), 28.5 (C-1) ppm.
Pt NMR (D
10Pt (539.41): calcd. C 24.49, H 4.48, N 5.19;
), 2.53 [t( JHH = 6.4 Hz) + d( JHPt = 34 Hz), found C 24.33, H 4.74, N 5.24.
2
O): δ =
1
.399 g, 97%. H NMR ([D
.46 (br. s, 3 H, NH
8 2 2
H, 1-H] ppm. CH I N Pt (496.99): calcd. C 2.42, H 1.62, N 5.64;
6
]acetone): δ = 3.99 (br. s, 2 H, NH
2
),
24 2
3629 ppm. C11H N O
3
3
3
(
(
OC-6-12)-Amminebis[(4-ethoxy)-4-oxobutanoato]dihydroxido-
methylamine)platinum(IV) (3e): The synthesis was carried out as
found C 2.46, H 1.53, N 5.37.
OC-6-12)-Ammine(cyclopentylamine)dihydroxidobis[(4-methoxy)-4-
oxobutanoato]platinum(IV) (3a): Compound 2a (533.7 mg,
.968 mmol) was dissolved in acetone (150 mL), and silver 4-meth-
(
described for 3a by using 2b (504 mg, 1.01 mmol) and silver 4-
ethoxy-4-oxobutanoate (513 mg, 2.03 mmol). The crude product
0
was purified by column chromatography (CH
2
Cl
2
/MeOH, 6:1).
oxy-4-oxobutanoate (462.9 mg, 1.937 mmol) was added. After 24 h
of stirring at 50 °C, the silver iodide formed was filtered off, and
1
Yield: 386 mg, 67%. H NMR ([D
4
]MeOH): δ = 4.12 (m, 4 H, 5Ј-
3
3
H), 2.67 [t( JHH = 6.8 Hz), 4 H, 2Ј-H], 2.58 [t( JHH = 6.8 Hz), 4
the filtrate was concentrated to dryness. H
5 mL, 30%) were added to the residue. After 16 h of stirring at
room temp., most of the H O/H mixture was evaporated, a bit
of acetone and then Et O were added to precipitate the white prod-
uct, which was subsequently collected by filtration and purified by
column chromatography (CH Cl /MeOH, 6:1). Yield: 269 mg,
]MeOH): δ = 3.66 (s, 6 H, 5Ј-H), 3.44 (m, 1 H,
2
O (30 mL) and H
2
O
2
3
3
H, 3Ј-H], 2.24 [s + d( JHPt = 23.5 Hz), 3 H, 1-H], 1.24 [t( JHH
=
(
13
7
1
(
.1 Hz), 6 H, 6Ј-H] ppm. C NMR ([D
4
]MeOH): δ = 182.8 (C-1Ј),
2
2 2
O
75.0 (C-4Ј), 61.7 (C-5Ј), 31.9 (C-2Ј), 30.9 (C-3Ј), 29.2 (C-1), 14.5
2
1 9 5
C- 6 Ј ) pp m.
10Pt (567.46): calcd. C 27.52, H 4.97, N 4.94; found C
7.26, H 4.72, N 4.87.
4
P t NM R ( [ D ] MeOH): δ = 36 01 ppm.
13 28 2
C H N O
2
2
2
1
4
1
7%. H NMR ([D
4
3
3
-H), 2.67 [t( JHH = 6.7 Hz), 4 H, 2Ј-H], 2.58 [t ( JHH = 6.7 Hz), 4
(OC-6-12)-Ammine(dihydroxido)methylaminebis[(4-propoxy)-4-oxo-
H, 3Ј-H], 2.04 (m, 2 H, 2-H), 1.77 (m, 2 H, 3-H), 1.70 (m, 2 H, 2- butanoato]platinum(IV) (3f): The synthesis was carried out as de-
H), 1.61 (m, 2 H, 3-H) ppm. 13C NMR ([D
]MeOH): δ = 182.9 (C- scribed for 3a by using 2b (757 mg, 1.52 mmol) and silver 4-pro-
Ј), 175.3 (C-4Ј), 56.7 (C-1), 52.2 (C-5Ј), 33.8 (C-2), 32.0 [s +
poxy-4-oxobutanoate (813 mg, 3.04 mmol). The crude product was
d( JCPt = 40 Hz), C-2Ј], 30.7 (C-3Ј), 25.1 (C-3) ppm. 195Pt NMR purified by column chromatography (CH Cl /MeOH, 6:1). Yield:
4
1
3
2
2
1
3
(
[D
4
]MeOH): δ = 3645 ppm. C15
H
30
N
2
O
10Pt (593.50): calcd. C
399 mg, 44%. H NMR ([D ]MeOH): δ = 4.03 [t( J
= 6.6 Hz), 4 H, 2Ј-H], 2.59 [t( J
.6 Hz), 4 H, 3Ј-H], 2.24 [s + d( JHPt = 24.0 Hz), 3 H, 1-H], 1.65
m, 4 H, 6Ј-H), 0.95 [t( JHH = 7.4 Hz), 6 H, 7Ј-H] ppm. C NMR
[D ]MeOH): δ = 182.8 (C-1Ј), 175.0 (C-4Ј), 67.3 (C-5Ј), 31.9 [s +
d( JCPt = 40 Hz), C-2Ј], 30.9 (C-3Ј), 29.2 (C-1), 23.0 (C-6Ј), 10.7 (C-
Ј) ppm. 195Pt NMR ([D
]MeOH): δ = 3601 ppm. C15H N O10Pt
32 2
HH
= 6.7 Hz),
4
3
3
30.36, H 5.10, N 4.72; found C 30.34, H 4.98, N 4.67.
4 H, 5Ј-H], 2.68 [t ( J
HH
=
HH
3
6
(
(
(
OC-6-12)-Ammine(cyclopentylamine)bis[(4-ethoxy)-4-oxobutano-
3
13
ato]dihydroxidoplatinum(IV) (3b): The synthesis was carried out as
described for 3a by using 2a (572 mg, 1.04 mmol) and silver 4-
ethoxy-4-oxobutanoate (525 mg, 2.08 mmol). The crude product
4
3
7
4
was purified by column chromatography (CH
2
Cl
]MeOH): δ = 4.13 (m, 4 H, 5Ј-
H), 3.44 (m, 1 H, 1-H), 2.67 [t( JHH = 6.7 Hz), 4 H, 2Ј-H], 2.57
2
/MeOH, 6:1).
1
(595.52): calcd. C 30.25, H 5.42, N 4.70; found C 30.37, H 5.39, N
4.66.
Yield: 390 mg, 61%. H NMR ([D
4
3
3
[
t( JHH = 6.7 Hz), 4 H, 3Ј-H], 2.04 (m, 2 H, 2-H), 1.77 (m, 2 H, 3-
(
(
OC-6-12)-Amminebis[(4-butoxy)-4-oxobutanoato]dihydroxido-
methylamine)platinum(IV) (3g): The synthesis was carried out as
3
H), 1.70 (m, 2 H, 2-H), 1.61 (m, 2 H, 3-H), 1.25 [t( JHH = 7.1 Hz),
H, 6Ј-H] ppm. 13C NMR ([D
]MeOH): δ = 182.9 (C-1Ј), 174.9
C-4Ј), 61.7 (C-5Ј), 56.7 (C-1), 33.8 (C-2), 31.9 [s + d( JCPt
6
4
described for 3a by using 2b (702 mg, 1.41 mmol) and silver 4-bu-
toxy-4-oxobutanoate (794 mg, 2.83 mmol). The crude product was
3
(
4
(
3
=
0 Hz), C-2Ј], 30.9 (C-3Ј), 25.1 (C-3), 14.5 (C-6Ј) ppm. 1 Pt NMR
[D ]MeOH): δ = 3645 ppm. C17 10Pt (621.55): calcd. C
2.85, H 5.51, N 4.51; found C 32.77, H 5.48, N 4.32.
95
purified by column chromatography (CH
2
Cl
2
/MeOH, 6:1). Yield:
4
H
34
N
2
O
1
3
3
4
14 mg, 36%. H NMR ([D ]MeOH): δ = 4.08 [t( JHH = 6.6 Hz),
4
3
3
H, 5Ј-H], 2.67 [t ( JHH = 6.7 Hz), 4 H, 2Ј-H], 2.58 [t( JHH
=
3
(OC-6-12)-Ammine(cyclopentylamine)dihydroxidobis[(4-propoxy)-4-
6.6 Hz), 4 H, 3Ј-H], 2.24 [s + d( JHPt = 23.6 Hz), 3 H, 1-H], 1.61
3
oxobutanoato]platinum(IV) (3c): The synthesis was carried out as
described for 3a by using 2a (406 mg, 0.74 mmol) and silver 4-prop-
oxy-4-oxobutanoate (393 mg, 1.47 mmol). The crude product was
(m, 4 H, 6Ј-H), 1.40 (m, 4 H, 7Ј-H), 0.95 [t( JHH = 7.4 Hz), 6 H,
1
3
8Ј-H] ppm. C NMR ([D
4
]MeOH): δ = 182.8 (C-1Ј), 175.0 (C-4Ј),
3
65.5 (C-5Ј), 31.9 [s + d( JCPt = 40 Hz, C-2Ј)], 31.8 (C-6Ј), 30.9 (C-
1
95
purified by column chromatography (CH
2
Cl
2
/MeOH, 6:1). Yield:
3Ј), 29.2 (C-1), 20.2 (C-7Ј), 14.2 (C-8Ј) ppm.
4
Pt NMR ([D ]-
Eur. J. Inorg. Chem. 2015, 1700–1708
1705
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
MeOH): δ = 3601 ppm. C17
H 5.82, N 4.49; found C 32.53, H 5.84, N 4.41.
H
36
N
2
O
10Pt (623.57): calcd. C 32.74,
DMSO): δ = 179.3 (C-1Ј), 178.9 (C-1ЈЈ), 172.7 (C-4Ј), 172.4 (C-4ЈЈ),
65.2 (C-5ЈЈ), 54.4 (C-1), 51.2 (C-5Ј), 31.9 (C-2), 31.4 (C-2ЈЈ), 30.5
(
C-2Ј), 30.0 (C-3ЈЈ), 29.4 (C-3Ј), 23.6 (C-3), 21.5 (C-6ЈЈ), 10.2 (C-
(
OC-6-13)-Acetato(ammine)cyclopentylamine(hydroxido)bis[(4-meth-
oxy)-4-oxobutanoato]platinum(IV) (4a): Compound 3a (60 mg,
.10 mmol) was suspended in DMF (5 mL), and acetic anhydride
12 μL, 0.13 mmol) was added. After 2.5 h of stirring at room
1
5
7
ЈЈ) ppm. N NMR ([D
6
]DMSO): –8.4 (NH ), –43.3 (NH
2
3
) ppm.
1
95
Pt NMR ([D
6
]DMSO): δ = 3792 ppm. C22H N O13Pt (735.65):
40 2
0
(
calcd. C 35.92, H 5.48, N 3.81; found C 35.96, H 5.50, N 3.68.
temp., a clear solution was obtained, and DMF was evaporated by
use of an oil pump. The residue was suspended in diethyl ether,
and the white product was collected by filtration and washed with
(OC-6-32)-Ammine[(4-butoxy)-4-oxobutanoato](cyclopentylamine)-
hydroxidobis[(4-methoxy)-4-oxobutanoato]platinum(IV) (4e): The
synthesis was carried out as described for 4a by using 3a (60 mg,
0.10 mmol) and 4-butoxy-4-oxobutanoic anhydride (42 mg,
1
diethyl ether. Yield: 58 mg, 71%. H NMR ([D
6
]DMSO): δ = 6.88
), 3.57 (s, 6 H, 5Ј-H), 3.25
m, 1 H, 1-H), 2.51 (m, 4 H, 2Ј-H), 2.46 (m, 4 H, 3Ј-H), 1.86 (s, 3
(
(
br. s, 2 H, NH
2
), 6.13 (br. s, 3 H, NH
3
0.13 mmol), with 2 h of stirring. White solid. Yield: 57 mg, 76%.
1
H NMR ([D
), 3.98 [t(3JHH = 6.7 Hz), 2 H, 5ЈЈ-H], 3.57 (s, 6 H, 5Ј-H),
3.24 (m, 1 H, 1-H), 2.49 (m, 4 H, 2Ј-H), 2.46 (m, 4 H, 3Ј-H), 2.43
C-1ЈЈ), 172.7 (C-4Ј), 54.3 (C-1), 51.2 (C-5Ј), 31.9 (C-2), 30.5 (C- (m, 2 H, 2ЈЈ-H/3ЈЈ-H), 2.41 (m, 2 H, 2ЈЈ-H/3ЈЈ-H), 1.85 (m, 2 H, 2-
6 2
]DMSO): δ = 6.86 (br. s, 2 H, NH ), 6.13 (br. s, 3
H, 2ЈЈ-H), 1.85 (m, 2 H, 2-H), 1.64 (m, 4 H, 2-H + 3-H), 1.47 (m, H, NH
3
2
H, 3-H) ppm. 13C NMR ([D
6
]DMSO): δ = 179.3 (C-1Ј), 177.9
(
2
1
5
Ј), 29.5 (C-3Ј), 23.7 (C-2ЈЈ), 23.6 (C-3) ppm. N NMR ([D
), –43.2 (NH ]DMSO): 3-H), 1.32 (m, 2 H, 7ЈЈ-H), 0.88 [t( JHH = 7.4 Hz), 3 H, 8ЈЈ-H] ppm.
) ppm. 195Pt NMR ([D
11Pt (635.54): calcd. C 32.13, H 5.08, N
.41; found C 32.09, H 5.03, N 4.30.
6
]- H), 1.64 (m, 4 H, 2-H + 3-H), 1.53 (m, 2 H, 6ЈЈ-H), 1.47 (m, 2 H,
3
DMSO): –8.6 (NH
δ = 3792 ppm. C17
2
3
6
1
3
H
32
N
2
O
C NMR ([D
4Ј), 172.4 (C-4ЈЈ), 63.4 (C-5ЈЈ), 54.4 (C-1), 51.2 (C-5Ј), 31.9 (C-2),
1.3 (C-2ЈЈ), 30.5 (C-2Ј), 30.2 (C-6ЈЈ), 30.0 (C-3ЈЈ), 29.4 (C-3Ј), 23.6
6
]DMSO): δ = 179.3 (C-1Ј), 178.9 (C-1ЈЈ), 172.7 (C-
4
3
(
OC-6–21)-Ammine(cyclopentylamine)hydroxidotris[(4-methoxy)-4-
1
5
(
(
C-3), 18.6 (C-7ЈЈ), 13.5 (C-8ЈЈ) ppm. N NMR ([D
NH ), –43.2 (NH ) ppm. Pt NMR ([D
2 3 6
6
]DMSO): –8.1
]DMSO): δ = 3792 ppm.
13Pt (749.68): calcd. C 36.85, H 5.65, N 3.74; found C
6.76, H 5.36, N 3.72.
oxobutanoato]platinum(IV) (4b): The synthesis was carried out as
described for 4a by using 3a (152 mg, 0.26 mmol) and 4-methoxy-
1
95
23 42 2
C H N O
3
4
-oxobutanoic anhydride (94 mg, 0.38 mmol), with 3 h of stirring.
1
White solid. Yield: 159 mg, 88%. H NMR ([D
6
]DMSO): δ = 6.84
(br. s, 2 H, NH
2
), 6.11 (br. s, 3 H, NH
3
), 3.57 (s, 6 H, 5Ј-H), 3.56
(OC-6-13)-Acetato(ammine)cyclopentylaminebis[(4-ethoxy)-4-oxo-
(s, 3 H, 5ЈЈ-H), 3.24 (m, 1 H, 1-H), 2.49 (m, 4 H, 2Ј-H), 2.46 (m, 4 butanoato]hydroxidoplatinum(IV) (4f): The synthesis was carried
H, 3Ј-H), 2.44 (m, 2 H, 2ЈЈ/-H3ЈЈ-H), 2.42 (m, 2 H, 2ЈЈ/-H3ЈЈ-H), out as described for 4a by using 3b (60 mg, 0.10 mmol) and acetic
.85 (m, 2 H, 2-H), 1.64 (m, 4 H, 2-H + 3-H), 1.47 (m, 2 H, 3-H) anhydride (11 μL, 0.12 mmol), with 3 h of stirring. White solid.
1
1
3
1
ppm. C NMR ([D
6
]DMSO): δ = 179.3 (C-1Ј), 178.8 (C-1ЈЈ), 172.8 Yield: 46 mg, 71%. H NMR ([D
C-4ЈЈ), 172.7 (C-4Ј), 54.4 (C-1), 51.2 (C-5Ј), 51.1 (C-5ЈЈ), 31.9 (C- NH ), 6.14 (br. s, 3 H, NH ), 4.04 (m, 4 H, 5Ј-H), 3.25 (m, 1 H, 1-
H), 2.48 (m, 4 H, 2Ј-H), 2.43 (m, 4 H, 3Ј-H), 1.86 (s, 3 H, 2ЈЈ-H),
) ppm. Pt 1.85 (m, 2 H, 2-H), 1.64 (m, 4 H, 2-H + 3-H), 1.47 (m, 2 H, 3-H),
6
]DMSO): δ = 6.89 (br. s, 2 H,
(
2
2
3
), 31.3 (C-2ЈЈ), 30.6 (C-2Ј), 29.8 (C-3ЈЈ), 29.4 (C-3Ј), 23.6 (C-3)
1
5
195
ppm. N NMR ([D
NMR ([D ]DMSO): δ = 3791 ppm. C20
C 33.95, H 5.13, N 3.96; found C 33.86, H 4.74, N 3.92.
6
]DMSO): –8.5 (NH
2
), –43.0 (NH
13Pt (707.60): calcd. 1.17 [t( JHH = 7.1 Hz), 6 H, 6Ј-H] ppm. C NMR ([D
= 179.4 (C-1Ј), 177.9 (C-1ЈЈ), 172.2 (C-4Ј), 59.8 (C-5Ј), 54.3 (C-1),
1.9 (C-2), 30.5 (C-2Ј), 29.7 (C-3Ј), 23.7 (C-2ЈЈ), 23.6 (C-3), 14.1
3
3
13
6
H
36
N
2
O
6
]DMSO): δ
3
(
(
OC-6-32)-Ammine(cyclopentylamine)[(4-ethoxy)-4-oxobutanoato]-
1
5
C-6Ј) ppm. N NMR ([D
ppm. 195Pt NMR ([D
]DMSO): δ = 3791 ppm. C19
663.59): calcd. C 34.39, H 5.47, N 4.22; found C 34.33, H 5.61, N
.19.
6 2 3
]DMSO): –8.8 (NH ), –43.1 (NH )
hydroxidobis[(4-methoxy)-4-oxobutanoato]platinum(IV) (4c): The
synthesis was carried out as described for 4a by using 3a (50 mg,
0
6
36 2
H N O11Pt
(
4
.08 mmol) and 4-ethoxy-4-oxobutanoic anhydride (29 mg,
.12 mmol), with 2.5 h of stirring. White solid. Yield: 50 mg, 82%.
(OC-6-13)-Ammine(cyclopentylamine)bis[(4-ethoxy)-4-oxobutano-
), 4.02 (m, 4 H, 5ЈЈ-H), 3.57 (s, 6 H, 5Ј-H), 3.24 (m, 1 H, ato]hydroxido[(4-methoxy)-4-oxobutanoato]platinum(IV) (4g): The
-H), 2.49 (m, 4 H, 2Ј-H), 2.46 (m, 4 H, 3Ј-H), 2.43 (m, 2 H, 2ЈЈ- synthesis was carried out as described for 4a by using 3b (50 mg,
0
1
H NMR ([D
6
]DMSO): δ = 6.86 (br. s, 2 H, NH
2
), 6.12 (br. s, 3
H, NH
1
3
H/-H3ЈЈ-H), 2.41 (m, 2 H, 2ЈЈ-H/3ЈЈ-H), 1.84 (m, 2 H, 2-H), 1.64
0.08 mmol) and 4-methoxy-4-oxobutanoic anhydride (29 mg,
3
(
3
(
(
m, 4 H, 2-H + 3-H), 1.47 (m, 2 H, 3-H), 1.16 [t( JHH = 7.1 Hz),
0.12 mmol), with 2 h of stirring. White solid. Yield: 44 mg, 73%.
H, 6ЈЈ-H] ppm. 1 C NMR ([D
3
]DMSO): δ = 179.4 (C-1Ј), 178.9
C-1ЈЈ), 172.7 (C-4Ј), 172.4 (C-4ЈЈ), 59.7 (C-5ЈЈ), 54.4 (C-1), 51.3 H, NH
3
1
H NMR ([D
), 4.04 (m, 4 H, 5Ј-H), 3.56 (s, 3 H, 5ЈЈ-H), 3.25 (m, 1 H,
C-5Ј), 31.9 (C-2), 31.3 (C-2ЈЈ), 30.6 (C-2Ј), 30.0 (C-3ЈЈ), 29.5 (C- 1-H), 2.49 (m, 4 H, 2Ј-H), 2.44 (m, 4 H, 3Ј-H), 2.43 (m, 2 H, 2ЈЈ-
6
6 2
]DMSO): δ = 6.86 (br. s, 2 H, NH ), 6.13 (br. s, 3
15
3
Ј), 23.6 (C-3), 14.1 (C-6ЈЈ) ppm. N NMR ([D
), –43.1 (NH ]DMSO): δ = 3791 ppm. 4 H, 2-H + 3-H), 1.47 (m, 2 H, 3-H), 1.17 [t( JHH = 7.1 Hz), 6 H,
) ppm. 195Pt NMR ([D
13Pt (721.63): calcd. C 34.95, H 5.31, N 3.88; found C
6
]DMSO): –8.4
H/3ЈЈ-H), 2.42 (m, 2 H, 2ЈЈ-H/3ЈЈ-H), 1.85 (m, 2 H, 2-H), 1.64 (m,
3
(NH
2
3
6
1
3
C
21
H
38
N
2
O
6Ј-H] ppm. C NMR ([D
6
]DMSO): δ = 179.4 (C-1Ј), 178.9 (C-
34.93, H 5.27, N 3.86.
1ЈЈ), 172.8 (C-4ЈЈ), 172.2 (C-4Ј), 59.8 (C-5Ј), 54.4 (C-1), 51.1 (C-
5
2
–
ЈЈ), 31.9 (C-2), 31.3 (C-2ЈЈ), 30.5 (C-2Ј), 29.8 (C-3ЈЈ), 29.6 (C-3Ј),
(
OC-6-32)-Ammine(cyclopentylamine)hydroxidobis[(4-methoxy)-4-
1
5
3.6 (C-3), 14.0 (C-6Ј) ppm. N NMR ([D
43.2 (NH ]DMSO): δ = 3790 ppm.
) ppm. 195Pt NMR ([D
13Pt (735.65): calcd. C 35.92, H 5.48, N 3.81; found C
5.85, H 5.62, N 3.77.
6 2
]DMSO): –8.7 (NH ),
oxobutanoato][(4-propoxy)-4-oxobutanoato]platinum(IV) (4d): The
synthesis was carried out as described for 4a by using 3a (50 mg,
0
3
6
22 40 2
C H N O
3
.08 mmol) and 4-propoxy-4-oxobutanoic anhydride (32 mg,
.12 mmol), with 2.5 h of stirring. White solid. Yield: 43 mg, 73%.
0
1
H NMR ([D
6
]DMSO): δ = 6.86 (br. s, 2 H, NH
2
), 6.14 (br. s, 3
(OC-6–21)-Ammine(cyclopentylamine)tris[(4-ethoxy)-4-oxobutano-
ato]hydroxidoplatinum(IV) (4h): The synthesis was carried out as
H, NH
3
), 3.94 [t(3JHH = 6.7 Hz), 2 H, 5ЈЈ-H], 3.57 (s, 6 H, 5Ј-H),
3.25 (m, 1 H, 1-H), 2.49 (m, 4 H, 2Ј-H), 2.46 (m, 4 H, 3Ј-H), 2.44 described for 4a by using 3b (75 mg, 0.12 mmol) and 4-ethoxy-4-
(
m, 2 H, 2ЈЈ-H/3ЈЈ-H), 2.42 (m, 2 H, 2ЈЈ-H/3ЈЈ-H), 1.85 (m, 2 H, 2- oxobutanoic anhydride (42 mg, 0.15 mmol), with 2 h of stirring.
1
H), 1.64 (m, 4 H, 2-H + 3-H), 1.57 (m, 2 H, 6ЈЈ-H), 1.47 (m, 2 H,
3
White solid. Yield: 74 mg, 82%. H NMR ([D
6
]DMSO): δ = 6.87
3
13
-H), 0.87 [t( JHH = 7.4 Hz), 3 H, 7ЈЈ-H] ppm. C NMR ([D
6
]- (br. s, 2 H, NH ), 6.13 (br. s, 3 H, NH ), 4.03 (m, 4 H, 5Ј-H), 4.02
2
3
Eur. J. Inorg. Chem. 2015, 1700–1708
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© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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FULL PAPER
(m, 2 H, 5ЈЈ-H), 3.25 (m, 1 H, 1-H), 2.49 (m, 4 H, 2Ј-H), 2.44 (m, Incubation with Ascorbic Acid: Reduction of complexes 3a, 3d, 4b,
4
1
1
H, 3Ј-H), 2.42 (m, 2 H, 2ЈЈ-H/3ЈЈ-H), 2.41 (m, 2 H, 2ЈЈ-H/3ЈЈ-H), 4i,
.84 (m, 2 H, 2-H), 1.64 (m, 4 H, 2-H + 3-H), 1.47 (m, 2 H, 3-H), (IV),
.17 [t( JHH = 7.1 Hz), 6 H, 6Ј-H], 1.16 [t( JHH = 7.1 Hz), 3 H, 6ЈЈ- oxobutanoato]platinum(IV) by ascorbic acid was monitored by H
(OC-6-44)-acetato(diammine)hydroxido(malonato)platinum-
and (OC-6-33)-diammine(malonato)bis[(4-methoxy)-4-
3
3
1
13
H] ppm. C NMR ([D
6
]DMSO): δ = 179.4 (C-1Ј), 178.9 (C-1ЈЈ),
NMR spectroscopy at ambient temperature. 1 mm solutions of the
O, pD
C-2), 31.3 (C-2ЈЈ), 30.5 (C-2Ј), 30.0 (C-3ЈЈ), 29.6 (C-3Ј), 23.6 (C- = 7.4), and H NMR spectra were recorded over a period of 24 h
1
(
72.3 (C-4ЈЈ), 172.2 (C-4Ј), 59.8 (C-5Ј), 59.7 (C-5ЈЈ), 54.4 (C-1), 31.9 compounds were prepared in 50 mm phosphate buffer (in D
2
1
15
3
–
C
3
), 14.0 (C-6Ј + C-6ЈЈ) ppm. N NMR ([D
43.0 (NH ]DMSO): δ = 3790 ppm. NMR spectra could generally not be seen [with the exception of
) ppm. 195Pt NMR ([D
13Pt (749.68): calcd. C 36.85, H 5.65, N 3.74; found C
6.83, H 5.80, N 3.61.
6
]DMSO): –8.6 (NH
2
),
in order to check the stability of the complexes; changes in the
3
6
23
H
42
N
2
O
(OC-6-44)-acetato(diammine)hydroxido(malonato)platinum(IV),
showing a small amount of hydrolysis]. Subsequently, ascorbic acid
1
(
25 mm) was added and H NMR spectra were recorded until com-
(
OC-6–21)-Ammine(hydroxido)tris[(4-methoxy)-4-oxobutanoato]-
methylamineplatinum(IV) (4i): Compound 3d (50 mg, 0.09 mmol)
was suspended in CHCl (5 mL), and 4-methoxy-4-oxobutanoic an-
plete reduction of the platinum(IV) complex was observed. The
process was monitored by following the decrease in intensity of the
3
CH
or in the case of (OC-6-44)-acetato(diammine)hydroxido(malon-
ato)platinum(IV), by following the decrease in intensity of the CH
2
signals of the coordinated succinic acid methyl ester chains,
hydride (29 mg, 0.12 mmol) was added. After 72 h of stirring at
room temp., a clear solution was obtained, diisopropyl ether was
added, and CHCl
3
3
was evaporated to yield a white solid (suspen-
signal of the acetato ligand. In all cases, integration of the signals
was performed relative to the sum of all signals deriving from the
respective (coordinated and non-coordinated) ligands.
sion in diisopropyl ether), which was collected by filtration and
1
washed with diethyl ether. Yield: 54 mg, 89%. H NMR ([D
DMSO): δ = 6.69 (br. s, 2 H, NH ), 6.14 (br. s, 3 H, NH ), 3.57 (s,
H, 5Ј-H), 3.56 (s, 3 H, 5ЈЈ-H), 2.49 (m, 4 H, 2Ј-H), 2.46 (m, 4 H, Biological Tests
Ј-H), 2.44 (m, 2 H, 2ЈЈ-H/3ЈЈ-H), 2.42 (m, 2 H, 2ЈЈ-H/3ЈЈ-H), 2.02
6
]-
2
3
6
3
3
13
Cell lines and culture conditions: CH1 cells (identified by STR pro-
filing as PA-1 ovarian teratocarcinoma cells by Multiplexion, Hei-
delberg, Germany; see also ref.[ ) were provided by Lloyd R.
Kelland, CRC Centre for Cancer Therapeutics, Institute of Cancer
Research, Sutton, UK. SW480 colon carcinoma and A549 non-
small cell lung cancer cells were provided by Brigitte Marian, Insti-
tute of Cancer Research, Department of Medicine I, Medical Uni-
versity of Vienna, Austria, and authenticated by Multiplexion, Hei-
[
1
5
t( JHH = 6.2 Hz), 3 H, 1-H] ppm. C NMR ([D
6
]DMSO): δ =
79.1 (C-1Ј), 178.6 (C-1ЈЈ), 172.9 (C-4ЈЈ), 172.3 (C-4Ј), 51.3 (C-5Ј),
1.1 (C-5ЈЈ), 31.3 (C-2ЈЈ), 30.5 (C-2Ј), 29.8 (C-3ЈЈ), 29.5 (C-3Ј), 27.7
48]
1
5
(
C-1) ppm. N NMR ([D
6
]DMSO): –34.2 (NH
]DMSO): δ = 3756 ppm. C16
653.51): calcd. C 29.41, H 4.63, N 4.29; found C 29.10, H 4.70, N
.23.
2 3
), –43.6 (NH )
ppm. 95Pt NMR ([D
1
6
30 2
H N O13Pt
(
4
(
OC-6–21)-Amminetris[(4-ethoxy)-4-oxobutanoato](hydroxido)meth- delberg, Germany. All cells were grown as monolayer cultures in
2
ylamineplatinum(IV) (4j): The synthesis was carried out as de-
75 cm culture flasks (CytoOne, Starlab, UK) in complete medium,
scribed for 4i by using 3e (80 mg, 0.14 mmol) and 4-ethoxy-4- that is, minimal essential medium (MEM) supplemented with 10%
oxobutanoic anhydride (48 mg, 0.18 mmol), with 2.5 h of stirring.
heat-inactivated fetal bovine serum, 1 mm sodium pyruvate, 4 mm
l-glutamine, and 1% v/v nonessential amino acids from 100ϫ
ready-to-use stock solution (all purchased from Sigma–Aldrich,
1
White solid. Yield: 92 mg, 94%. H NMR ([D
6
]DMSO): δ = 6.70
(
(
2
6
br. s, 2 H, NH ), 6.13 (br. s, 3 H, NH ), 4.04 (m, 4 H, 5Ј-H), 4.03
2
3
m, 2 H, 5ЈЈ-H), 2.49 (m, 4 H, 2Ј-H), 2.44 (m, 4 H, 3Ј-H), 2.43 (m, Austria). Cultures were maintained at 37 °C in a moist atmosphere
3
H, 2ЈЈ-H/3ЈЈ-H), 2.41 (m, 2 H, 2ЈЈ-H/3ЈЈ-H), 2.02 [t( JHH
=
2
containing 5% CO in air.
3
3
.1 Hz), 3 H, 1-H], 1.17 [t( JHH = 7.1 Hz), 6 H, 6Ј-H], 1.16 [t( JHH
7.1 Hz), 3 H, 6ЈЈ-H] ppm. 13C NMR ([D
Cytotoxicity tests in cancer cell lines: Cytotoxicity was determined
by the colorimetric 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-
tetrazolium bromide (MTT) assay in at least three independent ex-
periments. For this purpose, cells were harvested from culture
flasks by using trypsin-EDTA solution (Sigma–Aldrich, Austria)
and seeded into 96-well microculture plates (CytoOne, Starlab,
=
6
]DMSO): δ = 179.2 (C-
1
5
1
–
Ј), 178.6 (C-1ЈЈ), 172.4 (C-4ЈЈ), 172.2 (C-4Ј), 59.8 (C-5Ј), 59.7 (C-
ЈЈ), 31.3 (C-2ЈЈ), 30.5 (C-2Ј), 30.0 (C-3ЈЈ), 29.7 (C-3Ј), 27.7 (C-1),
15
4.1 (C-6Ј + C-6ЈЈ) ppm. N NMR ([D
6
]DMSO): –34.2 (NH
) ppm. 195Pt NMR ([D
6
]DMSO): δ = 3755 ppm.
2
),
43.8 (NH
3
C
19
H
36
N
2
O
13Pt (695.59): calcd. C 32.81, H 5.22, N 4.03; found C
3
UK) in the following cell numbers per well (in 100 μL each): 1ϫ10
(
32.52, H 5.38, N 3.99.
3
3
CH1), 2.5ϫ10 (SW480), 3ϫ10 (A549). Plates were incubated
(
OC-6–21)-Ammine(hydroxido)methylaminetris[(4-propoxy)-4-oxo- for 24 h, after which the test compounds were dissolved and serially
butanoato]platinum(IV) (4k): The synthesis was carried out as de-
scribed for 4a by using 3f (60 mg, 0.10 mmol) and 4-propoxy-4-
diluted in complete medium and dilutions added in triplicates of
100 μL per well. After exposure for 96 h, drug solutions were
replaced with 100 μL RPMI 1640 medium and 20 μL MTT in
phosphate-buffered saline (5 mg/mL). After incubation for 4 h, the
liquid was removed and the solid formazan product was dissolved
in 150 μL of DMSO per well. Optical densities at 550 nm (and a
oxobutanoic anhydride (38 mg, 0.13 mmol), with 2.5 h of stirring.
1
White solid. Yield: 59 mg, 79%. H NMR ([D
6
]DMSO): δ = 6.70
3
(br. s, 2 H, NH
2
), 6.14 (br. s, 3 H, NH
H, 5Ј-H], 3.94 [t( JHH = 6.4 Hz), 2 H, 5ЈЈ-H], 2.49 (m, 4 H, 2Ј-H),
3
), 3.95 [t( JHH = 6.5 Hz), 4
3
2
.46 (m, 4 H, 3Ј-H), 2.44 (m, 2 H, 2ЈЈ-H/3ЈЈ-H), 2.42 (m, 2 H, 2ЈЈ- reference wavelength of 690 nm) were measured with a microplate
3
H/3ЈЈ-H), 2.02 [t( JHH = 6.2 Hz), 3 H, 1-H], 1.57 (m, 4 H, 6Ј-H),
1
reader (Biotek ELx808), and IC50 values were calculated from con-
.56 (m, 2 H, 6ЈЈ-H), 0.873 [t( JHH = 7.4 Hz), 6 H, 6Ј-H], 1.16 centration-effect curves by interpolation.
3
3
13
[
1
6
(
(
t( JHH = 7.4 Hz), 3 H, 6ЈЈ-H] ppm. C NMR ([D
6
]DMSO): δ =
79.2 (C-1Ј), 178.6 (C-1ЈЈ), 172.4 (C-4ЈЈ), 172.3 (C-4Ј), 65.3 (C-5Ј),
5.2 (C-5ЈЈ), 31.3 (C-2ЈЈ), 30.5 (C-2Ј), 30.0 (C-3ЈЈ), 29.6 (C-3Ј), 27.7 Acknowledgments
15
C-1), 21.5 (C-6Ј + C-6ЈЈ), 10.2 (C-7Ј + C-7ЈЈ) ppm. N NMR
[D ]DMSO): –34.1 (NH ), –43.7 (NH
) ppm. 195Pt NMR ([D
13Pt (737.67): calcd. C 35.82,
6
2
3
6
]- The authors are very grateful for the support of the Austrian
Research Promotion Agency (FFG), the Austrian Council for Re-
search and Technology Development, the Austrian Science Fund
42 2
DMSO): δ = 3756 ppm. C22H N O
H 5.74, N 3.80; found C 35.64, H 5.41, N 3.82.
Eur. J. Inorg. Chem. 2015, 1700–1708
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© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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FULL PAPER
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