Metalcarbonyl complexes of acetylsalicylic acid as neo-anticancer agents

Article abstract of DOI:10.1016/j.ejmech.2010.08.028

[(Prop-2-ynyl)-2-acetoxybenzoate]dicobalthexacarbonyl (Co-ASS), a derivative of the nonsteroidal anti-inflammatory drug aspirin (ASS), demonstrated high cytotoxic potential against various tumor cells. The [acetylene]Co₂(CO)₆ cluster strongly increased the biological effects compared to aspirin. In this study we evaluated the use of [cyclopentadienyl]metalcarbonyl as cytotoxic moiety with a broader series of metals: molybdenum, manganese, cobalt and rhodium. All compounds were tested for cytotoxicity against breast (MCF-7, MDA-MB-231) and colon cancer (HT-29) cell lines. Their COX-1 and COX-2 inhibitory effects were evaluated at isolated isoenzymes. Additionally, the influence on the level of the major COX metabolite prostaglandin E₂ (PGE₂) was quantified in MDA-MB-231 breast cancer cells. Whereas the pure ligands or ASS did not show any cytotoxic effect, all metal complexes inhibited the tumor cell growth. The inhibitory effects at COX-1 and COX-2 enzymes were low. Only the Prop-Cp-ASS-Rh complex (10 μM) caused an important inhibition of COX-1 by 60% and COX-2 by 30%. ASS showed at the same concentration only a marginal repression of COX-1 activity (30%) and no effect on COX-2.

Full text of DOI:10.1016/j.ejmech.2010.08.028

European Journal of Medicinal Chemistry 45 (2010) 5157e5163
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
[Cyclopentadienyl]metalcarbonyl complexes of acetylsalicylic acid as
neo-anticancer agents
,c,
Gerhard Rubner a, Kerstin Bensdorf a, Anja Wellner a, Silke Bergemann a, Ingo Ott b, Ronald Gust a
*
a Institute of Pharmacy, Freie Universität Berlin, Königin-Luise-Str. 2 þ 4, 14195 Berlin, Germany
b Institute of Pharmacy, TU Braunschweig, Beethovenstr. 55, 38106 Braunschweig, Germany
c Institut für Pharmazie, Universität Innsbruck, Innrain 52, A-6020 Innsbruck, Austria
a r t i c l e i n f o
a b s t r a c t
Article history:
[(Prop-2-ynyl)-2-acetoxybenzoate]dicobalthexacarbonyl (Co-ASS), a derivative of the nonsteroidal anti-
inflammatory drug aspirinÒ (ASS), demonstrated high cytotoxic potential against various tumor cells. The
[acetylene]Co2(CO)6 cluster strongly increased the biological effects compared to aspirinÒ. In this study
we evaluated the use of [cyclopentadienyl]metalcarbonyl as cytotoxic moiety with a broader series of
metals: molybdenum, manganese, cobalt and rhodium. All compounds were tested for cytotoxicity
against breast (MCF-7, MDA-MB-231) and colon cancer (HT-29) cell lines. Their COX-1 and COX-2
inhibitory effects were evaluated at isolated isoenzymes. Additionally, the influence on the level of the
major COX metabolite prostaglandin E2 (PGE2) was quantified in MDA-MB-231 breast cancer cells.
Whereas the pure ligands or ASS did not show any cytotoxic effect, all metal complexes inhibited the
tumor cell growth. The inhibitory effects at COX-1 and COX-2 enzymes were low. Only the Prop-Cp-ASS-
Received 14 May 2010
Received in revised form
30 July 2010
Accepted 10 August 2010
Available online 18 August 2010
Keywords:
Transition metal complexes
Acetylsalicylic acid
Cyclopentadiene
Cytotoxicity
Rh complex (10 mM) caused an important inhibition of COX-1 by 60% and COX-2 by 30%. ASS showed at
COX inhibition
the same concentration only a marginal repression of COX-1 activity (30%) and no effect on COX-2.
Ó 2010 Elsevier Masson SAS. All rights reserved.
1. Introduction
the DNA (as known from other metal complexes) did not contribute to
the mode of action [13].
Despite thesuccessofcisplatinand closelyrelated platinum agents
in tumor therapy [1,2], there is an increasing interest in new metal-
based drugs for the second line therapy of platinum resistant tumors,
e.g. the mammary carcinoma using carrier ligands [3e8]. Especially
with complexes of ruthenium, rhodium or manganese promising
results were generated during the last years [9,10].
Furthermore, some nonsteroidal anti-inflammatory drugs (NSAIDs),
mainly aspirinÒ (ASS), have already demonstrated their activity in
prevention of colon cancer. ASS mediates its effects via interaction with
the cyclooxygenase enzymes COX-1 and COX-2 without showing
cytotoxic effects. In order to optimize ASS for the treatment of cancer
we focused our attention on its combination with a metal moiety.
[(Prop-2-ynyl)-2-acetoxybenzoate]hexacarbonyldicobalt (Co-ASS) was
already identified as a cytotoxic COX inhibitor [11]. The cobalt cluster
mediated cytotoxic properties and higher COX inhibition compared to
ASS [12]. Whether the inactivation of the COX caused cell death is still
unclear. However, it has been already verified that the interaction with
In a structureeactivity relationship (SAR) study we tried to
verify the significance of the metal and its binding mode to the ASS
moiety for cytotoxic and COX inhibitory effects. In the first part of
this study [14], we demonstrated that the [alkyne]Co2(CO)6
cluster caused maximal effects. Exchange of the Co2(CO)6 by Ru- or
Fe-carbonyls and the use of higher metal carbonyl cluster (e.g.
Co4(CO)10) led to active compounds but did not enhance the bio-
logical activity compared to Co-ASS [14]. Interestingly, the ferrocen
analogous was completely inactive.
In the present study, we used a cyclopentadiene moiety and
combined it with metalcarbonyls of cobalt, manganese, rhodium
and molybdenum. These compounds were easily available using
h
5-[(cyclopentadienyl)alkyl-2-acetoxybenzoate]thallium as inter-
mediate [15]. Furthermore, the alkyl chain was varied in length in
order to evaluate the significance of the distance between the
NSAID and the metal for cytotoxicity and COX inhibition.
The cytotoxic effects were investigated in vitro using HT-29 colon
carcinoma cells as well as MDA-MB-231 and MCF-7 breast cancer
cells. MCF-7 cells have a basal level of COX-1 and a barely detectable
and transient COX-2 inducible expression, whereas MDA-MB-231
cells show a low expression of COX-1 but a constitutive level of COX-
2 [16]. Further experiments included the COX inhibitory properties
* Corresponding author. Institut für Pharmazie, Universität Innsbruck, Innrain
52a, A-6020 Innsbruck, Austria. Tel.: þ43 512 507 5245; fax: þ43 512 507 2940.
E-mail address: Ronald.gust@uibk.ac.at (R. Gust).
0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.08.028

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G. Rubner et al. / European Journal of Medicinal Chemistry 45 (2010) 5157e5163
at isolated enzymes by ELISA and the quantification of the major
intracellular metabolite prostaglandine E2 (PGE2) in MDA-MB-231
cells after treatment with the drugs.
In order to clarify the importance of the aspirin-moiety for the biolo-
gical effects of Alkyl-Cp-ASS-Tl complexes, thallocen (cyclopentadienyl-
thallium) was synthesized as further reference compound [23].
2. Chemistry
3. Results and discussion
The (cyclopenta-1,3-dienyl)alkyl-2-acetoxybenzoates were prepared
by esterification of 2-acetylsalicoyl chloride, synthesized according
to Riegel and Wittcoff [17] or Weizmann et al. [18] with the
respective cyclopentadienyl alcohol [19] obtained from freshly
cracked cyclopentadiene after deprotonation with NaH in THF and
reaction with the chloroalcohol at 0 ꢀC (see Scheme 1).
3.1. Cytotoxicity
Antitumor activity was determined in vitro using MCF-7 and
MDA-MB-231 breast cancer cell lines as well as the colon carcinoma
cell line HT-29 (Table 1) in a crystal violet assay. In this test, the cell
biomass was quantified after an incubation time of 96 h under the
Attempts failed to achieve 2-cyclopentadienylethanol by reac-
tion of 2-chloroethanol and sodocen. Only bis(cyclopentadienyl)
ethane could be isolated. Therefore, we modified the procedure
described by Schroeder et al. [20]. Potassium-tert-butylat was used
as base and ethylene oxide as reactant. Cyclopentadienylethanol
was obtained as clear oil by vacuum distillation. It should be noted
that it was impossible up to now to get the methylene derivative.
The Alkyl-Cp-ASS compounds were characterized by 1H
NMR spectroscopy. Due to the tautomerism of the double bond, an
isomeric mixture was present in each case. A rapid degradation at
room temperature as described for related compounds [21] could
not be detected. Only 10% of the compounds degraded by Dielse
Alder-reactions within 4 months, while they were stable at ꢁ20 ꢀC
for more than a year.
Reaction of Alkyl-Cp-ASS with one equivalent of thallium eth-
oxide in n-hexane at ꢁ30 ꢀC afforded the corresponding thallium
complex (Alkyl-Cp-ASS-Tl, see Scheme 1), which was isolated as
beige solid and characterized by HR-EI-MS and elemental analyses.
The variation of the metal was performed on the example of
Prop-Cp-ASS. Treatment of Prop-Cp-ASS-Tl with MnBr(CO)5 in THF
yielded the manganese complex Prop-Cp-ASS-Mn as yellow oil,
reaction with [Rh2(CO)4Cl2] inTHF at ꢁ50 ꢀC gave Prop-Cp-ASS-Rh as
a dark brown solid (Scheme 2). TlBr or TlCl precipitated during the
reaction and were sucked off prior to the evaporation of the solvent.
Prop-Cp-ASS-Co was obtained by treatment of two equivalents of
Prop-Cp-ASS-Tl inTHF with the deep green reaction mixture of I2 and
Co2(CO)8 in THF at room temperature (Scheme 2) [22]. The resulting
deep yellow solid could be purified by column chromatography.
Finally, Prop-Cp-ASS was reacted with Mo(CO)3(NCMe)3 in
toluene to yield Prop-Cp-ASS-Mo, which was treated with a stoi-
chiometric amount of CHI3 in dichloromethane giving Prop-Cp-
ASS-Mo-I as dark red crystalline solid (see Scheme 2).
influence of vehicle (DMSO) or increasing amounts (0.1e10 mM) of
complexes. For each concentration the T/Ccorr value was calculated
(see Section 5.2.2). The IC50 value represents the concentration
causing 50% inhibition of growth inhibition (T/Ccorr ¼ 50%).
Cisplatin as a reference reduced the growth of all used cell lines
with IC50 values in the range of 2.0e3.3
selectivity for mammary carcinoma cells (MCF-7: IC50 ¼ 1.4
MDA-MB-231: IC50 ¼ 1.9 M) and was more active than cisplatin
(MCF-7: IC50 ¼ 2.0 M; MDA-MB-231: IC50 ¼ 3.3 M). Against HT-
29 cells an IC50 value of only 9.8 M was calculated. The cytotoxicity
mM. Co-ASS showed a clear
mM;
m
m
m
m
of Co-ASS was clearly mediated by the combination of ASS and the
[propargyl]Co2(CO)6 moiety. Both, ASS and the cobalt cluster alone
were inactive (IC50 > 50 mM).
Alkyl-Cp-ASS-metal complexes showed a comparable trend. The
free ligands and the reactants Mn(CO)5Br, Rh2(CO)4Cl2 and Mo
(CO)3NCMe did not cause cytotoxicity. Only thallocen was
marginally active at HT-29 cells (IC50 ¼ 23.9
mM).
Thallium complexes demonstrated cytotoxic properties at the
MCF-7 cell line dependent on the length of the alkyl spacer (Et
(IC50 ¼ 9.8
MDA-MB-231 cell line But-Cp-ASS-Tl (IC50 ¼ 20.7
active than its ethyl (IC50 ¼ 11.4 M) and propyl (IC50 ¼ 11.7
derivatives, while at the HT-29 cell line Et-Cp-Ass-Tl showed high
M).
m
M) < Prop (IC50 ¼ 7.3
m
M) < But (IC50 ¼ 5.4
M) was less
M)
mM)). At the
m
m
m
cytotoxicity (IC50 ¼ 4.6
m
Prop-Cp-ASS-Tl was selected for metal-variations. The exchange
of Tl by Co-, Mn-, Rh- and Mo-carbonyls slightly reduced the activity
at MCF-7 cells (IC50 ¼ 10e15
mM). An exception was Prop-Cp-ASS-
Mn which was distinctly less active at MCF-7 (IC50 ¼ 24.8
mM) cells
and completely inactive at the MDA-MB-231 cell line.
Generally, these compounds are less cytotoxic against MDA-MB-
231 cells. The IC50 values amounted to only 26e50 M. Effects at
m
HT-29 and MCF-7 cells were nearly identical (Table 1).
NaH, Cl-alkyl-OH, THF or
tert.-butOH, K, C2H4O
HO
+ 2-acetylsalicoylchloride,
pyridine
n
n = 1, 2, 3
+ isomers
Alkyl-Cp-OH
O
O
O
O
O
O
+ TlOC2H5, n-hexane
Tl
n
n
+ isomers
O
Alkyl-Cp-ASS
Alkyl-Cp-ASS-Tl
O
Scheme 1. Synthesis of Alkyl-Cp-ASS and related thallium complexes.

G. Rubner et al. / European Journal of Medicinal Chemistry 45 (2010) 5157e5163
5159
O
O
O
O
O
O
CHI3
Mo
Mo
OC
OC
I
O
OC
CO
CO
CO
Prop-Cp-ASS-Mo-I
Prop-Cp-ASS-Mo
O
Mo(CO)3(NCMe)3
O
O
MnBr(CO)5 , THF
O
O
Prop-Cp-
ASS-Tl
Mn
OC
CO
CO
½ [Rh2(CO)4Cl2]
THF
Prop-Cp-ASS-Mn
½ Co2(CO)8, I2
THF
O
O
O
O
O
O
O
O
Rh
Co
OC
CO
OC
CO
Prop-Cp-ASS-Rh
Prop-Cp-ASS-Co
Scheme 2. Metal exchange at Prop-ASS-Tl.
3.2. Determination of COX inhibitory effects
same concentration, none of the free ligands were able to inhibit
the enzymes.
Since it was very likely that the interference in the arachidonic
acid pathway does contribute to the mode of action, the effects of
the organometallic compounds on isolated COX-1 and COX-2
enzymes were quantified by ELISA. In an MDA-MB-231 cell based
assay we also quantified the PGE2 level as an indicator of interac-
tion with intracellular cyclooxygenase enzymes.
Prop-Cp-ASS-metal complexes showed inhibitoryeffects at COX-1
verysimilartoaspirinÒ. OnlyProp-Cp-ASS-Mo-Iwaslessactive, while
with Prop-Cp-ASS-Rh inhibitory effects of 57.3% were achieved.
At the COX-2 isoenzyme all Prop-Cp-ASS-metal complexes
were more active than aspirinÒ (Chart 1). Prop-Cp-ASS-Tl (42.3%
AspirinÒ was only marginally active in the ELISA at a concen-
tration of 10 mM (COX-1: 29% inhibition; COX-2: no effects). At the
Table 1
Cytotoxic effects (IC50 values given in mM) of Alkyl-Cp-ASS-metal complexes.
Compound
MCF-7
MDA-MB-231
HT-29
cisplatin
Co-ASS
thallocen
Mn(CO)5Br, Rh(CO)4Cl2
Mo(CO)3,NCMe
aspirin
Alkyl-Cp-ASS
Et-Cp-ASS-Tl
Prop-Cp-ASS-Tl
But-Cp-ASS-Tl
Prop-Cp-ASS-Mo
Prop-Cp-ASS-Mo-I
Prop-Cp-ASS-Mn
Prop-Cp-ASS-Co
Prop-Cp-ASS-Rh
2.0 ꢂ 0.3
1.4 ꢂ 0.3
3.3 ꢂ 0.5
1.9 ꢂ 0.3
>50
>50
>50
2.4 ꢂ 0.4
9.8 ꢂ 3.0
23.9 ꢂ 2.7
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
9.8 ꢂ 0.2
11.4 ꢂ 0.7
11.7 ꢂ 0.9
20.7 ꢂ 0.1
26.1 ꢂ 0.2
31.3 ꢂ 2.6
>50
4.6 ꢂ 0.5
12.1 ꢂ 2.3
10.5 ꢂ 0.2
13.8 ꢂ 2.6
12.0 ꢂ 1.6
30.4 ꢂ 4.0
12.3 ꢂ 2.6
9.2 ꢂ 1.7
7.3 ꢂ 2.0
5.4 ꢂ 0.2
14.0 ꢂ 3.6
13.7 ꢂ 2.4
24.8 ꢂ 3.6
10.8 ꢂ 2.3
10.2 ꢂ 3.4
34.4 ꢂ 7.3
26.6 ꢂ 0.5
Chart 1. COX inhibition of Prop-Cp-ASS-metal compounds.

5160
G. Rubner et al. / European Journal of Medicinal Chemistry 45 (2010) 5157e5163
Table 2
Pyridine was dried over KOH, dichloromethane over P2O5 and both
were stored over molecular sieves (4 Å and 3 Å). tert-Butanol was
dried over MgSO4 prior to use. Products were purified by flash
chromatography on silica gel (230e400 mesh, Merck). Melting
points: 510 Büchi (Flawil/Schweiz) capillary melting point apparatus.
IR spectra (KBr pellets): PerkineElmer Model 580 A (Rodgau-Jüge-
sheim/Germany). 1H and 13C NMR: Avance DPX-400 spectrometer
(Bruker, Karlsruhe/Germany) at 400 MHz (1H) or 100 MHz (13C);
(internal standard: TMS). Elemental analyses: Microlaboratory of
the Freie Universität Berlin on PerkineElmer 240C. Analyses indi-
cated bythe symbolsof the elementsor functions werewithin ꢂ0.4%
of the theoretical values. MS and HR-MS spectra: Finnigan MAT 711
(EI, 70 eV), MAT CH7A (EI, 80 eV, 3 kV), CH5DF (FAB, 80 eV, 3 kV) and
COX and PGE2 assay results of selected compounds.
Compound
aspirinÒ
Co-ASS
Et-Cp-ASS-Tl
Prop-Cp-ASS-Tl
But-Cp-ASS-Tl
Prop-Cp-ASS-Mo
Prop-Cp-ASS-Mo-I
Prop-Cp-ASS-Mn
Prop-Cp-ASS-Co
Prop-Cp-ASS-Rh
COX-1
COX-2
1% ꢂ 0.1
PGE
29.2% ꢂ 2.0
68.0% ꢂ 5.4
19.3% ꢂ 1.0
27.6% ꢂ 0.7
17.2% ꢂ 1.2
27.0% ꢂ 2.3
11.7% ꢂ 0.5
25.4% ꢂ 2.1
29.3% ꢂ 2.7
57.3% ꢂ 1.4
0
63.0% ꢂ 5.0
14.5% ꢂ 0.5
42.3% ꢂ 2.4
12.3% ꢂ 0.7
24.0% ꢂ 3.1
26.0% ꢂ 0.3
6.6% ꢂ 0.2
40.0% ꢂ 5.0
26.5% ꢂ 8.0
35.6% ꢂ 5.0
12.5% ꢂ 1.0
3.8% ꢂ 0.4
4.5% ꢂ 0.2
2.6% ꢂ 0.1
11.3% ꢂ 0.8
55.1% ꢂ 4.4
19.0% ꢂ 3.8
30.7% ꢂ 3.7
inhibition) and Prop-Cp-ASS-Mo-I (26.0% inhibition) even
exceeded their effects on COX-1 e (Table 2). The elongation or
reduction of the chain length reduced the effects at both
isoenzymes.
Agilent ESI-TOF 6210 (4 ml/min, 1 bar, 4000 V). Microplate reader:
FLASHscan S12 (AnalytikJena AG/Germany).
5.1.1. Preparation of cyclopentadienyl alcohol derivatives
The same trend was observed for Alkyl-Cp-ASS-Tl complexes on
the PGE2 level in MDA-MB-231 cells. Prop-Cp-ASS-Tl lowered the
PGE2 level more effectively (35.6%) than its ethyl (Et-Cp-ASS-Tl:
26.5%) or butyl derivative (But-Cp-ASS-Tl: 12.5%). Exchange of the
Tl by Mo, Mn or Co terminated the effects (0e5% inhibition). Only
the Prop-Cp-ASS-Rh complex showed increased inhibition (55.1%),
even higher than those obtained with Co-ASS.
The COX inhibitory effects of the Alkyl-Cp-ASS-metal complexes
did not correlate with the cytotoxicity against MDA-MB-231 and
MCF-7 cells. Therefore, it is very likely that the interference of
Alkyl-Cp-ASS-metal complexes in the arachidonic acid cascade
plays a subordinate role in the mode of action.
5.1.1.1. 2-(Cyclopenta-1,3-dienyl)ethanol (Cp-Et-OH). In 100 ml of dry
tert-butanol, 2.0 g of elemental potassium were dissolved under
hydrogen production in a wash-flask equipped with magnetic stirrer
and a ceramic frit in a glass tube. Temperature was controlled by
a water bath adjusted at 25e28 ꢀC to prevent crystallisation of the
alcohol. After dissolution was completed, argon was bubbled
through the apparatus for 30 min to create an inert atmosphere.
Afterwards 0.5 mol of freshly cracked cyclopentadiene (41.2 ml) was
added. The colour of the solution turned to red. About 20 g of
ethylene oxide were bubbled through the solution over a period of
4 h while the colour changed to dark gray. The main fraction of tert-
butanol was then evaporated on a rotavap. The residue was given in
a separating funnel and diluted with water and neutralized with 5%
H2SO4 and extracted twice with 100 ml of diethyl ether. The extracts
were washed once with water and dried over Na2SO4. Solvents were
removed under reduced pressure, leaving yellow oil which was
purified by vacuum distillation. The desired clear oil was obtained at
35 ꢀC at 5 ꢃ 10ꢁ3 T (3.8 g, 6.9%). MS (EI, 70 eV, 35 ꢀC): m/z (%) ¼ 110
(12) [Mþ], 80 (48) [Me(CH2OH)], 66 (100) [Cp]. 1H NMR (CDCl3):
The high COX inactivation observed by Prop-Cp-ASS-Rh did not
lead to strong cytotoxicity.
However, there have been several reports utilizing HT-29 cells in
which NSAIDs have been found to inhibit proliferation, cause cell
cycle quiescence, and induce apoptosis. There exist most probably
different pathways involving both COX-mediated and non-COX-
mediated mechanisms in the induction of apoptosis. Detailed
pharmacological studies are in progress and will be published in
a forthcoming paper.
d
¼ 2.74 (m, 2H, eCH2-Cp), 2.90 (m, 2H, ]CHeCH2eCH]), 3.60 (m,
2H, HOeCH2e), 6.06e6.45 (m, 3H, CpeR (alkenyl)).
4. Conclusion
5.1.1.2. 3-(Cyclopenta-1,3-dienyl)propanol(Cp-Prop-OH). To a mixture
of 0.25 mol of NaH (10 g of 60% dispersion in oil) in 100 ml of THF in
a large Schlenk tube one equivalent of freshly distilled cyclo-
pentadiene (20.7 ml) was added under argon atmosphere. The
mixture was stirred and cooled during the addition with an ice bath.
One equivalent of 3-chloropropanol (20.9 ml) was added to the
sodocen solution and stirred for 6 h at room temperature. The main
fraction of THF was distilled off at 30 ꢀC and the resulting solution
was diluted with 100 ml of ether, followed by slow addition of 150 ml
of water. The aqueous layer was separated and was extracted twice
with 50 ml of ether. Organic layers were combined and washed twice
with 50 ml of water and dried over Na2SO4. The solvent was removed
under reduced pressure followed by a vacuum distillation. The clear
oil was collected at 65 ꢀC at 10ꢁþ2 Torr. Yield: 4.7 g (15%). MS (EI, 70 eV,
35 ꢀC): m/z (%) ¼ 124 (44) [M ], 80 (59) [Cp-CH2], 66 (43) [Cp], 58
In a previous SAR study we already demonstrated that esterifi-
cation of aspirinÒ with a [propargyl]Co2(CO)6 moiety increased the
cytotoxicity and COX inhibitory properties. Co-ASS was identified as
lead structure, which was more active than cisplatin against MCF-7
and MDA-MB-231 cells. Not only the [alkyne]Co2(CO)6 moiety but
also a Cp-metal part increased the cytotoxicity of aspirinÒ. However,
compared to [alkyne]Co2(CO)6 in most cases lower cytotoxicity and
COX inhibition were observed. A clear conclusion whether the COX
enzyme inhibition participates in the mode of action cannot be
deduced from the results. Nevertheless, a series of very interesting
cytotoxic metal complexes were identified with preference for MCF-
7 breast cancer and HT‑29 colon carcinoma cells. Their mode of
action will be investigated in continuation of this study.
(100) [C3H6eO]. 1H NMR (CDCl3):
d
¼ 1.91 (m, 2H, eCH2eCH2-Cp),
5. Experimental
2.42 (m, 2H, eCH2-Cp), 2.92 (m, 2H, ]CHeCH2eCH]), 3.62 (m, 2H,
HOeCH2e), 6.06e6.45 (m, 3H, Cp-R (alkenyl)).
5.1. Chemistry
5.1.1.3. 4-(Cyclopenta-1,3-dienyl)butanol (Cp-But-OH). Analogously
to the procedure described above (Section 5.1.1.2). 4-Chlorobutanol:
27.2 g (25 ml)ꢁ;2cyclopentadiene: 21 ml. A clear oil was obtained at
105 ꢀC and 10 Torr. Yield: 3.1 g (9%). MS (EI, 35 ꢀC): m/z (%) ¼ 138
(42) [Mþ], 120 (9) [Me(OH)], 105 (22) [Me(CH2OH)], 91 (76) [Cp-
Commercially available chemicals were used without further
purification. C5H5Tl [21], Mo(CO)3(NCMe)3 [24] and MnBr(CO)5 [25]
were prepared by published procedures. Solvents were purified by
distillation from an appropriate drying agent: Tetrahydrofuran,
diethyl ether, toluene, pentane and n-hexane were dried over
sodium/potassium alloy and distilled under argon atmosphere.
C2H4], 79 (100) [Cp-CH2], 66 (56) [Cp]. 1H NMR (CDCl3):
d
¼ 1.67 (m,
2H, eCH2eCH2-Cp), 1.78 (m, 2H, eCH2eCH2eOe), 2.45 (m, 2H,

G. Rubner et al. / European Journal of Medicinal Chemistry 45 (2010) 5157e5163
5161
eCH2-Cp), 2.94 (m, 2H, ]CHeCH2eCH]), 3.57 (t, 3J ¼ 6.5 Hz, 2H,
HOeCH2-), 6.19e6.45 (m, 3H, Cp-R (alkenyl)).
(CH2eC]O)], 314 (18) [O-C2H4-Cp-Tl], 283 (2) [H3C-Cp-Tl], 269 (2)
[Cp-Tl], 205 (100) [Tl], 121 (4) [(C6H4)eCOO], 106 (1) [(C6H4)eCO].
HR-MS (EI, 70 eV, 140 ꢀC): [M- CH3-CO-] calcd. 434.06088; found
434.06037. Anal. C16H15O4Tl (C, H).
5.1.2. General preparation of (cyclopentadienyl)alkyl-2-
acetoxybenzoate
In an ice-cooled 100 ml round-bottom flask 0.025 mol of
cyclopentadienyl alcohol was mixed under stirring with 5 ml of abs.
pyridine. An amount of 0.03 mol of 2-acetylsalicoyl chloride (ASS-
Cl) [18] was solved in 40 ml of diethyl ether and added dropwise to
the reaction mixture over a period of 1 h. Then, the flask was
allowed to warm up to room temperature. In a separating funnel
the organic layer was washed with 1 N HCl and with saturated
sodium bicarbonate solution. The organic layer was dried over
Na2SO4 and the solvent was removed in vacuo. The crude product
was purified on a flash column with eluent petrol ether/diethyl
ether 5:1.
5.1.3.2. h
5-[3-((Cyclopentadienyl)propyl)-2-acetoxybenzoate]thallium
(Prop-Cp-ASS-Tl). Prop-Cp-ASS: 4.72 g (16.5 mmol), thallium eth-
oxide: 1.16 ml. Yield: 7.02 g (87%). MS (EI, 200 ꢀC): m/z (%) ¼ 490 (6)
[Mþ], 446 (2) [M-(CH2eC]O)], 355 (8) [O]CeOeC3H6-Cp-Tl], 326
(1) [OeC3H6-Cp-Tl], 269 (3) [Cp-Tl], 205 (22) [Tl], 121 (100) [(C6H4)e
COO],106 (92) [(C6H4)eCO]. MS (EI2, HR-MS,140 ꢀC): [MeCH3eCOe]
calcd. 446.07446; found 446.07413. Anal. C17H17O4Tl (C, H).
5.1.3.3.
h
5-[4-((Cyclopentadienyl)butyl)-2-acetoxybenzoate]thallium
(But-Cp-ASS-Tl). But-Cp-ASS: 2.70 g (16.5 mmol), thallium eth-
oxide: 0.62 ml. Yield 4.17 g (92%). MS (EI, 200 ꢀC): m/z (%) ¼ 488 (3)
[MeCH3], 462 (10) [Me(CH2eC]O)], 342 (3) [OeC4H8-Cp-Tl], 325
(2) [C4H8-Cp-Tl], 297 (2) [C2H4-Cp-Tl], 205 (95) [Tl], 121 (89)
[(C6H4)eCOO], 106 (20) [(C6H4)eCO], 92 (100) [(C6H4)eO]. MS (EI2,
200 ꢀC): m/z (%) ¼ 504 (1) [Mþ], 462 (4) [Me(CH2eC]O)], 342 (6)
[OeC4H8-Cp-Tl], 258 (2) [C4H4-Tl], 205 (65) [Tl], 120 (100) [(C6H4)e
COO], 105 (36) [(C6H4)eCO], 92 (74) [(C6H4)eO], 44 (76) [CH2eC]
O]. MS (EI2, HR-MS, 200 ꢀC): [MeCH3eCOe] calcd. 462.09219;
found 462.09184. Anal. C18H19O4Tl (C, H).
5.1.2.1. 2-(Cyclopenta-1,3-dienyl)ethyl-2-acetoxybenzoate
(Et-Cp-
ASS). Cp-Et-OH:2.8g(0.026mol),ASS-Cl:6.0g(0.03mol).Yield:6.3g
(89%) as colorless oil. MS (EI, 70 eV, 35 ꢀC): m/z (%) ¼ 272 (2) [Mþ],180
(10)[M-(Cp-C2H4)],163(13)[M-(Cp)-(Ac)],121 (36)[(C6H4)eCOO], 93
(100)[Cp-C2H4], 66(54)[Cp], 43(87)[Ac].1H NMR(CDCl3):
d
¼ 2.26(s,
3H, O]CeCH3), 2.74 (m, 2H, eCH2-Cp), 2.91 (m, 2H,
]
CHeCH2eCH]), 4.36 (t, 3J ¼ 7.0 Hz, 2H, eOeCH2e), 6.06e6.45 (m,
3H, Cp-R (alkenyl)), 7.04 (d, 3J ¼ 8.1 Hz,1H, 30-H), 7.23 (ddd, 3J ¼ 7.6 Hz,
3J ¼ 7.6 Hz, 4J ¼ 0.9 Hz, 1H, 50-H), 7.48 (ddd, 3J ¼ 8.0 Hz, 3J ¼ 7.5 Hz,
4J ¼ 1.6 Hz, 1H, 40-H), 7.92 (dd, 3J ¼ 7.9 Hz, 3J ¼ 7.9 Hz, 1H, 60-H).
5.1.4. Preparation of
2-acetoxybenzoate]tricarbonylmolybdenum (Prop-Cp-ASS-Mo)
resp.
5-[3-((cyclopentadienyl)propyl)-2-acetoxybenzoate]
h
5-[3-((cyclopentadienyl)propyl)-
h
5.1.2.2. 3-(Cyclopenta-1,3-dienyl)propyl-2-acetoxybenzoate (Prop-
Cp-ASS). Cp-Prop-OH: 3.1 g (0.025 mol), ASS-Cl: 5.2 g (0.026 mol).
Yield: 5.6 g (78%) as colorless oil. MS (EI, 100 ꢀC): m/z (%) ¼ 286 (3)
[Mþ], 163 (18) [M-(Ac)-(Cp-CH2)], 121 (100) [(C6H4)eCOO], 105 (96)
iodotricarbonylmolybdenum (Prop-Cp-ASS-Mo-I)
A solution of Prop-Cp-ASS (0.58 g, 2.0 mmol) in toluene (40 ml)
was added to a solution of Mo(CO)3(NCMe)3 (0.54 g, 2.0 mmol) in
toluene (40 ml) at 25 ꢀC. The reaction mixture was stirred for 2 h
and the resulting orange solution was filtered through celite. The
filtrate was concentrated to dryness. Half of the residue was put on
a silica gel column and was eluted with petrol ether/diethyl ether
[(C6H4)eCO], 43 (26) [Ac]. 1H NMR (CDCl3):
d
¼ 2.01 (m, 2H,
eCH2eCH2-Cp), 2.36 (s, 3H, O]CeCH3), 2.54 (m, 2H, eCH2-Cp),
2.95 (m, 2H, ]CHeCH2eCH]), 4.31 (t, 3J ¼ 6.6 Hz, 2H, eOeCH2e),
6.06e6.45 (m, 3H, Cp-R (alkenyl)), 7.11 (dd, 3J ¼ 8.0 Hz, 4J ¼ 1.0 Hz,
5:1. Yield: 0.31
g (67%). The second half was dissolved in
4
1H, 30-H), 7.31 (ddd, 3J ¼ 7.9 Hz, 3J ¼ 7.5 Hz, J ¼ 1.0 Hz, 1H, 50-H),
dichloromethane (50 ml). Solid CHI3 (0.39 g, 1.0 mmol) was added
to the dichloromethane solution and the colour immediately
turned to deep red. The reaction mixture was stirred for a further
30 min to ensure completion of the reaction and the solvent was
removed under vacuum. After chromatography with the same
solvent mentioned above, Prop-Cp-ASS-Mo-I was isolated as a dark
red solid. Yield: 0.42 g (71%). Prop-Cp-ASS-Mo: MS (EI2, 75 ꢀC): m/z
(%) ¼ 467 (6) [Mþ], 437 (8) [MeCO], 411 (1) [Me2(CO)], 381 (6)
[Me3(CO)], 341 (16) [Me3(CO)e(CH2eC]O)], 121 (41) [(C6H4)e
COO], 106 (100) [(C6H4)eCO]. Prop-Cp-ASS-Mo-I: MS (EI2, 90 ꢀC):
m/z (%) ¼ 594 (15) [Mþ], 566 (47) [MeCO], 510 (82) [Me3(CO)], 467
(60) [Me(I)], 440 (15) [Me(CO)e(I)], 394 (100) [Me(CH2]C]O)e
(CO)e(I)], 340 (23) [Me(CH2]C]O)-3(CO)e(I)], 120 (11) [(C6H4)e
COO], 106 (5) [(C6H4)eCO]. MS (EI2, HR-MS, 90 ꢀC): [Mþ] calcd.
587.90869; found 587.90871. Anal. C20H17O7MoI (C, H).
4
7.56 (ddd, 3J ¼ 7.9 Hz, 3J ¼ 7.6 Hz, J ¼ 1.7 Hz, 1H, 40-H), 8.01 (dd,
3J ¼ 7.8 Hz, 4J ¼ 1.8 Hz, 1H, 60-H).
5.1.2.3. 4-(Cyclopenta-1,3-dienyl)butyl-2-acetoxybenzoate (But-Cp-
ASS). Cp-But-OH: 2.8 g (0.02 mol), ASS-Cl: 4.4 g (0.022 mol). Yield:
4.9 g (82%) as colorless oil. MS (EI, 100 ꢀC): m/z (%) ¼ 300 (4) [Mþ],
257 (1) [M-(Ac)], 163 (15) [M-(Ac)-(Cp-CH2)], 120 (100) [(C6H4)e
COO], 105 (9) [(C6H4)eCO], 43 (26) [Ac]. 1H NMR (CDCl3):
d
¼ 1.70
(m, 2H, eCH2eCH2-Cp), 1.80 (m, 2H, eCH2eCH2eOe), 2.36 (s, 3H,
O]CeCH3), 2.49 (m, 2H, eCH2-Cp), 2.95 (m, 2H, ]CHeCH2eCH]),
4.31 (t, 3J ¼ 6.6 Hz, 2H, eOeCH2e), 6.19e6.45 (m, 3H, Cp-R
(alkenyl)), 7.11 (dd, 3J ¼ 8.1 Hz, 1H, 30-H), 7.33 (ddd, 3J ¼ 7.6 Hz, 1H,
4
50-H), 7.58 (ddd, 3J ¼ 7.4 Hz, J ¼ 1.6 Hz, 1H, 40-H), 8.03 (dd,
3J ¼ 7.8 Hz, 4J ¼ 1.5 Hz, 1H, 60-H).
5.1.3. General procedure for the preparation of
5.1.5. Preparation of h
5-[3-((cyclopentadienyl)propyl)-
h
5-[(cyclopentadienyl)alkyl-2-acetoxybenzoate]thallium
2-acetoxybenzoate]tricarbonylmanganese (Prop-Cp-ASS-Mn)
Solid MnBr(CO)5 (0.19 g, 0.7 mmol) was added to a stirred
solution of Prop-Cp-ASS-Tl (0.34 g, 0.7 mmol) in THF (40 ml) at
room temperature. The reaction mixture was stirred overnight and
the solvent was removed under vacuum. The residue was extracted
on a silica column with petrol ether/diethyl ether 5:1 to yield the
title compound as a waxy dark yellow solid. Yield: (81%). MS (EI,
150 ꢀC): m/z (%) ¼ 424 (6) [Mþ], 340 (11) [Me3(CO)], 298 (2) [Me3
(CO)e(CH2eC]O)], 222 (23) [Me(Cp-Mn-3CO)], 163 (2)
[H3CeCO2e(C6H4)eCO], 121 (42) [(C6H4)eCOO], 106 (34) [(C6H4)e
CO], 28 (100) [CO]. MS (EI2, HR-MS, 80 ꢀC): [Mþ] calcd. 424.03546;
found 424.03533. Anal. C20H17O7Mn (C, H).
Thallium ethoxide (10e17 mmol) was added dropwise at ꢁ30 ꢀC
under argon atmosphere to a pre-cooled solution of Cp-Alkyl-OH
(10e17 mmol) in n-hexane (200 ml). After stirring for 1 h at ꢁ30 ꢀC,
the reaction mixture was allowed to warm to room temperature
and stirred for further 16 h. A greyish yellow coloured precipitate
was separated by filtration and washed with diethyl ether to yield
the title compounds.
5.1.3.1.
h
5-[2-((Cyclopentadienyl)ethyl)-2-acetoxybenzoate]thallium
(Et-Cp-ASS-Tl). Et-Cp-ASS: 1.40 g (5.1 mmol), thallium ethoxide:
0.36 ml. Yield: 2.00 g (82%). MS (EI, 150 ꢀC): m/z (%) ¼ 434 (6) [M-

5162
G. Rubner et al. / European Journal of Medicinal Chemistry 45 (2010) 5157e5163
5.1.6. Preparation of
2-acetoxybenzoate]dicarbonylcobalt (Prop-Cp-ASS-Co)
h
5-[3-((cyclopentadienyl)propyl)-
were plated into each well and incubated for three days under
culture conditions. After the addition of various concentrations of
the test compounds, cells were incubated for another 96 h. Then the
medium was removed, the cells were fixed with glutardialdehyde
solution 1% and stored under phosphate buffered saline (PBS) at
Into an argon-purged 500 ml Schlenk tube equipped with
a magnetic stirrer was added 340 mg (1.0 mmol) of dicobaltocta-
carbonyl and 300 ml of THF. To this mixture was slowly added
250 mg (1.0 mmol) of iodine crystals, and the solution was stirred at
25 ꢀC for 3 h. To the resulting green solution, 980 mg (2.0 mmol) of
Prop-Cp-ASS-Tl was added, and stirring was maintained for addi-
tional 24 h. The reaction mixture was filtered through celite, and the
solvent was removed in vacuo. The residue was mixed with silica in
diethyl ether, the solvent was removed, and the coated product was
placed on a 2 ꢃ 35 cm dry-packed column of silica gel. Elution of the
column with petrol ether/diethyl ether 5:1 ceded the desired deep
yellow product with a yield of 510 mg (64%). MS (EI, 150 ꢀC): m/z
(%) ¼ 400 (4) [Mþ], 372 (6) [M-CO], 344 (27) [M-2(CO)], 302 (28) [M-
2(CO)e(CH2eC]O)], 121 (8) [(C6H4)eCOO], 106 (25) [(C6H4)eCO],
42 (100) [CH3eCO]. 28 (66) [CO]. MS (EI2, HR-MS, 90 ꢀC): [M-CO]
4
ꢀC. Cell biomass was determined by a crystal violet staining, fol-
lowed by extracting of the bound dye with ethanol and a photo-
metric measurement at 590 nm. Mean values were calculated and
the effects of the compounds were expressed as % Treated/Con-
trolcorr values according to the following equations:
T ꢁ C0
T=Ccorr½%ꢄ ¼
,100
C ꢁ C0
(C0 is the biomass of control cells at the time of compound addition;
C is the biomass of control cells at the time of the test end; T is the
biomass of probes/samples at the time of the test end).
The IC50 value was determined as the concentration causing 50%
inhibition of cell proliferation and calculated as mean of at least two
independent experiments.
calcd. ¼ 372.04080; found ¼ 372.04042. 1H NMR (CDCl3):
d
¼ 1.93
(m, 2H, -CH2eCH2-Cp), 2.28 (s, 3H, O]CeCH3), 2.61 (t, 3J ¼ 7.9 Hz,
2H, -CH2-Cp), 4.26 (t, 3J ¼ 6.2 Hz, 2H, eOeCH2e), 5.32 (t, 3J ¼ 2.1 Hz,
2H, Co(C5H4), 3040-H), 5.46 (t, 3J ¼ 2.1 Hz, 2H, Co(C5H4), 2050-H), 7.05
(d, 3J ¼ 7.6 Hz, 1H, 30-H), 7.26 (dd, 3J ¼ 7.9 Hz, 3J ¼ 7.6 Hz, 4J ¼ 1.0 Hz,
1H, 50-H), 7.53 (ddd, 3J ¼ 7.9 Hz, 3J ¼ 7.6 Hz, 4J ¼ 1.5 Hz, 1H, 40-H), 7.94
(dd, 3J ¼ 7.8 Hz, 4J ¼ 1.4 Hz, 1H, 60-H). Anal. C19H17O6Co (C, H).
5.2.3. Inhibition of COX-enzymes
The inhibition of isolated ovine COX-1 and human recombinant
COX-2 at 10 mMoftherespectivecompoundswasdeterminedbyELISA
(“COX Inhibitor Screening Assay”, Cayman Chemical). The experi-
ments were performed according to the manufacturer’s instructions.
Absorptionwasmeasured at 415 nm (Flashscan S12, AnalytikJena AG).
5.1.7. Preparation of h
5-[3-((cyclopentadienyl)propyl)-
2-acetoxybenz]dicarbonylrhodium (Prop-Cp-ASS-Rh)
Into an argon-purged 250 ml Schlenk tube was added 75 ml of
THF and 0.20 g (0.5 mmol) of dichlorotetracarbonyldirhodium [26].
After cooling the reaction mixture to ꢁ70 ꢀC, 0.49 g (1.0 mmol) of
Prop-ASS-Tl was added. The reaction mixture was allowed to warm
to room temperature and was stirred for additional 21 h. At the end
of this period, the mixture was filtered through celite and the filtrate
treated with 5 g of silica. The THF was removed in vacuo and the
coated product placed on a dry-packed silica column. Elution of the
column was performed with petrol ether/diethyl ether 5:1. Evapo-
ration of the solvent in vacuo gave 250 mg (56%) of yellow oil. MS (EI,
150 ꢀC): m/z (%) ¼ 416 (3) [MeCO], 388 (15) [Me2(CO)], 374 (27)
[MeCOe(CH2eC]O)], 346 (75) [Me2(CO)e(CH2eC]O)], 120 (100)
[(C6H4)eCOO],106 (90) [(C6H4)eCO], 42 (23) [CH3eCO], 28 (74) [CO].
5.2.4. PGE2-assay
MDA-MB-231 cells were grown in 24 well plates until at least 70%
confluency. The medium was then removed and replaced by fresh
DMEM containing the respective substances (10
were maintained in the absence of any compound. The cells were
incubated for 23 h followed by the addition of 100 M arachidonic
acid. 24 h after compound addition, the drug-containing medium
with the including prostaglandin E2 was removed and tested by ELISA
(“Prostaglandin E2 EIA Kit-Monoclonal”, Cayman Chemicals). Exper-
iments were performed according to the manufacturer’s instructions.
Absorptionwasmeasuredat415nm(FlashscanS12,AnalytikJenaAG).
mM); control cells
m
6. Elemental analyses
MS (EI, HR-MS, 150 ꢀC): [MeCO] calcd.
¼
416.01310;
found
¼
416.01292. MS (EI, HR-MS, 150 ꢀC): [Me2CO]
6.1.
h
5-[2-((Cyclopentadienyl)ethyl)-2-acetoxybenzoate]thallium
calcd. ¼ 388.01819; found ¼ 388.01803. 1H NMR (CDCl3):
d
¼ 2.00
(Et-Cp-ASS-Tl)
(m, 2H, eCH2eCH2-Cp), 2.36 (s, 3H, O]CeCH3), 2.68 (t, 3J ¼ 7.6 Hz,
2H, eCH2-Cp), 4.33 (t, 3J ¼ 6.3 Hz, 2H, eOeCH2e), 5.39 (t, 3J ¼ 1.9 Hz,
2H, Rh(C5H4), 3040-H), 5.53 (t, 3J ¼ 1.9 Hz, 2H, Rh(C5H4), 2050-H), 7.12
(d, 3J ¼ 8.0 Hz, 1H, 30-H), 7.33 (dd, 3J ¼ 7.6 Hz, 3J ¼ 7.6 Hz, 4J ¼ 1.0 Hz,
1H, 50-H), 7.56 (ddd, 3J ¼ 8.0 Hz, 3J ¼ 7.6 Hz, 4J ¼ 1.3 Hz,1H, 40-H), 8.01
(dd, 3J ¼ 7.8 Hz, 4J ¼ 1.2 Hz, 1H, 60-H). Anal. C19H17O6Rh (C, H).
Anal. calcd. for C16H15O4Tl: C, 40.40; H, 3.20; found: C, 40.29; H,
3.51%.
6.2.
h
5-[3-((Cyclopentadienyl)propyl)-2-acetoxybenzoate]thallium
(Prop-Cp-ASS-Tl)
5.2. Biological methods
Anal. calcd. for C17H17O4Tl: C, 41.70; H, 3.50; found: C, 41.49; H,
3.61%.
5.2.1. Cell culture
The human MCF-7 and MDA-MB-231 breastcancercell lines as well
as the HT-29 colon cancer cell line were obtained from the American
Type Culture Collection (ATCC, USA). Cell line banking and quality
control were performed according to the seed stock concept reviewed
by Hay [27]. All three cell lines were maintained in Dulbecco’sModified
6.3.
h
5-[4-((Cyclopentadienyl)butyl)-2-acetoxybenzoate]thallium
(But-Cp-ASS-Tl)
Anal. calcd. for C18H19O4Tl: C, 42.92; H, 3.80; found: C, 42.67; H,
3.81%.
Eagle Medium (DMEM) with 4.5 g/l glucose and L-glutamine (PAA,
Germany), supplemented with 5% fetal bovine serum (FBS; Biochrom,
Germany) at 37 ꢀC in a humidified atmosphere with 5% CO2.
6.4. h
5-[3-((Cyclopentadienyl)propyl)-2-acetoxybenzoate]
tricarbonylmolybdenum (Prop-Cp-ASS-Mo)
5.2.2. Cytotoxicity assay
In 96 well plates 100
7500 cells/ml (MCF-7 and MDA-MB-231) or 2500 cells/ml (HT-29)
m
l of a cell suspension in culture medium at
Anal. calcd. for C20H17O7Mo: C, 51.63; H, 3.68; found: C, 51.67; H,
3.95%.

G. Rubner et al. / European Journal of Medicinal Chemistry 45 (2010) 5157e5163
5163
6.5.
h
5-[3-((Cyclopentadienyl)propyl)-2-acetoxybenzoate]
References
iodotricarbonylmolybdenum (Prop-Cp-ASS-Mo-I)
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Anal. calcd. for C20H17O7MoI: C, 40.56; H, 2.89; found: C, 40.51;
H, 3.22%.
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6.6.
h
5-[3-((Cyclopentadienyl)propyl)-2-acetoxybenzoate]
tricarbonylmanganese (Prop-Cp-ASS-Mn)
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J. Am. Chem. Soc. 78 (1956) 120e124.
Anal. calcd. for C20H17O7Mn: C, 56.62; H, 4.04; found: C, 56.46;
H, 4.17%.
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(1985) 99e105.
6.7.
h
5-[3-((Cyclopentadienyl)propyl)-2-acetoxybenzoate]
dicarbonylcobalt (Prop-Cp-ASS-Co)
Anal. calcd. for C19H17O6Co: C, 57.01; H, 4.28; found: C, 57.12; H,
4.42%.
6.8.
h
5-[3-((Cyclopentadienyl)propyl)-2-acetoxybenzoate]
dicarbonylrhodium (Prop-Cp-ASS-Rh)
[20] A.S.R. Schröder, G. Zimmermann, M. Mühlstädt, J. Prakt. Chem. 315 (1973)
958e964.
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1196e1198.
Anal. calcd. for C19H17O6Rh: C, 51.37; H, 3.86; found: C, 51.44; H,
4.01%.
[23] C.C. Hunt, J.R. Doyle, Inorg. Nucl. Chem. Lett. 2 (1966) 283e288.
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Inorg. Syn. 8 (1966) 211e214.
Acknowledgements
The financial support of DFG e Deutsche Forschungsgemeinschaft
(project: FOR 630) is greatly appreciated.
[27] R.J. Hay, Anal. Biochem. 171 (1988) 225e237.