Novel organotin antibacterial and anticancer drugs

Article abstract of DOI:10.1016/j.poly.2008.09.009

From the reaction of 6-(p-methoxyphenyl) fulvene (1a), 6-(p-N,N-dimethylaminophenyl) fulvene (1b) and 6-(3,4-dimethoxyphenyl) fulvene (1c) with LiBEt₃H, lithiated cyclopentadienide intermediates (2a-c) were synthesised. These intermediates were

Full text of DOI:10.1016/j.poly.2008.09.009

Polyhedron 27 (2008) 3619–3624
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Novel organotin antibacterial and anticancer drugs
Brendan Gleeson, James Claffey, Daniel Ertler, Megan Hogan, Helge Müller-Bunz, Francesca Paradisi,
*
Denise Wallis, Matthias Tacke
Conway Institute of Biomolecular and Biomedical Research, Centre for Synthesis and Chemical Biology (CSCB), UCD School of Chemistry and Chemical Biology,
University College Dublin, Belfield, Dublin 4, Ireland
a r t i c l e i n f o
a b s t r a c t
Article history:
From the reaction of 6-(p-methoxyphenyl) fulvene (1a), 6-(p-N,N-dimethylaminophenyl) fulvene (1b)
and 6-(3,4-dimethoxyphenyl) fulvene (1c) with LiBEt3H, lithiated cyclopentadienide intermediates
(2a–c) were synthesised. These intermediates were then transmetallated to tin with SnCl4 to yield
tetra-substituted bis(cyclopentadienyl)tin dichloride complexes (3a–c). Further reaction with tin tetra-
chloride yielded the benzyl-substituted derivatives bis-[(p-methoxybenzyl)cyclopentadienyl] tin(IV)
dichloride (4a), bis-[(p-N,N-dimethylaminobenzyl)cyclopentadienyl] tin(IV) dichloride (4b), and bis-
[(3,4-dimethoxyphenyl)cyclopentadienyl] tin(IV) dichloride (4c). Preliminary antibacterial tests were
carried out using the Kirby–Bauer disk-diffusion method, in which 4a–c showed little to no activity
against the Gram-negative bacterium Escherichia coli, but medium activity against Gram-positive bacteria
(MRSA, MSSA). In addition, the organotin complexes had their cytotoxicity investigated through preli-
minary in vitro testing on the LLC-PK (pig kidney epithelial) cell line in order to determine their IC50 val-
ues. Compound 4c showed no cytotoxic activity, while 4a and 4b were found to have IC50 values of 15
Received 21 August 2008
Accepted 13 September 2008
Available online 18 October 2008
Keywords:
Anticancer drug
Antibacterial drug
Tin
Hydridolithiation
Fulvene
Gram-positive bacteria
LLC-PK
and 205 lM, respectively.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
lowed by transmetallation with titanium tetrachloride in the latter
two cases [7]. Hydridolithiation of 6-anisyl fulvene and subsequent
reaction with TiCl4 led to bis-[(p-methoxybenzyl)cyclopentadi-
enyl] titanium(IV) dichloride (Titanocene Y) [8], which has an
Beyond the field of platinum anti-cancer drugs there is signifi-
cant unexplored space for further metal-based drugs targeting can-
cer. Titanium-based reagents have significant potential against
solid tumors. Budotitane ([cis-diethoxybis(1-phenylbutane-1,3-
dionato)titanium(IV)]) looked very promising during its preclinical
evaluation, but did not go beyond Phase I clinical trials, although a
Cremophor ELÒ based formulation was found for this rapidly
hydrolysing molecule [1]. Much more robust in this aspect of
hydrolysis is titanocene dichloride (Cp2TiCl2), which shows med-
ium anti-proliferative activity in vitro but promising results
in vivo [2,3]. Titanocene dichloride reached clinical trials, but the
efficacy of Cp2TiCl2 in Phase II clinical trials in patients with meta-
static renal cell carcinoma [4] or metastatic breast cancer [5] was
too low to be pursued.
The field got renewed interest with P. McGowan’s elegant syn-
thesis of ring-substituted cationic titanocene dichloride deriva-
tives, which are water-soluble and show significant activity
against ovarian cancer [6]. More recently, novel methods starting
from fulvenes and other precursors allow direct access to antipro-
liferative titanocenes via reductive dimerisation with titanium
dichloride, carbolithiation or hydridolithiation of the fulvene fol-
IC50 value of 21 lM when tested on the LLC-PK cell line. This par-
ticular cell line was chosen as it has proven to be a good mimic of a
kidney carcinoma cell line and a reliable tool for the optimisation
of titanocenes against this type of cancer.
While the use of tin species are known to have an impact on the
environment [9], the biological activity and possible antibacterial/
antitumor applications of numerous organotin(IV) complexes have
been described in the literature [10–16]. A significant amount of
the work carried out on these Sn(IV) compounds was in relation
to their antibacterial activity against a wide range of both Gram-
negative and Gram-positive bacteria. While the results vary con-
siderably depending on the different substitution patterns at the
tin centre, a trend in activity emerges inclining towards the
Gram-positive bacteria, where a greater antibacterial effect is ob-
served compared to the Gram-negative bacteria [17–18].
With this in mind, and following on from the work carried out
on titanocene Y, we decided to substitute the titanium metal cen-
tre with tin in order to compare the difference in cytotoxicity be-
tween titanocene dichloride and bis(cyclopentadienyl)tin
dichloride derivatives, along with conducting preliminary antibac-
terial tests. The synthesis of these organotin compounds requires a
slightly different synthetic route than the titanocenes, where by a
* Corresponding author.
E-mail address: matthias.tacke@ucd.ie (M. Tacke).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.09.009

3620
B. Gleeson et al. / Polyhedron 27 (2008) 3619–3624
tetrakis cyclopentadienyl tin(IV) intermediate is produced, which
undergoes additional transmetallation to isolate the desired
organotin dichloride [19]. The reaction scheme can be viewed in
Scheme 1.
reliability factors. Suitable crystals of 5 were formed from the slow
evaporation of a saturated trichloromethane solution.
2.2. Synthesis
Within this paper we present the synthesis, preliminary cyto-
toxicity and antibacterial studies of a series of three organotin
dichloride derivatives, modelled on Titanocene Y.
6-(p-Methoxyphenyl) fulvene 1a, 6-(p-N,N-dimethylaminophe-
nyl) fulvene 1b and 6-(3,4-dimethoxyphenyl) fulvene 1c were syn-
thesised according to already published procedures [23–24].
2. Experimental
2.2.1. Synthesis of bis-[(p-methoxybenzyl)cyclopentadienyl] tin(IV)
dichloride, [g
1-C5H4–CH2–C6H4–O–CH3]2SnCl2 (4a)
2.1. General conditions
15.0 ml (15.0 mmol) of 1 M solution of Super Hydride (LiBEt3H)
in THF was concentrated by removal of the solvent by heating it to
60 °C under reduced pressure of 10À2 mbar for forty minutes and
then to 90 °C for 20 min in a Schlenk flask. The concentrated Super
Hydride was dissolved in 30 ml of dry diethyl ether to give a cloudy
white suspension. 2.40 g (13.0 mmol) of the red solid 1a was added
to a Schlenk flask and was dissolved in 90 ml dry diethyl ether to
give a red solution. The red fulvene solution was transferred to
the Super Hydride solution via cannula. The solution was left to stir
for 8 h to give a white precipitate of the lithium cyclopentadienide
intermediate and the solution had changed colour from orange/red
to colourless with a white precipitate formed. The precipitate was
filtered on to a frit and was washed with 20 ml of diethyl ether. The
white precipitate was dried briefly under reduced pressure and
Manipulations of air and moisture sensitive compounds were
performed under an inert atmosphere of nitrogen or argon using
standard Schlenk techniques. Tin tetrachloride (SnCl4 1.0 M solu-
tion in heptane) and Super Hydride (LiBEt3 H, 1.0 M solution in
THF) were obtained commercially from Sigma–Aldrich. All solvents
were dried and distilled according to standard methods. 1H and 13
C
NMR spectra were measured on a Varian 500 MHz spectrometer
with C6D6 as solvent and TMS as internal standard. 119Sn NMR
spectra were measured on a Varian 500 MHz spectrometer with
C6D6 as solvent and t-But2SnCl2 as internal standard. IR spectra
were recorded on a Perkin Elmer Paragon 1000 FT-IR Spectrometer
employing NaCl discs. UV/Vis spectra were recorded on a Unicam
UV4 Spectrometer. Electron spray mass spectrometry (MS) was
performed on a quadrupole tandem mass spectrometer (Quattro
Micro, Micromass/Water’s Corp., USA), using solutions made up
in 50% dichloromethane and 50% methanol. MS spectra were ob-
tained in the ES- (electron spray negative ionisation) mode for
compounds 4a and 4b. Compound 4c was obtained in ES+ (electron
spray positive) mode. X-ray diffraction data for compound 5 was
collected using a Bruker SMART APEX CCD area detector diffrac-
tometer. A full sphere of reciprocal space was scanned by phi–
omega scans. Pseudo-empirical absorption correction based on
redundant reflections was performed by the program SADABS [20].
The structures were solved by direct methods using SHELXS-97
[21] and refined by full matrix least-squares on F2 for all data using
SHELXL-97 [21]. In 5, hydrogen atoms were added at calculated posi-
tions and refined using a riding model. Their isotropic temperature
factors were fixed to 1.2 times (1.5 times for methyl groups) the
equivalent isotropic displacement parameters of its parent atom.
Anisotropic thermal displacement parameters were used for all
non-hydrogen atoms. The chloroform molecule could not be lo-
cated in the unit cell. Platon SQUEEZE [22] was used to compensate
for the spread electron density. The solvent is included in the over-
all formula, F(000), absorption coefficient and density. Further de-
tails about the data collection are listed in Table 2, as well as
was transferred to
a Schlenk flask under nitrogen. 2.06 g
(10.7 mmol, 82.2% yield) of the lithiated cyclopentadienide inter-
mediate 2a was obtained. 2.68 ml (2.68 mmol) of a 1 M solution
of tin tetrachloride in heptane was dissolved in 30 ml of dry tolu-
ene in a Schlenk flask. The lithium cyclopentadienide intermediate
was dissolved in 60 ml of dry toluene to give a colourless solution.
The solution of tin tetrachloride was added to the lithium cyclo-
pentadienide intermediate solution slowly at 0 °C via cannula to
give a yellow solution. The tin solution was allowed to stir for
16 h at room temperature followed by the removal of the solvent
under reduced pressure which yielded a yellow solid, tetrakis-
[g
1-(p-methoxybenzyl)cyclopentadienyl] tin(IV) intermediate 3a.
The yellow solid was dissolved in 30 ml of dry toluene and
2.68 ml (2.68 mmol) of a 1 M solution of tin tetrachloride in hep-
tane was added slowly at 0 °C. The solution was stirred at room
temperature for 2 h after which it was allowed to settle, followed
by filtration in an inert atmosphere of nitrogen using a frit. The
resulting clear yellow solution was reduced under vacuum to yield
the title compound as a light yellow, waxy and air sensitive solid
(0.960 g, 1.71 mmol, 31.9% yield) 4a.
1H NMR (d ppm C6D6, 500 MHz): 3.28 [s, 6H, C6H4–OCH3 ], 3.61
[s, 4H, C5H4–CH2], 5.15 [s, 4H, C5H4–CH2], 6.05 [s, 4H, C5H4–CH2],
6.75 [d, 4H, J 7.82 Hz, C6H4–OCH3], 7.04 [d, 4H, J 7.82 Hz, C6H4–
OCH3].
13C NMR (d ppm C6D6, 125 MHz, proton decoupled): 35.5
[C5H4–CH2], 54.4 [C6H4–OCH3], 97.1, 114.0, 123.3, 129.8, 132.3,
145.8, 158.4.
R
R
H
R
SnCl4
4LiBEt3H
4
4
Sn
119Sn NMR (d ppm C6D6, 186 MHz, proton decoupled): À36.5.
Et2O
-4BEt3
R
THF
H
H
-4LiCl(s)
MS (m/z, QMS-MS/MS): 559 [MÀH]À.
R
IR absorptions (NaCl, cmÀ1): 2996, 2905, 2833, 1610, 1575,
1511, 1463, 1431, 1300, 1247, 1176, 1036, 919, 803.
R
Li
1a-c
SnCl4
3a-c
2a-c
THF
UV–Vis (toluene, nm): k 216 (
49000), k 274 ( 39000), k 299 (
2000), k 425 ( 5900), kmax 555 (
e
56000), k 239 (
13000), k 321 (
600).
e
53000), k 266
e 7800), k 337
R
R
(
(
e
e
e
e
e
e
Cl
a = 4-OMe
Sn
2
Cl
b= 4-NMe2
c = 3,4-(OMe)2
2.2.2. Synthesis of bis-[(p-N,N-dimethylaminobenzyl)cyclopentadienyl]
tin(IV) dichloride, [
1-C5H4–CH2–C6H4–N–(CH3)2]2SnCl2 (4b)
g
15.0 ml (15.0 mmol) of 1 M solution of Super Hydride (LiBEt3H)
in THF was concentrated by removal of the solvent by heating it to
60 °C under reduced pressure of 10À2 mbar for forty minutes and
then to 90 °C for 20 min in a Schlenk flask. The concentrated Super
4a-c
Scheme 1. General reaction scheme for the synthesis of benzyl-substituted
organotin dichloride derivatives.

B. Gleeson et al. / Polyhedron 27 (2008) 3619–3624
3621
Hydride was dissolved in 30 ml of dry diethyl ether to give a cloudy
white suspension. 2.38 g (12.1 mmol) of the red solid 1b was
added to a Schlenk flask and was dissolved in 90 ml dry diethyl
ether to give a red solution. The red fulvene solution was trans-
ferred to the Super Hydride solution via cannula. The solution
was left to stir for 8 h to give a white precipitate of the lithium
cyclopentadienide intermediate and the solution had changed col-
our from orange/red to faint yellow. The precipitate was filtered on
to a frit and was washed with 20 ml of diethyl ether. The white
precipitate was dried briefly under reduced pressure and was
transferred to a Schlenk flask under nitrogen. 1.94 g (9.45 mmol,
78.2% yield) of the lithiated cyclopentadienide intermediate 2b
was obtained. 2.36 ml (2.36 mmol) of a 1 M solution of tin tetra-
chloride in heptane was dissolved in 30 ml of dry toluene in a
Schlenk flask. The lithium cyclopentadienide intermediate was dis-
solved in 60 ml of dry toluene to give a colourless solution. The
solution of tin tetrachloride was added to the lithium cyclopenta-
dienide intermediate solution slowly at 0 °C via cannula to give a
yellow solution with a white precipitate. The tin solution was al-
lowed to stir for 16 h at room temperature followed by the removal
of the solvent under reduced pressure which yielded a dark yellow
ether to give a cloudy white suspension. 2.40 g (11.2 mmol) of
the red solid 1c was added to a Schlenk flask and was dissolved
in 90 ml dry diethyl ether to give a red solution. The red fulvene
solution was transferred to the Super Hydride solution via can-
nula. The solution was left to stir for 8 h to give a white precipi-
tate of the lithium cyclopentadienide intermediate and the
solution had changed colour from orange/red to faint yellow with
a white precipitate formed. The precipitate was filtered on to a
frit and was washed with 20 ml of diethyl ether. The white pre-
cipitate was dried briefly under reduced pressure and was trans-
ferred to a Schlenk flask under nitrogen. 2.16 g (9.72 mmol, 86.8%
yield) of the lithiated cyclopentadienide intermediate 2c was ob-
tained. 2.43 ml (2.43 mmol) of a 1 molar solution of tin tetrachlo-
ride in heptane was dissolved in 30 ml of dry toluene in a Schlenk
flask. The lithium cyclopentadienide intermediate was dissolved
in 60 ml of dry toluene to give a colourless solution. The solution
of tin tetrachloride was added to the lithium cyclopentadienide
intermediate solution slowly at 0 °C via cannula to give a yellow
solution. The tin solution was allowed to stir for 16 h at room
temperature followed by the removal of the solvent under re-
duced pressure which yielded a dark brown solid, tetrakis-[g1
-
solid, tetrakis-[
g
1-(p-dimethylaminobenzyl)cyclopentadienyl] tin(IV)
(p-N,N-dimethylaminobenzyl)cyclopentadienyl] tin(IV) intermedi-
ate 3c. The dark yellow solid was dissolved in 30 ml of dry tolu-
ene and 2.43 ml (2.43 mmol) of a 1 M solution of tin tetrachloride
in heptane was added slowly at 0 °C. The solution was stirred at
room temperature for 2 h after which it was allowed to settle, fol-
lowed by filtration in an inert atmosphere of nitrogen using a frit.
The resulting clear brown solution was reduced under vacuum to
yield the title compound as a brown, waxy and air sensitive solid
(0.740 g 1.20 mmol, 24.6% yield) 4c.
intermediate 3b. The dark yellow solid was dissolved in 30 ml of
dry toluene and 2.36 ml (2.36 mmol) of a 1 M solution of tin tetra-
chloride in heptane was added slowly at 0 °C. The solution was
stirred at room temperature for 2 h after which it was allowed to
settle, followed by filtration in an inert atmosphere of nitrogen
using a frit. The resulting clear yellow solution was reduced under
vacuum to yield the title compound as a yellow, waxy and air sen-
sitive solid (1.21 g 2.06 mmol, 43.7% yield) 4b.
1H NMR (d ppm C6D6, 500 MHz): 2.23 [s, 12H, C6H4–N(CH3)2 ],
3.36 [s, 2H, C5H4–CH2], 3.43 [s, 2H, C5H4–CH2], 4.93 [s, 2H, C5H4–
CH2], 4.98 [s, 2H, C5H4–CH2], 5.72 [s, 2H, C5H4–CH2], 5.86 [s, 2H,
C5H4–CH2], 6.32 [d, 4H, J 8.31 Hz, C6H4–N(CH3)2], 6.82 [d, 4H, J
8.31 Hz, C6H4–N(CH3)2].
1H NMR (d ppm C6D6, 500 MHz): 3.14 [s, 6H, C6H3-(OCH3)2], 3.18
[s, 6H, C6H3–(OCH3)2], 3.46 [s, 4H, C5H4–CH2], 4.77 [s, 4H, C5H4–
CH2], 5.95 [s, 4H, C5H4–CH2], 6.37 [d, 2H, J 8.31 Hz, C6H3–(OCH3)2],
6.48 [s, 2H, C6H3–(OCH3)2], 6.52 [d, 2H, J 8.31 Hz, C6H3–(OCH3)2].
13C NMR (d ppm C6D6, 125 MHz, proton decoupled): 35.1
[C5H4–CH2], 54.2 [C6H3–(OCH3)2], 99.2, 111.7, 112.1, 120.0, 120.9,
131.7, 146.3, 149.2.
13C NMR (d ppm C6D6, 125 MHz, proton decoupled): 35.4
[C5H4–CH2], 40.2 [C6H4–N-(CH3)2], 97.0, 100.3, 113.0, 121.6,
123.4, 129.5, 146.3, 148.1, 149.3.
119Sn NMR (d ppm C6D6, 186 MHz, proton decoupled): À48.9.
119Sn NMR (d ppm C6D6, 186 MHz, proton decoupled): À26.8
MS (m/z, QMS-MS/MS): 621 [M+H]+.
MS (m/z, QMS-MS/MS): 585 [MÀH]À.
IR absorptions (neat, NaCl windows, cmÀ1): 2998, 2934, 2833,
1609, 1590, 1510, 1463, 1417, 1235, 1139, 1028, 804, 733.
IR absorptions (near, NaCl windows, cmÀ1): 3007, 2888, 2798,
1614, 1567, 1518, 1478, 1444, 1347, 1224, 1162, 1131, 947, 805.
UV–Vis (toluene, nm): k 213 (
55000), k 248 ( 56000), k 266 (
5600), k 426 ( 4300), kmax 555 (e
e
63000), k 230 (
58000), k 300 (
400) (see Fig. 1).
e
53000), k 240
e 8600), k 321
UV–Vis (toluene, nm): k 218 (
43000), k 246 ( 41000), k 263 (
8400), k 426 ( 4500), k 555 (weak).
e
42000), k 227 (
e
e
36000), k 236
20000), k 322
(
(
e
e
e
e
(
(
e
e
e
e
e
48000), k 299 (
e
2.3. Antibacterial Studies
2.2.3. Synthesis of bis-[(3,4-dimethoxybenzyl)cyclopentadienyl] tin(IV)
dichloride, [
1-C5H4–CH2–C6H3–(OCH3)2]2SnCl2 (4c)
g
Two different strains of the Gram-positive bacteria Staphylococ-
cus aureus (SA) were used; a clinical isolate of Methicillin-resistant
SA (MRSA identified as isolate CC), and the commercially available
Methicillin-sensitive SA (MSSA ATCC 6538). For comparison, a
Gram-negative bacterium was also tested (Escherichia coli, lab
strain BL21).
16.0 ml (16.0 mmol) of 1 molar solution of Super Hydride (Li-
BEt3H) in THF was concentrated by removal of the solvent by
heating it to 60 °C under reduced pressure of 10À2 mbar for
40 min and then to 90 °C for 20 min in a Schlenk flask. The con-
centrated Super Hydride was dissolved in 30 ml of dry diethyl
OMe
OMe
NMe2
OMe
Cl
Cl
Cl
Cl
Cl
Cl
Sn
Sn
Sn
OMe
NMe2
OMe
OMe
4a
4b
4c
Fig. 1. Structures of g1 organotin dichlorides 4a–c.

3622
B. Gleeson et al. / Polyhedron 27 (2008) 3619–3624
Table 1
line was chosen based on their regular and long-lasting growth
Zone of clearance for compounds 4a–c in mm
behaviour, which is similar to the one shown in kidney carcinoma
cells. It was obtained from the ATCC (American Tissue Cell Culture
Collection) and maintained in Dulbecco’s Modified Eagle Medium
containing 10% (v/v) FCS (foetal calf serum), 1% (v/v) penicillin
Bacteria
DMSO
4a (mm)
4b (mm)
4c (mm)
Gram-positive
MRSA
MSSA
N/A
N/A
5
8
10
8
14
14
streptomycin and 1% (v/v)
well plates containing 200
5000-cells/200 l of medium and were incubated at 37 °C for
L
-glutamine. Cells were seeded in 96-
ll microtitre wells at a density of
Gram–negative
E. coli
N/A
5
6
5
l
24 h to allow for exponential growth. Then the compounds used
for the testing were dissolved in the minimal amount of DMSO
(dimethylsulfoxide) possible and diluted with medium to obtain
stock solutions of 5 Â 10À4 M in concentration and less than 0.7%
of DMSO. The cells were then treated with varying concentrations
of the compounds and incubated for 48 h at 37 °C. Then, the solu-
tions were removed from the wells and the cells were washed with
PBS (phosphate buffer solution) and fresh medium was added to
the wells. Following a recovery period of 24 h incubation at
To assess the biological activity of compounds 4a–c, the Kirby–
Bauer disk-diffusion method was applied [25]. All bacteria were
individually cultured from a single colony in sterile LB medium
[26] overnight at 37 °C (orbital shaker incubator). All the work car-
ried out was performed under sterile conditions.
For each strain, 50 ll of culture were spread evenly on agar-LB
medium. Four 5 mm diameter paper discs were placed evenly sep-
arated on each plate. 50 mg of each sample (4a 0.089 M, 4b
0.085 M and 4c 0.081 M) were dissolved in 1 ml of DMSO to pre-
37 °C, individual wells were treated with a 200 ll of a solution of
MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bro-
mide) [27] in medium. The solution consisted of 30 mg of MTT in
30 ml of medium. The cells were incubated for 3 h at 37 °C. The
medium was then removed and the purple formazan crystals were
pare the drug formulation. 5
ll of 4a–c solution (250
lg) were
placed on the paper discs and 5
ll of DMSO was placed on the
fourth circle of filter paper as a control. The plates were covered
and placed in an incubator at 30 °C for 24 h. The plates were then
removed and the zone of clearance (defined as the diameter of
inhibited bacterial growth around the filter paper) for each sample
was measured in mm (see Table 1).
dissolved in 200 ll DMSO per well. A Wallac Victor (Multilabel HTS
Counter) Plate Reader was used to measure absorbance at 540 nm.
Cell viability was expressed as a percentage of the absorbance re-
corded for control wells. The values used for the dose response
curves represent the values obtained from four consistent MTT-
based assays for each compound tested.
2.4. Cytotoxicity studies
Preliminary in vitro cell tests were performed on the cell line
LLC-PK (long-lasting cells–pig kidney) in order to compare the
cytotoxicity of the compounds presented in this paper. This cell
3. Discussion
3.1. Synthesis
The lithium intermediates used in the synthesis of derivatives
4a–c were synthesised by the hydridolithiation reaction of aryl-ful-
venes with Super Hydride (LiBEt3H). This form of nucleophilic addi-
tion to the exocyclic double bond of the fulvene is highly selective
due to the increased polarity as a result of the inductive effect of
the corresponding phenyl ring. There is no nucleophilic attack seen
at the diene element of the aryl-fulvenes. The lithiated cyclopenta-
dienide intermediate was isolated with good yields of 79–87%.
Four equivalents of the lithiated cyclopentadienide intermedi-
ate were then transmetallated with one equivalent of tin tetrachlo-
ride to form a tetrakis cyclopentadienyl tin(IV) intermediate and
lithium chloride as a by-product. This tetrakis cyclopentadienyl ti-
n(IV) intermediate was isolated but not characterised due to ex-
treme air sensitivity. This was then further reacted with 1 equiv.
of tin tetrachloride to yield the organotin dichlorides 4a, 4b, and
4c in yields of 25–44%. Elemental analysis was not possible due
to the level of air and moisture sensitivity of the compounds.
Derivatives 4a, 4b, and 4c are soluble in organic non-chlori-
nated solvents, but decompose rapidly in chlorinated solvents such
as dichloromethane. The synthesis of organotin dichlorides is
dependent upon the solvent. The expected dichloride species were
formed only when toluene or benzene was used as the solvent.
A notable feature of the organotin species 4a, 4b, and 4c is the
Table 2
Crystal data and structure refinement for 5
Identification code
5
Empirical formula
Molecular formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C47H43N4O2Cl9Sn2
(C23H21N2OCl3Sn)2xCHCl3
1252.28
100(2)
0.71073
monoclinic
P21/n (#14)
14.7176(11)
8.2667(6)
20.4595(16)
90
96.649(2)
90
2472.5(3)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (Mg/m3)
1.682
1.540
1244
Absorption coefficient (mmÀ1
F(000)
)
Crystal size (mm3)
h range for data collection (°)
Index ranges
0.40 Â 0.05 Â 0.03
1.62–26.43
À18 ꢀ h ꢀ 18, À10 ꢀ k ꢀ 10,
À25 ꢀ l ꢀ 25
Reflections collected
21282
g
1-bonded Cp ligand in these molecules. This results in an interest-
ing 1H NMR spectrum, which appears to suggest a 5-bonding due
Independent reflections
Completeness to h = 26.43°
Absorption correction
Maximum and minimum transmission
Refinement method
5081 [R(int) = 0.0426]
99.8%
semi-empirical from equivalents
0.9553 and 0.7701
full-matrix least-squares on F2
5081/0/272
g
to the symmetry of two singlet peaks for the cyclopentadienyl
hydrogens, approximately 1 ppm apart. This can be rationalised
by fast sigma tropic shift in solution.
Data/restraints/parameters
Goodness-of-fit on F2
1.041
3.2. Structural discussion
Final R indices [I > 2sigma(I)]
R indices (all data)
R1 = 0.0347, wR2 = 0.0777
R1 = 0.0434, wR2 = 0.0805
0.907 and À0.536
Largest difference in peak and hole
Despite the effort to crystallise the organotin derivatives 4a-c,
no crystal structures were obtained. 2,2-Bipyridine was success-
(e ÅÀ3
)

B. Gleeson et al. / Polyhedron 27 (2008) 3619–3624
3623
fully used as a bidentate nitrogen base in an attempt to crystallise a
six co-ordinated tin complex for the organotin dichloride species.
This produced single crystals of the bipyridine adduct of
1-(p-
methoxybenzyl)cyclopentadienyl tin(IV) trichloride (5), where
one of the Cp ligands is replaced with a Cl atom, which can be
viewed in Fig. 2. This shows that the tin(IV) cyclopentadienyl chlo-
rides undergo more than one exchange reaction: The above men-
tioned sigma tropic shift and a ligand exchange in a Schlenk-type
equilibrium. The structure is monoclinic and contains CHCl3 sol-
vent molecules in the crystal (see Table 3).
The bond lengths for Sn–Cl(1) 2.420 Å, Sn–Cl(2) 2.442 Å, and
Sn–Cl(3) 2.414 Å of the six co-ordinated Sn species are slightly
longer when compared with other tin(IV) complexes [28], due to
the increased electron density surrounding the central Sn atom.
Also, the bond length of the Sn–C(3) 2.222 Å is comparable with
other organotin complexes such as Me2SnCl2 where the Sn–C bond
4a IC50 (1.5+/-0.2)E-5 M
4b IC50 (2.1+/-0.7)E-4 M
4c
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
g
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
C21
C20
Log10 Drug Concentration (M)
C17
C16
C22
C23
Fig. 3. Cytotoxicity curves from typical MTT assays showing the effect of
compounds 4a–c on the viability of LLC-PK cells.
C19
C18
C15
C8
Cl2
N2
C14
N1
C5
C9
C6
lengths are in the region of 2.210 Å [29]. This structure also dem-
onstrates the g1-bonded conformation for the Sn–C bond, which
is believed to be present in complexes 4a–c. The two double bonds
present in the cp ring are evident due to the shortening of the car-
bon-carbon bond lengths, C(1)–C(2) 1.349 Å and C(4)–C(5) 1.346 Å.
The longer single CC bonds within the Cp ring were; C(2)–C(3)
1.482 Å, C(3)–C(4) 1.460 Å, and C(1)–C(5) 1.453 Å. The structure
displays a distorted octahedral conformation, with the N(1)–Sn–
N(2) angle of 72.51° being compressed due to the co-ordinated
bipyridine ligand.
C7
C12
C4
C13
Sn
C1
C10
Cl1
O
C2
C3
Cl3
C11
Fig. 2. X-ray diffraction structure of 5; thermal ellipsoids are drawn on the 50%
probability level.
Table 3
Selected bond lengths and angles from the crystal structure of 5
3.3. Biological evaluation
Identification code
5
Bond
Sn–C(3)
Sn–N(1)
Sn–N(2)
Sn–Cl(3)
Sn–Cl(1)
Sn–Cl(2)
C(1)–C(2)
C(1)–C(5)
C(1)–C(6)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(6)–C(7)
N(1)–C(14)
N(1)–C(18)
C(19)–N(2)
C(19)–C(18)
C(23)–N(2)
Bond length (Å)
2.222
2.231
2.278
2.414
2.420
2.442
1.349
1.453
1.494
1.482
1.460
1.346
1.521
1.347
1.355
1.337
1.482
1.342
Almost no antibacterial effect was observed for complexes 4a–c
against the Gram-negative bacteria E. coli using the Kirby–Bauer
disk diffusion method. Against the Gram-positive bacteria MRSA
and MSSA however, a low to medium effect was observed with
the compounds 4b and 4c having the greatest effect over 24 h.
The solvent used to prepare the stock solutions (DMSO) played
no role in growth inhibition. These results are in keeping with
other organotin(IV) results found in the literature.
3.4. Cytotoxicity studies
As seen in Fig. 3, compounds 4a and 4b showed IC50 values 15
and 210
lM respectively. Complex 4c displayed no antitumor
activity. All three compounds suffered from very poor solubility
along with decomposition due to certain air sensitivity of the com-
pounds, which resulted in relatively large error margins for com-
pounds 4b and 4c. Compound 4a showed surprisingly good
Bond angles
C(3)–Sn–N(1)
C(3)–Sn–N(2)
N(1)–Sn–N(2)
C(3)–Sn–Cl(3)
N(1)–Sn–Cl(3)
N(2)–Sn–Cl(3)
C(3)–Sn–Cl(1)
N(1)–Sn–Cl(1)
N(2)–Sn–Cl(1)
Cl(3)–Sn–Cl(1)
C(3)–Sn–Cl(2)
N(1)–Sn–Cl(2)
N(2)–Sn–Cl(2)
Cl(3)–Sn–Cl(2)
Cl(1)–Sn–Cl(2)
91.73
95.38
72.51
93.98
93.59
163.44
92.82
165.49
93.34
99.83
176.83
85.48
82.34
87.72
89.53
results of 15
the titanium equivalent, Titanocene Y, which yielded an IC50 value
of 21 M. This result emphasises the importance of the p-methoxy
lM with reduced error margins when compared with
l
phenyl moiety that is present in both 4a and Titanocene Y. How-
ever the IC50 value for 4a did not reach the level set by cisplatin
with an IC50 value of 3.3 lM.
4. Conclusion and outlook
The hydridolithiation of 6-aryl substituted fulvenes followed by
transmetallation has been found to be a very effective and repro-
ducible way to medium to highly cytotoxic benzyl-substituted

3624
B. Gleeson et al. / Polyhedron 27 (2008) 3619–3624
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(2004) 288.
organotin complexes. Although preliminary anti-bacterial results
were lower than expected, 4a yielded a promising anti-tumour
IC50 value of 15 lM. While the possibility of 4a becoming a viable
anti-cancer drug are low due to high air sensitivity of 4a and gen-
eral toxicity of organotin compounds, these results are encourag-
ing enough to warrant further work in this area.
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CCDC 699232 contains the supplementary crystallographic data
for 5. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgements
[20] G.M. Sheldrick, SADABS Version 2.03, University of Göttingen, Germany, 2002.
[21] G.M. Sheldrick, SHELXS-97 and SHELXL-97, University of Göttingen, Germany,
1997.
The authors thank the Higher Education Authority (HEA), the
Centre for Synthesis and Chemical Biology (CSCB), University Col-
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for Anticancer Drug Research (CESAR) for funding.
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