Organotin flufenamates: Synthesis, characterization and antiproliferative activity of organotin flufenamates

Article abstract of DOI:10.1016/j.jorganchem.2005.02.004

The organotin flufenamates [Me₂(flu)SnOSn(flu)Me ₂]₂ (1), [Bu₂(flu)SnOSn(flu)Bu ₂]₂ (2) and [Bu₂Sn(flu)₂] (3) have been prepared and structurally characterized by means of vibrational and NMR (¹H, ¹³C and ¹¹⁹Sn) spectroscopy. The crystal structure of [Me₂(flu)SnOSn(flu)Me₂]₂ (1) has been determined by X-ray crystallography. Three distannoxane rings are present to the dimeric tetraorganodistannoxane of planar ladder arrangement. The structure is centro-symmetric and features a central rhombus Sn ₂O₂ unit with two additional tin atoms linked at the O atoms. Six-coordinated tin centers are present in the dimer distannoxane. This structure is self-assembled via π → π and C-H → π stacking interactions. Flufenamic acid and flufenamates were evaluated for antiproliferative activity in vitro. Among the compounds tested [Bu ₂(flu)SnOSn(flu)Bu₂]₂ (2) and [Bu ₂Sn(flu)₂] (3) exhibited high cytotoxic activity against the cancer cell line A549 (non-small cell lung carcinoma).

Full text of DOI:10.1016/j.jorganchem.2005.02.004

Journal of Organometallic Chemistry 690 (2005) 1800–1806
www.elsevier.com/locate/jorganchem
Organotin flufenamates: Synthesis, characterization and
antiproliferative activity of organotin flufenamates
a,
a
b
c
Dimitra Kovala-Demertzi *, Vaso N. Dokorou , Jerry P. Jasinski , Adam Opolski ,
a
Joanna Wiecek , Maria Zervou , Mavroudis A. Demertzis
d
a,
*
a
Inorganic and Analytical Chemistry, Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece
b
Department of Chemistry, Keene State College, 229 Main Street, Keene, NH 03435-2110, USA
c
Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, Weigla 12, 53-114 Wroclaw, Poland
d
National Hellenic Research Foundation, Institute of Organic and Pharmaceutical Chemistry, Vas. Constantinou 48, 11635 Athens, Greece
Received 2 February 2005; accepted 2 February 2005
Available online 16 March 2005
Abstract
The organotin flufenamates [Me2(flu)SnOSn(flu)Me2]2 (1), [Bu2(flu)SnOSn(flu)Bu2]2 (2) and [Bu2Sn(flu)2] (3) have been prepared
and structurally characterized by means of vibrational and NMR (1H, 13C and 119Sn) spectroscopy. The crystal structure of
[Me2(flu)SnOSn(flu)Me2]2 (1) has been determined by X-ray crystallography. Three distannoxane rings are present to the dimeric
tetraorganodistannoxane of planar ladder arrangement. The structure is centro-symmetric and features a central rhombus Sn2O2
unit with two additional tin atoms linked at the O atoms. Six-coordinated tin centers are present in the dimer distannoxane. This
structure is self-assembled via p ! p and C–H ! p stacking interactions. Flufenamic acid and flufenamates were evaluated for
antiproliferative activity in vitro. Among the compounds tested [Bu2(flu)SnOSn(flu)Bu2]2 (2) and [Bu2Sn(flu)2] (3) exhibited high
cytotoxic activity against the cancer cell line A549 (non-small cell lung carcinoma).
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Flufenamic acid; Diorganotin flufenamates; Crystal structure; Spectroscopic studies; Antitumor agents
1. Introduction
been isolated [1]. The increasing interest in organotin(IV)
carboxylates that has arisen in the last few decades is
attributed to their significantly important biological
properties. Several di- and tri-species have shown poten-
tial as antineoplastic and antituberculosis agents [2].
Flufenamic acid (N-[3-(trifluoromethyl)-phenyl]-
anthranilic acid), Hflu (Scheme 1), belongs to the class
of non-steroidal anti-inflammatory drugs, NSAIDs,
which are clinically used against a wide range of acute
and chronic disorders. The therapeutic activity of these
analgesics is believed to be due to their ability to inhibit
the biosynthesis of prostaglandins by competitive inter-
action with the cyclooxygenase–arachidonic acid com-
plex or by radical quenching agents that interfere with
the initiation of the cyclooxygenase reaction [3].
Additionally, Hflu produces inhibition of a variety of
Organotin compounds are of interest in view of their
considerable structural diversity. Among the com-
pounds, the most ubiquitous are the carboxylates [1].
The reactions of precursors with carboxylic acids have
been studied in considerable detail. Depending on the
carboxylic acid used and the stoichiometry of the reac-
tants, several products such as monomers, dimers, tetra-
mers, oligomeric ladders, and hexameric drums have
*
Corresponding authors. Tel.: +30 651 98425; fax: +30 651 98792
(D. Kovala-Demertzi), Tel.: +30 651 98425; fax: +30 651 44831 (M.A.
Demertzis).
E-mail addresses: dkovala@cc.uoi.gr (D. Kovala-Demertzi), mde-
mert@cc.uoi.gr (M.A. Demertzis).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.02.004

D. Kovala-Demertzi et al. / Journal of Organometallic Chemistry 690 (2005) 1800–1806
1801
HO
O
polyethylene disks (400–40 cmꢀ1). The 1H (250.13
MHz), 13C (62.90 MHz) NMR spectra were recorded
on a Bruker AMX-400 and on a Bruker AC-250 spec-
trometer. 119Sn spectra were recorded on a Bruker
AC-300 spectrometer operating at 111.9 MHz. The
spectra were acquired at room temperature (298 K).
The chemical shifts are reported in ppm with respect
to the references (external tetramethylsilane (TMS) for
1H and 13C NMR and neat tetramethyltin for 119Sn).
Samples were dissolved in CDCl3 and spectra were ob-
tained at room temperature with the signal of free
CDCl3 (at 7.24 ppm) as a reference. Elemental analyses
were carried out by the microanalytical service of the
University of Ioannina, Greece.
2'
2
CF3
H
N
3'
3
1
1'
4'
6'
4
6
5'
5
Scheme 1.
ion channel responses in a range of tissues. These actions
are capable of encompassing both anion and cation
channels and it appears that ion channels are the targets
of the drug [4,5]. Flufenamic acid was found to inhibit
the proliferation and migration of human aortic smooth
muscle cells (haSMCs) in vitro [5c]. The crystal structure
of Hflu [6] and of flufenamic acid with prostaglandin D
(2) 11-ketoreductase (AKR1C3) has been reported [7].
Given the pharmacological importance of flufenamic
acid and the potential biological activity of carboxylates,
it was thought of interest to explore the chemistry of/flu-
fenamic acid compounds. In order to widen the scope of
investigations on the coordination behavior of non-
steroidal anti-inflammatory drugs, NSAIDs, towards
organotins, we carried out systematic studies of organo-
tin(IV) derivatives of oxicams and fenamates [8,9], with
the final goal to develop new biologically active pharma-
ceuticals. Here, we report the synthesis and structural
studies of the novel complexes [R2(flu)SnOSn(flu)R2]2
R = Me (1), Bu (2) and [Bu2Sn(flu)2] (3). The complexes
have been structurally characterized by means of vibra-
2.2. Synthesis
2.2.1. [Me2(flu) SnOSn(flu)Me2]2 (1)
Dimethyltin(IV) oxide (0.198 g, 1.2 mmol) and flufen-
amic acid (0.281 g, 1.0 mmol) in benzene (40 ml) were
refluxed for 24 h under azeotropic removal of H2O
(Dean–Stark trap). The resulting clear solution was con-
centrated in vacuo to a small volume. The oily product
was chilled and triturated with diethyl ether (Et2O) to
give a yellow solid. The yellow powder was dried in va-
cuo over silica gel. Yield 26%; m.p. 216 ꢁC. IR: 3312
m(NH), 1611, 1585 mas(COO), 1395, 1462 msym(COO);
589, 577, 547 m(Sn–C); 648, 621 m(Sn–O)2; 300sh, 277
m(Sn–O); 176, 153 d(Sn–O). Crystals of 1 suitable for
X-ray analysis were obtained by slow evaporation of a
fresh tetrahydrofurane/acetone (1:1) solution Anal. calc.
for C64H60N4O10F12Sn4 (1747.8 g molꢀ1): C, 44.0; H,
3.5; N, 3.2. Found: C, 44.4; H, 3.6; N, 3.0%.
2.2.2. [Bu2(flu)SnOSn(flu)Bu2]2 (2) and [Bu2Sn(flu)2]
(3)
1
tional and H, 13C and 119Sn NMR spectroscopic stud-
Di-n-butyltin(IV) oxide (0.286 g, 1.15 mmol) and flu-
fenamic acid (0.281 g, 1.0 mmol) for 2 and (0.605 g,
2.15 mmol) for 3 in benzene (40 ml) were refluxed for
24 h under azeotropic removal of H2O (Dean–Stark
trap). The resulting clear solutions were concentrated
in vacuo to a small volume. The oily products were
chilled and triturated with trifluoroacetic acid (TFA)
to give a yellow and bright yellow powder, respectively,
for 2 and 3. The powders were dried in vacuo over silica
gel. [Bu2(flu)SnOSn(flu)Bu2]2 (2): Yield 82%; m.p. 52–
55 ꢁC. IR: 3317 m(NH), 1685, 1609 mas(COO), 1413,
1464 msym(COO); 544, 520, 482 m(Sn–C); 636, 617
m(Sn–O)2; 299, 285sh m(Sn–O); 171, 157 d(Sn–O). Anal.
calc. for C88H108N4O10F12Sn4 (2084.4 g molꢀ1): C,
50.7; H, 5.2; N, 2.7. Found: C, 51.0; H, 5.4; N, 2.6%.
[Bu2Sn(flu)2] (3): Yield 77%; m.p. 77–78 ꢁC; IR (KBr):
3314 m(NH), 1671 mas(COO), 1412 msym(COO); 543, 519
m(Sn–C); 302, 287sh m(Sn–O); 177, 154 d(Sn–O). Anal.
calc. for C36H36N2O4F6Sn1 (793.4 g molꢀ1): C, 54.5;
H, 4.6; N, 3.5. Found: C, 54.2; H, 4.5; N, 3.3%.
ies. The crystal and molecular structure of 1 is described.
The results of the cytotoxic activity of flufenamic and
flufenamates against the cancer cell line A549 (non-small
cell lung carcinoma) are also reported. These are the first
reported complexes and crystal structure of a flufenamic
complex.
2. Experimental
2.1. General and instrumental
The reagents (Aldrich, Merck, Sigma) were used as
supplied while the solvents were purified according to
standard procedures. Melting points were determined
in open capillaries and are uncorrected. Infrared and
far-infrared spectra were recorded on a Nicolet 55XC
Fourier transform spectrophotometer using KBr pellets
(4000–400 cmꢀ1) and nujol mulls dispersed between

1802
D. Kovala-Demertzi et al. / Journal of Organometallic Chemistry 690 (2005) 1800–1806
2.3. X-ray crystallography
culture medium. Afterwards, the tested compounds were
diluted in culture medium to reach the final concentra-
tions of 100, 10, 1, and 0.1 lg/ml. The solvent (DMSO)
in the highest concentration used in test did not reveal
any cytotoxic activity.
The crystallographic data for 1 are given in Table 1,
together with refinement details. All measurements were
performed on a Rigaku AFC6S diffractometer, with
graphite-monochromated Mo Ka radiation. The data
were collected in the x–2h scan technique to a maximum
2h value of 55.0ꢁ. The structure 1 was solved by direct
methods and expanded by Fourier techniques [10]. The
non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were refined in their calculated posi-
tions as ‘‘riding atoms’’. The two sets of fluoro atoms
were disorded and were refined anisotropically but in
2.4.2. Cells
The established in vitro human cancer cell line, A549
(non-small cell lung carcinoma), was applied: The line
was obtained from the American Type Culture Collec-
tion (Rockville, MD, USA) and is maintained in the Cell
Culture Collection of the Institute of Immunology and
Experimental Therapy, Wroclaw, Poland. Twenty-four
hours before addition of the tested agents, the cells were
plated in 96-well plates (Sarstedt, USA) at a density of
104 cells per well. The cells were cultured in the opti-
MEM medium supplemented with 2 mM glutamine,
streptomycin (50 lg/ml), penicillin (50 U/ml) and 5% fe-
tal calf serum. The cell cultures were maintained at
37 ꢁC in humid atmosphere saturated with 5% CO2.
˚
‘‘restrained format’’ (C–F distance 1.40 A and r
0.001). All calculations were performed with the teXsan
[10] crystallographic software package (Molecular
Structure Corporation), except for refinement, which
was performed with SHELXL-97 [11].
2.4. Antiproliferative assay in vitro
2.4.1. Compounds
2.4.3. SRB assay
Test solutions of the compounds tested (1 mg/ml)
were prepared ex tempore by dissolving the substance
in 100 ll of DMSO completed with 900 ll of tissue
The details of this technique were described by Ske-
han et al. [12]. The cytotoxicity assay was performed
after 72-h exposure of the cultured cells to varying con-
centrations (from 0.1 to 100 lg/ml) of the tested agents.
The cells attached to the plastic were fixed by gently lay-
ering cold 50% trichloroacetic acid (TCA) on the top of
the culture medium in each well. The plates were incu-
bated at 4 ꢁC for 1 h and then washed five times with
tap water. The background optical density was mea-
sured in the wells filled with culture medium, without
the cells. The cellular material fixed with TCA was
stained with 0.4% sulforhodamine B dissolved in 1%
acetic acid for 30 min. Unbound dye was removed by
rinsing (4·) with 1% acetic acid. The protein-bound
dye was extracted with 10 mM unbuffered Tris base
for determination of optical density (at 540 nm) in a
computer-interfaced, 96-well microtiter plate reader
Multiskan RC photometer (Labsystems, Helsinki, Fin-
land). Each compound in given concentration was tested
in triplicates in each experiment, which was repeated 3–5
times.
Table 1
X-ray crystal data and structure refinement
1
Crystallized from
Crystal size (mm)
Formula
THF/acetone
0.30 · 0.40 · 0.50
C
1747.8
64H60N4O10F12Sn4
Mr
T (K)
˚
Wavelength (A)
293(2)
0.71073
Triclinic
Crystal system
Space group
Cell dimensions
ꢀ
P1 (No. 2)
˚
a (A)
9.2782(19)
13.269(3)
˚
b (A)
˚
C (A)
15.530(3)
64.99(3)ꢁ
83.78(3)ꢁ
77.99(3)ꢁ
1694.4(6)
a (ꢁC)
˚
b (A)
˚
c (A)
3
˚
V (A )
Z
1
1.713
Dcalc (Mg mꢀ3
)
3. Results and discussion
Absorption coefficient (mmꢀ1
F(000)
)
1.548
860
1.72–27.50
3.1. Crystal structure of 1
h Range (ꢁ)
Ranges of hkl
ꢀ12 6 h 6 11, ꢀ17 6 k 6 0,
ꢀ20 6 l 6 18
8096
The molecular structure of 1 is shown in Fig. 1 and
selected interatomic parameters are collected in Table
2. Compound 1 is a centrosymmetric dimer distannox-
ane built up around the planar cyclic Sn2O2 unit. The
two oxygen atoms of this unit are tridentate as they link
three Sn centers, two endo-cyclic and one exo-cyclic.
The distance between the endocyclic and exocyclic tin
Reflections collected
Independent reflections [Rint
]
7760 [0.0911]
Full-matrix least-squares on F2
7760/54/492
Refinement
Data/restraints/parameters
Goodness-of-fit (F2)
0.959
0.0400, 0.0869
0.696 and ꢀ0.711
Final R1/w2 indices (I > 2rIꢀ) 3
˚
Largest diff. peak/hole (e A
)

D. Kovala-Demertzi et al. / Journal of Organometallic Chemistry 690 (2005) 1800–1806
1803
atoms is 3.732(1) and the distance between the two
endocyclic tin centers is 3.290(1). The additional links
between the endo- and exo-cyclic Sn atoms are provided
by bridging carboxylato ligands that form asymmetrical
differentiate the different modes of bonding of the car-
boxylate, i.e., bridging or chelating.
The phenyl rings are planar. The dihedral angles be-
tween the planes of the phenyl rings for 1 are 44.7(4)ꢁ
and 40.4(4)ꢁ for the bidentate bridging and the anisob-
identae chelating ligands, respectively. The angles be-
tween the two phenyl rings are 53ꢁ and 44ꢁ in the
two conformers of flufenamic [4]. The aminobenzoate
portion of each carboxylato ligand is effectively planar
which presumably facilitates the formation of
intramolecular hydrogen bonding N(1A)–Hꢁ ꢁ ꢁO(2A)
and N(1B)–Hꢁ ꢁ ꢁO(1B) interactions of 2.660(8) and
˚
bridges (Sn(1A)–O(1B) 2.340(5) A and Sn(1B)–O(2B)
˚
2.204(5) A). Each exocyclic Sn atom is also coordinated
by an anisobidentate chelating carboxylato ligand
˚
(Sn(1A)–O(1A) 2.172(5) A and Sn(1A)–O(2A) 2.783(5) A).
˚
This distance of 2.783(5) and the Sn(1B)–O(1Aa) dis-
˚
tance of 2.871(4) A are considered long to indicate sig-
nificant bonding interactions, however, the range of
˚
distances Sn–O of 2.61–3.02 A has been confidently re-
ported for intramolecular bonds [13].
˚
2.685(8) A, respectively. The crystal structure of 1 shows
The structures of dimeric distannoxane of anthranilic
acid, [Me2(NH2-o-H4C6CO2)SnOSn(NH2-o-H4C6CO2)-
Me2]2 [14] and of [Bu2(DMPA)SnOSn(DMPA)Bu2]2
HDMPA is 2-[bis(2,6-dimethylphenyl)amino]benzoic
acid [8d] have solid state structure closely resembling
the 1, both in the geometry of the central core
(Sn2O2)2, the coordination mode of anthranilic acid
and the presence of weaker interactions (2.736(9)–
2.918(6)). The anisobidentate chelated carboxylato of 1
ring-stacking interactions. The monomers are stacked
by a strong p ! p interaction and weaker C–H ! p
interactions. In this case complex 1 is self-assembled
via C–H ! p and p ! p stacking interactions. C–
H ! p, p ! p stacking and intramolecular hydrogen
interactions stabilize this structure, Table 3. The overall
geometry found in 1, allowing for differences in chemis-
try, is remarkably similar to compounds with the general
formula [R2(R0CO2)SnOSn(O2CR0)R2]2 [1b,1c].
˚
has a difference of 0.053 A between its C–O bonds while
for the bidentate bridged carboxylato this difference is
3.2. Spectroscopic studies
˚
only 0.019 A; the variations in the C–O bond distances
suggest charge delocalization over the carboxylato
group COO. The relevant bond lengths thus easily
In the IR spectrum of Hflu, the strong band at
3320 cmꢀ1 was assigned to the N–H stretching motion,
Fig. 1. Perspective view of 1 showing the atomic numbering scheme.

1804
D. Kovala-Demertzi et al. / Journal of Organometallic Chemistry 690 (2005) 1800–1806
Table 2
Table 3
C–H/p Interactions and intramolecular H-bonds and distances (ꢁ ꢁ ꢁ) for
˚
Bond lengths (A) and angles (ꢁ) for 1
1
Sn(1A)–O
2.024(4)
2.096(8)
2.111(8)
2.172(5)
2.340(5)
2.033(4)
2.092(8)
2.101(8)
2.154(5)
2.204(5)
Sn(1A)–C(2A)
Sn(1A)–C(1A)
Sn(1A)–O(1A)
Sn(1A)–O(1B)
Sn(1B)–O
X
H
Z
Hꢁ ꢁ ꢁZ
Xꢁ ꢁ ꢁZ
\(X–Hꢁ ꢁ ꢁZ)
C–H/p (1)
C(1A)i
H(1A)
Cg(6)a
2.967
3.088
3.199
3.680(9)
3.657(9)
3.814(12)
132.13
121.09
125.29
C(11A)ii
H(11A) Cg(3)a
C(13A)iii H(13A) Cg(4)a
Sn(1B)–C(2B)
Sn(1B)–C(1B)
Sn(1B)–O#1
Cg–Cgb bc
3.740(4) 11.42
CgI-Perpd CgJ-Perpd
Cg(6)iv ! Cg(6)
H-bonds (1)
3.666
3.666
Sn(1B)–O(2B)
N(1A)
N(1B)
C(5A)
C(5B)
H(1A)
O(2A)
O(1B)
O(1A)
O(2B)
2.07(9) 2.660(8)
2.00(7) 2.685(8)
141(8)
141(7)
101
O–Sn(1A)–C(2A)
O–Sn(1A)–C(1A)
110.2(3)
106.0(2)
142.6(3)
80.5(2)
96.8(3)
98.4(3)
91.5(2)
83.1(3)
86.7(3)
171.5(2)
105.8(3)
112.9(2)
140.7(3)
76.44(17)
99.0(3)
96.3(2)
89.1(2)
90.7(3)
83.5(3)
164.3(2)
H(1B)
H(5A)
H(5B)
2.42
2.37
2.750(10)
2.713(10)
C(2A)–Sn(1A)–C(1A)
O–Sn(1A)–O(1A)
101
˚
Distances in A, angles in degrees (ꢁ); X is a C-, O-, or N-atom, Z is
either a centroid (Cg) or an O-atom. See Fig. 1 for atom numbering.
C(2A)–Sn(1A)–O(1A)
C(1A)–Sn(1A)–O(1A)
O–Sn(1A)–O(1B)
a
Cg(3), Cg(4) and Cg(6) refer to the centroids C(4A)ꢁ ꢁ ꢁC(9A),
C(4B)ꢁ ꢁ ꢁC(9B) and (10B)ꢁ ꢁ ꢁC(15B).
C(2A)–Sn(1A)–O(1B)
C(1A)–Sn(1A)–O(1B)
O(1A)–Sn(1A)–O(1B)
O–Sn(1B)–C(2B)
b
Cg–Cg is the distance between ring centroids; symmetry transfor-
mations: (i) 1 + x,y,z; (ii) 2 ꢀ x, 2 ꢀ y, ꢀz; (iii) 2 ꢀ x, 1 ꢀ y, ꢀz; (iv)
1 ꢀ x, 1 ꢀ y, ꢀz.
c
b is the angle Cg(I) ! Cg(J).
O–Sn(1B)–C(1B)
C(2B)–Sn(1B)–C(1B)
O–Sn(1B)–O#1
C(2B)–Sn(1B)–O#1
C(1B)–Sn(1B)–O#1
O–Sn(1B)–O(2B)
d
CgI-Perp or CgJ-Perpis the perpendicular distance of Cg(I) on ring J.
are assigned to the Sn–O(COO) stretching modes. The
absorption bands at 540–500 cmꢀ1 are attributed to
m(Sn–C) stretching modes [8,9,15].
C(2B)–Sn(1B)–O(2B)
C(1B)–Sn(1B)–O(2B)
O#1–Sn(1B)–O(2B)
The H and 13C NMR data for flufenamic acid and
1
the complexes are summarized in Table 4. These re-
sults, together with the published data on flufenamic
acid [16], allowed complete assignment of all signals
in the spectra of both the flufenamic acid and com-
plexes. The downfield chemical shift for HN in flufen-
amic acid indicates that this proton is involved in
hydrogen bonding. The crystal structure of flufenamic
acid suggests the presence of hydrogen-bonded dimers
linked by two intermolecular O–H–O hydrogen bonds
and an intramolecular hydrogen bond between the
HN group and the carbonyl group of the carboxyl acid
Symmetry transformations used to generate equivalent atoms:
#1
ꢀx + 2, ꢀy + 1, ꢀz + 1.
and the broad band at ca. 2870 cmꢀ1 to the m(NHꢁ ꢁ ꢁO)
and m(OHꢁ ꢁ ꢁO) mode due to intra- and intermolecular
H-bonding, as confirmed by X-ray crystallography [6].
The absence of large systematic shifts of the m(NH)
and d(NH) bands in the spectra of the complexes com-
pared with those of the ligand indicates that there is
no interaction between the NH group and the metal
ions. The masym(COO) and msym(COO) bands appear at
ca. 1680–1580 and 1450–1300 cmꢀ1, respectively. The
mas(COO) bands appear at 1681, 1609 and at 1611,
1585 cmꢀ1for 1 and 2, respectively, and msym(COO) at
1413, 1464 and at 1395, 1462 cmꢀ1 for 1 and 2, respec-
tively. The difference D[mas(COO) ꢀ msym(COO)] between
these frequencies for 1 (276, 123 cmꢀ1) and 2 (272,
135 cmꢀ1) is close to that found for anisobidentate che-
late mode (276, 272 cmꢀ1) and bridging bidentate carb-
oxylato groups (123, 135 cmꢀ1). This is totally
consistent with the X-ray structure of 1. The masym(COO)
and msym(COO) bands appear at 1671 and 1412 cmꢀ1 for
3. The difference D[masym(COO) ꢀ msym(COO)] between
these frequencies is 259 cmꢀ1, which is close to that
found for the anisobidentate chelate carboxylato group.
Two bands at 650–620 cmꢀ1 for 1 and 2 are assigned to
symmetric and asymmetric (SnO)2 vibrations, indicating
nonlinear O–Sn–O moieties. The bands at 300–280 cmꢀ1
1
[6]. The existence of the HN resonance in the H NMR
spectra indicates that the nitrogen atoms remain pro-
1
tonated in 1–3. In the H NMR spectrum of 1, three
singlets appear in the region of the tin-bound methyl
groups, but integration shows that in the case of the
signal emerging at 1.25 ppm, two methyl groups are
present indicating accidental equivalence. Deshielding
of protons H(3) and H(4) is observed in complexes,
which should be related to the electrophilicity of the
tin. A r-charge donation from the COO-donor to the
tin center removes electron density from the ligand
and produces this deshielding which will attenuate at
positions remote from the metal. The remaining reso-
nances due to the aromatic carbon atoms do not shift
significantly on binding to Sn. The 13C NMR spectra
of 2 and 3 reveal resonance assignable to the CO2 nu-
cleus and coordination is confirmed by the fact that this
resonance exhibits a downfield shift. Involvement of the

D. Kovala-Demertzi et al. / Journal of Organometallic Chemistry 690 (2005) 1800–1806
1805
Table 4
1H, 13C and 119Sn NMR dataa
COOH
NH
H3
H4
H6
H5, H20, H40–H60
119Sn
Hfluc
1b
9.39s
9.87br
8.09dd
7.93br
6.74t
6.76br
7.29d
7.29d
7.32–7.51m
7.32–07.50m
Me2Sn
1.05s/1.54s
1.26s/1.26s
Bu2Sn
2
9.26br
8.47br
8.11d
8.13d
6.85t
6.86t
7.26d
7.26t
7.35–7.51m
7.33–7.50m
Hd: 0.91, Hc: 1.26
Hb: 1.80, Ha: 1.40
Bu2Sn
ꢀ121.5
ꢀ173.9
3
Hd: 0.91, Hc: 1.43
Hb: 1.85, Ha: 1.75
ꢀ112.9
COOH
Hflu 174.0
C1
C2
C3
C4
C5
C6
C10
C20
C30
C40
C50
C60
CF3
147.6 111.3 132.8 118.4 135.4 114.2 141.1 118.8 131.9 120.1 129.9
147.4 112.7 133.8 118.6 135.6 114.1 141.3 118.5 131.8 120.1 129.8
125.2 121.7
125.1 121.8
2
177.6
Bu2Sn Cd: 13.5, Cc: 22.7,
Cb: 29.7, Ca: 31.9
3c
Bu2Sn Cd: 13.4, Cc: 26.3,
Cb: 26.5, Ca: 29.8 COOO: 175.5
147.7 111.1 133.3 118.7 135.7 114.1 141.2 118.4 131.8 120.1 129. 9 125.2 122.5
a
Spectra recorded in CDCl3.
In CDCl3 and d6-DMSO insufficient solubility to record a measurable 13C and 119Sn NMR spectrum.
b
c
Carboxyl proton exchanged in CDCl3.
Table 5
The antiproliferative activity in vitro of Hflu, and flufenamates 2 and 3
carboxyl group in bonding to Sn is confirmed by the
resonance ascribed to C(2), which exhibit the greatest
shift upon coordination. The remaining resonances
due to the aromatic carbon atoms do not shift signifi-
cantly on binding to Sn. The 119Sn chemical shifts of
tin complexes appear to depend not only on coordina-
tion number, but also on the type of donor atoms
bonded to the metal ion. As reported in the literature,
(expressed as ID50) against A-549 lung human cancer cell linea
Compounds
ID50 SD (lg/ml)
Hflu
[Bu2(flu)SnOSn(flu)Bu2]2
30.0 1.0
0.24 0.1
0.35 0.1
108.0
[Bu2Sn(flu)2]
Carboplatin
a
Unsufficient solubility of 1 in DMSO to perform the antiprolifer-
[17a] chemical shifts in the range
d
ꢀ210 to
ative activity.
ꢀ400 ppm, ꢀ90 to ꢀ190 ppm and 200 to ꢀ60 ppm
have been associated with six-, five- and four-coordi-
nate tin centers, respectively. The 119Sn NMR spectrum
of 2 exhibits two distinct resonances at ꢀ121.5 and
ꢀ173.9 confirming endo- and exo-cyclic tin atoms
[1d]. The value of d ꢀ112.9 ppm for complex 3 is within
the range expected for five-coordinate complexes. The
chemical shift for complex 3 in CDCl3 indicates that
the six-coordinate Sn atom in the solid state structure
(as revealed by IR spectroscopy) is lost upon dissolu-
tion giving rise to a five-coordinate tin atom in solu-
tion. This change could be explained by the rupture
of the weak Sn–O bond in solution [17b,8d].
activity criterion for synthetic agents (4 lg/ml) [18].
Thus, compounds 2 and 3 are considered as agents with
potential antitumor activity, and can therefore be candi-
dates for further stages of screening in vitro and/or in
vivo.
3.4. Conclusions
Three novel flufenamates [Me2(flu)SnOSn(flu)Me2]2
(1), [Bu2(flu)SnOSn(flu)Bu2]2 (2) and [Bu2Sn(flu)2] (3)
have been prepared and structurally characterized by
1
means of vibrational, H NMR, 13C NMR and 119Sn
3.3. Antiproliferative activity in vitro of organotin
complexes
NMR spectroscopy. Based on spectroscopic data, di-
meric tetraorganostannoxanes are proposed for 1 and
2, and monomeric hexa-coordinate structure for 3,
respectively. The crystal structure of 1 was determined
by X-ray crystallography. Flufenamic acid and flufena-
mates 2 and 3 were evaluated for antiproliferative activ-
ity in vitro. Among the compounds tested 2 and 3
exhibited high cytotoxic activity against the cancer cell
line A549 (non-small cell lung carcinoma) and com-
pounds 2 and 3 are considered as agents with potential
The results of cytotoxic activity in vitro are expressed
as ID50 – the dose of compound (in lg/ml) that inhibits a
proliferation rate of the tumor cells by 50% as compared
to control untreated cells. Flufenamic acid, Hflu, and
flufenamates 2 and 3 exhibited cytotoxic activity against
the human lung cancer cell line A549 (see Table 5). The
ID50 value for 2 and 3 are lower to the international

1806
D. Kovala-Demertzi et al. / Journal of Organometallic Chemistry 690 (2005) 1800–1806
(b) N. Parij, A.-M. Nagy, P. Fondy, J. Neve, Eur. J. Pharmacol.
352 (1998) 299;
antitumor activity, and can therefore be candidates for
further stages of screening in vitro and/or in vivo.
(c) W. Schober, J. Wiskirchen, R. Kehlbach, R. Gebert, E.
Rodegerdts, A. Betsch, U. Johst, C.D. Claussen, S.H. Duda, J.
Vasc. Intervent. Radiol. 13 (1) (2002) 89.
4. Supplementary material
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Sect. B 38 (1982) 315.
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Koutsodimou, M. Kubicki, Helvet. Chim. Acta 83 (2000) 2787;
(b) A. Galani, M.A. Demertzis, M. Kubicki, D. Kovala-Demertzi,
Eur. J. Inorg. Chem. 9 (2003) 1761;
Crystallographic data for the structural analyses have
been deposited at Cambridge Crystallographic Data Cen-
tre, as deposition number CCDC-247773. Copies of
these data may be obtained, free of charge, from CCDC,
12 Union Road, Cambridge CB2 1EZ, UK, via fax:
(+44 1223 336 033), e-mail (deposit@ccdc.cam.ac.uk),
or internet (www.ccdc.cam.ac.uk).
(c) S.K. Hadjikakou, M.A. Demertzis, J.R. Miller, D. Kovala-
Demertzi, J. Chem. Soc., Dalton Trans. (1999) 663;
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[9] (a) V. Dokorou, Z. Ciunik, U. Russo, D. Kovala-Demertzi, J.
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Acknowledgments
(b) D. Kovala-Demertzi, N. Kourkoumelis, A. Koutsodimou, A.
Moukarika, E. Horn, E.R.T. Tiekink, J. Organomet. Chem. 620
(2001) 194;
This research was funded by the program ‘‘Heraklitos’’
of the Operational Program for Education and Initial
Vocational Training of the Hellenic Ministry of Educa-
tion under the 3rd Community Support Framework and
the European Social Fund.
(c) A. Galani, D. Kovala-Demertzi, N. Kourkoumelis, A.
Koutsodimou, V. Dokorou, Z. Ciunik, U. Russo, M.A. Demert-
zis, Polyhedron 23 (2004) 2021.
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