Palladium(II) complexes with 5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione : SSynthesis, thermogravimetric and cytotoxic investigation

Article abstract of DOI:10.1007/s10973-007-8937-3

Two new palladium(II) complexes with 5-methyl-5-(4-pyridyl)-2,4- imidazolidenedione(mpyh) were synthesized: cis-[Pd(mpyh)₂Cl ₂]?H₂O and cis-[Pd(mpyh)₂Br ₂]?2H₂O. The molecular formulae of t

Full text of DOI:10.1007/s10973-007-8937-3

Journal of Thermal Analysis and Calorimetry, Vol. 95 (2009) 1, 241–246
PALLADIUM(II) COMPLEXES WITH 5-METHYL-5-(4-PYRIDYL)-
2,4-IMIDAZOLIDENEDIONE
Synthesis, thermogravimetric and cytotoxic investigation
1*
Adriana Bakalova , H. Varbanov , R. Buyukliev , G. Momekov and D. Ivanov
1
2
3
1
1Department of Chemistry, Faculty of Pharmacy, Medical University, Sofia, 2 Dunav Str., 1000 Sofia, Bulgaria
2Department of Organic Chemistry, Faculty of Pharmacy, Medical University, Sofia, 2 Dunav Str., 1000 Sofia, Bulgaria
3Department of Pharmacology, Pharmacotherapy and Toxicology, Faculty of Pharmacy, Medical University, Sofia, 2 Dunav Str.
1000 Sofia, Bulgaria
Two new palladium(II) complexes with 5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione(mpyh) were synthesized:
cis-[Pd(mpyh)2Cl2]×H2O and cis-[Pd(mpyh)2Br2]×2H2O. The molecular formulae of the complexes were confirmed by elemental
analysis, IR, H NMR spectra and DTA study. The ligand is coordinated to the palladium ion with N-atom of the pyridine ring.
1
The spectroscopic data indicate a square planar geometry with two N-pyridine atoms and two halogene anions in cis position.
The final product of the thermal decomposition of cis-[Pd(mpyh)2Cl2]×H2O is metallic Pd, whereas for cis-[Pd(mpyh)2Br2]×2H2O the
residue consists of metallic Pd and C. The cytotoxic effects of the complexes were examined in vitro on some human tumor cell
lines. The cis-[Pd(mpyh)2Cl2]×H2O proved to be more active as compared to the cis-[Pd(mpyh)2Br2]×2H2O.
Keywords: cytotoxicity, hydantoins, Pd(II) complexes, synthesis, thermal analysis
Introduction
Based on the structural analogy between Pt(II) and
Pd(II) complexes, some studies on palladium com-
pounds as suitable drugs have been carried out [14].
The present study represents the synthesis,
physicochemical study and the pharmacological
investigation of Pd(II) complexes with 5-methyl-5-
(4-pyridyl)-2,4-imidazolidenedione in vitro as com-
pared to the clinically applied drug Cisplatin and
novel Pt(II) complexes with the same ligand [15].
The first transition metal to be used successfully as
anticancer agent was platinum. It was used in the
compound Cisplatin (cis-[Pt(NH3)2Cl2]), and its
ability to inhibit tumors was discovered by
Rosenberg et al. in 1969 [1, 2]. Cisplatin is known as
agent with strong anticancer potency [3]. It is widely
used for the chemotherapy of diverse solid tumours
such as head and neck, ovarian cancer, cervical
cancer, urinary bladder cancer etc. [4, 5]. Despite its
wide application as a therapeutic agent in chemo-
therapy, Cisplatin is associated with many serious
side toxic effects, such as nephrotoxicity, othotoxi-
city, allergy, peripheral neuropathy, etc. [6].
Experimental
Materials
The ligand 5-methyl-5-(4-pyridyl)-2,4-imidazoli-
denedione was synthesized according previously
described method [16]. K2[PdCl4] utilized for the
synthetic procedures was purchased from Fluka. All
of the other chemicals were of analytical grade.
Preparation of cis-dichloro-bis(5-methyl-5-
However, later it was shown that not only
platinum(II) complexes exhibited antitumor effects.
Numerous planar and octahedral platinum complexes
as well as compounds of other platinum group metals
such as ruthenium, rhodium, aurium, titanium or
palladium were characterized by cytotoxic activity
[7–9]. Although platinum complexes are still among
those most frequently studied in the search for new
metal based drugs, the ruthenium(III) complexes also
reach clinical level of trials [10]. Relatively few
palladium(II) and palladium(IV) complexes have
been investigated for their cytotoxic and antitumor
activity [10–13].
(4-pyridyl)-2,4-imidazolidenedionepalladium(II)
monohydrate – cis-[Pd(mpyh)2Cl2]×H2O
Two water solutions of K2[PdCl4] and 5-methyl-5-
(4-pyridyl)-2,4-imidazolidenedione(mpyh) were pre-
pared for the synthesis of the complex
cis-[Pd(mpyh)2Cl2]×H2O (1). The solution of the ligand
(0.1164 g, 0.6094 mmol) was added dropwise to the
water solution of K2[PdCl4] (0.1005 g, 0.3079 mmol)
*
Author for correspondence: adrigebk@abv.bg
1388–6150/$20.00
© 2008 Akadémiai Kiadó, Budapest
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands

BAKALOVA et al.
at constant stirring and after the addition of the ligand
FCS and Cisplatin was purchased from Sigma Co.
The stock solutions of tested compounds (20 mM)
were freshly prepared in DMSO, and stored at 4°C,
protected from light for a maximum period of 1 week.
The serial dilutions of the tested compounds were
prepared immediately before use. At the final
dilutions obtained the concentrations of DMSO never
exceeded 1%.
the homogenous solution was stirred for 1–2 h.
A bright-yellow product was obtained, which was fil-
tered, washed several times with water and dried in a
vacuum desiccator. The substance is soluble in DMSO
and weakly soluble in water and ethanol. The purity is
checked up by thin layer chromatography.
Yield: ca. 82%, m.p.: > 320°C (dec.).
1HNMR
8.78 (2H, py), 8.59 (NH-1), 7.65 (2H, py),
1.68 ppm (3H, s).
Preparation
(DMSO-d6):
11.08
(NH-3),
Cell lines and culture conditions
of
cis-dibromo-bis(5-methyl-
The cell line HL-60 (acute promyelocyte leukemia)
was supplied from DSMZ GmbH, Germany. SKW-3
human T-cell leukemia was supplied from DSMZ
GmbH, Germany and established from peripheral
blood of 61-year-old man with T-cell lymphocytic
leukemia.
5-(4-pyridyl)-2,4-imidazolidenedione)palladium(II)
dihydrate – cis-[Pd(mpyh)2Br2]×2H2O
The complex cis-[Pd(mpyh)2Br2]×2H2O (2) was pre-
pared according to a reported procedure [17].
0.1007 g K2[PdCl4] (0.3085 mmol) was mixed with a
saturated solution of potassium bromide (in excess)
(0.1906 g) and heated on a water bath for 5 min, thus
K2[PdCl4] was quantitatively converted into a solu-
tion of K2[PdBr4]. To this mixture 0.1173 g
(0.6141 mmol) of the ligand were added. The solution
was stirred for 1 h. Brown crystals were obtained and
filtered. The complex is weakly soluble in DMSO.
The purity is checked up by thin layer chromatogra-
phy. Yield. ca. 97%, m.p.: > 290°C (dec.).
Cells were cultured routinely in a controlled
environment: 37°C in 5% CO2 humidified atmo-
sphere. They were maintained in RPMI 1640 growth
medium supplemented with 2 mM L-glutamine and
10% fetal calf serum. HL-60 and SKW-3 cells were
subcultured twice weekly to maintain continuous
logarithmic growth.
Pharmacology
1HNMR (DMSO-d6): 11.08 (NH-3), 8.84 (2H, py),
8.77 (NH-1), 7.63 (2H, py), 1.68 ppm (3H, s).
Cytotoxicity assay
Cell survival was evaluated by using the MTT-dye re-
duction assay, which is based on the ability of viable
cells to metabolize a yellow tetrazolium salt to a vio-
let formazan product that can be detected
colorimetrically. The assay was carried out as previ-
ously described [18] with minor modifications [19].
In brief, exponentially growing cells were plated in
96-well sterile plates at a density of 104 cells/well in
100 m L of medium and were incubated for 24 h.
Thereafter the tested compounds were applied at con-
centrations ranging from 0.195 to 200 m M. After 72 h
continuous exposure 10 m L aliquots from a 5 mg mL–1
MTT solution were added to each well and the plates
were further incubated for 4 h at 37°C in a humidified
5% CO2 atmosphere. The formazan crystals yielded
were solubilized by addition of HCOOH (5%) acidi-
fied DMSO. The MTT-formazan absorbance was
read on a microprocessor controlled multiplate reader
(Labexim LMR-1).
Instrumentation
The carbon, nitrogen and hydrogen content of the
compounds were determined by elemental analysis.
The elemental analysis was carried out on an Elemen-
tar Analysensysteme GmbH VarioEl. The results
were within ± 0.5% of the theoretical values.
The IR spectra were recorded on IR IFS 113 v.
Bruker FTIR spectrophotometer in the range of
4000–400 cm–1 as KBr tablets and on FTIR-GX
PerkinElmer in the range of 400–220 cm–1 as CsI tab-
lets. The 1H-NMR spectra were registered on a
Bruker WM 250 (250 MHz) spectrometer in
DMSO-d6. Corrected melting points were determined
using a Bushi 535 apparatus. Thermal analysis were
performed on a C.MOM thermal analyzer (Budapest,
Hungary) with a simultaneous DTA-TG module us-
ing the following conditions: sample mass 50 mg,
heating range 20–900°C (293–1173 K), heating rate
5°C min–1, air atmosphere.
Results and discussion
In vitro assays; chemicals, solutions and other
materials
On the basis of the data from the elemental analysis
for the new complexes the following formulae can be
derived: cis-[Pd(C9H9N3O2)2Cl2]×H2O (1) and
cis-[Pd(C9H9N3O2)2Br2]×2H2O (2), where C9H9N3O2
The cell culture flasks and the 96-well microplates
were obtained from NUNCLON (Denmark). MTT,
242
J. Therm. Anal. Cal., 95, 2009

PALLADIUM(II) COMPLEXES WITH 5-METHYL-5-(4-PYRIDYL)-2,4-IMIDAZOLIDENEDIONE
Table 1 Chemical analysis of the complexes (1) and (2)
C/%
H/%
N/%
Pd/%
Compound
theor.
exp.
theor.
exp.
theor.
exp.
theor.
exp.
Complex (1)
Complex (2)
37.42
31.57
37.56
31.33
3.46
2.92
3.95
2.98
14.55
12.28
14.50
11.87
18.43
15.55
18.03
15.16
is 5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione as
a ligand (Table 1). Calculated data are in good
agreement with experimental values. In order to
evaluate the mode of coordination of the ligands to
the metal ion, the IR-spectra of the pure ligands as
well as of their Pd(II) complexes were recorded.
cis-[Pd(Him)2Cl2] (339, 335 cm–1), etc. (py=pyridine,
Him=imidazole) [26–28]. The presence of these bands
assigned to Pd-Cl and Pd-Br stretching vibrations indi-
cate coordination of the palladium(II) via Cl– and Br– in
cis geometry.
The bands related to the stretching vibrations of
the two carbonyl groups at 1776.2 and 1730.2 cm–1 of
the hydantoin ring remained unchanged in the
complexes. This fact is evidence that these groups are
not involved in the complex formation.
FTIR spectra
The assignment of the coordination mode of the
ligand with the palladium ion was done on the basis of
IR-spectra of mpyh, of the Pd(II) complexes with
mpyh, literature data for Pd(II) complexes with
pyridine derivatives [20, 21] as well as of our earlier
statements on platinum complexes with the same
ligand and with other N-containing heterocyclic
ligands [15, 22, 23].
1
H NMR spectra
In the 1H NMR spectra of complexes (1) and (2) the sig-
nals of the protons for H-2 and H-6 from the pyridine
ring were shifted from 8.56 ppm in the spectrum of the
ligand to 8.78 and 8.84 ppm in the spectra of the com-
plexes respectively. The differences between the chemi-
cal shifts of the protons of the ligand and these of the
corresponding complexes are shown as D d (in ppm).
The shifts are notice- able – D d =0.22 and 0.28 ppm. The
signals of the H-3 and H-5 protons from the pyridine
ring were shifted from 7.48 ppm in the ligand to 7.65
and 7.63 ppm in the complexes. The chemical shifts are
D d =0.17 and 0.15 ppm and are less than those registered
for the nearer to nitrogen atom protons of the pyridine
ring. This shows that the most probable bounding of the
ligand with the palladium ion in the complexes is real-
ized through the nitrogen atom from the pyridine ring,
similarly as it was found for platinum complexes with
the identical ligand [15]. The signals for the protons at
the nitrogen atoms from the hydantoin ring were not
shifted. This fact indicates that these atoms are not in-
volved in the complex formation to the palladium.
On the basis of the results from the physico-
chemical investigations, the following, most probable
schematic structures of the Pd(II) complexes with
mpyh could be proposed (Fig. 1).
The comparative analysis of the IR-spectra of
the complexes (1), (2) (Table 2) and of the free ligand
revealed that the absorption bands characteristic for
the stretching vibrations of –C=N– from the pyridine
ring were shifted towards the higher frequencies –
from 1605.3 cm–1 in the spectrum of the ligand to
1653.7 and 1652.4 cm–1 in the spectra of the com-
plexes respectively. The other characteristic bands of
the free ligand in the region 1414–1006 cm–1, related
to pyridine ring shift to higher frequencies upon
complexation likewise. This fact suggests that the ni-
trogen atom from the pyridine ring participates in the
coordination to the palladium ion [24, 25].
The far IR spectra of the complexes show ligand
vibrations as well as new bands originating from Pd-Cl
and Pd-Br stretching. In the IR spectra of the Pd(II)
complexes exhibited two new bands in the low-energy
region at 330–290 cm–1 which can be assigned to Pd-Cl
of (1) and Pd-Br of (2) stretching vibrations, because
they are in the range reported for other palladium com-
plexes e.g.: cis-[Pd(py)2Cl2] (342, 333 cm–1),
Table 2 IR data for the free ligand and for the complexes (1) and (2)
Compound
n (NH)
n (–C=N)
n (C=O)
n (Pd-Cl)
n (Pd-Br)
3203.2
3114.2
1605.3
1776.2
1730.2
Ligand (mpyh)
3440.6
3277.4
1653.7
1611.1
1770.3
1726.1
327.8
305.6
Complex (1)
Complex (2)
3189.4
3062.4
1652.4
1616.1
1783.1
1734.9
303.4
209.8
J. Therm. Anal. Cal., 95, 2009
243

BAKALOVA et al.
Thermogravimetric study
Fig. 2 TG, DTG and DTA curves of cis-[Pd(mpyh)2Cl2]×H2O
Fig. 1 Schematic structures of the investigated Pd(II) com-
plexes cis-[Pd(mpyh)2Cl2]×H2O (1) and
cis-[Pd(mpyh)2Br2]×2H2O (2)
Thermogravimetric analysis is a very valuable
method with which to study the thermal decom-
positions of solid substances, such as complex
compounds [29–32]. The curves obtained depict the
decrease in sample mass with linear increase in
treatment temperature.
Complex (1) is stable up to T=60°C (333 K).
(Fig. 2). After this temperature decomposition in two
stages begins. In the TG curve at T=100°C (373 K)
mass loss D m=9.8% is registered (theoretical mass
loss D m=9.3%) which corresponds to the discon-
nection of one molecule crystal water and one
chloride ion [33]. This is confirmed from the
endothermic effect in the DTA curve at the same
temperature. Endothermic effect at T=320°C (593 K)
in the DTA curve, which corresponds to an
undeviating part from the TG curve, includes further
decomposition of the complex. This suggests discon-
nection of the second chloride ion and initial
destroying of the two organic ligands leading to
palladium. At the beginning of these processes the
experimental mass loss D m=23.0% (theoretical mass
loss D m=23.0%). The final product of the decom-
position process is metallic Pd (D m=81.0%) [34].
Fig. 3 TG, DTG and DTA curves of cis-[Pd(mpyh)2Br2]×2H2O
Complex (2) is stable up to T=80°C (353 K).
(Fig. 3). In the TG curve at this temperature a mass loss
D m=4.9% is registered (theoretical mass loss D m=5.3%)
which corresponds to the disconnection of two mole-
cules crystal water. After this temperature begins grad-
ual decomposition. In the DTA curve endothermic ef-
fect with maximum at T=330°C (603 K) is observed. It
corresponds to the mass loss in the TG curve
D m=30.0%, which most probably due to the loss of one
bromide ion [29]. The theoretical calculated mass loss is
D m=29.6%. After this temperature decomposition of the
two organic ligands takes place.
After the T=330°C (603 K) in the DTA curve
one pronounced exothermic effect at T=580°C
(853 K) follows, which probably is a result from the
244
J. Therm. Anal. Cal., 95, 2009

PALLADIUM(II) COMPLEXES WITH 5-METHYL-5-(4-PYRIDYL)-2,4-IMIDAZOLIDENEDIONE
formation of new compounds. The final residue
consists of Pd and carbon as from the TG curve a
mass loss of 82.0% is registered. This statement is in
accordance with the results obtained about other
Pd(II) complexes [34].
Cytotoxic effect
The cytotoxic activity of the tested palladium com-
plexes and the referent cytotoxic drug cis-DDP was
evaluated by the MTT-dye reduction assay against the
human acute promyelocyte leukemia HL-60 and the
T-cell leukemia SKW-3. Evident from the concentra-
tion-response curves for HL-60 summarized in Fig. 4.
The referent drug induced strong, concentration-de-
pendent reduction of cell viability leading to almost total
eradication of malignant cells at concentrations exceed-
Fig. 5 Cytotoxic effects of the newly synthesized complexes
ing 50 m M (IC50=8.7 m M). The newly synthesized palla-
dium complexes exerted far less pronounced
cis-[Pd(mpyh)2Cl2], cis-[Pd(mpyh)2Br2] and cis-DDP
vs. the human T-cell leukemia SKW-3
cytotoxicity failing to reach 50% reduction of cell via-
bility up to concentration 200 m M. In order to allow
comparative assessment of their potency IC20 values
were calculated, as the concentrations reducing the cell
Statistical analysis
viability by 20%. The dichloro analogue (IC20
Student’s t-test performed using commercially available
=65.5 m M) proved to be more active as compared to the
software with p< 0.05 taken as significance level. The
cytotoxicity experiments were performed using eight
wells per concentration. The MTT-data processing –
non linear fitting (sigmoidal dose-response curves) and
calculation of IC50 and IC20 values were performed us-
ing Graph Pad Prizm software.
dibromo-complex (IC20=152.7 m M). The IC20 value of
Cisplatin was 3.33 m M.
The human T-cell leukemia SKW-3 proved to be
more sensitive to the novel compounds. The concen-
tration-response curves for SKW-3 summarized in
Fig. 5. The IC50 values obtained were 89.00 m M for
the dichloro-complex and 160.22 m M for the dibromo
analogue respectively. The referent antineoplastic
drug induced strong inhibitory activity with an IC50
value of 11.78 m M.
Conclusions
Two new Pd(II) complexes with 5-methyl-5-(4-pyri-
dyl)-2,4-imidazolidenedione and various halogen an-
ions were synthesized. The molecular formulae of the
complexes were confirmed by elemental, spectral
analysis as IR, 1H-spectra and DTA analysis. A NMR
study indicates that the palladium is coordinated via
N-atom of the pyridine ring. The infrared spectra in
the far region of metal-ligand bond stretching frequ-
encies indicates a square-planar cis geometry for
Pd(II) – halogene ions in the complexes. The thermal
decomposition of these complexes occurs in two con-
secutive steps and the final decomposition product
was Pd for complex (1) and Pd and carbon for com-
plex (2). The dichloro analogue proved to be more
active as compared to the dibromo-complex.
Acknowledgements
Fig. 4 Cytotoxic effects of the newly synthesized complexes
cis-[Pd(mpyh)2Cl2], cis-[Pd(mpyh)2Br2] and cis-DDP
vs. the human promyelocyte leukemia HL-60
The authors are grateful for the excellent technical assistance
of Mrs. Mariana Michailova.
J. Therm. Anal. Cal., 95, 2009
245

BAKALOVA et al.
19 S. Konstantinov, H. Eibl and M. Berger, Br. J. Haematol.,
References
107 (1999) 365.
20 P. C. Kong and F. D. Rochon, Can. J. Chem., 59 (1981) 3293.
21 J. Kuduk-Jaworska, A. Puszko, M. Kubiak and
M. Petczynska, J. Inorg. Biochem., 98 (2004) 1447.
22 A. Bakalova, R. Buyukliev, G. Momekov, D. Ivanov,
D. Todorov, S. Konstantinov and M. Karaivanova, Eur. J.
Med. Chem., 40 (2005) 590.
1 B. Rosenberg, L. Van Camp, J. E. Trosko and
V. H. Mansour, Nature, 222 (1969) 385.
2 B. Rosenberg and L. Van Camp, Cancer Res.,
304 (1979) 1799.
3 J. Reedijk, Curr. Opin. Chem. Biol., 3 (1999) 236.
4 A. Forastiere, W. Koch, A. Trotti and D. N. Sidranski,
Engl. J. Med., 345 (2001) 1890.
23 A. Bakalova, R. Buyukliev, I. Tcholakova, G. Momekov,
S. Konstantinov and M. Karaivanova, Eur. J. Med. Chem.,
38 (2003) 627.
5 A. Latorre, M. De Lena, A. Catino, E. Crucitta,
D. Sambiasi, M. Guida, A. Misino and V. Lorusso, Int. J.
Oncol., 20 (2002) 179.
24 N. S. Gill, R. H. Nuttal and D. E. Scaife, J. Inorg. Nucl.
Chem., 18 (1961) 79.
6 N. Markman, Exp. Opin. Drug Saf., 2 (2003) 597.
7 J. L. Bear, H. B. Gray, L. Rainen, I. M. Chang,
R. Howard, G. Serio and A. P. Kimball, Cancer
Chemother. Rep., 159 (1975) 611.
25 G. Zhao, H. Lin, P. Yu, H. Sun, Sh. Zhu and X. Su,
J. Inorg. Biochem., 73 (1999) 143.
26 K. Nakamoto, Infrared and Raman Spectra of Inorganic
and Coordination Compound, Wiley, New York 1978,
p. 197.
8 S. Giraldi, G. Sava, G. Bertoli, G. Mestroni and
G. Zassinovich, Cancer Res., 37 (1977) 2662.
9 R. D. Graham and D. R. Williams, J. Inorg. Nucl. Chem.,
41 (1979) 1245.
27 M. Pffefer, P. Braunstein and J. Dehand, Spectrochim.
Acta, A, 30 (1974) 331.
28 W. J. Geary, Coord. Chem. Rev., 7 (1971) 81.
29 B. A. Howell, D. Fan and L. Rakesh, J. Therm. Anal. Cal.,
85 (2006) 17.
10 D. Kovala-Demertzi, M. A. Demertzis, J. R. Miller,
C. S. Frampton, J. P. Jasinski and D. X. West, J. Inorg.
Biochem., 92 (2002) 137.
30 A. Bakalova and D. Ivanov, J. Therm. Anal. Cal.,
89 (2007) 257.
11 D. Kovala-Demertzi, M. A. Demertzis, E. Filiou,
A. A. Pantazaki, P. N. Yadav, J. R. Miller, Y. Zeng and
D. A. Kyriakidis, Biometals, 16 (2003) 411.
12 A. G. Quiroga and C. Navarro-Ranninger, Coord. Chem.
Rev., 248 (2004) 119.
31 F. Yakuphanoglu, A. KaradaÈ and M. Ÿekerci, J. Therm.
Anal. Cal., 86 (2006) 727.
32 V. ZeleÔák, Z. Vargová, K. Györyová, E. Ve¹erníková
and V. Balek, J. Therm. Anal. Cal., 82 (2005) 747.
33 N. El-Metwaly, Transition Met. Chem., 32 (2007) 88.
34 I. ˜akomska, M. BarwioÓek and E. SzÓyk, Transition Met.
Chem., 32 (2007) 70.
13 H. Hohman and R. Van Eldik, Inorg. Chim. Acta,
174 (1990) 87.
14 M. J. Cleare, P. C. Hydes, in H. Sigel (Ed.) Metal Ions in
Biological Systems, Marcel Dekker, New York 1980,
Vol. 11, Ch. 1.
15 A. Bakalova, H. Varbanov, R. Buyukliev, G. Momekov,
D. Ferdinandov, S. Konstantinov and D. Ivanov, Eur. J.
Med. Chem., 43 (2008) 958.
Received: December 20, 2007
Accepted: April 1, 2008
OnlineFirst: August 15, 2008
16 C.-C. Chu and P.C. Teague, J. Org. Chem.,
23 (1958) 1578.
17 S. Dhara, Indian J. Chem., 8 (1970) 193.
18 T. Mosmann, J. Immunol. Meth., 65 (1983) 55.
DOI: 10.1007/s10973-007-8937-3
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