Synthesis, structure, and biological activity of the cis-[4-amino-2,2,6,6- tetramethylpiperidine-N,N′]dichloropalladium(ii) complex

Article abstract of DOI:10.1007/s11172-013-0080-7

A previously unknown palladium complex was synthesized by the reaction of 4-amino-2,2,6,6-tetramethylpiperidine with PdCl₂. The X-ray diffraction study showed that the complex formed by 4-amino-2,2,6,6- tetramethylpiperidine with PdCl₂ is a chelate, in which the bidentate ligand adopts a boat conformation with the nitrogen atoms occupying cis positions at the palladium atom. The resulting cis-[4-amino-2,2,6,6- tetramethylpiperidine-N,N′]dichloro-palladium(ii) complex exhibits strong antimetastatic activity against experimental B16 melanoma at moderate toxicity.

Full text of DOI:10.1007/s11172-013-0080-7

Russian Chemical Bulletin, International Edition, Vol. 62, No. 2, pp. 572—574, February, 2013
572
Brief Communications
Synthesis, structure, and biological activity of
the cisꢀ[4ꢀaminoꢀ2,2,6,6ꢀtetramethylpiperidineꢀN,N´]dichloropalladium(II)
complex
B. S. Fedorov, M. A. Fadeev, G. I. Kozub, N. I. Golovina,† A. N. Utenyshev, G. V. Shilov,
S. M. Aldoshin, N. P. Konovalova, T. E. Sashenkova, and T. A. Kondrat´eva
Institute of Problems of Chemical Physics, Russian Academy of Sciences,
1 prosp. Akad. N. N. Semenova, 142432 Chernogolovka, Moscow Region, Russian Federation.
Fax: +7 (495) 785 7048. Eꢀmail: borisꢀ45@inbox.ru
A previously unknown palladium complex was synthesized by the reaction of 4ꢀaminoꢀ
2,2,6,6ꢀtetramethylpiperidine with PdCl2. The Xꢀray diffraction study showed that the comꢀ
plex formed by 4ꢀaminoꢀ2,2,6,6ꢀtetramethylpiperidine with PdCl2 is a chelate, in which the
bidentate ligand adopts a boat conformation with the nitrogen atoms occupying cis positions at
the palladium atom. The resulting cisꢀ[4ꢀaminoꢀ2,2,6,6ꢀtetramethylpiperidineꢀN,N´]dichloroꢀ
palladium(II) complex exhibits strong antimetastatic activity against experimental B16 melanoma
at moderate toxicity.
Key words: synthesis, complexation with PdCl2, metal complex, cisꢀ[4ꢀaminoꢀ2,2,6,6ꢀ
tetramethylpiperidineꢀN,N´]dichloropalladium(II), chelate, Xꢀray diffraction study, antimetaꢀ
static activity, toxicity.
Earlier,1—3 we have described complexes synthesized
from PtCl2 or PdCl2 and substituted amides of pyridineꢀ
carboxylic acids as ligands and revealed some characteristic
features of the complex formation reactions. Subsequently,
we have used these ligands to synthesize complexes with
platinum tetrachloride,4,5 which have cisꢀstereochemistry,
as was shown by Xꢀray diffraction analysis. While these
complexes are lowꢀtoxic (197—1000 mg kg–1) and do not
cause myelosuppression, they inhibit the experimental
metastasis of Lewis lung carcinoma and B16 melanoma
by 96—98%. In addition, it was experimentally shown that
the synthesized complexes act on Ca2+ꢀMg2+ꢀdependent
ATPase of the sarcoplasmic reticulum, thus inhibiting the
calcium transport across biological membranes.6 This leads
to the disturbance of the normal ratio of calcium ions on
the extraꢀ and intracellular membrane surfaces followed
by the inhibition of the aggregation of platelets (a critical
step in the metastatic process) and their binding to metaꢀ
static cells, which results in the loss of the cell adhesion to
bloodꢀvessel walls. However, these compounds cannot be
† Deceased.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 0570—0572, February, 2013.
1066ꢀ5285/13/6202ꢀ0572 © 2013 Springer Science+Business Media, Inc.

Synthesis and biological activity of the PdCl2 complex Russ.Chem.Bull., Int.Ed., Vol. 62, No. 2, February, 2013
573
recommended for the application to biological objects beꢀ
cause of their low solubility in water. Hence, a search for
C(9)
new highly efficient complexes, which are readily soluble
in water and have high activity, is a topical problem in the
chemistry of antitumor and antimetastatic drugs. In conꢀ
C(2)
Cl(1)
tinuation of our studies on the complexation in a series of
substituted pyridines, it was of interest to investigate the
complex formation reaction of palladium dichloride with
4ꢀaminoꢀ2,2,6,6ꢀtetramethylpiperidine, because pipeꢀ
ridines are physiologically active compounds and can acꢀ
tively participate in metabolic processes.
The aim of the present study is to synthesize a previꢀ
ously unknown waterꢀsoluble palladium complex with
the use of 4ꢀaminoꢀ2,2,6,6ꢀtetramethylpiperidine as the
ligand, which is supposed to have cisꢀstereochemistry, and
to determine the molecular structure of the resulting comꢀ
plex. It is known that complexes with cisꢀstereochemistry
have higher therapeutic activity compared to those with
transꢀgeometry.7
C(8)
C(1)
N(2)
Pd(1)
C(3)
C(4)
Cl(2)
N(1)
C(5)
C(6)
C(7)
Fig. 1. Molecular structure of complex 1.
Results and Discussion
1,3ꢀdiazoꢀ2ꢀpalladabicylco[2.2.2]octane framework. We
do not report the geometric parameters of complex 1 since
it is unreasonable to discuss them because of the low qualꢀ
ity of the crystals.
It was expected that the use of 4ꢀaminoꢀ2,2,6,6ꢀtetraꢀ
methylpiperidine as the ligand in the reaction with PdCl2
would make it possible to prepare complex 1 with
cisꢀstereochemistry (Scheme 1).
The biological activity of complex 1 was tested in mice
at the Laboratory of Experimental Tumor Chemotherapy
of the Institute of Problems of Chemical Physics of the
Russian Academy of Sciences. Complex 1 was shown to
have strong antimetastatic activity against experimental
metastatic B16 melanoma (the index of metastasis inhibiꢀ
tion (IMI) is 89%) at moderate toxicity (Table 1). For
comparison, IMI for cisplatin, which is the chemotherapy
drug widely used for the cancer treatment, is 92%.
To summarize, we synthesized new complex 1 starting
from palladium dichloride and 4ꢀaminoꢀ2,2,6,6ꢀtetrameꢀ
thylpiperidine. Moderate toxicity, fairly good solubility in
water, and strong antimetastatic activity of complex 1 sugꢀ
gest that this compound is a promising target for extensive
testing in biological materials.
Scheme 1
The Xꢀray diffraction study confirmed that comꢀ
pound 1 has the expected (see Scheme 1) molecular strucꢀ
ture (Fig. 1).
Compound 1 is a molecular complex, in which the
PdII atom is cisꢀcoordinated by two chlorine atoms and
two nitrogen atoms of the 4ꢀaminoꢀ2,2,6,6ꢀtetramethylpiꢀ
peridine molecule acting as a bidentate ligand (see Fig. 1).
In complex 1, the ligand adopts a boat conformation with
positions 1 and 4 of the heterocycle being in close proximꢀ
ity. The resulting chelate forms the 6,6,7,7ꢀtetramethylꢀ
Experimental
The IR spectrum was recorded on a PerkinꢀElmer Specꢀ
1
trumꢀ100 instrument. The H NMR spectra were measured on
a Brukerꢀ500 spectrophotometer.
Synthesis of cisꢀ[4ꢀaminoꢀ2,2,6,6ꢀtetramethylpiperidineꢀ
N,N´]dichloropalladium(II). 4ꢀAminoꢀ2,2,6,6ꢀtetramethylpipeꢀ
ridine (0.44 g, 2.8 mmol) was added with stirring to a suspension
of PdCl2 (0.5 g, 2.8 mmol) in water (30 mL) at 20 C. The
reaction mixture was stirred until PdCl2 was completely disꢀ
solved (24 h) and then concentrated in a fume hood using air
blowꢀoff until the precipitation of crystals started. After 10—12 h,
the paleꢀbrown precipitate was filtered off, washed with a small
amount of ice water and ethanol, and dried in air. Complex 1
was obtained in a yield of 0.8 g (80%), m.p. 174 C (decomp).
Table 1. Biological activity of preparations
Preparation
LD100
LD50
MTD/mg kg–1
Cisplatin
Complex 1
16
300
12.5
250
8.0
200

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Russ.Chem.Bull., Int.Ed., Vol. 62, No. 2, February, 2013
Fedorov et al.
Found (%) : C, 32.58; H, 5.71; N, 8.34; Pd, 32.43; Cl, 20.68.
C9H20N2PdCl2. Calculated (%): C, 32.5; H, 5.76; N, 8.42;
Pd, 31.99; Cl, 21.33. IR, /cm–1: 703 (w), 788 (m), 866 (m),
891 (m), 931 (s), 968 (s), 1018 (s), 1050 (s), 1068 (s), 1087 (s),
1160 (s), 1182 (s), 1221 (s), 1222 (s), 1269 (m), 1293 (w),
1307 (m), 1348 (m), 1363 (m), 1380 (s), 1392 (s), 1443 (s),
1475 (s), 1588 (s), 1609 (s), 2110 (w), 2468 (s), 2594 (s), 2652 (m),
2759 (s), 2830 (m), 2925 (w), 2946 (w), 3010 (m), 3184 (s),
3377 (s). 1H NMR (DMSOꢀd6): 1.35 (s, 6 H, CH3); 1.41 (s, 6 H,
CH3); 1.51 (m, 2 H, CH2); 2.23 (m, 2 H, –CH2–); 3.19 (m, 1 H,
CH); 7.94 (br.s, 2 H, NH2); 9.26 (br.s, 1 H, NH). The sample
for the Xꢀray diffraction study was obtained by the crystallization
from a mixture of acetonitrile and water in a ratio of 1 : 2.5.
Xꢀray diffraction study of complex 1. The unit cell parameters
for compound 1 were measured and the threeꢀdimensional Xꢀray
diffraction data set was collected on a KMꢀ4 fourꢀcircle diffractoꢀ
meter (KUMAꢀDiffraction, Poland) from a poorꢀquality crystal
with dimensions of 0.15×0.1×0.1 mm. Compound 1 crystallizes
in the monoclinic system: C9H20N2PdCl2, Mr = 333.57,
a = 12.814(3) Å, b = 11.519(2) Å, c = 17.803(4) Å,  = 91.97(3),
V = 2626(1) Å3, d = 1.687 g cm–3,  = 1.5418 Å, space group
of metastases in the control and test groups, respectively. The
preparations were administered intraperitoneally as aqueous soꢀ
lutions.
References
1. B. S. Fedorov, M. A. Fadeev, N. I. Golovina, A. B. Ereꢀ
meev, V. V. Arakcheeva, G. V. Strukov, G. V. Shilov,
R. F. Trofimova, L. O. Atovmyan, Russ. Chem. Bull. (Engl.
Transl.), 1998, 47, 510 [Izv. Akad. Nauk, Ser. Khim., 1998,
527].
2. B. S. Fedorov, N. I. Golovina, G. V. Strukov, V. V. Kedrov,
G. V. Shilov, L. O. Atovmyan, Russ. Chem. Bull. (Int. Ed.),
2000, 49, 566 [Izv. Akad. Nauk, Ser. Khim., 2000, 561].
3. B. S. Fedorov, M. A. Fadeev, N. I. Golovina, G. V. Strukov,
V. V. Kedrov, G. V. Shilov, G. N. Boiko, L. O. Atovmyan,
Russ. Chem. Bull. (Int. Ed.), 2001, 50, 520 [Izv. Akad. Nauk,
Ser. Khim., 2001, 499].
4. B. S. Fedorov, M. A. Fadeev, G. I. Kozub, C. M. Aldoshin,
Z. G. Aliev, L. O. Atovmyan, N. P. Konovalova, T. E. Cashꢀ
enkova, T. A. Kondrat´eva, S. V. Blokhina, Pharm. Chem.
(Engl Transl.), 2009, 43, 134 [Khim.ꢀfarm. Zh., 2009, 43,
No. 3, 12].
5. B. S. Fedorov, M. A. Fadeev, G. I. Kozub, A. N. Chekhlov,
N. P. Konovalova, T. E. Sashenkova, E. N. Berseneva, O. V.
Dobrokhotova, L. V. Tat´yanenko, Russ. Chem. Bull.
(Int. Ed.), 2011, 60, 1181 [Izv. Akad. Nauk, Ser. Khim., 2011,
1151].
6. L. V. Tat´yanenko, N. P. Konovalova, G. N. Bogdanov,
O. V. Dobrokhotova, B. S. Fedorov, Biomed. Chem.
(Moscow) (Engl. Transl.), 2006, 52, No. 1 [Biomed. Khim.,
2006, 52].
7. A. Sigel, H. Sigel, Metal Jons in Biological Systems, Marcel
Dekker, Inc., New York, 1996.
8. G. M. Sheldric, SHELXLꢀ97. Program for Refinement of
Crystal Structure, University of Göttingen, Göttingen, Gerꢀ
many, 1997.
C2/c, Z = 8,  = 14.88 mm–1
.
A total of 1591 reflections with F0 > 4(F0) were measured
for compound 1 in the angle range 3.5 <  < 80.5 using the
/2ꢀscan technique. The structure was solved by direct methods
using the SHELXLꢀ97 program package.8 The coordinates of
nonhydrogen atoms were refined by the fullꢀmatrix leastꢀsquares
method with anisotropic displacement parameters. The hydroꢀ
gen atoms were positioned geometrically and refined using
a riding model. The final R factor is 0.075.
Biological assays. Experiments were carried out in BDF1
hybrid mice with a weight of 22—24 g. Each group included
8—10 animals. The inoculum size for experimental B16 melanoꢀ
ma was 5•106 tumor cells. The B16 melanoma cells were injectꢀ
ed subcutaneously. The B16 melanomaꢀbearing mice were sacꢀ
rificed 24 days after the transplantation of tumor cells. The numꢀ
ber of lung metastases was determined, and then the index of
metastasis inhibition, which is an indicator of the antimetastatic
activity of the complex, was calculated according to the equation
where AC and A are the frequencies of metastasis in the control
and test groups, respectively, BC and B are the average numbers
Received October 12, 2012;
in revised form January 20, 2013