Synthesis, characterization, and biological activity of five new mixed-ligand palladium(II) complexes with ethylenediamine and 4-toluenesulfonyl-L-amino acid dianion

Article abstract of DOI:10.1080/00958972.2011.646999

Five new palladium(II) complexes with 4-toluenesulfonyl-L-amino acid dianion and en, [Pd(en)(TsserNO)] (1), [Pd(en)(TsglyNO)] (2), [Pd(en)(TsalaNO)]·1.5H₂O (3), [Pd(en)(TsleuNO)]·H ₂O (4), and [Pd(en)(TspheNO)]·2H₂O (5), have been synthesized and characterized by elemental analysis, IR, UV, ¹H NMR, and mass spectrometry. Crystal structure of 1 has been determined by X-ray diffraction analysis. The cytotoxicity was tested by MTT and SRB assays. The results indicate 1-5 exert cytotoxic effects against HL-60, Bel-7402, BGC-823, and KB cell lines and 5 displays the best cytotoxicity. The structure-activity relationships suggest that both amino acid and N-containing ligands have important effects on cytotoxicity. Copyright

Full text of DOI:10.1080/00958972.2011.646999

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Synthesis, characterization, and
biological activity of five new mixed-
ligand palladium(II) complexes
with ethylenediamine and 4-
toluenesulfonyl-L-amino acid dianion
Jinchao Zhang a , Lili Ma a , Fangfang Zhang a , Zhilei Zhang a
Luwei Li a & Shuxiang Wang a
,
a Key Laboratory of Chemical Biology of Hebei Province , College
of Chemistry & Environmental Science, Hebei University , Baoding
071002 , P.R. China
Published online: 22 Dec 2011.
To cite this article: Jinchao Zhang , Lili Ma , Fangfang Zhang , Zhilei Zhang , Luwei Li & Shuxiang
Wang (2012) Synthesis, characterization, and biological activity of five new mixed-ligand
palladium(II) complexes with ethylenediamine and 4-toluenesulfonyl-L-amino acid dianion, Journal
of Coordination Chemistry, 65:2, 239-250, DOI: 10.1080/00958972.2011.646999
To link to this article: http://dx.doi.org/10.1080/00958972.2011.646999
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Journal of Coordination Chemistry
Vol. 65, No. 2, 20 January 2012, 239–250
Synthesis, characterization, and biological activity of five new
mixed-ligand palladium(II) complexes with ethylenediamine
and 4-toluenesulfonyl-L-amino acid dianion
JINCHAO ZHANG*, LILI MA, FANGFANG ZHANG,
ZHILEI ZHANG, LUWEI LI and SHUXIANG WANG*
Key Laboratory of Chemical Biology of Hebei Province, College of Chemistry &
Environmental Science, Hebei University, Baoding 071002, P.R. China
(Received 29 May 2011; in final form 16 November 2011)
Five new palladium(II) complexes with 4-toluenesulfonyl-L-amino acid dianion and en,
[Pd(en)(TsserNO)] (1), [Pd(en)(TsglyNO)] (2), [Pd(en)(TsalaNO)] ꢀ 1.5H2O (3), [Pd(en)
(TsleuNO)] ꢀ H2O (4), and [Pd(en)(TspheNO)] ꢀ 2H2O (5), have been synthesized and charac-
terized by elemental analysis, IR, UV, 1H NMR, and mass spectrometry. Crystal structure of 1
has been determined by X-ray diffraction analysis. The cytotoxicity was tested by MTT and
SRB assays. The results indicate 1–5 exert cytotoxic effects against HL-60, Bel-7402, BGC-823,
and KB cell lines and 5 displays the best cytotoxicity. The structure–activity relationships
suggest that both amino acid and N-containing ligands have important effects on cytotoxicity.
Keywords: Palladium(II) complexes; 4-Toluenesulfonyl-L-amino acid; Ethylenediamine;
Cytotoxicity
1. Introduction
Cisplatin is one of the most successful antineoplastic drugs; carboplatin and oxaliplatin
have also received worldwide approval. Nedaplatin, lobaplatin, and heptaplatin have
gained regionally limited approval and a few platinum drugs continue to be evaluated
in clinical trials. Regardless of the achievements of current platinum drugs, they
have several major drawbacks, including cumulative toxicities of nephrotoxicity and
ototoxicity [1–5]. Besides the serious side effects, the therapeutic efficacy is also limited
by inherent or treatment-induced resistant tumor cells. These drawbacks have provided
the motivation for alternative chemotherapeutic strategies [6, 7].
Due to the structural and thermodynamic similarity between platinum(II) and
palladium(II) complexes, there is increased interest in palladium(II) derivatives as
potential anticancer drugs [8–13]. Ligands like pyridine, quinoline, phenanthroline, and
their derivatives have been widely used in metal-based anticancer drugs because they
have the ability to participate as DNA intercalators. Numerous palladium complexes
with aromatic N-containing ligands are effective against tumors. It was reported that
*Corresponding authors. Email: jczhang6970@yahoo.com.cn; wsx@hbu.edu.cn
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2011.646999

240
J. Zhang et al.
three planar palladium complexes trans-[PdCl2L2] (where L ¼ 3-hydroxypyridine,
2-hydroxypyridine and 4-hydroxypyridine) might be able to overcome resistance of
cisplatin [14]. Owing to higher lability of palladium versus platinum analogs, amino
acid ligands, which do not dissociate easily in aqueous solution, have been used to
synthesize palladium anticancer complexes [15]. The synthesis and cytotoxicity of nine
palladium(II) complexes [Pd(phen)(AA)]þ (where AA is an anion of L-gly, ala, leu, phe,
tyr, try, val, pro, or ser) were previously reported [16]. The palladium(II) complexes
exhibit growth inhibition of P388 lymphocytic leukemic cells. The IC50 values of the
palladium(II) complexes with gly and val are comparable to that of cisplatin, whereas
the other palladium(II) complexes show higher IC50 values [16]. We previously reported
the synthesis and cytotoxicity of eight palladium(II) complexes with 4-toluenesulfonyl-
L-amino acid dianion and aromatic N-containing ligands. The complexes had cytotoxic
effects and selectivity against BGC-823, Bel-7402, KB, and HL-60 cell lines [17].
Clinically used platinum-based anticancer drugs have aliphatic N-containing ligands as
carrier groups, but the cytotoxicity of mixed-ligand palladium(II) complexes with
aliphatic N-containing ligands and 4-toluenesulfonyl-L-amino acid dianions has not
been reported. To further explore the structure–activity relationships and discover new
metal-based anticancer drugs, the synthesis, characterization, and cytotoxicities of five
new palladium(II) complexes (1–5) with 4-toluenesulfonyl-L-amino acid dianion and en
are described in this work.
2. Experimental
2.1. Materials
4-Toluenesulfonyl chloride and K2[PdCl4] were of chemical grade; en was of analytical
grade. Commercially pure ser, gly, ala, leu, and phe were purchased from Sigma.
RPMI-1640 medium, trypsin, and fetal bovine serum were purchased from Gibco.
MTT, SRB, benzylpenicillin, and streptomycin were from Sigma. Four different human
carcinoma cell lines, HL-60 (immature granulocyte leukemia), Bel-7402 (liver carci-
noma), BGC-823 (gastrocarcinoma), and KB (nasopharyngeal carcinoma) were
obtained from American Type Culture Collection.
2.2. Instrumentation and measurement
Elemental analyses were determined on an Elementar Vario EL III elemental analyzer.
Melting points were determined on a Fisher-Johns apparatus and are uncorrected.
Electronic spectra in DMF were measured on a UV-3400 Toshniwal spectro-
photometer. IR spectra were recorded on a Perkin-Elmer Model-683 spectrophot-
ometer using KBr pellets. 1H NMR spectra were recorded on a Bruker AVIII 600 NMR
spectrometer. Mass spectra were measured by LC-MS Agilent 1200–6310. The single-
crystal X-ray structure was performed on a Bruker SMART APEX II CCD
diffractometer. The OD was measured on a microplate spectrophotometer (Bio-Rad
Model 680, USA).

Palladium(II) complexes
241
H2
NH2
NH2
Cl
N
H2O
K2[PdCl4]
Pd
+
N
Cl
H2
en
[Pd(en)Cl2]
O
S
N
O
H2N
HO
R
O
O
S
O
H2
N
R
O
[Pd(en)Cl2]
pH:8~9
NaOH
HN
R
+
O
S
O
Pd
Cl
O
N
H2
HO
O
TsCl
Amino Acid
Figure 1. The synthetic routes of 1–5.
1: R ¼ –CH2OH; 2: R ¼ –H; 3: R ¼ –CH3; 4: R ¼ –CH2CH(CH3)2; 5: R ¼ –CH2(C6H5).
2.3. Synthesis of compounds
[Pd(en)(TsserNO)] (1), [Pd(en)(TsglyNO)] (2), [Pd(en)(TsalaNO)] ꢀ 1.5H2O (3), [Pd(en)
(TsleuNO)] ꢀ H2O (4), and [Pd(en)(TspheNO)] ꢀ 2H2O (5) have been prepared by the
reaction of [Pd(en)Cl2] with 4-toluenesulfonyl-L-amino acids: TsserH2, TsglyH2,
TsalaH2, TsleuH2, or TspheH2 in a mixture of CH3OH/H2O (figure 1).
2.3.1. 4-Toluenesulfonyl-L-amino acids. To a rapidly stirred solution of ser (273 mg,
2.6 mmol) in 5.0 mL ꢀ H2O was added 2.6 mL NaOH (1 mol Lꢁ1). 4-Toluenesulfonyl
chloride (500 mg, 2.6 mmol) was added to the solution and then 2.6 mL NaOH
(1 mol Lꢁ1) was added dropwise over 0.5 h. After further 8 h, the solution was cooled
by ice and acidified to pH ¼ 3–4 with HCl solution. The resulting white precipitate
was collected by filtration, washed with cold H2O (50 mL), and dried to give
1
TsserH2. TsserH2: m.p.: 223.9–224.9ꢂC. H NMR (600 MHz, DMSO-d6) ꢀ(ppm) 7.89
(d, J ¼ 8.6 Hz, 1H, NH), 7.68 (d, J ¼ 7.9 Hz, 2H, ArH), 7.35 (d, J ¼ 7.9 Hz, 2H, ArH),
3.80–3.69 (m, 1H, CH), 3.53–3.45 (m, 2H, CH2), 2.37 (s, 3H, CH3).
TsglyH2, TsalaH2, TsleuH2, TspheH2 were carried out in an identical manner.
TsglyH2: m.p.: 149.2–150.8ꢂC. 1H NMR (600 MHz, DMSO-d6) ꢀ(ppm) 7.97
(t, J ¼ 6.1 Hz, 1H, NH), 7.68 (d, J ¼ 8.2 Hz, 2H, ArH), 7.38 (d, J ¼ 8.2 Hz, 2H, ArH),
3.55 (s, 2H, CH2), 2.38 (s, 3H, CH3). TsalaH2: m.p.: 133.2–135.4ꢂC. 1H NMR
(600 MHz, DMSO-d6) ꢀ(ppm) 8.04 (d, J ¼ 8.3 Hz, 1H, NH), 7.67 (d, J ¼ 7.9 Hz, 2H,
ArH), 7.37 (d, J ¼ 8.1 Hz, 2H, ArH), 3.78–3.69 (m, 1H, CH), 2.37 (s, 3H, CH3), 1.14 (d,
J ¼ 7.2 Hz, 3H, CH3). TsleuH2: m.p.: 119.4–120.7ꢂC. 1H NMR (600 MHz, CDCl3)
ꢀ(ppm) 7.73 (d, J ¼ 8.3 Hz, 2H, ArH), 7.28 (d, J ¼ 8.0 Hz, 2H, ArH), 5.33 (d, J ¼ 9.7 Hz,

242
J. Zhang et al.
1H, NH), 3.84–4.00 (m, 1H), 2.41 (s, 3H, CH3), 1.68–1.83 (m, 1H, CH), 1.59–1.42
(m, 2H, CH2), 0.89 (d, J ¼ 6.7 Hz, 3H, CH3), 0.81 (d, J ¼ 6.6 Hz, 3H, CH3). TspheH2:
1
m.p.: 150.4–152.9ꢂC. H NMR (600 MHz, DMSO-d6) ꢀ(ppm) 8.18 (d, J ¼ 5.0 Hz, 1H,
NH), 7.15–7.05 (m, 2H, ArH), 7.36–7.16 (m, 5H, ArH), 7.12 (m, 2H, ArH), 3.82–3.92
(m, 1H, CH), 3.00–2.87 (m, 1H, CH2), 2.83–2.66 (m, 1H, CH2), 2.34 (s, 3H, CH3).
2.3.2. [Pd(en)Cl2]. Precursor complex [Pd(en)Cl2] was synthesized according to a
published procedure [13]. Yield: 71.6%. Yellow solid. Anal. Calcd for C2H8Cl2N2Pd
(%): C, 10.12; H, 3.40; N, 11.80. Found (%): C, 10.20; H, 3.39; N, 11.64.
2.3.3. [Pd(en)(TsserNO)] (1). [Pd(en)Cl2] (15 mg, 0.063 mmol) was added to a 6 mL
CH3OH/H2O (volume 1 : 1) solution of TsserH2 (33 mg, 0.126 mmol), the mixture
was adjusted to pH ¼ 8–9 by NaOH solution, then heated to 48ꢂC and stirred for 3 h.
The solution was concentrated to about 80% of the original volume by reduced
pressure distillation. By evaporating the concentrated solution at room temperature,
yellow crystals suitable for X-ray diffraction were obtained after a few weeks and
separated from the solution. Yield: 61.9%. Yellow solid. IR (KBr, cm ꢁ 1): 1623, 1361,
1
587, 477. H NMR (600 MHz, DMSO-d6) ꢀ(ppm) 8.02 (d, J ¼ 8.1 Hz, 2H, ArH), 7.34
(d, J ¼ 8.1 Hz, 2H, ArH), 5.10–4.80 (m, 2H, NH2), 4.50–4.20 (m, 2H, NH2), 3.74–3.68
(t, J ¼ 3.71 Hz, 1H, OH), 3.65–3.57 (m, 1H, CH2), 3.57–3.52 (m, 1H, CH2), 3.30–3.15
(t, J ¼ 4.8 Hz, 1H, CH), 2.23–2.45 (m, 2H, CH2), 2.38 (s, 3H, CH3). ESI-MS: major
peak: 448.0 [M þ Na]þ; the relative abundance of isotope peaks match the expected
values, i.e., 447.1, 448.0, and 450.0. Anal. Calcd for C12H19N3O5PdS (%): C, 34.01;
H, 4.52; N, 9.92. Found: C, 34.25; H, 4.43; N, 10.21.
The other four complexes, [Pd(en)(TsglyNO)] (2), [Pd(en)(TsalaNO)] ꢀ 1.5H2O (3),
[Pd(en)(TsleuNO)] ꢀ H2O (4), and [Pd(en)(TspheNO)] ꢀ 2H2O (5), were prepared in an
identical manner.
[Pd(en)(TsglyNO)] (2): Yield: 58.0%. Yellow solid. IR (KBr, cmꢁ1): 1641, 1394, 587,
1
450. H NMR (600 MHz, DMSO-d6) ꢀ(ppm) 7.84 (d, J ¼ 8.2 Hz, 2H, ArH), 7.31 (d,
J ¼ 7.8 Hz, 2H, ArH), 4.97–4.92 (m, 2H, NH2), 4.72–4.65 (m, 2H, NH2), 3.24 (s, 2H,
CH2), 2.44–2.39 (m, 2H, CH2), 2.39–2.34 (m, 2H, CH2), 2.36 (s, 3H, CH3). ESI-MS:
major peak: 416.0 [M þ Na]þ; the relative abundance of isotope peaks match the
expected values, i.e., 415.1, 416.0, and 418.0. Anal. Calcd for C11H17N3O4PdS (%):
C, 33.55; H, 4.35; N, 10.67. Found: C, 33.61; H, 4.39; N, 10.64.
[Pd(en)(TsalaNO)] ꢀ 1.5H2O (3): Yield: 65.5%. Yellow solid. IR (KBr, cmꢁ1): 1603,
1
1372, 573, 404. H NMR (600 MHz, DMSO-d6) ꢀ(ppm) 7.98 (d, J ¼ 8.1 Hz, 2H, ArH),
7.32 (d, J ¼ 7.9 Hz, 2H, ArH), 5.05–4.80 (m, 2H, NH2), 4.45–4.30 (m, 2H, NH2), 3.31
(q, J ¼ 7.0 Hz, 1H, CH), 2.48–2.40 (m, 2H, CH2), 2.40–2.33 (m, 2H, CH2), 2.38 (s, 3H,
CH3), 1.25 (d, J ¼ 7.0 Hz, 3H, CH3). ESI-MS: major peak: 430.5 [M þ Na]þ; the relative
abundance of isotope peaks match the expected values, i.e., 429.9, 430.5, and 430.9.
Anal. Calcd for C12H19N3O4PdS (%): C, 33.15; H, 5.10; N, 9.66. Found: C, 33.16;
H, 4.80; N, 9.49.
[Pd(en)(TsleuNO)] ꢀ H2O (4): Yield: 63.8%. Yellow solid. IR (KBr, cmꢁ1): 1641,
1
1368, 587, 442. H NMR (600 MHz, DMSO-d6) ꢀ(ppm) 8.00 (d, J ¼ 8.1 Hz, 2H, ArH),
7.31 (d, J ¼ 7.9 Hz, 2H, ArH), 5.04–4.85 (m, 2H, NH2), 4.85–4.75 (m, 1H, NH2),
4.35–4.22 (m, 1H, NH2), 3.31 (dd, J ¼ 7.6, 5.7 Hz, 1H, CH), 2.48–2.42 (m, 2H, CH2),
2.42–2.32 (m, 2H, CH2), 2.37 (s, 3H, CH3), 1.99–1.90 (m, 1H, CH2), 1.66–1.59 (m, 1H,

Palladium(II) complexes
243
CH2), 1.55–1.45 (m, 1 H, CH), 0.89 (d, J ¼ 6.7 Hz, 3H, CH3), 0.85 (d, J ¼ 6.6 Hz, 3H,
CH3). ESI-MS: major peak: 472.1 [M þ Na]þ; the relative abundance of isotope
peaks match the expected values, i.e., 471.1, 472.1, and 474.1. Anal. Calcd for
C15H27N3O5PdS (%): C, 38.51; H, 5.82; N, 8.98. Found: C, 38.53; H, 5.73; N, 8.74.
[Pd(en)(TspheNO)] ꢀ 2H2O (5): Yield: 71.4%. Yellow solid. IR (KBr, cmꢁ1): 1582,
1
1380, 567, 497. H NMR (600 MHz, DMSO-d6) ꢀ(ppm) 7.97 (d, J ¼ 8.1 Hz, 2H, ArH),
7.54–7.09 (m, 7H, ArH), 4.90–4.70 (m, 2H, NH2), 4.60–4.40 (m, 1H, NH2), 4.40–4.20
(m, 1H, NH2), 3.54 (t, J ¼ 5.4 Hz, 1H, CH), 3.00–2.90 (m, 2H, CH2), 2.45–2.33 (m, 2H,
CH2), 2.33–2.23 (m, 2H, CH2), 2.34 (s, 3H, CH3). ESI-MS: major peak: 506.0
[M þ Na]þ, the relative abundance of isotope peaks match the expected values,
i.e., 505.1, 506.0, and 508.0. Anal. Calcd for C18H27N3O6PdS (%): C, 41.58; H, 5. 23;
N, 8.08. Found: C, 41.75; H, 5.02; N, 7.86.
2.4. X-ray structure determination of 1
The data collection of 1 was performed on a Bruker SMART APEX II CCD diffrac-
˚
tometer equipped with graphite monochromated Mo-Ka radiation (ꢁ ¼ 0.71073 A) at
296(2) K. Multi-scan absorption corrections were applied using SADABS. The structure
was solved by direct methods using SHELXS-97. Refinements on F2 were performed
using SHELXL-97 by full-matrix least-squares with anisotropic thermal parameters
for all non-hydrogen atoms. Table 1 lists crystallographic details.
2.5. Cell culture
Four different human carcinoma cell lines, HL-60, Bel-7402, BGC-823, and KB, were
cultured in RPMI-1640 medium supplemented with 10% fetal bovine serum, 100 units
per mL of penicillin and 100 mg ꢀ mLꢁ1 of streptomycin. Cells were maintained at 37ꢂC
in a humidified atmosphere of 5% CO2 in air.
Table 1. Crystallographic data for 1.
[Pd(en)TsserNO]
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimension (A)
a
b
C12H19N3O5PdS
423.76
296(2)
Orthorhombic
P2(1)2(1)2(1)
˚
7.9394(9)
10.7939(13)
c
17.753(2)
1521.3(3), 4
1.850
856
Volume (nm3), Z
Calculated density (Mg mꢁ3
F(000)
)
Crystal size (mm3)
0.55 ꢃ 0.46 ꢃ 0.35
ꢂ range for data collection (ꢂ)
hkl ranges
Data/parameters
2.21–28.28
ꢁ10 5 h 5 5; ꢁ14 5 k 5 14; ꢁ23 5 l 5 23
3715/202
1.082
Goodness-of-fit on F2
Final R indices [I 4 2ꢃ(I)]
R1 ¼ 0.0197; wR2 ¼ 0.0532

244
J. Zhang et al.
2.6. Solutions
The complexes were dissolved in DMSO at a concentration of 5 mmol ꢀ Lꢁ1 as stock
solution and diluted in culture medium at concentrations of 1.0, 10, 100, and
500 mmol ꢀ Lꢁ1 as working solutions. To avoid the cytotoxicity of DMSO, the
concentration of DMSO was less than 0.1% (v/v) in all experiments.
2.7. Cytotoxicity analysis
Cells harvested from exponential phase were seeded equivalently into a 96-well plate,
and then the complexes were added to the wells to achieve final concentrations. Control
wells were prepared by the addition of culture medium. Wells containing culture
medium without cells were used as blanks. All experiments were performed in
quintuplicate. The MTT assay for HL-60 cell line was performed as described by
Mosmann [18]. Upon completion of the incubation for 44 h, stock MTT dye solution
(20 mL, 5 mg ꢀ mLꢁ1) was added to each well. After 4 h incubation, 2-propanol (100 mL)
was added to solubilize the MTT formazan. The OD of each well was measured on
a microplate spectrophotometer at 570 nm. The SRB assays for Bel-7402, BGC-823,
and KB cell lines were performed as previously described [19]. Upon completion of the
incubation for 44 h, the cells were fixed in 10% trichloroacetic acid (100 mL) for 30 min
at 4ꢂC, washed five times and stained with 0.1% SRB in 1% acetic acid (100 mL) for
15 min. The cells were washed four times in 1% acetic acid and air dried. The stain was
solubilized in 10 mmol ꢀ Lꢁ1 unbuffered Tris base (100 mL) and OD was measured at
540 nm as above. The IC50 value was determined from plot of % viability against dose
of the complexes added.
3. Results and discussion
3.1. Characterization of the complexes
Complex 1 was observed in the ESI-MS as singly charged [M þ Na]þ ion of m/z 448.0.
The experimental isotope patterns for this ion matches theoretical predictions (figure 2).
ESI-MS of 2–5 are similar to that of 1. These results provide evidence for the formation
of 1–5. In addition, there is good agreement between calculated and measured values
for elemental analyses of 1–5.
UV-Vis spectroscopy shows that 4-toluenesulfonyl-L-amino acids have shoulders
at 267 and 273 nm. After formation of the complexes, the shoulders turn into a single
peak at 267 nm. In addition, there is also a broad LMCT peak at 303–400 nm for the
complexes, which further confirms the coordination of palladium(II) with en.
IR spectroscopy shows that the sulfonamide groups of TsserH2, TsglyH2, TsalaH2,
TsleuH2, and TspheH2 have a strong and sharp ꢄNH at 3273–3280 cmꢁ1. These bands
disappear for 1–5, indicating that the sulfonamide groups have been deprotonated.
This is further confirmed by the sulfonamide (I) shifting from ꢄ1630 cmꢁ1 to
ꢄ1550 cmꢁ1 and the disappearance of the sulfonamide (II). New bands appear at
440–470 cmꢁ1 and 560–585 cmꢁ1, which are assigned to ꢄPd–N and ꢄPd–NAr, respectively.
The carboxylates of 1–5 show two bands, an intense antisymmetric carboxylate stretch

Palladium(II) complexes
245
Theoretical
+
445.99802
448.0014
[C
H N O PdSNa]
12 19 3 5
100
80
60
40
20
0
+
[M+Na]
445.00021
449.99924
443.99796
446.99915
449.00473
450.99927
m/z
440
445
450
455
Intens.
µ10
Experimental
5
+MS, 0.5min #47
448.0
8
6
4
2
0
446.0
445.0
444.0
450.0
447.1
453.2
449.0
455.0
451.0
441.9
442
444
446
448
450
452
454
456
m/z
Figure 2. Experimental and theoretical isotope patterns of ESI-MS for 1.
ꢄ(as, cooꢁ) at 1620 cmꢁ1 and a symmetric carboxylate stretch ꢄ(s, cooꢁ) at 1380 cmꢁ1
.
The values of Dꢄ(cooꢁ)(ꢄ(as, cooꢁ)ꢁꢄ(s, cooꢁ)) of 1–5 are in the range 210–260 cmꢁ1, which
are greater than that of Dꢄ(cooꢁ) of the corresponding sodium carboxylates, so the
carboxylate group is monodentate [20]. This is further confirmed by the appearance
of ꢄPd–O. All the results are in agreement with the results revealed by X-ray crystal
analysis.
1H NMR spectra of the 4-toluenesulfonyl-L-amino acids are similar, TsserH2,
TsglyH2, TsalaH2, TsleuH2, and TspheH2 show a doublet at ꢀ ¼ 7.89 ppm, a triplet
at ꢀ ¼ 7.97 ppm, a doublet at ꢀ ¼ 8.04 ppm, a doublet at ꢀ ¼ 5.33 ppm, and a doublet
at ꢀ ¼ 8.18 ppm, respectively, which are assigned to the proton of the sulfonamide.
The protons of the aromatic ring appear at ꢀ ¼ 7.17–7.90 ppm. Although the overall
1
patterns of the H NMR spectra of 1–5 resemble very closely those of the free ligands,
the signals shift upon coordination. For example, the proton of sulfonamide of TsalaH2
shows a doublet at ꢀ ¼ 8.04 ppm, while it disappears for 3, showing deprotonation
of the sulfonamide. The ꢅ-hydrogen of TsalaH2 is a multiplet, but this proton is a
quartet in 3, also supporting deprotonation of sulfonamide (figures 3 and 4). 1H NMR
spectra of 1, 2, 4, and 5 are similar to that of 3. This provides further evidence that
the sulfonamide coordinates to palladium(II) through deprotonated sulfonamide
nitrogen.

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J. Zhang et al.
50,000
45,000
40,000
35,000
30,000
25,000
20,000
15,000
10,000
5000
5000
4000
3000
2000
1000
0
8000
6000
4000
2000
0
1
1
2
4
3
5
8.06 8.04 8.02
f1(ppm)
3.76 3.74 3.72
f1(ppm)
8
O
S
O
8
HN
6
7
4,5
2,3
HO
O
7
6
0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
f1(ppm)
Figure 3. 1H NMR spectra of TsalaH2 in DMSO-d6.
3.2. Structural studies
A view of the molecular structure of [Pd(en)(TsserNO)] (1) is shown in figure 5. The
selected bond lengths and angles are given in table 2. Palladium shows square-planar
coordination by two nitrogen atoms of en, one deprotonated sulfonamide nitrogen
atom, and one carboxylate oxygen atom in each molecule. The angle between planar
N(1)–Pd(1)–N(2) and planar O(1) –Pd(1) –N(3) is 4.143(62)ꢂ, which indicates that the
Pd(1)–O(1)–N(1)–N(2)–N(3) plane is slightly distorted. The Pd–N (deprotonated
˚
˚
˚
sulfonamide) length (2.029(2) A) is similar to the lengths (2.0355(19) A and 2.035(2) A)
˚
of Pd–N (en) bonds and longer than (1.9989(17) A) Pd–O (carboxylic oxygen). Sigel
et al. reported that the coordination qualities of the deprotonated amide were ‘‘O-like’’
as the deprotonated amide group was isoelectronic with carboxylate; this has been
confirmed by stability constants of some complexes [21]. Gong et al. also reported such
coordination of deprotonated amide nitrogen [22]. According to our experimental
results, the coordinating qualities of the deprotonated sulfonamide nitrogen might also
be ‘‘O-like’’.
3.3. Cytotoxic studies
As listed in table 3, 1–5 display cytotoxic effects against tested carcinoma cell lines with
a low IC50 value (550 mmol ꢀ Lꢁ1). Moreover, they have selectivity against tested
carcinoma cell lines, but none of the complexes show higher cytotoxicity than cisplatin.
The structure–activity relationships are summarized as follows: (1) the amino acids have

Palladium(II) complexes
247
50,000
1
45,000
40,000
35,000
30,000
25,000
20,000
15,000
10,000
5000
4000
3000
2000
1000
0
3
5
2
4
O
S
N
O
H
N
10
7
8
9
6
Pd
3.30
f1(ppm)
3.32
O
O
N
H
11
1
7
6
4,5
2,3
8,9
10,11
0
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
f1(ppm)
Figure 4. 1H NMR spectra of 3 in DMSO-d6.
Figure 5. Molecular structure and atom-labeling scheme for 1.
important effect on cytotoxicity; when the amino acid is phe, the complex has the
best cytotoxicity. For 1–5 with en and different amino acids, the cytotoxicity
against HL-60, BGC-823, Bel-7402, and KB cell lines decreases in the sequence:
phe 4 leu 4ala 4 gly 4 ser; phe 4 leu 4 gly 4 ala 4 ser; phe 4 leu 4 ala 4 gly 4 ser;

248
J. Zhang et al.
ꢂ
˚
Table 2. Selected bond lengths (A) and angles ( ) for 1.
[Pd(en)TsserNO]
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–N(3)
Pd(1)–O(1)
2.0355(19)
2.035(2)
2.029(2)
1.9989(17)
N(2)–Pd(1)–N(1)
O(1)–Pd(1)–N(3)
N(3)–Pd(1)–N(2)
O(1)–Pd(1)–N(1)
N(3)–Pd(1)–N(1)
O(1)–Pd(1)–N(2)
83.39(9)
83.85(8)
101.08(8)
91.80(8)
174.67(9)
174.51(8)
Table 3. The cytotoxicities of the complexes in vitro (n ¼ 5).a
IC50 ꢅ SD (mmol ꢀ Lꢁ1
)
Complexes
HL-60
BGC-823
Bel-7402
KB
1
2
3
4
5
6
7
8
26 ꢅ 1
23 ꢅ 1
48 ꢅ 2
38 ꢅ 2
45 ꢅ 1
35.8 ꢅ 0.9
33.9 ꢅ 0.6
33 ꢅ 2
32 ꢅ 2
37 ꢅ 2
15.9 ꢅ 0.5
12.9 ꢅ 0.9
12 ꢅ 1
41 ꢅ 1
12 ꢅ 1
35.8 ꢅ 0.8
34 ꢅ 2
15.6 ꢅ 0.9
11.8 ꢅ 0.5
36 ꢅ 3
28 ꢅ 1
19 ꢅ 2
21 ꢅ 1
36 ꢅ 3
30 ꢅ 2
7.5 ꢅ 0.9
22 ꢅ 1
23 ꢅ 2
28 ꢅ 3
18 ꢅ 2
38 ꢅ 3
5.4 ꢅ 0.8
37 ꢅ 3
9
10
11
Cisplatin
14 ꢅ 1
23 ꢅ 2
22 ꢅ 1
5.5 ꢅ 0.3
7.2 ꢅ 0.6
2.9 ꢅ 0.3
4.5 ꢅ 0.3
16 ꢅ 2
2.9 ꢅ 0.2
15 ꢅ 2
2.1 ꢅ 0.4
26 ꢅ 2
6.5 ꢅ 0.8
8 ꢅ 1
2.6 ꢅ 0.3
aThe IC50 (mmol ꢀ Lꢁ1) values of complexes [Pd(bipy)(TsalaNO)] ꢀ H2O (6), [Pd(bipy)
(TsleuNO)] ꢀ 1.5H2O (7), [Pd(bipy)(TspheNO)] (8), [Pd(phen(TsalaNO)] ꢀ 2.5H2O (9),
[Pd(phen)(TsleuNO)] ꢀ H2O (10), and [Pd(phen)(TspheNO)] ꢀ 2H2O (11) were cited
from [17].
and phe 4 ala 4 leu 4 ser 4 gly, respectively. (2) N-containing ligands also have
important effect on cytotoxicity, dependent on cell type. For 3, 6, and 9 with ala and
different N-containing ligands, the cytotoxicity against HL-60 and Bel-7402 cell lines
decreases in the sequence: phen 4 en 4 bipy, while the cytotoxicity against BGC-823
cell line decreases in the sequence: bipy 4 phen 4 en. For 4, 7, and 10 with leu and
different N-containing ligands, the cytotoxicity against HL-60 and KB cell lines
decreases in the sequence: phen 4 en 4 bipy, while the cytotoxicity against BGC-823
and Bel-7402 cell lines decreases in the sequence: phen 4 bipy 4 en. For 5, 8, and 11
with phe and different N-containing ligands, the cytotoxicity against HL-60 and
Bel-7402 cell lines decreases in the sequence: phen 4 en 4 bipy, while the cytotoxicity
against KB cell line decreases in the sequence: bipy 4 en 4 phen.
We previously reported the synthesis and cytotoxicity of five platinum(II) complexes
with 4-toluenesulfonyl-L-amino acid dianion and bipy. The results indicate that
both amino acids and N-containing ligands have important effects on cytotoxicity
and cytotoxicity is also related to cell type. [Pt(bipy)(TspheNO)] displays the best

Palladium(II) complexes
249
cytotoxicity against BGC-823, Bel-7402, and KB cell lines, while [Pt(bipy)(TsglyNO)]
has the best cytotoxicity against KB cell line. The cytotoxicity of these complexes
with bipy and different N-containing ligands against HL-60, BGC-823, Bel-7402, and
KB cell lines decreases in the sequence: gly ꢆ val 4 ser 4 leu 4 phe; phe 4 leu 4
ser ꢆ val 4 gly; phe 4 val 4 leu 4 ser 4 gly; and gly 4 phe 4 leu 4 val 4 ser, respec-
tively [23]. For palladium(II)/platinum(II) complexes with 4-toluenesulfonyl-L-amino
acid dianion and N-containing ligands, both amino acids and N-containing ligands
have important effects on cytotoxicity, moreover, the effects on cytotoxicity are related
to tumor cell type. Although the IC50 values do not show definite correlation with
variation of the amino acid and N-containing ligands, the palladium(II)/platinum(II)
complexes with phe display better cytotoxicities.
4. Conclusion
Five new palladium(II) complexes with 4-toluenesulfonyl-L-amino acid dianion and
en were synthesized and characterized. The cytotoxic experiment indicates that the
complexes display cytotoxic effects against HL-60, Bel-7402, BGC-823, and KB cell
lines; both amino acids and N-containing ligands have important effects on cytotox-
icity. When the amino acid is phe, the complex has better cytotoxicity, but none
of the complexes is more active than cisplatin. The palladium(II) complexes with
4-toluenesulfonyl-L-amino acid dianions and en may be promising metal-based
antitumor agents. Current studies are ongoing in our laboratory to gain insight
in the mechanism of action of these complexes, which may be helpful for the design
of new metal-based antitumor agents.
Supplementary material
Crystallographic data for the structural analysis of 1 have been deposited with the
Cambridge Crystallographic Data Centre, CCDC – 760941. Copies of this information
may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (Fax: þ44 1223 336033; E-mail: deposit@ccdc.cam.ac.uk or http://
www.ccdc.cam.ac.uk).
Acknowledgments
This work was supported by the Special Foundation for State Major New Drug
Research Program of China (Grant No. 2009ZX09103-139), the National Basic
Research 973 Program (Grant No. 2010CB534913), Hebei Province Nature Science
Fund for Distinguished Young Scholars (Grant No. B2011201164), the Nature Science
Fund of Hebei Province (Grant No. B2011201135), the Key Basic Research Special
Foundation of Science Technology Ministry of Hebei Province (Grant No.
11966412D), and the Key Research Project Foundation of Department of Education
of Hebei Province (Grant No. ZD2010142).

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