Synthesis, characterization, and cytotoxicity of complexes of platinum(u) with 2,2'-bipyridine and N-benzoyl-L-amino acid dianion

Article abstract of DOI:10.1080/00958972.2012.689293

Four new platinum(II) complexes (1-4) with N-benzoyl-L-amino acid and bipy were synthesized and characterized by elemental analysis, IR, UV, ¹H NMR, and mass spectra. The crystal structure of 1 was determined by X-ray diffraction analysis. Cytotoxicities were measured by MTT and SRB assays. Complexes 1-4 exert cytotoxicity with selectivity against HL-60, Bel-7402, BGC-823, and KB cell lines. This suggests that amino acids and acylated groups have important effects on cytotoxicity; the cytotoxicity is also related to the species of tumor cells, but the IC₅₀ values do not show definite correlation with the variation of amino acids and acylated groups.

Full text of DOI:10.1080/00958972.2012.689293

Journal of Coordination Chemistry
Vol. 65, No. 12, 20 June 2012, 2159–2169
Synthesis, characterization, and cytotoxicity of complexes
of platinum(II) with 2,29-bipyridine and N-benzoyl-L-amino
acid dianion
JINCHAO ZHANG*yz, FANGFANG ZHANGyz, LIWEI WANGyz,
JIANLONG DUyz, SHUXIANG WANG*yz and SHENGHUI LIyz
yCollege of Chemistry & Environmental Science, Chemical Biology Key Laboratory of
Hebei Province, Hebei University, Baoding 071002, China
zKey Laboratory of Medicinal Chemistry and Molecular Diagnosis of the Ministry of
Education, Hebei University, Baoding 071002, China
(Received 9 January 2012; in final form 14 March 2012)
Four new platinum(II) complexes (1–4) with N-benzoyl-L-amino acid and bipy were
synthesized and characterized by elemental analysis, IR, UV, 1H NMR, and mass spectra.
The crystal structure of 1 was determined by X-ray diffraction analysis. Cytotoxicities were
measured by MTT and SRB assays. Complexes 1–4 exert cytotoxicity with selectivity against
HL-60, Bel-7402, BGC-823, and KB cell lines. This suggests that amino acids and acylated
groups have important effects on cytotoxicity; the cytotoxicity is also related to the species of
tumor cells, but the IC50 values do not show definite correlation with the variation of amino
acids and acylated groups.
Keywords: Mixed-ligand platinum(II) complexes; N-Benzoyl-L-amino acid dianion;
2,20-Bipyridine; Synthesis; Cytotoxicity
1. Introduction
The landmark discovery of cisplatin by Rosenberg in 1965 heralded a new era of
anticancer drug research based on metallopharmaceuticals [1]. Cisplatin is still one of
the world’s best-selling anticancer drugs with carboplatin and oxaliplatin also receiving
worldwide approval. Nedaplatin, lobaplatin, and heptaplatin have gained regional
approval and a few platinum drugs continue to be evaluated in clinical studies. There
are some major drawbacks of current platinum drugs, including a limited range of
cancers, acquired or intrinsic resistance, and severe side-effects [2–4]. These problems
have prompted chemists to develop new platinum anticancer drugs.
It was reported that 2,20-bipyridine (bipy), quinoline, 1,10-phenanthroline (phen),
and their derivatives have ability to participate as DNA intercalators. Amino acids
are the fundamental material of life and the basis of metabolism. Introducing amino
*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/10.1080/00958972.2012.689293

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J. Zhang et al.
acid into an antitumor drug can improve selectivity to tumor cells, enhance their
liposolubility, and remit their toxicity to normal cells, thus widely used in platinum
anticancer drugs as ligands. Jin and Ranford [5]. synthesized and characterized nine
complexes of platinum(II) with phen and amino acids (where amino acids are glycine
(Gly), L-histidine (His), L-cysteine (Cys), L-isoleucine (Ile), L-alanine (Ala), L-proline
(Pro), L-serine (Ser), L-aspartic acid (Asp), and L-glutamic acid (Glu)). Most of the
complexes were less cytotoxic than cisplatin. The IC50 of [Pt(phen)(Pro)]Cl ꢀ 2H2O is
similar to cisplatin. Mital and Srivastava [6] reported the cytotoxicities of some
platinum(II) complexes with phen and amino acids (where amino acids are Gly, Ala,
L-leucine (Leu), and L-tyrosine (Tyr)). These complexes exhibit a growth inhibition of
P388 lymphocytic leukemic cells, but the IC50 values for the platinum(II) complexes
are higher than cisplatin. Puthraya et al. [7] have tested several platinum(II)
complexes with bipy and amino acids against tumor cells; the results indicated that
some complexes had good cytotoxicity. Cytotoxicities of platinum(II) complexes with
bipy and N-benzoyl-L-amino acid dianion has not been reported. In order to develop
new platinum anticancer drugs, in this work, we present the synthesis, characteriza-
tion, and cytotoxicity of four mixed-ligand platinum(II) complexes with N-benzoyl
amino acid dianion and bipy.
2. Experimental
2.1. Materials
Benzoyl chloride and K2[PtCl4] were of chemical grade and bipy was of analytical
grade. Commercially pure L-tryptophan (Trp), L-valine (Val), Leu, and L-phenylal-
anine (Phe) were purchased from Sigma. RPMI-1640 medium, trypsin, and fetal bovine
serum were purchased from Gibco. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazo-
lium bromide (MTT), sulforhodamine B (SRB), benzyl penicillin, and streptomycin
were from Sigma. Four different human carcinoma cell lines, HL-60 (immature
granulocyte leukemia), Bel-7402 (liver carcinoma), 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 an UV-3400 Toshniwal spectro-
photometer. IR spectra were recorded using KBr pellets and a Perkin-Elmer Model-683
1
spectrophotometer. H NMR spectra were recorded on a Bruker AVIII 600 NMR
spectrometer. Mass spectra were measured by LC-MS apparatus Agilent 1200-6310.
X-ray single-crystal structure was performed on a Bruker SMART APEX II CCD
diffractometer. The optical density (OD) was measured on a microplate spectro-
photometer (Bio-Rad Model 680, USA).

Platinum(II) with N-benzoyl-L-amino acid dianion
2161
N
N
N
45-48 oC
Cl
Pt
+
K2PtCl4
Vethanol :Vwater=1:1
N
Cl
bipy
N
N
Cl
Cl
Cl
Pt
C
N
O
R
C O
H2N
HO
C
O
Vwater:Vacetone=2:1 pH 3-4
R
+
N
N
NaOH; 0 oC
HCl
R
O
pH 9-10; 54-60 o
C
HN
.
nH2O
O
Pt
Vmethanol:Vwater=1:2
O
O
L-Amino Acid
Benzoyl chloride
HO
n =
1 ;
0 ;
4.5 ;
1
CH3
CH3
CH3
CH3
H
CH2
C
C
H2C
=
HC
R
;
;
;
H2
NH
4
2
3
1
Figure 1. The synthetic routines of 1–4.
2.3. Synthesis of compounds
[Pt(bipy)(Bzleu-N,O)] ꢀ H2O
(1),
[Pt(bipy)(Bzval-N,O)]
(2),
[Pt(bipy)(Bzphe-
N,O)] ꢀ 4.5H2O (3), and [Pt(bipy)(Bztrp-N,O)] ꢀ H2O (4) have been prepared by the
reaction of [Pt(bipy)Cl2] with N-benzoyl-L-amino acids: benzoyl-L-leucine (BzleuH2),
benzoyl-valine (BzvalH2), benzoyl-L-phenylalanine (BzpheH2), and benzoyl-L-trypto-
phan (BztrpH2), in a mixed solution of CH3OH/H2O (figure 1) [8].
2.3.1. Benzoyl-L-amino acids. To a stirred solution of Leu (200 mg, 1.5 mmol) in
1.5 mL H2O, 1.5 mL of NaOH aqueous solution (1 mol Lꢁ1) was added. Benzoyl
chloride (0.18 mL, 1.5 mmol) dissolved in 8 mL of CHCl3 and 8 mL of NaOH
(0.5 mol Lꢁ1) aqueous solution were added slowly to the solution at the same time under
ice bath. After the reaction was complete, the reaction mixture was acidified to
pH ¼ 3–4 with HCl (0.5 mol Lꢁ1). The organic layer was separated and the aqueous
layer was extracted with 8 mL CHCl3. The combined organic layers were washed with
water (2 ꢂ 5 mL), dried over MgSO4, filtered, and concentrated to 3 mL by a rotary
evaporator at 40ꢃC; then white solid was precipitated. The collected solid was
recrystallized twice from an ethanol–water mixture (V/V ¼ 1 : 1) and dried to give
1
BzleuH2. m.p.: 135–137ꢃC; IR (KBr, cmꢁ1): 3378, 1635, 1535, 1720, 1244. H NMR
(600 MHz, CDCl3) ꢀ ppm 7.81–7.79 (d, 2H, J ¼ 7.6 Hz), 7.54–7.51 (t, 1H, J ¼ 7.8 Hz),
7.45–7.43 (t, 2H, J ¼ 7.8 Hz), 6.62–6.60 (d, 1H, J ¼ 7.8 Hz), 4.85–4.82 (m, 1H), 1.85–1.78
(m, 2H), 1.74–1.69 (m, 1H), 1.00–0.98 (q, 6H, J ¼ 3.0 Hz).
BzvalH2, BzpheH2, and BztrpH2 were carried out in an identical manner. BzvalH2:
1
m.p.: 129–130ꢃC; IR (KBr, cmꢁ1): 3364, 1640, 1546, 1726, 1206. H NMR (600 MHz,
CDCl3) ꢀ ppm 7.80–7.78 (d, 2H, J ¼ 7.2 Hz), 7.55–7.52 (t, 1H, J ¼ 7.8 Hz), 7.46–7.44

2162
J. Zhang et al.
(t, 2H, J ¼ 7.8 Hz), 6.63–6.61 (d, 1H, J ¼ 7.8 Hz), 4.62–4.60 (m, 1H), 2.37–2.25 (m, 1H),
1.07–1.02 (q, 6H, J ¼ 3.0 Hz). BzpheH2: m.p.: 184–186ꢃC; IR (KBr, cmꢁ1): 3327, 1612,
1
1538, 1722, 1228. H NMR (600 MHz, CDCl3) ꢀ ppm 7.78–7.70 (d, 2H, J ¼ 7.2 Hz),
7.54–7.52 (t, 1H, J ¼ 7.8 Hz), 7.47–7.45 (t, 2H, J ¼ 7.8 Hz), 7.30–7.24 (m, 5H), 6.64–6.62
(d, 1H, J ¼ 7.8 Hz), 4.61–4.58 (m, 1H), 3.24–3.20 (m, 2H). BztrpH2: m.p.: 193–195ꢃC;
1
IR (KBr, cmꢁ1): 3396, 1624, 1543, 1724, 1234. H NMR (600 MHz, CDCl3) ꢀ ppm
10.82–10.78 (s, 1H), 7.78–7.75 (d, 2H, J ¼ 7.2 Hz), 7.54–7.52 (t, 1H, J ¼ 7.8 Hz), 7.48–
7.46 (t, 2H, J ¼ 7.8 Hz), 7.20–7.10 (d, 2H, J ¼ 7.2 Hz), 7.10–6.96 (d, 2H, J ¼ 7.8 Hz),
6.96–6.80 (s, 2H), 6.64–6.62 (d, 1H, J ¼ 7.8 Hz), 4.80–4.60 (m, 1H), 3.30–3.25 (m, 2H).
2.3.2. [Pt(bipy)Cl2]. Precursor complex [Pt(bipy)Cl2] was synthesized according to a
published procedure [9]. Yield: 87.7%. Yellow solid. Anal. Calcd for C10H8Cl2N2Pt
(%): C, 28.45; H, 1.91; N, 6.64. Found (%): C, 28.56; H, 1.98; N, 6.80.
.
2.3.3. [Pt(bipy)(Bzleu-N,O)] H2O (1). BzleuH2 (22 mg, 0.094 mmol) dissolved in
5.0 mL of NaOH (0.047 mmol) water solution was added to a suspension of
[Pt(bipy)Cl2] (20 mg, 0.047 mmol) in 6 mL mixture of CH3OH/H2O (V/V ¼ 1 : 2). The
reaction mixture was adjusted to pH ¼ 9–10 with a NaOH solution and stirred for 6 h at
56ꢃC until a clear solution was formed. The clear solution was filtered and concentrated
to 2 mL at 40ꢃC. By slowly evaporating the solution after several days at room
temperature, a yellow crystalline solid was separated, and collected by filtration,
washed with a small amount of cold methanol and diethyl ether, and dried under
vacuum at 60ꢃC. Yield: 70.2%. Yellow solid. IR (KBr, cmꢁ1): 3446, 1560, 1634, 1394,
1
556, 455. H NMR (600 MHz, DMSO-d6) ꢀ(ppm) 0.80 (d, J ¼ 6.59 Hz, 3H, CH3), 0.83
(d, J ¼ 6.48 Hz, 3H, CH3), 1.87–1.81 (m, 1H, CH), 2.06 (d, J ¼ 7.50 Hz, 2H, CH2), 4.25
(dd, J ¼ 8.97, 5.79 Hz, 1H, CH), 7.00–9.33 (13H, Ar-H). ESI-MS: 584.53 [M]þ. Anal.
Calcd for C23H25N3O4Pt (%): C, 45.85; H, 4.18; N, 6.97. Found (%): C, 45.85; H, 3.94;
N, 7.12.
2.3.4. [Pt(bipy)(Bzval-N,O)] (2). The synthesis of 2 was carried out similar to 1,
starting from [Pt(bipy)Cl2] (19 mg, 0.045 mmol) and BzvalH2 (23 mg, 0.090 m mol).
Yield: 68.4%. Yellow green solid. IR (KBr, cmꢁ1): 3427, 1587, 1645, 1384, 562, 447. 1H
NMR (600 MHz, DMSO-d6) ꢀ(ppm) 1.10 (d, J ¼ 6.97 Hz, 3H, CH3), 1.20 (d, J ¼ 6.68 Hz,
3H, CH3), 3.99 (d, J ¼ 6.56 Hz, 1H, CH), 5.26 (d, J ¼ 6.53 Hz, 1H, CH), 6.99–8.20 (13H,
Ar-H). ESI-MS: 593.50 [MþNa]þ. Anal. Calcd for C22H21N3O3Pt (%): C, 46.32; H,
3.71; N, 7.37. Found (%): C, 46.31; H, 3.62; N, 7.43.
.
2.3.5. [Pt(bipy)(Bzphe-N,O)] 4.5H2O (3). The synthesis of 3 was carried out similar
to 1, starting from [Pt(bipy)Cl2] (19 mg, 0.045 mmol) and BzpheH2 (25 mg,
0.094 m mol). Yield: 65.6%. Red brown solid. IR (KBr, cmꢁ1): 3427, 1597, 1645,
1
1384, 570, 463. H NMR (600 MHz, DMSO-d6) ꢀ (ppm) 3.19 (d, J ¼ 5.88 Hz, 1H, CH2),
3.22 (d, J ¼ 4.49 Hz, 1H, CH2), 5.32–5.28 (m, 1H, CH), 7.18–8.74 (18 H, Ar-H). ESI-
MS: 641.54 [MþNa]þ. Anal. Calcd for C26H30N3O7.5Pt (%): C, 44.64; H, 4.32; N, 6.01.
Found (%): C, 44.60; H, 3.98; N, 6.43.

Platinum(II) with N-benzoyl-L-amino acid dianion
2163
.
2.3.6. [Pt(bipy)(Bztrp-N, O)] H2O (4). The synthesis of 4 was carried out similar to 1,
starting from [Pt(bipy)Cl2] (19 mg, 0.045 mmol) and BztrpH2 (29 mg, 0.094 m mol).
Yield: 74.2%. Deep green solid. IR: 3460, 1550, 1670, 1397, 555, 471. 1H NMR
(600 MHz, DMSO-d6) ꢀ(ppm) 3.16–3.14 (m, 1H, CH2), 3.18–3.16 (m, 1H, CH2), 5.77–
5.75 (m, 1H, CH), 7.04–8.64 (18H, Ar-H), 10.45–10.41 (m, 1H, indole-NH). ESI-MS:
696.56 [MþK]þ. Anal. Calcd for C28H24N4O4Pt (%): C, 49.77; H, 3.55; N, 8.29. Found
(%): C, 49.73; H, 3.41; N, 7.93.
.
2.4. X-ray structure determination of [Pt(bipy)(Bzleu-N, O)] H2O (1)
Data collection for 1 was performed on a Bruker SMART APEX II CCD
diffractometer equipped with graphite monochromated Mo-Ka radiation
˚
(ꢁ ¼ 0.71073 A) at 296(2) K. Multi-scan absorption corrections were applied using
SADABS and the structure was solved by direct methods using the SHELXS-97
program. 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 an RPMI-1640 medium supplemented with 10% fetal bovine serum,
100 unit mLꢁ1 of penicillin and 100 mg mLꢁ1 of streptomycin. Cells were maintained at
37ꢃC in a humidified atmosphere of 5% CO2 in air.
Table 1. Crystallographic data for 1.
1
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimensions (A)
a
b
C92H105N12O18Pt4
2435.10
296(2)
Triclinic
ꢀ
P1
˚
10.1503(9)
21.152(2)
c
21.974(2)
4.6362(7), 8
1.753
2394
Volume (nm3), Z
Calculated density (Mg mꢁ3
F(000)
)
Crystal size (mm3)
0.55 ꢂ 0.33 ꢂ 0.09
ꢂ range for data collection (ꢃ)
Limiting indices
Data/parameters
0.94–28.38
ꢁ10 ꢄ h ꢄ 13; ꢁ28 ꢄ k ꢄ 27; ꢁ29 ꢄ l ꢄ 28
22,952/1144
0.966
R1 ¼ 0.0458, wR2 ¼ 0.1082
Goodness-of-fit on F2
Final R indices [I 4 2ꢃ(I)]

2164
J. Zhang et al.
2.6. Solutions
The complexes were dissolved in DMSO at a concentration of 5 mM as stock solution
and diluted in culture medium at concentrations of 1.0, 10, 100, and 500 mM as
working-solutions. To avoid dimethyl sulfoxide (DMSO) toxicity, the concentration of
DMSO was less than 0.1% (V/V) in all experiments.
2.7. Cytotoxicity analysis
The cells harvested from the 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 was performed as described by Mosmann for HL-60
[10]. 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 assay was performed as previously
described for Bel-7402, BGC-823, and KB [11]. Upon completion of the incubation for
44 h, the cells were fixed in 10% trichloroacetic acid (100 mL) for 30 min at 4ꢃC, 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 mM unbuffered Tris base (100 mL) and OD was measured at 540 nm as mentioned
above. The IC50 value was determined from the plot of % viability against dose of
compounds added.
3. Results and discussion
3.1. Characterization of the complexes
The elemental analysis data of 1–4 are in agreement with the calculated values. Mass
spectra of 1–4 also provide support for the suggested composition and structures of the
complexes. Bipy has a maximum absorption at 282 nm, assigned to ꢄ–ꢄ* transition.
After the formation of the complexes, the absorption red shifts by 23–42 nm for 1–4
compared with bipy, caused by charge transfer transition (metal-ligand) from platinum
d-orbital to a ꢄ*-orbital of bipy.
The amide groups of BzleuH2, BzvalH2, BzpheH2, and BztrpH2 have strong and sharp
ꢅNH at 3327–3396 cmꢁ1, which disappears for the complexes, showing that the amide
groups have been deprotonated. This is further confirmed by both the amide (I) shifting
from 1612–1640 cmꢁ1 to 1550–1597 cmꢁ1 and the disappearance of the amide (II) from
ꢅ1540 cmꢁ1. A new band assigned to ꢅPt–N appears at 560 cmꢁ1. The carboxylates of 1–4
ꢁ
ꢁ
at 1720 and
show two bands, an intense antisymmetric ꢅ
and a symmetric ꢅ
ðas, coo
ðcoo
Þ
ðs, coo Þ
1230 cmꢁ1, respectively. The values of Dꢅ
ꢅ
of 1–4 are 240–
ꢁ
ꢁ
Þ
ðas, coo
ðs, cooꢁÞ
Þ ꢁ ꢅ
270 cmꢁ1, greater than Dꢅ(cooꢁ) of the corresponding sodium carboxylate, so the
carboxylate is monodentate, coordinated with Pt(II) through oxygen [12]. This is further

Platinum(II) with N-benzoyl-L-amino acid dianion
2165
confirmed by the appearance of ꢅPt–O (Supplementary material). These results are in
agreement with the results revealed by the X-ray crystal analysis.
BzLeuH2, BzvalH2, BzpheH2, and BztrpH2 shows a doublet at ꢀ ¼ 7.8–8.1, which is
associated with a proton of the amide, however this peak disappeared for 1–4, showing
1
that the amide groups have been deprotonated. The methylene H resonances (amino
acid) for 1–4 shifted downfield as a result of deprotonated benzoylamide nitrogen
coordinating to Pt(II).
3.2. Structural studies
A view of the molecular structure of [Pt(bipy)(Bzleu-N,O)] ꢀ H2O (1) is shown in
figure 2. Selected bond lengths and angles of 1 are given in table 2. The Pt–N bond
˚
length varies from 1.992(5) to 2.012(5) A. The bond angles of O(1)–Pt(1)–N(1), O(1)–
Pt(1)–N(2), N(1)–Pt(1)–N(2), N(1)–Pt(1)–N(3), N(2)–Pt(1)–N(3), and N(1)–Pt(1)–N(2)
are 80.32(19)ꢃ, 95.03(18)ꢃ, 175.3(2)ꢃ, 104.4(2)ꢃ, 80.2(2)ꢃ, and 175.3(2)ꢃ, respectively. The
platinum is square-planar from two nitrogen atoms of bipy, one deprotonated amide
nitrogen, and one carboxylate oxygen. The torsion angles of Pt(1)–N(1)–C(2)–C(1) and
Pt(1)–O(1)–C(1)–C(2) are 40.108(552)ꢃ and 6.642(747)ꢃ, indicating that N-benzoyl-L-
leuline coordinates to Pt(II) in a distorted five-membered ring. The bond length
Figure 2. Molecular structure and atom-labeling scheme for 1 (H2O is omitted for clarity).
Table 2. Selected bond lengths and angles for 1.
Pt(1)–N(1)
Pt(1)–N(2)
Pt(1)–N(3)
Pt(1)–O(1)
2.012(5)
1.992(5)
1.999(5)
2.004(4)
N(1)–Pt(1)–N(2)
N(2)–Pt(1)–N(3)
N(3)–Pt(1)–O(1)
O(1)–Pt(1)–N(1)
O(1)–Pt(1)–N(2)
N(1)–Pt(1)–N(3)
175.3(2)
80.2(2)
174.60(19)
80.32(19)
95.03(18)
104.4(2)

2166
J. Zhang et al.
Figure 3. View showing the weak interactions of 1.
˚
(2.012(5) A) of Pt–N (deprotonated amide) is longer than the bond lengths of Pt–N
˚
˚
(bipy) (1.992(5) and 1.999(5) A) and close to the bond length (2.004(4) A) of Pt–O
(carboxylate), in good agreement with Sigel’s report [13].
There are some intramolecular interactions between phenyl and bipy rings in 1. The
edge of N3–C23–C22 on bipy is close to the edge of C9–C8–C13 on phenyl ring, causing
the ligand to twist at nitrogen of the N-benzoyl amino acid. This weak interaction also
exists intermolecularly. There are weak ꢄ ꢀ ꢀ ꢀ ꢄ stacking interactions between the
benzene rings of one molecular and pyridyl rings of another, with an average
ꢃ
˚
interplanar separation and dihedral angle of 4.672 A and 23.485 (figure 3). The water
in the crystal cell does not form hydrogen bonds, hence we omit it for clarity.
3.3. Cytotoxic studies
In this work, as shown in table 3 and figure 4, compounds 1–4 exert cytotoxic effects
with a low IC50 value (540 mM), have selectivity against tested carcinoma cell lines, but
none showed higher cytotoxicity than cisplatin. The structure–activity relationships are
summarized as follows: (1) the amino acids have important effect on the cytotoxicity.
For 1–4, the cytotoxicity against KB cell line decreases in the sequence:
Phe 4 Val 4 Trp ꢆ Leu, the cytotoxicity against BGC-823 cell line decreases in the
sequence: Trp 4 Val 4 Leu 4 Phe, the cytotoxicity against Bel-7402 cell line decreases
in the sequence: Trp 4 Leu 4 Val 4 Phe, the cytotoxicity against HL-60 cell line
decreases in the sequence: Val 4 Trp 4 Leu 4 Phe. For platinum(II) complexes (5–7)
with 4-toluenesulfonyl-L-amino acid dianion and bipy, the cytotoxicity against KB and
BGC-823 cell lines decreases in the sequence: Phe 4 Leu 4 Val, the cytotoxicity against
Bel-7402 cell line decreases in the sequence: Phe 4 Val 4 Leu, the cytotoxicity against
HL-60 cell line decreases in the sequence: Val 4 Leu 4 Phe. (2) The acylated groups

Platinum(II) with N-benzoyl-L-amino acid dianion
Table 3. The cytotoxicities of 1–7 in vitro (n ¼ 5).
2167
IC50 (mM)
Complexes
KB
BGC-823
Bel-7402
HL-60
Cisplatin
[Pt(bipy)Cl2]
2.6 ꢇ 0.3
85 ꢇ 2
20 ꢇ 1
18 ꢇ 1
12 ꢇ 1
19 ꢇ 1
14 ꢇ 1
16 ꢇ 1
7 ꢇ 1
6.5 ꢇ 0.8
43 ꢇ 1
8 ꢇ 1
44 ꢇ 2
29 ꢇ 2
30 ꢇ 3
33 ꢇ 3
26 ꢇ 2
26 ꢇ 2
24 ꢇ 2
14 ꢇ 1
2.9 ꢇ 0.3
32 ꢇ 2
25 ꢇ 2
20 ꢇ 2
26 ꢇ 3
23 ꢇ 2
26 ꢇ 2
18 ꢇ 2
28 ꢇ 2
1
2
3
4
5
6
7
34 ꢇ 3
25 ꢇ 2
39 ꢇ 2
11.9 ꢇ 0.6
22 ꢇ 2
27 ꢇ 2
10 ꢇ 2
The IC50 (mM) values of [Pt(bipy)(Tsleu-N, O)] (5), [Pt(bipy)(Tsval-N, O)] (6), and [Pt(bipy)(Tsphe-N, O)] (7)
were cited from our previous work [14].
KB
11
BGC-823
Bel-7402
HL-60
10
9
8
7
6
5
4
3
2
1
0
0.1
1
10
Concentration (uM)
Figure 4. The dose–response curve for 1 against HL-60, Bel-7402, BGC-823, and KB cell lines.
have important impact on the cytotoxicity of complexes. For 1 and 5, the cytotoxicities
against KB, BGC-823 and Bel-7402 cell lines decrease in the sequence: Ts 4 Bz; the
cytotoxicity against HL-60 cell line decreases in the sequence: Bz 4 Ts. For 2 and 6, the
cytotoxicity against KB, HL-60, and Bel-7402 cell lines decreases in the sequence:
Ts 4 Bz; the cytotoxicity against BGC-823 cell line decreases in the sequence: Bz 4 Ts.
For 3 and 7, the cytotoxicity against KB, BGC-823 and Bel-7402 cell lines decreases in
the sequence: Ts 4 Bz; the cytotoxicity against HL-60 cell line decreases in the
sequence: Bz 4 Ts. In summary, both amino acids and acylated groups have important
effects on cytotoxicity, but the IC50 values do not show definite correlation with the

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J. Zhang et al.
variation of amino acids and acylated groups; the cytotoxicity of complexes is also
related to tumor cell species.
4. Conclusions
Four new platinum(II) complexes with N-benzoyl-L-amino acid and bipy 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 acylated groups have important effect on cytotoxicity, but none of the
complexes is more active than cisplatin. The platinum(II) complexes with N-benzoyl-L-
amino acid and bipy may be a promising source of 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-780368. 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 Departement of
Education of Hebei Province (Grant No. ZD2010142).
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