Synthesis, Characterization, and Cytotoxicity of Palladium(II) Complexes with Diimine/Diamine and N-Carbonyl-L-Phenylalanine Dianion

Article abstract of DOI:10.1080/15533174.2013.862652

Six palladium(II) complexes, [Pd(bipy)(Bzphe-N,O)] (I-a), [Pd(bipy)(p-Mbzphe-N,O)]·2H₂O (I-b), [Pd(bipy)(p-Nbzphe-N,O)]·2H₂O (I-c), [Pd(phen)(Bmined by X-ray diffraction. The cytotoxicity test indicates that the complexes exert cytot

Full text of DOI:10.1080/15533174.2013.862652

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Synthesis, Characterization, and Cytotoxicity of
Palladium(II) Complexes With Diimine/Diamine and N-
Carbonyl-L-Phenylalanine Dianion
Li-Wei Wanga, Si-Yuan Liua, Jin-Jie Wanga, Wen Penga, Sheng-Hui Liab, Guo-Qiang Zhouab, Xin-
Ying Qinab, Shu-Xiang Wangab & Jin-Chao Zhangab
a Key Laboratory of Chemical Biology of Hebei Province, College of Chemistry &
Environmental Science, Hebei University, Baoding, P. R. China
b Key Laboratory of Medicinal Chemistry and Molecular Diagnosis of the Ministry of
Education, Hebei University, Baoding, P. R. China
Accepted author version posted online: 13 Jan 2015.
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To cite this article: Li-Wei Wang, Si-Yuan Liu, Jin-Jie Wang, Wen Peng, Sheng-Hui Li, Guo-Qiang Zhou, Xin-Ying Qin, Shu-Xiang
Wang & Jin-Chao Zhang (2015) Synthesis, Characterization, and Cytotoxicity of Palladium(II) Complexes With Diimine/Diamine
and N-Carbonyl-L-Phenylalanine Dianion, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry,
45:7, 1049-1056, DOI: 10.1080/15533174.2013.862652
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry (2015) 45, 1049–1056
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2013.862652
Synthesis, Characterization, and Cytotoxicity of Palladium(II)
Complexes With Diimine/Diamine and N-Carbonyl-L-
Phenylalanine Dianion
LI-WEI WANG1, SI-YUAN LIU1, JIN-JIE WANG1, WEN PENG1, SHENG-HUI LI1,2, GUO-QIANG ZHOU1,2
XIN-YING QIN1,2, SHU-XIANG WANG1,2 and JIN-CHAO ZHANG1,2
,
1Key Laboratory of Chemical Biology of Hebei Province, College of Chemistry & Environmental Science, Hebei University, Baoding,
P. R. China
2Key Laboratory of Medicinal Chemistry and Molecular Diagnosis of the Ministry of Education, Hebei University, Baoding,
P. R. China
Received 28 July 2013; accepted 2 November 2013
Six palladium(II) complexes, [Pd(bipy)(Bzphe-N,O)] (I-a), [Pd(bipy)(p-Mbzphe-N,O)]¢2H2O (I-b), [Pd(bipy)(p-Nbzphe-N,O)]¢2H2O
(I-c), [Pd(phen)(Bmined by X-ray diffraction. The cytotoxicity test indicates that the complexes exert cytotoxic effects against KB,
BGC-823, Bel-7402, and HL-60, but none of them shows higher cytotoxicity than cisplatin. The structure-activity relationship
suggests that bomined by X-ray diffraction. The cytotoxicity test indicates that the complexes exert cytotoxic effects against KB,
BGC-823, Bel-7402, and HL-60, but none of them shows higher cytotoxicity than cisplatin. The structure-activity relationship
suggests that both N-containing ligands and N-carbonyl reagent have important effect on cytotoxicity, however, the IC50 values do
not show definite correlation with their variation.
Keywords: Palladium (II) complex, N-carbonyl-L-phenylalanine dianion, diimine, cytotoxicity
Introduction
rapid, thus the complexes dissociate readily in solution lead-
ing to very reactive species that are unable to reach their
The landmark discovery of cisplatin heralded a new era of pharmacological targets. This implies that if anticancer palla-
anticancer drug research based on metallopharmaceuticals.[1] dium drugs will be developed, they must be stabilized by
Now cisplatin, carboplatin, and oxaliplatin are commonly strongly coordinated nitrogen ligands and suitable leaving
used for the treatment of lung, colorectal, ovarian, breast, ligands. Amino acid, bipy, and phen or their derivatives have
head and neck, bladder, and testicular cancers. In addition, been widely used to synthesize palladium anticancer com-
nedaplatin, lobaplatin, and heptaplatin have gained regional plexes because amino acid ligands do not dissociate easily in
approval, a few platinum drugs continue to be evaluated in aqueous solution and bipy or phen has the ability to partici-
clinical studies. The major drawbacks of current platinum pate as DNA intercalator.[7,8] Numerous palladium com-
drugs, including a limited range of cancers, acquired or plexes with aromatic N-containing and L-amino acid ligands
intrinsic resistance, and severe side effects prompted chemists were shown to be effective against tumors. For example,
to develop new metal anticancer drugs.[2,3]
Puthraya et al.[9] reported the synthesis and cytotoxicity of
Due to the structural and thermodynamic similarities palladium(II) complexes of the formula [Pd(bipy)(AA)]nC
between palladium(II) and platinum(II) complexes, there is (where AA is an anion of Cys, Asp, Glu, Met, His, Arg, Phe,
an increased interest in the study of palladium(II) derivatives Tyr, or Try, and n D 0 or 1). The results indicated that these
as potential anticancer drugs.[4–6] It was found that the hydro- palladium(II) complexes showed growth inhibition against
lysis of the leaving ligands in palladium complexes was too L1210 lymphoid leukemic, P388 lymphocytic leukemic, Sar-
cama 180, and Ehrlich ascites tumor cells. IC50 values of
some complexes were comparable to or lower than that of cis-
platin.[9] Mital et al.[10] reported the synthesis and cytotoxic-
Address correspondence to Jin-Chao Zhang and Shu-Xiang
ity of palladium(II) complexes of type [Pd(phen)(AA)]C
Wang, Key Laboratory of Chemical Biology of Hebei Province,
(where AA is an anion of Gly, Ala, Leu, Phe, Tyr, Try, Val,
College of Chemistry & Environmental Science, Hebei Univer-
Pro, or Ser), only two complexes, [Pd(phen)(Gly)]C and [Pd
sity, Baoding, P. R. China. E-mail: jczhang6970@163.com;
(phen)(Val)]C, showed comparable cytotoxicity as cis-
wsx@hbu.edu.cn
platin.[10] The cytotoxic study of [Pd(AMBI)(AA)]nC (where
AA is an anion of Gly, Ala, Cys, Met, or Ser) was reported
Color versions of one or more of the figures in the article can be
found online at www.tandfonline.com/lsrt.

1050
Wang et al.
by El-Sherif.[11] The results indicated that [Pd(AMBI)(Met)] N-Carbonyl-L-Phenylalanine Ligands
Cl¢H2O showed significant activity against HCT116 cells
N-carbonyl-L-pheylalanine was prepared by a modified
method.[13] To a vigorously stirred solution of L-phenylala-
nine (200 mg, 1.2 mmol) and 6.0 mL of NaOH
(0.2 molꢁL¡1) water solution in an ice bath, benzoyl chloride
(0.15 mL, 1.2 mmol) dissolved in 8 mL of CHCl3 and 6 mL
of NaOH (0.2 molꢁL¡1) solution were added slowly at the
same time. The reaction was held for 5-6 h. Then the solution
was acidified to pH D 3»4 with HCl (0.2 molꢁL¡1) and the
aqueous layer was extracted with CHCl3 (3 £ 8 mL). Organic
layers were combined, dried with anhydrous sodium sulfate,
and concentrated to 3 mL by a rotary evaporator at 40ꢀC.
By evaporating the solution at room temperature, white solid
was generated. After filtration, the white solid was recrystal-
lized twice from ethanol-water (V/V D 1:1) mixtureand dried
to give BzpheH2, m.p: 185»186ꢀC (found); 187ꢀC (lit[13]); IR
(KBr, cm¡1): n(NH-amide) 3327, n(AmideⅠ) 1612, n(Amide P) 1538,
n(OCO)a 1722, n(OCO)s 1228.
with IC50 value of 0.74 mg¢mL¡1, while [Pd(AMBI)(Cys)]
Cl¢H2O showed cytotoxicity against HEP2 cells with IC50
value of 0.60 mg¢mL¡1 [11]
.
We previously reported the syn-
thesis and cytotoxicity of four platinum(II) complexes with
bipy and N-benzoyl-L-amino acid dianion. The results indi-
cated that these complexes exerted cytotoxicity against HL-
60, Bel-7402, BGC-823, and KB cell lines.[12] In order to
develop new metal anticancer drugs, in this study, we present
the synthesis, characterization, and cytotoxicity of six palla-
dium(II) complexes with diimine (phen and bipy) or diamine
(en) and N-carbonyl-L-phenylalanine dianion for the first
time.
Experimental
Materials
p-MbzpheH2 was prepared following a procedure similar
to BzpheH2. IR (KBr, cm¡1): n(NH-amide) 3324, n(AmideⅠ)
Benzoyl chloride, p-methyl benzoyl chloride, p-nitro benzoyl
chloride, and K2[PdCl4] were of chemical grade: bipy, en,
and phen were of analytical grade. MTT, SRB, benzylpenicil-
lin, streptomycin, and Phe were purchased from Sigma.
RPMI-1640 medium, trypsin, and fetal bovine serum were
purchased from Gibco. Four different human carcinoma cell
lines: HL-60 (immature granulocyte leukemia), Bel-7402
(liver carcinoma), BGC-823 (gastric carcinoma), and KB
(nasopharyngeal carcinoma) were obtained from American
Type Culture Collection.
1
1618, n(Amide P) 1544, n(OCO)a 1718, n(OCO)s 1232; H NMR
(600 MHz, CDCl3) d (ppm): 2.39 (s, 3H, CH3), 3.29 (dd, J D
14.1, 5.7 Hz, 1H, CH2-H), 3.38 (dd, J D 14.1, 5.7 Hz, 1H,
CH2-H), 5.11 (dd, J D 13.2, 6.0 Hz, 1H, CH), 6.52 (d, J D
7.2 Hz, 1H, NH), 7.22 (t, J D 7.2 Hz, 4H, Ar-H), 7.33–7.30
(m, 1H, Ar-H), 7.60 (d, J D 8.4 Hz, 2H, Ar-H), 7.99 (d, J D
8.4 Hz, 2H, Ar-H).
p-NbzpheH2 was prepared following a procedure similar
to BzpheH2. IR (KBr, cm¡1): n(NH-amide) 3351, n(AmideⅠ)
1
1600, n(Amide P) 1530, n(OCO)a 1710, n(OCO)s 1299; H NMR
(600 MHz, CDCl3) d (ppm): 3.33–3.27 (m, 1H, CH2-H), 3.40
(dd, J D 14.4, 5.4 Hz, 1H, CH2-H), 5.13 (dd, J D 13.2,
5.4 Hz, 1H, CH), 6.64 (d, J D 7.8 Hz, 1H, NH), 7.20 (d, J D
6.6 Hz, 2H, Ar-H), 7.35–7.29 (m, 2H, Ar-H), 7.85 (d, J D
8.4 Hz, 2H, Ar-H), 8.29–8.26 (m, 2H, Ar-H), 8.33 (d, J D
9.0 Hz, 1H, Ar-H).
Instrumentation and Measurement
Elemental analysis was determined on an Elementar Vario
EL III elemental analyzer. The electronic spectra in DMF
were measured on an UV-3400 Toshniwal spectrophotome-
ter. The IR spectra were recorded using KBr pellets and a
1
Perkin Elmer Model-683 spectrophotometer. The H NMR
was recorded on a Bruker AVIII 600 NMR spectrometer.
The mass spectra were measured by LC-MS apparatus Agi-
Precursor Complexes
lent 1200-6310. X-ray single-crystal structure was performed Precursor complexes [Pd(bipy)Cl2], [Pd(phen)Cl2], and [Pd
on a Bruker SMART APEX II CCD diffractometer. The (en)Cl2] were synthesized according to published proce-
OD was measured on a microplate spectrophotometer (Bio- dures.[14,15] [Pd(bipy)Cl2]: Yellow solid, yield 63%. Anal.
Rad Model 680, USA).
Calcd. for C10H8Cl2N2Pd: C, 36.01; H, 2.42; N, 8.40. Found:
C, 36.28; H, 2.63; N, 8.50. [Pd(phen)Cl2]: Yellow solid, yield
95%. Anal. Calcd. for C12H8Cl2N2Pd: C, 40.31; H, 2.26; N,
7.88. Found: C, 40.51; H, 2.32; N, 7.79. [Pd(en)Cl2]: Brown
yellow solid, yield 84%. Anal. Calcd. for C12H6Cl2N2Pd: C,
10.12; H, 3.40; N, 11.80. Found: C, 10.16; H, 3.41; N, 11.65.
Synthesis of Compounds
Six palladium(II) complexes [Pd(bipy)(Bzphe-N,O)] (I-a), [Pd
(bipy)(p-Mbzphe-N,O)]¢2H2O (I-b), [Pd(bipy)(p-Nbzphe-N,
O)]¢2H2O (I-c), [Pd(phen)(Bzphe-N,O)]¢2H2O (P-a), [Pd(en)
(Bzphe-N,O)]¢H2O (S-a), and [Pd(en)(p-Nbzphe-N,O)]¢
2H2O (S-c) were prepared by adding precursor complex [Pd
[Pd(bipy)(Bzphe-N, O)] (I-a)
(bipy)Cl2], [Pd(phen)Cl2] or [Pd(en)Cl2] with N-carbonyl-L- To a vigorously stirred solution of BzpheH2 (32.32 mg,
pheylalanine in a mixed solution of CH3OH/H2O at 50ꢀC 0.12 mmol) in 8 mL CH3OH/H2O (V:V D 1:1), [Pd(bipy)
and pH 8–9. The mixture was stirred till to a clear solution. Cl2] (20 mg, 0.06 mmol) was added. The mixture was heated
Then the solution was filtered and concentrated to 3 mL at to 50ꢀC and adjusted to pH D 8–9 by NaOH solution, and
50ꢀC by a rotary evaporator. By evaporating the filtered solu- then stirred for 2 h. The solution was concentrated to about
tion (or the filtrate) at room temperature, yellow crystal or 80% of the original volume. The complex I-a was separated
sediment was obtained in 1–2 weeks (Figure 1).
from the solution after a few days. Yellow crystalline, yield:

Palladium(II) Complexes
1051
Fig. 1. The synthesis routes of the six Pd(II) complexes.
68%. IR (KBr, cm¡1): n(Amide&)1551, n(OCO)a 1632, n(OCO)a NbzpheH2 (37.71 mg, 0.12 mmol). Yield: 62%, yellow solid.
1383, n(Pd-N) 566, n(Pd-O) 465. 1H NMR (600 MHz, d6- IR (KBr, cm¡1): n(OH) 3428, n(Amide&) 1552, n(OCO)a 1640,
1
DMSO) d (ppm): 3.08 (dd, J D 13.1, 4.5 Hz, 1H, CH2-H), n(OCO)a 1397, n(Pd-N) 565, n(Pd-O) 479. H NMR (600 MHz,
3.29 (dd, J D 13.1, 4.5 Hz, 1H, CH2-H), 5.08–5.05 (m, 1H, CDCl3) d (ppm): 3.11 (dd, J D 12.9, 5.7 Hz, 1H, CH2-H),
CH), 6.65 (t, J D 7.5 Hz, 1H, Ar-H), 6.73 (t, J D 7.5 Hz, 2H, 3.44 (dd, J D 12.9, 5.7 Hz, 1H, CH2-H), 5.12–5.06 (m, 1H,
Ar-H), 7.09 (d, J D 3.0 Hz, 3H, Ar-H), 7.13 (d, J D 5.4 Hz, CH-H), 7.19–7.13 (m, 2H, Ar-H), 7.27 (d, J D 7.2 Hz, 2H,
1H, Ar-H), 7.23 (d, J D 7.2 Hz, 2H, Ar-H), 7.28 (d, J D Ar-H), 7.31 (d, J D 5.4 Hz, 1H, Ar-H), 7.81–7.74 (m, 2H,
5.4 Hz, 1H, Ar-H), 7.78–7.75 (m, 1H, Ar-H), 8.02 (t, J D Ar-H), 7.95 (d, J D 9.0 Hz, 2H, Ar-H), 8.03 (t, J D 8.1 Hz,
7.8 Hz, 1H, Ar-H), 8.26 (d, J D 7.8 Hz, 1H, Ar-H), 8.30 (t, J 1H, Ar-H), 8.35–8.26 (m, 4H, Ar-H), 8.43 (d, J D 8.4 Hz,
D 6.9 Hz, 4H, Ar-H), 8.42 (d, J D 7.8 Hz, 1H, Ar-H). ESI- 1H, Ar-H), 8.52 (d, J D 8.4 Hz, 2H, Ar-H). ESI-MS: 592.05
MS: 568.03 [MCK]C. Anal. Calcd. for [Pd(bipy)(Bzphe-N, [M]C. Anal. Calcd. for [Pd(bipy)(p-Nbzphe-N, O)]¢H2O
O)] (C26H21N3O3Pd, 529.06): C, 58.93; H, 3.99; N, 7.93. (C26H22N4O6Pd, 592.06): C, 52.67; H, 3.74; N, 9.45. Found:
Found: C, 58.84; H, 4.04; N, 7.84.
C, 52.75; H, 3.89; N, 9.29.
[Pd(bipy)(p-Mbzphe-N, O)]¢2H2O (I-b)
[Pd(phen)(Bzphe-N, O)]¢2H2O (P-a)
The synthesis of I-b was carried out in an identical manner to The synthesis of P-a was carried out in an identical manner
I-a starting from [Pd(bipy)Cl2] (20 mg, 0.06 mmol) and p- to I-a starting from [Pd(phen)Cl2] (20 mg, 0.056 mmol) and
MbzpheH2 (34.00 mg, 0.12 mmol). Yellow solid, yield: 62%. BzpheH2 (30.16 mg, 0.112 mmol). Yield: 66%, yellow crys-
IR (KBr, cm¡1): n(OH) 3430, n(Amide&) 1530, n(OCO)a 1641, talline. IR (KBr, cm¡1): n(OH) 3428, n(Amide&) 1549, n(OCO)a
1
n(OCO)a 1385, n(Pd-N) 572, n(Pd-O) 455. H NMR (600 MHz, 1637, n(OCO)a 1384, n(Pd-N) 562, n(Pd-O) 474. 1H NMR
CDCl3) d (ppm): 2.07 (s, 3H, CH3), 3.07 (dd, J D 14.1, (600 MHz, CDCl3) d (ppm): 3.14 (dd, J D 14.1, 5.7 Hz, 1H,
5.7 Hz, 1 H, CH2-H), 3.09 (dd, J D 14.1, 5.7 Hz, 1H, CH2- CH2-H), 3.31 (dd, J D 14.1, 5.7 Hz, 1H, CH2-H), 5.13–5.08
H), 5.05–5.02 (m, 1H, CH), 6.65 (t, J D 7.2 Hz, 1H, Ar-H), (m, 1H, CH), 6.26 (d, J D 7.2 Hz, 1H, Ar-H), 6.52 (t, J D
6.72 (t, J D 7.2 Hz, 2H, Ar-H), 6.89 (d, J D 7.8 Hz, 3H, Ar- 7.4 Hz, 2H, Ar-H), 7.07 (d, J D 4.8 Hz, 3H, Ar-H), 7.23 (d, J
H), 7.15–7.11 (m, 1H, Ar-H), 7.22 (d, J D 7.2 Hz, 3H, D 7.2 Hz, 2H, Ar-H), 7.50 (s, 1H, Ar-H), 8.08 (dd, J D 7.8,
Ar-H), 7.27 (d, J D 4.8 Hz, 1H, Ar-H), 7.78–7.74 (m, 1H, 5.2 Hz, 1H, Ar-H), 8.13 (d, J D 8.8 Hz, 1H, Ar-H), 8.20 (d, J
Ar-H), 8.04 (t, J D 7.5 Hz, 1H, Ar-H), 8.21 (d, J D 7.8 Hz, D 8.8 Hz, 1H, Ar-H), 8.39 (m, 2H, Ar-H), 8.65 (dd, J D 12.8,
2H, Ar-H), 8.26 (d, J D 7.8 Hz, 1H, Ar-H), 8.41 (d, J D 5.2 Hz, 2H, Ar-H), 8.91 (d, J D 8.0 Hz, 1H, Ar-H). ESI-MS:
8.4 Hz, 1H, Ar-H). ESI-MS: 580.11 [MCH]C. Anal. Calcd. [MCH]C 590.10. Anal. Calcd. for [Pd(phen)(Bzphe-N, O)]¢
for
[Pd(bpy)(p-Mbzphe-N,O)]¢2H2O
(C27H27N3O5Pd, 2H2O (C28H25N3O5Pd, 589.08): C, 57.01; H, 4.27; N, 7.12.
579.10): C, 55.92; H, 4.69; N, 7.25. Found: C, 56.91; H, 4.68; Found: C, 57.11; H, 4.17; N,7.05.
N, 7.25.
[Pd(en)(Bzphe-N, O)]¢H2O (S-a)
The synthesis of S-a was carried out in an identical manner
[Pd(bipy)(p-Nbzphe-N, O)]¢H2O (I-c)
The synthesis of I-c was carried out in an identical manner to to I-a starting from [Pd(en)Cl2] (20 mg, 0.084 mmol) and
I-a starting from [Pd(bipy)Cl2] (20 mg, 0.06 mmol) and p- BzpheH2 (45.24 mg, 0.168 mmol). Yield: 66%, yellow

1052
Wang et al.
powder. IR (KBr, cm¡1): n(OH) 3430, n(Amide&) 1535, n(OCO)a
1640, n(OCO)a 1380, n(Pd-N) 552, n(Pd-O) 460. 1H NMR
(600 MHz, CDCl3) d (ppm): 1.97 (s, 2H), 2.33 (s, 2H), 2.83
(dd, J D 12.80, 5.8 Hz, 2H), 2.97 (dd, J D 12.80, 5.8 Hz, 2H),
3.12 (dd, J D 12.8, 6.4 Hz, 1H), 3.24 (dd, J D 12.8, 6.4 Hz,
1H), 4.48–4.42 (m, 1H), 6.63 (d, J D 7.2 Hz, 3H), 6.97–6.88
(m, 3H), 7.28 (d, J D 5.6 Hz, 2H), 7.37 (d, J D 7.2 Hz, 1H),
7.66 (d, J D 7.2 Hz, 1H). ESI-MS: [M]C 451.08. Anal. Calcd.
for [Pd(en)(Bzphe-N, O)]¢H2O (C18H23N3O4Pd, 451.07): C,
47.85; H, 5.13; N, 9.30. Found: C, 47.75; H, 5.05; N, 9.27.
Table 1. Crystallographic data for the complex I-a
Complex
I-a
Chemical formula
Formula weight
T/K
C24H24N3O3Pd
508.86
296(2)
Crystal dimensions/mm
Crystal system
0.46 £ 0.37 £ 0.33
Monoclinic
P2(1)/c
Space group
ꢀ
a/A
10.4931(4)
18.9224(7)
11.6646(5)
90
ꢀ
b/A
ꢀ
c/A
a (ꢀ)
b (ꢀ)
[Pd(en)(p-Nbzphe-N, O)]¢2H2O (S-c)
103.8690(10)
90
2248.54(15)
4
The synthesis of S-c was carried out in an identical manner
to I-a starting from [Pd(en)Cl2] (20 mg, 0.084 mmol) and p-
NbzpheH2 (52.80 mg, 0.168 mmol). Yield: 82%, yellow pow-
der. IR (KBr, cm¡1): n(OH) 3427, n(Amide&) 1528, n(OCO)a
1636, n(OCO)a 1398, n(Pd-N) 566, n(Pd-O) 465. 1H NMR
(600 MHz, CDCl3) d (ppm): 1.94 (s, 2H), 2.31 (s, 2H), 2.87
(dd, J D 12.8, 5.8 Hz, 2H), 2.94 (dd, J D 12.8, 5.8 Hz, 2H),
3.15 (dd, J D 12.8, 6.4 Hz, 1H), 3.21 (dd, J D 12.8, 6.4 Hz,
1H), 4.39–4.52 (m, 1H), 6.59 (d, J D 7.2 Hz, 3H), 6.93–6.78
(m, 3H), 7.31 (d, J D 5.6 Hz, 2H), 7.68 (d, J D 7.2 Hz, 1H).
ESI-MS: [MCNa]C 537.06. Anal. Calcd. for [Pd(en)(p-
Nbzphe-N, O)]¢2H2O (C18H24N4O7Pd, 514.07): C, 41.99; H,
4.70; N, 10.88. Found: C, 41.86; H, 4.72; N, 10.83.
g (ꢀ)
ꢀ
V/A3
Z
Dc/gꢁcm¡3
1.503
1036
F(000)
u range for collection (ꢀ)
Reflections collected
Independent reflections
Parameters/restraints
R (int)
2.00–28.30
16315
5585
298/0
0.0181
R,WR2 (all)
0.0357, 0.0958
0.0305, 0.0917
1.052
R,WR2[I>2s(I)]
GOF on F2
Crystallography
measured on a microplate spectrophotometer at a wavelength
of 570 nm. The SRB assay was performed for Bel-7402,
BGC-823, and KB.[17] Upon completion of the incubation
for 44 h, the cells were fixed in 10% trichloroacetic acid
(100 mL) for 30 min at 4ꢀC, 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 staining was solubilized in 10 mM unbuffered Tris base
(100 mL) and OD was measured at 540 nm as mentioned pre-
viously. The IC50 value was determined from plot of% viabil-
ity against dose of complexes.
The data collection of the complex I-a was performed on a
Bruker SMART APEX II CCD diffractometer equipped
with a graphite monochromatized Mo Ka radiation (λ D
ꢀ
0.71073 A) at 296(2) K. Multi-scan absorption corrections
were applied using the SADABS program. The structures
were solved by the direct method using the SHELXS-97 pro-
gram. Refinements on F2 were performed using SHELXL-97
by the full-matrix least-squares method with anisotropic ther-
mal parameters for all non-hydrogen atoms. Table 1 lists
crystallographic details.
Cytotoxicity Analysis
Results and Discussion
The complexes were dissolved in DMSO at a concentration
of 5 mM as stock solution, and diluted in culture medium at
concentrations of 1, 10, 100, and 500 mM as working solu-
Characterization of Complexes
tion. To avoid DMSO toxicity, the concentration of DMSO The elemental analysis showed that there was good agree-
was less than 0.1% (V/V) in all experiments. ment between calculated and found values for six complexes,
The cells harvested from exponential phase were seeded this indicated that all the complexes were of high purity.
equivalently into a 96-well plate, then the complexes were Bipy and Phen have a strong absorption peak at 282 and
added to the wells to achieve final concentrations. Control 273 nm, respectively, which is assigned to internal p-p* tran-
wells were prepared by addition of culture medium. Wells sition. After formation of the complexes, the absorption peak
containing culture medium without cells were used as blanks. red shifts by ca. 32 nm for complexes (I-a » I-c and P-a)
All experiments were performed in quintuplicate. The MTT compared with that of bipy or phen, which may be caused by
assay was performed as described by Mosmann for HL- charge transfer transition (metal » ligand) from palladium d-
60.[16] Upon completion of the incubation for 44 h, stock orbital to p* orbital of bipy or phen.
MTT dye solution (20 mL, 5 mg/mL) was added to each
The amide groups of BzpheH2, p-MbzpheH2, and p-
well. After 4 h incubation, DMSO (100 mL) was added to NbzpheH2 have a strong sharp yNH near 3320 cm¡1, which
solubilize the MTT formazan. The OD of each well was disappears after formation of the complexes, showing that

Palladium(II) Complexes
1053
Fig. 2. Molecular structure and atom-labeling scheme for the complex I-a.
the amide groups have been deprotonated. This is also further stacking is also observed between the benzene rings of Phe
confirmed by the amide (I) shifting from »1610 cm¡1 to and bipy ligands considering that the intermolecular cen-
ꢀ
1530»1551 cm¡1 and the disappearance of the amide (II) in troid-centroid distance is 4.317 A (Figure 3).
the »1540 cm¡1 region. New bands appear at
564»572 cm¡1 and are assigned to yPd-N. The carboxylate
group of these complexes shows two ban¡ds, an intense anti-
Cytotoxicity Studies
symmetric carboxylate stretching y(as, coo and a symmetric
)
¡
As listed in Table 3, the six complexes exerted cytotoxic
carboxylate stretching y(s,
,
at about 1640¡ and
coo
)
1380 cm¡1, respectively. The values of Dy(coo¡)(y(as, coo ) -y(s,
effects against HL-60, BGC-823, Bel-7402, and KB. How-
ever, none of them showed higher cytotoxicity than cisplatin.
Comparing to other complexes, the complexes P-a and PI-a
exerted higher cytotoxicity against HL-60 with IC50 values of
8.50 and 5.95 mmol/L. For BGC-823, complex I-c displayed
higher cytotoxity. For Bel-7402 and KB, complex II-a dis-
played higher cytotoxity.
¡)) of these complexes are in the range 241–256 cm¡1
,
coo
which is greater than Dy(coo-) of the corresponding sodium
carboxylates, so the carboxylate group may be monodentate
coordinated through oxygen atoms.[18] This is further con-
firmed by the appearance of the peaks of yPd-O. These results
are in good agreement with the results revealed by X-ray crys-
tal analysis.
For [Pd(bipy)(AA)]nC complexes, Puthraya et al.[9]
reported that side chain of the amino acids might affect the
inhibitory activity. This inhibitory activity was found to be in
decreasing order as follows: nonpolar hydrophobic > polar
uncharged > charged side groups.[9] However, for [Pd(phen)
(AA)]C complexes, Mital et al.[10] reported that the IC50 val-
ues did not show definite correlation with variation of the
amino acid side chains.[10] El-Sherif[11] reported that the cyto-
toxicity of [Pd(AMBI)(Met)]Cl¢H2O against HCT116 and
HEP2 decreased in the sequences: Met > Ser > Ala > Gly >
Cys, and Cys > Ser > Ala > Met > Gly, respectively.[11] We
BzpheH2, p-MbzpheH2 and p-NbzpheH2 show signal as
1
doublet at d D »6.5 in H NMR, which are associated with
the proton of the amide groups, but these peaks disappeared
for these complexes, which further confirmed that the amide
groups had been deprotonated. The methylene 1H resonances
(amino acid) of the complexes shifted to the lower field as a
result of deprotonated amide nitrogen coordinating to Pd(II).
X-Ray Structure of the Complex I-a
ꢀ
The crystal structure and numbering scheme of complex I-a
were shown in Figure 2. Selected bond distances and angles
were listed in Table 2. Complex I-a crystallized in a mono-
clinic unit cell, space group P2(1)/c. The geometry around
Pd(II) is approximately square planar, composed of two
nitrogen atoms from the bipy, one carbonyl amide nitrogen
atom, and one carboxylic oxygen atom of the amino acid
molecule.
Table 2. Selected bond lengths (A) and angles (ꢀ) for the complex
I-a
ꢀ
Bond distances/A
Angles/ꢀ
O(1)-Pd-N(1)
O(1)-Pd-N(3)
N(2)-Pd-N(3)
O(1)-Pd-N(2)
N(1)-Pd-N(2)
N(3)-Pd-N(1)
Pd–O(1)
1.9953(17)
2.0095(19)
2.019(2)
94.18(8)
81.40(8)
104.47(8)
172.20(8)
80.08(8)
175.30(8)
Pd–N(1)
Pd–N(2)
Pd–N(3)
2.0030(19)
For complex I-a, there is weak interaction between bipy
ring side and the other bipy ring side from the neighborꢀmole-
cule, which happens in the distance of 3.548 and 3.664 A. p-p

1054
Wang et al.
Fig. 3. View showing the weak pairing of the complex I-a.
previously reported the synthesis and cytotoxity of palladium 60 decreases in the sequence: phen > bqu > bipy > 1,4-dab,
(II) complexes with 4-toluenesulfonyl-L-amino acid dianion and the cytotoxicity against Bel-7402 decreases in the
and diimine/diamine ligands. Our results indicated that these sequence: 1,4-dab > bqu > bipy > phen. For the palladium
complexes exerted cytotoxic effects with selectivity against (II) complexes with ser and different diimine/diamine
tested carcinoma cell lines, some complexes displayed better ligands, the cytotoxicity against HL-60 and Bel-7402
cytotoxity than cisplatin. Both amino acids and diimine/ decreases in the sequences: 1,4-dab > bqu> 1,3-dap > en,
diamine ligands have important effect on cytotoxicity, but and 1,4-dab > 1,3-dap > bqu > en. For the palladium(II)
the IC50 values do not show definite correlation with varia- complexes with phe and different diimine/diamine ligands,
tion of the amino acids and diimine/diamine ligands, the the cytotoxicity against HL-60 decreases in the sequence:
cytotoxicity of complexes is also related to tumor cell spe- phen> bqu > en > bipy >1,4-dab, the cytotoxicity against
cies.[19–24] For example, for palladium(II) complexes with Bel-7402 decreases in the sequence: phen > bqu >1,4-dab >
1,4-dab and different amino acids, the cytotoxicity against en > bipy. In this study, for palladium(II) complexes with N-
Bel-7402 and HL-60 decreases in the sequences: Gly > Ser > carbonyl-L-amino acid dianion and diimine/diamine ligands,
Ile > Val > Phe > Thr > Leu and Ser > Gly > Val > Thr > the nature of diimine/diamine and N-carbonyl reagent have
Phe > Leu > Ile, respectively. For palladium(II) complexes important effects on cytotoxicity. For palladium(II) com-
with bipy and different amino acids, the cytotoxicity against plexes (I-a, II-a, and III-a) with Bzphe and different diimine/
HL-60 decreases in the sequence: Val > Phe > Ala > Leu, diamine, the cytotoxicity against BGC-823, Bel-7402 and KB
but the cytotoxicity against Bel-7402 decreases in the decreases in the sequence: phen > bipy > en, the cytotoxicity
sequence: Leu > Ala > Phe > Val. For palladium(II) com- against HL-60 decreases in the sequence: en > phen > bipy.
plexes with phen and different amino acids, when the amino For palladium(II) complexes (I-c and III-c) with p-Nbzphe
acid is Leu, the complex has the best cytotoxicity against HL- and different diimine/diamine, the cytotoxicity against HL-
60 and Bel-7402. For palladium(II) complexes with en and 60 and BGC-823 cell lines decreases in the sequence: bipy >
different amino acids, the cytotoxicity against HL-60 and en; the cytotoxicity against Bel-7402 and KB cell lines
Bel-7402 decreases in the same sequence: Phe > Leu > Ala > decreases in the sequence: en > bipy. For palladium(II) com-
Gly > Ser. For the palladium(II) complexes with Val and dif- plexes (I-a, I-b, and I-c) with bipy and different N-carbonyl-
ferent diimine/diamine ligands, the cytotoxicity against HL- L-phenylalanine dianion, the cytotoxicity against HL-60 and
Table 3. The cytotoxicities of the complexes in vitro
IC50 (mmol/L)
No.
Compound
HL-60
BGC-823
Bel-7402
KB
Cisplatin
I-a
I-b
I-c
P-a
S-a
S-c
V-4
Cis-[Pt(NH3)2Cl2]
[Pd(bipy)(Bzphe-N,O)]
2.89
16.98
15.33
17.31
8.50
5.95
27.45
26
6.48
37.89
18.49
13.35
24.85
47.32
23.33
39
8.12
38.31
29.21
57.59
19.74
42.85
35.45
33
2.65
23.57
50.08
22.17
10.19
44.51
17.41
12
[Pd(bipy)(p-Mbzphe-N,O]¢2H2O
[Pd(bipy)(p-Nbzphe-N,O)]¢H2O
[Pd(phen)(Bzphe-N,O)]¢2H2O
[Pd(en)(Bzphe-N,O)]¢H2O
[Pd(en)(p-Nbzphe-N,O)]¢2H2O
[Pt(bipy)(Bzphe-N,O)]¢4.5H2O [12]

Palladium(II) Complexes
1055
Ser D L-serine
Bel-7402 decreases in the sequence: p-Mbzphe > Bzphe > p-
Nbzphe; the cytotoxicity against BGC-823 decreases in the
sequence: p-Nbzphe > p-Mbzphe > Bzphe; the cytotoxicity
against KB decreases in the sequence: p-Nbzphe > Bzphe >
p-Mbzphe. For palladium(II) complexes (III-a and III-c)
with en and different N-carbonyl-L-phenylalanine dianion,
the cytotoxicity against HL-60 decreases in the sequence:
Bzphe > p-Nbzphe; the cytotoxicity against BGC-823
decreases in the sequence: p-Nbzphe > Bzphe; the cytotoxic-
ity against Bel-7402 and KB decreases in the sequence: p-
Nbzphe > Bzphe. In addition, the metal ion has also impor-
tant effect on cytotoxicity. For complexes (I-a and V-4) with
bipy and Bzphe, the cytotoxicity against HL-60 and BGC-
823 decreases in the sequence: Pd > Pt; the cytotoxicity
against Bel-7402 and KB decreases in the sequence: Pt >
Pd.[12]
Ile D L-isoleucine
BzpheH2 D N- benzoyl-L-pheylalanine
p-MbzpheH2 D N-p-methylbenzoyl-L-phenylalanine
p-NbzpheH2 D N-p-nitrolbenzoyl-L-phenylalanine
DMF D dimethyl formamide
DMSO D dimethyl sulfoxide
MTT D 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-
tetrazolium bromide
SRB D sulforhodamine B
OD D optical density
Supplementary Material
Crystallographic data for the structural analysis of I-a have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC-870815. Copies of this information may be
obtained free of charge from The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (Fax: C44 1223 336033; E-
mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.
uk)
In summary, the nature of N-containing ligands and N-
carbonyl reagent has important effect on cytotoxicity. How-
ever, the IC50 values do not show definite correlation with
variation of N-containing ligands and N-carbonyl reagent,
the cytotoxicity of complexes is related to tumor cell species.
Funding
Conclusion
The authors gratefully acknowledge financial support by the
Nature Science Foundation for Distinguished Young Schol-
ars of Hebei Province (No. B2011201164), Natural Science
Foundation of Hebei Province (No. B2011201135), the Key
Basic Research Special Foundation of Science Technology
Ministry of Hebei Province (No. 11966412D, 12966418D),
the Key Research Project Foundation of Department of Edu-
cation of Hebei Province (No. ZH2012041), the Pharmaceu-
tical Joint Research Foundation of the Natural Science
Foundation of Hebei Province and China Shiyao Pharma-
ceutical Group Co., LTD (No. B2012201044, B2011201174).
ne (phen and bipy) or diamine (en). The crystal structure of
complex I-a was determined by single-crystal X-ray diffrac-
tine (phen and bipy) or diamine (en). The crystal structure of
complex I-a was determined by single-crystal X-ray diffrac-
tion. Cytotoxic studies showed that six complexes exhibited
cytotoxity against different cell lines, but none of them
showed higher cytotoxicity than cisplatin. The results suggest
that both N-containing ligands and N-carbonyl reagent have
important effect on the cytotoxity.
Abbreviations
en D ethylenediamine
bipy D 2,2’-bipyridine
phen D 1,10-phenanthroline
AMBI D 2-aminomethyl benzimidazole
1,4-Dab D 1,4-diaminobutane
Bqu D 2, 20-biquinoline
1,3-Dap D 1,3-diaminopropane
Ala D L-alanine
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