Water-soluble platinum(II) complexes of reduced amino acid Schiff bases: Synthesis, characterization, and antitumor activity

Article abstract of DOI:10.1007/s11164-012-0593-y

A series of water-soluble platinum(II) complexes of reduced amino acid Schiff bases were synthesized as potential anticancer agents and characterized by ¹H NMR, EA, MS, IR, and molar conductivity. These compounds were tested for their DNA inter

Full text of DOI:10.1007/s11164-012-0593-y

Res Chem Intermed (2013) 39:733–746
DOI 10.1007/s11164-012-0593-y
Water-soluble platinum(II) complexes of reduced
amino acid Schiff bases: synthesis, characterization,
and antitumor activity
•
Li-Jun Li Cheng Wang Chao Tian
•
•
•
Xiao-Yan Yang Xing-Xing Hua Jian-Long Du
•
Received: 11 March 2012 / Accepted: 3 May 2012 / Published online: 30 May 2012
Ó Springer Science+Business Media B.V. 2012
Abstract A series of water-soluble platinum(II) complexes of reduced amino acid
Schiff bases were synthesized as potential anticancer agents and characterized by H
1
NMR, EA, MS, IR, and molar conductivity. These compounds were tested for their DNA
interaction with salmon sperm DNA, and their in vitro anticancer activities have been
validated against HL-60, KB, BGC-823, and Bel-7402 cell lines by the MTT assay. The
cytotoxicity of one complex (5g) is better than that of cisplatin against BGC-823 and
HL-60 cell lines, and show close cytotoxic effect against Bel-7402 cell line.
Keywords Water-soluble platinum(II) complexes Á Reduced amino acid Schiff
bases Á DNA interaction Á Antitumor activity
Introduction
The biological activity of cisplatin was discovered fortuitously in 1965 during
studies of the effect of an electric current on Escherichia coli [1]. Currently,
cisplatin is being used as an anticancer agent in several human cancers, particularly
ovarian, testicular, bladder, and head and neck cancers [2–4]. However, structural
analogues to cisplatin have not yet overcome cisplatin’s clinical limitations,
particularly with regard to a dose-limiting toxicity and the lower activity (acquired
resistance) in some of the most common cancers, and therefore, many platinum
complexes have been designed and synthesized to overcome such disadvantages of
cisplatin [5–7]. A drug that could be effectively delivered orally is strongly
desirable, as it would allow substantial flexibility in dosing and increase the
potential for the use of platinum drugs. However, an effective oral formulation of
L.-J. Li (&) Á C. Wang Á C. Tian Á X.-Y. Yang Á X.-X. Hua Á J.-L. Du
Chemical Biology Key Laboratory of Hebei Province, Hebei University,
Baoding 071002, People’s Republic of China
e-mail: llj@hbu.edu.cn
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L.-J. Li et al.
cisplatin is not achievable at the clinical level because of its poor water solubility
and low level of bioavailability [8]. Overcoming the adverse effects and eventual
resistance, the Pt(II) compounds should be tailored to meet the various requirements
such as water solubility, chemical stability, biodegradability, tumor targeting,
and so on.
Over the last few decades, transition metal complexes have been well studied for
their application as artificial nucleases, because of their diverse structural features
and the possibility to tune their redox potential through the choice of ligands [9–11].
Transition metal complexes containing Schiff-base ligands and their reduced
products are often used as artificial chemical nucleases and some of such complexes
have proved to be efficient DNA cleavage reagents [12, 13]. Most of the model
studies of the metal complexes of Schiff-base ligands containing salicylaldehyde
and amino acids have focused upon the binding mode of these ligands [14–16].
Structural studies on the metal complexes of reduced Schiff-base ligands, derived
from various amino acids and salicylaldehyde, are well documented [17–19].
Compared to Schiff bases, the corresponding reduced ones are expected to be more
stable and adaptable to form conformationally flexible five- or six-membered rings
upon complexation as they are not constrained to be planar. Although there are
numerous reports on transition metal complexes of reduced Schiff bases derived
from amino acids [17, 20], information on the corresponding derivatives of
platinum(II) is still very scanty. We have prepared a series of reduced amino acid
Schiff bases coordinated to platinum(II), the interaction between salmon sperm
DNA and these water-soluble complexes was investigated by ultraviolet spectrum
and their antitumor activities have also been tested on HL-60, Bel-7402, BGC-823,
and KB cell lines in vitro.
Results and discussion
Ligands 4a–h are synthesized from salicylaldehyde and 5-bromsalicylaldehyde with
L-amino acid: Gly, Phe, Ser, Thr, and Leu. The platinum(II) complexes 5a–h are
prepared by the reaction of K2PtCl4 with reduced amino acid Schiff bases in
CH3OH/H2O at room temperature (See Scheme 1).
Comparison of the IR spectra of the free ligands with that of their Pt(II)
complexes, the (N–H) stretching frequencies were found in free ligands at about
3,370–3,450 cm-1, while in complexes shifted to high wavenumbers at about
3,410–3,480 cm-1. On the other hand, the (COO-)carboxyl asymmetric stretching
frequency and symmetric stretching frequency was found at about
1,580–1,630 cm-1 and 1,450–1,480 cm-1 in the free ligands, whereas shifted to
about 1,600–1,650 cm-1 and 1,380–1,480 cm-1 in the complexes. In the spectra of
a metal complexes, the bands for the phenolic group (C–O) shifted from about
1,250–1,290 cm-1 to 1,260–1,340 cm-1, comparing to the free ligands. New bands
appeared at about 610–630 cm-1, 510–550 cm-1 and 430–480 cm-1 and were may
assigned to tPt–OAr and tPt–N, and tPt–OOC, respectively. The IR spectra of 4g and 5g
was shown in Fig. 1. All of these indicated that nitrogen atoms of the imino groups
123

Platinum(II) complexes
735
R2
N
O
O
NH2
2
CHO
R2
KOH
OK
OH
R1
OH
+
CH3CH2OH
R1
OH
1
3
R2
O
R2
O
NH
O
O
NH OK
OH
K+
NaBH4
CH3OH
K2PtCl4
pH=8~9
Pt
R1
R1
Cl
4
5
a: R1 = H, R2 = H;
b: R1 = H, R2 = benzyl;
d: R1 = H, R2 = Bui;
g: R1 = Br, R2 = Bui;
e: R1 = H, R2 = -CH(OH)CH3; h: R1 = Br, R2 = H;
c: R1 = H, R2 = -CH2OH; f: R1 = Br, R2 = -CH2OH;
Scheme 1 Synthetic pathway for the preparation of compounds
4g
5g
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers (cm-1)
Fig. 1 The IR spectrum of 4g and 5g
and oxygen atoms of the carboxyl groups and phenolic groups are coordinated to the
metal ion (see Table 1).
Although the overall pattern of the 1H NMR spectra of the complexes (5a–h) was
very closely to that of the free ligands, the signals have been shifted to lower fields. The
mass spectra of the complexes (5a–h) have molecular peaks and the elemental analysis
data were in good agreement with the calculated values. The conductivity data of all
complexes were measured. The molar conductance values of platinum(II) complexes
123

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L.-J. Li et al.
Table 1 Main IR absorptions of ligands and complexes (cm-1
)
t (N–H)
tas (COO-)
ts (COO-)
t (ph-O)
t (Pt–OAr)
t (Pt–N)
t (Pt-OOC)
4a
4b
4c
4d
4e
4f
3381
3420
3414
3378
3417
3445
3418
3371
3417
3471
3421
3414
3438
3422
3471
3426
1613
1589
1618
1591
1594
1624
1583
1613
1638
1642
1648
1643
1610
1604
1645
1650
1455
1454
1478
1459
1450
1473
1470
1464
1474
1480
1384
1447
1453
1413
1418
1471
1254
1257
1270
1255
1283
1281
1274
1255
1264
1269
1265
1270
1271
1269
1331
1263
4g
4h
5a
5b
5c
5d
5e
5f
622
616
615
615
632
627
623
617
517
533
525
544
525
512
547
516
476
478
476
477
468
434
480
476
5g
5h
in deionized water are in the range of 1.32–1.60 S cm2 mol-1. All complexes
therefore formulated as 1:1 electrolytes having one non-bonded K? counter ion.
Interaction between complexes and DNA
The interactions between DNA and complexes were characterized by UV spectra.
Some of DNA binding drugs produce direct DNA strand breaks: Some possess
planar multiring chromophores and are also able to bind noncovalently to DNA by
intercalation between base pairs; Other drugs bind into the minor groove of DNA
[21]. In the wavelength range of 200–400 nm, DNA with different concentrations of
complexes (5b, 5c, and 5e) were determined (See Figs. 2, 4). As can be seen from
Fig. 2, there was one positive peak at 258 nm (A = 1.3293) due to the absorption of
DNA. With the increased concentration of complexes 5b (c5b:cDNA = 0.1, 0.3 and
0.5), the absorbance values were increased (A = 1.3906, 1.4730, and 1.5168), and
the abosorption at 258 nm shifted to low wavelength (k = 257, 256 and 255 nm).
Also, in Fig. 3, there was one similar positive peak at 258 nm (A = 1.3563). When
the concentration of complexes 5c (c5c:cDNA = 0.1, 0.3 and 0.5) was increased, the
absorbance values were enhanced (A = 1.3977, 1.4256 and 1.4773); meanwhile,
the abosorption at 258 nm shifted to low wavelength (k = 257, 256, and 256 nm).
In addition, with the same increased concentration of complexes 5e (Fig. 4), the
absorbance values were improved (A = 2.0658, 2.1559, and 2.3337); the abosorp-
tion shifted to low wavelength (k = 257, 256, and 256 nm). It might be due to that
the complex was inserted into the DNA double-helix structure and stacking with
DNA base pairs where p-electron accumulation occurred, thus the absorbance value
increased and maximum absorption wavelength occurred blue-shifted. The results
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Platinum(II) complexes
737
confirmed that hyperchromicity occurred after coordination and the binding mode of
complexes with DNA was might for intercalation [22–24].
In vitro cytotoxic activity
The cytotoxic activities of 5a–h were evaluated against four human cancer cell lines
consisting of HL-60, BGC-823, KB, and Bel-7402, and the results are listed in
Table 2. As shown in Table 2, almost all the complexes (except 5f) exerted
cytotoxic effects against tested carcinoma cell lines with a lower IC50 value
(\50 lM), moreover, they have selectivity against tested carcinoma cell lines.
Complex 5g displayed the best cytotoxicity among the eight complexes against
tested carcinoma cell lines. It can be seen that complex 5g was more active against
BGC-823 and HL-60 cell lines than cisplatin, fairly active against Bel-7402, but less
active than cisplatin against KB cell line. The complexes (5c, 5d, and 5g) were more
active than cisplatin against HL-60 cell line, and the 5g had the best antitumor
activity against HL-60 cell line. The complexes (5b–5e, 5g–5h) demonstrated
higher cytotoxicity than cisplatin against BGC-823 cell line and the 5c had the best
antitumor activity. Only 5g displayed fairly anticancer activity against Bel-7402
compared to cisplain. However, 5a and 5f did not show any better activity than
cisplain against all four cell lines, all the complexes had a little cytotoxicity against
KB cell line in compared with cisplatin.
Conclusions
In this study, eight platinum(II) complexes with reduced amino acid Schiff bases
were synthesized and characterized. All complexes were tested for their DNA
3.0
c5b:cDNA = 0.5
2.5
c5b:cDNA = 0.3
c5b:cDNA = 0.1
2.0
DNA Blank
1.5
1.0
0.5
0.0
200
250
300
350
400
Wavelength (nm)
Fig. 2 Ultraviolet spectrum of interaction between 5b and salmon sperm DNA
123

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L.-J. Li et al.
3.0
2.5
2.0
1.5
1.0
0.5
0.0
c5c:cDNA = 0.5
c5c:cDNA = 0.3
c5c:cDNA = 0.1
DNA Blank
200
250
300
350
400
Wavelength (nm)
Fig. 3 Ultraviolet spectrum of interaction between 5c and salmon sperm DNA
4.0
c5e:cDNA = 0.5
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
c5e:cDNA = 0.3
c5e:cDNA = 0.1
DNA Blank
200
250
300
350
400
Wavelength (nm)
Fig. 4 Ultraviolet spectrum of interaction between 5e and salmon sperm DNA
interaction ability with the salmon sperm DNA using UV. The results informed that
hyperchromicity occurred after coordination and the binding mode of complexes
with DNA was might for intercalation. The in vitro anticancer activities of the
platinum compounds have been validated against the HL-60, KB, BGC-823, and the
Bel-7402 cell lines by the MTT assay and the results show that the complexes
(5a–h) have selectivity against tested carcinoma cell lines. Complex 5g has the best
123

Platinum(II) complexes
739
Table 2 The cytotoxicity of complexes in vitro (IC50
)
Complex
IC50 (lM)
HL-60
BGC-823
KB
Bel-7402
5a
10.71
4.80
2.85
2.24
3.93
34.71
2.83
4.00
2.89
39.78
6.36
3.47
5.30
4.79
84.16
4.63
5.68
6.48
26.03
9.98
7.75
7.35
4.47
91.10
8.60
10.61
2.65
20.74
20.21
33.91
19.25
13.58
253.45
8.26
5b
5c
5d
5e
5f
5g
5h
22.98
8.12
Cisplatin
cytotoxicity among the eight complexes, moreover its cytotoxicity is better than that
of cisplatin against BGC-823 and HL-60 cell lines, and displays close cytotoxic
effect against the Bel-7402 cell line. Platinum(II) complexes with reduced amino
acid Schiff bases might be a promising source of metal-based antitumor agents.
Experimental
All reagents and chemicals were purchased from commercial sources and used as
received. Salicylaldehyde and K2PtCl4 were of chemical grade, L-amino acids were
of analytical grade, and MTT and salmon sperm DNA 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.
Elemental analysis were determined on an Elemental Vario EL III elemental
analyzer. The IR spectra were recorded using KBr pellets and a Perkin-Elmer
Model-683 spectrophotometer. The 1H NMR spectra were recorded in DMSO-d6 on
a Bruker AVIII 600 NMR spectrometer. The mass spectra were measured by Bruker
apex-ultra 7.0T. The interaction between DNA and complexes was measured on a
UV-3400 Toshniwal spectrophotometer. The conductivity values were determined
on a DDSJ-308A conductivity meter. The molar conductivity of 8 9 10-4 mol/L
solutions of the complexes 5a–h in deionized water (K = 0.785 ls/cm) was
measured at 10 °C.
Ligand synthesis: general procedure
5-Bromosalicylaldehyde was synthesized according to a published procedure [25].
Amino acid Schiff bases (3a–h), reduced amino acid Schiff bases (4a–h) were
synthesized according to published procedures [25] and [26], respectively.
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L.-J. Li et al.
Platinum complexes (5a–h) were synthesized in the following method: K2PtCl4
(20 mg, 0.0482 mmol) was added to a CH3OH/H2O (v/v = 1/1, 4 mL) solution of
reduced Schiff bases (4a–h) (0.0461 mmol) at room temperature, the mixture was
adjusted to pH = 8–9 at the beginning, then stirred for 24 h and the pH was down
to about 7. The solution was heated in vacuo and recrystallized from CH3OH/
CH3COOC2H5 with N2 protection.
Potassium 2-(2-hydroxybenzylideneamino)acetate (3a)
1
Light yellow solid (62.21 %): H NMR: d 14.40 (s, 1H, Ar–OH), 8.285 (s, 1H,
–CH=N–), 6.650–7.310 (m, 4H, Ar–H), 3.895 (s, 2H, –CH2–); IR: 3411,
1644(C=N), 1604(COO-)as, 1510, 1384(COO-)s, 1308, 1218(ph-O), 1187, 734,
563, 523 cm-1. Anal. Calc. for C9H8NO3K: C, 49.75; H, 3.71; N, 6.45. Found: C,
49.42; H, 3.95; N, 6.71.
Potassium 2-(2-hydroxybenzylideneamino)-3-phenylpropanoate (3b)
1
Light yellow solid (80.30 %): H NMR: d 14.30 (s, 1H, Ar–OH), 8.09 (s, 1H,
–CH=N–), 7.180–7.220 (m, 4H, Ar–H), 6.650–7.170 (m, 5H, Ar–H), 3.800–3.840
(dd, 1H, CH–H), 3.260–3.300 (dd, 1H, CH–H), 2.900–2.950 (dd, 1H, C–H); IR:
3406, 1630(C=N), 1605(COO-)as, 1512, 1371(COO-)s, 1215(ph-O), 1145, 1074,
743, 700, 477 cm-1. Anal. Calc. for C16H14NO3K: C, 62.52; H, 4.59; N, 4.56.
Found: C, 62.35; H, 4.25; N, 4.80.
Potassium 3-hydroxy-2-(2-hydroxybenzylideneamino)propanoate (3c)
Light yellow solid (78.01 %): 1H NMR: d 14.20 (s, 1H, Ar–OH), 8.35 (s, 1H, –CH=
N–), 6.69–7.35 (m, 4H, Ar–H), 3.681–3.702 (t, 1H, C–H), 3.544–3.572 (dd, 1H, CH–
H), 3.727–3.754 (dd, 1H, CH–H); IR: 3175, 1633(C=N), 1609(COO-)as, 1493,
1382(COO-)s, 1233(ph-O), 1147, 1094, 758, 727, 672, 567 cm-1. Anal. Calc. for
C10H10NO4K: C, 48.57; H, 4.08; N, 5.66. Found: C, 48.72; H, 4.42; N, 5.31.
Potassium 2-(2-hydroxybenzylideneamino)-4-methylpentanoate (3d)
1
Light yellow solid (70.14 %): H NMR: d 14.50 (s, 1H, Ar–OH), 8.364 (s, 1H,
–CH=N–), 6.660–7.320 (m, 4H, Ar–H), 3.700–3.723 (dd, 1H, N–CH–), 1.692–1.737
(m, 1H, –CH–H), 1.571–1.618 (m, 1H, –CH–H), 1.485–1.551 (m, 1H, CH3–C–H),
0.879–0.890 (d, 3H, –CH3), 0.849–0.859 (d, 3H, –CH3); IR: 3422, 1640(C=N),
1604(COO-)as, 1516, 1374(COO-)s, 1217(ph-O), 1142, 1018, 741, 578, 539 cm-1
.
Anal. Calc. for C13H16NO3K: C, 57.12; H, 5.90; N, 5.12. Found: C, 57.41; H, 5.47;
N, 5.44.
Potassium 3-hydroxy-2-(2-hydroxybenzylideneamino)butanoate (3e)
1
Light yellow solid (58.33 %): H NMR: d 14.33 (s, 1H, Ar–OH), 8.37 (s, 1H,
–CH=N–), 6.74–7.36 (m, 4H, Ar–H), 1.031–1.041 (d, 3H, CH3), 3.815–3.852 (m,
123

Platinum(II) complexes
741
1H, O–CH–), 3.618–3.624 (d, 1H, N–CH–); IR: 3382, 1638(C=N), 1609(COO-)as,
1513, 1375(COO-)s, 1280, 1225(ph-O), 1128, 1005, 762, 697 cm-1. Anal. Calc. for
C11H12NO4K: C, 50.56; H, 4.63; N, 5.36. Found: C, 50.22; H, 4.97; N, 5.14.
Potassium 2-(5-bromo-2-hydroxybenzylideneamino)-3-hydroxypropanoate (3f)
1
Light yellow solid (62.49 %): H NMR: d 8.299 (s, 1H, –CH=N–), 6.618–7.507
(m, 3H, Ar–H), 3.739–3.766 (dd, 1H, –CH–H), 3.521–3.550 (dd, 1H, –CH–H),
3.700–3.721 (t, 1H, N–CH–); IR: 3424, 1638(C=N), 1607(COO-)as, 1485,
1378(COO-)s, 1308, 1230(ph-O), 1164, 1025, 826, 775, 617 cm-1. Anal. Calc.
for C10H9NO4BrK: C, 36.82; H, 2.78; N, 4.29. Found: C, 36.48; H, 2.54; N, 4.57.
Potassium 2-(5-bromo-2-hydroxybenzylideneamino)-4-methylpentanoate (3g)
1
Light yellow solid (74.52 %): H NMR: d 8.323 (s, 1H, –CH=N–), 6.585–7.479
(m, 3H, Ar–H), 3.706–3.728 (dd, 1H, N–CH–), 1.684–1.729 (m, 1H, –CH–H),
1.553–1.599 (m, 1H, –CH–H), 1.481–1.527 (m, 1H, –CH–), 0.872–0.883 (d, 3H, –
CH3), 0.849–0.860 (d, 3H, –CH3); IR: 3432, 1638(C=N), 1613 (COO-)as, 1493,
1378(COO-)s, 1219(ph-O), 1062, 1018, 868, 827, 615, 560 cm-1. Anal. Calc. for
C13H15NO3BrK: C, 44.32; H, 4.29; N, 3.98. Found: C, 44.06; H, 4.57; N, 3.64.
Potassium 2-(5-bromo-2-hydroxybenzylideneamino)acetate (3h)
1
Light yellow solid (81.02 %): H NMR: d 8.314 (s, 1H, –CH=N–), 6.712–7.603
(m, 3H, Ar–H), 4.290 (s, 2H, –CH2–); IR: 3428, 1630(C=N), 1612(COO-)as, 1483,
1374(COO-)s, 1310, 1224(ph-O), 1056, 837, 725 cm-1. Anal. Calc. for
C9H7BrNO3K: C, 36.50; H, 2.38; N, 4.73. Found: C, 36.31; H, 2.57; N, 4.45.
Potassium 2-(2-hydroxybenzylamino)acetate (4a)
1
White solid (82.01 %): H NMR: d 6.916–6.951 (m, 2H, Ar–H), 6.509–6.523 (d,
1H, Ar–H), 6.421–6.440 (t, 1H, Ar–H), 3.587 (s, 2H, Ar–CH2), 2.895 (s, 2H, –CH2–);
IR: 3381(N–H), 2367, 1613(COO-)as, 1455(COO-)s, 1254(ph-O), 1163, 1071, 930,
756, 727 cm-1. Anal. Calc. for C9H10NO3K: C, 49.30; H, 4.60; N, 6.39. Found: C,
49.52; H, 3.92; N, 6.64.
Potassium 2-(2-hydroxybenzylamino)-3-phenylpropanoate (4b)
White solid (87.04 %): 1H NMR: d 7.131–7.243 (m, 5H, Ar–H), 6.494–6.985
(m, 4H, Ar–H), 3.712–3.733 (d, 1H, Ar–CH–H), 3.319–3.339 (d, 1H, Ar–CH–H),
3.016–3.037 (m, 2H, –CH2–), 2.595–2.631 (dd, 1H, N–CH–); IR: 3420(N–H),
1589(COO-)as, 1454(COO-)s, 1398, 1257(ph-O), 1017, 866, 754, 700 cm-1. Anal.
Calc. for C16H16NO3K: C, 62.11; H, 5.21; N, 4.53. Found: C, 62.53; H, 4.97; N,
5.61.
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L.-J. Li et al.
Potassium 3-hydroxy-2-(2-hydroxybenzylamino)propanoate (4c)
1
White solid (80.11 %): H NMR: d 6.705–7.173 (m, 4H, Ar–H), 3.969–3.991 (d,
1H, Ar–CH–H), 3.300–3.352 (d, 1H, Ar–CH–H), 1.693–1.772 (m, 1H, –CH–),
3.244–3.272 (dd, 1H, CH–H), 3.527–3.554 (dd, 1H, CH–H); IR: 3414(N–H),
1618(COO-)as, 1478(COO-)s, 1406, 1270(ph-O), 1129, 1037, 875, 759 cm-1
.
Anal. Calc. for C10H12NO4K: C, 48.18; H, 4.85; N, 5.62. Found: C, 47.89; H, 4.48;
N, 5.81.
Potassium 2-(2-hydroxybenzylamino)-4-methylpentanoate (4d)
1
White solid (84.13 %): H NMR: d 6.614–7.048 (m, 4H, Ar–H), 3.773–3.794 (d,
1H, Ar–CH–H), 3.494–3.516 (d, 1H, Ar–CH–H), 2.761–2.785 (dd, 1H, N–CH–),
1.698–1.777 (m, 1H, –CH–), 1.367–1.412 (m, 1H, CH–H), 1.217–1.263 (m, 1H,
CH–H), 0.807–0.818 (d, 3H, –CH3), 0.844–0.855 (d, 3H, –CH3); IR: 3378(N–H),
1591(COO-)as, 1459(COO-)s, 1336, 1255(ph-O), 1117, 1003, 941, 826, 753 cm-1
.
Anal. Calc. for C13H18NO3K: C, 56.70; H, 6.59; N, 5.09. Found: C, 56.43; H, 6.76;
N, 5.46.
Potassium 3-hydroxy-2-(2-hydroxybenzylamino)butanoate (4e)
1
White solid (81.07 %): H NMR: d 6.670–7.290 (m, 4H, Ar–H), 3.935–3.957 (d,
1H, Ar–CH–H), 3.660–3.682 (d, 1H, Ar–CH–H), 2.978–2.990 (d, 1H, N–CH–),
3.804–3.837 (q, 1H, O–CH), 1.053–1.142 (m, 3H, –CH3); IR: 3417(N–H),
1594(COO-)as, 1450(COO-)s, 1347, 1283(ph-O), 1114, 978, 878, 757 cm-1
.
Anal. Calc. for C11H14NO4K: C, 50.17; H, 5.36; N, 5.32. Found: C, 50.37; H, 5.52;
N, 5.14.
Potassium 2-(5-bromo-2-hydroxybenzylamino)-3-hydroxypropanoate (4f)
1
White solid (78.17 %): H NMR: d 6.427–7.055 (m, 3H, Ar–H), 3.679–3.731 (m,
2H, Ar–CH2–), 3.554–3.582 (t, 1H, CH–H), 3.350–3.379 (t, 1H, CH–H),
2.793–2.815 (t, 1H, –CH–); IR: 3445(N–H), 1624(COO-)as, 1473(COO-)s,
1407, 1281(ph-O), 1102, 873, 820 cm-1. Anal. Calc. for C10H11BrNO4K: C,
36.60; H, 3.38; N, 4.27. Found: C, 36.32; H, 3.51; N, 4.71.
Potassium 2-(5-bromo-2-hydroxybenzylamino)-4-methylpentanoate (4g)
1
White solid (83.12 %): H NMR: d 7.064–7.558 (m, 3H, Ar–H), 4.395–4.417 (d,
1H, Ar–CH–H), 3.946–3.968 (d, 1H, Ar–CH–H), 3.507–3.530 (dd, 1H, N–CH),
2.203–2.259 (m, 1H, –CH–), 1.981–2.025 (m, 1H, CH–H), 1.842–1.888 (m, 1H,
CH–H), 1.310–1.321 (d, 3H, –CH3), 1.284–1.295 (d, 3H, –CH3); IR: 3418(N–H),
1583(COO-)as, 1470(COO-)s, 1404, 1274(ph-O), 1120, 1037, 999, 819, 770 cm-1
.
Anal. Calc. for C13H17BrNO3K: C, 44.07; H, 4.84; N, 3.95. Found: C, 44.31; H,
4.53; N, 3.66.
123

Platinum(II) complexes
743
Potassium 2-(5-bromo-2-hydroxybenzylamino)acetate (4h)
1
White solid (81.02 %): H NMR: d 6.564–7.140 (m, 3H, Ar–H), 3.625 (s, 2H, Ar–
CH2), 2.835 (s, 2H, CO–CH2), 1.608 (s, 1H, NH); IR: 3371(N–H), 1613(COO-)as,
1464(COO-)s, 1409, 1255(ph-O), 1007, 816 cm-1. Anal. Calc. for C9H9BrNO3K:
C, 36.25; H, 3.04; N, 4.70. Found: C, 36.53; H, 3.41; N, 4.52.
K[Pt(2-(2-hydroxybenzylamino)acetoxyl)Cl] (5a)
Yellow Solid (63.46 %): 1H NMR: d 6.464–6.997 (m, 4H, Ar–H), 3.598 (s, 2H, Ar–
CH2), 2.889 (s, 2H, –CH2–); IR: 3417(N–H), 1638(COO-)as, 1474(COO-)s, 1404,
1342, 1264(ph-O), 1026, 622(Pt–OAr), 517(Pt–N), 476(Pt–OOC) cm-1. ESI–MS:
471.9433 [M ? Na]?. Anal. Calc. for C9H9ClNO3KPt: C, 24.09; H, 2.02; N, 3.12.
Found: C, 24.33; H, 2.45; N, 3.22. Km = 1.36 S cm2 mol-1
.
K[Pt(2-(2-hydroxybenzylamino)-3-phenylpropanyloxy)Cl] (5b)
1
Yellow Solid (65.78 %): H NMR: d 7.124–7.238 (m, 5H, Ar–H), 6.536–7.028
(m, 4H, Ar–H), 3.720–3.742 (d, 1H, Ar–CH–H), 3.326–3.348 (d, 1H, Ar–CH–H),
3.012–3.035 (m, 2H, –CH2–), 2.598–2.636 (dd, 1H, N–CH–); IR: 3471(N–H),
1642(COO-)as, 1480(COO-)s, 1372, 1269(ph-O), 1151, 1030, 867, 754, 616(Pt–
OAr), 533 (Pt–N), 478(Pt–OOC) cm-1. ESI–MS: 561.9934 [M ? Na]?. Anal. Calc.
for C16H15ClNO3KPt: C, 35.66; H, 2.81; N, 2.60. Found: C, 35.24; H, 2.51; N, 2.33.
Km = 1.41 S cm2 mol-1
.
K[Pt(3-hydroxy-2-(2-hydroxybenzylamino)propionyloxy)Cl] (5c)
1
Yellow Solid (66.41 %): H NMR: d 6.736–7.208 (m, 4H, Ar–H), 3.974–3.995 (d,
1H, Ar–CH–H), 3.306–3.359 (d, 1H, Ar–CH–H), 1.688–1.768 (m, 1H, –CH–),
3.242–3.268 (dd, 1H, CH–H), 3.524–3.552 (dd, 1H, CH–H); IR: 3421(N–H),
1648(COO–)as, 1384(COO–)s, 1265(ph-O), 615(Pt–OAr), 525(Pt–N), 476(Pt–
OOC) cm-1. ESI–MS: 501.9556 [M ? Na]?. Anal. Calc. for C10H11ClNO4KPt:
C, 25.08; H, 2.32; N, 2.93. Found: C, 25.31; H, 2.57; N, 2.58. Km
1.32 S cm2 mol-1
=
.
K[Pt(2-(2-hydroxybenzylamino)-4-methylpentanyloxy)Cl] (5d)
1
Yellow Solid (70.32 %): H NMR (600 M Hz, DMSO-d6): d 6.636–7.081 (m, 4H,
Ar–H), 3.760–3.795 (q, 1H, Ar–CH–H), 3.491–3.525 (q, 1H, Ar–CH–H),
2.524–2.530 (t, 1H, N–CH–), 1.603 (s, 1H, NH), 0.883–0.906 (m, 1H, –CH–),
1.220–1.254 (m, 1H, CH–H), 1.047–1.085 (m, 1H, CH–H), 0.655–0.859 (m, 6H,
CH3); IR: 3414(N–H), 2957, 1643(COO-)as, 1447(COO-)s, 1270(ph-O), 1027,
758, 615(Pt–OAr), 544(Pt–N), 477(Pt–OOC) cm-1. ESI–MS: 528.0074 [M ? Na]?.
Anal. Calc. for C13H17ClNO3KPt: C, 30.92; H, 3.39; N, 2.77. Found: C, 31.21; H,
3.52; N, 2.43. Km = 1.47 S cm2 mol-1
.
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744
L.-J. Li et al.
K[Pt(3-hydroxy-2-(2-hydroxybenzylamino)butanyloxy)Cl] (5e)
1
Yellow Solid (68.44 %): H NMR: d 6.712–7.336 (m, 4H, Ar–H), 3.944–3.968
(d, 1H, Ar–CH–H), 3.665–3.688 (d, 1H, Ar–CH–H), 2.974–2.985 (d, 1H, N–CH–),
3.802–3.838 (q, 1H, O–CH), 1.051–1.139 (m, 3H, –CH3); IR: 3438(N–H),
1610(COO-)as, 1453(COO-)s, 1385, 1271(ph-O), 1117, 874, 759, 632(Pt–OAr),
525(Pt–N), 468(Pt–OOC) cm-1. ESI–MS: 476.0235 [M ? Na]?. Anal. Calc. for
C11H13ClNO4KPt: C, 26.81; H, 2.66; N, 2.84. Found: C, 26.52; H, 2.84; N, 2.51.
Km = 1.48 S cm2 mol-1
.
K[Pt(2-(5-bromo-2-hydroxybenzylamino)-3-hydroxypropanyloxy)Cl] (5f)
1
Yellow Solid (60.27 %): H NMR: d 6.468–7.096 (m, 3H, Ar–H), 3.689–3.748
(m, 2H, Ar–CH2–), 3.551–3.579 (t, 1H, CH–H), 3.347–3.375 (t, 1H, CH–H),
2.795–2.818 (t, 1H, –CH–); IR: 3422(N–H), 2169, 1604(COO-)as, 1413(COO-)s,
1269(ph-O), 1161, 819, 627(Pt–OAr), 512(Pt–N), 434(Pt–OOC) cm-1. ESI–MS:
579.8648 [M ? Na]?. Anal. Calc. for C10H10BrClNO4KPt: C, 21.54; H, 1.81; N,
2.51. Found: C, 21.35; H, 1.64; N, 2.77. Km = 1.42 S cm2 mol-1
.
K[Pt(2-(5-bromo-2-hydroxybenzylamino)-4-methylpentanyloxy)Cl] (5g)
1
Yellow Solid (64.45 %): H NMR: d 7.106–7.613 (m, 3H, Ar–H), 4.408–4.431 (d,
1H, Ar–CH–H), 3.956–3.977 (d, 1H, Ar–CH–H), 3.504–3.525 (dd, 1H, N–CH),
2.205–2.263 (m, 1H, –CH–), 1.984–2.030 (m, 1H, CH–H), 1.838–1.882 (m, 1H,
CH–H), 1.313–1.325 (d, 3H, –CH3), 1.286–1.297 (d, 3H, –CH3); IR: 3471(N–H),
2957, 1645(COO-)as, 1418(COO-)s, 1331(ph-O), 1120, 1024, 822, 623(Pt–OAr),
547(Pt–N), 480(Pt–OOC) cm-1. ESI–MS: 605.9154 [M ? Na]?. Anal. Calc. for
C13H16BrClNO3KPt: C, 26.75; H, 2.76; N, 2.40. Found: C, 26.41; H, 2.89; N, 2.13.
Km = 1.43 S cm2 mol-1
.
K[Pt(2-(5-bromo-2-hydroxybenzylamino)acetoxyl)Cl] (5h)
1
Yellow Solid (61.13 %): H NMR: d 6.610–7.188 (m, 3H, Ar–H), 3.637 (s, 2H,
Ar–CH2), 2.841 (s, 2H, CO–CH2); IR: 3426(N–H), 2921, 1650(COO-)as,
1471(COO-)s, 1263(ph-O), 1122, 1027, 820, 617(Pt–OAr), 516(Pt–N), 476(Pt–
OOC) cm-1. ESI–MS: 549.8545 [M ? Na]?. Anal. Calc. for C9H8BrClNO3KPt:
C, 20.48; H, 1.53; N, 2.65. Found: C, 20.14; H, 1.82; N, 2.33. Km
1.60 S cm2 mol-1
=
.
Determination of UV absorption spectra
An UV-3400 Toshniwal spectrophotometer emitting UV light was used mainly
between 200 and 400 nm. The salmon sperm DNA (M = 208.8 g/mol) was
dissolved in Tris–HCl (pH = 7.5) buffer solution, and rested in 24 h at 4 °C. Then
complexes (5b, 5c, and 5e) were added in buffer solution in different concentrations
123

Platinum(II) complexes
745
(ccomplex:cDNA) = 0.1, 0.3, and 0.5), and rested in 24 h at 4 °C again. The UV
absorption spectra was determined at room temperature (Dt = 1 s, n = 3.).
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 U/mL of penicillin, and 100 lg/mL of streptomycin. Cells were maintained at
37 °C in a humidified atmosphere of 5 % CO2 in air.
Solutions
The complexes were dissolved in DMSO at a concentration of 5 mM as stock
solution, and diluted in culture medium at concentrations of 0.1, 1.0, and 10 lM as
working solution. To avoid DMSO toxicity, the concentration of DMSO was less
than 0.1 % (v/v) in all experiments.
Cytotoxicity analysis
The 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 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 [27]. Upon completion of the incubation for 44 h, stock MTT
dye solution (20 mL, 5 mg/mL) 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 a wavelength of 570 nm.
The IC50 value was determined from plot of % viability against dose of compounds
added.
Acknowledgments This work was supported by the Natural Science Foundation of Hebei Province
(No. B2010000223) and Doctoral fundation of Hebei University (No. 2009-164).
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