Synthesis, characterization and cytotoxicity of gold(III) complexes with deprotonated pyridyl carboxamide

Article abstract of DOI:10.1002/aoc.2888

Six new gold(III) complexes [Au(bzpam)Cl₂] (1, bzpamH = N-benzyl picolinamide), [Au(hetpam)Cl₂] (2, hetpamH = N-(2-hydroxyethyl) picolinamide), [Au(pypam)Cl]AuCl₄ (3, pypamH = N-(pyridin-2-ylmethyl) picolinamide), [Au(dmepam)Cl]AuCl₄ (4, dmepamH = N-(2-(dimethylamino)ethyl) picolinamide), [Au(bhetpydam)Cl] (5, bhetpydamH ₂ = N,N'-bis(2-hydroxyethyl) pyridine- 2,6-dicarboxamide) and [Au₂(hedam)Cl₄] (6, hedamH₂ = N,N'-(hexane-1,6-diyl) dipicolinamide) with deprotonated pyridyl carboxamide were synthesized and characterized by elemental analysis, molar conductivity, IR, H¹ NMR and C¹³ NMR techniques. The analytical data showed that deprotonated pyridyl carboxamide coordinated with gold(III) ions through a nitrogen atom. The cytotoxicity against Bel-7402 and HL-60 cell lines was tested by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and SRB (sulforhodamine B) assays. The results indicated that the complexes exerted cytotoxic effects against Bel-7402 and HL-60 cell lines, complex 6 had better cytotoxicity than cisplatin, and complex 3 displayed similar cytotoxicity to cisplatin against Bel-7402 cell line. The results suggested that the characteristics of ligands had an important effect on cytotoxicity of complexes. Copyright

Full text of DOI:10.1002/aoc.2888

Full Paper
Received: 19 October 2011
Revised: 12 April 2012
Accepted: 26 April 2012
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.2888
Synthesis, characterization and cytotoxicity of
gold(III) complexes with deprotonated pyridyl
carboxamide
Shuxiang Wanga*, Yanan Shia, Wenqing Shaoa, Jianlong Dua, Haiying Weia,
Jinchao Zhanga*, Ke Wangb, Shigang Shena, Shenghui Lia, Jitai Lia and
Yangyang Zhaoa
Six new gold(III) complexes [Au(bzpam)Cl2] (1, bzpamH = N-benzyl picolinamide), [Au(hetpam)Cl2] (2, hetpamH = N-(2-
hydroxyethyl) picolinamide), [Au(pypam)Cl]AuCl4 (3, pypamH = N-(pyridin-2-ylmethyl) picolinamide), [Au(dmepam)Cl]
AuCl4 (4, dmepamH = N-(2-(dimethylamino)ethyl) picolinamide), [Au(bhetpydam)Cl] (5, bhetpydamH2 = N,N0-bis(2-hydro-
xyethyl) pyridine- 2,6-dicarboxamide) and [Au2(hedam)Cl4] (6, hedamH2 = N,N0-(hexane-1,6-diyl) dipicolinamide) with
deprotonated pyridyl carboxamide were synthesized and characterized by elemental analysis, molar conductivity, IR,
H1 NMR and C13 NMR techniques. The analytical data showed that deprotonated pyridyl carboxamide coordinated
with gold(III) ions through a nitrogen atom. The cytotoxicity against Bel-7402 and HL-60 cell lines was tested by MTT
(3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and SRB (sulforhodamine B) assays. The results indicated
that the complexes exerted cytotoxic effects against Bel-7402 and HL-60 cell lines, complex 6 had better cytotoxicity
than cisplatin, and complex 3 displayed similar cytotoxicity to cisplatin against Bel-7402 cell line. The results suggested
that the characteristics of ligands had an important effect on cytotoxicity of complexes. Copyright © 2012 John Wiley &
Sons, Ltd.
Keywords: gold(III) complex; deprotonated amide; cytotoxicity
within the ’metals in medicine’ community owing to their
Introduction
outstanding antiproliferative properties,[13–15] and are being
Nowadays cisplatin and its derivatives are the most widely used
clinical anticancer drugs. However, they have several major
drawbacks. Common problems include cumulative toxicities of
nephrotoxicity and ototoxicity.[1,2] In addition to the serious side
effects, the therapeutic efficacy is also limited by inherent or
treatment-induced resistant tumor cells.[3,4] These drawbacks
have provided the motivation for alternative chemotherapeutic
strategies.
intensely investigated as a rich source of innovative cytotoxic
drugs for cancer treatment.[16–18] We previously reported
cytotoxic properties of eight gold(III) complexes of 5-aryl-3-(pyridin-
2-yl)-4,5-dihydropyrazole-1-carbothioamide (with one Au-S and
two Au-N bonds). Five of these complexes have better
cytotoxicity than cisplatin against HeLa cell line. The structure
and properties of ligands show an important influence on
cytotoxicity of complexes.[15]
In the search of new therapies avoiding these drawbacks,
special attention has been paid to gold(III) complexes because
they show chemical features that are very close to those of
clinically employed platinum(II) complexes, such as the prefer-
ence for square-planar coordination and the typical d8 electronic
configuration. However, the high redox potential and relatively
poor stability of gold(III) compounds make their use rather
problematic under physiological conditions. In recent years, by
implementation of appropriate ligand selection strategies, a
number of gold(III) compounds have been obtained, exhibiting
sufficient stability under physiological-like conditions and
manifesting cytotoxic properties in vitro. The main types of gold
(III) complexes have shown activity as follows: coordination
compounds with N-polydentate, macrocyclic ligands, bioligands
or dithiocarbamato ligands;[5–8] organometallic compounds with
an Au-C bond or CNC-pincer backbone.[9–12] Most of the above-
mentioned compounds turned out to be highly cytotoxic, with
IC50 values generally falling in the low micromolar range. There-
fore, gold compounds are drawing a great deal of attention
It has been reported that deprotonated amide as ligands could
decrease the redox potential of the gold(III) center and thereby
stabilize the gold(III) complexes.[19–22] In order to further explore
the structure–activity relationships and discover new metal-
based anticancer drugs, the synthesis, characterization and
cytotoxicity of six new gold(III) complexes with deprotonated
pyridyl carboxamide ligands are described in the present work
for the first time. The results of the cytotoxicity experiments
*
Correspondence to: Shuxiang Wang, Jinchao Zhang, Chemical Biology Key
Laboratory of Hebei Province, College of Chemistry and Environmental Science,
Hebei University, Baoding 071002, Hebei, People’s Republic of China. E-mail:
wsx@hbu.edu.cn(S. Wang); jczhang6970@yahoo.com.cn(J. Zhang)
a Chemical Biology Key Laboratory of Hebei Province, College of Chemistry and
Environmental Science, Hebei University, Baoding 071002, People’s Republic
of China
b Shijiazhuang Center for Disease Control and Prevention, Shijiazhuang 050011,
Hebei, People’s Republic of China
Appl. Organometal. Chem. (2012)
Copyright © 2012 John Wiley & Sons, Ltd.

Shuxiang Wang et al.
indicate that the gold(III) complexes with deprotonated pyridyl
carboxamide ligands exerted cytotoxic effects against Bel-7402
and HL-60 cell lines, and the structural characteristic of ligands
had an influence on cytotoxicity of complexes.
was added. The mixture was heated to 70 ꢃC and kept for 6 h,
and the resulting red precipitate was filtered. The collected solid
was recrystallized in acetonitrile to give 2. Red solid; yield 77.4%;
IR (KBr, cmꢁ1) 3730 (O-H), 3109–3030 (C-H, py), 1639 (C = O), 1633
(C = C), 1604 (C = N), 418 (Au-N); UV (acetonitrile, nm) 205 (C = O),
212 (C = N), 260 (C = C), 310 (LMCT); 1 H NMR (600 MHz, DMSO-d6)
d 9.31 (d, J = 6.0 Hz, 1 H, 6-H, py), 8.51 (dd, J = 7.8 Hz, 7.8 Hz, 1 H,
4-H, py), 8.03 (dd, J = 7.8 Hz, 6.0 Hz, 1 H, 5-H, py), 7.99 (d, J = 7.8 Hz,
1 H, 3-H, py), 4.69 (brs, 1 H, OH), 3.57 (t, J = 6.0 Hz, 2 H, NCH2), 3.52
(t, J = 6.0 Hz, 2 H, CH2O); 13 C NMR (150 MHz, DMSO-d6) d 49.0
(-N-CH2-), 59.9 (-CH2OH), 128.6 (3-C, py), 130.4 (5-C, py), 145.4
(4-C, py), 145.5 (6-C, py), 149.3 (2-C, py), 171.5 (-CON-); Anal. Calcd
for C8H9N2O2AuCl2: C, 22.19; H, 2.09; N, 6.47. Found: C, 22.11; H,
2.03; N, 6.12; Λm (acetonitrile, S m2 molꢁ1) 3.1.
Experimental
Materials
All chemicals and reagents were of analytical grade. RPMI-1640
medium, trypsin and fetal bovine serum were purchased
from Gibco. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
bromide (MTT), sulforhodamine B (SRB), benzyl penicillin and
streptomycin were from Sigma. Two different human carcinoma
cell lines
– HL-60 (immature granulocyte leukemia) and
[Au(pypam)Cl]AuCl4 (3)
Bel-7402 (liver carcinoma) – were obtained from the American
To a rapidly stirred solution of K[AuCl4]ꢂH2O (80 mg, 0.2 mmol) in
1.5 ml H2O, the solution of L3 (21 mg, 0.1 mmol) in 1.5 ml EtOH
was added. The mixture was heated to 70 ꢃC and kept for 6 h,
and the resulting yellow precipitate was filtered. The collected
solid was recrystallized in acetonitrile to give 3. Yellow solid;
yield 79.4%, IR (KBr, cmꢁ1): 3103–2927 (C-H, py), 1665 (C = O),
1635 (C = C), 1607 (C = N), 411 (Au-N); UV (acetonitrile, nm): 198
(C = O), 214 (C = N), 263 (C = C), 320 (LMCT); 1 H NMR (600 MHz,
DMSO-d6) d 9.13 (d, J = 6.0 Hz, 1 H, 6-H, pyridyl carboxamide),
9.04 (d, J = 6.0 Hz, 1 H, 60-H, py), 8.64 (dd, J = 7.8 Hz, 6.0 Hz,
1 H, 4-H, pyridyl carboxamide), 8.50 (dd, J = 7.8 Hz, 6.0 Hz, 1 H, 40-
H, py), 8.15 (td, J = 8.4 Hz, 1.2 Hz, 1 H, 5-H, pyridyl carboxamide),
8.12 (dd, J = 7.8 Hz, 7.8 Hz, 1 H, 50-H, py), 8.08 (d, J = 7.8 Hz, 1 H,
3-H, pyridyl carboxamide), 8.02 (d, J = 7.8 Hz 1 H, 30-H, py), 5.40
(s, 2 H, CH2); 13 C NMR (150 MHz, DMSO-d6) d 40.5 (CH2), 123.5
(2 C, 3,30-C, py), 128.9 (2 C, 5,50-C, py), 139.2 (2 C, 4,40-C, py),
148.6 (2 C, 6,60-C, py), 149.5 (2 C, 2,20-C, py), 162.2 (-CON-); Anal.
Calcd for C12H10N3OAu2Cl5: C, 18.40; H, 1.29; N, 5.36. Found: C,
18.48; H, 1.04; N, 4.89; Λm (acetonitrile, S m2 molꢁ1) 145.4.
Type Culture Collection.
Analytical and Physical Measurements
Elemental analyses were determined on an Elementar Vario EL III
elemental analyzer. Conductivity measurements were made on
freshly prepared 1 ꢀ 10ꢁ3 mol lꢁ1 solutions in acetonitrile or
DMF at room temperature using a DDS-12DW type conductivity
meter. IR spectra were recorded using KBr pellets and a PerkinElmer
model 683 spectrophotometer. UV–visible spectra at room temper-
ature were measured in acetonitrile solution using a TU-1901
double-beam UV–visible spectrophotometer (Beijing Purkinje
General Instrument Co., Ltd). 1 H NMR and 13 C NMR spectra were
recorded on a Bruker AVIII 600 NMR spectrometer. Optical density
(OD) was measured on a microplate spectrophotometer (Bio-Rad
Model 680, USA).
Preparation of Ligands and Gold(III) Complexes
Ligands L1–L6 were prepared as described in the literature.[23–27]
Gold(III) complexes were prepared by the reaction of pyridyl
carboxamides with K[AuCl4]ꢂH2O in a mixture of C2H5OH/H2O (v/v, 1:1).
[Au(dmepam)Cl]AuCl4 (4)
To a rapidly stirred solution of K[AuCl4]ꢂH2O (80 mg, 0.2 mmol) in
1.5 ml H2O, the solution of L4 (19 mg, 0.1 mmol) in 1.5 mL EtOH
was added. The mixture was heated to 70 ꢃC and kept for 6 h,
and the resulting yellow precipitate was filtered. The collected
solid was recrystallized in acetonitrile to give 4. Yellow solid;
yield 76.9%; IR (KBr, cmꢁ1): 3116–2928 (C-H, py), 1671 (C = O),
1659 (C = C), 1607 (C = N), 422 (Au-N); UV (acetonitrile, nm): 195
(C = O), 214 (C = N), 265 (C = C), 314 (LMCT); 1 H NMR (600 MHz,
DMSO-d6) d 9.00 (d, J = 6.0 Hz, 1 H, 6-H, py), 8.59 (dd, J = 7.8 Hz,
7.8 Hz, 1 H, 4-H, py), 8.06 (dd, J = 7.8 Hz, 6.0 Hz, 1 H, 5-H, py), 8.04
(d, J = 7.8 Hz, 1 H, 3-H, py), 3.66 (t, J = 6.0 Hz, 2 H,-CONCH2-), 3.61
(t, J = 6.0 Hz, 2 H,-CH2NMe2), 3.25 (s, 6 H, 2CH3); 13 C NMR
(150 MHz, DMSO-d6) d 41.1 (CH2), 43.4 (CH3), 57.0 (CH2), 128.9
(3-C, py), 130.7 (5-C, py), 145.5 (4-C, py), 145.8 (6-C, py), 149.8
(2-C, py), 172.2 (-CON-); Anal. Calcd for C10H14N3OAu2Cl5: C,
15.73; H, 1.85; N, 5.50. Found: C, 16.15; H, 1.76; N, 5.30; Λm (aceto-
nitrile, S m2 molꢁ1) 155.2.
[Au(bzpam)Cl2] (1)
To a rapidly stirred solution of K[AuCl4].H2O (40 mg, 0.1 mmol) in
1.5 ml H2O, the solution of L1 (21 mg, 0.1 mmol) in 1.5 ml EtOH
was added. The mixture was heated to 70 ꢃC and kept for 6 h,
and the resulting red precipitate was filtered. The collected solid
was recrystallized in acetonitrile to give 1. Red solid; yield 77.6%;
IR (KBr, cmꢁ1) 3101–3056 (C-H, py), 1639 (C = O), 1633 (C = C),
1604 (C = N), 421 (Au-N); UV (acetonitrile, nm) 200 (C = O), 208
(C = N), 260 (C = C), 310 (LMCT); 1 H NMR (600MHz, DMSO-d6) d
9.31 (d, J = 6.0Hz, 1 H, 6-H, py), 8.52 (dd, J = 7.8 Hz, 7.8Hz, 1 H, 4-H,
py), 8.04 (dd, J = 7.8Hz, 6.0 Hz, 1 H, 5-H, py), 8.01 (d, J = 7.8Hz, 1 H,
3-H, py), 7.40 (d, J = 7.8Hz, 2 H, 20,60-H, ph), 7.25 (dd, J = 7.8Hz,
7.8 Hz, 2 H, 30,50-H, ph), 7.20 (dd, J = 7.8Hz, 7.8Hz, 1 H, 40-H, ph),
4.74 (s, 2 H, CH2); 13 C NMR (150 MHz, DMSO-d6) d 49.5 (CH2),
126.5 (40-C, ph), 127.0 (20,60-C, ph), 128.0 (30,50-C, ph), 128.3 (3-C,
py), 130.0 (5-C, py), 139.3 (10-C, ph), 145.0 (4-C, py), 145.1 (6-C, py),
148.4 (2-C, py), 171.1 (-CON-); Anal. Calcd for C13H11N2OAuCl2:
C, 32.57; H, 2.30; N, 5.84. Found: C, 32.55; H, 2.18; N, 5.64; Λm
(acetonitrile, S m2 molꢁ1) 12.2.
[Au(bhetpydam)Cl] (5)
To a rapidly stirred solution of K[AuCl4]ꢂH2O (40 mg, 0.1 mmol) in
1.5 ml H2O, the solution of L5 (25 mg, 0.1 mmol) in 1.5 ml EtOH
was added. The mixture was heated to 70 ꢃC and kept for 6 h,
and the resulting yellow precipitate was filtered. The collected
solid was recrystallized in acetonitrile to give 5. Yellow solid; yield
75.8%; IR (KBr, cmꢁ1): 3340 (O-H), 3074–3051 (C-H, py), 1661 (C= O),
[Au(hetpam)Cl2] (2)
To a rapidly stirred solution of K[AuCl4]ꢂH2O (40 mg, 0.1 mmol) in
1.5 ml H2O the solution of L2 (17 mg, 0.1 mmol) in 1.5 ml EtOH
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Copyright © 2012 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. (2012)

Gold(III) complexes with deprotonated pyridyl carboxamide
1636 (C= C), 1604 (C= N), 428 (Au-N); 1 H NMR (600 MHz, DMSO-d6)
d 8.58 (dd, J = 7.8 Hz, 7.8 Hz, 1 H, 4-H, py), 8.00 (d, J = 7.8 Hz, 2 H,
3,5-H, py), 4.69 (t, J= 6.0 Hz, 2 H, 2OH), 3.59 (t, J= 6.8 Hz, 4 H, 2CH2),
3.52 (dd, J= 12.8, 6.8 Hz, 4 H, 2CH2); 13 C NMR (150MHz, DMSO-d6)
d 49.0 (NCH2), 60.0 (CH2OH), 128.2 (2C, 3,5-C, py), 146.5(4-C,py),
147.1(2 C, 2,6-C, py), 171.0 (-CON-); Anal. Calcd for C11H13N3O4AuCl:
C, 27.32; H, 2.71; N, 8.69. Found: C, 27.01; H, 2.36; N, 8.46; Λm
(acetonitrile, S m2 molꢁ1) 4.2.
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 product. The
OD of each well was measured on a microplate spectrophotome-
ter at a wavelength of 570 nm. The IC50 value was determined
from the plot of percent viability against dose of compounds
added. The SRB assay was performed as previously described for
Bel-7402.[29] Upon completion of the incubation for 44 h, the cells
were fixed in 10% trichloroacetic acid (100 ml) for 30 min at 4 ꢃC,
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 mmollꢁ1
unbuffered Tris base (100ml) and OD was measured at 492 nm
as above.[30] The IC50 value was determined from plot of percent
viability against dose of compounds added.
[Au2(hedam)Cl4] (6)
To a rapidly stirred solution of K[AuCl4]ꢂH2O (80 mg, 0.2 mmol) in
1.5 ml H2O, the solution of L6 (26 mg, 0.1 mmol) in 1.5 ml EtOH
was added. The mixture was heated to 70 ꢃC and kept for 6 h,
and the resulting red precipitate was filtered. The collected solid
was recrystallized in acetonitrile to give 6. Red solid; yield 82.6%;
IR (KBr, cmꢁ1): 3108–2932 (C-H, py), 1641 (C= O), 1629 (C= C), 1602
(C= N), 423 (Au-N); UV (acetonitrile, nm): 203 (C= O), 209 (C= N),
268 (C = C), 304 (LMCT); 1 H NMR (600 MHz, DMSO-d6) d 9.29 (d,
J= 6.0 Hz, 2 H, 6-H, py), 8.50 (dd, J= 7.8 Hz, 7.8 Hz, 2 H, 4-H, py), 8.01
(dd, J= 7.8 Hz, 6.0 Hz, 2 H, 5-H, py), 7.97 (d, J= 7.8 Hz, 2 H,
3-H, py), 3.44 (t, J = 7.2 Hz, 4 H, 10-H, 2CH2), 1.58 (s, 4 H, 20-H, 2CH2),
1.33 (s, 4 H, 30-H, 2CH2); 13 C NMR (150MHz, DMSO-d6) d 26.6
(30-C, CH2), 30.3 (20-C, CH2), 47.1 (10-C, CH2), 128.6 (3-C, py),
130.3 (5-C, py), 145.5 (4-C, py), 145.6 (6-H, py), 149.4 (2-C, py),
171.0 (-CON-); Anal. Calcd for C18H20N4O2Au2Cl4: C, 25.14; H, 2.34;
N, 6.51. Found: C, 25.47; H, 2.38; N, 6.30; Λm (DMF, S m2 molꢁ1) 4.5.
Results and Discussion
Synthesis and Characterization
The ligands L1–L6 (as shown in Fig. 1) were prepared following
reported procedures.[23–27] Their structure and purity were estab-
lished by comparing their melting points, IR and NMR data with
those reported in the literature.
Gold(III) complexes (1–6) with deprotonated pyridyl carboxa-
mide were synthesized as described in the Experimental section
(as shown in Scheme 1). Treatment of the free pyridyl carboxa-
mide ligands (L1–L4) with K[AuCl4].H2O in a C2H5OH–H2O
mixture affords complexes (1–4) in ~80% yield (Scheme 1, Route
1). Reaction of bis(pyridyl) carboxamide (L5) with K[AuCl4]ꢂH2O
affords complex 5 in ~83% yield (Scheme 1, Route 2). Using
dipyridyl carboxamide (L6) as ligand affords complex 6 in ~83%
yield (Scheme 1, Route 3). Complexes 1 and 2 contain two
Au-N bonds, complexes 3, 4 and 5 contain three Au-N bonds,
whereas complex 6 is a binuclear complex. When the ratio of
ligand to KAuCl4 was 2:1, 1:1 or 1:2, the mixture of L3 or L4 with
K[AuCl4]ꢂH2O produced the same gold(III) complex (3 or 4) with
anion [AuCl4]ꢁ. The excess ligand in the reaction mixture was
found by thin-layer chromatography when the ratio of ligand to
KAuCl4 was 2:1 or 1:1. Heating the gold(III) complex 3 (or 4) with
KPF6 in water (or alcohol), or heating L3 (or L4), K[AuCl4]ꢂH2O
with KPF6 in a C2H5OH/H2O mixture, pure gold(III) complex was
not isolated as their PF6- salt.
Cytotoxic Studies
Cell culture
Two different human carcinoma cell lines – HL-60 and Bel-7402 –
were cultured in RPMI-1640 medium supplemented with 10%
fetal bovine serum, 100 units mlꢁ1 penicillin and 100 mg mlꢁ1
streptomycin. Cells were maintained at 37 ꢃC in a humidified
atmosphere of 5% CO2 in air.
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
solution. To avoid DMSO toxicity, the concentration of DMSO
was less than 0.1% (v/v) in all experiments.
Cytotoxicity analysis
The complexes were soluble in DMF, DMSO and acetonitrile,
poorly soluble in MeOH, and insoluble in some common organic
solvents. Attempts to obtain a single crystal suitable for X-ray
determination were unsuccessful. Structural analogies of the title
compounds, [Au(Quinpy)Cl]Cl, [Au(Quingly)Cl]Cl and [Au(Quinala)
Cl]Cl with three Au-N bonds (where Hquinpy = N-(8-quinolyl)
pyridine-2-carboxamide; Hquingly = N-(8-quinolyl)-glycine-car-
boxamide; Hquinala = N-(8-quinolyl)-L-alanine-carboxamide) were
The cells harvested from exponential phase were seeded equiva-
lently 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
previously described for HL-60.[28] Upon completion of the
O
O
O
N
O
O
N
NH
HN
R
H
N
N
N
H
H
N
N
HO
OH
R= Ph, CH2OH, Py, CH2N(CH3)2
L2
L3
L4
L6
L1
L5
Figure 1. Structures of the ligands
Appl. Organometal. Chem. (2012)
Copyright © 2012 John Wiley & Sons, Ltd.
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Shuxiang Wang et al.
Route 1 For the gold(III) complexes with pyridyl carboxamide
O
N
O
N
Cl
Cl
Au
N
Cl
Cl
Au
N
O
O
N
70 oC
N
K[AuCl4] +
N
O
+ KCl +HCl
R1
HN
Au
Cl
Cl
OH
[Au(hetpam)Cl ]
[Au(bzpam)Cl ]
2:
R1
O
2
1:
2
+
+
+
O
N
O
N
N
N
N
N
70 oC
-
-
AuCl4
AuCl4
Au
- +2KCl +HCl
Cl
N
N
Cl
Cl
2 K[AuCl4] +
AuCl4
N
HN
N
Cl
Cl
Au
Au
Cl
R2
Me2N
[Au(dmepam)Cl]AuCl
4:
[Au(pypam)Cl]AuCl
4
R2
3:
4
Route 2 For the gold(III) complexes with bis(pyridyl) carboxamide
O
O
O
O
N
70 oC
HO
N
K[AuCl4] +
HO
N
N
+ KCl + 2 HCl
Au
NH
HN
OH
[Au(bhetpydam)Cl]
Cl
OH
5:
Route 3 For the binuclear gold(III) complex with pyridyl carboxamide
O
O
O
O
70 oC
N
N
N
N
+ 2 KCl +2HCl
2 K[AuCl4]
+
H
H
N
N
N
N
Au
Cl
[Au2(hedam)Cl4]
Au
Cl
Cl
Cl
6:
Scheme 1. Synthetic routes for the gold(III) complexes with deprotonated amide
synthesized by Yang et al.[19] The crystal structures of complexes
[Au(Quingly)Cl]Cl and [Au(Quinala)Cl]Cl revealed that gold(III) is
coordinated by three nitrogen atoms from the ligand, one of
which is deprotonated amide nitrogen. Hill et al.[31] synthesized
a dichloro(pyridine-2-carboxamido-N1,N2) gold(III) complex. Its
X-ray crystal structure showed that the ligand had been deproto-
nated after complexation.
The structures of the synthesized gold(III) complexes were
established with the help of elemental analyses data, and IR, UV
and NMR spectra.
As shown in Table 1, elemental analysis data of the complexes
are in good agreement with the calculated values. The molar
conductance values in acetonitrile or DMF for the complexes 1, 2,
5 and 6 correspond to non-electrolyte, while complexes 3 and 4
correspond to 1:1 electrolyte type.[32] This can be accounted for
the coordination of gold (III) with different nitrogen atoms..
Comparison of the IR spectra of the ligands and complexes
provided information about the mode of bonding of the ligands
in gold(III) complexes. The significant data are given in Table 2.
The bands of υC O (amide) in 1677–1657 cmꢁ1 shifted to 1671–
1639 cm-1 after complexation. The stretching frequency υNH of
amide which appeared at 3382–3300 cmꢁ1 in the spectra of free
ligands disappeared in the spectra of all gold complexes. In addi-
tion, the complexes exhibited new bands assigned to υAu-N appeared
at 424–411 cmꢁ1, indicating that the ligands had been deprotonated
after complexation. The bands of υC N (pyridyl) at 1640–1617 cmꢁ1
shifted to a lower frequency by 15–36 cmꢁ1, and the strong and
sharp bands of υC-H (pyridyl) at 3082–2853 cmꢁ1 shifted to 3116–
Table 1. Analytical and physical data of the complexes
Complex
Formula
Color
Found (calculated) (%)
H
Molar conductance
(S cm2 molꢁ1
)
C
N
1
2
3
4
5
6
C13H11AuCl2N2O
C8H9AuCl2N2O2
Red
32.55 (32.59)
22.11 (22.19)
18.48 (18.40)
16.15 (15.73)
27.01 (27.32)
25.47 (25.14)
2.18 (2.31)
2.03 (2.09)
1.04 (1.29)
1.76 (1.85)
2.36 (2.71)
2.38 (2.34)
5.64 (5.85)
6.12 (6.47)
4.89 (5.36)
5.30 (5.50)
8.46 (8.69)
6.30 (6.51)
Acetonitrile, 12.2
Acetonitrile, 3.1
Acetonitrile, 145.4
Acetonitrile, 155.2
Acetonitrile, 4.2
Red
C
C
C
C
12H10Au2Cl5N3O
10H14Au2Cl5N3O
11H13AuClN3O4
18H20Au2Cl4N4O2
Yellow
Yellow
Yellow
Red
Dimethyllformamide, 4.5
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Appl. Organometal. Chem. (2012)

Gold(III) complexes with deprotonated pyridyl carboxamide
Table 2. Infrared spectral data of ligand and its complexes (cm-1)
Compound n(N-H) n(C-H, Py ) n(C O) n(C N, Py) n(Au-N) n(O-H)
4.38 ppm down-field, and the chemical shift of the carbon of C2
(py, at 150.81 ppm picolinamide) shifted 11.66 ppm down-field after
complexation. The conclusions drawn from these studies lend further
support to the mode of bonding discussed in IR spectra.
Based on all the above physical and spectral studies, we
propose a tentative structure for the complexes as shown in Fig. 3.
L1
L2
L3
L4
L5
L6
1
3300 3082–3026 1667
3366 3093–3015 1657
3369 3058–2853 1677
3382 3045–2853 1677
3282 2968–2856 1665
3372 3071–2920 1657
3101–3056 1639
1640
1628
1620
1634
1617
1617
1604
1604
1607
1607
1604
1602
3730
3407
3730
3340
Cytotoxic Studies
Previous investigations had already revealed favorable cytotoxic
properties for some gold(III) complexes. However, the data pres-
ent in the literature about gold(III) complexes with deprotonated
amide ligands are still very scarce. Hill et al. synthesized and
characterized an N,N0-bis-coordinated gold(III) aurocycle.[31] How-
ever, they did not evaluate the cytotoxic activity of the gold(III)
complex. Yang et al.[19] reported three gold(III) complexes ([Au
(Quinpy)Cl]Cl, [Au(Quingly)Cl]Cl and [Au(Quinala)Cl]Cl) with
deprotonated amide ligands, which were tested against B16-
BL6, P388, HL-60, A-549 and BEL-7402 cell lines. The cytotoxicity
of [Au(Quinpy)Cl]Cl against A549 cells is about three times higher
than that of cisplatin. [Au(Quinala)Cl]Cl is active against B16-BL6
421
418
411
422
428
423
2
3109–3030 1639
3
3103–2927 1665
4
3116–2928 1671
5
3074–3051 1661
6
3108–2932 1641
2927 cm-1, suggesting that pyridyl coordinated with gold through
nitrogen atom.[33] The band of υAu-Cl is not observed in
far-infrared region.[11] Hill et al. reported that the bands of υC O
(amide) in 1678 cmꢁ1 shifted to 1650.8 cmꢁ1 after complexation.[31]
The UV–visible spectra of ligands and gold(III) complexes in
acetonitrile were measured. At a concentration of 1 ꢀ 10ꢁ4 mol
with an inhibition rate of 67.52% at a concentration of 10ꢁ7 mol Lꢁ1
.
In the present work, in the search for novel gold compounds
as potential anticancer treatments, we synthesized two gold(III)
complexes (1 and 2) containing two Au-N bonds, three complexes
(3, 4 and 5) containing three Au-N bonds, and a binuclear complex
(6). The cytotoxicity of ligands and their metal complexes was tested
by MTT and SRB assays, and the results obtained with gold(III)
complexes are presented in Table 3. The corresponding ligands
had no cytotoxicity against Bel-7402 and HL-60 cell lines (IC50 > 200
mmol lꢁ1), whereas the gold(III) complexes exerted cytotoxic effects
against Bel-7402 and HL-60 cell lines. Most complexes showed lower
IC50 values (<20 mmol lꢁ1); complex 6 had better cytotoxicity than
cisplatin; complex 3 displayed similar cytotoxicity to cisplatin against
Bel-7402 cell line; complex 3 also showed the highest cytotoxic
activity against HL-60 cell line among the six complexes. Com-
plexes 1, 3 and 6 exhibited comparable cytotoxicity to cisplatin,
and they demonstrated similar or better cytotoxicity than that of
gold(III) compounds containing bis(pyridyl) carboxamide ligands
(IC50 =10–30 mM)[34] and [PtL2Cl] (where HL = N-(4-methylphenyl)-
2-pyridine-carboxamide). In HL-60, Bel-7402, P388 and A-549
cell lines, the growth inhibitory rates of [PtL2Cl] were 81.7%,
47.7%, 99.5% and 87.5%, respectively, at a concentration of
l
ꢁ1, three main absorption peaks at about 196, 220 and 262 nm
for ligands are assigned to C O, C N and C C, respectively. The
peak at 220 nm blue shifts by about 8 nm, indicating that py
coordinates with gold(III) ion through a nitrogen atom. Gold(III)
complexes give high-intensity bands at about 310 nm which
can be assigned to ligand–metal charge transfer.
The 1 H NMR spectra of ligands and gold(III) complexes were
recorded in DMSO-d6. All the protons were found to be in their
expected regions and numbers of protons calculated from the
integration curves agreed with those obtained from the values
of C, H, and N element analyses. In comparison 1 H NMR of the
gold(III) complexes with that of the free ligands, a broad signal
of-CONH- (at 8.05–8.77 ppm) disappeared in the complexes,
indicating that the ligands had been deprotonated due to
coordination with gold ion. For example, the proton signal at
8.77 ppm attributed to-CONH- (1 H) of L1 disappeared in complex 1.
The chemical shift of the protons which are near the coordi-
nated pyridine nitrogen shifted 0.07–0.54 ppm down-field
compared to free ligands.
The 13 C NMR (DMSO-d6) spectra further provide support for the
structure of the complexes, e.g. chemical shifts of complex 1 differ-
ing from L1 (Fig. 2). The chemical shift of the carbon of-C O (at
159.1 ppm in pyridyl carboxamide) moves down-field by 12.0 ppm;
the chemical shift of the carbon of C2 (py, at 144.9 ppm in pyridyl
carboxamide) moves down-field by 3.5 ppm; and the chemical shift
of the carbon of-NHCH2Ph (at 38.8 ppm in pyridyl carboxamide)
moves down-field by 10.7 ppm after complexation. A similar result
was obtained by Hill et al.[31] They reported that the chemical shift
of the carbon of-CONH- (at 166.89 ppm in picolinamide) shifted
10ꢁ5 mol lꢁ1 [35]
.
The experimental results indicated that the characteristics of
ligands had an important effect on cytotoxicity of gold(III)
complexes. In general, the cytotoxicty of these gold(III) complexes
with deprotonated pyridyl carboxamide decreased in sequences
as follows: binuclear complex> mononuclear complex; complex
wherein R is an aromatic group on picolinamide > complex
wherein R is an aliphatic group.
The binuclear complex 6 with two Au-N bonds per unit showed
higher cytotoxicity than mononuclear complexes (1 and 2) with
two Au-N bonds.
For mononuclear complexes with two Au-N bonds, complex 1,
wherein R is an aromatic group on picolinamide, exhibited higher
cytotoxicity than complex 2, wherein R is an aliphatic group. For
mononuclear complexes with three Au-N bonds, a similar result is
obtained: complex 3, wherein R is an aromatic group on picolina-
mide, showed higher cytotoxicity than complexes (4 and 5)
wherein R is an aliphatic group. A similar result was obtained by
Yang et al.[19] They reported that [Au(Quinpy)Cl]Cl with
O
6'
3
1'
4
5
5'
4'
N
2
H
N
2'
1
6
3'
Figure 2. Numbering of carbons of L1
Appl. Organometal. Chem. (2012)
Copyright © 2012 John Wiley & Sons, Ltd.
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Shuxiang Wang et al.
+
+
O
O
N
O
O
N
N
Cl Au
Cl
O
O
O
O
N
N
N
N
N
N
N
-
-
AuCl4
AuCl4
Au
Cl
N
N
N
Cl
Cl
N
N
N
Cl Au
Au
Au
Cl
Au
Au
Cl
Cl
Cl
Cl
Cl
OH
OH
Me2N
HO
Cl
[Au(dmepam)Cl]AuCl4 [Au(bhetpydam)Cl]
4
[Au2(hedam)Cl4]
[Au(hetpam)Cl ][Au(pypam)Cl]AuCl
[Au(bzpam)Cl2]
2
1
2
3
4
5
6
Figure 3. Suggested structures of gold(III) complexes
Acknowledgments
Table 3. The cytotoxicity of the complexes against HL-60 and
Bel-7402 cell lines (n = 3)
This work was supported by the Natural Science Foundation of
Hebei Province (No. B2011201135), the Special Foundation
for State Major New Drug Research Program of China (No.
2009ZX09103-139), the National Basic Research 973 Program
(No. 2010CB534913), the Nature Science Foundation for Distin-
guished Young Scholars of Hebei Province (No. B2011201164), the
Key Basic Research Special Foundation of the Science Technology
Ministry of Hebei Province (No. 11966412D), the Key Research Project
Foundation of the Department of Education of Hebei Province
(No. ZD2010142), and the Foundation of Openend Laboratory of
Hebei University (No. 2010015).
Complexes
IC50 ꢄ SD (mmol lꢁ1
)
HL-60
Bel-7402
1
11.47 ꢄ 0.17
39.93 ꢄ 1.44
9.45 ꢄ 0.18
30.39 ꢄ 1.21
35.43 ꢄ 0.22
10.47 ꢄ 0.24
2.89 ꢄ 0.18
11.77 ꢄ 0.23
17.37 ꢄ 0.24
8.55 ꢄ 0.18
14.81 ꢄ 0.22
13.43 ꢄ 0.18
6.03 ꢄ 0.14
8.12 ꢄ 0.20
2
3
4
5
6
Cisplatin
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