Synthesis, structural characterization and anticancer activity of some new complexes of 6-amino-4-hydroxy-2-thiopyrimidine

Article abstract of DOI:10.1016/j.molstruc.2012.05.073

New complexes of 6-amino-4-hydroxy-2-thiopyrimidine (Hahtp), [Zn(ahtp) ₂(H₂O)₂], [Zn(ahtp)₂(PPh ₃)(H₂O)], [Zn(Hahtp)(bpy)Cl₂], [Pd(phen)(ahtp]Cl, [Pd(Hahtp)(PPh₃)₂]Cl₂, [Ag(ahtp)(H₂O)₂], [Ag(ahtp)(PPh₃)(H ₂O)], [Ag(ahtp)L] (L = bpy, phen), have been synthesized and characterized on the basis of spectral (IR, ¹H-NMR, ESI-mass and UV-visible), elemental analysis, thermal and molar conductivity measurements. Three modes of chelations have been observed for Hahtp; as a neutral bidentate ligand through cyclic nitrogen and thione sulfur atoms, mononegative bidentate ligand through either the deprotonated cyclic nitrogen and thione sulfur atoms or the deprotonated hydroxy and cyclic nitrogen atoms; all forming four-membered chelating rings. The free Hahtp and its complexes, [Zn(ahtp)₂(H ₂O)₂], [Zn(Hahtp)₂(PPh₃)(H ₂O)], [Zn(Hahtp)(bpy)Cl₂], [Pd(phen)(Hahtp]Cl and [Ag(Hahtp)(PPh₃)(H₂O)] have been tested against the human breast cancer MDA-MB231 cell line. The [Ag(ahtp)(PPh₃)(H ₂O)] complex exhibits the highest efficacy with a mean IC ₅₀ value of 4.7 μM.

Full text of DOI:10.1016/j.molstruc.2012.05.073

Journal of Molecular Structure 1028 (2012) 208–214
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structural characterization and anticancer activity of some new
complexes of 6-amino-4-hydroxy-2-thiopyrimidine
Shadia A. Elsayed a, Bertrand J. Jean-Claude b, Ian S. Butler c, Sahar I. Mostafa d,
⇑
a Chemistry Department, Faculty of Science, Damietta, Mansoura University, Egypt
b Royal Victoria Hospital, Department of Medicine, Montreal, QC, Canada H3A 1A1
c Department of Chemistry, McGill University, Montreal, QC, Canada H3A 2K6
d Chemistry Department, Faculty of Science, Mansoura, Mansoura University, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
New complexes of 6-amino-4-hydroxy-2-thiopyrimidine (Hahtp), [Zn(ahtp)2(H2O)2], [Zn(ahtp)2
(PPh3)(H2O)], [Zn(Hahtp)(bpy)Cl2], [Pd(phen)(ahtp]Cl, [Pd(Hahtp)(PPh3)2]Cl2, [Ag(ahtp)(H2O)2],
[Ag(ahtp)(PPh3)(H2O)], [Ag(ahtp)L] (L = bpy, phen), have been synthesized and characterized on the basis
of spectral (IR, 1H-NMR, ESI-mass and UV–visible), elemental analysis, thermal and molar conductivity
measurements. Three modes of chelations have been observed for Hahtp; as a neutral bidentate ligand
through cyclic nitrogen and thione sulfur atoms, mononegative bidentate ligand through either the
deprotonated cyclic nitrogen and thione sulfur atoms or the deprotonated hydroxy and cyclic nitrogen
atoms; all forming four-membered chelating rings. The free Hahtp and its complexes, [Zn(ahtp)2(H2O)2],
[Zn(Hahtp)2(PPh3)(H2O)], [Zn(Hahtp)(bpy)Cl2], [Pd(phen)(Hahtp]Cl and [Ag(Hahtp)(PPh3)(H2O)] have
been tested against the human breast cancer MDA-MB231 cell line. The [Ag(ahtp)(PPh3)(H2O)] complex
Received 10 March 2012
Received in revised form 28 May 2012
Accepted 29 May 2012
Available online 23 June 2012
Keywords:
Hahtp
Silver
Zinc
Palladium
Anticancer
exhibits the highest efficacy with a mean IC50 value of 4.7 lM.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
water soluble complexes, [Pd(bpy)(dahmp)]Cl and [Ag(bpy)(H-
dahmp)]NO3, display a significant anticancer activity against Ehr-
lich ascites tumor cells (EACs). In continuation of our search for
potent active anticancer complexes, it was considered worthwhile
to synthesize a variety of novel complexes of 6-amino-4-hydroxy-
2-thiopyrimidine (Hahtp) with Zn(II), Pd(II) and Ag(I). The struc-
tures of the resulting complexes have been discussed on the bases
of elemental analysis, spectral (IR, UV–visible, 1H-NMR, mass),
thermal and molar conductivity measurements. In addition, the
anticancer activity of Hahtp and the complexes, [Zn(ahtp)2(H2O)2],
[Zn(Hahtp)(bpy)Cl2], [Zn(ahtp)2(PPh3)(H2O)], [Pd(ahtp)(phen)]Cl,
[Pd(Hahtp)(PPh3)2]Cl2 and [Ag(ahtp)(PPh3)(H2O)] have been tested
against the human breast cancer MDA-MB231 cell line.
Pyrimidine constitutes are known as important component of
nucleic acids and are reported as building blocks in pharmaceutics
for the synthesis of antiviral, anticancer, antibacterial and anti-
fungal agents [1–3]. Thus, the synthesis of new transition metal
complexes with pyrimidine derivatives is a matter of interest be-
cause of their well known anti-cancer, anti-metastase and anti-
microbial activity [4,5]. The pharmacological activity of these com-
plexes comes from synergic effects by the transition metal ion and
thiopyrimidine, once the coordinated molecule dissociates in the
target tissue [6–8]. 2-Thiopyrimidine and 4,6-dimethyl-2-thiopy-
rimidine behave as unsymmetrical ambidentate ligands, when
coordinate with metal ions, generate linkage isomerism due to ste-
ric-repulsion-interactions [9]. Palladium(II) thiopyrimidine com-
plexes are of great interest due to the significant Pd(II)–S
interactions in biological system [10]. During the past few years,
our laboratory has been actively involved in the synthesis of a
variety of complexes of 4,6-diamino-5-hydroxy-2-mercaptopyrim-
idine (Hdahmp) [11–13] and 5,6-diamino-2,4-dihydroxypyrimi-
dine (Hahp) [14]. Some complexes of 4,6-diamino-5-hydroxy-2-
mercaptopyrimidine have been evaluated for their antibacterial,
antifungal [11,13] and anticancer activity [12]. Among them, the
2. Experimental
2.1. Materials and measurements
All reagents and solvents were purchased from Alfa/Aesar and
all manipulations were performed under aerobic conditions using
materials and solvents as received. [M(PPh3)2Cl2] [15], [M(bpy)Cl2],
[M(phen)Cl2] (M(II) = Pd, Pt) [16]. DMSO-d6 was used for the NMR
measurements referenced against TMS.
The human breast carcinoma MDA-MB-231 cell line was ob-
tained from the American Type Culture Collection (ATCC catalog
number). Cells were maintained in Dulbecco’s Modified Eagle Med-
⇑
Corresponding author. Tel.: +20 100 8502625; fax: +20 50 2246781.
E-mail address: sihmostafa@yahoo.com (S.I. Mostafa).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.05.073

S.A. Elsayed et al. / Journal of Molecular Structure 1028 (2012) 208–214
209
ium (Wisent Inc., St-Bruno, Canada) supplemented with 10% FBS,
10 mM HEPES, 2 mM -gultamine and 100 g/ml penicillin/strep-
tomycin (GibcoBRL, Gaithersburg, MD). In all assays cells were pla-
anol containing KOH (0.014 g, 0.25 mmol; 10 cm3). The reaction
mixture was stirred with warming for 96 h. The yellow precipitate
was filtered off, washed with methanol and air-dried. Yield: 64%.
Anal. Calcd. for C16H12ClN5OPdS: C, 43.9; H, 3.3; N, 14.1; S, 6.5%,
L
l
ted 24 h before drug treatment.
Infrared spectra were recorded on a Nicolet 6700 Diamond ATR
spectrometer in the 4000–200 cmꢀ1 range. 1H-NMR spectra were
recorded on VNMRS 200 and 500 MHz spectrometer in DMSO-d6
using TMS as reference. Mass spectra (ESI-MS) were recorded using
LCQ Duo and double focusing MS25RFA instruments, respectively.
Electronic spectra were recorded in DMF using a Hewlett–Packard
8453 spectrophotometer. Thermal analysis measurements were
made in the 20–800 °C range at a heating rate of 20 °C minꢀ1 using
Ni and NiCo as references, on a on a TA instrument TGA model
Q500Analyzer TGA-50. Molar conductivity measurements were
carried out at room temperature on a YSI Model 32 conductivity
bridge.
Found: C, 43.6; H, 3.2; N, 14.0; S, 6.3%. Conductivity data (10ꢀ3
M
in DMF): KM = 96.0
X
ꢀ1. IR (cmꢀ1): 3423, 3316, 2953, 1613,
1541, 1373, 500, 432. 1H NMR (d6-DMSO/TMS, ppm), d: 11.22 (s,
1H, N(1)H); 4.56 (s, 1H, C(5)H); 5.66 (s, 2H, NH2). ESI-MS (m/z):
430 [Pd(ahtp)(phen)]+, 285 [Pd(phen)]+.
2.2.5. [Pd(Hahtp)(PPh3)2Cl2]
[Pd(PPh3)2Cl2] (0.14 g, 0.2 mmol) was added to Hahtp (0.03 g,
0.2 mmol) in dichloromethane (10 cm3). The mixture was heated
under reflux for 48 h. The green-yellow precipitate was filtered
off, washed with dichlromethane and air-dried. Yield: 59%. Anal.
Calcd. for C40H35Cl2N3OP2PdS: C, 56.8; H, 4.1; N, 4.9; S, 3.8%, Found:
C, 56.1; H, 3.8; N, 4.3; S, 3.7%. Conductivity data (10ꢀ3 M in DMF):
2.2. Preparations
KM = 98.0
X
ꢀ1. IR (cmꢀ1): 3334, 3425, 3316, 2960, 1606, 1504,
1378, 442, 333. 1H NMR (d6-DMSO/TMS, ppm), d: 11.22 (s, 1H,
2.2.1. [Zn(ahtp)2(H2O)2].2H2O
N(1)H) ; 11.59 (s, 1H, O(4)H); 4.65 (s, 1H, C(5)H); 6.35 (s, 2H,
Zinc chloride (0.136 g, 1 mmol) in water (2 cm3) was added to
Hahtp (0.143 g, 1 mmol) in methanol containing KOH (0.056 g,
1 mmol; 15 cm3). The reaction mixture was heated under reflux
for 4 h, during which an off-white precipitate was obtained. This
precipitate was filtered off, washed with water, methanol and
air-dried. Yield: 81%. Anal. Calcd. for C11H22N6O6S2Zn: C, 26.5; H,
4.4; N, 18.7; S, 14.3 %, Found: C, 26.9, H, 4.2; N, 17.9; S, 13.8%. Con-
ductivity data (10ꢀ3 M in DMF): KM = 9.0 Xꢀ1 . IR (cmꢀ1), 3320,
3416, 3318, 1621, 1521, 1377, 438, 332; 1H NMR (d6-DMSO/TMS,
ppm), d: 11.38 (s, 1H, O(4)H); 4.65 (s, 1H, C(5)H); 6.21 (s, 2H,
NH2).
ESI-MS
(m/z):
774
[Pd(Hahtp)(PPh3)2]+,
511.0
[Pd(PPh3)(Hahtp)]+.
2.2.6. [Ag(ahtp)(H2O)2].H2O
Silver nitrate (0.17 g, 1 mmol) in water (2 cm3) was added to
Hahtp (0.143 g, 1 mmol) in methanol containing KOH (0.056 g,
1 mmol; 10 cm3). The reaction mixture was heated with stirring
for 4 h in the dark and the white precipitate was filtered off,
washed with water, methanol and air-dried in dark. Yield: 81%.
Anal. Calcd. for C4H8AgN3O3S: C, 15.7; H, 3.2; N, 13.7; S, 10.6%,
NH2), ESI-MS: m/z, 385.0 [Zn(ahtp)2(H2O)2]+ 349.5 [Zn(ahtp)2]+,
,
Found: C, 15.2, H, 3.0 N, 13.4; S, 10.5%. Conductivity data (10ꢀ3
M
207.5[Zn(ahtp)]+.
in DMF): KM = 9.0
X
ꢀ1. IR (cmꢀ1): 3322, 3426, 3317, 1623, 1548,
1396, 437, 331. 1H NMR (d6-DMSO/TMS, ppm), d: 12.08 (s, 1H,
O(4)H), 4.84 (s, 1H, C(5)H) ; 6.61 (s, 2H, NH2). ESI-MS (m/z):
2.2.2. [Zn(ahtp)2(PPh3)(H2O)]
[ZnCl2(PPh3)2] was prepared by refluxing a mixture of ZnCl2
(0.136 g, 1 mmol) and triphenylphosphine (0.524 g, 2 mmol) in
THF. Upon reducing the volume, white crystals were obtained.
[Zn(PPh3)2Cl2] (0.33 g, 0. 5 mmol) in dichloromethane (10 cm3)
was added to Hahtp (0.072 g, 0.5 mmol) in methanol (10 cm3). The
reaction mixture was heated under refluxed for 24 h and the white
precipitate was filtered off, washed with methanol, dichlorometh-
ane and air-dried. Yield: 68%. Anal. Calcd.. for C28H29N6O3PS2Zn:
Calcd.: C, 51.1; H, 4.4; N, 12.7; S, 9.7%, Found: C, 50.6; H, 3.8; N,
290.0 [Ag(ahtp)(H2O)2]+ 167.0 [Ag(ahtp-C3H4N2O)]+.
,
2.2.7. [Ag(ahtp)(PPh3)(H2O)]
In the dark, silver nitrate (0.087 g, 0.5 mmol) in water (2 cm3)
was added to PPh3 (0.131 g, 0.5 mmol) in methanol (15 cm3) and
the colorless solution was stirred for 3 h. This solution was added
to Hahtp (0.07 g, 0.5 mmol) in methanol containing KOH
(0.028 g, 0.5 mmol; 10 cm3). The reaction was stirred for 48 h.
The white solid was filtered off, washed with water, methanol
and air-dried. Yield: 79%. Anal. Calcd. for C22H21AgN3O2PS: C,
49.8; H, 3.9; N, 7.9; S, 6.0%. Found: C, 49.2; H, 4.1; N, 8.5; S, 5.4%.
12.1; S, 9.3%. Conductivity data (10ꢀ3 M in DMF): KM = 7.0 Xꢀ1
.
IR (cmꢀ1), 3538, 3432, 3323, 1595, 1505, 1381, 429, 326. 1H NMR
(d6-DMSO/TMS, ppm), d: 11.40 (s, 1H, O(4)H); 4.66 (s, 1H,
C(5)H); 6.24 (s, 2H, NH2).
Conductivity data (10ꢀ3 M in DMF): KM = 8.0
X
ꢀ1. IR (cmꢀ1):
3343, 3429, 3344, 1638, 1512, 1360, 444,329. 1H NMR (d6-
DMSO/TMS, ppm), d: 11.25 (s, 1H, O(4)H); 4.69 (s, 1H, C(5)H),
6.25 (s, 2H, NH2). ESI-MS (m/z): 535 [Ag(PPh3)(ahtp)(H2O)]+,
371.0 [Ag(PPh3)]+.
2.2.3. [Zn(Hahtp)(bpy)Cl2]
ZnCl2 (0.068 g, 0.5 mmol) in water (2 cm3) was added to basic
methanolic solution {KOH (0.028 g, 0.5 mmol; 10 cm3)} of Hahtp
(0.072 g, 0.5 mmol). To the colorless solution, bpy (0.078 g,
0.5 mmol) in ethanol (10 cm3) was added drop by drop with con-
stant stirring. The reaction mixture was heated under reflux for
20 h. The white precipitate was filtered off, washed with methanol
and air-dried. Yield: 76%. Anal. Calcd. for C14H13Cl2N5OSZn: C, 38.6;
H, 3.0; N, 16.1; S, 7.3%, Found: C, 38.3; H, 2.6; N, 16.3; S, 6.8%. Con-
2.2.8. [Ag(ahtp)L] (L = bpy, phen)
A similar procedure as for the [Ag(PPh3)(Hahtp)(H2O)] analogue
was applied using bpy (0.078 g, 0.5 mmol) or phen (0.09 g,
0.5 mmol) instead of PPh3. The white (bpy) or yellow (phen) pre-
cipitate was filtered off, washed with water, methanol and air-
dried.
ductivity data (10ꢀ3 M in DMF): KM = 8.0
X
ꢀ1. IR (cmꢀ1), 3331,
3412, 3329, 1626, 1523, 1377, 439, 341. 1H NMR (d6-DMSO/TMS,
ppm), d: 11.42 (s, 1H, N(1)H); 11.35 (s, 1H, O(4)H); 4.70 (s, 1H,
C(5)H); 6.37 (s, 2H, NH2). ESI-MS (m/z): 436.0 [Zn(Hahtp)(b-
py)Cl2]+, 363.0 [Zn(bpy)]+.
2.2.8.1. For [Ag(bpy)(ahtp)]. Yield: 80%. Anal. Calcd. for C14H12Ag-
N5OS: C, 41.4; H, 2.9; N, 17.2; S, 7.8%, Found: C, 41.1; H, 2.2; N,
17.2, S, 7.3%.Conductivity data (10ꢀ3 M in DMF): KM = 6.0
X
ꢀ1. IR
2.2.4. [Pd(phen)(ahtp]Cl
(cmꢀ1): 3314, 3430, 3320, 1622, 1517, 1380, 436, 332. 1H NMR
(d6-DMSO/TMS, ppm), d: 11.83 (s, 1H, O(4)H), 4.81 (s, 1H, C(5)H),
6.65 (s, 2H, NH2). ESI-MS (m/z): 405 [Ag(bpy)(ahtp)]+.
[Pd(phen)Cl2] (0.085 g, 0.25 mmol) in methanol–benzene
(3:2 V/V, 5 cm3) was added to Hahtp (0.036 g, 0.25 mmol) in meth-

210
S.A. Elsayed et al. / Journal of Molecular Structure 1028 (2012) 208–214
2.2.8.2. For [Ag(phen)(ahtp)]. Yield: 78%. Anal. Calcd. for C16H12Ag-
plexes are reported in the experimental section. The IR spectral
data of Hahtp support its existence in the thione form (Scheme 1).
N5OS: C, 44.4; H, 3.3; N, 16.3; S, 7.4%. Found: C, 44.0; H, 3.2; N,
15.8; S, 7.0%. Conductivity data (10ꢀ3 M in DMF): KM = 6.0 Xꢀ1
.
This conclusion is supported by the presence of the
at 2950 cmꢀ1 [19], the absence of the
(SH) mode near
2600 cmꢀ1, and the production of the characteristic thioamide
bands due to extensive coupling of d(NH), (C@N), (NCS), and
(C@S) at 1623, 1585, and (1375, 1268, 1179) cmꢀ1, respectively
[20–22]. The bands at 3422 and 3317 cmꢀ1 are due to
as(NH2)
m(NH) stretch
IR (cmꢀ1): 3321, 3422, 3328, 1646, 1510, 1392, 457, 342. 1H
NMR (d6-DMSO/TMS, ppm), d: 12.14 (s, 1H, O(4)H), 4.85 (s, 1H,
C(5)H), 6.59 (s, 2H, NH2). ESI-MS (m/z): 431 [Ag(phen)(ahtp)]+.
m
m
m
m
m
2.3. Biological assay
and
ms(NH2) stretching vibration, respectively, while the strong
band at 3315 cmꢀ1 is associated with the
tion [12,14,23].
m(OH) stretching vibra-
Growth inhibition assay; MDA-MB-231 cells were plated at
2500 cells/well in 96-well flat-bottomed microliter plates (Costar,
Corning, NY). After 24 h incubation, the cells were exposed to dif-
ferent concentrations of each compound continuously for 5 days.
In the complexes, [Zn(ahtp)2(H2O)2], [Zn(ahtp)2(PPh3)(H2O)],
[Ag(ahtp)(H2O)2], [Ag(ahtp)(PPh3)(H2O)], [Ag(ahtp)L] (L = bpy,
phen), Hahtp acts as a mononegative bidentate ligand, coordinat-
ing the metal ions through the thione sulfur and the deprotonated
cyclic nitrogen N(1) atoms [9,12,14]. This feature is evidenced by
Briefly, following drug treatment, the cells were fixed using 50 ll
of cold trichloroacetic acid (50%) for 2 h at 4 °C, washed with water,
stained with sulforhodamine B (SRB 0.4%) overnight at room tem-
perature, rinsed with 1% acetic acid and allowed to dry overnight
the shift observed in the
as well as the absence of the
Moreover, the existence of s(NH2),
m
(C@S) and
(NH) and d(NH) stretches [12,14].
as(NH2), and (OH) stretches
m(NAC@S) stretching modes
m
[17]. The resulting colored residue was dissolved in 200 ll Tris
m
m
m
base (10 mM, pH 10.0) and optical density was recorded at
490 nm using a microplate reader ELx808 (BioTek Instruments).
The results were analyzed by GraphPad Prism (GraphPad Software,
Inc., San Diego, CA) and the sigmoidal dose response curve was
used to determine 50% cell growth inhibitory concentration
(IC50). Each point represents the average of two independent
experiments performed in triplicate [17].
more or less in the same position as in the free ligand [20,24,25].
These results indicate the replacement of the acidic hydrogen by
the metal ion, forming four-membered chelate ring [9]. The same
feature have been observed and support by X-ray crystal structures
of [Pd2(Tu)(PPh3)3Cl2] and trans–cis–cis-[Ru(AsPh3)2(Tpy)] (Tu = 2-
thiouracil, Tpy = 2-thiopyrimidine) complexes [9,20]. Figs. 1 and
2 show the structures of [Zn(ahtp)2(H2O)2] and [Ag(ahtp)(bpy)],
respectively.
3. Results and discussion
In the [Pd(ahtp)(phen)]Cl complex (Fig. 3), the
vibration at 3315 cmꢀ1 in the free ligand is missing, while the
bands arising from (C@N) are shifted to lower wavenumber
[26,27]. The bands arising from the as(NH2), s(NH2), (NH),
d(NH), (NCS) and
m(OH) stretching
The experimental section describes the synthesis of some new
complexes of 6-amino-4-hydroxy-2-thiopyrimidine (Hahtp). The
elemental analyses of the complexes are in excellent agreement with
the assigned formulae. The molar conductivities (KM) in DMF at
room temperature suggest all complexes to be non-electrolytes ex-
cept for, [Pd(ahtp)(phen)]Cl and [Pd(Hahtp)(PPh3)2]Cl2, which show
1:1 and 1:2 electrolytes, respectively [12,18]. The complex, [Zn(aht-
p)2(H2O)2] was prepared from Hahtp and ZnCl2 in methanol under
basic conditions. [Zn(ahtp)2(PPh3)(H2O)] and [Pd(Hahtp)(PPh3)]Cl2
were isolated from the reaction of [M(PPh3)2Cl2] (M(II) = Zn, Pd)
and Hahtp in CH2Cl2 under reflux. The complex, [Zn(Hahtp)(bpy)Cl2],
was prepared from ZnCl2, Hahtp and 2,20-bipyridyl under basic con-
ditions. The reaction of Hahtp and [Pd(phen)Cl2] in basic methanol–
benzene produced [Pd(phen)(ahtp]Cl. The complex, [Ag(aht-
p)(H2O)2], was isolated from the reaction of Hahtp and AgNO3 in ba-
sic methanol in the dark while the complexes, [Ag(ahtp)(PPh3)(H2O)]
and [Ag(ahtp)L] (L = bpy, phen) were formed from the reaction of
AgNO3 with Hahtp in presence of PPh3, bpy or phen in methanol un-
der basic conditions in the dark.
m
m
m
m
m
m(C@S) modes are not affected by complexation.
This feature supports the coordination of ahtpꢀ through the depro-
tonated hydroxy oxygen and cyclic nitrogen N(3) centers without
any participation of the thione sulfur atom due to the observation
of a band near 1178 cmꢀ1 ariseing from the
mains unchanged [11,13,14].
m(C@S) stretch that re-
The IR spectra of the [Zn(bpy)(Hahtp)Cl2] and [Pd(Hahtp)-
(PPh3)2]Cl2 complexes (Fig. 4) show that Hahtp functions as a
neutral bidentate ligand coordinating Zn(II) or Pd(II) through the
thione sulfur and cyclic nitrogen N(3) atoms. This mode of chela-
tion is evidenced by the shifts observed for
m
(C@N),
(NAC@S) stretches, while the bands arising from (OH),
s(NH2), (NH) and d(NH) are found more or less in the same posi-
m
(C@S) and
m
m
m
m
as(NH2),
m
tions as in the free ligand [12].
As expected, the presence of coordinated PPh3 in the
complexes [Zn(ahtp)2(PPh3)(H2O)], [Pd(Hahtp)(PPh3)2]Cl2 and
[Ag(ahtp)(PPh3)(H2O)] is indicated by strong IR bands near 1100
and 750 cmꢀ1 due to
m(PAC) and d(CCH) vibrations, respectively
3.1. Vibrational spectra
[13,28]. Also, the IR bands near 1590, 1510, 1480 and 1423 cmꢀ1
in the complexes, [Pd(ahtp)(phen)]Cl and [Ag(ahtp)(phen)], are
due to the phen stretching vibrations [29]. These bands are at high-
The characteristic IR bands and vibrational assignments
observed for 6-amino-4-hydroxy-2-thiopyrimidine (Hahtp) com-
NH2
NH2
6
6
1
N
1
5
4
5
4
NH
2
2
HO
N
3
SH
HO
N
3
S
Thione form
Thiol form
Scheme 1. Thione-thiol form of 6-amino-4-hydroxy-2-thiopyrimidine (Hahtp).

S.A. Elsayed et al. / Journal of Molecular Structure 1028 (2012) 208–214
211
H2N
NH2
H2O
Zn
S
N
N
OH
OH
NH
N
N
S
Cl2
OH2
N
HO
S
NH2
Pd
Fig. 1. Structure of [Zn(ahtp)2(H2O2)2].
PPh3
Ph3P
Fig. 4. Structure of [Pd(Hahtp)](PPh3)2]Cl2.
NH2
N
NH2
N
Ag
6
N
1
NH
N
HO
S
5
2
Fig. 2. Structure of [Ag(ahtp)(bpy)].
4
HO
N
S
3
NH2
NH
Fig. 5. Structure of 6-amino-4-hydroxy-2-thiopyrimidine (Hahtp).
shifted upfield. This feature supports coordination of ahtpꢀ
through the deprotonated hydroxy and cyclic nitrogen N(3) atoms
[11–14].
In spectra of the complexes, [Zn(Hahtp)(bpy)Cl2] and
[Pd(Hahtp)(PPh3)2]Cl2 , the four singlets are observed with upfield
shifts for the OH(4) and NH(1) protons indicating the coordination
of Hahtp to Zn(II) or Pd(II) through the thione and cyclic nitrogen
N(3) atoms [12,20]. The signals for H(5) and H(6) are shifted up-
field, which may be attributed to the decrease in the electron den-
sity in the pyrimidine ring upon complexation [34].
O
N
N
S
Cl
Pd
N
Fig. 3. Structure of [Pd(Hahtp)(phen)]Cl.
3.3. Electronic spectra
er wavenumbers compared with those for the free phen ligand
indicating chelation. Also, in the complexes, [Zn(Hahtp)(bpy)Cl2]
and [Ag(ahtp)(bpy)], the bands near 840, 750 and 725 cmꢀ1 are as-
signed to coordinated bpy [30].
The electronic spectra of the complexes were recorded in DMSO
in the 200–800 nm range. The electronic spectra of the diamag-
netic silver(I) complexes, [Ag(ahtp)(H2O)2], [Ag(PPh3)(ahtp)] and
[Ag(ahtp)L] (L = bpy, phen), show bands near 445 and 380 nm;
the latter may arise from charge transfer of the type li-
The spectra of the complexes show several bands near 500, 420,
350 and 290 cmꢀ1 due to
m(MAO), m(MAN), m(MAS) and m(MACl)
stretches, respectively [13,31]. In the complex [Zn(Hahtp)(bpy)Cl2],
one sharp band is observed at 300 cmꢀ1, corresponding to the pres-
ence of the trans-ZnCl2 moiety [11,32].
gand(p r
) ? b1g (Ag+) and ligand ( ) ? b1g (Ag+), respectively, in dis-
torted square planar environment around the metal ion [35].
The electronic spectra of the diamagnetic [Pd(phen)(ahtp)]Cl
and [Pd(PPh3)2(ahtp)]Cl2 complexes show bands near 475 and
330 nm due to 1A1g ? 1B1g and 1A1g ? 1E1g transitions in
a
3.2. NMR spectra
square-planar configuration [12,34,36]. The absorption band near
375 nm is assigned to combination of charge-transfer transitions
from the Pd(II) d-orbital to the pꢁ-orbital of phen or PPh3 [37].
The 1H-NMR data for the free Hahtp ligand and some of its com-
plexes in DMSO-d6 are given in the experimental section. The 1H-
NMR spectrum of Hahtp shows four singlets at d 4.67, 6.35, 11.51
and 11.60 ppm arising from H(5), NH2(6), NH(1) and OH(4),
respectively (see Fig. 5 for numbering scheme).
3.4. Mass spectra
In the 1H NMR spectra of the complexes, [Zn(ahtp)2(PPh3)(-
H2O)], [Zn(ahtp)2(H2O)2], [Ag(ahtp)(H2O)2], [Ag(ahtp)(PPh3)
(H2O)] and [Ag(ahtp)L] (L = bpy, phen), the NH(1) singlet is not ob-
served, while that of NH2 appears upfield confirming the coordina-
tion of ahtpꢀ through the thione sulfur and deprotonated cyclic
N(1) atoms [9,12,14,33].
The mass spectra of the complexes, [Zn(ahtp)2(H2O)2],
[Zn(Hahtp)(bpy)Cl2], [Pd(phen)(ahtp)]Cl, [Pd(PPh3)2(Hahtp)]Cl2,
[AgL(ahtp)] (L = bpy, phen), [Ag(ahtp)(H2O)2] and [Ag(ahtp)(PPh3)-
(H2O)], are reported in the experimental section and their molecu-
lar ion peaks are in agreement with their assigned formulae. The
mass spectrum of [Zn(ahtp)2(H2O)2] shows fragmentation patterns
corresponding to the successive degradation of the complex. The
first peak at m/z 385.0 with 6% abundance represents the molecu-
In the spectrum of the complex, [Pd(ahtp)(phen)]Cl, the hydro-
xy proton, OH(4), signal is not observed while the H(5) signal is

212
S.A. Elsayed et al. / Journal of Molecular Structure 1028 (2012) 208–214
represents the molecular peak of the complex, [Ag(ahtp)(H2O)2]+.
The spectrum exhibits one more peak at 167 (Calcd. 166) corre-
sponding [Ag(ahtp-C3H4N2O)]+ [14]. The mass spectrum of [Ag(P-
Ph3)(ahtp)(H2O)] exhibits the first signal at m/z 535 (Calcd. 530)
corresponding to [Ag(ahtp)(PPh3)(H2O)]+ while the second one at
371 (Calcd. 370) corresponding to [Ag(PPh3)]+ fragment [12,14].
The mass spectra of [Ag (ahtp)L] (L = bpy, phen) show peaks at
m/z 405 and 431 (Calcd. 406 and 430) with 5% and 10% abundance,
respectively.
Table 1
Anticancer activity of 6-amino-4-hydroxy-2-
thiopyrimidine and its complexes against
human breast cancer MDA-MB-231 cell line.
Compound
IC50 (lM)
Hahtp
>100
>100
49.6
>100
7.7
24.5
4.7
8.7
[Zn(bpy)(Hahtp)Cl2]
[Zn(ahtp)2(PPh3)(H2O)]
[Zn(ahtp)2(H2O)2]
[Pd(phen)(ahtp)]Cl
[Pd(Hahtp)(PPh3)2]Cl2
[Ag(ahtp)(PPh3)(H2O)]
Cis-platin
3.5. Thermal measurements
The thermal stability and degradation behavior of some re-
ported complexes, [Zn(Hahtp)(bpy)Cl2], [Zn(ahtp)2(PPh3)(H2O)],
[Pd(phen)(ahtp)]Cl.2H2O, [Pd(PPh3)2(Hahtp)]Cl2 and [Ag(P-
Ph3)(ahtp)(H2O)] were studied using the thermogravimetric (TG)
technique. The weight loss observed below 130 °C is due to dehy-
dration as the colors changed from pale to deeper [33,39].
The thermogram of [Pd(PPh3)2(Hahtp)]Cl2, shows four TG
inflections in the 35–210, 211–270, 271–520 and 525–800 °C re-
gions. These weight losses may arise from the release of chlorine
molecule (Calcd. 8.4, Found 8.3), three Ph (Calcd. 27.4, Found
27.2%), two P, three Ph and N2 fragments (Calcd. 38.0, Found
38.3%), and C4H5S (Calcd. 10.1, Found 9.5%) fragments, respectively
[33], leaving a residue of palladium oxide and nitride (18.1%). The
thermogram of [Zn(Hahtp)(bpy)Cl2], is characterized by four
weight losses in the 50–300, 301–420, 421–500 and 501–800 °C
regions. These weight losses are due to the elimination of Cl2
(Calcd. 16.3, Found 16.1%) [12], C3H5N2 (Calcd. 15.8, Found
15.4%), CNS (Calcd. 13.3, Found 13.2%) and 1/2 bpy (Calcd. 17.9,
Found 18.2%) fragments, respectively, leaving ZnO contaminated
lar ion (Calcd. 385.5). The peaks at 349.5 and 207.5 correspond to
[Zn(ahtp)2]+ and [Zn(ahtp)]+ fragments, respectively. The mass
spectrum of [Zn(Hahtp)(bpy)Cl2] shows a peak at m/z 436.0 (Calcd.
435.5), in agreement with the molecular ion of the complex,
[Zn(Hahtp)(bpy)Cl2]+, with 3.2% abundance. There are signals
which represent the loss of Cl2 and C3H4N2O fragments (Calcd.
364.5) and [Zn(bpy)]+ with m/z 221 (Calcd. 221.5), respectively.
The mass spectrum of [Pd(phen)(ahtp)]Cl displays a signal at m/z
430 (Calcd. 328.4) with 100% abundance, in agreement with the
molecular ion of the complex, [Pd(ahtp)(phen)]+. The fragmenta-
tion patterns indicate ahtp loss to [Pd(phen)]+ at 285 (Calcd.
286.4). The mass spectrum of the [Pd(PPh3)2(Hahtp)]Cl2 complex
shows first the molecular ion peak at m/z 774 (Calcd. 773.4) with
35% abundance, in agreement with the molecular ion,
[Pd(Hahtp)(PPh3)2]+. The fragmentation patterns indicate the loss
of PPh3, [Pd(PPh3)(Hahtp)]+ at 511 (Calcd. 511.4), [16,38]. The mass
spectrum of [Ag(ahtp)(H2O)2] shows signal at m/z 290 (Calcd. 286)
Fig. 6. Anticancer activity of of Hahtp and its complexes against the human breast cancer MDA- MB231 cell line.

S.A. Elsayed et al. / Journal of Molecular Structure 1028 (2012) 208–214
213
with carbide residue at 700 °C (31.7%) [12,33]. The TG thermogram
of [Pd(phen)(ahtp)]Cl.2H2O shows the first endothermic weight
loss step between 25 and 265 °C, corresponding to the release of
crystal lattice water and 1/2Cl2 (Cacld. 14.3, Found 14.8%). The sec-
ond decomposition step occurs between 266 and 430 °C, this
weight loss is attributed the loss of C4H3N2S fragment (Calcd.
22.2, Found 22.3%). The third TG inflection between 431 and
800 °C is attributed to the loss of C6H2 and 1/2N2 fragments (Calcd.
17.6, Found 17.0%), leaving PdO and carbide residue representing
(45.9%). In some reported transition metal complexes, the thermal
decomposition residue is mainly metal or metal oxide, but in the
presence of non-stoichiometric oxide, unburned carbon or nitrogen
is observed [23].
The thermal decomposition of the complex [Zn(ahtp)2(PPh3)(-
H2O)], shows two TG inflections in the ranges of 75–326 and
327–800 °C. The exothermic weight losses may arise from the re-
lease of coordinated water, PPh3, 1/2O2 and two C4H4N3S frag-
ments (Calcd. 87.1, Found 86.9%), and zinc oxide residue (Calcd.
13.1, Found 12.9%), respectively [33].
The TG thermogram of the complex [Ag(ahtp)(PPh3)(H2O)], dis-
plays three TG weight losses in the ranges 200–275 °C, 276–345
and 346–800 °C. The first exothermic weight loss may arise from
the release of coordinated water, three Ph and 1/2N2 fragments
(Calcd. 49.6, Found 50.2%). The second one is due to the loss of
one P (Calcd. 5.8, Found 5.7%) while the third is indicating the loss
of C4H4O1/2S fragment (Calcd. 17.4, Found 17.2%), leaving silver
oxide residue (26.9%) [12].
that, the water soluble complex, [Pd(phen)(ahtp)]Cl may able to
reach DNA as a cellular target, which can be determined by intra-
cellular transport factors [45]. On the other side, the highest effi-
cacy of the silver complex, [Ag(ahtp)(PPh3)(H2O)], is expected,
since Ag(I) has been reported as a wound healing stimulator [46–
48].
4. Conclusions
In conclusion, new complexes of Hahtp have been prepared and
characterized. The Hahtp ligand shows different coordination
modes-mononegative bidentate, through either thione sulfur and
deprotonated cyclic nitrogen N(1) centers or deprotonated hydro-
xy oxygen and cyclic nitrogen N(3) centers, and neutral bidentate
thione sulfur and cyclic nitrogen N(3) centers. The free hahtp li-
gand and its complexes, [Zn(bpy)(Hahtp)Cl2], [Zn(ahtp)2(PPh3)
(H2O)],
[Zn(ahtp)2(H2O)2],
[Pd(phen)(ahtp)]Cl,
[Pd(Hahtp)-
(PPh3)2]Cl2 and [Ag(ahtp)(PPh3)(H2O)], have been tested as
anticancer agents against MDA-MB231 breast cancer cells and
the silver(I) complex, [Ag(ahtp)(PPh3)(H2O)], shows high efficacy.
Acknowledgements
We are grateful to the Ministry of Higher Education in Egypt
(ES) and NSERC (Canada) Discovery Grant (ISB) for the financial
support of this work.
3.6. Anti-cancer activity
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