Synthesis, antiamoebic activity and thermal study of copper complexes of 1-formyl-2-pyrazolines

Article abstract of DOI:10.1007/s10973-011-2168-3

Copper complexes of 1-formyl-2-pyrazolines were prepared by the reaction of 1-formyl-2-pyrazolines with copper chloride and nitrate with methanol. The structures of copper complexes 1a-3a have been established by elemental analysis, FT-IR, UV and thermogr

Full text of DOI:10.1007/s10973-011-2168-3

J Therm Anal Calorim (2013) 111:549–552
DOI 10.1007/s10973-011-2168-3
Synthesis, antiamoebic activity and thermal study
of copper complexes of 1-formyl-2-pyrazolines
•
Pramod Singh Jagmohan S. Negi
•
•
M. S. M. Rawat Geeta Joshi nee Pant
Received: 8 November 2011 / Accepted: 15 December 2011 / Published online: 6 January 2012
´
´
Ó Akademiai Kiado, Budapest, Hungary 2012
Abstract Copper complexes of 1-formyl-2-pyrazolines
were prepared by the reaction of 1-formyl-2-pyrazolines
with copper chloride and nitrate with methanol. The
structures of copper complexes 1a–3a have been estab-
lished by elemental analysis, FT-IR, UV and thermo-
gravimetric analysis. These compounds were tested against
HM1:IMSS strain of Entamoeba histolytica by the micro-
dilution method. Complexes 2a and 3a are more active
than other complexes.
allows its participation in biological transport [5]. Cu(II) and
Ni(II) 1,3-bis(thiosemicarbazonato) complexes were syn-
thesised by the reaction of the metal acetates with pyrazoline
proligands [6]. Metal complexes of 3-(2-hydroxy-1-naph-
thyl)-5-(4-X-phenyl-2-pyrazolines have been reported by
Athappan et al. [7]. Metal complexes of 3,30-thiodipropionic
acid
bis(4-amino-5-ethylimino-2,3-dimethyl-1-phenyl-3-
pyrazoline) were evaluated for their antifungal and antibac-
terial activities against three fungi, Alternaria brassicae,
Aspergillus niger and Fusarium oxysporum and two bacteria,
i.e. Xanthomonas compestris and Pseudomonas aeruginosa
[8]. Copper (II) complexes of N-1-isonicotinoyl-3-methyl-4-
(p-hydroxybenzilidene)-2-pyrazolin-5-one derivatives show
considerable activity against tumour [9]. Literature survey
revealed that copper (II) complexes as anti-inflammatory
drugs are often more active than the parent ligands [10].
Copper complexes of 5-(20-hydroxyphenyl)-3-(4-X-phenyl)
pyrazolines show good antimicrobial and anti-inflammatory
activities [11]. A copper (II) complex, [Cu(phen)(L-Thr)
(H2O)](ClO4) (phen = 1,10-phenanthroline, L-Thr = L-thre
onine), has exhibited potent cytotoxic effects against the
human leukaemia cell line HL-60 and human stomach cancer
cell line SGC-7901 with inhibition rates of over 90% [12].
Palladium (II) coordination compounds containing isonico-
tinamide were synthesized and characterized by spectro-
scopic and thermal analysis which have been reported by
Rodrigo et al. [13]. The copper and zinc (II) complexes of
1-phenyl-3-methyl-4-benzoyl-5-pyrazolone have been syn-
thesized by Dey et al. [14]. The antifungal and antibacterial
activities of copper (II) complexes have been evaluated
against several pathogenic fungi and bacteria [15–17].
Palladium (II) complexes of pyrazole 3,5-dimethyl-4-iodo-
pyrazole (HdmIPz) have been synthesized and their antitumour
activity tested against murine mammary adenocarcinoma
(LM3) and lung adenocarcinoma (LP07) cell lines [18].
Keywords 1-Formyl-2-pyrazolines ꢀ Copper complexes ꢀ
Thermal analysis ꢀ Antiamoebic activity
Introduction
Metal complexes derived from pyrazole have attracted
considerable interest not only due to their extensive coor-
dination chemistry, but also to their catalytic and biological
properties [1, 2]. Metal ions are known to accelerate drug
action and the efficacy of a therapeutic agent may be
enhanced upon coordination with a metal ion [3]. The
coordination bonds between transition metal ions and
nitrogen containing heterocyclic ligands have proved to be
useful for the construction of solid-state architectures and
inorganic crystal engineering [4].
Copper (II) is an important biologically active essential
ion. Its chelating ability and positive reduction potential
P. Singh (&) ꢀ J. S. Negi ꢀ M. S. M. Rawat ꢀ G. J. nee Pant
Department of Chemistry, HNB Garhwal University, Srinagar,
Garhwal, Uttarakhand 246 174, India
e-mail: negi_pramod04@rediffmail.com
M. S. M. Rawat
e-mail: msmrawat@gmail.com
123

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P. Singh et al.
Amoebiasis is an infection of the mucous membrane of
UV/VIS kmax nm. 263, 327, 538; IR (KBr) cm-1: 1655
(C=O), 1592 (C=N), 1231 (C–N); ESI-MS: 634 (M?H)?,
656 (M?Na)?, 672 (M?K)?.
the large intestine where E. histolytica is a causative
organism. Amoebiasis afflicts millions of individuals in
developing countries. Estimated death toll from amoebiasis
[19] is 40,000-1000,000 annually. Abnormal pain, anor-
exia, fever, hepatomegaly and weight loss are caused by
E. histolytica present in intestine in the form of trophozo-
ites and cysts [20]. Synthesis and thermal studies of Cu (II)
complexes with different ligands have been reported [21,
22]. Here, we report synthesis and antiamoebic activity of a
new series of complexes of N1-formyl pyrazolines.
Compound 1b (C32H28N6O6Cu)
Green crystals; crystallized in methanol; yield 48%, m.p.
310–312 °C. Anal. calcd. for C32H28N6O6Cu (%):C, 55.90;
H, 4.07; N, 12.23. Found: C, 55.93; H, 4.06; N, 12.19; UV/
VIS kmax nm. 268, 335, 542; IR (KBr) cm-1: 1662 (C=O),
1598 (C=N), 1242 (C–N); ESI-MS: 656 (M?H)?,
679 (M?Na)?, 695 (M?K)?.
Materials and methods
Compound 2a (C32H26N4O2CuCl4)
Materials
Green crystals; crystallized in methanol; yield 45%; m.p.
305–307 °C. Anal. calcd. for C32H26N4O2CuCl4 (%): C,
54.62; H, 3.70; N, 7.96. Found: C, 54.59; H, 3.66; N, 7.92;
UV/VIS kmax nm. 265, 339, 540; IR (KBr) cm-1: 1658
(C=O), 1610 (C=N), 1228 (C–N); ESI-MS: 702 (M?H)?,
724 (M?Na)?, 740 (M?K)?.
The progress of reaction was monitored by TLC plate (Merck,
silica gel 60 F254) using chloroform:methanol (7:3) as mobile
phase. All the starting materials were of GR quality, Merck.
Solvents were distilled before using. Melting points were
recorded in open capillary with Metzer apparatus and are
uncorrected. IR spectra were recorded with KBr in Perkin
Elmer FT-IR-RX-01 Spectrophotometer. UV Spectra were
recorded on Perkin Elmer double beam UV–Visible Spectro-
photometer (k-25) in chloroform. Elemental analyses were
performed by Central Drug Research Institute, Lucknow, using
Heraeus Vario EL III analyzer, and the results were within 0.3%
of the theoretical values. Thermograms were recorded on
simultaneous DT-TG Shimadzu thermal analyzer, DT-40 inair.
Compound 3a (C32H26N4O2CuCl4)
Green crystals; crystallized in methanol; yield 70%; m.p.
308–309 °C. Anal. calcd. for C32H26N4O2CuCl4 (%): C,
54.62; H, 3.70; N, 7.96. Found: C, 54.59; H, 3.66; N, 7.94;
UV/VIS kmax nm. 268, 339, 544; IR (KBr) cm-1: 1670
(C=O), 1615 (C=N), 1364 (C–N); ESI-MS: 702 (M?H)?,
724 (M?Na)?, 740 (M?K)?.
Biological activity
Preparation method
Antiamoebic activity was done by the reported method in
literature [24, 25].
Ligands
Ligands (1-formyl-2-pyrazolines) 1–3 were synthesized by
reported method [23].
Results and discussion
Synthesis of copper complexes of 2-pyrazolines
Chemistry
Copper complexes 1a–3a was prepared by mixing of ligands
and copper chloride and nitrate in hot methanol with contin-
uous stirring. The reaction mixture was refluxed for 6 h. The
solution was kept at 0 °C for crystallization. The crystalline
products were separated after 6–7 days by filtration, and finally
washed with methanol and dried in vacuum.
Ligands were prepared by the reported methods [23] in
moderate yields about 60–80%. Chloride and nitrate of
copper (II) were used for the synthesis of complexes 1a–3a
(Scheme 1). Ligands and metals were mixed in equimolar
ratio (1:1) in methanol. All complexes were sparingly sol-
uble in chloroform but soluble in DMSO. The metal com-
plexes were characterized by spectral and thermal studies.
Compound 1a (C32H28N4O2CuCl2)
Infrared and electronic spectral studies
Green crystals; crystallized in methanol; yield 72%; m.p.
320–322 °C. Anal. calcd. for C32H28N4O2CuCl2(%): C,
60.66; H, 4.42; N, 8.84. Found: C, 60.62; H, 4.38; N, 8.80;
The IR spectra of complexes (1a–3a) showed strong bands
in the region between 1,670 and 1,658 cm-1 due to the
123

Synthesis, antiamoebic activity and thermal study of copper complexes
551
193.40 °C
–7.350%
100.00
80.00
60.00
40.00
DTA
TGA
DTG
1
–52.571%
'
C
N
CH CH2
N
R
R
2.00
0.00
325.82 °C
150.00
100.00
50.00
CHO
–2.00
–4.00
362.47 °C
–2.37 mg/min
326.96 °C
Ligands 1-3
–4.299%
619.10 °C
368.31 °C
466.58 °C
776.18 °C
'
200.00
400.00
600.00
800.00
R
Temperature/°C
CuX2
MeOH
1
Fig. 1 Thermal curve of compound 1a
R
H
C
O
Table 1 Antiamoebic activity of metal complexes of 2-pyrazolines/
1a–3a
N
X
N
Cu
N
S. no.
Compounds
IC50/lM SD*
X
N
1
2
3
4
5
1a
0.501 0.10
0.508 0.08
0.390 0.08
0.422 0.04
0.226 0.06
O
C
1b
H
2a
1
3a
R
MNZ
MNZ metronidazole, SD standard deviation
* Significant (P \ 0.05)
'
R
Complexes 1a-3a
Scheme 1 Synthesis of complexes 1a–3a. 1a: R0 = R1= H, X = Cl;
1b: R0 = R1= H, X = NO2; 2a: R0 = Cl, R1= H, X = Cl; 3a:
R0 = H, R1 = Cl, X = Cl
a solvent. Twofold serial dilutions were made of either the free
ligand or the corresponding complexes 1a–3a in 96-well
microtiter plates and were incubated for 72 h. The concentra-
tion of drug for IC50 was determined by the microdilution
method [26]. The experimental results are summarized in the
Table 1. The results show 50% inhibitory concentration in
carbonyl groups. Other bands in the range between
1,615–1,558 and 1,364–1,228 cm-1 show presence of C=N
and C–N groups. Chelation weakens the bonds that are
involved in coordination bringing a shift to lower fre-
quencies in comparison to ligands. The electronic spectra
of complexes (1a–3a) showed bands in the region between
265–273, 327–339 and 538–544 nm.
comparison to the standard drug metronidazole (IC50
=
0.266 lM). All compounds show activity against the test
organism E. histolytica with IC50 values in the range between
0.390 and 0.508 lM. Among these, 2a with IC50 0.390 lM is
the most active. The null hypothesis was tested using t test and
the significance of the differences among the IC50 values of
metronidazole, 1a, 1b, 2a and 3a was evaluated.
Thermal studies
Complex 2a is more active than 1a with lower MIC
value. Difference in the anion did not influence the activity
much as the MIC values of 1a and 1b are comparable.
Copper complex of 1-formyl-2-pyrazoline 1a showed about
eleven times high activity than ligand 1 [1-formyl-2-pyraz-
oline (5.62 lM)] which may be due to enhanced solubility.
Complex 2a is more active than 3a because of the chloro
group attached with different phenyl rings of the pyrazoline.
In the thermal curve (Fig. 1) of complex (1a), the TG curve
of complex of composition CuCl2 (C32H28O2N4) has
shown that it is stable up to 193.40 °C after which tem-
perature it seems to undergo continuous decomposition in
single step in 193.40–776.18 °C temperature range. This is
substantiated by single peak at 362.47 °C in DTG curve.
The 64.22% weight loss may be accounted for the forma-
tion of copper oxide (CuO). The complex has shown
endothermic peaks at 326.96 and 368.31 °C.
Conclusions
Antiamoebic activity
We have synthesized four novel copper complexes of
1-formyl-2-pyrazolines. The complexes were screened
against E. histolytica using metronidazole as standard drug.
Antiamoebic activity of pyrazolines complexes 1a–3a against
HM1:IMSS strain of E. histolytica was carried out in DMSO as
123

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P. Singh et al.
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All the complexes show good activity against the test
organism with IC50 values in the range between 0.390 and
0.508 lM. Among all these compounds, 2a is more active.
Cytotoxicity profile, thermal and single crystal studies of
the compounds is in progress.
Acknowledgements The authors are thankful to Dr. Amir Azam,
Jamia Milia Islamia University, New Delhi, for screening biological
activity of the synthesized compounds. This study was supported by
UGC New Delhi [Grant No. F.4-3/2006(BSR)/11-84/2008 (BSR)].
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