Diorganotin(IV) derivatives of ONO tridentate Schiff base: Synthesis, crystal structure, in vitro antimicrobial, anti-leishmanial and DNA binding studies

Article abstract of DOI:10.1016/j.ejmech.2010.03.015

Six new diorganotin(IV) derivatives of N′-(2-hydroxybenzylidene) formohydrazide (H₂L) with general formula R₂SnL, where R = Ph (1), Me (2), Bu (3), Oct (4), t-Bu (5), Et (6), and L = [OC ₆H₄CHNNCHO] have been sy

Full text of DOI:10.1016/j.ejmech.2010.03.015

European Journal of Medicinal Chemistry 45 (2010) 2902e2911
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Diorganotin(IV) derivatives of ONO tridentate Schiff base: Synthesis, crystal
structure, in vitro antimicrobial, anti-leishmanial and DNA binding studies
,
a
Shaukat Shujha a, Afzal Shah a, Zia-ur-Rehman a, Niaz Muhammad a, Saqib Ali a , Rumana Qureshi ,
*
Nasir Khalid b, Auke Meetsma c
a Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan
b Chemistry Division, Pakistan Institute of Nuclear Science and Technology, PO Nilore, Islamabad, Pakistan
c Crystal Structure Center, Chemical Physics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747 AG Groningen, The Netherlands
a r t i c l e i n f o
a b s t r a c t
Six new diorganotin(IV) derivatives of N0-(2-hydroxybenzylidene)formohydrazide (H2L) with general
formula R2SnL, where R ¼ Ph (1), Me (2), Bu (3), Oct (4), t-Bu (5), Et (6), and L ¼ [OC6H4CHNNCHO] have
been synthesized and characterized by different analytical techniques. Crystal structure of Me2SnL (2)
authenticated distorted square-pyramidal geometry around the Sn atom. The CV and UVeVis spectro-
scopic data indicated intercalation of complexes into DNA with binding affinity varying in the sequence:
Article history:
Received 12 August 2009
Received in revised form
11 March 2010
Accepted 15 March 2010
Available online 18 March 2010
3 (1.69 ꢀ 104 Mꢁ1) > 1 (1.10 ꢀ 104
M
ꢁ1) > 2 (9.61 ꢀ 103
M
ꢁ1). Some of these compounds were found to
be good antibacterial, antifungal and leishmanicidal agents.
Keywords:
Ó 2010 Elsevier Masson SAS. All rights reserved.
N0-(2-Hydroxybenzylidene)formohydrazide
Diorganotin(IV) complexes
Crystal structure
DNA-binding
1. Introduction
report on the in vitro evaluation of the binding parameters of
organotin(IV) schiff base complexes with DNA by electrochemical
and spectroscopic techniques.
The study of organotin(IV) complexes has gained growing
interest in the last four decades due to their ability to interact with
DNA, indicating their potential candidature in cancer chemo-
therapy [1e4]. Several organotin(IV) Schiff base complexes have
been investigated for their structural diversity and biocidal activi-
ties [5e7]. Cagnoli et al. found some organotin(IV) complexes to be
even more active in vitro than the clinically used cis-platin [8]. Some
other workers have established the quantitative structure/activity
and structure/property relationships of these compounds [9].
However, little work has been carried out on the ONO donor
tridentate chelating ligands, derived from the condensation of
salicylaldehyde with hydrazides [10]. The present work is centered
on the synthesis of diorganotin(IV) Schiff base derivatives of formic
hydrazide and their characterization by different analytical tech-
niques. Some of these compounds have good antimicrobial activi-
ties. Keeping the anticancer activity of dibutyltin(IV) complexes
[11] in view, we selected three potential antitumor organotin(IV)
complexes, with the one having dibutyltin(IV) moiety to evaluate
their DNA binding parameters. Up to our knowledge, this is the first
2. Results and discussion
2.1. Synthesis
The ligand was synthesized by direct reaction of formic hydra-
zide with salicylaldehyde in ethanol. The yellow organotin(IV)
complexes were prepared by reacting together ligand, organotin
(IV) dichloride, triethylamine in 1:1:2 and ligand, dioctyltin(IV)
oxide in 1:1 ratios in dry toluene. All the compounds were obtained
in good yield. The detailed syntheses and physical data are
presented in Experimental section.
2.2. Spectroscopic studies
In the ligand the vibration bands appearing at 3345, 3184 and
1689 cmꢁ1 were assigned to nNeH
, nOeH and nC]O vibration modes,
respectively. Due to enolization and deprotonation of the ligand on
complexation with diorganotin moiety, these bands disappeared.
The shifting of nC]N band at 1613 cmꢁ1 to lower energy suggested
* Corresponding author. Tel.: þ925190642208; fax: þ92512873869.
E-mail address: drsa54@yahoo.com (S. Ali).
0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.03.015

S. Shujha et al. / European Journal of Medicinal Chemistry 45 (2010) 2902e2911
2903
Table 1
the coordination of azomethine nitrogen with Sn atom [12]. The
shifting of nNeN band from 1053 cmꢁ1 to 1072e1082 cmꢁ1 on
complexation is attributed to the decrease in repulsion of the lone
pairs of electrons on the nitrogen atoms [13]. New bands were also
Crystal data and structure refinement parameters for Me2SnL (2).
Empirical formula
Formula mass
Crystal system
Space group
a (Å)
C10H12N2O2Sn
310.93
Tetragonal
I41/a, 88
13.4693(4)
13.4693(4)
24.9037(17)
4518.1(4)
16(1)
observed in the region of 500e555 cmꢁ1 nSneO) and 450e470 cmꢁ1
(
(nSneN) [14].
The 1H NMR spectral data showed signals at 10.12, 11.67 and
b (Å)
c (Å)
8.68 ppm due to eOH, eCHO and eNHN] protons, respectively. All
these signals were absent from the spectra of complexes owing to
the conversion of the aldo-imine form of ligand to imine-ol form
and subsequent deprotonation. The coordination of azomethine
nitrogen with Sn atom shifted the CH]N proton resonance signal
down field to 8.60e8.65 ppm with 3J (119Sn, 1H) coupling constant
value of 38e51 Hz. All the other protons of the ligand and the R
groups bonded to Sn atom appeared in the expected region. The
2J (119Sn, 1H) coupling constant (79 Hz) of complex 2 corresponding
to CeSneC angel of 129.6ꢂ was evaluated by Lockhart’s equation,
V (Å3)
Z(Z0)
Crystal habit/size (mm)
T (K)
Block/0.35 ꢀ 0.29 ꢀ 0.15
100(1)
r
(g cmꢁ3
)
1.828
22.44
2432
19718
2799
2749
0.0223
0.0558
m
(Mo Ka) (cmꢁ1
)
F(000)
Total reflections
Independent reflections
For (Fo ꢃ 4.0
s
(Fo))
P
P
RðFÞ ¼ ðjjFoj ꢁ jFcjjÞ= jFoj for Fo > 4.0
s
(Fo)
P
P
wRðF2Þ ¼ ½ ½wðFo2 ꢁ Fc2Þ2ꢄ=½ wðFo2Þ2ꢄꢄ1=2
q
¼ 0.0161 [2J]2 ꢁ 1.32 [2J] þ 133.4 [15]. Thus, confirmed five-
Goodness-of-fit
1.043
coordinate Sn atom in solution. In 13C NMR, the angle calculated
q
Range (ꢂ)
2.69e29.28
2799/0/139
ꢁ0.12 and 0.17(4)
(127.4e133.4ꢂ) for compounds 2, 3, 5 and 6, using equation
Data/restrictions/params
1J ¼ 10.7
qe778 [16], affirmed penta-coordination of Sn in solution.
Largest diff. peak and hole (e Åꢁ3
)
In all complexes, the signals observed in 13C NMR are in conformity
with expected composition.
The presence of a single 119Sn peak for complexes 1e6 in the
range ꢁ163.2 to ꢁ337 ppm is in conformity with the formation of
a single species having penta-coordinated Sn atom [17].
bond distances and angles of the complex 2 are comparable with
the values for analogous compounds [18]. The structure of
complex 2 consists of a deprotonated ONO dibasic tridentate
ligand bonded to the (CH3)2Sn(IV) moiety via two oxygen and
a nitrogen atom, forming a O2NC2 core around the Sn atom.
The ligand is non-planar, probably due to the steric requirements
of the five and six membered chelate rings formed. The
geometry around Sn atom can be characterized by the value of
2.3. Mass spectrometry
The ligand and its complexes showed molecular ion peak of
significant intensity with the characteristic peak pattern of Sn. The
proposed fragmentation pattern of ligand and complex 2 is depic-
ted in Scheme 6. The initial fragmentation is due to the loss of
a methyl group, which then gave a base peak [C8H6N2O2Sn]þ in the
spectrum due to the elimination of a second methyl group. The
other fragments with significant abundances were [CH3Sn]þ,
[CH3Sn]þ and [Sn]þ. The rest of the diorganotin(IV) compounds
followed almost the same fragmentation route as 2, the mass
spectral data is given in the Experimental section.
s
¼ (
b
ꢁ
a)/60, where b is the largest and a the second largest
basal angles around the Sn atom. The
s
value is zero for perfect
square pyramid (
pyramidal geometry
a
¼
b
¼ 180ꢂ) and unity for a perfect trigonal
(
a
¼
120ꢂ) [19]. For compound
2
(
s
b
¼ O1eSneO2 ¼ 152.9ꢂ and
a
¼ C9eSneC10 ¼ 140.7ꢂ) the
value (0.2) indicates a distorted square-pyramidal geometry
with two enolic oxygens and two methyl carbons in the equa-
torial positions and the azomethinic nitrogen at the apical
position. The tendency of going from trigonal-bipyramidal
geometry towards a square-pyramidal one is most probably
associated with secondary intermolecular Sn/O interactions
(Fig. 2). The SneO1 and SneO2 bond lengths (2.110 and 2.169 Å)
are less than the sum of Van der Waals radii of Sn and O (2.8 Å).
The O1eSneN1, and O2eSneN1 angles are 82.25ꢂ and 72.47ꢂ,
2.4. Crystal structure
The molecular structure with atomic numbering scheme for
compound 2 is given in Fig. 1. The crystallographic data, selected
bond lengths and angles are listed in the Tables 1 and 2. The
respectively. The C9eSneC10 angle (140.70ꢂ) show
a large
deviation from the linear value (180ꢂ) and the angle calculated
from 2J(119Sne1H) (129.6ꢂ) and 1J[119Sne13C] (133.4ꢂ) by Lockhart
Table 2
Selected bond lengths (Å) and angles (ꢂ) for Me2SnL (2).
SneO1
SneO2
SneN1
SneC9
2.110(2)
2.169(2)
2.184(2)
2.106(4)
2.112(4)
152.89(9)
82.25(9)
88.93(13)
96.55(10)
72.47(9)
93.36(13)
98.63(10)
115.96(13)
103.34(11)
140.70(14)
O1eC1
O2eC8
N1eN2
N1eC7
1.312(4)
1.302(4)
1.409(3)
1.295(4)
1.289(4)
115.6(2)
110.0(3)
119.0(3)
123.2(2)
129.21(18)
113.12(18)
116.97(18)
127.13(19)
126.2(3)
127.1(3)
SneC10
N2eC8
O1eSneO2
O1eSneN1
O1eSneC9
O1eSneC10
O2eSneN1
O2eSneC9
O2eSneC10
N1eSneC9
N1eSneC10
C9eSneC10
N2eN1eC7
N1eN2eC8
O1eC1eC2
O1eC1eC6
SneO1eC1
SneO2eC8
SneN1eN2
SneN1eC7
N1eC7eC6
O2eC8eN2
Fig. 1. ORTEP view of Me2SnL (2) with atomic numbering scheme. Thermal ellipsoids
are drawn at the 50% probability level. Hydrogen atoms are shown as spheres of
arbitrary radii.

2904
S. Shujha et al. / European Journal of Medicinal Chemistry 45 (2010) 2902e2911
to the simplicity in the cell wall of these strains [22]. The dimethyl-
(2) and dibutyltin(IV)-(3) complexes show highest activity, which
subsides as the alkyl chain length increases [23,24].
2.5.2. Antifungal activity
The antifungal activity of synthesized compounds were tested
in vitro against human pathogenic fungal strains including yeasts
(Candida albicans ATCC 2192, Candida glabrata ATCC 90030),
dermatophytes (Microsporum canis ATCC 9865, Trichphyton
longifusus ATCC 22397), opportunistic moulds (Aspergillus flavus
ATCC 1030 and Fusarium solani ATCC 11712) by using the agar
tube dilution test. Micoanazole (200
(200 g/ml) were used as standards drugs. The percent growth
mg/ml) and Amphotericin B
m
inhibition of the compounds is summarized in Table 4. All the
fungal strains except A. flavus are resistant to the ligand. Activity of
compounds 1, 2 and 6 is fairly good while for the rest of the
compounds low activity was observed.
2.5.3. Cytotoxicity
The in vivo lethality to brine shrimp nauplii was used to assess
the cytotoxicity of synthesized compounds [25]. The results are
presented in Table 5. Compound 3 show highest toxicity larger than
Fig. 2. The molecular packing of Me2SnL (2) showing the arrangement of monomeric
units.
the standard drug with LD50 0.691 mg/ml.
equation [14,15]. The SneN1 bond distance is 2.184 Å, closer to
the sum of covalent radii of Sn and N (2.15 Å) and significantly
less than the sum of van der waals radii (3.75 Å). The C1eO1,
C8eO2 bond length (1.313 Å, 1.302 Å) and C1eN1eN2 angle
(109.99ꢂ) for compound 2 are match-well with the reported
values [17].
2.5.4. Anti-leishmanial activity
The Anti-leishmanial activity of ligand and complexes (1e6)
were obtained against the pathogenic Leishmania major, using
Amphotericin B (0.50
mg/ml) and Pentamidine (5.78 mg/ml) as
standard drugs. The data are presented in Table 6. The reported
compounds produced a significant reduction in viable promas-
tigotes. Compound 6 has the highest potential as leishmanicidal
agent with IC50 0.90
m
g/ml followed by compound
3
2.5. Biological activity
(IC50 0.96 g/ml) and 5 (IC50 0.98
m
m
g/ml). The activity of these
compounds is excellent and far exceed the level for the reported
organotin(IV) compounds [26].
2.5.1. Antibacterial activity
The Schiff base ligand and its diorganotin(IV) derivatives were
screened for their antibacterial activity against 2 gram positive
(Bacillus subtilis, Staphylococcus aureus) and 4 gram negative
bacteria (Eschericha coli, Shigella flexenari, Pseudomonas aeruginosa,
Salmonella typhi), Table 3. Despite the reported antibacterial
activity of various Schiff bases [20,21], the synthesized ligand was
found inactive against all bacterial strains. Most of the diorganotin
(IV) derivatives significantly inhibit gram-positive bacteria growth.
This may be due to the ease of permeation of the complexes owing
2.6. Voltammetric study of complex-DNA interaction
The cyclic voltammetric behavior of 3.00 mM complex 1 in the
absence and presence of 50 mM DNA at bare GCE is shown in Fig. 3A.
The voltammogram of the free complex 1 shown in Fig. 3A(a)
featured a single well defined and stable cathodic peak at ꢁ1.531 V
versus SCE in 10% aqueous DMSO at 25 ꢂC. The absence of anodic
peak in the reverse scan indicated the irreversibility of the elec-
trochemical process. The electrochemical signal at ꢁ1.531 V is
attributed to the reduction of Snþ4 to Snþ2 state. The broadness of
the peak as indicated by jEp ꢁ Ep/2j ¼ 70 mV, may be due to the
overlap of two 1eꢁ reduction peaks. The cyclic voltammogram of
Table 3
Antibacterial activityaed (diameter of inhibition zone) of N0-(2-hydrox-
ylbenzylidene) formohydrazide and its diorganotin(IV) derivatives.
Bacterium (ATCC No.)
Inhibition zone diameter (mm)
Reference
drug
complex 1 in the presence of 50 mM DNA (Fig. 3A(b)), underwent
H2L
1
2
3
4
5
6
Bacillus subtillis (11774)
Staphylococcus aureus
(25923)
Eschericha coli (11229)
Shigella flexenari (10782)
Pseudomonas aeruginosa
(10145)
e
e
18 15 20 10
20 15
e
12 37
Table 4
e
e
10
9
26
Antifungal activity a,b,c (% inhibition) of N0-(2-hydroxybenzylidene)formohydrazide
and its diorganotin(IV) derivatives.
e
e
e
15 10 18 11 12
17 14 11
9
30
e
9
e
10 36
11 32
Fungus (ATCC No.)
Inhibition %
MIC
g/ml)
10 12
9
e
(m
H2L
1
2
3
4
5
6
Salmonella typhi (10749)
e
e
e
17
e
15
30
Candida albicans (2129)
Aspergeilus flavus (1030)
Microsporum canis (9865)
Fusarium solani (11712)
Trichophyton longifusus
(22397)
0
40
0
0
0
0
35
45
0
40
20
0
10
0
20
0
30
0
10
0
10
0
20
0
20
40
0
30
0
110.8
20.0
98.4
73.2
70.0
50
10
0
a
In vitro agar well-diffusion method, conc. 1 mg mLꢁ1 DMSO.
Reference drug, Imipenum 10
Zone diameter (Activity): 3e6 mm (non significant), 7e9 mm (low), 10e12 mm
b
c
mg/disc.
40
0
0
(good), >12 mm (significant).
d
Clinical Implication: Escherichia coli, infection of wounds, urinary tract and
Candida glabrata (90 030)
0
50
0
0
5
0
35
110.8
dysentery; Bacillus subtilis, food poisoning; Shigella flexenari, blood diarrhea with
fever and severe prostration; Staphylococcus aureus, food poisoning, scaled skin
syndrome, endocarditis; Pseudomonas aeruginosa, infection of wounds, eyes, septi-
cemia, Salmonella typhi, typhoid fever, localized infection [25].
a
Concentration: 200 m
g mLꢁ1 of DMSO.
MIC: Minimum inhibitory concentration.
% (standard drug) ¼ 100.
b
c

S. Shujha et al. / European Journal of Medicinal Chemistry 45 (2010) 2902e2911
2905
Table 5
-17
a
A
Brine Shrimp (Artemia salina) lethality bioassay of N0-(2-ydroxybenzylidene)
formohydrazide and its diorganotin(IV) complexes.
-14
-11
-8
-5
-2
1
Sample Code
LD50 g/ml
H2L
1
2
3
4
5
6
b
m
e
e
95.70
0.691
e
e
88.30
Standard drug Etoppside LD50 7.46
mg/mL.
31.46% decrease in peak current and 79 mV positive shift in peak
potential. The substantial diminution in peak current can presum-
ably be due to the decrease in free drug concentration due to the
formation of slowly diffusing, heavy molecular weight 1-DNA
adduct. The obvious positive peak potential shift could be attrib-
uted to the intercalation of 1 into the stacked base pair pockets of
DNA as reported by the previous investigators [27,28]. The
voltammetric parameters obtained from the cyclic voltammograms
of 3.00 mM 2 and 3 with and without DNA (Fig. 3B and C) are listed
in Table 7.
4
-1.2
-1.4
-1.6
-1.8
E / V vs. SCE
-12
-9
-6
-3
0
B
a
b
The greater decrease in peak current (33.65%) of 3 as compared
to 2 (24.88%) by the addition of 50 mM DNA is due to the lower
diffusion coefficient of 3eDNA complex as compared to 2eDNA,
which will be discussed thoroughly in subsequent section. The
positive shift in peak potentials of both the compounds by the
addition of DNA reflects intercalation as the dominant mode of
interaction, in which the drug inserts itself into the stacked base
pairs domain of DNA.
3
-1.4
-1.6
-1.8
E / V vs. SCE
-2
The gradual decay in peak current of 1, 2 and 3 by the addition of
varying concentration of DNA, ranging from 10 to 60 mM, can be
used to quantify the binding constants of 1-DNA, 2-DNA and 3-DNA
adducts by the application of the following equation [29].
-14
-10
-6
C
a
log ð1=½DNAꢄÞ ¼ log K þ log ðIHꢁG=ðIG ꢁ IHꢁGÞÞ
(1)
b
where, K is the binding constant, IG and IHꢁG are the peak currents
of the free guest (G) and the adduct (H ꢁ G), respectively.
The plots of log (1/[DNA]) versus log (IHꢁG/(IG ꢁ IHꢁG)) (Fig. 4)
yielded K ¼ 1.10 ꢀ 104 Mꢁ1, 9.61 ꢀ 103 Mꢁ1 and 1.69 ꢀ 104 Mꢁ1 for
1-DNA, 2-DNA and 3-DNA complexes, respectively. The greater K
value of 1 as compared to 2 is attributed to the presence of
extended aromatic system which may bind strongly with DNA
bases [30]. The strong affinity of 3 for DNA, indicated by its greater
intercept (Fig. 4) as compared to 1 could be assigned to the addi-
tional hydrophobic interactions of the bulky butyl moiety with the
nucleotide bases. The K values of these diorganotin(IV) e DNA
adducts are greater than those observed for similar DNA-inter-
-2
2
-1.4
-1.6
-1.8
E / V vs. SCE
-2
Fig. 3. A. Cyclic voltammograms of 3.00 mM Ph2SnL (1) in 10% aqueous DMSO with
0.1 M TBAP as supporting electrolyte in the absence (a) and presence of 50 mM DNA (b)
calating Cr and Ru complexes, [CrCl2(dicnq)2]þ and [Ru(dicnq)3]þ2
,
at 25 ꢂC. Working electrode: Glassy carbon with a geometric area of 0.071 cm2, scan
for which the binding constants have been reported as 1.20 ꢀ 103
rate 100 mV/s. B. Cyclic voltammograms of 3.00 mM Me2SnL (2) in 10% aqueous DMSO
and 9.70 ꢀ 103
M
ꢁ1, respectively [31e33].
with 0.1 M TBAP as supporting electrolyte in the absence (a) and presence of 50 mM
DNA (b) at 25 ꢂC. Working electrode: Glassy carbon with a geometric area of 0.071 cm2,
scan rate 100 mV/s. C. Cyclic voltammograms of 3.00 mM Bu2SnL (3) in 10% aqueous
DMSO with 0.1 M TBAP as supporting electrolyte in the absence (a) and presence of
To know whether the electrochemical process is diffusion
controlled or adsorption controlled, the values of peak current,
I were plotted vs. the square root of the scan rate (n
1/2) in the
50
m
M DNA (b) at 25 ꢂC. Working electrode: Glassy carbon with a geometric area of
0.071 cm2, scan rate 100 mV/s.
presence and absence of DNA using RandleseSevcik equation for
irreversible process [34,35].
I ¼ 2:69 ꢀ 105nð
a
nÞ1=2ACoꢅD1=2n1=2
(2)
Table 6
Anti-leishmanial activity of N0-(2-hydroxybenzylidene)formohydrazide and its
Where I is the peak current (A), A is the surface area of the
diorganotin(IV) complexes.
electrode (cm2), Coꢅ is the bulk concentration (mol cmꢁ3) of the
Sample Code
IC50
(
m
g/ml) ꢆ S.D
electroactive species, D is the diffusion coefficient (cm2
s
ꢁ1),
a
is
the transfer coefficient with a value of 0.34 as obtained from
n and
is the scan rate (V sꢁ1).
H2L
1
2
3
4
24.0 ꢆ 0.02
6.50 ꢆ 0.04
2.08 ꢆ 0.04
0.96 ꢆ 0.02
4.26 ꢆ 0.04
0.98 ꢆ 0.02
0.90 ꢆ 0.02
jEpeEp/2j ¼ 47.7 mV/
a
n
The linearity of the plots demonstrates that the main mass
transport of these complexes (Fig. 4A) and their DNA adducts
(Fig. 4B), to the electrode surface is controlled by diffusion step [36].
The diffusion coefficients of the free and DNA bound adducts of
5
6

2906
S. Shujha et al. / European Journal of Medicinal Chemistry 45 (2010) 2902e2911
Table 7
2.7. UVeVis absorption study of complex-DNA interaction
Voltammetric parameters of compound 1e3 in the absence and presence of DNA.
The interaction of diorganotin(IV) complexes with DNA was also
examined by UVeVis spectroscopy for getting some further clues
about the mode of interaction and binding strength. The effect of
Substance
n
/V sꢁ1 [DNA]/
m
M
I/
m
A
Epc/V
Shift in
Epc/m V in I
% Decrease
1
0.1
0.1
0.1
0.1
0.1
0.1
0
50
0
50
0
ꢁ15.63 ꢁ1.531 79
ꢁ10.71 ꢁ1.452
31.46
24.88
33.65
1-DNA
2
2-DNA
3
varying concentration of DNA (5e25
mM) on the electronic
ꢁ10.85 ꢁ1.710 46
ꢁ8.15 ꢁ1.664
absorption spectra of 0.2 mM of 1, 2 and 3 is shown in Fig. 5AeC.
The strong absorption of these compounds in the near UV region
(292e330 nm) is attributed to the long-living triplet excited state of
the aromatic system. The underlying principle behind the broad
absorption bands in the region (350e470 nm) is the transition
ꢁ12.67 ꢁ1.713 52
ꢁ8.41 ꢁ1.661
3-DNA
50
diorganotin(IV) complexes (Table 8) were determined from the
slopes of RandleseSevcik plots. The lower diffusion coefficients of
the DNA bound species are responsible for the decay of peak
currents in cyclic voltammograms shown in Fig. 3.
between
pep* and nep* energy levels of the tridentate ligand
N0-(2-hydroxybenzylidene)formohydrazide. The absorption spec-
tra of 1, 2 and 3 recorded a 68.26, 62.83 and 65.91% decrease in peak
intensities accompanied with 2, 5 and 3 nm red shift, by the
addition of 25 mM DNA. The peculiar hypochromic effects can be
5
associated with the interaction of electronic states of the inter-
calating chromophore and those of the stacked base pairs of DNA
[37,38]. The slight bathochromic shifts can best be described by the
1
2
3
lowering in
pep* and nep* transition energy of the ligands in
diorganotin(IV) complexes due to their ordered stacking between
the DNA base pairs after intercalation.
4.6
Based upon the decrease in absorbance, the binding constants
were calculated according to the following equation [39,40].
A0
A ꢁ A0
3G
3HꢁG
3G
3G 3HꢁG
1
¼
þ
(3)
ꢁ
ꢁ
3G K½DNAꢄ
4.2
0.15
0.65
1.15
1.65
Where K is the binding constant, A0 and A are absorbances of the
free and DNA bound diorganotin(IV) complexes while 3G and 3HꢁG
are their absorption coefficients respectively.
log(IH-G)/(IG-IH-G))
-40
-30
-20
-10
0
A
The binding constants, with values of 1.54 ꢀ 104, 8.19 ꢀ 103 and
2.59 ꢀ 104 Mꢁ1 for the interaction of 1, 2 and 3 with DNA were
obtained from the slope to intercept ratio of the plots (Fig. 6)
between A0/(A ꢁ A0) vs. 1/[DNA]. The results tabulated in Table 8,
indicate a very close agreement in the values obtained from CV and
UVeVis spectroscopy. An examination of Table 8 reflects that the
interaction of these drugs with DNA is a spontaneous process as
3
1
attested by the negative values of DG.
2
3. Conclusions
Spectroscopic data and X-ray single crystal study confirmed
tridentate coordination of ligand with diorganotin moiety. Due to
the presence of intermolecular Sn/O interactions in compound 2,
the structure has a tendency towards a square-pyramidal geometry.
The dibutyltin(IV) derivative exhibited significant inhibitory effects
on gram positive bacterial strains, leshminia major and brine
shrimp larvae. The results of CV and UVeVis. spectroscopy revealed
intercalative mode of interaction of these complexes with DNA as
the dominant mode. The negative values of standard Gibbs energy
0.2
0.4
0.6
0.8
υ1/2(V/s)1/2
-30
-20
-10
0
B
changes (
D
G ¼ ꢁRTlnK) indicated the spontaneity of these inter-
actions. This study is expected to throw light in understanding the
molecular mechanism of the drug action and designing of DNA
targeted drugs.
1
3
2
4. Experimental
0.2
0.4
0.6
0.8
υ1/2(V/s)1/2
4.1. Materials and methods
Fig. 4. Plots of log (IHꢁG/(IG ꢁ IHꢁG)) vs. log (1/[DNA]) used to calculate the binding
constants of 1-DNA, 2-DNA and 3-DNA adducts. A. Plots of I vs.
1/2, for the determi-
nation of diffusion coefficients of the free drugs (3.00 mM 1e3). Scan rates 0.1e0.6 V/s
with a difference of 0.1 V/s. B. Plots of I vs.
1/2, for the determination of the diffusion
All reagents of analytical grade were obtained from Aldrich
chemicals (USA). Tetrabutylammonium perchlorate (TBAP, Fluka,
99% purity) was further purified by recrystallization using meth-
anol as a solvent. DMSO, ethanol and toluene were procured from
E. Merck (Germany). Toulene was dried before use with standard
n
n
coefficients of the DNA bound drugs by taking 3.00 mM 1e3 and 60
0.1e0.6 V/s with a difference of 0.1 V/s.
mM DNA. Scan rate

S. Shujha et al. / European Journal of Medicinal Chemistry 45 (2010) 2902e2911
2907
Table 8
The binding constants and Gibbs free energies of 1-DNA, 2-DNA and 3-DNA adducts as determined by voltammetry and UVeVis. spectroscopy along with the diffusion
coefficients of the free and DNA bound species.
Drug-DNA
adduct
CV
Spectroscopy
107Df/cm2 sꢁ1
108Db/cm2 sꢁ1
K/Mꢁ1
ꢁ
23.05
22.72
24.11
D
G/kJ molꢁ1
K/Mꢁ1
ꢁ
23.39
22.33
25.18
D
G/kJ molꢁ1
1-DNA
2-DNA
3-DNA
2.37
2.05
2.29
0.15
6.49
7.89
1.10 ꢀ 104
9.61 ꢀ 103
1.69 ꢀ 104
1.54 ꢀ 104
8.19 ꢀ 103
2.59 ꢀ 104
procedure [41]. The melting points were determined on an elec-
trothermal melting point apparatus, model MP-D Mitamura Riken
Kogyo (Japan) by using capillary tubes and are uncorrected.
Elemental analyses were performed using Leco CHNS-932
elemental analyzer (USA). The IR spectra of all samples were
recorded as KBr discs or in NaCl cells using Bio-Rad Excaliber FT-IR,
A
1.6
1.2
0.8
0.4
0
model FTS 300 MX spectrometer (USA) in range of 4000e400 cmꢁ1
.
NMR (1H and 13C) spectra were obtained on a Brucker 300 MHz FT
NMR spectrometer using CDCl3 as solvent. 119Sn NMR spectra were
obtained with Me4Sn as an external reference. The cyclic voltam-
metric experiments were performed by PGSTAT 302 with Autolab
GPES version 4.9 Eco Chemie, Utrecht, the Netherlands. Measure-
ments were carried out in a conventional three electrode cell with
saturated calomel electrode (SCE) from Fisher scientific company
(Cat No. 13-639-51) as a reference electrode, a thin Pt wire of
thickness 0.5 mm with an exposed end of 10 mm as the counter
280
330
380
430
480
Wavelength/nm
electrode and
a geometric area of 0.071 cm2 as the working electrode. Prior to
experiments, the GCE was polished with 0.25 m diamond paste on
a bare glassy carbon electrode (GCE) with
B
1.8
m
a nylon buffing pad. For electrochemical measurements the test
solution was kept in an electrochemical cell (model K64 PARC)
connected to the circulating thermostat LAUDA model K-4R. Argon
was used for flushing out oxygen before every electrochemical
assay. Absorption spectra were measured on a UVeVis Spectrom-
eter; Shimadzu 1601. Table Top Centrifuge, Model PLC-05 (Taiwan)
was used for the extraction of DNA.
1.5
1.2
0.9
0.6
0.3
0
4.2. Synthesis
4.2.1. Synthesis of Schiff base ligand
280
330
380
430
480
An ethanolic solution of salicylaldehyde (0.1 mol, 12.2 g) was
added slowly to the solution of formic hydrazide (0.1 mol, 6.0 g) in
ethanol with constant stirring. The mixture was refluxed for 1 h and
on cooling crystalline solid product was obtained (Scheme 1). The
structure of ligand and numbering scheme are given in Scheme 2.
Wavelength/nm
2
1.5
1
C
-7
-6
-5
-4
-3
-2
-1
0
2
1
3
0.5
0
280
330
380
430
480
Wavelength/nm
Fig. 5. A Absorption spectra of 0.2 mM Ph2SnL (1) in the absence (a) and presence of
M, (b) 10 M, (c) 15 M, (d) 20 M, (e), and 25 M DNA (f). The arrow direction
indicates increasing concentrations of DNA. B. Absorption spectra of 0.2 mM Me2SnL
(2) in the absence (a) and presence of 5 M, (b) 10 M, (c) 15 M, (d) 20 M, (e), and
25 DNA (f). The arrow direction indicates increasing concentrations of DNA.
C. Absorption spectra of 0.2 mM Bu2SnL (3) in the absence (a) and presence of 5 M, (b)
10 M, (c) 15 M, (d) 20 M, (e), and 25 M DNA (f). The arrow direction indicates
increasing concentrations of DNA.
5
m
m
m
m
m
0
0.05
0.1
1/[DNA]/(
0.15
M)-1
0.2
0.25
μ
m
m
m
m
m
M
m
Fig. 6. Plots of Ao/(A ꢁ Ao) vs. 1/[DNA] for the determination of binding constants of
Complex-DNA adducts by taking 0.2 mM drug and 5e25 M DNA with a difference of
M aliquot of DNA.
m
m
m
m
m
5
m

2908
S. Shujha et al. / European Journal of Medicinal Chemistry 45 (2010) 2902e2911
O
C
H
C
H
C
H
O
N
H
N
H
H
N
N
-H2O
H C NHNH2
+
OH
O
OH
OH
OH
aldo-imine form
imine-ol form
Scheme 1. Synthesis of ligand (H2L).
4.2.1.1. 2.2.1.1.N0-(2-hydroxybenzylidene)formohydrazide. Yield 82%,
m.p. 187e189 ꢂC. Anal. Calc. for C8H8N2O2 (M ¼ 164): C, 58.53; H,
4.91; N, 17.06. Found: C, 58.49; H, 4.89; N, 17.03%. EI-MS, m/z (%):
[C8H8N2O2]þ 164 (50), [C7H7N2O]þ 135 (8), [C7H6NO]þ 120 (80),
[C7H5NO]þ 119 (100), [C7H7O]þ 107 (11), [C6H5]þ 77 (44), [C5H5]þ 65
[
119Sne13C] ¼ 56 Hz, C-
g
: 129.0 3J[119/117Sne13C] ¼ 97, 89 Hz, C-
d:
130.7 4J[119Sne13C] ¼ 17 Hz, 119Sn NMR:
d
¼ ꢁ337 Hz
4.2.2.2. Dimethyltin(IV) [N-(2-oxidobenzylidene)-N0-(oxidomethylene)
hydrazine] (2). Yield 80%, m.p. 116e118 ꢂC. Anal. Calc. for
C10H12N2O2Sn (M ¼ 312): C, 38.63; H, 3.89; N, 9.01. Found: C, 38.59;
H, 3.85; N, 9.03%. EI-MS, m/z (%): [C10H12N2O2Sn]þ 312 (84),
[C9H9N2O2Sn]þ 297 (80), [C8H6N2O2Sn]þ 282 (100), [C8H8N2O2]þ
164 (6), [C7H9N2O]þ 137 (27), [C7H6NO]þ/[Sn]þ 120 (51), [C7H5NO]þ
119 (23), [C6H5]þ 77 (23), [C4H3]þ 51 (48), [C2H6Sn]þ 150 (5),
(24), [C4H9]þ 57 (3), [C4H3]þ 51 (38) FT-IR (cmꢁ1, KBr): 3355m, nNeH
;
3184m, nOeH; 1701s, nC¼O; 1613m, nC¼N; 1053m, nNeN.
1H NMR
3
(ppm): H-2: 6.89 (d, 1H, phenyl, JHeH ¼ 8.4), H-3: 7.24 (t, 1H,
phenyl, 3JHeH ¼ 7.6), H-4: 6.85 (t, 1H, phenyl, 3JHeH ¼ 7.8), H-5: 7.60
3
(d, 1H, phenyl, JHeH ¼ 7.6), H-7: 8.32 (s, 1H, CH]N), H-8: 11.67
(s, 1H, CHO), NH: 8.68 (s, 1H, NH), OH: 10.12 (s, 1H, OH), 13C NMR
(ppm): C-7: 148.1 (HC]N); C-8: 165.2 (CHONH); 157.4, 116.8, 132.3,
120.1, 131.6, 119.1 (Ph-C)
[CH3Sn]þ 135 (71) FT-IR (cmꢁ1,KBr): 1605s, nC]N; 563m, nSneO
;
1072m, nNeN, 484w,nSneN
.
1H NMR (ppm): H-2: 6.77 (d, 1H, phenyl, 3JHeH ¼ 8.1), H-3: 7.36
3
3
(t, 1H, phenyl, JHeH ¼ 7.8), H-4: 6.75 (t, 1H, phenyl, JHeH ¼ 7.8),
3
4.2.2. Synthesis of the complexes (1e6)
The diorganotin(IV) complexes were synthesized by two
method.
H-5: 7.18 (d, 1H, phenyl, JHeH ¼ 7.8), H-7: 8.62 [(s, 1H, CH]N),
3J(119Sne1H) ¼ 46 Hz], H-8: 7.63 (s, 1H, N]OCH), H-
a: 0.83 (s, 6H,
2CH3), 2J(119/117Sne1H) ¼ 79, 76 Hz 13C NMR (ppm): C-7: 162.8
(HC]N), C-8: 166.6 (CO]N), 163.7, 135.8, 134.5, 121.8, 117.3, 116.2
(Ph-C), Ca: 1.55 1J[119/117Sne13C] ¼ 650, 620 Hz, 119Sn NMR:
Method I: A 3.0 mmol (0.49 g) of N0-(2-hydroxybenzylidene)
formohydrazide, 6 mmol (0.83 ml) triethylamine and dialkylltin
dichloride (3.0 mmol) were mixed together in 100 ml toluene. After
5 h stirring at room temperature, the yellow solution was filtered
off to remove the Et3NHCl salt. The filtrate was rotary evaporator to
get a yellow product (Scheme 3).
d
¼ ꢁ163 Hz
4.2.2.3. Dibutyltin(IV) [N-(2-oxidobenzylidene)-N0-(oxidomethylene)
hydrazine] (3). Yield 78%, m.p. viscous liquid. Anal. Calc. for
C16H24N2O2Sn (M ¼ 396): C, 48.64; H, 6.12; N, 7.09. Found: C, 48.61;
H, 6.10; N, 7.06%. EI-MS, m/z (%): [C16H24N2O2Sn]þ 396 (32),
[C12H15N2O2Sn]þ 339 (76), [C8H6N2O2Sn]þ 282 (100), [C8H8N2O2]þ
164 (21), [C7H9N2O]þ 137 (26), [C7H6NO]þ/[Sn]þ 120 (26),
[C7H5NO]þ 119 (16), [C4H9]þ 57 (99), [C4H3]þ 51 (6), [C8H18Sn]þ 234
Method II: The dioctyltin(IV) complex was synthesized by sus-
pending the dioctyltin(IV) oxide and ligand in stoichiometric
amounts in dry toluene. The mixture was refluxed for 3 h, and
water formed during the reaction was removed by the Dean and
Stark apparatus. Yellow oily product was obtained by removing
solvent under reduce pressure (Scheme 4).
(12). FT-IR (cmꢁ1, KBr): 1609s, nC]N; 565m, nSneO; 1080m, nNeN
;
The structure and numbering template of diorganotin(IV)
complexes is illustrated in Scheme 5.
481w, nSneN, 1H NMR (ppm): H-2: 6.77 (d, 1H, phenyl, 3JHeH ¼ 8.1),
3
H-3: 7.35 (t, 1H, phenyl, JHeH ¼ 7.8), H-4: 6.73 (t, 1H, phenyl,
3JHeH ¼ 7.8), H-5: 7.16 (d, 1H, phenyl, 3JHeH ¼ 7.8), H-7: 8.61 [(s, 1H,
4.2.2.1. Diphenyltin(IV) [N-(2-oxidobenzylidene)-N0-(oxidomethylene)
hydrazine] (1). Yield 84%, m.p. 160e162 ꢂC. Anal. Calc. for
C20H16N2O2Sn (M ¼ 436): C, 55.21; H, 3.71; N, 6.44. Found: C, 55.19;
H, 3.72; N, 6.39%. EI-MS, m/z (%): [C20H16N2O2Sn]þ 436 (56),
[C14H11N2O2Sn]þ 359 (22), [C8H6N2O2Sn]þ 282 (100), [C8H8N2O2]þ
165 (11), [C7H9N2O]þ 137 (11), [C7H6NO]þ/[Sn]þ 120 (37),
[C7H5NO]þ 119 (11), [C6H5]þ 77 (36), [C4H9]þ 57 (5) [C4H3]þ 51 (27),
CH]N), 3J(119Sne1H) ¼ 43 Hz], H-8: 7.66 (s, 1H, N]OCH), H-
a:
1.60e1.69 (m, 4H, 2CH2), H-b: 1.48e1.54 (m, 4H, 2CH2), H-g: 1.36
(m, 4H, 2CH2), H-
C-7: 162.7 (HC]N), C-8: 167.2 (CO]N), 164.0, 135.6, 134.5, 121.7,
d
: 0.89 (t, 6H, 2CH3, 3JHeH ¼ 7.2), 13C NMR (ppm):
117.0, 116.2 (Ph-C), C-
a
: 22.4 1J[119/117Sne13C] ¼ 600, 575 Hz, C-
b
:
:
26.8 2J[119Sne13C] ¼ 36 Hz, C-
g
: 26.2 3J[119Sne13C] ¼ 90 Hz, C-
d
13.6 (SneBu). 119Sn NMR:
d
¼ ꢁ202 Hz
[C6H5Sn]þ 197 (48) FT-IR (cmꢁ1, KBr): 1609s, nC]N; 567m, nSneO
;
1074m, nNeN; 486w, nSneN. 1H NMR (ppm): H-2: 7.12 (d, 1H, phenyl,
3JHeH ¼ 8.4), H-3: 7.41e7.50 (m, 1H, phenyl), H-4: 6.81 (t, 1H,
phenyl, 3JHeH ¼ 7.8), H-5: 7.21 (d, 1H, phenyl, 3JHeH ¼ 7.8), H-7: 8.65
[(s, 1H, CH]N), 3J(119Sne1H) ¼ 51 Hz], H-8: 7.38e7.51 (m, 1H,
4.2.2.4. Dioctyltin(IV) [N-(2-oxidobenzylidene)-N0-(oxidomethylene)
hydrazine] (4). Yield 77%, m.p. Viscous liquid. Anal. Calc. for
C24H40N2O2Sn (M ¼ 508): C, 56.82; H, 7.95; N, 5.52. Found: C, 56.79;
H, 7.92; N, 5.49%. EI-MS, m/z (%): [C24H40N2O2Sn]þ 508 (4),
[C16H23N2O2Sn]þ 395 (14), [C8H7N2O2Sn]þ 283 (64), [C8H6N2O2Sn]þ
282 (32), [C8H8N2O2]þ 164 (10), [C7H9N2O]þ 137 (13), [C7H6NO]þ/
[Sn]þ 120 (9), [C7H5NO]þ 119 (7), [C6H5]þ 77 (4), [C4H9]þ 57 (100),
[C4H3]þ 51 (4). FT-IR (cmꢁ1, KBr): 1603s, nC]N; 566m, nSneO; 1082m,
N]CH), H-b: 7.84e7.90 (m, 4H, phenyl), H-g, H-d: 7.38e7.51 (m, 6H,
phenyl), 13C NMR (ppm): C-7: 163.0 (HC]N), C-8: 167.5 (CO]N),
163.6, 135.8, 134.7, 122.2, 11.7, 116.3 (Ph-C); C- : 139.0, C-
: 136.7 2J
a
b
nNeN; 489w, nSneN,
1H NMR (ppm): H-2: 6.76 (d, 1H, phenyl,
3JHeH ¼ 8.1), H-3: 7.35 (t, 1H, phenyl, 3JHeH ¼ 7.8), H-4: 6.70 (t, 1H,
phenyl, 3JHeH ¼ 7.8), H-5: 7.16 (d, 1H, phenyl, 3JHeH ¼ 7.8), H-7: 8.61
[(s, 1H, CH]N), 3J(119Sne1H) ¼ 41 Hz], H-8: 7.66 (s, 1H, N]OCH),
H
C
7
H
5
N
H
6
1
8
4
N
O
H-a: 1.65e1.72 (m, 4H, 2CH2), H-b: 1.49e1.58 (m, 4H, 2CH2), H-g- :
g0
3
OH
2
1.23e1.46 (br, 16H, 2CH2 CH2CH2 CH2), H-d
0: 0.88 (t, 6H, 2CH3,
Scheme 2. Numbering scheme of ligand (H2L).
3JHeH ¼ 7.2), 13C NMR (ppm): C-7: 162.6 (HC]N), C-8: 167.2

S. Shujha et al. / European Journal of Medicinal Chemistry 45 (2010) 2902e2911
2909
H
C
H
N
H
C
N
R
H
N
N
+
R2SnCl2
+
2Et3N
+
2Et3NHCl
OH
O
Sn
OH
O
R
R = C6H5, CH3, n-C4H9, t-C4H9, C2H5
Scheme 3. Synthesis of diorganotin(IV) derivatives (1e5).
(CO]N), 164.0, 135.6, 134.5, 121.8, 117.0, 116.2 (Ph-C); C-
a
: 22.1, C-
b
:
by Patterson method, extension of the model was accomplished by
direct method and applied to different structure factors using the
program DIRDIF [43]. Crystal data and numerical details on data
collection and refinement are given in Table 1. Selected bond
lengths and angles are provided in Table 2. All refinement calcu-
lations and graphics were performed with the program packages
SHELXL [44], a locally modified version of the program PLUTO and
PLATON package [45,46].
24.65, 2J[119Sne13C] ¼ 36 Hz, C-
g
g
: 33.4, 3J[119Sne13C] ¼ 82 Hz, C-
d:
29.2, C-
a
0: 29.1, C-
b
0: 31.8, C-
0: 22.7, C-
d
0: 14.1. 119Sn NMR:
d
¼ ꢁ180 Hz
4.2.2.5. Di-ter-butyltin(IV) [N-(2-oxidobenzylidene)-N0-(oxidometh-
ylene)hydrazine] (5). Yield 78%, m.p. Viscous liquid. Anal. Calc. for
C16H24N2O2Sn (M ¼ 396): C, 48.64; H, 6.12; N, 7.09. Found: C, 48.59;
H, 6.09; N, 7.12%. EI-MS, m/z (%): [C16H24N2O2Sn]þ 396 (19),
[C12H15N2O2Sn]þ 339 (6), [C8H6N2O2Sn]þ 282 (100), [C8H8N2O2]þ
164 (5), [C7H6NO]þ/[Sn]þ 120 (5), [C4H9]þ 57 (29), FT-IR (cmꢁ1
,
4.4. Antibacterial and antifungal activities
KBr): 1601s, nC]N; 561m, nSneO; 1080m, nNeN; 478w, nSneN
;
1H NMR (ppm): H-2: 6.83 (d, 1H, phenyl, 3JHeH ¼ 8.4), H-3: 7.35
The antibacterial an antifungal screening were performed by
using the agar well-diffusion and agar tube dilution methods,
respectively [47].
3
3
(t, 1H, phenyl, JHeH ¼ 7.8), H-4: 6.70 (t, 1H, phenyl, JHeH ¼ 7.2),
3
H-5: 7.14 (d, 1H, phenyl, JHeH ¼ 7.8), H-7: 8.6 [(s, 1H, CH]N),
3J(119Sne1H) ¼ 38 Hz], H-8: 7.74 (s, 1H, N]OCH), H-
6CH3) 3J(119/117Sne1H) ¼ 111, 106 Hz]
b: 1.33 [(s, 18H,
4.5. Cytotoxicity
13C NMR (ppm): C-7: 162.4 (HC]N), C-8: 168.2 (CO]N), 164.0,
135.4, 134.3, 121.8, 116.6, 116.3 (Ph-C), C-
a
:
40.8 1J[119/
¼ ꢁ220 Hz
Cytotoxicity of the compounds was studies by the Brine shrimp
lethality bioassay [47]. Data were analyzed with Finney’s probit
analysis to determine the LD50 [48].
117Sne13C] ¼ 586, 559 Hz, C-
b d
: 29.6. 119Sn NMR:
4.2.2.6. Diethyltin(IV) [N-(2-oxidobenzylidene)-N0-(oxidomethylene)
hydrazine] (6). Yield 80%, m.p. Viscous liquid. Anal. Calc. for
C12H16N2O2Sn (M ¼ 340): C, 42.52; H, 4.76; N, 8.26. Found: C, 42.48;
H, 4.79; N, 8.23%. EI-MS, m/z (%): [C12H16N2O2Sn]þ 340 (64),
[C10H11N2O2Sn]þ 311 (100), [C8H6N2O2Sn]þ 282 (75), [C8H8N2O2]þ
164 (17), [C7H9N2O]þ 137 (10), [C7H6NO]þ/[Sn]þ 120 (22),
4.6. Leishmanicidal activity
Leishmania major (MHOM/PK/88/DESTO) promastigotes, culti-
vated in bulk were aseptically sedimented down at 300 rpm,
counted with the help of improved Neubaver chamber under the
microscope and diluted with the fresh medium to a final concen-
tration of 2 ꢀ 106 parasites/ml. The compounds to be checked were
dissolved to a final concentration of 1.0 mg in 0.1 ml of PBS
(Phosphate Buffered Saline, pH 7.4 containing 0.5% MeOH, 0.5%
DMSO). In a 96-well microtiter plate, 90 ml of the parasite culture
(2 ꢀ 106 parasites/ml) was added in different wells. 10 ml of the
experimental compound was added in culture and serially diluted
so that minimum concentration of the compound is 0.1 mg/ml
10 ml of PBS (Phosphate buffered saline, pH 7.4 containing 0.5%
MeOH, 0.5% DMSO) was added as negative control while
glucantime, amphotericin B, pentamidine and ampicilline to a final
concentration of 1.0 mg/ml was added separately as positive
control. The plate was incubated between 21 and 22 ꢂC in dark for 5
days during which control organisms multiply 6 times. The culture
was examined microscopically on an improved neubaver chamber
and IC50 values of compounds possessing anti-leishmanial activity
were calculated [49].
[C7H5NO]þ 119 (24), [C6H5]þ 77 (6), [C4H9]þ 57 (8), FT-IR (cmꢁ1
,
KBr): 1602s, nC]N; 577m, nSneO; 1077m, nNeN; 475w, nSneN. 1H NMR
3
(ppm): H-2: 6.78 (d, 1H, phenyl, JHeH ¼ 8.7), H-3: 7.35 (t, 1H,
phenyl, 3JHeH ¼ 7.6), H-4: 6.70 (t, 1H, phenyl, 3JHeH ¼ 7.8), H-5: 7.15
3
(d, 1H, phenyl, JHeH
¼
7.8), H-7: 8.62 [(s, 1H, CH]N),
3J(119Sne1H) ¼ 42 Hz], H-8: 7.67 (s, 1H, N]OCH), H-
a: 1.44e1.52
(m, 4H, 2CH2), H-
b
: 1.29 (t, 6H, 2CH3, 3JHeH ¼ 7.8), 13C NMR (ppm):
C-7: 162.9 (HC]N), C-8: 167.1 (CO]N), 164.0, 135.6, 134.5, 121.7,
117.0, 116.2 (Ph-C); C-
a
: 14.5, 1J[119/117Sne13C] ¼ 616, 589 Hz, C-
b:
9.2, 2J[119Sne13C] ¼ 44 Hz 119Sn NMR:
d
¼ ꢁ171 Hz.
4.3. X-ray crystallography
X-ray diffraction data were collected on a Bruker SMART APEX
CCD diffractometer, equipped with a 4K CCD detector. Data inte-
gration and global cell refinement was performed with the
program SAINT [42]. The program suite SAINTPLUS was used for
space group determination (XPREP) [42]. The structure was solved
H
H
N
H
C
C
N
H
N
N
+
H2O
(C8H17)2SnO
+
O
OH
Sn
O
OH
C8H17
C8H17
Scheme 4. Synthesis of dioctyltin(IV) derivative (6).

2910
S. Shujha et al. / European Journal of Medicinal Chemistry 45 (2010) 2902e2911
H
C
5
N
H
6
1
8
4
N
7
O
Sn
3
O
2
R
R
γ
β
′
′
′
′
γ
α
γ
γ
α
β
β
α
α
α
β
α
δ
β
δ
β
δ
α
δ
,
,
,
CH2CH2CH2CH3
C(CH3)3 CH2CH3
,
R =
CH3
,
CH2CH2CH2CH2CH2CH2CH2CH3
Scheme 5. Numbering scheme of organic groups and ligand.
H
N
N
H
H
N
-C8H6N2O2
m/z 150 (5.3%)
+
N
[Sn(CH3)2]
Sn
O
O
O
CH3
OH
H3C
m/z 312 (84.8%)
m/z 164 ( 49.6%)
-COH
-CH3
NH
N
H
H
N
+
-C8H6N2O2
N
[SnCH3]
Sn
O
m/z 135 (70.8%)
OH
O
m/z 135 (7.8%)
H3C
m/z 297 (79.8%)
-NH
-CH3
N
N
N
Sn
OH
8
O
6
2
2
m/z 120 (79.2%)
O
+
[Sn]
m/z 282 (100%)
-H
-CH2NO
m/z 120 (51.3%)
N
4
7
N
m/z 77 (43.8%)
OH
Sn
m/z 119 (100.0%)
O
m/z 238 (26.4%)
Scheme 6. Proposed mass fragmentation pattern of ligand and complex 2.
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DNA was extracted from chicken blood by Falcon method [50].
The purity of DNA was checked from the ratio of absorbance at 260
and 280 nm (A260/A280 ¼ 1.85). The concentration of the DNA stock
solution (2.5 mM in nucleotide phosphate, NP) was determined by
monitoring the absorbance at 260 nm using the molar extinction
coefficient (
3 .
) of 6600 Mꢁ1 cmꢁ1
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Inorg. Chim. Acta 325 (2001) 103e114.
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre, CCDC
No. 698809 for Me2SnL (2), Copy of this information may be
obtained free of charge from the Director, CCDC, 12 Union Road,
Cambridge, CBZ 1EZ, UK (fax: þ44 1223 336 033; email: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
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ꢀ
ꢀ
ꢀ
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Acknowledgements
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