Synthesis, characterization and cytotoxic activity of S- benzyldithiocarbazate Schiff bases derived from 5-fluoroisatin, 5-chloroisatin, 5-bromoisatin and their crystal structures

Article abstract of DOI:10.1007/s10870-011-0151-2

Schiff bases were prepared from S-benzyldithiocarbazate with 5-fluro-, 5-chloro- and 5-bromoisatin. All are potential tridentate nitrogen, oxygen, sulfur donors. They were found to be selectively active against MCF-7 cell line (Human non-metastatic mammary gland adenocarcinoma cell line). The bromide and fluoride compounds were the most active with IC₅₀ values of 6.40 μM (2.6 μg/mL) and 9.26 μM (3.2 μg/mL) respectively while the chloride derivative was weakly active with an IC₅₀ value of 38.69 μM (14.0 μg/mL). The cytotoxic activity of the halo substituted isatins against the breast cancer cell lines tested is in the order of Br > F > Cl. Planarity of the isatin ring in the Schiff bases can be arranged in the following order SB5FISA > SB5ClISA > SB5BrISA while the perpendicularity of the benzyl ring towards the dithiocarbazate plane can be ordered as follows, SB5FISA > SB5BrISA > SB5ClISA.

Full text of DOI:10.1007/s10870-011-0151-2

J Chem Crystallogr (2011) 41:1630–1641
DOI 10.1007/s10870-011-0151-2
ORIGINAL PAPER
Synthesis, Characterization and Cytotoxic Activity
of S-Benzyldithiocarbazate Schiff Bases Derived
from 5-Fluoroisatin, 5-Chloroisatin, 5-Bromoisatin
and Their Crystal Structures
•
Mohd Abdul Fatah Abdul Manan Karen A. Crouse
•
•
M. Ibrahim M. Tahir Rozita Rosli Fiona N.-F. How
•
•
•
David J. Watkin Alexandra M. Z. Slawin
Received: 16 April 2011 / Accepted: 9 June 2011 / Published online: 23 June 2011
Ó Springer Science+Business Media, LLC 2011
Abstract Schiff bases were prepared from S-benzyldithioc-
arbazate with 5-fluro-, 5-chloro- and 5-bromoisatin. All are
potential tridentate nitrogen, oxygen, sulfur donors. They
were found to be selectively active against MCF-7 cell line
(Human non-metastatic mammary gland adenocarcinoma
cell line). The bromide and fluoride compounds were the
most active with IC50 values of 6.40 lM (2.6 lg/mL) and
9.26 lM (3.2 lg/mL) respectively while the chloride
derivative was weakly active with an IC50 value of
38.69 lM (14.0 lg/mL). The cytotoxic activity of the halo
substituted isatins against the breast cancer cell lines tested
is in the order of Br [ F [ Cl. Planarity of the isatin ring in
the Schiff bases can be arranged in the following order
SB5FISA [ SB5ClISA [ SB5BrISA while the perpen-
dicularity of the benzyl ring towards the dithiocarbazate
plane can be ordered as follows, SB5FISA [ SB5BrISA [
SB5ClISA.
Keywords Dithiocarbazate Á Schiff base Á Isatin Á
MCF-7 Á Structure
Introduction
Dithiocarbazate, NH2NHCS2-, is a chelating agents
derived from S-alkyl esters of dithiocarbazic acid, the
metal complexes of which have been extensively studied
over the past two decades, not only because of their
behaviour as ligands in transition metal complexes, but also
have been shown to exhibit interesting physico-chemical
and potentially chemotherapeutic properties [1–3].
Isatin is an endogenous compound isolated in 1988 and
reported to possess a wide range of activities involving the
central nervous system [4–7]. Schiff bases and Mannich
bases derived from isatin have been reported to possess
antibacterial [8–17], antifungal [11–13, 15, 17], antiviral
[10, 14], anti-HIV [11–13, 15, 17], antiprotozoal [18, 19],
and antihelminthic activities [20, 21].
M. A. F. A. Manan (&)
Faculty of Applied Sciences, Universiti Teknologi MARA,
40450 UiTM Shah Alam, Selangor, Malaysia
e-mail: abdfatah@salam.uitm.edu.my
K. A. Crouse Á M. I. M. Tahir Á F. N.-F. How
Department of Chemistry, Faculty of Science, Universiti Putra
Malaysia, 43400 Serdang, Selangor, Malaysia
Varieties of halogenated compounds particularly fluo-
rine-containing aromatic compounds have drawn much
attention because of their biological activities [22]. Many
of them are used as pharmaceuticals and pesticides or have
found use as precursors for the synthesis of biologically
active compounds. In 2006, SU11248 (Sutent), a 5-fluoro-
3-substituted-2-oxoindole, was approved by the US FDA
for the treatment of gastrointestinal stromal tumors [23]
and advanced renal-cell carcinoma [24].
R. Rosli
Department of Obstetrics and Gynaecology, Faculty of Medicine
and Health Sciences, Universiti Putra Malaysia, 43400 Serdang,
Selangor, Malaysia
D. J. Watkin
Chemical Chemistry Research Laboratory, University of Oxford,
South Parks Road, Oxford OX1 3QA, UK
Although much attention has been directed to study of
Schiff base and Mannich bases derived from isatin [8, 9,
12, 13, 15–17] no investigations have appeared in the
A. M. Z. Slawin
Molecular Structure Laboratory, School of Chemistry,
University of St. Andrews, St. Andrews, Fife KY16 9ST, UK
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J Chem Crystallogr (2011) 41:1630–1641
1631
literature to describe the Schiff bases derived from dith-
iocarbazate with 5-haloisatins. Furthermore, only limited
studies have been done on dithiocarbazato Schiff bases
having nitrogen, oxygen, sulfur (NOS) donor sequences.
Therefore, as part of our ongoing study on Schiff bases
derived from S-benzyldithiocarbazate, we report herein the
synthesis, characterization and cytotoxic activity of Schiff
bases formed from the condensation of S-benzyldithiocar-
bazate with 5-fluroisatin, 5-chloroisatin and 5-bromoisatin
that are potential NOS donor ligands.
Table 1 Summary of crystal data and structure refinement parame-
ters for SB5FISA
Chemical formula
Formula weight
Crystal class
C16H12F1N3O1S2
345.42
Monoclinic
P21
Space group
˚
a (A)
4.576(3)
9.688(7)
17.119(12)
90
˚
b (A)
˚
c (A)
a (o)
b (o)
c (o)
94.615(19)
90
Experimental
3
˚
V (A )
756.4(9)
2
Z
Physical Measurements
˚
Mo Ka (A)
0.7107
T (K)
qcalc (mg m-3
l (mm-1
93
All the chemicals, reagents and solvents for the synthesis of
compounds were analytical grade and used without further
purification. Microanalyses for carbon, hydrogen, nitrogen
and sulfur were carried out using a LECO CHNS-932
instrument. The IR spectra, as KBr pellets were recorded
using a Perkin–Elmer FT IR 1750X spectrophotometer
(4000–400 cm-1). NMR spectra were acquired on a JOEL-
JNM ECA 400 MHz spectrometer, where proton (1H) and
carbon (13C) spectra were obtained at 300 and 100 MHz
respectively. Spectra were recorded in DMSO-d6 with
TMS as the internal standard. All chemical shift values
were recorded in ppm (d).
)
1.52
)
0.370
Crystal dimension (mm)
F (000)
0.01 9 0.02 9 0.20
356
Theta range for data collection (°)
Limiting indices
2–29
(-5 B h B 5)
(-11 B k B 10)
(-20 B l B 17)
5038/2542
0.57, 1.00
2536/1/209
0.87
Reflections collected/unique
Maximum & minimum transmission
Data/restrains/parameters
Goodness-of-fit on F2
Minimum & maximum residual electron
-3
-0.58, 0.57
X-ray Structure Determination
˚
density (e A
)
R, Rw (%)
6.5, 15.3
Dark orange crystals of SB5FISA, brownish orange crys-
tals of SB5ClISA and orange crystals of SB5BrISA formed
after EtOH solutions were allowed to slowly evaporate
over a few weeks. Data for the SB5FISA (Table 1) was
collected at 93 K using a Rigaku MM007 High brilliance
RA generator (Mo Ka radiation, confocal optics) and
Mercury CCD system at Molecular Structure Laboratory,
School of Chemistry, University of St. Andrews. At least a
full hemisphere of data was collected using x scans.
Intensities were corrected for Lorentz-polarisation and for
absorption. Selected crystals of SB5BrISA and SB5FISA
were mounted on glass fiber using perfluropolyether oil and
cooled rapidly to 150 K in a stream of cold N2 using
Oxford Cryosystems CRYOSTREAM unit at the Chemis-
try Research Laboratory, University of Oxford. Diffraction
data were measured using an Enraf–Nonius Kappa CCD
diffractometer (graphite-monochromatic Mo Ka radiation,
F/F2 was carried out using CRYSTALS Program Suite [27]
Coordinates and anisotropic thermal parameters of all non-
hydrogen atoms were refined. Hydrogen atoms were posi-
tioned geometrically after each cycle of refinement.
Refinement converged satisfactorily to give good R and Rw
values with the best residual electron density minimum and
maxima. Tables 1, 2 and 3 summarizes crystal data and
structure refinement results of the Schiff bases.
Cell Culture
Two types of cell lines were used: MCF-7 (Human non-
metastatic mammary gland adenocarcinoma cell line.) and
MDA-MB-231 (Human metastatic mammary gland ade-
nocarcinoma cell line.). All the cell lines were obtained
from the National Cancer Institute, USA. MCF-7 was
cultured in RPMI-1640 medium supplemented with 10%
fetal bovine serum while MDA-MB-231 was cultured in
DMEM medium supplemented with 10% foetal bovine
˚
k = 0.71073 A). Intensity data were processed using the
DENZO-SMN package [25]. The crystal structures of all
three Schiff bases were solved using the direct-methods
program SIR92 [26] which located all non-hydrogen
atoms. Subsequent full-matrix least-squares refinement of
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J Chem Crystallogr (2011) 41:1630–1641
Table 2 Summary of crystal data and structure refinement parame-
ters for SB5ClISA
Table 3 Summary of crystal data and structure refinement parame-
ters for SB5BrISA
Chemical formula
Formula weight
Crystal class
C16H12Cl1N3O1S2
361.88
Chemical formula
Formula weight
Crystal class
C16H12Br1N3O1S2
406.33
Triclinic
Triclinic
Space group
P - 1
Space group
P - 1
˚
a (A)
˚
a (A)
6.4447(2)
8.0844(3)
15.8506(6)
94.3189(16)
99.2169(17)
92.0591(17)
811.90(5)
2
6.5350(2)
8.0867(2)
15.9265(5)
92.9504(12)
99.2083(12)
92.0396(14)
828.89(4)
2
˚
b (A)
˚
b (A)
˚
c (A)
˚
c (A)
a (o)
b (o)
c (o)
a (o)
b (o)
c (o)
3
3
˚
V (A )
˚
V (A )
Z
Z
˚
˚
Mo Ka (A)
0.7107
Mo Ka (A)
0.7107
T (K)
qcalc (mg m-3
l (mm-1
150
T (K)
qcalc (mg m-3
l (mm-1
150
)
1.48
)
1.63
)
0.499
)
2.738
Crystal dimension (mm)
F (000)
0.20 9 0.26 9 0.40
372
Crystal dimension (mm)
F (000)
0.20 9 0.30 9 0.40
408
Theta range for data collection (°)
Limiting indices
5–28
Theta range for data collection (°)
Limiting indices
5 to 27
(-8 B h B 7)
(-10 B k B 10)
(-20 B l B 19)
6118/3793
0.88, 0.91
3126/0/208
1.077
(-8 B h B 7)
(-10 B k B 10)
(-20 B l B 20)
6556/3786
0.44, 0.58
3184/0/208
1.082
Reflections collected/unique
Maximum & minimum transmission
Data/restrains/parameters
Reflections collected/unique
Maximum & minimum transmission
Data/restrains/parameters
Goodness-of-fit on F2
Goodness-of-fit on F2
Minimum & maximum residual electron
-3
-0.33, 0.39
Minimum & maximum residual electron
-3
-0.56, 1.17
˚
density (e A
˚
density (e A
)
)
R, Rw (%)
3.8, 3.7
R, Rw (%)
3.2, 3.4
culture plates were incubated for 4 days in an atmosphere
of 5% CO2 and 100% relative humidity at 37 °C. The end
point was measured using MTT assay as explained below.
serum. Both cells were incubated in an atmosphere of 5%
CO2 and 100% relative humidity at 37 °C.
Treatments and Sample Dilutions
3-[4,5-Dimethylthiazo-2-yl]-2,5-diphenyltetrazolium
bromide (MTT) Assay
Cells from the cell lines were counted, diluted and inocu-
lated onto sterile 96-well microtiter plates. Cells were
inoculated in a volume of 100 lL per well at densities
between 5000 and 7500 cells per well. The microtiter
plates containing the cells were preincubated overnight at
37 °C in an atmosphere of 5% CO2 and 100% relative
humidity to allow stabilization prior to addition of
compounds.
Cytotoxicity was evaluated using MTT (3-[4,5-dim-
ethylthiazo-2-yl]-2,5-diphenyltetrazolium bromide) (Sigma,
USA) assay as reported by Mosmann [28]. The MTT assay
is based on the metabolic reduction of (3-[4,5-dim-
ethylthiazo-2-yl]-2,5-diphenyltetrazolium bromide) (MTT).
A 40 lL aliquot of MTT solution (2.5 mg MTT in 1 mL of
PBS solution) was added directly to all the appropriate
microtiter plate wells containing cells, complete growth
media and test agents as prepared above. The culture was
then incubated for 4 h to allow for MTT to metabolise to
formazan. The supernatant was pipetted out and 200 lL of
DMSO was added to dissolve the formazan. The plates
Stock solutions of the compounds (10 mg/mL) were
prepared using DMSO. The compounds were then diluted
with complete medium ranging from 100 to 0.3 lg/mL.
Immediately after preparation of these intermediate dilu-
tions, 100 lL aliquots of each dilution were added to the
appropriate microtiter plate wells. The treated microtiter
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J Chem Crystallogr (2011) 41:1630–1641
1633
were agitated on a plate shaker to ensure homogeneity of
the solution and the optical densities were read on an
automated spectrophotometric plate reader (model MRX II
microplate Elisa reader) at a test wavelength of 570 nm and
a reference wavelength of 630 nm. Cytotoxicity is shown
as the minimum concentration required to reduce the
absorbance of treated cells by 50% with reference to the
untreated cells (IC50). Tamoxifen, was the cytotoxic
standard.
DMSO-d6): d 199.5 (C=S), 162.6 (C=O), 129.36 (C=N),
108.1–157.2 (aromatic), 38.2 (S-CH2) ppm. Anal. Calcd.
For C16 H12F1N3O1S2: C, 55.63; H, 3.50; N, 12.17; S,
18.57. Found; C, 55.35; H, 3.44; N, 12.12; S, 18.38.
(CCDC reference 696006).
S-Benzyl 2-(5-chloro-2-oxoindolin-
3-ylidene)hydrazinecarbodithioate (SB5ClISA)
The compound was obtained as brownish orange powder in
a yield of 80%; mp 247–248 °C. FTIR (KBr, cm-1) 3250
m(M–H); 1694 m(C=O); 1586 m(C=N); 1076 m(C=S), 1150
Chemistry
1
m(N–N); H NMR (300 MHz, DMSO-d6): d 13.88 (s, 1H,
Preparation of S-Benzyldithiocarbazate (SBDTC)
NHdithiocarbazate), 11.46 (s, 1H, NHisatin), 7.35–7.50 (m, 8H,
aromatic), 4.55 (s, 2H, CH2) ppm; 13C NMR (100 MHz,
DMSO-d6): d 199.5 (C=S), 162.3 (C=O), 131.8 (C=N),
113.0–142.1 (aromatic), 38.2 (S-CH2) ppm. Anal. Calcd.
For C16 H12Cl1N3O1S2: C, 53.11; H, 3.31; N, 11.61; S,
17.72. Found; C, 53.05; H, 3.32; N, 11.45; S, 17.67.
(CCDC reference 696008).
This compound was synthesized as previously reported
[29]. Potassium hydroxide (22.8 g, 0.4 mol) was dissolved
completely in 90% ethanol (140 mL) and the mixture was
cooled in ice bath. To the mixture, hydrazine hydrate (20 g,
0.4 mol) was added slowly with stirring. Carbon disulfide
(30.4 g, 0.4 mol) was then added dropwise with vigorous
stirring. The temperature of the reaction mixture was not
allowed to rise above 6 °C during the period of addition of
carbon disulfide. The resulting yellow oil was separated by
means of a separatory funnel and dissolved in 40% ethanol
(40 mL) and the solution was cooled in ice. Benzyl chlo-
ride (58 g, 0.4 mol) was added slowly with vigorous stir-
ring. The white product was separated by filtration, washed
with water and dried in air. The crude product was
recrystallized from ethanol. Yield, 20 g (40%). The melt-
ing point was 124 °C (Lit. 124–125 °C) [30].
S-Benzyl 2-(5-bromo-2-oxoindolin-
3-ylidene)hydrazinecarbodithioate (SB5BrISA)
The compound was obtained as dark orange powder in a
yield of 80%; mp 249–250 °C. FTIR (KBr, cm-1) 3300
m(M–H); 1696 m(C=O); 1616 m(C=N); 1066 m(C=S), 1148
1
m(N–N); H NMR (300 MHz, DMSO-d6): d 13.86 (s, 1H,
NHdithiocarbazate), 11.45 (s, 1H, NHisatin), 7.32–7.49 (m, 8H,
aromatic), 4.54 (s, 2H, CH2) ppm; 13C NMR (100 MHz,
DMSO-d6): d 199.5 (C=S), 162.1 (C=O), 129.3 (C=N),
114.5–142.4 (aromatic), 38.2 (S-CH2) ppm. Anal. Calcd.
For C16 H12Br1N3O1S2: C, 47.30; H, 2.98; N, 10.34; S,
15.78. Found; C, 47.10; H, 2.84; N, 10.29; S, 15.28.
(CCDC reference 696007).
Preparation of Schiff Bases
S-benzyldithiocarbazate, SBDTC (1.36 g, 0.01 mol) was
dissolved in hot ethanol (35 mL) and to this solution was
added an equimolar amount of 5-fluorosatin (1.65 g,
0.01 mol), 5-chloroisatin (1.81 g, 0.01 mol) or 5-bromoi-
satin (2.26 g, 0.01 mol). The mixtures were heated while
being stirred for 15 min and later allowed to stand for
*20 min until product formed. Solids were filtered,
washed with ethanol and recrystallized from ethanol.
Yields were high, ca 80%.
Result and Discussion
Chemistry
The results of elemental analyses (carbon, hydrogen,
nitrogen, and sulfur) obtained are in good agreement with
calculated values.
S-Benzyl 2-(5-fluoro-2-oxoindolin-
3-ylidene)hydrazinecarbodithioate (SB5FISA)
Fourier-Transform Infrared Data for the Schiff Bases
The compound was obtained as dark orange powder in a
yield of 80%; mp 235–236 °C. FTIR (KBr, cm-1) 3280
m(M–H); 1686 m(C=O); 1628 m(C=N); 1056 m(C=S), 1136
m(N–N); H NMR (300 MHz, DMSO-d6): d 13.93 (s, 1H,
NHdithiocarbazate), 11.36 (s, 1H, NHisatin), 7.30–7.44 (m, 8H,
aromatic), 4.53 (s, 2H, CH2) ppm; 13C NMR (100 MHz,
Bands in the region 3300–3250 cm-1 are attributable to
NH stretching. The Schiff bases contain a thione group
(C=S) with protons adjacent to it. Although it has been
noted that the thione group (C=S) is relatively unstable in
the monomeric form and tends to convert to a stable C–S
single bond by enethiolization if there is at least one
1
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J Chem Crystallogr (2011) 41:1630–1641
X
[32]. The cluster of peaks obtained in the region of
7.30–7.50 ppm is associated with the aromatic hydrogen in
the aromatic ring.
X
The 13C NMR spectra of the Schiff bases showed a
signal at 199.5 ppm which is attributed to the thioamide
carbon. The low intensity is due to the deshielding effect of
the nitrogen and two sulfur atoms adjacent to the carbon.
These electronegative elements produce a large downfield
shift since they are directly attached to the carbon atom.
Another downfield signal observed in each spectrum at
162.1–162.6 ppm is ascribed to the carbonyl group (C=O)
of the isatin derivatives. The remaining signals observed in
the region of 108.1–157.2 ppm may be assigned to carbons
in the aromatic ring.
NH
H
NH
S
N
S
N
N
N
O
SH
O
S
a ; X=F,Cl,Br
b ; X=F,Cl,Br
(Thione form)
(Thiol form)
Fig. 1 Thione-thiol tautomerism of the Schiff bases
hydrogen atom adjacent to the C=S bond [30]. The IR spectra
of the Schiff bases did not display m(S–H) at ca. 2570 cm-1
indicating that in the solid-state they remain in the thione
form (Fig. 1a). However, equilibrium with the thiolo
tautomeric form (Fig. 1b) may be established in solution.
m(C=S) bands were observed at 1056–1076 cm-1 while
m(C=N), m(N–N) and m(C=O) bands were observed at
Single Crystal X-ray Analyses of SB5FISA, SB5ClISA
and SB5BrISA
1586–1628 cm-1, 1136–1150 cm-1 and 1686–1694 cm-1
as expected for these SBDTC Schiff bases.
,
The crystal structures of the Schiff bases with their atom
numbering schemes, intramolecular and intermolecular
hydrogen bonds are shown in Figs. 2, 3, 4, 5, 6, 7. Selected
bond lengths and bond angles of the Schiff bases are listed
in Table 4. The structures of SB5ClISA and SB5BrISA
feature centrosymmectric H-bonded dimeric motifs which
are held by the strong intermolecular hydrogen bonds of
(N–H–O). These hydrogen bond motifs are different to that
observed in SB5FISA which is held by the weak inter-
molecular hydrogen bond of (C–H–O). Variations in these
hydrogen bonding motifs would give a different packing of
molecules in a crystal [33].
Nuclear Magnetic Resonance (NMR) Spectroscopy
The signal at 4.53–4.55 ppm was attributed to the methy-
lene hydrogen (CH2). The methylene hydrogen shift is
generally in the range 1.2–1.4 ppm [31]. The downfield
shift of methylene hydrogen in all the Schiff bases can be
ascribed to the deshielding effect of electronegative sulfur
and the aromatic ring. The signal at 13.86–13.93 ppm was
assigned to the secondary proton from the dithiocarbazate
and the singlet peak at 11.36–11.46 ppm can be assigned to
NH in the pyrrole group of the isatin ring. The NH signal
from the isatin ring appears upfield to NH from the dith-
iocarbazate indicating intermolecular hydrogen bonding
In SB5FISA (Fig. 2), the six- and five-membered rings of
the isatin moieties which consist of C1–C8–C7–C6–C5–C4
and C2–C1–C4–N1–C3 are almost perfectly coplanar with
dihedral angle of 0.78° between the two mean planes. The
H15
Fig. 2 ORTEP diagram and
numbering scheme of SB5FISA
H14
C15
C16
C14
F1
H16
H8
C13
C7
C8
C11
H6
C6
H13
S2
H102
C12
C1
N2
C5
C10
C4
H12
C9
C2
H5
H101
N3
N1
C3
H3
S1
H1
O1
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Cl10
Fig. 3 ORTEP diagram and
numbering scheme of
SB5ClISA
H191
C8
H71
C19
C7
H201
H91
H181
C9
C20
C18
C6
C1
C17
C21
C22
H61
C5
S15
H161
N12
C2
H211
C16
N4
C14
H221
H162
N13
H2
C3
H1
O11
S23
Br10
H211
C8
H71
C21
C22
H201
C7
H91
C9
H221
C20
C6
C1
C19
C17
C5
H61
S15
H162
H191
N12
C18
C16
C2
N4
N13
C14
H181
H161
C3
H3
H2
O11
S23
Fig. 4 ORTEP diagram and numbering scheme of SB5BrISA
planarity of the molecules was stabilized by a strong
˚
The N2–N3–C9–S1 and N3–C9–S2–C10 chains adopt
intramolecular hydrogen bond N3–H3ÁÁÁO1 = 2.690(9) A
trans conformation with the torsion angles of 174.58°
and -176.82° respectively whereas the S1–C9–S2–C10
chain adop cis conformation with the torsion angle of 2.70°.
The S-benzyldithiocarbazate moiety is in the Z configuration
with respect to C2=N2 double bond (torsion angle C2–C3–
N2–N3 = 1.18°), as a consequence of formation of the
(Table 5) leading to the formation of the pseudo
six-membered ring. The benzyl ring C10–C11–C12–C13–
C14–C15–C16 is nearly perpendicular to the methylene-
dithiocarbazate plane consisting of atoms N2–N3–C9–S1–
S2 with the dihedral angle between the two mean planes of
83.12°. The isatin moiety is trans to the C9–N3 and C9–S1
bonds while the benzyl group is cis to the C9–N3 and
C9–S2 bonds respectively.
˚
intramolecular hydrogen bond N3–H3ÁÁÁO1 = 2.690(9) A
(Table 5) and intermolecular hydrogen bond C5–H5ÁÁÁO1 =
˚
3.209(9) A (Table 6).
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Fig. 5 Intramolecular and
intermolecular hydrogen bonds
of SB5FISA
F 1
H3
(a) Intramolecular hydrogen bond of SB5FISA
O1
H5
O1
F1
H5
O1
F1
(b) Intermolecular hydrogen bond of SB5FISA
In SB5ClISA (Fig. 3) and SB5BrISA (Fig. 4), the six-
and five-membered rings of the isatin moieties which
consist of C1–C5–C6–C7–C8–C9 and C1–C2–C3–N4–C5
are not exactly planar with the dihedral angle of 1.50° and
1.70° respectively. The benzyl ring of SB5ClISA and
SB5BrISA, C16–C17–C18–C19–C20–C21–C22 are nearly
perpendicular to the methylene-dithiocarbazate plane con-
sisting of atoms N12–N13–C14–S23–S15 with the dihedral
angle between the two mean planes of 72.84° and 74.79°
respectively. Both of the isatin moieties in SB5ClISA and
SB5BrISA are trans to the C14–N13 and C14–S23 bonds
while the benzyl groups are cis to the C14–N13 and
C14–S15 bonds respectively. A similar configuration also
was reported for SBDTC [34, 35].
In these compounds, the N12–N13–C14–S23 and N13–
C14–S15–C16 chains adopt trans conformation with the
torsion angles of (173.51° and 177.53° for SB5ClISA) and
(172.81° and 176.91° for SB5BrISA) respectively. The
S-23-C14-S15-C16 chains adop cis conformation with the
torsion angle of -3.80° and -5.18° for SB5ClISA and
SB5BrISA respectively. Both of the S-benzyldithiocar-
bazate moieties are in the Z configuration with respect
to C2=N12 double bond (torsion angle C2–C3–N12–
N13 = -1.57° for SB5ClISA and -3.04° for SB5BrISA),
123

J Chem Crystallogr (2011) 41:1630–1641
1637
Fig. 6 Intramolecular and
intermolecular hydrogen bonds
of SB5ClISA
Cl10
H2
O11
(a) Intramolecular hydrogen bond of SB5ClISA
Cl10
H1
O11
O11
H1
Cl10
(b) Intermolecular hydrogen bond of SB5ClISA
as a consequence of formation of the intramolec-
˚
The bond length increased in the following order C–Br [
C–Cl [ C–F in order electronegativity as expected.
The C–S (Table 8) bond lengths in all the Schiff bases
ular hydrogen bonds N13–H2ÁÁÁO11 = 2.771(2) A for
˚
SB5ClISA and 2.772(2) A for SB5BrISA (Table 5), and
˚
are intermediate between 1.82 A for C–S single bond and
˚
1.56 A for C=S double bond [34] and are in agreement with
intermolecular hydrogen bonds N4–H1ÁÁÁO11 = 2.825(2)
˚
˚
A for SB5ClISA and N4–H3ÁÁÁO11 = 2.826(2) A for
SB5BrISA (Table 6) respectively. Comparisons of the
torsional angles of the Schiff bases are presented in
Table 7.
the reported value in SBDTC [35]. Thus, the compound
exists in the thioketo tautomeric form. Due to delocaliza-
tion of electrons in the isatin ring, the N–N (Table 8) bond
distances are slightly shorter than the corresponding bond
˚
The C–Br bond length of 1.894 A is slightly longer
˚
compared to C–Cl (1.744 A) and C–F (1.374 A) (Table 4).
˚
˚
length in unsubstituted SBDTC (1.406(3) A) [35].
123

1638
J Chem Crystallogr (2011) 41:1630–1641
Fig. 7 Intramolecular and
intermolecular hydrogen bonds
of SB5BrISA
Br10
H2
O11
(a) Intramolecular hydrogen bond of SB5BrISA
Br10
O11
H3
H3
O11
Br10
(b) Intermolecular hydrogen bond of SB5BrISA
Table 9 shows the comparison of the dihedral angles
between two selected planes. The isatin ring in SB5FISA is
almost nearly planar with dihedral angles of 0.78° followed
by SB5ClISA (1.50°) and SB5BrISA (1.70°). The planarity
of the isatin ring in the Schiff bases can be arranged in
the following order SB5FISA [ SB5ClISA [ SB5BrISA.
The benzyl ring of SB5FISA is almost perpendicular to the
dithiocarbazate plane with the dihedral angle of 83.12°
123

J Chem Crystallogr (2011) 41:1630–1641
1639
˚
Table 4 Selected bond lengths (A) and bond angles (°) for SB5FISA, SB5ClISA and SB5BrISA
SB5FISA
SB5ClISA
SB5BrISA
Bond length
C(10)–S(2)
C(9)–S(2)
C(9)–S(1)
C(3)–O(1)
C(2)–N(2)
N(2)–N(3)
C(9)–N(3)
C(7)–F(1)
1.828(6)
1.734(6)
1.676(6)
1.223(8)
1.295(7)
1.374(7)
1.347(7)
1.374(7)
C(16)–S(15)
C(14)–S(15)
C(14)–S(23)
C(3)–O(11)
C(2)–N(12)
N(12)–N(13)
C(14)–N(13)
C(8)–Cl(10)
C(8)–Br(10)
1.802(17)
1.748(17)
1.644(17)
1.234(2)
1.290(2)
1.349(2)
1.366(2)
1.744(17)
–
1.824(2)
1.748(2)
1.649(2)
1.239(3)
1.290(3)
1.353(3)
1.365(3)
–
1.894(2)
Bond angles
C(9)–S(2)–C(10)
C(9)–N(3)–N(2)
N(3)–C(9)–S(1)
N(3)–C(9)–S(2)
S(1)–C(9)–S(2)
C(3)–N(1)–C(4)
C(2)–C(3)–N(1)
N(1)–C(3)–O(1)
C(2)–C(3)–O(1)
102.2(3)
121.9(4)
118.4(4)
115.3(4)
126.3(3)
110.8(4)
105.2(5)
126.6(5)
128.1(5)
C(16)–S(15)–C(14)
C(14)–N(13)–N(12)
N(13)–C(14)–S(23)
N(13)–C(14)–S(15)
S(23)–C(14)–S(15)
C(3)–N(4)–C(5)
102.86(8)
103.20(11)
119.40(18)
119.54(17)
112.06(16)
128.37(14)
111.18(18)
106.46(19)
127.20(2)
126.30(2)
119.43(14)
119.62(13)
111.92(12)
128.45(10)
111.20(13)
106.31(14)
127.96(15)
125.73(15)
C(2)–C(3)–N(4)
N(4)–C(3)–O(11)
C(2)–C(3)–O(11)
˚
Table 5 Intramolecular hydrogen bonds (A, °)
Compound
D–HÁÁÁA
D–H
HÁÁÁA
DÁÁÁA
D–HÁÁÁA
SB5FISA
SB5ClISA
SB5BrISA
N3–H3ÁÁÁO1
N13–H2ÁÁÁO11
N13–H2ÁÁÁO11
0.85
0.86
0.85
2.00
2.16
2.12
2.690(9)
138
129
133
2.771(2)
2.772(2)
D donor, A acceptor, H hydrogen
˚
Table 6 Intermolecular hydrogen bonds (A, °)
Compound
D–HÁÁÁA
D–H
HÁÁÁA
DÁÁÁA
D–HÁÁÁA
SB5FISA
SB5ClISA
SB5BrISA
C5–H5ÁÁÁO1
N4–H1ÁÁÁO11
N4–H3ÁÁÁO11
0.92
0.89
0.87
2.46
1.95
1.98
3.209(9)
2.825(2)
2.826(2)
138
166
166
D donor, A acceptor, H hydrogen
Table 7 Comparison of the
torsional angles (°) of the Schiff
bases
Plane
SB5FISA
SB5ClISA
SB5BrISA
Torsional angles
N2–N3–C9–S1
174.58
-176.82
2.70
–
–
–
–
–
–
N3–C9–S2–C10
S1–C9–S2–C10
C2–C3–N2–N3
1.18
N12–N13–C14–S23
N13–C14–S–15–C16
S23–C14–S15–C16
C2–C3–N12–N13
173.51
177.53
-3.80
-1.57
172.81
176.91
-5.80
-3.04
123

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J Chem Crystallogr (2011) 41:1630–1641
Table 8 C–S and N–N bond
˚
lengths (A) for SB5FISA,
SB5ClISA and SB5BrISA
SB5FISA
SB5ClISA
SB5BrISA
C–S Bond length
C(9)–S(1)
1.676(6)
–
–
–
C(14)–S(23)
N–N Bond length
N(2)–N(3)
1.644(17)
1.649(2)
1.374(7)
–
–
–
N(12)–N(13)
1.349(2)
1.353(3)
Table 9 Comparison of the dihedral angles (°) between two selected planes
Plane
SB5FISA
SB5ClISA
SB5BrISA
Dihedral angles
C1–C8–C7–C6–C5–C4 and C2–C1–C4–N1–C3 (isatin ring)
C10–C11–C12–C13–C14–C15–C16 (benzyl ring) and N2–N3–C9–S1–S2 (dithiocarbazate)
C1–C5–C6–C7–C8–C9 and C1–C2–C3–N4–C5 (isatin ring)
C16–C17–C18–C19–C20–C21–C22 (benzyl ring) and N12–N13–C14–S23–S15 (dithiocarbazate)
0.78
83.12
–
–
–
–
–
1.50
72.84
1.70
74.79
–
Table 10 Cytotoxicity data (lg/mL)
Sample
MW
MCF-7
IC50 (lM)
MDA-MB-231
IC50 (lM)
SB5FISA
SB5ClISA
SB5BrISA
Tamoxifen
345.42
361.88
406.33
371.51
3.2
14.0
2.6
9.26
38.69
6.40
Inact
Inact
Inact
8.0
Inact
Inact
Inact
21.53
5.0
13.46
Values are shown as IC50 (concentration required to inhibit a 50% of the cell growth) in lg/mL. Inact inactive, IC50 \ 5.0 lg/mL (Strongly
active), IC50 = 5.0–10.0 lg/mL (moderately active), IC50 = 10–25.0 lg/mL (weakly active), IC50 [ 25.0 lg/mL (inactive), MCF-7 Human
non-metastatic mammary gland adenocarcinoma cell line, MDA-MB-231 Human metastatic mammary gland adenocarcinoma cell line
followed by SB5BrISA (74.79°) and SB5ClISA (72.84°).
The perpendicularity of the benzyl ring towards the dith-
iocarbazate plane can be ordered as follows, SB5FISA [
SB5BrISA [ SB5ClISA.
isatins against the MCF-7 breast cancer cell lines tested is
in the order of Br [ F [ Cl.
Supplementary Material
CCDC 696006, 696007 and 696008 contain the supple-
mentary crystallography data for SB5FISA, SB5BrISA and
SB5ClISA Schiff bases. This data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.
html, or from the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB21EZ, UK; fax: (?44)1223-
336-033; or email:deposit@ccdc.cam.ac.uk.
Cytotoxic Activity
The Schiff bases were evaluated in vitro using MDA-MB-
231 (Human metastatic mammary gland adenocarcinoma
cell line) and MCF-7 Human non-metastatic mammary
gland adenocarcinoma cell line. Measurement for cyto-
toxicity was in IC50, where IC50 corresponds to the con-
centration required to inhibit a 50% of the cell growth [36].
The IC50 of the Schiff bases are shown in Table 10. The
Schiff bases were found to be selectively active towards the
MCF-7 cell lines with the IC50 values of 6.40 lM, for
SB5BrISA, 9.26 lM for SB5FISA and 38.69 lM for
SB5ClISA. The cytotoxic activity of the halo substituted
Acknowledgments We thank the Department of Chemistry, Uni-
versiti Putra Malaysia for the provision of laboratory facilities. This
work was funded by a grant from the Ministry of Science, Technology
and Innovation under the Intensification of Research in Priority Area
program (Grant no. 09-02-04-0755-EA001). Support from Universiti
Teknologi MARA (UiTM) and the Ministry of Higher Education
(MOHE) for MAFA Manan is also gratefully acknowledged.
123

J Chem Crystallogr (2011) 41:1630–1641
1641
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