Syntheses and anti-depressant activity of 5-amino-1, 3, 4-thiadiazole-2-thiol imines and thiobenzyl derivatives

Article abstract of DOI:10.1016/j.bmc.2008.07.056

A number of new imine derivatives of 5-amino-1, 3, 4-thiadiazole-2-thiol have been synthesized, and their anti-depressant activity was tested using imipramine as reference drug. Two compounds namely 5-{[1-(4-chlorophenyl)-3-(4-methoxy-phenyl)prop-2-en-1-ylidene]-amino}-5-benzylthio-1, 3,4 -thiadiazole 4i(b) and 5-{[1-(4-chlorophenyl)-3-(4-dimethyl-aminophenyl)-prop-2-en-1-ylidene]amino}-5-benzylthio-1,3,4-thiadiazole 4i(c) have shown significant anti-depressant activity, which decreased immobility time by 77.99% and 76.26% compared to the standard imipramine (82%). All the compounds in the series have passed neurotoxicity tests.

Full text of DOI:10.1016/j.bmc.2008.07.056

Bioorganic & Medicinal Chemistry 16 (2008) 8029–8034
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Bioorganic & Medicinal Chemistry
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Syntheses and anti-depressant activity of 5-amino-1, 3, 4-thiadiazole-2-thiol
imines and thiobenzyl derivatives
*
Mohammad Yusuf, Riaz A. Khan, Bahar Ahmed
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Antihepatotoxic Research Laboratory, Jamia Hamdard, Hamdard Nagar, New Delhi 110062, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A number of new imine derivatives of 5-amino-1, 3, 4-thiadiazole-2-thiol have been synthesized, and
their anti-depressant activity was tested using imipramine as reference drug. Two compounds namely
5-{[1-(4-chlorophenyl)-3-(4-methoxy-phenyl)prop-2-en-1-ylidene]-amino}- 5-benzylthio-1, 3,4 -thiadi-
azole 4i(b) and 5-{[1-(4-chlorophenyl)-3-(4-dimethyl-aminophenyl)-prop-2-en-1-ylidene]amino}-5-
benzylthio-1,3,4-thiadiazole 4i(c) have shown significant anti-depressant activity, which decreased
immobility time by 77.99% and 76.26% compared to the standard imipramine (82%). All the compounds
in the series have passed neurotoxicity tests.
Received 22 May 2008
Revised 21 July 2008
Accepted 22 July 2008
Available online 24 July 2008
Keywords:
Imines
5-Amino-1, 3, 4-thiadiazole-2-thiol
Thiobenzyl
Ó 2008 Elsevier Ltd. All rights reserved.
Anti-depressant
Neurotoxic
MAO inhibitors
1. Introduction
and electron- donating groupson both terminals of the two aromatic
substitutions.
A topographical comparison also provided the
During recent years intense investigations on different classes
of thiadiazole compounds for CNS disorders have been re-
ported.1–3 Brufani et al.1 have synthesized a series of 2-amino-
5-sulfanyl-1, 3, 4-thiadiazoles as aldehyde dehydrogenase inhibi-
tors and observed significant effects on the CNS as well as
anti-depressant activity. Clerici et al.2 reported the synthesis of
2-amino-5-sulfanyl-1, 3, 4-thiadiazoles and their anti-depressant
and anxiolytic activities. Srivastava et al.3 reported triazolo-thiadi-
azole and carbazolyl-thiadiazole-2-oxaazetidines as alternate
compounds with moderate CNS activity. The reports on the
diathiazole substitution prompted us to investigate the imine
substitution in the moiety. A preliminary SAR, as discussed for
the diathiazoles1, has suggested the 2-amino substitution for
better activity. Our efforts have been on the major substitution
on the imine. The substitution of bulkier aliphatic group on the
diathiazoles does not have much effect on the antidepressant activ-
ity. However, the benzyl substitution provided much impetus to the
activity profile, and a substitution in the aromatic ring proved more
beneficial to the activity enhancement. The features for the diathiaz-
ole-linked substitution for desired level of bioactivity have been
retained in all the derivatives. The findings suggested designing
amino substitution with bulkier aromatic groups with the electron-
donating substitution for activity mapping. We have designed a
series of amino-substituted compounds with electron-withdrawing
chlorobenzyl difference in the series developed by us. Keeping this
in view, we have synthesized some new imine derivatives of 5-ami-
no-1, 3, 4-thiadiazole-2-thiol for their anti-depressant activity.
2. Results and discussion
The compounds were synthesized starting from chalcones and
5-amino-1, 3, 4-thiadiazole-2-thiols. The 5-amino-1, 3, 4-thiadia-
zole-2-thiol was synthesized from carbon disulfide addition to thi-
osemicarbazide under reflux. The series 2a–2e were synthesized in
single step by addition of different chalcones to the 2-amino-5-
mercapto-1, 3, 4-thiadiazoles under reflux for 5 to 8 hrs. The com-
pounds of 2a–2e and benzyl chloride/4-chloro-benzyl chloride in
ethanolic alkali were refluxed to give the desired 4i and 4ii series
of compounds (Fig. 1). Concerning the characterization of com-
pounds, infrared spectra were scanned in KBr on Bio-Red FTIR-
spectrophotometer. Nuclear magnetic resonance spectra were
scanned on Bruker model DRX-400 MHz, in CDCl3 using tetrameth-
ylsilane (TMS) as the internal reference and Mass spectra was re-
corded on a JOEL SX 102nDA-6000 mass spectrometer using
ArgonnXenon as FAB gas in matrix of m-nitro benzyl alcohol with
an accelerating voltage of 10 kV.
The IR spectra of compounds exhibited absorption bands in the
range of 3390–3318 cmꢀ1 due to trans-ene CAH stretching bonds,
2600–2550 cmꢀ1 due to SH, 1600–1550 cmꢀ1 due to aromatic CAH
groups, 1540–1500 cmꢀ1 due to imine C@N stretching and 800–
720 cmꢀ1 due to aromatic CAH deformation. The NMR peaks in
* Corresponding author. Tel.: +91 11 26059686x5623; fax: +91 11 26059686.
E-mail address: baharchem@yahoo.com (B. Ahmed).
0968-0896/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.07.056

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M. Yusuf et al. / Bioorg. Med. Chem. 16 (2008) 8029–8034
R1
O
R1
N
N
N
SH
S
R2
HN NH2
S
N
N
S
R2
+
S
H2N
C
Carbon
SH
S
H2N
2a-2e)
(
5-amino-1,3,4-thiadiazole-2-thiol
Thiosemicarbazide
Cl
disulfide
Cl
R1 = H, OCH3, (CH3)2N, Cl, OH
R2 = H, Cl
Cl
S
S
S
S
N
N
N
N
N
N
Cl
4iia-4iie
(
)
R1
4ia-4ie)
(
R2
R1
R2
Figure 1. Synthesis of 5-amino-1,3,4-thiadiazole-2-thiol imine and imino-thiobenzyl derivatives.
the range of 6.5–8.00 ppm were due to different aromatic protons.
8–10 ppm was characteristic to imino proton; and 10–13.1 ppm
was assigned to thiol-proton. The peaks in the range of 3.8–
4.9 ppm were also found due to methylene group. Two doublets
in the range of 7.5–8 ppm having coupling constant 15.6 Hz were
very characteristic due to trans-proton of the ethylene group.
The conventional tricyclic anti-depressants inhibit the neuronal
reuptake of neurotransmitters and metabolize to effective inhibi-
tors of both norepinephrine and serotonin by dealkylation. The tri-
cyclics have been analyzed for their lack of co-planarity in the
molecular structure and effects of substitutions in side chains pri-
marily responsible for alternating activity profile. However, the
structural similarities among non-tricyclic antidepressants are less
obvious. The aryl, aryloxy-alkylamines, flouxetin and viloxazine
antidepressants have their own structural parameters with less
interrelation. However, a broader look suggested a spatial mini-
mality, wherein the contraction (or expansion) of available
structural entities pointed out toward a spatial dimension occupa-
tion similar to that of tricyclic compounds with lesser consider-
ations for the substitutions. The observation of minimum
structural feature as presence of an aromatic ring and an aliphatic
nitrogen with aliphatic chain of 4 atoms does not distinguish be-
tween inhibitors of dopamine, norepinephrine and serotonin up-
takes, but does have interaction with other uptake receptor sites.
As ‘the amine hypothesis of mood’ postulates, the brain amines,
particularly norepinephrine (NE) and serotonin (5-HT), are neuro-
Figure 2. Possible interaction of norepinephrine and the test drug pharmacophore with MAO Enzyme.5–14

M. Yusuf et al. / Bioorg. Med. Chem. 16 (2008) 8029–8034
8031
Figure 3. Space-filling models for 4i & 4ii series compounds.
in its observance of non-co-planarity. The remarkable difference
was the extended spatial dimensions with electron-withdrawing
groups as nuclear substitution in both the aromatic rings in the rest
of the structure. These spatial and molecular attributes correlation
suggested a different biological activity receptor site. (Figs. 3–6).
The observations that the products did not show any side ef-
fects with the neurological deficit have indicated the non-involve-
ment of cross-over activity through the specific receptor sites.
Figure 4. A Space-filling model for 4i & 4ii series compounds substituted with
OCH3 and Cl. The extra second Cl is colored green.
3. Conclusion
Compounds of 4i and 4ii series were tested for their anti-
depressant activity using imipramine as a standard drug. The
parameter ‘% immobility’ was calculated through forced swimming
test in albino mice. All the test and standard compounds were
administered at dose of 10 mg/kg intraperitoneally. Compound
4ib and 4id have decreased the immobility time by 77.99% and
76.26% compared to the standard drug (imipramine), which
showed 82% decrease in immobility time. Hence, these compounds
have superior anti-depressant activity as compared to standard
drug (imipramine). Although 4iib and 4iid also decreased the
immobility time by 84.20% and 87.57%, it was less than that of
the standard drug imipramine.
transmitters in pathways and function in the expression of mood.
A functional decrease in the activity of such amines would result in
depression and a functional increase of activity would result in
mood elevation.4
MAO oxidizes the amines having hydrogen at
the nitrogen, which are bonded with the amino acid carboxy (C)
terminus, where the oxidation of -carbon takes place by FAD
cofactor. FAD itself reduces to FADH and oxidizes the -H against
a-position against
a
a
the nitrogen to Schiff (imine) compound after being hydrolyzed
to give aldehyde or ketone and an amine.5–9
We have synthesized a number of MAO inhibitors, which abol-
ished the enzyme activity by one electron mechanism,10 chelating
the Zn2+ ions to interact with enzyme, creating non-availability of
a
-hydrogen against the nitrogen,11,12or by oxidation of trans ene
4. Experimental
proton and attachment to cysteine residue13,14 as shown in Fig. 2.
The SAR has also been suggested for the aromatic ring and side
chain amine. The aromatic substitution with electron-withdrawing
groups and heterocyclic of 2-thienyl, 2-pyridyl, 2-furyl, and 2-pyr-
azinyl nature increases the potency. Thus, the minimum structure
requirement includes an electron-rich moiety separated in the
plane of aromatic ring by a distance of 5.25° A from its center. A
QSAR molecular attribute estimate and 3D spatial orientation as
well as electronic arrangements in the molecules obtained by the
geometrical optimizations could not be interrelated with the activ-
ity profile of products in 4i and 4ii series. The products in 2a-e and
4i and 4ii series were found to be non-planer in their stereo-
orientation.
4.1. Synthesis of chalcones15,16
A solution of 2 g of sodium hydroxide in 20 mL of water and
10 g (12.5 mL) of rectified spirit was refluxed under stirring. It
was cooled to room temperature and poured in freshly distilled
acetophenone (0.04 mol). Benzaldehyde was added slowly under
stirring at 25 °C for 2 h and it was kept in refrigerator overnight be-
tween 0 and 5 °C. The crystals obtained were filtered, washed with
cold water until they were neutral and again were washed with
ice-cold n-hexane. The product was recrystallized from n-hexane.
TLC, (silica gel), Rf 0.5 in benzene: acetone (9:1).
4.2. Synthesis of 5-amino-1, 3, 4-thiadiazole-2-thiol17
These observations suggested the structural correlation of con-
jugated methoxy-benzyl and chloro-benzyl groups as the larger
substituents for aliphatic amine side chain in relation to the tricy-
clic and aryl-oxy antidepressant group of compounds. The struc-
tural entity minus the conjugated benzyl functionality is distinct
Thiosemicarbazide 45.5 g (0.25 mol) was suspended in absolute
ethanol and anhydrous sodium carbonate (24 g) and carbon disul-
phide 0.25 mol (46 g) were added slowly. The mixture was stirred
Figure 5. Brufani et al. JMC, 2001, 44, 931.936, the most potent thiadizole, 3k and 5g, 3d.

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M. Yusuf et al. / Bioorg. Med. Chem. 16 (2008) 8029–8034
Figure 6. 3D Optimized di-chloro and methoxy substituted 4i series compound.
under reflux for 1 h and later heated at 75–80 °C for 4 h. Solvent
was removed and the residue was dissolved in water (200 mL),
acidified with conc. HCl to give the product as hydrochloride salt,
TLC (silica gel), TEF 5:4:1, mp 232 °C, yield 84% (54 g). 1H NMR
(400 MHz, DMSO-d6, TMS) d ppm 7.99 (2H, s, NH2), 12.93 (H, s,
SH). FTIR (KBr) mmax cmꢀ1 2553 (SAHstr, thiol).
265, 131. Anal. Calcd. for C17H11Cl2N3S2: C, 52.04; H, 2.83; N,
10.16. Found: C, 52.08; H, 2.81; N, 10.13.
4.3.5. 2-{-3-(4-Chlorophenyl)-3-[(5-mercapto-1,3,4-thiadiazol-
2-yl)imino]-prop-1-en-1-yl} phenol (2e)
Yield 45%, mp 126–129 °C; 1H NMR (400 MHz, CDCl3, TMS) d
ppm 4.92 (1H, s, OH), 7.52 (1H, d, J = 15.6 Hz, trans-ene-H), 7.77
(1H, d, J = 15.6 Hz, trans-ene-H), 12.19 (1H, s, SH) 7.05–7.84(m,
8H, Ar–Bz). FTIR (KBr) mmax cmꢀ1 3019 (CAHstr, trans-ene), 2548
(SAHstr, thiol), 1672 (imine, C@Nstr), 960 (CAHdef, trans-ene), 739
(CAHdef, o-disubst. Bz), 693 (CAHdef, monosubst. Bz), 614 (Ar
4.3. Syntheses of various imines (2a-2e)
2-Amino-5-mercapto-1, 3, 4-thiadiazole (0.02 mol) was sus-
pended in 25 mL absolute ethanol and 0.02 mol of different chal-
cones were added, refluxed for 5–8 h, and then left overnight.
The solvent was evaporated in vacuum and the residue was recrys-
tallized from methanol.
CAClstr
, Bz). FABMS m/z 372, 246, 131. Anal. Calcd. for
C17H12ClN3OS2: C, 54.61; H, 3.24; N, 11.24. Found: C, 54.62; H,
3.21; N, 11.23.
4.3.1. 5-{[1, 3-Diphenylprop-2-en-1-ylidene] amino}-1,3,4-
thiadiazole-2-thiol (2a)
4.4. Thio-thiadiazole imine derivatives of aromatic chalcones
(4a–4e)
Yield 70%, mp 58–60 °C; 1H NMR (400 MHz, CDCl3, TMS) d ppm
7.73 (1H, d, J = 15.6 Hz, trans-ene-H), 7.94 (1H, d, J = 15.6 Hz, trans-
ene-H), 12.37 (1H, s, SH) 6.97–7.76 (m, 10H, Ar–Bz). FTIR (KBr) mmax
cmꢀ1 3018 (CAHstr, trans-ene), 2545 (SAHstr, thiol), 1680 (imine,
C@Nstr), 968 (CAHdef, trans-ene), 706 (CAHdef, monosubst. Bz). FAB-
MS m/z 325, 210, 131. Anal. Calcd. for C17H13N3S2: C, 63.13; H,
4.05; N, 12.99. Found: C, 63.10; H, 4.06; N, 12.97.
A mixture of Fig. 2 compounds namely 2a–2e (0.005 mol) and
0.005 mol of benzyl chloride/4-chloro-benzyl chloride in ethanolic
alkali (0.08 g KOH in 20 mL EtOH) was refluxed till the completion
of reaction (as indicated by TLC using silica gel as stationary phase
and TEF 5:4:1 as mobile phase). On cooling, the reaction mixture
was poured into crushed ice, and a crude precipitate was obtained,
which was filtered and then recrystallized from acetone.
4.3.2. 5-{[1-(4-Chlorophenyl)-3-[4-(methoxyphenyl)-prop-2-
en-1-ylidene]amino}- 1,3,4-thiadiazole-2-thiol (2b)
4.4.1. 5-(Benzylthio)-N-[1,3-diphenylprop-2-en-1-ylidene]-
1,3,4-thiadiazol-2-amine (4ia)
Yield 62%, mp 81–83 °C. 1H NMR (400 MHz, CDCl3, TMS) d ppm
7.44 (1H, d, J = 15.6 Hz, trans-ene-H), 7.57 (1H, d, J = 15.6 Hz, trans-
ene-H), 12.17 (1H, s, SH) 7.02–7.82 (m, 8H, Ar–Bz). FTIR (KBr) mmax
cmꢀ1 3015 (CAHstr, trans-ene), 2543 (SAHstr, thiol), 1677 (imine,
C@Nstr), 964 (CAHdef, trans-ene), 808 (CAHdef, p-disubst. Bz), 698
(CAHdef, monosubst. Bz), 612 (Ar CAClstr, Bz). FABMS m/z 390,
273, 131. Anal. Calcd. for C18H14ClN3OS2: C, 55.73; H, 3.64; N,
10.83. Found: C, 55.71; H, 3.63; N, 10.84.
Yield 47%, mp 46 °C; 1H NMR (400 MHz, CDCl3, TMS) d ppm 4.81
(2H, s, CH2), 7.89 (1H, d, J = 15.6 Hz, trans-ene-H), 7.65 (1H, d,
J = 15.6 Hz, trans-ene-H), 6.98–7.81 (m, 15H, Ar–Bz). FTIR (KBr)
mmax cmꢀ1 3021 (CAHstr, trans-ene) 1687 (C@Nstr), 1462 (methy-
lene, CAHstr), 976 (CAHdef, trans-ene), 709 (CAHdef, monosubst.
Bz). FABMS m/z 415, 274, 209. Anal. Calcd. for C24H19N3S2: C,
69.70; H, 4.63; N, 10.16. Found: C, 69.71; H, 4.62; N, 10.14.
4.3.3. 5-{[1-(4-Chlorophenyl)-3-[4-(dimethylamino)phenyl-
prop- 2-en-1-ylidene]amino}-1,3,4-thiadiazole-2-thiol (2c)
Yield 73%, mp 130–134 °C; 1H NMR (400 MHz, CDCl3, TMS) d
ppm 7.36 (1H, d, J = 15.6 Hz, trans-ene-H), 7.49 (1H, d, J = 15.6 Hz,
trans-ene-H), 12.15 (1H, s, SH) 7.04–7.86 (m, 8H, Ar–Bz). FTIR
(KBr) mmax cmꢀ1 3016 (CAHstr, trans-ene), 2544 (SAHstr, thiol),
1680 (imine, C@Nstr), 967 (CAHdef, trans-ene), 810 (CAHdef, p-dis-
ubst. Bz), 703 (CAHdef, monosubst. Bz), 615 (Ar CAClstr, Bz). FABMS
4.4.2. 5-{[1-(4-Chloro phenyl)-3-(4-methoxyphenyl)prop-2-en-
1-ylidene]amino}-5-benzylthio-1,3, 4-thiadiazole (4ib)
Yield 50%, mp 80 °C; 1H NMR (400 MHz, CDCl3, TMS) d ppm 4.83
(2H, s, CH2), 7.66 (1H, d, J = 15.6 Hz, trans-ene-H), 7.86 (1H, d,
J = 15.6 Hz, trans-ene-H) 6.91–7.68 (m, 13H, Ar–Bz). FTIR (KBr) mmax
cmꢀ1 3027 (CAHstr, trans-ene), 1689 (C@Nstr), 1466 (methylene,
CAHstr), 976 (CAHdef, trans-ene), 815 (CAHdef, p-disubst. Bz), 712
(CAHdef, monosubst. Bz), 610 (Ar CAClstr, Bz). FABMS m/z 478,
271, 208. Anal. Calcd. for C25H20ClN3OS2: C, 62.81; H, 4.22; N,
8.79. Found: C, 62.79; H, 4.21; N, 8.78.
m/z 402, 272, 131. Anal. Calcd. for C19H17ClN4S2: C, 56.92; H, 4.27;
N, 13.97. Found: C, 56.87; H, 4.26; N, 13.94.
4.3.4. 5-{[1,3-bis-(4-Chlorophenyl)-prop-2-en-1-
ylidene]amino}-1,3,4-thiadiazole-2-thiol (2d)
4.4.3. 5-{[1-(4-Chlorophenyl)-3-(4-dimethylaminophenyl)-
prop-2-en-1- ylidene]amino}-5-benzylthio-1,3,4-thiadiazole
(4ic)
Yield 69%, mp 75–79 °C; 1H NMR (400 MHz, CDCl3, TMS) d ppm
7.68 (1H, d, J = 15.6 Hz, trans-ene-H), 7.91 (1H, d, J = 15.6 Hz, trans-
ene-H), 12.21 (1H, s, SH) 7.10–7.92 (m, 8H, Ar–Bz). FTIR (KBr) mmax
cmꢀ1 3020 (CAHstr, trans-ene), 2547 (SAHstr, thiol), 1679 (imine,
C@Nstr), 965 (CAHdef, trans-ene), 805 (CAHdef, p-disubst. Bz), 696
(CAHdef, monosubst. Bz), 618 (Ar CAClstr, Bz). FABMS m/z 409,
Yield 48%, mp 95 °C; 1H NMR (400 MHz, CDCl3, TMS) d ppm 4.79
(2H, s, CH2) 7.65 (1H, d, J = 15.6 Hz, trans-ene-H), 7.89 (1H, d,
J = 15.6 Hz, trans-ene-H) 6.93-7.72 (m, 13H, Ar–Bz). FTIR (KBr) mmax
cmꢀ1 3023 (CAHstr, trans-ene), 1682 (C@Nstr), 1461 (methylene,
CAHstr), 973 (CAHdef, trans-ene), 812 (CAHdef, p-disubst. Bz), 709

M. Yusuf et al. / Bioorg. Med. Chem. 16 (2008) 8029–8034
8033
(CAHdef, monosubst. Bz), 605 (Ar CAClstr, Bz). FABMS m/z 491, 285,
209. Anal. Calcd. for C26H23ClN4S2: C, 63.59; H, 4.72; N, 8.43.
Found: C, 63.56; H, 4.71; N, 8.43.
cmꢀ1 3012 (CAHstr, trans-ene). 1680 (C@Nstr), 1457 (methylene,
CAHstr), 964 (CAHdef, trans-ene), 601 (Ar CAClstr, Bz). FABMS m/z
518, 275, 242. Anal. Calcd. for C24H16Cl3N3S2: C, 55.77; H, 3.12;
N, 8.13. Found: C, 55.76; H, 3.08; N, 8.11.
4.4.4. 5-Benzylthio-N-[1,3-bis(4-chlorophenyl)prop-2-en-1-
ylidene]-1,3,4- thiadiazol-2-amine (4id)
4.4.10. 2-[3-{[5-(4-Chlorobenzylthio)-1,3,4-thiadiazol-2-
yl]imino}- 3-(4-chlorophenyl)prop-1-en-1-yl] phenol (4iie)
Yield 25%, mp 90 °C; 1H NMR (400 MHz, CDCl3, TMS) d ppm,
4.66 (1H, s, OH), 4.95 (2H, s, CH2) 7.61 (1H, d, J = 15.6 Hz, trans-
ene-H), 7.85 (1H, d, J = 15.6 Hz, trans-ene-H) 6.96-7.72 (m, 12H,
Ar–Bz). FTIR (KBr) mmax cmꢀ1 3031 (CAHstr, trans-ene), 1691
(C@Nstr), 1459 (methylene, CAHstr), 975 (CAHdef, trans-ene), 816
(CAHdef, p-disubst. Bz), 715 (CAHdef, monosubst. Bz), 612 (Ar
Yield 39%, mp 51 °C; 1H NMR (400 MHz, CDCl3, TMS) d ppm 4.80
(2H, s, CH2) 7.63 (1H, d, J = 15.6 Hz, trans-ene-H), 7.88 (1H, d,
J = 15.6 Hz, trans-ene-H) 6.98–7.76 (m, 13H, Ar–Bz). FTIR (KBr) mmax
cmꢀ1 3028 (CAHstr, trans-ene), 1688 (C@Nstr), 1465 (methylene,
CAHstr), 976 (CAHdef, trans-ene), 815 (CAHdef, p-disubst. Bz), 711
(CAHdef, monosubst. Bz), 607 (Ar CAClstr, Bz). FABMS m/z 525,
276, 209. Anal. Calcd. for C24H17Cl2N3S2: C, 59.75; H, 3.55; N,
8.71. Found: C, 59.73; H, 3.56; N, 8.70.
CAClstr
, Bz). FABMS m/z 499, 258, 243. Anal. Calcd. for
C24H17Cl2N3OS2: C, 57.83; H, 3.44; N, 8.43. Found: C, 57.76; H,
4.4.5. 2-[3-{[5-(Benzylthio)-1,3,4-thiadiazol-2-yl]imino}-3-(4-
chlorophenyl)prop-1-en-1-yl]phenol (4ie)
3.43; N, 8.39.
Yield 52%, mp 101 °C; 1H NMR (400 MHz, CDCl3, TMS) d ppm
4.75 (2H, s, CH2), 4.88 (1H, s, OH), 7.61 (1H, d, J = 15.6 Hz, trans-
ene-H), 7.85 (1H, d, J = 15.6 Hz, trans-ene-H) 7.04–7.70 (m, 13H,
Ar–Bz). FTIR (KBr) mmax cmꢀ1 3030 (CAHstr, trans-ene), 1692
(C@Nstr), 1460 (methylene, CAHstr), 977 (CAHdef, trans-ene), 817
(CAHdef, p-disubst. Bz), 717 (CAHdef, monosubst. Bz), 613 (Ar
4.5. Biological screening
4.5.1. Anti-depressant activity18,19
Anti-depressant activity was measured with imipramine as
standard drug using the Forced Swimming Test in albino mice. Al-
bino mice were placed in a vertical Plexiglas cylinder filled with
water, maintained at 25 °C, for 15 min. Five to six minutes later
immobility reached a plateau, where the mice remained immobile
for approximately 80% of the time. After 15 min in the water, the
mice were removed and allowed to dry in a heated enclosure
(32 °C) before being returned to their home cages. They were again
placed in the cylinder for 24 h later, and the total duration of
immobility was measured during a 5-min test (Table 1).
CAClstr, Bz). FABMS m/z 463, 258, 208. Anal. Calcd. for
C24H18ClN3OS2: C, 62.12; H, 3.91; N, 9.06. Found: C, 62.11; H,
3.92; N, 9.10.
4.4.6. 5-(4-Chlorobenzylthio)-N-[1,3-diphenylprop-2-en-1-
ylidene]-1,3,4- thiadiazol-2-amine (4iia)
Yield 23%; 1H NMR (400 MHz, CDCl3, TMS) d ppm 4.96 (2H, s,
CH2), 7.64 (1H, d, J = 5.6 Hz, trans-ene-H), 7.9 (1H, d, J = 15.6 Hz,
trans-ene-H) 7.09–7.73 (m, 14H, Ar–Bz). FTIR (KBr) mmax cmꢀ1
3014 (CAHstr, trans-ene), 1683 (C@Nstr), 1466 (methylene, CAHstr),
971 (CAHdef, trans-ene), 704 (CAHdef, monosubst. Bz), 609 (Ar
4.5.2. Neurotoxicity test
The disruptive effects on motor coordination were assessed
using the Rotarod Tread20 mill mouse test and Ethanol Potentia-
tion2 Test in male albino mice.
CAClstr
24H18ClN3S2: C, 64.34; H, 4.05; N, 9.38. Found: C, 64.32; H, 4.02;
N, 9.33.
, Bz). FABMS m/z 447, 207, 244. Anal. Calcd. for
C
4.5.2.1. Rotarod test20
.
The animals were placed on a
rotating rod (24 rpm) and then observed for 5 min. The skeletal
4.4.7. 5-{[1-(4-Chlorophenyl)-3-(4-methoxyphenyl)-prop-2-en-
1-ylidene]amino}- 5-(4-chlorobenzylthio)-1,3,4-thiadiazole
(4iib)
Table 1
Antidepressant activity of test drug compared with that of imipramine by the Forced
Swimming test in albino mice
Yield 39%, mp 72 °C; 1H NMR (400 MHz, CDCl3, TMS) d ppm 5.1
(2H, s, CH2), 7.71 (1H, d, J = 15.6 Hz, trans-ene-H), 7.94 (1H, d,
J = 15.6 Hz, trans-ene-H) 6.96–7.63 (m, 12H, Ar–Bz). FTIR (KBr) mmax
cmꢀ1 3027 (CAHstr, trans-ene) 1689 (C@Nstr), 1464 (methylene,
CAHstr), 976 (CAHdef, trans-ene), 813(CAHdef, p-disubst. Bz), 604
(Ar CACl str, Bz). FABMS m/z 513, 273, 243. Anal. Calcd. for
Compound
Dose (mg/kg)
Immobility time SEM
% Immobility
Vehicle
4ib
4id
4iib
4iid
—
235.9 5.7
184.0 12.1*
179.9 5.6*
198.7 9.9
206.6 10.7
215.3 13.1
176.3 14.9
100
10
10
10
10
—
77.99
76.26
84.23
87.57
100.00
82.00
C25H19Cl2N3OS2: C, 58.59; H, 3.74; N, 8.20. Found: C, 58.54; H,
Vehicle
Imipramine
10
3.71; N, 8.21.
Test compounds and imipramine (reference) were administered ip 60 min before
the test. Each group consisted of eight mice.
P < 0.01 vs respective vehicle group.
4.4.8. 5-{[1-(4-Chlorophenyl)-3-(4-dimethylaminophenyl)-
prop-2-en-1- ylidene]amino}-5-(4- chlorobenzylthio)-1,3,4-
thiadiazole (4iic)
*
Yield 41%, mp 81 °C; 1H NMR (400 MHz, CDCl3, TMS) d ppm 4.98
(2H, s, CH2), 7.67 (1H, d, J = 15.6 Hz, trans-ene-H), 7.93 (1H, d,
J = 15.6 Hz, trans-ene-H) 7.01–7.78 (m, 12H, Ar–Bz). FTIR (KBr) mmax
cmꢀ1 3014 (CAHstr, trans-ene) 1678 (C@Nstr), 1454 (methylene,
CAHstr), 969 (CAHdef, trans-ene), 603 (Ar CAClstr, Bz). FABMS m/z
527, 285, 242. Anal. Calcd. for C26H22Cl2N4S2: C, 59.42; H, 4.22;
N, 10.66. Found: C, 59.39; H, 4.18; N, 10.59.
Table 2
Neurotoxic activity of the test compounds by Rotarod an Ethanol Potentiation test in
albino mice
Compound
Dose (mg/kg)
Number of
mice
Result of
Result of Ethanol
Potentiation testb
Rotarod testa
4ib
4id
4iib
4iid
10
10
10
10
6
6
6
6
(+)
(+)
(+)
(+)
(+)
(+)
(+)
(+)
4.4.9. 5-(4-Chlorobenzylthio)-N-[1,3-bis(4-chlorophenyl)prop-
2-en-1-ylidene]-1, 3,4-thiadiazol-2-amine (4iid)
The (+) sign indicates 50% or more passed the neurotoxicity testing.
Yield 22%, mp 40 °C; 1H NMR (400 MHz, CDCl3, TMS) d ppm 5.12
(2H, s, CH2), 7.69 (1H, d, J = 15.6 Hz, trans-ene-H), 7.97 (1H, d,
J = 15.6 Hz, trans-ene-H) 6.98–7.65 (m, 12H, Ar–Bz). FTIR (KBr) mmax
a
Dose was administered ip and neurotoxicity was measured after 30 min.
Mice were treated with the test compounds and 1 h later with ethanol 2.5 gnkg
b
ip neurotoxicity was measured after 30 min.

8034
M. Yusuf et al. / Bioorg. Med. Chem. 16 (2008) 8029–8034
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Mice were treated with the
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The authors are thankful to the NMR Section Jamia Hamdard,
New Delhi for scanning the NMR spectra. Arbro Pharmaceuticals,
New Delhi, for scanning IR spectra; and CDRI Lucknow for MASS
spectra. One of the authors (M.Y.) is thankful to UGC, New Delhi,
for granting GATE Scholarship.
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