1,3,4-Thiadiazole derivatives. Synthesis, structure elucidation, and structure-antituberculosis activity relationship investigation

Article abstract of DOI:10.1021/jm0495632

A series of 2,5-disubstituted-1,3,4-thiadiazoles were synthesized, the compounds structures were elucidated and screened for the antituberculosis activity against Mycobacterium tuberculosis H37Rv using the BACTEC 460 radiometric system. Among the tested compounds, 2-phenylamino-5-(4-fluorophenyl) -1,3,4-thiadiazole 22 showed the highest inhibitory activity. The relationships between the structures of compounds and their antituberculosis activity were investigated by the Electronic-Topological Method (ETM) and feed forward neural networks (FFNNs) trained with the back-propagation algorithm. As a result of the approach, a system of pharmacophores and anti-pharmacophores has been found that effectively separates compounds of the examination set into groups of active and inactive compounds. The system can be applied to the screening and design of new active compounds possessing skeletons similar to those used in the present study.

Full text of DOI:10.1021/jm0495632

6760
J. Med. Chem. 2004, 47, 6760-6767
1,3,4-Thiadiazole Derivatives. Synthesis, Structure Elucidation, and
Structure-Antituberculosis Activity Relationship Investigation
Elc¸in E. Oruc¸,† Sevim Rollas,*,† Fatma Kandemirli,‡ Nathaly Shvets,§,| and Anatholy S. Dimoglo§,
Faculty of Pharmacy, Department of Pharmaceutical Chemistry, Marmara University, Istanbul, 81010, Turkey,
Department of Chemistry, Kocaeli University, Izmit, 41400, Turkey, Institute of Technology,
PK-141, Gebze, Kocaeli, 41400, Turkey, Institute of Mathematics, Academy of Sciences of Moldova, Kishinev, 2028, Moldova,
and Institute of Chemistry, Department of Quantum Chemistry, Kishinev, 2028, Moldova
Received June 5, 2004
A series of 2,5-disubstituted-1,3,4-thiadiazoles were synthesized, the compounds structures
were elucidated and screened for the antituberculosis activity against Mycobacterium tuber-
culosis H37Rv using the BACTEC 460 radiometric system. Among the tested compounds,
2-phenylamino-5-(4-fluorophenyl)-1,3,4-thiadiazole 22 showed the highest inhibitory activity.
The relationships between the structures of compounds and their antituberculosis activity were
investigated by the Electronic-Topological Method (ETM) and feed forward neural networks
(FFNNs) trained with the back-propagation algorithm. As a result of the approach, a system
of pharmacophores and anti-pharmacophores has been found that effectively separates
compounds of the examination set into groups of active and inactive compounds. The system
can be applied to the screening and design of new active compounds possessing skeletons similar
to those used in the present study.
Introduction
activity, the better are the results of pattern recognition
and separation of the molecules into active and inactive
ones. The ETM can be considered as belonging to the
class of structure-based approaches17-21 for the struc-
ture-activity relationship (SAR) study. As a conse-
quence of the choice, the ETM is capable of taking into
account any individual properties of separate atoms and
bonds that is very important for revealing details of
interactions between a biologic receptor and an active
molecule.
Many enough published studies have used ETM to
find SAR models involving a representative list of
activities and thousands of compounds belonging to
different chemical classes (some of them are given as
an example22-25). The ETM software has also undergone
considerable development, so as the method itself.26-28
The new ETM-based system capable of unifying Web-
based SAR resources and using Internet communica-
tions in the frameworks of a project named ETOSAR
makes the ETM a valuable tool for SAR studies and
provides rules for the synthesis of new potentially active
compounds. For the analysis of data on the pharma-
cophores in this study we have used one of the most
well-known NNsthe feed forward neural networks
(FFNNs) trained with the back-propagation algo-
rithm.29,30
During recent years there has been intense investiga-
tion of different classes of thiadiazole compounds, many
of which known to possess interesting biological proper-
ties such as antimicrobial,1-3 antituberculosis,4 anti-
inflammatory,5-7 anticonvulsant,8,9 antihypertensive,10,11
local anesthetic,12 anticancer,13,14 and hypoglycemic
activities.15
Increasingly, the treatment of mycobacterial infec-
tions, especially tuberculosis, has become an important
problem due to the emergence of multidrug-resistance.
The 1,3,4-thiadiazole derivatives were synthesized with
the aim of new antituberculosis drugs development. In
our previous study, one of thiadiazole derivatives,
namely 2-(4-chlorophenylamino)-5-(4-aminophenyl)-
1,3,4-thiadiazole, showed 57% inhibition against Myco-
bacterium tuberculosis.16 This observation had an im-
pact on our further work on the synthesis and search
for some new thiadiazoles with the antituberculosis
activity. The structures of the synthesized compounds
were elucidated using UV, IR, 1H NMR, mass spectros-
copy, and elemental analysis. The Tuberculosis Anti-
microbial Acquisition and Coordinating Facility (TAACF)
of the Southern Research Institute screened the com-
pounds for antituberculosis activity.
The present study that uses both the Electronic-
Topological Method (ETM) and Neural Network (NN)
methods aims also in finding new antituberculosis
compounds. The better is the description of a molecule
in terms of structural parameters representing its
Results and Discussion
Chemistry. In our research, 4-substituted benzoic
acid hydrazides 2a-d being the starting materials were
prepared by etherification of 4-substituted benzoyl
chloride with phenol in sodium hydroxide, followed by
refluxing with hydrazine hydrate in dry methanol
(Scheme 1). After treatment with different arylisothio-
cyanates in ethanol or acetonitrile, compounds 2a-e
and isoniazid gave the thiosemicarbazides 3, which were
cyclized into the thiadiazoles as the result of a ring
* Corresponding authors: S. Rollas, Phone: +90 216 414 2962.
Fax: +90 216 345 2952. E-mail: sevim@sevimrollas.com; A. Dimoglo,
E-mail: dimoglo@gyte.edu.tr.
† Marmara University.
‡ Kocaeli University.
§ Institute of Technology.
| Institute of Mathematics, Academy of Sciences of Moldova.
Institute of Chemistry, Academy of Sciences of Moldova.
10.1021/jm0495632 CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/02/2004

1,3,4-Thiadiazole Derivatives
Journal of Medicinal Chemistry, 2004, Vol. 47, No. 27 6761
Scheme 1a
method (MMP2) and semiempirical quantum chemistry
method (AM1), respectively. Diagonal elements of the
matrixes called Electronic-Topological Matrixes of
Contiguity (ETMC, for short) reflect one or more atomic
properties (represented by a separate value or by a
vector of characteristics). Off-diagonal elements char-
acterize bonds between pairs of atoms, if they exist, or
distances, otherwise. (Usually, only the upper triangle
of each matrix is used in calculations because of the
symmetry of bonds.) Also, more that one property can
be taken for bonds. However, the ETM calculations use
only by one property for atoms and bonds, for simplicity.
If there are more than one property for atoms and
bonds, the ETM calculations can be repeated for each
property but separately. In our case, effective charges
on atoms are taken as diagonal elements, and the values
of Wiberg’s index represent off-diagonal elements cor-
responding to bonds; if no bond, then off-diagonal
elements are distances for corresponding pairs of atoms.
Computational part of the ETM is a sequence of the
following steps:
a Reagents and conditions: (a) NaOH; (b) NH2NH2, CH3OH.
Scheme 2a
• Conformational analysis
• Quantum-chemistry calculations
• The ETMCs formation
• The search for structural features, responsible for
the compounds activity/inactivity (the features are
referenced as pharmacophores/anti-pharmacophores,
correspondingly). To find pharmacophores, a template
active compound and the rest of compounds are com-
pared as weighted graphs; to find anti-pharmacophores,
an inactive compound is used as a template for the
comparison. At the same time, the molecules flexibility
is taken into account by the comparison of atomic and
bond weights.
The last two steps represent the essential part of the
ETM. The main advantages of the ETM are that its
molecular descriptions reflect the molecules electronic
and 3D conformational properties of compounds and do
not depend on the atoms numeration and sorts.
Thus, for each template compound (active or inactive),
its ETMC was compared with the ETMCs of the rest of
compounds in both classes of the series taken for this
study. The comparison resulted in a few common
structural fragments for the two cases. The fragments
were found as submatrixes of the ETMCs corresponding
to templates (they will be referenced as electron-
topological submatrixes of contiguity, or ETSCs, for
short). Consequently, all pharmacophores and anti-
pharmacophores found from the ETM calculations form
a system for the activity identification. For the series
studied the system includes 15 pharmacophores and 10
anti-pharmacophores. From the compound 22 taken as
the template active compound, an activity feature 1 (or
the Ph1 pharmacophore) was found. It is given in
Figure 1 with the corresponding ETSC, which describes
electronic-topological characteristics of the fragment
(see Figure 1a). As seen from the Ph1 pharmacophore
structure, it consists of five atoms (C1, C10, C16, H19, F20),
which relate structurally to the substituents attached
to the thiadiazole ring. Charges on C10 and C16 atoms,
which are situated at a distance of 11.16 Å, are -0.15ej
and -0.16ej, respectively. The charge on the atom H19,
which is chemically bonded to the nitrogen atom, is
0.24ej.
a Reagents and conditions: (a) 4-RC6H4NCS, C2H5OH or CH3CN;
(b) concentrated H2SO4.
closure reaction with concentrated sulfuric acid at room
temperature. The synthetic pathway of the compounds
is represented in Scheme 2.
The antituberculosis tests indicated that compound
22 exhibited the highest inhibitory activity (69% inhib)
against in vitro growing Mycobacterium tuberculosis at
a concentration >6.25 µL/mL (MIC). These compounds,
while not active enough to be considered as therapeu-
tics, are definitely lead compounds in the search for
novel agents to combat resistance.
Structure-Activity Relationship (SAR) Investi-
gation. Data Sets. Compounds under study (66 mol-
ecules) are shown in Table 1. Molecules under study
were classified as high activity compounds (28 molecules
with % inhib g 35), low activity compounds (18 mol-
ecules with 35 > % inhib > 18) and inactive compounds
(20 molecules with % inhib e 18).
To identify activity features (or pharmacophores),
ETM calculations were carried out twice: first, low
activity compounds were considered as belonging to the
active class, and then as belonging to the inactive class.
The Search for Pharmacophores (Ph) and An-
tipharmacophores (APh) by Using ETM. Confor-
mational analysis and quantum chemistry calculations
were carried out by means of molecular mechanics

6762 Journal of Medicinal Chemistry, 2004, Vol. 47, No. 27
Table 1. Antituberculosis Activity of Compounds (4-69)a
Oruc¸ et al.
no.
Ar
R
% inhib
no.
Ar
R
% inhib
4
C6H5
C6H5
65
36
30
50
21
18
0
33
33
42
31
43
50
34
32
54
42
44
69
40
42
52
39
8
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
4-C6H4N
4-C6H4N
4-C6H4N
4-FC6H4
4-CH3C6H4
4-NO2C6H4
CH3
49
38
18
29
34
0
41
37
16
57
3
5
C6H5
4-BrC6H4
4-ClC6H4
4-FC6H4
4-CH3C6H4
4-NO2C6H4
C6H5
6
C6H5
7
C6H5
4-NH2C6H4
8
C6H5
4-NH2C6H4
C2H5
9
C6H5
4-NH2C6H4
C3H7
C6H11
CH2C6H5
C6H5
4-ClC6H4
4-FC6H4
4-CH3OC6H4
2-CH3C6H4
4-CH3C6H4
4-NO2C6H4
C3H7
C6H11
CH2C6H5
C6H5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
4-BrC6H4
4-BrC6H5
4-BrC6H4
4-BrC6H4
4-BrC6H4
4-BrC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-FC6H4
4-FC6H4
4-FC6H4
4-FC6H4
4-FC6H4
4-FC6H4
4-NO2C6H4
4-NO2C6H4
4-NO2C6H4
4-NO2C6H4
4-NO2C6H4
4-NO2C6H4
4-C6H4N
4-C6H4N
4-C6H4N
4-NH2C6H4
4-BrC6H4
4-ClC6H4
4-FC6H4
4-CH3C6H4
4-NO2C6H4
C6H5
4-BrC6H4
4-ClC6H4
4-FC6H4
4-CH3C6H4
4-NO2C6H4
C6H5
4-BrC6H4
4-ClC6H4
4-FC6H4
4-CH3C6H4
4-NO2C6H4
C6H5
4-BrC6H4
4-ClC6H4
4-FC6H4
4-CH3C6H4
4-NO2C6H4
C6H5
4-NH2C6H4
4-NH2C6H4
4-NH2C6H4
4-NH2C6H4
4-NH2C6H4
7
0
4-NH2C6H4
4-NH2C6H4
22
37
6
67
16
1
32
0
5
3
46
39
36
11
0
0
15
0
4-NH2C6H4
4-C6H5NH CSNHC6H4
4-C6H5NH CSNHC6H4
4-C6H5NH CSNHC6H4
4-C6H5NH CSNHC6H4
4-C6H5NH CSNHC6H4
4-C6H5NH CSNHC6H4
4-C6H5NH CSNHC6H4
4-C6H5NH CSNHC6H4
(CH3CO)2CdNNHC6H4
(CH3CO)2CdNNHC6H4
(CH3CO)2CdNNHC6H4
(CH3CO)2CdNNHC6H4
(CH3CO)2CdNNHC6H4
(CH3CO)2CdNNHC6H4
(CH3CO)2CdNNHC6H4
(CH3CO)2CdNNHC6H4
(CH3CO)2CdNNHC6H4
(CH3CO)2CdNNHC6H4
4-ClC6H4
4-FC6H4
4-CH3OC6H4
2-CH3C6H4F
CH3
39
26
29
30
33
20
38
53
59
C2H5
C3H7
C6H11
CH2C6H5
C6H5
4-ClC6H4
4-FC6H4
2-CH3C6H4
4-CH3C6H4
4-BrC6H4
4-ClC6H4
5
0
a The data on the antituberculosis activity of 40-69 are taken from studies.16,52
Submatrix given in Fig. 1 is found after setting some
allowable limits for finding equivalent matrix elements.
The limits are δ1 ) (0.05 for its diagonal elements and
δ2 ) (0.15 for the off-diagonal ones. The pharmacophore
found from the ETM-calculations is realized in 34 active
compounds, and the probability PA of its realization in
this class is about 0.95.
The pharmacophore Ph2 (see Figure 1b) was calcu-
lated from template compound 36. Ph2 includes C8, C9,
C14, N17, and C18 atoms. Ph2 is found in 34 active and
two inactive compounds. Thus, the probability of its
realization is 0.92. One common use for the structural
methods criterion (CA) that evaluates the probability of
a pharmacophore (Ph) occurrence in the series under
study is given by the following formula31:
sponding templates after which the anti-pharmaco-
phores are found.
As seen from Figure 2a, APh1 (after template inactive
compound 49) consists of atoms N5, N6, C16, and H21.
APh1 is present in 17 inactive molecules and two active
molecules, and probability of its realization is 0.84. For
the anti-pharmacophore APh2, inactive compound 69
was selected as template compound, and the probability
of APh2 realization is 0.89, respectively.
When comparing the structures of the pharmaco-
phores and anti-pharmacophores, one can pay attention
to the differences in their spatial and electron charac-
teristics. Thus, the pharmacophores and anti-pharma-
cophores, used together, play an important role in the
activity prediction in the process of a new drug search.
In this way, the set of activity/inactivity fragments,
found as the result of this study, forms a basis for the
development of a system for the antituberculosis activity
prediction.
Neural Network Application. Artificial Neural
Networks (ANNs) is a group of methods that are
increasingly being used in drug design to study quan-
titative/qualitative SAR (QSAR). This method is able
to elucidate SARs and take into account any nonlinear
character of these relationships. Thus, this method can
be of significant interest in three-dimensional (3D)
QSAR studies.
CA(Ph) ) (nA + 1)/(nA + nIA + 2)
(1)
where nA, nIA are numbers of active/inactive compounds,
respectively, which contain the Ph. For an anti-phar-
macophore (APh), (nIA+1) is to be used at place of (nA+1)
in the formula (1). The rest of pharmacophores, Ph3-
Ph15, were found analogously, and the probabilities of
their realization in the class of active compounds varied
in the limits of 0.86-0.95.
To determine anti-pharmacophores, ETMCs of some
inactive compounds were taken as templates. Ten
pharmacophores, APh1-APh10, were found, in the
total. ETSCs that correspond to APh1 and APh2 are
given in Figure 2 along with structures of the corre-
The architecture of the artificial supervised NN
applied to our study consists of three layers, with five

1,3,4-Thiadiazole Derivatives
Journal of Medicinal Chemistry, 2004, Vol. 47, No. 27 6763
Figure 1. The Ph1 (a) and Ph2 (b) pharmacophores found
relative to active molecules 22 and 36, respectively.
Figure 2. The APh1 (a) and APh2 (b) anti-pharmacophore
found relative to inactive molecules 49 and 69, respectively.
neurons in one hidden layer. A single output node was
used to code activities of inhibitors. The bias neuron was
presented on the input and hidden layers. At least M )
200 independent FFNNs were trained to analyze each
set of variables. The values predicted for each analyzed
case were averaged over all M networks predictions, and
the means were used to calculate statistical coefficients
with targets. The other details of the algorithm can be
found elsewhere.32,33
out on the training set with q2 value (introduced by
Cramer et al.34) defined as
q2 ) (SD - press)/SD
In the equation, SD represents the variance of a
target value relative to its mean and ‘press’ is the
average squared errors of predicted values obtained
from the LOO procedure.
The avoidance of overfitting/overtraining has been
shown to be an important factor for improving the
predictive ability and correct selection of variables in
the FFNNs. The Early Stopping over Ensemble (ESE)
technique was used in the current study to accomplish
this. We used a subdivision of the initial training set
into two equal learning/validation subsets. The first set
was used to train the neural network, while the second
one was used to monitor the training process measured
by root-mean-square error. An early stopping point
determined as a best fit of a network to the validation
set was used to stop the neural network learning. Thus,
statistical parameters calculated at the early stopping
point were used. The training was terminated by
limiting the network run to 10 000 epochs (total number
of epochs) or after 2000 epochs (local number of epochs)
following the last improvement of root-mean-square
error in the early stopping point. The root-mean-square
error E was computed as a criterion for network
learning to determine the stop points of a training
procedure. The quality of the model was tested by the
leave-one-out (LOO) cross-validation procedure carried
The LOO cross-validation procedure, which was used
to supervise the predictive performance of the ANN, has
shown that pruning algorithms35,36 can be used to
optimize the number of input parameters for the ANNs
training and to select the most significant ones. These
algorithms operate in a manner similar to stepwise
multiple regression analysis and, at each step, exclude
by one input parameter that has been estimated as a
nonsignificant one. The pruning algorithms were used
in the current study to determine significant parameters
of input data points of the analyzed molecules as
described in references.
As the second stage, we decided to examine if all 25
molecular fragments (pharmacophores and anti-phar-
macophores) are relevant for the antituberculosis activ-
ity prediction. For these 25 fragments and 85 com-
pounds in the series studied, a table of weights was
formed as consisting of 85 rows of 25 elements being 1
(the fragment is present in the corresponding molecular
structure) or 0 (the fragment is absent).
Application of pruning methods allowed for the selec-
tion of only five the most appropriate parameters
responsible for the antituberculosis inhibitory activity.

6764 Journal of Medicinal Chemistry, 2004, Vol. 47, No. 27
Oruc¸ et al.
MS at 70 eV. All new compounds were analyzed for C, H, N
and the results were in an acceptable range (1H NMR, mass
spectra, and elemental analysis were provided by the Scientific
and Technical Research Council of Turkey, Tu¨bitak).
General Procedure for the Synthesis of 4-Substituted
Phenyl Benzoate (1). To the solution of 0.1 mol of phenol in
100 mL of 10% of sodium hydroxide, 0.1 mol of 4-substituted
benzoyl chloride was added and stirred for 30 min. The solid
product was washed with distilled water and crystallized from
ethanol.37
General Procedure for the Synthesis of 4-Substituted
Benzoic Acid Hydrazides (2a-d). To the solution of 0.05
mol of 1 in 3 mL of methanol was added 0.1 mol of 99%
hydrazine hydrate. The mixture was refluxed on a water bath
for 30 min. After cooling, the precipitate was collected, washed
with distilled water, and recrystallized from ethanol.37
General Procedure for the Synthesis of 4-Nitroben-
zoic Acid Hydrazide (2e). To the solution of 0.05 mol of
4-nitrobenzoyl chloride in 75 mL of methanol was added 0.1
mol of 99% hydrazine hydrate. The mixture was refluxed on a
water bath for 6 h. After cooling, the precipitate was collected,
washed with distilled water, and recrystallized from ethanol.38
General Procedure for the Synthesis of 1-Aroyl-
4-arylthiosemicarbazides (3). To the solution of 0.0075 mol
of 4-substituted benzoic acid hydrazides 2a-e or isoniazid in
30 mL of ethanol or acetonitrile was added 0.0075 mol of the
appropriate arylisothiocyanate. The mixture was refluxed on
a water bath for 3 h. The solid product, obtained on cooling,
was washed with distilled water and recrystallized from
ethanol.38-40
General Procedure for the Synthesis of 2,5-Disubsti-
tuted-1,3,4-thiadiazoles (4-39). To 0.001 mol of appropriate
1-aroyl-4-arylthiosemicarbazides 3 was added concentrated
sulfuric acid (1 mL) dropwise. The mixture was stirred at room
temperature for 30 min. The reaction content was poured into
ice-water mixture. The precipitated solid was washed with
sodium carbonate solution followed by water and recrystallized
from ethanol.39-41
Figure 3. Neural network leave-one-out cross validation
inhibitory activity against M. tuberculosis H37Rv results.
The calculated result shows that the reduction of the
initially obtained seven parameters to five of them did
not decrease the cross-validated q2 coefficient (0.86 (
0.01). As illustrated in Figure 3, there was a good
concordance between the predicted and experimental
values of the antituberculosis activities. This result
confirms our hypothesis on that only both pharmaco-
phores and anti-pharmacophores taken as parameters
can be used for identifying active molecules and building
the system for the antituberculosis activity prediction.
Conclusion
A series of 2,5-disubstituted-1,3,4-thiadiazoles were
synthesized, their structures were elucidated and
screened for antituberculosis activity against Mycobac-
terium tuberculosis H37Rv.
2-Phenylamino-5-phenyl-1,3,4-thiadiazole (4): 91% yield,
mp 176-180 °C (lit..42 mp 199-200 °C).Retention time (tR) 2.47
min. IR (KBr) 3252, 3198 (NH), 1620 (CdN), 1031 (N-N); 689
The systematic SAR study was carried out by the
ETM application to the synthesized series of compounds
capable of demonstrating antituberculosis activity. Data
obtained from conformation and quantum-chemistry
calculations were used to form electronic-topological
matrixes. These matrixes were effectively used in the
search for a system of pharmacophores and anti-
pharmacophores capable of effective separation of com-
pounds from the examination set into groups of active
and inactive compounds. Low activity molecules are
badly responsive to the activity prognostication, because
they form a buffer zone consisting of compounds that
can include both pharmacophores and anti-pharma-
cophores. The system mentioned is supposed to be
applied to screening and design of new active com-
pounds possessing skeletons similar to those used in the
present study.
(C-S-C) cm-1
.
2-(4-Bromophenylamino)-5-phenyl-1,3,4-thiadiazole
(5): 63% yield, mp 178-182 °C. tR 2.63 min. IR (KBr) 3240
(NH), 1620 (CdN), 1070 (Ar-Br), 1050 (N-N), 680 (C-S-C)
1
cm-1. H NMR (DMSO-d6) δ 7.52-7.88 (m, 9H, Ar-protons),
10.95 (s, 1H, NH). MS (EIMS) m/z 331 (M+).
2-(4-Chlorophenylamino)-5-phenyl-1,3,4-thiadiazole
(6): 85% yield, mp 222-224 °C.43 tR 3.42 min. IR (KBr) 3260,
3200 (NH), 1620 (CdN), 1090 (Ar-Cl), 685 (C-S-C) cm-1
.
2-(4-Fluorophenylamino)-5-phenyl-1,3,4-thiadiazole
(7): 80% yield, mp 200-202 °C. tR 2.52 min. IR (KBr) 3250,
3210 (NH), 1620 (CdN), 1225, 1160 (Ar-F), 685 (C-S-C)
1
cm-1. H NMR (DMSO-d6) δ 7.22 (t, 2H, meta-protons to F),
7.50-7.55 (m, 3H, meta- and para-protons to thiadiazole),
7.67-7.71 (m, 2H, ortho-protons to F), 7.85-7.87 (m, 2H,
ortho-protons to thiadiazole), 10.57 (s, 1H, NH); MS (EIMS)
m/z 271 (M+). Anal. (C14H10FN3S) C, H, N, S.
2-(4-Methylphenylamino)-5-phenyl-1,3,4-thiadiazole
(8): 59% yield, mp 176-180 °C.37 tR 3.15 min. IR (KBr) 3260,
3200 (NH), 1620 (CdN), 690 (C-S-C) cm-1
.
Experimental Section
2-(4-Nitrophenylamino)-5-phenyl-1,3,4-thiadiazole (9):
All chemicals and solvents were purchased from Merck,
Aldrich, and Fluka. Melting points were taken on apparatus
Buchi 530 in open capillaries and were uncorrected. The purity
of the synthesized compounds was checked on HPLC using
acetonitrile-water (65:35, v/v) as the mobile phase (Agilent
1100 series-Diode Array Dedector). UV spectra were recorded
on a Beckman DU 530 spectrophotometer. IR spectra were
obtained using a Perkin-Elmer 1600 FT-IR spectrophotometer
53% yield, mp 216-220 °C. tR 2.63 min. IR (KBr) 3260, 3220
(NH), 1630 (CdN), 1580, 1325 (Ar-NO2), 685 (C-S-C) cm-1
.
1H NMR (DMSO-d6) δ 7.54-7.55 (m, 3H, meta-protons to NO2
and para-proton to thiadiazole), 7.87-7.92 (m, 4H, ortho- and
meta-protons to thiadiazole), 8.28 (d, 2H, ortho-protons to
NO2), 11.25 (s, 1H, NH). MS (EIMS) m/z 298 (M+). Anal.
(C14H10N4O2S‚H2O) C, H, S.
1
using KBr pellets. H NMR spectra were recorded in DMSO
2-Phenylamino-5-(4-bromophenyl)-1,3,4-thiadiazole
(10): 86% yield, mp 338-339 °C.45 tR 3.74 min. IR (KBr) 3347,
3243 (NH), 1613 (CdN), 1070 (Ar-Br), 1047 (N-N), 683 (C-
on a Bruker AVANC-DPX-400 spectrometer and chemical
shifts were given in δ ppm with tetramethylsilane (TMS). Mass
spectra were run on a Fisons Instruments VG, Platform LC-
S-C) cm-1
.

1,3,4-Thiadiazole Derivatives
Journal of Medicinal Chemistry, 2004, Vol. 47, No. 27 6765
670 (C-S-C) cm-1 1H NMR (DMSO-d6) δ 7.53 (d, 2H, J )
8.5 Hz, ortho-protons to Cl), 7.81 (d, 2H, J ) 9.2 Hz, meta-
protons to NO2), 7.86 (d, 2H, J ) 8.5 Hz, meta-protons to Cl),
8.21 (d, 2H, J ) 9.2 Hz, ortho-protons to NO2), 11.13 (s, 1H,
NH). MS (EIMS) m/z 332 (M+). Anal. (C14H9ClN4O2S) C, H,
N, S.
2-(4-Bromophenylamino)-5-(4-bromophenyl)-1,3,4-thi-
adiazole (11): 73% yield, mp 244-247 °C. tR 6.28 min. IR
(KBr) 3250 (NH), 1620 (CdN), 1070 (Ar-Br), 660 (C-S-C)
.
1
cm-1. H NMR (DMSO-d6) δ 7.49 (d, 2H, J ) 8.9 Hz, ortho-
protons to sec. amine), 7.59 (d, 2H, J ) 8.9 Hz, meta-protons
to sec. amine), 7.66 (d, 2H, J ) 8.5 Hz, meta-protons to
thiadiazole), 7.76 (d, 2H, J ) 8.5 Hz, ortho-protons to thia-
diazole), 10.67 (s,1H, NH). MS (EIMS) m/z 411 (M+). Anal.
(C14H9Br2N3S) C, H, N, S.
2-Phenylamino-5-(4-fluorophenyl)-1,3,4-thiadiazole
(22): 63% yield, mp 258-262 °C. tR 2.53 min. IR (KBr) 3240,
3180 (NH), 1615 (CdN), 1170 (Ar-F), 690 (C-S-C) cm-1. 1H
NMR (DMSO-d6) δ 7.03 (t, 1H, para-proton to sec. amine),
7.34-7.39 (m, 4H, ortho-protons to sec. amine and meta-
protons to F), 7.65 (d, 2H, J ) 7.8 Hz, meta-protons to sec.
amine), 7.90-7.94 (m, 2H, ortho-protons to F), 10.49 (br.s, 1H,
NH). 13C NMR (DMSO-d6) δ 117.09, 117.31 (ortho-carbons to
F), 118.38 (meta-carbons to sec. amine), 122.96 (ipso-carbon
to sec. amine), 127.69 (para-carbons to F), 129.85, 129.93
(meta-carbons to F), 130.02(o- carbons to sec. amine), 141.36
(para-carbon to sec. amine), 157.29 (thiadiazole C5), 162.69
(ipso-carbon to F), 165.05 (thiadiazole C2); MS (EIMS) m/z 271
2-(4-Chlorophenylamino)-5-(4-bromophenyl)-1,3,4-thi-
adiazole (12): 76% yield, mp 248-250 °C. tR 5.59 min. IR
(KBr) 3260 (NH), 1620 (CdN), 1090 (Ar-Br), 660 (C-S-C)
cm-1 1H NMR (DMSO-d6) δ 7.37 (d, 2H, J ) 8.9 Hz, meta-
;
protons to Cl), 7.63-7.67 (m, 4H, ortho-protons to Cl and Br),
7.76 (d, 2H, J ) 8.5 Hz, meta-protons to Br), 10.67 (s, 1H, NH).
MS (EIMS): m/z 367 (M+). Anal. (C14H9BrClN3S) C, H, N, S.
2-(4-Fluorophenylamino)-5-(4-bromophenyl)-1,3,4-thi-
adiazole (13): 63% yield; mp 235-237 °C. tR 3.86 min. IR
(KBr) 3280, 3220 (NH), 1630 (CdN), 1160, 1120 (Ar-F), 1090
1
(M+). Anal. (C14H10FN3S. /2 H2O) C, H, N, S.
(Ar-Br), 670 (C-S-C) cm-1 1H NMR (DMSO-d6) δ 7.22 (t,
.
2H, meta-protons to F), 7.67-7.72 (m, 4H, ortho-protons to F
and Br), 7.81 (d, 2H, J ) 8.5 Hz, meta-protons to Br), 10.60
(s, 1H, NH). MS (EIMS) m/z 349 (M+). Anal. (C14H9BrFN3S)
C, H, N, S.
2-(4-Bromophenylamino)-5-(4-fluorophenyl)-1,3,4-thia-
diazole (23): 76% yield, mp 230-236 °C. tR 3.92 min. IR (KBr)
3244 (NH), 1619 (CdN), 1157 (Ar-F), 1078 (Ar-Br), 696 (C-
S-C) cm-1 1H NMR (DMSO-d6) δ 7.37-7.41 (m, 2H, meta-
.
protons to F), 7.55-7.58 (m, 2H, meta-protons to Br), 7.65-
7.68 (m, 2H, ortho-protons to Br), 7.93-7.97 (m, 2H, ortho-
protons to F), 10.70 (s, 1H, NH). MS (EIMS) m/z 349 (M+).
Anal. (C14H9BrFN3S) C, H, N, S.
2-(Methylphenylamino)-5-(4-bromophenyl)-1,3,4-thia-
diazole (14): 68% yield, mp 218-219 °C.46 tR 5.03 min. IR
(KBr) 3240 (NH), 1610 (CdN), 1070 (Ar-Br), 635 (C-S-C)
cm-1
.
2-(4-Chlorophenylamino)-5-(4-fluorophenyl)-1,3,4-thi-
adiazole (24): 53% yield, mp 238-240 °C. tR 3.47 min. IR
(KBr) 3250, 3190 (NH), 1620 (CdN), 1230, 1155 (Ar-F), 1090
(Ar-Cl), 670 (C-S-C) cm-1. 1H NMR (DMSO-d6) δ 7.34-7.43
(m, 4H, meta-protons to Cl and F), 7.70 (d, 2H,J ) 8.8 Hz,
ortho-protons to Cl), 7.91-7.94 (2d, 2H, ortho-protons to F),
10.68 (s, 1H, NH). MS (EIMS) m/z 305 (M+). Anal. (C14H9-
ClFN3S) C, H, N, S.
2-(4-Nitrophenylamino)-5-(4-bromophenyl)-1,3,4-thia-
diazole (15): 68% yield, mp 293-294 °C. tR 3.93 min. IR (KBr)
3270, 3220 (NH), 1625 (CdN), 1580, 1330 (Ar-NO2), 670 (C-
S-C) cm-1 1H NMR (DMSO-d6) δ 7.74-7.76 (m, 2H, meta-
.
protons to NO2), 7.85-7.90 (m, 4H, ortho- and meta-protons
to Br), 8.28-8.30 (m, 2H, ortho-protons to NO2), 11.31 (s, 1H,
NH). MS (EIMS) m/z 376 (M+). Anal. (C14H9BrN4O2S) C, H,
N, S.
2-Phenylamino-5-(4-chlorophenyl)-1,3,4-thiadiazole
(16): 50% yield, mp 216-217 °C (lit..43,46,47 mp 220-222 °C)‚
tR 3.52 min. IR (KBr) 3241, 3192 (NH), 1614 (CdN), 1092 (Ar-
2-(4-Fluorophenylamino)-5-(4-fluorophenyl)-1,3,4-thia-
diazole (25): 74% yield, mp 226-228 °C. tR 2.60 min. IR (KBr)
3210 (NH), 1626 (CdN), 1231, 1155 (Ar-F), 670(C-S-C) cm-1
.
Cl), 1034 (N-N), 683 (C-S-C) cm-1
.
1H NMR (DMSO-d6) δ 7.23 (t, 2H, ortho-protons to sec. amine),
7.36-7.40 (m, 2H, meta-protons to F), 7.69-7.72 (m, 2H, meta-
protons of phenyl to sec. amine), 7.92-7.95 (m, 2H, ortho-
protons to F), 10.53 (s, 1H, NH). MS (EI MS) m/z 289 (M+).
Anal. (C14H9F2N3S) C, H, N, S.
2-(4-Bromophenylamino)-5-(4-chlorophenyl)-1,3,4-thi-
adiazole (17): 68% yield, mp 248-250 °C. tR 5.61 min. IR
(KBr) 3250 (NH), 1620 (CdN), 1090 (Ar-Cl), 1075 (Ar-Br),
660 (C-S-C) cm-1 1H NMR (DMSO-d6) δ 7.53 (d, 2H, J )
.
8.9 Hz, meta-protons to Br), 7.57 (d, 2H, J ) 8.6 Hz, ortho-
protons to Cl), 7.64 (d, 2H, J ) 8.9 Hz, ortho-protons to Br),
7.87 (d, 2H, J ) 8.6 Hz, meta-protons to Cl), 10.54 (br.s, 1H,
NH). MS (EIMS) m/z 367 (M+). Anal. (C14H9BrClN3S) C, H,
N, S.
2-(4-Methylphenylamino)-5-(4-fluorophenyl)-1,3,4-thi-
adiazole (26): 71% yield, mp 210-214 °C. tR 3.20 min. IR
(KBr) 3245 (NH), 1617 (CdN), 1229 (Ar-F), 673 (C-S-C)
1
cm-1. H NMR (DMSO-d6) δ 2.30 (s, 3H, CH3), 7.20 (d, 2H, J
) 8.1 Hz, ortho-protons to sec. amine), 7.35-7.40 (m, 2H, meta-
protons to F), 7.55 (d, 2H, J ) 8.3 Hz, meta-protons to sec.
amine), 7.91-7.95 (m, 2H, ortho-protons to F), 10.41 (s, 1H,
NH). MS (EI MS) m/z 285 (M+). Anal. (C15H12FN3S) C, H, N,
S.
2-(4-Chlorophenylamino)-5-(4-chlorophenyl)-1,3,4-thi-
adiazole (18): 65% yield, mp 236-240 °C (lit.46 mp 242 °C)‚
tR 4.99 min. IR (KBr) 3260, 3200 (NH), 1620 (CdN), 1090 (Ar-
Cl), 1020 (N-N), 660 (C-S-C) cm-1
.
2-(4-Nitrophenylamino)-5-(4-fluorophenyl)-1,3,4-thia-
diazole (27): 92% yield, mp 296-298 °C. tR 2.61 min. IR (KBr)
3212 (NH), 1627 (CdN), 1587, 1336 (Ar-NO2), 1235 (Ar-F),
2-(4-Fluorophenylamino)-5-(4-chlorophenyl)-1,3,4-thi-
adiazole (19): 70% yield, mp 232-234 °C. tR 3.60 min. IR
(KBr) 3260, 3220 (NH), 1625 (CdN), 1230, 1160 (Ar-F), 1090
1
676 (C-S-C) cm-1. H NMR (DMSO-d6) δ 7.39 (t, 2H, meta-
(Ar-Br), 670 (C-S-C) cm-1 1H NMR (DMSO-d6) δ 7.19 (t,
.
protons to F), 7.87 (d, 2H, J ) 9.1 Hz, meta-protons to
NO2),7.95-7.98 (2d, 2H, ortho-protons to F), 8.27 (d, 2H, J )
9.1 Hz, ortho-protons to NO2), 11.10 (br.s, 1H, NH). MS (EIMS)
m/z 316 (M+). Anal. (C14H9FN4O2S) C, H, N, S.
2H, meta-protons to F), 7.57 (d, 2H, J ) 8.5 Hz, ortho-protons
to Cl), 7.65-7.67 (m, 2H, ortho-protons of phenyl to F), 7.87
(d, 2H, J ) 8.5 Hz, meta-protons to Cl), 10.50 (br.s, 1H, NH).
13C NMR (DMSO-d6) δ 116.46, 116.69 (meta-carbons to F),
120.12, 120.21 (ortho-carbons to F), 129.25 (ortho-carbons to
Cl), 130.18 (meta-carbons to Cl), 135.56 (para-carbon to F),
137.83 (para-carbon to Cl), 157.06 (ipso-carbon to Cl), 157.22
(thiadiazole C5); 159.43 (ipso-carbon to F), 165.33 (thiadiazole
C2). MS (EIMS) m/z 305 (M+). Anal. (C14H9ClFN3S) C, H, N,
S.
2-Phenylamino-5-(4-nitrophenyl)-1,3,4-thiadiazole
(28): 67% yield, mp 275-277 °C (lit.43,47 mp 272-273 °C)‚tR
2.57 min. IR (KBr) 3196 (NH), 1621 (CdN), 1573, 1331 (Ar-
NO2), 680 (C-S-C) cm-1
.
2-(4-Bromophenylamino)-5-(4-nitrophenyl)-1,3,4-thia-
diazole (29): 68% yield, mp 322-324 °C. tR 1.23 min. IR (KBr)
3253 (NH), 1623 (CdN), 1565, 1376 (Ar-NO2), 1075 (Ar-Br),
2-(4-Methylphenylamino)-5-(4-chlorophenyl)-1,3,4-thi-
adiazole (20): 57% yield, mp 213-214 °C (lit.46 mp 223 °C)‚
tR 4.53 min. IR (KBr) 3250 (N-H), 1615 (CdN), 1090 (Ar-
687 (C-S-C) cm-1 1H NMR (DMSO-d6) δ 7.46 (d, 2H, J )
.
8.9 Hz, meta-protons to Br), 7.56 (d, 2H, J ) 8.9 Hz, ortho-
protons to Br), 8.04 (2d, 2H, J ) 8.8 Hz, meta-protons to NO2),
8.25 (d, 2H, J ) 8.8 Hz, ortho-protons to NO2), 10.75 (br.s,
1H, NH). MS (EIMS) m/z 376 (M+). Anal.(C14H9BrN4O2S.1/
2H2O) C, H, N, S.
Cl), 670 (C-S-C) cm-1
.
2-(4-Nitrophenylamino)-5-(4-chlorophenyl)-1,3,4-thia-
diazole (21): 61% yield, mp 300-302 °C. tR 3.58 min. IR (KBr)
3220 (NH), 1625 (CdN), 1585, 1330 (Ar-NO2), 1090 (Ar-Cl),

6766 Journal of Medicinal Chemistry, 2004, Vol. 47, No. 27
Oruc¸ et al.
2-(4-Chlorophenylamino)-5-(4-nitrophenyl)-1,3,4-thia-
diazole (30): 53% yield, mp 334-335 °C. tR 1.20 min. IR (KBr)
3260, 3200 (NH), 1625 (CdN), 1565, 1335 (Ar-NO2), 670 (C-
primary screening (MIC > 6.25 µg/mL) were not generally
evaluated further.
S-C) cm-1 1H NMR (DMSO-d6) δ 7.49 (d, 2H, J ) 8.9 Hz,
.
Acknowledgment. This research was supported by
The Research Fund of Marmara University, project
number HEA-DYD-029/201501. We thank Dr. Joseph
A. Maddry from Tuberculosis Antimicrobial Acquisition
and Coordinating Facility (TAACF) Southern Research
Institute for his assistance.
meta-protons to Cl), 7.77 (d, 2H, J ) 8.9 Hz, ortho-protons to
Cl), 8.19 (d, 2H, J ) 8.8 Hz, meta-protons to NO2), 8.40 (d,
2H, J ) 8.8 Hz, ortho-protons to NO2), 10.91 (s, 1H, NH). MS
(EIMS) m/z 332 (M+). Anal. (C14H9ClN4O2S.1/2H2O) C, H, N.
2-(4-Fluorophenylamino)-5-(4-nitrophenyl)-1,3,4-thia-
diazole (31): 38% yield, mp 322-324 °C. tR 1.19 min. IR (KBr)
3270, 3220 (NH), 1630 (CdN), 1510, 1345 (Ar-NO2), 670 (C-
S-C) cm-1 1H NMR (DMSO-d6) δ 7.26-7.30 (m, 2H, meta-
.
Supporting Information Available: Elemental analyses
of compounds; NMR and MS spectra of compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
protons to F), 7.73-7.77 (m, 2H, ortho-protons to F), 8.18 (d,
2H, J ) 8.9 Hz, meta-protons to NO2), 8.39 (d, 2H, J ) 8.9
Hz, ortho-protons to NO2), 10.76 (s, 1H, NH). MS (EIMS) m/z
316 (M+). Anal. (C14H9FN4O2S‚H2O) C, S.
References
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diazole (32): 63% yield, mp 280-284 °C (lit.44 mp 243 °C)‚tR
3.16 min. IR (KBr) 3244 (NH), 1616 (CdN), 1568, 1368 (Ar-
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NO2), 683 (C-S-C) cm-1
.
2-(4-Nitrophenylamino)-5-(4-nitrophenyl)-1,3,4-thia-
diazole (33): 64% yield, mp 368 °C. tR 2.72 min. IR (KBr)
3362 (NH), 1595 (CdN), 1563, 1330 (Ar-NO2), 687 (C-S-C)
1
cm-1. H NMR (DMSO-d6) δ 7.79 (d, 2H, J ) 9.0 Hz, ortho-
protons to sec. amine), 8.09 (d, 2H, J ) 8.8 Hz, meta-protons
to NO2), 8.19 (d, 2H, J ) 9.0 Hz, meta-protons to sec. amine),
8.27 (d, 2H, J ) 8.8 Hz, ortho-protons to NO2), 11.40 (br.s,
1H, NH). MS (EIMS) m/z 343 (M+). Anal. (C14H9N5O4S) C, H,
N, S.
2-Phenylamino-5-(4-pyridyl)-1,3,4-thiadiazole (34): 22%
yield, mp 238-240 °C.48 tR 2.83 min. IR (KBr) 3199 (NH), 1624
(CdN), 689 (C-S-C) cm-1
.
2-(4-Bromophenylamino)-5-(4-pyridyl)-1,3,4-thiadi-
azole (35): 82% yield, mp 278-280 °C.48,49 tR 3.77 min. IR
(KBr) 3241 (NH), 1616 (CdN), 1073 (Ar-Br), 691 (C-S-C)
cm-1
.
2-(4-Chlorophenylamino)-5-(4-pyridyl)-1,3,4-thiadi-
azole (36): 74% yield, mp 238-240 °C.48,49 tR 3.53 min. IR
(KBr) 3174 (NH), 1597 (CdN), 1091 (Ar-Cl), 1047 (N-N), 695
(C-S-C) cm-1
.
2-(4-Fluorophenylamino)-5-(4-pyridyl)-1,3,4-thiadi-
azole (37): 81% yield, mp 246-248 °C.49 tR 2.75 min. IR (KBr)
3392 (NH), 1626 (CdN), 1224, 1168 (Ar-F), 642 (C-S-C)
cm-1
.
2-(4-Methylphenylamino)-5-(4-pyridyl)-1,3,4-thiadi-
azole (38): 78% yield, mp 238-240 °C.50 tR 3.34 min. IR (KBr)
3245 (NH), 1631 (CdN), 670 (C-S-C) cm-1, 1H NMR (DMSO-
d6) δ 2.30 (s, 3H, CH3), 7.20 (d, 2H, J ) 8.3 Hz, ortho-protons
to sec. amine), 7.54 (d, 2H, J ) 8.3 Hz, meta- protons to sec.
amine), 8.04 (d, 2H, J ) 6.0 Hz, ortho-protons of pyridyl to
thiadiazole), 8.79 (d, 2H, J ) 6.0 Hz, meta-protons of pyridyl
to thiadiazole),10.67 (br.s, 1H, NH), MS (EIMS) m/z 268 (M+).
2-(4-Nitrophenylamino)-5-(4-pyridil)-1,3,4-thiadi-
azole (39): 86% yield, mp 302-304 °C.tR 2.37 min. IR (KBr)
3267 (NH), 1596 (CdN), 1512, 1328 (Ar-NO2), 701 (C-S-C)
1
cm-1. H NMR (DMSO-d6) δ 7.78 (d, 2H, J ) 6.0 Hz, ortho-
protons of pyridyl to thiadiazole), 7.81 (d, 2H, J ) 9.0 Hz, meta-
protons to NO2), 8.20 (d, 2H, J ) 9.0 Hz, ortho-protons to NO2),
8.65 (d, 2H, J ) 6.0 Hz, meta-protons of pyridyl to thiadiazole),
11.31 (s, 1H, NH). 13C NMR (DMSO-d6) δ 122.90 (para-carbon
to NO2), 126.34, 126.52 (ortho-carbons of pyridyl to thiadi-
azole), 131.14 (ipso-carbon to thiadiazole), 142.44 (meta-
carbons to NO2), 146.73 (ortho-carbons to NO2), 151.67 (ipso-
carbon to NO2), 156.36 (thiadiazole C5), 163.05 (thiadiazole C2),
170.01 (meta-carbons of pyridyl to thiadiazole). MS (EIMS) m/z
299 (M+). Anal. (C13H9N5O2S) C, H, N, S.
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and Coordinating Facility (TAACF) Southern Research Insti-
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