Synthesis and antituberculosis activity of new N-phenyl-N′-[4-(5-alkyl/arylamino-1,3,4-thiadiazole-2-yl)phenyl] thioureas

Article abstract of DOI:10.1016/S0014-827X(02)01252-1

In this study, eight original N-phenyl-N′-[4-(5-alkyl/arylamino-1,3,4-thiadiazole-2-yl)phenyl] thiourea derivatives were synthesized and tested for antituberculosis activity. Antituberculosis activities of the synthesized compounds were screened in vitro

Full text of DOI:10.1016/S0014-827X(02)01252-1

Il Farmaco 57 (2002) 577–581
www.elsevier.com/locate/farmac
Synthesis and antituberculosis activity of new N-phenyl-
N%-[4-(5-alkyl/arylamino-1,3,4-thiadiazole-2-yl)phenyl]thioureas
S. Karakus¸, S. Rollas*
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Marmara Uni6ersity, Tibbiye cad. No. 49, 81010, Haydarpas¸a, Istanbul, Turkey
Received 22 January 2002; accepted 26 January 2002
Abstract
In this study, eight original N-phenyl-N%-[4-(5-alkyl/arylamino-1,3,4-thiadiazole-2-yl)phenyl]thiourea derivatives were synthe-
sized and tested for antituberculosis activity. Antituberculosis activities of the synthesized compounds were screened in vitro using
BACTEC 460 Radiometric System against Mycobacterium tuberculosis H37Rv at 6.25 mg/ml. The highest inhibition observed with
´
the synthesized compounds is 67% for N-phenyl-N%-[4-(5-cyclohexylamino-1,3,4-thiadiazole-2-yl)phenyl]thiourea. © 2002 Editions
scientifiques et me´dicales Elsevier SAS. All rights reserved.
Keywords: 1,3,4-Thiadiazole; Thiourea; Antituberculosis activity
1. Introduction
with hydrazine hydrate to prepare 4-(benzoylamino)-
benzoylhydrazine. 1-[4-(benzoylamino)benzoyl]-4-alkyl/
arylthio-semicarbazides (IIIa–k) were then synthesized
by the addition of methyl, ethyl, propyl, cyclohexyl,
phenyl, benzyl, 4-fluorophenyl, 4-chlorophenyl, 2-
methylphenyl, 4-methylphenyl, 4-methoxyphenyl and 4-
nitrophenyl isothiocyanates to 4-(benzoylamino)-
benzoylhydrazine [8]. From (IIIa–k), 2-(4-amino-
Tuberculosis has become a particularly important
social problem in the recent years. It is known that
compounds that contain thiourea structure show anti-
tuberculosis activity [1–5]. In a previous work in our
laboratory, N-allyl-N%-{4-[3-[(2,4-dichlorobenzyl)thio]-
4-methyl-4H-1,2,4-triazole-5-yl]phenyl}thiourea
was
shown to possess a potent inhibitory activity against
Mycobacterium tuberculosis H37Rv by a MIC value of
6.25 mg/ml [6]. Therefore, we synthesized eight com-
pounds bearing the same thiourea pharmacophore with
a different heterocyclic ring system.
phenyl)-5-alkyl/arylamino-1,3,4-thiadiazoles
(IVa–k)
were synthesized by using a new method more econo-
mically in this study. In the second part, N-phenyl-N%-
[4-(5 - alkyl/arylamino - 1,3,4 - thiadiazole - 2 - yl)phenyl]-
thioureas (Vc–e, Vg–i, Vj) were obtained from the
addition of aromatic primary amine to phenyl isothio-
cyanate in dry acetone.
All the synthesized compounds were characterized by
UV, IR, H NMR (for Ve, Vf, Vg and Vj) and mass
2. Chemistry
1
(for Vc, Ve, Vf and Vi) spectral methods besides ele-
mental analysis. The UV spectra of Vc–e, Vg–i, Vj
showed two absorption maxima as at 249.4–277.5 and
The general formulae of the synthesized compounds
are presented in Fig. 1. In the first part of research,
compounds in the form of 2-(4-aminophenyl)-5-alkyl/
arylamino-1,3,4-thiadiazoles were prepared from ben-
zoyl chloride and ethyl 4-aminobenzoate according to
the literature [7]. The product obtained was reacted
1
298.9–337.6 nm. The H NMR (DMSO-d6) spectra of
Ve, Vf, Vg and Vj displayed NH resonance at 9.51–
10.37 and 10.58–9.91 and 9.54 ppm, 10.00 and 10.06
ppm and 11.05 and 13.92 ppm. Mass spectra of com-
pounds Vc, Ve and Vi gave molecular ion peaks at m/z:
370 (M.W.: 370); m/z: 403 (M.W.: 403.1); m/z: 417
* Corresponding author
E-mail address: sevim@sevimrollas.com (S. Rollas).
´
0014-827X/02/$ - see front matter © 2002 Editions scientifiques et me´dicales Elsevier SAS. All rights reserved.
PII: S0014-827X(02)01252-1

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S. Karakus¸, S. Rollas / Il Farmaco 57 (2002) 577–581
compounds similar fragmentation patterns as observed
previously for either thioureas such as losing the perti-
nent ArꢀNH2 or ArꢀNCS from the molecular ion. The
mass fragmentation pathway of compound Vf is shown
in Scheme 1. Other characteristic data for compounds
are given in Table 1.
3. Experimental
3.1. Chemistry
Acetone, benzocaine, hydrazine hydrate were pur-
chased from Merck. All other chemicals were pur-
chased from Fluka. Melting points were determined by
using a Bu¨chi-530 melting point apparatus (open capil-
laries) and uncorrected. Elemental analyses were per-
formed on a Carlo Erba 1106. UV spectra were
determined on a Shimadzu UV 2100 S spectrophotome-
ter. IR spectra were run a Perkin–Elmer 1600 spec-
Fig. 1. The synthetic route of N-phenyl-N%-[4-(5-alkyl/arylamino-
1,3,4-thiadiazole-2-yl)phenyl]thiourea derivatives.
1
trophotometer as KBr pellets. H NMR spectra were
obtained on a Bruker DP X-400 spectrometer at MHz
using TMS as the internal reference. Mass spectra were
determined at 70 eV on a VG Zabspec Double Fo-
cussing Magnetic Sectot spectrometer.
(M.W.: 417.1). The molecular ion was not detected in
the mass spectrum of compound Vf. All the synthesized
Scheme 1.

S. Karakus¸, S. Rollas / Il Farmaco 57 (2002) 577–581
579
Table 1
Physical and spectral data of Vc–e, Vg–i, Vj
Comp.
M.p. (°C)
Yields (%)
Molecular formula
Elemental analysis
UV (EtOH)
IR (KBr) (cm−1
)
(Calc./Found)
umax (nm)
C
H
N
Vc
Vd
Ve
Vf
Vg
Vh
Vi
184
61.43
50.94
45.71
52.20
53.89
48.86
46.73
54.70
C
18H19N5S2
C21H23N5S2·12H2O
21H17N5S2·1/2H2O
C21H16CIN5S2
58.51
57.76
5.14
4.84
18.95
18.22
330.6
250.0
3201, 1537, 1314, 1261, 991
3201, 1543, 1320, 1267, 985
3272, 3201, 1543, 1314, 1267, 985
3213, 1531, 1314, 1090, 973
3319, 3213, 1531, 1308
189–190
203–205
203–205
175–177
217–218
209–210
224–226
60.25
59.48
5.78
4.85
16.73
16.14
330.7
283.5
C
61.14
61.13
4.39
4.08
16.97
16.17
277.5
57.59
57.86
3.68
3.80
15.99
15.44
298.9
C
C
22H19N5S2
63.28
63.16
4.59
4.22
16.77
16.48
331.3
249.4
21H16FN5S2·3/2H2O
56.23
56.89
4.27
3.52
15.61
14.48
334.4
260.8
3213, 1537, 1318, 1290, 1186, 973
3619, 3285, 1587, 1319, 979
3225, 1537, 1331, 1255, 973
C22H19N5S2·2H2O
22H19N5OS2·3H2O
58.26
58.03
5.11
4.96
15.44
14.83
337.6
260.4
Vj
C
54.19
53.84
5.17
5.04
14.36
13.70
308.3
225.5
3.1.1. General procedure for the preparation of N-
phenyl-N%-[4-(5-alkyl/arylamno-1,3,4-thiadiazole-2-yl)-
phenyl]thioureas [Vc–e, Vg–i, Vj ]
A solution of the 0.001 mol phenyl isothiocyanate in
1.2 ml anhydrous C3H6O was added dropwise to the
solution of 0.001 mol amine in 1.2 ml anhydrous C3H6O
[9]. The solution was refluxed for 4–5 h. The mixture
was evaporated and the precipitated product was
purified by washing with petroleum ether and boiled
EtOH.
the same manner as a BACTEC positive vial, when
growth from a solid medium was used. Each vial was
tested immediately on a BACTEC instrument to
provide CO2 in the headspace. The vials were incubated
at 37 °C and tested daily with a BACTEC instrument.
When the GI in the control reads at least 30, the
increase in GI (DGI) from the previous day in the
control was compared with that in the drug vial [10,11].
The following formula was used to interpret results:
DGI control\DGI drug=susceptible
DGI controlBDGI drug=resistant
3.2. Biological acti6ity
Antituberculosis activities of the synthesized com-
pounds were screened in vitro using BACTEC 460
Radiometric System against M. tuberculosis H37Rv at
6.25 mg/ml. Primary antituberculosis activity screening
results of these compounds are shown in Table 2.
4. Results and discussion
Antituberculosis activities of the synthesized com-
pounds were screened in vitro using BACTEC 460
Radiometric System against M. tuberculosis H37Rv at
6.25 mg/ml. Rifampicin was used as the standard in
these tests. The compound Vd has cyclohexyl group
showed the highest inhibition with 67%. While the
compound Vf has chlorine on the fourth position of
aromatic ring showed 32% inhibition against M. tuber-
culosis H37Rv, the compound Vg has fluorine on the
fourth position of aromatic ring did not exhibited inhi-
bition. Other compounds showed varying degrees of
inhibition in the primary screen. We concluded from
our investigation that Vd may be considered promising
for the development of new antituberculosis agents.
3.2.1. BACTEC radiometric method of susceptibility
testing
Inocula for susceptibility testing were either from a
positive BACTEC isolation vial with a growth index
(GI) of 500 or more, or a suspension of organisms
isolated earlier on a conventional medium. The culture
was well mixed with a syringe and 0.1 ml of a positive
BACTEC culture was added to each of the vials con-
taining the test drugs. The drug vials contained ri-
fampicin (0.25 mg/ml). A control vial was inoculated
with 1:100 dilution of the culture. A suspension equiva-
lent to a McFarland No. 1 standard was prepared in

580
S. Karakus¸, S. Rollas / Il Farmaco 57 (2002) 577–581
Table 2
Antimycobacterial activity of Vc–e, Vg–i and Vj
Acknowledgements
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We thank Dr Joseph A. Maddry from the Tuberculo-
sis Antimicrobial Acquisition and Coordinating Facility
(TAACF) for the in vitro evaluation of antimycobacte-
rial activity using M. tuberculosis H37R6. This work
was supported by the Research Fund of Marmara
"
University. Project Number: SAG-65/1998.
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