Synthesis, characterization, and anti-inflammatory evaluation of 1,2,4-oxadiazoles combined with thiosemicarbazide and 1,3,4-oxadiazole moieties

Article abstract of DOI:10.1002/jhet.133

(Chemical Equation Presented) The reaction of 1,2,4-oxadiazole carbohydrazides 1a-h with phenyl isothiocyanate led to an unexpected ring cyclisation of the thiosemicarbazide derivatives 2a-h, giving compounds 3a-h as side products. These two new series we

Full text of DOI:10.1002/jhet.133

722
Synthesis, Characterization, and Anti-Inflammatory
Evaluation of 1,2,4-Oxadiazoles Combined with
Thiosemicarbazide and 1,3,4-Oxadiazole Moieties
Vol 46
a
Jose M. dos Santos Filho, * Jose G. de Lima, and Lucia F. C. C. Leite
b
c
´
´
´
aDepartment of Chemical Engineering, Federal University of Pernambuco,
Recife, PE, 50740-521, Brazil
bDepartment of Pharmaceutical Sciences, Federal University of Pernambuco,
Recife, PE, 50740-521, Brazil
cDepartment of Chemistry, Catholic University of Pernambuco, Recife, PE, 50050-900, Brazil
*E-mail: mauricio_santosfilho@yahoo.com.br
Received June 12, 2008
DOI 10.1002/jhet.133
Published online 13 July 2009 in Wiley InterScience (www.interscience.wiley.com).
The reaction of 1,2,4-oxadiazole carbohydrazides 1a-h with phenyl isothiocyanate led to an
unexpected ring cyclisation of the thiosemicarbazide derivatives 2a-h, giving compounds 3a-h as side
products. These two new series were preliminarily evaluated for their anti-inflammatory activity, using
the carrageenin induced edema protocol.
J. Heterocyclic Chem., 46, 722 (2009).
INTRODUCTION
phoric group in our studies. Starting with 1,2,4-oxadia-
zole carbohydrazides 1a-h, it was possible to introduce
thiosemicarbazide and 1,3,4-oxadiazole residues at the
C-5 position of the 1,2,4-oxadiazole ring, so as to obtain
the designed substances. On the basis of the approach to
the synthesis of 1,2,4-oxadiazole derivatives largely
explored in our group, it was possible to synthesize
compounds 1a-h, which are the adequate starting mate-
rials for our purposes [23].
Non-steroidal anti-inflammatory drugs (NSAIDs) have
been used remarkably widely in the treatment of pain,
fever, and inflammatory diseases, in particular rheuma-
toid arthritis [1–3]. However, severe side effects like
gastrointestinal (GI) ulceration, bleeding, and nephrotox-
icity are associated with the chronic use of NSAIDs
[4,5]. Since most NSAIDs possess a carboxylic group or
a 1,3-diketone moiety capable of forming an enol, they
have the potential to have a topical effect on the stom-
ach walls, leading to GI damage [6,7]. In addition, the
inhibition of enzyme cyclooxygenases (COXs), which is
the main NSAID action mechanism, also inhibits tissue
prostraglandin production, undermining its physiological
cytoprotective role in maintaining GI health [8–11].
Substances containing heterocyclic and/or heteroali-
phatic moieties have been found to exhibit a large spec-
trum of biological responses, including anti-inflamma-
tory activity. It has been reported in the literature that
certain compounds possessing 1,2,4-oxadiazole [12–14],
1,3,4-oxadiazole [15–19] or thiosemicarbazide [20–22]
moieties exhibit significant anti-inflammatory properties.
This led us to investigate the planning and synthesis of
new series of substances whose structures fuse two of
these groups with the consequent study of their biologi-
cal responses. In our attempt to discover new and useful
agents for the treatment of inflammation diseases, we
selected the 1,2,4-oxadiazole ring as the main pharmaco-
During the synthesis of the thiosemicarbazide deriva-
tives 2a-h, their spontaneous ring closure was observed,
leading to 1,3,4-oxadiazole derivatives 3a-h. To our best
knowledge, this unusual outcome for this condensation
reaction was never observed before and is possible due
to the structural features of compounds 2a-h. All iso-
lated compounds were preliminary tested for their anti-
inflammatory activity as part of our studies on new
NSAIDs drugs.
RESULTS AND DISCUSSION
1,2,4-Oxadiazole hydrazides 1a-h provided access to
the designed heterogeneous chains and heterocyclic sys-
tems. Their synthesis was already described by our
group and can be achieved in three easy and efficient
steps [23]. Preparation of thiosemicarbazide derivatives
has usually been carried out by condensation of hydra-
zides with appropriate isothiocyanates in a polar protic
C
V
2009 HeteroCorporation

July 2009
Synthesis, Characterization, and Anti-Inflammatory Evaluation of 1,2,4-Oxadiazoles
Combined with Thiosemicarbazide and 1,3,4-Oxadiazole Moieties
723
Scheme 1
ence of base [24] or selective activation of the sulfur
moiety by coupling reagents such as DCC [25] under
reflux. No references to a spontaneous process have
been found in the literature. This suggests that the ring
closure process is possibly associated with the specific
structural features of the thiosemicarbazides 2a-h. In
order to investigate the effect of the solvent on this cyc-
lisation, the reaction of hydrazides 1a-h with phenyl
isothiocyanate was carried out in THF/MeOH 7:3. No
difference in the results was observed, indicating that
the reaction doesn’t depend on using an aprotic or protic
solvent. On the other hand, solutions of pure phenyl thi-
osemicarbazides 2a-h in THF produce 1,3,4-oxadiazole
derivatives 3a-h very slowly at room temperature. By
means of TLC control, traces of 1,3,4-oxadiazole were
identified only after 10 days. Refluxing these solutions
over several hours under argon, a mixture of decomposi-
tion products could be observed, confirming the thermal
instability of the thiosemicarbazides. However, transfor-
mation into tetracyclic compounds 3a-h was not
solvent under reflux. However, it was not possible to
transform 1,2,4-oxadiazole hydrazides 1a-h into their
thiosemicarbazide derivatives 2a-h under these condi-
tions. First, educts were poorly soluble in ethanol or
methanol even at their boiling points. Solubility was
increased after addition of phenyl isothiocyanate and
reflux. After reaction times, a complex mixture of prod-
ucts was observed when using TLC, but none of them
could be isolated or identified. Access to the desired thi-
osemicarbazides 2a-h was possible using dry THF as
solvent and refluxing for only short periods of time
(Scheme 1). Despite the satisfactory outcome, this meth-
odology led to a result different from that usually
reported in the literature. Thiosemicarbazide adducts 2a-
h have been formed in a mixture with their correspond-
ing ring closed 1,3,4-oxadiazole derivatives 3a-h as by-
products in yields ranging from 2 to 10%, as determined
after isolation (Tables 1 and 2).
1
increased, as observed by H-NMR analysis. Hence, the
cyclisation process should occur mainly during the for-
mation of the thiosemicarbazides. Analysing the mecha-
nism of this reaction, depicted in Scheme 2, it can be
assumed that the formation of intermediate A is a criti-
cal step for understanding its outcome. After the break-
ing of the C¼¼N bond, an electron pair of thiol group
(pathway a) easily establishes the thiocarbonyl bond,
leading to the thiosemicarbazide products 2a-h, as nor-
mally described. Ring closure should otherwise occur as
a consequence of a nucleophilic attack by the carbonyl
oxygen on the carbon atom of the imine group, as
shown in pathway b. However, this oxygen atom is usu-
ally not basic enough to undergo such a nucleophilic
addition. It is reasonable to assume that the conjugated
3-aryl-1,2,4-oxadiazol-5-yl substituent attached to the
Cyclisation of thiosemicarbazide moiety exclusively
into the 1,3,4-oxadiazole nucleus has been reported
under oxidative iodine-mediated conditions in the pres-
Table 1
Physical and pharmacological data for the derivatives N1-[3-(4-substituted-aryl)-1,2,4-oxadiazol-5-yl carbonyl]-N4-phenyl thiosemicarbazides 2a-h.
Molecular
weight
CFE, % inhibn ꢁ
Comp.
X
Molecular formula
Yield (%)
M.p. (ꢀC)
S.E.M.a,b
2a
2b
2c
2d
2e
2f
H
CH3
F
C16H13N5SO2
C17H15N5SO2
C16H12N5SO2F
C16H12N5SO2Cl
C16H12N5SO2Br
C17H15N5SO3
C16H12N6SO4
C16H13N5SO3
339
353
357
373
418
369
384
355
81
75
88
82
194–196
192–193
193–194
193–194
203–204
184–186
211–212
229–230
29.5 ꢁ 7.2
28.9 ꢁ 2.5
20.7 ꢁ 2.5
23.5 ꢁ 1.5
26.4 ꢁ 2.5
18.3 ꢁ 1.8
30.7 ꢁ 4.8
32.9 ꢁ 3.2
Cl
Br
OCH3
NO2
OH
80
85
90
2g
2h
75
75.0 ꢁ 5.7
Diclofenac sodiumc
a Percentage of inhibition on carrageenin-induced rat paw edema at the dosis of 25 mg/kg. The result is the mean value ꢁ S.E.M. for each test
group.
b P < 0.001 and P < 0.01 represented a significant difference when compared with control group.
c At the dosis of 2 mg/kg.
Journal of Heterocyclic Chemistry
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724
J. M. dos Santos Filho, J. G. de Lima, and L. F. C. C. Leite
Vol 46
Table 2
Physical and pharmacological data for derivatives 5-[3-(4-substituted-aryl)-1,2,4-oxadiazol-5-yl]-2-(N-phenylamino)-1,3,4-oxadiazoles 3a-h.
Molecular
formula
Molecular
weight
Yield
(%)a
M.p.
(ꢀC)
CFE, %inhibn
ꢁ S.E.M.b,c
Comp.
X
3ꢀ
H
CH3
F
C16H11N5O2
C17H13N5O2
C16H10N5O2F
C16H10N5O2Cl
C16H10N5O2Br
C17H13N5O3
C16H10N6O4
C16H11N5O3
305
319
323
339
384
335
350
321
75 (10)
80 (9)
73 (7)
90 (8)
84 (6)
93 (7)
85 (2)
89 (8)
238–240
236–237
225–227
49.6 ꢁ 5.8
48.6 ꢁ 2.8
47.9 ꢁ 2.3
49.9 ꢁ 4.9
41.4 ꢁ 5.7
39.2 ꢁ 0.54
61.3 ꢁ 2.4
59.2 ꢁ 8.1
3b
3c
3d
3e
3f
Cl
Br
OCH3
NO2
OH
229–230
232–233
225–227 (dec.)
259–260 (dec.)
218–220 (dec.)
3g
3h
Diclofenac sodiumd
75.0 ꢁ 5.7
a Values in parenthesis report the percentage of the compound obtained as side product after isolation in the reaction to obtain 2a-h.
b Percentage of inhibition on carrageenin-induced rat paw edema at the dosis of 25 mg/kg. The result is the mean value ꢁ S.E.M. for each test
group.
c P < 0.001 and P < 0.01 represented a significant difference when compared with control group.
d At the dosis of 2 mg/kg.
carbonyl group acts as a good electron-donating group,
enhancing the nucleophilicity of the oxygen atom. Thus,
the reaction described by pathway b can take place in
addition to the pathway a. Protons migration, elimina-
tion of the thiol group, and aromatisation of the five-
membered ring should be a specially favoured and rapid
process, owing to the direct conjugation between 1,3,4-
oxadiazole and the other two aromatic rings.
are more effective in edema inhibition. It was found that
the presence of NO2 and OH groups, in products 3g and
3h respectively, promotes better biological responses.
In the light of these results, we envisage introducing
structural modifications in compounds 3a-h to identify
Scheme 2
The nature of the para-substituents on the phenyl ring
influences the quantity of products formed. The strong
electron-withdrawing nitro-substituent doubtless affects
the cyclisation reaction, since it decreases the stabilising
effect of the aromatic rings on the carbonyl group, lead-
ing to only 2% of compound 3g as a by-product. The
other substituents seem to influence the ring closure pro-
cess to almost the same extent, as suggested by the
yields for isolated products (Table 2).
To obtain appropriate amounts of compounds 3a-h,
thiosemicarbazides 2a-h were treated with DCC in dry
THF, leading to the well known oxidative process of
ring closure with good yields. The characterization and
results of pharmacological tests for compounds 2a-h and
3a-h are given in Tables 1 and 2 as well as in the exper-
imental protocols.
The anti-inflammatory activity of synthesized com-
pounds 2a-h and 3a-h was evaluated using the carragee-
nin induced edema method [26]. The compounds were
tested at a 25 mg/kg oral dose and compared with the
standard drug diclofenac sodium in a dose of 2 mg/kg.
Comparing the results in Tables 1 and 2 it can easily be
concluded that compounds exhibiting the thiosemicarba-
zide moiety 2a-h have a low level of activity. In con-
trast to these poor results, compounds 3a-h, possessing
the two oxadiazole rings directly linked to each other
Journal of Heterocyclic Chemistry
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July 2009
Synthesis, Characterization, and Anti-Inflammatory Evaluation of 1,2,4-Oxadiazoles
Combined with Thiosemicarbazide and 1,3,4-Oxadiazole Moieties
725
N1-(3-Phenyl-1,2,4-oxadiazol-5-ylcarbonyl)-N4-phenyl thio-
more potent substances, which can then be submitted to
further biological studies.
semicarbazide (2a). IR (m, cmꢂ1): 3302, 3207 (NAH), 1683
~
1
(C¼¼O), 1226 (C¼¼S); H-NMR (DMSO-d6, ppm): 11.5 (s, 1H,
In summary, a set of 16 new compounds were
designed and synthesized to evaluate their anti-inflamma-
tory profiles and to correlate them with molecular proper-
ties of these products. Although compounds bearing a
thiosemicarbazide moiety 2a-h are practically inactive,
their derivatives 3a-h showed better biological response
to the carrageenin footpad edema (CFE) test, so that they
can serve as models for designing a new series of deriva-
tives, expected to be more effective as NSAIDs drugs.
Compounds 3g and 3h were especially active, suggesting
that groups capable of establishing hydrogen bonds
should be crucial for the biological response. Studies of
GI effects of these products were not carried out because
of the limitation of their anti-inflammatory profiles.
The spontaneous ring closure of compounds bearing
the thiosemicarbazide group 2a-h leading to compounds
3a-h was observed for the first time for this kind of
transformation, constituting an interesting subject for
further experimental and theoretical studies.
CONH), 10.0 (s, 1H, CSNH), 9.85 (s, 1H, NH), 8.10–8.05 (m,
2H, ortho-oxadiazole ArH), 7.63–7.58 (m, 3H, ArH), 7.42–
7.29 (m, 4H, ArH), 7.16 (t, 1H, J ¼ 7.1 Hz, para-amino ArH);
MS (m/z, %): 339 (Mþꢃ, 24), 305 (8), 204 (21), 193 (39), 135
(94), 77 (100); HRMS, Calc. (Found) for C16H13N5SO2:
339.07900 (339.07970); Anal. Calcd.: C, 56.62; H, 3.86; N,
20.64. Found: C, 56.69; H, 4.07; N, 20.84.
N1-[3-(4-Tolyl)-1,2,4-oxadiazol-5-ylcarbonyl]-N4-phenyl
thiosemicarbazide (2b). IR (m, cmꢂ1): 3326, 3220, 3151
~
(NAH), 1689 (C¼¼O), 1231 (C¼¼S); 1H-NMR (DMSO-d6,
ppm): 11.5 (s, 1H, CONH), 10.0 (s, 1H, CSNH), 9.84 (s, 1H,
NH), 7.96 (d, 2H, AB-System, J ¼ 8.0 Hz, ortho-oxadiazole
ArH), 7.43–7.33 (m, 6H, ArH), 7.16 (t, 1H, J ¼ 6.8 Hz, para-
amino ArH), 2.48 (s, 3H, CH3); MS (m/z, %): 353 (Mþꢃ, 21),
218 (12), 193 (27), 132 (81), 77 (100); HRMS, Calc. (Found)
for C17H15N5SO2: 353.09465 (353.09573); Anal. Calcd.: C,
57.77; H, 4.28; N, 19.82. Found: C, 57.78; H, 4.29; N, 20.23.
N1-[3-(4-Fluorophenyl)-1,2,4-oxadiazol-5-ylcarbonyl]-N4-
phenylthiosemicarbazide (2c). IR (m, cmꢂ1): 3306, 3226,
~
3159 (NAH), 1688 (C¼¼O), 1227 (C¼¼S); 1H-NMR (DMSO-
d6, ppm): 11.6 (s, 1H, CONH), 10.1 (s, 1H, CSNH), 9.84 (s,
1H, NH), 8.12 (dd, 2H, J ¼ 8.4 Hz, ortho-oxadiazole ArH),
7.51–7.29 (m, 6H, ArH), 7.16 (t, 1H, J ¼ 7.1 Hz, para-amino
ArH); MS (m/z, %): 357 (Mþꢃ, 13), 222 (13), 193 (17), 136
(100), 77 (56); HRMS, Calc. (Found) for C16H12N5SO2F:
357.06957 (357.07017); Anal. Calcd.: C, 53.77; H, 3.38; N,
19.60. Found: C, 53.50; H, 3.49; N, 19.46.
EXPERIMENTAL
Melting points were determined on a Gallenkamp capillary
apparatus and are uncorrected. Infrared spectra were recorded
using KBr discs on a Perkin-Elmer Paragon 500 FT-IR spec-
trometer. 1H-NMR spectra were recorded on a Bruker DPX-
200 spectrometer, with chemical shifts d reported in ppm uni-
ties relative to the internal standard TMS. Mass spectra were
obtained by using a Finnigam MAT 8200 or MAT 95 mass
spectrometer. Values for High resolution mass spectrometry
(HRMS) lie within the permitted limit intervals with resolution
of 10,000. Reactions were generally run under an argon atmos-
phere. Elemental analysis was performed on a Carlo Erba EA
1110 elemental analyzer. Organic solutions were concentrated
at vacuum on a rotary evaporator at room temperature or at
60ꢀC. Column chromatography was performed with ICN Bio-
medicals silica gel 60, 32–63 lm.
N1-[3-(4-Chlorophenyl)-1,2,4-oxadiazol-5-ylcarbonyl]-N4-
phenyl thiosemicarbazide (2d). IR (m, cmꢂ1): 3325, 3221,
~
3158 (NAH), 1687 (C¼¼O), 1232 (C¼¼S); 1H-NMR (DMSO-
d6, ppm): 11.6 (s, 1H, CONH), 10.1 (s, 1H, CSNH), 9.82 (s,
1H, NH), 8.08 (d, 2H, AB-System, J ¼ 8.5 Hz, ortho-oxadia-
zole ArH), 7.70 (d, 2H, AB-System, J ¼ 8.8 Hz, meta-oxadia-
zole ArH), 7.39–7.29 (m, 4H, ArH), 7.16 (t, 1H, J ¼ 7.0 Hz,
para-amino ArH); MS (m/z, %): 375 (Mþꢃþ2, 11), 373 (Mþꢃ
,
25), 238 (13), 193 (48), 135 (100), 77 (79); HRMS, Calc.
(Found) for C16H12N5SO235Cl: 373.04002 (373.03986); Anal.
Calcd.: C, 51.41; H, 3.23; N, . Found: C, 51.49; H, 3.40; N,
18.80.
N1-[3-(4-Bromophenyl)-1,2,4-oxadiazol-5-ylcarbonyl]-N4-
~
Compounds 3-(4-substitutedaryl)-1,2,4-oxadiazol-5-yl carbo-
hydrazide (1a-h) were prepared by the procedure given in
literature [23].
phenyl thiosemicarbazide (2e). IR (m, cmꢂ1): 3319, 3187,
3099 (NAH), 1688 (C¼¼O), 1219 (C¼¼S); 1H-NMR (DMSO-
d6, ppm): 11.6 (s, 1H, CONH), 10.1 (s, 1H, CSNH), 9.83 (s,
1H, NH), 8.00 (d, 2H, AB-System, J ¼ 8.4 Hz, ortho-oxadia-
zole ArH), 7.84 (d, 2H, AB-System, J ¼ 8.7 Hz, meta-oxadia-
zole ArH), 7.42–7.29 (m, 4H, ArH), 7.16 (t, 1H, J ¼ 6.9 Hz,
General procedure for the preparation of N1-[3-(4-substi-
tutedaryl)-1,2,4-oxadiazol-5-yl carbonyl]-N4-phenyl thiose-
micarbazides (2a-h). A solution of hydrazides 1a-h (0.5
mmol) in 2.5 mL THF was gently heated at 50ꢀC, then phenyl
isothiocyanate (0.5 mmol, 0.068 g) was added and the reaction
was allowed to proceed at reflux under inert atmosphere for 30
min before cooling to room temperature. Solvent was removed
in vacuo and the crude products were recrystallized from THF/
petroleum ether (30–60ꢀC) to afford, after filtration, the thiose-
micarbazides 2a-h as main products, whose yields, melting
points and results of biological evaluation are given in Table
1. The filtrate was concentrated and the residue was eluted on
a silica gel column using CH2Cl2/MeOH 10:0.2 as eluent to
give the secondary ring closed products 3a-h, and their yields
were reported in Table 2.
para-amino ArH); MS (m/z, %): 419 (Mþꢃþ2, 11), 417 (Mþꢃ
,
11), 284/282 (13/13), 196 (55), 135 (100), 77 (52); HRMS,
Calc. (Found) for C16H12N5SO281Br: 418.98746 (418.98777);
Anal. Calcd.: C, 45.94; H, 2.89; N, 16.74. Found: C, 45.90; H,
2.90; N, 16.85.
N1-[3-(4-Methoxyphenyl)-1,2,4-oxadiazol-5-ylcarbonyl]-
N4-phenyl thiosemicarbazide (2f). IR (m, cmꢂ1): 3301,
~
3220, 3163 (NAH), 1686 (C¼¼O), 1226 (C¼¼S); 1H-NMR
(DMSO-d6, ppm): 12.3 (s, 1H, CONH), 10.9 (s, 1H, CSNH),
10.7 (s, 1H, NH), 8.84 (d, 2H, AB-System, J ¼ 9.1 Hz, ortho-
oxadiazole ArH), 8.23 (m, 4H, ArH), 7.98 (broad m, 3H,
ArH), 4.67 (s, 3H, OCH3); MS (m/z, %): 369 (Mþꢃ, 4), 234
Journal of Heterocyclic Chemistry
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726
J. M. dos Santos Filho, J. G. de Lima, and L. F. C. C. Leite
Vol 46
(13), 193 (6), 148 (100), 135 (67), 77 (48); HRMS, Calc.
(Found) for C17H15N5SO3: 369.08956 (369.08884); Anal.
Calcd.: C, 55.27; H, 4.09; N, 18.96. Found: C, 55.12; H, 4.05;
N,19.05.
100), 163 (8), 120 (32), 92 (9), 77 (24); HRMS, Calc. (Found)
for C16H10N5O2F: 323.08185 (323.08104); Anal. Calcd.: C,
59.44; H, 3.12; N, 21.66. Found: C, 59.32; H, 3.23; N, 21.79.
5-[3-(4-Chlorophenyl)-1,2,4-oxadiazol-5-yl]-2-(N-phenyla-
N1-[3-(4-Nitrophenyl)-1,2,4-oxadiazol-5-ylcarbonyl]-N4-
mino)-1,3,4-oxadiazole (3d). IR (m, cmꢂ1): 3290 (NAH),
~
phenyl thiosemicarbazide (2g). IR (m, cmꢂ1): 3329, 3223,
1640 (C¼¼C), 1613 (C¼¼N); 1H-NMR (DMSO-d6, ppm): 11.3
(s, 1H, NH), 8.09 (d, 2H, AB-System, J ¼ 8.5 Hz, ortho-oxa-
diazole ArH), 7.69 (d, 2H, AB-System, J ¼ 8.8 Hz, meta-oxa-
diazole ArH), 7.62 (d, 2H, AB-System, J ¼ 7.9 Hz, ortho-
amino ArH), 7.40 (t, 2H, J ¼ 7.6 Hz, meta-amino ArH), 7.08
(t, 1H, J ¼ 7.3 Hz, para-amino ArH); MS (m/z, %): 341
(Mþꢃþ2, 35), 339 (Mþꢃ, 100), 181/179 (3/8), 120 (56), 92
(30), 77 (76); HRMS, Calc. (Found) for C16H10N5O235Cl:
339.05230 (339.05128); Anal. Calcd.: C, 56.56; H, 2.97; N,
20.61. Found: C, 56.70; H, 3.18; N, 20.70.
~
3157 (NAH), 1690 (C¼¼O), 1220 (C¼¼S); 1H-NMR (DMSO-
d6, ppm): 11.6 (s, 1H, CONH), 10.1 (s, 1H, CSNH), 9.83 (s,
1H, NH), 8.46 (d, 2H, AB-System, J ¼ 8.1 Hz, ortho-oxadia-
zole ArH), 8.33 (d, 2H, AB-System, J ¼ 8.7 Hz, meta-oxadia-
zole ArH), 7.42–7.13 (m, 4H, ArH), 7.17 (t, 1H, J ¼ 7.0 Hz,
para-amino ArH); MS (m/z, %): 384 (Mþꢃ, 2), 249 (23), 135
(100), 77 (67); HRMS, Calc. (Found) for C16H12N6SO4:
384.06407 (384.06372); Anal. Calcd.: C, 49.99; H, 3.15; N,
21.86. Found: C, 50.02; H, 3.24; N, 21.89.
N1-[3-(4-Hydroxyphenyl)-1,2,4-oxadiazol-5-ylcarbonyl]-
5-[3-(4-Bromophenyl)-1,2,4-oxadiazol-5-yl]-2-(N-phenyl-
N4-phenyl thiosemicarbazide (2h). IR (m, cmꢂ1): 3289,
amino)-1,3,4-oxadiazole (3e). IR (m, cmꢂ1): 3292 (NAH),
~
~
3183 (broad, NAH), 1694 (C¼¼O), 1220 (C¼¼S); 1H-NMR
(DMSO-d6, ppm): 11.5 (s, 1H, CONH), 10.3 (s, 1H, OH), 10.0
(s, 1H, CSNH), 9.84 (s, 1H, NH), 7.90 (d, 2H, AB-System, J ¼
8.8 Hz, ortho-oxadiazole ArH), 7.42–7.29 (m, 4H, ArH), 7.16 (t,
1H, J ¼ 7.1 Hz, para-amino ArH), 6.94 (d, 2H, AB-System, J ¼
8.8 Hz, meta-oxadiazole ArH); MS (m/z, %): 355 (Mþꢃ, 0.4),
220 (13), 134 (100), 77 (37); HRMS, Calc. (Found) for
C16H13N5SO3: 355.07391 (355.07361); Anal. Calcd.: C, 54.07;
H, 3.69; N, 19.71. Found: C, 53.91; H, 3.82; N, 19.67.
General procedure for the preparation of 5-[3-(4-substi-
tutedaryl)-1,2,4-oxadiazol-5-yl]-2-(N-phenylamino)-1,3,4-
oxadiazoles (3a-h). Thiosemicarbazides 2a-h (0.5 mmol) were
dissolved in 5 mL of dry THF together with DCC (0.75 mmol,
1.5 eq.), and the solution was refluxed under inert atmosphere
for 2 h. After solvent evaporation under vacuum, crude products
were digested in CH2Cl2/petroleum ether (30–60ꢀC) 1:1, cooled
in ice bath, filtered and washed with cold CH2Cl2/ petroleum
ether 1:1. All products were purified by column chromatography
on silica gel using CH2Cl2/MeOH 10:0.2 as eluent.
1621 (C¼¼C), 1584 (C¼¼N); 1H-NMR (DMSO-d6, ppm): 11.3
(s, 1H, NH), 8.01 (d, 2H, AB-System, J ¼ 8.3 Hz, ortho-oxa-
diazole ArH), 7.82 (d, 2H, AB-System, J ¼ 8.6 Hz, meta-oxa-
diazole ArH), 7.61 (d, 2H, AB-System, J ¼ 7.7 Hz, ortho-
amino ArH), 7.40 (t, 2H, J ¼ 7.5 Hz, meta-amino ArH), 7.07
(t, 1H, J ¼ 7.4 Hz, para-amino ArH); MS (m/z, %): 385
(Mþꢃþ2, 99), 383 (Mþꢃ, 100), 227/225 (5/5), 120 (42), 92 (9),
77 (36); HRMS, Calc. (Found) for C16H10N5O279Br:
383.00179 (383.00193); Anal. Calcd.: C, 50.02; H, 2.62; N,
18.23. Found: C, 50.23; H, 2.80; N, 18.32.
5-[3-(4-Methoxyphenyl)-1,2,4-oxadiazol-5-yl]-2-(N-phenyl-
amino)-1,3,4-oxadiazole (3f). IR (m, cmꢂ1): 3286 (NAH),
~
1639 (C¼¼C), 1614 (C¼¼N); 1H-NMR (DMSO-d6, ppm): 11.3
(s, 1H, NH), 8.03 (d, 2H, AB-System, J ¼ 8.3 Hz, ortho-oxa-
diazole ArH), 7.60 (d, 2H, AB-System, J ¼ 7.7 Hz, ortho-
amino ArH), 7.40 (t, 2H, J ¼ 7.5 Hz, meta-amino ArH), 7.14
(d, 2H, AB-System, J ¼ 8.7 Hz, meta-oxadiazole ArH), 7.07
(t, 1H, para-amino ArH), 3.84 (s, 3H, OCH3); MS (m/z, %):
335 (Mþꢃ, 100), 175 (4), 120 (10), 92 (6), 77 (15); HRMS,
Calc. (Found) for C17H13N5O3: 335.10184 (335.10141); Anal.
Calcd.: C, 60.89; H, 3.91; N, 20.88. Found: C, 60.64; H, 3.97;
N, 20.89.
5-(3-Phenyl-1,2,4-oxadiazol-5-yl)-2-(N-phenylamino)-1,3,4-
oxadiazole (3a). IR (m, cmꢂ1): 3172 (NAH), 1672 (C¼¼C), 1638
~
(C¼¼N); 1H-NMR (DMSO-d6, ppm): 11.3 (s, 1H, NH), 8.07
(broad s, 2H, ortho-oxadiazole ArH), 7.61 (broad d, 5H, J ¼ 6.4
Hz, ArH), 7.39 (t, 2H, J ¼ 7.6 Hz, meta-oxadiazole ArH), 7.07
5-[3-(4-Nitrophenyl)-1,2,4-oxadiazol-5-yl]-2-(N-phenylamino)-
1,3,4-oxadiazole (3g). IR (m, cmꢂ1): 3372 (NAH), 1611
~
(t, 1H, J ¼ 7.1 Hz, para-amino ArH); MS (m/z, %): 305 (Mþꢃ
,
(C¼¼C), 1580 (C¼¼N); H-NMR (DMSO-d6, ppm): 11.6 (s, 1H,
1
100), 145 (18), 120 (46), 92 (15), 77 (71); HRMS, Calc. (Found)
for C16H11N5O2: 305.09127 (305.09170); Anal. Calcd.: C,
62.95; H, 3.63; N, 22.94. Found: C, 62.80; H, 3.66; N, 23.15.
5-[3-(4-Tolyl)-1,2,4-oxadiazol-5-yl]-2-(N-phenylamino)-
NH), 8.45 (d, 2H, AB-System, J ¼ 8.6 Hz, ortho-oxadiazole
ArH), 8.34 (d, 2H, AB-System, J ¼ 9.0 Hz, meta-oxadiazole
ArH), 7.63 (d, 2H, AB-System, J ¼ 7.9 Hz, ortho-amino
ArH), 7.41 (t, 2H, J ¼ 8.2 Hz, meta-amino ArH), 7.09 (t, 1H,
J ¼ 7.6 Hz, para-amino ArH); MS (m/z, %): 350 (Mþꢃ, 100),
190 (3), 120 (26), 92 (8), 77 (17); HRMS, Calc. (Found) for
C16H10N6O4: 350.07635 (350.07591); Anal. Calcd.: C, 54.85;
H, 2.88; N, 23.99. Found: C, 54.53; H, 2.99; N, 23.69.
1,3,4-oxadiazole (3b). IR (m, cmꢂ1): 3258 (NAH), 1636
~
1
(C¼¼C), 1621 (C¼¼N); H-NMR (DMSO-d6, ppm): 11.3 (s, 1H,
NH), 8.15 (dd, 2H, J ¼ 5.2 Hz, ortho-oxadiazole ArH), 7.60
(d, 2H, AB-System, J ¼ 7.6 Hz, ArH), 7.45 (m, 4H, ArH),
7.09 (t, 1H, J ¼ 7.3 Hz, para-amino ArH), 2.39 (s, 3H, CH3);
MS (m/z, %): 319 (Mþꢃ, 100), 160 (13), 120 (13), 92 (6), 77
(13); HRMS, Calc. (Found) for C17H13N5O2: 319.10692
(319.10594); Anal. Calcd.: C, 63.94; H, 4.10; N, 21.93. Found:
C, 63.96; H, 4.17; N, 21.93.
5-[3-(4-Hydroxyphenyl)-1,2,4-oxadiazol-5-yl]-2-(N-phenyl-
amino)-1,3,4-oxadiazole (3h). IR (m, cmꢂ1): 3298 (broad,
~
1
NAH), 1626 (C¼¼C); H-NMR (DMSO-d6, ppm): 11.2 (s, 1H,
NH), 10.3 (s, 1H, OH), 7.90 (d, 2H, AB-System, J ¼ 9.3 Hz,
ortho-oxadiazole ArH), 7.61 (d, 2H, AB-System, J ¼ 8.2 Hz,
ortho-amino ArH), 7.39 (t, 2H, J ¼ 7.4 Hz, meta-amino ArH),
7.07 (t, 1H, J ¼ 7.3 Hz, para-amino ArH), 6.94 (d, 2H, AB-Sys-
tem, J ¼ 8.8 Hz, meta-oxadiazole ArH); MS (m/z, %): 321
(Mþꢃ, 100), 161 (12), 120 (13), 92 (10), 77 (26); HRMS, Calc.
(Found) for C16H11N5O3: 321.08619 (321.08603); Anal. Calcd.:
C, 59.81; H, 3.45; N, 21.80. Found: C, 59.56; H, 3.63; N, 21.66.
5-[3-(4-Fluorophenyl)-1,2,4-oxadiazol-5-yl]-2-(N-phenyl-
amino)-1,3,4-oxadiazole (3c). IR (m, cmꢂ1): 3286 (NAH),
~
1639 (C¼¼C), 1614 (C¼¼N); 1H-NMR (DMSO-d6, ppm): 11.3 (s,
1H, NH), 8.15 (dd, 2H, J ¼ 5.2 Hz, ortho-oxadiazole ArH), 7.63
(d, 2H, AB-System, J ¼ 7.6 Hz, ArH), 7.45 (m, 4H, ArH), 7.09
(t, 1H, J ¼ 7.3 Hz, para-amino ArH); MS (m/z, %): 323 (Mþꢃ
,
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

July 2009
Synthesis, Characterization, and Anti-Inflammatory Evaluation of 1,2,4-Oxadiazoles
Combined with Thiosemicarbazide and 1,3,4-Oxadiazole Moieties
727
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Acknowledgments. The authors gratefully acknowledge partial
financial support from the Brazilian Funding agencies CAPES
and CNPq. Their special thanks to the Institutes of Biology and
Chemistry of the University of Bremen, Germany, for laboratory
facilities and characterization of new compounds.
[14] Bezerra, N. M. M.; de Oliveira, S. P.; Srivastava, R. M.;
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet