Synthesis of new 4[4-(4-nitrophenoxy)phenyl]-5-substituted-2H-1,2,4-triazole-3-thiones and their evaluation as anthelmintics

Article abstract of DOI:10.1007/s11164-015-2123-1

A library of novel 4-[4-(4-nitrophenoxy)phenyl]-5-substituted-2H-1,2,4-triazole-3-thiones containing different substituents at the 5-position is synthesized. The mechanochemical treatment is followed to synthesize target compounds 8 (a-p), and the yields are compared by both the grinding method and the conventional method. The structure of the intermediate, isothiocyanato-4-(4-nitrophenoxy)benzene 6, is analyzed by single crystal X-ray studies. The title compounds are characterized by spectral and elemental analyses and further evaluated for their efficacy as anthelmintics in vitro. Compounds 8c, 8j, 8k, 8l, and 8m exhibit significant anthelmintic activity.

Full text of DOI:10.1007/s11164-015-2123-1

Res Chem Intermed
DOI 10.1007/s11164-015-2123-1
Synthesis of new 4[4-(4-nitrophenoxy)phenyl]-5-
substituted-2H-1,2,4-triazole-3-thiones and their
evaluation as anthelmintics
2
3
•
B. Namratha1 Dinesh Bilehal V. ShyamKumar
•
•
Santosh L. Gaonkar1
Received: 21 March 2015 / Accepted: 29 May 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract A library of novel 4-[4-(4-nitrophenoxy)phenyl]-5-substituted-2H-1,2,4-
triazole-3-thiones containing different substituents at the 5-position is synthesized.
The mechanochemical treatment is followed to synthesize target compounds 8 (a–
p), and the yields are compared by both the grinding method and the conventional
method. The structure of the intermediate, isothiocyanato-4-(4-nitrophenoxy)ben-
zene 6, is analyzed by single crystal X-ray studies. The title compounds are char-
acterized by spectral and elemental analyses and further evaluated for their efficacy
as anthelmintics in vitro. Compounds 8c, 8j, 8k, 8l, and 8m exhibit significant
anthelmintic activity.
Keywords Anthelmintic Á Grinding Á Nitroscanate Á Triazole
Introduction
Nitroscanate, chemically called isothiocyanato-4-(4-nitrophenoxy)benzene is an
anthelmintic drug active against nematodes and cestodes in cats and dogs. Close
intimacy of the immunocompromised human population with cats and dogs has
Electronic supplementary material The online version of this article (doi:10.1007/s11164-015-2123-1)
contains supplementary material, which is available to authorized users.
&
Santosh L. Gaonkar
gaonkarslg@rediffmail.com
1
2
3
Department of Chemistry, Manipal Institute of Technology, Manipal University,
Manipal 576104, India
Department of Chemistry, Reva Institute of Technology and Management, Bangalore 560064,
India
Department of Biotechnology, Karnataka University, Dharwad 580003, India
123

B. Namratha et al.
considerably increased the risk of transmission of parasitic infections [1, 2].
Nitroscanate is structurally related to an herbicide named nitrofen, which is
described to be a carcinogen [3] and a teratogen [4]. It belongs to the nitro phenyls
class of anthelmintic drugs, a class that comprises a number of anthelmintics like
amoscanate, amocarzine, and nitrodan [5]. Pharmacological profiles of the nitroaryls
and nitroheterocycles include the antibacterials and anthelmintics [6]. These
activities are ascribed to their ability to undergo cytochrome P-450 dependent
reduction to form reactive species like Ar–NHOH and Ar–NH2, which interact with
DNA and perturb its normal functions in different pathogens. This property of nitro
compounds is certainly related to their ability to kill a variety of microbes and
parasites; concurrently it may impart to them mutagenicity [7] and carcinogenicity
[8]. This is the reason why some of the nitro phenyl drugs are withdrawn from the
market. There are findings suggesting that while designing a drug with a biphenyl
ether moiety, the simultaneous presence of –NO2 and –NCS functions should be
avoided. The presence of the latter group may enhance the genetic toxicity of the
former while any modification of –NCS function leads to a greater reduction of
mutagenicity [9]. Hence, we have tried to modify –NCS function for mercapto
triazoles, considering the high biological significance of the triazole moiety [10–15].
In congruence with microwave-assisted synthesis [16], grinding-accelerated
synthesis is gaining recognition. It is the chemical synthesis [17, 18] using
mechanical force [19]. Shorter reaction times, higher yields, environmental
friendliness, and operational simplicity form the salient features of the grinding
synthesis. In continuance of our work on the synthesis of interesting five-membered
heterocycles [20–23], we report the study describing the grinding synthesis of novel
4[4-(4-nitrophenoxy)phenyl]-5-substituted-2H-1,2,4-triazole-3-thiones, their char-
acterization, and progression of their in vitro anthelmintic activities.
Results and discussion
Chemistry
The target compounds are synthesized as per Scheme 1. P-Hydroxy acetanilide 1 is
condensed with p-chloronitrobenzene 2 in DMF at 135–140 °C in presence of
anhydrous K2CO3. The excess amount of unreacted p-hydroxy acetanilide 1 is
removed by washing with hot water. The second step involves hydrolysis of N-[4-
(4-nitrophenoxy)phenyl]acetamide 3 with hydrochloric acid in methanol. The 4-(4-
Nitrophenoxy)aniline 4 is converted to 4-(4-Nitrophenoxy)phenyl thiourea 5 in an
environmentally benign method by heating 4 with ammonium thiocyanate in water
at 100 °C. The 4-(4-nitrophenoxy)phenyl thiourea 5 is refluxed in a nonpolar
solvent, xylene, in the presence of pyridine to afford isothiocyanato-4-(4-nitrophe-
noxy)benzene 6. Thus, the use of hazardous chemicals like thiophosgene, CS2, and
NaOCl for the conversion of 4-(4-nitrophenoxy)aniline 4 to isothiocyanato-4-(4-
nitrophenoxy)benzene 6 can be avoided. Isothiocyanato-4-(4-nitrophenoxy)benzene
6 is then treated with different synthesized aryl carbohydrazides to yield N-[4-(4-
nitrophenoxy)phenyl]-2-(phenylcarbonyl)hydrazinecarbothioamide
7
(a–p).
123

Synthesis of new 4[4-(4-nitrophenoxy)phenyl]-5…
NHCOCH 3
NO2
O
O
MeOH / HCl
DMF / K2CO3
+
O2N
NH2
O2N
NHCOCH 3
OH
Cl
4
3
1
2
NH4SCN
H
N
S
O
H
O
N
H
N
O
RCONHNH2
MeOH
R
Xylene / Pyridine
O2N
O2N
NCS
NHCSNH 2
6
5
O
O2N
H
N
N
Basic medium
7 (a - p)
S
R
N
O
O2N
8 (a - p)
Scheme 1 Where R = a phenyl, b 4-methylphenyl, c 4-methoxyphenyl, d 4-nitrophenyl, e 4-
bromophenyl, f 4-chlorophenyl, g 2-furyl, h 2-thiophenyl, i 3-methoxyphenyl, j 2,4-dimethoxyphenyl,
k 3,4-dimethoxyphenyl, l 4-fluorophenyl, m 2-benzofuryl, n 3-chlorophenyl, o 3-bromophenyl, p 2,4-
dichlorophenyl
Cyclodehydration of 7 (a–p) in basic medium affords 4[4-(4-nitrophenoxy)phenyl]-
5-substituted-2H-1,2,4-triazole-3-thiones 8 (a–p). This reaction is carried out by
both the grinding method and the conventional method. The grinding method is a
solid-phase synthesis which requires a shorter time (12 min) and occurs at room
temperature resulting in comparable yields. On the other hand, conventional
synthesis needs heating in a solvent at 80 °C for about an hour. A comparison of the
yields obtained by grinding and conventional methods is given in Table 1. In the IR
spectra of compounds 8 (a–p), there is NH stretching in the characteristic region of
1
3400 cm-1. Their H NMR signals for NH emerging downfield around d 14.0
authenticates the existence of the ring in thione form. In the 13C NMR spectra, C-3
carbons have shown up around d 168 and C-5 carbons around d 162 denoting the
formation of target compounds. Other signals are observed in the respective regions.
Crystal structure analysis
In order to confirm the orientation of biphenyl groups, crystal structure analysis of
compound 6 is undertaken. Figure 1 displays the ORTEP diagram of 6 at 50 %
probability with atom numbering while Fig. 2 depicts its packing diagram viewed
along the b-axis. X-ray data of compound 6 was obtained to characterize the
123

B. Namratha et al.
Table 1 Physical data of
synthesized compounds 8 (a–p)
Compound
Melting point (°C)
Yield (%)
Conventional
Grinding
8a
8b
8c
8d
8e
8f
192–194
226–228
248–250
268–270
230–232
254–256
202–204
212–214
236–238
250–252
260–262
218–220
206–208
244–246
240–242
218–220
80
89
87
74
81
79
82
84
85
82
82
85
84
76
82
74
82
93
89
75
84
83
85
89
87
85
84
88
88
76
83
74
8g
8h
8i
8j
8k
8l
8m
8n
8o
8p
compound and to know the orientation of biphenyl groups. The C6–O1–C5 bond
angle is 119°. This shows that the two biphenyl groups are out of the plane.
Biology
The results of the anthelmintic activity exhibited by compounds 8(a–p) and standard
drug on Pheretima posthuma are shown in Table 2. The anthelmintic activity
screening data reveal that compound 8c with a p-OMe phenyl group attached to the
5th position of 3-mercapto-1,2,4-triazole ring exhibits significant anthelmintic
activity compared to nitroscanate, the standard drug. This suggests that besides the
nitro group, perhaps the p-OMe phenyl group is also influential in exhibiting
anthelmintic activity. Duplication of the methoxy groups as in 8j and 8k has caused
similar results as in the monosubstituted compound. Similarly, there is no much
variation in the result of the compound 8i monomethoxylated at the meta position.
Compound 8l with p-fluoro phenyl group has induced a pronounced anthelmintic
activity with respect to the standard. This effect can be attributed to the presence of
a p-fluoro group as in the anthelmintic drug flubendazole. Compounds 8a and 8d
have shown moderate activities. Meanwhile, compounds 8b, 8e, and 8f have
demonstrated better activities owing to the presence of p-Me, p-Br, and p-Cl phenyl
groups, respectively. Similar results are observed with the meta substitutions of
chloro 8n and bromo 8o groups as well as with the duplication of chloro groups 8p.
The replacement of phenyl group with the heteroaryl moiety has created varied
effects. Compounds 8g and 8h have shown average activities but the presence of the
benzofuran unit as in 8m demonstrated potent anthelmintic activity.
123

Synthesis of new 4[4-(4-nitrophenoxy)phenyl]-5…
Experimental
Chemistry
The melting points were ascertained on Thomas Hoover apparatus and remain
uncorrected. IR (KBr) spectra were recorded on a Shimadzu 8300 Fourier transform
Fig. 1 ORTEP diagram of 6 at 50 % probability with atom numbering
Fig. 2 Packing diagram of 6 viewed along b-axis
123

B. Namratha et al.
Table 2 Effects of compounds 8 (a–p) and standard drug on Pheretima posthuma
Compound
Paralysis time (min)
25 mg/50 mL
Death time (min)
25 mg/50 mL
50 mg/50 mL
50 mg/50 mL
Control
–
–
–
–
8a
20.04 0.003
10.44 0.006
9.52 0.012
21.03 0.008
11.35 0.006
11.50 0.028
15.42 0.014
17.18 0.020
10.05 0.012
9.57 0.006
9.52 0.010
9.43 0.014
9.50 0.026
12.13 0.015
11.50 0.025
11.55 0.011
9.45 0.024
17.38 0.015
12.06 0.005
6.12 0.014
18.32 0.033
8.49 0.035
9.09 0.015
12.04 0.028
15.10 0.008
7.12 0.023
6.16 0.024
6.15 0.005
6.01 0.020
6.17 0.015
9.24 0.008
9.00 0.010
9.15 0.025
6.05 0.017
25.23 0.037
17.17 0.008
15.05 0.006
27.12 0.014
16.09 0.003
18.18 0.053
21.35 0.006
24.08 0.035
15.045 0.010
15.03 0.010
15.15 0.015
14.16 0.013
15.00 0.010
18.36 0.025
16.20 0.036
18.10 0.036
14.17 0.014
22.23 0.008
19.17 0.042
12.17 0.037
23.16 0.006
12.53 0.018
14.29 0.037
17.19 0.008
20.07 0.014
12.50 0.024
12.16 0.009
12.25 0.020
11.34 0.017
11.55 0.029
14.50 0.010
13.03 0.005
14.25 0.005
11.36 0.023
8b
8c
8d
8e
8f
8g
8h
8i
8j
8k
8l
8m
8n
8o
8p
Nitroscanate
1
infrared spectrometer. H NMR spectra were recorded on a Bruker AM 400 MHz
spectrometer and 13C NMR spectra on a Bruker AM 100 MHz spectrometer using
DMSO-d6 as solvent and TMS as an internal standard (Chemical shift in ppm). ESI
mass spectra were recorded on an Agilent 6520 ESIQTOF instrument at ionization
potential of 110 V and acetonitrile as solvent. Elemental analyses were obtained on
a Vario-EL instrument. Thin layer chromatography (TLC) was conducted on
0.25 mm silica gel plates (60F254, Merck). Visualization is made with ultraviolet
light (UV. R-340). The solvents were evaporated with a Buchi rotary evaporator.
N-[4-(4-Nitrophenoxy)phenyl]acetamide (3)
p-Hydroxy acetanilide 1 (6.00 g,
0.039 mol) was dissolved in DMF (20 mL) under room temperature (r.t.) stirring.
The p-Chloronitrobenzene (6.26 g, 0.039 mol) 2 and anhydrous K2CO3 (2.75 g,
0.0198 mol) were then added to the reaction mixture. This brown reaction mass was
stirred at r.t. for 30 min. The temperature of the reaction mass was slowly raised to
135–140 °C under stirring. This temperature was maintained at 135–140 °C for 1 h
as monitored by TLC (hexane: EtOAc; 1:1). The reaction mass was cooled and the
yellow precipitate that formed was washed with 25 % NaOH solution. The solid
was suck dried upon a hot water wash and crystallized from methanol to afford N-
[4-(4-nitrophenoxy)phenyl]acetamide 3 as yellow solid (10.17 g, 94 %); mp
146–148 °C; Rf 0.81 (hexane: EtOAc; 1:1); IR (KBr): mmax 3291, 1656, 1342,
123

Synthesis of new 4[4-(4-nitrophenoxy)phenyl]-5…
1
1235 cm-1; H NMR (DMSO-d6, 400 MHz,): d = 8.32 (2H, d, ArH, J = 8 Hz),
8.24 (2H, d, ArH, J = 8 Hz), 7.76 (1H, s, NH), 7.64 (2H, d, ArH, J = 8 Hz), 7.36
(2H, d, ArH, J = 8 Hz), 2.20 (3H, s, CH3). 13C NMR (DMSO-d6, 100 MHz,) :
d = 186.7, 162.4, 153.6, 143.5, 128.2, 126.9, 126.1, 121.3, 117.5; Anal. Calcd. for
C14H12N2O4: C, 61.76; H, 4.44; N, 10.29. Found: C, 61.72; H, 4.49; N, 10.27.
4-(4-Nitrophenoxy)aniline (4) Refluxed N-[4-(4-Nitrophenoxy)phenyl]acetamide
3 (8.00 g, 0.029 mol) and Conc. HCl (18 mL) in methanol (16 mL) for 20 min.
Upon completion of reaction as marked by TLC (hexane: EtOAc; 1:1), reaction
mass was cooled down and the yellow solid formed was washed with chilled water.
This solid was crystallized from methanol to yield 4-(4-nitrophenoxy)aniline 4
(6.94 g, 89 %); mp 228–230 °C; Rf 0.76 (hexane: EtOAc; 1:1); IR (KBr): mmax
3120, 1451, 1335, 1244 cm-1; 1H NMR (DMSO-d6, 400 MHz,) : d = 8.26 (2H, d,
ArH, J = 8 Hz), 7.58(2H, d, ArH, J = 8 Hz), 7.25 (2H, d, ArH, J = 8 Hz), 7.14
(2H, d, ArH, J = 8 Hz), 3.71 (2H, bs, NH2); 13C NMR (DMSO-d6, 100 MHz,) :
d = 162.2, 154.6, 143.7, 128.4, 127.3, 126.5, 121.1, 118.1; Anal. Calcd. for
C12H10N2O3: C, 62.60; H, 4.38; N, 12.17. Found: C, 62.55; H, 4.33; N, 12.13.
4-(4-Nitrophenoxy)phenyl thiourea (5) Ammonium thiocyanate (4.27 g, 0.056 mol)
was stirred in water (20 mL) for 15 min at r.t. to get a clear solution. Added 4-(4-
nitrophenoxy)aniline 4 (5.00 g, 0.018 mol) and refluxed at 100 °C for 2 h. As
indicated by TLC (hexane: EtOAc; 1:1), the yellow solid formed was cooled,
filtered off, and washed with hot water. Recrystallized from methanol to offer 4-(4-
nitrophenoxy)phenyl thiourea 5 (4.60 g, 85 %); mp 190–192 °C; Rf 0.4; IR (KBr):
1
mmax 3352, 3280, 1428, 1351, 1328, 1212 cm-1; H NMR (DMSO-d6, 400 MHz,):
d = 9.02 (2H, s, NH), 8.99 (1H, bs, NH), 8.26 (2H, d, ArH, J = 8 Hz), 7.44 (2H, d,
ArH, J = 8 Hz), 7.26 (2H, d, ArH, J = 8 Hz), 7.13 (2H, d, ArH, J = 8 Hz); 13C
NMR (DMSO-d6, 100 MHz,) d = 172.5, 166.4, 153.7, 143.5, 127.7, 127.3, 126.1,
121.9, 117.3; Anal. Calcd. for C13H11N3O3S:C, 53.97; H, 3.83; N, 14.52. Found: C,
53.99; H, 3.80; N, 14.56.
Isothiocyanato-4-(4-nitrophenoxy)benzene (6) Dissolved 4-(4-nitrophenoxy)phenyl
thiourea 5 (4.0 g, 0.013 mol) in xylene (20 mL) and added catalytic amount of
pyridine (0.1 mL), refluxed at 140 °C for 45 min as indicated by TLC (hexane:
EtOAc; 1:1). Gradually cooled the reaction mass and stirred at r.t. for 30 min.
Filtered off the insoluble solid and removed xylene in vacuo. The yellow solid thus
obtained was crystallized from methanol to provide isothiocyanato-4-(4-nitrophe-
noxy)benzene 6 (3.08 g, 82 %); mp 120–122 °C; Rf 0.73 (hexane: EtOAc; 1:1); IR
(KBr): mmax 2115, 1489, 1358, 1238, 842 cm-1
;
1H NMR (DMSO-d6,
400 MHz,):d = 8.26 (2H, d, ArH, J = 8 Hz), 7.51(2H, d, ArH, J = 8 Hz), 7.25
(2H, d, ArH, J = 8 Hz), 7.14 (2H, d, ArH, J = 8 Hz); 13C NMR (DMSO-d6,
100 MHz,): d = 162.4, 153.9, 143.1, 134.1, 128.4, 127.2, 126.3, 121.1, 117.7; Anal.
Calcd. for C13H8N2O3S:C, 57.35; H, 2.96; N, 10.29. Found: C, 57.30; H, 2.99; N,
10.22.
Representative procedure for N-[4-(4-nitrophenoxy)phenyl]-2-(phenylcarbonyl)hy-
drazinecarbothioamide 7 (a–p): Refluxed an equimolar proportion of compound 6 and
123

B. Namratha et al.
aryl carbohydrazide in methanol (10 vol.) for 1 h. Upon cooling, the resulting solid was
filtered off and crystallized from methanol to afford pure N-[4-(4-nitrophenoxy)phenyl]-
2-(phenylcarbonyl)hydrazinecarbothioamide 7 (a–p).
Characterization data of N-[4-(4-nitrophenoxy)phenyl]-2-[(4-methoxyphenyl)-
carbonyl]hydrazinecarbothioamide (7c): Rf 0.21 (toluene: EtOAc; 2:1); IR (KBr):
1
mmax 3021, 1499, 1311, 1240 cm-1; H NMR (DMSO-d6, 400 MHz,): d = 10.41
(1H, s, NH), 9.84(1H, s, NH), 9.73 (1H, s, NH), 8.26 (2H, d, ArH, J = 8 Hz), 7.93
(2H, d, ArH, J = 8.8 Hz), 7.56 (2H, d, ArH, J = 6.4 Hz), 7.11–7.17 (4H, m, ArH),
7.04 (2H, d, ArH, J = 8 Hz), 3.82 (3H, s, CH3); 13C NMR (DMSO-d6, 100 MHz,):
d = 166.0, 163.5, 162.5, 154.8, 151.5, 142.6, 137.1, 130.2, 128.2, 126.6, 125.1,
120.4, 117.6, 113.9, 55.9; Anal. Calcd. for C21H18N4O5S:C, 56.46; H, 4.03; N,
13.17. Found: C, 56.41; H, 4.08; N, 13.14.
4-[4-(4-nitrophenoxy)phenyl]-5-substituted-2H-1,2,4-triazole-3-thiones 8 (a–
p): typical procedure
Conventional method
Refluxed hydrazinecarbothioamide 7 (a–p) (0.3 mmol) with aqueous 5 % NaOH
solution (10 mL) for 1 h; checked the clear solution with TLC (toluene: EtOAc;
2:1). Cooled and acidified with 6 N HCl and crystallized from ethanol.
Grinding method
Ground hydrazinecarbothioamide 7 (a–p) (0.3 mmol) and NaOH pellets (0.6 mmol)
in a porcelain mortar with a pestle for 12 min at r.t. Monitored the pasty reaction
mixture by TLC (toluene: EtOAc; 2:1), poured into ice cold water, and acidified
with 6 N HCl. Filtered off the crude solid and crystallized from ethanol.
4-[4-(4-Nitrophenoxy)phenyl]-5-phenyl-2H-1,2,4-triazole-3-thione (8a) Rf 0.57 (Toluene:
1
EtOAc; 2:1); IR (KBr): mmax 3474, 3142, 1554, 1542, 1358, 1224 cm-1; H NMR
(DMSO-d6, 400 MHz,):d = 14.07 (1H, s, NH), 8.36 (2H, d, ArH, J = 8 Hz), 8.12
(2H, d, ArH, J = 7.5), 7.68 (2H, d, ArH, J = 8 Hz), 7.64 (2H, d, ArH, J = 8 Hz),
7.61 (1H, t, ArH, J = 7.2), 7.56 (2H, t, ArH, J = 7.6), 7.40 (2H, d, ArH, J = 8 Hz);
13C NMR (DMSO-d6, 100 MHz,): d = 167.4, 160.2, 156.7, 149.3, 143.1, 131.6,
130.6, 129.1, 128.6, 128.5, 128.3, 126.9, 122.6, 118.7; Anal. Calcd. for C20H14-
N4O3S:C, 61.53; H, 3.61; N, 14.35. Found: C, 61.57; H, 3.63; N, 14.38.
4-[4-(4-Nitrophenoxy)phenyl]-5-(4-methylphenyl)-2H-1,2,4-triazole-3-thione
(8b) Rf
0.68 (Toluene: EtOAc; 2:1); IR (KBr): mmax 3452, 3052, 1526, 1502, 1326,
1240 cm-1; 1H NMR (DMSO-d6, 400 MHz,): d = 14.12 (1H, s, NH), 8.32 (2H, d,
ArH, J = 8 Hz), 7.61 (2H, d, ArH, J = 8 Hz), 7.32 (2H, d, ArH, J = 8 Hz), 7.25
(2H, d, ArH, J = 8 Hz), 7.21 (2H, d, ArH, J = 8 Hz), 6.98 (2H, d, ArH, J = 8 Hz),
2.68 (3H, s, CH3); 13C NMR (DMSO-d6, 100 MHz,): d = 168.5, 161.4, 160.7,
155.2, 143.4, 138.3, 132.7, 130.2, 129.6, 128.7, 126.1, 122.6, 118.2, 116.8, 21.5;
123

Synthesis of new 4[4-(4-nitrophenoxy)phenyl]-5…
Anal. Calcd. for C21H16N4O3S:C, 62.36; H, 3.99; N, 13.85. Found: C, 62.35; H,
3.91; N, 13.80.
4-[4-(4-Nitrophenoxy)phenyl]-5-(4-methoxyphenyl)-2H-1,2,4-triazole-3-thione (8c) Rf
0.62 (Toluene: EtOAc; 2:1); IR (KBr): mmax 3448, 3247, 1596, 1504,1334,
1249 cm-1; 1H NMR (DMSO-d6, 400 MHz,): d = 14.07 (1H, s, NH), 8.33 (2H, d,
ArH, J = 8 Hz), 7.47 (2H, d, ArH, J = 8 Hz), 7.32 (2H, d, ArH, J = 8 Hz), 7.27
(2H, d, ArH, J = 8 Hz), 7.21 (2H, d, ArH, J = 9.2 Hz), 6.96 (2H, d, ArH,
J = 8 Hz), 3.71(3H, s, OCH3); 13C NMR (DMSO-d6, 100 MHz,): d = 168.8,
162.4, 161.1, 155.3, 150.9, 143.2, 131.9, 131.5, 130.2, 126.8, 121.2, 118.5, 118.3,
114.5, 55.7; Mass spectrum, m/z (Irel, %): 421 [M ? H] ? (19), 374 (100), 344
(24), 283 (3.9), 210 (3.7), 149 (5.1), 77 (2.4). Anal. Calcd. for C21H16N4O4S: C,
59.99; H, 3.84; N, 13.33. Found: C, 59.91; H, 3.87; N, 13.39.
4-[4-(4-Nitrophenoxy)phenyl]-5-(4-nitrophenyl)-2H-1,2,4-triazole-3-thione (8d) Rf 0.61
(Toluene: EtOAc; 2:1); IR (KBr): mmax 3409, 3070, 1596, 1504, 1334, 1242 cm-1
;
1H NMR (DMSO-d6, 400 MHz,): d = 14.21 (1H, s, NH), 8.34 (2H, d, ArH,
J = 8 Hz), 8.16 (2H, d, ArH, J = 8 Hz), 7.54 (2H, d, ArH, J = 8 Hz), 7.42 (2H, d,
ArH, J = 8 Hz), 7.26–6.99 (4H, m, ArH); 13C NMR (DMSO-d6, 100 MHz,):
d = 170.1, 164.8, 155.5, 150.2, 148.6, 145.3, 135.2, 130.7, 130.1, 129.9, 126.4,
123.7, 122.8, 119.9; Anal. Calcd. for C20H13N5O5S: C, 55.17; H, 3.01; N, 16.08.
Found: C, 55.12; H, 3.08; N, 16.03.
4-[4-(4-Nitrophenoxy)phenyl]-5-(4-bromophenyl)-2H-1,2,4-triazole-3-thione (8e) Rf
0.71 (Toluene: EtOAc; 2:1); IR (KBr): mmax 3389, 1589, 1514, 1366, 1241 cm-1; 1H
NMR (DMSO-d6, 400 MHz,): d = 14.14 (1H, s, NH), 8.30 (2H, d, ArH, J = 8 Hz),
7.82 (2H, d, J = 7.5, ArH); 7.70 (2H, d, J = 7.5, ArH), 7.60 (2H, d, ArH,
J = 8 Hz), 7.40 (2H, d, ArH, J = 8 Hz), 7.21 (2H, d, ArH, J = 8 Hz); 13C NMR
(DMSO-d6, 100 MHz,): d = 167.2, 163.6, 161.9, 154.6, 148.3, 143.6, 134.5, 133.6,
132.0, 128.1, 123.5, 122.1, 118.6, 114.2; Anal. Calcd. for C20H13BrN4O3S: C,51.18;
H, 2.79; N, 11.94. Found: C, 51.14; H, 2.75; N, 11.89.
4-[4-(4-Nitrophenoxy)phenyl]-5-(4-chlorophenyl)-2H-1,2,4-triazole-3-thione (8f) Rf
0.73 (Toluene: EtOAc; 2:1); IR (KBr): mmax 3415, 3072, 1591, 1507, 1340, 1251,
1
745 cm-1; H NMR (DMSO-d6, 400 MHz,): d = 14.21 (1H, s, NH), 8.34 (2H, d,
ArH, J = 8 Hz), 7.81 (2H, d, ArH, J = 8 Hz), 7.68 (2H, d, ArH, J = 8 Hz), 7.48 -
7.28 (6H, m, ArH); 13C NMR (DMSO-d6, 100 MHz,): d = 169.6, 162.1, 154.8,
149.7, 143.4, 135.4, 132.6, 131.8, 130.2, 129.9, 127.4, 126.4, 121.5, 116.7; Anal.
Calcd. for C20H13ClN4O3S: C, 56.54; H, 3.08; N, 13.19. Found: C, 56.60; H, 3.06;
N, 13.10.
4-[4-(4-Nitrophenoxy)phenyl]-5-(furan-2-yl)-2H-1,2,4-triazole-3-thione (8g) Rf
0.63 (Toluene: EtOAc; 2:1); IR (KBr): mmax 3438, 3042, 1591, 1504, 1334,
1244 cm-1; 1H NMR (DMSO-d6, 400 MHz,): d = 14.24 (1H, s, NH), 8.26 (2H, d,
ArH, J = 8 Hz), 8.02 (2H, d, H Furan, J = 4.3 Hz), 7.68 (2H, d, ArH, J = 8 Hz),
7.62 (2H, d, ArH, J = 8 Hz), 7.25 7(1H, t, H Furan, J = 4.0 Hz), 7.36 (2H, d, ArH,
J = 8 Hz); 13C NMR (DMSO-d6, 100 MHz,): d = 168.2, 162.5, 158.8, 151.6,
123

B. Namratha et al.
149.5, 143.7, 140.9, 132.3, 130.6, 127.9, 122.8, 117.5, 110.3, 106.1; Anal. Calcd. for
C18H12N4O4S:C, 56.84; H, 3.18; N, 14.73. Found: C, 56.80; H, 3.11; N, 14.75.
4-[4-(4-Nitrophenoxy)phenyl]-5-(thiophen-2-yl)-2H-1,2,4-triazole-3-thione (8h)
Rf
0.63 (Toluene: EtOAc; 2:1); IR (KBr): mmax 3432, 3241, 1573, 1512, 1339,
1245 cm-1; 1H NMR (DMSO-d6, 400 MHz,): d = 14.18 (1H, s, NH), 8.14 (2H, d,
ArH, J = 8 Hz), 7.88 (2H, d, H Thiophene, J = 4.8 Hz), 7.76 (2H, d, ArH,
J = 8 Hz), 7.68 (2H, d, ArH, J = 8 Hz), 7.46 (2H, d, ArH, J = 8 Hz), 7.25 (1H, t,
H Thiophene, J = 4.0 Hz); 13C NMR (DMSO-d6, 100 MHz,): d = 169.1, 162.6,
158.2, 149.9, 144.7, 133.3, 130.4, 129.3, 126.6, 126.0, 124.3, 122.8, 118.3, 117.6;
Anal. Calcd. for C18H12N4O3S2: C, 54.53; H, 3.05; N, 14.13. Found: C, 54.59; H,
3.01; N, 14.16.
4-[4-(4-Nitrophenoxy)phenyl]-5-(3-methoxyphenyl)-2H-1,2,4-triazole-3-thione(8i)
Rf 0.61 (Toluene: EtOAc; 2:1); IR (KBr): mmax 3436, 3240, 1588, 1503, 1368,
1226 cm-1; 1H NMR (DMSO-d6, 400 MHz,): d = 14.03 (1H, s, NH), 8.36 (2H, d,
ArH, J = 8 Hz), 7.44 (2H, d, ArH, J = 8 Hz), 7.33 (2H, d, ArH, J = 8 Hz), 7.26
(2H, d, ArH, J = 8 Hz), 7.11-6.83 (4H, m, ArH), 3.75(3H, s, OCH3); 13C NMR
(DMSO-d6, 100 MHz,): d = 167.9, 162.1, 160.9, 155.3, 150.6, 145.7, 131.8, 131.5,
130.5, 126.9, 122.4, 119.1, 118.2, 114.5, 53.2; Anal. Calcd. for C21H16N4O4S: C,
59.99; H, 3.84; N, 13.33. Found: C, 59.90; H, 3.86; N, 13.37.
4-[4-(4-Nitrophenoxy)phenyl]-5-(2,4-dimethoxyphenyl)-2H-1,2,4-triazole-3-thione
(8j) Rf 0.62 (Toluene: EtOAc; 2:1); IR (KBr): mmax 3413, 3245, 1587, 1513, 1345,
1268 cm-1; 1H NMR (DMSO-d6, 400 MHz,): d = 14.01 (1H, s, NH), 8.15 (2H, d,
ArH, J = 8 Hz), 7.25 (2H, d, ArH, J = 8 Hz), 7.16 (2H, d, ArH, J = 8 Hz), 7.08
(2H, d, ArH, J = 8 Hz), 6.88–6.80 (3H, m, ArH), 3.02 (6H, s, OCH3); 13C NMR
(DMSO-d6, 100 MHz,): d = 164.8, 161.4, 160.9, 159.0, 154.2, 150.6, 147.9, 130.7,
127.6, 126.8, 124.0, 123.7, 119.3, 116.1, 115.1, 114.8, 54.7; Anal. Calcd. for
C22H18N4O5S: C, 58.66; H, 4.03; N, 12.44. Found: C, 58.60; H, 4.05; N, 12.49.
4-[4-(4-Nitrophenoxy)phenyl]-5-(3,4-dimethoxyphenyl)-2H-1,2,4-triazole-3-thione
(8k) Rf 0.62 (Toluene: EtOAc; 2:1); IR (KBr): mmax 3455, 3211, 1579, 1498,
1
1328, 1214 cm-1; H NMR (DMSO-d6, 400 MHz,): d = 14.01 (1H, s, NH), 8.10
(2H, d, ArH, J = 8 Hz), 7.61 (2H, d, ArH, J = 8 Hz), 7.18 (2H, d, ArH, J = 8 Hz),
6.88 (2H, d, ArH, J = 8 Hz), 6.73–6.68 (3H, m, ArH), 3.11 (6H, s, OCH3); 13C
NMR (DMSO-d6, 100 MHz,): d = 165.2, 162.4, 157.9, 153.3, 150.2, 146.2, 145.5,
144.5, 133.7, 127.6, 125.5, 121.8, 119.1, 114.8, 113.6, 113.2, 51.1; Anal. Calcd. for
C22H18N4O5S: C, 58.66; H, 4.03; N, 12.44. Found: C, 58.62; H, 4.09; N, 12.41.
4-[4-(4-Nitrophenoxy)phenyl]-5-(4-fluorophenyl)-2H-1,2,4-triazole-3-thione (8l)
Rf 0.69 (toluene: EtOAc; 2:1); IR (KBr): mmax 3448, 3078, 1596, 1504, 1342,
1242 cm-1; 1H NMR (DMSO-d6, 400 MHz,): d = 14.23 (1H, s, NH), 8.33 (2H, d,
ArH, J = 8 Hz), 7.65 (2H, d, ArH, J = 8 Hz), 7.49 (2H, d, ArH, J = 8 Hz),
7.33–7.20 (6H, m, ArH); 13C NMR (DMSO-d6, 100 MHz,): d = 169.4, 162.6,
154.8, 149.9, 143.1, 132.9, 132.0, 131.3, 130.1, 126.9, 126.6, 123.4, 121.1, 118.4;
123

Synthesis of new 4[4-(4-nitrophenoxy)phenyl]-5…
Anal. Calcd. for C20H13FN4O3S: C, 58.82; H, 3.21; N, 13.72. Found: C, 58.86; H,
3.21; N, 13.79.
4-[4-(4-Nitrophenoxy)phenyl]-5-(benzofuran-2-yl)-2H-1,2,4-triazole-3-thione (8m)
Rf
0.66 (Toluene: EtOAc; 2:1); IR (KBr): mmax 3481, 3042, 1565, 1492, 1313,
1
1269 cm-1; H NMR (DMSO-d6, 400 MHz,): d = 14.20 (1H, s, NH), 8.24(2H, d,
ArH, J = 8 Hz), 7.81 (1H, d, H Benzofuran, J = 7.6 Hz); 7.79 (1H, s, H
Benzofuran), 7.75 (1H, d, H Benzofuran, J = 8.0 Hz), 7.66 (2H, d, ArH, J = 8 Hz),
7.60 (2H, d, ArH, J = 8 Hz), 7.55–7.51 (1H, t, H Benzofuran, J = 7.6 Hz),
7.41–7.37 (1H, t, H Benzofuran, J = 7.6 Hz), 7.32 (2H, d, ArH, J = 8 Hz); 13C
NMR (DMSO-d6, 100 MHz,): d = 167.9, 161.5, 156.0, 155.7, 149.1, 143.2, 134.6,
130.9, 127.9, 127.8, 127.3, 126.9, 125.4, 124.7, 123.2, 117.3, 113.5, 111.7; Anal.
Calcd. for C22H14N4O4S: C, 61.39; H, 3.28; N, 13.02. Found: C, 61.38; H, 3.24; N,
13.05.
4-[4-(4-Nitrophenoxy)phenyl]-5-(3-bromophenyl)-2H-1,2,4-triazole-3-thione (8n)
Rf
0.71 (Toluene: EtOAc; 2:1); IR (KBr): mmax 3476, 1586, 1504, 1342, 1242,
1
667 cm-1; H NMR (DMSO-d6, 400 MHz,): d = 14.26 (1H, s, NH), 8.64 (2H, d,
ArH, J = 8 Hz), 7.91(2H, d, ArH, J = 8 Hz), 7.68 (2H, d, ArH, J = 8 Hz), 7.48
(2H, d, ArH, J = 8 Hz), 7.18-7.10 (4H, m, ArH); 13C NMR (DMSO-d6, 100 MHz,):
d = 168.1, 164.8, 154.8, 148.3, 146.1, 140.2, 136.7, 132.9, 130.2, 127.6, 126.6,
123.9, 120.9, 114.8, 114.1, 112.2; Anal. Calcd. for C20H13BrN4O3S: C, 51.18; H,
2.79; N, 11.94. Found: C, 51.19; H, 2.70; N, 11.92.
4-[4-(4-Nitrophenoxy)phenyl]-5-(3-chlorophenyl)-2H-1,2,4-triazole-3-thione (8o)
Rf
0.73 (Toluene: EtOAc; 2:1); IR (KBr): mmax 3428, 3065, 1587, 1413, 1244,
1
781 cm-1; H NMR (DMSO-d6, 400 MHz,): d = 14.23 (1H, s, NH), 8.34(2H, d,
ArH, J = 8 Hz), 7.64 (2H, d, ArH, J = 8 Hz), 7.50 (2H, d, ArH, J = 8 Hz),
7.31(2H, d, ArH, J = 8 Hz), 7.29-7.20 (4H, m, ArH); 13C NMR (DMSO-d6,
100 MHz,): d = 169.4, 161.8, 159.7, 150.3, 143.4, 140.9, 139.0, 135.6, 130.2,
128.7, 128.5,126.9, 126.7, 124.6, 121.5, 117.0; Anal. Calcd. for C20H13ClN4O3S: C,
56.54; H, 3.08; N, 13.19. Found: C, 56.56; H, 3.10; N, 13.13.
4-[4-(4-Nitrophenoxy)phenyl]-5-(2,4-dichlorophenyl)-2H-1,2,4-triazole-3-thione (8p)
Rf 0.73 (Toluene: EtOAc; 2:1); IR (KBr): mmax 3430, 3012, 1515, 1489, 1246,
1
730 cm-1; H NMR (DMSO-d6, 400 MHz,): d = 14.19 (1H, s, NH), 8.31 (2H, d,
ArH, J = 8 Hz), 7.72(2H, d, ArH, J = 8 Hz), 7.58 (2H, d, ArH, J = 8 Hz), 7.39
(2H, d, ArH, J = 8 Hz), 7.22-7.14 (3H, m, ArH); 13C NMR (DMSO-d6, 100 MHz,):
d = 167.4, 161.4, 154.9, 146.1, 143.2, 136.3, 135.9, 135.0, 134.0, 129.7, 129.5,
128.8, 128.6, 126.9, 123.5, 116.6; Anal. Calcd. for C20H12Cl2N4O3S: C, 52.30; H,
2.63; N, 12.20. Found: C, 52.28; H, 2.60; N, 12.26.
X-ray data collection
Suitable crystals are obtained by dissolving the title compound in ether followed by
slow evaporation. A specimen of C13H8N2O3S 6 is used for the X-ray crystallo-
graphic analysis. The X-ray intensity data are measured. The total exposure time is
123

B. Namratha et al.
3.96 h. The frames are integrated with the Bruker SAINT software package using a
narrow-frame algorithm. The structure is solved and refined using the Bruker
SHELXTL Software Package, using the space group P -1, with Z = 2 for the
formula unit, C13H8N2O3S. This structure is deposited with the Cambridge
Structural Data Base having CCDC NO. 1006102 as a supplementary publication.
Biology
Anthelmintic activity
We have adopted the anthelmintic assay as per the method already illustrated [24,
25] with the necessary modifications. Indian earthworm Pheretima posthuma is used
for this study due to its anatomical and physiological resemblance with the
roundworms. The earthworms of 5–6 cm length and 0.3–0.4 cm width are used for
all experimental protocols. The worms are divided into ten sets with one earthworm
per Petri dish at r.t. Nitroscanate solution is used as a standard drug and saline water
as control. The test compounds 8(a–p) and Nitroscanate are dissolved in a minimum
quantity of dimethyl sulfoxide (DMSO) in a 50 mL standard flask and made up to
the mark with saline water. All the test solutions and standard solution are prepared
freshly before beginning an experiment. Then 50 mL of test solution is poured into
each Petri dish. Each experiment is repeated thrice and the results are expressed as
mean S.E.M [26]. We have observed the time taken for paralysis and death of
individual worms (Table 2). The stage of paralysis is the time when no movement
can be observed while the worms are shaken vigorously. Death is concluded to have
occurred when the worms are observed to have lost their motility even when poked
with a needle.
Conclusion
We report the interesting compounds, 4-[4-(4-nitrophenoxy)phenyl]-5-substituted-
2H-1,2,4-triazole-3-thiones. The crystal structure of the key intermediate, isothio-
cyanato-4-(4-nitrophenoxy)benzene 6 has been presented. All the target compounds
are characterized by analytical techniques. Target compounds 8(a–p) are synthe-
sized by solid-phase grinding synthesis as well as by the conventional method.
Grinding synthesis has offered comparable yields in a shorter reaction time at room
temperature. Preliminary structure–activity relationship studies have helped to
highlight the effectiveness of 4-[4-(4-nitrophenoxy)phenyl]-5-substituted-2H-1,2,4-
triazole-3-thiones as anthelmintics in vitro compared to nitroscanate.
Acknowledgements We gratefully acknowledge the laboratory facilities from Manipal Institute of
Technology (MIT), Manipal and XRD from Karnatak University, Dharwad. One of the authors
(Namratha) thanks the Manipal University for a fellowship under a MU-structured PhD programme.
123

Synthesis of new 4[4-(4-nitrophenoxy)phenyl]-5…
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