Mercury(II) chloride-mediated desulphurization of amidinothioureas: Synthesis and antimicrobial activity of 3-amino-1,2,4-triazole derivatives

Article abstract of DOI:10.1002/jhet.1890

The synthesis of 3-amino-1,2,4-triazole via mercury(II) chloride-mediated cyclization of amidinothiourea is described. This procedure offers a general and efficient route to synthesize the title compound by 3 + 2 annulation reaction. On the basis of the l

Full text of DOI:10.1002/jhet.1890

Month 2014
Mercury(II) Chloride-Mediated Desulphurization of Amidinothioureas:
Synthesis and Antimicrobial Activity of 3-Amino-1,2,4-triazole Derivatives
a
b
c
d
d
*
Swapnil G. Yerande, Chetna D. Baviskar, Kiran M. Newase, Wei Wang, Kan Wang,
and Alexander Dömlingd,e
aAcoris Research Ltd, 3A International Biotech Park, Hinjewadi, Pune 411 057
bDepartment of Pharmaceutical Chemistry, Progressive Education Society’s, Modern College of Pharmacy, Sector 21,
Yamunanagar, Nigdi, Pune, 411044 (M.S.), India
cBanasthali Vidyapith, P.O. Banasthali Vidyapith, Rajasthan 304022
dDepartment of Pharmaceutical Sciences, University of Pittsburgh, PA 15261, USA
eDept. of Pharm. Chemistry (PG), Chair of Drug Design, University of Groningen Antonius Deusinglaan 1, 9713 AV
Groningen, The Netherlands
*
E-mail: swapnil_yerande@acorisresearch.com
Received June 29, 2012
DOI 10.1002/jhet.1890
Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com).
The synthesis of 3-amino-1,2,4-triazole via mercury(II) chloride-mediated cyclization of amidinothiourea
is described. This procedure offers a general and efficient route to synthesize the title compound by 3 + 2
annulation reaction. On the basis of the literature precedence, the mechanism for the formation of
3-amino-1,2,4-triazole is proposed. When the synthesized compounds were tested for their antimicrobial
activity showed promising inhibition against tested microbes.
J. Heterocyclic Chem., 00, 00 (2014).
INTRODUCTION
heterocycles [9–11]. We hypothesized that amidinothiourea
will react with binucleophilic phenyl hydrazine in the presence
of strong thiophile mercury(II) chloride and will furnish the
targeted 3-amino-1,2,4-triazole derivatives.
Aminotriazole have established unique place in the
world of heterocyclic chemistry by acting as antiviral
agents [1], CCK-A agonists [2], urinary tract antibacterial
agents [3], and antiasthmatic agents [4].
RESULT AND DISCUSSION
Literature search revealed that 3-amino-1,2,4-triazole are
prepared on solid support either by reaction of hydrazine with
immobilized N-acyl-1H-benzotriazole-1-carboximidamides
[5a], or by reaction of hydrazine with resin-bound S-
methyl-N-acylisothioureas [5b]. Various methods have been
developed for the solution phase synthesis of 3-amino-1,2,
4-triazole. These include the reaction of amidrazones with
carbodiimides [6a, 6b], cyclization of aminoguanidines [7],
and reaction of alkylhydrazine with N-acyl-N0,N0-dialkyl-S-
methylisothiourea [8].
This work represents our concise strategy for the prepara-
tion of 3-amino-1,2,4-triazole scaffold using amidi-
nothiourea as a key starting material. Amidinothiourea is a
versatile intermediate having two strategically placed leaving
groups and has been used for the synthesis of different
Our investigation began with the synthesis of amidi-
nothioureas (Scheme 1). The addition reaction of N,
N-diethyl amidine with arylisothiocynate in acetone gave
amidinothioureas. These amidinothioureas (1 equiv) were
treated with phenyl hydrazine (1 equiv); in the presence of
triethylamine (2equiv), mercury(II) chloride (1.2 equiv)
allowed the formation of the target compounds at RT. Here,
the desulfurization of amidinothiourea was monitored
visually on the basis of the formation of black precipitate
of mercury sulfide. Desired 3-amino-1,2,4-triazoles were
obtained after column chromatographic purification in
moderate yields. The results are summarized in Scheme 1.
All the target compounds synthesized were characterized
by spectroscopic methods. For example, 1,5-diphenyl-N-p-
© 2014 HeteroCorporation

S. G. Yerande, C. D. Baviskar, K. M. Newase, W. Wang, K. Wang, and A. Dömling
Vol 000
Scheme 1
tolyl-1H-1,2,4-triazol-3-amine (4e) gave IR absorption
bands at 3282 (—NH, broad), 3199 (aromatic C—H
stretching), 1608 (C═N stretching), and 1551 (aromatic
1,2,4-triazole derivatives (Scheme 2), both of which should
involve an initial activated species 5 formed by complexion
of amidinothiourea with Hg2+. In the absence of HgCl2,
desired product did not form. In pathway A, amidinothiourea
(2) may undergo nucleophilic attack from phenyl hydrazine
in the presence of triethylamine to form intermediate 6,
followed by elimination of diethylamine to afford target
product 4. Alternatively, in pathway B, compound 5 under-
goes desulfurization to form a carbodiimide intermediate 7,
which is trapped by phenyl hydrazine in the presence of
triethylamine and subsequent elimination of the diethylamine
by nucleophilic nitrogen, will give the target product 4.
All the newly synthesized 3-amino-1,2,4 triazoles were
tested for their antimicrobial activity [14–16]. The antibacte-
rial activity was compared with standard drug azithromycin
(Fig. 1), and antifungal activity was compared with standard
1
C═C stretching). H-NMR spectrum showed a singlet at
d 2.35 ppm for three protons confirmed the presence of
CH3 group, singlet at d 6.8 ppm for NH proton, and multi-
plet in the region of d 7.1–7.7 ppm corresponding to 14 ar-
omatic protons were in accordance with the structure of
target compound. 13C-NMR gave characteristic signal at
20.67 for methyl carbon, signals at 152.29 and 160.12
corresponding to carbons of 1,2,4 triazole ring. The HRMS
spectrum revealed actual mass 327.1579 corresponding to
molecular formula of C21H18N4 (M + 1)+.
On the basis of the literature [12,13] precedent for the
formation of Guanidine from thiourea, two mechanistic
pathways may be postulated for the formation of 3-amino-
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2014
Mercury(II) Chloride-Mediated Desulphurization of Amidinothioureas: Synthesis and
Antimicrobial Activity of 3-Amino-1,2,4-triazole Derivatives
Scheme 2. Plausible mechanism for the formation of 3-amino-1,2,4-triazole.
Figure 1. Antibacterial activity of 3-amino-1,2,4-triazole. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
drug fluconazole (Fig. 2). In all the compounds tested from
3-amino-1,2,4-triazole series, the results revealed that com-
pound 4j containing trityl group was most active
compound against all the tested microorganisms strains.
When compared with standard antifungal drug fluconazole,
4j showed better antifungal activity. Although compound
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

S. G. Yerande, C. D. Baviskar, K. M. Newase, W. Wang, K. Wang, and A. Dömling
Vol 000
Figure 2. Antifungal activity of 3-amino-1,2,4-triazole. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
chromatography was performed using SiO2 60 (particle size
0.040–0.055 mm, 230–400 mesh). Proton and carbon NMR
spectra were obtained on Bruker Avance 600 MHz NMR
41–4f did not show antifungal activity, all these tested
compounds showed moderate antibacterial activity.
spectrometer. Chemical shifts are reported as d values in parts
per million as referenced to residual solvent. 1H-NMR spectra
are tabulated as follows: chemical shift, multiplicity (s = singlet
CONCLUSION
In conclusion, we have described synthesis of 3-amino-
1,2,4-triazole derivatives via mercury(II) chloride-mediated
3 + 2 annulation of amidinothioureas with binucleophilic
phenyl hydrazine. The reaction was fast, and in most cases,
the 3-amino-1,2,4-triazole derivatives were isolated in
synthetically useful yields. All the synthesized compounds
showed moderate antimicrobial activity. Compound 4j
showed antifungal activity greater than standard drug
fluconazole. This approach is compatible with a wide range
of functional groups, which is a valuable advantage over
previously reported methods. Moreover, it can be imagined
that the trityl-protected derivative (4j) after deprotection will
furnish 3-amino-1,2,4-triazole derivative that can serve as a
starting material for the synthesis of various 3-acyl or 3-alkyl-
amino-1,2,4-triazole analogs. Availability of a diverse
collection of isothiocynates and amidines makes this route
suitable for the preparation of large numbers of 3-amino-
1,2,4-triazole derivatives.
and m = multiplet). High resolution mass spectra were obtained
at the University of Pittsburgh Mass Spectrometry facility.
Antimicrobial activity was carried out as per the reported
protocol [14–16].
General procedure for the synthesis of 3-amino-1,2,4-
oxadiazole (4). Amidinothiourea (3) (1.0 equiv) was taken in
DMF in round-bottomed flask. To it, phenyl hydrazine
(1.1 equiv) was added followed by triethylamine (2.2 equiv).
The reaction mixture was then cooled between 0 and 5ꢀC, and
mercury(II) chloride (1.1 equiv) was added to it. Reaction
mixture was maintained at same temperature for 20 min. The
reaction was then monitored by TLC, and after completion,
precipitate of mercury sulfite was filtered through celite bed.
The filtrate was then poured in cold water and stirred for
10 min. The precipitated product was filtered and was purified
by column chromatography using suitable combination of
hexane and ethyl acetate.
CAUTION: HgCl2 is very toxic, and both the reagent and
the crude product must be manipulated carefully. Although the
by-product of the reaction, mercury sulfite, is a highly water
insoluble, the solid residue retained in the short celite column must
be disposed of in a suitable flask. The appropriate disposal of celite
and SiO2 used in the purification process must also be considered.
EXPERIMENTAL
Characterization.
N,1,5-Triphenyl-1H-1,2,4-triazol-3-
General methods. All reactions were under air atmosphere.
All other reagents and solvents are purchased from Avra
chemicals Hyderabad, India and used without further
purification. TLC was performed on precoated aluminum plate
with silica gel 60 F254 available from Merck. Flash column
amine (4a). White solid, mp 198–200ꢀC, Rf: 0.5 (hexane:ethyl
acetate 1.5:0.5), IR (KBr, cmꢁ1 : 3287.07, 3054.69, 1618.95,
1572.66, 1505.18, 1349.28), 1H-NMR (600 MHz, CDCl3) d
(ppm): 6.92 (s, 1H, —NH—); 6.9–7.6 (m, 15H, ArH). 13C-NMR
Journal of Heterocyclic Chemistry
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Month 2014
Mercury(II) Chloride-Mediated Desulphurization of Amidinothioureas: Synthesis and
Antimicrobial Activity of 3-Amino-1,2,4-triazole Derivatives
(150MHz, CDCl3) d (ppm): 116.38, 120.56, 125.27, 127.90,
128.33, 128.59, 128.90, 129.05, 130.04, 138.30, 140.71, 152.34,
159.92. HRMS (TOFMS ES+) Calcd for C20H16N4 (M+ 1)+
313.1453, found 313.1441.
129.23, 129.96, 130.57, 138.38, 146.78, 152.26, 159.90. HRMS
(TOFMS ES+) Calcd for C21H18N4O (M + 1)+ 343.1559, found
343.1525.
N-(4-Bromophenyl)-1,5-diphenyl-1H-1,2,4-triazol-3-amine
5-Methyl-N,1-diphenyl-1H-1,2,4-triazol-3-amine (4b). White
(4i).
White solid, mp 256–258ꢀC, Rf: 0.5 (hexane:ethyl acetate
solid, mp 168–170ꢀC, Rf: 0.3 (hexane:ethyl acetate 1.5:0.5),
1.5:1), IR (KBr, cmꢁ1: 3276.47, 3198.73, 2362.37, 1882.18,
IR (KBr, cmꢁ1
:
3256.22, 3091.33, 1598.70, 1557.24,
1608.34, 1287.11.), H-NMR (600 MHz, CDCl3) d (ppm): 6.8 (s,
1
1494.56,1340.28.), 1H-NMR (600 MHz, CDCl3) d (ppm): 2.52 (s,
3H, —CH3); 6.92 (s, 1H, —NH—); 6.93–7.54 (m, 10H, ArH).
13C-NMR (150 MHz, CDCl3) d (ppm): 13.0, 117.0, 120.0, 123,
129, 130.1, 139.1, 140.1, 156, 160. GC–MS (M+) 250.
1H, —NH—); 7.3–7.7 (m, 13H, ArH). 13C-NMR (150MHz,
CDCl3) d (ppm): 112.65, 118.02, 125.26, 128.84, 125.26, 128.49,
128.61, 128.84, 129.33, 130.13, 131.88, 139.78. HRMS (TOFMS
ES+) Calcd for C20H15BrN4 (M+ 1)+ 391.0558, found 391.0587.
1,5-Diphenyl-N-trityl-1H-1,2,4-triazol-3-amine (4j). White
solid, mp 160–162ꢀC, Rf: 0.6 (hexane:ethyl acetate 1.5:1), IR
(KBr, cmꢁ1 : 3245.61, 3061.44, 2931.27, 1541.81, 1174.44,
772.351.), 1H-NMR (600 MHz, CDCl3) d (ppm): 2.1 (s, 3H, —CH3);
5.6 (s, 1H, —NH—); 7.1–7.7 (m, 21H, ArH). 13C-NMR
(150 MHz, CDCl3) d (ppm): 14.32, 72.07, 123.96, 127.01,
127.93, 128.08, 128.77, 129.98, 136.81, 145.01, 153.03,
158.63. HRMS (TOFMS ES+) Calcd for C28H24N4 (M + Na)+
439.1899, found 439.1934.
N-(4-Chlorophenyl)-1,5-diphenyl-1H-1,2,4-triazol-3-amine
(4c).
White solid, mp 240–242ꢀC, Rf: 0.5 (hexane:ethyl acetate
1.5:1), IR (KBr, cmꢁ1: 3276.47, 3199.33, 3070.12, 1887.97, 1603.52,
1
1551.45.), H-NMR (600 MHz, CDCl3) d (ppm): 6.92 (s, 1H, —
NH—); 7.23–7.50 (m, 14H, ArH). 13C-NMR (150 MHz, CDCl3) d
(ppm): 117.59, 125.26, 127.74, 128.48, 128.62, 128.86, 128.94,
129.32, 130.14, 138.19, 139.34, 152.46, 159.62. HRMS (TOFMS ES
+) Calcd for C20H15ClN4 (M + 1)+ 347.1063, found 347.1074.
N-(4-Chlorophenyl)-5-methyl-1-phenyl-1H-1,2,4-triazol-3-
amine (4d).
White solid, mp 190–192ꢀC, Rf: 0.4 (hexane:ethyl
acetate 1.5:1), IR (KBr, cmꢁ1 : 3266.82, 2931.27, 1557.24,
1334.50, 1097.30, 823.455.), 1H-NMR (600 MHz, CDCl3) d
(ppm): 2.50 (s, 3H, —CH3); 6.85 (s, 1H, —NH—); 7.24–7.54 (m,
9H, ArH). 13C-NMR (150MHz, CDCl3) d (ppm): 13.30, 117.56,
124.28, 125.20, 128.25, 128.95, 129.39, 137.53, 139.40, 150.88,
159.20. HRMS (TOFMS ES+) Calcd for C15H13ClN4 (M+ 1)+
285.0907, found 285.0899.
1,5-Diphenyl-N-p-tolyl-1H-1,2,4-triazol-3-amine (4e). White
solid, mp 225–228ꢀC, Rf: 0.6 (hexane:ethyl acetate 1.5:1), IR
(KBr, cmꢁ1: 3282.25, 3199.33, 3075.90, 1960.29, 1882.18, 1551.45.),
1H-NMR (600 MHz, CDCl3) d (ppm): 2.35 (s, 3H, —CH3);
6.8 (s, 1H, —NH—); 7.1–7.7 (m, 14H, ArH). 13C-NMR
(150 MHz, CDCl3) d (ppm): 20.67, 117.51, 125.25, 127.98,
128.56, 128.88, 129.24, 129.54, 129.92, 129.98, 137.53,
138.34, 152.29, 160.12. HRMS (TOFMS ES+) Calcd for
C21H18N4 (M + 1)+ 327.1610, found 327.1579.
1,5-Diphenyl-N-o-tolyl-1H-1,2,4-triazol-3-amine (4f). White
solid, mp 138–140ꢀC, Rf: 0.46 (hexane:ethyl acetate 1.5:1), IR
(KBr, cmꢁ1 : 3437.49, 3281.29, 3062.41, 1556.27, 1447.31,
1321.96.), 1H-NMR (600 MHz, CDCl3) d (ppm): 2.4 (s, 3H, —CH3);
6.6 (s, 1H, —NH—); 6.9–8.4 (m, 14H, ArH) 13C-NMR
(150 MHz, CDCl3) d (ppm): 17.85, 116.31, 120.65, 123.61,
125.25, 127.17, 127.92, 128.83, 129.27, 128.85, 129.27, 130.03,
130.23, 138.21, 138.95, 152.37, 160.02. HRMS (TOFMS ES+)
Calcd for C21H18N4 (M + 1)+ 327.1610, found 327.1612.
N-(4-Methoxyphenyl)-1,5-diphenyl-1H-1,2,4-triazol-3-amine
(4g). White solid, mp 232–234ꢀC, Rf: 0.4 (hexane:ethyl acetate
1.5:1), IR (KBr, cmꢁ1 : 3282.25, 2997.82, 1614.13, 1237.11.),
1H-NMR (600 MHz, CDCl3) d (ppm): 3.8 (s, 3H, —OCH3); 6.9
(s, 1H, —NH—); 7.2–7.7 (m, 14H, ArH). 13C-NMR (150 MHz,
CDCl3) d (ppm): 55.62, 114.40, 118.02, 125.24, 127.99, 128.24,
128.55, 128.88, 129.23, 129.97, 134.43, 138.34, 152.33, 153.98,
160.36. HRMS (TOFMS ES+) Calcd for C21H18N4O (M+ 1)+
343.1559, found 343.1527.
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N-(2-Methoxyphenyl)-1,5-diphenyl-1H-1,2,4-triazol-3-amine
(4h). White solid, mp 130–132ꢀC, Rf: 0.5 (hexane:ethyl acetate
1.5:1), IR (KBr, cmꢁ1 : 3421.10, 3390.24, 3054.69, 2925.48,
1887.97, 1603.52, 1241.93.), 1H-NMR (600 MHz, CDCl3) d
(ppm): 3.95 (s, 3H, —OCH3); 7.0 (s, 1H, —NH—); 6.9–7.7 (m,
14H, ArH). 13C-NMR (150 MHz, CDCl3) d (ppm): 55.71, 109.70,
115.75, 119.90, 121.22, 125.23, 128.03, 128.24, 128.54, 128.87,
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet