Convenient synthesis of 4H-1,2,4-triazole-3-thiols using di-2-pyridylthionocarbonate

Article abstract of DOI:10.1016/j.tetlet.2007.09.094

We report here the convenient synthesis of 4H-1,2,4-triazole-3-thiols using di-2-pyridyl-thionocarbonate as the thiocarbonyl transfer reagent. This method is suitable for microplate parallel synthesis and produces samples in screening-ready condition. It

Full text of DOI:10.1016/j.tetlet.2007.09.094

Available online at www.sciencedirect.com
Tetrahedron Letters 48 (2007) 8157–8162
Convenient synthesis of 4H-1,2,4-triazole-3-thiols using
di-2-pyridylthionocarbonate
Rebecca F. Deprez-Poulain,* Julie Charton, Virginie Leroux and Benoit P. Deprez
INSERM U761 Biostructures and Drug Discovery, Lille F-59006, France
Faculte´ de Pharmacie, Universite´ Lille 2, Lille F-59006, France
Institut Pasteur de Lille, Lille F-59000, France
Received 14 July 2007; revised 11 September 2007; accepted 14 September 2007
Available online 20 September 2007
Abstract—We report here the convenient synthesis of 4H-1,2,4-triazole-3-thiols using di-2-pyridyl-thionocarbonate as the thiocar-
bonyl transfer reagent. This method is suitable for microplate parallel synthesis and produces samples in screening-ready condition.
It uses two large sets of building-blocks: amines and hydrazides.
Ó 2007 Elsevier Ltd. All rights reserved.
Five-membered rings are highly prevalent in the
pharmacopoeia and more generally in collections of bio-
active compounds. Since long we have been interested in
the parallel synthesis of five-membered heterocycles.1,2
Not only is ring closure usually entropically favoured,
but also they are compact scaffold for the distribution
of pharmacophore elements in space. Amongst five-
membered rings, 1,2,4-triazole-3-thiols and derivatives
(series A–E in Fig. 1) appear pharmacologically relevant
since they are found in many bioactive compounds.
Matrix-MetalloProteinases (MMPs) and A Disintegrin
and Metallo Domain (ADAMs) enzymes.6 S-alkylated
derivatives have been shown to antagonize Angiotensin
II receptors (AT-1) or more recently to inhibit cyclo-
oxygenase-2 (COX-2).7,8 Other compounds in these
series display anti-bacterial properties.9,10
More generally a survey in MDDR database11 retrieves
245 molecules in series A–E, among which 63 are free-
thiol derivatives (series A and B).
For example, D and E derivatives have been developed
as memory enhancers, or sphingomyelinase inhibitors.3,4
Recently CXCR2 antagonists displaying a triazolethiol
moiety have been described.5 Such heterocycles have
also been developed as inhibitors of the large family of
Suritozole and mitratapide (Fig. 2)12 are two examples
of bioactive 1,2,4-triazole-3-thiols.
Among the compounds presented in Figure 1, we were
interested in type B compounds because they display
structures complementary to those of linear carbox-
amides. Indeed, whereas the energetically favoured con-
formation of amide is the trans conformation, the
substituents brought by the parent acid and amine in
4H-1,2,4-triazole-3-thiols are in a cis configuration rela-
R 3
S
S
R
R
D: R1, R2, R4 = not H
E: R2 = H
A: R2,R3 =H
B: R3 =H
2 N
2 N
N R
N
4
N
N
R
R
C: R1, R2, R3 =not H
1
1
N
N
Figure 1. Markush formulas of 1,2,4-triazole-3-thiols derivatives.
O
N
N
O
S
N
O
S
N
N
Keywords: Triazol-3-thiols; Parallel synthesis; DPT; Solubility;
cis-Amides.
N
O
1
2
F
*
Cl
Corresponding author. Address: INSERM U761 Biostructures and
N
N
Drug Discovery, 3 rue du Pr. Laguesse, Lille F-59006, France. Tel.:
+33 320 964 948; fax: +33 320 964 709; e-mail: rebecca.deprez@
univ-lille2.fr
N
Figure 2. Structures of suritozole (1) and mitratapide (2).
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.09.094

8158
R. F. Deprez-Poulain et al. / Tetrahedron Letters 48 (2007) 8157–8162
tive to the NC bond. Thus from a diversity viewpoint,
using the same parent reagents, series B populates a
region of space complementary to that of amides (Fig. 3).
The synthesis of 4H-1,2,4-triazole-3-thiols proceeds
in two steps.26 As shown in Scheme 1, the first step
consists in the in situ formation of the isothiocyanate
from the amine followed by reaction with the required
hydrazide.27
4H-1,2,4-Triazole-3-thiols can be prepared from two
reagent sets and in the end display three pharmacophore
motives: two from the reagents and a thiol function.
The general synthesis procedures of 4H-1,2,4-triazole-
3-thiols proceed through the preparation of the
corresponding acylthiosemicarbazides that are further
cyclized under basic conditions (Fig. 3). Interestingly
these intermediates can be used for the synthesis of other
heterocycles.13,14 Acylthiosemicarbazide intermediates
are usually obtained by acylation of 2-substituted thio-
semicarbazates with acid chlorides (Fig. 3, route 1), or
by reaction of hydrazides with the corresponding
thioisocyanate (Fig. 3, route 2).15,16 Route 2 uses
hydrazides that can easily be obtained from the corre-
sponding carboxylic acid in two steps using tert-butyl-
carbazate, if they are not commercially available.17 An
analysis of commercially available reagents showed that
amines and hydrazides were more represented in
databases than acid chlorides or thiosemicarbazates.18
We thus developed a procedure following Route 2
(Fig. 3).
Inversion of the sequence of introduction of reagents in
the first step yielded 3H-1,3,4-oxadiazole-2-thione
quantitatively (compound 5 in Fig. 4). Another frequent
by-product is the symmetrical thiourea from the amine
(compound 6, Fig. 4).28
Table 1 compares results obtained using either TCDI or
DPT. Under the same conditions, TCDI proved to be
less efficient than DPT. Also, in our hands, the use of
TCDI was hampered by a hardly preventable decompo-
sition that makes difficult the measure of stoichiometric
amounts. Furthermore, TCDI produces imidazole as a
by-product (pKa 6.95) whereas DPT produces 2-pyri-
done (pKa 0.75). Thus conditions using DPT are milder
and pyridone by-product can be more easily removed in
water than imidazole.22
Cyclization of the acylthiosemicarbazide into 1,2,4-tri-
azole-3-thiones proceeds under basic conditions. The use
of bases such as carbonate, hydrogenocarbonate and
hydroxide has been reported.5,8,29 Solubility in DMSO
The synthesis of isothiocyanates from amines requires
the use of thiocarbonyl transfer reagents such as carbon
disulfide. Nevertheless, toxicity of CS2 to human and
environment is a real problem.19 Moreover, its physical
properties make it unusable in automated chemistry.20
K+
S
S
H
R
b.
a.
N,N0-Thiocarbonyldiimidazole (TCDI) is
a
usual
N
R
1
+
2 N
R
NH2
H2N
R
N
NH
HN
2
N
2
surrogate of CS2.21 More recently, di-2-pyridylthiono-
carbonate (DPT) and its equivalent 1,l0-thiocarbonyl-
2,20-pyridone were also used.22,23 We were interested
in evaluating the use of TCDI or DPT as thiocarbonyl
transfer reagents in the synthesis of our target com-
pounds. In particular our goal was to develop a protocol
for both microplate synthesis (15 lmol) and larger scale
synthesis, which would not require the purification of
the intermediate isothiocyanate.24,25
H
O
O
N
R
1
3
4
R
1
Scheme 1. Reaction and conditions: (a) (i) Thiocarbonyl transfer
reagent 0.25 M in DMF (1.05 equiv), amine (free base) 0.1 M in DMF
(1 equiv), 55 °C, 1.5 h (ii) hydrazide (free base), 0.1 M in DMF
(1 equiv) 55 °C, 1.5 h, solvent evaporation; (b) KOH 0.1 M in H2O/
EtOH (40/60) 85 °C, 5 h.
O
H
H
R
S
N
N
1
R
R
2
2
N
N
R 1
Cl
S
H
5
6
O
+
S
Figure 4. Structures of potential by-products.
R 2
H2N
S
C N
R 2
N
N
H
H
OH
R 1
ROUTE 1
S
H
N
Table 1. Comparison of the use of TCDI or DPT at 5 lmol scalea
O
R 1
R 2
N
N
+
H
H
O
S
H
H2N R 2
ROUTE 2
H
N
a.
N
R
1
+
R
NH2
R
+
H2N
R
N
NH
HN
2
2
2
H
H
N
R
2
R 1
N
O
O
H
NH2
S
O
R
SH
N
3
6
1
+
R
R
2 N
S
C N
R 2
2
HN
R1
% 3 (% 6)b
N
O
R
R
1
1
B
Ph
2-Thienyl
Amides
1,2,4-triazole-3-thiols
TCDI
DPT
74 (26)
91 (9)
72 (28)
99 (1)
pharmacophore groups
"trans" pharmacophore
"cis" pharmacophore
Figure 3. Routes to access 4H-1,2,4-triazole-3-thiols, mimicks of
cis-amides.
a R2-NH2 used was 4-chloro-phenethylamine.
b Relative proportions of 3 and 6 evaluated in 215 nm HPLC-MS.

R. F. Deprez-Poulain et al. / Tetrahedron Letters 48 (2007) 8157–8162
8159
Table 2. Scope of the amine set31
K+
S
R
NH2
2
R
O
2 N
H
H
+
N
N
N
R
N
R
2
N
1
H
O
R
S
1
NH2
7a-14a
7b-14b
N
R
1
H
7-12 : R1 = C6H5-
13-14 : R1 = pCl-C6H4-O-CH2-
Amine R2–NH2
Yield (purity)a
Acylthiosemi-carbazide
Yield (purity)b
Product
K+
S
Cl
N
Cl
7a
8a
78 (100)
7b
8b
72 (100)
N
NH2
N
K+
S
N
45 (95)c
40 (97)d
N
NH2
N
K+
9a
43 (100)c
9b
42 (97)d
S
N
N
N
NH2
N
N
K+
S
N
10a
11a
12a
45 (100)c
10b
11b
12b
50 (96)d
72 (95)
87 (95)
NH2
N
N
K+
S
N
96 (96)
N
NH2
N
K+
S
N
NH2
94 (100)
N
N
K+
S
N
N
NH2
13a
85 (100)
N
13b
80 (97)
O
Cl
K+
S
S
N
N
S
N
14a
74 (100)
14b
90 (99)
NH2
O
Cl
a 300 lmol scale; isolated yield of acyl-thiosemicarbazide; purity was assessed by HPLC at 215 nm.
b Isolated yield of the cyclization step; purity was assessed by HPLC at 215 nm.
c Purified by thick layer chromatography.
d Cyclized with 2 equiv of KOH and purified by extraction.

8160
R. F. Deprez-Poulain et al. / Tetrahedron Letters 48 (2007) 8157–8162
of final compounds is critical for high-throughput
screening; we evaluated the solubility of sodium and
potassium salts of our final thiols.30 In this context, we
found that potassium salts were more soluble than their
sodium counterparts.31 We thus decided to use potas-
sium hydroxide for the cyclization step.
(compounds 10a or 11a). Unexpectedly, a-substituted
primary amines gave acylthiosemicarbazides in only
moderate yields and the symmetrical thiourea by-prod-
uct was produced in high proportions.
Cyclization efficiency was also a function of the amine
precursor. Steric hindrance at the amine function seems
critical at this step. Good to excellent yields were
obtained for compounds 7b, 11b–14b (72–90%).
Using this optimized protocol, we evaluated the scopes
of both reagent sets at a larger scale.32 Various amines
were evaluated for their ability to form the acylthio-
semicarbazide and the ability of the latter to undergo
cyclization (Table 2).33 Benzylamines and phenethyl-
amines were converted quantitatively and the resulting
acylthiosemicarbazides were obtained in very good
yields (compounds 12a, 13a, 7a). Interestingly anilines
gave heterogenous results depending on the substituents
Cyclization of 8a–10a into 8b–10b was slower than for
other acylthiosemicarbazides and addition of higher
amounts of KOH was required to complete the reaction.
Various hydrazides such as aliphatic, benzylic or hetero-
aromatic were also tested (Table 3). They all gave target
Table 3. Scope of the hydrazide set31
K+
S
R2 NH2
R
O
2 N
H
H
+
N
N
N
R
N
R
N
1
2
H
O
R
S
1
NH2
7b; 15b-18b
7a; 15a-18a
N
R1
H
7; 15-16 : R2 = pCl-C6H4-CH2-CH2-
17-18 : R2 = pC6H5-C6H4-CH2-
Hydrazide R1-CONHNH2
Yield (purity)a
Acylthiosemi-carbazide
Yield (purity)b
Product
K+
N
S
O
Cl
Cl
NH2
7a
78 (100)
7b
72 (100)
N
N
H
N
K+
S
O
N
N
15a
73 (100)
15b
70 (97)
NH2
N
N
H
K+
S
O
Cl
64 (100)c
16b
17b
60 (98)
80 (95)
NH2
16a
17a
N
O
N
N
H
N
O
H
O
O
N
N
K+
S
65 (100)
N
H
NH2
O
N
N
N
N
N
N
N
N
N
O
K+
H
N
NH2
O
S
18a
58 (100)
18b
71 (100)
N
N
N
O
a 300 lmol scale; isolated yield of acyl-thiosemicarbazide; purity was assessed by HPLC at 215 nm.
b Isolated yield of the cyclization step; purity was assessed by HPLC at 215 nm.
c Purified by thick layer chromatography.

R. F. Deprez-Poulain et al. / Tetrahedron Letters 48 (2007) 8157–8162
8161
8. Navidpour, L.; Shafaroodi, H.; Abdi, K.; Amini, M.;
Ghahremani, M. H.; Dehpour, A. R.; Shafiee, A. Bioorg.
Med. Chem. 2006, 14, 2507–2517.
9. Kucukguzel, I.; Kucukguzel, S. G.; Rollas, S.; Kiraz, M.
Bioorg. Med. Chem. Lett. 2001, 11, 1703–1707.
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H.; Shafiee, A. Bioorg. Med. Chem. Lett. 2005, 15, 1023–
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products in good yield. Interestingly, tert-butylcarbazate
gave good results and allows the synthesis of
5-thioxo-1,2,4-triazolidin-3-one 16b. Synthesis of such
compounds is only poorly described and uses either
semicarbazide and thioisocyanate or thiobisureas and
carbamoylthiosemicarbazide.34,35
At last, compound 12b, a prototypal example of these
series, was found to have a measured pKa of 7.95.36 This
value is in the range of published pKas.37
11. Search updated in December 2006 within MDL Drug
Data Report from Prous Science Publisher.
12. Mitratapide is a lipid-lowering agent used for treatment of
dog obesity.
13. Kilburn, J. P.; Lau, J.; Jones, R. C. F. Tetrahedron Lett.
2003, 44, 7825–7828.
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S. K. U.S. Patent 5,723,624, 1998.
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73–93.
In conclusion, we developed a facile synthesis of 4H-
1,2,4-triazole-3-thiols in two steps that is suitable for
both one-pot parallel synthesis in microplates and larger
scale synthesis. This method can be used for various sets
of hydrazides including tert-butylcarbazate. The most
reactive amines are benzylamines, phenethylamines
and linear alkylamines but this method can also be used
with anilines and a-substituted amines.
18. We performed an analysis of.sdf files from different
providers using PipelinePilotTM from ScitegicÒ. Initial files
contained reagents from Sigma–Aldrich–Fluka; Acros;
Matrix; Maybridge; Fischer and Enamine, available at the
gram scale for a price lower than 80 €. The search
retrieves, respectively, 30 thiosemicarbazides (NH–CO–
NH–NH2); 214 hydrazides (C–CO–NH–NH2); 236 acid
chlorides (C–CO–Cl) and 832 primary amines (not[O,S]–
C–NH2). Similar results were obtained using the whole
MDLTM Available Chemical Directory.
19. Tan, X.; Peng, X.; Wang, Y.; Wang, F.; Joyeux, M.;
Hartemann, P. Ecotoxicol. Environ. Saf. 2003, 55, 168–
172.
20. Flash point: ꢀ30 °C; Auto-ignition temperature: 90 °C.
21. Larsen, C.; Steliou, K.; Harpp, D. N. J. Org. Chem. 1978,
43, 337–339.
Acknowledgments
The authors would like to thank Allison Millon and
Romain Paraye for technical assistance. We are grateful
to the institutions that support our laboratory (Inserm,
Universite de Lille2 and Institut Pasteur de Lille). NMR
spectra were recorded in the ‘Laboratoire d’Application
´
´
´
RMN’ (LARMN) at Universite de Lille2, Faculte des
Sciences Pharmaceutiques de Lille. Data management
was performed using Pipeline PilotTM from ScitegicÒ.
We also thank the following sponsoring institutions or
companies: CAMPLP and VARIAN. France.
22. Kim, S.; Yi, K. Y. J. Org. Chem. 1986, 51, 2613–
2615.
23. Kilburn, J. P.; Lau, J.; Jones, R. C. F. Tetrahedron 2002,
58, 1739–1743.
Supplementary data
Full characterizations of compounds. Supplementary
data associated with this article can be found, in the
online version, at doi:10.1016/j.tetlet.2007.09.094.
24. Ronsisvalle, G.; Prezzavento, O.; Marrazzo, A.; Vittorio,
F.; Massimino, M.; Murari, G.; Spampinato, S. J. Med.
Chem. 2002, 45, 2662–2665.
25. Huang, S. C.; Undem, B.; Korlipara, V. Bioorg. Med.
Chem. Lett. 2004, 14, 4779–4782.
26. Protocol for the synthesis at 15 lmol scale using DPT in
MatrixTM 1.5 mL PP-tubes: To 63 lL of a solution of
0.25 M di-pyridyl-thiocarbonate in DMF (1.05 equiv) was
added 150 lL of 0.1 M amine (free base) in DMF
(1 equiv). The reaction mixture was heated at 55 °C for
1.5 h. Then 150 lL of a solution of 0.1 M hydrazide (free
base) in DMF (1 equiv) was added. The reaction mixture
was heated at 55 °C for 1.5 h to allow the synthesis of the
thiosemicarbazide. Solvent was removed under reduced
pressure; 300 lL of 0.1 M KOH in H2O/EtOH (40/60) was
added. Acyl-thiosemicarbazide may poorly dissolve in
0.1 M KOH in H2O/EtOH (40/60). Each hour, it is
required to sonicate the product to dissolve the interme-
diate and to complete the reaction. The reaction mixture
was heated at 85 °C for 5 h until complete cyclization.
Solvents were removed under reduced pressure.
27. Hydrazides used were commercially available or synthe-
sized using classical methods from t-butylcarbazate. See
Supplementary data for details.
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28. It was observed that old DMF containing dimethylamine
(characteristic fishy smell) yielded mainly the symmetrical

8162
R. F. Deprez-Poulain et al. / Tetrahedron Letters 48 (2007) 8157–8162
thiourea instead of the desired acyl-thiosemicarbazide. It
is thus essential that DMF be stored on 4 A molecular
chloroform–diethylic ether (7/3) as eluent) to remove
by-products and (1,3,4-oxadiazol-2-thione and
˚
5
6
sieves.
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(1 equiv or 2 equiv). The reaction mixture was heated at
85 °C for 2–8 h until complete cyclization. Solvents were
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31. Compound 7a was cyclized using KOH to give 7b or
NaOH to give the corresponding Na salt. Both com-
pounds were solubilized at 10ꢀ2 M in DMSO. DMSO
solutions were centrifuged. A 10 lL aliquot was diluted in
MeOH and analyzed by HPLC at 215 nm. The potassium
salt was more soluble than its sodium salt counter part
(Area: 2,549,782 versus 1,588,948).
32. Protocol for the synthesis at 300 lmol scale using DPT. In
this case, the reactions are performed 20 times under the
same conditions (15 lmol scale) and acylthiosemicarbaz-
ides pooled in CH2Cl2 or AcOEt. The organic layer is
washed three times with water to remove pyridone, dried
over MgSO4 and evaporated under reduced pressure. If
necessary, acylthiosemicarbazides are recrystallized from
petroleum ether or purified on silica gel (thick layer
chromatography on silica gel:using DCM/MeOH (9/1) or
33. Unfortunately, reaction with ammonia or precursors of
ammonia yielded the corresponding 3H-1,3,4-oxadiazole-
2-thione by-product (Fig. 4, compound 5) quantitatively.
The desired product can be obtained by reaction of
hydrazide with thiocyanic acid, potassium salt (Yehya, E.;
Korany, A.; Ahmad, F. Phosphorus, Sulfur Silicon Relat.
Elem. 2006, 181, 2037– 2049) or by reaction of activated
carboxylic acid with thiosemicarbazide, followed by
cyclization.
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