S-Aryltriazole acyclonucleosides: Synthesis and biological evaluation against hepatitis C virus

Article abstract of DOI:10.1016/j.bmcl.2010.04.115

Novel S-aryltriazole acyclonucleosides were designed as structural analogs based on the previously identified antiviral aryltriazole acyclonucleosides in our laboratories. These S-aryltriazole nucleosides were synthesized in excellent yields via S_N

Full text of DOI:10.1016/j.bmcl.2010.04.115

Bioorganic & Medicinal Chemistry Letters 20 (2010) 3610–3613
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
S-Aryltriazole acyclonucleosides: Synthesis and biological evaluation
against hepatitis C virus
Yang Liu a, Yi Xia b, Wei Li a, Mei Cong a, Alain Maggiani b, Pieter Leyssen c, Fanqi Qu a, Johan Neyts c,
Ling Peng b,
*
a State Key Laboratory of Virology, College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, PR China
b Département de Chimie, CINaM CNRS UPR 3118, 163, Avenue de Luminy, 13288 Marseille Cedex 09, France
c Rega Institute for Medical Research, Minderbroedersstraat 10, B-3000 Leuven, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel S-aryltriazole acyclonucleosides were designed as structural analogs based on the previously iden-
tified antiviral aryltriazole acyclonucleosides in our laboratories. These S-aryltriazole nucleosides were
synthesized in excellent yields via SNAr-mediated S-arylation, followed by subsequent ammonolysis.
X-ray structural analysis revealed special structural feature brought by the S-linkage, which may repre-
sent an unfavorable factor contributing to the lack of anti-HCV activity for this family of triazole
nucleosides.
Received 1 April 2010
Revised 26 April 2010
Accepted 26 April 2010
Available online 28 April 2010
Keywords:
Acyclonucleosides
S-arylation
Ó 2010 Elsevier Ltd. All rights reserved.
S-arylated triazole nucleosides
Triazole nucleosides
Hepatitis C virus
Synthetic nucleoside mimics with modified nucleobase and/or
sugar moieties are of considerable importance in the search for
new structural leads exhibiting biologically interesting activity.1
Appending aromatic systems to a nucleobase has been shown to
create nucleosides with unique properties and biological activities.
The resulting enlarged aromatic system may confer stronger and
more efficient binding properties to the corresponding nucleoside
for interaction with biological targets, leading to novel mechanism
of action. One successful example is HEPT (Fig. 1) an acyclonucle-
oside analog displaying the potent and selective anti-HIV activity.2
Of particular importance is the appended phenylthio group which
is attached on the pyrimidine nucleobase of HEPT at the 6-position.
This aryl interacts with the amino acid residues Tyr188 and Leu100
of the HIV reverse transcriptase enzyme, leading to the conforma-
tional change and consequent inhibition of HIV replication. The
mode of action for HEPT is therefore completely different from that
of the conventional nucleoside analogs.3
Over the last five years we have been interested in developing
structurally novel and diverse triazole nucleosides bearing
aromatic systems anchored onto the triazole nucleobases.4–12 By
O
O
O
NH2
NH
N
N
N
Ar
NH2
S
F
N
N
S
N
O
N
HO
HO
HO
O
O
O
S-Aryltriazole
acyclonucleosides
1
HEPT
Figure 1. Chemical structure of HEPT, 1 and proposed S-aryltriazole acyclonucleoside compounds.
* Corresponding author. Tel.: +33 491 82 91 54; fax: +33 491 82 93 01.
E-mail address: ling.peng@univmed.fr (L. Peng).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.04.115

Y. Liu et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3610–3613
3611
O
O
O
N
N
N
N
N
OCH3
R
OCH3
R
NH2
Br
S
S
N
N
N
N
RSH
NH3
AcO
AcO
HO
K2CO3, CH3CN
CH3OH
O
O
O
2
4
3
Scheme 1. Synthesis of S-aryltriazole acyclonucleosides 3 and 4 starting with 2 followed by subsequent ammonolysis.
Table 1
Synthesis of S-aryltriazole acyclonucleosides 3 and 4 via direct S-arylation on 2 followed by subsequent ammonolysis.
O
O
O
N
N
N
N
N
N
OCH3
R
OCH3
R
NH2
Br
S
S
N
N
N
RSH
NH3
AcO
AcO
HO
K2CO3, CH3CN
IMW, 100 oC
30 min
OH
2 days
CH3
O
O
O
2
4
3
Entry
1
R
Products
Yields (%)
99
Products
Yields (%)
3a
4a
84
99
CH3
2
3b
91
4b
H3C
H3C
3
4
5
3c
3d
3e
98
97
98
4c
4d
4e
95
73
99
OCH3
H3CO
H3CO
6
7
8
3f
93
99
99
4f
67
81
94
3g
3h
4g
4h
F
F
F
9
3i
96
92
98
4i
99
79
77
10
11
3j
4j
CF3
3k
4k
F3C
12
3l
96
4l
61
13
14
15
3m
3n
3o
92
79
92
4m
4n
4o
85
80
95
F3C
Cl
16
3p
93
4p
76
F3C
17
18
3q
3r
93
96
4q
4r
63
86

3612
Y. Liu et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3610–3613
Figure 2. Crystal structure of 4j in comparison with those of 16 and HEPT.2
combining the intrinsic properties of the triazole ring13 with the
appended aromatic moieties in an enlarged aromatic system,14
we aimed to identify novel triazole nucleoside analogs displaying
advantageous binding properties with the corresponding biological
targets via aromatic interactions and thus novel mechanism of ac-
tion. Some of these compounds indeed show promising antiviral
and anticancer activities.4–8,12b Of particular interest, acyclic nucle-
oside lead 1 (Fig. 1) elicits significant in vitro antiviral activity
against the hepatitis C virus (HCV).6
mainly ascribed to the much stronger nucleophilicity of the thiol
compared to the amine functionality.
Further treatment of 3 in NH3/MeOH at room temperature re-
sulted in the deprotection of the sugar moiety and amination of
the carboxylester group, affording the corresponding deprotected
nucleoside 4 in good to excellent yields (Table 1).16 Some com-
pounds were obtained in only moderate yields due to their rela-
tively poor solubility leading to considerable loss during the
purification process.
Based on the identified anti-HCV lead compound 16 and in-
spired by the structural features of HEPT,3 we decided to synthe-
size S-aryltriazole acyclonucleosides (Fig. 1) in the view to
undertake a study on structure–activity relationship and explore
their anti-HCV activity as well. Whereas this family of compounds
do share some features with 1, that is, the presence of aryl ap-
pended triazole heterocycle as the nucleobase, there are some
structural differences, that is, the aryl moiety is linked to the tria-
zole ring via structurally flexible S-linkage rather than the rigid tri-
ple bond bridge in 1. In this way, they may resemble HEPT which
has an aryl moiety appended on the nucleobase via S-linkage. Here
we report the synthesis and the anti-HCV activity of these S-aryl-
triazole acyclonucleosides.
The synthesis of the corresponding S-arylation nucleosides was
performed via SNAr-mediated S-arylation reaction between the
bromotriazole nucleoside 210 and various thiols to provide the
nucleosides 3,15 which were then subjected to subsequent ammo-
nolysis to furnish the corresponding deprotected nucleosides 4
(Scheme 1).16
We first optimized the S-arylation of 2 using 4-methylbenze-
nethiol as a thiol counterpart. We were pleased to find that the
S-arylation proceeded readily, which was in line with the results
observed by Liu and Robins for S-arylation on 6-halopurine nucle-
oside analogs.17 By systematically varying the bases (K2CO3,
Na2CO3, Li2CO3, triethylamine, etc.), solvents (CH3CN, THF, toluene
etc.), reaction temperature and microwave irradiation duration
(data not shown), we determined the most suitable conditions
for S-arylation, namely, treating 2 with thiol in the presence of
two equivalent K2CO3 in CH3CN under microwave irradiation at
100 °C for 30 min. Most S-arylation reactions proceeded in almost
quantitative yields,15 except for that with 4-chlorothiophenol (Ta-
ble 1, entry 14). The relatively lower yield for 3n was probably due
to the incomplete transformation, for a small amount of 2 re-
mained in the reaction mixture, as revealed by TLC analysis. It
should be noted that the presence of the electron-donating (Table
1, entries 5–7) or electron-withdrawing groups (Table 1, entries 8–
13) on thiophenol did not significantly affect the yield of S-aryla-
tion, and that no steric effect was observed (Table 1, entries 2, 5,
and 11). Alkyl thiols also gave excellent yields (Table 1, entries
17 and 18). The overall high-yielding S-arylation was significantly
different from the N-arylation on 2.12a This difference can be
Finally, we obtained single crystals of 4j and determined its
structure by X-ray analysis (Fig. 2).18 To our great surprise, the phe-
nyl ring in 4j adopted very different orientations compared to that
in 1 and in HEPT. In addition, the carboxylamide group in 4j also
projected in an almost opposite direction with respect to that in
1. All these structural deviations can be directly ascribed to the
S-linkage introduced between the appended aryl group and tria-
zole ring in 4j.
All the synthesized S-aryltriazole acyclonucleosides were sub-
jected to an antiviral assay against hepatitis C virus using a HCV
subgenomic RNA replicon test in Huh-5-2 cells.19,20 Unfortunately,
none of the synthesized compounds elicited any notable antiviral
activity. Based on earlier identified anti-HCV activity of lead 1 as
well as on the different structural features revealed by the crystal
structures of 4j, 1 and HEPT, we can reasonably assume that the S-
linkage introduced between the appended aromatic groups and tri-
azole ring might represent an unfavorable factor contributing to
the lack of anti-HCV activity.
In conclusion, we synthesized and characterized a novel family
of S-arylated triazole acyclonucleosides. The aromatic groups were
introduced directly at the 5-position on the triazole ring via a
simple and efficient SNAr-mediated S-arylation procedure, giving
the corresponding products in excellent yields. Due to the special
structure feature brought by the S-linkage, none of the synthesized
S-arylated triazole nucleosides elicited any significant antiviral
activity against HCV. However, the easy and efficient S-arylation
reaction presented in this study will allow us to prepare structur-
ally diverse S-aryltriazole nucleoside analogs in the view to under-
take a detailed structure–activity relationship analysis in our
future drug discovery program based on triazole nucleoside
analogs.
Acknowledgments
Financial supports from the Ministry of Science and Technology
of China (Nos. 2003CB114400, 2003AA2Z3506), National Science
Foundation of China (Nos. 20372055, 20473112), Wuhan Univer-
sity, CNRS and the Geconcerteerde Onderzoeksactie (KULeuven)
and the Fonds voor Wetenschappelijk Onderzoek Vlaanderen
(G.0728.09N) are gratefully acknowledged. We thank Mrs. Katrien
Geerts for anti-HCV evaluation, and Mrs. Emily Witty for English

Y. Liu et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3610–3613
3613
13. Loakes, D. Nucleic Acids Res. 2001, 29, 2437.
correction of manuscript. Dr. Yi Xia is supported by a post-doctoral
fellowship from la Fondation pour la Recherche Médicale.
14. Xia, Y.; Wan, J. Q.; Qu, F. Q.; Peng, L. Synthesis of Nucleoside Analogues with
Aromatic Systems Appended on the Triazole Nucleosides. In Chemistry of
Nucleic Acid Components; Hocek, M., Ed.; Collection Symposium Series;
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the
Czech Republic: Prague, 2008; Vol. 10, pp 224–228.
Supplementary data
15. General procedure for preparing 3: Methyl 1-((2-acetoxyethoxy)methyl)-5-
1H NMR and 13C NMR spectra of all the new compounds de-
scribed. Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.bmcl.2010.04.115.
bromo-1H-1,2,4-triazole-3-carboxylate
(32.2 mg,
0.1 mmol),
the
corresponding thiol (0.12 mmol), and K2CO3 (27.6 mg, 0.2 mmol) were
suspended in 2 mL of fresh distilled CH3CN under argon. The vessel was
sealed and the reaction was carried out under microwave irradiation at 100 °C
for 30 min, and then cooled to room temperature. The reaction mixture was
concentrated under reduced pressure and the crude residue was purified by
flash chromatography on silica gel (petroleum ether/ethyl acetate, 2:1). The
purified material was dried in vacuo to afford the corresponding product 3 as
colorless oil.
References and notes
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16. General procedure for preparing 4: The corresponding starting material 3 was
dissolved in 12 mL of a saturated NH3/MeOH solution and stirred at room
temperature for 2 days. Then the solvent was removed and the residue was
washed three times with CH2Cl2. The washed residue was dried in vacuo to
afford the corresponding product 4.
17. Liu, J. Q.; Robins, M. J. J. Am. Chem. Soc. 2007, 129, 5962.
18. Single crystals of product 4j suitable for X-ray crystallographic analysis were
obtained via slow evaporation of CH2Cl2–CH3OH solution. Crystallographic
data of 4j: Mw = 312.32, monoclinic, space group P2(1)/n, a = 7.3609(9) Å,
b = 27.335(3) Å, c = 7.7357(9) Å,
V = 1383.5(3) Å3, Z = 4, Dcalcd = 1.499 g/cm3,
wR2 = 0.0712 (I > 2 (I)), GOF = 1.005. CCDC 762236 contains the
a
= 90.00°, b = 117.268(2)°,
c = 90.00°,
l
= 0.262 mmÀ1, R1 = 0.0330 and
r
supplementary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Center, 12, Union Road, Cambridge CB2 1EZ, UK; fax:
+44 1223 336033.
19. Anti-HCV assay in Huh-5-2 cells: Huh-5-2 cells were seeded at a density of 5000
per well in
Canberra, Canada) in complete Dulbecco’s modified Eagle’s medium
(DMEM) supplemented with 250 g/mL G418. After incubation for 24 h at
a tissue culture-treated white 96-well view plate (Packard,
l
37 °C (5% CO2), medium was removed and threefold serial dilutions in
complete DMEM (without G418) of the test compounds were added in a
total volume of 100 lL. After 4 days of incubation at 37 °C, cell culture
medium was removed and luciferase activity was determined using the
Steady-Glo luciferase assay system (Promega, Leiden, The Netherlands); the
luciferase signal was measured using a Luminoskan ascent (Thermo, Vantaa,
Finland).
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20. (a) Paeshuyse, J.; Kaul, A.; De Clercq, E.; Rosenwirth, B.; Dumont, J.-M.; Scalfaro,
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