Discovery and synthesis of c-nucleosides as potential new anti-HCV agents

Article abstract of DOI:10.1021/ml500077j

Nucleoside analogues have long been recognized as prospects for the discovery of direct acting antivirals (DAAs) to treat hepatitis C virus because they have generally exhibited cross-genotype activity and a high barrier to resistance. C-Nucleosides have

Full text of DOI:10.1021/ml500077j

Letter
pubs.acs.org/acsmedchemlett
Discovery and Synthesis of C‑Nucleosides as Potential New Anti-HCV
Agents
Alistair G. Draffan,†,* Barbara Frey,† Brett Pool,† Carlie Gannon,† Edward M. Tyndall,† Michael Lilly,†
Paula Francom,† Richard Hufton,† Rosliana Halim,† Saba Jahangiri,† Silas Bond,† Van T. T. Nguyen,†
Tyrone P. Jeynes,† Veronika Wirth,† Angela Luttick,† Danielle Tilmanis,† Jesse D. Thomas,†
Melinda Pryor,† Kate Porter,† Craig J. Morton,† Bo Lin,† Jianmin Duan,‡ George Kukolj,‡
Bruno Simoneau,‡ Ginette McKercher,‡ Lisette Lagace,‡ Ma’an Amad,‡ Richard C. Bethell,‡
́
and Simon P. Tucker†
†Biota Scientific Management Pty. Ltd., 10/585 Blackburn Road, Notting Hill, Victoria 3168, Australia
‡Research and Development, Boehringer Ingelheim (Canada), Ltd., 2100 rue Cunard, Laval, Queb
́
ec H7S 2G5, Canada
S
* Supporting Information
ABSTRACT: Nucleoside analogues have long been recognized as
prospects for the discovery of direct acting antivirals (DAAs) to treat
hepatitis C virus because they have generally exhibited cross-
genotype activity and a high barrier to resistance. C-Nucleosides have
the potential for improved metabolism and pharmacokinetic
properties over their N-nucleoside counterparts due to the presence
of a strong carbon−carbon glycosidic bond and a non-natural
heterocyclic base. Three 2′CMe-C-adenosine analogues and two
2′CMe-guanosine analogues were synthesized and evaluated for their anti-HCV efficacy. The nucleotide triphosphates of four of
these analogues were found to inhibit the NS5B polymerase, and adenosine analogue 1 was discovered to have excellent
pharmacokinetic properties demonstrating the potential of this drug class.
KEYWORDS: C-Nucleoside, HCV, NS5B polymerase
epatitis C virus (HCV) is a major cause of chronic viral
hepatitis that often leads to liver cirrhosis and
variation possible in the heterocyclic base, offers the potential
for improved drug metabolism and pharmacokinetic properties.
As part of an effort to investigate new nucleoside agents for
HCV, C-nucleoside adenosine analogues 1−3 and guanosine
analogues 4 and 5 were targeted. Reported herein are the
synthesis and biological characterization of these compounds
(Figure 1).
Pyrrolo[2,1-f ][1,2,4]triazine-4-amine adenosine analogue, 1,
was first synthesized using the linear route shown in Scheme 1.
This is a highly modified approach to that used by Patil et al.,
for the synthesis of the unsubstituted ribo-analogue (4-aza-7,9-
dideazaadenosine).15 The 3,5-bis-dichlorobenzyl protected
2′CMe-riboside 7 was protected at the 2′-position to afford
8, then hydrolyzed under acidic conditions to afford 9. The key
glycosylation reaction was performed using a procedure
adapted from a method reported for the reaction of pyrroles
with O-glycosylimidates.16 Riboside 9 was converted to the
activated trichloroacetimidate 10. Slow addition of pyrrole to
10 at low temperature in the presence of BF3·Et2O afforded an
anomeric mixture of the pyrrolo-nucleoside, 11. Modest
improvement in β-selectivity was achieved at higher temper-
H
hepatocellular carcinoma.1,2 In 2011 the protease inhibitors
boceprevir and telaprevir became available to treat HCV
infection with genotype 1 in combination with ribavirin and
pegylated interferon.3,4 The recent approval of two new direct
acting antivirals (DAAs), simeprevir and sofosbuvir,5 will
significantly enhance the available armory, but there remains
a need for new DAAs for use in safe and effective combination
therapies.
Nucleoside and nucleotide inhibitors of HCV (NIs) are a
class of DAA that tend to demonstrate broad activity across
HCV genotypes and a high barrier to the emergence of viral
resistance. Structural modifications have been made to both the
carbohydrate (“sugar”) and heterocyclic base components of
natural nucleosides to develop potent and selective antiviral
analogues.6 The early promise of 2′CMe-7-deaza-adenosine
(Figure 1) and, more recently, the excellent clinical success of
sofosbuvir have validated the use of NIs as anti-HCV DAAs.5,7,8
Structural analogues that have attracted relatively little
attention to date for application to HCV are C-nucleosides,9−14
which comprise a sugar moiety and non-natural heterocylic
base connected by a carbon−carbon bond. This strong
glycosidic bond makes C-nucleosides more resistant to
enzymatic and hydrolytic cleavage than their N-nucleoside
counterparts. This feature, combined with the broad structural
Received: February 20, 2014
Accepted: April 10, 2014
Published: April 10, 2014
© 2014 American Chemical Society
679
dx.doi.org/10.1021/ml500077j | ACS Med. Chem. Lett. 2014, 5, 679−684

ACS Medicinal Chemistry Letters
Letter
Figure 1. Structures of sofosbuvir, 2′CMe-7-deaza-adenosine, and target C-nucleoside analogues.
α
Scheme 1. Synthesis of 1
α
Reagents and conditions: (a) NaH, 2,4-dichlorobenzyl chloride; (b) TFA/water 9:1; (c) Cl3CCN, Cs2CO3; (d) (i) 4 Å mol. sieves, DCM, 2 h, rt,
(ii) pyrrole, BF3·OEt2, −50 °C (60% yield, β/α 2:1) or −78 °C (80% yield, β/α 1:1), (iii) NH3 in MeOH, −78 °C; (e) ClSO2NCO, CH3CN/DMF,
0 °C; (f) BF3·OEt2, DCM, reflux; (g) (i) NaH, THF, 0 °C, (ii) Ph2P(O)ONH2, THF, 0 °C; (h) formamidine acetate, DMA, 140 °C, 1−2 h; (i) H2,
Pd−C (10%), 45 °C, 18 h, NaOAc, MeOH, HOAc.
α
ature (−50 °C, α/β = 1:2, 60% yield), but at the cost of yield
(−78 °C, α/β = 1:1, 80% yield). Because pyrrolo-nucleoside 11
decomposed slowly on standing, it was immediately converted
to the more stable pyrrolonitrile nucleoside 12 by reaction with
chlorosulfonyl isocyanate in DMF. The α/β mixture was
separated at this stage by flash chromatography, and more of
the desired β-anomer (12b) recovered after BF3·Et2O catalyzed
anomerization of the purified α-anomer (12a). The β-
stereochemistry was established at this stage by the observation
of strong NOE between the H4′ and the H1′ protons.
Electrophilic amination of the pyrrole nitrogen, ring closure
with formamidine actetate, followed by buffered hydrogenolysis
afforded the free adenosine analogue 1.
Scheme 2. Convergent Synthesis of A-Analogue 2
An analogous linear route toward the pyrrolo[2,1-f][1,2,4]-
triazine-4-amine guanosine analogue 4 was attempted. Evidence
was obtained that this may be achieved via hydrolysis of the 2,6-
diamino analogue of 1 under strongly basic conditions at high
temperature. However, this approach was abandoned in favor
of the convergent synthesis described below.
Imidazo[2,1-f ][1,2,4]triazine-4-amine adenosine analogue, 2,
was synthesized using a convergent approach, which utilized
the direct coupling of a bicyclic heterocycle, as shown in
Scheme 2. After selective bromination of 15, the bromo-base 16
was coupled with ribolactone 17. Amine displacement of the
α
Reagents and conditions: (a) NBS, DMF, 86 °C, 1 h; (b)(i) nBuLi,
−78 °C, THF, (ii) 17, −78 °C; (c) NH3 in MeOH, RT to reflux; (d)
BF3·OEt2, Et3SiH, DCM, −78 °C to RT, 3 h; (e) H2, Pd−C (10%), 60
°C, 18 h, NaOAc, MeOH/DCM (9:1), AcOH.
thiomethyl group followed by selective lactol reduction yielded
the desired β-nucleoside 20 and subsequently the free
nucleoside 2 after hydrogenolysis. A similar convergent
680
dx.doi.org/10.1021/ml500077j | ACS Med. Chem. Lett. 2014, 5, 679−684

ACS Medicinal Chemistry Letters
Letter
synthesis of the pyrrolo analogue 1 was developed for large
scale synthesis. Convergent methods for 1 and 2 have also been
reported by others since we completed this work.12
Guanosine analogues 4 and 5 were prepared using an
analogous approach, as shown in Scheme 3. Compounds 21
Because of the anion instability of the intermediate
organolithium base, formed from 23, the synthesis of 4 was
only possible in small, low milligram quantities using the
method outlined in Scheme 3. A more robust procedure was
therefore developed, which is shown in Scheme 4. The
α
α
Scheme 3. Convergent Synthesis of G-Analogues 4 and 5
Scheme 4. Improved Synthesis of 4
α
Reagents and conditions: (a) TEA, DMAP, Boc2O, MeCN, RT, 46 h;
(b) NBS, DCE, −10 to 0 °C, 1 h; (c)(i) nBuLi, THF −100 °C, 23 or
28 (ii) 17; (d) BF3·OEt2, Et3SiH, MeCN, −78 °C to RT, 3 h; (e) H2
(60 psi) Pd−C (10%), 60 °C, 18 h, NH4OAc, MeOH/EtOAc (13:2)
or BBr3, −78 °C to −30 °C (30 to 5); (f) DMF-dimethylacetal,
DCM/MeCN, RT to 60 °C.
α
Reagents and conditions: (a) nBuLi, BnOH, −10 °C to RT, THF;
and 26 were chosen as appropriate starting heterocycles. Under
standard conditions for Boc-protection, N-Boc protection was
achieved for both starting materials, together with tBu-
protection of the 4-oxygen, a surprising transformation that
has been observed for other guanine analogues.17 After selective
bromination, the direct glycosylation of the bromo-bases 23
and 28 with the lactone 17 was achieved at very low
temperature (−100 °C). It was noted that the anions of
these guanosine base analogues were much less stable than the
anions of the corresponding adenosine base analogues. The
coupling thus required careful, slow addition of the lactone to
the organolithium base to maintain a low temperature and
minimize anion quenching. The protecting groups on the base
were removed in the subsequent stereoselective lactol reduction
to afford DCB-protected β-nucleosides 25 and 30. The β-
stereochemistry of 25 was established at this stage by the
observation of an interaction between H1′ and H4′ in the
NOESY spectrum. Such unambiguous signals were not
observed for 30; so, the formamidine analogue 31 was prepared
under mild conditions. The observation of a strong interaction
between H1′ and H4′ in the NOESY spectrum of this
compound provided evidence of β-stereochemistry. The free
guanosine nucleoside analogues 4 and 5 were obtained upon
hydrogenolysis of the 2,4-dichlorobenzyl groups under buffered
conditions.
(b) NBS, DCM, −10 °C to RT; (c)(i) nBuLi, −100 °C, 2-Me-THF,
(ii) 34 containing C7 isomer, −100 °C to RT; (d) BF3·OEt2, Et3SiH,
DCM, −78 °C, 15 min; (e) acetamide, Pd2(dba)2, xantphos, Cs2CO3,
130 °C, 1 h; (f) H2, MeOH, Pd−C (10%), RT to 50 °C, 70 h; (g)
NaOMe, RT to 80 °C.
heterocycle 35 was chosen for glycosidic coupling and
subsequent transformation to nucleoside 4 based on observa-
tions made during the initial synthesis of 4. These included the
relative instability of anions on heterocycles bearing a protected
nitrogen at the 2-position, the requirement for O4 protection to
enable good metalation, and the susceptibility of the 2,4-
dihalides to uncontrolled hydrolysis. Heterocycle 35 was
prepared from the bis-chloro analogue 32 by displacement of
the 4-chloro with BnOLi followed by bromination with NBS in
DCE to yield an inseparable mixture of 35 along with its C7
isomer (3:1). As the C7 isomer was found to be inert in the
glycosylation reaction, the mixture was used without separation.
Glycosylation of the per-benzylated lactone 34 was achieved in
60% yield based on 35. After selective reduction of the lactol 36
to afford β-nucleoside 37, the 2-amino was installed by applying
cross-coupling chemistry,18 which also resulted in partial
deprotection of the 4-oxygen to afford a mixture of 38 and
39. The benzyl groups were cleaved under hydrogenolysis and
681
dx.doi.org/10.1021/ml500077j | ACS Med. Chem. Lett. 2014, 5, 679−684

ACS Medicinal Chemistry Letters
Letter
the acetamide group cleaved under basic conditions to afford
the free guanosine nucleoside 4.
Application of the convergent chemistry used for the
pyrrolo[2,1-f ][1,2,4]triazine and imidazo[2,1-f][1,2,4]triazine
bases was unsuccessful for the synthesis of pyrazolo[1,5-a]-
1,3,5-triazine adenosine 3. Scheme 5 shows its successful linear
recognized by the NS5B enzyme. The adenosine analogues 1
and 2 were furthermore active in the replicon assay, although
the imidazotriazine analogue, 2, also showed some cytotoxicity.
The corresponding guanosine analogues 4 and 5 were inactive
in the cell-based replicon assay, a result consistent with the
relatively poor activity reported for N-nucleoside guanosine
analogues 2′CMe-G (EC50 = 2−4 μM) and 7-deaza-2′CMe-G
(EC50 > 50 μM).7,21 The activity of the corresponding NTP
suggests they were not efficiently phosphorylated by host
kinases. In contrast, the poor enzyme activity observed for the
pyrazolotriazine adenosine analogue, 3, is consistent with its
poor activity in the replicon assay. On the basis of these initial
results, 1 was selected for further investigation as a potential
HCV DAA.
α
Scheme 5. Synthesis of Pyrazolo-Nucleoside 3
Compound 1 displayed excellent activity against HCV
genotypes 1a, 2a, 2b, 3a, 4a, 5a, 6a, and 7a. EC50 and IC50
values ranged from 0.39 to 1.0 μM (see Supporting Information
for details) demonstrating its potential suitability as part of a
pan-genotypic HCV therapy.
Because the nucleotide triphosphate is the compound
responsible for anti-HCV activity, it is important to measure
the ability of relevant cells to anabolize the parent nucleoside.
The in vitro anabolism of 1 was studied in adherent Huh-7 cells
and plated primary human hepatocytes. Following incubation
of Huh-7 cells with 10 μM initial concentration of 1 for 24 h,
the intracellular concentration of 1-NTP reached 9.3 pmol/
million cells. Surprisingly, primary human hepatocytes
generated much higher (∼50-fold) intracellular levels of 1-
NTP (487 pmol/million cells) after 24 h with the same starting
concentration, offering the promise of enhanced HCV antiviral
activity in humans. Intracellular levels of 1 were found to be
comparable in Huh-7 cells and hepatocytes, but the mono- and
diphosphate species were about 10-fold lower in the replicon
cell line suggesting that the first and second phosphorylation
α
Reagents and conditions: (a) NaH, DME, 41, 0 °C to RT; (b)
(CH3)3COCH[N(CH3)2]2, DMF, 60 °C, 15 h; (c) NH2NH2·HCl,
EtOH, 105 °C, 2 h; (d) ethyl N-cyanoformimidate, 85 °C, toluene; (e)
H2, MeOH, Pd−C (10%), 45 °C, 17 h.
synthesis, which adopts similar methodology reported by Klein
et al. for the synthesis of the unsubstituted riboside
analogue.19,20 Condensation of 2-diethoxyphosphoryl-
acetonitrile, 41, with the tris-benzyl riboside 9 afforded the
C-nucleoside intermediate 42. Separation of the anomers was
possible at this stage but unnecessary, as interchange between
anomers was observed under reaction conditions for the
dimethylamine adduct 43 and for the amino-pyrazole
intermediate 44. In situ condensation of 44 with ethyl
cyanoimidoformate afforded the protected nucleoside 45. The
anomers were separated, and the β-stereochemistry was
established by the observation of an interaction between H1′
and H4′ in the NOESY spectrum. The pyrazolotriazine
adenosine analogue 3 was obtained after hydrogenolysis.
The in vitro anti-HCV results for the parent C-nucleosides
1−5 are shown in Table 1. The low IC50 values observed for
the pyrrolotriazine and imidazotriazine adenosine and
guanosine nucleoside triphosphates show they are well
steps are more efficient in hepatocytes. The decay half-life (t1/2
)
of 1-NTP displays a biphasic profile in both replicon cells and
primary human hepatocytes: a rapid initial decay t1/2 (0.7 and
3.3 h, respectively), followed by a prolonged elimination phase
(t1/2 ≥ 35 h).
The pharmacokinetic properties of 1 were determined in
male Sprague−Dawley rats, beagle dogs, and cynomolgus
monkeys. Compound 1 displayed excellent cross-species
pharmacokinetics with elimination t1/2 ranging from 4 to 7.6
h and high bioavailabilities (33−96%). On the basis of these
data, the drug may have sufficient PK properties for a once daily
dosing regimen in humans taking into account the long
intracellular half-life of its triphosphate in hepatocytes.
Compound 1 was evaluated in a range of in vitro safety
assays to assess its suitability for progression into animal
toxicity studies. In a mitochondrial toxicity study over 14 days
in HepG2 cells, 1 showed no increase in lactate production or
decrease in mtDNA up to 10 μM. Low levels of cytotoxicity
were observed in rat cells (CC50 = 190 μM for liver epithelial
cells and CC50 > 250 μM for kidney fibroblasts and heart
myoblasts). Compound 1 did not inhibit erythroid and myeloid
progenitor proliferation in human bone marrow cells up to 100
μM and was negative in an AMES mutagenicity test. In
addition, compound 1 triphosphate did not inhibit human
DNA polymerases (IC50 >100 μM for α, β, and γ enzymes).
Despite this promising in vitro profile, unacceptable adverse
effects, including death, were observed during single oral dose
toxicity studies in rats (dosed up to 400 mg/kg). This result
caused us to focus development efforts on derivatives of 1 with
Table 1. Inhibitory Potency (EC50) of Nucleosides on HCV
RNA Replication in Replicon Assay; Cytotoxicity (CC50);
and Inhibitory Potency (IC50) of Corresponding Nucleoside-
Triphosphate (NTP) on NS5B Polymerase Enzyme (WT
GT1b(Con1))
GT1b EC50
NTP IC
c50
a
b
compd
(μM)
CC50 (μM)
>100,
(μM)
2′CMe-7
0.20, 0.3 (lit.)21
0.20, 0.07 (lit.)21
-deaza-A
>100 (lit.)21
pyrrolo-A (1)
pyrrolo-G (4)
imidazo-A (2)
imidazo-G (5)
pyrazolo-A (3)
1.6, 1.98 (lit.)12
>100
1.3, 1.28 (lit.)12
>100, 85 (lit.)12
>100
34, >89 (lit.)12
0.37, 0.31 (lit.)12
0.21
0.55, 2.1 (lit.)12
>100, >89 (lit.)12 >100, >89 (lit.)12 0.31, 0.19 (lit.)12
>100
>100
33
a
Measured using subgenomic replicon cell lines described by Blight et
al.22 See Supporting Information for methods. Measured using Huh-7
b
c
derived replicon cell lines with MTT as the vital dye indicator. See
Supporting Information for methods.
682
dx.doi.org/10.1021/ml500077j | ACS Med. Chem. Lett. 2014, 5, 679−684

ACS Medicinal Chemistry Letters
Letter
Potent and Selective Inhibitor of Hepatitis C Virus Replication with
Excellent Pharmacokinetic Properties. Antimicrob. Agents Chemother.
2004, 48 (10), 3944−3953.
a potentially improved safety margin. Since the completion of
this work, the results of safety pharmacology and toxicology
studies of 1 have been published.11
(8) Osinusi, A.; Meissner, E. G.; Lee, Y.-J.; Bon, D.; Heytens, L.;
Nelson, A.; Sneller, M.; Kohli, A.; Barrett, L.; Proschan, M.; Herrmann,
E.; Shivakumar, B.; Gu, W.; Kwan, R.; Teferi, G.; Talwani, R.; Silk, R.;
Kotb, C.; Wroblewski, S.; Fishbein, D.; Dewar, R.; Highbarger, H.;
Zhang, X. X.; Kleiner, D.; Wood, B. J.; Chavez, J.; Symonds, W. T.;
Subramanian, M.; McHutchison, J.; Polis, M. A.; Fauci, A. S.; Masur,
H.; Kottilil, S. Sofosbuvir and Ribavirin for Hepatitis C Genotype 1 in
Patients With Unfavorable Treatment Characteristics: A Randomized
Clinical Trial. JAMA 2013, 310 (8), 804−811.
In summary, the synthesis and anti-HCV activity of a series
of C-nucleoside purine analogue inhibitors of HCV NS5B
polymerase have been investigated. Four of the five nucleosides
showed excellent enzyme activity as their triphosphates, with
two adenosine analogues showing activity in the cell-based
replicon assay. The enzyme active guanosine analogues were,
however, inactive in the whole cell assay, presumably due to
inefficient anabolism to their nucleotide triphosphates. The
pyrrolotriazine adenosine analogue 1 was chosen for further
profiling because it showed excellent cross-genotype activity,
low in vitro toxicity, good anabolism, and excellent
pharmacokinetic properties in three species. Compound 1
incorporates the key structural features of a 2′CMe-ribose
moiety with a pyrrolotriazine 7-deazaadenine base mimic,
connected by a highly stable C−C bond. Unfortunately, the
observation of adverse effects in rat safety studies caused us to
re-evaluate our pursuit of 1 as a drug candidate. Despite this,
these results demonstrated the potential for C-nucleosides to
be used in new antiviral HCV therapies provided a sufficient
therapeutic margin can be established.
(9) Biota Scientific Management & Boehringer Ingelheim Interna-
tional GMBH. Bicyclic Nucleosides and Nucleotides as Therapeutic
Agents. WO2010/002877, January 7, 2010.
(10) Butora, G.; Olsen, D. B.; Caroll, S. S.; McMasters, D. R.;
Schmitt, C.; Leone, J. F.; Stahlhut, M.; Burlein, C.; MacCoss, M.
Synthesis and HCV Inhibitory Properties of 9-Deaza-and 7,9-Dideaza-
7-oxa-2′-C-methyladenosine. Bioorg. Med. Chem. 2007, 15, 5219−
5229.
(11) Cho, A.; Zhang, L.; Xu, J.; Lee, R.; Butler, T.; Metobo, S.;
Aktoudianakis, V.; Lew, W.; Ye, H.; Clarke, M.; Doerffler, E.; Byun, D.;
Wang, T.; Babusis, D.; Carey, A. C.; German, P.; Sauer, D.; Zhong, W.;
Rossi, S.; Fenaux, M.; McHutchison, J. G.; Perry, J.; Feng, J.; Ray, A.
S.; Kim, C. U. Discovery of the First C-Nucleoside HCV Polymerase
Inhibitor (GS-6620) with Demonstrated Antiviral Response in HCV
Infected Patients. J. Med. Chem. 2014, 57, 1812−1825.
(12) Cho, A.; Zhang, L.; Xu, J.; Babusis, D.; Butler, T.; Lee, R.;
Saunders, O. L.; Wang, T.; Parrish, J.; Perry, J.; Feng, J. Y.; Ray, A. S.;
Kim, C. U. Synthesis and Characterization of 2′-C-Me Branched C-
Nucleosides as HCV. Bioorg. Med. Chem. Lett. 2012, 22, 4127−4132.
(13) Feng, J. Y.; Cheng, G.; Perry, J.; Barauskas, O.; Xu, Y.; Fenaux,
M.; Eng, S.; Tirunagari, N.; Peng, B.; Yu, M.; Tian, Y.; Lee, Y.-J.;
Stepan, G.; Lagpacan, L. L.; Jin, D.; Hung, M.; Ku, K. S.; Han, B.
Inhibition of Hepatitis C Virus Replication by GS-6620, A Potent C-
Nucleoside Monophosphate Prodrug. Antimicrob. Agents Chemother.
2014, 58, 1930−1942.
(14) Murakami, E.; Wang, T.; Babusis, D.; Lepist, E.-I.; Sauer, D.;
Park, Y.; Vela, J. E.; Shih, R.; Birkus, G.; Stefanidis, D.; Kim, C. U.;
Cho, A.; Ray, A. S. Metabolism and Pharmacokinetics of the Anti-
HCV Nucleotide Prodrug GS-6620. Antimicrob. Agents Chemother.
2014, DOI: 10.1128/AAC.02350-13.
ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental procedures, analytical data, and the description
and results of in vitro assays and in vivo pharmacokinetics. This
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*(A.G.D.) Tel: +61 (0)3 9915 3735. E-mail: a.draffan@biota.
com.au.
■
Author Contributions
All authors have given approval to the final version of the
manuscript.
Notes
(15) Patil, S. A.; Otter, B. A.; Klein, R. S. 4-Aza-7,9-
Dideazaadenosine, a New Cytotoxic Synthetic C-Nucleoside Analogue
of Adenosine. Tetrahedron Lett. 1994, 35, 5339−5342.
The authors declare no competing financial interest.
(16) Hungerford, N. L.; Armitt, D. J.; Banwell, M. G. Syntheses of
Showdomycin and Its Anomer Using N-(Triisopropylsilyl)pyrrole as a
Synthetic Equivalent for the Maleimide C3-Anion. Synthesis 2003, 12,
1837−1843.
REFERENCES
■
(1) Centers for Disease Control and Prevention. Hepatitis C
Information for Health Professionals. http://www.cdc.gov/hepatitis/
HCV/HCVfaq.htm (accessed October 11, 2013).
(17) Wang, R.-W.; Gold, B. A Facile Synthetic Approach to 7-
Deazaguanine Nucleosides via a Boc Protection Strategy. Org. Lett.
2009, 11, 2465−2468.
(2) Lavanchy, D. The Global Burden of Hepatitis C. Liver Int. 2009,
74−81.
(3) Poordad, F.; Dieterich, D. Treating Hepatitis C: Current
Standard of Care and Emerging Direct-Acting Antiviral Agents. J.
Viral Hepatitis 2012, 19, 449−524.
(18) Bosch, L.; Cialîcu, I.; Caner, J.; Ariza, X.; Costa, A. M.; Terrazas,
M.; Vilarrasa, J. Pd-Catalysed Amidation of 2,6-Dihalopurine Nucleo-
sides. Replacement of Iodine at 0°C. Tetrahedron Lett. 2012, 53,
1358−1362.
(19) Tam, S. Y.-K.; Hwang, J.-S.; de Las Heras, F. G.; Klein, R. S.;
Fox, J. J. Nucleosides CV. Synthesis of the 8-(β-D-ribofuranosyl)-
pyrazolo[1,5-a]-1,3,5-triazine Isosteres of Adenosine and Inosine. J.
Heterocycl. Chem. 1976, 13, 1305−1308.
(20) Tam, S. Y. K.; Klein, R. S.; Wempen, I.; Fox, J. J. Nucleosides.
112. Synthesis of Some New Pyrazolo[1,5-a]-1,3,5-triazines. J. Org.
Chem. 1979, 44, 4547−4553.
(21) Eldrup, A. B.; Allerson, C. R.; Bennett, C. F.; Bera, S.; Bhat, B.;
Bhat, N.; Bosserman, M. R.; Brooks, J.; Burlein, C.; Carroll, S. S.;
Cook, P. D.; Getty, K. L.; MacCoss, M.; McMasters, D. R.; Olsen, D.
B.; Prakash, T. P.; Prhavc, M.; Song, Q.; Tomassini, J. E.; Xia, J.
Structure−Activity Relationship of Purine Ribonucleosides for
(4) Pawlotsky, J.-M. Hepatitis C Virus: Standard-of-Care Treatment.
Adv. Pharmacol. 2013, 67, 169−215.
(5) US Food and Drug Administration. Viral Hepatitis Therapies.
h t t p : / / w w w . f d a . g o v / F o r C o n s u m e r s / B y A u d i e n c e /
ForPatientAdvocates/ucm151494.htm (accessed December 23, 2013).
(6) Sofia, M. J.; Chang, W.; Furman, P. A.; Mosley, R. T.; Ross, B. S.
Nucleoside, Nucleotide, and Non-Nucleoside Inhibitors of Hepatitis C
Virus NS5B RNA-Dependent RNA-Polymerase. J. Med. Chem. 2012,
55, 2481−2531.
(7) Olsen, D. B.; Eldrup, A. B.; Bartholomew, L.; Bhat, B.;
Bosserman, M. R.; Ceccacci, A.; Colwell, L. F.; Fay, J. F.; Flores, O.
A.; Getty, K. L.; Grobler, J. A.; LaFemina, R. L.; Markel, E. J.;
Migliaccio, G.; Prhavc, M.; Stahlhut, M. W.; Tomassini, J. E.; MacCoss,
M.; Hazuda, D. J.; Carroll, S. S. A 7-Deaza-Adenosine Analog Is a
683
dx.doi.org/10.1021/ml500077j | ACS Med. Chem. Lett. 2014, 5, 679−684

ACS Medicinal Chemistry Letters
Letter
Inhibition of Hepatitis C Virus RNA-Dependent RNA Polymerase. J.
Med. Chem. 2004, 47, 2283−2295.
(22) Blight, K. J.; Kolykhalov, A. A.; Rice, C. M. Efficient Initiation of
HCV RNA Replication in Cell Culture. Science 2000, 290, 1972−1974.
684
dx.doi.org/10.1021/ml500077j | ACS Med. Chem. Lett. 2014, 5, 679−684