Towards the second generation of Boceprevir: Dithianes as an alternative P2 substituent for 2,2-dimethyl cycloproyl proline in HCV NS3 protease inhibitors

Article abstract of DOI:10.1016/j.bmcl.2010.01.037

Hepatitis C (HCV) infection is a global health crisis leading to chronic liver disease. In our efforts towards a second generation HCV NS3 serine protease inhibitor with improved profile, we have undertaken SAR studies in various regions of Boceprevir inc

Full text of DOI:10.1016/j.bmcl.2010.01.037

Bioorganic & Medicinal Chemistry Letters 20 (2010) 1689–1692
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Towards the second generation of Boceprevir: Dithianes as an alternative
P2 substituent for 2,2-dimethyl cycloproyl proline in HCV NS3 protease
inhibitors
*
Latha G. Nair , Stephane Bogen, Sumei Ruan, Weidong Pan, Russel Pike, Xiao Tong, Kuo-Chi Cheng,
Zhuyan Guo, Ronald J. Doll, F. George Njoroge
Merck Research Laboratories, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Hepatitis C (HCV) infection is a global health crisis leading to chronic liver disease. In our efforts towards
a second generation HCV NS3 serine protease inhibitor with improved profile, we have undertaken SAR
studies in various regions of Boceprevir including P2. Herein, we report the synthesis and structure–activ-
ity relationship studies of inhibitors with (S)-1,4-dithia-7-azaspiro[4.4]nonane-8-carboxylic acid 2 as P2
substituent replacing the (1R,2S,5S)-6,6-dimethyl 3-azabicyclo[3.1.0]hexane-2-carboxylic acid. The sys-
tematic investigation led to the discovery of highly potent inhibitor 25 (Kꢀi = 7 nM, EC90 = 30 nM) with
Received 2 November 2009
Revised 8 January 2010
Accepted 11 January 2010
Available online 20 January 2010
Keywords:
HCV protease
Dithianes
improved rat exposure of 2.56 lM h.
Ó 2010 Published by Elsevier Ltd.
Glutarimides
The hepatitis C virus is a major health hazard affecting over 170
million individuals worldwide1a and its infection is a leading cause
of chronic liver disease in the United States.1b–d The current stan-
dard of care treatment is a combination of subcutaneous pegylated
tered in the process, intensive efforts have been focused on NS3
serine protease and a number of novel inhibitors have been
reported.8 More recently, peptidomimetics like BILN-20619, VX-
95010 and MK-700911 are reported to show the antiviral activity
by inhibiting the replication of the virus along with our clinical
candidate SCH 503034 (Fig. 1).12 Currently, the most advanced can-
didates are Telapravir (VX-950) from Vertex and Boceprevir (SCH
503034) from Schering-Plough which are in phase III clinical trials.
Synthesis of inhibitors with dithiane at P2 (Fig 2) starting from
4-oxo proline derivative 313 was achieved according to the general
Scheme 1. Refluxing 3 with 1,2-dithioethane and a catalytic
amount of PTSA in glacial acetic acid resulted in the thioketal 4
in 56% isolated yield. The hydrobromide 4 was coupled with
various N-Boc protected P3 amino acid under the HATU conditions
interferon-
a
with oral nucleoside drug ribavirin.2 Response rates
for HCV patients having genotypes 2 or 3 on a 24 week treatment
of this is 80%, whereas those with genotype 1 are treated for
48 weeks with response rates of less than 50%. With the opportu-
nity to improve response rates, especially for genotype 1 patients,
and given the side effects associated with the current therapy, it is
necessary to search for novel potent and drug like inhibitors of NS3
enzyme of HCV with the intent of improving treatment outcomes
and potentially shorten treatment duration.
The NS3 protease which is located at N-terminal portion of NS3
protein has a demonstrated vital role in the replication of the HCV
virus.3 Hence there are compelling evidences4 to suggest that the
inhibition of NS3 protease would be a viable strategy for the devel-
opment of small molecules as antiviral agents. It has been deter-
mined that the HCV NS3 protease belongs to the trypsin or
chymotrypsin super family of serine protease.5 For efficient pro-
cessing, the protease forms a complex with a small polypeptide
co-factor NS4A.6 The structure data of the protease have revealed
a shallow and solvent exposed substrate binding region, where
the binding energy is mainly derived from weak lipophilic and
electrostatic interactions.7 Despite tremendous difficulty encoun-
p2
p1'
cap
N
O
N
NH2
N
O
O
N
O
Ki* = 14nM
EC90 =350nM
O
p1
p3
* Corresponding author.
E-mail address: latha.nair@spcorp.com (L.G. Nair).
Figure 1. Boceprevir (SCH 503034).
0960-894X/$ - see front matter Ó 2010 Published by Elsevier Ltd.
doi:10.1016/j.bmcl.2010.01.037

1690
L. G. Nair et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1689–1692
Table 1
S
( )n
S
SAR of dithianes and primary amides
n = 1,2
S
N
O
S
O
O
NH2
N
N
H
N
O
O
Figure 2. Dithiane P2.
N
P1
O
O
P3
Kiꢀ
(lM)
Entry
P3
P1
O
S
S
a, b
c, d
S
8
0.600
0.400
0.300
0.200
OMe
OH
OMe
N
N
HBr
H
Cbz O
O
9
10
11
4
3
S
S
e
S
OH
H
H
N
N
N
N
O
P3
O
P1
O
P3
O
O
O
S
NH
O
NH
6
5
O
O
P3 replacement (11, Kꢀi = 200 nM) to achieve a threefold improve-
ment in potency compared to 8. Assessment of resistance mutation
selected by Boceprevir suggested that larger flexible P2 could pro-
vide better results for V170A mutant profile by retaining more
interaction between Arg 155 and the inhibitor.22 Structural model-
ling predicted that the side chain of Val 170 was in Van der Waals
contact with the side chain of Arg 155.22 Although the initial re-
sults from analogs 8–11 were disappointing, we decided to con-
tinue the SAR studies and quickly identified compounds with
desired potency by incorporating P3 caps (Table 2).
S
O
H
H
N
N
f, g, h
N
P3
O
P1
O
O
O
NH
NH
7
P4
We have reported in the 2,2-dimethyl proline P2 series that
extension of the P3 unit resulted in additional interaction with
Cys159 and hence improved the potency.23 Since it was known
from our previous SAR studies which led to the discovery of 1 that
allyl amide P10 provided inhibitors with good rat PK profile12, we
kept allyl amides at P10 for our P4 and P3 optimization studies.
As observed before, extending the P3 unit to P4 with cyclopropyl
Scheme 1. Synthesis of the dithiane inhibitors. Reagents and conditions: (a) 1,2-
dithioethane, PTSA, glacial acetic acid, reflux; (b) 20% HBr, acetic acid; (c) HATU,
DIPEA, P3 Boc amino acid; (d) 1 N LiOH (aq); (e) HATU, DIPEA, P1 hydroxy
allylamide hydrochloride; (f) 4 M HCl/dioxane; (g) P4 isocyanate, triethylamine; (h)
DMSO, dichloroacetic acid, EDACꢁHCl.
to get a dipeptide which up on hydrolysis with LiOH afforded the
acids of type 5. Acid 5 were reacted with P1 hydroxy allyl amides
under the standard coupling conditions to afford the hydroxy allyl
amide intermediates 6. tert-Butyl carbamates 6 were progressed to
the P4 extended ureas 7 by Boc deprotection and reaction with iso-
cyanates14followed by Moffat oxidation (Scheme 1).15
ester resulted in inhibitor 13 (Kꢀ = 84 nM, EC90 = 300 nM) with
i
ninefold improvement in potency compared to their urea analog
(11, Kꢀi = 700 nM). Changing the P3 to cyclohexyl glycine did not
Table 2
SAR of P3 cap
All inhibitors were tested in the HCV continuous enzymatic as-
say16 using the NS4A-tethered single chain NS3 serine protease.17
The Kꢀi values reflected the equilibrium constant determined by
the reversible covalent bond formed between the ketone and ser-
ine and other interactions between the inhibitors and the en-
zyme.18 The concentration required for inhibition of 90% of virus
replication, EC90, was obtained as a measure of replicon cellular po-
tency.19 Inhibitors were tested for the activity against one of the
structurally close related serine protease, human neutrophil elas-
tase (HNE) to determine the selectivity between HCV and HNE.
Results from our previous structural studies showed that intro-
duction of a hydrophobic sulfide moiety at P2 provided some
improvement in binding potency.20The initial set of compounds
for the current study were primary amides 8–11 (Table 1). The ex-
act dithiane analog of Boceprevir (8, Kꢀi = 600 nM) was less active. It
was known from our previous SAR studies that cyclohexyl at P3
improved the potency.21 Although tertiary butyl P3 replacement
with cyclohexyl enhanced the potency (9, Kꢀi = 400 nM), it was
not potent enough to pursue further. We had observed earlier that
cyclopropyl alanine at P1 improved potency.20 Thus, a twofold
improvement in the potency was observed with inhibitor 10
(Kꢀi = 300 nM). Further enhancement was achieved with cyclohexyl
S
O
S
H
N
N
N
H
N
O
O
N
P4
O
O
P3
Kiꢀ
(lM)
Entry
P3
P4
HNE/HCV
NA
EC90
NA
(lM)
12
0.700
O
O
13
14
0.084
0.072
40
15
0.300
0.300
O
O
O
N
15
16
0.021
0.018
290
200
0.070
0.050
O
O
N
O

L. G. Nair et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1689–1692
1691
improve the activity (14, Kꢀ = 72 nM, EC90 = 300 nM) albeit showed
low selectivity. Replacing the ester P3 cap of 13 with the glutari-
Table 4
i
SAR of inhibitors with sulfone as P4
mide demonstrated a profound effect in potency (15, Kꢀi = 21 nM,
EC90 = 70 nM) and eightfold improvement in selectivity. In order
to benefit from potency enhancement (Table 1, in primary amide
series) of the cyclohexyl and the selectivity advantage of the ter-
tiary butyl group we used b-methyl cyclohexyl group, a combina-
tion of these two, at P3. We found the imide 16 (Kꢀi = 18 nM,
EC90 = 50 nM) showed a slight improvement in potency but suf-
fered from loss of selectivity compared to 15.
S
( )n
O
S
H
N
N
N
H
N
O
O
N
P1
S
O
O
O
O
P3
Kiꢀ
(
lM)
Entry
P3
P1
n
EC90
(
lM)
HNE/HCV
Our next focus was to optimize the P1 unit keeping 4,4-dimethyl
glutarimide as P4. From our previous structure–activity studies,12 it
was demonstrated that combination of norvaline at P1 with allyl
amideatP10 providedbetterratexposure.Thus, changingtheP1from
21
1
0.019
0.100
10
cyclopropyl (16) to norvaline afforded 17 (Kꢀ = 6 nM, EC90 = 40 nM)
22
23
24
25
1
1
2
2
0.011
0.033
0.018
0.007
0.070
0.100
0.050
0.030
50
40
i
with similar potency in cellular assays and improvement in enzy-
matic potency and HNE selectivity. Replacement of P3 with tertiary
butyl retained the potency with two to threefold enhancement in
selectivity (18, Kꢀ = 5 nM, EC90 = 40 nM). From our previous struc-
130
128
i
ture–activity studies,12 it was demonstrated that norleucine at P1
improvedtheHNEselectivity. IndeedchangingtheP1fromnorvaline
(18) to norleucine boosted the selectivity by twofold. But this
replacement was detrimental to the potency (19, Kꢀi = 13 nM,
EC90 = 100 nM) with more than twofold loss in both enzymatic and
cellular potencies. Since it was known that longer P1 residues were
optimal for HNE selectivity12 we synthesized the homocyclopropyl
as a combination of cyclopropyl and norleucine at P1. However,
profile, the selectivity for these compounds had to be further
improved.
The SAR above clearly showed that a spirocyclohexyl with an ap-
pended tert-butyl sulfone at P4 improved DMPK properties. Then we
decided to change the ring size of the dithiane and selected analogs
were synthesized to evaluate their effect on selectivity. Thus, the six
inhibitor 20 (Kꢀ = 13 nM, EC90 = 70 nM) was similar to their norleu-
i
cinecounterpart19inpotencyandselectivity(Table3). Wecouldim-
prove both the enzymatic and cellular potency by incorporating the
P4 imide cap and P10 allyl amide. However, none of those inhibitors
showed better rat PK profile compared to 1 (Table 5).
membered dithiane analog 24 (Kꢀ = 18 nM, EC90 = 50 nM) with
i
cyclopropyl P1 improved the potency twofold both in enzymatic
and cellular assays with a threefold augmentation in selectivity
Encouraged by the results obtained from P3 cap exploration we
further studied different P3 cap units, identified in 2,2-dimethyl pro-
line P2 series23 to improve PK. Sulfones24emerged out as one of the
best class of capping group. The sulfone analog of 17 (21,
and a much improved rat exposure of 1.69 lM h. Changing the P1
unit to norvaline (25, Kꢀ = 7 nM, EC90 = 30 nM) further improved
i
the potency threefold maintaining the selectivity and improved rat
exposure (2.56 lM h) (Table 4). Thus, by systematic investigations
on different regions of the molecule we identified a potent dithiane
Kꢀ = 19 nM, EC90 = 100 nM) showed 2–3-fold loss in potency and
i
poor selectivity. However, there was a profound effect on the oral
rat exposure for this compound with 33-fold improvement (21, Ta-
ble 5). As observed before change of P3 to tertiary butyl further im-
proved the selectivity (fivefold) and potency (22, Kꢀi = 11 nM,
EC90 = 70 nM), but exhibited lower exposure. The cyclopropyl P1
inhibitor with enhanced potency and DMPK profile.
From the model of compound 25 bound to the active site of HCV
NS3/4A protease, it was evident that the dithiane P2 fitted into the
S2 pocket very well (Fig. 3). The inhibitor is represented as stick
model, and the protein as surface. The S1–S4 subsites and the ami-
no acid residues forming the S2 pocket are labeled. The larger size
flexible P2 of inhibitor 25 reaches more towards R155 compared to
smaller P2 residue. The resistance profiles of these inhibitors are
yet to be studied.
congener 23 (Kꢀ = 33 nM, EC90 = 100 nM) was less active in the enzy-
i
matic assay and cellular assay compared to 22. Even though we
could identify compounds with desired potency and acceptable PK
In conclusion, we identified a new class of compounds as potent
HCV NS3 serine protease inhibitors. Replacement of the 2,2-di-
methyl cyclopropyl proline with the spiro dithiane proline P2 in
compound 1 resulted in loss of activity. However, by the system-
atic SAR studies of the different regions of the molecule we could
achieve an improvement in replicon activity by 12-folds (25,
Table 3
SAR of P1 substituents
S
O
S
H
N
N
O
N
H
N
O
O
N
P1
N
O
O
P3
Kiꢀ
O
Table 5
Rapid rat PO AUC of selected analogs
Entry
P3
P1
EC90
(l
M)
HNE/HCV
240
(lM)
Kꢀi (nM)
Compound
EC90
(
lM)
PO AUC lM h (10 mpk)
16
17
18
6
0.070
0.040
0.040
0.100
0.100
0.100
0.100
0.050
0.030
0.350
0.20
0.04
0.06
0.2
1.34
0.57
0.77
1.69
2.56
0.14
17
0.006
0.005
0.040
18
5
19
21
22
23
24
25
13
19
11
33
18
7
18
19
20
0.040
0.100
0.070
630
1500
1700
0.013
0.013
SCH503034 (1)
14

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L. G. Nair et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1689–1692
J. P.; Windsor, W. T. Bioorg. Med. Chem. Lett. 2002, 12, 1005–1008; (j)
Ingallinella, P.; Fattori, D.; Altamura, S.; Steinkuhler, C.; Koch, U.; Cicero, D.;
Bazzo, R.; Cortese, R.; Bianchi, E.; Pessi, A. Biochemistry 2002, 41, 5483–5492;
(k) Beevers, R.; Carr, M. G.; Jones, P. S.; Jordan, S.; Kay, P. B.; Lazell, R. C.;
Raynham, T. M. Bioorg. Med. Chem. Lett. 2002, 12, 641–643; (l) Venderville, S.;
Nilsson, M.; de Kock, H.; Lin, T-I.; Antonov, D.; Classon, B.; Ayesa, S.; Ivanov, V.;
Johansson, P-O.; Kahnberg, P.; Eneroth, A.; Wikstrom, K.; Vrang, L.; Edlund, M.;
Lindstrom, S.; Vreken, W. V. De.; McGowan, D.; Tahri, A.; Ku, L.; Lenz, O.;
Delouvroy, F.; Dooren, M. V.; Kindermans, N.; Surleraux, D.; Wigerinck, P.;
Rosenquist, A.; Samuelsson, B.; Simmen, K.; Raboisson, P. Biorg. Med. Chem. Lett.
2008, 18, 6189.
9. For BILN-2061, see: (a) Lamarre, D.; Anderson, P. C.; Bailey, M.; Beaulieu, P.;
Bolger, G.; Bonneau, P.; Bös, M.; Cameron, D. R.; Cartier, M.; Cordingley, M. G.;
Faucher, A-M.; Goudreau, N.; Kawai, S. H.; Kukolj, G.; Lagacé, L.; LaPlante, S. R.;
Narjes, H.; Poupart, M.-A.; Rancourt, J.; Sentjens, R. E.; George, T. S.; Simoneau,
B.; Steinmann, G.; Thibeault, D.; Tsantrizos, Y. S.; Weldon, S. M.; Yong, C.-L.;
Llinàs-Brunet, M. Nature 2003, 426, 186–189; (b) Tsantrizos, Y. S.; Bolger, G.;
Bonneau, P.; Cameron, D. R.; Gordreau, N.; Kukolj, G.; LaPlante, S. R.; Llinas-
Brunet, M.; Nar, H.; Lamarre, D. Angew. Chem., Int. Ed. 2003, 42, 1355–1360.
10. For VX-950, see: (a) Yip, Y.; Victor, F.; Lamar, J.; Johnson, R.; Wang, Q.; May, G.;
John, I.; Yumibe, N.; Wakulchik, M.; Munroe, J.; Chen, S.-H. Bio. Med. Chem. Lett.
2004, 14, 5007–5011; (b) Perni, R. Gordon Research Conference, New London,
New Hampshire, 2005, August 7–12.
11. MK-7009 referneces: (a) Anon Nat. Rev. Drug Discovery 2009, 8, 11; (b) Harper,
S.; Ferrara, M.; Crescenzi, B.; Pompei, M.; Palumbi, M. C.; Di Muzio, J. M.;
Donghi, M.; Fiore, F.; Koch, U.; Liverton, N. J.; Pesci, S.; Petrocchi, A.; Rowley,
M.; Summa, V.; Gardelli, C. J. Med. Chem. 2009, 52, 4820–4837.
12. For Boceprevir: Venkatraman, S.; Bogen, S.; Arasappan, A.; Bennet, F.; Chen, K.;
Jao, E.; Liu, Y.-T.; Lovey, R.; Hendreta, S.; Huang, Y.; Pan, W.; Parekh, T.; Pinto,
P.; Popov, V.; Pike, R.; Ruan, S.; Santhanam, B.; Vibulbhan, B.; Wu, W.; Yang, W.;
Kong, J.; Liang, X.; Wong, J.; Liu, R.; Butkiewicz, N.; Chase, R.; Hart, A.; Agrawal,
S.; Ingravallo, P.; Pichardo, J.; Kong, R.; Baroudy, B.; Malcolm, B.; Guo, Z.;
Prongay, A.; Madison, V.; Broske, L.; Cui, X.; Cheng, K.-C.; Hsieh, T. Y.; Brisson,
J.-M.; Prelusky, D.; Korfmacher, W.; White, R.; Bogdanowich-Knipp, S.;
Pavlovsky, A.; Bradley, P.; Saksena, A. K.; Ganguly, A.; Piwinski, J.;
Girijavallabhan, V.; Njoroge, F. G. J. Med. Chem. 2006, 49, 6074.
Figure 3. Model of compound 25 bound to the active site of HCV NS3/4A protease.
Kꢀ = 7 nM, EC90 = 30 nM). All of the inhibitors with sulfone as P3
i
cap showed improved pharmacokinetic properties compared to 1
in rat model. Our SAR studies with (S)-6, 10-dithia-2-azaspi-
ro[4.5]decane-3-carboxylic acid (2, n = 2) as the new P2 culmi-
nated potent inhibitor, 25, with excellent potency (Kꢀi = 7 nM,
EC90 = 30 nM) and good rat exposure with acceptable selectivity
against elastase.
13. Smith, E. M.; Swiss, G. F.; Neustard, B. R.; Gold, E. H.; Sommer, J. A.; Brown, A.
D.; Deeter, J. B. J. Org. Chem. 1994, 59, 4327–4331.
Acknowledgment
14. (a) Chen, K. X.; Arasappan, A.; Njoroge, F. G.; Vibulbhan, B.; Buevich, A.; Chan,
T.-M.; Girijavallabhan, V. J. Org. Chem. 2002, 67, 2730–2733; (b) Arasappan, A.;
Chen, K. X.; Njoroge, F. G.; Parekh, T. N.; Girijavallabhan, V. J. Org. Chem. 2002,
67, 3923–3926.
15. Pfitzner, K. E.; Moffatt, J. C. J. Am. Chem. Soc. 1991, 113, 7277–7287.
16. Zhang, R.; Beyer, B. M.; Durkin, J.; Ingram, R.; Njoroge, F. G.; Windsor, W. T.;
Malcolm, B. A. Anal. Biochem. 1999, 270, 268–275.
The authors wish to thank virology, DMPK and Structural
Chemistry group of Schering-Plough Research Institute for their
help in in vitro, in vivo and X-ray crystal studies, respectively.
References and notes
17. Taremi, S. S.; Beyer, B.; Maher, M.; Yao, N.; Prosise, W.; Weber, P. C.; Malcolm,
B. A. Protein Sci. 1998, 7, 2143.
18. For a definition of Kꢀi and discussions, see: Morrison, J. F.; Walsh, C. T. In Adv.
Enzymol., Meister, A., Ed.; Interscience: NY, 1988, Vol. 61, pp 201–301.
19. (a) Chung, v.; Carroll, A. R.; Gray, N. M.; Parry, N. R.; Thommes, P. A.; Viner, K.
C.; D’Souza, E. A. Antimicrob. Agents Chemother. 2005, 49, 1381–1390; (b) Blight,
K. J.; Kolykhalov, A. A.; Rice, C. M. Science 2000, 290, 1972–1974; (c) Lohmann,
V.; Körner, F.; Koch, J.-O.; Herian, U.; Theilmann, L.; Bartenschlager, R. Science
1999, 285, 110–113.
20. Bogen, S.; Saksena, A. K.; Arasappan, A.; Gu, H.; Njoroge, F. G.; Girijavallabhan,
V.; Pichardo, J.; Butkiewicz, N.; Prongay, A.; Madison, V. Biorg. Med. Chem. Lett.
2005, 15, 4515–4519.
21. Bogen, S.; Saksena, A.; Bennett, F.; Chen, K.; Jao, E.; Liu, Y.-T.; Lovey, R. G.;
Venkatraman, S.; Pan, W.; Parekh, T.; Pike, R. E.; Ruan, S.; Liu, R.; Baroundy, B.;
Agrawal, S.; Chase, R.; Ingravallo, P.; Pichardo, J.; Prongay, A.; Brisson, J.-M.;
Hsieh, T. Y.; Cheng, K.-C.; Kemp, S. J.; Levy, O. E.; Lim-Wilby, M.; Tamura, S. Y.;
Saksena, A. K.; Girijavallabhan, V.; Njoroge, F. G. J. Med. Chem 2006, 49, 2750–
2757.
22. Tong, X.; Bogen, S.; Chase, R.; Girijavallabhan, V.; Guo, Z.; Njoroge, F. G.;
Prongay, A.; Saksena, A.; Skelton, A.; Xia, E.; Ralston, R. Antiviral Res. 2008, 177–
185.
23. (a) Arasappan, A.; Padilla, A. I.; Jao, E.; Bennett, F.; Bogen, S. L.; Chen, K. X.; Pike,
R. E.; Sannigrahi, M.; Soares, J.; Venkatraman, S.; Vibulbhan, B.; Saksena, A. K.;
Girijavallabhan, V.; Tong, X.; Cheng, K.-C.; Njoroge, F. G. J. Med. Chem. 2009, 52,
2806–2817; (b) Chen, K. X.; Nair, L.; Vibulbhan, B.; Yang, W.; Arasappan, A.;
Bogen, S. L.; Venkatraman, S.; Bennett, F.; Pan, W.; Blackman, M. L.; Padilla, A.
I.; Prongay, A.; Cheng, K.-C.; Tong, X.; Shih, N.-Y.; Njoroge, F. G. J. Med. Chem.
2009, 52, 1370–1379; (c) Venkatraman, S.; Blackman, M.; Wu, W.; Nair, L.;
Arasappan, A.; Padilla, A.; Bogen, S.; Bennett, F.; Chen, K.; Pichardo, J.; Tong, X.;
Prongay, A.; Cheng, K.-C.; Girijavallabhan, V.; George, N. F. Bioorg. Med. Chem.
2009, 17, 4486–4495.
1. (a) Cohen, J. Science 1999, 285, 26–30; (b) Alter, M. J.; Cresson-Moran, D.;
Nanina, O. V.; McMullan, G. M.; GAO, F.; Moyer, L. A.; Maslow, R. A.; Margolis,
H. S. N. Engl. J. Med. 1999, 341, 556–562; (c) Cuthbert, J. A. Clint. Microbial. Rev.
1994, 7, 505–532; (d) Monte, A.; Wright, T. L. Semen. Once. 2001, 441.
2. (a) Neumann, A. U.; Lam, N. P.; Datary, H.; Retch, D. R.; Wiley, T. E.; Leyden, T. J.;
Per Elson, A. S. Science 1998, 282, 103–107; (b) Rosen, H. R.; Retch, D. R. Mol.
Med. Today 1999, 5, 393–399; (c) Di Bisceglie, A. M.; McHutchison, J.; Rice, C. M.
Hepatology 2002, 35, 224–231.
3. Lindenbach, B. D.; Rice, C. M. Nature 2005, 436, 933–938.
4. Kolykhalov, A. A.; Mihalik, K.; Feinstone, S. M.; Rice, C. M. J. Virol. 2000, 74,
2046–2051.
5. Lesk, A. M.; Fordham, W. D. J. Mol. Bio. 1996, 258, 501–537.
6. De Francesco, R.; Steinkuhler, C. Curr. Top. Microbiol. Immunol. 2000, 242, 149–
169.
7. (a) Yan, Y.; Li, Y.; Munshi, S.; Sardana, V.; Cole, J. L.; Sardana, M.; Steinkuehler,
C.; Tomei, L.; De Francesco, R.; Kuo, L. C.; Chen, Z. Protein Sci. 1998, 7, 837–847;
(b) Di Marco, S.; Rizzi, M.; Volpari, C.; Walsh, M. A.; Narjes, F.; Colarusso, S.; De
Francesco, R.; Matassa, V. G.; Sollazzo, M. J. Biol. Chem. 2000, 275, 7152–7157.
8. (a) De Francesco, R.; Migliaccio, G. Nature 2005, 436, 953–960; (b) Tan, S.-L.; He,
Y.; Huang, Y.; Gale, M., Jr. Curr. Opin. Pharmacol. 2004, 4, 465–470; (c)
Malancona, S.; Colarrusso, S.; Ontoria, J. M.; Marchetti, A.; Poma, M.; Stansfield,
I.; Laufer, R.; Marco, A. D.; Taliani, M.; Verdirame, M.; Gonzalez-paz, O.;
Matassa, V. G.; Narjes, F. Bioorg. Med. Chem. Lett. 2004, 14, 4575–4579; (d)
Llinas-Brunet, M.; Bailey, M. D.; Ghiro, E.; Gorys, V.; Halmos, T.; Poirier, M.;
Rancourt, J.; Goudreau, N. J. Med. Chem. 2004, 47, 6584–6594; (e) Andrews, D.
M.; Barnes, M. C.; Dowle, M. D.; Hind, S. L.; Johnson, M. R.; Jones, P. S.; Mills, G.;
Patikis, A.; Pateman, T. J.; Redfern, T. J.; Ed Robinson, J.; Slater, M. J.; Trivedi Org.
Lett. 2003, 5, 4631–4634; (f) Zhang, X. Idrugs 2002, 5, 154–158; (g) Dymock, B.
W. Expert Opin. Emerg. Drugs 2001, 6, 13–42; (h) Dymock, B. W.; Jones, P. S.;
Wilson, F. X. Antiviral. Chem. Chemother. 2000, 11, 79–96; (i) Zhang, R.; Durkin,
24. Unpublished results, Schering-Plough Research Institute.