Novel potent inhibitors of hepatitis C virus (HCV) NS3 protease with cyclic sulfonyl P3 cappings

Article abstract of DOI:10.1016/j.bmcl.2008.12.111

Extensive SAR studies of the P3 capping group led to the discovery of a series of potent inhibitors with sultam and cyclic sulfonyl urea moieties as the P3 capping. The bicyclic thiophene-sultam or phenyl-sultam cappings were selected for further SAR development. Modification at the P3 side chain determined that the tert-butyl group was the best choice at that position. Optimization of P1 residue significantly improved potency and selectivity. The combination of optimal moieties at all positions led to the discovery of compound 33. This compound had the best overall profile in potency and PK profile: excellent K_i^* of 5.3 nM and activity in replicon (EC₉₀) of 80 nM, extremely high selectivity of 6100, and a good rat PO AUC of 1.43 μM h.

Full text of DOI:10.1016/j.bmcl.2008.12.111

Bioorganic & Medicinal Chemistry Letters 19 (2009) 1105–1109
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Novel potent inhibitors of hepatitis C virus (HCV) NS3 protease
with cyclic sulfonyl P3 cappings
*
Kevin X. Chen , Bancha Vibulbhan, Weiying Yang, Latha G. Nair, Xiao Tong,
Kuo-Chi Cheng, F. George Njoroge
Infectious Disease Tumor Biology, Schering-Plough Research Institute, 2015 Galloping Hill Road, K-15-A-3545, 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:
Extensive SAR studies of the P3 capping group led to the discovery of a series of potent inhibitors with
sultam and cyclic sulfonyl urea moieties as the P3 capping. The bicyclic thiophene-sultam or phenyl-sul-
tam cappings were selected for further SAR development. Modification at the P3 side chain determined
that the tert-butyl group was the best choice at that position. Optimization of P1 residue significantly
improved potency and selectivity. The combination of optimal moieties at all positions led to the discov-
ery of compound 33. This compound had the best overall profile in potency and PK profile: excellent Ki* of
5.3 nM and activity in replicon (EC90) of 80 nM, extremely high selectivity of 6100, and a good rat PO AUC
Received 29 September 2008
Revised 23 December 2008
Accepted 31 December 2008
Available online 8 January 2009
Keywords:
HCV
Protease inhibitor
Serine protease
Ketoamide
of 1.43 lM h.
Ó 2009 Elsevier Ltd. All rights reserved.
Hepatitis C virus (HCV) infection is a principle cause of chronic
liver disease that leading to cirrhosis, hepatocellular carcinoma or
liver failure in humans.1 HCV has infected more than 170 million
people worldwide and it has emerged as a major global health
503034)8 from Schering–Plough. Both are in late stage (phase III)
clinical trials.
Our first generation HCV NS3 protease inhibitor, compound 1
(Boceprevir, Fig. 1), is a potent inhibitor of the NS3 protease with
problem. Currently available therapy is
or in combination with ribavirin. The latest combination therapy
with pegylated -interferon and ribavirin generates sustained viro-
a-interferon, either alone
activity in enzyme assay (Ki*) of 14 nM and replicon assay (EC90
)
of 350 nM.8 It has a favorable pharmacokinetic (PK) profile in rats
and dogs (26% and 34% bioavailability, respectively) but low bio-
availability in monkeys (4–11%). Our goal for a next generation
inhibitor was to improve the potency by at least fivefold while
a
logical response in only 50% of infected patients.2 These existing
therapies are also associated with considerable side effects. The
limited efficacy and adverse side effects of the current therapies
has clearly demonstrated that there is a dire need to develop more
effective antiviral agents, and has stimulated intensive research in
finding potent and orally bioavailable small molecule drug
candidates.3
P2
P'
NH2
Cap
O
The HCV viral RNA genome encodes a polyprotein which con-
sists of structural and nonstructural (NS) proteins. The chymotryp-
sin-like serine protease located at N-terminal of NS3 nonstructural
protein is essential for viral replication.4 It has been a valuable tar-
get for which a number of inhibitors have been reported in litera-
ture.5 Several drug candidates have or are being progressed into
clinical trials in human beings. The earliest entry, BILN-2061,6 an
NS3 protease inhibitor from Boehringer–Ingelheim, failed in phase
I clinical trials due to toxicity. Currently, the most advanced candi-
dates are Telaprevir (VX-950)7 from Vertex and Boceprevir (SCH
H
N
N
H
H
N
O
O
N
O
O
P1
P3
1
Boceprevir (SCH503034)
Ki*= 14 nM
EC90 = 350 nM
Ratbioavail. 26%
Monkey bioavail. 4-11%
Dog bioavail. 30%
* Corresponding author. Tel.: +1 908 740 7556; fax: +1 908 740 7152.
E-mail address: kevin.chen@spcorp.com (K.X. Chen).
Figure 1. Boceprevir: the HCV protease inhibitor that is in phase III clinical trials.
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.12.111

1106
K. X. Chen et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1105–1109
O
maintain or improve upon PK profile. Modeling studies based on X-
ray crystal structure of compound 1 revealed that there was ample
room for the P3 cap to be extended beyond current tert-butyl
group. The Cys159 amino acid residue of the protein backbone in
the S4 region provided an opportunity for additional hydrogen
bonding interaction. We envisioned that an extended P3 cap hav-
ing sulfonyl or carbonyl groups at right position could engage in
a hydrogen bonding with Cys159. In the course of our extensive
search for the optimal functionality to establish the hydrogen
bond, we discovered that sultams and cyclic sulfonyl ureas derived
from tert-leucinol provided potent P3 capped inhibitors. Thus, a
number of mono-cyclic and bicyclic sultams and sulfonyl ureas
were studied. We also systematically investigated SAR at other
sites of the inhibitor, namely P3, P1 and P0 residues. The combina-
tion of the best moieties at all positions gave rise to a potent inhib-
itor with favorable PK profile. Herein, we report our SAR
development and the identification of a novel potent sultam-based
HCV NS3 protease inhibitor.
O
NHBoc
R"
H2N
a, b
S
NHBo c
R"
+
N
Cl
SO2Cl
R'
n
R'
n
7
8
9
O
S
O
NHBoc
N
SO2Cl
CO2Me
10
a, c-e
R' R"
11
+
8
O
O
S
NHBoc
R"
N
CbzHN
f
a
H
ClSO2NHCbz
+
R'
12
8
O
O
O
O
S
NHBoc
R' R"
N
(Me)
S
NHBoc
H
CbzN
N
H
N
e, g, (h)
R'
14
R"
The general synthesis of the inhibitors is outlined in Scheme 1.
It has been described in details in our previous publications.8,9
Starting from our unique gem-dimethylcyclopropylproline P2 core
2 and a Boc-protected P3 amino acid, dipeptide 3 was obtained
through a standard EDC mediated coupling. Removal of the Boc
protecting group and subsequent reaction with a capping isocya-
nate afforded compound 4. Hydrolysis of the methyl ester to a car-
Br
13
O
O
S
N=C=O
N
i, j
9, or 11, or 14
R' R"
n
15
boxylic acid 5 and its coupling to a P1
gave rise to a tripeptide. Dess–Martin periodinane10 oxidation of
the hydroxyamide furnished the desired -ketoamide 6. Since
our early research indicated the difficulty in obtaining acceptable
PK from primary ketoamides (R0 = H), we decided to perform all
SAR studies on secondary ketoamides. Among various R0 groups
investigated, allyl group was one of the best moieties for potency
and PK. Thus, R0 was fixed as allyl group for current study.
Synthesis of the capping group, the focus of the current SAR
development, is shown in Scheme 2. Thus, the amino acid derived
a-hydroxy-b-aminoamide
Scheme 2. Reagents and conditions: (a) Et3N, CH2Cl2; (b) NaH, DMF; (c) DIBAL-H,
toluene; (d) MsCl, Et3N, CH2Cl2; (e) Cs2CO3, DMF; (f) 3-bromopropanol, DIAD, PPh3,
CH2Cl2; (g) H2, Pd–C, EtOH; (h) Cs2CO3, MeI, DMF; (i) 4 M HCl, p-dioxane; (j)
phosgene, NaHCO3, H2O/CH2Cl2.
a
the amine was followed by an in-situ intra-molecular cyclization to
form the desired sultam 9. Similarly, o-aromatic sulfonyl chloride
carboxylic esters were reacted with 8 to give sulfonamides. The es-
ters were reduced to alcohols which were then converted to mesy-
lates or chlorides. Finally, intra-molecular cyclization afforded
bicyclic aromatic sultams 11. To gain access to the cyclic sulfonyl
urea of type 14, amine 8 was first treated with Cbz-amino sulfonyl
chloride to give sulfonyl urea 12, which was then alkylated with 3-
bromopropanol under Mitsunobu reaction conditions to give 13,
cyclized, and finally hydrogenated to remove Cbz-protecting
group. The intermediate sultams 9, 11 and cyclic sulfonyl urea 14
were treated with 4 M HCl to remove the Boc group and then re-
acted with phosgene to provide key isocyanate intermediates of
type 15, which were used to make final targets 6 (Scheme 1). All
compounds were isolated as mixture of two diastereomers at P1
a,b-di-amine (8), which could be obtained from commercial pro-
tected amino acid through a reduction to amino alcohol, a Mitsun-
obu reaction11 with phthalimide and subsequent removal of the
phthaloyl group with hydrazine, was treated with chloroalkyl sul-
fonyl chloride (7) in the presence of triethylamine. Sulfonylation of
OMe
b, c
N
a
H
N
OMe
O
a-center. The ratio of two isomers varied between 2:1 and 1:2.
O
N
H
O
O
R3
All inhibitors synthesized were tested in HCV continuous as-
O
say12 using the NS4A-tethered single chain NS3 serine protease.13
The Ki* values in the assay reflected the equilibrium constant deter-
mined by the reversible covalent bond formed between the ketone
and serine and other interactions between the inhibitors and the
enzyme.14 Compounds with good potency were then evaluated in
a replicon assay.15 EC90, the concentration required for inhibition
of 90% of replicon replication, was obtained as a measure of activity
in replicon. To address the issue of selectivity among serine prote-
ases, all inhibitors were assayed against human neutrophil elastase
(HNE), a serine protease with most structural similarity to HCV
NS3 serine protease. The ratio of activity in these two proteases
(HNE/HCV) was used as a measure of the selectivity. Previously,
a multiplex Taqman RT reaction was done to measure both HCV
and endogenous GAPDH RNA levels for analogous compounds.
GAPDH RNA level did not change when measured up to a maxi-
2
3
OH
OMe
d
N
N
H
H
N
H
H
N
O
N
O
O
N
O
O
Cap
Cap
R3
R3
O
O
5
4
O
H
H
N
N
R'
N
e, f
H
H
N
R1
O
N
Cap
O
R3
O
6
mum concentration of 5 lM. Thus, cytotoxicity was never an issue
for this class of inhibitors, and GAPDH was not measured for most
recent compounds.
Scheme 1. Reagents and conditions: (a) Boc-tert-leucine, EDC, HOOBt, DMF/CH2Cl2;
(b) 4 M HCl; p-dioxane; (c) appropriate isocyanate, i-Pr2NEt, CH2Cl2; (d) LiOH, THF/
MeOH/H2O; (e) P1-a-hydroxy-b-aminoamide, EDC, HOOBt, DMF/CH2Cl2; (f) Dess–
Martin periodinane, CH2Cl2.

K. X. Chen et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1105–1109
1107
P3 capping SAR: Discovery of sultam and sulfonyl urea as potent
capping moiety. As demonstrated by X-ray structure of compound
1 bound to the protein, the S4 pocket and Cys159 were potential
targets for additional interactions. After extensive exploration with
the moieties that could both reach into the S4 pocket and form
hydrogen bonding with Cys159, compounds with sulfonyl func-
tionality were proved to be promising. Among them, cyclic sulfon-
amides (sultams) and sulfonyl ureas were found to be more
interesting. Thus, a set of inhibitors with these types of P3 capping
were prepared and evaluated (Table 1). The P1 side chain was fixed
as n-propyl for this study.
A number of structure variations were incorporated into the P3
capping group as shown in Table 1. The caps in compounds 16–20
were mono-cyclic alkyl sultams or sulfonyl ureas, while those in
compounds 21–25 were bicyclic fused aromatic sultams. Most of
the caps were derived from tert-leucine amine (8, R0 = H,
R00 = tert-butyl), except those in compounds 18/24 and 22, where
amine 8 was prepared from cyclohexyl glycinol and 1-amino-1-
cyclohexylmethanol, respectively. We started with compound 16
which had a tert-leucine derived 5-membered sultam P3 cap. It
had good potency in both enzyme assay (Ki* = 11 nM) and replicon
assay (EC90 = 200 nM), but had a moderate selectivity against hu-
man neutrophil elastase (HNE/HCV = 230). This compound had
poor rat PK with oral area-under-curve (PO AUC) of only
0.09 lM h. Expanding the sultam ring size to six led to compound
17. Enzyme potency, selectivity and oral PK AUC were improved
significantly over that of 16, while activity in replicon remained
the same at 200 nM. Replacement of the tert-butyl side chain of
the P3 cap with a cyclohexyl gave group compound 18 which re-
sulted in a loss in both enzyme and activity in replicon (20 and
250 nM, respectively), lower selectivity (50) and rat PO AUC
(0.18 lM h). It was hoped that addition of more heteroatoms to
the P3 cap rings might increase the opportunity of additional
hydrogen bonding, thus improving potency. Initial result from a
Table 1
P3 capping SAR development
O
H
H
N
N
O
N
H
O
N
O
Cap
Compound
P3 cap
Ki* (nM)
HNE/HCV
230
EC90 (nM)
200
Rat PO AUCa
0.09
(lM h)
O
H
N
O
S
N
16
11
O
O
O
O
O
N
H
N
S
S
17
18
6
650
50
200
250
0.67
0.18
O
O
N
H
N
30
O
O
H
S
S
HN
N
N
19
20
21
59
14
10
80
350
150
150
—
O
O
N
O
N
H
N
490
150
0.20
0.43
O
O
O
S
H
N
O
N
S
O
S
H
N
O
N
22
23
41
3
130
650
400
150
—
O
S
O
S
H
N
O
N
N
0.37
O
O
O
S
H
N
O
24
18
15
55
NA
—
—
O
O
H
N
S
N
25
310
230
O
O
a
3 mg/kg, 0.4% MC.

1108
K. X. Chen et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1105–1109
6-membered sulfonyl urea ring (compound 19) was not encourag-
ing (Ki* = 59 nM, EC90 = 350 nM).
However, methylation of the nitrogen gave compound 20 with
enhanced potency and selectivity. It had one of the best activity
in replicon among all mono-cyclic alkyl sulfonyl capped inhibitors
in Table 1.
The fused bicyclic aromatic sulfonyl moieties were of great
interest because of their potential to improve PK properties. Thus,
bicyclic thiophene-sultam analog of 16 was synthesized. Com-
pound 21 maintained enzyme activity (Ki* = 10 nM) but lost some
selectivity (HNE/HCV = 150). However, it had better activity in rep-
licon (EC90 = 150 nM) than 16. The same bicyclic thiophene sultam
did not work well with the 1,1-disubstituted-cyclohexyl moiety in
compound 22, as evidenced by the drop in potency and selectivity.
Changing from 5,5- to 6,5-ring system resulted in the fused bicyclic
phenyl-sultam analog 23. This compound had the best overall pro-
file among all the inhibitors discussed so far. It was the most po-
tent in both enzyme and replicon assays (3 and 150 nM,
respectively) and it had the highest selectivity of 650. It also had
compounds had small ring side chains. Compound 30 had the same
cyclobutylalanine P1 residue as compound 1. Unfortunately, in the
enzyme assay it was substantially less potent (Ki* = 30 nM) than
similar analogs in Table 2, even though its selectivity (HNE/
HCV = 1500) was much higher than that of compound 23. The
smaller ring analog, compound 31, however, had very good en-
zyme potency of 7 nM, along with good activity in replicon
(150 nM). The profile of 31 was comparable to that of 23, except
that selectivity was more than twofold higher. We then investi-
gated terminal alkyne P1 side chain as shown in compound 32. It
definitely improved enzymatic activity by several fold, but selec-
tivity and activity in replicon decreased. Finally, inhibitor with nor-
leucine as P1 residue was prepared (33). The side chain was one
carbon longer than that of 23. We were delighted that compound
had excellent potency in enzyme assay (Ki* = 5 nM) and extremely
high selectivity (HNE/HCV = 6100). More importantly, it achieved
the best activity in replicon (EC90 = 80 nM). This compound (33)
clearly had the best overall profile in potency and selectivity.
Besides a compound’s biological activity, equally important is
its pharmacokinetic properties. PK profile determines whether a
chemical entity has the desired characteristics of a drug. Along
our SAR development, selected promising compounds were evalu-
ated in PK studies. The oral AUC in rats for three most interesting
compounds is listed in Table 3. Both compounds 31 and 23 had
moderate rat PK AUC (0.34 lM h). When this phenyl-sultam moi-
ety was combined with cyclohexyl glycine amine as in compound
24, significant loss of potency and selectivity were observed. We
also investigated inhibitors with bicyclic phenyl acyl sulfonamide
capping (25). Compared to 23, this compound was inferior in both
potency and selectivity.
rat PO AUC below 1.0
lM h. Fortunately, compound 33, the most
Based on these results, we decided that tert-leucine amine-de-
rived thiophene- and phenyl-sultam P3 capping groups (in com-
pounds 21 and 23, respectively) were most interesting for further
SAR development. Optimization at other positions was thus per-
formed with these two capping moieties.
potent of the series, demonstrated good rat PO AUC of 1.43
l
M h.
Thus, through the combination of the novel phenyl-sultam P3
cap, tert-butyl P3 side chain and norleucine P1 residue, a potent
HCV NS3 protease inhibitor with good PK was discovered. It had
best overall profile: Ki* of 5 nM, EC90 of 80 nM, excellent selectivity
P3 side chain modifications. Both X-ray structures16 and our ear-
lier SAR studies indicated that the S3 pocket of HCV NS3 protease
was highly lipophilic and the P3 moiety bound to the enzyme
mainly through hydrophobic interactions. As a result, possible
modifications to the P3 side chain was very limited. Branched alkyl
or carbocyclic groups were among the best options. In the current
study, three P3 residues were incorporated: tert-leucine, cyclo-
hexyl glycine and b-methyl cyclohexyl glycine. They were com-
bined with either thiophene or phenyl-sultam P3 cappings. The
results are summarized in Table 2.
HNE/HCV of 6100, and a favorable rat PK of 1.43 lM h PO AUC. This
Table 2
P3 side chain modifications
O
H
N
H
N
N
H
N
O
O
Cap
O
In the series with thiophene-sultam P3 cap, compounds having
cyclohexyl and b-methylcyclohexyl P3 side chains (26 and 27)
achieved better activity in replicon (EC90 = 100 nM). Compound
27 had better enzyme potency as well (Ki* = 3 nM). However, both
of these compounds were less selective against elastase with HNE/
HCV of 10 and 68, respectively. When phenyl-sultam P3 cap was
incorporated, all three compounds (23, 28, 29) had good activity
in replicon (EC90 = 150 nM) and excellent Ki* (3–7 nM). However,
the selectivity against elastase decreased significantly for com-
pounds 28 and 29 (HNE/HCV = 19 and 50, respectively). Based on
the results from these two series, cyclohexyl and b-methyl cyclo-
hexyl P3 side chains did not provide much improvement in activity
in both enzyme and replicon assays, but resulted substantial loss in
elastase selectivity. Judging from the overall profile of these com-
pounds, inhibitor 23 appeared to the most interesting. A decision
was tentatively made to perform further SAR studies using com-
pound 23 as a template, with P3 cap as phenyl-sultam and P3 side
chain as tert-butyl group.
P1residue optimization. The X-ray structure of the HCV NS3 pro-
tease revealed that the S1 pocket was small and narrow.16 The pre-
ferred P1 side chain is either a short linear alkyl chain or a small
ring attached to a short alkyl chain. Compound 1 had a cyclobutyl
methyl P1 side chain, which was one of the largest group the S1
pocket could accommodate. Compound 23 had a smaller n-propyl
side chain. It could serve as the starting point for further modifica-
tions. The results of this study are listed in Table 3. The first two
R3
Compound P3
P3
Ki* (nM) HNE/HCV EC90 (nM)
O
O
H
S
N
21
N
10
14
3
150
10
150
100
100
S
O
26
27
68
O
O
N
H
N
S
23
28
3
650
150
O
7
19
150
29
5
50
150

K. X. Chen et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1105–1109
2. Monto, A.; Wright, T. L. Semin. Oncol. 2001, 441.
1109
Table 3
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J.; Perelson, A. S. Science 1998, 282, 103; (b) Rosen, H. R.; Gretch, D. R. Mol. Med.
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Mihalik, K.; Feinstone, S. M.; Rice, C. M. J. Virol. 2000, 74, 2046.
Modifications on P1 side chains
O
H
N
H
N
N
O
H
N
H
N
O
S
N
O
O
5. (a) De Francesco, R.; Migliaccio, G. Nature 2005, 436, 953; (b) Tan, S.-L.; He, Y.;
Huang, Y.; Gale, M., Jr. Curr. Opin. Pharmacol. 2004, 4, 465; (c) Malancona, S.;
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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; (b) Tsantrizos, Y. S.; Bolger, G.;
Bonneau, P.; Cameron, D. R.; Gordreau, N.; Kukolj, G.; LaPlante, S. R.; Llinas-
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7. 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. Bioorg. Med. Chem.
Lett. 2004, 14, 5007; (b) Perni, R. Presented at the Gordon Research Conference,
New London, New Hampshire, August, 2005.
P1
O
O
Compound
P1
Ki* (nM)
HNE/HCV
1500
EC90 (nM)
NA
Rat PO AUCa
NA
(lM h)
30
30
7
31
23
32
1600
650
150
150
250
80
0.705
0.373
NA
3
0.9
5
380
33
6100
1.43
a
8. For SCH 503034, see: (a) Njoroge, F. G.; Chen, K. X.; Shih, N.-Y.; Piwinski, J. J. Acc.
Chem. Res. 2008, 41, 50; (b) Venkatraman, S.; Bogen, S. L.; Arasappan, A.;
Bennett, F.; Chen, K.; Jao, E.; Liu, Y.-T.; Lovey, R.; Hendrata, S.; Huang, Y.; Pan,
W.; Parekh, T.; Pinto, P.; Popov, V.; Pike, R.; Ruan, S.; Santhanam, B.; vibulbhan,
B.; Wu, W.; Yang, W.; Yang, W.; Kong, J.; Liang, X.; Wong, J.; Liu, R.; Butkiewicz,
N.; Chase, R.; Hart, A.; Agarwal, S.; Ingravallo, P.; Pichardo, J.; Kong, R.; Baroudy,
B.; Malcolm, B.; Guo, Z.; Prongay, A.; Madision, V.; Broske, L.; Cui, X.; Cheng, K.-
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3 mg/kg, 0.4% MC.
compound is under further evaluation and will serve as the lead
compound for future SAR development.
In summary, a number of novel and potent HCV protease inhib-
itors with various sultam or sulfonyl urea P3 capping groups were
synthesized and investigated. The tert-leucine amine-derived thio-
phene-sultam or phenyl-sultam cappings were the most interest-
ing. The capping group SAR study identified compound 23 as a
starting point for further optimization. Modification on the P3 side
chain established that the tert-butyl group was the best moiety for
that position. With the optimum combination of the phenyl-sul-
tam P3 cap and tert-butyl P3 side chain, an SAR investigation on
the P1 residues significantly improved potency and selectivity fur-
ther. The combination of optimal moieties at all positions led to the
discovery of compound 33, which had the best overall profile in
potency and PK properties: excellent Ki* (5 nM) and activity in rep-
licon (EC90 = 80 nM), extremely high selectivity against elastase
10. Dess, D. B.; Martin, J. C. J. Am. Chem. Soc. 1991, 113, 7277.
11. (a) Hughes, D. L. Org. React. 1992, 42, 335; (b) Mitsunobu, O. Synthesis 1981, 1.
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Malcolm, B. A. Anal. Biochem. 1999, 270, 268. The substrate Ac-DTEDVVP(Nva)-
O-PAP was used in the present study..
13. Taremi, S. S.; Beyer, B.; Maher, M.; Yao, N.; Prosise, W.; Weber, P. C.; Malcolm,
B. Protein Sci. 1998, 7, 2143.
14. For a definition of Ki* and discussions, see: Morrison, J. F.; Walsh, C. T. In
Meister, A., Ed.; Adv. Enzymol.; 1988; Vol. 61, pp 201–301.
15. (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; (b) Blight, K. J.;
Kolykhalov, A. A.; Rice, C. M. Science 2000, 290, 1972; (c) Lohmann, V.; Körner,
F.; Koch, J.-O.; Herian, U.; Theilmann, L.; Bartenschlager, R. Science 1999, 285,
110.
16. (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; (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.
(HNE/HCV = 6100), and a good rat oral PK AUC of 1.43 lM h.
References and notes
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