Finger loop inhibitors of the HCV NS5b polymerase. Part II. Optimization of tetracyclic indole-based macrocycle leading to the discovery of TMC647055

Article abstract of DOI:10.1016/j.bmcl.2012.04.113

Optimization of a novel series of macrocyclic indole-based inhibitors of the HCV NS5b polymerase targeting the finger loop domain led to the discovery of lead compounds exhibiting improved potency in cellular assays and superior pharmacokinetic profile. F

Full text of DOI:10.1016/j.bmcl.2012.04.113

Bioorganic & Medicinal Chemistry Letters 22 (2012) 4437–4443
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Finger loop inhibitors of the HCV NS5b polymerase. Part II. Optimization
of tetracyclic indole-based macrocycle leading to the discovery of TMC647055
⇑
Sandrine Vendeville , Tse-I. Lin, Lili Hu, Abdellah Tahri, David McGowan, Maxwell D. Cummings,
Katie Amssoms, Maxime Canard, Stefaan Last, Iris Van den Steen, Benoit Devogelaere,
Marie-Claude Rouan, Leen Vijgen, Jan Martin Berke, Pascale Dehertogh, Els Fransen, Erna Cleiren,
Liesbet van der Helm, Gregory Fanning, Kristof Van Emelen, Origène Nyanguile, Kenny Simmen,
Pierre Raboisson
Janssen Infectious Diseases BVBA, 30 Turnhoutseweg, B-2340 Beerse, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 30 April 2012
Optimization of a novel series of macrocyclic indole-based inhibitors of the HCV NS5b polymerase
targeting the finger loop domain led to the discovery of lead compounds exhibiting improved
potency in cellular assays and superior pharmacokinetic profile. Further lead optimization performed
on the most promising unsaturated-bridged subseries provided the clinical candidate 27-cyclohexyl-
12,13,16,17-tetrahydro-22-methoxy-11,17-dimethyl-10,10-dioxide-2,19-methano-3,7:4,1-dimetheno-
1H,11H-14,10,2,9,11,17-benzoxathiatetraazacyclo docosine-8,18(9H,15H)-dione, TMC647055 (compound
18a). This non-zwitterionic 17-membered ring macrocycle combines nanomolar cellular potency (EC50 of
Keywords:
Hepatitis C virus
NS5b polymerase
Allosteric inhibitor
Macrocycle
82 nM) with minimal associated cell toxicity (CC50 >20
lM) and promising pharmacokinetic profiles in
rats and dogs. TMC647055 is currently being evaluated in the clinic.
Ó 2012 Elsevier Ltd. All rights reserved.
An estimated 3% of the worldwide population is infected by
Hepatitis C virus (HCV), a major cause of acute hepatitis and
chronic liver disease, ultimately leading to cirrhosis, liver failure,
and hepatocellular carcinoma.1,2 The current standard of care
treatment, incorporating ribavirin and PEG-interferon alpha, suf-
fers from several drawbacks including limited efficacy, treatment
related side-effects and long treatment period, especially in pa-
tients infected by genotype 1 virus.3,4 In the search for novel HCV
direct antiviral agents (DAA), inhibition of the NS5b RNA-depen-
dant RNA-polymerase is of particular interest as this enzyme was
shown to be essential for viral replication5,6 and has no mamma-
lian counterpart.
potent, bioavailable, and non zwitterionic inhibitors, as exemplified
by compound 3 (Fig. 1).22
Here we report our lead optimization of a novel series of mac-
rocyclic inhibitors which have been further rigidified with the
introduction of a bridge between the indole ring and its C2 phenyl
substituent. Indeed, we hypothesized that this approach could
eventually improve the drug-like properties of our lead series by
(i) increasing the potency by bringing the torsion angle between
the phenyl and indole moiety in a pre-bound conformation of
46° as previously determined by X-ray crystallography,18 (ii)
improving the metabolic stability by increasing the overall rigidity
of the molecule, which becomes less accessible to cytochromes and
(iii) balancing the lipophilicity of the cyclohexylindole moiety by
introducing polar functions in the macrocycle. This lead optimiza-
tion effort culminated with the identification of the clinical candi-
date TMC647055 (18a).
Several classes of nucleoside and non nucleoside inhibitors,7,8
targeting the different allosteric sites NNI-1 to 4, have demon-
strated efficacy in clinical trials.9–12 The so-called thumb domain I
or finger loop region13 is an especially attractive target, as
compounds targeting this site enable a broad genotypic coverage.
Several classes of indole-based inhibitors targeting the NNI-1 site
have been discovered and optimized,14–19 with a particular focus
on zwitterionic structures, such as compounds 120 and 221 (Fig. 1).
We have previously reported our strategy towards a new series of
macrocyclic indole-based compounds, leading to the discovery of
The synthesis of the macrocyclic indole derivatives 18a–k, 26a
and 27a (Tables 1 and 2) was performed using either the unsatu-
rated acids 8a–d (Scheme 1) or the cyclopropyl acids 13a,b
(Scheme 2) as starting materials. The cinnamic acid analogs 8a–d
were readily prepared from the 2-bromoindole derivative 423 fol-
lowing the procedures outlined in Scheme 1.
Activation of 423 with pinacolborane followed by the reaction of
the so-formed boronic ester 5 with the substituted 2-bromoben-
zaldehydes in presence of palladium acetate afforded the
⇑
Corresponding author.
E-mail address: svendev1@its.jnj.com (S. Vendeville).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.04.113

4438
S. Vendeville et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4437–4443
N
N
N
N
O
O
O
O
N
S
O
N
OH
NH
OH
O
N
N
O
O
N
O
Cl
1
2
3
EC50 = 127 nM
EC50 = 140 nM
EC50 = 190 nM
Figure 1. Finger loop inhibitors of NS5b polymerase.
Table 1
Effect of the type of bridge on potency in cellular HCV assays, metabolic stability and rat PK parameters
No.
EC50 (nM)
RLMb
HLMb
In vivo rat PK parametersa
[Liver]d (ng/mL)
Clc (L/h/kg)
L/Pe
F (%)f
3
190
82
40
800
79
3830
50
30
72
nd
42
nd
65
35
95
nd
63
nd
7.7
3.2
5.2
—
3.2
—
1717
7807
3200
—
898
—
64
46
38
—
22
—
21
>66
51
—
15
–
18a
26a
27a
25a
25b
a
b
c
d
e
f
Vehicle iv (2 mpk) PEG400/saline 70/30; po (10 mpk) PEG400/2% vitE-TPGS; n = 3.
RLM and HLM: resp. rat and human liver microsomes stability expressed as % of compound metabolized after 15 min at a concentration of 5 lM.
Plasma clearance.
Liver concentrations after oral administration 7 h post-dosing.
Liver/plasma ratio after oral administration 7 h post-dosing.
Oral bioavailability.
corresponding aldehydes 6a–b, which were subsequently reacted
with methyl 2-(dimethoxyphosphoryl)acetate in presence of ce-
sium carbonate to afford the corresponding esters 7a–b in high
yields (72–94%). Alternatively, aldehydes 6c–d could be obtained
via a one step procedure by reacting the bromoindole derivative
4 with commercially available 2-formyl-4 or 5-Cl-phenylboronic
acids, in the presence of potassium carbonate. The acid intermedi-
ates 8a–d were obtained by saponification of the corresponding es-
ters 7a–d in almost quantitative yields.
provide intermediates 16a–k in moderate to good yields (50–
90%). Finally, after the deprotection of the tert-butylester, the
macrocyclisation was achieved by a tandem of reactions involving
the activation of the carboxylic acid in the presence of CDI, fol-
lowed by subsequent intramolecular nucleophilic attack of the
sulfamide moiety in presence of DBU resulting in the target com-
pounds 18a–k. Similarly, this route was applied to the
cyclopropyl carboxylic acids 13a and 13b, to provide compounds
26a and 27a, respectively.
Alternatively, the ester 7a was reacted with trimethylsulfoxoni-
um iodide in presence of sodium hydride to give the cyclopropyl
ester 9, which was saponified to the corresponding acid 10 in
93% yield as shown in Scheme 2. The enantiomerically pure car-
boxylic acids 13a and 13b were obtained via the transformation
of the racemic mixture of 10 into the pair of diastereoisomers
12a and 12b, using (S)-4-benzyl-2-oxazolidinone as chiral auxil-
iary followed by a separation by column chromatography and the
subsequent removal of the chiral auxiliary under basic conditions
in quantitative yields.
Starting from the mono-protected indole derivatives 8a–d and
13a,b two routes were used to introduce the linkers as shown in
Schemes 3 and 4. The first route (Scheme 3) allowed the intro-
duction of the bis-amino linker on the carboxylic acids 8a–d
using either mono-protected bis-amines 14f–h or symmetrical
unprotected bis-amines 14a–e to afford the amides 15a–k in
good yields (>80%). The formation of dimers with the unprotected
bis-amines 14a–e was minimal when an excess of amine was
Alternatively, the target macrocyclic indoles 24a–d were pre-
pared from the corresponding mono-Boc protected bis-amines
20a–d as depicted in Scheme 4. Deprotection of the tert-butyl ester
7a in presence of trifluoroacetic acid followed by the introduction
of the sulfonamides 21a–d, which were readily accessible via a one
step synthesis from the corresponding amines 20a–d, afforded the
open intermediates 22a–d in 53–68% yield. The ester and Boc pro-
tecting groups were successively cleaved by saponification and
treatment with TFA, respectively, leading to the acidamino deriva-
tives 23a–d, which were subsequently macrocyclized to the target
products 24a–d using a CDI/DBU standard procedure. Eventually,
the pure enantiomers possessing a saturated bridge 25a and 25b
(Scheme 5), were synthesized by catalytic hydrogenation of the
olefin bridge of compound 18a, resulting in a mixture of enantio-
mers which were separated by chiral SFC.
Anti-HCV activities (EC50) of final macrocyclic compounds were
determined in the Huh-7 replicon cell line containing the subge-
nomic bicistronic HCV genotype 1b replicon clone ET with a lucifer-
ase read out and compared with the cytotoxicity measured in MT4
and Huh-7 cell lines24 (see Tables 1 and 2). None of the compounds
showed significant cytotoxicity, with selectivity indexes range from
70 to over 400. In addition to potency and selectivity index, meta-
bolic stability and in vivo rat PK parameters were also measured
used in diluted conditions. After
a deprotection step, with
thiophenol in the presence of cesium carbonate in dimethylform-
amide or trifluoroacetic acid in dichloromethane to remove,
respectively, the nosyl or the Boc protecting group, intermediates
15a–k were refluxed in dioxane with an excess of sulfamide to

S. Vendeville et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4437–4443
4439
Table 2
Effect of the linker and phenyl substitution on potency and metabolic stability in the unsaturated-bridged series
O
O
Linker
N
O
S
HN
O
R1
R2
No.
R1
R2
H
Linker
EC50 (nM)
82
SIa
RLMb
30
HLMb
18a
OMe
>300
35
99
N
N
O
N
N
N
18b
18c
OMe
OMe
H
H
160
82
150
46
26
N
>330
56
N
18d
18e
18f
18g
OMe
OMe
OMe
OMe
H
H
H
H
680
470
130
550
72
>68
28
23
27
18
7
N
H
N
H
N
N
H
N
>400
>58
32
N
N
H
N
N
H
N
18h
OMe
H
860
>40
16
10
N
N
N
N
N
18i
18j
Cl
F
H
H
280
72
150
22
37
16
38
N
O
O
>250
N
18k
24a
H
Cl
H
14,480
912
>2
30
13
29
20
N
N
OMe
>40
NH
H
N
24b
24c
OMe
OMe
H
H
N
550
180
>58
25
17
27
26
N
N
>170
N
N
24d
OMe
H
330
>100
12
80
N
a
SI (selectivity index) in Huh-7 cells (CC50/EC50).
RLM and HLM: resp. rat and human liver microsomes stability expressed as% of compound metabolized after 15 min at a concentration of 5 lM.
b
and used to prioritize the different subseries, characterized by a
different bridge. Thus, a first series of analogs having the same lin-
ker in common and only differing by their bridge, namely an
unsaturated bridge for compound 18a, a cyclopropyl bridge for
diastereoisomers 26a and 27a and a saturated bridge for enantio-
macrocycle 3, resulting in very potent inhibitors. Of note, the anti-
HCV activity observed with 26a and 25a was highly enantiospecific,
with a reduction of 20- and 48-fold in potency for the (S)-
enantiomers 27a and 25b, respectively. Compound 18a and active
enantiomers 26a and 25a were further evaluated for rat PK analysis.
The plasma kinetics, oral bioavailability together with liver tissue
distribution in male Sprague–Dawley rats were determined after
a single oral administration of 10 mg/kg of the dosed compounds
using PEG400 2% vitamin E-TPGS as vehicle. These data were ana-
lyzed and compared with those obtained after a single intravenous
(iv) administration of 2 mg/kg in PEG400/saline, 70:30. These re-
sults are reported in Table 1.
mers 25a and 25b, was synthesized and evaluated in vitro (EC50
,
RLM and HLM) and in vivo after a single iv and oral administration
of 2 and 10 mg/kg of macrocyclic compound, respectively (Table 1).
The introduction of a bridge was beneficial for potency, whatever
the type of bridge used (compare 18a, 26a and 25a with 3). Indeed,
more than a two fold increase in replicon inhibition was measured
with the new macrocycles compared with our first generation

4440
S. Vendeville et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4437–4443
c
H
O
O
O
O
H
N
H
N
H
N
O
O
O
O
b
R1
a
O
Br
B
R2
6a-d
HO
4
5
O
O
O
O
O
P
OMe
O
O
OMe
N
N
O
O
O
R1
e
R1
d
R2
R2
7a-d
8a-d
,
,
: R1 = OMe, R2 = H
6a 7a 8a
6b, 7b, 8b: R1 = F, R2 = H
6c, 7c, 8c: R1 = Cl, R2 = H
1
6d 7d 8d
,
,
: R = H, R2 = Cl
Scheme 1. Reactions and conditions: (a) (i) Pinacolborane, TEA, THF, RT; (ii) biphenyl-2-yldicyclohexylphosphine, Pd(OAc)2, 80 °C; (b) 2-Br-4-(R2)-5-(R1)benzaldehyde
1.2 equiv (R1 = OMe, R2 = H and R1 = F, R2 = H), Na2CO3 3 equiv, Pd(PPh3)4 0.05 equiv, DME/H2O 4/1, 70 °C, 1 h; (c) 2-CHO-4-(R1)-5-(R2)phenylboronic acid 1.2 equiv (R1 = Cl,
R2 = H and R1 = H, R2 = Cl), K2CO3 2.4 equiv, PdCl2(PPh3)2 0.05 equiv, DME/H2O 4/1, 70 °C, 3 h; (d) Cs2CO3, DMF, 60 °C; (e) LiOH, H2O/THF/MeOH, RT.
HO
N
O
O
O
O
O
N
O
c
O
b
a
7a
OMe
OMe
10
9
O
O
O
N
HO
N
O
e
O
O
O
Cl
N
O
N
NH
O
O
O
OMe
OMe
O
O
d,
12a
13a
OMe
O
N
11
O
O
HO
O
O
O
e
N
N
O
O
OMe
OMe
12b
13b
Scheme 2. Reactions and conditions: (a) (i) Trimethylsulfoxonium iodide, NaH, DMSO, RT; (ii) 7a, 50 °C; (b) LiOH, H2O/THF/MeOH, RT.; (c) (COCl)2, DMF, THF, 0 °C; (d) (i) (S)-
4-benzyl-2-oxazolidinone (1.1 equiv), n-BuLi (1.1 equiv), THF, À78 °C, (ii) 11, THF, À78 °C, (iii) flash chromatography; (d) NaOH 1 N, MeOH/THF, RT.
All three compounds exhibited an improved in vivo clearance
compared with compound 3. Compounds 18a and 25a although
having a similar clearance of 3.2 L/h/kg, exhibited marked differ-
ences after oral administration. The saturated bridged-analog 25a
resulted in reduced absorbtion compared with its unsaturated
counterpart 18a (oral bioavailability of 15% for 25a vs >66% for
18a), and also displayed a lower distribution to the liver (liver
to plasma ratio being 22 and 46, respectively). Although the
cyclopropyl bridged-analog 26a combines a good oral bioavail-
ability of 51% with a high liver to plasma ratio (38), its clearance
was high (5.2 L/h/kg), above rat hepatic blood flow. Overall, 18a
exhibited the best PK profile with a high bioavailability of at least
66%, an acceptable plasma clearance of 3.2 L/h/kg, and a high he-
patic exposure of 7807 ng/mL at 7 h post oral administration, cor-
responding to approximately 20 times the value of the EC50
measured in the presence of 40% human serum. Of note, the

S. Vendeville et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4437–4443
4441
NH2
S
O
O
H
Linker
N
O
O
Linker
N
O
O
e
d
a, b or c
O
O
8a-d
R1
R1
R2
R2
15a-k
16a-k
NH2
S
O
O
S
O
HN
O
Linker
Linker
O
O
OH
f
N
N
O
O
R1
R1
R2
R2
18a-k
(Table 2)
17a-k
O
O
N
N
N
O
N
O
O S
O S
NH
NH
O
O
O
O
N
N
a, d, e, f
13a-b
OMe
OMe
+
26a
27a
H-linker-H
R-linker-H
H2N
NH2
14a
14b
14e
14f
N
N
N
N
H
H
O
H
N
N
NH2
N
H
Nosyl
Nosyl
14c
14d
14g
14h
NH2
N
N
H
N
H
NH2
Boc N
N
N
N
H
H
Scheme 3. Reactions and conditions: (a) 14a–e, HATU, DIPEA,THF; (b) (i) 14f–g, HATU, DIPEA, THF; (ii) thiophenol, Cs2CO3, DMF, RT (c) (i) 14h, HATU, DIPEA, THF; (ii) TFA/
DCM, (d) sulfamide, dioxane 100 °C; (e) TFA/DCM; (f) CDI, dry THF, RT, then DBU, THF.
excellent distribution to the liver (L/P ratio of 46) observed with
18a is a key parameter toward in vivo efficacy for an anti-HCV
drug given that the virus replicates primarily in hepatocytes.
These results prompted the selection of the unsaturated subseries
for further structure–activity studies.
with 18c). Replacement of the methyl group on the sulfamide nitro-
gen by a bulkier isopropyl group (24d) also led to decreased po-
tency (EC50 = 330 nM) and HLM stability (80% metab.) when
compared with 18c (EC50 = 82 nM, 56% metab.). This reduced activ-
ity might be explained by the steric hindrance of the isopropyl moi-
ety which would disturb the optimal binding conformation of the
acylsulfonamide moiety. Finally, introduction of a basic amine in
the macrocycle resulted in compounds 18e, g, h and 24c which
were all less potent than 18a but were metabolically more stable.
This loss of potency contrasts with the observations from other in-
dole series, where a fivefold gain in potency was measured.15 Anal-
ysis of the published X-ray structure suggests that a small
substituent in position R1 or R2 would be tolerated.18 Although a
fluoro atom in R1 (18j) was found equipotent compared with the
lead 18a (EC50 = 72 and 81 nM, respectively), the introduction of a
chlorine led to 18i, which is approximately three times less potent
than the methoxy analog 18a. The introduction of a chloro atom in
R2 position led to an almost inactive compound (18k,
Two main variations were then considered (see Table 2): the lin-
ker (length, presence of heteroatoms, substitution on the nitrogen)
with the synthesis of compounds 18b–h and 24a–d and the substi-
tution of the phenyl moiety (18i–k). Both the length of the linker
and the substitution on the amines had an impact on potency and
metabolic stability. The optimal macrocycle size was found to be
a 16- to 17-membered ring where 18a, 18c, 18f and 24c were all po-
tent inhibitors (EC50 <200 nM). Although the ring constriction led
reduced potency (18d, EC50 = 680 nM) with a good human liver
microsome stability (18% metab.), the ring extension had little im-
pact on potency (18b, EC50 = 160 nM) but resulted in a dramatic
loss of liver microsome stability (99% metab.). Interestingly similar
effect of macrocycle ring size was observed with our previously
published HCV NS3 serine protease analogs. We hypothesize that
a more rigid macrocycle results in a reduced accessibility to the ac-
tive site of cytochromes leading to reduced metabolism and im-
proved stability. In particular, the removal of either methyl group
on the nitrogens of the linker yielded less active compounds,
although these were more stable in HLM (compare 24a and 24b
EC50 = 14 lM).
Based on their overall profile, 18c, f, j and 24c were selected
and compared with the lead 18a for their PK profile in rats
(Table 3). The zwitterionic compound 24c showed overall sub-
optimal PK properties: poor oral bioavailability (F = 3%)
associated with extensive clearance (Cl = 9.4 L/h/kg) and low

4442
S. Vendeville et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4437–4443
H-linker-Boc
20a-d
Boc
b
Linker
O
O
O
MeO
N
linker-Boc
MeO
N
O
O
S
S
H2N
O
21a-d
OH
NH
O
O
a
d, e
c
OMe
OMe
7a
19
22a-d
H
O
Linker
O
O
Linker
N
HO
O
O
S
S
O
HN
NH
N
f
O
O
OMe
OMe
24a-d
23a-d
H-linker-Boc
n°
N
Boc
20a
20b
20c
20d
H
H
H
N
H
H
N
Boc
N
N
N
N
N Boc
Boc
H
N
Scheme 4. Reagents and conditions: (a) TFA/DCM, RT; (b) sulfamide, dioxane, 100 °C; (c) CDI (1.3 equiv), ACN, 60 °C then 21a–d, DBU (1.5 equiv), 60 °C; (d) LiOH, H2O/THF/
MeOH, RT; (e) TFA/DCM, RT; (f) DIPEA, HATU, dry DMF, 0 °C then RT.
O
O
O
N
N
N
N
O S
O
O
N
O S
O
N
O S
O
O
O
NH
NH
NH
N
N
N
O
O
O
a
OM
e
OMe
OMe
+
18a
25a
25b
Scheme 5. Reagents and conditions: (a) H2, 10% Pd/C, MeOH, THF; chiral separation of enantiomers by SFC using a CHIRALCEL OD-H column.
Table 3
hepatic concentration measured 7 h post dosing ([liver] = 299 ng/
Pharmacokinetic parameters of selected macrocyclic analogs (2 mg/kg iv, 10 mg/kg
po; vehicle iv PEG400/saline 70/30; po PEG400/2% vitE-TPGS, n = 3)
mL). This discrepancy between in vitro rat liver microsome stabil-
ity and in vivo clearance indicates that metabolism may not be
No.
Cla (L/h/kg)
Cmax (ng/mL)
[Liver]b (ng/mL)
L/Pc
F (%)d
the main mechanism of clearance, but bile excretion is most
probably also involved. A poor oral bioavailability (F = 6%) associ-
ated with high clearance (Cl = 4.2 L/h/kg) was also measured with
the analog 18f, although a good liver distribution was observed,
leading to a very high liver to plasma ratio of 341. Somewhat
more encouraging, 18c and 18j displayed a very similar rat PK
profile compared with the lead 18a, however with no major
advantage.
18a
18c
18f
18j
24c
3.2
2.4
4.2
3.7
9.4
440
800
30
272
6
7800
5000
6317
6560
299
46
23
341
62
>66
76
6
52
3
108
a
b
c
Plasma clearance.
Liver concentrations after oral administration at 7 h post-dosing.
Liver/plasma ratio after oral administration 7 h post-dosing.
Oral bioavailability.
d
Further preclinical characterizations were performed on 18a. In
dogs, 18a also showed an acceptable PK profile, characterized by
high oral bioavailability (F = 87%) and high systemic exposure
(Cmax = 10.2
of 10 mg/kg, combined with
l
M and AUC0–inf = 25.8
l
M h) after single oral dosing
(Cl = 0.54 L/h/kg) and low volume of distribution (Vdss = 0.32 L/
kg). Furthermore, and contrary to other series of indole-based
a
moderate plasma clearance

S. Vendeville et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4437–4443
4443
inhibitors containing a carboxylic acid,20,21 in vivo metabolism of
compound 18a in rats did not produce any phase two metabolites,
such as undesirable reactive acyl glucuronides. Further character-
ization of 18a showed a high selectivity towards other polymerases
and a panel of enzymes and receptors, as well as an acceptable
profile in assays measuring cytotoxicity, genotoxicity and cardio-
vascular effects, with little potential to cause drug–drug interac-
tion since no major inhibition of cytochromes CYP450 has been
detected.
In summary, we have described the discovery of macrocyclic
bridged-indoles as very potent inhibitors of HCV replication in
vitro. Modulation of the type of bridge linking the indole moiety
to the C2-phenyl, the macrocycle linker, and the substitution on
the phenyl ring, resulted in the discovery of promising inhibitors
(e.g., 18a, 18c and 18j), which combine potent activity in cellular
HCV assays (EC50 <100 nM), encouraging pharmacokinetic proper-
ties, and acceptable profiles in a panel of preclinical assays. Taken
together, these data enabled us to select 18a (TMC647055) for
further pre-clinical and clinical characterization. This HCV NS5b
polymerase inhibitor is currently being evaluated in phase 2 clini-
cal trials.
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