Discovery of novel tricyclic indole derived inhibitors of HCV NS5B RNA dependent RNA polymerase

Article abstract of DOI:10.1016/j.bmc.2013.01.024

The characterization of HCV genome has identified various vital functional proteins involved in the life cycle of hepatitis C virus. This has resulted in many novel enzymatic targets that are potential for development of therapeutic agents. The HCV RNA de

Full text of DOI:10.1016/j.bmc.2013.01.024

Bioorganic & Medicinal Chemistry 21 (2013) 2007–2017
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Discovery of novel tricyclic indole derived inhibitors of HCV NS5B
RNA dependent RNA polymerase
⇑
Srikanth Venkatraman , Francisco Velazquez, Stephen Gavalas, Wanli Wu, Kevin X. Chen,
Anilkumar G. Nair, Frank Bennett, Yuhua Huang, Patrick Pinto, Yueheng Jiang, Oleg Selyutin,
Bancha Vibulbhan, Qingbei Zeng, Charles Lesburg, Jose Duca, Hsueh-Cheng Huang, Sony Agrawal,
Chuan-kui Jiang, Eric Ferrari, Cheng Li, Joseph Kozlowski, Stuart Rosenblum, Neng-Yang Shih
F. George Njoroge
Merck Research Laboratories, Mail Stop RY121E-28, 126 East Lincoln Avenue, Rahway, NJ 07065-0900, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The characterization of HCV genome has identified various vital functional proteins involved in the life
cycle of hepatitis C virus. This has resulted in many novel enzymatic targets that are potential for devel-
opment of therapeutic agents. The HCV RNA dependent RNA polymerase (HCV NS5B) is one such essen-
tial enzyme for HCV replication that has been well characterized and studied by various groups to
develop novel therapies for hepatitis C. In this paper, we describe our efforts towards the identification
and structure–activity relationship (SAR) of novel tricyclic indole derivatives that bind close to the palm
site of the NS5B polymerase. X-ray crystal structure of an inhibitor bound to the polymerase is also
described.
Received 10 September 2012
Revised 3 January 2013
Accepted 11 January 2013
Available online 23 January 2013
Keywords:
HCV
NS5B
Tricyclic Indole
Pyridone
Replicon
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
and Vaniprevir9 from our laboratories. HCV NS5B polymerase is a
RNA dependent RNA polymerase enzyme which is essential for viral
Approximately 3% of world population has been infected with
hepatitis C virus (HCV) which belongs to the hepacivirus genus
and Flaviviridae family.1,2 The vast majority (ꢀ80%) of these infec-
tions turn chronic, resulting in cirrhosis of the liver and hepatocel-
lular carcinoma. HCV infections are the primary causes of liver
transplantation in the United States. Current standard of care for
the treatment of patients with gt1 infections is a combination of
pegylated interferon, ribavirin and a protease inhibitor which has
resulted in improved management of the disease. About 60–70%
of the patients infected with the major genotype 1 virus demon-
strate sustained virologic response (SVR).3,4 The suboptimal re-
sponse obtained in treating genotype 1 infected patients and non-
responders has prompted experimental new therapies for the treat-
ment of HCV. Characterization of HCV genome has resulted in iden-
tification of various proteins and their functions in the viral life
cycle, providing many novel targets for drug interference. Of these,
the quintessential enzyme HCV NS3 protease5,6 has been widely
studied and many novel inhibitors have been identified and pro-
gressed to clinical evaluation including Boceprevir,7 Narlaprevir8
replication that has been extensively studied as a potential target
for therapeutic intervention. Numerous non-nucleoside (NNI) and
nucleotide (NI) inhibitors targeting various sites of the enzyme
have been identified and progressed to clinical evaluation.
Proof of concept was initially demonstrated with NS5B inhibitor
Nesbuvir10 (HCV-796) resulting in significant viral load reductions
in humans. However, it was discontinued from further develop-
ment due to its adverse side effects. Many nonnucleoside inhibitors
such as filibuvir11, GS-9190,12 ANA598,13 VCH-75914 A83709315 are
currently undergoing or completed clinical evaluations and have
demonstrated robust viral load reductions. Nucleoside derived
polymerase inhibitors such has GS797716 and INX-18917 have dem-
onstrated clinical efficacy and are currently undergoing phase-2
studies. We recently disclosed novel indole derived inhibitors of
HCV NS5B polymerase.18,19 These compounds bind to the NS5B en-
zyme close to the palm site. The X-ray structure of the inhibitor
bound to enzyme indicated novel interactions that contributed to
its specific binding (Fig. 1). 5-Chloroindole derivative 1, functional-
ized with a pyridone at C(3) and benzyl acylsulfonamide at C(2)
demonstrated good enzyme potency (IC50 = 10 nM) and modest
replicon cellular potency (EC50 = 1.0
carboxylic acid analog containing N1 2,4-difluorobenzyl moiety
lM). The corresponding C(2)
⇑
Corresponding author.
E-mail address: Srikanth.Venkatraman@merck.com (S. Venkatraman).
0968-0896/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2013.01.024

2008
S. Venkatraman et al. / Bioorg. Med. Chem. 21 (2013) 2007–2017
S
S
S
Tyr448
Ile447
NH
O
b
a
COOR
Br
CHO
4
N3
Cl
H
O
S
5
2
N
6a R = CH3
6b R = C2H5
4
5
N
O
1
O
S
S
I
F
d
c
F
1
COOR
COOR
N
H
N
H
Cys366
IC50 = 10 nM; EC50 =1.0 uM
7a R = CH3
7b R = C2H5
8a R = CH3
8b R = C2H5
Figure 1.
N
N
S
N
OMe
COOR
S
OMe
COOR
displayed an IC50 = 35 nM and EC50 = 10
l
M). The X-ray structure of
MeO
N
1 bound in the enzyme revealed characteristic hydrogen bonding
interactions of C(3)-pyridone to the protein backbone. The pyridone
oxygen atom accepts a hydrogen bond from tyr448, whereas the
pyridone NH donates hydrogen bond to Ile447. In addition to these
interactions, the chlorine atom at the C(5) position is buried into a
lipophilic channel and the aryl ring of the 2, 5-difluorophenyl
makes close contact with Cys366.
It was clear from the soaked X-ray structure of 1 that the pocket
occupied by the C(5) chlorine was large and could be replaced with
other substitutions, potentially improving potency. We envisioned
syntheses of novel tricyclic indole derivatives by fusing an addi-
tional ring at C(4)–C(5) positions to improve potency. In this paper,
we describe the syntheses and evaluation of NS5B polymerase
inhibitors that culminated in the identification of a novel furan de-
rived tricyclic indoles resulting in improved enzyme binding and
cellular activity.
B(OH)2
e
9
f
N
H
F
10a R = CH3
F
10b R = C2H5
11a R = CH3
11b R = C2H5
N
NH
S
S
OMe
O
O
h or i
g
O
N
OH
N
R
F
F
F
F
13 R = OH
14 R = NHSO2CH3
12
Scheme 1. Reagents and conditions: (a) (i) n-BuLi, ether, À78 °C, 15 min; (ii) DMF,
À78 °C ? rt; (b) N3CH2COOC2H5, NaOMe, methanol, 0 °C ? rt; (c) xylenes, reflux;
(d) NIS, DMF, 0 °C ? rt; (e) Pd(dppf)Cl2, K2CO3, H2O, DME, reflux (f) Cs2CO3, DMF,
2,5-difluorobenzyl bromide, (g) aq LiOH, THF, reflux; (h) 4 M HCl, dioxane, reflux (i)
(i) CH3SO2NH2, CDI, DBU reflux; (ii) 4 M HCl, dioxane.
2. Chemistry
Syntheses of inhibitors used to construct tricyclic ring systems
are outlined in schemes below. Scheme 1 outlines the syntheses
of inhibitors derived from the 6H-thieno[2,3-e]indole core.
Isomeric thiazole fused indole derived inhibitors 20 and 26
were synthesized using palladium catalyzed Heck cyclization and
Fischer indole synthesis,23 as outlined in Scheme 2. Regioselective
iodination of 6-aminobenzothiazole (15) with iodine and silver sul-
fate resulted in formation of 7-iodobenzo[d]thiazol-6-amine (16)
in modest yields.24 The iodinated aniline 16 was converted to ethyl
6H-thiazolo[5,4-e]indole-7-carboxylate (17) by heating with ethyl
pyruvate and palladium acetate in the presence of DABCO.25 Indole
17 was then converted to inhibitor 20 following iodination, Suzuki
coupling, N-alkylation and demethylation in a similar sequence as
outlined in scheme 1. The regioisomeric thiazole compound 26 was
initiated from hydrazide 21. Condensation of 21 with ethylpyru-
vate followed by acid catalyzed cyclization using HCl in ethanol26
resulted in the formation of indole 23 that was converted to inhib-
itor 26 using similar reactions described in Scheme 1.
Scheme 3 outlines syntheses of 4,5-furan fused indole deriva-
tives. Alkylation of commercially available ethyl 5-hydroxy-1H-in-
dole-2-carboxylate (27) with bromoacetaldehyde diethyl acetal
resulted in O-alkylated intermediate 28. Attempts to induce furan
cyclization with intermediate 28 only resulted in polymerization
and intractable mixtures. However, iodination of indole 28 with
NIS resulted in iodo derivative 29 which underwent smooth cycli-
zation to form ethyl 8-iodo-6H-furo[3,2-e]indole-7-carboxylate 30
upon heating with polyphosphoric acid. The furan-derived indole
30 was converted to target 32 following similar reactions previ-
ously described.
Commercially available 7-bromobenzo[b]thiophene (4) was
converted to aldehyde 5 by treatment with n-butyl lithium at
À78 °C to affect bromine–lithium exchange followed by treatment
with DMF. Aldehyde 5 was then subjected to Hemetsberger–Knit-
tel20 reaction to assemble the indole core. Condensation of alde-
hyde 5 with ethyl azidoacetate using sodium methoxide resulted
in azido acrylate derivatives 6a and 6b. Azido compounds 6a and
6b were identified as methyl and ethyl esters arising from trans-
esterification of the ethyl ester with sodium methoxide. The mix-
tures of esters were heated in refluxing xylenes to induce indole
formation. Upon cooling the desired indole products precipitated
from the reaction mixture yielding 6H-thieno[2,3-e]indole-7-car-
boxylate esters (7a and 7b). The facile access to aldehyde 5 fol-
lowed by scalability of the Hemetsberger–Knittel synthesis made
this method desirable and robust for syntheses of indoles. Tricyclic
indoles (7a and 7b) were converted to inhibitor 14 by functionali-
zing the indole at C(3) position using Suzuki coupling followed by
nitrogen alkylation. Thus, a mixture of 7a and 7b were selectively
iodinated at C(3) with NIS to form iodoindoles 8a and 8b. Coupling
of iodo compounds with 2-methoxypyridin-3-ylboronic acid (9)
using Pd(dppf)Cl2 installed methoxypyridine, as a masked pyri-
done moiety.21 N(1) alkylation of indoles 10a and 10b was accom-
plished by treatment with 2,5-difluorobenzyl bromide and Cs2CO3
which were subsequently hydrolyzed to the acid 12 using aqueous
lithium hydroxide. Demethylation of pyridine methyl ether 12
with refluxing 4 M HCl in dioxane yielded pyridone analog 13.
Alternatively, carboxylic acid 12 was coupled with methyl sulfon-
amide using carbonyl diimidazole followed by demethylation with
4 M HCl in dioxane to yield methyl acyl sulfonamide analog 14.22
The regioisomeric furan fused indole 36 was synthesized start-
ing from commercially available methyl 4-methoxy-1H-indole-2-
carboxylate (33). Demethylation of 33 with BBr3 resulted in
hydroxy indole 34, which was alkylated with bromoacetaldehyde

S. Venkatraman et al. / Bioorg. Med. Chem. 21 (2013) 2007–2017
2009
N
S
OC2H5
OC2H5
N
S
A
b
a
HO
NH2
NH2
a
O
b
COOC2H5
I
N
H
COOC2H5
15
16
N
H
N
27
S
28
S
OC2H5
N
N
OCH3
c
I
d
COOC2H5
OC2H5
COOC2H5
I
O
N
O
d
N
H
c
COOC2H5
NH
H
COOC2H5
17
N
18
N
H
H
30
N
NH
O
29
S
S
N
OCH3
COOH
N
e
N
COOH
O
O
N
N
e
O
O
COOH
N
COOC2H5
N
F
F
H
F
32
31
F
F
19
F
20
COOC2H5
S
N
S
N
OH
f
g
OMe
B
N
N
H
NHNH2
a
b
COOCH3
COOCH3
22
N
N
21
N
H
H
34
N
33
N
S
c
c
C2H5O
C2H5O
S
OCH3
O
COOC2H5
O
COOC2H5
N
H
c
d
N
COOCH3
23
d
COOCH3
H
N
H
24
N
H
N
NH
35
36
NH
O
N
N
S
OCH3
S
O
COOH
e
COOH
N
O
N
N
O
e
O
COOH
F
F
N
F
COOCH3
F
N
H
F
25
26
37
F
Scheme 2. Reagents and conditions: (a) (i) Ag2SO4, I2, ethanol, 47%; (b) ethyl
pyruvate, Pd(OAc)2, DABCO, tetramethylene hexammine, DMF, 33%; (c) (i) NIS,
DMF; (ii) 9, Pd(dppf)Cl2, K2CO3, H2O, DME, reflux; (d) (i) Cs2CO3, DMF, 2,5-
difluorobenzyl bromide or 2,4 difluorobenzyl bromide; (ii) aq LiOH, THF, reflux; (e)
4 M HCl/dioxane reflux, 71% (f) ethylpyruvate, HCl; (g) HCl in ethanol reflux.
38
Scheme 3. (A) Reagents and conditions: (a) BrCH(OC2H5)2, Cs2CO3, DMF, 150 °C; (b)
NIS, DMF; (c) PPA, benzene, reflux, 1 h; (d) 9, Pd(dppf)Cl2, K2CO3, H2O, DME, reflux;
(e) (i) 2,5-difluorobenzyl bromide, Cs2CO3, DMF; (ii) aq LiOH, THF; (iii) 4 M HCl/
dioxane reflux. (B) Reagents and conditions: (a) BBr3, CH2Cl2, À78 ? 0 °C; (b)
BrCH(OC2H5)2, Cs2CO3, DMF, 150 °C; (c) Amberlyst-15, benzene, reflux; (d) (i) NIS,
DMF; (ii) 9, Pd(dppf)Cl2, K2CO3, H2O, DME, reflux; (e) (i) 2,5-difluorobenzyl
bromide, Cs2CO3, DMF; (ii) aq LiOH, THF; (iii) 4 M HCl/dioxane reflux.
diethylacetal using conditions previously described. Cyclization of
35 to methyl 6H-furo[2,3-e]indole-7-carboxylate was accom-
plished by refluxing 35 in benzene with strongly acidic resin
amberlyst-15 to obtain indole 36. Tricyclic indole 36 was con-
verted to inhibitor 38 using similar set of reactions outlined in
scheme 1.
47, which were converted to inhibitors of type 49 using methodol-
ogy previously described.
2-Methyl substituted indole 51 was synthesized using metal
catalyzed Claisen rearrangement methodology. Thus, alkylation of
methyl 4-hydroxy indole 2-carboxylate 34 with allyl bromide,
formed O-allylated compound 50. Refluxing 50 with Pd(CH3CN)2Cl2
and benzophenone in the presence of potassium carbonate induced
cyclization to tricyclic indole 51, by a metallo-Claisen rearrange-
ment followed by intramolecular ring closure reaction.27 Versatile
intermediate 51 was progressed to inhibitor 54, following reaction
conditions previously outlined
Furan fused indoles bearing substitutions at two and three posi-
tions of furan were synthesized using methodology outlined in
schemes 4 and 5. The synthesis of methyl 3-chloro-6H-furo[2,3-
e]indole-7-carboxylate (43) was initiated from 2-bromophenol
(39). Alkylation of 39 with 2-bromoacetaldehyde diethylacetal, fol-
lowed by acid catalyzed cyclization afforded 7-bromobenzofuran
40. Chlorination of 40 with chlorine gas followed by treatment
with sodium hydroxide provided 7-bromo-3-chlorobezofuran 41.
Halogen metal exchange of 41 followed by treatment with DMF
yielded aldehyde 42 that was converted to indole 43 using
Hemetsberger–Knittel synthesis. Indole 43 was converted to inhib-
itor 45 using similar protocol previously described. Syntheses of 3-
alkyl substituted indoles were accomplished starting from methyl
4-hydroxyindole-2-carboxylate 34. Alkylation of phenolic oxygen
with bromo acetone or 1-bromobutane-2-one followed by acid cat-
alyzed cyclization resulted in 3-alkyl substituted indoles of type
Synthesized inhibitors were evaluated in NS5B enzyme assay28
for their ability to inhibit the initiation of polymerization using a
NS5BDCT21 polymerase enzyme by 50%. Potent compounds in this
assay were evaluated in the cellular based replicon assay29 to ob-
tain EC50 defined as the concentration required reducing 50% of vir-
al RNA levels in replicon infected hepatoma cells. Cellular toxicity
of inhibitors was evaluated using GAPDH as the internal control
and/or using MTS toxicity assays. Compounds demonstrating

2010
S. Venkatraman et al. / Bioorg. Med. Chem. 21 (2013) 2007–2017
Table 1
OH
39
O
O
c
b
Br
Cl
Br
a
Br
Cl
Entry
Compound
IC50 (nM)
EC50 (nM)
AUCa
104
(lM h)
40
41
NH
O
O
O
55
27
3.5
d
e
CHO
Cl
COOH
COOCH3
N
N
H
43
R1
42
F
NH
F
O
NH
O
O
O
O
56
20
26
14
32
38
57
7
2.0
N
OMe
COOCH3
COOH
Cl
O
R
N
COOH
R1
Cl
f
N
NH
N
H
F
S
44
F
O
N
S
1700c
—
104
45
COOH
N
R1
O
O
NH
O
R
a
b
N
COOCH3
34
COOCH3
O
N
H
47
N
H
9
0.7
5.2
3.1
0.16
0.46
COOH
46
N
R1
NH
N
O
NH
O
O
R
c
S
c
OCH3
O
R
COOH
67
34
31
8
63
N
COOCH3
COOH
N
N
H
R1
F
48
F
NH
49
O
O
Scheme 4. Reagents and conditions: (i) Cs2CO3, BrCH(OC2H5)2, DMF, 150 °C; (ii)
PPA, toluene reflux; (b) Cl2 gas, acetic acid, 0 °C ? rt, (ii) NaOH, methanol; (c) (i)
BuLi, ether, À78 °C; (ii) DMF, À78 °C ? rt; (d) N3CHCOOC2H5, NaOMe, MeOH; (ii)
xylenes, reflux; (e) (i) NIS, DMF; (ii) Pd(dppf)Cl2, K2CO3, H2O, DME, reflux; (f) (i) 2,5-
difluorobenzyl bromide, Cs2CO3, DMF; (ii) aq LiOH, THF; (iii) 4 M HCl/dioxane
reflux.
COOH
N
R1
NH
O
O
O
146
11
COOH
N
R1
CH3
NH
O
O
O
a
b
34
COOCH3
COOCH3
NH
COOH
N
H
N
H
N
R1
50
N
51
O
CH3
b
N
CH3
All compounds demonstrated CC50 >10
lM.
a
O
10 mg/Kg of compound in 0.4% HPMC was dosed to rats orally.
O
O
c
R1 = 2, 4 difluorobenzyl.
e
c
COOH
COOCH3
N
R
52 R =H
53 R = 2, 5 difluorobenzyl
F
d
3. Discussion
F
54
Table 1 summarizes tricyclic indole inhibitors that were synthe-
sized as initial screen for the inhibition of HCV NS5B polymerase.
Previous N(1) SAR studies had shown that a 2,5 difluorobenzyl
group and C(2) carboxylic acid as preferred moieties. Synthesis of
cyclopentyl fused indole resulted in compound 55 (IC50 = 27 nM
Scheme 5. Reagents and conditions: (a) Cs2CO3, allylbromide, DMF, 63%; (b)
Pd(CH3CN)2Cl2, benzoquinone, K2CO3, THF, reflux, 32%; (c) (i) NIS, DMF, (ii) 9,
Pd(dppf)Cl2, K2CO3, H2O, DME reflux; (d) 2,5-difluorobenzyl bromide, Cs2CO3, DMF,
(e) (i) aq LiOH/THF/MeOH, (ii) 4 M HCl/dioxane reflux.
and EC50 = 3.5 lM), with loss in enzyme and replicon activity
poorer than 1. Even though the activity was lower than 1 this
clearly demonstrated that introduction of a five-membered fused
ring at C(4)–C(5) was tolerated and could be optimized to obtain
compound with acceptable activity. Replacement of cyclopentyl
ring in 55 with difluorodioxolane ring resulted in analog 56 that
potent inhibition in enzyme assay and replicon based cellular assay
were evaluated for oral exposure using a rapid rat assay.30 The area
under the curve integrated over 0–6 h after single oral administra-
tion of 10 mg/kg was defined as AUC0–6 h enabling ranking of com-
pounds for further evaluation.

S. Venkatraman et al. / Bioorg. Med. Chem. 21 (2013) 2007–2017
2011
Table 3
demonstrated improved potency IC50 = 7 nM and EC50 = 2 lM. This
was a marginal improvement compared to the cyclopentane ana-
log 55. We next evaluated incorporation of a series of five-mem-
bered heterocycles. Incorporation of a 6H-thiazolo[5,4-e]indole
into the inhibitor scaffold resulted in analog 20 (IC50 = 1700 nM)
that was not well tolerated. However, the introduction of a regio-
NH
O
O
O
isomeric thiazole resulted in analog 26 (IC50 = 9 nM; EC50 = 0.7
that was more potent than the chloro derivative 1.
lM)
O
N
O
HN
S
R5
We next evaluated the introduction of thiophene and furans at
this position. The thiophene derived analog 14 demonstrated
F
F
acceptable potency with IC50 = 67 nM and EC50 = 5.2 lM. Even
though the enzyme potency of this analog was good its potency
in the cellular assay was modest. The introduction of furan rings
resulted in analogs 32 and 38. Inhibitor 32 derived from 6H-
furo[3,2-e]indole-7-carboxylic acid was potent in the enzyme as-
say with IC50 = 34 nM, but demonstrated poor cellular activity with
Entry
R5
IC50 (nM)
EC50 (nM)
AUC (lM h)
60
61
62
63
CH3
9
6
8
0.05
0.11
0.05
0.05
11
0.7
1.0
—
C2H5
(CH3)2CH
cPr
EC50 = 3.1 lM whereas, the regio isomeric furan containing com-
pound 38 demonstrated much improved cellular potency. Thus,
16
analog 38 containing 6H-furo[2,3-e]indole-7-carboxylic acid had
a potency an IC50 = 31 nM and an EC50 = 0.16 lM. This was a signif-
icant improvement in cellular potency compared to the chloro ana-
log 1. The furan derived analog 38 was further reduced to the
dihydrofuran derivative 57 that improved potency but had a weak-
methyl groups are similar in size and display similar lipophilic
properties. The chlorine substituted compound 45 also demon-
strated good oral pharmacokinetics in the rapid rat assay with an
er cellular potency (IC50 = 8 nM; EC50 = 0.46 lM). From the activity
of compounds in Table 1, it is clear that the presence of oxygen at
the four position of the indole is important for potency. Replace-
ment of this group with a sulfur (analog 14) or CH (analog 32) re-
sulted in reduced cellular activity. It is unclear if this loss in activity
is an electronic or steric effect. Tricyclic indole derived analogs
were evaluated for plasma exposure in rats dosed orally at
10 mg/kg in methyl cellulose. The tricyclic inhibitors were readily
absorbed in rats and demonstrated excellent plasma exposure. The
AUC0–6 h = 16 lM h when dosed at 10 mg/kg. We next evaluated
the activity of 2-methyl substituted furano-indole resulting in
compound 53. The methyl substitution at 2-postion was well toler-
ated with compound 53 inhibiting the polymerase enzyme with
IC50 = 21 nM, however it had a weak cellular activity (EC50 = 2 lM);
an 18-fold loss in activity compared to unsubstituted compound 38
(see Table 3.)
All attempts to improve cellular potencies of these inhibitors by
incorporating substitutions on the furan ring only lead to com-
pounds that were less potent than the hydrogen derivative. We
therefore decided to investigate acid isostere modifications at
C(2) carboxylic acid of indole ring. Various alkyl derived acyl sulfon-
amides of the lead compound 38 were synthesized and evaluated in
the binding and cellular assays (Table 3). Thus, functionalization of
C(2) carboxylic acid with methyl acylsulfonamide resulted in ana-
log 60 which demonstrated an enzyme activity of IC50 = 9 nM and
furan derivative 38 demonstrated excellent AUC0–6 h = 146
lM h
and the dihydrofuran derivative had an AUC0–6 h = 11 M h. Having
l
identified the furan fused analog 38 as a potential lead with im-
proved enzyme and cellular activity we evaluated the effect of sub-
stitutions on the furan ring.
The syntheses of substituted furan fused indoles are outlined in
scheme 4 and their inhibitory activities are described in Table 2.
Incorporation of a methyl or ethyl substitution at C(3) position of
the furan ring resulted in analogs 58 (IC50 = 2900 nM) and 59
(IC50 >5000 nM) with significant loss in enzyme potency compared
to the hydrogen analog 38; clearly demonstrating alkyl substitu-
tion was not tolerated at this position. However, the introduction
of a chlorine group (compound 45) displayed high potencies
cellular activity of EC50 = 0.05
acceptable oral rat PK with an AUC0–6 h = 11
10 mg/Kg. Homologation of methyl to ethyl acyl sulfonamide re-
sulted in analog 61 (IC50 = 6 nM, EC90 = 0.11 M) which demon-
strated low oral PK (AUC0–6 h = 0.7 M h). The incorporation of
lM. This analog also demonstrated
l
M h, when dosed at
l
l
(IC50 = 7 nM) and potent cellular activity (EC50 = 0.12
an interesting observation given the fact that both chlorine and
l
M. This is
branched acyl sulfonamide groups had a positive effect on binding
with isopropyl acyl sulfonamide and cyclopropyl acyl sulfonamides
compounds 62 and 63 having IC50’s of 8 and 16 nM and EC50’s of
Table 2
0.05
to analog 1.
Having identified methylacyl sulfonamide as desirable moiety
lM respectively. This is a 20-fold improvement in comparison
R4
NH
at C(2) position of indole, we next explored replacement of N(1)
2,5-difluorobenzyl group with other benzylic moieties. Table 4 out-
lines the results of these modifications. Replacement of 2,5-difluo-
robenzyl group of 60 with 2,4 difluoro benzyl moiety resulted in
O
O
R3
COOH
N
analog 64 (IC50 = 31 nM, EC50 = 0.08 lM) demonstrating dimin-
ished cellular potency compared to 2,5-difluoro analog 60. Intro-
duction of the 2-fluorobenzyl moiety resulted in inhibitor 65
with excellent enzyme inhibition (IC50 = 8 nM) and modest cellular
F
F
activity (EC50 = 0.1
oral exposure in rats (AUC0–6 h = 9.5
2,4 difluorobenzyl analog 64. Introduction of 2,4 dimethylbenzyl
group resulted in analog 66 (IC50 = 6 nM; EC50 = 0.06 M) which
had a similar activity to the 2,5-difluorobenzyl analogs. We next
evaluated the replacement of 2,5-difluorobenzyl group with 2-
methylbenzyl group resulting in compound 67 (IC50 = 10 nM;
l
M). The 2-fluorobenzyl analog had a better
l
M h) than the corresponding
Entry
R3
R4
IC50 (nM)
EC50 (nM)
58
59
45
53
CH3
C2H5
Cl
H
H
H
CH3
2900
>5000
7
—
—
0.12
2.00
l
H
21

2012
S. Venkatraman et al. / Bioorg. Med. Chem. 21 (2013) 2007–2017
Table 4
70 (IC50 = 3 nM; EC50 = 0.05 lM) that had improved enzyme and
cellular profiles than 60. However, the oral exposure of 67 and
69 were poor with an AUC0–6 h = 1.2 and 0.3 lM h, possibly due
to increased metabolism of the methyl group.
HN
O
The X-ray structure of inhibitor 68 bound to HCV NS5B poly-
merase was solved and characteristic interactions responsible for
specific binding with the enzyme were identified (Fig. 2). The
inhibitor bound close to the palm region of the enzyme. The oxy-
gen of the pyridone at C(3) accepted a hydrogen bond from NH
of Ile447 and NH of pyridone in turn donated a hydrogen bond
to Tyr448 making these interactions specific. The aryl ring of the
indole was oriented orthogonal to the pyridone ring and formed
lipophilic interactions with the protein. The C(3)–C(4) fused furan
ring was buried in a lipopholic pocket and was in close proximity
to Tyr415, Met414, Pro197 and Leu384.
O
CH3
O
HN
O
S
O
N
R1
Entry
R1
IC50 (nM)
31
EC50 (nM)
0.08
AUC (
lM h)
64
2.4
The aryl ring of the N(1) benzyl group made lipophilic contact
with the sulfur of cys366 and the carboxamide group interacts
with side chain hydroxyl of Ser367. In addition oxygen of an amide
interacted with Tyr415 and Arg386 via a water molecule.
F
F
65
66
8
6
0.10
0.06
9.5
—
F
4. Conclusions
CH3
H3C
In an effort to improve potency and cellular activity of indole
derived inhibitor 1, novel tricyclic indole scaffolds were synthe-
sized and evaluated for inhibition of HCV NS5B polymerase.
C(4)–C(5) ring fused indoles were prepared and incorporated into
inhibitor scaffold. Five-membered C(4)–C(5) ring fusion was
well-tolerated and yielded compounds with good enzyme activi-
ties and modest cellular potencies. Expanding the SAR of the fused
five-membered rings identified 38, a 6H-furo[2,3-e]indole-7-car-
boxylic acid derived compound that contained a C(4)–C(5) fused
furan with good potency (IC50 = 31 nM) and cellular activity
67
68
10
10
0.05
0.03
1.2
CH3
H2NOC
F
69
70
3
3
0.03
0.05
0.3
F
CH3
(EC50 = 0.16 lM). Further SAR exploration of substitution on the
furan demonstrated that chlorine at C(3) was tolerated. Investiga-
tion of substitutions at indole C(2) showed acyl sulfonamide deriv-
atives were more potent than corresponding carboxylic acids. It
was discovered that methyl acyl sulfonamide was equipotent to
cyclopropyl acyl sulfonamide derivatives. A systematic investiga-
tion of N(1) substitutions in C(2) methyl acyl sulfonamide series
identified N(1) benzyl groups substituted with 2-fluoro and 5-car-
Cl
Tyr448
boxamide, compounds 68 (EC50 = 0.03 lM) demonstrating excel-
lent enzyme activities and cellular potencies.
The X-ray structure of 68 bound to the HCV polymerase enzyme
revealed key hydrogen bonding interactions to the backbone,
which correlated with the enhancement of potency. The interac-
tion of the carboxamide with hydroxyl of Ser367, and oxygen to
Tyr415 and Arg386 via a bound water molecule is worth mention.
We have demonstrated the identification of a novel tricyclic indole
scaffold that inhibits HCV NS5B polymerase in low nanomolar con-
centration and display excellent cellular activities and acceptable
PK. Further optimization of the furan scaffold leading to potent
inhibitors with excellent PK and developable clinical candidates
will be disclosed in future communications.
Ile447
Ser367
5. Experimental
5.1. General
Cys366
Figure 2. X-ray structure of 68 bound to HCV NS5B polymerase.
Dry solvents were purchased from Aldrich or Acros and used
without further purification. Other solvents or reagents were used
as obtained except when otherwise noted. Analytical thin layer
chromatographies (TLC) were performed on pre-coated silica gel
plates available from Analtech. Column chromatography were per-
EC90 = 0.05
of 60 with primary carboxamide derivative yielded inhibitor 68
(IC50 = 10 nM; EC50 = 0.03 M); with improved cellular potency
lM). The replacement of N(1) 2, 5-fluorobenzyl moiety
l
relative to 2,5-dilfuorobenzyl derivatives. Replacement of N(1)
formed using Merck silica gel 60 (particle size 0.040–0.055
lm,
with 2-fluoro-3-methylbenzyl and 2-chlorobenzyl moieties
230–400 mesh), or using Biotage or Isco chromatographic systems
yielded compounds 69 (IC50 = 3 nM; EC50 = 0.03 lM) and inhibitor

S. Venkatraman et al. / Bioorg. Med. Chem. 21 (2013) 2007–2017
2013
with prepacked silica columns. Final compounds were purified by
reverse phase HPLC using C18 column in a Varian HPLC instrument.
Elution was achieved using water, and acetonitrile or water con-
taining 0.1% TFA and THF system. (Column: Waters: Delta Pk, P/
10 mmol), Pd(dppf)Cl2ÁCH2Cl2 (324 mg) and stirred at rt under
nitrogen for 0.25 h. The reaction mixture was treated with a solu-
tion of potassium carbonate (2.77 g, 20.1 mmol) in 25 mL of water
and heated at 90 °C. After 1 h, analysis of TLC of reaction mixture
indicated complete consumption of starting material. The reaction
mixture was diluted with EtOAc (300 mL), and washed with water.
The combined organic layers were dried (MgSO4), filtered, concen-
trated in vacuo and purified by chromatography using EtOAc/hex-
anes (0 ? 70%) to yield 10a and 10b.
No 11805, Wat 011805, 300 mm  30 mm (L/ID) C18, 15
lM,
300 Å, 343K16006 (W): 30 mL/min flow; 30–70% ramp water/ace-
tonitrile; 0 ? 40 min). Visualization was accomplished with UV
light or by staining with basic KMnO4 solution, methanolic H2SO4
or Vaughn’s reagent. NMR spectra were recorded in CDCl3 or
DMSO-d6 unless otherwise noted either in a 400 or 500 MHz (1H
NMR), or 100 or 125 MHz (13C NMR). Mass spectra were obtained
using electron spray ionization methods. Where applicable 13C
NMRs are reported as fluorine coupled spectra unless otherwise
indicated.
5.1.5. 6-(2,5-Difluorobenzyl)-8-(2-oxo-1,2-dihydropyridin-3-yl)-
6H-thieno[2,3-e]indole-7-carboxylic acid (13)
A solution of 10a and 10b (300 mg, 0.90 mmol) in DMF (10 mL)
were treated with cesium carbonate (585 mg, 1.80 mmol), 2,5-
difluorobenzyl bromide (372 mg, 1.80 mmol) and stirred at rt for
12 h. The reaction mixture was diluted with EtOAc (250 mL) and
washed with brine (2 Â 100 mL). The EtOAc layer was dried
(MgSO4), filtered, concentrated in vacuo and purified by chroma-
tography using SiO2 (EtOAc/hexanes) and once again with ace-
tone/CH2Cl2 to yield N(1) alkylated products 10a and 10b as a
colorless solid. The solid were taken in THF (20 mL) and water
(20 mL), treated with lithium hydroxide and refluxed. The disap-
pearance of starting material was followed by TLC. On complete
consumption of starting material the mixture was diluted with
EtOAc (200 mL) washed with water, brine and dried (MgSO4), fil-
tered concentrated in vacuo to yield 12 that was used as is.
A solution of the acid 12 (100 mg, 0.23 mmol) in HCl (4 M solu-
tion in dioxane, 5.0 mL) was treated with 1 mL of methanol and
heated at 90 °C for 3 h. The reaction mixture was concentrated in
vacuo and the residue was dissolved in EtOAc. On treatment with
5.1.1. Benzo[b]thiophene-7-carbaldehyde (5)
A solution of commercially available 7-bromobenzo[b]thio-
phene (8.0 g, 37.5 mmol) in ether (50.0 mL) was cooled to À78 °C
was and treated dropwise with BuLi (1.6 M solution in Hexanes,
21 mL, 37.5 mmol) and stirred at À78 °C for 20 min. The reaction
mixture was treated with DMF (5.4 g, 67.4 mmol) and stirred at
À78 °C for 1 h. The reaction mixture was diluted with water and
extracted with ether. The combined organic layer were washed
with water, dried (MgSO4) filtered concentrated in vacuo and puri-
fied by chromatography (SiO2, EtOAc/Hexanes) to yield 5 as a col-
orless oil. 1H NMR (400 MHz, CDCl3) d 10.25 (s, 1H), 8.12 (d, 1 H,
J = 7.6 Hz), 7.90 (d, 1H, J = 7.2 Hz), 7.67 (d, 1H, J = 5.6 Hz), 7.59 (t,
1H, J = 7.6 Hz), 7.45 (d, 1H, J = 5.6 Hz).
5.1.2. (Z)-Methyl 2-azido-3-(benzo[b]thiophen-7-yl)acrylate (6)
A solution of freshly made sodium methoxide by dissolving
(1.42 g, 62.0 mmol) of sodium in methanol (30 mL) was added
dropwise to a solution of ethylazido acetate (7.99 g, 62 mmol),
and 5.1 g (31 mmol) of aldehyde 5 in methanol (30 mL) at
À20 °C. The reaction mixture was slowly warmed to room temper-
ature and stirred for 3 h. The reaction mixture was concentrated in
vacuo and diluted with EtOAc. The organic layers were washed
with water and dried (MgSO4), filtered, concentrated in vacuo
and purified by chromatography using SiO2 (EtOAc/hexanes) to
yield 6 (3 g) of yellow solid. It was further purified by crystalliza-
tion using ether and hexanes to yield pure product (1.95 g). 1H
NMR (400 MHz, CDCl3) d 8.21 (d, 1H, J = 7.6 Hz), 7.81 (d, 1H,
J = 8.4 Hz), 7.44 (d, 1H, J = 6.0 Hz), 7.42 (t, 1H, J = 8.0 Hz), 7.38 (d,
1H, J = 5.6 Hz), 7.19 (s, 1H), 3.97 (s, 3H).
hexanes
a colorless solid separated out which was filtered
(45 mg) to yield 6-(2,5-difluorobenzyl)-8-(2-oxo-1,2-dihydropyri-
din-3-yl)-6H-thieno[2,3-e]indole-7-carboxylic acid (13) 1H NMR
(500 MHz in DMSO-d6), d 12.88 (b, 1H), 11.78 (s, 1H), 7.81 and
7.62 (AB, 2H, J = 9.0 Hz), 7.61 (dd, 1H, J = 6.5 and 2.0 Hz), 7.51
and 7.48 (AB, 2H, J = 5.3 Hz), 7.52–7.48 (m, 1 H), 7.33 (dt, 1 H,
J = 4.5 and 9.5 Hz), 7.18–7.13 (m, 1H), 6.37–6.33 (m, 2H), 6.04
and 5.95 (AB, 2H, J = 17.5 Hz).13C NMR (125 MHz in DMSO-d6) d
162.6, 161.4, 158.1 (d, JC–F = 242 Hz), 156.0 (d, JC–F = 242 Hz),
140.8, 134.7, 131.5, 124.1, 123.8, 121.2, 120.4, 118.4, 116.9 (dd,
JC–F = 24 and 8.8 Hz), 115.3 (dd, JC–F = 24 and 8.4 Hz), 113.9 (dd,
JC–F = 24 and 6 Hz), 108.9, 104.7, 41.9 (dd, JC–F = 4.1 Hz). LR MS
(ESI) 437 [(M+1)+, 44], 493 [(M+1ÀCO2)+, 100].
5.1.6. Ethyl-6H-thiazolo[5,4-e]indole-7-carboxylate (17)
5.1.3. Methyl 6H-thieno[2,3-e]indole-7-carboxylate (7)
A solution of azido ester 6 (1.9 g, 7.4 mmol) in xylenes was
heated at reflux for 30 min, when the starting material completely
disappears as indicated by TLC. On cooling the solution to room
temperature and partial concentration of the xylenes, indole 7
(1.1 g) precipitated out of solution as a colorless solid. 1H NMR
(400 MHz, DMSO-d6) d, 7.72 (d, 1H, J = 8.8 Hz), 7.57 (d, 1H,
J = 5.2 Hz), 7.48 (d, 1H, J = 5.2 Hz), 7.44 (d, 1H, J = 8.8 Hz), 7.33 (s,
1H), 3.87 (s, 3H).
A
solution of 7-iodobenzo[d]thiazol-6-amine31 (16) (1.7 g,
6.16 mmol) in DMF (15 mL) was extensively degassed and treated
with ethylpyruate (0.965 g, 8.4 mmol), DABCO, Pd(OAc)2 (139 mg,
0.616 mmol) and heated at 105 °C for 12 h. The reaction mixture
was poured into water and extracted with ethyl acetate (an emul-
sion was formed which was painstakingly separated). The organic
layer was dried (MgSO4) filtered concentrated in vacuo and puri-
fied by chromatography SiO2 (EtOAc/hexanes 0–70%) to yield in-
dole 17 (500 mg) as a tan colored solid. 1H NMR (400 MHz,
CDCl3), d 9.63 (s, 1H), 8.93 (s, 1H), 8.06 (s, 1H, J = 8.8 Hz), 7.57 (d,
1H, J = 8.8 Hz), 7.41 (br d, 1H, J = 1.7 Hz), 4.46 (q, 2H, J = 7.3 Hz),
5.1.4. Methyl, 8-(2-methoxypyridin-3-yl)-6H-thieno[2,3-
e]indole-7-carboxylate (10)
1.44 (t, 3H, J = 7.3 Hz); LR-MS (ESI): calcd for
C12H11N2O2S
A solution of indole 7 (1.00 g, 4.33 mmol) in DMF (20 mL) was
treated with N-iodosuccinimide (1.07 g, 4.76 mmol) and stirred
at rt for 12 h. The reaction mixture was concentrated in vacuo, di-
luted with water, and extracted in EtOAc (300 mL). The combined
organic layers were dried (MgSO4), filtered, concentrated in vacuo
and purified by chromatography (SiO2, EtOAc/hexanes) to yield
iodinated compounds 8a and 8b as a colorless solid.
[M+H]+ 247, found 247 (100), 201 (50%).
5.1.7. Methyl-6H-furo[2,3-e]indole-7-carboxylate (36)
A solution of methyl-4-hydroxy indole carboxylate 34 (2.5 g,
13.1 mmol) in DMF (50 mL) was treated with Cs2CO3 (5.12 g,
15.72 mmol),
bromoacetaldehye
diethyl
acetal
(12.90 g,
65.6 mmol) and stirred at reflux for 2 h. The reaction mixture
was cooled to room temperature, treated with aq NaOH (1 M,
50 mL) and extracted into EtOAc (250 mL). The organic layers were
A solution of iodide (1.2 g, 3.35 mmol) in DME (25 mL) was
treated with 2-methoxypyridin-3-ylboronic acid
9
(1.52 g,

2014
S. Venkatraman et al. / Bioorg. Med. Chem. 21 (2013) 2007–2017
dried (MgSO4), filtered, concentrated in vacuo (high vacuum to
distill out DMF and bromoacetaldehyde) and purified by chroma-
tography (SiO2, hexanes/EtOAc 0 ? 100%) to yield methyl 4-(2,2-
diethoxyethoxy)-1H-indole-2-carboxylate 35 (3.5 g, 88%). 1H
NMR (500 MHz, DMSO-d6) d 11.96 (s, 1H), 7.17 (t, 1H, J = 7.6 Hz),
7.08 (dd, 1H, J = 1.0 and 2.2 Hz), 7.05 (d, 1H, J = 8.2 Hz), 6.57 (d,
1H, J = 7.6 Hz), 4.91 (t, 1H, J = 5.1 Hz), 4.07 (d, 2H, J = 5.0 Hz), 3.87
(s, 3H), 3.76–3.61 (m, 4H), 1.17 (t, 6H, J = 7.0 Hz). 13C NMR
(125 MHz, DMSO-d6) d 161.4, 152.5, 138.7, 125.7, 118.0, 105.7,
104.8, 100.5, 100.0, 68.3, 62.1, 51.6, 15.2.
J = 7.2 Hz). A solution of the azido ester (2.8 g, 10.8 mmol) in xy-
lenes (20 mL) was heated at reflux for 20 min until all the ester
was consumed as indicated by TLC (20% EtOAc/hexanes). On cool-
ing the solution to rt, indole 43 crystallized out, which was filtered
and washed with hexanes (500 mg, ꢀ 20%). 1H NMR (400 MHz,
DMSO-d6), d, 12.47 (s, 1H), 8.26 (s, 1H), 7.50 and 7.46 (AB, 2H,
J = 9.0 Hz), 7.35–7.34 (m, 1H), 4.37 (q, 2 H, J = 7.2 Hz), 1.36 (t, 3H).
5.1.11. Methyl-3-ethyl-6H-furo[2,3-e]indole-7-carboxylate (47,
R = C2H5)
A solution of methyl 4-(2,2-diethoxyethoxy)-1H-indole-2-car-
boxylate 35 (4.5 g, 14.7 mmol) in benzene (60 mL) was treated
with strongly acidic resin amberlyst-15 (4.5 g) and heated at
70 °C. The reaction mixture was monitored by TLC (10% EtOAc/hex-
anes). After 4 h, the reaction mixture was cooled, diluted with
EtOAc (300 mL) and washed with saturated aq NaHCO3. The com-
bined organic layers were dried (MgSO4), filtered, concentrated in
vacuo and purified by chromatography (SiO2) EtOAc/Hexanes
(0 ? 30%) to yield indole 36 (1.2 g). 1H NMR (400 MHz, DMSO-
d6), d, 12.31 (s, 1H), 7.93 (d, 1H, J = 2.1 Hz), 7.53 (d, 1H,
J = 8.8 Hz), 7.37 (d, 1H, J = 8.1 Hz), 7.32 (d, 1H, J = 2.0 Hz), 7.00 (br
d, 1H), 3.89 (s, 3H).
A solution of methyl 4-hydroxy indole 2-carboxylate (34,
500 mg, 2.62 mmol) in DMF (4.00 mL) was treated with bromobu-
tanone (789 mg, 5.20 mmol) and Cs2CO3 (936 mg, 2.88 mmol) and
heated at 70 °C for 3 h. The reaction mixture was diluted with
water (100 mL) and extracted into EtOAc (200 mL). The combined
organic layers were dried (MgSO4), filtered concentrated in vacuo
and purified by chromatography (SiO2, EtOAc/hexanaes) to yield
46 (320 mg, 47%). A solution of ketone 46 (3.5 g, 13.4 mmol) in tol-
uene (30.00 mL) was treated with 6.5 g of Amberlyst-15 strongly
acidic resin and heated at 80 °C for 3 h. The reaction mixture was
diluted with EtOAc (300 mL), filtered, washed with aq sodium
bicarbonate, dried (MgSO4), filtered, concentrated in vacuo, and
purified by chromatography to yield indole 47 as a colorless solid.
1H NMR (500 MHz, CDCl3), d, 9.11 (s, 1H), 7.48 (d, 1H, J = 8.5 Hz),
7.45 (dd, 1 H, J = 1.0 and 1.0 Hz), 7.43 (t, 1H, J = 1.0 Hz), 7.30 (dd,
1 H, J = 8.5 and 1.0 Hz), 3.97 (s, 3 H), 2.75 (dq, 2 H, J = 7.5 and
1.5 Hz), 1.36 (t, 3 H, J = 7.5 Hz).
5.1.8. 3-Chloro-7-bromobenzofuran (41)
A solution of 7-bromobenzofuran 40 (20 g, 101 mmol) in acetic
acid (150 mL) was cooled to 15 °C and a gentle stream of chlorine
was passed through the mixture for 0.5 h. The reaction mixture
was concentrated in vacuo, diluted with water and extracted with
ether (1 L). The ether layer was washed with water, dried (MgSO4),
filtered and concentrated in vacuo. KOH (28 g) was dissolved in
methanol (300 mL) and a solution of the crude dichlorinated com-
pound was added dropwise into the base. The reaction mixture
was stirred at room temperature for 20 min. The reaction mixture
was concentrated in vacuo when a colorless solid precipitated out.
The solid was filtered washed with water and dried to yield 41
(14 g, 60%) as a colorless solid. 1H NMR (400 MHz, CDCl3), d, 7.72
(s, 1H), 7.55 (d, 1H, J = 7.6 and 1.2 Hz), 7.53 (d, 1H, J = 7.6 and
1.2 Hz), 7.21 (t, 1H, J = 7.6 Hz).
5.1.12. Methyl-4-(allyloxy)-1H-indole-2-carboxylate (50)
A solution of methyl-4-hydroxy-1H-indole-2-carboxylate, 34
(2.9 g, 15 mmol) and Cs2CO3 (5.4 g, 16 mmol) in DMF (45 mL),
was treated with allyl bromide (1.6 mL, 18 mmol) and heated at
60 °C for 2 h. The reaction mixture was concentrated in vacuo
and the residue diluted with EtOAc (200 mL). The organic layer
was washed with water, brine, dried (MgSO4), filtered and concen-
trated in vacuo. The crude mixture was purified by chromatogra-
phy (SiO2 EtOAc/Hexanes) to yield methyl 4-(allyloxy)-1H-
indole-2-carboxylate 50 (2.2 g, 63%). 1H NMR (400 MHz, CH3OH-
d4), d, 7.22 (s, 1H), 7.15 (t, 1H, J = 7.3 Hz), 7.02 (d, 1H, J = 7.0 Hz),
6.50 (d, 1H, J = 8.1 Hz), 6.19–6.01 (m, 1H), 5.47 (td, 1H, J = 19 and
1.5 Hz), 5.28 (td, 1H, J = 11.6 and 1.6 Hz) 4.66 (s, 2H, J = 5.1 Hz),
3.90 (s, 3H). LR-MS (ESI), relative intesity 312 (40), 272 (20), 232
[(M+1)+, 100], 199 (20).
5.1.9. 3-Chloro-benzofuran-7-carbaldehyde (42)
A
solution of 3-chloro-7-bromobenzo furan 41 (10 g,
43.2 mmol) in ether (100 mL) at À78 °C was treated with BuLi
(15.5 mL, 38.9 mmol, 2.5 M soln.) and stirred À78 °C. After
10 min, dimethylformamide (9 g, 123 mmol) was added to the
mixture and stirred for 0.5 h. The reaction was quenched with a
solution of saturated ammonium chloride and aq HCl (30 mL)
and extracted into ether (700 mL). The combined organic layers
were dried (MgSO4) filtered concentrated in vacuo and purified
by chromatography (SiO2, EtOAc/hexanes) to yield aldehyde 42.
1H NMR (400 MHz, CDCl3), d, 10.42 (s, 1 H), 7.90–7.87 (m, 2 H),
7.80 (s, 1 H), 7.49 (t, 1 H, J = 7.6 Hz).
5.1.13. Methyl-2-methyl-6H-furo[2,3-e]indole-7-carboxylate
(51)
A solution of methyl-4-(allyloxy)-1H-indole-2-carboxylate 50
(2.2 g, 9.5 mmol), p-benzoquinone (1.00 g, 9.5 mmol) and K2CO3
(1.3 g, 9.5 mmol) in dioxane (15.0 mL) was degassed and treated
with bis(acetonitrile)palladium(II) chloride (200 mg, 0.9 mmol)
and heated at reflux for 5 h. The reaction mixture was diluted with
water and extracted into EtOAc (300 mL). The combined organic
layers were washed with aq NaOH (1 M, 300 mL). The organic layer
was dried (MgSO4), filtered, concentrated in vacuo and purified by
chromatography (SiO2, EtOAc/hexanes) to yield methyl-2-methyl-
6H-furo[2,3-e]indole-7-carboxylate 51 (702 mg, 32%) as a colorless
solid 1H NMR (400 MHz, CD3OD) d, 7.35 (d, 1H, J = 8.8 Hz), 7.27 (d,
1 H, J = 8.1 Hz), 7.25 (s, 1H), 6.44 (s, 1H), 3.92 (s, 3H), 2.47 (s, 3H).
5.1.10. Methyl-3-chloro-6H-furo[2,3-e]indole-7-carboxylate
(43)
Metallic sodium (1.43 g, 61.9 mmol) was added carefully to
methanol (60 mL) and stirred for 20 min till a homogenous solu-
tion was obtained. This was added dropwise to a solution of alde-
hyde 42 (5.00 g, 27.68 mmol) and ethyl azido acetate (8 g,
61.9 mmol) in 30 mL of methanol at À20 °C. The reaction mixture
was stirred at rt for 2 h and quenched with aq saturated ammo-
nium chloride and concentrated in vacuo. The mostly aqueous
layer was extracted with EtOAc (700 mL) and purified by chroma-
tography (SiO2, EtOAc/hexanes) to yield azido ester as a colorless
solid. 1H NMR (400 MHz, CDCl3), d, 8.29 (td, 1H, J = 7.6, 0.4 and
0.4 Hz), 7.68 (s, 1H), 7.58 (dd, 1H, J = 8.0 and 1.2 Hz), 7.42 (s, 1H),
7.37 (t, 1H, J = 7.6 and 0.4 Hz), 4.41 (q, 2H, J = 7.2 Hz), 1.43 (t, 3H,
5.1.14. 6-(2,5-Difluorobenzyl)-8-(2-oxo-1,2-dihydropyridin-3-
yl)-6H-thiazolo[5,4-e]indole-7-carboxylic acid (20)
1H NMR (400 MHz in DMSO-d6) d, 9.17 (s, 1 H), 8.01 and 7.79
(AB, 2 H, J = 9.00 Hz), 7.60 (dd, 1H, J = 7.0 and 2.5 Hz), 7.51 (dd,
1H, J = 6.5 and 2.0 Hz), 7.32–7.27 (m, 1H), 6.97 (dt, 1H, J = 8.5 and
2.0 Hz), 6.76–6.71 (m, 1H), 6.37 (t, 1H, J = 6.5 Hz), 6.06–5.95 (AB,
2 H, J = 15.8 Hz); 13C NMR (125 MHz, DMSO-d6, F-coupled), d

S. Venkatraman et al. / Bioorg. Med. Chem. 21 (2013) 2007–2017
2015
162.5, 162.4, 162.3, 161.2, 160.5, 160.4, 160.3, 158.5, 158.4, 152.3,
149.2, 141.1, 135.1, 134.8, 129.0, 128.96, 128.93, 128.88, 126.9,
125.3, 125.1, 121.7, 121.6, 121.53, 121.50, 120.1, 119.7, 118.4,
111.59, 111.56, 111.42, 111.39, 110.5, 104.9, 104.1, 103.9, 103.8,
103.6, 41.7, 41.65, LR-MS (ESI): calcd for C22H14F2N3O3S [M+H]+
438, found 438 (100), 394 (30)
1H, J = 6.8 Hz), 6.15–6.10 (m, 1H), 5.96 (s, 2H), 2.28 (s, 3H); LR-MS
(ESI): calcd for C24H17F2N2O4 [M+H]+ 435, found 435 (100).
5.1.20. 6-(2,5-Difluorobenzyl)-3-ethyl-8-(2-oxo-1,2-
dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-carboxylic acid
(59)
1H NMR (400 MHz, DMSO-d6), d 13.2 (s, 1H), 11.92 (s, 1H), 7.75
(d, 1H, J = 6.6 Hz), 7.57 and 7.44 (AB, 2 H, J = 8.8 Hz), 7.50 (d, 1H,
J = 6.6 Hz), 7.47 (s, 1H), 7.30 (dt, 1H, J = 4.4 and 4.3 Hz), 7.15–7.09
(m, 1H), 6.35 (t, 1H, J = 6.6 Hz), 6.16–6.13 (m, 1H), 6.00 (s, 2H),
5.1.15. 3-(2,5-Difluorobenzyl)-1-(2-oxo-1,2-dihydropyridin-3-
yl)-3,6,7,8-tetrahydrocyclopenta[e]indole-2-carboxylic acid (55)
1H NMR (400 MHz, DMSO-d6) d above 12 (1 H), 11.6 (s, broad,
1H), 7.43 (dd, 1H, J = 2 and 6.5 Hz), 7.39 (dd, 1H, J = 2 and
6.5 Hz), 7.30 (d, 1H, J = 8.5 Hz), 7.27 (dt, 1H, J = 4.5, 9.3 and
9.3 Hz), 7.20 (d, 1H, J = 8.5 Hz), 7.11 (m, 1H), 6.36 (m, 1H), 6.27
(t, 1H, J = 6.5 Hz), 5.85 (br, 2 H), 2.86 (t, J = 7.6 Hz, 2 H), 2.72 (br,
2 H), 1.98 (br, 2 H). 13C NMR (125 MHz, DMSO-d6, F-coupled spec-
tra), d, 162.8, 161.8, 158.9, 157.0, 156.4, 154.5, 140.5, 136.9, 136.1,
135.9, 134.1, 127.8, 127.7, 127.67, 127.6, 126.9, 126.2, 123.3, 121.6,
118.6, 116.8, 116.7, 116.6, 116.5, 115.2, 115.1, 115.0, 114.9, 114.04,
114.0, 113.84, 113.80, 108.5, 104.6, 41.51, 41.48, 39.9, 39.8, 39.6,
39.4, 39.2, 39.1, 38.9, 31.6, 31.2, 24.5. HR-MS (ESI): calcd. for
2.77 (q, 2H, J = 7.3 Hz), 1.18 (t,
3
H, J = 7.3 Hz). 13C NMR
(125 MHz, DMSO-d6, F-coupled), d 162.3, 159.9, 159.0, 157.1,
156.4, 154.5, 147.1, 145.5, 141.0, 138.0, 136.0, 127.7, 127.5,
121.8, 120.3, 117.4, 116.99, 116.92, 116.8, 116.7, 115.34, 115.28,
115.0, 113.6, 113.4, 111.8, 106.5, 105.8, 104.9, 41.8, 17.2, 14.5.
LR-MS (ESI): calcd for C25H19F2N2O4 [M+H]+ 449, found 449 (100)
5.1.21. 3-Chloro-6-(2,5-difluorobenzyl)-8-(2-oxo-1,2-
dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-carboxylic acid
(45)
C
24H19F2N2O3 [M+1]+ 421.1363, found 421.1360.
1H NMR (400 MHz, DMSO-d6), d 13.11 (s, 1H), 11.76 (s, 1H), 8.18
(s, 1H), 7.69 (dd, 1H, J = 2.2 and 4.4 Hz), 7.63 and 7.49 (AB, 2H,
J = 8.8 Hz), 7.41 (d, 1H, J = 5.5 Hz), 7.30 (dt, 1H, J = 4.4 and
4.3 Hz), 7.17–7.11 (m, 1H), 6.38–6.33 (m, 1H), 6.32 (t, 1H,
J = 6.6 Hz), 5.95 (s, 2H). 13C NMR (125 MHz, DMSO-d6, F-coupled),
d 162.6, 161.3, 159.0, 157.1, 157.1, 156.5, 156.5, 154.6, 147.5,
140.4, 139.5, 136.6, 134.3, 127.4, 127.3, 127.2, 127.1, 125.6,
118.3, 117.0, 116.98, 116.85, 116.78, 115.5, 115.5, 115.3, 115.3,
115.0, 114.1, 114.08, 113.9, 113.87, 112.7, 112.0, 108.2, 104.8,
42.1, 42.1. LR-MS (ESI): calcd for C23H14ClF2N2O4 [M+H]+ 455,
found 455 (30), 411 (100)
5.1.16. 6-(2,5-Difluorobenzyl)-8-(2-oxo-1,2-dihydropyridin-3-
yl)-6H-furo[3,2-e]indole-7-carboxylic acid (32)
1H NMR (400 MHz, in DMSO-d6): d above 12 (1H), 11.81 (br s,
1H), 7.95 (s, 1H), 7.60 (d, 2H, J = 8.8 Hz), 7.5 (d, 1H, J = 9.5 Hz),
7.46 (d, 1H, J = 6.6 Hz), 7.30 (ddd, 1H, J = 4.4, 8.8, 9.5 Hz), 7.13 (m,
1H), 6.57 (s, 1H), 6.36–6.31 (m, 2 H), 5.95 (s, 2 H); LR-MS (ESI):
calcd for C23H15F2N2O4 [M+H]+ 421, found 421.
5.1.17. 6-(2,5-Difluorobenzyl)-8-(2-oxo-1,2-dihydropyridin-3-
yl)-6H-furo[2,3-e]indole-7-carboxylic acid (38)
1H NMR (400 MHz, DMSO-d6), d 12.8 (s, 1H), 11.74 (s, 1H), 7.85
(d, 1H, J = 1.5 Hz), 7.68 (dd, 1H, J = 2.2 and 6.6 Hz), 7.56 and 7.47
(AB, 2 H, J = 8.8 Hz), 7.40 (d, 1H, J = 5.2 Hz), 7.30 (dt, 1H, J = 4.4
and 5.0 Hz), 7.16–7.11 (m, 1H), 6.97 (d, 1H, J = 2.2 Hz), 6.36–6.31
(m, 2H), 5.93 (s, 2H). 13C NMR (125 MHz, DMSO-d6, F-coupled
spectra), d 162.7, 161.4, 158.9, 157.0, 156.4, 154.5, 147.8, 143.5,
140.4, 136.0, 134.1, 127.59, 127.53, 127.4, 127.3, 126.3, 126.0,
120.2, 118.3, 117.0, 116.9, 116.8, 116.7, 115.4, 115.39, 115.32,
115.27, 115.20, 114.08, 114.05, 113.88, 113.85, 112.7, 107.1,
106.8, 104.9, 41.97, 41.94 LR-MS (ESI): calcd for C23H15F2N2O4
[M+H]+ 421, found 421 (50), 377 (100).
5.1.22. 6-(2,5-Difluorobenzyl)-2-methyl-8-(2-oxo-1,2-
dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-carboxylic acid
(53)
1H NMR (400 MHz, DMSO-d6), d above 12.97 (s, 1H), 11.75 (s,
1H), 7.70 (dd, 1H, J = 1.8 and 6.8 Hz), 7.44 and 7.38 (AB, 2 H,
J = 8.7 Hz), 7.45–7.36 (m, 1H), 7.29 (dt, 1H, J = 4.6 and 9.1 Hz),
7.15–7.10 (m, 1H), 6.57 (d, 1H, J = 0.9 Hz), 6.34 (t, 1H, J = 6.8 Hz),
6.35–6.30 (m, 1H), 5.89 (s, 2H), 2.34 (s, 3H). 13C NMR (125 MHz,
DMSO-d6, F-coupled), d 162.8, 161.5, 158.0 (d, JC–F = 238 Hz),
155.5 (d, JC–F = 238 Hz), 152.4, 147.1, 140.4, 135.5, (dd, JC–F = 24
and 8.3 Hz), 126.4, 125.9, 121.6, 117.6, 116.9 (d, JC–F = 24 and
9.3 Hz), 114.7, 114.0 (dd, JC–F = 25.9 and 5.5 Hz), 112.4, 106.3,
104.9, 103.0, 41.8 (dd, JC–F = 3.7 Hz), 13.5. LR-MS (ESI): calcd for
5.1.18. 6-(2,5-Difluorobenzyl)-8-(2-oxo-1,2-dihydropyridin-3-
yl)-3,6-dihydro-2H-furo[2,3-e]indole-7-carboxylic acid (57)
1H NMR (400 MHz, in DMSO-d6): d 12.92 (1H, br s), 11.67 (1H,
br s), 7.50 (1H, dd, J = 1.5, 6.6 Hz), 7.34 (1H, d, J = 5.1 Hz), 7.30
(1H, dt, J = 4.4, 8.8 Hz), 7.18 (1H, d, J = 8.8 Hz), 7.14 (1H, m), 6.99
(1H, d, J = 8.8 Hz), 6.34 (1H, m), 6.27 (1H, t, J = 6.6 Hz), 5.79 (2H,
s), 4.54 (2H, t, J = 8.8 Hz), 3.16 (2H, t, J = 8.8 Hz); 13C NMR
(125 MHz, in DMSO-d6): d 162.9, 161.5, 158.0 (d, JC–F = 240.4 Hz),
155.5 (d, JC–F = 240.4 Hz), 153.2, 140.6, 138.8, 133.7, 127.6 (dd,
JC–C–F = 17.5 Hz, JC–C–C–F = 7.3 Hz), 126.6, 125.9, 121.7, 116.9 (dd,
JC–C–F = 24.0 Hz, JC–C–C–F = 8.3 Hz), 116.8, 115.5, 115.3 (dd, JC–C–
F = 24.0 Hz, JC–C–C–F = 8.3 Hz), 114.0 (dd, JC–C–F = 24.9 Hz, JC–C–
F = 5.5 Hz), 112.1, 104.8, 102.2, 71.9, 41.7 (d, JC–C–F = 3.6 Hz),
28.7 ppm. LR-MS (ESI): calcd for C23H17F2N2O4 [M+H]+ 423.12,
found 422.99.
C
24H17F2N2O4 [M+H]+ 435, found 435 (100), 391 (50).
5.1.23. 6-(2,5-Difluorobenzyl)-N-(methylsulfonyl)-8-(2-oxo-1,2-
dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-carboxamide (60)
1H NMR (400 MHz, DMSO-d6), d 12.6 (s, 1H), 12.7 (s, 1H), 7.99
(d, 1H, J = 6.6 Hz), 7.85 (s, 1H), 7.69–7.65 (m, 1H), 7.60 and 7.49
(AB, 2H, J = 8.8 Hz), 7.33–7.24 (m, 1H), 7.18–7.13 (m, 1H), 6.99
(s, 1H), 6.63–6.53 (m, 2H), 5.78 (s, 2H), 3.24 (s, 3H) LR-MS (ESI):
calcd for C24H18F2N3O5S [M+H]+ 498, found 498 (30), 435 (100),
377 (30).
5.1.24. 6-(2,5-Difluorobenzyl)-N-(ethylsulfonyl)-8-(2-oxo-1,2-
dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-carboxamide (61)
1H NMR (400 MHz, DMSO-d6) d above 12 (2H), 8.00 (d, 1H,
J = 7.2 Hz), 7.84 (dd, 1H, J = 2.0 and 7.2 Hz), 7.69 (t, 1H,
J = 6.4 Hz), 7.61 and 7.53 (AB, 2H, J = 9.2 Hz), 7.30 (dt, 1H, J = 4.0
and 8.8 Hz), 7.18–7.13 (m, 1H), 6.99 (dd, 1H, J = 1.2 and 2.4 Hz),
6.64 (t, 1H, J = 7.6 Hz), 6.57–6.53 (m, 1H), 5.79 (s, 2H), 3.35 (q,
2H, J = 8.0 Hz), 1.04 (d, 3H, J = 7.6 Hz). 13C NMR (125 MHz, DMSO-
d6, F-coupled spectra), d 163.5, 161.7, 159.9, 158.0, 157.6, 155.6,
5.1.19. 6-(2,5-Difluorobenzyl)-3-methyl-8-(2-oxo-1,2-
dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-carboxylic acid
(58)
1H NMR (400 MHz, DMSO-d6), d above 12 (s, 1H), 11.94 (s, 1H),
7.77 (dd, 1H, J = 2.0 and 8.5 Hz), 7.54 and 7.47 (AB, 2 H, J = 8.8 Hz),
7.54–7.44 (m, 2 H), 7.33–7.27 (m, 1H), 7.17–7.08 (m, 1 H), 6.35 (t,

2016
S. Venkatraman et al. / Bioorg. Med. Chem. 21 (2013) 2007–2017
148.5, 145.9, 144.6, 140.8, 137.1, 136.8, 129.0, 127.8, 127.8, 127.7,
127.6, 124.0, 121.6, 119.8, 117.9, 117.7, 117.8, 116.7, 116.7, 116.5,
115.7, 115.7, 115.5, 115.5, 113.7, 113.6, 108.2, 108.1, 108.0, 47.7,
43.0, 43.0, 8.2. LR-MS (ESI): calcd for C25H20F2N3O5S [M+H]+ 512,
found 512 (30), 435 (50), 402 (30), 377 (100).
5.1.29. 6-(2,4-Dimethylbenzyl)-N-(methylsulfonyl)-8-(2-oxo-
1,2-dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-carboxamide
(66)
1H NMR (400 MHz, DMSO-d6), d 12.70 (s, 1H), 12.59 (d, 1H,
J = 5.4 Hz), 7.99 (dd, 1H, J = 1.9 and 4.9 Hz), 7.85 (t, 1H,
J = 1.5 Hz), 7.66 (t, 1H, J = 4.9 Hz), 7.54 and 7.35 (AB, 2H,
J = 8.8 Hz), 7.00 (br s, 1H), 6.98 (d, 1H, J = 2.5 Hz), 6.76 (d, 1H,
J = 7.8 Hz), 6.62 (t, 1H, J = 6.4 Hz), 6.14 (d, 1H, J = 7.8 Hz), 5.66 (s,
2H), 3.10 (s, 3H), 2.31 (s, 3H), 2.18 (s, 3H). LR-MS (ESI): calcd for
5.1.25. 6-(2,5-Difluorobenzyl)-N-(isopropylsulfonyl)-8-(2-oxo-
1,2-dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-carboxamide
(62)
C
26H24N3O5S (M+1)+ 490, found 490 (60), 427(60), 395 (35), 369
1H NMR (400 MHz, DMSO-d6), d above 12 (2H), 8.00 (td, 1H,
J = 1.6 and 6.8 Hz), 7.84 (m, 1H), 7.71 (t, 1H, J = 6.8 Hz), 7.62 and
7.54 (AB, 2 H, J = 8.8 Hz), 7.30 (dt, 1H, J = 4.4 and 8.8 Hz), 7.18–
7.13 (m, 1H), 6.99–6.98 (m, 1H), 6.64 (t, 1H, J = 7.2 Hz), 6.54–6.49
(m, 1H), 5.80 (s, 2H), 3.63–3.55 (m, 1H), 1.14 (d, 6 H, J = 7.2 Hz).
13C NMR (125 MHz, DMSO-d6, F-coupled spectra), d 162.6, 160.7,
159.0, 157.1, 154.7, 147.6, 145.1, 143.7, 136.2, 135.9, 128.0,
126.9, 126.8, 123.0, 120.7, 118.9, 117.1, 117.0, 116.9, 115.7,
115.6, 115.5, 114.7, 114.5, 112.8, 112.6, 107.4, 107.3, 107.2,
107.1, 52.6, 42.1, 42.0, 15.1. LR-MS (ESI): calcd for C26H22F2N3O5S
[M+H]+ 526, found 526 (100), 377 (60).
(100).
5.1.30. 6-(2-Methylbenzyl)-N-(methylsulfonyl)-8-(2-oxo-1,2-
dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-carboxamide (67)
1H NMR (400 MHz, DMSO-d6), d 12.69 (s, 1H), 12.60 (s, 1H), 8.00
(dd, 1H, J = 1.5 and 5.4 Hz), 7.85 (d, 1H, J = 2.5 Hz), 7.66 (t, 1H,
J = 5.9 Hz), 7.55 and 7.36 (AB, 2H, J = 8.8 Hz), 7.19 (d, 1H,
J = 7.3 Hz), 7.10 (t, 1H, J = 7.3 Hz), 6.98 (d, 1H, J = 2.0 Hz), 6.95 (t,
1H, J = 7.8 Hz), 6.62 (t, 1H, J = 6.8 Hz), 6.22 (d, 1H, J = 7.8 Hz), 5.71
(s, 2H), 3.09 (s, 3H), 2.37 (s, 3H). 13C NMR (125 MHz, DMSO-d6) d
173.8, 173.3, 172.7, 172.2, 159.2, 155.9, 154.9, 154.8, 151.2,
147.8, 147.5, 147.7, 146.9, 145.9, 145.8, 141.2, 138.0, 137.3,
138.1, 136.1, 135.2, 131.6, 129.9, 129.7, 126.3, 118.8, 118.6, 62.8,
30.1, 30.0; LR-MS (ESI): calcd for C25H22N3O5S [M+H]+ 476. found
498 [(M+Na)+ 10]. 476 (50). 355 (100).
5.1.26. N-(Cyclopropylsulfonyl)-6-(2,5-difluorobenzyl)-8-(2-
oxo-1,2-dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-
carboxamide (63)
1H NMR (400 MHz, DMSO-d6), d above 12 (2H), 7.98 (dd, 1H,
J = 2.0 and 7.2 Hz), 7.84 (d, 1H, J = 2.0 Hz), 7.69 (t, 1H, J = 5.2 Hz),
7.61 and 7.52 (AB, 2 H, J = 8.4 Hz), 7.30 (dt, 1H, J = 5.2 and
9.6 Hz), 7.19–7.13 (m, 1H), 6.99 (d, 1H, J = 2.0 Hz), 6.63 (t, 1H,
J = 6.4 Hz), 6.60–6.56 (m, 1H), 5.80 (s, 2 H), 2.96–2.89 (m, 1H),
0.96 (d, 4 H, J = 6.4 Hz). 13C NMR (125 MHz, DMSO-d6, F-coupled
spectra), d 162.5, 160.6, 159.0, 157.1, 154.8, 147.6, 144.9, 143.7,
136.1, 135.8, 128.1, 123.1, 120.6, 118.8, 117.0, 116.9, 116.8,
115.8, 115.8, 115.6, 115.6, 114.9, 114.8, 114.7, 114.6, 112.6,
112.6, 107.2, 107.1, 41.9, 30.5, 5.3. LC-MS (ESI, water [0.1% TFA]/
acetonitrile): calcd for C26H20F2N3O5S [M+H]+ 524, found 524
(100).
5.1.31. 6-(5-Carbamoyl-2-fluorobenzyl)-N-(methylsulfonyl)-8-
(2-oxo-1,2-dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-
carboxamide (68)
1H NMR (400 MHz, DMSO-d6), d above 12 (2H), 7.98 (dt, 1H,
J = 2.4 and 7.2 Hz), 7.86 (s, 1H), 7.82–7.80 (m, 2H), 7.68 (t, 1H,
J = 6.0 Hz), 7.59, 7.52 (AB, 2H, J = 3.2 Hz), 7.53–7.51 (m, 1H), 7.33
(s, 1H), 7.30 (t, 1H, J = 9.2 Hz), 6.98–6.96 (m, 1H), 6.63 (t, 1H,
J = 7.2 Hz), 5.81 (s, 2H), 3.25 (s, 3H). LR-MS (ESI): calcd. for
C
25H20FN4O6S [M+H]+ 523, found 523 (100).
5.1.32. 6-(2-Fluoro-3-methylbenzyl)-N-(methylsulfonyl)-8-(2-
oxo-1,2-dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-
carboxamide (69)
5.1.27. 6-(2,4-Difluorobenzyl)-N-(methylsulfonyl)-8-(2-oxo-1,2-
dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-carboxamide (64)
1H NMR (400 MHz, DMSO-d6), d 12.8 (s, 1H), 12.9 (s, 1H), 7.96
(d, 1H, J = 6.6 Hz), 7.84 (d, 1H, J = 2.2 Hz), 7.66 (bt, 1H), 7.59 and
7.51 (AB, 2 H, J = 8.8 Hz), 7.28 (dt, 1H, J = 2.2 and 8.8 Hz), 6.98 (d,
1H, J = 2.2 Hz), 6.98–6.87 (m, 2H), 6.61 (t, 1H, J = 6.6 Hz), 5.77 (s,
3H), 3.25 (s, 3H); 13C NMR (150 MHz, DMSO-d6) d 162.4, 160.9,
160.5, 160.4, 158.8, 158.74, 147.6, 144.6, 143.6, 136.1, 135.6,
129.9, 129.8, 128.2, 123.2, 121.1, 121.0, 120.6, 118.7, 112.6,
111.6, 111.4, 107.2, 107.1, 104.1, 103.9, 103.8, 41.7, 41.1. LR-MS
(ESI): calcd for C24H18F2N3O5S [M+H]+ 498, found 498 (30), 377
(15), 337 (25), 169 (40), 107 (100).
1H NMR (400 MHz, DMSO-d6), d above 12 (2H), 7.97 (dd, 1H,
J = 1.6 and 6.8 Hz), 7.84–7.83 (m, 1H), 7.66 (t, 1H, J = 6.4 Hz), 7.58
and 7.48 (AB, 2 H, J = 8.8 Hz), 7.16 (t, 1H, J = 8.5 Hz), 6.98–6.97
(m, 1H), 6.92 (t, 1H, J = 7.6 Hz), 6.61 (t, 1H, J = 6.8 Hz), 6.57 (t, 1H,
J = 7.2 Hz), 5.79 (s, 2H), 3.22 (s, 3H), 2.23 (s, 3H). 13C NMR
(125 MHz, DMSO-d6, F-coupled spectra), d 162.4, 160.9, 158.9,
157.0, 147.5, 144.5, 143.5, 136.1, 135.6, 130.5, 128.2, 125.7,
124.4, 124.2, 123.9, 123.2, 120.5, 118.5, 112.4, 107.3, 107.2,
107.0, 42.2, 42.1, 41.0, 13.9, LR-MS (ESI): calcd for C25H21FN3O5S
[M+H]+ 494, found 494 (30), 373 (100).
5.1.28. 6-(2-Fluorobenzyl)-N-(methylsulfonyl)-8-(2-oxo-1,2-
dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-carboxamide (65)
1H NMR (400 MHz, DMSO-d6) d 12.77 (br s, 1H), 12.61 (br s, 1H),
7.98 and 7.96 (d, J = 6.04 Hz, 2H), 7.86–7.83 (m, 1H), 7.67 (s, 1H),
7.60 and 7.58 (d, J = 7.7 Hz, 1H), 7.51 and 7.49 (d, J = 8.3 Hz, 1H),
7.32–7.27 (m, 1H), 7.21 (t, J = 8.8 Hz, 1H), 7.05 (t, J = 7.7 Hz, 1H),
6.82 (t, J = 7.7 Hz, 1H), 6.67–6.60 (m, 1H), 5.81 (s, 2H), 3.22 (s,
3H). 13C NMR, (125 MHz, DMSO-d6, F-coupled spectra), d 162.4,
160.8, 160.4, 158.5, 147.5, 144.5, 143.5, 136.1, 135.5, 129.3,
129.2, 128.4, 128.4, 124.6, 124.5, 124.4, 120.5, 118.5, 115.2,
115.1, 112.5, 112.4, 107.2, 107.1, 107.0, 42.0, 41.0; LR-MS (ESI):
calcd for C24H19FN3O5S (M+1)+: 480.3; Found 502 [(M+Na)+, 5],
480 (10), 417 (10), 359 (25), 251 (100).
5.1.33. 6-(2-Chlorobenzyl)-N-(methylsulfonyl)-8-(2-oxo-1,2-
dihydropyridin-3-yl)-6H-furo[2,3-e]indole-7-carboxamide (70)
1H NMR (500 MHz, DMSO-d6), d 12.77 (br s, 1H) 12.67 (d, 1H,
J = 6.5 Hz), 8.02 (dd, 1H, J = 2.5 and 7 Hz), 7.87 (d, 1H, J = 2.5 Hz),
7.68 (dt, 1H, J = 2 and 6 Hz), 7.57 (d, 1H, J = 9 Hz), 7.51 and 7.33
(AB, 2 H, J = 8.5 Hz), 7.29 (dt, 1H, J = 8 and 2.0 Hz), 7.15 (dt, 1H,
J = 7.5 and 1.0 Hz), 7.01 (d, 1H, J = 2.0 Hz), 6.64 (t, 1H, J = 7 Hz),
6.40 (d, 1H, J = 8.0 Hz), 5.79 (s, 2H), 3.17 (s, 3H). 13C NMR
(125 MHz, DMSO-d6), d 162.5, 160.8, 147.6, 144.7, 143.7, 136.2,
135.7, 135.2, 130.1, 129.2, 128.8, 127.4, 127.1, 120.7, 118.9,
113.1, 112.5, 107.2, 107.1, 46.0, 41.0. LR-MS (ESI): calcd for
C
24H19ClN3O5S [M+H]+ 496, found 496 (20), 400 (10) 375 (100).

S. Venkatraman et al. / Bioorg. Med. Chem. 21 (2013) 2007–2017
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