Inhibitors of HCV NS5B polymerase: Synthesis and structure-activity relationships of unsymmetrical 1-hydroxy-4,4-dialkyl-3-oxo-3,4-dihydronaphthalene benzothiadiazine derivatives

Article abstract of DOI:10.1016/j.bmcl.2007.01.072

Substituted 1-hydroxy-4,4-dialkyl-3-oxo-3,4-dihydronaphthalene benzothiadiazine derivatives were investigated as inhibitors of genotype 1 HCV polymerase. Structure-activity relationship patterns for this class of compounds are discussed. It was found that

Full text of DOI:10.1016/j.bmcl.2007.01.072

Bioorganic & Medicinal Chemistry Letters 17 (2007) 2289–2292
Inhibitors of HCV NS5B polymerase: Synthesis and structure–
activity relationships of unsymmetrical 1-hydroxy-4,4-dialkyl-
3-oxo-3,4-dihydronaphthalene benzothiadiazine derivatives
A. Chris Krueger,* Darold L. Madigan, Brian E. Green, Douglas K. Hutchinson,
Wen W. Jiang, Warren M. Kati, Yaya Liu, Clarence J. Maring, Sherie V. Masse,
Keith F. McDaniel, Tim R. Middleton, Hongmei Mo, Akhteruzzaman Molla,
Debra A. Montgomery, Teresa I. Ng and Dale J. Kempf
Infectious Disease Research, Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, IL 60064, USA
Received 12 December 2006; revised 15 January 2007; accepted 18 January 2007
Available online 27 January 2007
Abstract—Substituted 1-hydroxy-4,4-dialkyl-3-oxo-3,4-dihydronaphthalene benzothiadiazine derivatives were investigated as inhib-
itors of genotype 1 HCV polymerase. Structure–activity relationship patterns for this class of compounds are discussed. It was found
that the saturated alkane dialkyl units provided the most active analogs.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Hepatitis C virus (HCV) is a (+)-strand RNA virus of the
Flaviviridae family that was first identified in 1989.1 HCV
is a common pathogen that can lead to cirrhosis, hepato-
cellular carcinoma (HCC) and liver failure. It is estimat-
ed that 170 million people were infected worldwide in the
year 2000, and that the virus is responsible for at least
10,000 deaths annually in the United States alone.2
HCV has six major genotype classes, with genotypes 1
and 2 being the most prevalent in the United States, Eur-
ope, and Japan.3 Currently combination drug treatment
of genotype 2 or 3 is more successful than treatment of
genotype 1 infection.4,5 Moreover, existing therapies
are hampered by drug-related toxicities. Therefore there
is a particular need for new therapies directed toward
genotype 1 HCV infection.6
hydroxyquinolon-3-yl-benzothiadiazine series into a
dialkyl naphthalene unit.9 We refer to this related series
as the 1-hydroxy-4,4-dialkyl-3-oxo-3,4-dihydronaphtha-
lenes. Upon generation of a small set of 1-hydroxy-4,4-
dialkyl-3-oxo-3,4-dihydronaphthalene analogs, the SAR
data initially suggested that the most potent analogs
contain an unsymmetrical dialkyl unit in the B ring as
shown in Table 1.10
These data imply that the two alkyl groups are binding
into different pockets or environments within the HCV
polymerase enzyme. The data also imply that one of
the two enantiomers of a racemic mixture should be
more active than the other. Thus we embarked upon a
strategy to assemble a set of unsymmetrical 1-hydroxy-
4,4-dialkyl-3-oxo-3,4-dihydronaphthalene analogs in
order to optimize both the biochemical (recombinant
HCV polymerase) and antiviral (HCV subgenomic
replicon)11 potencies of this series. We felt that we would
be able to construct a number of these desired analogs
by employing a late stage olefin metathesis reaction
upon the allyl group of thiadiazine 4, represented in
Figure 1. This paper highlights the efforts directed
toward that strategy.
Our research group has been pursuing inhibition of the
HCV NS5B RNA-dependent RNA polymerase (RdRp)
enzyme by hydroxyquinolon-3-yl-benzothiadiazines.7
Other groups have reported nucleoside as well as other
non-nucleoside inhibitors of this viral enzyme.8 We
have also recently transformed the B ring in the
Keywords: HCV; NS5B; Polymerase; 1-Hydroxy-4,4-dialkyl-3-oxo-3,4-
dihydronaphthalene benzothiadiazine.
*
The chemistry utilized to prepare the 1-hydroxy-4,4-
dialkyl-3-oxo-3,4-dihydronaphthalene analogs is shown
Corresponding author. Tel.: +1 847 938 2944; fax: +1 847 938
2756; e-mail: a.chris.krueger@abbott.com
0960-894X/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.01.072

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A. C. Krueger et al. / Bioorg. Med. Chem. Lett. 17 (2007) 2289–2292
benzenesulfonamide.12 Reduction of the nitro moiety
followed by a chemo-selective mesylation gave the
desired benzothiadiazine precursor 5.
Table 1. Biochemical and cell culture replicon potency of analogs 1–3
O
O
H
N
S
C
OH
N
S
D
O O
Scheme 2 depicts the synthetic transformations employed
to prepare many of the unsymmetrical 1-hydroxy-4,4-
dialkyl-3-oxo-3,4-dihydronaphthalene analogs. Com-
mercially available 1-methyl-2-tetralone was allylated
with palladium catalysis employing a racemic mixture of
the cyclohexyl 2-DPPBA ligand developed by Trost in or-
der to accelerate the reaction.13 This reaction provided
dialkylated tetalone 6, from which the corresponding enol
ether (7) was made followed by oxidation and hydrolysis
to the unsymmetrical dialkyl diketone (9). Formation of
the dithioketene acetal (10) allowed a mild, neutral
coupling to amino-sulfonamide 5, which provided the
methyl, allyl-benzothiadiazine 4. Reaction of this materi-
al (4) with a variety of alkenes employing the Hoveyda–
Grubbs 2nd generation catalyst produced a number
of differentially substituted alkene analogs (11a–11f).
These alkene analogs could then be transformed easily
into the corresponding alkane analogs (12a–12e) by
simple hydrogenation.
N
A
B
H
O
1-3
R1 R2
Compound R1
R2
Polymerase 1a, Replicon 1a,
a
IC50 (nM)
a,b
EC50 (nM)
1
2
3
Me
Me
933
68
—
423
184
Isoamyl Isoamyl
Me n-Propyl
20
a IC50 and EC50 values in all tables are means of at least two inde-
pendent determinations, standard deviation 10%. Detailed proto-
cols can be found in Supplementary material.
b Assay run with 5% fetal calf serum.
O
O
H
N
S
OH
N
S
O O
N
H
Analogs 13 and 14 were both produced upon hydrochlo-
ric acid treatment of alkene 11a. The methyl cyclopropyl
analog 15 was generated by reacting 4 with diazome-
thane and palladium acetate. This reaction generates
the requisite cyclopropyl group along with the 1-methyl
ether in ring B. This methyl ether was then hydrolyzed
back to the enol functionality upon heating with
base. Additionally, two hydroxylated analogs (16,
17) were also produced from the methyl allyl compound
O
4
Analog
Synthesis
O
O
H
N
S
OH
N
S
O O
4 via hydroboration and osmylation, respectively
(Scheme 2).
N
H
O
The racemic unsymmetrical 1-hydroxy-4,4-dialkyl-3-
oxo-3,4-dihydronaphthalene analog 11a could be sepa-
rated into the corresponding enantiomeric isomers
(11aR and 11aS) by use of chiral chromatography
(Scheme 3). The absolute configuration of each isomer
was tentatively assigned as shown.
R'
R
Figure 1. Synthetic strategy for producing C-4 dialkyl analogs.
in Scheme 1–3. First, the bis-sulfonamide aniline, 5, was
prepared as shown in Scheme 1. 2-Chloro-5-nitroben-
zene-sulfonamide was converted into 2-amino-5-nitro-
Table 2 details the biochemical potencies of the unsym-
metrical 1-hydroxy-4,4-dialkyl-3-oxo-3,4-dihydronaph-
thalene analogs against genotypes 1b and 1a. In
addition the activities against the HCV genotype 1a
subgenomic replicon in tissue culture are included. All
of the analogs are more potent against genotype 1a ver-
sus genotype 1b in the biochemical assay. Two of the
analogs, 11f and 17, which contain more polar ester
and diol functionalities respectively, are less potent than
other analogs that contain hydrophobic functionalities.
This suggests that the binding pocket in this region is
hydrophobic in nature.7a Analogs 11b and 12b each
containing a phenyl group, are exceptions to this trend,
suggesting that they are too sterically encumbered to fit
well within this hydrophobic pocket.
O
O
O
O
S
NO2
S
NH2
a,b
H2N
H2N
Cl
H2N
c
O
O
H
N
S
H2N
H2N
Amino-sulfonamide (5)
S
O O
In every case the saturated alkane analogs are several
fold more active than the corresponding alkene analogs
(11a–11e vs 12a–12e) in both biochemical and replicon
assays. When the isoamyl group in compound 12a was
Scheme 1. Reagents and conditions: (a) (NH4)2CO3, CuSO4, NH4OH,
120 ꢁC, 4 h, sealed tube, 90%; (b) Na2S2O4, 1 N NaOH, 70%; (c)
MeSO2Cl, CH2Cl2, pyridine, 18 h, 68%.

A. C. Krueger et al. / Bioorg. Med. Chem. Lett. 17 (2007) 2289–2292
2291
O
O
c
b
a
d
O
O
O
O
O
7
6
9
8
e
O
O
O
O
H
N
H
N
S
S
OH
N
S
OH
N
S
O
SMe
SMe
O O
O O
g
f
N
H
N
H
O
O
O
4
11a-11f
10
R2
H
R1
H
l or m
j, k
O
h or i
O
O
O
H
O
O
H
N
S
N
H
N
OH
N
S
S
S
OH
N
S
OH
N
S
O O
O O
O O
N
H
N
N
H
H
O
O
O
12a-12e, 13, 14
R2
16, 17
R3
15
R1
1 R3
R
Scheme 2. Reagents and conditions: (a) allyl acetate, 0.25 mol % Pd2dba3, Cs2CO3, 0.5 mol % racemic Trost ligand [1,2-diaminocyclohexane-N,N0-
bis(20-diphenylphosphinobenzoyl)], THF, 24 h, 90%; (b) (MeO)3CH, 5% toluene sulfonic acid, methanol, 60 ꢁC, 2 h, 75%; (c) pyridinium dichromate,
tert-butylhydroperoxide, Celite, benzene, 1 h, 25%; (d) 1 N aq NaOH, MeOH, reflux, 16 h, 80%; (e) (MeS)3C+ MeSO4ꢀ, pyridine, dioxane, 100 ꢁC,
1.5 h, 96%; (f) dioxane, sulfonamide 5, 85 ꢁC, 18 h, 46%; (g) 20 equiv substituted alkene, 4 mol % Hoveyda–Grubbs 2nd generation catalyst, CH2Cl2,
sealed tube, 70 ꢁC, 18–120 h, 11a–11f, (27–72%); (h) 10% Pd/C, MeOH, THF, hydrogen balloon, 18–24 h, 12a–12e, (50–100%); (i) when R1, R2 = Me,
dioxane, 6 N aq HCl, 65 ꢁC, 3 h, 13 (14%) and 14 (9%); (j) Pd(OAc)2, CH2N2, THF, 3 h; (k) 1 N aq NaOH, dioxane, reflux, 15, (23%, two steps (j and
k)); (l) borane–THF complex, THF, 16 h, 16, (58%); (m) OsO4, NMO, acetone, water, 18 h, 17, (19%).
O
O
H
N
O
O
O
O
H
N
H
N
S
S
S
OH
N
S
OH
N
S
OH
N
S
O O
O O
O O
N
H
N
H
N
H
+
O
O
O
11aR
11aS
11a
Scheme 3. Racemic 11a was chromatographed on a Chiralcel OD (4.6 · 250 cm) column using a mobile phase of Hex/EtOH/MeOH/TFA
(70:15:15:0.1) to yield 11aR (43%, 92% ee) and 11aS (42%, >99% ee).
lengthened to the larger ethyl cyclobutyl (12c), ethyl
cyclopentyl (12d), and ethyl cyclohexyl (12e), both the
biochemical and cell culture activities decreased in that
same order. When a slightly smaller methyl cyclopropyl
compound (15) was tested, it demonstrated activity
comparable to the ethyl cyclobutyl (12c) compound.
Thus, the most potent compound produced in this set
was the methyl isoamyl analog (12a) with an EC50 value
of 17 nM in the replicon assay. As expected, when the
two enantiomers 11aR and 11aS of a racemic analog
(11a) were tested separately, one of them was substan-
tially more active than the other in the biochemical
assay (approx. 35-fold).
In summary, a number of unsymmetrical 1-hydroxy-
4,4-dialkyl-3-oxo-3,4-dihydronaphthalene analogs were
synthesized by employing a late stage olefin metathesis
reaction. These analogs were assessed for inhibitory
potency against genotype 1 HCV polymerase. Overall
we observed that the saturated dialkyl analogs displayed
the most potent biochemical and cell culture replicon
activities.

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A. C. Krueger et al. / Bioorg. Med. Chem. Lett. 17 (2007) 2289–2292
Table 2. Biochemical and cell culture replicon potency of analogs 4 and 11–17
Compound
R1
R2
R3
Polymerase 1b, IC50 (nM)
Polymerase 1a, IC50 (nM)
Replicon 1a, EC50 (nM)
4
H
H
—
—
—
—
—
—
—
H
225
147
1850
425
550
910
5870
7
18
38
690
237
—
11a
11b
11c
11d
11e
11f
12aa
12b
12c
12d
12e
13
Me
Ph
Me
H
460
87
Cyclobutyl
Cyclopentyl
Cyclohexyl
1120
1490
—
93
195
1080
4
COOEt
H
>10,000
17
—
Me
Ph
Me
H
H
280
36
115
16
Cyclobutyl
Cyclopentyl
Cyclohexyl
H
190
320
2710
8000
2170
160
860
—
H
70
32
57
H
194
193
70
Me
Me
Me
Me
OH
Cl
43
39
14
15
Methyl cyclopropyl
—
—
40
21
16
17
OH
OH
Me
Me
H
—
—
—
OH
—
450
19
11aR
11aS
Me
Me
32
134
—
—
—
702
a See Ref. 14.
D. J.; Kohlbrenner, W. Bioorg. Med. Chem. Lett. 2005, 15,
1577; (b) Krueger, A. C.; Madigan, D. L.; Jiang, W. W.;
Kati, W. M.; Liu, D.; Liu, Y.; Maring, C. J.; Masse, S.;
McDaniel, K. F.; Middleton, T.; Mo, H.; Molla, A.;
Montgomery, D.; Pratt, J. K.; Rockway, T. W.; Zhang,
R.; Kempf, D. J. Bioorg. Med. Chem. Lett. 2006, 16, 3367;
(c) Rockway, T. W.; Zhang, R.; Liu, D.; Betebenner, D.
A.; McDaniel, K. F.; Beno, D.; Montgomery, D.; Jiang,
W. W.; Masse, S.; Kati, W. M.; Middleton, T.; Molla, A.;
Maring, C. J.; Kempf, D. J. Bioorg. Med. Chem. Lett.
2006, 16, 3833.
Detailed biological protocols for biochemical IC50
determinations and cell culture replicon assay EC50
determinations are available in Supplementary data.
Acknowledgment
We thank Chong Chen from the GPRD Process Chem-
istry Group for helping with the chiral chromatography.
8. (a) Powers, J. P.; Piper, D. E.; Li, Y.; Mayorga, V.;
Anzola, J.; Chen, J. M.; Jaen, J. C.; Lee, G.; Liu, J.;
Peterson, M. G.; Tonn, G. R.; Ye, Q.; Walker, N. P. C.;
Wang, Z. J. Med. Chem. 2006, 49, 1034; (b) Tedesco, R.;
Shaw, A. N.; Bambal, R.; Chai, D.; Concha, N. O.;
Darcy, M. G.; Dhanak, D.; Fitch, D. M.; Gates, A.;
Gerhardt, W. G.; Halegoua, D. L.; Han, C.; Hofmann,
G. A.; Johnston, V. K.; Kaura, A. C.; Liu, N.; Keenan,
R. M.; Lin-Goerke, J.; Sarisky, R. T.; Wiggall, K. J.;
Zimmerman, M. N.; Duffy, K. J. J. Med. Chem. 2006, 49,
971; (c) Fitch, D. M.; Evans, K. A.; Chai, D.; Duffy, K.
J. Org. Lett. 2005, 7, 5521; (d) Gordon, C. P.; Keller, P.
A. J. Med. Chem. 2005, 48.
Supplementary data
Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/j.bmcl.
2007.01.072.
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