Highly functionalized 7-azaindoles as selective PPARγ modulators

Article abstract of DOI:10.1016/j.bmcl.2008.07.103

A series of highly functionalized 3-aroyl and 3-phenoxy-2-methyl-7-azaindoles have been identified, which are potent selective PPARγ modulators (SPPARγMs). Addition of substituents at the 6-position of the 7-azaindoles improves in vitro potency and pharmacokinetics. 7-Azaindoles have significantly improved off-target profiles compared to the parent indole series.

Full text of DOI:10.1016/j.bmcl.2008.07.103

Bioorganic & Medicinal Chemistry Letters 18 (2008) 4798–4801
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Highly functionalized 7-azaindoles as selective PPARc modulators
*
Sheryl D. Debenham , Audrey Chan , Fiona WaiYu Lau, Weiguo Liu, Harold B. Wood, Karen Lemme,
Lawrence Colwell, Bahanu Habulihaz, Taro E. Akiyama, Monica Einstein, Thomas W. Doebber,
Neelam Sharma, Chaunlin F. Wang, Margaret Wu, Joel P. Berger, Peter T. Meinke
Merck Research Laboratories, PO Box 2000, Rahway, NJ 07065, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of highly functionalized 3-aroyl and 3-phenoxy-2-methyl-7-azaindoles have been identified,
Received 9 June 2008
Revised 22 July 2008
Accepted 24 July 2008
Available online 30 July 2008
which are potent selective PPAR
c modulators (SPPARcMs). Addition of substituents at the 6-position
of the 7-azaindoles improves in vitro potency and pharmacokinetics. 7-Azaindoles have significantly
improved off-target profiles compared to the parent indole series.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
PPAR
Azaindole
Indole
Selective PPAR modulator
SPPARM
Type 2 diabetes (T2DM) has been identified as a significant
health threat to the aging population of industrialized societies.1
that the relatively high logD values of the functionalized indoles
contributed to their affinity for off-target receptors. In an effort
Peroxisome proliferator-activated receptor gamma (PPAR
c
) is a
to find SPPARcMs that have fewer potential off-target liabilities,
member of a large family of ligand-activated nuclear hormone
receptors, and is known to mediate adipocyte differentiation and
moderate glucose levels in individuals with T2DM.2 Rosiglitazone
a nitrogen was incorporated into the core structure at the 7-posi-
tion of the indole.
The general route for the preparation of appropriately substi-
tuted 3-aroyl-2-methyl-7-azaindoles (7a–j) is shown in Scheme
and pioglitazone are full agonists of PPARc that are currently used
in the clinic to treat patients with T2DM. However, the efficacy of
these compounds is tempered by a range of mechanism-based ad-
verse effects (AEs), which include weight gain, edema, and ane-
mia.3 Additionally, the use of rosiglitazone and pioglitazone is
contraindicated in insulin-dependent T2DM patients as well as
H
R
N
N
1 R' = SCH3
2 R' = H
3 R' = p-anisoyl
a
b
c
those with congestive heart failure. A PPARc agonist devoid of
R'
R = H, CH3, OCH3
these AEs and available to a larger T2DM patient population is
therefore desirable.
Recently, compounds that act as selective PPAR
c modulators
(SPPAR
c
Ms) have been reported.4,5 In animal models, partial ago-
R
N
O
N
R
N
nists such as indole 13 display potent glucose lowering activity,
but unlike full agonists these do not cause cardiac hypertrophy
and attenuate brown adipose tissue weight increases.6,7 Unfortu-
nately, many members of this indole-based class have moderate
OR"
e
N
CO2R'
O
O
OCH3
6 R' = CH3
7 R' = H
levels of cytochrome P450 liabilities (1–20
lM on 2C9, 3A4, and
OCH3
2D6) as well as binding to off-target enzymes (<10
lM) as mea-
4 R" = Ac
5 R" = H
f
d
sured by a commercial screening laboratory. It was hypothesized
Scheme 1. Synthesis of 7-azaindoles 7a–j. Reagents and conditions: (a) Raney
Nickel, EtOH, rt, 80%; (b) EtMgBr, ZnCl2, p-anisoyl chloride, 64%; (c) 3-bromomethyl
phenylacetate, Cs2CO3, DMF, 70%; (d) K2CO3, aq MeOH; (e) methyl (R)-lactate,
DEAD, PPh3; (f) KOH 36% (3 steps).
* Corresponding author. Tel.: +1 732 594 9618; fax: +1 732 594 9556.
E-mail address: sheryl_debenham@merck.com (S.D. Debenham).
Present address: Cubist Pharmaceuticals, Lexington, MA 02421, USA.
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.07.103

S. D. Debenham et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4798–4801
4799
by hydrolysis of the lactoyl ester gave the desired acid 12 (ꢀ18%
overall yield for three steps).
N
O
O
The synthesis and biological activity of functionalized 6-substi-
O
R
NH
N
tuted-2-methyl-indoles as potent SPPAR
reported.6 Many members of the indole class are cytochrome
P450 inhibitors (1–10 M), and inhibit 15–43 enzymes (<10 M)
cMs has been previously
b
Cl
a
Cl
R
8
9
l
l
on a customized panel of 168 assorted radioligand binding and
enzymatic assays.11 It was postulated that nitrogen incorporated
into the indole ring of the lead class may decrease the off-target
activity of these molecules by decreasing the hydrophobicity of
H
N
N
R
N
O
N
c
CO2R'
the molecules while retaining SPPARcM in vitro and in vivo po-
O
O
10
tency. Gratifyingly, 7-azaindoles displayed markedly reduced CYP
inhibition and off-target activity. For example, indole 13, which
is characteristic of the series, was moderately potent 2C9 inhibitor
Cl
R = H, F, Cl, CF3
Cl
11 R' = CH3
12 R' = H
(IC50 = 5.6
enzymes (IC50, Ki < 10
to inhibit CYP 3A4 and 2C9 (IC50 > 100
only one off-target enzyme in the commercial screen (TxA2 64%
@ 10 M).
l
M) and the R enantiomer of 13 inhibited 26 off-target
M).11 In contrast, the azaindoles, 7b failed
M) and 7c inhibited
d
l
l
Scheme 2. Synthesis of 7-azaindoles 12a–h. Reagents and conditions:
(a) 2-pyridylhydrazine; (b) H3PO4, 35%; (c) methyl (2S)-2-[3-(bromomethyl)phen-
oxy]propanoate, Cs2CO3, DMF; (d) KOH, 50% (2 steps).
l
As compared to 13, 3-aroyl- or 3-phenoxy-2-methyl-7-azain-
doles lost some potency in the SPA and transactivation assays
(TA) (Table 1).12 However, all of the compounds retained their
1. Synthesis of 2-methyl-3-thiomethyl-7-azaindole starting mate-
rial (1) has been described previously.8 The 3-thiomethyl group
of 1 was removed upon treatment with Raney Nickel in good yield.
Following the procedure of Bergman et al. acylation of the in situ
transmetallated indole-Grigard occurred smoothly to give moder-
ate yields of the 3-aroylated indole (3).9 Benzylation of the N1
nitrogen provides the desired core structure 4.10 After hydrolysis
of the acetate protecting group on the phenol, a Mitsunobu reac-
tion was employed to install the R- or S-lactoyl group stereoselec-
tively in excellent yield (6). Simple hydrolysis of the ester allows
for isolation of the desired carboxylic acid 7 in modest overall yield
(ꢀ10% 6 steps).
partial agonism of PPARc as defined by reaching 20–60% of the
maximal activation of rosiglitazone in TA. In most cases, the
S enantiomer was more potent than the R enantiomer (7a and
7b, respectively). Additionally, the R enantiomer of many azain-
doles was active on the human and/or murine PPAR
a
isoform,
while the
S enantiomer was selective for PPARc (data not
shown).13 Substitution of the N-benzyl ring with a halide either
ortho- or para- to the O-lactoyl moiety increased the intrinsic
potency approximately 10-fold, with the fluorinated 7c being equi-
potent to 13.
Having identified potent and selective SPPARcMs with im-
proved off-target profiles, pharmacokinetic characteristics and in
vivo efficacy of 7b were examined in Sprague–Dawley rats and
db/db mice, respectively (Table 1).14 The PK profile of 7b was dom-
inated by very high clearance rates. Not surprisingly, after once
daily oral dosing for 11 days at 10 mpk in db/db mice, 7b failed
Synthesis of the 2-methyl-3-phenoxy-7-azaindoles (12a–h)
was accomplished in four steps from 1-(4-chlorophenoxy)acetone
(8) (Scheme 2). Standard Fischer indole synthesis provided the
7-azaindole (10) in modest yield (35%). Benzylation on N1 followed
Table 1
In vitro human PPAR
c
activity of 2-methyl-7-azaindoles (7a–d, 12a–c)
R
R'
N
N
F3CO
O
N
O
CO2H
CO2H
Y
O
X
Cl
7a-d, 12a-c
13
TA
Compound
X
Y
R
R0
Stereochem
SPA
SD rat pharmacokineticsc
% maxb
Clp/mL/min/kg
21.7
t1/2 (h)
AUCd
(lM h)
F (%)
a
IC50
EC50
13
7a
7b
7c
S
R
S
S
S
S
S
S
1
726
66
5
10
25
54
106
1
24
23
32
43
47
36
19
19
1.5
0.7
45
OCH3
OCH3
OCH3
OCH3
Cl
CO
CO
CO
CO
O
H
H
F
H
Cl
F
H
H
H
F
H
H
F
2926
27
115
31.7
2.0
1.8
0.1
0.6
29
51
3
3
36
156
140
7d
12a
12b
12c
21.8
22.1
1.2
1.6
1.0
1.3
61
77
Cl
Cl
O
O
H
All values are in nM.
a
IC50 is measured by the complete displacement of a radio-labeled full agonist indicating competitive binding to the receptor.
The EC50 is reported; this is the compound concentration at which 50% of a given compound intrinsic maximal response has been reached. Activation levels that reach
b
nearly equivalent maximal activation to rosiglitazone are considered full agonists, while those reaching 20–60% of rosiglitazone maximal activation are deemed partial
agonists.
c
All pharmacokinetic studies were preformed in Sprague–Dawley rats at dose of 0.5 mg iv, 2.0 mg po.
Dose normalized AUC.
d

4800
S. D. Debenham et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4798–4801
Table 2
In vitro human PPAR
c
activity, in vivo db/db mouse, and pharmacokinetic data of 6-substituted 7-azaindoles 7e–j, 12d–h
R'
R'
R"
R"
R
N
R
N
N
N
O
O
CO2H
CO2H
O
O
Cl
OCH3
12d-h
7e-j
Compound
R
R0
R00
SPAa
IC50
TAb
db/db mouse
(% glc corr)c
SD rat pharmacokineticsc
EC50
% max
Dose
Clp/mL/min/kg
t1/2 (h)
AUCd
(
l
M h)
F (%)
7e
7f
7g
7h
7i
CH3
CH3
OCH3
OCH3
OCH3
OCH3
F
F
F
Cl
CF3
H
F
F
H
H
H
F
H
Cl
H
Cl
F
16
4
2
1
2
<1
15
3
23
3
9
2
1
1
2
1
4
4
94
4
35
27
14
29
23
25
37
21
22
20
26
10
10
10,30,50
10
30
—
—
30
—
42
63
33,35,34
23
32
—
—
30
—
28
32
7,4
2.4
1.9
1.4
1.0
1.1
1.7
80
105
37
H
Cl
H
Cl
H
H
H
H
7j
12d
12e
12f
12g
12h
23
0.8
0.7
47
Cl
Cl
10,30
20,50
32,44
18,56
27
12.4
1.2
1.9
6.8
1.5
56
61
22
23
All values are in nM.
a
IC50 is measured by the complete displacement of a radio-labeled full agonist indicating competitive binding to the receptor.
The EC50 is reported; this is the compound concentration at which 50% of a given compound intrinsic maximal response has been reached. Activation levels that reach
b
nearly equivalent maximal activation to rosiglitazone are considered full agonists, while those reaching 20–60% of rosiglitazone maximal activation are deemed partial
agonists.
c
Rosiglitazone was used as a control in the db/db mouse studies (10 mpk, 77–85% glucose correction). All pharmacokinetic studies were preformed in Sprague–Dawley rats
at dose of 0.5 mg iv, 2.0 mg po.
d
Dose normalized AUC.
to correct glucose levels compared to the 10 mpk rosiglitazone
control (29% vs 82%, respectively). The more potent halogenated
compounds (such as 7c, 12a, and 12b) had improved SD rat PK.
into the indole ring also eliminates CYP inhibition on 2C9 and
3A4, and drastically reduces off-target liabilities as compared to
the parent indole series. Furthermore, substitution at the 6-posi-
tion of the 7-azaindole provides compounds that have moderately
improved pharmacokinetic properties as compared to the parent
7-azaindoles. Further characterization and preparation of 4-, 5-,
However, 7c at
a dose of 20 mpk (dose normalized AUC
21.8 M h) resulted in a modest 44% glucose correction in db/db
l
mouse study, whereas a 10-mpk rosiglitazine control reduced glu-
cose to 90%.
6-, and 7-azaindole SPPARcMs continues in an effort to explore
In an effort to develop 7-azaindole-based agonists with more
desirable in vivo activity, substitution at the 6-position was intro-
duced on the 7-azaindole core to more closely mimic the parent in-
dole series (Table 2). Generally, 6-substitution resulted in an
the possibility that compounds with these features may afford
beneficial glycaemic control in humans with reduced AEs. These
results will be reported in due course.
overall increase in potency without loss of desired SPPAR
acteristics. Exceptions occurred with 7f which was active on the
murine PPAR receptor (500 nM, 28% max) and 7h (489 nM human
PPAR ; 222 nM murine PPAR ). The in vitro activity of 6-methoxy-
3-anisoyl-7-azaindoles (7g–j) as measured in the db/db mouse is
comparable to 13, which exhibited 26% and 36% glucose correction
at doses of 10 and 30 mpk, respectively.
cM char-
Acknowledgments
a
We acknowledge the skills and hard work of the many scientists
on the PPAR team who provided technical support in support of
this project. Additional thanks to Amy F. Hasler who provided
assistance with the preparation of the manuscript.
a
a
Substitution at the 6-position of the 7-azaindoles resulted in
moderately improved pharmacokinetics in the SD rat as compared
to the unsubstituted 7-azaindoles (Tables 1 and 2). Unfortunately,
low exposure in the db/db mouse resulted in modest glucose cor-
rection for all azaindoles tested. 7-Azaindoles were still unable to
completely correct glucose in the db/db mouse even at high doses
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2008.07.103.
References and notes
(7g and 12h @ 50 mpk). SPPAR
at doses of 10, 30, and 50 mpk. Drug levels in animal dosed at
30 mpk were low (dose normalized AUC 1.6 M h). Both 7f (dose
normalized AUC 0.38 M h) and 12e (dose normalized AUC
2.6 M h) were found to be low exposure compounds. Surprisingly,
cM 7g corrected glucose to only 34%
1. Centers for Disease Control and Prevention. National diabetes fact sheet:
general information and national estimates on diabetes in the United States,
2003, Rev ed. U.S. Department of Health and Human Services, Centers for
Disease Control and Prevention: Atlanta, GA, 2004.
l
l
l
2. Reviews on PPARc and insulin resistance: (a) Olefsky, J. M.; Saltiel, A. R. Trends
7f had the lowest drug exposure of the azaindoles tested, but the
best in vivo efficacy as a dose of 10 mpk had 63% glucose correction
(10 mpk rosiglitazone control reduced glucose 83%).
In summary, incorporation of a nitrogen at the 7-position of the
indole ring results in compounds that have similar in vitro potency
to the parent indole series. Additionally, the inclusion of nitrogen
Endocrinol. Metab. 2000, 11, 362; (b) Berger, J.; Wagner, J. A. Diabetes Technol.
Therap. 2002, 4, 163; (c) Berger, J.; Moller, D. E. Annu. Rev. Med. 2002, 53, 409;
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351, 1106.
11. Off-target data were obtained using commercial screening laboratories. In
enzyme assays, significant inhibition by the enantiomer of 13 by the
following enzymes was observed (IC50 values in parentheses): 5-LO
R
4. (a) Acton, J. J., III; Black, R. M.; Jones, A. B.; Moller, D. E.; Colwell, L.; Doebber, T.
W.; MacNaul, K. L.; Berger, J.; Wood, H. B. Bioorg. Med. Chem. Lett. 2005, 15, 357;
(b) Thor, M.; Beierlein, K.; Dykes, G.; Gustavsson, A. L.; Heidrich, J.; Jendeberg,
L.; Lindqvist, B.; Pegurier, C.; Roussel, P.; Slater, M.; Svensson, S.; Sydow-
Backman, M.; Thornstrom, U.; Uppenberg, J. Bioorg. Med. Chem. Lett. 2002, 12,
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Metabolism 2000, 49, 1417; (d) Östberg, T.; Svensson, S.; Selén, G.; Uppenberg,
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P.; Meinke, P. T.; Shi, G. Q. Bioorg. Med. Chem. Lett. 2005, 15, 5035.
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M.; Tschirret-Guth, R.; Colwell, L.; Liu, C.; Wu, M.; Wang, C. F.; MacNaul, K. L.;
McCann, M. E.; Moller, D. E.; Berger, J. P.; Meinke, P. T.; Jones, A. B.; Wood, H. B.
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(1.64
HERG (3.23
FP (2.73 M), IP (6.34
l
M), PDE2 (29.1
l
M), PDE3 (22.5
l
M), EGF receptor (2.24
l
l
M),
M),
lM), Prostanoid: DP (8.45
lM), EP3 (1.22 l
M), EP4 (3.7
l
l
M). In radioligand binding assays, significant
displacement of radioligand from the following binding sites was
observed (with estimated Ki values in parentheses): adrenergic: a2A
(1.65
transporter (2.16
(0.837 M),dopamine transporter (3.41
Muscarinic M4 (1.34 M), Opiate (1.69
(1.86 M), Serotonin 5-HT2B (1.14 M), serotonin transporter (0.97
Tachykinin NK2 (0.53 M), TXA2 (2.03 M).
l
M), a2B (0.77
M), dopamine: D1 (1.53
M), Muscarinic M3 (1.56
M), opiate (3.48 M), opiate
M),
l
M), b1 (4.07
l
M), b3 (4.86
l
M), norepinephrine
M), D3
M),
l
l
M), D25 (3.55
l
l
l
l
l
d
l
j
l
l
l
l
l
l
l
12. Procedures for the SPA and transactivation assay are described in:
Berger, J. P.; Petro, A. E.; MacNaul, K.; Kelly, L. E.; Zhang, B. B.;
Richards, K.; Elbrecht, A.; Johnson, B.; Zhou, G.; Doebber, T. W.; Biswas,
C.; Parikh, M.; Sharma, N.; Tanen, M. R.; Thompson, M.; Ventre, J.;
Adams, A. D.; Mosley, R.; Surwit, R. S.; Moller, D. E. Mol. Endocrinol.
2003, 17, 662; Berger, J.; Liebowitz, M. D.; Doebber, T. W.; Elbrecht, A.;
Zhang, B.; Zhou, G.; Biswas, C.; Cullinan, C. A.; Hayes, N. S.; Li, Y.;
Tanen, M.; Ventre, J.; Wu, M. S.; Berger, G. D.; Mosley, R.; Marquis, R.;
Santini, C.; Sahoo, S. P.; Tolman, R. L.; Smith, R. G.; Moller, D. E. J. Biol.
Chem. 1999, 274, 6718.
7. Berger, J. P.; Petro, A. E.; MacNaul, K. L.; Kelly, L. J.; Zhang, B. B.; Richards, K.;
Elbrecht, A.; Johnson, B. A.; Zhou, G.; Doebber, T. W.; Biswas, C.; Parikh, M.;
Sharma, N.; Tanen, M. R.; Thompson, G. M.; Ventre, J.; Adams, A. D.; Mosley, R.;
Surwit, R. S.; Moller, D. E. Mol. Endocrinol. 2003, 17, 662.
8. Debenham, S. D.; Chan, A.; Liu, K.; Price, K.; Wood, H. B. Tetrahedron Lett. 2005,
46, 2283.
9. Bergman, J.; Venemalm, L. Tetrahedron 1990, 46, 6061.
10. Benzylation on N1 vs N7 was confirmed using NOE studies:
13. With the exception of 7f and 7h, the
azaindoles described above do not bind to PPAR
(IC50 > 50 M).
14. db/db mice were used as described in: Berger, J.; Bailey, P.; Biswas, C.; Cullinan,
C. A.; Doebber, T. W.; Hayes, N. S.; Saperstein, R.; Smith, R. G.; Liebowitz, M. D.
Endocrinology 1996, 137, 4189.
S
enantiomers of the 7-
a
and PPARd
l
H
Ar
Ar
H
H
N
H
H
N
N
N
H
R'
R'
.