Discovery of an androgen receptor modulator pharmacophore based on 2-quinolinones

Article abstract of DOI:10.1016/j.bmcl.2007.01.007

A series of alkylamino-2-quinolinone compounds (3) was discovered as androgen receptor modulators based on an early linear tricyclic quinoline pharmacophore (1). The series demonstrated selective high binding affinity to androgen receptor and potent recep

Full text of DOI:10.1016/j.bmcl.2007.01.007

Bioorganic & Medicinal Chemistry Letters 17 (2007) 1523–1526
Discovery of an androgen receptor modulator
pharmacophore based on 2-quinolinones
Arjan van Oeveren, Barbara A. Pio, Christopher M. Tegley, Robert I. Higuchi, Min Wu,
*
´
Todd K. Jones, Keith B. Marschke, Andres Negro-Vilar and Lin Zhi
Discovery Research, Ligand Pharmaceuticals, 10275 Science Center Drive, San Diego, CA 92121, USA
Received 29 November 2006; revised 23 December 2006; accepted 2 January 2007
Available online 13 January 2007
Abstract—A series of alkylamino-2-quinolinone compounds (3) was discovered as androgen receptor modulators based on an early
linear tricyclic quinoline pharmacophore (1). The series demonstrated selective high binding affinity to androgen receptor and potent
receptor modulating activities in the cotransfection assays.
Ó 2007 Elsevier Ltd. All rights reserved.
The androgen receptor (AR) is a transcription factor
CF3
CF3
R
6
R
that androgens depend upon to play their diverse and
complex physiological and pathophysiological roles.
As a validated drug target, many therapies have been
developed based on AR actions. Numerous synthetic
steroidal androgens were developed decades ago to
mimic the activity of natural hormones, testosterone
and dihydrotestosterone (DHT), with improved potency
or oral bioavailability in the absence of understanding
the mechanism of action at the molecular level. Despite
many potential risks, the steroidal androgens have been
used to treat many diseases associated with androgen
deficiency or have been abused as anabolic agents.1,2
Separation of the beneficial activities of androgens, such
as on bone and muscle, and the potential risks on pros-
tate has been the focus of multiple research groups in re-
cent years to develop new androgens, named selective
androgen receptor modulators (SARM).3–7 On the side
of blocking AR actions, bicalutamide has been used to
treat prostate carcinoma by binding to and antagonizing
AR.8 Development of better and safer antagonists,
named selective AR antagonists, has also been attempt-
ed9–11 (Fig. 1).
R"
0-1
C
O
N
H
N
O
N
H
N
H
R'
8
H
1
2
CF3
6
NRR'
O
N
H
3
Figure 1. Nonsteroidal AR modulators: (1) AR antagonists; (2) AR
agonists; and (3) new compounds.
on the C-ring.13–16 It was found that the bisalkyl groups
at the 8 position were responsible for the AR antagonist
activity and a small alkyl group at the 6 or 7 positions or
combinations at 6- and 7- or 7- and 8-positions were
good for AR agonist activities. In the optimization of
the AR lead pharmacophore, the SAR studies were
encumbered due to the nonconvergent synthetic
sequence of many analogs of the series as illustrated
by compound 6 in Scheme 1. The tetrahydroquinoline
4 related intermediates were prepared from aniline in
four to six steps to setup targeted substitution pattern
and then were nitrated to provide compound 5 after
hydrogenation. The Knorr cyclization afforded target
compound 6. In addition to the linear synthesis of the
C-ring modified analogs and relatively low yield of the
Based on our AR antagonist pharmacophore (1),12 we
successfully developed AR agonists, such as molecules
of structure 2, by modifying the substitution pattern
Keywords: Androgen receptor; SARM; 2-Quinolinone; AR antagonist.
*
Corresponding author. Tel.: +1 858 550 7663; fax: +1 858 550
7249; e-mail: lzhi@ligand.com
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.01.007

1524
A. van Oeveren et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1523–1526
nitrogen to mimic the 8-gemdimethyl at the C-ring of
a), b), c), d)
e), f)
pharmacophore 1. In Scheme 3, quinoline 8a was isolat-
ed in the synthesis of compound 8 as a minor byproduct
and was alkylated with the special amide bromide18 to
facilitate the formation of the nitrogen quaternary car-
bon bond followed by methylation to give 8b. Hydroly-
sis of compound 8b to the quinolinone intermediate and
reduction of the amide to an aldehyde followed by Wit-
tig olefination provided compound 9h. Hydrogenation
afforded compound 9g. The binding affinity of the com-
pounds to human AR and their functional activity were
measured by a competitive whole cell binding assay and
the cotransfection assay in CV-1 cells.19 The results are
summarized in Table 1. We used the functional assay re-
sults to drive the SAR studies and the binding affinity to
assure the interaction with AR.
N
Et
NH2
H
4
CF3
g)
H2N
N
H
Et
O
N
N
Et
H
H
5
6
Scheme 1. Reagents and conditions: (a) 2-pentenoic acid, toluene,
reflux 20 h (72%); (b) neat PPA, 110 °C, 6 h (43%); (c) NaBH4, MeOH,
rt, 3 h (80%); (d) Et3SiH–BF3-OEt2, CH2Cl2, 50 °C, 15 h (71%); (e)
HNO3, H2SO4, 0 °C, 20 min (85%); (f) H2, Pd/C, EtOAc, rt, 15 h
(92%); (g) CF3COCH2CO2Et, ZnCl2, EtOH, reflux, 8 h (30%).
Knorr reaction at the last step, there are three potential
stereogenic centers of the molecules to be addressed for
any scale-ups. In the process of the synthesis, compound
7 was isolated as a contaminant and was found to be a
reasonable AR antagonist in our assays. The unexpected
result prompted us to think about the possibility of
opening the C-ring of the tricyclic template to simplify
the skeleton and the synthesis (Fig. 2).
Compound 6 was prepared as a structural isomer of
compound 1 reported previously from the linear tricyclic
tetrahydroquinoline series15 and tested as a racemate.
The 7-alkylamino-2-quinolinone lead compound 7 dem-
onstrated AR antagonist activity and binding affinity
similar to those of compounds 1 and 6, which indicates
that breaking the C-ring of the tricyclic structure does
not have significant impact on the activities of the series
on AR. Additional analogs of compound 7 provide con-
sistent results to further support the hypothesis. The
unsubstituted aminoquinolone compound 8 had weak
binding to AR and some partial activity in the function-
al assay. The monoalkylamine analogs (compounds
9a–9h) showed good antagonist activities comparable
to reference compound bicalutamide in the cotransfec-
tion assay. The smaller alkyl groups apparently showed
better potency than those of bulkier analogs and the best
example is the increased IC50 of the cycloalkyl analogs
from 9i (cyclobutyl), 9j (cyclopentyl), to 9k (cyclohexyl).
The fluoroalkyl analogs (9l and 9m) showed similar
activity as those of alkyl analogs. However, the trifluo-
roacetamido analog (9n) had no activity in the testing
range. The bisalkylamino compounds (10a–10d) were
generally weaker antagonists in the assays.
A number of the 7-alkylamino-2-quinolinone analogs
were prepared by a much more efficient synthetic route
as described in Scheme 2. Knorr reaction of 1,3-pheny-
lenediamine and the trifluoromethylketo ester using
p-toluenesulfonic acid as a catalyst provided the 7-ami-
no-2-quinolinone 8 in good yield. Reductive alkylation
of intermediate 8 afforded analogs of structure 9 and
the second alkylation gave bisalkylated analogs of struc-
ture 10.17 Compounds 9g and 9h were prepared differ-
ently to install the quaternary carbon next to the
CF3
CF3
C-ring opening
O
N
H
N
Et
O
N
H
N
Et
H
H
Compounds of structure 11 are analogs of different dis-
section of the C-ring of pharmacophore 1 and were pre-
pared by the chemistry similar to that of structure 9. As
6
7
Figure 2. Development of the alkylamino-2-quinolinone series.
CF3
CF3
CF3
O
N
a), b)
Ph
a)
b)
Et
Et
O
N
N
H
O
N
NH2
O
N
NH2
H2N
NH2
8b
8a
H
CF3
8
CF3
c), d), e)
f)
CF3
CF3
O
N
H
N
H
b)
O
N
N
H
H
R
R
9g
9h
O
N
H
N
O
N
N
R1
H
H
Scheme 3. Reagents and conditions: (a) BrC(CH3)2CONHPh, NaH,
THF, rt, 1 h (75%); (b) NaH, MeI, THF, rt, 2 h (95%); (c) 57%
aqueous HI, 40 °C, 3 h (50%); (d) DIBAL, THF, À78 to À50 °C, 1 h
(40%); (e) Ph3PCH3Br, NaN(SiMe3)2, THF, rt, 1 h (85%); (f) H2, Pd/C,
EtOAc, rt, 15 h (90%).
9
10
Scheme 2. Reagents and conditions: (a) CF3COCH2CO2Et, TsOH,
EtOH, reflux, 8 h (75%); (b) an aldehyde or a ketone, NaB(CN)H3,
AcOH, rt, 15 h (50–95%).

A. van Oeveren et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1523–1526
1525
Table 1. Cotransfection and competitive binding data for the new analogs and reference compoundsa
R
N
CF3
CF3
CF3
CF3
CF3
R1
R1
R
R
R
R
O
N
N
O
N
H
O
O
N
O
N
H
N
H
O
N
H
N
H
H
R1
R1
11
9
10
12
13
Compound
R
R1
hAR agonist hAR agonistb hAR antagonist hAR antagonistc hAR whole cell
EC50 (nM)
Eff. (%)
IC50 (nM)
Eff. (%)
binding Ki (nM)
1
H
—
—
—
—
—
58
—
—
—
—
—
—
—
—
—
—
—
27
14
32
28
30
5
3
7
5
7
74
55
86
53
79
77
86
87
86
88
93
92
89
89
90
61
76
—
94
88
90
79
89
75
51
2
5
1
9
5
2
2
1
2
2
2
1
2
73 11
11
6 ( )
7
3
—
1300
37 19
407
8
9a
CH3
CH2CH3
—
—
83
29
50
7
9
7
9b
9c
35 10
67 11
56 10
CH2CH2CH2CH3
CH(CH3)2
CH2CH(CH3)2
CH2C(CH3)3
C(CH3)2CH2CH3
C(CH3)2CH=CH2
Cyclobutyl
Cyclopentyl
Cyclohexyl
CH2CF3
—
—
9d
9e
79 27
65 23
134 29
—
—
74 1
98 15
9f
9g
—
—
209
122 30
6
110
3
9h
9i
118 46
161
1000
—
—
43
149
507
21
9
9j
9k
—
905 154
1000
15
9l
29
0
5
9
4
2
3
9m
9n
CH2CF2CF3
COCF3
CH2Ph
—
—
—
58
—
36 14
—
—
—
—
—
—
—
—
9o
—
—
294 21
1160
591
1
163 77
761
463
10a
10b
10c
10d
11a
11b
11c
11d ( )
11e
11f
11g
11h
12a
12b
13a
13b
13c
13d
13e
13f
13g
13h
CH3
CH3
CH2CH3
CH2CH3
CH2CH2CH3
H
CH2CH3
CH2CF3
CH2CF3
CH3
—
—
—
42
549 452
30
241
2
1
3
—
76
23
7
0
30
H
CH2CH3
CH2CH2CH3
593 436
83 24
65 16
—
27
1
2
8
20
9
4
2
2
H
26
40
—
—
—
—
—
21
—
—
19
14
34 14
H
CH(CH3)CH2CH3
CH3
0
23
93
83
98
91
70
63
28
84
3
13
CH2CH2CH3
CH2CH(CH3)2
CH3
674
641 359
650 350
CH3
CH2CH3
CH2CH3
—
—
301 97
504
216 54
5
869
157 153
CH2CF3
CH2CF3
—
—
4
4
4
7
H
CH2CF3
50
7
na
na
CH2CF3
H
73 31
—
—
4
63 23
26
111
H
—
na
CH2CH3
CH2CF3
H
H
108 36
246
—
24 10
89
—
18 12
39 13
16
78
CH2CF2CF3
Cyclopentyl
CH2CH(CH3)2
CH2C(CH3)3
COCF3
H
17
42
5
8
63
82
61
2
2
7
H
74
59
H
404
—
21
—
22 18
H
27
—
72
56
—
H
CH2CF3
—
—
—
—
—
85
13i (LGD2226) CH2CF3
DHT
Bicalutamide
0.20 0.02
5.1 0.1
—
95
100
—
2
—
—
1.5
0.20 0.02
151 36
162 99
9
a Values with standard errors represent the mean value of at least two separate experiments with triplicate determinations. ‘—’ indicates not active
(an efficacy of <20% and/or a potency of >10,000 nM). ‘na’ means not available.
b Agonist efficacies were determined relative to DHT (100%).
c Antagonist efficacies (%) were determined as a function of maximal inhibition of DHT at the EC50 value.
size increases of the 6-alkyl group, the 7-amino analog
functional activities shifted from AR antagonism
toward partials (compounds 11a–11d). Monoalkylation
of the amino group does not make better AR modula-
tors (compounds 11e–11h). A couple of 7-alkylamino-
coumarin analogs were also prepared similarly and
their functional activities are in parallel with the
2-quinolones.
The 6-alkylamino compounds (13) were synthesized in a
similar fashion as described previously20 and have a very
intriguing SAR. The parent compound 13a did not show

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A. van Oeveren et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1523–1526
8. Wirth, M.; Tyrrell, C.; Delaere, K.; Sanchez-Chapado,
M.; Ramon, J.; Wallace, D. M.; Hetherington, J.; Pina, F.;
Heyns, C.; Borchers, T.; Morris, T.; Armstrong, J.
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Kamikubo, T.; Imamura, M.; Matsuhisa, A.; Samizu, K.;
Kawanimani, E.; Niimi, T.; Hamada, N.; Koutoku, H.;
Furutani, T.; Kudoh, M.; Okada, M.; Ohta, M.; Tsukam-
oto, S. J. Med. Chem. 2006, 49, 716.
10. Hwang, D. J.; Yang, J.; Xu, H.; Rakov, I. M.; Dalton, J.
T.; Miller, D. D. Bioorg. Med. Chem. 2006, 14, 6525.
11. Allan, G.; Lai, M.-T.; Sbriscia, T.; Linton, O.; Haynes-
Johnson, D.; Bhattacharjee, S.; Dodds, R.; Fiordeliso, J.;
Lanter, J.; Sui, Z.; Lundeen, S. J. Steroid Biochem. Mol.
Biol. 2007, 103(1), 76.
much AR related activity and the monoalkylamino
analogs (13b–13g) demonstrated good AR antagonist
activities similar to their 7-alkylamino counterparts.
In addition, some of the analogs showed partial
agonist activity, especially for compound 13d. Once
the 6-amino group is bisalkylated, the series becomes a
highly potent AR agonist pharmacophore. Compound
13i (LGD2226) as a representative analog of the series
has high specific binding affinity to AR and demonstrat-
ed functional activity in the cotransfection assay more
potent than DHT. In additional in vitro and in vivo as-
says, compound 13i was characterized as an orally avail-
able highly potent tissue-selective AR modulator.20,21
12. Hamann, L. G.; Higuchi, R. I.; Zhi, L.; Edwards, J. P.;
Wang, X.; Marschke, K. W.; Kong, J.; Farmer, L. J.;
Jones, T. K. J. Med. Chem. 1998, 41, 623.
13. Hamann, L. G.; Mani, N. S.; Davis, R. L.; Wang, X.-N.;
Marschke, K. B.; Jones, T. K. J. Med. Chem. 1999, 42,
210.
14. Edwards, J. P.; West, S. J.; Pooley, C. L. F.; Marschke, K.
M.; Farmer, L. J.; Jones, T. K. Bioorg. Med. Chem. Lett.
1998, 8, 745.
15. Zhi, L.; Tegley, C. M.; Marschke, K. B.; Jones, T. K.
Bioorg. Med. Chem. Lett. 1999, 9, 1009.
A group of the representative compounds (9a, 9b, 9d, 9l,
9m, 10c, 11b, 11c, 13c, and 13e) were tested in other
related steroidal hormone receptor cotransfection assays
in both agonist and antagonist modes to check their
receptor selectivity. All of the compounds showed more
than 100-fold separation from the modulating activities
of estrogen, glucocorticoid, and mineralocorticoid
receptors, and more than 10-fold separation from the
progesterone receptor activities.
16. Higuchi, R. I.; Edwards, J. P.; Caferro, T. R.; Ringgen-
berg, J. D.; Kong, J. W.; Hamann, L. G.; Arienti, K. L.;
Marschke, K. M.; Davis, R. L.; Farmer, L. J.; Jones, T. K.
Bioorg. Med. Chem. Lett. 1999, 9, 1335.
In summary, the alkylamino-2-quinolinone series was
developed as an AR modulator template from the linear
tricyclic pharmacophore. The series demonstrated many
synthesis-friendly features, which significantly facilitated
the development of the SAR. Several new antagonist
analogs were assessed in a typical rodent model and
unfortunately no antiandrogenic activity was observed
due to the significantly lower exposure relative to that
of bicalutamide (data not shown). The AR agonists of
the series did show excellent in vivo activity and tissue
selectivity. More detailed SAR studies around the
6-bisalkylamino AR agonist analogs are discussed in
the following manuscript.22
17. Preparation of 9l as an example: 1,3-Phenylenediamine
(5.4 g, 50 mmol) and CF3COCH2CO2Et (11 g, 60 mmol)
in EtOH (100 mL) were heated at reflux overnight to give
rise to a yellow slurry. P-TsOH (0.19 g, 1.0 mmol) was
added and the reaction mixture was stirred at reflux for
additional 24 h. The reaction mixture was cooled to room
temperature and filtration afforded compound 8 as a
yellowish solid (8.5 g, 75%): 1H NMR (400 MHz, acetone-
d6) 10.91 (br s, 1H), 7.47 (dq, J = 6.7 and 2.4, 1H), 6.70
(dd, J = 6.7 and 2.2, 1H), 6.65 (d, J = 2.2, 1H), 6.50 (s,
1H), 5.65 (br s, 2H). A solution of compound 8 (100 mg,
0.45 mmol) in TFA (3 mL) was treated with NaBH4 and
the mixture was heated at 60 °C for 4 h. The mixture was
quenched with 10% NaOH and extracted with EtOAc.
Chromatography provided compound 9l (45 mg, 33%) as
a yellow solid: mp 238–239 °C, 1H NMR (400 MHz,
acetone-d6) 10.95 (br s, 1H), 7.56 (dq, J = 9.0 and 1.5, 1H),
6.86 (dd, J = 9.0 and 2.1, 1H), 6.80 (d, J = 2.1, 1H), 6.60
(s, 1H), 6.50 (br s, 1H), 4.05 (m, 2H). Anal. (C12H8F6N2O)
C, 46.46; H, 2.60; N, 9.03. Found: C, 46.36; H, 2.55; N,
8.89.
Acknowledgment
We thank the Department of New Leads for performing
the cotransfection and binding assays.
References and notes
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mide and a highly active alpha lactam may be involved in
the alkylation reaction.
19. Detailed assay conditions were described previously in our
early publications.
20. van Oeveren, A.; Motamedi, M.; Mani, N. S.; Marschke,
K. B.; Lopez, F. J.; Schrader, W. T.; Negro-Vilar, A.; Zhi,
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