Serendipitous discovery of novel imidazolopyrazole scaffold as selective androgen receptor modulators

Article abstract of DOI:10.1016/j.bmcl.2006.10.035

A novel imidazolopyrazole derivative has been fortuitously discovered as potent selective androgen receptor modulator with in vivo efficacy.

Full text of DOI:10.1016/j.bmcl.2006.10.035

Bioorganic & Medicinal Chemistry Letters 17 (2007) 439–443
Serendipitous discovery of novel imidazolopyrazole scaffold as
selective androgen receptor modulators
Xuqing Zhang,* Xiaojie Li, George F. Allan, Tifanie Sbriscia, Olivia Linton,
Scott G. Lundeen and Zhihua Sui
Drug Discovery, Johnson & Johnson Pharmaceutical Research and Development, LLC, 665 Stockton Drive, Exton, PA 19341, USA
Received 24 August 2006; revised 10 October 2006; accepted 12 October 2006
Available online 17 October 2006
Abstract—A novel imidazolopyrazole derivative has been fortuitously discovered as potent selective androgen receptor modulator
with in vivo efficacy.
Ó 2006 Elsevier Ltd. All rights reserved.
Androgens control sexual function in males and are cen-
tral to the anabolic processes that underlie the develop-
ment of male sexual and physiological characteristics.
Natural androgen testosterone (T) and its metabolite-di-
hydrotestosterone (DHT) act via the androgen receptor
(AR), which is a member of the nuclear receptor super-
family. While T and its esters were approved for a lim-
ited number of therapeutic applications, including
primary or hypogonadotropic hypogonadism and de-
layed puberty, fear of exacerbating nascent prostate dis-
ease has limited more extensive legitimate use of these
natural ligands.1 The successful marketing of drugs such
as raloxifene, a selective estrogen receptor modulator
(SERM), has raised the possibility of generating non-
steroidal AR ligands with tissue selectivity.2 The term
selective androgen receptor modulators (SARMs) is
chosen after the terminology used for similar ligands
targeting estrogen receptor. An ideal SARM is an antag-
onist or weak agonist in the prostate, but an agonist in
muscle, which has potentially less side effects compared
to T. Therefore, SARMs have potential for treating
muscle wasting, hypogonadism of aging, osteoporosis,
and female sexual dysfunction.3
vent castration caused tissue weight loss and behave as
partial agonists in the prostate but full agonists in the
levator ani. muscle in the castrated rat model. Here we
describe our discovery of a novel imidazolopyrazole
scaffold as SARM. The lead compound 10c is a tissue-
selective non-steroidal androgen receptor ligand with
agonist activity in rat muscle and mixed agonist and
antagonist activity in the rat prostate. The synthesis
and in vivo SAR studies of this novel series of bicyclic
structures are presented.
Recently, we have identified a novel series of pyrazolines
(III) as SARMs.5 The potential of metabolic instability
of the amide bond in structure III led us to consider
replacement with an amidate linkage as effective bioiso-
stere. The goal of this design was to probe the influence
of the amidate portion of the molecule and identify
those features that could improve metabolic stability,
while maintaining the efficacy as seen in structure III.
The syntheses of amidates 8 are described in Scheme
1. Preparation of 5 utilized an efficient 1,3-dipolar cyclo-
addition between the a,b-unsaturated alkenes 3 and the
hydrazones 4 (R5CH@NNHTs) in the presence of NaH
to afford pyrazolines 5 in moderate to good yields. The
alkene precursors 3 were obtained by coupling of meth-
ylacryl acid 2 with the corresponding anilines 1 in the
presence of thionyl chloride. Compounds 5 were then
transformed into their thio-amide analogs 6 by treat-
ment with Lawesson’s reagent. Alkylations of 6 with
EtI in the presence of K2CO3 afforded the corresponding
thio-imidates 7. Nucleophilic displacements of
SEt group with nitrogen-containing nucleophiles
Progress has been made in identifying novel pharmaco-
phores of non-steroidal SARMs by structural modifica-
tion of non-steroidal antiandrogens (Fig. 1).4 S-4 (I) and
BMS-564929 (II) are two leading SARMs that can pre-
Keywords: SARMs; Imidazolopyrazole; Tissue selectivity.
*
Corresponding author. Tel.: +1 610 458 4137; fax: +1 610 458
8249; e-mail: xzhang5@prdus.jnj.com
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.10.035

440
X. Zhang et al. / Bioorg. Med. Chem. Lett. 17 (2007) 439–443
O
O
OH
NHAc
NC
H
N
n(R)
O2N
F3C
H
N
O
N
O
N
H
N
N
H
O
OH
Cl
R'
I, S-4
II, BMS-564929
III
Figure 1.
R1
R2
R1
R2
R1
R2
O
O
4H
N
a
b
R
R4
O
R4
HO
NH
NH2
+
N
R3
NH
R3
R3
R5
1
2
3
5
R1
R2
A
B
R
R1
R2
R1
R2
Et
S
N
4H
N
S
4H
N
C
R
d
4H
N
e
R
N
NH
N
N
R3
N
R3
N
R3
R5
R5
R5
7
8
6
Scheme 1. Reagents and conditions: (a) SOCl2, 0 °C–rt, 2–4 h; (b) R5CH@NNHTs (4), NaH, 0 °C, 30 min then 70 °C 4–6 h, 55–70%; (c) Lawesson
reagent, 120 °C, 6–10 h, 42–60%; (d) K2CO3, EtI, acetone, 50–70 °C, 1–2 h, 75–85%; (e) A–NH–B (extra), dioxane in seal tube, 100 °C or A–NH–B,
1
DMF, K2CO3, rt, or A–NH–B, K2CO3, dioxane, 80 °C, 1–4 h, 35–80%. All compounds were characterized by H NMR and LC–MS. LC purity is
>95%.
Table 1. SAR at substitutions A and B of structure 8a
A
N
B
NC
N
H
N
N
F3C
CF3
8
Compound
A
B
Levator ani. stimulation (%)
100
Prostate stimulation (%)
100
Prostate inhibitione (%)
TPb
Bicalutamidec
70
20
8a
8b
8c
8d
8e
8f
H
H
Me
76
17
39
H
<10d
<10
14
15
18
H
Et
50
23
H
OMe
OH
SO2Me
Et
<10
<10
<10
<10
<10
H
<10
<10
32
<10
<10
22
H
Et
8g
8h
–(CH2)4–
<10
<10
a All compounds were administered via po (vehicle: 20% cyclodextrin) once daily at a dose rate of 2 mg/day for 5 days. The data were normalized to
control group administer with vehicle (N = 3/group).
b Testosterone propionate was administered subcutaneously by injection at the nape of the neck at 5 mg/kg, in a volume of 0.1 mL in sesame oil.
c Average value based on 10 tests.
d Inhibition at a dose rate of 2 mg/day.
e Compounds were dosed via po in the presence of 0.1 mg/day (approximately 1.3 mg/kg) testosterone propionate (subcutaneous dosing, vehicle:
sesame oil).
(A–NH–B) under the conditions described in Scheme 1
led to a series of amidates 8.
able compound amount (ꢀ40 mg for each test), and sim-
plified data analysis. The data indicate the combination
of compound’s ADME properties and intrinsic efficacy,
which allows us to advance potent compound into ma-
ture rat efficacy model. Thus, all compounds were
screened in immature castrated male Sprague–Dawley
rats agonist and antagonist assays. In these studies, the
As described in our recent communication, a modified
Hersherberger assay as an in vivo screening protocol
was utilized to evaluate all compounds.6 We found this
strategy provided us with fast turnaround time, reason-

X. Zhang et al. / Bioorg. Med. Chem. Lett. 17 (2007) 439–443
441
NHR6
N
4H
N
R1
R2
R1
Et
R
NH2CN, K2CO3
dixoane, 80oC
R1
S
HN
4H
R
N
5-exo
N
N
R2
N
N
N
R2
N
N
N
R3
R3
R4
R5
R3
yield, 45-81%
R5
R5
7
9
10
Scheme 2.
bolic and antiandrogenic activities for compounds 8 con-
taining amidate functionality. In castrated immature rat
agonist assay, compound 8a showed tissue-selective in vi-
vo pharmacologic activity at a po dose of 2 mg/day, with
anabolic activity on levator ani. muscle weight stimula-
tion to 76% and androgenic activity on ventral prostate
weight stimulation to 39%. Interestingly, when further
tested in an immature rat antagonist assay, 8a presented
weak inhibition on the ventral prostate weight to 20% in
TP treated immature rat, which secured its selectivity be-
tween anabolic and androgenic tissues. SAR around the
amidate structure suggested that the size of the amidate
as a bioisostere was critical for activity, as indicated by
the data in Table 1. Any modifications on substituent
B by adding size or hydrophilicity resulted in either par-
tial or complete loss of the agonist activity on levator ani.
and prostate (8b–8f). Moreover, bis-substitutions on A
and B were detrimental to the activity and led to ineffica-
cious compounds 8g and 8h.
Figure 2. X-ray crystal structure of 10c.
weights of the ventral prostate and seminal vesicle were
used as the indicators of androgenic activity, while the
weight of levator ani. muscle was used as the indicator
of anabolic activity. Table 1 summarizes the in vivo ana-
Table 2. SAR at substitutions R1–R6 of structures 10a
R6
HN
R1
N
N
N
R2
N
R4
R5
R3
10
Compound
R1
R2 R3 R4 R5
R6
Levator ani. stimulation (%) Prostate stimulation (%) Prostate inhibition (%)
TP
100
100
Bicalutamideb
10a
10b
70
CN CF3
CN CF3
CN CF3
CN CF3
H
H
H
H
Me
H
H
H
H
H
H
H
H
<10
<10
91d
72d
19
<10
<10
36c
<10
<10
30
Me CO2Et
Me CF3
Me CF3
10c (R)
10d (S)
10e
29c
<10
<10
<10
<10
31
CN CF3 Et Me CF3
<10
<10
<10
55
10f
10g
CN CF3
CN CF3
CN CF3
H
H
H
H
H
H
Me per-F–Ph
Et CF3
Me CF3
Me CF3
Me CF3
Me CF3
21
16
10h
10i
CF3CO 61
Cl
Br
Cl
CF3
H
H
H
<10
<10
<10
<10
55
31
10j
10k
<10
<10
29
<10
<10
<10
NO2 CF3
10l
NH
O
NC
N
N
F3C
N
Me
CF3
a All footnotes in Table 1 apply in this table.
b Bicalutamide, average value based on 10 tests.
c stimulation at the dose of 3 mg/day.
d 10c and 10d were followed up with a five point dose-dependent study at doses from 0.03, 0.1, 0.3, 1 to 3 mg/day to generate ED50 value on levator
ani.: ED50 for 10c, 0.07 mg/day; ED50 for 10d, 0.85 mg/day.

442
X. Zhang et al. / Bioorg. Med. Chem. Lett. 17 (2007) 439–443
#
#
1.25
1.00
0.75
0.50
0.25
0.00
Ventral prostate
Levator ani
#
#
#
#
#
#
#
*
Vehicle
0.03 0.1 0.3
1
3
0.3
1
3
10
30
Testosterone propionate
(sc, mg/kg)
10C
(po, mg/kg)
ED50 prostate 0.25 mg/kg
ED50 lev. ani. 0.17 mg/kg
ED50 prostate > 30 mg/kg
ED50 lev. ani. 2.8 mg/kg
Figure 3. Effect of 10c on muscle and prostate weights in castrated mature rats (#p < 0.01 and *p < 0.05, means SD, n = 3, tissue weights relative to
body weight).
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
antagonist activity on prostate. Interestingly, 10c acted
as the eutomer that contributed the observed in vivo effi-
cacy, while its S-enantiomer-10d was a weaker agonist
showing ED50 0.85 mg/day on levator ani. muscle and
29% stimulation on prostate at the same dose in the cas-
trated immature rat agonist assay. Brief survey of the
substitutions of structure 10 revealed that this scaffold
generally was not well tolerated for in vivo efficacy.
Any modification on R1, R2, R3, R4, and R5 seemed
to be detrimental to the activity and led to inactive com-
pounds, as exemplified by 10a–b, 10e–g, and 10i–k in
Table 1. Compound 10h with trifluoro acetyl substitu-
tion on R6 was an exception that maintained agonistic
activity on levator ani muscle and prostate. Compound
10l, O-analog of 10c with a unique pyrazolooxazole
structure, also showed strong potency on levator ani.
muscle.
Prostate
levator ani
10C
Figure 4. Effect of daily six-week treatment with 10c on prostate and
muscle wet weights in intact adult male rats (means SD, n = 3).
As a logic extension of the amidate series, the cyano
amidate functionality was considered an effective
replacement of the amide bond in structure III. A clean
product originally assigned as structure 9 was obtained
by reaction of compounds 7 and NH2CN in the presence
of K2CO3 (Scheme 2). Beyond our anticipation, dis-
placement of the thio-imidate group of compounds 7
with cynamide followed by an intramolecular 5-exo
cyclization of the corresponding intermediates 9 oc-
curred to afford the bicyclic imidazolopyrazole deriva-
tives 10 in good yields. Structures 10 were
differentiated from the amidate structures 8 initially by
the spectroscopic data and later were confirmed by X-
ray single crystallography of compound 10c7 (Fig. 2).
Intramolecular 5-exo cyclization of a nucleophile to
cynamide was not unprecedented in the literature.8
Compound 10c (R configuration) was tested in castrated
immature male rats agonist and antagonist assays (Ta-
ble 2). It presented dose-dependent pharmacological
responses in both anabolic (levator ani.) and androgenic
(prostate) tissues. In the absence of testosterone, 10c was
a tissue-selective androgen agonist, with ED50 0.07 mg/
day on levator ani. muscle and 36% stimulation at
3 mg/day on prostate (Table 2). On the other hand, in
the presence of exogenous testosterone, 10c at a single
dose of 2 mg/day inhibited stimulation of prostate
weight by 30%, which exhibited its mixed agonist and
Compound 10c was further tested in castrated mature
male rats for its ability to stimulate prostate and muscle
weights in the absence of endogenous testosterone
(Fig. 3).9 Compound 10c had an ED50 on prostate of
>30 mg/kg (31% stimulation at 30 mg/kg) and on leva-
tor ani. of 2.8 mg/kg. For comparison, TP had an
ED50 on prostate of 0.25 mg/kg while it presented
EC50 0.17 mg/kg on levator ani. muscle. In the intact
mature male rat assay (Fig. 4),10 compound 10c was able
to reduce prostate weight dose-dependently, with 26%
reduction at 30 mg/kg in the presence of endogenous tes-
tosterone. At the same time, there was no significant
dose-dependent effect on muscle weight. For compari-
son, the androgen antagonist bicalutamide in the same
assay reduced both prostate and levator ani weights by
60% at 30 mg/kg (Figure not shown here). These data
strongly indicated that 10c was a tissue-selective non-
steroidal androgen receptor ligand with agonist activity
on rat muscle and mixed agonist and antagonist activity
on the rat prostate.
In summary, we conducted SAR through modification
on structure III by replacement of the amide bond with
amidate structures. This led to the identification of a un-
ique imidazolopyrazole derivative 10c as potent SARMs
with oral efficacy.

X. Zhang et al. / Bioorg. Med. Chem. Lett. 17 (2007) 439–443
443
inhibition of testosterone-enhanced tissue weights, with a
vehicle-treated control group set to 100% and a testoster-
one alone-treated control group set to 0%; (c) Agonist
assay: Test compound activity was determined as the
percent stimulation of tissue weight, with the vehicle-
treated control group set to zero percent and the testos-
terone alone-treated control group set to 100%; Synthesis
and SAR of novel hydantoin derivatives as selective
androgen receptor modulators: (d) Zhang, X.; Allan, G.
F.; Sbriscia, T.; Linton, O.; Lundeen, S. G.; Sui, Z. Bioorg.
Med. Chem. Lett. 2006, 16, 5763; The discovery of a
potent orally efficacious indole androgen receptor antag-
onist through in vivo screening: (e) Lanter, J. C.; Fiordel-
iso, J. J.; Jiang, W.; Allan, G. F.; Lai, M.-T.; Linton, O.;
Hahn, D.-W.; Lundeen, S. G.; Sui, Z. Bioorg. Med. Chem.
Lett. 2006. doi:10.1016/j/bmcl.2006.09. 086.
Acknowledgment
We thank Dr. Alexandra Shedlow and Dr. Derek Beau-
champ for coordination on obtaining the X-ray crystal-
lographic data.
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.bmcl.2006.10.035.
References and notes
7. Compound 10c was prepared from its enantiomeric pure
precursor of 6 obtained from Chiral Pak column separa-
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X-ray crystallography data for 10c (HCl salt) have been
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(CCDC). CCDC 623419 contains the supplementary
crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_re-
quest/cif, or by emailing data_request@ccdc.cam.ac.uk, or
by contacting The Cambridge Crystallographic Data
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were treated once daily for two weeks with test
compound in 20% cyclodextrin. The activity was deter-
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agonist assay.
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