Synthesis and antihormonal properties of novel 11β-benzoxazole- substituted steroids

Article abstract of DOI:10.1016/j.bmcl.2011.12.110

Early studies led to the identification of 11β-aryl-4×,5 times;-dihydrospiro[estra-4,9-diene-17β,4 times;-oxazole] analogs with potent and more selective antiprogestational activity compared to antiglucocorticoid activity than mifepristone. In the present

Full text of DOI:10.1016/j.bmcl.2011.12.110

Bioorganic & Medicinal Chemistry Letters 22 (2012) 1705–1708
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antihormonal properties of novel
11b-benzoxazole-substituted steroids
Chunyang Jin , Scott E. Fix, John A. Kepler , C. Edgar Cook z
⇑
⇑
Center for Organic and Medicinal Chemistry, Research Triangle Institute, PO Box 12194, Research Triangle Park, NC 27709-2194, USA
a r t i c l e i n f o
a b s t r a c t
Early studies led to the identification of 11b-aryl-40,50-dihydrospiro[estra-4,9-diene-17b,40-oxazole] ana-
logs with potent and more selective antiprogestational activity compared to antiglucocorticoid activity
than mifepristone. In the present study, we replaced the 40-dimethylaminophenyl group of mifepristone
with the benzoxazol group to give 5a–d. We also prepared the 17b-formamido analogs 6a,b using a new
synthetic strategy via the intermediate epoxide 21. These compounds were evaluated for their antagonist
hormonal properties using the T47D cell-based alkaline phosphatase assay and the A549 cell-based func-
tional assay. Compound 5c showed potent antagonist activity at GR with better selectivity for GR versus
PR than mifepristone and is a promising lead for further development.
Article history:
Received 7 October 2011
Revised 20 December 2011
Accepted 21 December 2011
Available online 30 December 2011
Keywords:
Glucocorticoid receptor
Progesterone receptor
Antagonist
Ó 2011 Elsevier Ltd. All rights reserved.
11b-Arylsteroids
Mifepristone
Nuclear receptors play crucial roles in development, homeosta-
sis and other biological processes in mammals.1 A subset of these
receptors binds specific steroids and related ligands to mediate
the effects by influencing transcription of target genes.2 One such
receptor, the glucocorticoid receptor (GR), acts primarily via bind-
ing to cortisol in humans and is crucially involved in the normal
development and maintenance of basal and stress-related homeo-
stasis.3 Potent and selective GR antagonists have been suggested
for the possible treatment of depression,4 diabetes,5 glaucoma,6
hypertension7 and Cushing’s disease.8 The well-known steroidal
GR antagonist, mifepristone (RU 486, 1, Fig. 1), was introduced
by the Roussel-Uclaf group in 1980s.9 A serious drawback of mife-
pristone is its abortifacient effects due to its potent progesterone
receptor (PR) antagonism.10 Since the discovery of mifepristone,
hundreds of analogs have been synthesized to optimize the
potency and selectivity for GR or PR.11 Nonetheless, mifepristone
remains the most used drug to date for the study of biology involv-
ing GR.
SAR studies from our laboratory as well as others have shown that
combinations of specific substitutions at the 11- and 17-positions
have a marked influence on the antihormonal properties at GR and
PR.11,15–24 For example, replacement of the N,N-dimethylamino
group of mifepristone with a diethoxyphosponyl group led to a po-
tent and selective GR antagonist 2.22 Interestingly, substitution of
the methyl on the propynyl group with dialkyl or dialkoxyphospho-
nyl groups resulted in selective PR antagonists.21 Some time ago, we
found that various nitro25 and amido (3)26 substituents on the 17b-
position could also generate potent antihormonal effects, in some
cases, with dissociated activities at GR versus PR. We also showed
that replacement of the 17b-hydroxyl and 17a-propynyl groups
with a substituted 17,17-spiro-oxazole group (4) led to potent
antagonism at PR with considerably reduced activity at GR.24
Oxazoles have been suggested as bioisosteres for the carboxylic es-
ter group.27 We envisioned that oxazole could also serve as a bioiso-
stere in steroids for the N,N-dimethylamino group in mifepristone or
the diethoxyphosponyl group in 2. In this Letter, we describe the
synthesis of several 11b-benzoxazole-substituted 17b-hydroxy- or
17b-formamido-steroids, and report their antagonist activities at
GR and PR.
Retrosynthetic analysis suggested that dieneketal 10 was a suit-
able starting material for making the target compounds with the
major question being the order of introduction of the substituents
to give intermediate 8 or 9 (Scheme 1). The synthesis of 11b-benzox-
azole-substituted 17b-hydroxy-steroids 5a–d is presented in
Scheme 2. Regioselective 5,10-epoxidation of commercial dienek-
etal 10 using hexafluoroacetone hydroperoxide, generated in situ
from hexafluoroacetone trihydrate and hydrogen peroxide, afforded
Steroid receptors are closely related in the structure and their
mechanism of action.12 Crystal structures of mifepristone bound
to GR and PR have recently been solved.13,14 Superposition of mife-
pristone bound to GR and PR ligand binding domains (LBD)
revealed its different binding interactions in GR and PR, indicating
that modification of the steroidal structure would have a profound
effect on the affinity and activity for the corresponding receptors.14
⇑
Corresponding authors. Tel.: +1 919 541 6328; fax: +1 919 541 8868.
E-mail address: cjin@rti.org (C. Jin).
Dr. C. Edgar Cook is deceased.
z
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.12.110

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C. Jin et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1705–1708
O
EtO
P
O
N
O
EtO
OH
HN
R
OH
Ar
CH3
CH3
CH3
O
O
2
3
1
R
R
O
R
O
N
N
O
O
N
OH
HN
H
Ar
CH3
CH3
O
O
O
4
5a R = H
6a R = H
6b R = CF3
5b R = CH3
5c R = C2H5
5d R = CF3
Figure 1. Structures of mifepristone (1) and 11b-arylsteroids.
epoxide 11 in 53% yield.25 Original attempts to generate the Grig-
nard or lithiate reagent from the corresponding 5-bromobenzoxaz-
oles followed by addition to epoxide 11 were not successful. It was
therefore necessary to introduce the oxazole moiety at a later stage
in the synthesis. Thus, treatment of diallyamino-2-allyloxy-5-bro-
mobenzene, prepared from 2-amino-4-bromophenol with ally bro-
mide and potassium hydroxide, with magnesium in tetrahydrofuran
(THF) afforded the required Grignard reagent. Subsequent addition
of the Grignard reagent to a solution of 11 in THF in the presence
of CuI gave 12 in 85% yield.28 Deprotection of the allyl groups was
achieved in 69% yield by using N,N0-dimethylbarbituric acid and cat-
alytic Pd(PPh3)4 to give aminophenol 13.29 Ring formation with s-tri-
azine30 or an appropriate ortho ester31 provided oxazoles 14a–c in
57–73% yields. The trifluoromethyl analog 14d was synthesized in
67% yield using freshly prepared 2,2,2-trifluoroacetimidic acid
methyl ester.32,33 Addition of 1-propynylmagnesium bromide fol-
lowed by deketalization and dehydration with trifluoroacetic acid
R1
O
R2
Ar
Ar
O
O
O
OH
7
8
R1
O
R2
O
O
O
O
9
10
Scheme 1. Retrosynthesis of 11b-aryl 17,17-disubstituted steroids.
NH2
N
HO
O
O
O
O
O
a
O
O
b
c
O
O
O
O
OH
13
O
O
O
OH
12
10
11
R
O
R
O
R
O
N
N
N
OH
O
OH
CH3
d
e
CH3
f
O
O
O
O
OH
O
OH
5a R = H
15a R = H
14a R = H
5b R = CH3
15b R = CH3
15c R = C2H5
15d R = CF3
14b R = CH3
14c R = C2H5
14d R = CF3
5c R = C2H5
5d R = CF3
Scheme 2. Reagents and conditions: (a) CF3COCF3, Na2HPO4, H2O2, 0 °C, 53%; (b) diallylamino-2-allyloxy-5-bromobenzene/Mg, THF, CuI, 0 °C, 85%; (c) Pd(PPh3)4, N,N0-
dimethylbarbituric acid, CH2Cl2, 40 °C, 69%; (d) 14a: s-triazine, toluene, reflux, 57%; 14b: triethyl orthoacetate, DMF, 100 °C, 73%; 14c: triethyl orthopropionate, DMF, 100 °C,
69%; 14d: 2,2,2-trifluoroacetimidic acid methyl ester, CHCl3, rt, then toluene, reflux, 67%; (e) 1-propynylmagnesium bromide, THF, rt, 80–87%; (f) TFA, CH2Cl2, H2O, 0 °C, 70–
83%.

C. Jin et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1705–1708
1707
O
N
N
N
Br
CH3
c,d
a
b
O
O
O
O
O
O
O
O
10
16
17
18
O
O
NH2
HN
H
HN
H
CH3
CH3
CH3
e
f
g
O
O
O
O
O
O
O
19
21
20
Scheme 3. Reagents and conditions: (a) allylamine, p-TsOH, benzene, reflux; (b) allyl bromide, CH2Cl2, rt; (c) KCN, MeOH, rt; (d) 1-propynylmagnesium bromide, THF, rt, 25%
over 4 steps; (e) Pd(PPh3)4, N,N0-dimethylbarbituric acid, CH2Cl2, 35 °C, 84%; (f) cyanomethyl formate, CH2Cl2, rt, 75%; (g) CF3COCF3, Na2HPO4, H2O2, 0 °C, 90%.
N
NH2
O
O
O
O
O
HO
O
HN
H
HN
H
HN
H
CH3
CH3
CH3
a
b
O
O
O
O
OH
22
O
OH
23
21
R
O
R
N
N
O
O
O
O
HN
H
HN
H
CH3
CH3
d
c
O
O
OH
24a R = H
24b R = CF3
6a R = H
6b R = CF3
Scheme 4. Reagents and conditions: (a) diallylamino-2-allyloxy-5-bromobenzene/Mg, THF, CuI, 0 °C, 71%; (b) Pd(PPh3)4, N,N0-dimethylbarbituric acid, CH2Cl2, 40 °C, 77%; (c)
24a: s-triazine, toluene, reflux, 79%; 24b: 2,2,2-trifluoroacetimidic acid methyl ester, CHCl3, rt, then toluene, reflux, 77%; (d) TFA, CH2Cl2, H2O, 0 °C, 92–98%.
(TFA) furnished the title compounds 5a–d in 56–72% yields over two
steps.
in 77% yield. Oxazole ring formation with s-triazine or 2,2,2-triflu-
oroacetimidic acid methyl ester gave 24a,b in 79% and 77% yield,
respectively. Finally, deketalization and dehydration with TFA pro-
vided 17b-formamido analogs 6a,b in 92–98% yields. All synthe-
sized steroids 5a–d and 6a,b were ꢀ98% pure as determined by
HPLC analyses. The 1H NMR and HRMS analyses of the compounds
were in agreement with the assigned structures.36
Compounds 5a–d and 6a,b were evaluated for GR antagonist
activity based on the ability to inhibit dexamethasone-induced
transcription from a glucocorticoid response element (GRE)-linked
luciferase reporter gene in the human lung carcinoma cell line
A549.37 Their PR antagonist activity was tested on the ability to
block progesterone induction of alkaline phosphatase activity in
the human breast cancer cell line T47D.37 The IC50 values of the
tested compounds were determined using regression analysis of
the luminescent data and are listed in Table 1. The ratio of the
T47D IC50 to the A549 IC50 was also calculated as a measure of the
separation of GR and PR antagonism. The commercial drug mifepri-
stone was tested as a control. Compounds 5a–d are potent GR antag-
onists with similar or better selectivity, though less potent, than
mifepristone. The best selectivity (fivefold) in differentiating GR
The synthesis of 17b-formamido analogs 6a,b was investigated
next. Attempts to convert the 17-keto group of intermediate 12 or
14 to the 17a
-propynyl-17b-formamido26 functionalities were
not successful. Therefore, an alternative synthetic strategy, outlined
in Schemes 3 and 4, was pursued, in which the 17-substituents
were introduced first. Reaction of dieneketal 10 with allylamine fol-
lowed by excess allyl bromide afforded the iminium salt 17
(Scheme 3). Addition of potassium cyanide to the iminium moiety
followed by substitution with 1-propynylmagesium bromide under
Bruylants reaction conditions34 provided the 17b-diallylamino-
17a-propynyl derivative 18 in 25% yield over four steps. Pd(0)-cat-
alyzed deprotection of the ally groups afforded amine 19 in 84%
yield. Formylation of 19 with cyanomethyl formate35 followed by
epoxidation gave the key epoxide 21 in 67% yield. Following a sim-
ilar procedure analogous to that for preparing 5a–d, CuI-catalyzed
addition of the Grignard reagent, generated from diallyamino-2-
allyloxy-5-bromobenzene, to 21 afforded the Grignard adduct 22
in 71% yield (Scheme 4). Ally groups deprotection using N,N0-dim-
ethylbarbituric acid and catalytic Pd(PPh3)4 gave aminophenol 23

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C. Jin et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1705–1708
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R
O
R
O
N
N
O
OH
HN
H
CH3
CH3
O
O
5a-d
6a,b
Compound
R
A549 (GR) and T47D (PR) activity
A549 IC50 (nM)
T47D IC50 (nM)
Ratio (PR/GR)
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Mifepristonea
1.6
45
23
13
61
60
1.4
101
35
65
85
41
46
0.9
2.2
1.5
5.0
1.4
0.7
0.3
5a
5b
5c
5d
6a
6b
H
CH3
C2H5
CF3
H
CF3
142
a
Data taken from Ref. 37.
from PR was realized when R = Et (5c). Compound 5c is also the most
potent compound in the series at GR with an IC50 value of 13 nM. It is
interesting to note that the 17b-amido analogs 6a,b are slightly
more selective than mifepristone toward PR.
In summary, a series of novel 11b-benzoxazole-substituted
17b-hydroxy- or 17b-formamido-steroids were synthesized and
evaluated for their antihormonal properties at GR and PR. Although
all the compounds in this series were less potent than mifepri-
stone, representative compound demonstrated a better selectivity
for GR versus PR. Further modification of 5c is underway to gain
additional SAR information for potent and selective GR antagonist.
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J.; Zhu, P. F.; Gunnet, J.; Demarest, K.; Lundeen, S.; Sui, Z. H. Steroids 2006, 71,
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Acknowledgment
This research was supported by the R. W. Johnson Pharmaceu-
tical Research Institute.
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