ERβ ligands. Part 5: Synthesis and structure-activity relationships of a series of 4′-hydroxyphenyl-aryl-carbaldehyde oxime derivatives

Article abstract of DOI:10.1016/j.bmcl.2006.11.066

A series of 4′-hydroxyphenyl-aryl-carbaldehyde oximes (5b) was prepared and found to have high affinity (4 nM) and modest selectivity (39-fold) for estrogen receptor-β (ERβ). Substitution of one of the core rings of the scaffold based around these novel ligands further expanded our knowledge in the quest toward achieving high affinity and selectivity for ERβ. An X-ray co-crystal of structure 11 revealed that the oxime moiety was mimicking the C-ring of genistein, as previously predicted by SAR and docking studies.

Full text of DOI:10.1016/j.bmcl.2006.11.066

Bioorganic & Medicinal Chemistry Letters 17 (2007) 902–906
ERb ligands. Part 5: Synthesis and structure–activity relationships
of a series of 40-hydroxyphenyl-aryl-carbaldehyde oxime derivatives
Richard E. Mewshaw,a,* S. Marc Bowen,a Heather A. Harris,b Zhang B. Xu,c
Eric S. Manasd and Stephen T. Cohne
aChemical and Screening Sciences, Wyeth Research, 500 Arcola Road, Collegeville, PA 19426, USA
bWomen’s Health and Musculoskeletal Biology, Wyeth Research, 500 Arcola Road, Collegeville, PA 19426, USA
cStructural Biology and Computational Chemistry, Wyeth Research, 200 Cambridge Park Drive, Cambridge, MA 02140, USA
dComputational, Analytical and Structural Sciences, GlaxoSmithKline, 709 Swedeland Road, King of Prussia, PA 19406, USA
eEncysive Pharmaceuticals, 7000 Fannin Suite 1920, Houston, TX 77030, USA
Received 11 October 2006; revised 13 November 2006; accepted 20 November 2006
Available online 1 December 2006
Abstract—A series of 40-hydroxyphenyl-aryl-carbaldehyde oximes (5b) was prepared and found to have high affinity (4 nM) and
modest selectivity (39-fold) for estrogen receptor-b (ERb). Substitution of one of the core rings of the scaffold based around these
novel ligands further expanded our knowledge in the quest toward achieving high affinity and selectivity for ERb. An X-ray co-crys-
tal of structure 11 revealed that the oxime moiety was mimicking the C-ring of genistein, as previously predicted by SAR and dock-
ing studies.
Ó 2006 Elsevier Ltd. All rights reserved.
Estrogens are known to play important roles in the reg-
ulation of growth, development, and maintenance of a
diverse range of tissues.1 Two forms of the estrogen
receptor (ER) have been identified, designated ERa
and ERb, which are major mediators of the biologic
effects of estrogens.2 While the utility of estrogen-based
therapies such as oral contraceptives and hormone
replacement is well-established, the role of ERb is still
being unraveled.3 Crystal structures of the ERa
and ERb binding domains reported in the literature4–6
reveal two conservative residue substitutions in the
binding site: ERa Leu334 ! ERb Met336 and ERa
Met421 ! ERb Ile373. Several laboratories have exploit-
ed these residue substitutions, resulting in a wide variety
of structures and ranges of ERb selectivity.7 Recently
developed non-steroidal selective ERb agonists in
our laboratories [i.e., ERB-041 (1)3,8 and WAY-202196
(2)9 ( Fig. 1)] have demonstrated remarkable anti-in-
flammatory activities but lack classical estrogenic activ-
ity in a variety of models. One strategy that our
laboratory has embraced was to try to mimic the phar-
macophore of genistein (3) by employing either the sim-
pler phenylnaphthalene9,10 (e.g., 2) or the biphenyl
scaffold11,12 (e.g., 5a) in place of the isoflavone moiety.
Modeling studies predicted that an oxime moiety at-
tached to the biphenyl scaffold could potentially mimic
OH
OH
C
N
C
B
B
A
A
A
O
HO
HO
CN
1
2
F
F
OH
O
B
OH
D
C
C
A
B
O
OH
HO
HO
3
4
Cl
OH
OH
N
N
B
Ar
Cl
A
F
5a
5b
HO
HO
Keywords: Estrogen receptor ligands; Oximes.
*
X
Corresponding author. Tel.: +1 484 865 2910; fax: +1 484 865
9399; e-mail: mewshar@wyeth.com
Figure 1. Compounds of interest.
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.11.066

R. E. Mewshaw et al. / Bioorg. Med. Chem. Lett. 17 (2007) 902–906
903
of genistein) until our report in Part 2.12 In fact, oxime
5a was discovered to have similar ERb affinity
(IC50 = 9 nM) and selectivity (31-fold selective) to those
of genistein.
R2
R1
Br
X
b
In order to further expand our knowledge-based around
these novel oxime ligands, we report in this letter our re-
sults toward replacement of the B-ring of the previously
reported biphenyl oximes with other aryl groups (i.e.,
5b). Our strategy was to attempt to induce ERb selectiv-
ity using the larger aryl rings that project toward the
ERa Met421 ! ERb Ile373 residue substitution.
CHO
8 R1= H, R2= OTBS
9 R1= F; R2= OMe
10 R1= F; R2=OH
6 X=Br
7 X=CHO
a
c
OH
OH
d, e
F
d
The synthesis of naphthalene oximes 11 and 12 is shown
in Scheme 1 beginning with dibromo 6. Formylation,
followed by Suzuki coupling,14 afforded the aldehydes
8 and 9. Compound 8 was reacted with hydroxylamine
and deprotected to afford 11. Deprotection of 9 with
pyridine hydrochloride followed by treatment with
hydroxylamine led to 12.
N
N
12
11
OH
OH
Benzofurans and benzothiophenes were prepared
according to Scheme 2. Triflation of the commercially
available ketone 13 led to 14, which upon Suzuki cou-
pling and aromatization afforded 16. The corresponding
isomer was prepared from the known benzothiophene
18 using Suzuki conditions. Both 16 and 17 were bromi-
nated and formylated to afford aldehydes 28 and 29,
which were deprotected and treated with hydroxylamine
to afford oximes 36 and 37. The benzofurans were pre-
pared beginning with the known phenols 2015 and 2316
that were converted into their respective regioisomers
26 and 27 in two steps. Oxidation17 to the corresponding
aldehydes followed by demethylation and treatment
with hydroxylamine gave the phenolic oximes 38 and 39.
Scheme 1. Reagents and conditions: (a) i—n-BuLi, ii—DMF; (b)
Pd[P(Ph3)]4, ArBr, Na2CO3, DME/H2O, 85 °C; (c) C6H5NÆHCl,
190 °C; (d) NH2OHÆHCl, MeOH; (e) TBAF/THF.
the hydroxyl group on the C-ring of genistein. Though,
the oxime moiety has been recently employed as a mimic
of the A-ring phenol of estradiol (4),13 it had never been
utilized as a mimic of the D-ring of estradiol (i.e., C-ring
Indoles 50–52 were prepared in a straight-forward
manner as depicted in Scheme 3. Briefly, commercially
Scheme 2. Reagents and conditions: (a) Tf2O, DCM, 2,6-lutidine,
0 °C; (b) Pd2(dba)3, ArBr, KF, P(Cy)3, 60 °C; (c) MnO2/toluene; (d)
Br2 DCM, ꢀ20 °C; (e) Pd[P(Ph3)]4, ArBr, Na2CO3, DME/H2O, 85 °C;
(f) i— n-BuLi; ii—DMF; (g) BBr3, DCM, ꢀ78 °C, rt; (h) C6H5NÆHCl,
190 °C; (i) NH2OHÆHCl, MeOH; (j) BrCH2CH(OMe)2, NaOEt/EtOH;
(k) PPA, ClC6H5; (l) Pd[P(Ph3)]4, ArBr, Na2CO3, DME/H2O, 85 °C;
(m) i—NBS, AIBN; ii—K2SeO2, K2HPO4.
Scheme 3. Reagents and conditions: (a) K2CO3, NMP, CuBr, ArBr;
(b) POCl3, DMF, 80 °C; (c) NH2OHÆHCl, MeOH; (d) i—Pd(OAc)2,
Et3SiH, TEA; ii—TBAF/THF.

904
R. E. Mewshaw et al. / Bioorg. Med. Chem. Lett. 17 (2007) 902–906
Table 1. Biaryl carboxaldehyde oximes of interest
a
ERb IC50 (nM)
a
ERa IC50 (nM)
Compound
X
H
Y
a/b
11
5
2
95 12
20
12
36
37
38
39
50
51
F
4
1
148 145
39
5
H
H
H
H
H
H
F
4
20
S
4
1
37
1
10
15
3
S
10
1
155 21
O
457 122
202 124
1330 198
1905 997
270 12
O
N
9
Me
12
1
23
N
Me
N
52
3
8.05
9.7
298
37
41
1
Genistein
4
395 181
3.2 1.0
270 157
4
Estradiol
3.6 1.6
Cl
512
9
3
31
Cl
a Values are means of three experiments SEM (performed in triplicate, determined from eight concentrations).
available indoles 40 and 41 were exposed to Ullman ary-
lation conditions by reacting with the appropriately
substituted phenyl iodide to afford 42–44. Formylation
of 43 and 44 led to aldehydes 45 and 46, respectively.
Aldehydes 42, 45, and 46 were converted to their respec-
tive oximes and the phenols were unmasked using a deb-
enzylation sequence employing palladium acetate and
triethylsilane followed by desilylation to afford indole
oximes 50–52. As discussed in our previous paper, the
(E)-geometry was assigned to all of the oximes.12
of all compounds of interest using a competitive radioli-
gand binding assay.18 In our previous oxime study,
employing the biphenyl motif allowed us to identify 5a
as one of the most interesting oximes (ERb
IC50 = 9 nM).11 However, as noted above replacing the
substituted phenyl group with an unsubstituted naph-
thalene moiety resulted in a twofold increase in ERb
affinity (i.e., 11 and 12) and similar ERb selectivity to 5a.
As observed in earlier studies,8–12,19 the ortho-fluoro
substituent resulted in a slight improvement in selectivi-
ty (e.g., 11 versus 12). Replacement of the naphthalene
nucleus with the benzothiophene moiety gave similar
Shown in Table 1 are the affinities (as measured by
IC50s) and selectivities for human ERa or ERb LBD

R. E. Mewshaw et al. / Bioorg. Med. Chem. Lett. 17 (2007) 902–906
905
affinity for ERb (36 and 37 versus 1). However, ERb
selectivity was not maintained due to an improvement
in ERa affinity. A slight loss in affinity was observed
for benzofuran 38 (versus 11, 36, and 37). In contrast,
the isomeric benzofuran 39 had a dramatic loss in affin-
ity compared to its isomer 38. One possible explanation
is that intramolecular hydrogen bonding may be occur-
ring between the oxygen of the furan ring of 39 and the
hydroxyl of the oxime moiety, preventing hydrogen
bonding with the His475 moiety of ERb. Incorporation
of the unsubstituted indole ring as part of the scaffold
(i.e., 50) led to only modest ERb affinity. However con-
formational analysis (using the MMFF94 forcefield and
a GBSA solvation model, as implemented in Macro-
model; Schro¨dinger, LLC) suggested that the oxime
moiety spends the greatest amount of time (by roughly
5-fold) in an alternate conformation where it is unable
to access ERb His475. This led us to attach a 2-methyl
substituent, in an attempt to energetically stabilize the
bioactive conformation relative to the alternate one.
While this resulted in a 17-fold increase in ERb affinity
(i.e., 51 versus 50), the improvement may be the result of
several factors in addition to conformational preferences
of the oxime, including increased lipophilicity and/or a
change in the electronic nature of the indole ring. Upon
attachment of an ortho-fluoro substituent to 51, a slight
increase in ERb selectivity was again achieved (i.e., 51
versus 52).
ulated by 17b-estradiol in human prostate cancer cells
(LNCaPLN3) engineered to express either ERa or
ERb and thus can be used to determine agonist activi-
ty.11 Analog 11 was tested at 1 lM and was compared
to that of 10 nM 17b-estradiol. It was 24% as efficacious
as 17b-estradiol via ERa and was about 50% as effica-
cious as 17b-estradiol via ERb. The results thus suggest
that 11 is a weak partial agonist for both ERs at 1 lM.
In summary, we have expanded our knowledge of the
type of scaffolds that can be employed to identify novel
ER ligands, which embrace the oxime moiety as a C-ring
mimic of genistein. The most selective compounds (i.e.,
12 and 52) had a slight improvement in both ERb affin-
ity and selectivity with respect to genistein. Finally, an
X-ray co-crystal structure of 11 verified that the oxime
moiety was hydrogen bonded to the His475 residue and
mimicking the D-ring of estradiol, as predicted from
our previous modeling studies. Efforts are continuing
in our laboratories to discover novel ERb scaffolds
and understand their modes of binding in order to ratio-
nally design highly selective ligands to further unravel
the precise roles of ERb.
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Figure 2. Unbiased 2fo–fc electron density difference map, indicating
the binding mode of 11 in the ERb LBD.

906
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