Analogs of methyl-piperidinopyrazole (MPP): Antiestrogens with estrogen receptor α selective activity

Article abstract of DOI:10.1016/j.bmcl.2008.11.006

Methyl-piperidino-pyrazole (MPP), an estrogen receptor α (ERα)-selective antagonist we developed, has a basic side chain (BSC) attached to an ERα-selective agonist ligand, methyl-pyrazole-triol (MPT) through an ether linkage. To remove the possibility tha

Full text of DOI:10.1016/j.bmcl.2008.11.006

Bioorganic & Medicinal Chemistry Letters 19 (2009) 108–110
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Analogs of methyl-piperidinopyrazole (MPP): Antiestrogens with estrogen
receptor
a selective activity
Hai-Bing Zhou a, , Kathryn E. Carlson a, Fabio Stossi b, Benita S. Katzenellenbogen b,
John A. Katzenellenbogen a,
*
a Department of Chemistry, University of Illinois, Urbana, IL 61801, USA
b Departments of Molecular and Integrative Physiology, Cell and Developmental Biology, University of Illinois, Urbana, IL 61801, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Methyl-piperidino-pyrazole (MPP), an estrogen receptor
a basic side chain (BSC) attached to an ERa-selective agonist ligand, methyl-pyrazole-triol (MPT) through
an ether linkage. To remove the possibility that metabolic cleavage of the BSC in MPP would regenerate
MPT, we have replaced the N-piperidinylethoxy moiety with an N-piperidinylpropyl group, giving MPrP.
a (ERa)-selective antagonist we developed, has
Received 22 September 2008
Revised 28 October 2008
Accepted 3 November 2008
Available online 6 November 2008
This new analog retains the high ER
a
-selective binding affinity and antagonist potency of MPP.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Estrogen receptor antagonist
Antiestrogen
Subtype-selective ligand
PPT
Propyl piperidino triol
Estrogens can have remarkable tissue-selective effects, and this
has led to the development of compounds termed selective estro-
gen receptor modulators (SERMs), which function as estrogen ago-
nists in some tissues (bone, brain and the cardiovascular system)
but as antagonists in others (uterus and breast).1,2 Estrogen recep-
tors (ERs) can bind a variety of steroidal and non-steroidal ligands,
and the search for better SERMs has driven efforts to increase the
chemical diversity of these compounds, especially the non-steroi-
dal ones. In fact, subtle changes in ligand structure can have a dra-
matic impact on receptor conformation and the resulting biological
activities.3–7 A prominent feature of SERMs is a basic side chain
(BSC), typically an aminoethyl group, appended to a core non-ste-
roidal ER ligand by a phenyl ether linkage. The precise structure
and orientation of the BSC can modulate SERM activity.8,9
ing a BSC onto members of the pyrazole triol family of non-
steroidal ER ligands, we obtained antagonist compounds that re-
tained this affinity and potency preference for ERa 18
Of the seven
.
BSC-pyrazole combinations that we investigated, the most selec-
tive was a methyl-piperidino-pyrazole, which we termed MPP
(Scheme 1). In binding and transcription activation assays, MPP
is very ERa selective, with its antagonistic activity on ERa being
complete at concentrations at which it has neither agonist nor
antagonist activity on ERb.18
While MPP appeared to be a complete ER
based assay systems and has been widely used by others to evalu-
ate the role of ER in various estrogen-responsive systems, it
a antagonist in cell-
a
resembles a SERM. Therefore, it was not surprising that we (unpub-
lished) and others19 found MPP to have some agonist activity in
certain animal models of estrogenic activity.
Estrogen action is mediated through two ER subtypes, ERa and
ERb, which have distinct target tissue distributions and functional
activities.10–14 Classical SERMs (e.g., tamoxifen and raloxifene),
however, have essentially no selectivity for either ER subtype.
Structurally, MPP is based on and prepared from a pyrazole
triol, methyl-pyrazole-triol (MPT; Scheme 1), which is an ERa ago-
nist, though of modest potency.16 Thus, in principle, metabolic
cleavage of the BSC might reveal latent agonist activity in an
MPT metabolite. To investigate this possibility, we synthesized
two MPP analogs in which the side chain was modified so as to
preclude an ether metabolic cleavage that could convert MPP to
MPT. The best of these analogs, MPrP, maintains excellent selectiv-
Compounds capable of stimulating ERa very selectively have been
developed,15–17 and we found that members of the triarylpyrazole
class, such as propyl-pyrazole-triol (PPT), have ca. 1000-fold high-
er affinity and agonist potency on ERa
than on ERb.16,17 By attach-
ity for ER
transcription activation assays.
a in terms of binding affinity and antagonist potency in
* Corresponding author. Tel.: +1 217 333 6310; fax: +1 217 333 7325.
E-mail address: jkatzene@uiuc.edu (J.A. Katzenellenbogen).
Present address: State Key Laboratory of Virology, College of Pharmacy, Wuhan
University, Wuhan 430072, China.
Notably, other SERMs having aminoethoxy BSCs could, in prin-
ciple, also be metabolized to more agonistic phenols,20 and while
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.11.006

H.-B. Zhou et al. / Bioorg. Med. Chem. Lett. 19 (2009) 108–110
109
OH
OH
ERα : 12+2
ERα : 5.1+1.7
ERβ : 0.016+0.001
α/β : 320
ER
β
: 0.05+0.01
α/β
: 240
N
N
N
N
O
CH3
MPP
CH3
N
N
HO
HO
1 (MPrP)
OH
OH
ER
ER
α
β
: 5.4+1.7
: 0.039+0.027
ER
ER
α
β
: 1.6+0.5
: 0.015+0.005
α/β : 140
α/β : 110
N
N
N
O
N
OH
N
CH3
CH3
HO
HO
MPT
2
Scheme 1. Structures and ERa and ERb relative binding affinity (RBA, estradiol = 100%) values of MPP, its precursor MPT, and analogs 1 (MPrP) and compound 2. RBA values
are the average of duplicate or triplicate determinations SD.
this possibility has been considered as a mechanism for tamoxifen
resistance in breast cancer,21,22 we have found only one case in
which the propyl for ethoxy group substitution in a SERM has been
made.23 This compound, however, was characterized only as a po-
tent antifertility agent, similar in activity to the SERM nafoxidine.23
To prepare the BSC-pyrazole 1 (MPrP) and its analog 2, we first
performed an aldol condensation of 1-(4-methoxy-phenyl)-pro-
pan-1-one 3 and p-hydroxybenz aldehyde 4, according to a modi-
fied literature procedure (Scheme 2).24 The highly crystalline
enone 5 underwent reaction with 4-methoxylphenylhydrazine 6
under vigorous conditions to give pyrazole 7 from which the tri-
flate 8 was obtained. Heck-type coupling with ethyl acrylate and
a catalytic amount of (PhCN)2PdCl2 in toluene afforded the desired
pyrazole ester 10 in 82% yield. Piperidinolysis with stoichiometric
dimethyl-aluminum chloride in CH2Cl2 then gives compound 11 in
good yield. Hydrogenation gave the saturated amide 12, which was
O
O
OHC
OMe
EtOH, H2SO4
HCl gas, neat
+
+
reflux, 4 days
80 ºC, 4h
CH3
CH3
OH
H2NHN
MeO
OH
MeO
3
4
5, 41%
6
OMe
OMe
OMe
CO2Et
9
Tf2O, PyH
MeO
N
N
N
CO2Et
N
N
N
OTf
(PhCN)2PdCl2
OH
CH3
CH3
CH3
MeO
MeO
OH
7, 60%
8, 92%
10, 82%
OMe
O
O
N
Me2AlCl
.
BF3 Me2S
N
N
N
piperidine
N
CH2Cl2, rt
N
CH3
CH3
HO
MeO
11, 78%
2, 89%
Pd/C EtOH/EtOAc
OH
OMe
OMe
N
N
O
N
.
BF3 Me2S
N
N
N
BH3, THF
N
N
CH2Cl2, rt
N
overnight, rt
CH3
CH3
CH3
12, 93%
HO
MeO
MeO
13, 85%
Scheme 2. Synthesis of MPP analogs 1 (MPrP) and 2.
1 (MPrP), 81%

110
H.-B. Zhou et al. / Bioorg. Med. Chem. Lett. 19 (2009) 108–110
compounds are ER
a antagonists with no significant agonist or
A
B
C
antagonist activity on ERb. The potency of analog 1 (MPrP) appears
to be somewhat higher than that of MPP itself, and it also lacks the
ERβ Antagonist
100
50
residual, low ER
a partial agonist activity of MPP. The potency of
OH
amide (2) is somewhat lower.
In this study, we have developed a synthetic strategy to gener-
ate 1 (MPrP), a novel analog of our ERa-selective antagonist MPP,
in which the 2-(N-piperidino)ethoxy moiety has been replaced by
the 3-(N-piperidino)propyl moiety, removing a potential metabolic
liability that might engender agonist activity. This new analog re-
ERα Antagonist
N
N
O
CH3
MPP
N
HO
ERβ Agonist
ERα Agonist
tains the high affinity and antagonist potency selectivity for ER
of the parent ligand and should be a useful probe for the biological
activity of ER
a
0
a.
ERβ Antagonist
Acknowledgments
100
OH
Supported by grants from the NIH (PHS 5R37 DK15556 to J.A.K.
and 5R01 CA11819 to B.S.K.). Funding for NMR and MS instrumen-
tation is from the Keck Foundation, NIH and NSF. We are grateful to
Dr. Sung Hoon Kim and Dr. William A. Boulanger for helpful
comments.
ERα Antagonist
N
N
50
CH3
1, MPrP
N
HO
ERα Agonist
ERβ Agonist
References and notes
0
1. Park, W. C.; Jordan, V. C. Trends Mol. Med. 2002, 8, 82.
2. Sato, M.; Grese, T. A.; Dodge, J. A.; Bryant, H. U.; Turner, C. H. J. Med. Chem. 1999,
42, 1.
3. Zhou, H. B.; Nettles, K. W.; Bruning, J. B.; Kim, Y.; Joachimiak, A.; Sharma, S.;
Carlson, K. E.; Stossi, F.; Katzenellenbogen, B. S.; Greene, G. L.;
Katzenellenbogen, J. A. Chem. Biol. 2007, 14, 659.
ERβ Antagonist
100
OH
ERα Antagonist
4. Fink, B. E.; Mortensen, D. S.; Stauffer, S. R.; Aron, Z. D.; Katzenellenbogen, J. A.
Chem. Biol. 1999, 6, 205.
5. Barlaam, B.; Bernstein, P.; Dantzman, C.; Warwick, P. In PCT Int. Appl.;
(Astrazeneca AB, Swed.). Wo, 2002; p. 71.
6. Teo, C. C.; Kon, O. L.; Sim, K. Y.; Ng, S. C. J. Med. Chem. 1992, 35, 1330.
7. Palkowitz, A. D.; Glasebrook, A. L.; Thrasher, K. J.; Hauser, K. L.; Short, L. L.;
Phillips, D. L.; Muehl, B. S.; Sato, M.; Shetler, P. K.; Cullinan, G. J.; Pell, T. R.;
Bryant, H. U. J. Med. Chem. 1997, 40, 1407.
N
50
0
O
N
N
CH3
HO
2
ERα Agonist
ERβ Agonist
8. Zhou, H. B.; Sheng, S.; Compton, D. R.; Kim, Y.; Joachimiak, A.; Sharma, S.;
Carlson, K. E.; Katzenellenbogen, B. S.; Nettles, K. W.; Greene, G. L.;
Katzenellenbogen, J. A. J. Med. Chem. 2007, 50, 399.
-12
-11
-10
-9
-8
-7
-6
-5
Concentration (Log M)
9. Wallace, O. B.; Bryant, H. U.; Shetler, P. K.; Adrian, M. D.; Geiser, A. G. Bioorg.
Med. Chem. Lett. 2004, 14, 5103.
10. Kuiper, G. G.; Enmark, E.; Pelto-Huikko, M.; Nilsson, S.; Gustafsson, J. A. Proc.
Natl. Acad. Sci. U.S.A. 1996, 93, 5925.
Figure 1. Transcription activation through ER
of compounds MPP, 1 (MPrP), and 2. HEC-1 cells were transfected with expression
plasmids for ER or ERb and the estrogen-responsive gene 2xERE-pS2-Luc and were
a (solid lines) and ERb (dotted lines)
a
incubated with the indicated ligand for 24 h. Antagonist assays were done in the
presence of 1 nM estradiol (E2). Values are the mean ( SD) of two or more
11. Mosselman, S.; Polman, J.; Dijkema, R. FEBS Lett. 1996, 392, 49.
12. Pettersson, K.; Gustafsson, J. A. Annu. Rev. Physiol. 2001, 63, 165.
13. Dechering, K.; Boersma, C.; Mosselman, S. Curr. Med. Chem. 2000, 7, 561.
14. Katzenellenbogen, B. S.; Montano, M. M.; Ediger, T. R.; Sun, J.; Ekena, K.;
Lazennec, G.; Martini, P. G.; McInerney, E. M.; Delage-Mourroux, R.; Weis, K.;
Katzenellenbogen, J. A. Recent Prog. Horm. Res. 2000, 55, 163. discussion 194.
15. Larrea, F.; Garcia-Becerra, R.; Lemus, A. E.; Garcia, G. A.; Perez-Palacios, G.;
Jackson, K. J.; Coleman, K. M.; Dace, R.; Smith, C. L.; Cooney, A. J. Endocrinology
2001, 142, 3791.
16. Stauffer, S. R.; Coletta, C. J.; Tedesco, R.; Nishiguchi, G.; Carlson, K.; Sun, J.;
Katzenellenbogen, B. S.; Katzenellenbogen, J. A. J. Med. Chem. 2000, 43, 4934.
17. Kraichely, D. M.; Sun, J.; Katzenellenbogen, J. A.; Katzenellenbogen, B. S.
Endocrinology 2000, 141, 3534.
experiments, expressed as a percent of the activity of ER
which is set at 100%. IC50 values from the antagonist profiles: MPP, ER
compound 1 (MPrP), ER 20 nM, and compound 2, ER M.
a
and ERb with 1 nM E2,
a
80 nM,
a
a 1 l
reduced by borane to the corresponding amine 13. Methyl ether
cleavage with BF3ÁMe2S gave from 13 the desired product 1 (MPrP)
in 81% yield and from 11, the unsaturated amide 2.
The ER
a and ERb binding affinities, determined by a competi-
tive radiometric binding assay,25,26 shown in Scheme 1, are ex-
pressed as relative binding affinity (RBA) values (estradiol =
100%). The nature of the BSC affects binding affinity, and com-
18. Sun, J.; Huang, Y. R.; Harrington, W. R.; Sheng, S.; Katzenellenbogen, J. A.;
Katzenellenbogen, B. S. Endocrinology 2002, 143, 941.
19. Davis, A. M.; Ellersieck, M. R.; Grimm, K. M.; Rosenfeld, C. S. Mol. Reprod. Dev.
2006, 73, 1034.
pound 1 (MPrP) has an ER
than that of MPP (12%), but because its ERb binding is further re-
duced from that of MPP, MPrP has a somewhat increased ER
binding selectivity (320-fold). The ER selectivity of MPrP is also
about 2.3-fold greater than that of the triol agonist MPT, which
was the parent of MPP. The binding of the unsaturated amide (2)
is markedly lower.
a
binding affinity (5.1%) slightly lower
20. Murphy, C. S.; Langan-Fahey, S. M.; McCague, R.; Jordan, V. C. Mol. Pharmacol.
1990, 38, 737.
21. Osborne, C. K.; Jarman, M.; McCague, R.; Coronado, E. B.; Hilsenbeck, S. G.;
Wakeling, A. E. Cancer Chemother. Pharmacol. 1994, 34, 89.
22. Wolf, D. M.; Langan-Fahey, S. M.; Parker, C. J.; McCague, R.; Jordan, V. C. J. Natl.
Cancer Inst. 1993, 85, 806.
23. Lednicer, D.; Lyster, S. C.; Duncan, G. W. J. Med. Chem. 1967, 10, 78.
24. Huang, Y. R.; Katzenellenbogen, J. A. Org. Lett. 2000, 2, 2833.
25. Carlson, K. E.; Choi, I.; Gee, A.; Katzenellenbogen, B. S.; Katzenellenbogen, J. A.
Biochemistry 1997, 36, 14897.
26. Katzenellenbogen, J. A.; Johnson, H. J., Jr.; Myers, H. N. Biochemistry 1973, 12,
4085.
a
a
The ERa and ERb transcriptional activity of MPP and com-
pounds 1 (MPrP) and 2 was determined by estrogen-responsive re-
porter gene cotransfection assays in human endometrial cancer
cells (HEC-1; Fig. 1; IC50 values are given in the legend).27 All three
27. Sun, J.; Meyers, M. J.; Fink, B. E.; Rajendran, R.; Katzenellenbogen, J. A.;
Katzenellenbogen, B. S. Endocrinology 1999, 140, 800.