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J. Med. Chem. 2006, 49, 3362-3367
Discovery of a Novel, Orally Active, Small Molecule Gonadotropin-Releasing Hormone (GnRH)
Receptor Antagonist
Haitao Li,* Kenna L. Anderes, Eugenia A. Kraynov, David R. Luthin, Quyen-Quyen Do, Yufeng Hong, Eileen Tompkins,
Eric T. Sun, Ranjan Rajapakse, Ved P. Pathak, Lance C. Christie, Haresh Vazir, Rosemary Castillo, Margaret L. Gregory,
Mary Castro, Karen Nared-Hood, Genevieve Paderes, and Mark B. Anderson
Department of Medicinal Chemistry, Research Pharmacology, and Pharmacokenetics, Dynamics & Metabolism, Pfizer Global Research &
DeVelopment, 10770 Science Center DriVe, San Diego, California 92121
ReceiVed January 5, 2006
Gonadotropin releasing hormone (GnRH) plays an important role in the biology of reproduction. The use
of GnRH receptor antagonists has been reported in the literature for the treatment of breast, ovarian, and
prostate cancers. In this article, we report the synthesis, in vitro characterization, pharmacokinetics, and
pharmacodynamics of an orally bioavailable, potent, small molecule GnRH receptor antagonist N-{4,6-
dimethoxy-2-[(3-morpholin-4-ylpropyl)amino]pyrimidin-5-yl}-5-[3,3,6-trimthyl-2,3-dihydro-1H-inden-5-
yl)oxy]-2-furamide (compound 1).
Introduction
Results and Discussion
Gonadotropin-releasing hormone (GnRH) plays an important
role in the biology of reproduction.1 The GnRH decapeptide
(pyro-Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2) is pro-
duced in the hypothalamus. The decapeptide is released into
the pituitary, where GnRH interacts with high-affinity receptors
(7-transmembrane G-Protein coupled receptors). In the pituitary,
GnRH triggers the release of luteinizing hormone (LH) and
follicle-stimulating hormone (FSH).2 GnRH, as the primary
regulator of LH, is consequently the primary regulator of the
sex hormones testosterone and estrogen.3 GnRH and its
analogues have stimulated much interest because of their
potential therapeutic benefit in treating sex-hormone-dependent
diseases, such as prostate, ovarian, and breast cancer as well as
endometriosis, uterine fibroids, benign prostate hyperplasia,
fertility disorders, and precocious puberty.4-7
GnRH receptor agonists have been clinically used in the
treatment of sex-steroid-dependent diseases. The agonists mimic
GnRH to stimulate receptors on the pituitary gland, mediating
the release of LH and FSH. After a transient rise in hormone
production or the flare effect, the administration of GnRH
receptor agonists results in a down-regulation of GnRH recep-
tors. GnRH receptor down-regulation leads to a decrease in
circulating levels of LH, testosterone, and estrogen.
In recent years, peptide GnRH receptor antagonists have been
available for clinical evaluation. They directly lower the
hormones levels without the observed flare effect associated
with the agonists.8 Several laboratories have reported active
nonpeptide GnRH receptor antagonists;9-17 few have shown oral
activity in animal models.18-21 In this article, we report the
synthesis, in vitro characterization, pharmacokinetics, and
pharmacodynamics of an orally bioavailable, potent, small
molecule GnRH receptor antagonist (compound 1). Our effort
toward the discovery of small molecule GnRH receptor antago-
nists started with the screening of our exploratory library.
Compound 2 was obtained as an initial lead.22,23 Following this
discovery, an efficient combination of targeted library syntheses
and medicinal chemistry approaches resulted in compound 1
as a potent, orally active GnRH receptor antagonist.
Chemistry. The synthesis of compound 1 is outlined in
Scheme 1. Friedel-Crafts alkylation of o-cresol 3 with 3,3-
dimethylacrylic acid provided indanone 4, which was reduced
by hydrogenation to yield indanol 5. Alkylation of phenol 5
with methyl 5-bromo-2-furoate afforded 6. Saponification of 6
provided furoic acid 7, which was acylated with 4,6-dimethoxy-
N-(3-morpholin-4-yl-propyl)-pyrimidine-2,5-diamine (11) to
furnish compound 1. The synthesis of diamine 11 is shown in
Scheme 2. Nitration of 2-chloro-4,6-dimethoxy-pyrimidine (8)
provided nitro-pyrimidine 9. Nucleophilic aromatic substitution
of 9 with 3-morpholin-4-yl-propylamine afforded compound 10.
The nitro group was then reduced by hydrogenation to provide
compound 11.
In Vitro Characterization. Compound 1 was characterized
in competition radioligand-binding assays utilizing 125I-GnRH-A
as previously described.24 Compound 1 bound to rat pituitary
and recombinant human GnRH receptors with identical binding
Ki values of 0.4 ( 0.1 nM. In cell-based functional assays,
compound 1 was an antagonist of GnRH-stimulated total inositol
phosphate accumulation with IC50 values of 3.3 ( 0.9 nM (Hill
coefficient of 0.96 ( 0.08; 1 nM GnRH in assay) and 8.8 (
1.5 nM (Hill coefficient of 0.83 ( 0.15; 100 nM GnRH in assay)
for recombinant human and rat receptors, respectively. GnRH
stimulated increases in total inositol phosphates with EC50 values
of 53 ( 16 nM (N ) 4; Hill coefficient of 1.2 ( 0.2) and 1.0
( 0.2 (N ) 4; Hill coefficient of 0.72 ( 0.2) for recombinant
rat and human receptors, respectively. In selectivity assays,
compound 1 was examined in 54 different assays including ion
channels, GPCRs, and monoamine transporters. The Ki values
were determined for hits at 10 µM. These are depicted in Table
1. With the exceptions of the Ca2+ channel assays, GnRH
selectivity of compound 1 was more than 1000-fold for all 54
assays examined. Compound 1 was subsequently profiled for
effects on basal (agonist) and KCl-stimulated Ca2+ channel
activity. Compound 1 produced no effect on basal Ca2+ channel
activity and inhibited KCl-stimulated Ca2+ flux with an IC50
value of 6.3 µM (nH 1.6), suggesting that although compound
1 readily binds to these channels, it has only modest effects as
a Ca2+ channel antagonist. Compound 1 has low potential for
drug-drug interactions mediated by CYP 1A2, 2C19, 2D6, and
* To whom correspondence should be addressed. Tel: 858-526-4659.
Fax: 858-526-4508. E-mail: haitao.li@pfizer.com.
10.1021/jm060012g CCC: $33.50 © 2006 American Chemical Society
Published on Web 04/26/2006