A potent, nonpeptidyl 1H-quinolone antagonist for the gonadotropin-releasing hormone receptor.

Extensive development of the structure-activity relationships of a screening lead determined three important pharmacophores for gonadotropin-releasing hormone (GnRH) receptor antagonist activity. Incorporation of the 3,4,5-trimethylphenyl group at the 3-position, 2-(2(S)-azetidinyl)ethoxy group at the 4-position, and N-4-pyrimidinylcarboxamide at the 6-position of the quinolone core resulted in the identification of 4-(2-(azetidin-2(S)-yl)ethoxy)-7-chloro-2-oxo-3-(3,4,5-trimethylphenyl)-1,2-dihydroquinoline-6-carboxylic acid pyrimidin-4-ylamide (1) as a potent antagonist of the GnRH receptor. A 10(4)-fold increase in in vitro binding affinity is observed for the GnRH receptor as compared to the initial screening lead. Compound 1 exhibits nanomolar binding activity and functional antagonism at the human receptor and is 7-fold less active at the rhesus receptor. Intravenous administration of compound 1 to rhesus monkeys results in a significant decrease of the serum levels of downstream hormones, luteinizing hormone (79% decrease in area under the curve) and testosterone (92% decrease in area under the curve), at a dose of 3 mg/kg. Quinolone 1 is a potent nonpeptidyl antagonist for the human GnRH receptor that is efficacious for the suppression of luteinizing hormone and testosterone in primates.

Quinolones as gonadotropin releasing hormone (GnRH) antagonists: simultaneous optimization of the C(3)-aryl and C(6)-substituents.

A series of 3-arylquinolones was prepared and evaluated for their ability to act as gonadotropin releasing hormone (GnRH) antagonists. A variety of substitution patterns of the 3-aryl substituent are described. The 3,4,5-trimethylphenyl substituent (23h) was found to be optimal.

Identification of Phe313 of the gonadotropin-releasing hormone (GnRH) receptor as a site critical for the binding of nonpeptide GnRH antagonists.

The dog GnRH receptor was cloned to facilitate the identification and characterization of selective nonpeptide GnRH antagonists. The dog receptor is 92% identical to the human GnRH receptor. Despite such high conservation, the quinolone-based nonpeptide GnRH antagonists were clearly differentiated by each receptor species. By contrast, peptide antagonist binding and functional activity were not differentiated by the two receptors. The basis of the differences was investigated by preparing chimeric receptors followed by site-directed mutagenesis. Remarkably, a single substitution of Phe313 to Leu313 in the dog receptor explained the major differences in binding affinities and functional activities. The single amino acid replacement of Phe313 of the human receptor with Leu313 resulted in a 160-fold decrease of binding affinity of the nonpeptide antagonist compound 1. Conversely, the replacement of Leu313 of the dog receptor with Phe313 resulted in a 360-fold increase of affinity for this compound. These results show that Phe313 of the GnRH receptor is critical for the binding of this structural class of GnRH antagonists and that the dog receptor can be "humanized" by substituting Leu for Phe. This study provides the first identification of a critical residue in the binding pocket occupied by nonpeptide GnRH antagonists and reinforces cautious extrapolation of ligand activity across highly conserved receptors.

Potent antagonists of gonadotropin releasing hormone receptors derived from quinolone-6-carboxamides.

SAR studies which focused upon the C-6 position of a recently described series of quinolone gonadotropin releasing hormone antagonists are reported. Synthetic access to diverse quinolone-6-carboxamides was achieved via the palladium-catalyzed amino-carbonylation reactions of iodide 4 with various amines. Amides related to 9y were especially potent, functional antagonists of rat and human GnRH receptors.

Identification and initial structure-activity relationships of a novel non-peptide quinolone GnRH receptor antagonist.

Screening of the Merck sample collection for non-peptide compounds with binding affinity for the rat GnRH receptor led to the identification of the substituted quinolone (1) as a lead compound in the search for a non-peptide GnRH receptor antagonist. Substantial improvements in potency (approximately 300 fold) were achieved by addition of an alkyl amine at the 4-position, a 3,5-dimethylphenyl group at the 3-position and 6-nitro-7-chloro-substitution of the 1 H-quinolone core.

Investigation of the 4-O-alkylamine substituent of non-peptide quinolone GnRH receptor antagonists.

Synthesis and in vitro activity of the enantiomers of quinolone GnRH antagonist (+/-)-1 are reported. Chiral amino alcohols were prepared from the appropriate cyclic D- or L-amino acids by the Amdt-Eistert homologation followed by reduction of the resulting esters. Incorporation of these pharmacophores was achieved via a novel Mitsunobu alkylation of 4-hydroxyquinolones. The key amine pharmacophore for binding to the rat GnRH receptor was most active in the S-configuration. Ring size was not important for potency with 4, 5, 6, and 7-membered ring amines exhibiting similar potency.

A potent, orally bioavailable benzazepinone growth hormone secretagogue.

The identification of L-739,943 (8b), a potent, orally bioavailable benzolactam growth hormone secretagogue, is obtained from zwitterionic L-692,429 through modification of its amino acid side chain and replacement of the acidic 2'-tetrazole with the neutral and potency enhancing 2'-(N-methylaminocarbonylamino)methyl substituent. L-739,943 is orally active for the release of growth hormone in beagle dogs at doses as low as 0.5 mg/kg. Oral bioavailability in dogs of 8b is 24% at a dose of 2 mg/kg with a mean drug Cmax of 145 +/- 46 ng/mL. L-739,943 represents a significant breakthrough in terms of both potency and oral bioavailability as compared to the prototype benzolactam L-692,429.

Small molecule mimetics of GHRP-6.

In 1981, Bowers reported that xenobiotic peptides, derived from the Leu- and Met- enkephalins, demonstrated novel growth hormone (GH) secretory activity. The most potent peptide reported, GH releasing peptide-6 (GHRP-6), was shown to release GH by a different pathway to the known signalling peptide, growth hormone releasing hormone (GHRH). The discovery of a peptidyl GH secretagogue laid the foundation for the search for smaller, orally active mimetics of GHRP-6, as well as for its mechanism of action. This review focuses on the recent developments in the field of small molecule GH secretagogues from a medicinal chemistry perspective, and discusses various structural classes of mimetics recently reported in the literature.

Synthesis and antiarrhythmic activity of novel 3-alkyl-1-[omega-[4-[(alkylsulfonyl)amino]phenyl]-omega- hydroxyalkyl]-1H-imidazolium salts and related compounds.

Novel 3-alkyl-1-[omega-[4-[(alkylsulfonyl)amino]phenyl]-omega-hydroxyalkyl]-1H -imidazolium salts were synthesized and investigated for their class III electrophysiological activity on isolated canine cardiac Purkinje fibers and ventricular muscle tissue. Structure-activity relationships are discussed for a series of 25 compounds. Compound 3, 1-[2-hydroxy-2-[4-[(methylsulfonyl)amino]phenyl]ethyl]-3-methyl-1H- imidazolium chloride, prolonged the functional refractory period in anesthetized dogs when given intraduodenally and was also effective in preventing reentrant ventricular tachycardia induced by programmed electrical stimulation when administered intravenously in anesthetized dogs 24 h after an acute myocardial infarction. Both enantiomers of 3 were synthesized. No enantioselectivity was found in the electrophysiological effects of 3.