Novel benzothiophene H1-antihistamines for the treatment of insomnia.

SAR of lead benzothiophene H(1)-antihistamine 2 was explored to identify backup candidates with suitable pharmacokinetic profiles for an insomnia program. Several potent and selective H(1)-antihistamines with a range of projected half-lives in humans were identified. Compound 16d had a suitable human half-life as demonstrated in a human microdose study, but variability in pharmacokinetic profile, attributed to metabolic clearance, prevented further development of this compound. Compound 28b demonstrated lower predicted clearance in preclinical studies, and may represent a more suitable backup compound.

Allosteric ligands for the corticotropin releasing factor type 1 receptor modulate conformational states involved in receptor activation.

Allosteric modulators of G-protein-coupled receptors can regulate conformational states involved in receptor activation ( Mol Pharmacol 58: 1412-1423, 2000 ). This hypothesis was investigated for the corticotropin-releasing factor type 1 (CRF(1)) receptor using a novel series of ligands with varying allosteric effect on CRF binding (inhibition to enhancement). For the G-protein-uncoupled receptor, allosteric modulation of CRF binding was correlated with nonpeptide ligand signaling activity; inverse agonists inhibited and agonists enhanced CRF binding. These data were quantitatively consistent with a two-state equilibrium underlying the modulation of CRF binding to the G-protein-uncoupled receptor. We next investigated the allosteric effect on CRF-stimulated G-protein coupling. Ligands inhibited CRF-stimulated cAMP accumulation regardless of their effect on the G-protein-uncoupled state. The modulators reduced CRF E(max) values, suggesting that they reduced the efficacy of a CRF-bound active state to couple to G-protein. Consistent with this hypothesis, the modulators inhibited binding to a guanine nucleotide-sensitive state. Together, the results are quantitatively consistent with a model in which 1) the receptor exists in three predominant states: an inactive state, a weakly active state, and a CRF-bound fully active state; 2) allosteric inverse agonists stabilize the inactive state, and allosteric agonists stabilize the weakly active state; and 3) antagonism of CRF signaling results from destabilization of the fully active state. These findings imply that nonpeptide ligands differentially modulate conformational states involved in CRF(1) receptor activation and suggest that different conformational states can be targeted in designing nonpeptide ligands to inhibit CRF signaling.

Identification of novel, water-soluble, 2-amino-N-pyrimidin-4-yl acetamides as A2A receptor antagonists with in vivo efficacy.

Potent adenosine hA2A receptor antagonists are often accompanied by poor aqueous solubility, which presents issues for drug development. Herein we describe the early exploration of the structure-activity relationships of a lead pyrimidin-4-yl acetamide series to provide potent and selective 2-amino-N-pyrimidin-4-yl acetamides as hA2A receptor antagonists with excellent aqueous solubility. In addition, this series of compounds has demonstrated good bioavailability and in vivo efficacy in a rodent model of Parkinson's disease, despite having reduced potency for the rat A2A receptor versus the human A2A receptor.

2-Amino-N-pyrimidin-4-ylacetamides as A2A receptor antagonists: 1. Structure-activity relationships and optimization of heterocyclic substituents.

Previously we have described a novel series of potent and selective A 2A receptor antagonists (e.g., 1) with excellent aqueous solubility. While these compounds are efficacious A 2A antagonists in vivo, the presence of an unsubstituted furyl moiety was a cause of some concern. In order to avoid the potential metabolic liabilities that could arise from an unsubstituted furyl moiety, an optimization effort was undertaken with the aim of replacing the unsubstituted furan with a more metabolically stable group while maintaining potency and selectivity. Herein, we describe the synthesis and SAR of a range of novel heterocyclic systems and the successful identification of a replacement for the unsubstituted furan moiety with a methylfuran or thiazole moiety while maintaining potency and selectivity.

2-Amino-N-pyrimidin-4-ylacetamides as A2A receptor antagonists: 2. Reduction of hERG activity, observed species selectivity, and structure-activity relationships.

Previously we have described a series of novel A 2A receptor antagonists with excellent water solubility. As described in the accompanying paper, the antagonists were first optimized to remove an unsubstituted furyl moiety, with the aim of avoiding the potential metabolic liabilities that can arise from the presence of an unsubstituted furan. This effort identified a series of potent and selective methylfuryl derivatives. Herein, we describe the further optimization of this series to increase potency, maintain selectivity for the human A 2A vs the human A 1 receptor, and minimize activity against the hERG channel. In addition, the observed structure-activity relationships against both the human and the rat A 2A receptor are reported.

2,6-Diaryl-4-phenacylaminopyrimidines as potent and selective adenosine A(2A) antagonists with reduced hERG liability.

In this report, the design and synthesis of a series of pyrimidine based adenosine A(2A) antagonists are described. The strategy and outcome of expanding SAR exploration to attenuate hERG and improve selectivity over A(1) are discussed. Compound 33 exhibited excellent potency, selectivity over A(1), and reduced hERG liability.

2,6-Diaryl-4-acylaminopyrimidines as potent and selective adenosine A(2A) antagonists with improved solubility and metabolic stability.

In this report, the strategy and outcome of expanding SAR exploration to improve solubility and metabolic stability are discussed. Compound 35 exhibited excellent potency, selectivity over A(1) and improved solubility of >4 mg/mL at pH 8.0. In addition, compound 35 had good metabolic stability with a scaled intrinsic clearance of 3 mL/min/kg (HLM) and demonstrated efficacy in the haloperidol induced catalepsy model.

Synthesis of N-pyrimidinyl-2-phenoxyacetamides as adenosine A2A receptor antagonists.

A series of N-pyrimidinyl-2-phenoxyacetamide adenosine A(2A) antagonists is described. SAR studies led to compound 14 with excellent potency (K(i) = 0.4 nM), selectivity (A(1)/A(2A) > 100), and efficacy (MED 10 mg/kg p.o.) in the rat haloperidol-induced catalepsy model for Parkinson's disease.

CoMFA, synthesis, and pharmacological evaluation of (E)-3-(2-carboxy-2-arylvinyl)-4,6-dichloro-1H-indole-2-carboxylic acids: 3-[2-(3-aminophenyl)-2-carboxyvinyl]-4,6-dichloro-1H-indole-2-carboxylic acid, a potent selective glycine-site NMDA receptor antagonist.

(E)-3-(2-Carboxy-2-phenylvinyl)-4,6-dichloro-1H-indole-2-carboxylic acid, 1, is a potent and selective antagonist of the glycine site of the N-methyl-d-aspartate (NMDA) receptor. Using 3D comparative molecular field analysis (CoMFA) to guide the synthetic effort, a series of aryl diacid analogues of 1 were synthesized to optimize in vivo potency, duration of action, and binding activity. It was found that the incorporation of a substituted aromatic with an electron withdrawing group or a heterocyclic group at the 2-position of the 3-propenyl moiety of 1 gave compounds with better affinity and potency in the murine stroke model. Ultimately this led to the discovery of 3-[2-(3-aminophenyl)-2-carboxyvinyl]-4,6-dichloro-1H-indole-2-carboxylic acid, 19, as a new potent selective glycine-site NMDA receptor antagonist.

Potent, orally active corticotropin-releasing factor receptor-1 antagonists containing a tricyclic pyrrolopyridine or pyrazolopyridine core.

Two new classes of tricyclic-based corticotropin-releasing factor (CRF(1)) receptor-1 antagonists were designed by constraining known 1H-pyrrolo[2,3-b]pyridine and 1H-pyrazolo[3,4-b]pyridine ligands. Pyrrole- and pyrazole-based molecules 19g and 22a, respectively, were discovered that potently bind the recombinant CRF(1) receptor (K(i) = 3.5, 2.9 nM) and inhibit adrenocorticotropic hormone (ACTH) release from rat pituitary cell culture (IC(50) = 14, 6.8 nM). These compounds show good oral bioavailabity (F = 24%, 7.0%) and serum half-lives in rats (t(1/2) = 6.3, 12 h) and penetrate the rat brain ([brain]/[plasma] = 0.27, 0.52) but tend toward large volumes of distribution (V(D) = 38, 44 L kg(-1)) and rapid clearances (CL = 70, 43 mL min(-1) kg(-1)). When given orally, both the pyrazole and the pyrrole leads dose-dependently inhibit stress-induced ACTH release in vivo. ACTH reductions of 84-86% were observed for 30 mg kg(-1) doses.

Design and synthesis of tricyclic imidazo[4,5-b]pyridin-2-ones as corticotropin-releasing factor-1 antagonists.

The synthesis and SAR studies of tricyclic imidazo[4,5-b]pyridin-2-ones as human corticotropin-releasing factor receptor (CRF(1)) antagonists are discussed herein. Compound 16g was identified as a functional antagonist that inhibited CRF-stimulated cyclic adenosine monophosphate production and CRF-induced adrenocorticotrophic hormone release. Pharmacokinetics studies in rats showed that 16g was orally bioavailable, had good brain penetration, and had a moderate half-life. In our effort to identify CRF(1) antagonists with improved pharmacokinetics properties, 16g exhibited a favorably lower volume of distribution.

Design and synthesis of tricyclic corticotropin-releasing factor-1 antagonists.

Antagonists of the corticotropin-releasing factor (CRF) neuropeptide should prove to be effective in treating stress and anxiety-related disorders. In an effort to identify antagonists with improved physicochemical properties, new tricyclic CRF(1) antagonists were designed, synthesized, and tested for biological activity. As a result of studies aimed at establishing a relationship between structure and CRF(1) binding affinity, NBI 35965 (12a) was identified as a high-affinity antagonist with a pK(i) value of 8.5. Compound 12a proved to be a functional CRF(1) antagonist with pIC(50) values of 7.1 and 6.9 in the in vitro CRF-stimulated cAMP accumulation and ACTH production assays, respectively, and 12a also reduced CRF or stress induced ACTH production in vivo.

N-[6-amino-2-(heteroaryl)pyrimidin-4-yl]acetamides as A2A receptor antagonists with improved drug like properties and in vivo efficacy.

In the present article, we report on a strategy to improve the physical properties of a series of small molecule human adenosine 2A (hA2A) antagonists. One of the aromatic rings typical of this series of antagonists is replaced with a series of aliphatic groups, with the aim of disrupting crystal packing of the molecule to lower the melting point and in turn to improve the solubility. Herein, we describe the SAR of a new series of water-soluble 2,4,6-trisubstituted pyrimidines where R1 is an aromatic heterocycle, R2 is a short-chain alkyl amide, and the typical R3 aromatic heterocyclic substituent is replaced with an aliphatic amino substituent. This approach significantly enhanced aqueous solubility and lowered the log P of the system to provide molecules without significant hERG or CYP liabilities and robust in vivo efficacy.

Characterization of novel selective H1-antihistamines for clinical evaluation in the treatment of insomnia.

Analogues of the known H(1)-antihistamine R-dimethindene were profiled as potential agents for the treatment of insomnia. Several highly selective compounds were efficacious in rodent sleep models. On the basis of overall profile, indene 1d and benzothiophene 2a had pharmacokinetic properties suitable for evaluation in night time dosing. Compound 2a did not show an in vivo cardiovascular effect from weak hERG channel inhibition.

Lead optimization of 4-acetylamino-2-(3,5-dimethylpyrazol-1-yl)-6-pyridylpyrimidines as A2A adenosine receptor antagonists for the treatment of Parkinson's disease.

4-Acetylamino-2-(3,5-dimethylpyrazol-1-yl)-pyrimidines bearing substituted pyridyl groups as C-6 substituents were prepared as selective adenosine hA2A receptor antagonists for the treatment of Parkinson's disease. The 5-methoxy-3-pyridyl derivative 6g (hA2A Ki 2.3 nM, hA1 Ki 190 nM) was orally active at 3 mg/kg in a rat HIC model but exposure was poor in nonrodent species, presumably due to poor aqueous solubility. Follow-on compound 16a (hA2A Ki 0.83 nM, hA1 Ki 130 nM), bearing a 6-(morpholin-4-yl)-2-pyridyl substituent at C-6, had improved solubility and was orally efficacious (3 mg/kg, HIC) but showed time-dependent cytochrome P450 3A4 inhibition, possibly related to morpholine ring metabolism. Compound 16j (hA2A Ki 0.44 nM, hA1 Ki 80 nM), bearing a 6-(4-methoxypiperidin-1-yl)-2-pyridyl substituent at C-6, was sparingly soluble but had good oral exposure in rodent and nonrodent species, had no cytochrome P450 or human ether-a-go-go related gene channel issues, and was orally efficacious at 1 mg/kg in HIC and at 3 mg/kg for potentiation of l-dopa-induced contralateral rotations in 6-hydroxydopamine-lesioned rats.

Characterization of the interaction of indiplon, a novel pyrazolopyrimidine sedative-hypnotic, with the GABAA receptor.

Clinically used benzodiazepine and nonbenzodiazepine sedative-hypnotic agents for the treatment of insomnia produce their therapeutic effects through allosteric enhancement of the effects of the inhibitory neurotransmitter GABA at the GABA(A) receptor. Indiplon is a novel pyrazolopyrimidine sedative-hypnotic agent, currently in development for insomnia. Using radioligand binding studies, indiplon inhibited the binding of [(3)H]Ro 15-1788 (flumazenil) to rat cerebellar and cerebral cortex membranes with high affinity (K(i) values of 0.55 and 0.45 nM, respectively). [(3)H]Indiplon binding to rat cerebellar and cerebral cortex membranes was reversible and of high affinity, with K(D) values of 1.01 and 0.45 nM, respectively, with a pharmacological specificity consistent with preferential labeling of GABA(A) receptors containing alpha1 subunits. In "GABA shift" experiments and in measurements of GABA-induced chloride conductance in rat cortical neurons in culture, indiplon behaved as an efficacious potentiator of GABA(A) receptor function. In both the radioligand binding and electrophysiological experiments, indiplon had a higher affinity than zolpidem or zaleplon. These in vitro properties are consistent with the in vivo properties of indiplon as an effective sedative-hypnotic acting through allosteric potentiation of the GABA(A) receptor.

In vivo pharmacological characterization of indiplon, a novel pyrazolopyrimidine sedative-hypnotic.

Indiplon (NBI 34060; N-methyl-N-[3-[3-(2-thienylcarbonyl)-pyrazolo[1,5-alpha]pyrimidin-7-yl]phenyl]acetamide), a novel pyrazolopyrimidine and high-affinity allosteric potentiator of GABA(A) receptor function, was profiled for its effects in rodents after oral administration. In mice, indiplon inhibited locomotor activity (ED(50) = 2.7 mg/kg p.o.) at doses lower than the nonbenzodiazepine hypnotics zolpidem (ED(50) = 6.1 mg/kg p.o.) and zaleplon (ED(50) = 24.6 mg/kg p.o.), a sedative effect that was reversed by the benzodiazepine site antagonist flumazenil. Indiplon inhibited retention in the mouse passive avoidance paradigm over a dose range and with a temporal profile that coincided with its sedative activity. Indiplon, zolpidem, and zaleplon were equally effective in inhibiting locomotor activity in the rat and produced dose-related deficits on the rotarod. In a rat vigilance paradigm, indiplon, zolpidem, and zaleplon produced performance deficits over a dose range consistent with their sedative effects, although indiplon alone showed no significant increase in response latency. Indiplon produced a small deficit in the delayed nonmatch to sample paradigm at a dose where sedative effects became apparent. Indiplon was active in the rat Vogel test of anxiety, but it showed only a sedative profile in the mouse open field test. The pharmacokinetic profile of indiplon in both rat and mouse was consistent with its pharmacodynamic properties and indicated a rapid T(max), short t(1/2), and excellent blood-brain barrier penetration. Therefore, indiplon has the in vivo profile of an efficacious sedative-hypnotic, in agreement with its in vitro receptor pharmacology as a high-affinity allosteric potentiator of GABA(A) receptor function, with selectivity for alpha1 subunit-containing GABA(A) receptors.