Discovery of Selective M4 Muscarinic Acetylcholine Receptor Agonists with Novel Carbamate Isosteres.

It has been hypothesized that selective muscarinic acetylcholine receptor (mAChR) M4 subtype activation could provide therapeutic benefits to a number of neurological disorders while minimizing unwanted cholinergic side effects observed due to nonselective mAChR activation. Given the high sequence and structural homology of the orthosteric binding sites among mAChRs, achieving M4 subtype-selective activation has been challenging. Herein, we describe the discovery of a series of M4 subtype-selective agonists bearing novel carbamate isosteres.

Harnessing biosynthesis and quantitative NMR for late stage functionalization of lead molecules: Application to the M1 positive allosteric modulator (PAM) program.

A facile method for late stage diversification of lead molecules for the M1 PAM program using biosynthesis is described. Liver microsomes from several species are screened to identify a high turnover system. Subsequent incubations using less than 1 mg of substrate generate nanomole quantities of drug metabolites that are purified, characterized by microcryoprobe NMR spectroscopy, and quantified to known concentrations to enable rapid biology testing.

The Discovery of a Novel Phosphodiesterase (PDE) 4B-Preferring Radioligand for Positron Emission Tomography (PET) Imaging.

As part of our effort in identifying phosphodiesterase (PDE) 4B-preferring inhibitors for the treatment of central nervous system (CNS) disorders, we sought to identify a positron emission tomography (PET) ligand to enable target occupancy measurement in vivo. Through a systematic and cost-effective PET discovery process, involving expression level (B) and biodistribution determination, a PET-specific structure-activity relationship (SAR) effort, and specific binding assessment using a LC-MS/MS "cold tracer" method, we have identified 8 (PF-06445974) as a promising PET lead. Compound 8 has exquisite potency at PDE4B, good selectivity over PDE4D, excellent brain permeability, and a high level of specific binding in the "cold tracer" study.

Discovery and Characterization of (R)-6-Neopentyl-2-(pyridin-2-ylmethoxy)-6,7-dihydropyrimido[2,1-c][1,4]oxazin-4(9H)-one (PF-06462894), an Alkyne-Lacking Metabotropic Glutamate Receptor 5 Negative Allosteric Modulator Profiled in both Rat and Nonhuman Primates.

We previously observed a cutaneous type IV immune response in nonhuman primates (NHP) with the mGlu negative allosteric modulator (NAM) 7. To determine if this adverse event was chemotype- or mechanism-based, we evaluated a distinct series of mGlu NAMs. Increasing the sp character of high-throughput screening hit 40 afforded a novel morpholinopyrimidone mGlu NAM series.

Design and Synthesis of γ- and δ-Lactam M Positive Allosteric Modulators (PAMs): Convulsion and Cholinergic Toxicity of an M-Selective PAM with Weak Agonist Activity.

Recent data demonstrated that activation of the muscarinic M receptor by a subtype-selective positive allosteric modulator (PAM) contributes to the gastrointestinal (GI) and cardiovascular (CV) cholinergic adverse events (AEs) previously attributed to M and M activation. These studies were conducted using PAMs that also exhibited allosteric agonist activity, leaving open the possibility that direct activation by allosteric agonism, rather than allosteric modulation, could be responsible for the adverse effects. This article describes the design and synthesis of lactam-derived M PAMs that address this hypothesis.

Characterization of a Novel M1 Muscarinic Acetylcholine Receptor Positive Allosteric Modulator Radioligand, [3H]PT-1284.

Selective activation of the M1 muscarinic acetylcholine receptor (mAChR) via a positive allosteric modulator (PAM) is a new approach for the treatment of the cognitive impairments associated with schizophrenia and Alzheimer's disease. Herein, we describe the characterization of an M1 PAM radioligand, 8-((1S,2S)-2-hydroxycyclohexyl)-5-((6-(methyl-t3)pyridin-3-yl)methyl)-8,9-dihydro-7H-pyrrolo[3,4-hour]quinolin-7-one ([(3)H]PT-1284), as a tool for characterizing the M1 allosteric binding site, as well as profiling novel M1 PAMs. 8-((1S,2S)-2-Hydroxycyclohexyl)-5-((6-methylpyridin-3-yl)methyl)-8,9-dihydro-7H-pyrrolo[3,4-hour]quinolin-7-one (PT-1284 ( 1: )) was shown to potentiate acetylcholine (ACh) in an M1 fluorometric imaging plate reader (FLIPR) functional assay (EC50, 36 nM) and carbachol in a hippocampal slice electrophysiology assay (EC50, 165 nM).

Discovery of the Potent and Selective M1 PAM-Agonist N-[(3R,4S)-3-Hydroxytetrahydro-2H-pyran-4-yl]-5-methyl-4-[4-(1,3-thiazol-4-yl)benzyl]pyridine-2-carboxamide (PF-06767832): Evaluation of Efficacy and Cholinergic Side Effects.

It is hypothesized that selective muscarinic M1 subtype activation could be a strategy to provide cognitive benefits to schizophrenia and Alzheimer's disease patients while minimizing the cholinergic side effects observed with nonselective muscarinic orthosteric agonists. Selective activation of M1 with a positive allosteric modulator (PAM) has emerged as a new approach to achieve selective M1 activation. This manuscript describes the development of a series of M1-selective pyridone and pyridine amides and their key pharmacophores.

Design and optimization of selective azaindole amide M1 positive allosteric modulators.

Selective activation of the M1 receptor via a positive allosteric modulator (PAM) is a new approach for the treatment of the cognitive impairments associated with schizophrenia and Alzheimer's disease. A novel series of azaindole amides and their key pharmacophore elements are described. The nitrogen of the azaindole core is a key design element as it forms an intramolecular hydrogen bond with the amide N-H thus reinforcing the bioactive conformation predicted by published SAR and our homology model.

The discovery and characterization of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor potentiator N-{(3S,4S)-4-[4-(5-cyano-2-thienyl)phenoxy]tetrahydrofuran-3-yl}propane-2-sulfonamide (PF-04958242).

A unique tetrahydrofuran ether class of highly potent α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor potentiators has been identified using rational and structure-based drug design. An acyclic lead compound, containing an ether-linked isopropylsulfonamide and biphenyl group, was pharmacologically augmented by converting it to a conformationally constrained tetrahydrofuran to improve key interactions with the human GluA2 ligand-binding domain. Subsequent replacement of the distal phenyl motif with 2-cyanothiophene to enhance its potency, selectivity, and metabolic stability afforded N-{(3S,4S)-4-[4-(5-cyano-2-thienyl)phenoxy]tetrahydrofuran-3-yl}propane-2-sulfonamide (PF-04958242, 3), whose preclinical characterization suggests an adequate therapeutic index, aided by low projected human oral pharmacokinetic variability, for clinical studies exploring its ability to attenuate cognitive deficits in patients with schizophrenia.

Discovery and preclinical characterization of 1-methyl-3-(4-methylpyridin-3-yl)-6-(pyridin-2-ylmethoxy)-1H-pyrazolo-[3,4-b]pyrazine (PF470): a highly potent, selective, and efficacious metabotropic glutamate receptor 5 (mGluR5) negative allosteric modulator.

A novel series of pyrazolopyrazines is herein disclosed as mGluR5 negative allosteric modulators (NAMs). Starting from a high-throughput screen (HTS) hit (1), a systematic structure-activity relationship (SAR) study was conducted with a specific focus on balancing pharmacological potency with physicochemical and pharmacokinetic (PK) properties. This effort led to the discovery of 1-methyl-3-(4-methylpyridin-3-yl)-6-(pyridin-2-ylmethoxy)-1H-pyrazolo[3,4-b]pyrazine (PF470, 14) as a highly potent, selective, and orally bioavailable mGluR5 NAM.

Discovery and characterization of a novel dihydroisoxazole class of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor potentiators.

Positive allosteric modulators ("potentiators") of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPAR) enhance excitatory neurotransmission and may improve the cognitive deficits associated with various neurological disorders. The dihydroisoxazole (DHI) series of AMPAR potentiators described herein originated from the identification of 7 by a high-throughput functional activity screen using mouse embryonic stem (mES) cell-derived neuronal precursors. Subsequent structure-based drug design using X-ray crystal structures of the ligand-binding domain of human GluA2 led to the discovery of both PF-04725379 (11), which in tritiated form became a novel ligand for characterizing the binding affinities of subsequent AMPAR potentiators in rat brain homogenate, and PF-04701475 (8a), a prototype used to explore AMPAR-mediated pharmacology in vivo.

Positive allosteric modulation of AMPA receptors from efficacy to toxicity: the interspecies exposure-response continuum of the novel potentiator PF-4778574.

α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) positive allosteric modulation (i.e., "potentiation") has been proposed to overcome cognitive impairments in schizophrenia, but AMPAR overstimulation can be excitotoxic.

1-[(1-methyl-1H-imidazol-2-yl)methyl]-4-phenylpiperidines as mGluR2 positive allosteric modulators for the treatment of psychosis.

A novel series of mGluR2 positive allosteric modulators (PAMs), 1-[(1-methyl-1H-imidazol-2-yl)methyl]-4-phenylpiperidines, is herein disclosed. Structure-activity relationship studies led to potent, selective mGluR2 PAMs with excellent pharmacokinetic profiles. A representative lead compound (+)-17e demonstrated dose-dependent inhibition of methamphetamine-induced hyperactivity and mescaline-induced scratching in mice, providing support for potential efficacy in treating psychosis.

3-Benzyl-1,3-oxazolidin-2-ones as mGluR2 positive allosteric modulators: Hit-to lead and lead optimization.

The discovery, synthesis and SAR of a novel series of 3-benzyl-1,3-oxazolidin-2-ones as positive allosteric modulators (PAMs) of mGluR2 is described. Expedient hit-to-lead work on a single HTS hit led to the identification of a ligand-efficient and structurally attractive series of mGluR2 PAMs. Human microsomal clearance and suboptimal physicochemical properties of the initial lead were improved to give potent, metabolically stable and orally available mGluR2 PAMs.

3-(Imidazolyl methyl)-3-aza-bicyclo[3.1.0]hexan-6-yl)methyl ethers: a novel series of mGluR2 positive allosteric modulators.

The synthesis and structure-activity relationship (SAR) of a novel series of 3-(imidazolyl methyl)-3-aza-bicyclo[3.1.0]hexan-6-yl)methyl ethers, derived from a high throughput screening (HTS), are described.

Synthesis of novel pyrrolo[3,4-d]pyrazole-dicarboxylic acids and evaluation of their interaction with glutamate receptors.

Chiral pyrazoline amino acids (3aR,4S,6aR)-1a and (3aR,4S,6aR)-1b, and (3aS,6S,6aS)-2a and (3aS,6S,6aS)-2b, which are conformationally constrained analogues of glutamic and homoglutamic acid, respectively, were prepared via a strategy based on the 1,3-dipolar cycloaddition of a nitrile imine to methyl N-Boc-3,4-didehydro-(S)-prolinate. The new 'amino acids' were tested for activity at ionotropic glutamate receptors. Solely the derivative (3aR,4S,6aR)-1a, which is structurally related to the previously described 4,5-dihydroisoxazole analogue (S)-CIP-A, turned out to be a potent and selective agonist for the AMPA receptors.