ABSTRACT
The positive allosteric modulator (PAM) binding site for metabotropic glutamate receptor subtype 5 (mGlu(5)) lacks a readily available radio-labeled tracer fordetailed structure-activity studies. This communication describes a selective mGlu(5) compound, 7-methyl-2-(4-(pyridin-2-yloxy)benzyl)-5-(pyridin-3-yl)isoindolin-1-one (PBPyl) that binds with high affinity to human mGlu(5) and exhibits functional PAM activity. Analysis of PBPyl by FLIPR revealed an EC(50) of 87 nM with an 89% effect in transfected HEK293 cells and an EC(50) of 81 nM with a 42% effect in rat primary neurons. PBPyl exhibited 5-fold higher functional selectivity for mGlu(5) in a full mGlu receptor panel. Unlabeled PBPyl was tested for specific binding using a liquid chromatography mass spectrometry (LC/MS/MS)-based filtration binding assay and exhibited 40% specific binding in recombinant membranes, a value higher than any candidate compound tested. In competition binding studies with [(3)H]MPEP, the mGlu(5) receptor negative allosteric modulator (NAM), PBPyl exhibited a k(i) value of 34 nM. PBPyl also displaced [(3)H]ABP688, a mGluR(5) receptor NAM, in tissue sections from mouse and rat brain using autoradiography. Areas of specific binding included the frontal cortex, striatum and nucleus accumbens. PBPyl was radiolabeled to a specific activity of 15 Ci/mmol and tested for specific binding in a filter plate format. In recombinant mGlu(5b) membranes, [(3)H] PBPyl exhibited saturable binding with a K(d) value of 18.6 nM. In competition binding experiments, [(3)H] PBPyl was displaced by high affinity mGlu(5) positive and negative modulators. Further tests showed that PBPyl displays less than optimal characteristics as an in vivo tool, including a high volume of distribution and ClogP, making it more suitable as an in vitro compound. However, as a first report of direct binding of an mGlu(5) receptor PAM, this study offers value toward the development of novel PET imaging agents for this important therapeutic target.
Subject(s)
Isoindoles/pharmacology , Pyridines/pharmacology , Receptors, Metabotropic Glutamate/metabolism , Allosteric Regulation , Allosteric Site , Animals , Dose-Response Relationship, Drug , Excitatory Amino Acid Antagonists/pharmacology , HEK293 Cells , Humans , Isoindoles/chemistry , Isoindoles/metabolism , Male , Mass Spectrometry , Mice , Oximes/pharmacology , Protein Binding , Pyridines/chemistry , Pyridines/metabolism , Radioactive Tracers , Radioligand Assay , Rats , Rats, Sprague-Dawley , Receptor, Metabotropic Glutamate 5 , Receptors, Metabotropic Glutamate/antagonists & inhibitorsABSTRACT
A series of 4-piperidin-4-ylidenemethyl-benzamide δ-opioid receptor agonists is described with an emphasis on balancing the potency, subtype selectivity and in vitro ADME and safety properties. The three sites impacting SAR are substitutions on the aryl group (R(1)), the piperidine nitrogen (R(2)), and the amide (R(3)). Each region contributes to the balance of properties for δ opioid activity and a desirable CNS profile, and two clinical candidates (20 and 24) were advanced.
Subject(s)
Benzamides/pharmacology , Central Nervous System/drug effects , Piperidines/pharmacology , Receptors, Opioid, delta/agonists , Benzamides/chemistry , Central Nervous System/metabolism , Dose-Response Relationship, Drug , Ether-A-Go-Go Potassium Channels/antagonists & inhibitors , HEK293 Cells , Humans , Molecular Structure , Piperidines/chemistry , Receptors, Opioid, delta/metabolism , Stereoisomerism , Structure-Activity RelationshipABSTRACT
A novel series of piperazine derivatives exhibits sub-nanomolar binding and enhanced subtype selectivity as δ-opioid agonists. The synthesis and SAR are described as well as the application of computational models to improve in vitro ADME and safety properties suitable for CNS indications, specifically microsomal clearance, permeability, and hERG channel inhibition.
Subject(s)
Central Nervous System/drug effects , Piperazines/pharmacology , Receptors, Opioid, delta/agonists , Animals , Central Nervous System/metabolism , Computer Simulation , Dogs , Dose-Response Relationship, Drug , Ether-A-Go-Go Potassium Channels/antagonists & inhibitors , Humans , Molecular Structure , Piperazines/chemical synthesis , Piperazines/chemistry , Receptors, Opioid, delta/metabolism , Stereoisomerism , Structure-Activity RelationshipABSTRACT
Novel in vitro mGlu(5) positive allosteric modulators with good potency, solubility, and low lipophilicity are described. Compounds were identified which did not rely on the phenylacetylene and carbonyl functionalities previously observed to be required for in vitro activity. Investigation of the allosteric binding requirements of a series of dihydroquinolinone analogs led to phenylacetylene azachromanone 4 (EC(50) 11.5 nM). Because of risks associated with potential metabolic and toxicological liabilities of the phenylacetylene, this moiety was successfully replaced with a phenoxymethyl group (27; EC(50) 156.3 nM). Derivation of a second-generation of mGlu(5) PAMs lacking a ketone carbonyl resulted in azaindoline (33), azabenzimidazole (36), and N-methyl 8-azaoxazine (39) phenylacetylenes. By scoping nitrogen substituents and phenylacetylene replacements in 39, we identified phenoxymethyl 8-azaoxazine 47 (EC(50) 50.1 nM) as a potent and soluble mGlu(5) PAM devoid of both undesirable phenylacetylene and carbonyl functionalities.
Subject(s)
Drug Design , Receptors, Metabotropic Glutamate/metabolism , Allosteric Regulation , Inhibitory Concentration 50 , Receptor, Metabotropic Glutamate 5ABSTRACT
Positive allosteric modulation of metabotropic glutamate receptor 5 (mGluR5) is regarded as a potential novel treatment for schizophrenic patients. Herein we report the synthesis and SAR of 4-aryl piperazine and piperidine amides as potent mGluR5 positive allosteric modulators (PAMs). Several analogs have excellent activity and desired drug-like properties. Compound 2b was further characterized as a PAM using several in vitro experiments, and produced robust activity in several preclinical animal models.
