First-Time Disclosure of CVN424, a Potent and Selective GPR6 Inverse Agonist for the Treatment of Parkinson's Disease: Discovery, Pharmacological Validation, and Identification of a Clinical Candidate.

Parkinson's disease (PD) is a chronic and progressive movement disorder with the urgent unmet need for efficient symptomatic therapies with fewer side effects. GPR6 is an orphan G-protein coupled receptor (GPCR) with highly restricted expression in dopamine receptor D2-type medium spiny neurons (MSNs) of the indirect pathway, a striatal brain circuit which shows aberrant hyperactivity in PD patients. Potent and selective GPR6 inverse agonists (IAG) were developed starting from a low-potency screening hit (EC50 = 43 µM). Herein, we describe the multiple parameter optimization that led to the discovery of multiple nanomolar potent and selective GPR6 IAG, including our clinical compound CVN424. GPR6 IAG reversed haloperidol-induced catalepsy in rats and restored mobility in the bilateral 6-OHDA-lesioned rat PD model demonstrating that inhibition of GPR6 activity in vivo normalizes activity in basal ganglia circuitry and motor behavior. CVN424 is currently in clinical development to treat motor symptoms in Parkinson's disease.

Development of CVN424: A Selective and Novel GPR6 Inverse Agonist Effective in Models of Parkinson Disease.

GPR6 is an orphan G-protein-coupled receptor that has enriched expression in the striatopallidal, indirect pathway and medium spiny neurons of the striatum. This pathway is greatly impacted by the loss of the nigro-striatal dopaminergic neurons in Parkinson disease, and modulating this neurocircuitry can be therapeutically beneficial. In this study, we describe the in vitro and in vivo pharmacological characterization of (R)-1-(2-(4-(2,4-difluorophenoxy)piperidin-1-yl)-3-((tetrahydrofuran-3-yl)amino)-7,8-dihydropyrido[3,4-b]pyrazin-6(5H)-yl)ethan-1-one (CVN424), a highly potent and selective small-molecule inverse agonist for GPR6 that is currently undergoing clinical evaluation. CVN424 is brain-penetrant and shows dose-dependent receptor occupancy that attained brain 50% of receptor occupancy at plasma concentrations of 6.0 and 7.4 ng/ml in mice and rats, respectively. Oral administration of CVN424 dose-dependently increases locomotor activity and reverses haloperidol-induced catalepsy. Furthermore, CVN424 restored mobility in bilateral 6-hydroxydopamine lesion model of Parkinson disease. The presence and localization of GPR6 in medium spiny neurons of striatum postmortem samples from both nondemented control and patients with Parkinson disease were confirmed at the level of both RNA (using Nuclear Enriched Transcript Sort sequencing) and protein. This body of work demonstrates that CVN424 is a potent, orally active, and brain-penetrant GPR6 inverse agonist that is effective in preclinical models and is a potential therapeutic for improving motor function in patients with Parkinson disease. SIGNIFICANCE STATEMENT: CVN424 represents a nondopaminergic novel drug for potential use in patients with Parkinson disease.

Discovery of a Novel and Brain-Penetrant O-GlcNAcase Inhibitor via Virtual Screening, Structure-Based Analysis, and Rational Lead Optimization.

O-GlcNAcase (OGA) has received increasing attention as an attractive therapeutic target for tau-mediated neurodegenerative disorders; however, its role in these pathologies remains unclear. Therefore, potent chemical tools with favorable pharmacokinetic profiles are desirable to characterize this enzyme. Herein, we report the discovery of a potent and novel OGA inhibitor, compound 5i, comprising an aminopyrimidine scaffold, identified by virtual screening based on multiple methodologies combining structure-based and ligand-based approaches, followed by sequential optimization with a focus on ligand lipophilicity efficiency. This compound was observed to increase the level of O-GlcNAcylated protein in cells and display suitable pharmacokinetic properties and brain permeability. Crystallographic analysis revealed that the chemical series bind to OGA via characteristic hydrophobic interactions, which resulted in a high affinity for OGA with moderate lipophilicity. Compound 5i could serve as a useful chemical probe to help establish a proof-of-concept of OGA inhibition as a therapeutic target for the treatment of tauopathies.

Stereocontrolled intramolecular iron-mediated diene/vinyl ether cyclocoupling reactions.

A stereocontrolled intramolecular iron-mediated diene/olefin cyclocoupling reaction has been explored using vinyl ethers as the olefin partners. Spirolactams with functionalized (alkoxymethyl) side chains can be formed under thermal conditions. With a methoxy substituent on the diene, demetalation and hydrolysis of the cyclocoupling product afforded a single diastereomer.

Stereoselective synthesis of a model C(18)-C(35) spiroketal fragment of integramycin.

A highly stereoselective synthesis of a model C(18)-C(35) spiroketal unit (7) of integramycin has been accomplished via an enantioselective stannyl-crotylboration reaction and an N-iodosuccinimide-mediated spiroketalization of 19a.

An iron-promoted aldehyde-diene cyclocoupling reaction.

A stereospecific intramolecular iron tricarbonyl-promoted aldehyde-diene cyclocoupling reaction was investigated by using simple substrates 6 and more complicated substrates 30a/30b. Demetalation of the initial products converts all complexed dienes to their pure organic counterparts. In addition, the nickel-catalyzed carbonyl-ene reaction and the Prins reaction were investigated with two different substrates.

Dynamic diastereoselectivity during iron carbonyl mediated spirocyclization reactions.

Dynamic diastereoselectivity during Fe(CO)3 promoted [6+2] ene spirocyclization of 35a and 35b, having a chiral center on the pendent side chain, was investigated and gave rise to products 28a and 28b instead of four possible isomers. From this reaction, two chiral centers are generated, with absolute stereochemistry determined by the double bond geometry and the chiral center already present. 28a/b and the diene product from demetallation of 28a are proposed as potential intermediates for total synthesis of 18-deoxycytochalasin H. Furthermore, a stepwise second cyclization and a tandem double cyclization mediated by the Fe(CO)3 moiety was investigated.

Synthesis and herbicidal activity of 2-cyano-3-substituted-pyridinemethylaminoacrylates.

Two series of 2-cyano-3-substituted-pyridinemethylaminoacrylates, namely 12 new (Z)-2-cyano-3-methylthio-3-substituted-pyridinemethaneaminoacrylates and 10 new (Z)-2-cyano-3-alkyl-3-substituted-pyridinemethaneaminoacrylates, were synthesized as herbicidal inhibitors of photosystem II (PSII) electron transport. All of these compounds were confirmed by (1)H NMR, elemental, IR, and mass spectrum analyses. Their herbicidal activities were evaluated. Some compounds exhibited excellent herbicidal activities, even at a dose of 75 g/ha. A suitable substituent at the 2-position of the pyridine ring and the well-fit group at the 3-position of acrylate were essential for high herbicidal activity. 2-Cyanoacrylates containing a substituted pyridine ring provide higher herbicidal activities than parent compounds containing phenyl. These PSII inhibitor herbicides are safe to corn, which is a major crop in China.