Discovery, Synthesis, and Structure–Activity Relationship Development of a Series of <i>N</i>-4-(2,5-Dioxopyrrolidin-1-yl)phenylpicolinamides (VU0400195, ML182): Characterization of a Novel Positive Allosteric Modulator of the Metabotropic Glutamate Receptor 4 (mGlu₄) with Oral Efficacy in an Antiparkinsonian Animal Model

There is an increasing amount of literature data showing the positive effects on preclinical antiparkinsonian rodent models with selective positive allosteric modulators of metabotropic glutamate receptor 4 (mGlu₄). However, most of the data generated utilize compounds that have not been optimized for druglike properties, and as a consequence, they exhibit poor pharmacokinetic properties and thus do not cross the blood–brain barrier. Herein, we report on a series of <i>N</i>-4-(2,5-dioxopyrrolidin-1-yl)­phenylpicolinamides with improved PK properties with excellent potency and selectivity as well as improved brain exposure in rodents. Finally, ML182 was shown to be orally active in the haloperidol induced catalepsy model, a well-established antiparkinsonian model