Acyl dihydropyrazolo[1,5-a]pyrimidinones as metabotropic glutamate receptor 5 positive allosteric modulators.

We report the optimization of a series of metabotropic glutamate receptor 5 (mGlu 5 ) positive allosteric modulators (PAMs) from an acyl dihydropyrazolo[1,5- a ]pyrimidinone class. Investigation of exocyclic amide transpositions with this unique 5,6-bicyclic core were conducted in attempt to modulate physicochemical properties and identify a suitable backup candidate with a reduced half-life. A potent and selective PAM, 1-(2-(phenoxymethyl)-6,7-dihydropyrazolo[1,5- a ]pyrimidin-4(5 H )-yl)ethanone ( 9a , VU0462807), was identified with superior solubility and efficacy in the acute amphetamine-induced hyperlocomotion (AHL) rat model with a minimum effective dose of 3 mg/kg. Attempts to mitigate oxidative metabolism of the western phenoxy of 9a through extensive modification and profiling are described. [ABSTRACT FROM AUTHOR]