Discovery of the First Potent and Orally Available Agonist of the Orphan G-Protein-Coupled Receptor 52

G-protein-coupled receptor 52 (GPR52) is an orphan Gs-coupled G-protein-coupled receptor. GPR52 inhibits dopamine D2 receptor signaling and activates dopamine D1/N-methyl-d-aspartate receptors via intracellular cAMP accumulation, and therefore, GPR52 agonists may have potential as a novel class of antipsychotics. A series of GPR52 agonists with a bicyclic core was designed to fix the conformation of the phenethyl ether moiety of compounds 2a and 2b. 3-[2-(3-Chloro-5-fluorobenzyl)-1-benzothiophen-7-yl]-N-(2-methoxyethyl)benzamide 7m showed potent activity (pEC50 = 7.53 ± 0.08) and good pharmacokinetic properties. Compound 7m significantly suppressed methamphetamine-induced hyperactivity in mice after oral administration of 3 mg/kg without disturbance of motor function.