Discovery of the First M5-Selective and CNS Penetrant Negative Allosteric Modulator (NAM) of a Muscarinic Acetylcholine Receptor: (S)-9b-(4-Chlorophenyl)-1-(3,4-difluorobenzoyl)-2,3-dihydro-1H-imidazo[2,1-a]isoindol-5(9bH)-one (ML375)

A functional high throughput screen and subsequent multidimensional, iterative parallel synthesis effort identified the first muscarinic acetylcholine receptor (mAChR) negative allosteric modulator (NAM) selective for the M-5 subtype. ML375 is a highly selective M-5 NAM with submicromolar potency (human M-5 IC50 = 300 nM, rat M-5 IC50 = 790 nM, M1-M4 IC50 > 30 mu M), excellent multispecies PK, high CNS penetration, and enantiospecific inhibition.