SAGE-718: A First-in-Class <i>N</i>‑Methyl‑d‑Aspartate Receptor Positive Allosteric Modulator for the Potential Treatment of Cognitive Impairment

N-Methyl-d-aspartate receptor (NMDAR) positive allosteric modulators (PAMs) have received increased interest as a powerful mechanism of action to provide relief as therapies for CNS disorders. Sage Therapeutics has previously published the discovery of endogenous neuroactive steroid 24­(S)-hydroxycholesterol as an NMDAR PAM. In this article, we detail the discovery of development candidate SAGE-718 (5), a potent and high intrinsic activity NMDAR PAM with an optimized pharmacokinetic profile for oral dosing. Compound 5 has completed phase 1 single ascending dose and multiple ascending dose clinical trials and is currently undergoing phase 2 clinical trials for treatment of cognitive impairment in Huntington’s disease.