In our efforts to develop CGRP receptor antagonists as backups to MK-3207, 2, we employed a scaffold hopping approach to identify a series of novel oxazolidinone-based compounds. The development of a structurally diverse, potent (20, cAMP + HS IC50 = 0.67 nM), and selective compound (hERG IC50 = 19 μM) with favorable rodent pharmacokinetics (F = 100%, t1/2 = 7 h) is described. Key to this development was identification of a 3-substituted spirotetrahydropyran ring that afforded a substantial gain in potency (10 to 35-fold).

The field of small-molecule orexin antagonist research has evolved rapidly in the last 15 years from the discovery of the orexin peptides to clinical proof-of-concept for the treatment of insomnia. Clinical programs have focused on the development of antagonists that reversibly block the action of endogenous peptides at both the orexin 1 and orexin 2 receptors (OX1R and OX2R), termed dual orexin receptor antagonists (DORAs), affording late-stage development candidates including Merck's suvorexant (new drug application filed 2012). Full characterization of the pharmacology associated with antagonism of either OX1R or OX 2 R alone has been hampered by the dearth of suitable subtype-selective, orally bioavailable ligands. Herein, we report the development of a selective orexin 2 antagonist (2-SORA) series to afford a potent, orally bioavailable 2-SORA ligand. Several challenging medicinal chemistry issues were identified and overcome during the development of these 2,5-disubstituted nicotinamides, including reversible CYP inhibition, physiochemical properties, P-glycoprotein efflux and bioactivation. This article highlights structural modifications the team utilized to drive compound design, as well as in vivo characterization of our 2-SORA clinical candidate, 5''-chloro-N-[( 5,6-dimethoxypyridin-2-yl) methyl]-2,2':5',3''-terpyridine-3'-carboxamide (MK-1064), in mouse, rat, dog, and rhesus sleep models.