Surveying heterocycles as amide bioisosteres within a series of mGlu 7 NAMs: Discovery of VU6019278

This letter describes a diversity-oriented library approach to rapidly assess diverse heterocycles as bioisosteric replacements for a metabolically labile amide moiety within a series of mGlu negative allosteric modulators (NAMs). SAR rapidly honed in on either a 1,2,4- or 1,3,4-oxadizaole ring system as an effective bioisostere for the amide. Further optimization of the southern region of the mGlu NAM chemotype led to the discovery of VU6019278, a potent mGlu NAM (IC = 501 nM, 6.3% L-AP Min) with favorable plasma protein binding (rat f = 0.10), low predicted hepatic clearance (rat CL = 27.7 mL/min/kg) and high CNS penetration (rat K = 4.9, K = 0.65).