Herein we describe the design, synthesis, and evaluation of a novel series of oxadiazine-based gamma secretase modulators obtained via isosteric amide replacement and critical consideration of conformational restriction. Oxadiazine lead 47 possesses good in vitro potency with excellent predicted CNS drug-like properties and desirable ADME/PK profile. This lead compound demonstrated robust Aβ42 reductions and subsequent Aβ37 increases in both rodent brain and CSF at 30 mg/kg dosed orally. [ABSTRACT FROM AUTHOR]