γ-Secretase modulator 12 (Compound 1a) is a γ-secretase modulator that can selectively decrease amyloid-β42 (Aβ42) levels ( IC 50 of 0.39 µM). γ-Secretase modulator 12 can be used for Alzheimer’s disease research. γ-Secretase modulator 12 has a good brain/plasma ratio (Kp, brain = 0.72) in mice.