An inhibitor of γ-secretase (IC50s = 6.2 and 1.2 nM, respectively, in an enzyme assay and in whole cells); does not induce Notch-related toxicity (EC50s = 1,300-3,000 nM for B cells in fetal thymic organ cultures); reduces the level of Aβ40 fragments in mouse brain three hours following 1 to 18 mg/kg doses and the level of Aβ42 fragments levels at 9 or 18 mg/kg; reduces Aβ fragments when at 0.3-3 mg/kg per day for five days