Cell-permeable. A potent and selective γ-secretase inhibitor (IC₅₀ = 17 nM) .Displays > 50-fold selectivity over a range of aspartyl, serine and cysteine proteases. Exhibits equal potency for inhibition of Aβ40 and Aβ42 peptides (IC₅₀ values are 48 and 67 nM respectively in human neuroblastoma cells).