δ-Secretase inhibitor 11 (compound 11) is an orally active, potent, BBB-penetrated, non-toxic, selective and specific δ-secretase inhibitor, with an IC50 of 0.7 μM. δ-Secretase inhibitor 11 interacts with both the active site and allosteric site of δ-secretase. δ-Secretase inhibitor 11 attenuates tau and APP (amyloid precursor protein) cleavage. δ-Secretase inhibitor 11 ameliorates synaptic dysfunction and cognitive impairments in tau P301S and 5XFAD transgenic mouse models. δ-Secretase inhibitor 11 can be used for Alzheimer's disease research.