Potent, selective inhibitor of O-GlcNAcase (Ki = 21 nM for human O-GlcNAcase). Increases levels of O-GlcNAc-modified proteins in cellular assays and in vivo. Suppresses phosphorylation of tau protein in rat cortex and hippocampus1. Stabilizes tau against aggregation and slows neurodegeneration2. Prevents cognitive decline and amyloid plaque formation in bigenic tau/APP mutant mice3. Elevates soluble tau species and reduces tauopathy in mouse models4. Active in vivo and blood brain barrier permeable.