O-GlcNAcase-IN-2 (compound 81) is an orally effective, blood-brain barrier-permeable OGA inhibitor ( IC 50 =4.93 nM). O-GlcNAcase-IN-2 can increase the O-GlcNAcylation level of proteins and phosphorylation of tau (p-Ser199, p-Thr205 and p-Ser396) in the OA-damaged SH-SY5Y cell model. O-GlcNAcase-IN-2 can also improve cognitive impairment in APP/PS1 mice and has potential anti-Alzheimer's disease (AD) effects.