Glutaminyl Cyclase Inhibitor 3 (compound 212 ), a designed anti-Alzheimer’s compound, is a potent human Glutaminyl Cyclase (GC) inhibitor, with an IC 50 of 4.5 nM. Glutaminyl Cyclase-IN-1 (compound 212) significantly reduced the brain concentrations of pyroform Aβ and total Aβ and restored cognitive functions.