MAO-B-IN-9 (compound 16) is a potent, selective, BBB-penetrated, irreversible and time-dependent MAO-B ( monoamine oxidase B) inhibitor, with an IC 50 of 0.18 μM. MAO-B-IN-9 prevents Aβ 1-42 -induced neuronal cell death. MAO-B-IN-9 shows neuroprotective effects, which may be the result of its Aβ 1-42 anti-aggregation effects. MAO-B-IN-9 is a click chemistry reagent, itcontains an Alkyne group and can undergo copper-catalyzed azide-alkyne cycloaddition (CuAAc) with molecules containing Azide groups.