Amyloid β (Aβ) aggregates in the brains of patients with Alzheimer's disease (AD) and accumulates
via oligomerization and subsequent fiber elongation processes. These toxicity-induced neuronal
damage and shedding processes advance AD progression. Therefore, Aβ aggregation-inhibiting
substances may contribute to the prevention and treatment of AD. We screened for Aβ42 aggregation
inhibitory activity using various plant extracts and compounds, and found high activity for a
Geranium thunbergii extract (EC50 = 18 μg/mL). Therefore, we screened for Aβ42 aggregation
inhibitors among components of a G. thunbergii extract and investigated their chemical properties in
this study. An active substance was isolated from the ethanol extract of G. thunbergii based on the
Aβ42 aggregation inhibitory activity as an index, and the compound was identified as geraniin (1)
based on spectral data. However, although geraniin showed in vitro aggregation-inhibition activity,
no binding to Aβ42 was observed via saturation transfer difference-nuclear magnetic resonance
(STD-NMR). In contrast, the hydrolysates gallic acid (2) and corilagin (5) showed aggregationinhibiting
activity and binding was observed via STD-NMR. Therefore, the hydrolysates produced
under the conditions of the activity test may contribute to the Aβ42 aggregation-inhibition activity of
G. thunbergii extracts. Geraniin derivatives may help prevent and treat AD.journal articl
