β-Secretase inhibition by C-methylisoflavones from Abronia nana

The methanol extract of Abronia nana suspension cultures were subjected to column chromatography to identify potential inhibitors of β-secretase, which is a major factor in Alzheimer's disease development. Two new C-methylisoflavones boeravinone T (1) and U (4) were isolated with three knowns boeravinone B (2), J (3) and X (5). The half-maximal inhibitory concentration (IC₅₀) values of compounds 1-5 were 18.29, 8.57, 7.87, 12.02 and 5.30 μM, respectively. The most potent 5, non-competitively inhibited β-secretase [inhibition constant (K) = 3.79 μM]. Compounds 1-5 did not inhibit other proteases such as chymotrypsin, trypsin and elastase at concentrations up to 1 mM, indicating that they were relatively specific inhibitors of β-secretase. A free hydroxyl group at C-3 position of the C-methylisoflavone skeleton appeared to be responsible for the stronger inhibitory activity against β-secretase.