Antidiabetic complications and anti-Alzheimer activities of sophoflavescenol, a prenylated flavonol from Sophora flavescens, and its structure-activity relationship.

It was previously reported that prenylated flavonols from Sophora flavescens are inhibitors of rat lens aldose reductase (RLAR), human recombinant aldose reductase (HRAR), advanced glycation endproducts (AGE), β-secretase (BACE1) and cholinesterases (ChE). Based upon structure-activity relationships, 3,4'-dihydroxy flavonols with a prenyl or lavandulyl group substitution at the C-8 position, and a hydroxy group at the C-5, are important for such inhibition. In our ongoing study to isolate active principles from S. flavescens by an activity-guided isolation procedure, further detailed phytochemical investigations of the CH(2)Cl(2) fraction were conducted via repeated chromatography over silica gel and Sephadex LH-20 columns. This ultimately resulted in the isolation of a promising active sophoflavescenol with higher inhibitory activities among the current prenylated flavonols isolated from S. flavescens against RLAR, HRAR, AGE, BACE1 and ChEs. The results further support that 3,4'-dihydroxy flavonols with a prenyl or lavandulyl substitution at the C-8 position and a methoxy group at C-5 represent a new class of RLAR, HRAR and AGE inhibitors. Nevertheless, the C-5 hydroxyl group of prenylated flavonoids is important for inhibition of BACE1 and ChEs, indicating that the hydroxyl group at C-5 might be the main contributor to the augmentation and/or modification of prenylated flavonol activity.