Anti-acetylcholinesterase activity of the aglycones of phenolic glycosides isolated from Leonurus japonicus

Objective: To find the genuine structure with anti-acetylcholinesterase (anti-AChE) from the phenolic glycosides abundant in Leonurus japonicus (Lamiaceae). The assay for anti-AChE activity is often used to lead anti-Alzheimer's drugs. Methods: The five phenolic glycosides, tiliroside, leonurusoside C, 2 '''-syringoylrutin, rutin, and lavanduliofolioside were isolated from L. japonicus. The activities of the glycosides were relatively low. Seven compounds including p-coumaric acid, caffeic acid, hydroxytyrosol, salidroside, syringic acid, kaempferol, and quercetin, which are produced by the hydrolysis of the five glycosides, were also assayed for anti-AChE activity. Results: Of those seven compounds, the five compounds other than salidroside and syringic acid exhibited potent anti-AChE activities. In particular, the IC(50)s of caffeic acid and quercetin were (1.05 +/- 0.19) and (3.58 +/- 0.02) mu g/mL, respectively. Rutin was the most abundant flavonoid in the extract (9.18 mg/g as measured by HPLC). Conclusion: The substances with potent anti-AChE were caffeic acid, quercetin, p-coumaric acid, kaempferol, and hydroxytyrosol that can be produced from their glycosides.