Isolation of cholinesterase-inhibiting flavonoids from Morus lhou.

Cholinesterases are key enzymes that play important roles in cholinergic transmission. Nine flavonoids displaying cholinesterase inhibitory activity were isolated from the root bark of Morus lhou L., a cultivated edible plant. The isolated compounds were identified as a new flavone (1), 5′-geranyl-5,7,2′,4′-tetrahydroxyflavone (2), kuwanon U (3), kuwanon E (4), morusin (5), morusinol (6), cyclomorusin (7), neocyclomorusin (8), and kuwanon C (9). All compounds apart from compound 6 inhibited cholinesterase enzyme in a dose-dependent manner with Ki values ranging between 3.1 and 37.5 μM and between 1.7 and 19.1 μM against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes, respectively. The new compound was charactierized as 5′-geranyl-4′-methoxy-5,7,2′-trihydroxyflavone (1). It showed the most potent inhibitory activity (Ki = 3.1 μM for AChE, Ki = 1.74 μM for BChE). Lineweaver−Burk and Dixon plots and their secondary replots indicated that flavones (5−9) with prenyl substitution on C-3 we...