New diterpenoids isolated from Leonurus japonicus and their acetylcholinesterase inhibitory activity

Three new labdane diterpenoids, leojaponicone A ( 1 ), isoleojaponicone A ( 2 ) and methylisoleojaponicone A ( 3 ), were isolated from the herb of Leonurus japonicus. The chemical structures of these secondary metabolites were elucidated on the basis of 1D and 2D NMR, including HMQC, and HMBC spectroscopic techniques. All the new compounds were tested in vitro for their acetylcholinesterase and α-glucosidase inhibitory activity. Compounds 1 - 3 exhibited low inhibitory effects on α-glucosidase with respect to acarbose and exhibited high inhibitory effects on acetylcholinesterase with respect to huperzine A.