New di-spirocyclic labdane diterpenoids from the aerial parts of Leonurus japonicus

Phytochemical investigation on the ethanol extract of a well-known medicinal herb Leonurus japonicus,led to the separation of 18 labdane type diterpenoids(1-18).Through comprehensive spectroscopic analyses and quantum chemical calculations,these compounds were structurally characterized as six new interesting 5,5,5-di-spirocyclic ones(1-6),two new(7 and 8)and six known(13-18)interesting 6,5,5-di-spirocyclic ones,a new rare 14,15-dinor derivative(9),and three new ones incorporating a y-lactone unit(10-12).An in vitro neuroprotective assay in RSC96 cells revealed that compounds 7 and 12 exhibited neuroprotective activity in a concentration-dependent way,comparable to the reference drug N-acetylcysteine.