Bioactive constituents from the leaves of Lonicera japonica

Six new isolates including three new alkaloids (1-3), one new secoiridoid glycoside (4) and one new 11-delactonization-secoiridoid glycoside (5), and one new organic acid (6) were identified from the leaves of Lonicera japonica, among which 1 and 2 assigned as a pair of configurational isomers possessed two oxazolidin-2-one fragments connected through NN bond. The structures were elucidated by the NMR data and ICD analysis. All the compounds (1-6) were tested for their antioxidant and hepatoprotective activities using cell models of ABAP-induced HepG₂ cell and APAP-induced HepG₂ cell by the MTT method. Outstandingly, compound 2 exhibited remarkable antioxidative activity with inhibitory rate of 117.2%, and compounds 2, 4, 6 exhibited significant effects with inhibitory rates of 68.1%, 69.3%, 69.2%, respectively.