Ent-kaurane diterpenoids isolated from Sideritis congesta

► This study reports the isolation of one new and eight known ent-kaurane diterpenoids. ► Structure elucidation of the new and known diterpenoids was made based on NMR and mass spectroscopic analyses. ► The bioactivity, including antioxidant and anticholinesterase activity, was evaluated for the pure compounds, except for compound 7. ► Among the tested ent-kauranes, compounds 3 and 6 were found to possess higher BChE inhibitory activity than the standard galanthamine. while all compounds exhibited only weak AChE inhibitory activity.