New diterpenes leojaponins G–L from Leonurus japonicus

Six new diterpenes, leojaponins G–L (1–6) along with 19 known compounds (7–25) were isolated from Leonurus japonicus. Their structures were elucidated by NMR, MS, IR, UV, and ECD spectroscopic data. Anti-melanogenesis assay indicated that 7 could safely and dose-dependently decrease melanin production in B16F10 melanoma cell with an IC50 value of 59.1 μM, but moderately inhibit tyrosinase activity. Without cytotoxicities at 20 μM, compounds 11,...