Cytotoxic Diterpenoids from Caryopteris aureoglandulosa

Seven new (1-7) and 11 known diterpenoids were isolated and identified from Caryopteris aureoglandulosa. These diterpenoids were structurally determined by HRESIMS and NMR spectroscopic analyses, single-crystal X-ray diffraction, and ECD data. Structurally, aureoglandulosin A (1) is a highly oxygenated abietane diterpenoid with an unprecedented 7/6/6/5-ring system. Aureoglandulosins B (2) and C (3) represent naturally occurring new diterpenoids with an unusual 6/6/6/5-ring system. Additionally, the configurations of two known abietane diterpenoids 11 and 12 were determined by X-ray crystallographic data analysis for the first time. A plausible biosynthetic pathway for compounds 1-3 is proposed. The cytotoxicity of all isolates was evaluated, and compounds 1 and 11 exhibited significant cytotoxic activity against some cell lines with IC₅₀ values in the range 1.6-8.2 μM.