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.