Cunlanceloic acids A–D: unprecedented labdane diterpenoid dimers with AChE inhibitory and cytotoxic activities from Cunninghamia lanceolata

Cunlanceloic acid A (1), a symmetric terpenoid peroxide bearing an unprecedented dimeric labdane backbone linked through C-16/C-16′ bonds, and cunlanceloic acids B–D (2–4), three asymmetric diterpenoid dimers with a new carbon skeleton linked through C12/C-13′ and C-15/C-16′ bonds between two labdane units, were isolated from the cones of Cunninghamia lanceolata. Their structures including absolute configurations were determined by extensive NMR spectroscopy, X-ray diffraction analysis, and chemical transformations. Compound 1 exhibited potent AChE inhibitory activity with an IC50 value of 6.14 ± 0.66 μM and compounds 2 and 3 showed remarkable cytotoxic activities against A-549 and SMMC-7721 cell lines with IC50 values of 5.90–9.21 μM.