Annotinolides A–C, Three Lycopodane-Derived 8,5-Lactones with Polycyclic Skeletons from Lycopodium annotinum

Three novel 7,8-seco-lycopodane-derived 8,5-lactones (annotinolides A–C, 1–3) were isolated from Lycopodium annotinum. Their structures were elucidated by spectroscopic methods and single-crystal X-ray diffraction. Compound 1 possesses an unusual cyclopropane ring constructed through a hitherto unknown C-6/C-12 bond. Compound 2 represents the first 7,8-seco-lycopodane-derived alkaloid with a rare cyclobutane ring formed by a new C-12/C-15 linkage, while the C-8/C-15 bond remains. Compound 3 contains an unprecedented 12-spiro-9,12-γ-lactone moiety. Their plausible biosynthetic pathways and antiaggregation effects on amyloid-β1–42 are also presented.