Variecolortins A–C, Three Pairs of Spirocyclic Diketopiperazine Enantiomers from the Marine-Derived Fungus Eurotium sp. SCSIO F452

Three pairs of spirocyclic diketopiperazine enantiomers, variecolortins A–C (1–3), were isolated from marine-derived fungus Eurotium sp. SCSIO F452. Compound 1 possesses an unprecedented highly functionalized seco-anthronopyranoid carbon skeleton featuring a 2-oxa-7-azabicyclo[3.2.1]octane core. Compounds 2 and 3 represent rare examples of a 6/6/6/6 tetracyclic cyclohexene–anthrone carbon scaffold. Their structures were determined by spectroscopic analyses, X-ray diffraction, and ECD calculations. Their enantiomers exhibited different antioxidative and cytotoxic activities, and their modes of action were investigated.