Emeridones A–F, a Series of 3,5-Demethylorsellinic Acid-Based Meroterpenoids with Rearranged Skeletons from an Endophytic Fungus Emericella sp. TJ29

Six new 3,5-demethylorsellinic acid-based meroterpenoids, emeridones A–F (1–6), and eight known analogues (7–14) were isolated from Emericella sp. TJ29. Their structures and absolute configurations were elucidated by comprehensive spectroscopic analyses, single-crystal X-ray diffraction experiments, and electronic circular dichroism calculations. Emeridone A (1) represents the first meroterpenoid featuring a unique rigid 6/6/5/6 tetracyclic carbon ring system with two additional lactone rings. Emeridones B and C (2 and 3) possess a 2,6-dioxabicyclo[2.2.1]heptane and a spiro[bicyclo[3.2.2]nonane-2,1′-cyclohexane] moiety, respectively, and both functionalities were found for the second time in meroterpenoids. These new compounds were evaluated for their cytotoxic activities against five human cancer cells, and compounds 2, 4, and 6 exhibited moderate cytotoxic activities, with IC50 values ranging from 8.19 to 18.80 μM.