Photeroids A and B, unique phenol-sesquiterpene meroterpenoids from the deep-sea-derived fungus Phomopsis tersa

Photeroids A (1) and B (2), two structurally fascinating meroterpenoids, were isolated from the deep-sea-derived fungus Phomopsis tersa FS441. Their structures were sufficiently established by a comprehensive interpretation of the spectroscopic data, NMR spectra, and ECD calculation. Photeroids A and B represented the first phenolic sesquiterpene meroterpenoids featuring a highly fused 6/6/6/6 tetracyclic ring system derived through a rarely-occurring hetero-Diels-Alder reaction via an orthoquinone methide intermediate. Additionally, they were also evaluated for their cytotoxic activities against four human cancer cells, wherein compounds 1 and 2 exhibited moderate cytotoxic activities.