Cytotoxic Norsesquiterpene Peroxides from the Endophytic Fungus <i>Talaromyces flavus</i> Isolated from the Mangrove Plant <i>Sonneratia apetala</i>

Four new norsesquiterpene peroxides, named talaperoxides A–D (1–4), as well as one known analogue, steperoxide B (5, or merulin A), have been isolated from a mangrove endophytic fungus, Talaromyces flavus. Their structures were elucidated mainly by 1D and 2D NMR. Structures of 1, 2, and 5 were further confirmed by single-crystal X-ray diffraction, and their absolute configurations were also determined using copper radiation. Cytotoxic activities of compounds 1–5 were evaluated in vitro against human cancer cell lines MCF-7, MDA-MB-435, HepG2, HeLa, and PC-3. Compounds 2 and 4 showed cytotoxicity against the five human cancer cell lines with IC50 values between 0.70 and 2.78 μg/mL.