Talachalasins A—C, Undescribed Cytochalasans with a 16 β ‐Methyl or 2‐Oxabicyclo [3.3.1]nonan‐3‐one unit from the Deep‐Sea‐Derived Fungus Talaromyces muroii sp. SCSIO 40439

Comprehensive Summary Talachalasins A—C ( 1 — 3 ), three new cytochalasans (CYTs), were isolated from deep‐sea‐derived fungus Talaromyces muroii sp. SCSIO 40439. The structures of 1 — 3 , including absolute configurations, were determined based on HRESIMS, NMR spectroscopic data, ECD comparison, and single crystal X‐ray diffraction analysis. Talachalasins A—C ( 1 — 3 ) represented the first examples of cytochalasans possessing a unique 16 β ‐methyl group, distinct from >500 reported CYTs. Talachalasin C ( 3 ) was an unprecedented 20,21‐ seco ‐cytochalasans characterized by a 2‐oxabicyclo[3.3.1]nonan‐3‐one unit. Talachalasin A ( 1 ) displayed moderate cytotoxic activity against four tumor cell lines (IC 50 3.40—10.02 μM). Talachalasin B ( 2 ) showed comparable anti‐RSV and HSV‐1 activities (IC 50 12.5 μM or IC 50 20.0 μM).