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

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 cyto-chalasans possessing a unique 168-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 (IC50 3.40-10.02 mu M). Talachalasin B (2) showed comparable anti-RSV and HSV-1 activities (IC50 12.5 p.M or IC50 20.0 mu M).