New Cytochalasins from the Marine‐Derived Fungus Xylaria sp. SCSIO 156

Two new cytochalasins, 18‐deoxycytochalasin Q (1) and 21‐O‐deacetylcytochalasin Q (2), together with four known analogues, cytochalasin Q (3), 19,20‐epoxycytochalasin Q (4), 21‐O‐deacetyl‐19,20‐epoxycytochalasin Q (5), and cytochalasin D (6), were isolated from the fungus Xylaria sp. SCSIO156 originated from the South China Sea marine sediment. The structures of 1 and 2 were elucidated by MS and 1D‐ and 2D‐NMR data analyses, and comparison with known compounds. The known compounds 3–6 were identified by comparison of their MS and NMR data with those reported in the literature. In the in vitro antitumor assay, compounds 2–6 showed mild cytotoxicity against three tumor cell lines (MCF‐7, SF‐268, and NCI‐H460).