Thiocytochalasins A−D, four sulfur-containing cytochalasans from an endophytic fungus Phoma multirostrata XJ-2-1

Four unprecedented sulfur-containing cytochalasans, thiocytochalasins A−D ( 1 − 4 ), were isolated from an endophytic fungus Phoma multirostrata XJ-2-1. Thiocytochalasins A ( 1 ) and B ( 2 ) feature a novel 5/6/14/5 tetracyclic scaffold, which are the first examples of cytochalasan containing a thiophene moiety. Thiocytochalasins C ( 3 ) and D ( 4 ) are epimeric cytochalasan homodimers formed via a thioether bridge. Their structures with absolute configurations were established by detailed analysis of the HRESIMS, NMR, and X-ray crystallography. The plausible biogenetic pathway of 1 − 4 was postulated. Compounds 3 and 4 exhibited significant cytotoxicity against CT26 cells with IC 50 values of 0.85 and 0.76 µmol/L, respectively.