Periconiasins A–C, New Cytotoxic Cytochalasans with an Unprecedented 9/6/5 Tricyclic Ring System from Endophytic Fungus Periconia sp.

Periconiasins A–C (1–3), new cytochalasans with an unprecedented 9/6/5 tricyclic ring system, were isolated from the endophytic fungus Periconia sp. F-31. Their structures and absolute configurations were elucidated by extensive spectroscopic and X-ray crystallographic analyses. Their biosynthesis is proposed to occur from an unusual seven acetate/malonate polyketide backbone attached to one leucine moiety by a PKS-NRPS followed by Diels–Alder and other reactions. 1 and 2 showed significant cytotoxicity against human HCT-8 cancer cells.