Janthinoid A, an unprecedented tri-nor-meroterpenoid with highly modified bridged 4a,1-(epoxymethano)phenanthrene scaffold, produced by the endophyte of Penicillium janthinellum TE-43

Janthinoid A (1), an unprecedented C22 meroterpenoid featuring a highly modified bridged 4a,1-(epoxymethano)phenanthrene scaffold incorporating eight continuous quaternary carbons, along with its biosynthetic-related C25 analogue andrastone I (2), were isolated from the endophytic fungus Penicillium janthinellum TE-43. Their structures were unambiguously established by comprehensive analyses of spectroscopic data, quantum chemical calculations, and X-ray diffraction. The tri-nor-meroterpenoid skeleton of 1 was produced by a unique biosynthetic pathway, involving the ring cleavage and continuous carbon degradations of the aromatic polyketide precursor, which distinct from the commonly-observed meroterpenoids both structurally and biogenetically, representing a new type of meroterpenoid. Both compounds showed significant in vivo anti-tumor activities against NSCLC cells A549.