Indole diterpenoids with fungal resistance reversal activity from the plant endophytic fungus Penicillium sp. DG23.

Eighteen undescribed indole diterpenoids (1-18), serially named after schipenindolene, along with six known ones (19-24), were isolated from the plant endophytic fungus Penicillium sp. DG23, which was derived from Schisandra macrocarpa. Their structures and absolute configurations were established through extensive spectroscopic data, NMR calculation with DP4+ probability analysis, electronic circular dichroism calculations, semisynthesis, and single crystal X-ray diffraction. Among them, schipenindolene M (1), containing an unusual trisubstituted furan ring, was successfully semisynthesized from 7-hydroxy-13-dehydroxypaxilline (21) using Lewis acid catalysis. Schipenindolenes N1 and N2 (2 and 3) are characterized by a distinctive 6/5/5/6/6/6 hexacyclic ring system with a rare pyrrolo[1,2-a]indole motif. Schipenindolenes O1 and O2 (4 and 5) possess a 6/5/5/6/6/7 hexacyclic ring system bearing an oxepan ring. Compounds 1, 7, 9, 15, 16 and 19 indicated promising fungal resistance reversal activity as a newly discovered biological function for indole diterpenoids.