Polyketide-Terpene Hybrid Metabolites from an Endolichenic Fungus Pestalotiopsis sp.

Five new polyketide-terpene hybrid metabolites ( 1 - 5 ) with highly functionalized groups, together with six known derivatives ( 6 - 11 ), were isolated from the endolichenic fungus Pestalotiopsis sp. Their structures were elucidated by extensive NMR experiments including ¹ H, ¹³ C, HMQC, COSY, and HMBC. The relative configurations of the new compounds were determined by analysis of coupling constants and ROESY correlations. The absolute configurations especially the secondary alcohol at C-15 in 1 and secondary alcohol at C-14 in 5 were established via the CD experiments of the in situ formed [Rh ₂ (OCOCF ₃ ) ₄ ] complex with the acetonide derivatives. These compounds were tested for their inhibition activity against six plant pathogens. Compounds 1 and 5 exhibited pronounced efficiency against Fusarium oxysporum , and compounds 5 and 6 potently inhibited Fusarium gramineum with MIC value of 8  µ g/mL, which revealed the plausible ecological role of endolichenic fungus in providing chemical protection for its host lichen in the fungus-plant relationship. The biosynthetic pathway of compounds 1 - 11 was postulated for the first time, which paved the way for its further biosynthesis research.