Polyketide-Terpene Hybrid Metabolites from an Endolichenic Fungus<i> Pestalotiopsis</i> sp.

Abstract

Five new polyketide-terpene hybrid metabolites (<b>1</b>-<b>5</b>) with highly functionalized groups, together with six known derivatives (<b>6</b>-<b>11</b>), were isolated from the endolichenic fungus <i>Pestalotiopsis</i> sp. Their structures were elucidated by extensive NMR experiments including ¹H, ¹³C, 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 <b>1</b> and secondary alcohol at C-14 in <b>5</b> were established via the CD experiments of the in situ formed [Rh₂(OCOCF₃)₄] complex with the acetonide derivatives. These compounds were tested for their inhibition activity against six plant pathogens. Compounds <b>1</b> and <b>5</b> exhibited pronounced efficiency against <i>Fusarium oxysporum</i>, and compounds <b>5</b> and <b>6</b> potently inhibited <i>Fusarium gramineum</i> with MIC value of 8 <i>µ</i>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 <b>1</b>-<b>11</b> was postulated for the first time, which paved the way for its further biosynthesis research.