Stereochemical Assignment of the Fungal Metabolites Pestalotiopsones D and E through Enantiopure Synthesis

The pestalotiopsones are fungal metabolites isolated from an endophytic fungus Pestalotiopsis sp. found in the mangrove Rhizophora mucronata, used in traditional Chinese medicine to treat symptoms of dysentery. The absolute configurations of pestalotiopsones D (4) and E (5) were elucidated through total synthesis of both the R and S enantiomers, allowing for the assignment of the stereochemistry of the natural compounds as the (+)-S enantiomers. The key steps include homologation of a substituted benzoic acid to the appropriate phenylacetate derivative using Birch reductive alkylation, an oxa-Michael cyclization induced by microwave irradiation to form the chromanone substructure, and an IBX-mediated dehydrogenation yielding the chromone skeleton. Assessment of the synthetic compounds against clinical pathogens was performed.