Taxonomy Driven Discovery of Polyketides from Aspergillus californicus

Five new polyketides were isolated from the rare filamentous fungus Aspergillus californicus IBT 16748 including calidiol A (1); three phthalide derivatives califuranones A₁, A₂, and B (2-4); and a pair of enantiomers (-)-calitetralintriol A (-5) and (+)-calitetralintriol A (+5) together with four known metabolites (6-9). The structures of the new products were established by extensive spectroscopic analyses including HRMS and 1D and 2D NMR. The absolute configurations of two diastereomers 2 and 3 and the enantiomers (-5) and (+5) were assigned by comparing their experimental and calculated ECD data, whereas the absolute configuration of 4 was proposed by analogy. Compound 1 showed moderate activity against methicillin-resistant Staphylococcus aureus.