Synergizing a Metabolic Blockade and Non-reducing Polyketide Synthase Substrate Flexibility Expand Depsidone Diversity in a Marine-Derived Aspergillus Species

Depsidones are structurally diverse polyketides with significant pharmacological potential. Their structural variability in the marine-derived fungus Aspergillus sp. SCSIO SX7S7 stems from the substrate promiscuity of key enzymes, particularly the starter-unit acyltransferase (SAT) domain of non-reducing polyketide synthase (NR-PKS). In this study, we combined a metabolic blockade with the inherent biosynthetic flexibility to access rare depsidone derivatives. Inactivation of the highly reducing polyketide synthase (HR-PKS) gene depD redirected metabolic flux to potential branching pathways, leading to the isolation of (i) aspergillol A (1), an unprecedented depsidone featuring a unique benzene substitution, (ii) four new orsellinic acid homodimer-derived depsidones aspergillol B–E (2–5), (iii) a new diphenyl ether derivative aspergillol F (6), and (iv) two known compounds (7 and 8) but lacking complete NMR data from a previous publication. Further structure–activity relationship analyses revealed that the ester linkage in compounds 1–5 is essential for antimicrobial activities, while the distinctive benzene extension in compound 1 is responsible for its significantly enhanced activity. These findings not only expand the known structural diversity of fungal depsidones but also reveal the complex metabolic network underlying their biosynthesis while establishing an effective approach for discovering bioactive natural product scaffolds through rational pathway manipulation.