Westersidones A–C: Antimicrobial Depsidones From the Deep‐Sea Cold Seep‐Derived Endozoic Fungus Westerdykella dispersa CS‐734

Eight depsidone derivatives (1-8), including three new compounds designated as westersidones A-C (1-3), were isolated from Westerdykella dispersa CS-734, an endozoic fungus derived from the deep-sea cold seep mussel Gigantidas platifrons. Their structures were elucidated through extensive spectroscopic analysis, including HRESIMS, NMR, and single-crystal X-ray diffraction. Remarkably, compound 1 represents a rare and unprecedented hybrid natural product formed by the fusion of a depsidone and a naphtho-γ-pyrone skeleton. The antibacterial activities against human and aquatic pathogens of the isolated compounds were assayed. Notably, compound 8 exhibited the most potent activity against several tested strains, with MICs 4-16 µg/mL, underscoring the critical role of the C-4 aldehyde group in enhancing antimicrobial potency.