Secondary metabolites from the oyster-derived fungus Trichoderma sp. QCML7-3.

Chemical investigation of the oyster-associated fungus Trichoderma sp. QCML7-3 afforded a novel γ-pyrone analogue, crotonylkojate (1), alongside 22 previously reported compounds (2-23). The structure of 1 was elucidated as 2-(acetoxymethyl)-4-oxo-4H-pyran-5-yl (E)-but-2-enoate based on comprehensive 1D and 2D NMR spectroscopic analyses, HRESIMS data, and comparison with related kojic acid derivatives. The known compounds were identified by comparison with reported spectroscopic data. The cytotoxicity of all obtained compounds against BV2 microglial cells was evaluated using the CCK-8 assay. Compounds 1 and 16 ((22E)-3β-hydroxy-5α,9α-peroxy-ergosta-6,8(14),22-triene) showed no detectable cytotoxicity at 20 μM in a 24-h assay. Subsequent evaluation showed that 1 and 16 dose-dependently inhibited lipopolysaccharide (LPS)-stimulated nitric oxide (NO) generation in BV2 cells, with preliminary IC50 values of 13.89 and 8.04 μM, respectively. These findings highlight the chemical diversity of metabolites from oyster-associated Trichoderma species and the potential of crotonylkojate and related metabolites as inhibitors of LPS‑induced NO production in microglial cells.