New Bioactive Polyketides from the Mangrove-Derived Fungus Daldinia eschscholzii HJX1P2

Three new naphthalene-chroman dimer derivatives, daldinaphchromes A-C (1-3), two new chroman derivatives, daldichromes A (5) and B (6), along with five known compounds (4, 7-10) were isolated from the mangrove-derived fungus Daldinia eschscholzii HJX1P2. Their structures and stereochemistries were elucidated through detailed NMR and MS analyses, calculated electronic circular dichroism, and comparison with previously reported data. Compound 1 demonstrated inhibitory effects on nitric oxide (NO) production in LPS-induced RAW 264.7 cells, with an IC₅₀ value of 62.9 µM, and more effectively suppressed the expression of interleukin (IL)-6 than dexamethasone. A further mechanistic study suggested that 1 could prohibit the expression of iNOS in RAW 264.7 cells, and the molecular docking study suggested a possible interaction between 1 and the iNOS protein. Compounds 7 and 8 exhibited moderate to potent DPPH radical scavenging activity, with IC₅₀ values of 117.4 and 46.2 µM, respectively, compared with the positive control ascorbic acid (IC₅₀ = 45.6 µM). Compounds 4 and 10 showed ABTS⁺ radical scavenging activity, with IC₅₀ values of 66.6 and 33.2 µM, respectively, which were equal to or lower than that of the positive control vitamin C (IC₅₀ = 59.7 µM). Compounds 1-3, 7, and 9 showed antibacterial activity against three Staphylococcus aureus strains, with MIC values of 74.4-390.6 μM.