Phytotoxic Tetramic Acid and Plumbagic Acid Lactone Derivatives from the Marine-Derived Fungus <i>Cladosporium</i> sp. DLT-87

Five new tetramic acid derivatives, cladosins P–T (1–5), and a new plumbagic acid lactone derivative (6), alongside eight known compounds (7–14), were isolated from the marine-derived fungus Cladosporium sp. DLT-87. Their structures were elucidated by comprehensive spectroscopic analysis, as well as NMR, ECD, and optical rotation computations. Compounds 1, 2, 6–10, and 13 inhibited the seedling growth of Arabidopsis thaliana, with IC50 values of 55.16–142.30 μM for fresh weight and 47.54–172.00 μM for root length. Evans blue and propidium iodide staining revealed that compounds 1, 6, and 8 damaged cell membrane integrity and induced cell death in root tips. Transcriptome analysis indicated that compound 6 primarily acted by disrupting photosynthesis-related pathways, a mechanism supported by the molecular docking and molecular dynamics simulation studies of 6 with the PSII D1 protein. Notably, no toxicity was observed for compounds 1, 6, and 8 toward earthworms.