A Novel Cytotoxic Compound From the Endolichenic Fungus, Xylaria psidii Inhabiting the Lichen, Amandinea medusulina

The lichen host, Amandinea medusulina, collected from mangrove habitats in Sri Lanka, and its associated endolichenic fungi were isolated and identified by rDNA-ITS sequence analysis and morphological features. One of the fungal strains frequently isolated from the lichen thalli was identified as Xylaria psidii. This study aimed at the isolation and identification of the cytotoxic compounds present in this fungus. Secondary metabolites of X. psidii were first extracted into ethyl acetate and subsequently subjected to bioassay-guided fractionation to isolate the bioactive compounds. Sulforhodamine B assay against a lung cancer (NCI-H292) cell line was used to determine the differential cytotoxic activity. Bioassay-guided fractionation led to the isolation of an active compound, SS/02/29/08, showing moderate cytotoxicity (IC₅₀ = 27.2 µg/mL). Its structure was elucidated by IR, 1D- and 2D-NMR, and ¹³C-NMR spectrophotometry and MS, in combination with HRMS, ¹³C NMR, HSQC, HMBC, and DQF-COSY. The structure of SS/02/29/08 was determined as (Z)-3-{(3-acetyl-2-hydroxyphenyl)diazenyl}-2,4-dihydroxybenzaldehyde and identified as a new compound. This novel compound has promising differential cytotoxic activity against human lung cancer cell line (NCI-H292).