Bioactive Secondary Metabolites Isolated from the Antarctic Lichen Himantormia lugubris

Two new depsidones, himantormiones A and B (1 and 2) were isolated and identified from the Antarctic lichen, Himantormia lugubris (Parmeliaceae), with seven known compounds (3-9). The structures of two new compounds (1 and 2) were determined by means of spectroscopic analyses, including 1D and 2D NMR and HR-MS. The isolated compounds were tested for antimicrobial and cytotoxic activities, where himantormione B (2) exhibited inhibitory effect against Staphylococcus aureus with the IC₅₀ value of 7.01±0.85 mM. Compound 2 also exhibited strong cytotoxic activity against HCT116 cells (colon cancer) with the EC₅₀ value of 1.11±0.85 μM, where that of the positive control, 5-fluouracil, was 9.4±1.90 μM.