New γ -Lactone Carboxylic Acids from the Lichen Parmotrema praesorediosum (Nyl.) Hale, Parmeliaceae

From the lichen Parmotrema praesorediosum (Nyl.) Hale, Parmeliaceae, collected in Vietnam, five new (1, 2, 3, 5, 6) and one known (4) g -lactonic acids were isolated. The structures of the new compounds were established by 1D and 2D NMR spectroscopy, as well as high resolution-electrospray ionization (HR-ESI)-MS analysis. The absolute configuration of new compounds was determined by ultraviolet circular dichroism spectroscopy. Compounds were evaluated for their cytotoxic activity against HeLa (human epithelial carcinoma), NCI-H460 (human lung cancer) and MCF-7 (human breast cancer) cell lines at the concentration of 100 µg/mL. Among six compounds, 1 possessed medium activity against MCF-7 cell line with the inhibition of 52.5%. Meanwhile, the rest showed no cytotoxic activity against three surveyed cancer cell lines.