1H and13C-NMR and biological activity investigations of four lichen-derived compounds

The lichen-derived natural products, atranorin (1), hopane-6α, 22-diol (2), usnic acid (3), and vulpinic acid (4) were analysed by both one and two-dimensional (1H, 13C)-NMR. Experiments employed included COSY, NOESY, XHCO, HMQC and HMBC. For 1 and 2, fully assigned proton NMR data are reported for the first time; the reassigned 13C NMR data for both 1 and 2 are also reported. For 3, cross-peaks were observed in the HMBC spectrum that suggest that CH long-range coupling through H bonds is occurring. Biological activity investigations of each compound indicated hopane-6α, 22-diol (2) to have anti-tubercular activity (MIC 8 µg/mL) and usnic acid (3) to be very weakly cytotoxic (ED50 13 µg/mL).