Bioactive Terphenyls Isolated from the Antarctic Lichen Stereocaulon alpinum

Three p-terphenyls (2–4)—2-hydroxy-3,5-dimethoxy-p-terphenyl (2), 2-hydroxy-3,6-dimethoxy-p-terphenyl (3), and 2,3,5,6-tetramethoxy-p-terphenyl (4)—were isolated for the first time as natural products along with seven known compounds (1, 5–10) from the Antarctic lichen Stereocaulon alpinum. Structures of the new compounds were elucidated by comprehensive analyses of 1D and 2D NMR and HREIMS experiments. Compound 3 exhibited cytotoxicity against HCT116 cells with the IC(50) value of 3.76 ± 0.03 μM and also inhibited NO production in LPS-induced RAW264.7 macrophages with the IC(50) value of 22.82 ± 0.015 μM.