Biguaiascorzolides A and B: Two novel dimeric guaianolides with a rare skeleton, from Scorzonera austriaca

The root of Scorzonera austriaca has been used in indigenous cuisines as a delicious food and in the Tibetan traditional medicine in northwestern China. Two novel dimeric guaianolides linked by a carbon–carbon bond with a rare carbon skeleton, termed biguaiascorzolides A (1) and B (2), respectively, have been isolated from roots of S. austriaca. Acetylation of 1 gave 1a. The structures of 1, 1a and 2 were characterised by HR-ESI-MS, EI-MS, UV, IR, and 1D- and 2D-NMR techniques (1H and 13C NMR, 1H-1H COSY, HMQC, HMBC, and NOESY experiments). The cytotoxicity of 1a was assayed against selected cancer cell lines, including the human erythroleukaemia adriamycin-resistant subline (K562/ADM) and human stomach carcinoma (MGC-803) cell lines. Compound 1a exhibits a moderate activity against K562/ADM cell lines (IC50 39.8 μm) and is inactive towards MGC-803 cell lines.