Altaicalarins A-D, Cytotoxic Bisabolane Sesquiterpenes from Ligularia altaica

Four new bisabolane sesquiterpenes, altaicalarins A-D (1-4), and three known analogues (5-7) were isolated front the roots and rhizomes of Ligularia altaica. The structures were elucidated by spectroscopic methods including 2D NMR techniques, and the structure of I was confirmed by single-crystal X-ray diffraction. The isolated compounds were also evaluated for cytotoxic activity against human carcinoma (A-549), human breast adenocarcinoma (MCF-7), epidermoid carcinoma of the nasopharynx (KB), and vincristine-resistant nasopharyngeal (KBVIN) cell lines, and I was found to show significant cytotoxicity, with EC50 values of 3.4, 0.8, 1.0, and 0.9 mu g/mL, respectively.