New 29-nor-cycloartanes with a 3,4-seco- and a novel 2,3-seco-structure from the leaves of Sinocalycanthus chinensis

Eight new triterpenoids, including sinocalycanchinensins A-E (1-5) with a 3,4-seco-29-nor-cycloartane skeleton, sinocalycanchinensin F (6) possessing a novel 2,3-seco-29-nor-cycloartane skeleton, and 29-nor-cycloartanes, sinocalycanchinensins G and H (7 and 8), have been isolated from the leaves of Sinocalycanthus chinensis. Their structures were elucidated on the basis of spectroscopic examinations. The cytotoxicities of the isolated new triterpenes against a panel of human cancer cell lines, including multi-drug resistant (MDR) cancer cell lines, were also evaluated. Compound 5 demonstrated enhanced cytotoxicity against MDR KB cells in the presence of colchicine, although all the compounds showed moderate or no cytotoxicities.