Sesquiterpene esters from Celastrus orbiculatus and their structure-activity relationship on the modulation of multidrug resistance

Six new (1-6) and three known (7-9) sesquiterpene esters were isolated from the roots of Celastrus orbiculatus. The structures of the new compounds were elucidated as 1 beta-acetoxy-6 alpha-furoyloxy-9 alpha-benzoyloxydihydro-beta-agarofuran (1), 1 beta-acetoxy-6 alpha-benzoyloxy-9 alpha-furoyloxydihydro-beta-agarofuran (2), 1 beta-acetoxy-6 alpha,9 alpha-difuroyloxydihydro-beta-agarofuran (3), 1 beta,2 beta-diacetoxy-6 alpha-furoyloxy-9 alpha-benzoyloxydihydro- beta-agarofuran (4), 1 beta-acetoxy-2 beta,6 alpha-difuroyloxy-9 alpha-benzoyloxydihydro beta-agarofuran (5), and 1 beta-acetoxy-2 beta,6 alpha,9 alpha-tribenzoyloxydihydro-beta-agarofuran (6). Compounds 4, 5, and 7-9 were shown to be more active than verapamil in reversing vinblastine resistance in multidrug-resistant KB-V1 cells.