Novel Zierane- and Guaiane-Type Sesquiterpenes from the Root of Melicope denhamii

Two novel zierane-type sesquiterpenes, named melicodenones A and B (1 and 2, resp.), and three new guaiane-type sesquiterpenes, named melicodenones CE (35), were isolated from the root of Melicope denhamii (Seem.) T. G. Hartley together with zierone (6). Their structures were established by extensive NMR-spectroscopic analyses. Compounds 16 were tested for cytotoxicity using human colon cancer DLD-1 cells, and melicodenone A (1) was found to exhibit moderate activity.