Parviflorenes B–F, novel cytotoxic unsymmetrical sesquiterpene-dimers with three backbone skeletons from Curcuma parviflora

Five novel natural products classified as dimeric sesquiterpenes, named parviflorenes B–F (), possessing three types of novel backbone frameworks, have been isolated from Curcuma parviflora (Zingiberaceae). The structures of were elucidated by means of spectroscopic studies, and the structure of was further unambiguously established by X-ray crystallographic analysis. Compounds , , and have an unsymmetrical bis-cadinane skeleton, while compound is a dimer of cadinane and iso-cadinane, and compound possesses another novel carbon framework consisting of two cadinanes with different bond-connection. These new compounds with novel carbon skeletons showed cytotoxicity against tumor cell lines.