A series of lathyranediterpeneswere isolated or synthesized,and established on the basis of extensive spectroscopic methods,including two-dimensional NMR techniques.Stereo configuration and conformation of Euphorbia factors L1,L2,L7a,L7b,L8and derivatives of L3were analyzed by X-ray diffraction for the first time.The configuration of the unique isolathyrolditerpeneEuphorbia factorL7bwas rectified from S* to R* at C-5.All compounds were examined as modulators of multidrug resistance on MCF-7/ADM cell lines in vitro.To obtain sufficient information on the structural characteristics of this class of compounds,the detailed fragmentation patterns of the lathyranediterpenes were studied with collision-induced dissociation(CID)–MS/MS using an ESI–quadrupole time-of-flight(QTOF)–MS/MS hybrid instrument in positive-ion mode.