17-nor-Cephalotane-Type Diterpenoids from Cephalotaxus fortunei

Seventeen new 17-nor-cephalotane-type diterpenoids, fortalpinoids A–Q (1–17), were isolated from the seeds of Cephalotaxus fortunei var. alpine. Compound 12 represents the first 17-nor-cephalotane-type diterpenoid featuring an 8-oxabicyclo[3.2.1]oct-2-ene moiety. The absolute configuration of fortunolide A (18) was determined for the first time, and the structure of cephinoid Q was revised to 14-epi-cephafortoid A (24) by X-ray crystallographic data analysis. Some of the compounds showed significant cytotoxicity against A549 and HL-60 cells, and the structure–activity relationship of this compound class is discussed.