Cephanolides A–J, Cephalotane-Type Diterpenoids from Cephalotaxus sinensis

Ten new cephalotane-type diterpenoids, cephanolides A–J (1–10), and two known analogues were isolated and characterized from Cephalotaxus sinensis. Compounds 1–3 represent the first examples of A-ring-contracted cephalotane-type dinorditerpenoids, and compound 4 is an A-ring-contracted norditerpenoid. The biosynthetic pathways for compounds 1–4 are postulated with the coexisting cephalotane-type troponoids as the precursors. Compounds 11 and 12 showed significant cytotoxicities against a panel of tumor cell lines (A549, KB, HL-60, and HT-29) with IC50 values ranging from 0.464 to 6.093 μM.