Octacyclic and decacyclic ent-abietane dimers with cytotoxic activity from Euphorbia fischeriana steud

A novel Diels-Alder adduct possesses a 6/6/6/5/6/6/6/6 octacyclic skeleton featured with bicy-clo[2.2.2]octane moiety,biseupyiheoid A(1),along with another decacyclic 6/6/6/3/5/6/5/6/6/6 fused diterpenoid dimer,bisfischoid C(2),were isolated from Euphorbia fischeriana.Their structures were de-termined by spectroscopic,X-ray crystallographic approaches,and quantum mechanical calculations.The structural features of 1 and 2 were hypothesized to involve intramolecular Diels-Alder reactions with dif-ferent coupling patterns.Dimer 1 showed antiproliferative activity through apoptosis activation in LoVo cells.