Fischdiabietane A, an Antitumoral Diterpenoid Dimer Featuring an Unprecedented Carbon Skeleton from .

Fischdiabietane A (), a novel asymmetric diterpenoid dimer with a unique nonacyclic 6/6/6/5/7/6/6/6/6 ring system possessing unprecedented 2-oxaspiro[4.5]decane-1-one and 2-oxabicyclo[3.2.2]nonane frameworks in D/E/F rings, was isolated from the roots of . Its structure was determined by spectroscopic techniques, electronic circular dichroism calculations, and X-ray diffraction experiments. Notably, is the first abietane-type [4 + 2] Diels-Alder dimer identified from nature. The IC of against T47D cells was about sixfold higher than that of cisplatin (the positive control). Furthermore, induced apoptosis in T47D cells through the activation of caspase-3 and the degradation of poly(ADP-ribose) polymerase.