Dolabrane Diterpenoids from the Chinese Liverwort Notoscyphus lutescens

Nine new dolabrane-type diterpenoids, notoscarins A-I (1-9), including an unprecedented 6,18-cyclo-dolabrane-type diterpenoid (1) obtained through intramolecular cyclization, two rare 19-nor-2-chloro-dolabrane diterpenoids (2 and 3), six new related dolabrane-type diterpenoids (4-9), and one new butyrolactone derivative (10), were isolated from the Chinese liverwort Notoscyphus lutescens. The 6,18-cyclo-dolabrane and 19-nor-dolabrane carbon skeletons are reported for the first time. The structures of these compounds were determined on the basis of MS and NMR spectroscopic data, single-crystal X-ray diffraction, and electronic circular dichroism calculations. Preliminary bioassays showed that compounds 1-10 exhibited moderate to weak quinone reductase-inducing activity in Hepa-1c1c7 cells.