Biscroyunoid A, an Anti-Hepatic Fibrotic 19- nor -Clerodane Diterpenoid Dimer with a C-16-C-12' Linkage from Croton yunnanensis .

Biscroyunoid A ( 1 ), a 19- nor -clerodane diterpenoid dimer featuring a unique C-16-C-12' linkage and containing an unusual 4,7-dihydro-5 H -spiro[benzofuran-6,1'-cyclohexane] motif, together with its biosynthetic precursor, croyunoid A ( 2 ), were isolated from Croton yunnanensis . Their structures were determined by spectroscopic, computational, and single-crystal X-ray diffraction methods. Compound 1 exerted an antihepatic fibrosis effect in LX-2 cells via inhibition of TGFβ-Smad2/3 signaling.