Daphniphyanoids A-C, three triterpenoids with uncommon 5/6/6/6/5-pentacyclic system from Daphniphyllum calycinum Benth.

Three new carbon-skeleton triterpenoids, named daphniphyanoids A-C (1-3), featuring an uncommon A-ring rearranged 5/6/6/6/5-pentacyclic nucleus, along with two biogenetically related known lupane-type triterpenoids (4 and 5), have been isolated from Daphniphyllum calycinum Benth. The determination of their structures was based on the extensive spectroscopic analysis, X-ray single crystal diffraction analysis, and chemical conversion. A plausible biosynthetic pathway for compounds 1-5 was proposed, involving a pinacol rearrangement, Wagner-Meerwein rearrangement, oxidation, and esterification. In in vitro bioassays, the methylated derivative (1a) of compound 1 exhibited preliminary selective PPAR-γ agonistic activity with an EC50 value of 5.46 μM, promoting both glucose uptake and mild lipid accumulation.