Humulane-type sesquiterpenoids from Pilea cavaleriei subsp. crenata

Nine new, uncommon humulane-type sesquiterpenoids (1, 2, 4, 6-11), together with two known derivatives, were isolated from extracts of the plant Pilea cavaleriei subsp. crenata. The structures of these compounds were fully elucidated by extensive analyses of spectroscopic data (MS, 1D- and 2D-NMR), use of the Mosher method, and by X-ray crystallographic analysis, in combination with chemical conversions. An ene reaction was discovered during the chemical transformations, which might provide an explanation for the wide distribution of the allylic hydroperoxide group in natural products.