Portulene acetal, a novel minor constituent of Portulaca grandiflora with significance for the biosynthesis of portulal

A new clerodane diterpenoid (6) with a caged hemiacetal ring has been isolated as a minor constituent from Portulaca grandiflora and its structure elucidated by extensive spectral studies. The compound might be of significance in the biosynthesis and in the chemosystematics of constituents of the genus Portulaca. The structural features of 6 provide important clues for the proposal of a chemically reasonable scheme for the biosynthesis of portulal (1).