Isoleojaponin, a New Halimane Diterpene Isolated from Leonurus japonicus

Leojaponin ( 2), a labdane diterpene, was isolated from the EtOH extract of the herb of Leon urus japonicus together with a new halimane diterpene named isoleojaponin ( 1). Isoleojaponin has a new diterpene skeleton with a unique cross-conjugated α,β-unsaturated ketone system, Their structures were elucidated by physical and spectroscopic analysis, and the relative configuration of the chiral C-9 carbon was determined by a computational method, and analysis of its possible biogenesis pathways.