Abstract
Nodosin, a new diterpenoid isolated from Isodon trichocarpus KUDO and I. Japonicus HARA, was converted to the keto lactone acetal X via several steps of reactions. The conversion made it possible to propose the structure II for nodosin. The remaining hydroxyl group proved to be located at C-11 and to have the β-configuration on the basis of a detailed NMR investigation. Thus, the structure and absolute configuration of nodosin were established as formula XIX.
