Diterpene Alkaloids with an Aza-ent-kaurane Skeleton from Isodon rubescens

Two compounds belonging to a new group of diterpene alkaloids, kaurines A and B (1 and 2), and an alkaloid bearing a succinimide moiety (3) were obtained from Isodon rubescens. Their structures and absolute configurations were determined by spectroscopy and quantum-chemical computational C-13 NMR and ECD data analysis. These alkaloids differ from known diterpene alkaloids and diterpenoids and are presumably biosynthesized from ent-kaurane diterpenoids.