Grayanane diterpenoids from the leaves of Rhododendron dauricum

Phytochemical investigations on the leaves of Rhododendron dauricum L. (Ericaceae) resulted in the isolation of thirteen known grayanane diterpenoids (1-13). Their structures were determined by spectroscopic data analysis and comparison with the literature. The structure and absolute configuration of grayanotoxin VI (1) was determined by single-crystal X-ray diffraction analysis for the first time. This is the first time to report the isolation of grayanane diterpenoids 1-10, 12, and 13 from Rhododendron dauricum. Grayanotoxin VI (1) was isolated from the genus of Rhododendron for the first time. The chemotaxonomic significance of grayanane diterpenoids (1-13) was discussed.