Structures of New Seven-Membered Ring Vibsane-Type Diterpenes Isolated from Leaves of Viburnum awabuki

Abstract

Five new vibsane-type diterpenes, vibsanin G, vibsanin H, vibsanin K, 18-O-methylvibsanin K and 15, 18-di-O-methylvibsanin H were isoalted from the leaves of Viburnum awabuki (Caplifoliaceae). Their structures were elucidated by analyses of spectroscopic data involving comparison of their ¹³C-NMR data with those of the previously known vibsanin C, and the structure of vibsanins H and K were confirmed by X-ray crystallographic analysis and chemcial transformation, respectively. All five new compounds differ from the seven-membered ring vibsane-type diterpene, vibsanin C, only in the C-12-C-17 side chain.