Inunicosides A−K, rare polyacylated ent-kaurane diterpenoid glycosides from the flowers of Inula japonica.

Inunicosides A−K (1–11), eleven unusual polyacylated ent -kaurane diterpenoid glycosides, were isolated from the flowers of a traditional Chinese herbal plant Inula japonica. Their structures with absolute configurations were determined on the basis of comprehensive spectroscopic analyses, chemical degradation, enzymatic hydrolysis and ECD experiments. Among these isolates, inunicoside K (11) showed mild antibacterial activity against Staphylococcus aureus ATCC 25923. Diterpene constituents have been rarely reported in the Inula species, and thus the discovery of this panel of compounds greatly enriches the chemical diversity of metabolites from the genus Inula. Image 1 • Eleven unusual 18-norditerpenoid glycosides were isolated from the flowers of Inula japonica. • The absolute configurations were determined via chemical derivatization, enzymatic hydrolysis and ECD analysis. • An intact diterpenoid glycoside with 4-geminal carboxyl groups showed moderate antibacterial activity. • The discovery of these compounds enriches the chemical diversity of metabolites from Inula species. [ABSTRACT FROM AUTHOR]