Norclerodane diterpenoids from rhizomes of Dioscorea bulbifera.

Three norclerodane diterpenoids, diosbulbins K-M, and one analogous enolglycoside, diosbulbinoside G, together with four norclerodane diterpenoids, diosbulbins B, E, F and G, were isolated from rhizomes of Dioscorea bulbifera. Their structures were established by spectroscopic and chemical methods, including 1H and 13C NMR, NOESY, HSQC, HMBC, and HRMS analyses. The relative configurations of diosbulbins K and L, and diosbulbin F were confirmed by X-ray crystallographic diffraction analysis, and the absolute stereochemistry of diosbulbin K was determined by a modified Mosher's method. The 13C NMR spectroscopic data for diosbulbins E, F and G were also measured for the first time. The compounds did not show significant cytotoxic and anti-bacterial activities.