In Vitro Hypoglycemic Diterpenoids from the Roots of Croton yunnanensis .

Fifteen compounds including nine new diterpenes were isolated from the roots of . By HRESIMS, NMR, ECD data, and X-ray diffraction analysis, the new compounds were characterized as eight -clerodane diterpenes (compounds -) and one 15,16-dinor--pimarane diterpene (). All diterpenes were assayed for their hypoglycemic activities. Compounds -, , , and promoted glucose uptake activity in insulin-resistant 3T3-L1 adipocytes. Compounds and showed insulin sensitizing activity, potentiating conspicuously their glucose uptake activity at a concentration of 20 μM when treated synergistically with low-concentration insulin at 1 nM.