Minor Humulane and Eremophilane Sesquiterpenoids from Syringa pinnatifolia and Their Protective Effect Against Oxidative Injuries in H9c2 Cells

Abstract As a part of systematic research, an ongoing phytochemical investigation of the sesquiterpenoid‐containing fraction led to the isolation of five new sesquiterpenoids from the peeled stems of Syringa pinnatifolia , including two pairs of enantiomeric humulane‐type (±)‐alashanoids A 1 and B 1 ( 1 and 2 ) and one eremophilane‐type alashanoid C 1 ( 3 ). These structures were elucidated by the analysis of extensive spectroscopic data, including ESI‐MS and 1D and 2D NMR, and the absolute configuration was determined by comparing its experimental and calculated electronic circular dichroism and calculated NMR. These isolates exhibited moderate in vitro cardioprotective effects against oxidative injuries in H9c2 cells.