Saudiarabicains A-E, bioactive 19-acetoxyingol diterpenoids from Euphorbia saudiarabica

Abstract Five new 19-acetoxyingols were isolated from the aerial parts of Euphorbia saudiarabica. They included two uncommon pentacyclic acetoxyingols (1, 2) and two 2,3-diepimers (3, 4), representing the first report of 19-acetoxyingols epimers. Their structures were determined by analysis of extensive 1D and 2D NMR spectroscopic data. The absolute configurations were established by experimental and calculated CD analysis. Compounds 3–5 showed α-glucosidase inhibitory effects superior to the positive control, acarbose (IC50 9.1, 8.0, 1.8 vs 147 µM, respectively). Compounds 1, 2, 4, and 5 showed inhibitory effects on human P-glycoprotein comparable to the positive control, valspodar (IC50 0.1–1.4 vs 0.2 µM, respectively).