Arnebinfuranoids A–G, seven unique heterodimers of meroterpenoids from Arnebia euchroma

Seven previously undescribed heterodimers (1–7) with unusual carbon-carbon bond linkages for monomeric meroterpenoids and a known compound (8) were isolated from the roots of Arnebia euchroma (Royle) Johnst. Their structures were elucidated by extensive spectroscopic methods and quantum chemical calculations of electronic circular dichroism spectra. Further careful NMR analysis revealed that the chemical shift differences of the methylene protons affected by remote chirality were related to the relative configurations of the heterodimers (1–6). Compounds 2–5 and 8 significantly ameliorated PC12 cell damage induced by H₂O₂ and glutamate in vitro comparable to edaravone.