Structurally Diverse Cytotoxic Dimeric Chalcones from Oxytropis chiliophylla

Ten isomeric cyclobutane- and cyclohexene-containing chalcone dimers, oxyfadichalcones A–G, were isolated from the aerial parts of Oxytropis chiliophylla. These included six new compounds and three pairs of enantiomers that are being reported from natural sources for the first time. The relative configurations were elucidated by spectroscopic data analysis, while the absolute configurations were determined by comparing the experimental and calculated electronic circular dichroism spectra. Quantitative LC-MS analysis of the main dimers from different parts of the plant revealed their characteristic accumulation in the viscous secretion and provided supporting evidence for the hypothesized photochemical biosynthesis. In addition, the cytotoxic activities of all isolates against the PC-3 human prostate cancer cell line are reported.