Phytotoxic constituents from Bunias orientalis leaves

Aqueous extracts of Bunias orientalis leaves showed considerable germination inhibition in petri-dish bioassays. As major B. orientalis leaf constituents with known allelopathic activity bound forms of p-coumaric, ferulic and sinapic acids as well as two C-13-norisoprenoids, i.e. 3-hydroxy-beta-ionone and 3-hydroxy-5,6-epoxy-beta-ionone, were identified in XAD-2 isolates. After separation of the glycosidic isolate by counter-current chromatography/HPLC, 3-hydroxy-5,6-epoxy-beta-ionyl-beta-D-glucoside and the glucose ester of sinapic acid were isolated in pure form and their structures elucidated from H-1 and C-13 NMR spectral data. The corresponding aglycones were found to be major constituents in leaf leachate solutions of B. orientalis, together with the known allelochemic loliolide.