Two polycyclic geranylhydroquinone-derived metabolites from roots of Arnebia hispidissima (Lehm.) DC.

A phytochemical investigation of the least polar organic extracts of Arnebia hispidissima (Lehm.) DC. roots has led to the isolation of two unique polycyclic geranylhydroquinone-derived metabolites, arnebacene (1) and arnebidin (2), along with some known phenolic metabolites viz., arnebin-7 (3) and vanillic acid (4). The chemical identification of the new isolated compounds, including their relative stereochemistry, was achieved via spectroscopic analyses, including 2D NMR, and spectral comparison with related compounds. A biosynthetic pathway is proposed for the new compounds on the basis of their structure-relationship with previously isolated metabolites.