Aromatic plants of tropical Central Africa. Part XXXI. Tricyclic sesquiterpenes from the root essential oil ofEchinops giganteus var.lelyi C. D. Adams

The essential oil from the roots of Echinops giganteus var. lelyi C. D. Adams from Cameroon was investigated by GC, GC–MS and NMR spectroscopy. The oil contains exclusively sesquiterpenes, two-thirds of which are hydrocarbons. Eighteen components, representing 83% of the oil, could be identified; 14 of them (80%) are tricyclic sesquiterpenes with presilphiperfolane, silphiperfolane, isocomane and modhephane skeletons. The main constituent is silphiperfol-6-ene (26.9%), accompanied by presilphiperfol-7(8)-ene (9.4%) which is found for the first time as a natural product. Only one of the four silphiperfolan-6-ol stereoisomers I–IV detected has been described previously. All constituents identified seem to be generated by the same biogenetic pathway.