Isogermacrene A, a proposed intermediate in sesquiterpene biosynthesis

A sesquiterpene hydrocarbon, isogermacrene A ( 5), which is structurally related to the gorgonanes and zieranes, was isolated from the essential oil of Saccogyna viticulosa (Hepaticae). This monocyclic compound is proposed as the biogenetic intermediate of some rare sequiterpene skeletons. In the essential oil of the liverwort Saccogyna viticulosa, collected on the island of Madeira, the new sesquiterpene hydrocarbons isogermacrene A ( 5) and its Cope rearrangement product iso-β-elemene ( 6) were identified. 5 is proposed to act as the biogenetic precursor of several new sesquiterpenes identified in the volatiles of S. viticulosa. These include iso-α-humulene, α-gorgonene, gorgona-1,4(15),11-triene and gorgon-11-en-4-ol. In addition, the Cope product of zierene, isozierene, allo-aromadendra-4(15),10(14)-diene, aromadendra-4(15),10(14)-dien-1-ol and a prenylguaiane diterpene alcohol, named viticulol, were identified as new natural products.