Isogermacrene A, a proposed intermediate in sesquiterpene biosynthesis.

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-beta-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-alpha-humulene, alpha-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.