Addressing the Chemistry of Germacrene A by Isotope Labeling Experiments.

Despite the central role of germacrene A in sesquiterpene biosynthesis and its widespread occurrence in nature, its complete NMR characterization is still pending. This problem was solved through enzymatic preparation of germacrene A isotopomers that allowed for a full signal assignment to all three conformers. The obtained materials gave insights into the stereochemical course of the Cope rearrangement to β-elemene and uncovered the Cope rearrangement as a new EI-MS fragmentation reaction.