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. Author manuscript; available in PMC: 2014 Dec 16.
Published in final edited form as: Chembiochem. 2013 Oct 24;14(18):10.1002/cbic.201300349. doi: 10.1002/cbic.201300349

Scheme 2. Cyclization pathways for the production of Δ-6 protoilludene, germacrene A and β-elemene.

Scheme 2

A metal ion mediated dephosphorylation of (2E,6E)-FPP yields a reactive carbocation, followed by a specific ring closure. A 1,11-cyclization mechanism produces a trans-humulyl cation, a precursor to a wide range of sesquiterpenes. The trans-humulyl cation can undergo a 1,2 hydride shift followed by two cyclizations and loss of a proton, resulting in Δ-6 protoilludene 7. A 1,10-cyclization mechanism yields a E,E-germacradienyl cation, and loss of a proton leads to germacrene A. β-elemene 8 is the heat induced Cope rearrangement product of germacrene A. Relative stereochemistries of sesquiterpenes are shown.