Biosynthesis of Sesquiterpenes by the Fungus Fusarium verticillioides

The volatiles of the fungus Fusarium verticillioides were analysed by GC-MS. Sesquiterpenes dominated, with trichodiene as the principle component. Several other sesquiterpenes were detected in low amounts that were unambiguously identified from their mass spectra and retention indices. The absolute configurations of (R)-beta-bisabolene, (R)-cuparene, (+)-beta-barbatene, (-)-alpha-cedrene, (+)-beta-cedrene, and (+)-alpha-funebrene originating from different key cationic intermediates, were determined by chiral GC-MS and proved to be related to the trichodiene stereostructure. The unusual compound (E)-iso-gamma-bisabolene was also found corroborating a previously suggested mechanism for the cyclisation of the bisabolyl to the cuprenyl cation that is based on quantum mechanical calculations (Y.J. Hong, D.J. Tantillo, Org. Lett. 2006, 8, 4601-4604). These analyses resulted in a revised biosynthesis scheme to trichodiene and the side products of the responsible terpene cyclase, trichodiene synthase, an enzyme that is well characterised from Fusarium sporotrichioides. Feeding studies with several deuterated mevalonolactone isotopomers unravelled stereochemical aspects of the late cyclisations towards trichodiene.