Which Is More Likely in Trichodiene Biosynthesis:  Hydride or Proton Transfer?

The mechanisms proposed for enzyme-catalyzed formation of the sesquiterpene natural product trichodiene consistently include a step involving a 1,4-hydride transfer. Using quantum chemical methods (B3LYP/6-31+G(d,p) and mPW1PW91/6-31+G(d,p)), we discovered two alternative pathways for transformation of the intermediate bisabolyl cation to the cuprenyl cation, one of which--a proton-transfer pathway--appears to be much more energetically favorable (by more than 10 kcal/mol) than the hydride transfer pathways usually proposed.