A potential energy surface bifurcation in terpene biosynthesis

Terpenes comprise a class of natural products that includes molecules with thousands of distinct structurally and stereochemically complex molecular architectures. The core hydrocarbon frameworks of these molecules are constructed via carbocation rearrangements promoted by terpene synthase (cyclase) enzymes. Although many mechanistic details for such reactions have been uncovered, the factors that control which carbocation intermediates and transition-state structures form are not well understood. Here we show that rearrangement pathways that pass through particular transition-state structures can bifurcate after the transition state. The resulting pathways lead to terpenes with distinctly different skeletons from each other. Although these types of bifurcating pathways have been described previously for some small molecules, the possibility that they may have an important role in the production of complex molecules in nature has, to our knowledge, not previously been considered.