title: Challenges posed to bornyl diphosphate synthase: diverging reaction mechanisms in monoterpenes.
abstract: The simplest form of terpenoid chemistry is found for the monoterpenes, which give plants fragrance, flavor, and medicinal properties. Monoterpene synthases employ geranyl diphosphate as a substrate to generate an assortment of cyclic products. In the current study we present a detailed analysis of the multiple gas-phase reaction pathways in the synthesis of bornyl cation from geranyl diphosphate. Additionally, the fate of the proposed bornyl cation intermediate in the bornyl diphosphate synthase reaction is investigated by molecular dynamics simulations. We employ accurate density functional theory (DFT) methods after careful validation against high-level ab initio data for a set of model carbocations. The gas-phase results for the monoterpene reactions indicate a diverging reaction mechanism with multiple products in the absence of enzymatic control. This complex potential energy surface includes several possible bifurcation points due to the presence of secondary cations. Additionally, the suggested bornyl cation intermediate in the bornyl diphosphate synthase reaction is studied by molecular dynamics simulations employing a hybrid quantum mechanics (DFT)-molecular mechanics potential energy function. The simulations suggest that the bornyl cation is a transient species as in the gas phase and that electrostatic steering directs the formation of the final product, bornyl diphosphate.
authors.affiliation: Department of Chemistry and the Lise Meitner-Minerva Center of Computational Quantum Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel.
authors.forename: Michal
authors.initials: M
authors.lastname: Weitman
authors.forename: Dan Thomas
authors.initials: DT
authors.lastname: Major
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000737:chemistry / Q000378:metabolism*; D005740:Gases / Q000737:chemistry; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D039821:Monoterpenes / Q000737:chemistry / Q000378:metabolism*; D011789:Quantum Theory; D027543:Salvia officinalis / Q000201:enzymology; D013816:Thermodynamics
chemical_list: D005740:Gases; D039821:Monoterpenes; D019883:Alkyl and Aryl Transferases