Biosynthesis of Cyclic Monoterpenoids -The Role of Bivalent Metal Cations in the Cyclization of Acyclic Allylic Diphosphates

Abstract

The role of bivalent metal cations in the cyclization of acyclic allylic diphosphates to cyclic monoterpenoids was investigated. The reaction of linalyl diphosphate (LPP) with the bivalent metal ions was found to give much more amount of a-terpineol than in the cases of neryl diphosphate (NPP) and gerany diphosphate (GPP) with the metal ions. The reaction of these allylic diphosphates with Mn²⁺ ion was traced by the ¹H-NMR spectroscopy, and a change in the intensity of the C-9 methyl proton signal was observed only in the case of LPP. This change was found to result from the coordination of Mn²⁺ ion with the diphosphate moiety. The structure analysis pf LPP chelated with Mn²⁺ ion was carried out by CNDO/2 calculation, and the analysis indicated that the C-0 bond of LPP is weakened by the chelation of Mn²⁺ ion.
It was thus establishe d that the bivalent metal cation chelates the diphosphate moiety of LPP and plays a role in the production of linalyl cation by pulling out the diphosphate moiety.