Biosynthesis of Cyclic Monoterpenoids. Involvement of Stereochemically Specified Linalyl Cation in the Cyclization of C10-Prenyl Chain

Abstract
Incubation of geranyl diphosphate (GPP) and the enantiomers and racemate of linalyl diphosphate (LPP) with the limonene synthetase isolated from Mentha spicata resulted in the conversion of GPP and (S)-LPP into (S)-limonene; this can be taken as evidence that linalyl cation having not only the (S)-LPP-like configuration but also C-1 and C-6 double bonds situated in the anti spatial arrangement is involved in the process of the cyclization of GPP to (S)-limonene. The intermediacy of the linalyl cation was supported by the evaluation of the potential energy of the cation with the MO calculation.