Biosynthetic pathway of β-thujaplicin in the Cupressus lusitanica cell culture

The biosynthesis pathway of β-thujaplicin, which has a unique conjugated seven-membered ring structure, was investigated using the Cupressus lusitanica cell culture. We also examined a transformation of the carbon skeleton during its biosynthesis. Incorporation of [10-¹⁴C]geraniol into β-thujaplicin in the cell culture revealed that this compound was biosynthesized via geranylpyrophosphate (GPP) and hence is a monoterpenoid. The biosynthesis pathway from glucose to GPP and a skeletal rearrangement of GPP to β-thujaplicin are proposed, based on the NMR analysis of β-thujaplicin biosynthesized in C. lusitanica cells from [1-¹³C]-, [2-¹³C]- and [U-¹³C]-glucose. β-Thujaplicin was produced in the C. lusitanica cell from GPP, which was almost solely produced through the GAP/pyruvate pathway; contribution of the classical mevalonate pathway must be negligible, contrary to our previous conclusion. In addition, it was assumed that GPP was transformed to β-thujaplicin via the limonane type skeleton, which is a common intermediate of cyclic monoterpene.