GC-MS and 13C-NMR studies on the biosynthesis of terpenoid defensive secretions by the larvae of papilionid butterflies ( Luehdorfia and Papilio)

Abstract

The biosynthetic pathway of some terpenic hydrocarbons present in the larval osmeterial secretions of Luehdorfia (homogeneous type) and Papilio (heterogeneous type) species was examined by in vivo experiments, using 13C-labelled acetic acid which was topically applied to the everted osmeteria. GC-MS investigation demonstrated that 13C was incorporated into mono- and/or sesquiterpene hydrocarbons with the enrichment factor of approx. 0.5% ( L. puziloi), 1.0% ( P. protenor) and 2.9% ( P. helenus) by treatment with 1,2- 13C-enriched acetic acid, thereby substantiating de novo biosynthesis of terpenes from acetate precursors by these larvae. The incorporation pattern of [2- 13C]- or [1,2- 13C]acetic acid into the carbon framework of β-myrcene ( L. puziloi) and (E)-β-farnesene ( P. helenus) as revealed by 13C-NMR spectroscopy definitely elucidated the biosyntheses of terpenic compounds in both species by the familiar terpenoid synthetic system with the isoprenoid skeletal units that is widely known in plants. Partial correction of previous assignment of 13C-NMR spectra of β-myrcene and (E)-β-farnesene is also made.