Chemical compositions of essential oils of five introduced conifers in Corsica

Abstract The aim of this survey was to determine the chemical composition of essential oils (EO) of five conifers acclimated in Corsica by GC(RI), GC–MS and 13C NMR. L. decidua needle and wood EOs contained as majors components: α- and β-pinenes, germacrene D (needles) and bornyl acetate (wood). The EOs of needles, wood and cones of P. menziesii were characterised by β- and α-pinenes, terpinen-4-ol, sabinene, terpinolene (needles and wood), Δ-3-carene (wood) and limonene (cones). Needles and wood EOs of P. ponderosa contained as major components: β- and α-pinenes, Δ-3-carene (wood) and estragole (needles). S. giganteum EOs of foliage and wood were rather similar and dominated by α-pinene, and safrole. The EOs of leaf, wood and cones from C. japonica were very similar, and exhibited α-pinene, sabinene, β-elemol and kaurene as major constituents. It appeared that EO compositions of some species were different from reported literature data.


Plant material, isolation of essential oil
The essential oil samples have been isolated by hydro distillation using a Clevenger-type apparatus from different parts of individual tree (500 g; yields given in table 1) harvested on the experimental forest plot, in which each planted tree is individually numbered, of l'Ospedalesoutheast of the Corsica (P. menziesii, P. ponderosa, S. giganteum, C. japonica), and the managed natural forests of Vizzavona-center of Corsica (P. menziesii) and Verde -center of Corsica (L. decidua) ( Figure S1).

Gas Chromatography
Analyses were performed on a Clarus 500 PerkinElmer (PerkinElmer, Courtaboeuf, France) system equipped with a FID and two fused-silica capillary columns (50m x 0.22 mm, film thickness 0.25 mm), BP-1 (polydimethylsiloxane) and BP-20 (polyethylene glycol). The oven temperature was programmed from 60 °C to 220 °C at 2 °C/min and then held isothermal at 220 °C for 20 min; injector temperature: 250 °C; temperature detector: 250 °C; carrier gas: helium (0.8 mL/min); split: 1/60; injected volume: 0.5 L (50 L in 350 L of CHCl 3 ). The relative amounts of the oil constituents were expressed as percentages obtained by peak-area normalisation, without using correcting factors.
Retention indices (RI) were determined relative to the retention times of a series of n-alkanes with linear interpolation (Target Compounds software from PerkinElmer).

Nuclear Magnetic Resonance
All NMR spectra were recorded on a Bruker AVANCE 400 (100.623 MHz for 13 C) equipped with a 5mm probe, in deuterated chloroform (CDCl 3 ), with all shifts referred to internal tetramethylsilane (TMS). The 1 H NMR spectra were recorded with the following parameters, pulse width (PW), 4.3 ms; acquisition time, 2.6 s for 32 K data table with a spectral width (SW) of 6000 Hz (15 ppm). 13 C NMR spectra were recorded with the following parameters: pulse width (PW), 4 µs (flip angle 45°); acquisition time, 2.7 s for 128 K data table with a spectral width of 24000 Hz (240 ppm); total repetition time, 2.8 s; CPD (composite pulse decoupling) mode decoupling; digital resolution, 0.183 Hz/point.

Identification and quantification of individual components
Identification of individual components was based: i) on comparison of their GC retention indices (RI) on polar and apolar columns, with those of authentic compounds (König et al. 2001) ii) on computer search using digital libraries of mass spectral data and comparison with published data (McLafferty & Stauffer 1994, König et al. 2001, Adams 2007 iii) on comparison of the signals in the 13 C NMR spectra of the mixtures with those of reference spectra compiled in the laboratory spectral library, with the help of a laboratory-made software (Tomi and Casanova 2006, Bighelli andCasanova 2009).