Chemical Variability of Litsea cubeba Leaf Oil from Vietnam

Journal of Essential Oil Research: JEOR, Jan/Feb 2005 by Bighelli, Ange, Muselli, Alain, Casanova, Joseph, Tam, Nguyen Thi, Et al

Abstract

The chemical composition of Litsea cubeba essential oils obtained from leaves harvested in six provinces of Vietnam were investigated using a combination of capillary GC, GC/MS and ^sup 13^C-NMR spectroscopy. Three compositions were found, dominated by 1,8-cineole (0.2-51.7%), linalool (0.4-91.1%) and sabinene (0-48.1%).

Key Word Index

Litsea cubeba, Lauraceae, essential oil composition, linalool, 1,8-cineole, sabinene, α-terpineol.

Introduction

Litsea cubeba (Lour.) Pers. (syn. Litsea citrata Blume), Lauraceae, is an evergreen tree (5-8 m high), wide spread in eastern Asia (1). Even though the fruits give the highest yield, all parts of the plant produce an essential oil, which exhibits diverse compositions reviewed by Lawrence (2-4) and Choudhury et al. (5).

Two main compositions were reported for fruit oils: citral alone (6,7) or associated with Iimonene (4) and citronellal (5,8). The compositions of flower, branch, bark and root oils were dominated by sabinene/citronellal (5), citronellol/citronelIaI (5), citronellol/linalool/citronellal (8), and citronellal (9), respectively. Finally, three compositions were reported for L. cubeba leaf oils: i) linalool (78%, India)(8); ii) linalool/citronellal (40-50/30-40%, Java)(10); iii) 1,8-cineole (50-66%, Java and Taiwan)(3).

As part of our on going work on the characterization of Vietnamese aromatic plants, we investigated the chemical composition of the essential oils obtained from leaves of L. cubeba harvested in six provinces of Vietnam. We report here on the chemical variability of these oils.

Experimental

Plant material and oil isolation: The leaves were collected in July 1998, in six Provinces of Vietnam: Bavi (A), Langson (B), Thai Nguyen (C), Thanh Hoa (D), Yen Bai (E) and Dien Bien (F). Fresh plant material was submitted to hydrodistillation for 4 h using a Clevenger-type apparatus. The oil yield (w/w vs dry material) varied to 0.3-6.6% (see Table I). A voucher specimen has been deposited at the Herbarium of the Department of Botany, Faculty of Pharmacy, Hanoi, Vietnam.

GC and GC/MS analysis: GC analysis was carried out using a Perkin-Elmer Autosystem apparatus equipped with FID and fused-silica capillary columns (50 m × 0.22 mm, film thickness 0.25 µm), BP-1 (dimethyl siloxane) and BP-20 (polyethylene glycol) as previously reported (11,12).

GC/MS analysis was performed on a Hewlett Packard Type 5972. The Chromatograph was equipped with a BPX5 column (20 m × 0.20 mm) and was programmed from 50°-220°C at 3°C/min; injector temperature: 200°C; detector temperature: 240°C. The detector ionization potential was 70 eV.

^sup 13^C-NMR analysis: Spectra were recorded on a Bruker AC 200 Fourier Transform spectrometer operating at 50.323 MHz, equipped with a 10 mm probe, in CDCl^sub 3^, with all shifts referred to internal TMS. Other parameters were as previously reported (11,12).

Identification of components: Identification of the components was based i) on their GC retention indices (RI) on polar and apolar columns, determined relative to the retention time of a series of n-alkanes with linear interpolation with those of authentic compounds; ii) on computer matching with mass spectral libraries (13) and comparison of spectra with literature data (14,15); iii) and by ^sup 13^C-NMR following the methodology first reported by Fonnacek and Kubeczka (16) and improved and computerized in our laboratory (17). All samples were investigated by GC, GC/MS as well as by ^sup 13^C-NMR spectroscopy.

Results and Discussion

The composition of six samples of L. cubeba leaf oil is reported in the Table I. Thirty-three compounds have been identified by combination of capillary GC, GC/MS and ^sup 13^C-NMR spectroscopy: 26 monoterpenes, one normonoterpene and six sesquiterpenes, which represented 75.3-98.2% of the oils. Among them, 14 were hydrocarbons and 19 oxygenated compounds. These oils were characterized by the presence of a high content of oxygenated compounds such as acyclic aldehydes, cyclic alcohols, ketones and oxides.

Three compositions were observed for L. cubeba leaf oils (Table I): 1,8-cineole (23.4-51.7%) was the major constituent of leaf oils from the provinces of Langson (B), Thai Nguyen (C), Than Hoa (D) and Yen Bai (E), which contained also appreciable amounts of α-terpineol (6.1-11.9%) and sabinene (0.9-14.8%). One sample contained a small amount of geranic acid possibly due to the oxidation of geraniol. Linalool(91.1%) and sabinene (48.1%) were the major components of the oils obtained from the provinces of Bavi (A) and Dien Bien (F), respectively. Sesquiterpenes were present at moderate contents except caryophyllene oxide (6.1% in sample C).

It has to be mentioned that ^sup 13^C-N MR spectroscopy ensured the identification of the furan form of the linalool oxides and that the quantification of 1,8-cineole and β-phellandrene, which co-eluted on the polar and apolar columns used, was carried out by combination of GC and NMR (percentage of both compounds on the polar column and relative intensities of selected peaks on the NMR spectrum).