Advances in the Chemical Composition of Essential Oils from Illicium griffithii Hook. f. et Thoms. from Vietnam(a)

Abstract

The chemical composition of essential oils from several parts of a type of Illicium griffithii (short peduncle) harvested in Vietnam was investigated using GC, GC/MS and ^sup 13^C-NMR spectroscopy. These oils contained mostly oxygenated phenylpropanoids, essentially safrole (51.6-65.3%) and 4-methoxysafrole (19.6%, root bark oil). Oils from aerial parts and bark of root oil differed significantly.

Key Word Index

Illicium griffithii, Illiaceae, essential oil composition, 1,8-cineole, linalool, safrole, 4-methoxysafrole.

Introduction

As part of our ongoing work on the aromatic and medicinal Vietnamese plants, we investigated the Illiaceae family which comprises several species. The well known member of this family is Illicium verum Hooker, whose fruit is used to produce star anise oil, characterized by the dominance of (E)-anethole,

In Vietnam, eight Illicium species are known (1). Among these, Illicium griffithii Hook. f. et Thorns, growing wild in different localities is well represented. Illicium griffithii is a tree 6-15 m high, its leaves are persistent and grouped at the hitch in false-whorl. The flowers are borne singly at the axis of the leaves, with 12-13 carpels. Three types can be found in Vietnam, two of which exhibit a long peduncle (2-4 cm) could be differentiated accordingto the color of the flowers (yellowish or pink), the third is characterized by a short peduncle (1-1.5 cm) and by the color of the young flowers (purple for this type and green for the two others).

Recently, we described the chemical composition of leaf and branch oils of the two types of I. griffithii that exhibit a long peduncle. One oil was characterized by an appreciable amount of methyl eugenol followed by safrole. Conversely, safrole was the single major component of the second oil (2). One other study about the fruit oil of I. griffithii harvested in Vietnam reported α-pinene, linalool, limonene and 1,8-cineole as main components (3).

As a continuation of our phytochemical studies on the Illiaceae family, we investigated the chemical composition of oils from several parts (leaves, branches, fruits and root-bark) of the short peduncle type of I. griffithii, by GC, GC/MS and ^sup 13^C-NMR spectroscopy.

Experimental

Plant material and oil isolation: Wild plant material was harvested in Langson Province, Vietnam. All samples were collected at the flowering stage and subjected to water distillation for 4 h using a Clevenger-type apparatus. A voucher specimen has been deposited at the Herbarium of the Department of Botany, Faculty of Pharmacy, Hanoi, Vietnam. The oil yields (w/w vs. diy material) varied from 1.0-4.8% (see Table I).

The chemical composition of the oils obtained from the leaves, branches, fruits and root-bark was investigated by a combination of GC, GC/MS and ^sup 13^C-NMR spectroscopy.

GC: GC analyses were carried out using a Perkin-Elmer Autosystem apparatus equipped with FID and fused capillary columns (50 m × 0.22 mm, film thickness 0.25 µm), BP-1 (polydimethyl siloxane) and BP-20 (polyethylene glycol). The oven temperature was programmed for 60°-22°CC at 2°C/min and then held isothermal at 220°C for 20 min; injector temperature: 250°C; detector temperature: 250°C; carrier gas: helium (20 psi); mode split 1/60.

GC/MS: Samples were analyzed with a Perkin Elmer Turbo mass detector, directly coupled to a Perkin Elmer Autosystem XL equipped with a fused-silica capillary column, BP-1 (polydimethylsiloxane, 50 m × 0.22 mm, film thickness 0.25 µm) or Rtx-WAX (polyethyleneglycol, 60 m × 0.25 mm, film thickness 0.25 µm). Ion source temperature: 150°C; energy ionization: 70 eV; electron ionization mass spectra were acquired over the mass range 35-350 Da. Split: 1/80. Other GC conditions were the same as described under GC.

^sup 13^C-NMR: ^sup 13^C-NMR spectra were recorded on a Bruker AC 200 Fourier Transform spectrometer operating at 50.323 MHz equipped with a 10 mm probe, in deuterated chloroform, with all shifts referred to internal tetramethylsilane (TMS). The spectra were recorded with the following parameters: pulse width (PW): 5.0 µs (flip angle 45°); acquisition time: 1.3 s for 32 K data table with a spectral width (SW) of 12 500 Hz (250 ppm); CPD mode decoupling; digital resolution: 0.763 Hz/pt. The number of accumulated scans was 5,000 for each sample (200 mg of the oil in 2 mL CDCP). An exponential multiplication of the free induction decay with the line broadening of 1.0 Hz was applied before Fourier transformation. This technique allows the identification of individual components to a content of 0.5-1% without any previous purification. The identification is based on comparison of the chemical shift values in the mixture with those of the reference spectra compiled in our laboratory spectral library with the help of a laboratory made software (4).

Identification of components: Identification of the components of the four samples was based on i) comparison of their GC retention indices (RI) on apolar and polar columns, determined relative to the retention time of a series of n-alkanes with linear interpolation, with those of authentic compounds; ii) computer matching with mass spectral libraries including our own library and iii) by ^sup 13^C-NMR following the aforementioned method.