Chemical Composition of Teucrium alopecurus Essential Oil from Tunisia

Abstract

The chemical composition of the essential oil obtained from Teucrium alopecurus De Noé, an endemic limited to Matmata (southern Tunisia) was analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS). Fifty-seven components were identified; the predominant compounds of the oil of Teucrium alopecurus were mainly sesquiterpenes hydrocarbons (61.3%) and oxygenated sesquiterpenes (26.9%); δ-cadinene (13.4%), nerolidyl acetate (12.3%), α-humulene (12.3%), α-guaiene (10.3%) and β-caryophyllene (8.2%).

Key Word Index

Teucrium alopecurus, Lamiaceae, essential oil composition, δ-cadinene, nerolidyl acetate, α-humulene, α-guaiene.

Introduction

The genus Teucrium (Lamiaceae family) comprises some 200 species (1) mostly in die Mediterranean basin with 220 taxa (2), nineteen of which grow in Tunisia (3-5).

Teucrium alopecurus de Noé is an endemic limited to the region of Matmata (southern Tunisia) (2). This species grows wild in lower arid mediterranean bioclimate widi moderate winter. T. alopecurus is a small under-shrub with grey rosy trained branches, having reddish, dense floral clusters looking like a fox tail, and for that it's called "Germandrée queue de renard" in French. It is found in calcareous rocky regions and rocky steppes (5).

Various species of the genus Teucrium are known for their medicinal value in folk medicine for more than 2,000 years (6,7). In Tunisia, (8) as in many other countries such as Corsica, Iran, Italy, Turkey, Egypt, Spain, Portugal and Cyprus (7, 9-16), this genus has often been used as an antispasmodic, antimalarial, antipyretic, antibacterial and anti-inflammatory drug.

Several morphological, caryological and chemical studies have been reported about the Teucrium genus which has a very complex taxonomy depending on places and regions where it grows.

Experimental

Plant Material: Aerial parts of T. alopecurus were collected at flowering stage in the south of Tunisia, 31 km from the region of Matmata in April 2005. The plant was identified by Z. Ghrabi, Institut National Agronomique de Tunisie, Université de Tunis. Voucher specimens of this plant have been deposited at the Herbarium of the Institut National Agronomique de Tunis.

Isolation of the essential oil: The oil was isolated from fresh plant material (850 g) by steam distillation in an all-glass apparatus, for 4 h in 0.02% v/w yield. The oil was dried over anhydrous sodium sulphate and stored at +4°C until tested and analyzed.

Gas chromatography: Gas chromatographic analysis was carried out using a Hewlett Packard 6890 (Agilent Technologies ) , gas Chromatograph equipped with a flame ionization detector (FID). The analysis was performed on two fused silica capillary columns: a non polar HP-I (polydimetiiylsilicone, 30m × 0.25mm, film thickness 0.25 µm) and a polar column Innowax (polyethyleneglycol, 30m × 0.25mm, film thickness 0.25 µm). Oven temperature program, 60°-240°C (2°C/min), 240°C (20.0 min); injector temperature, 220°C ; carrier gas; He at 1mL/min flow rate; split ratio (1/40); detector temperature, 240°C.

Gas chromatography-Mass spectrometry: GC-HRMS analysis were performed on an Autospec 610-M mass spectrometer coupled to a gas Chromatograph from Agilent Technologies 6890. The analysis was performed on two fused silica capillary columns: HP-1 (polydimethylsilicone, 30m × 0.25mm, film thickness 0.25 µm) and Innowax (polyethyleneglycol, 30m × 0.25mm, film thickness 0.25 µm). Oven temperature program; 60°-240°C (2°C/min), 240°C (20.0 min); injectortemperature, 220°C; carrier gas, He at 1 mL/min flow rate; split ratio ( 1/40); detector temperature, 240°C.

Qualitative and quantitative analysis: The identity of the components was assigned by comparison of their Retention Indices (RI) on both HP-1 and Innowax columns and from their mass spectra. The RIs were calculated using a mixture of C^sub 8^-C^sub 30^ hydrocarbons. Acquired mass spectra were compared to the NIST and Wiley mass spectra databases and to literature data (15). Relative amounts of individual components were also calculated on the basis of GC (FID) peak areas.

Results and Discussion

Fifty-seven (57) compounds were identified in T. alopecurus oil. The qualitative and quantitative composition of the oils are given in Table I, where the components are fisted according to their elution on the Innowax column.

Retention data acquired in the two different polarity columns combined with data from mass spectra was crucial for the identification of most of the compounds; only (2.7%) were not identified.

Oil isolated from T. alopecurus consisted mainly of sesquiterpenes, either hydrocarbons (61.3%) or oxygenated compounds (26.9%), such as δ-cadinene (13.4%), nerolidyl acetate (12.3%), α-humulene (12.3%), α-guaiene (10.3%), β-caryophyllene (8.2%) and germacrene D (5.1%).

Among monoterpenes, the hydrocarbons were detected at 5.4% with β-pinene at 2.6% and limonene at 1.4% being the most abundant monoterpene hydrocarbons.