Caractérisation des huiles essentielles de Tetraclinis articulata (Vahl) Masters (Thuya de Barbarie) de la région de Tlemcen et étude de leurs activités biologiques

Résumé

In order to promote Algerian medicinal plants, we were interested in this work by the chemical characterization by CG (Ir), CG-SM and 13C NMR of the essential oils obtained from the aerial parts as well as the cone of Tetraclinis articulata (Vahl) Masters (Barbary Thuya), growing in a spontaneous state in the region of Tlemcen on one hand, and the determination of the biological activities of these essential oils on the other hand. The first part concerned the chemical characterization of the essential oil of Tetraclinis articulata brought to Tlemcen in eight stations. The essential oil yields are very variable. The cone (0.17-1.13%) are rich in essential oils than the aerial parts (leaves and flowers), from 0.03 to 0.86%. A detailed analysis of aerial parts essential oil, using the combination of chromatographic and spectroscopic techniques, leads to the identification of 35 compounds. This essential oil is rich in monoterpens which α- pinene (23.6%), bornyl acetate (20.7%) and the camphor (17.3%) being the main constituents. The analysis of 50 samples of aerial parts essential oil, associated with statistical treatment of the results (PCA and Dendrogram), suggested the occurrence of a chemical variability. Samples are divided into two groups (I and II which is subdivided in two sub-groups) based on their contents in camphor (groupe I), in α-pinene (sub-groups IIA) and in association α-pinene/bornyl acetate (sub-groups IIB). In parallel, we followed the chemical composition of leaves essential oils collected on the same foot during one year and noted that the essential oil yields varied from one month to another, ranging between (0.16 à 0.66%) with the most important values observed for December and June. The composition remains qualitatively homogeneous but present quantitative differences. This variability also concerned to major compounds, namely: α-pinene (11.1-24.6%), bornyl acetate (8.6-411%) and camphor (2.2-16.4%). We continued our work by the determination of the chemical composition of the cone essential oils of Tetraclinis articulata isolated from the same stations. A detailed analysis of six samples of the cone’s essential oil leads to the identification of 38 compounds, of which the chemical composition are dominated by the α-pinene (47.1-73.6%), limonene (6.5-21.9%) and myrcene (up to 11.6%). The analysis of 40 samples of the cone’s essential oil, associated with statistical treatment, suggested the occurrence of a chemical variability. Thus, samples are divided into two independent groups characterized by α-pinene (group I) and association α-pinene/limonene (group II). The second part concerned the study of the antimicrobial and antioxidant activity of these essential oils. Essential oils of the aerial parts of Tetraclinis articulata presenting three different chemical compositions (α-pinene, or camphor or bornyl acetate majority), displayed the highest activity against both Staphylococcus aureus and Aspergillus fumigatus, with diameters of the zones of inhibition ranging between 20 and 38.5 mm. However, essential oil with camphor as major component was th CMIs ranging between 1 and 3 μL/mL. While, essential oil with α-pinene remains the less effective, with CMIs ranging between 2 and 6 μL/mL, against to the same micro-organisms. Finally, we tested the antioxidant activity with three methods: DPPH, β-carotene and FRAP, with respect to three samples of essential oil of the aerial parts and twelve of cones exhibiting three different chemical compositions, according to the percentages of α-pinene and limonene. The results obtained revealed a weak antioxidant capacity for the whole essential oils by comparison with the reference compounds.

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