Caractérisation chimique d'huiles essentielles de Corse et du Vietnam. La RMN du carbone-13, outil d'analyse des mélanges naturels.

摘要

In recent years products derived from plant biomass have become increasingly popular in many industries (aromatherapy, cosmetics, food, etc.). The aim of our study was twofold. First, it was to study the chemical composition of essential oils isolated from different species from Vietnam, adapting the analytical strategy to the complexity of the mixture. Secondly, we want to contribute to a better understanding of the volatiles by two species of the type Myrtus : M. nivellei, endemic in the Sahara, the chemical composition of the essential oil had never been previously described and M. communis, through the analysis of essential oils from different sources around the Mediterranean and their aroma. The first part concerns the essential oils of 7 species from Vietnam. Among these, the essential oils of Clausena indica, C. anisum-olens, Cunninghamia konishii, Asarum glabrum, A. cordifolium et Cupressus tonkinensis (EO stems) were analysed by GC(RI), GC-MS and 13C NMR, without prior splitting. In contrast, the essential oils of C. tonkinensis (EO leaves) and Xanthocyparis vietnamensis, more complex than the preceding, required one or more fractionation steps by short open column chromatography of silica prior to analysis by GC(RI), GC-MS and 13C NMR and sometines 2D NMR. This work has contributed to a better understanding of the chemical compositions of these essential oils and has enriched our NMR spectra library « Terpènes » of 8 compounds, two of which had never been identified or described in the literature: the 10-epi-nor-g-eudesmen-11-one and the 12-hydroxy-isodihydroagarofuran. The second and final part deals with essential oils of M. nivellei and of M. communis. The essential oil of leaves of M. nivellei was studied by combination of different techniques (CC, GC-MS, GC(RI), 13C NMR and 2D NMR). We identified 26 compounds representing 94.7% of the overall chemical composition, including the two major compounds are 1,8-cineole (37,5%) and limonene (25,0%). We managed to determine the structure of two new compounds: the 1-hydroxy-1-(3-methylbutoxy)-2-acetoxy-3,5,5-trimethyl-3-cyclopentene (4,3%) et le 1-hydroxy-1-(3-methyl-2-butenoxy)-2-acetoxy-3,5,5-trimethyl-3-cyclopentene (0,9%). Finally, the essential oils of M. communis (65 samples) from Corsica and other areas of the Mediterranean (Algeria, Portugal, Morocco, Tunisia and Sardinia) were analyzed by GC-MS, GC(RI) and 13C NMR, giving special importance to minority oxygenates. Four short chain esters, very rarely reported in the literature, have been systematically identified, regardless of the chemical group to which the essential oil belongs: the isobutyl isobutyrate, the isobutyl 2-méthylbutyrate, the 2-méthylbutyl isobutyrate and the 2-méthylbutyl 2-méthylbutyrate. Their individual contents vary from 0,1 to 2,2%. A sensory analysis has noted the contribution of these esters, with varying intensity, with a fruity top note from the essential oils of myrtle.