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DOI: 10.1055/s-0035-1565790
Comparative study of natural and synthetic linalool isolated from Ginger (Zingiber officinale) using photochemical reactions
Ginger (Zingiber officinale Roscoe) is very important plant for its medical properties from ancient time and used as spicy herb all over the world. This study was designed to examine the chemical composition of the hydrodistillated-essential oils and various solvent crude extracts (n-hexane, chloroform and ethanol) of fresh ginger rhizomes as well. 38 chemical compounds of different concentration were isolated and identified by gas chromatography-mass spectroscopy in the essential oils as citral (11.4%), curcumene (10.67%), zingiberene (28.6%), and linalool (15.0%) which represent the major chemical compounds. However, some other minor chemical constituents were also identified from the essential oil. Based on its chemical complexity comfirmed by TLC, the hexane crude extract was selected for GC-MS analysis, and the results revealed the presence of several volatile compounds such as terpineol (13.96%), farnesol, 6-gingerol (14.3%) and linalool (11.4%) as main components. Further investigation on the structure elucidation of the selected bioactive compound (linalool) using IR, GC-MS and NMR techniques compared to authenticated linalool were studied. Linalool was subjected to purification using preparative and column chromatography. Then linalool has been epoxidized using m-chloroperbenzoic acid (mcpba) at 0 °C (thermal reaction) and the results revealed the presence of two cyclic oxygenated products which are 2,2,6-trimethyl-6-vinyle-tetrahydropyran-3-ol and 2-(5-methyl-5-vinyl-tetrahydro-furan-2-yl) as a stereospecific product. Another photo-epoxidation was carried out on linalool in the presence of florescent lamps and H2O2 and the results revealed the presence of the same above mentioned two cyclic oxygenated products and a new photo-epoxide compound named 2,8-trimethyl-6-oxinyl-tetrahydro-pyran-3-ol. Oxidation process is enhanced by irradiation and results in the formation of epoxide derivatives, which may be subjects of biological investigations.