A Study Of The Oxidation Products Of Sesamol - A Naturally Occuring Antioxidant

This investigation was undertaken to determine the oxidation products of sesamol in a variety of oxidising systems and to postulate a possible mechanism for their formation. Initially a literature review was completed concerning oxidation products derived from synthetic and natural antioxidants, and the role antioxidants have in inhibiting lipid autoxidation. A literature survey of the oxidation methods employed in various antioxidant studies was also performed. A complete spectroscopic study of sesamol was performed (IR/UV/MS/NMR) and the first unequivocal assignment of the 3¢ NMR spectra of sesamol was achieved using a variety of pulse sequences. The use of high-performance-liquid-chromatography (HPLC) was investigated in this study to separate the oxidation products derived from sesamol. A number of HPLC systems were investigated employing both isocratic and gradient elution to optimise separations. The influence of the methanol content on the peak shape of phenolic species is discussed. The oxidation methods of sesamol employed in this study were: (1) Ultra-violet irradiation; (ii) Horseraddish Peroxidase/Hydrogen Peroxide; (iii) Alkaline Potassium Ferricyanide; and (iv) Autoxidising Unsaturated Fatty Acid Methyl Esters. The products from these. oxidations were monitored using HPLC. Semi-preparative HPLC and Prep TLC were employed to isolate pure fractions for spectroscopic studies. This HPLC method was used in both the analytical and semi-preparative mode; thin layer chromatography (TLC) and column chromatography were also employed in this study to achieve preparative isolation of products. A number of novel oxidation products were isolated and employing spectroscopic techniques their structures were determined as two distinctly different dimeric structures and a spiroketal trimeric structure. Mechanisms for their formation have been proposed. A number of minor products were also isolated in sufficient quantities for mass spectral investigations only. Mass spectral data would indicate trimeric and tetrameric structures of sesamol. Employing autoxidising unsaturated fatty acid methyl esters showed that the formation of sesamol/sesamol oxidation products was only a minor oxidation route. It is proposed that the major oxidation route for sesamol in these systems involves the formation of sesamol/lipid adducts.