Natural Deuterium Distribution in Fatty Acids Isolated from Peanut Seed Oil: A Site-Specific Study by Quantitative 2H NMR Spectroscopy

Quantitative 2H NMR spectroscopy has been used to measure the distribution of deuterium at natural abundance in long‐chain fatty acids extracted from the same vegetable oil. Peanut seed oil was selected, due to its suitable oleic and linoleic acid content. The methyl esters of the fatty acids were prepared by transesterification and isolated by modified argentation column chromatography on silica. In order to measure the natural isotopic fractionation of deuterium (D) at the maximum number of positions, the purified methyl oleate and methyl linoleate were chemically cleaved and the (D/H)i values determined by quantitative 2H NMR spectroscopy. It was thus possible to demonstrate that fractionation in deuterium occurs during the desaturation of oleate to linoleate. Furthermore, the previously observed distribution of deuterium at the sites of desaturation is confirmed, as is the alternating pattern of (D/H)i, which relates to the origin of the pertinent hydrogen atoms. The data obtained are discussed in terms of the kinetic isotopic effects intrinsic to the enzymes—synthetases and desaturases—involved in the biosynthesis of fatty acids. The site‐specific distribution of 2H in fatty acids isolated from peanut oil has been measured by quantitative 2H NMR spectroscopy. The distribution is shown to be nonstatistical (see picture). It is shown that, during the desaturation of oleate to linoleate, kinetic isotope effects give rise to a relative enrichment in 2H in the substrate.