Abstract
A combination of selective 1D Total Correlation Spectroscopy (TOCSY) and 1H-13C Heteronuclear Multiple Bond Correlation (HMBC) NMR techniques has been employed for the identification of methyl linolenate primary oxidation products without the need for laborious isolation of the individual compounds. Complex hydroperoxides and diastereomeric endo-hydroperoxides were identified and quantified. Strongly deshielded C–O–O–H 1H-NMR resonances of diastereomeric endo-hydroperoxides in the region of 8.8 to 9.6 ppm were shown to be due to intramolecular hydrogen bonding interactions of the hydroperoxide proton with an oxygen atom of the five-member endo-peroxide ring. These strongly deshielded resonances were utilized as a new method to derive, for the first time, three-dimensional structures with an assignment of pairs of diastereomers in solution with the combined use of 1H-NMR chemical shifts, Density Functional Theory (DFT), and Our N-layered Integrated molecular Orbital and molecular Mechanics (ONIOM) calculations.
Highlights
Polyunsaturated fatty acids (PUFAs) are a broad and diverse group of naturally occurring biomolecules with numerous physicochemical and biological properties, and diverse roles in health and nutrition [1,2,3]
Methyl linolenate was selected as a suitable representative of omega-3 fatty acids that contains three methylene intruded cis double bonds
Since no X-ray structures of the hydroperoxides of fatty acids have so far been reported, it would be of interest to investigate three-dimensional structures of hydroperoxides of the present work, which are based on the combined use of quantum chemical calculations and 1 H-NMR chemical shifts
Summary
Polyunsaturated fatty acids (PUFAs) are a broad and diverse group of naturally occurring biomolecules with numerous physicochemical and biological properties, and diverse roles in health and nutrition [1,2,3]. PUFAs are susceptible to oxidation upon exposure of thermal stress, light, photosensitizing pigments, and metal ions This results in primary oxidation products, such as hydroperoxides, endo-hydroperoxides, hydroperoxide bis cyclic peroxides, and polymeric hydroperoxides. Complex hydroperoxides and endo-hydroperoxides of methyl linolenate were identified and quantified, with the combination of selective 1D TOCSY and 1 H-13 C HMBC NMR techniques without laborious isolation of the individual components Their three-dimensional (3D) structures with assignment of pairs of diastereomers in solution were elucidated, for the first time, with the combined use of 1 H-NMR chemical shifts, Density Functional Theory (DFT) and Our N-layered Integrated molecular Orbital and molecular Mechanics (ONIOM) calculations
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