Synthesis and enantiospecific analysis of enantiostructured triacylglycerols containing n-3 polyunsaturated fatty acids

Marika Kalpio,Jóhann D Magnússon,Haraldur G Gudmundsson,Kaisa M Linderborg,Heikki Kallio,Gudmundur G Haraldsson,Baoru Yang

doi:10.1016/j.chemphyslip.2020.104937

Marika Kalpio, Jóhann D Magnússon + Show 5 more

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https://doi.org/10.1016/j.chemphyslip.2020.104937

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Abstract

The stereospecific structure of triacylglycerols (TAGs) affects the bioavailability of fatty acids. Lack of enantiopure reference compounds and effective enantiospecific methods have hindered the stereospecific analysis of individual TAGs. Twelve novel enantiostructured AAB-type TAGs were synthesized containing one of the three n-3 polyunsaturated fatty acid: α-linolenic acid (ALA), eicosapentaenoic acid (EPA), or docosahexaenoic acid (DHA) in sn-1 or sn-3 position. These compounds formed six enantiomer pairs, which were separated with recycling high-performance liquid chromatography using chiral columns and UV detection. The chromatographic retention behavior of the enantiomers and the stereospecific elution order were studied. The enantiomer with an n-3 PUFA in the sn-1 position eluted faster than the enantiomer with the n-3 PUFA in the sn-3 position, regardless of the carbon chain length and number of double bonds of the PUFA. TAG enantiomers containing DHA exhibited highly different retention on the chiral column and were separated after the first column, whereas recycling was needed to separate the enantiomer pairs containing ALA or EPA. The system using two identical columns and one mobile phase, without sample derivatization, proved to be very effective also for peak purity assessment, confirming the enantiopurity of the synthesized structured TAGs being higher than 98 % (96 % ee).

Highlights

There is an increasing interest in the health effects of n-3 poly unsaturated fatty acids (PUFAs). α-Linolenic acid (18:3n-3, acid: α-linolenic acid (ALA)) is an essential fatty acid and a precursor for synthesis of other long-chain n-3 PUFAs
We address a new challenge in the synthesis and analysis of enantiostructured AAB type TAGs pos sessing n-3 PUFAs with 3–6 double bonds (DBs) (ALA, eicosapentaenoic acid (EPA), or docosahexaenoic acid (DHA)) in one of the enantiomeric sn-1/sn-3 positions along with pure stearic (C18:0) or palmitic acids (C16:0) in the remaining positions
Six pairs of TAG enantiomers were formed, all of the AAB type containing one n-3 PUFA (ALA, EPA or DHA) attached to the terminal sn-1 or sn-3 position of the glycerol backbone along with two palmitic or stearic acids located in the remaining positions

Summary

Introduction

There is an increasing interest in the health effects of n-3 poly unsaturated fatty acids (PUFAs). α-Linolenic acid (18:3n-3, ALA) is an essential fatty acid and a precursor for synthesis of other long-chain n-3 PUFAs. There is an increasing interest in the health effects of n-3 poly unsaturated fatty acids (PUFAs). In TAGs, the fatty acyl groups are covalently attached by ester bonds in the glycerol backbone in one of the three stereospecifically distinct locations termed sn-1, sn-2 and sn-3 (IUPAC-IUB Commission on Biochemical Nomenclature, 1977). When the two terminal primary hydroxyl groups of a glycerol are esterified with different fatty acids, the resulting TAG displays chiral asymmetry and has two en antiomers. The stereospecific distribution of fatty acids in TAGs of natural fats and oils is under genetic control, making the positional distribution of fatty acids not random (Brockerhoff, 1971; Vichi et al, 2007)

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