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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)., (Copyright © 2020 The Author(s). Published by Elsevier B.V. All rights reserved.)

Lack of synthetic enantiospecific triacylglycerols (TAGs) has hindered our understanding of the impact of TAG structure on the absorption and metabolic fate of fatty acids (FAs). In a five-day feeding trial with mildly (n-3) deficient rats, the bioavailability of docosahexaenoic acid [22:6(n-3), DHA] and stearic acid (18:0) from the two different enantiomers of TAG: sn-22:6(n-3)-18:0-18:0 and sn-18:0-18:0-22:6(n-3), and their regioisomeric TAG: sn-18:0-22:6(n-3)-18:0 was compared. Less secretion of fecal DHA was detected from the sn-2 position compared with the sn-1 and sn-3 positions, but no difference was found in DHA content of the fasting plasma or in the weight of the body or organs. 18:0 was lost to feces mainly as cleaved from the primary positions but also as glycerol-bound. The 5-day intervention in rats was long enough to modify the fatty acid profile of plasma phospholipids., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Enantiomers of racemic triacylglycerol (TAG) mixtures were separated using two chiral HPLC columns with a sample recycling system and a UV detector. A closed system without sample derivatisation enabled separation and identification by using enantiopure reference compounds of eleven racemic TAGs with C12-C22 fatty acids with 0-2 double bonds. The prolonged separation time was compensated for by fewer pretreatment steps. Presence of one saturated and one unsaturated fatty acid in the asymmetric TAG favoured the separation. Enantiomeric resolution, at the same time with stronger retention of TAGs, increased with increasing fatty acid chain length in the sn-1(3) position. Triunsaturated TAGs containing oleic, linoleic or palmitoleic acids did not separate. The elution order of enantiomers was determined by chemoenzymatically synthesised enantiopure TAGs with a co-injection method. The method is applicable to many natural fats and oils of low unsaturation level assisting advanced investigation of lipid synthesis and metabolism., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

This report demonstrates the first asymmetric synthesis of enantiopure structured triacylglycerols (TAGs) of the ABC type presenting three non-identical fatty acids, two of which are unsaturated. The unsaturated fatty acids included monounsaturated oleic acid (C18:1 n-9) and polyunsaturated linoleic acid (C18:2 n-6). This was accomplished by a six-step chemoenzymatic approach starting from (R)- and (S)-solketals. The highly regioselective immobilized Candida antarctica lipase (CAL-B) played a crucial role in the regiocontrol of the synthesis. The synthesis also benefited from the use of the p-methoxybenzyl (PMB) ether protective group, which enabled the incorporation of two different unsaturated fatty acids into the glycerol skeleton. The total of six such TAGs were prepared, four constituting the unsaturated fatty acids in the sn-1 and sn-2 positions, with a saturated fatty acid in the remaining sn-3 position of the glycerol backbone. In the two remaining TAGs, the different unsaturated fatty acids accommodated the sn-1 and sn-3 end positions, with the saturated fatty acid present in the sn-2 position. Enantiopure TAGs are urgently demanded as standards for the enantiospecific analysis of intact TAGs in fats and oils. [ABSTRACT FROM AUTHOR]

This report describes synthesis of novel structured triacylglycerols (TAGs) and diacylglyceryl ethers (DAGEs) of the 1- O-alkyl- sn-glycerol type constituting EPA and DHA as the sole fatty acids. One of two TAGs was comprised of a pure EPA located at the 1,3-positions with pure DHA at the 2-position and the other had it reversed with a pure DHA at the 1,3-positions and pure EPA at the 2-positions. The similarly structured DAGEs were derived from chimyl-, batyl-, and selachyl alcohols constituting pure EPA at their sn-3 position with pure DHA at the sn-2 position as well as the opposite composition with pure DHA at the sn-3 position and EPA at the sn-2 position, the total of six such DAGE products. The syntheses of these compounds were brought about by a two-step chemoenzymatic process involving a highly regioselective immobilized Candida antarctica lipase to incorporate EPA or DHA activated as acetoxime esters exclusively into the 1,3-positions of glycerol and the sn-3 position of the 1- O-alkyl- sn-glycerols. The second PUFA acyl groups were subsequently introduced to the remaining 2-positions by EDCI coupling agent to accomplish the title compounds highly efficiently in very high to excellent yields (86-92%). Practical applications: The work described is based on a previously reported methodology to introduce n-3 PUFAs activated as oxime esters exclusively into the terminal 1,3-positions of glycerol and 1- O-alkyl- sn-glycerols to prepare reversed structured TAGs and DAGEs by use of immobilized Candida antarctica lipase. The methodology is ideal for introducing isotopically labeled fatty acids into predetermined positions of TAGs and DAGEs. Novel structured triacylglycerols (TAGs) and diacylglyceryl ethers (DAGEs), constituting EPA and DHA as the sole fatty acids, were obtained by a two-step chemoenzymatic synthesis comprised of an exclusive incorporation of EPA or DHA, activated as acetoxime esters, into the terminal positions of glycerol and 1- O-alkyl- sn-glycerols by use of immobilized Candida antarctica lipase, and a subsequent introduction of a second PUFA acyl group to the remaining 2-positions by EDCI coupling agent. [ABSTRACT FROM AUTHOR]

Background: n-3 polyunsaturated fatty acids, namely docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), reduce the risk of cardiovascular disease and can ameliorate many of obesity-associated disorders. We hypothesised that the latter effect will be more pronounced when DHA/EPA is supplemented as phospholipids rather than as triglycerides. Methodology/Principal Findings: In a 'prevention study', C57BL/6J mice were fed for 9 weeks on either a corn oil-based high-fat obesogenic diet (cHF; lipids ∼35% wt/wt), or cHF-based diets in which corn oil was partially replaced by DHA/EPA, admixed either as phospholipids or triglycerides from marine fish. The reversal of obesity was studied in mice subjected to the preceding cHF-feeding for 4 months. DHA/EPA administered as phospholipids prevented glucose intolerance and tended to reduce obesity better than triglycerides. Lipemia and hepatosteatosis were suppressed more in response to dietary phospholipids, in correlation with better bioavailability of DHA and EPA, and a higher DHA accumulation in the liver, white adipose tissue (WAT), and muscle phospholipids. In dietary obese mice, both DHA/EPA concentrates prevented a further weight gain, reduced plasma lipid levels to a similar extent, and tended to improve glucose tolerance. Importantly, only the phospholipid form reduced plasma insulin and adipocyte hypertrophy, while being more effective in reducing hepatic steatosis and low-grade inflammation of WAT. These beneficial effects were correlated with changes of endocannabinoid metabolome in WAT, where phospholipids reduced 2-arachidonoylglycerol, and were more effective in increasing anti-inflammatory lipids such as N-docosahexaenoylethanolamine. Conclusions/Significance: Compared with triglycerides, dietary DHA/EPA administered as phospholipids are superior in preserving a healthy metabolic profile under obesogenic conditions, possibly reflecting better bioavalability and improved modulation of the endocannabinoid system activity in WAT. [ABSTRACT FROM AUTHOR]

• First study on the oxidative stability of DHA in regio- and enantiopure TAGs. • DHA in sn -2 was the most stable structure with or without RRR -α-tocopherol. • Without tocopherol, oxidative stability of DHA in sn -1 and sn- 3 was comparable. • With RRR -α-tocopherol, higher stability of DHA in sn -1 compared to sn -3. • Diastereomeric interactions between RRR -α-tocopherol and DHA in sn -1 is proposed. Docosahexaenoic acid (DHA) is essential for health but easily oxidized. Yet the influence of DHA's exact location (sn -1, sn -2, or sn -3) in triacylglycerols on oxidative stability is currently unknown. This is the first study comparing oxidative stability of DHA in regio- and enantiopure triacylglycerols with or without RRR -α-tocopherol. Headspace solid-phase micro-extraction with gas chromatography–mass spectrometry, liquid chromatography–mass spectrometry, and nuclear magnetic resonance spectroscopy were applied. DHA in sn -2 was the most stable with or without added RRR -α-tocopherol resulting in differences in hydroperoxide formation. Without antioxidant, stability of DHA in sn -1 and sn -3 was mainly similar, with slight tendency towards better stability in sn -3. With RRR -α-tocopherol higher stability in sn -1 compared to sn -3 was observed. This points to diastereomeric interactions between RRR -α-tocopherol and DHA in sn -1. These results are highly relevant for enzymatic restructuring processes of DHA-rich fish or microalgae oil concentrates aimed for food supplements or food fortification. [ABSTRACT FROM AUTHOR]

This report describes synthesis of reversed structured triacylglycerols (TAGs) of the LML type, possessing pure EPA or DHA located at the terminal 1,3-positions of the glycerol backbone along with pure even number saturated fatty acids (C6:0–C16:0) occupying the 2-position. These compounds were synthesized by a two-step chemoenzymatic route involving a highly regioselective immobilized Candida antarctica lipase to incorporate EPA or DHA activated as acetoxime esters exclusively into the 1,3-positions of glycerol. The saturated fatty acyl groups were subsequently introduced to the remaining 2-position by EDCI coupling agent to accomplish the title compounds highly efficiently. This is the first report on reversed structured TAGs possessing the long-chain n-3 polyunsaturated fatty acids. It is anticipated that these novel compounds and their synthetic methodology will find various important uses such as analytical standards, in screening for bioactivity and in the pharmaceutical area as prodrugs. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of nine enantiopure structured triacylglycerols (TAGs) of the AAB type is described, all possessing the (S)-absolute configuration. Six of them possess one saturated and two identical unsaturated fatty acyl chains, whereas the remaining three possess two identical saturated fatty acids along with one unsaturated fatty acid. The former group was synthesized by a five-step chemoenzymatic route involving a highly regioselective immobilized Candida antarctica lipase, starting from enantiopure (R)-solketal. The second group was prepared by a fully chemical five-step approach based on the same chiral precursor. Such enantiopure TAGs are strongly required as standards for the enantiospecific analysis of intact TAGs in fats and oils. [Copyright &y& Elsevier]

The synthesis of twelve enantiopure structured triacylglycerols (TAGs) of the ABC type possessing three different fatty acids is described by a six-step chemoenzymatic approach starting from (S)-solketal. Eight of the TAGs possess two different saturated fatty acyl groups located in the sn -1 and sn -2 positions with an unsaturated fatty acyl group in the remaining sn -3 position of the glycerol skeleton, whereas the remaining four possess two different saturated acyl groups in the terminal sn -1 and sn -3 positions with an unsaturated acyl group in the sn -2 position. The former group was synthesised by a six-step chemoenzymatic route involving a highly regioselective immobilised Candida antarctica lipase. The second group was prepared by a similar six-step approach, that required two separate lipase steps. Such enantiopure TAGs are strongly demanded as standards for enantiospecific analysis of intact TAGs in fats and oils. Image 1 • Twelve enantiostructured ABC type triacylglycerols (TAGs) were synthesised. • Unique TAGs as standards for chiral separation. • Facile methodology to synthesise both enantiomers of ABC type TAGs. • Highly regioselective lipase. [ABSTRACT FROM AUTHOR]