Search

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]

Abstract: A novel approach has been developed for activating the highly bioactive long-chain n-3 polyunsaturated fatty acids EPA and DHA as oxime esters and incorporating them exclusively to the end-positions of glycerol and enantiopure 1-O-alkylglycerols. The Candida antarctica lipase B was observed to display a superb regioselectivity when using the acetoxime esters of EPA and DHA as acyldonors under mild condition to keep acyl-migration side-reaction under complete control. Regiopure 1,3-diacylglycerols, 1-O-alkyl-3-acyl-sn-glycerols and their antipodes possessing EPA and DHA were afforded in very high purity and yields. [Copyright &y& Elsevier]

Abstract: Synthesis of symmetrically structured triacylglycerols possessing bioactive n−3 polyunsaturated fatty acids (eicosapentaenoic acid or docosahexaenoic acid) at the 2-position and a short-chain fatty acid (C2, C4, C6) located at the end-positions by a highly efficient two-step chemoenzymatic process is described. Full regiocontrol devoid of any acyl-migration side reactions was obtained in both a lipase promoted step to introduce the short-chain fatty acids exclusively into the primary alcohol positions of glycerol using activated vinyl esters at low temperature and a subsequent coupling reaction involving free EPA and DHA using EDAC as a coupling agent. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

• Twelve enantiopure asymmetric TAGs containing ALA, EPA and DHA were synthesized. • Unique TAGs offer reference material e.g. for bioavailability studies of n-3 PUFAs. • Chiral separation of structured TAG enantiomers was performed by chiral R-HPLC. • New information about stereospecific resolution of TAGs was received. • R-HPLC was applied to study enantiopurity (>98 %). 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). [ABSTRACT FROM AUTHOR]