Marcel S. F. Lie Ken Jie

13C-NMR of methyl, methylene and carbonyl carbon atoms of methyl alkenoates and alkynoates

Abstract The carbon magnetic resonance spectra of 102 fatty acid methyl esters with cis and trans double bonds and triple bonds at various positions and in many different combinations have been investigated. A comprehensive set of chemical shift parameters has been developed for the various substituents. With the aid of these parameters, the chemical shifts of all methyl, methylene carbonyl carbon atoms can be predicted with an accuracy of ±0.1 ppm or better.

13C-NMR of double and triple bond carbon atoms of unsaturated fatty acid methyl esters.

The carbon magnetic resonance spectra of many fatty acid methyl esters with cis and trans double bonds and triple bonds at various positions and in many different combinations have been investigated. The influence of the ester group on double and triple bonds in the fatty acid chain depends strongly on the positions of these bonds. For a given position the influence is constant, even if one or more other double or triple bonds are present. Together with the evaluated chemical shift parameters for the effects of double and triple bonds on each other, complete assignments are possible and spectra of various types of unsaturated esters can be predicted with high accuracy (+/- 0.1 ppm).

High-resolution nuclear magnetic resonance spectroscopy —Applications to fatty acids and triacylglycerols

During the past two decades, nuclear magnetic resonance spectroscopy (NMR) has played an ever-increasing role in the structural determination of fatty acids, fatty acid derivatives and analogues, and in the analysis of the structures of triacylglycerols including the quantitative analysis of lipid mixtures. This article discusses some of the results obtained through the application of the NMR technique to lipid molecules and reviews the literature. To maintain brevity, this article does not cover the underlying theory of NMR spectroscopy as numerous books devoted to modern NMR spectroscopy have been published.

1H-Nuclear magnetic resonance spectroscopic studies of saturated, acetylenic and ethylenic triacylglycerols

Abstract The 1H-NMR spectroscopic properties of 15 synthetic homologous saturated triacylglycerols of type AAA and 16 mixed saturated triacylglycerols of type ABA and AAB have been studied. Triacylglycerols containing short-chain fatty acids (2:0–6:0) are readily identified. Triacylglycerols containing medium- and long-chain fatty acid components are not differentiated. From the analysis of 19 acetylenic triacylglycerols of type AAA, ABA and AAB (containing positional isomers of acetylenic fatty acids), it is only possible to characterize triacylglycerols with acyl groups containing the acetylenic bond at the Δ2−Δ5 position. 1H-NMR analysis could not confirm the positions (α- or β-acyl) of the acetylenic acids in mixed triacylglycerols. In the study of 22 ethylenic triacylglycerols of type AAA containing positional isomers of (Z)- or (E)-ethylenic acids, molecules containing an ethylenic bond in the Δ2 position of the acyl chains were readily characterized, as the ethylenic protons in the α- and β-acyl chains were fully resolved. Triacylglycerols containing an unsaturated center at the position were characterized by the shifts of the 2-H protons. The spectra of the remaining triacylglycerol molecules were very similar and the position of the ethylenic system could not be determined by this technique.

Synthesis and nuclear magnetic resonance properties of all geometrical isomers of conjugated linoleic acids

Pure geometric isomers of conjugated linoleic acid were prepared from castor oil as the primary starting material. Methyl octadeca-9Z, 11E-dienoate (2) and methyl octadeca-9Z, 11Z-dienoate (4) were obtained by zinc reduction of methyl santalbate (1, methyl octadec-11E-en-9-ynoate) and methyl octadec-11 Z-en-9-ynoate (3), respectively, as the key intermediates. Methyl octadeca-9E, 11E-dienoate (8) and methyl octadeca-9E, 11Z-dienoate (9) were prepared by demesylation of the mesyloxy derivative of methyl ricinelaidate (6, methyl 12-hydroxy-octadec-9 E-enoate). A study of the nuclear magnetic resonance spectral properties was carried out and the shifts of the olefinic carbon atoms of 18:2(9Z, 11E) (2) and 18:2(9E, 11Z) (9) were readily identified by a combination of incredible natural abundance double quantum transfer experiment, heteronuclear multiple bond correlation, and 1H−13C correlation spectroscopy correlation techniques. Doubts remain in the absolute identification of the individual olefinic carbon atoms of the 18:2(9Z, 11Z) (4) and 18:2(9E, 11E) (8), except the fact that the shifts of the “inner” (C-10 and C-11) and “outer” (C-9 and C-12) positioned olefinic carbon atoms of the conjugated diene system are distinguishable.

5c, 11c, 14c-Eicosatrienoic acid and 5c, 11c, 14c, 17c-eicosatetraenoic acid ofBiota orientalis seed oil affect lipid metabolism in the rat

The effects of 5c, 11c, 14c-eicosatrienoic acid (20∶3BSO) and 5c, 11c, 14c, 17c-eicosatetraenoic acid (20∶4BSO), polyunsaturated fatty acids (PUFA) contained inBiota orientalis seed oil (BSO), on lipid metabolism in rats were compared to the effects of fats rich in linoleic acid (LA) or α-linolenic acid (ALA) under similar conditions. The potential effect of ethyl 20∶4BSO as an essential fatty acid also was examined in comparison with the ethyl esters of LA. ALA and γ-linolenic acid (GLA). BSO- and ALA-rich fat decreased the concentration of plasma total cholesterol, high density lipoprotein cholesterol, triglyceride and phospholipid as compared to LA-rich fat. BSO was more effective in reducing plasma cholesterol concentrations than was the ALA-rich fat. Dietary BSO markedly decreased the hepatic triglyceride concentration as compared to the LA-rich or ALA-rich fats. Aortic production of prostaglandin I2 tended to decrease in rats fed BSO or ALA-rich fat compared to those fed the LA-rich fat. Adenosine diphosphate-induced platelet aggregation was similar in the three groups. The proportion of arachidonic acid (AA) in liver phosphatidylcholine (PC) of rats fed BSO was lowest compared to that of rats fed ALA-rich or LA-rich fats. Administration of 20∶4BSO, ALA or GLA to essential fatty acid-deficient rats decreased the ratio of 20∶3n−9 to AA in liver PC to the same extent; administration of LA was more effective. The results indicate that the effects of specific PUFA contained in BSO on lipid metabolism are different from those of LA and ALA. It is also suggested that 20∶4BSO may exhibit some essential fatty acid effects.

The use of a microwave oven in the chemical transformation of long chain fatty acid esters

The use of a microwave oven as an energy source allowed transformation of fatty acid derivatives to be complete in a few minutes. Hydrolysis of triglycerides, esterification of free fatty acids, epoxidation of unsaturated fatty acid esters, cyclization of dioxostearates and oxounsaturated fatty acid esters into furanoid derivatives, conversion of epoxystearate to oxostearate derivatives, and substitution of a tosyl group by an azide all took about five min to complete and were in very high yields. The most sluggish reaction encountered was the acid catalyzed hydrolysis (ring opening) reaction of a furanoid ester to the corresponding 1,4-dioxo derivative, which required three 10-min periods of heating. The use of microwaves not only decreased the reaction time considerably but also allowed smaller volumes of solvent and lower quantities of reagents to be used as compared with the conventional methodologies reported.

Ultrasound-assisted synthesis of santalbic acid and a study of triacylglycerol species inSantalum album (Linn.) seed oil

Methyl ricinoleate (1) was treated with bromine and the dibromo derivative (2) was reacted with ethanolic KOH under ultrasonic irradiation to give 12-hydroxy-octadec-9-ynoic acid upon acidification with dil. HCl. The latter compound was methylated with BF3/methanol to give methyl 12-hydroxy-octadec-9-ynoate (3). Compound3 was treated with methanesulfonyl chloride in the presence of triethylamine in CH2Cl2 to give methyl 12-mesyloxy-octadec-9-ynoate (4). Reaction of methyl 12-mesyloxy-octadec-9-ynoate with aqueous KOH under ultrasonic irradiation (20 kHz) gave (11E)-octadecen-9-ynoic acid (5, santalbic acid, 40%) and (11Z)-octadecen-9-ynoic acid (6, 60%) on acidification with dil. HCl. These isomers were separated by urea fractionation. The13C nuclear magnetic resonance (NMR) spectroscopic properties of the methyl ester and the triacylglycerol (TAG) esters of these enynoic fatty acid isomers were studied. The carbon shifts of the unsaturated carbon nuclei of the methyl ester of theE-isomer were unambiguously assigned as 88.547 (C-9), 79.287 (C-10), 109.760 (C-11), and 143.450 (C-12) ppm while the unsaturated carbon shifts of the (Z)-enynoate isomer appeared at 94.277 (C-9), 77.561 (C-10), 109.297 (C-11), and 142.668 (C-12) ppm. In the13C NMR spectral analysis of the TAG molecules of type AAA containing either the (Z)-or (E)-enyne fatty acid, the C-1 to C-6 carbon atoms on the α- and β-acyl positions were differentiated. The unsaturated carbon atoms in the α- and β-acyl chains were also resolved into two signals except that of the C-11 olefinic carbon. Sandal (Santalum album) wood seed oil (a source of santalbic acid) was separated by silica chromatography into three fractions. The least polar fraction (7.2 wt%) contained TAG which had a random distribution of saturated and unsaturated fatty acids, of which oleic acid (69%) was the predominant component. The second fraction (3.8 wt%) contained santalbic acid (58%) and oleic acid (28%) together with some other normal fatty acids. Santalbic acid in this fraction was found in both the α- and β-acyl positions of the glycerol “backbone”. The most polar fraction (89 wt%) consisted of TAG containing santalbic acid only. The distribution of the various fatty acids on the glycerol “backbone” was supported by the results from the13C NMR spectroscopic analysis.

Ultrasound-assisted epoxidation reaction of long-chain unsaturated fatty esters

Abstract Ultrasound (20 kHz)-assisted epoxidation of unsaturated fatty esters with m-chloroperoxybenzoic acid (MCPBA) in water was successfully carried out in less than 30 min. Epoxidation of unsaturated fatty esters containing an internal ethylenic system was more readily accomplished than with substrates containing a terminal ethylenic bond. The rate of epoxidation of the same unsaturated fatty esters using magnesium monoperoxyphthalate in aqueous ethanol was much slower than reactions with MCPBA.

13C-NMR studies of polyunsaturated triacylglycerols of type AAA and mixed triacylglycerols containing saturated, acetylenic and ethylenic acyl groups

Abstract The 13C-NMR spectroscopic properties of eight triacylglycerols of type AAA containing polyunsaturated fatty acids, viz. 18:2(9Z,12Z) 18:2(9Z,12E), 18:2(9E,12Z) 18:2(9E,12E), 18:2(8E,12Z) 18:3(9Z,12Z,15Z) 20:3(5Z,11Z,14Z) and 20:4(5Z,11Z,14Z,17Z), have been studied. From the carbon shift values of the various carbon atoms, it is possible to confirm the position and geometry of the unsaturated centers in the acyl chains. Many of the similarly positioned carbon atoms from C-1 to C-14, whether arising from methylene or ethylenic carbon nuclei in the α- and β-acyl chains, are resolved to give characteristic pairs of signals. By making use of the differences in shift values for carbon atoms of similarly positioned carbon atoms in the α- and β-acyl chains, the assignment of the chemical shifts of the various nuclei is readily achieved. A further 21 mixed triacylglycerols containing a mixture of saturated (18:0) acetylenic [18:1(5A), 18:1(6A) or 18:1(7A)], mono-ethylenic [18:1(5Z) 18:1(6Z), 18:1(7Z), 18:1(7E) or 18:1(9Z)] and diethylenic [18:2(9Z,12Z)] acyl groups have been studied. The nature (type of unsaturation and position of unsaturated centers) and distribution of the various acyl groups on the glycerol ‘backbone’ of these mixed triacyl glycerols are determined by this technique.