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

Isolation of a series of fatty acid components of Ongokea gore seed (Isano) oil and their detailed structural analysis

The total oil production capacity of isano oil is estimated at about 10,000 tons annually. Previous studies of this oil revealed that it is rich in fatty acids including a conjugated diyne moiety. This makes isano oil an excellent candidate for sustainable applications development. However, only a few of its fatty acids have been isolated and identified so far. In this study, we have reinvestigated this oil by characterizing its physicochemical properties and isolating several of its fatty acids as ethyl esters for their detailed structural analysis and identification. Six ethyl esters of fatty acids constituting isanic oil were isolated by flash column chromatography and semipreparative HPLC. The detailed structural analysis of these fatty acid esters by infrared, high resolution, mass spectroscopy, and nuclear magnetic resonance (1-D and 2-D) allowed determining unequivocally their chemical structure. The main fatty acid component of the oil (35.7 %) was identified as isanic acid. Four minor acids were found to possess also two conjugated triple bonds, while the sixth fatty acid does not contain carbon-carbon triple bonds nor double bonds but possessed a cis epoxide function. Results obtained in this study are currently being used to explore potential applications of isano oil.

Atkamine: a new pyrroloiminoquinone scaffold from the cold water Aleutian Islands Latrunculia sponge

A new pyrroloiminoquinone alkaloid, named atkamine, with an unusual scaffold was discovered from a cold, deep water Alaskan sponge Latrunculia sp. collected from the Aleutian Islands. Olefin metathesis was utilized to determine the location of the double bond in the hydrocarbon chain. The absolute configuration was determined by using computational approaches combing with the ECD (electronic circular dichroism) spectroscopy.

Geometrical trans Lipid Isomers: A New Target for Lipidomics

Evidence that lipids play different roles in the biological environment, particularly in dealing with metabolic regulation and cell signaling, has led to a growing interest in these molecules, and nowadays the research field of lipid structures and functions is called lipidomics. The term describes diverse research areas, from mapping the entire spectrum of lipids in organisms to describing the function and metabolism of individual lipids. Recent investigations on geometrical trans isomers of fatty acid derivatives, which have the double bonds in the same position as the natural compounds but with the trans instead of the naturally occurring cis geometry, highlighted these compounds as a new target for lipidomics. In addition to the identification of their structures and functions, research in a multidisciplinary context aims at understanding the biochemical significance of cis and trans lipid geometry, and a chemical biology approach can be envisaged to explore the role of the geometry change as either an alteration or a signal that can perturb a biological system and induce a cellular response.

Synthesis of all-trans arachidonic acid and its effect on rabbit platelet aggregation

A simple and high-yielding method to convert natural all-cis PUFA derivatives to the corresponding all-trans geometrical isomers is described. The method is based on the thiyl radical-catalyzed cis-trans isomerization. The all-trans isomer of arachidonic acid was found to cause rabbit platelet aggregation at concentrations higher than 0.1 mM and inhibition of PAF-induced platelet aggregation in a concentration dependent manner with an IC(50) in the micromolar range.

Arachidonate geometrical isomers generated by thiyl radicals: the relationship with trans lipids detected in biological samples

The presence of trans fatty acids in mammalians is attributed to exogenous sources; nevertheless, trans isomers could be easily formed by free radical-catalyzed isomerization processes in vivo. The isomerization of methyl arachidonate (all-cis isomer) catalyzed by thiyl radical is proposed as a methodology applicable in biochemical laboratories, which produces mono- and di-trans isomers. Carbon-13 nuclear magnetic resonance spectroscopy shows that the carbon atom in position 15 is characteristic for each mono- and di-trans isomer. Antioxidants, such as alpha-tocopherol and all-trans-retinol acetate, inhibited the isomerization process. Trans phospholipids are formed in erythrocyte membranes by exposing blood to gamma-irradiation in the presence of thiols, which is in contradiction with the known role of these compounds as radioprotectors. Trans isomers are also analyzed in tissues harvested from breast cancer patients and compared to the adipose breast tissue taken a few centimeters from the edge of the tumor from the same patient. This work is generally aimed at contributing to the debate on trans fatty acids and stimulating a reconsideration of the current view on the exclusive presence of cis double bonds in cell membranes by studying radical processes that could affect or protect this natural configuration.

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.

Detection of [U-13C]eicosapentaenoic acid in rat liver lipids using 13C nuclear magnetic resonance spectroscopy

Fatty acid carbons are well-resolved in 13C nuclear magnetic resonance (NMR) spectra of lipid extracts, but application of this methodology to the metabolism of 13C-labelled fatty acids has not yet been reported. In the present study, 13C NMR was used to monitor the presence of 98% [U-13C]eicosapentaenoic acid (EPA) in liver and carcass lipids 24 h after it had been injected into the stomach of a rat. Natural abundance 13C NMR spectra of liver total fatty acid extracts were obtained from four control rats for comparison. At 24 h post-injection, quantitative high resolution 13C NMR showed 13C enrichment in liver fatty acid extracts was present mainly at olefinic and at the n-1 to n-4 carbons, but 13C signal intensities for C-1 to C-4 of [U-13C]EPA were markedly reduced or absent. Small 13C resonances, possibly indicative of some 13C incorporation into docosahexaenoic acid and saturated or monounsaturated fatty acids, were present in spectra of liver fatty acids. Liver and carcass fatty acid composition was similar in both the controls and the EPA-injected rat, suggesting little accumulation of the injected [U-13C]EPA after 24 h. We conclude that the carbon-specific data provided by 13C NMR of lipid extracts may be useful in monitoring the fate of individual carbons during tracer studies using 13C-labelled fatty acids.

Effects of bis homoallylic and homoallylic hydroxyl substitution on the olefinic 13C resonance shifts in fatty acid methyl esters

Substitution of a hydroxyl group at the bis homoallylic position (OH group located three carbons away from the olefinic carbon) in C18 unsaturated fatty acid esters (FAE) induces a 0.73 +/- 0.05 ppm upfield and a 0.73 +/- 0.06 ppm downfield shift on the delta and epsilon olefinic 13C resonances relative to the unsubstituted FAE, respectively. If the hydroxyl group is located on the carboxyl side of the double bond of the bis homoallylic hydroxy fatty acid esters (BHAHFA), the olefinic resonances are uniformly shifted apart by [formula: see text] where delta delta dbu represents the absolute value of the double bond resonance separation in the unsubstituted FAE and 1.46 ppm is the sum of the absolute values of the delta and epsilon shift parameters. With hydroxyl substitution on the terminal methyl side of the double bond, the olefinic shift separation is equal to [formula: see text] In homoallylic (OH group located two carbons away from the olefinic carbon) substituted FAE the gamma and delta induced hydroxyl shifts for the cis double bond resonances are +3.08 and -4.63 ppm, respectively while the trans double bond parameters are +4.06 and -4.18 ppm, respectively. The double bond resonance separation in homoallylic hydroxy fatty acid esters (HAHFA) can be calculated from the formula [formula: see text] for cis and [formula: see text] for the trans case when the OH substitution is on the carboxyl side of the double bond. Conversely, when the OH resides on the terminal methyl side, the double bond shift separations for cis and trans isomers are [formula: see text] and [formula: see text] respectively.(ABSTRACT TRUNCATED AT 250 WORDS)