Rapid determination of double-bond positions in monoenoic fatty acids by periodate-permanganate oxidation

Tetramethylammonium hydroxide has been used in the extraction and pyrolysis methylation of the carboxylic acids produced by periodate-permanganate oxidation of monounsaturated fatty acid methyl esters. This modification of the von Rudloff procedure allows rapid determination of double-bond positions and analysis of mixtures of positional isomers of monoenoic fatty acids.     

The mass spectrometry of iso and anteiso monoenoic fatty acids

The normal, iso, and anteiso Δ⁸- and Δ⁹-17:1 fatty acid methyl esters were synthesized and their electron impact-induced fragmentation was studied by mass spectrometry. The mass spectra of the preterminal branched monoenoic fatty acid methyl esters present characteristic fragment ions, now understood to be indicative of the position of the methyl group. These fragment ions are in the iso compound m/e 227 [M-55]⁺, m/e 195 [M-87]⁺, and m/e 177 [M-105]⁺, while in the anteiso compound these fragments are shifted by 14 mass units to m/e 213, m/e 181, and m/e 163. The 15-D-iso Δ⁸- and Δ⁹-17:1 methyl esters were synthesized because the characteristic fragment ions in the methyl branched compounds indicated a key role of the tertiary hydrogen atom in the rearrangement process. A fragmentation mechanism consisting of a double bond migration triggered by the tertiary hydrogen and an allylic cleavage assuming a displacement mechanism is proposed.     

Determining double-bond positions in monoenoic 2-hydroxy fatty acids of glucosylceramides by gas chromatography-mass spectrometry

We applied a gas chromatography-mass spectrometry (GC-MS) method using dimethyl disulfide (DMDS) adducts and were able to determine the double-bond positions in monounsaturated 2-hydroxy fatty acids (2-HFA). 2-HFA methyl esters, prepared from the hydrolysate ofArabidopsis thaliana leaf glucosylceramides, were acetylated and methylthiolated. GC-MS analysis of the resulting DMDS adducts showed simple mass spectra with recognizable molecular ions and a series of key fragment ions indicating the original double-bond positions in the aliphatic chain. Based on this GC-MS elucidation, we confirmed thatArabidopsis leaf glucosylceramides have C₂₂, C₂₃, C₂₄, C₂₅, and C₂₆ chain length 2-HFA with monounsaturation, and all their double bonds are placed at the n−9 position. This procedure is simple, time efficient, and highly sensitive.     

Antioxidant effect of naturally occurring furan fatty acids on oxidation of linoleic acid in aqueous dispersion

Naturally occurring furan fatty acids were synthesized and their antioxidant activity has been studied during the oxidation of linoleic acid in the phosphate buffer, pH 6.9, in the dark. The extent of the oxidation was followed both by the accumulation of conjugated diene and by the measurement of the residual amounts of linoleic acid. The tetra-alkylsubstituted furan fatty acids were found to suppress the oxidation. The trialkylsubstituted compound also showed antioxidant activity, being about 50% as effective as the tetra-alkylsubstituted ones. The di-alkylsubstituted one revealed no significant activity. The antioxidant activity of furan fatty acids depended on the number of substituents on the furan ring. Therefore, a tetra-alkylsubstituted furan ring may be necessary for the antioxidant action of furan fatty acids. The tetra-alkylsubstituted furan fatty acids reduced 1,1-diphenyl-2-picrylhydrazyl, reacted with the peroxyl radical generated from the thermal decomposition of a radical initiator, 2,2′-azobis(2-amidinopropane)hydrochloride (AAPH), and also suppressed the AAPH-induced oxidation of linoleic acid, indicating that, by scavenging, the peroxyl radical furan fatty acids inhibit the oxidation.     

Desaturation of positional and geometric isomers of monoenoic fatty acids by microsomal preparations from rat liver

A range ofcis- andtrans-monoenoic fatty acids was tested as substrates for desaturation in microsomal preparations from rat liver.Trans-monoenoic acids were generally desaturated in the Δ9 position to the same extent as stearic acid. Acids with Δ7-trans- and Δ11-trans-olefinic unsaturation produced Δ7-trans,9-cis- and Δ9-cis,11-trans-conjugated dienoic acids, respectively, but the Δ8-trans- and Δ10-trans-monoenoic acids did not give Δ8,9- or Δ9,10-allenes. Of thecis-monoenoic acids examined, only those with double bonds at or beyond the Δ14 position gave any measurable Δ9 desaturation. When Δ9 desaturation of long chain saturated acids was inhibited by adding sterculic acid, these saturated acids were desaturated at the Δ5 and Δ6 positions. Many of the monoenoic acids tested were also desaturated at the Δ5 and/or Δ6 positions, although the percentage conversions were always low. Δ9-cis,11-trans-, Δ9-cis,12-trans- and Δ9-cis,13-trans-dienoic acids, produced in situ by Δ9 desaturation of the corresponding monoenoic acids, were extensively desaturated in the Δ6 position. These results are discussed in terms of: (a) the various models proposed to explain the substrate specificities of the desaturases, and (b) the metabolism of unnatural fatty acids ingested from dietary sources.     

Hydrogenation of cyclopropenoid fatty acids occurring in cottonseed oil

The hydrogenation of cyclopropenoid acids and their relative reactivities during hydrogenation as compared to linoleic and oleic acids were examined. Pure methyl sterculate and purifiedSterculia foetida oil and its methyl esters, which have a cyclopropene content more than 60 times that of cottonseed oil, were used for the hydrogenation experiments. Nickel, palladium and platinum catalysts were used. The effect of temperature and type of catalyst were demonstrated in a series of hydrogenation experiments of safflower andS. foetida oil mixtures, and methyl oleate and methyl dihydrosterculate mixtures. Partial hydrogenation of methyl sterculate formed as many as twenty compounds in addition to the cyclopropenoid derivatives. Most of these compounds were monounsaturated. The cyclopropene group hydrogenated very readily compared to the 9,12-diene system in linoleate. The cyclopropane group obtained by hydrogenating the cyclopropenoid acids group was quite resistant to further attack by hydrogen and nickel catalyst had little effect. With palladium catalyst, a temperature of 180 C was necessary for the reaction to go to completion. Platinum in acetic acid was a good system for hydrogenolysis of the cyclopropane group at 80 C. Retired.     

Autoxidation rates of 5-olefinic monoenoic and denoic fatty acids from sea urchin lipids and meadoefoam oils

Autoxidation rates of the 5-olefinic monoenoic and dienoic fatty acids from sea urchin lipids and meadow-foam oils were compared with those of normal monoenoic and dienoic fatty acids by gas-liquid Chromatographic determination of the unoxidized fatty acid methyl esters remaining through the autoxidation period. The fatty acids are classified into five groups shown below according to the oxidation rate of their methyl esters: I 5-olefinic monoenoic acids (c5-18:l, c5-20:l and c5-22:1), II normal monoenoic acids (c9-18:l, cll-18:l, c9-20:1, cl3-20:l and cl3-22:l), III 5-olefinic dienoic acids (c5,cll-20:2, c5,cl3-20:2 and c5,cl3-22:2), IV 7-olefinic dienoic acids (c7,cl3-22:2 and c7,cl5-22:2) and V normal dienoic acids (c6,c9-18:2, c9,cl2-18:2 and cll,cl4-20:2). The oxidation rates of these groups increased during autoxidation in order from I to V. These results show that the 5-olefinic monoenoic and dienoic acids are more stable to autoxidation than the normal monoenoic and dienoic acids, respectively. The higher stabilities of the 5-olefinic monoenoic and dienoic acids in organisms are shown from these results.     

Studies on the inhibition of the desaturases by cyclopropenoid fatty acids

Unwashed rat liver microsomes were used to study the inhibition of the Δ⁶ and Δ⁹ desaturases by cyclopropenoid fatty acids with the ring structure about the 9,10 or 6,7 carbon atoms. The 9,10 cyclopropenoid acid (sterculic acid) is shown to be an effective inhibitor of only Δ⁹ desaturase and then only in the presence of MgCl₂ and coenzyme A (prepresence of MgCl₂ and coenzyme A (presumably due to the formation of sterculoyl-CoA). Two 6,7 cyclopropenoid acids of different chain lengths showed no marked inhibition of either the Δ⁶ or Δ⁹ desaturase. By the use of [³H]-sterculic acid, it has been shown that under conditions of high inhibition of the Δ⁹ desaturase the inhibitor is not covalently attached to the enzyme at any point. This disproves older ideas on the mechanism of inhibition that assumed reaction between the cyclopropenoid ring and sulphydryl groups on the enzymes. Cyclopropenoid fatty acids are named according to the number of carbon atoms in the chain; thus sterculic acid is a C₁₈ cyclopropenoid fatty acid.     

Serum apolipoproteins B and A-I and naturally occurring fatty liver in dairy cows

Serum lipids and apolipoprotein (apo) B and A-I concentrations were determined in 164 dairy cows which had undergone liver biopsy in early lactation. The animals were divided into groups according to fatty liver severity on the basis of hepatic triglyceride content. The serum free fatty acid (FFA) concentration was higher in cows that developed fatty livers than in normal cows, and it correlated highly with liver triglycerides. Serum total cholesterol and triglyceride levels did not correlate with hepatic triglycerides. Both apo B and apo A-I levels were significantly decreased in fatty liver cows. In particular, apo B levels showed a strongly negative correlation with liver triglycerides. The present results suggest that hepatic apolipoprotein synthesis is impeded in fatty liver cows.     

The fatty acid composition of small and large naturally occurring milk fat globules

Native milk fat globules of various mean diameters, ranging from d₄₃ = 1.5 to 7.3 μm, were obtained using microfiltration of raw whole milk acquired in winter and spring. After total lipid extraction, fatty acid composition was characterized by methyl and butyl ester analysis using gas chromatography. The oleic and linoleic acid content of milk obtained in winter increased with fat globule size, whereas myristic and palmitic acid decreased. There was significantly more lauric, myristic and palmitoleic acid, and less stearic acid in small fat globules compared to large fat globules in milk obtained in both winter and spring. The relative content of oleic and linoleic acids were found to depend on fat globule size and season. Results are interpreted on the basis of the relative content of milk fat globule membrane depending on fat globule size, and on consequences of compositional variations on milk fat globule melting behavior.     

The regiospecific position of 18∶1 cis and trans monoenoic fatty acids in milk fat triacylglycerols

TAG of butterfat were fractionated according to the type and degree of unsaturation into six fractions by silver-ion HPLC. The fractions containing TAG with either cis-or trans-monoenoic FA were collected and fractionated further by reversed-phase HPLC to obtain fractions containing cis TAG of ACN:DB (acyl carbon number:double bonds) 48∶1, 50∶1, and 52∶1 as well as trans 48∶1, 50∶1, and 52∶1. The FA compositions of these fractions were elucidated by GC. The MW distribution of each fraction was determined by ammonia negative-ion CI-MS. Each of the [M-H]⁻ parent ions was fractionated further by collision-induced dissociation with argon, which gave information on the location of cis-and trans-FA between the primary and secondary positions of TAG. The results suggest that the sn-positions of the monoenoic cis-and trans-FA depend on the two other FA present in the molecule. With 14∶0 FA in the TAG molecule, the 18∶1 FA in the sn-2 position are mostly present as cis-isomers. When there is no 14∶0 in the TAG molecule, the trans-18∶1 isomers seem to be more common in the sn-2 position. Also when other long-chain FA are present, the trans-isomers are more likely to be located in the secondary (sn-2) position.     

Triacylglycerols of winter butterfat containing configurational isomers of monoenoic fatty acyl residues. I. Disaturated monoenoic triacylglycerols

The triacylglycerols of winter butterfat were fractionated according to the type and degree of unsaturation into six fractions by silver ion high-performance liquid chromatography (Ag-HPLC). The acyl carbon number distribution of the triacylglycerols in each fraction was elucidated by reversed-phase HPLC and mass spectrometry (MS). The MS analysis of each fraction gave deprotonated triacylglycerol [M - H]⁻ ions which were produced by chemical ionization with ammonia. The daughter spectrum of each of the [M - H]⁻ ions provided information on its fatty acid constituents. Successful fractionation of triacylglycerols differing in the configuration of one fatty acyl residue by Ag-HPLC was important because geometrical isomers could not be distinguished by the MS system used. In addition to the fatty acid compositions, reversed-phase HPLC analysis demonstrated the purity of the collected fractions: molecules having acis-trans difference were separated nearly to the baseline. Triacylglycerols differing in the configuration of one fatty acyl residue were not equally distributed in relation to their acyl carbon numbers. This indicates that during the biosynthesis of triacylglycerols,cis- andtrans-fatty acids are processed differently. Although the fatty acid compositions of the corresponding molecular weight species of disaturatedtrans- and disaturatedcis-monoenoic triacylglycerols were similar, there may be differences in the amounts of different fatty acid combinations or in the distribution of fatty acids between the primary and secondary glycerol positions. In addition to the main components, it was possible to analyze minor triacylglycerols, such as molecules containing one odd-chain fatty acid, by the MS system used.     

Two novel naturally occurring α-methoxy acids from the phospholipids of two caribbean sponges

The novel (5Z)-2-methoxy-5-hexadecenoic acid (1) was identified in the phospholipids of the spongeTethya crypta while the also novel acid (6Z)-2-methoxy-6-hexadecenoic acid (2) was found in the phospholipids of the Caribbean spongeSpheciospongia cuspidifera. The methoxy-fatty acids were mainly associated with phosphatidylethanolamine. The double bond positions were determined by gas chromatography/mass spectrometry on the corresponding dimethyl-disulfide adducts and the double bond stereochemistry was ascertained by gas chromatography/Fourier transform infrared spectroscopy. The fatty acid composition of the two sponges is reported.     

Behavioral responses of western corn rootworm larvae to naturally occurring and synthetic hydroxamic acids

Hydroxamic acids have been shown to be toxic to many pest insects and pathogens. In this study, the behavioral responses of western corn rootworm larvae to naturally occurring and synthetic hydroxamic acids were investigated. In a choice test between corn roots treated with hydroxamic acids and roots treated with distilled water (control), western corn rootworm larvae chose to burrow into the control roots significantly more often than compoundtreated roots. In addition, when corn roots were treated with different hydroxamic acids in a designed searching-behavior test, neonate larvae of western corn rootworm responded by significantly reducing the number of turns, while the area searched and locomotor rate significantly increased. The responses were dependent on the concentrations of the test compounds. These results suggested that hydroxamic acids were acting as behavior-modifying and possibly feeding-deterrent chemicals.     

Tuna fatty acids: I. initial studies on the composition of the light and dark meats of bluefin tuna (Thunnus thynnus)-structural isomers of the monoenoic fatty acids

Bluefin tuna (Thunnus thynnus) is consumed in substantial amounts by humans. However, little has been reported on the fatty acid composition of bluefin body oil and on the isomeric structures of the unsaturated fatty acids. Because of the probable nutritional significance of unsaturated fatty acids, the present work was undertaken as an introductory study of the composition and structure of the fatty acids of tuna. The fatty acid composition of the light and dark meats from three bluefin tuna was determined by gas-liquid chromatography. A wide variety of saturated and polyunsaturated fatty acids were present in the oil from the meat of these speciments. the monoemoic fatty acid fraction, which comprises 34% of the total fatty acids was isolated and the isomers determined. Isomers found werecis-9-hexadecenoic acid,cis-9-octadecenoic acid,cis-11-octadecenoic acid,cis-9-eicosenoic acid,cis-11-eicosenoic acid,cis-11-docosenoic acid, andcis-13-docosenoic acid. Division of Industrial Research, U.S. Fish and Wildlife Service, Department of the Interior.     

Sponge fatty acids. 3. Occurrence of series of n−7 monoenoic andiso-5,9 dienoic long-chain fatty acids in the phospholipids of the marine spongeCinachyrella aff.schulzei keller

The fatty acid composition of phospholipids from the New Caledonian spongeCinachyrella aff.schulzei Keller was studied. More than 60 fatty acids were identified as methyl esters andN-acyl pyrrolidides by gas chromatography and gas chromatography/mass spectrometry. Two isoprenoid fatty acids also were shown to be present, namely 4,8,12-trimethyltridecanoic and 5,9,13-trimethyltetradecanoic acids. The unusual 6-tetradecenoic, 6-pentadecenoic, 12-nonadecenoic and 26-methylheptacosanoic (iso-28∶0) acids were found for the first time in sponge phospholipids. A series of six n−7 monoenoic long-chain fatty acids (C₂₃ to C₂₈) were identified, including the rare 16-tricosenoic, 18-pentacosenoic and 21-octacosenoic acids. Fifteen fatty acids possessing the typical 5,9 dienoic moiety accounted for 30% of the total fatty acid mixture. Two new fatty acids were identified, namely 5(Z)-octacosenoic and 27-methyl-5(Z),9(Z)-octacosadienoic (iso-5,9-29∶2). Based on gas chromatography/Fourier transform infrared experiments, the double bonds were assigned the (Z) configuration. For part 2 of this series, see Reference 1.     

Fatty acid desaturase systems of hen liver and their inhibition by cyclopropene fatty acids

Hen liver preparations which desaturate stearic acid at the 9,10 position to form oleic acid have been found to desaturate other saturated fatty acids of carbon chain length from 12 to 20 and 22. The 9,10-monoenoic fatty acid of the same chain length as the substrate fatty acid is the major product formed. Minor amounts of the 10,11- and 11, 12-monoenoic acids are also formed. Maximum desaturation occurred with the C₁₄ fatty acid substrate and with the fatty acids C₁₇ and C₁₈, suggesting the presence of at least two desaturating systems. The cyclopropene fatty acids, sterculic and malvalic acids, inhibited the desaturation of all thefatty acids at the 9,10 position but desaturation at the 10,11 and 11, 12 positions was affected only slightly. The effect is not due to inhibition of the primary activating enzyme, the long chain acyl CoA synthetase. Sterculic acid is a more effective inhibitor than either malvalic acid or sterculyl alcohol, probably because these cyclopropene compounds do not block the desaturating site of the enzyme as completely as sterculic acid.