Α-Linolenic acid

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α-Linolenic acid
ALAnumbering.svg
Linolenic-acid-3D-vdW.png
Names
Preferred IUPAC name
(9Z,12Z,15Z)-Octadeca-9,12,15-trienoic acid [1]
Other names
ALA; LNA; Linolenic acid; cis,cis,cis-9,12,15-Octadecatrienoic acid; (9Z,12Z,15Z)-9,12,15-Octadecatrienoic acid; Industrene 120
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.006.669 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
UNII
  • InChI=1S/C18H30O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18(19)20/h3-4,6-7,9-10H,2,5,8,11-17H2,1H3,(H,19,20)/b4-3-,7-6-,10-9- Yes check.svgY
    Key: DTOSIQBPPRVQHS-PDBXOOCHSA-N Yes check.svgY
  • InChI=1/C18H30O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18(19)20/h3-4,6-7,9-10H,2,5,8,11-17H2,1H3,(H,19,20)/b4-3-,7-6-,10-9-
    Key: DTOSIQBPPRVQHS-PDBXOOCHBH
  • O=C(O)CCCCCCC\C=C/C\C=C/C\C=C/CC
  • CC/C=C\C/C=C\C/C=C\CCCCCCCC(=O)O
Properties
C18H30O2
Molar mass 278.436 g·mol−1
Density 0.9164 g/cm3
Melting point −11 °C (12 °F; 262 K) [2]
Boiling point 232 °C (450 °F; 505 K) at 17.0 mmHg [2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

α-Linolenic acid, also known as alpha-linolenic acid (ALA) (from Greek alpha meaning "first" and linon meaning flax), is an n−3, or omega-3, essential fatty acid. ALA is found in many seeds and oils, including flaxseed, walnuts, chia, hemp, and many common vegetable oils.

In terms of its structure, it is named all-cis-9,12,15-octadecatrienoic acid. [3] In physiological literature, it is listed by its lipid number, 18:3 (n−3). It is a carboxylic acid with an 18-carbon chain and three cis double bonds. The first double bond is located at the third carbon from the methyl end of the fatty acid chain, known as the n end. Thus, α-linolenic acid is a polyunsaturated n−3 (omega-3) fatty acid. It is a regioisomer of gamma-linolenic acid (GLA), an 18:3 (n−6) fatty acid (i.e., a polyunsaturated omega-6 fatty acid with three double bonds).

Etymology

The word linolenic is an irregular derivation from linoleic, which itself is derived from the Greek word linon (flax). Oleic means "of or relating to oleic acid" because saturating an omega-6 double bond of linoleic acid produces oleic acid. Similarly saturating one of linolenic acid's double bonds produces linoleic acid.

Dietary sources

Seed oils are the richest sources of α-linolenic acid, notably those of hempseed, chia, perilla, flaxseed (linseed oil), rapeseed (canola), and soybeans. α-Linolenic acid is also obtained from the thylakoid membranes in the leaves of Pisum sativum (pea leaves). [4] Plant chloroplasts consisting of more than 95 percent of photosynthetic thylakoid membranes are highly fluid due to the large abundance of ALA, evident as sharp resonances in high-resolution carbon-13 NMR spectra. [5] Some studies state that ALA remains stable during processing and cooking. [6] However, other studies state that ALA might not be suitable for baking as it will polymerize with itself, a feature exploited in paint with transition metal catalysts. Some ALA may also oxidize at baking temperatures. [7] ALA percentages in the table below refer to the oils extracted from each item.

Common nameAlternate nameLinnaean name% ALA(of oil)ref.
Chia chia sageSalvia hispanica64% [8]
Kiwifruit seedsChinese gooseberryActinidia chinensis62% [8]
Perilla shisoPerilla frutescens58% [8]
Flax linseedLinum usitatissimum55% [8]
Lingonberry cowberryVaccinium vitis-idaea49% [8]
Camelina camelinaCamelina sativa37% [9]
Purslane portulacaPortulaca oleracea35% [8]
Cuckoo flower mayflowerCardamine pratensis35% [10]
Cranberry American cranberryVaccinium macrocarpon35% [10]
Sea buckthorn seaberryHippophae rhamnoides L.32% [11]
Raspberry raspberryRubus idaeus31% [10]
Blueberry bilberry Vaccinium myrtillus L.29% [10]
Hemp cannabisCannabis sativa20% [8]
Walnut English walnut / Persian walnutJuglans regia10.4% [12]
Rapeseed canolaBrassica napus10% [3]
Soybean soyaGlycine max8% [3]
 average value

Metabolism

Flax is a rich source of a-linolenic acid. Bekladnadsvaxter, Linum usitatissimum, Nordisk familjebok.png
Flax is a rich source of α-linolenic acid.

α-Linolenic acid can be obtained by humans only through their diets. Humans lack the desaturase enzymes required for processing stearic acid into A-linoleic acid or other unsaturated fatty acids.

Dietary α-linolenic acid is metabolized to stearidonic acid, a precursor to a collection of polyunsaturated 20-, 22-, 24-, etc fatty acids (eicosatetraenoic acid, eicosapentaenoic acid, docosapentaenoic acid, tetracosapentaenoic acid, 6,9,12,15,18,21-tetracosahexaenoic acid, docosahexaenoic acid). [13] Because the efficacy of n−3 long-chain polyunsaturated fatty acid (LC-PUFA) synthesis decreases down the cascade of α-linolenic acid conversion, DHA synthesis from α-linolenic acid is even more restricted than that of EPA. [14] Conversion of ALA to DHA is higher in women than in men. [15]

Stability and hydrogenation

Compared to many other oils, α-linolenic acid is more susceptible to oxidation. It becomes rancid more quickly in air. Oxidative instability of α-linolenic acid is one reason why producers choose to partially hydrogenate oils containing α-linolenic acid, such as soybean oil. [16] Soybeans are the largest source of edible oils in the U.S., and, as of a 2007 study, 40% of soy oil production was partially hydrogenated. [17]

Hydrogenation of ALA-containing fats can introduce trans fats. Consumers are increasingly avoiding products that contain trans fats, and governments have begun to ban trans fats in food products, including the US government as of May 2018. [18] These regulations and market pressures have spurred the development of soybeans low in α-linolenic acid. These new soybean varieties yield a more stable oil that often do not require hydrogenation for many applications. [19]

Health

ALA consumption is associated with a lower risk of cardiovascular disease and a reduced risk of fatal coronary heart disease. [20] [21] Dietary ALA intake can improve lipid profiles by decreasing triglycerides, total cholesterol, high-density lipoprotein, and low-density lipoprotein. [22] A 2021 review found that ALA intake is associated with a reduced risk of mortality from all causes, cardiovascular disease, and coronary heart disease but a slightly higher risk of cancer mortality. [23]

History

In 1887, linolenic acid was discovered and named by the Austrian chemist Karl Hazura of the Imperial Technical Institute at Vienna (although he did not separate its isomers). [24] α-Linolenic acid was first isolated in pure form in 1909 by Ernst Erdmann and F. Bedford of the University of Halle an der Saale, Germany, [25] and by Adolf Rollett of the Universität Berlin, Germany, [26] working independently, as cited in J. W. McCutcheon's synthesis in 1942, [27] and referred to in Green and Hilditch's 1930s survey. [28] It was first artificially synthesized in 1995 from C6 homologating agents. A Wittig reaction of the phosphonium salt of [(Z-Z)-nona-3,6-dien-1-yl]triphenylphosphonium bromide with methyl 9-oxononanoate, followed by saponification, completed the synthesis. [29]

See also

Related Research Articles

<span class="mw-page-title-main">Fat</span> Esters of fatty acid or triglycerides

In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food.

<span class="mw-page-title-main">Lipid</span> Substance of biological origin that is soluble in nonpolar solvents

Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins, monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing energy, signaling, and acting as structural components of cell membranes. Lipids have applications in the cosmetic and food industries, and in nanotechnology.

Omega−3 fatty acids, also called omega−3 oils, ω−3 fatty acids or n−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond three atoms away from the terminal methyl group in their chemical structure. They are widely distributed in nature, being important constituents of animal lipid metabolism, and they play an important role in the human diet and in human physiology. The three types of omega−3 fatty acids involved in human physiology are α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ALA can be found in plants, while DHA and EPA are found in algae and fish. Marine algae and phytoplankton are primary sources of omega−3 fatty acids. DHA and EPA accumulate in fish that eat these algae. Common sources of plant oils containing ALA include walnuts, edible seeds, and flaxseeds as well as hempseed oil, while sources of EPA and DHA include fish and fish oils, and algae oil.

Essential fatty acids, or EFAs, are fatty acids that are required by humans and other animals for normal physiological function that cannot be synthesized in the body.⁠ As they are not synthesized in the body, the essential fatty acids – alpha-linolenic acid (ALA) and linoleic acid – must be obtained from food or from a dietary supplement. Essential fatty acids are needed for various cellular metabolic processes and for the maintenance and function of tissues and organs. These fatty acids also are precursors to vitamins, cofactors, and derivatives, including prostaglandins, leukotrienes, thromboxanes, lipoxins, and others.

<span class="mw-page-title-main">Linseed oil</span> Oil obtained from the dried, ripened seeds of the flax plant

Linseed oil, also known as flaxseed oil or flax oil, is a colourless to yellowish oil obtained from the dried, ripened seeds of the flax plant. The oil is obtained by pressing, sometimes followed by solvent extraction.

<span class="mw-page-title-main">Omega-6 fatty acid</span> Fatty acids where the sixth bond is double

Omega−6 fatty acids are a family of polyunsaturated fatty acids that have in common a final carbon-carbon double bond in the n−6 position, that is, the sixth bond, counting from the methyl end.

γ-Linolenic acid or GLA is an n−6, or omega-6, fatty acid found primarily in seed oils. When acting on GLA, arachidonate 5-lipoxygenase produces no leukotrienes and the conversion by the enzyme of arachidonic acid to leukotrienes is inhibited.

Linoleic acid (LA) is an organic compound with the formula HOOC(CH2)7CH=CHCH2CH=CH(CH2)4CH3. Both alkene groups are cis. It is a fatty acid sometimes denoted 18:2 (n−6) or 18:2 cis-9,12. A linoleate is a salt or ester of this acid.

In biochemistry and nutrition, a monounsaturated fat is a fat that contains a monounsaturated fatty acid (MUFA), a subclass of fatty acid characterized by having a double bond in the fatty acid chain with all of the remaining carbon atoms being single-bonded. By contrast, polyunsaturated fatty acids (PUFAs) have more than one double bond.

<span class="mw-page-title-main">Eicosapentaenoic acid</span> Chemical compound

Eicosapentaenoic acid (EPA; also icosapentaenoic acid) is an omega−3 fatty acid. In physiological literature, it is given the name 20:5(n−3). It also has the trivial name timnodonic acid. In chemical structure, EPA is a carboxylic acid with a 20-carbon chain and five cis double bonds; the first double bond is located at the third carbon from the omega end.

<span class="mw-page-title-main">Soybean oil</span> Oil obtained from seeds of soya plant

Soybean oil is a vegetable oil extracted from the seeds of the soybean. It is one of the most widely consumed cooking oils and the second most consumed vegetable oil. As a drying oil, processed soybean oil is also used as a base for printing inks and oil paints.

<span class="mw-page-title-main">Polyunsaturated fat</span> Type of fatty acid defined by molecular bonds

In biochemistry and nutrition, a polyunsaturated fat is a fat that contains a polyunsaturated fatty acid, which is a subclass of fatty acid characterized by a backbone with two or more carbon–carbon double bonds. Some polyunsaturated fatty acids are essentials. Polyunsaturated fatty acids are precursors to and are derived from polyunsaturated fats, which include drying oils.

Fatty acid desaturases are a family of enzymes that convert saturated fatty acids into unsaturated fatty acids and polyunsaturated fatty acids. For the common fatty acids of the C18 variety, desaturases convert stearic acid into oleic acid. Other desaturases convert oleic acid into linoleic acid, which is the precursor to alpha-linolenic acid, gamma-linolenic acid, and eicosatrienoic acid.

<span class="mw-page-title-main">Essential fatty acid interactions</span>

There is a wide variety of fatty acids found in nature. Two classes of fatty acids are considered essential, the omega-3 and omega-6 fatty acids. Essential fatty acids are necessary for humans but cannot be synthesized by the body and must therefore be obtained from food. Omega-3 and omega-6 are used in some cellular signaling pathways and are involved in mediating inflammation, protein synthesis, and metabolic pathways in the human body.

α-Eleostearic acid Chemical compound

α-Eleostearic acid or (9Z,11E,13E)-octadeca-9,11,13-trienoic acid, is an organic compound, a conjugated fatty acid and one of the isomers of octadecatrienoic acid. It is often called simply eleostearic acid although there is also a β-eleostearic acid. Its high degree of unsaturation gives tung oil its properties as a drying oil.

<span class="mw-page-title-main">Punicic acid</span> Chemical compound

Punicic acid is a polyunsaturated fatty acid, 18:3 cis-9, trans-11, cis-13. It is named for the pomegranate,, and is obtained from pomegranate seed oil. It has also been found in the seed oils of snake gourd.

<span class="mw-page-title-main">Linoleoyl-CoA desaturase</span> Class of enzymes

Linoleoyl-CoA desaturase (also Delta 6 desaturase, EC 1.14.19.3) is an enzyme that converts between types of fatty acids, which are essential nutrients in the human body. The enzyme mainly catalyzes the chemical reaction

α-Parinaric acid Chemical compound

α-Parinaric acid is a conjugated polyunsaturated fatty acid. Discovered by Tsujimoto and Koyanagi in 1933, it contains 18 carbon atoms and 4 conjugated double bonds. The repeating single bond-double bond structure of α-parinaric acid distinguishes it structurally and chemically from the usual "methylene-interrupted" arrangement of polyunsaturated fatty acids that have double-bonds and single bonds separated by a methylene unit (−CH2−). Because of the fluorescent properties conferred by the alternating double bonds, α-parinaric acid is commonly used as a molecular probe in the study of biomembranes.

Only two essential fatty acids are known to be essential for humans: alpha-linolenic acid and linoleic acid. The biological effects of the ω-3 and ω-6 fatty acids are mediated by their mutual interactions. Closely related, these fatty acids act as competing substrates for the same enzymes. The biological effects of the ω-3 and ω-6 fatty acids are largely mediated by essential fatty acid interactions. The proportion of omega-3 to omega-6 fatty acids in a diet may have metabolic consequences. Unlike omega-3 fatty acids and omega-6 fatty acids, omega-9 fatty acids are not classed as essential fatty acids because they can be created by the human body from monounsaturated and saturated fatty acids, and are therefore not essential in the diet.

<span class="mw-page-title-main">Cooking oil</span> Oil consumed by humans, of vegetable or animal origin

Cooking oil is a plant or animal liquid fat used in frying, baking, and other types of cooking. Oil allows higher cooking temperatures than water, making cooking faster and more flavorful, while likewise distributing heat, reducing burning and uneven cooking. It sometimes imparts its own flavor. Cooking oil is also used in food preparation and flavoring not involving heat, such as salad dressings and bread dips.

References

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  25. See:
    • Erdmann E, Bedford F (1909). "Über die im Leinöl enthaltene Linolensäure" [On linolenic acid [that's] contained in flax oil]. Berichte der Deutschen Chemischen Gesellschaft (in German). 42: 1324–1333. doi:10.1002/cber.190904201217. Archived from the original on 26 January 2021. Retrieved 31 October 2020. On p. 1329 they distinguish one of the isomers of linolenic acid: "Wir bezeichnen diese in Leinöl vorhandene Linolensäure, welche das feste Hexabromid liefert, zum Unterschied von einer später zu erwähnenden Isomeren als α-Linolensäure." (We designate this linolenic acid, which the solid hexabromide [of linolenic acid] provides, as α-linolenic acid in order to distinguish [it] from an isomer [that will be] mentioned later.)
    • Erdmann E, Bedford F, Raspe F (1909). "Konstitution der Linolensäure" [Structure of linolenic acid]. Berichte der Deutschen Chemischen Gesellschaft (in German). 42: 1334–1346. doi:10.1002/cber.190904201218. Archived from the original on 1 February 2021. Retrieved 31 October 2020. The structure of α-linolenic acid appears on p. 1343.
  26. Rollett, A. (1909). "Zur Kenntnis der Linolensäure und des Leinöls" [[Contribution to our] knowledge of linolenic acid and flax oil]. Zeitschrift für physiologische Chemie. 62 (5–6): 422–431. doi:10.1515/bchm2.1909.62.5-6.422. Archived from the original on 18 March 2020. Retrieved 1 July 2019.
  27. J. W. McCutcheon (1955). "Linolenic acid". Organic Syntheses ; Collected Volumes, vol. 3, p. 351.
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  29. Sandri, J., Viala, J. (1995). "Direct preparation of (Z,Z)-1,4-dienic units with a new C6 homologating agent: synthesis of α-linolenic acid". Synthesis . 1995 (3): 271–275. doi:10.1055/s-1995-3906. S2CID   196696819.