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α-Linolenic acid

Names
Preferred IUPAC name (9Z,12Z,15Z)-Octadeca-9,12,15-trienoic acid
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
CAS Number	463-40-1
3D model (JSmol)	Interactive image Interactive image
ChEBI	CHEBI:27432
ChEMBL	ChEMBL8739
ChemSpider	4444437
DrugBank	DB00132
ECHA InfoCard	100.006.669
IUPHAR/BPS	1049
PubChem CID	5280934
UNII	0RBV727H71
CompTox Dashboard (EPA)	DTXSID7025506
InChI 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-Key: DTOSIQBPPRVQHS-PDBXOOCHSA-N 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
SMILES 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
Chemical formula	C18H30O2
Molar mass	278.436 g·mol
Density	0.9164 g/cm
Melting point	−11 °C (12 °F; 262 K)
Boiling point	232 °C (450 °F; 505 K) at 17.0 mmHg
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is  ?) Infobox references

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. 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). 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. Some studies state that ALA remains stable during processing and cooking. 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. ALA percentages in the table below refer to the oils extracted from each item.

Metabolism

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). 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. Conversion of ALA to DHA is higher in women than in men.

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. 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.

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. 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.

Health

ALA consumption is associated with a lower risk of cardiovascular disease and a reduced risk of fatal coronary heart disease. Dietary ALA intake can improve lipid profiles by decreasing triglycerides, total cholesterol, high-density lipoprotein, and low-density lipoprotein. 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.

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). 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, and by Adolf Rollett of the Universität Berlin, Germany, working independently, as cited in J. W. McCutcheon's synthesis in 1942, and referred to in Green and Hilditch's 1930s survey. It was first artificially synthesized in 1995 from C6 homologating agents. A Wittig reaction of the phosphonium salt of triphenylphosphonium bromide with methyl 9-oxononanoate, followed by saponification, completed the synthesis.

See also

• Canola oil
• Flax seed oil
• γ-Linolenic acid
• Drying oil
• Essential fatty acid
• List of n−3 fatty acids
• Essential nutrient
• Wheat germ oil

References

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24. Hazura K (1887). "Über trocknende Ölsäuren IV. Abhandlung" [On drying oily acids 4th paper]. Monatshefte für Chemie (in German). 8: 260–270. doi:10.1007/BF01510049. S2CID 197767239. Archived from the original on 18 January 2021. Retrieved 1 November 2020. Linolenic acid is named on p. 265: "Für die Säure C₁₈H₃₂O₂ schlage ich den Namen Linolsäure, für die Säure C₁₈H₃₀O₂ den Namen Linolensäure vor." (For the acid C₁₈H₃₂O₂ I suggest the name "linolic acid"; for the acid C₁₈H₃₀O₂ the name "linolenic acid".) Linolenic acid is discussed on pp. 265-268.
25. See:
    • Erdmann E, Bedford F (1909). "Über die im Leinöl enthaltene Linolensäure" [On linolenic acid 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 provides, as α-linolenic acid in order to distinguish from an isomer 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.
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• Fatty acids
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