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α-Tocopherol

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α-Tocopherol (alpha-tocopherol) is a type of vitamin E. Its E number is "E307". Vitamin E exists in eight different forms, four tocopherols and four tocotrienols. All feature a chromane ring, with a hydroxyl group that can donate a hydrogen atom to reduce free radicals and a hydrophobic side chain, along with an aromatic ring is situated near the carbonyls in the fatty acyl chains of the phospholipid bilayer, allows for penetration into biological membranes.[2] It is found most in the membrane's non-raft domains, associated with omega-3 and 6 fatty acids, to partially prevent oxidation.[3] The most prevalent form, α-tocopherol, is involved in molecular, cellular, biochemical processes closely related to overall lipoprotein and lipid homeostasis. Compared to the others, α-tocopherol is preferentially absorbed and accumulated in humans.

α-Tocopherol[1]
Names
Preferred IUPAC name
(2R)-2,5,7,8-Tetramethyl-2-[(4R,8R)-4,8,12-trimethyltridecyl]-3,4-dihydro-2H-1-benzopyran-6-ol
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.000.375 Edit this at Wikidata
EC Number
  • 200-412-2
E number E307a (antioxidants, ...)
UNII
  • InChI=1S/C29H50O2/c1-20(2)12-9-13-21(3)14-10-15-22(4)16-11-18-29(8)19-17-26-25(7)27(30)23(5)24(6)28(26)31-29/h20-22,30H,9-19H2,1-8H3/t21-,22-,29-/m1/s1 checkY
    Key: GVJHHUAWPYXKBD-IEOSBIPESA-N checkY
  • InChI=1/C29H50O2/c1-20(2)12-9-13-21(3)14-10-15-22(4)16-11-18-29(8)19-17-26-25(7)27(30)23(5)24(6)28(26)31-29/h20-22,30H,9-19H2,1-8H3/t21-,22-,29-/m1/s1
    Key: GVJHHUAWPYXKBD-IEOSBIPEBS
  • Cc1c(O)c(C)c(CC[C@](CCC[C@@H](CCC[C@@H](CCCC(C)C)C)C)(C)O2)c2c1C
Properties
C29H50O2
Molar mass 430.71 g/mol
Appearance yellow-brown viscous liquid
Density 0.950 g/cm3
Melting point 2.5 to 3.5 °C (36.5 to 38.3 °F; 275.6 to 276.6 K)
Boiling point 200 to 220 °C (392 to 428 °F; 473 to 493 K) at 0.1 mmHg
insoluble
Solubility soluble in alcohol, ether, acetone, oils
Pharmacology
A11HA03 (WHO)
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
1
0
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Vitamin E is found in a variety of tissues, being lipid-soluble, and taken up by the body in a wide variety of ways. Ongoing research is believed to be "critical for manipulation of vitamin E homeostasis in a variety of oxidative stress-related disease conditions in humans."[4] One of these disease conditions is the α-tocopherol role in the use by malaria parasites to protect themselves from the highly oxidative environment in erythrocytes.[5] A second of these disease conditions is the α-tocopherol antioxidant properties' role cardiovascular heart disease. In preventing LDL (low-density lipoprotein) oxidation, it is able to decrease chances of atherosclerosis and arterial build-up.[6]

Synthesis

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To synthesize the ⍺-diastereomer selectively, tocol acetate is transformed to the naturally occurring, kinetically favored α-Tocopherol after being catalyzed by the lipase enzyme. This reaction occurs under biological conditions, commonly in the digestive system.[7]

Stereoisomers

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α-Tocopherol has three stereocenters, so it is a chiral molecule.[8] The eight stereoisomers of α-tocopherol differ in the configuration of these stereocenters. RRR-α-tocopherol is the natural one.[9] The older name of RRR-α-tocopherol is d-α-tocopherol, but this d/l naming should no longer be used, because whether l-α-tocopherol should mean SSS enantiomer or the SRR diastereomer is not clear, from historical reasons. The SRR may be named 2-epi-α-tocopherol, the diastereomeric mixture of RRR-α-tocopherol and 2-epi-α-tocopherol may be called 2-ambo-α-tocopherol (formerly named dl-α-tocopherol). The mixture of all eight diastereomers is called all-rac-α-tocopherol.[10] The α-Tocopherol is the most active diastereomer biologically, while being maintained at a high level in plasma and tissues of many different animal species.[11]

One IU of tocopherol is defined as 2⁄3 milligram of RRR-α-tocopherol (formerly named d-α-tocopherol). 1 IU is also defined as 0.9 mg of an equal mix of the eight stereoisomers, which is a racemic mixture, all-rac-α-tocopheryl acetate. This mix of stereoisomers is often called dl-α-tocopheryl acetate.[12] Starting with May 2016, the IU unit is made obsolete, such that 1 mg of "Vitamin E" is 1 mg of d-alpha-tocopherol or 2 mg of dl-alpha-tocopherol.[13]


References

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  1. ^ Merck Index, 11th Edition, 9931.
  2. ^ Burton, G. W.; Ingold, K. U. (1 June 1986). "Vitamin E: application of the principles of physical organic chemistry to the exploration of its structure and function". Accounts of Chemical Research. 19 (7): 194–201. doi:10.1021/ar00127a001.
  3. ^ Atkinson, Jeffrey; Harroun, Thad; Wassall, Stephen R.; Stillwell, William; Katsaras, John (May 2010). "The location and behavior of α‐tocopherol in membranes". Molecular Nutrition & Food Research. 54 (5): 641–651. doi:10.1002/mnfr.200900439.
  4. ^ Rigotti A (2007). "Absorption, transport, and tissue delivery of vitamin E". Molecular Aspects of Medicine. 28 (5–6): 423–36. doi:10.1016/j.mam.2007.01.002. PMID 17320165.
  5. ^ Shichiri M, Ishida N, Hagihara Y, Yoshida Y, Kume A, Suzuki H (2019). "Probucol induces the generation of lipid peroxidation products in erythrocytes and plasma of male cynomolgus macaques". Journal of Clinical Biochemistry and Nutrition. 64 (2): 129–142. doi:10.3164/jcbn.18-7. PMC 6436040. PMID 30936625.
  6. ^ Singh, U.; Devaraj, S.; Jialal, I. (21 August 2005). "VITAMIN E, OXIDATIVE STRESS, AND INFLAMMATION". Annual Review of Nutrition. 25 (1): 151–174. doi:10.1146/annurev.nutr.24.012003.132446.
  7. ^ Mizuguchi, Eisaku; Takemoto, Masumi; Achiwa, Kazuo (January 1993). "An enzyme-catalyzed synthesis of natural α-tocopherol". Tetrahedron: Asymmetry. 4 (9): 1961–1964. doi:10.1016/s0957-4166(00)82239-9.
  8. ^ Jensen SK, Lauridsen C (2007). "Alpha-tocopherol stereoisomers". Vitamins and Hormones. 76: 281–308. doi:10.1016/S0083-6729(07)76010-7. ISBN 9780123735928. PMID 17628178.
  9. ^ Brigelius-Flohé R, Traber MG (July 1999). "Vitamin E: function and metabolism". FASEB Journal. 13 (10): 1145–55. doi:10.1096/fasebj.13.10.1145. PMID 10385606. S2CID 7031925.
  10. ^ IUPAC Nomenclature of Tocopherols and Related Compounds, from https://www.degruyter.com/document/doi/10.1351/pac198254081507/pdf
  11. ^ Jensen, Søren K.; Nørgaard, Jan V.; Lauridsen, Charlotte (March 2006). "Bioavailability of α-tocopherol stereoisomers in rats depends on dietary doses of all-rac - or RRR-α-tocopheryl acetate". British Journal of Nutrition. 95 (3): 477–487. doi:10.1079/bjn20051667. Retrieved 31 October 2024.
  12. ^ "Composition of Foods Raw, Processed, Prepared USDA National Nutrient Database for Standard Reference, Release 20" (PDF). USDA. February 2008. Archived from the original (PDF) on 2012-02-19.
  13. ^ "Unit Conversions". National Institutes of Health. Retrieved 2018-11-21.
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