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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.cite-ref-2[2] It is found most in the membrane's non-raft domains, associated with omega-3 and 6 fatty acids, to partially prevent oxidation.cite-ref-3[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.

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."cite-ref-4[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.cite-ref-5[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.cite-ref-6[6]

• Synthesis

• Stereoisomers

• References

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.cite-ref-7[7]

α-Tocopherol has three stereocenters, so it is a chiral molecule.cite-ref-8[8] The eight stereoisomers of α-tocopherol differ in the configuration of these stereocenters. RRR-α-tocopherol is the natural one.cite-ref-9[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.cite-ref-iupac1-10-0[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.cite-ref-11[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.cite-ref-12[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.cite-ref-nih-calc-13-0[13]

cite-note-11. Merck Index, 11th Edition, 9931.

cite-note-22. ↑ citerefburtoningold1986Burton, 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.

cite-note-33. ↑ citerefatkinsonharrounwassallstillwell2010Atkinson, 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. PMID 20166146.

cite-note-44. ↑ citerefrigotti2007Rigotti 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.

cite-note-55. ↑ citerefshichiriishidahagiharayoshida2019Shichiri 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.

cite-note-66. ↑ citerefsinghdevarajjialal2005Singh, 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. PMID 16011463.

cite-note-77. ↑ citerefmizuguchitakemotoachiwa1993Mizuguchi, 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.

cite-note-88. ↑ citerefjensenlauridsen2007Jensen 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.

cite-note-99. ↑ citerefbrigelius-floh-traber1999Brigelius-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.

cite-note-iupac1-1010. ↑ IUPAC Nomenclature of Tocopherols and Related Compounds, from https://www.degruyter.com/document/doi/10.1351/pac198254081507/pdf

cite-note-1111. ↑ citerefjensenn-rgaardlauridsen2006Jensen, 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. PMID 16512933. Retrieved 31 October 2024.

cite-note-1212. ↑ "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.

cite-note-nih-calc-1313. ↑ "Unit Conversions". National Institutes of Health. Retrieved 2018-11-21.