Chemistry:Α-Tocopherol
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.[1] It is found most in the membrane's non-raft domains, associated with omega-3 and 6 fatty acids, to partially prevent oxidation.[2] 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."[3] 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.[4] 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.[5]
Synthesis
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.[6]
Stereoisomers
α-Tocopherol has three stereocenters, so it is a chiral molecule.[7] The eight stereoisomers of α-tocopherol differ in the configuration of these stereocenters. RRR-α-tocopherol is the natural one.[8] 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.[9] 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.[10]
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.[11] 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.[12]
References
- ↑ 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.
- ↑ 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. PMID 20166146.
- ↑ "Absorption, transport, and tissue delivery of vitamin E". Molecular Aspects of Medicine 28 (5–6): 423–36. 2007. doi:10.1016/j.mam.2007.01.002. PMID 17320165.
- ↑ "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. 2019. doi:10.3164/jcbn.18-7. PMID 30936625.
- ↑ 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. PMID 16011463.
- ↑ 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.
- ↑ "Alpha-tocopherol stereoisomers". Vitamins and Hormones 76: 281–308. 2007. doi:10.1016/S0083-6729(07)76010-7. ISBN 9780123735928. PMID 17628178.
- ↑ "Vitamin E: function and metabolism". FASEB Journal 13 (10): 1145–55. July 1999. doi:10.1096/fasebj.13.10.1145. PMID 10385606. http://www.fasebj.org/cgi/pmidlookup?view=long&pmid=10385606.
- ↑ IUPAC Nomenclature of Tocopherols and Related Compounds, from https://www.degruyter.com/document/doi/10.1351/pac198254081507/pdf
- ↑ 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. PMID 16512933. https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/bioavailability-of-tocopherol-stereoisomers-in-rats-depends-on-dietary-doses-of-allrac-or-rrrtocopheryl-acetate/921CFDBA1B7B2923CD5937F2069BE1BA. Retrieved 31 October 2024.
- ↑ "Composition of Foods Raw, Processed, Prepared USDA National Nutrient Database for Standard Reference, Release 20". USDA. February 2008. https://www.ars.usda.gov/ARSUserFiles/80400525/Data/SR20/SR20_doc.pdf.
- ↑ "Unit Conversions". National Institutes of Health. https://dietarysupplementdatabase.usda.nih.gov/Conversions.php.
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