α-Tocopherol
Chemical compound
From Wikipedia, the free encyclopedia
α-Tocopherol (alpha-tocopherol) is a type of vitamin E.[2][3]
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| Names | |
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| Preferred IUPAC name
(2R)-2,5,7,8-Tetramethyl-2-[(4R,8R)-4,8,12-trimethyltridecyl]-3,4-dihydro-2H-1-benzopyran-6-ol | |
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3D model (JSmol) |
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| DrugBank | |
| ECHA InfoCard | 100.000.375 |
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| E number | E307a (antioxidants, ...) |
PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| 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) | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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It is found most in the membrane's non-raft domains, associated with omega-3 and 6 fatty acids, to partially prevent oxidation.[4] The most prevalent form, α-tocopherol, is involved in molecular, cellular, biochemical processes closely related to overall lipoprotein and lipid homeostasis.[2] Compared to the others, α-tocopherol is preferentially absorbed and accumulated in humans.[3]
Vitamin E exists in 8 different forms: 4 tocopherols and 4 tocotrienols.[2][3] Each form has a chromane ring, and an alkyl side chain, which is hydrophobic. The chromane ring contains a hydroxyl group that can donate a hydrogen atom to free radicals. This reaction helps reduce oxidative damage. In this way, a vitamin E acts as an antioxidant. The hydrophobic side chain helps vitamin E enter biological membranes. In the membrane, the aromatic ring of the chromane (the chromanol ring) lies near the carbonyl groups of the fatty chains of phospholipids. This allows vitamin E to concentrate from the surrounding aqueous solution into biological membranes.[5]
Because vitamin E is lipid-soluble, it is found in many tissues.[2] The body absorbs and distributes vitamin E through several pathways.[3][6] Malaria parasites may use α-tocopherol to protect themselves from the highly oxidative environment in erythrocytes.[7] In cardiovascular disease, α-tocopherol acts as an antioxidant. It can help prevent oxidation of low-density lipoprotein (LDL). Lower levels of oxidation of LDL may reduce atherosclerosis and arterial plaque formation.[8]
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.[9]
Stereoisomers
α-Tocopherol has three stereocenters, so it is a chiral molecule.[10] The eight stereoisomers of α-tocopherol differ in the configuration of these stereocenters. RRR-α-tocopherol is the natural one.[11] 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.[12] 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.[13]
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.[14] 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.[15]