α-Tocopherol is a type of
vitamin E. It has
E number
E numbers ("E" stands for "Europe") are codes for substances used as food additives, including those found naturally in many foods such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...
"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 which allows for penetration into biological membranes. 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. The most prevalent form, α-tocopherol, is involved in molecular, cellular, biochemical processes closely related to overall
lipoprotein and
lipid homeostasis. Ongoing research is believed to be "critical for manipulation of vitamin E homeostasis in a variety of oxidative stress-related disease conditions in humans." 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.
Stereoisomers
α-Tocopherol has three
stereocenters, so it is a
chiral molecule. The eight
stereoisomers of α-tocopherol differ in the configuration of these stereocenters. ''RRR''-α-tocopherol is the natural one. The older name of ''RRR''-α-tocopherol is ''d''-α-tocopherol, but this ''d/l'' naming should be no longer 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.
[IUPAC Nomenclature of Tocopherols and Related Compounds](_blank)
from https://www.degruyter.com/document/doi/10.1351/pac198254081507/pdf
One IU of tocopherol is defined as 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
In chemistry, a racemic mixture, or racemate (), is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as racemates. ...
,
''all''-''rac''-α-tocopheryl acetate. This mix of stereoisomers is often called ''dl''-α-tocopheryl acetate.
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.
References
{{DEFAULTSORT:Tocopherol, Alpha-
Vitamin E