α-Tocopherol is a type of

vitamin E Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vitami ...

. 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

tocopherol Tocopherols (; TCP) are a class of organic chemical compounds (more precisely, various methylated phenols), many of which have vitamin E activity. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rat ...

s 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 Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vitami ...

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 Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids incl ...

homeostasis In biology, homeostasis (British English, British also homoeostasis) Help:IPA/English, (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physics, physical, and chemistry, chemical conditions maintained by organism, living systems. Thi ...

. 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 Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or deat ...

parasites to protect themselves from the highly oxidative environment in

erythrocytes Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

Stereoisomers

α-Tocopherol has three

stereocenter In stereochemistry, a stereocenter of a molecule is an atom (center), axis or plane that is the focus of stereoisomerism; that is, when having at least three different groups bound to the stereocenter, interchanging any two different groups cr ...

s, so it is a

chiral Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from i ...

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
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