α-Tocopherol (''alpha''-tocopherol) is a type of

vitamin E Vitamin E is a group of eight compounds related in molecular structure that includes four tocopherols and four tocotrienols. The tocopherols function as fat-soluble antioxidants which may help protect cell membranes from reactive oxygen speci ...

. Its

E number E numbers, short for Europe numbers, 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 ...

is "E307". Vitamin E exists in eight different forms, four

tocopherol Tocopherols (; TCP) are a class of organic compounds comprising 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 rats, it was named ''t ...

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, 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. It is found most in the membrane's non-raft domains, associated with omega-3 and 6 fatty acids, to partially prevent oxidation. The most prevalent form, α-tocopherol, is involved in molecular, cellular, biochemical processes closely related to overall

lipoprotein A lipoprotein is a biochemical assembly whose primary function is to transport hydrophobic lipid (also known as fat) molecules in water, as in blood plasma or other extracellular fluids. They consist of a triglyceride and cholesterol center, sur ...

and

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

homeostasis In biology, homeostasis (British English, British also homoeostasis; ) is the state of steady internal physics, physical and chemistry, chemical conditions maintained by organism, living systems. This is the condition of optimal functioning fo ...

. Compared to the others, α-tocopherol is preferentially absorbed and accumulated in humans.

Vitamin E Vitamin E is a group of eight compounds related in molecular structure that includes four tocopherols and four tocotrienols. The tocopherols function as fat-soluble antioxidants which may help protect cell membranes from reactive oxygen speci ...

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." One of these disease conditions is the α-tocopherol role in the use by

malaria Malaria is a Mosquito-borne disease, mosquito-borne infectious disease that affects vertebrates and ''Anopheles'' mosquitoes. Human malaria causes Signs and symptoms, symptoms that typically include fever, Fatigue (medical), fatigue, vomitin ...

parasites to protect themselves from the highly oxidative environment in

erythrocytes Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood cel ...

. A second of these disease conditions is the α-tocopherol antioxidant properties' role cardiovascular heart disease. In preventing LDL (low-density

) oxidation, it is able to decrease chances of atherosclerosis and arterial build-up.

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.

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 language, Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is dist ...

molecule. The eight

stereoisomers In stereochemistry, stereoisomerism, or spatial isomerism, is a form of isomerism in which molecules have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms i ...

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 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.IUPAC Nomenclature of Tocopherols and Related Compounds
from https://www.degruyter.com/document/doi/10.1351/pac198254081507/pdf 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. 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 a mixture that has equal amounts (50:50) 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 r ...

, ''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