alpha-Tocopherol

α-Tocopherol is a type of vitamin E. It has E number '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. α-Tocopherol is a type of vitamin E. It has E number '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. α-Tocopherol has three stereocenters, so it is a chiral molecule. The eight stereoisomers of α-tocopherol differ the configuration on these stereocenters. RRR-α-tocopherol is the natural one. 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 One IU of tocopherol is defined as ⅔ milligrams of RRR-α-tocopherol (formerly named d-α-tocopherol, or sometimes ddd-α-tocopherol). 1 IU is also defined as 1 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. However, 1 IU of this mixture of diastereomers is not now considered equivalent to 1 IU of natural RRR-α-tocopherol, and the Institute of Medicine and the USDA now convert IUs of the racemic mixture to milligrams of equivalent RRR using 1 IU racemic mixture = 0.45 'mg α-tocopherol'.