Tocotrienols

Tocotrienols are members of the vitamin E family. An essential nutrient for the body, vitamin E is made up of four tocopherols (alpha, beta, gamma, delta) and four tocotrienols (alpha, beta, gamma, delta). The slight difference between tocotrienols and tocopherols lie in the unsaturated side chain having three double bonds in its farnesyl isoprenoid tail. Tocotrienols are natural compounds found in select vegetable oils, wheat germ, barley, saw palmetto, and certain types of nuts and grains. This variant of vitamin E typically only occurs at very low levels in nature.

Chemically, vitamin E in all of its forms functions as an antioxidant. All of the tocotrienol and tocopherol isomers have this antioxidant activity due to the ability to donate a hydrogen atom (a proton plus electron) from the hydroxyl group on the chromanol ring, to a free radical in the body. This process inactivates ("quenches") the free radical by effectively donating a single unpaired electron (which comes with the hydrogen atom) to the radical. Although the many vitamers of vitamin E have different distributions and metabolic fates, there is as yet no accepted evidence that any of the active forms of vitamin E are able to do any essential function in the body that each of the others is not also able to do. Specifically, symptoms caused by alpha-tocopherol deficiency can be alleviated by tocotrienols. Thus, tocotrienols may be viewed as being members of the natural vitamin E family not only structurally but also functionally. Thus, one model for the function of vitamin E in the body is that it protects cell membranes, active enzyme sites, and DNA from free radical damage.

While the majority of research on vitamin E has focused on alpha-tocopherol, studies into tocotrienols account for less than 1% of all research into vitamin E. More recently, tocotrienols have reached a new measure of scientific recognition, with nearly 30% of peer-reviewed research articles on the vitamin published within the last two years (2009–2010). The first-ever scientific compilation of tocotrienol research, Tocotrienols: Vitamin E Beyond Tocopherols, was published in 2008 by CRC and AOCS Press, while a second edition has been approved for publication in May 2012.

Tocotrienols are named by analogy to tocopherols (from Greek words meaning to bear a pregnancy (see tocopherol); but with this word changed to include the chemical difference that tocotrienols are trienes, meaning that they share identical structure with the tocopherols except for the addition of three double bonds to their side chains.

Tocotrienols extracted from natural sources are d-tocotrienols. Tocotrienols have only a single chiral center, which exists at the 2' chromanol ring carbon, at the point where the isoprenoid tail joins the ring; the other two corresponding centers in the phytyl tail of the corresponding tocopherols, do not exist due to tocotrienol's unsaturation at these sites. In theory, tocotrienol stereoisomers may thus exist in the natural d-tocotrienol form, or as the unnatural isomeric 'l-tocotrienols' which have a 2S (rather than 2R) configuration at the molecules' single chiral center. In practice, however, tocotrienols are extracted from natural sources, and synthetic l and d,l forms are not marketed as supplements.