Tocopherol stmcture

Vitamin E was first described ia 1922 and the name was originally applied to a material found ia vegetable oils. This material was found to be essential for fertility ia tats. It was not until the early 1980s that symptoms of vitamin E deficiency ia humans were recognized. Early work on the natural distribution, isolation, and identification can be attributed to Evans, Butt, and Emerson (University of California) and MattiU and Olcott (University of Iowa). Subsequentiy a group of substances (Eig. 1), which fall iato either the family of tocopherols or tocotrienols, were found to act like vitamin E (1 4). The stmcture of a-tocopherol was determined by degradation studies ia 1938 (5). 

The term vitamin E refers to two groups of compoxmds, the tocopherols and the tocotrienols. The stmctuies of these compoimds appear in Figure 9.90. All forms of the vitamin contain two parts, a "head" and a "tail." The head consists of an aromatic ring stmcture, called chroman or chromanol, and is the site of antioxidant action. The tail of tocopherols is a phytyl group, while the tail of tocotrienols is a polyisoprenoid group. The tail of vitamin E serves to anchor the vitamin in lipid membranes, in the lipids of adipose tissue, and in the lipid surface and core of the lipoproteins. 

Alpha-tocopherol (3.53) is an example of a chroman derivative. It is found in vegetable oils and is one of several related stmctures constituting the human growth factor Vitamin E. 

Triketones with Heterocyclic Substituents. Triketones represent a well-studied, but still developing, family of herbicides. Some with pyiidyl substituents are among the most active. Much of the research in this area has been reviewed. The triketones are inhibitors of the plant enzyme 4-hydroxyphenylpymvate dioxygenase (HPPD), which plays a key role in the biosynthesis of plastoquinone and tocopherol. Compound 11.6, which is known as nicotinoyl syncarpic acid, is shown as a typical structure of this type. Its potent herbiddal activity led to synthetic work that has yielded many related stmctures in an effort to improve selectivity in the herbicidal action. 

MRF A is an antioxidant and a potent inhibitor of lipid peroxidation [66-68]. MRF A showed inhibitory activity on NADPH-dependent lipid peroxidation (1C50 = 2.8 mcM) in rat hver microsomes, being 30 times and 70 times stronger than alpha-tocopherol (1C50 = 87 mcM) and ascorbic acid (1C50 = 200 mcM), respectively. Indole (1C50 = 330 mcM) and tryptamine (1C50 = 260 mcM), the partial stmctures of MRF A, had much weaker effects on lipid peroxidation [67]... 

Vitamins are organic compounds required as vital nutrients in small amounts by a given organism. Vitamins cannot be synthesized in sufficient quantities by the body and have to be provided with the diet to avoid characteristic diseases (e.g., scurvy in the case of human shortage of vitamin C). The three most important vitamins (by their industrial production capacities) are vitamin C, vitamin B3 (nicotinic acid amide) and vitamin E (tocopherol). These three vitamins represent, from their stmcture and synthesis, typical fine chemicals. However, they are produced on a multi-10000 ton-scale per year. To give an example that also fulfils the capacity criterion of fine chemicals. Table 5.3.19, shows vitamin B2 (riboflavin). The latter is produced both by chemical synthesis and fermentation on the order of 10 000 tons yr . Riboflavin is required for a wide variety of cellular processes and is used for therapeutic purposes and as food additive. 

Actually, a redox reaction takes place. It is due to the reducing properties of para and ortho diphenols, stmctures that were masked in a-tocopherol. Hence, the driving force of this particular reaction is the formation of a quinone. It is sufficiently strong to induce the break of the ether-oxide bond of pyran. This is remarkable. The identification reaction of a-tocopherol is called Emmeri-Engel s reaction. 

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