Vitamin E family

Tocopherols and tocotrienols belong to the vitamin E family of compounds, which are potent antioxidants. The four isomers of tocotrienols (a-T3, P-T3, y-T3, 8-T3) are structurally related to their corresponding homologues of tocopherols (a-T, p-T, y-T, 8-T), but differ in their side-chain in that T3... 

A closely related and important family of chro-manols are the tocopherols or vitamins E (Fig. 15-24, Box 15-G). Tocopherols are plant products found primarily in plant oils and are essential to proper nutrition of humans and other animals. a-Tocopherol is the most abundant form of the vitamin E family smaller amounts of the P, 8, and y forms occur, as do a series of tocotrienols which contain unsaturated isoprenoid units.495 The configuration of a-tocopherol is 2R,4 R,8 R as indicated in Fig. 15-24. When a-toco-pherol is oxidized, e.g., with ferric chloride, the ring can be opened by hydrolysis to give tocopherolquinones (Fig. 15-24), which can in turn be reduced to tocopherol-hydroquinones. Large amounts of the tocopherolquinones have been found in chloroplasts. 

Rice bran oil and palm oil are the only readily available oils that contain significant levels (about 1000 ppm) tocotrienols (99). Tocotrienols belong to the Vitamin E family and have similar chemical stmcmres. According to Tomeo et al. (100), tocotrienols are powerful antioxidants. Commercially available RBO may contain 980 ppm y-tocotrienol (101). 

Vitamins are divided into two major categories. They are fat-soluble (A, D, E and K) and water-soluble vitamins (B-complex and vitamin C). B complex vitamins include thiamine (Bi), riboflavin (B2), pantothenic acid (B3), niacin (B5), pyridoxine (Be), biotin (By), folic acid (B9), and cobalamin (Biy). Inositol, cholic and para-aminobenzoic acid are vitamin-like substances sometimes classified as part of the B complex, but no convincing evidence has been shown so far to be included as vitamins. All the fat-soluble vitamins and some B vitamins exist in multiple forms. The active forms of vitamin A are retinol, retinal and retinoic acid and vitamin D is available as ergocalciferol (D2) and cholecalciferol (D3). The vitamin E family includes four tocopherols and four tocotrienols but a-tocopherol being the most abundant and active form. The multiple forms of vitamins are interconvertible and some are interchangeable. 

Chemistry. The vitamin E family I )nsists of tocopherols and tocotrienols. There been considerable debate as to whether b RRR isomer is the only biologically active arm cf the vitamin. The vitamin of commerce a-tocopheroi, either as a racemic synthetic... 

Vitamin K comprises derivatives of 1,4-naphthoquinone. Naturally occurring forms are equipped with structures possessing the unsaturated isoprenoid side chain linked to naphthoquinone at carbon-3 (Figure 7.5). Vitamin Kj, phylloquinone (2 methyl-3 phytyl-1,4-naphthoquinone), is one of the natural forms. Similar to compounds belonging to the vitamin E family, those included in the vitamin K group have the isoprenoid side chain consisting of 20 carbon atoms with one double bond. This side chain is derived from plant diterpenoic alcohol (C20H39OH). These compounds have been detected in alfalfa oil. 

Within the vitamin E family, there has been significant focus on TCPs relative to that of TCTs. Current developments in vitamin E research show that each member of... 

Well-known naturally occurring antioxidants are vitamin C (ascorbic acid), which are contained in many citrus fruits, or on the other hand manbers of vitamin E family, which appear for example in nnts and snnflower seeds. Also P-carotene and lycopine, which also belong to the family of caro-tenoides, are further examples of natural antioxidants. On the other hand, there are many synthetic... 

Another impressive example of dienamine-iminium cascade catalysis was developed during the total synthesis of a-tocopherol 59 by Liu et al. [31]. This natural product is a member of the vitamin E family and possesses remarkable biological activity. The key step in the total synthesis of this natural product involved an organocatalytic aldol/oxa-Michael cascade reaction for construction of the core... 

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