Chromanol ring

In normal-phase HPLC on a silica column, separation is based on the number and position of methyl substituents on the chromanol ring. In reversed-phase HPLC on a Cl8 column, separation is based on the structure of the side chain and the number of methyl substituents. It is therefore difficult to completely separate [3-and y-tocopherol and (3- and y-tocotrienols by reversed-phase HPLC, because both have the same side-chain structure and number of methyl substituents on the chromanol ring. Only six peaks are usually found in the reversed-phase HPLC method. Thus, reversed-phase HPLC is recommended for samples from animal tissues, which contain little or no P and y vitamers. 

In reversed-phase HPLC on a Cl8 column, only six peaks are usually found, and their order of elution is 5-tocotrienol, (3- and y-to-cotrienols, a-tocotrienol, 5-tocopherol, (3- and y-tocopherol, and a-tocopherol. Figure D 1.5.4 is an example of a reversed-phase chromatograph of tocopherols and tocotrienols in rice bran oil. The tocols with unsaturated side chain have shorter retention time than those with saturated side chain. The methyl substituents on the chromanol ring also affect the retention times of tocopherols and tocotrienols. However, the effect is reversed, compared with the normal-phase HPLC method. 

Tocopherols comprise a methyl-substituted chroman-6-ol ring attached at C-2 to a saturated iso-prenoid side chain. Tocotrienols are analogous structures whose side chains contain three trans double bonds. The tocopherols and tocotrienols are designated as a, (S, y, and 8, according to the number and position of the methyl substituents in the chromanol ring (Fig. 5). 

These compounds can be divided into two types, tocols and trienols. Although both types have the 6-chromanol ring structure and a phytol-like... 

Table 5.6. STRUCTURE-ACTIVITY RELATIONSHIP FOR COMPOUNDS CONTAINING THE PHYTOL SIDE-CHAIN AND CHROMANOL RING STRUCTURES RELATED TO VITAMIN E...

Figure 5. Chromanol ring and isoprenoid side chains in tocopherols, tocotrienols (n = 3), and plastochromanol-8 (n=8, R)=H, R2=CH3 ) in vegetable oils (for systematic names, see Table 6).

Vitamin E is the term used for eight naturally occurring fat-soluble nutrients (Fritsma, 1983). Four compounds bear a saturated phytyl side chain and differ only with respect to number and position of methyl groups at the chromanol ring (a-,... 

The term vitamin E describes a family of eight antioxidants, a-, P-, y-, and 5-tocopherol and a-, P-, y-, and 5-tocotrienol, which are synthesized only by plants. Tocopherols and tocotiienols are characterized by a substituted hydroxylated ring system (chromanol ring). However, tocotrienols have an unsaturated side chain, while tocopherols have a saturated side chain with three asymmetric carbon atoms (Figure 21.2). Out of eight possible tocopherol stereoisomers, only the AAA-stereoisomer occurs naturally. ... 

Chemical structure (Figure 4). Compounds composed of a chromanol-ring system, with two to four... 

A diastereoselective synthesis of a-tocopherol 87 features a Shi epoxidation with ent-2 and a carefully controlled intramolecular epoxide opening cyclization for the formation of the chromanol ring. Good conversion and high enantioselectivity have been achieved in the epoxidation step. ... 

Vitamin E has eight biologically active forms [1] four tocopherols (saturated isoprenoid side chain) and four tocotrienols (imsaturated iso-prenoid side chain), designed as a-, P-, y-, and 5-according to the number and position of methyl groups on the chromanol ring. Of these, a-tocopherol is the most important (plant sources) and active. 

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