Vitamin E Vitamers And Units Of Activity

As shown in Figure 4.1, there are eight vitamers of vitamin E; the tocopherols and the tocotrienols differ in that the tocopherols have a saturated side chain,

Figure 4.1. Vitamin E vitamers, tocopherols and tocotrienols, and the synthetic water-soluble vitamin E analog, Trolox. Relative molecular masses (Mr): «-tocopherol, 430.7 (acetate 488.8, succinate 546.8); p-tocopherol, 419.7; y-tocopherol, 416.7; ¿-tocopherol, 402.7; a-tocotrienol, 424.7; p-tocotrienol, 410.7; y-tocotrienol, 410.7; S-tocotrienol, 396.7; and Trolox, 250.3.

Figure 4.1. Vitamin E vitamers, tocopherols and tocotrienols, and the synthetic water-soluble vitamin E analog, Trolox. Relative molecular masses (Mr): «-tocopherol, 430.7 (acetate 488.8, succinate 546.8); p-tocopherol, 419.7; y-tocopherol, 416.7; ¿-tocopherol, 402.7; a-tocotrienol, 424.7; p-tocotrienol, 410.7; y-tocotrienol, 410.7; S-tocotrienol, 396.7; and Trolox, 250.3.

whereas the tocotrienols have an unsaturated side chain. The different tocopherols and tocotrienols (a, p, y, and S) differ in the methylation of the chromanol ring. Tocotrienols occur in foods as both the free alcohols and also as esters; tocopherols occur naturally as the free alcohols, but acetate and succinate esters are used in pharmaceutical preparations because of their greater stability against oxidation. Trolox is a synthetic water-soluble compound with vitamin E activity.

Table 4.1 Relative Biological Activity of the Vitamin E Vitamers

Fetal Resorption Bioassay

Binding to

Relative

a -Tocopherol

IU/mg

Activity

Transfer Protein

d-a-tocopherol (RRR)

1.49

1.0

1.0

d-p-tocopherol (RRR)

0.75

0.50

0.38

d-7-tocopherol (RRR)

0.15

0.10

0.09

d-S-tocopheroi (RRR)

0.05

0.03

0.02

d-a-tocotrienol

0.75

0.50

0.12

d-p-tocotrienol

0.08

0.05

d-7-tocotrienol

d-S-tocotrienol

l-a-tocopherol (SRR)

0.46

0.31

0.11

RRS-a-tocopherol

1.34

0.90

SRS-a-tocopherol

0.55

0.37

RSS-a-tocopherol

1.09

0.73

SSR-a-tocopherol

0.31

0.21

RSR-a-tocopherol

0.85

0.57

SSS-a-tocopherol

1.10

0.60

RRR-a-tocopheryl

1.36

0.91

acetate

RRR-a-tocopheryl acid

1.21

0.81

succinate

All-rac-a-tocopherol

1.10

0.74

0.02

All-rac-a-tocopheryl

1.00

0.67

acetate

All-rac-a-tocopheryl

0.89

0.60

acid succinate acid succinate

Based on biological assay in vitamin E-deficient rats, the vitamers have widely varying biological activity. The original international unit (iu) of vitamin E potency was equated with the activity of 1 mg of (synthetic) DL-a-tocopherol acetate; on this basis, pure D-a-tocopherol (RRR-a-tocopherol, the most potent vitamer) is 1.49 iu per mg. The precise mixture of stereoisomers in this original standard is unknown, and the different stereoisomers have very different biological activities, so that different preparations may differ considerably.

It is now usual to express the vitamin E content of foods in terms of milligram-equivalents of (RRR)-a-tocopherol, based on their biological activities. In Table 4.1, the biological activity is shown in iuper milligram and relative to D-a-tocopherol on a molar basis. For the major vitamers present in foods, total a-tocopherol equivalent is calculated as the sum of mg a-tocopherol +

OH3 CH3 CH3

OH3 CH3 CH3

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