Y-tocopherol

Fig. 1. The four naturally occutting tocopherols (a-tocopherol, E.E.E. [59-02-9] jall-rac [2074-53-5] (1) p-tocopherol [148-03-8] (2) y-tocopherol [54-28-4] (3) 8-tocopherol [119-13-1] (4)), a-tocotrienol [1721 -51 -3] (5), and p-tocotrienol [14101-61-2] (6) where asterisks denote asymmetric centers and the...

Oil source Total tocopherols a-Tocopherol y-Tocopherol (3-Tocopherol 5-Tocopherol... 

It has been established that carotenoid structure has a great influence in its antioxidant activity for example, canthaxanthin and astaxanthin show better antioxidant activities than 3-carotene or zeaxanthin. 3- 3 3-Carotene also showed prooxidant activity in oil-in-water emulsions evaluated by the formation of lipid hydroperoxides, hexanal, or 2-heptenal the activity was reverted with a- and y-tocopherol. Carotenoid antioxidant activity against radicals has been established. In order of decreasing activity, the results are lycopene > 3-cryptoxanthin > lutein = zeaxanthin > a-carotene > echineone > canthaxanthin = astaxanthin. ... 

The stabilization of the zwitterionic o-QM precursors is due to electrostatic interactions. It was reasonable to assume that also the other methods of stabilizing the zwitterions might be viable, and indeed it was confirmed that both steric and electronic effects are able to stabilize such intermediates. In 5-(4-octyl)-y-tocopherol (5a-butyl-5a-propyl-a-tocopherol, 21), the octyl group acts as a flywheel, which impedes the rotation of the C-5a moiety into the ring plane as compared to the parent zwitterions with the unsubstituted exocyclic methylene group. The situation is... 

The methano-dimer of a-tocopherol (28)50 was formed by the reaction of o-QM 3 as an alkylating agent toward excess y-tocopherol. It is also the reduction product of the furano-spiro dimer 29, which by analogy to spiro dimer 9 occurred as two interconvertible diastereomers,28 see Fig. 6.23. However, the interconversion rate was found to be slower than in the case of spiro dimer 9. While the reduction of furano-spiro dimer 29 to methano-dimer 28 proceeded largely quantitatively and independently of the reductant, the products of the reverse reaction, oxidation of 28 to 29, depended on oxidant and reaction conditions, so that those two compounds do not constitute a reversible redox pair in contrast to 9 and 12. 

Treatment of methano-dimer 28 with elemental bromine revealed a remarkable reactivity at low temperatures it proceeded quantitatively to the furano-spiro dimer 29, by analogy with the ethano-dimer 12 giving spiro dimer 9 upon oxidation. With increasing temperatures, the reaction mechanism changed, however, now affording a mixture of 5-bromo-y-tocopherol (30) and spiro dimer 9 (Fig. 6.24). Thus, the methano-dimer 28 fragmented into an a-tocopherol part, in the form of o-QM 3 that dimerized into 9, and a /-tocopherol part, which was present as the 5-bromo derivative 30 after the reaction. Thus, the overall reaction can be regarded as oxidative dealkylation. 

FIGURE 6.45 Inability of 5a-substituted derivatives to form structures analogous to o-QM 3 causes increased oxidative stability as in compounds 71 and 72. 5-(p-Hydroxyphenyl)-y-tocopherol (73) is oxidized to the conjugatively stabilized o-QM 74, the phenylogous a-tocored (75). 

FIGURE 6.46 Oxidation chemistry of 5-(4-methylphenyl)- y-tocopherol (76), establishing a reaction system phenylogous to a-tocopherol (1), with quinone methide 77 and benzyl bromide 78 being the conjugatively stabilized, phenylogous counterparts of o-QM 3 and 5a-bromo-a-tocopherol (46), respectively. 

FIGURE 6.47 Oxidation of styryl-y-tocopherol 79 to the stable o-QM 80, a styrylogous o-QM 3. 

Dallacker, F. Eisbach, R. Holschbach, M. Derivatives of vitamin E series 1. Preparation and reaction of all-rac-5-formyl-y-tocopherol. Chem. Ztg. 1991, 115(4), 113-116. 

The presence of tocopherols,114 as well as caffeic acid,108 accounts for the remarkable stability of green coffee bean oils toward oxidation. In coffee beans from different origins, a-tocopherol concentrations are in the range 89 to 188 pg/kg and (p + y)-tocopherol concentrations are in the range 252 to 530 pg/kg.114 Since p- and y-tocopherols have better antioxidant properties than a-tocopherol,114 it is not surprising to see coffee oil patented as an antioxidant material.115117... 

Haila KM, Lievonen SM and Heinon IM. 1996. Effects of lutein, lycopene, annatto, and -y -tocopherol on oxidation of triglycerides. J Agric Food Chem 44 2096-2100. 

Figure 9 Antiradical capacity in the lipid phase of blood plasma (ACL) determined with the PCL method versus vitamin E (VE) as a sum of a- and y-tocopherols determined with HPLC. (From Ref. 28.)...

Tocopherols are not as effective as antioxidants as the synthetic antioxidants, e.g. BHA or BHT. The antioxidant effect of tocopherols is increased by mixing them with ascorbyl palmitate, ascorbic acid, lecithin or citric acid. Typical confectionery applications are the use of tocopherols with ascorbyl palmitate or lecithin or citric acid in the fat phase of toffees or caramels. Chewing gum base can be treated with a- and y-tocopherol to extend the shelf life. 

Scheme 6 Asymmetric synthesis of y-tocopherol from the triene...

Figure 15.14 Structural formula of a-tocopherol. In P-tocoph-erol, the 7-methyl group is absent, in y-tocopherol the 5-methyl group is absent, and in 5-tocopherol, both methyl groups are absent. In the tocotrienols, the side-chain at position 2 is replaced by ...

Vitamin E, a natural antioxidant, is essential for growth, disease prevention, tissue integrity and reproduction in all fauna. Natural vitamin E, as it occurs in plants, consists mainly of a-tocopherol (III, R = H) with minor amounts of y-tocopherol (IV), although this ratio can vary as for example in the vegetable oil composition shown in Fig. 5a. In animal husbandry, such as dairy farms or cattle feed lots, the stock diets are commonly supplemented with vitamin E, because processed grain-based cereal fodder, hay, and silage are deficient in vitamin This results in higher levels of a-tocopherol... 

Consequently, soil samples from feedlots have a dual origin of toco-pherols. This is illustrated with the GC-MS data of a study done in the San Joaquin Valley of California (Fig. 5b, ). The y-tocopherol is derived exclusively from the vegetation fodder, while a-tocopherol is derived from both vegetation and the hydrolysis of the tocopheryl acetate feed supplement. Excess a-tocopherol acetate, not hydrolyzed in the animal gut, is also present. Because a-tocopherol acetate is relatively stable, its presence in soil dust samples indicates the level of its usage as a feed supplement. A significant metabolite of a-tocopherol elutes after the acetate and the... 

In spite of the obvious advantages of elevated temperature, there are examples of cases where better separation is achieved at a reduced temperature, even for simple solutes. Craft et al. [20] recently demonstrated an improved separation of P and y tocopherol at -20°C in THF/acetonitrile when compared to the ambient temperature separation of the compounds in Acetonitrile water. Bohm [21] reported the temperature dependence of the separation of a mixture of five xanthophylls and six carotenes on a C-30 column. The optimum temperature in this case was 23°C with a coelution of some peaks at temperatures below 20°C and others above 35°C. In a study using a 300 A pore C-18 column, Bohm [22] reported dramatic changes in the elution order over the temperature range -7°C to 35°C. On this column, the optimal separation was achieved at low temperatures... 

Owing to good antioxidant properties, a-tocopherol is also a much sought target for enhanced production. This was achieved by enhancing the level of the a-tocopherol biosynthetic precursor, Y-tocopherol, and over-expressing y-tocopherol methyltransferase in seeds of the plant Arabidopis thaliana (Shintani 1998). 

Wehmeyer et al. (1969) published results on the content of B vitamins (thiamine, riboflavin, and nicotinic acid), vitamin C, and p-carotene and foimd that the morama bean is a good source of both B vitamins and vitamin C, but a poor source of p-carotene. Holse et al. (2010) investigated the content of the eight vitamin E isomers and found that the vitamin E composition in morama beans is dominated by y-tocopherol with 59-234 ng/g, followed by a- and p-tocopherols with 14- 8 gg/g and 1.1-3.3 ng/g, respectively. Eurthermore, traces of 8-tocopherol as well as p- and y-tocotrienols were present in some samples. The remaining two tocotrienols (a- and 8-) were not present in the beans. The presence of a-, p-, and y-tocopherols in the morama bean was also foimd by Mitei et al. (2009) who examined morama oil and by Dubois et al. (1995) who examined two samples of T.fassoglense. 

The vitamin E components have numerous health benefits. The high content of y-tocopherol is of particular biological relevance as it has shown potential anticarcinogenic and anti-inflammatory activities (Brigelius-Flohe, 2006 Saldeen and Saldeen, 2005). 

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