A-Tocotrienol

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...

The yield of the more active RRR-a-tocopherol can be improved by selective methylation of the other tocopherol isomers or by hydrogenation of a-tocotrienol (25,26). Methylation can be accompHshed by several processes, such as simultaneous halo alkylation and reduction with an aldehyde and a hydrogen haUde in the presence of staimous chloride (27), amino alkylation with ammonia or amines and an aldehyde such as paraformaldehyde followed by catalytic reduction (28), or via formylation with formaldehyde followed by catalytic reduction (29). 

RAEDERSTORFF D, ELSTE V, AEBiscHER c, WEBER p (2002) Effect of either gamma-tocotrienol or a tocotrienol mixture on the plasma lipid profile in hamsters. Ann Nutr Metab, 46 17-23. 

In normal-phase HPLC on a silica column, the order of elution of tocopherols and tocotrienols is a-tocopherol, a-tocotrienol, [3-tocopherol, (3-tocotrienol, y-tocopherol, y-tocotrienol, 8-tocopherol, and 5-tocotrienol. Figure Dl.5.3 is an example of a normal-phase chromatograph of tocopherols and tocotrienols in rice bran oil. 

Research Council defined 1 mg of a-tocopherol as 1 unit of a-TE (mg x 1). The activities as a-TE of other vitamers were (3-tocopherol, mg x 0.5 y-tocopherol, mg xO. 1 8-tocopherol, mg x 0.03 a-tocotrienol, mg x 0.3 and (3-to-cotrienol, mg x 0.05. The activities of y- and 8-tocotrienol were undetectable. The Recommended Dietary Allowances (RDAs) are only based on intake of the 2R-stereoisomeric forms of a-tocopherol (RRR-, RSR-, RRS-, and RSS-tocopherol) from food, fortified food, and vitamin supplements (Food and Nutrition Board, 2000). The 2S-stereoisomeric forms of a-tocopherol and the other tocopherols ((3-, y-, and 5-tocopherol) and tocotrienols are not used to estimate the RDAs. 

Fig. 13 HPLC of vitamin E. (A) Standards of vitamin E vitamers. Column, 5-p.m Supelcosil LC-Si (250 X 4.6-mm ID) mobile phase, isooctane/ethyl acetate (97.5 2.5), 1.6 ml/min fluorescence detection, excitation 290 nm, emission 330 nm. Peaks (1) a-tocopherol (2) a-tocotrienol (3) /3-tocopherol (4) y-tocopherol (5) /3-tocotrienol (6) y-tocotrienol (7) 5-tocopherol (8) 5-tocotrienol. (B) Saponified rice bran sample. Chromatographic conditions as in (A) except for mobile phase isooctane/ethyl acetate/2,2-dimethoxypropane (98.15 0.9 0.85 0.1). (From Ref. 228. AOCS Press.)...

Fig. 9.5 Chemical structures of low molecular weight antioxidants Melatonin (a) ascorbic acid (Vitamin C) (b) glutathione (c) lipoic acid (d) a-tocopherol (Vitamin E) (e) and a-tocotrienol (f)...

Osakada F., Hashino A., Kume T., Katsuki H., Kaneko S., and Akaike A. (2004). a-Tocotrienol provides the most potent neuroprotection among vitamin E analogs on cultured striatal neurons. Neuropharmacology 47 904-915. 

In the rat foetal resorption and haemolysis tests, a-tocotrienol had respectively 29% and between 17-25% of the activity of vitamin E [4], The tocotrienols also have a dependence on the presence of methyl groups in the benzene ring for their activity. Thus, 5,8-dimethyltocotrienol shows negligible activity compared with 5,7,8-trimethyltocotrienol and indeed (RRR)-a-toco-pherol [55-57], Unsaturation of the side-chain causes the activity to decrease [58]. 

The other five molecules which were identified using continuous-flow HPLC-1 H NMR spectroscopy at an observation frequency of 400 MHz were a-tocoenol with a mass of 428 (a double bond at Cl 1 ), a-tocotrienol with a mass of 424 (double bonds at C3, Cl and Cll ), (3-tocotrienol with a mass of 410 (double bonds at C3, Cl and Cl V, but with loss of a methyl on the phenyl ring), y-tocotrienol, also with a mass of 410 (like (3-tocotrienol but with loss of a different methyl group on the phenyl ring) and 8-tocotrienol with a mass of 396 (like (3-tocotrienol but with the loss of two methyl groups from the phenyl ring). 

Extraction method a-Tocopherol a-Tocotrienol P- + y-Tocopherol 5-Tocopherol... 

The a-tocotrienol has a number of isolated double bonds on the alkyl chain and also has the double bonds of the aromatic ring. The isolated double bonds are easier to reduce by catalytic hydrogenation as the aromatic ring would prefer to retain its resonance energy from aromaticity. Thus, low-pressure hydrogenation and the use of simple catalysts like Pt will selectively reduce the isolated double bonds of a-tocotrienol to a-tocopherol. 

Tocopherols and tocotrienols are precursors of vitamin E and are important antioxidants in oils. Their reactivity means that they are not stable to many oil processing procedures, including deodorization, which reduces levels by up to 15%. Levels of tocopherols in cocoa butter are usually about 100-300 mg/kg, with the y-isomer (IV) being the major component (about 90%), but they can be entirely absent (Lipp et al., 2001) (Figure 3.3). Tocotrienols have a similar structure with unsaturation of alternate bonds along the alkyl chain. Only y-tocotrienol is found in cocoa butter and this at low levels (< 5 mg/kg). Palm oil is notably high in tocopherols and tocotrienols, of which a-tocopherol and a-tocotrienol make up 20% to 30% each with most of the remainder as y-tocotrienol. 

Much less is known on the antioxidant activity of tocotrienols than tocopherols. Tocotrienols were shown to have similar reactivities to peroxyl radicals and antioxidant activities than tocopherols in solution and membranes (Yoshida et ah, 2003) also, in general, y-tocotrienol was a better antioxidant than a-tocotrienol, and tocotrienols were better than tocopherols in oil systems (Seppanen et ah, 2010). Recently, Muller et ah (2010) conducted a comparative study to investigate the four tocopherols, four tocotrienols, and a-tocopheryl acetate on their antioxidant activities in five different popular in vitro assays (FRAP, a-TEAC, DPPH, ORAC, and CL), which were adapted to nonpolar antioxidants. Most notably, they found that a-tocopheryl acetate, a popular ingredient in supplements, had no significant antioxidant activity in vitro. However, once ingested, tocol esters are hydrolyzed and antioxidant activities are retained. Overall, the eight tocols performed similarly in the five assays. The authors concluded that in vitro antioxidant assays performed in polar solvents are not a good way to predict in vivo antioxidant activity. 

Figure 4.1. Vitamin E vitamers, tocopherois and tocotrienois, and the synthetic water-soluble vitamin E analog, Trolox. Relative molecular masses (Mr) a-tocopherol, 430.7 (acetate 488.8, succinate 546.8) , 6-tocopherol, 419.7 y-tocopherol, 416.7 5-tocopherol, 402.7 a-tocotrienol, 424.7 , 6-tocotrienol, 410.7 y-tocotrienol, 410.7 5-tocotrienol, 396.7 and Trolox, 250.3.

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