Tocopherol derivatives

The occurrence of a 5a-C-centered tocopherol-derived radical 10, often called chromanol methide radical or chromanol methyl radical, had been postulated in literature dating back to the early days of vitamin E research,12 19 which have been cited or supposedly reconfirmed later (Fig. 6.5).8,20-22 In some accounts, radical structure 10 has been described in the literature as being a resonance form (canonic structure) of the tocopheroxyl radical, which of course is inaccurate. If indeed existing, radical 10 represents a tautomer of tocopheroxyl radical 2, being formed by achemical reaction, namely, a 1,4-shift of one 5a-proton to the 6-oxygen, but not just by a shift of electrons as in the case of resonance structures (Fig. 6.5). In all accounts mentioning... 

FIGURE 6.8 Hypothetical disproportionation of two a-tocopherol-derived radicals 2 and 10 in the absence of other coreactants to account for the formation of typical two-electron oxidation products (o-QM 3, a-tocopherol spiro dimer 9). 

Detailed Formation Pathway and Stabilization of the Tocopherol-Derived o-QM 3 and Other o-QMs... 

REACTIONS OF THE COMMON TOCOPHEROL-DERIVED OR77/0-QUINONE... 

Spiro Oligomerization/Spiro Polymerization of Tocopherol Derivatives... 

Spiro dimerization of the tocopherol-derived o-QM seemed to be a quite favored process, which proceeds also in the case of moderately bulky substituents at C-5a. 

While tocopherylacetic aicd (51), the lower Crhomologue of 3-(5-tocopheryl)-propionic acid (50) showed a changed redox behavior (see Section 6.5.1), compound 50 displayed the usual redox behavior of tocopherol derivatives, that is, formation of both ortho- and para-quinoid oxidation intermediates and products depending on the respective reaction conditions. Evidently, the electronic substituent effects that... 

FORMATION OF TOCOPHEROL-DERIVED o-QMs INVOLVING OTHER POSITIONS THAN C-5A... 

Rosenau T. PhD Thesis, Novel tocopherol derivatives. Dresden University of Technology, Dresden. 1997. 

GC analyses of the pupal secretion of E. borealis have indicated the presence of vitamin E acetate and other tocopherol derivatives [49,50]. However, in tests with ants, these compounds proved to be essentially inactive, whereas the secretion itself was potently deterrent. To find and identify the active components in the pupal Epilachna borealis secretion, NMR spectroscopic studies on the fresh secretion were carried out. One and two-dimensional NMR experiments revealed that the tocopheryl acetates account for only a relatively small percentage of the beetles5 total secretion (20%), whereas the major components represented a group of previously undetected compounds. By analysis of the COSY, HSQC and HMBC spectra of the mixture, these components were shown to be esters and amides derived from three (co-l)-(2-hydroxyethylamino)alka-noic acids 44-46. HPLC analyses coupled to a mass spectrometric detector revealed that the secretion contain a highly diverse mixture of macrocyclic polyamines, the polyazamacrolides (PAMLs) 47-52 (Fig. 8). 

Vitamin E a-Tocopherol Any of several tocopherol derivatives Antioxidant l... 

Vitamin E (a-tocopherol) has as its active form any of several tocopherol derivatives. It functions as an antioxidant. Vitamin E deficiency is rarely seen, but can lead to red blood cell fragility that leads to hemolytic anemia. It has no known toxicity. 

More recently, this same group have used a combination of HPLC-NMR and HPLC-MS to identify analogues of vitamin E found in a palm oil extract rich in such tocopherol derivatives [46]. For the MS, a new technique called coordination ion spray was used in which the addition of silver ions to the HPLC eluent caused the enhanced formation of ions of such non-polar compounds. In addition, the HPLC utilised a C30 column in order to gain suitable chromatographic resolution. The compounds in the mixture comprised vitamin E itself, tocopherol, and five related compounds, some of which were isomeric. Tocopherol has the structure shown below ... 

Rate constants for the reactions of S0o with a wide variety of organic compounds are summarized in Table 2. The sulfite radical was found to oxidize ascorbate, trolox (a water soluble tocopherol derivative), methoxyphenol, hydroquinone and other phenolic compounds, sulfonated hydroquinones, phenylenediamines, and phenothiazines with rate constants ranging to 1 CrM 1 s. ... 

---