5-Trideuteromethyl-α-tocotrienol and 5-14CH3-α-tocotrienol as biological tracers of tocotrienols

Tocopherol activity correlates with its location in a membrane: a new perspective on the antioxidant vitamin E

We show evidence of an antioxidant mechanism for vitamin E which correlates strongly with its physical location in a model lipid bilayer. These data address the overlooked problem of the physical distance between the vitamin's reducing hydrogen and lipid acyl chain radicals. Our combined data from neutron diffraction, NMR, and UV spectroscopy experiments all suggest that reduction of reactive oxygen species and lipid radicals occurs specifically at the membrane's hydrophobic-hydrophilic interface. The latter is possible when the acyl chain "snorkels" to the interface from the hydrocarbon matrix. Moreover, not all model lipids are equal in this regard, as indicated by the small differences in vitamin's location. The present result is a clear example of the importance of lipid diversity in controlling the dynamic structural properties of biological membranes. Importantly, our results suggest that measurements of aToc oxidation kinetics, and its products, should be revisited by taking into consideration the physical properties of the membrane in which the vitamin resides.

Assignment of the 1H and 13C NMR of tocotrienols

Vitamin E is a family of chromanols that vary by the degree of methylation of the chroman ring as well as the nature of the hydrophobic side chain at C2 that serves to anchor these lipids in biological membranes. The tocopherols contain saturated side chains, whereas the tocotrienols contain three sites of unsaturation and are derived from geranylgeranyl diphosphate. A growing interest in the unique biological activities of the tocotrienols has led us to begin syntheses of isotopically substituted forms and other derivatives that will be useful for probing the metabolism and membrane behavior of the tocotrienols. In order to be certain of our ability to selectively modify sites on the parent molecules it was necessary to make as complete an assignment of the 1H and 13C NMR as possible. Herein we report multidimensional NMR data (HSQC, COSY, ADEQUATE(1,1), C--H HMBC, and NOESY) that have allowed us to assign the identity of almost all the resonances for alpha-, beta-, gamma-, and delta-tocotrienol.

Synthesis of Vitamin E

Vitamin E compounds are biologically essential fat-soluble antioxidants derived from 6-chromanol. This chapter covers the representative literature on the preparation of various stereoisomeric forms and homologues of tocopherols and tocotrienols, and of respective starting materials and intermediates. The industrially most relevant (all-rac)-alpha-tocopherol is generally built up by coupling of arenes with aliphatic precursors. For the synthesis of optically active vitamin E components, various strategies are compiled. In approaches to chiral chroman and side chain building blocks, a broad variety of methods from the repertoire of asymmetric synthesis were applied, that is optical resolution and use of chiral pool starting materials and chiral auxiliaries in stoichiometric as well as catalytic amounts, including catalysis by metal complexes, microorganisms, and enzymes. Most efforts were directed to (2R,4'R,8'R)-alpha-tocopherol due to its prominent biological activity. Syntheses of different stereoisomers (and mixtures thereof) and (beta-, gamma-, delta-) homologues of tocopherols and tocotrienols, as well as methods for their interconversion, are also described.