Improvements in the Synthesis of a Key α-tocopherol, Intermediate[sbnd] (s)-(−)-3,4-Dihydro-6-Hydroxy-2,5,7,8-Tetramethyll-2H-1-Benzopyran-2-Acetic Acid

Top-down control analysis of the cadmium effects on molluscan mitochondria and the mechanisms of cadmium-induced mitochondrial dysfunction

Cadmium (Cd) is a toxic metal and an important environmental pollutant that can strongly affect mitochondrial function and bioenergetics in animals. We investigated the mechanisms of Cd action on mitochondrial function of a marine mollusk (the eastern oyster Crassostrea virginica) by performing a top-down control analysis of the three major mitochondrial subsystems (substrate oxidation, proton leak, and phosphorylation). Our results showed that the substrate oxidation and proton leak subsystems are the main targets for Cd toxicity in oyster mitochondria. Exposure to 12.5 μM Cd strongly inhibited the substrate oxidation subsystem and stimulated the proton conductance across the inner mitochondrial membrane. Proton conductance was also elevated and substrate oxidation inhibited by Cd in the presence of a mitochondrially targeted antioxidant, MitoVitE, indicating that Cd effects on these subsystems were to a large extent ROS independent. Cd did not affect the kinetics of the phosphorylation system, indicating that it has negligible effects on F₁, F(O) ATP synthase and/or the adenine nucleotide transporter in oyster mitochondria. Cd exposure altered the patterns of control over mitochondrial respiration, increasing the degree of control conferred by the substrate oxidation subsystem, especially in resting (state 4) mitochondria. Taken together, these data suggest that Cd-induced decrease of mitochondrial efficiency and ATP production are predominantly driven by the high sensitivity of substrate oxidation and proton leak subsystems to this metal.

Racemic and optically active tocopherol analogues with a modified side chain: Synthesis and biological activity (Review)

Information on the synthesis and biological activity of natural and synthetic analogues of alpha-tocopherol with a modified side chain is systematized. These compounds are of interest as vitamin E metabolites, hydrophilic antioxidants, and precursors of drugs with combined pharmacological properties useful in therapy of pathological disorders caused by oxidative stress.

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.

Tocopherol as singlet oxygen scavenger in photosystem II

Singlet oxygen is formed in the photosystem II reaction center in the quench of P680 triplets, and the yield is dependent on light intensity and the reduction level of plastoquinone. Singlet oxygen in PS II triggers the degradation of the D1 protein. We investigated the participation of tocopherol as a singlet oxygen scavenger in this system. For this purpose, we inhibited tocopherol biosynthesis at the level of the HPP-dioxygenase in the alga Chlamydomonas reinhardtii under conditions in which plastoquinone did not limit the photosynthesis rate. In the presence of the inhibitor and in high light for 2 h, photosynthesis in vivo and photosystem II was inactivated, the D1 protein was degraded, and the tocopherol pool was depleted and fell below its turnover rate/h. The inhibited system could be fully resuscitated upon the addition of a chemical singlet oxygen quencher (diphenylamine), and partly by synthetic cell wall permeable short chain alpha- and gamma-tocopherol derivatives. We conclude that under conditions of photoinhibition and extensive D1 protein turnover tocopherol has a protective function as a singlet oxygen scavenger.

Selective targeting of an antioxidant to mitochondria

Mitochondrial oxidative damage contributes significantly to a range of human disorders, including neurodegenerative diseases, ischaemia-reperfusion injury and ageing-associated dysfunction. To prevent this damage we have delivered a molecule containing the active antioxidant moiety of vitamin E to mitochondria. This was carried out by covalently coupling the antioxidant moiety to a lipophilic triphenylphosphonium cation. This mitochondrially targeted antioxidant, 2-[2-(triphenylphosphonio)ethyl]-3,4-dihydro-2, 5,7,8-tetramethyl-2H-1-benzopyran-6-ol bromide (TPPB), accumulated several-hundred fold within the mitochondrial matrix, driven by the organelle's large membrane potential. When cells were incubated with micromolar concentrations of TPPB, they accumulated millimolar concentrations within their mitochondria. The amount of TPPB taken up by mitochondria was approximately 80-fold greater than endogenous levels of vitamin E. Consequently the targeted derivative of vitamin E protected mitochondrial function from oxidative damage far more effectively than vitamin E itself. The mitochondrially targeted antioxidant TPPB has potential as an antioxidant therapy for disorders involving mitochondrial oxidative damage. It also suggests a new family of mitochondrially targeted antioxidants, redox-active and pharmacologically active molecules designed to prevent damage or manipulate mitochondrial function.