As an indispensable factor in the mitochondrial respiratory chain, the role of coenzyme Q has been conclusively established. However, the details of the mechanism of how it functions are under investigation. The proton motive Q cycle theory proposed by Mitchell has stimulated the research on topology of coenzyme Q in mitochondrial membranes. The biosynthesis of coenzyme Q is considered in relation to that of cholesterol because they are derived from the same precursor, mevalonate. The clinical application of coenzyme Q10 to diseases supposed to be brought about by mitochondrial dysfunction has been developed, particularly in Japan. The physiological significance of exogenous coenzyme Q10 is discussed as a supplier of coenzyme Q10 to endogenous coenzyme Q pool in mitochondria, a membrane stabilizer and an antioxidant.
Synthesis of pseudo- hexopyranoses (2, 3, 4, 5- tetrahydroxy-1-cyclohexanemethanols) and their derivatives are reviewed. In addition, synthetic studies on naturally occurring antibiotics validamycins and α-amylase inhibitors, amylostatins, adiposins, etc., which are considered to be composed of the pseudo-sugar components, are described.
Interest in the structural dependence of the tautomerism between cycloheptatriene derivatives and their norcaradiene tautomers dates back to the proposal of the norcaradiene structure for “Buchner's ester”. Today, the tautomerism is recognized as a typical example of electrocyclic reactions. Very recently, the spectroscopic detection of the elusive parent norcaradiene (C7H8) has been reported. In the meantime, various factors have been found to affect the equilibrium between the cycloheptatriene and the norcaradiene form. The stabilization of the norcaradiene form by a π-acceptor group on C (7) is well recognized, both experimentally and theoretically, but there still remains the possibility that a π-donor group might also stabilize the norcaradiene form. Recently, steric factors have been shown to shift the equilibrium to the norcaradiene side. So far, thirteen systems have been subjected to structural analysis by X-ray, microwave, or electron-diffraction method ; however, the prediction of the structure - norcaradiene or cycloheptatriene-in crystal appears difficult for the equilibrating systems in solution. As reactions of interest the endoperoxide formation from cycloheptatriene-norcaradiene systems and singlet oxygen, stereochemistry of the Berson-Willcott rearrangement, and solvolytic reactions are reviewed.
Some of the photochemical reactions of γ, δ-epoxyenones of the ionone series which have been investigated by ETH-group during the years 1968-1984 are reviewed. In particular the influence of the various functional groups in the neghbourhood of the oxirane on the photochemical behavior is discussed. On n, π*-excitation, in general, the γ, δ-epoxyenones undergo (E/Z) -isomerization and/or product formation via cleavage of the C (γ), O-bond of the oxirane. Selective π, π*-excitation, however, also causes reactions which include cleavage of the C (γ), C (δ) -bond of the oxirane leading to ylide and carbene intermediates which undergo various reactions with participation of neighbouring groups. The types and the distribution of the isolated products dramatically depends on the functional group placed in ε-position. On vapor phase thermolysis, in general, the epoxyenones undergo a 1, 5-homosigmatropic H-shift with cleavage of the C (γ), C (δ) -bond of the oxirane leading in high yields to divinyl ethers. Furthermore, thermal rearrangements via ylide intermediates were also observed resulting in the same products as obtained on photolysis.
This is a review on the antioxidant action of transition metal dialkyldithiophosphates and dialkyldithiocarbamates in autoxidation of hydrocarbon. These complexes interrupt autoxidation by trapping chain-propagating peroxy radicals and by decomposition of hydroperoxides into non-radical products. Trapping peroxy radicals occurs at sulphur atom or at central metal atom of these complexes. Hydroperoxide decomposition proceeds in three stages, i. e. a fast homolytic decomposition followed by an induction period, and a fast heterolytic decomposition. In the first or the second stage, these complexes change into ionic catalysts which are responsible for the heterolytic decomposition of the third stage. The kinetics, the products and the mechanisms of inhibition by these complexes are summarized.
Diphosphorus tetraiodide (P2I4) is the only known stable halogeno derivative of diphosphine, which possesses a unique affinity for oxygen and thus behaves as a mild, efficient deoxygenating and dehydrating agent in the presence of various functionalities. In this brief article, potential aspects of P2I4 as organic reagent have been surveyed with an emphasis on the coverage of recent works.