YS-Oxidation

The higher nucleophilicity of the yS-oxide ion may be attributed to a steric factor in combination with a kinetically effective stereoelectronic effect that results from repulsions of lone electron pairs, dipole effects, or both (Scheme 5) (45,46). This effect should be more pronounced in anomericy3-oxide ions... 

Acyl CoA dehydrogenases in fatty acid yS-oxidation. These enzymes eue especially sensitive to riboflavin depletion, and riboflavin deficiency is chtuacterized by impaired fatty acid oxidation and orgtinic aciduria (Section 7.4.1). These tue tdso the enzymes eiffected in riboflavin-responsive orgtinic acidurias. 

Enoyl-CoA hydratase (ECH commonly known as crotonase), that catalyzes the cofactor-independent hydration of conjugated enoyl-CoA esters in yS-oxidation, has been the subject of considerable debate regarding the timing of bond-making reactions and, therefore, the importance of a thioester enolate anion on the reaction coordinate. The active site contains Glu 144 and Glu 164 as the only possible acid-base catalysts. In the nonphysiological dehydration direction, the value of the pKa... 

Brigham CJ, Budde CF, Mahan AE, Rha C, Sinskey AJ (2010) Elucidation of yS-oxidation pathways in Ralstonia eutropha H16 by examination of global gene expression. J Bacteriol 192 5454-5464... 

Houten, SM Wanders, RJA. A general introduction to the biochemistry of mitochondrial fatty acid yS-oxidation. J Inherit Metab Dis, 2010 33 469-77. 

The yS-oxidation of fatty acids was the first metabolic process in which labelled compounds were used for its investigation. Knoop s classic experiments at the turn of the century were later confirmed and extended by others to reveal the details of the process (for references see Greville and Tubbs, 1968 Wakil,... 

Although it was known that the intermediates of the yS-oxidation cycle are chaimelled towards PHA biosynthesis, only recently the precursor sources were identified. In A. caviae, the y3-oxidation intermediate, trans-2-tnoy -CoA is converted to (R)-3-hydroxyacyl-CoA via (R)-specific hydration catalysed by an (R)-specific enoyl-CoA hydratase [125, 126]. Subsequently, Tsuge and co-workers [127] reported the identification of similar enoyl-CoA hydratases in Pseudomonas aeruginosa. In the latter case, two different enoyl-CoA hydratases with different substrate specificities channelled both SCL and MCL enoyl-CoA towards PHA biosynthesis. In recombinant . coli it was further shown that 3-ketoacyl-CoA intermediates in the )8-oxidation cycle can also be channelled towards PHA biosynthesis by a nicotinamide adenine dinucleotide phosphate dependent (NADPH-dependent) 3-ketoacyl-ACP reductase [128]. A similar pathway was also identified in P. aeruginosa [129]. In addition, it was also reported that the acetoacetyl-CoA reductase (PhaB) of R. eutropha can also carry out the conversion of 3-ketoacyl-CoA intermediates in Pathway II to the corresponding (R)-3-hydroxyacyl- CoA in E. coli [130]. The results clearly indicate that several channelling pathways are available to supply substrates from the y3-oxidation cycle to the PHA synthase. This explains why it was not possible to obtain mutants that completely lack PHA accumulation ability, unless the mutation occurred in the PHA synthase gene [131]. 

Like mitochondria, peroxisomes contain pathways for the /3-oxidation of fatty acids. The mechanism by which fatty acids enter peroxisomes is unclear but does not appear to involve the CPTl-CACT-CPT2 pathway. Long-chain and very-long-chain acyl-CoA synthetase activities are associated with peroxisomes, but it has not been established whether fatty acids or fatty acyl-CoAs traverse the peroxisomal membrane. The basic reactions of peroxisomal /3-oxidation resemble those found in mitochondria, but the peroxisomal and mitochondrial enzymes are distinct proteins (Figure 4). In fact, peroxisomes contain two sets of yS-oxidation enzymes, which appear to function with distinct substrates. 

Huang YS, Chen YE (1988) Electronic-structure study of RuS2. Phys Rev B 38 7997-8002 Salvador P, Alonso-Vante N, Tributsch H (1998) Photoelectrocatalytic study of water oxidation at n-RuS2 electrodes. J Electrochem Soc 145 216-225... 

Jerkiewicz G, Vatankhah G, Lessard J, Soriaga MP, Park YS. 2004. Surface-oxide growth at platinum electrodes in aqueous H2SO4 Reexamination of its mecharusm through combined cyclic-voltammetry, electrochemical quartz-crystal nanobalance, and Auger electron spectroscopy measurements. Electrochim Acta 49 1451-1459. 

Procedure 2 Oxidation of jS-Hydroxy Sulfides to yS-Hydroxy Sulfoxides Catalyzed by CHMO... 

The stereochemical trends discussed above are not limited to a, yS-unsaturated carbonyl compounds other Michael acceptors such as nitroalkenes and unsaturated phosphane oxides display similar behavior. A representative example for the nitroalkene class of Michael acceptors is shown with substrate 70 in Scheme 6.13 [28]. The best results were thus obtained for arylcuprates. Other organocuprates were much less selective, which severely restricts their application in organic synthesis. 

As shown by these equations, the different deprotonation pathways differ in their transition-state structures a 2/1 base-oxirane trimer of type 30 for a-deprotonation, compared with a 1/1 base-oxirane dimer of type 31 for yS-deprotonation (Scheme 13). Similar results have been reported for the -deprotonation of cyclohexene oxide by proline-derivated amides. ... 

We have explored two types of carbon-carbon bond forming reactions operated under almost neutral conditions. Both reactions are initiated by the formation of an H-Rh-Si species through oxidative addition of a hydrosilane to a low-valence rhodium complex. Aldol-type three-component couphngs are followed by the insertion of an a,yS-unsatu-rated carbonyl compound into a Rh-H bond, whereas silylformylation is accomplished by the insertion of an acetylenic moiety into a Rh-Si bond. 

Vogt H, Balej J, Bennett JE, et al. 1986. Chlorine oxides and chlorine oxygen acids. In GerhartzW, Yamamoto YS, Campbell FT, et al., eds. Ullman s encyclopedia of industrial chemistry. Vol. A6. New York, NY VCH, 483-500. 

Through the application of the general Eqs. (3)-(5) to complexes of the type [MgL2] and the related [MgL L] ones presenting a suitable auxiliary MgL j metal site with the basic Mg core, it has been possible to establish [20] relationships from which Eg and yS of the (MgLj center (Eqs. 9 and 10, respectively), as well as the oxidation potential of the complexes [MgL2] (Eq. 11), can be predicted, provided that one knows the oxidation potential of the dicarbonyl [Mg(CO)2], the Eg and /J of the auxiliary MgL site, and the Pi values of L and the auxiliary L ligand. 

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