Oxidations enzymatic

Enzymatic fat splitting Enzymatic hydrolysis Enzymatic methods Enzymatic oxidation Enzymatic resolutions... 

Adipoyl moiety is first attached ia order to provide an appropriately spaced proximal carbonyl group. The esters are oxidized enzymatically and then deacylated. The procedure results ia the synthesis of diols (119) with excellent enantiomeric purity (ee 96—98%) ia 72—92% yield. 

Monosaccharides can be oxidized enzymatically at C-6, yielding uronic acids, such as D-glucuronic and L-iduronic acids (Figure 7.10). L-Iduronic acid is similar to D-glucuronic acid, except for having an opposite configuration at C-5. Oxidation at both C-1 and C-6 produces aldaric acids, such as D-glucaric... 

Much of the chemistry of monosaccharides is the familiar chemistry of alcohols and aldehydes/ketones. Thus, the hydroxyl groups of carbohydrates form esters and ethers. The carbonyl group of a monosaccharide can be reduced with NaBH4 to form an alditol, oxidized with aqueous Br2 to form an aldonic acid, oxidized with HNO3 to form an aldaric acid, oxidized enzymatically to form a uronic acid, or treated with an alcohol in the presence of acid to form a glycoside. Monosaccharides can also be chain-lengthened by the multistep Kiliani-Fischer synthesis and can be chain-shortened by the Wohl degradation. 

Figure 10.19 Oxidative enzymatic generation of dihydroxyacetone phosphate in situ for stereoselective aldol reactions using DHAP aldolases (a), and extension by pH-controlled, integrated precursor preparation and product liberation (b).

Belkner et al. [32] demonstrated that 15-LOX oxidized preferably LDL cholesterol esters. Even in the presence of free linoleic acid, cholesteryl linoleate continued to be a major LOX substrate. It was also found that the depletion of LDL from a-tocopherol has not prevented the LDL oxidation. This is of a special interest in connection with the role of a-tocopherol in LDL oxidation. As the majority of cholesteryl esters is normally buried in the core of a lipoprotein particle and cannot be directly oxidized by LOX, it has been suggested that LDL oxidation might be initiated by a-tocopheryl radical formed during the oxidation of a-tocopherol [33,34]. Correspondingly, it was concluded that the oxidation of LDL by soybean and recombinant human 15-LOXs may occur by two pathways (a) LDL-free fatty acids are oxidized enzymatically with the formation of a-tocopheryl radical, and (b) the a-tocopheryl-mediated oxidation of cholesteryl esters occurs via a nonenzymatic way. Pro and con proofs related to the prooxidant role of a-tocopherol were considered in Chapter 25 in connection with the study of nonenzymatic lipid oxidation and in Chapter 29 dedicated to antioxidants. It should be stressed that comparison of the possible effects of a-tocopherol and nitric oxide on LDL oxidation does not support importance of a-tocopherol prooxidant activity. It should be mentioned that the above data describing the activity of cholesteryl esters in LDL oxidation are in contradiction with some earlier results. Thus in 1988, Sparrow et al. [35] suggested that the 15-LOX-catalyzed oxidation of LDL is accelerated in the presence of phospholipase A2, i.e., the hydrolysis of cholesterol esters is an important step in LDL oxidation. 

G. Palmieri, G. Cennamo and G. Sannia, Remazol Brilliant Blue R decolorisation by the fungus Pleurotus ostreatus and its oxidative enzymatic system. Enz. Microbiol. Technol., 36 (2005) 17-24. 

Eor example, in the intestinal tract and liver of both humans and animals DEHP is rapidly hydrolyzed by esterases to yield mono-(2-ethylhexyl) phthalate (MEHP) and 2-ethylhexanol [25]. The latter metabolite is subsequently oxidized enzymatically to 2-ethyl hexanoic acid (2-EHXA) [26]. MEHP, 2-hethylhexanol, and/or their metabolites are the immediate inducers of the majority of enzymes known to be affected by exposure of DEHP [27]. Due to the high importance of the primary and secondary PAE metabolites in the human exposure smdies, during the last years a big number of smdies have been conducted to prove that some of them are appropriate biomarkers to calculate human PAE intake [28-30] and that their determination is easier than calculate it through food intake, which are more time consuming and subjects to several error sources. 

CO the oxygen which is oxidized enzymatically. This was done by comparing the kinetics of demethylation of the unsymnetrical trideuterated DMN, undeuterated DMN and hexadeuterated DMN. The kinetic characteristics of Z-DMN-d3 were similar to OMN-d and different from DMN-d0. Equilibrated DMN-d3 (equal amounts of the Z and E isomers) exhibited kinetics intermediate between DMN-djj and DMN-d0. 

Foodstuff Mai Hard Reaction Oxidation Enzymatic Degradation other Reactions... 

Oxidation of xanthine and hypoxanthine Xanthine and hypoxanthine can he oxidized enzymatically with xanthine oxidase to produce uric acid. 

One hundred grams of fresh beets from five randomly selected roots are used for analysis. The tissue is blended for 1 min with 100 ml ethanol/water mixture (50 50, v/v) under a stream of nitrogen to lessen oxidative enzymatic reactions. The blender walls are washed with 100 ml of water, and the mixture is blended for an additional 5 min under nitrogen. Fifty grams of this homogenate are removed, filtered over a 10-g bed of celite, and washed with 300-400 ml of water until the tissue-celite mixture is colorless. The filtrate is quantitatively transferred to a 500-ml volumetric flash and brought to volume. An adequate dilution (1 5) of this sample is used for HPLC analysis. 

Toluene tends to enter brain tissue, which it affects, and accumulates in adipose tissue. Unlike benzene, toluene possesses an aliphatic side chain that can be oxidized enzymatically, leading to products that are readily excreted from the body. The metabolism of toluene is thought to proceed via oxidation of the methyl group and formation of the conjugate compound hippuric acid, as shown in Figure 13.9. 

The hydrodimers D 3 are also oxidized enzymatically with the horseradish peroxid-ase-H202 system, the reactions being considerably more rapid in this case. Under these conditions, the methylated dimers D2 and D3 are quantitatively transformed to the parent monomers. In the case of dimer Dl5 however, formation of the monomer... 

Lipids do not escape damage by reactive intermediates. Lipids are oxidized in number of ways. They may be oxidized enzymatically, or via free-radical interaction (enzyme independent), or they can also be oxidized in a free-radical-independent,... 

When comparing chemical and biocatalytic methods, one could say that, especially for asymmetric oxidations, enzymatic methods enter the scene. This is most evident in the area of asymmetric Baeyer-Villiger oxidation, where biocatalysts take the lead and homogeneous chiral catalysts lag far behind in terms of ee values. Significant progress can be expected in the area of biocatalysis due to the advancement in enzyme production technologies and the possibility of tailor-made enzymes. 

Similar to biologic oxidation, enzymatic oxidation of drugs opened a way to studies on the preparation of optically active sulfoxides by enzymatic procedures. Among numerous reports a typical example is the oxidation of aryl aminoalkyl sulfides by dopamine -hydoxylase (DBH) in Ae presence of some electron donors to afford the sulfoxide with high enantioselectivity (equation 54). °... 

Pascal, S., Taton, M. and Rahier, A. (1993) Plant sterol biosynthesis. Identification and characterization of two distinct microsomal oxidative enzymatic systems involved in sterol C4-demethylation. /. Biol. Chem., 268,11639-54. 

Thioredoxin from E. coli is a heat stable small acidic protein (pi 4.4—4.5) with a molecular weight of about 12,000 (37, 115—118). It consists of a single polypeptide chain with 108 amino acid residues the complete amino acid sequence has been determined (Fig. 2). Thioredoxin can occur in the oxidized or reduced state. Reduced thioredoxin contains two cysteine residues in positions 32 and 35 which can be oxidized enzymatically or chemically to the disulfide bridge of cystine. Only two... 

It might then be oxidized enzymatically with hydrogen peroxide to produce a polymer, as described in Chap. 9. A final cure with diisocyanates or bisoxazolines would yield the equivalent of a phenol-formaldehyde resin without use of the carcinogenic formaldehyde. Terephthalic acid for polyethylene terephthalate) might be made by the oxidation of p-cymene, although two carbon atoms would be... 

Heterocydes are common motifs in natural products, which may occur as single, tandem, and multiple moieties within a given molecule (Scheme 8.5) [35-37]. These motifs often provide molecular interaction with nudeotide and protein targets. In the biosynthesis of NRPs, an oxazoline was usually formed from a dipeptide containing serine in the second position upon dehydration (Scheme 8.5) [38]. The syntheses of a thiazoline from cysteine and a 2-methyloxazoline from threonine follow a similar mechanism. These heterocycles can be further custom-made to provide thiazolidines/oxazolidines upon reduction or thiazoles/oxazoles upon oxidation. Enzymatic heterocyclization can be portable, as demonstrated in the synthesis of novel chiral heterocyclic carboxylic adds by hybrid enzymes [39]. 

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