Reduction of hydroperoxides

Extensive studies have established that the catalytic cycle for the reduction of hydroperoxides by horseradish peroxidase is the one depicted in Figure 6 (38). The resting enzyme interacts with the peroxide to form an enzyme-substrate complex that decomposes to alcohol and an iron-oxo complex that is two oxidizing equivalents above the resting state of the enzyme. For catalytic turnover to occur the iron-oxo complex must be reduced. The two electrons are furnished by reducing substrates either by electron transfer from substrate to enzyme or by oxygen transfer from enzyme to substrate. Substrate oxidation by the iron-oxo complex supports continuous hydroperoxide reduction. When either reducing substrate or hydroperoxide is exhausted, the catalytic cycle stops. 

The fast reduction of hydroperoxide by Sn(II) is used in stannometric technique of hydroperoxide estimation. 

Polarography is successfully used for the estimation of hydroperoxides and peracids [60], The reduction of hydroperoxide proceeds according to the electrochemical equation ... 

Enthalpies, Activation Energies, and Rate Constants of the Reduction of Hydroperoxides by Alkyl Radicals Calculated by I PM Model [68]... 

Peroxidases are heme iron-containing proteins similar in structure to that of cytochromes P450. The major difference is that peroxidases have histidine as the axial ligand instead of cysteine, and there are also other polar amino acids close to the heme iron that help to catalyze the peroxidase function of the enzyme (41). The result is that the peroxidases very rapidly catalyze the reduction of hydroperoxides to alcohols (or water in the case of... 

By selective modification of the serine 221 at the active site of the protease sub-tilisin Carlsberg to its seleno derivative, peroxidase activity was achieved and utilized for the enantioselective reduction of hydroperoxides (Table 6). In con-... 

The reduction of hydroperoxides may be coupled with the oxidation of phenol in the presence of 4-aminoantipyrine (81) to yield a quinoneimine dye (186), determined... 

The reduction of hydroperoxides with LiAlH, yields the corresponding alcohols probably via an LiAl(OR)4 intermediate. However this reaction with Bz202 resulted in an explosion (Ref 1) Cumene hydroperoxide (91-95% pure) will not detonate even when strongly boostered. However, it is easily ignitable can burn with sufficient violence to rupture steel distillation equipment (Ref 4)... 

Reduction of carboxylic acids 9-42 Reduction of carboxylic esters 9-43 Reduction of carboxylic esters with titanocene dichloride 9-44 Reduction of anhydrides 9-45 Reduction of acyl halides 9-53 Reduction of nitriles 9-57 Reduction of hydroperoxides 9-60 Reduction of peroxides 9-69 Reaction between aldehydes and base (Cannizzaro)... 

The zinc dithiophosphates (7) appear to be active antioxidants they produce sulfur acids by reduction of hydroperoxides and also act as radical scavengers (B-79MI11502). 

Figure 30. Enantioselective reductions of hydroperoxides to alcohols for the synthesis of...

As already mentioned, one of the products of action of hydroxyl radicals on proteins is protein hydroperoxides (G6). Valine and lysine residues are particu-larily susceptible to hydroperoxide formation. Reduction of hydroperoxides produces respective hydroxy derivatives of amino acids. Three valine hydroxides derived from hydroperoxides of this amino acid have been characterized structurally as p-hydroxyvaline [(2S)-2-amino-3-hydroxy-3-methyl-butanoic acid], (2S,3S)-y-hydroxyvaline [(2S,3S)-2-amino-3-hydroxymethyl-butanoic acid], and (2S,3R)-y -hydroxyvaline [(2S,3R)-2-amino-3-hydroxymethyl-butanoic acid (Fig. 12). They are suggested to be possible markers of protein peroxidation (F21). 

The oxygen-oxygen bond of peroxides is easily reduced and many standard reducing agents are capable of cleaving the bond efficiently. Catalytic and other methods have been reviewed. Whereas the reduction of hydroperoxides leads to the formation of alcohols, considerable selectivity is possible in the products derived from disubstituted peroxides. Hydroperoxides and disubstituted peroxides are, therefore, discussed separately below, even though some of the reduction methods are identical. Reductive ozonolysis of alkenes has also been included as a separate third category. 

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