Biochemical oxidations examples

In addition to their role in the formation of DNA and RNA (see Section 27.2), nucleotides have other important biological functions. For example, adenosine triphosphate (ATP) is an important energy carrier in biochemical reactions, and nicotinamide adenine dinucleotide is a coenzyme that is often involved in biochemical oxidation-reduction reactions. 

The Baeyer-Villiger reaction is also effected by biochemical oxidation using the enzyme cyclohexanone oxygenase from Acinetobacter strain NCIB 9871. Cyclohexanone is thus converted into e-caprolactone [1043], and phenylacetone (l-phenyl-2-propanone) is transformed into benzyl acetate. The formation of benzyl acetate from phenylacetone involves the same migration as that in oxidation with peroxytrifluoroacetic acid (equation 387) [1034]. More examples of biochemical Baeyer-Villiger reactions occur in diketones and steroids see equation 397). 

Nitrites occur as the simple NO anion. It is formed particularly by biochemical oxidation of ammonia nitrogen or biochemical reduction of nitrates. Some industrial wastewaters are very rich in nitrites, for example those from the production of some dyestuffs or from engineering works employing cutting liquids for cooling of machine tools such liquids contain nitrites as corrosion inhibitors. Nitrites in waters occur with nitrates and ammonia nitrogen only at low concentrations since they are biochemically and chemically labile. In clean ground- and surface waters only trace... 

It would be well to point out a few examples which illustrate the overlap of asymmetric reduction studies and molecular biochemistry. Diphosphopyridine nucleotide (DPN) and triphospho-pyridine nucleotide (TPN) are important coenzymes in biochemical oxidation reduction reactions. Certain enzymes function as catalysts for the reversible transfer of hydrogen between these nucleotides and a substrate for which the enzyme is specific. For example, DPN and the enzyme, alcohol dehydrogenase (ADH), form a redox system with ethanol. Using deuterium labeled reducing agent and substrate, Westheimer, Vennesland,... 

Moving to the kinetics, the addition of a catalyst is normally intended to increase the reaction rate. A small but important class of catalyst, termed inhibitors, acts to lower the rate, however. Such is the case for antioxidants which scavenge the radical intermediates in chain oxidation processes or preservatives that inhibit biochemical oxidation and consequent spoilage of food. The antioxidant vitamins C and E are well-known examples. 

Xanthophylls are the main carotenoids of plants. They primarily arise as products of biochemical oxidation (hydroxylation and epoxidation) of carotenes. Xanthophylls derived from acyclic carotenes occur in foods in small quantities. For example, tomatoes contain as minor pigments 1,2-epoxylycopene, 5,6-epoxylycopene, 1,2-epoxyphytoene and some other compounds. Much more common are monohydroxysubstituted alicyclic derivatives of carotenes called cryptoxanthins. Most plant materials contain small amounts of a-cryptoxanthin also called zeinoxanthin, derived from a-carotene (9-182) and P-cryptoxanthin, derived from... 

An example of the aerobic biochemical oxidation of acetic acid is thus CH3COOH + 20 -I- bacteria 2CO2 -I- H O... 

An example of the anaerobic biochemical oxidation of acetic acid is ... 

In many biochemical oxidation-reduction reactions, the transfer of hydrogen atoms is necessary for the production of energy in the cells. For example, methyl alcohol (CH3OH), a poisonous substance, is metabolized in the body by the following reactions ... 

As described in Section 4-1. one important class of chemical reactions involves transfers of protons between chemical species. An equally important class of chemical reactions involves transfers of electrons between chemical species. These are oxidation-reduction reactions. Commonplace examples of oxidation-reduction reactions include the msting of iron, the digestion of food, and the burning of gasoline. Paper manufacture, the subject of our Box, employs oxidation-reduction chemishy to bleach wood pulp. All metals used in the chemical industry and manufacturing are extracted and purified through oxidation-reduction chemistry, and many biochemical pathways involve the transfer of electrons from one substance to another. 

Type I MCRs are usually reactions of amines, carbonyl compounds, and weak acids. Since all steps of the reaction are in equilibrium, the products are generally obtained in low purity and low yields. However, if one of the substrates is a bi-funchonal compound the primarily formed products can subsequently be transformed into, for example, heterocycles in an irreversible manner (type II MCRs). Because of this final irreversible step, the equilibrium is forced towards the product side. Such MCRs often give pure products in almost quantitative yields. Similarly, in MCRs employing isocyanides there is also an irreversible step, as the carbon of the isocyanide moiety is formally oxidized to CIV. In the case of type III MCRs, only a few examples are known in preparative organic chemistry, whereas in Nature the majority of biochemical compounds are formed by such transformations [3]. 

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