Oxidations sugars

Other possible chemical synthesis routes for lactic acid include base-cataly2ed degradation of sugars oxidation of propylene glycol reaction of acetaldehyde, carbon monoxide, and water at elevated temperatures and pressures hydrolysis of chloropropionic acid (prepared by chlorination of propionic acid) nitric acid oxidation of propylene etc. None of these routes has led to a technically and economically viable process (6). 

A number of mechanistic pathways have been identified for the oxidation, such as O-atom transfer to sulfides, electrophilic attack on phenols, hydride transfer from alcohols, and proton-coupled electron transfer from hydroquinone. Some kinetic studies indicate that the rate-determining step involves preassociation of the substrate with the catalyst.507,508 The electrocatalytic properties of polypyridyl oxo-ruthenium complexes have been also applied with success to DNA cleavage509,5 and sugar oxidation.511... 

Uronic acids are found in nature, but they are formed enzymically by selective oxidation of the primary alcohol function of a sugar. Oxidation takes place not on the free sugar, but on UDPsugar... 

The kinetics and mechanisms of the oxidation of DNA, nucleic acid sugars, and nucleotides by [Ru(0)(tpy)(bpy)] and its derivatives have been reported. " The Ru =0 species is an efficient DNA cleavage agent it cleaves DNA by sugar oxidation at the 1 position, which is indicated by the termini formed with and without piperidine treatment and by the production of free bases and 5-methylene-2(5//)-furanone. Kinetic studies show that the I -C— activation is rate determining and a hydride transfer mechanism is proposed. The Ru =0 species also oxidizes guanine bases via an 0x0 transfer mechanism to produce piperidine-labile cleavages. 

Figure 3. Ozone alteration of dehydrogenases active in sugar oxidation in soybean leaves. Each mean is based on eight observations.

Farrer BT, Thorp HH (2000) Redox pathways in DNA oxidation kinetic studies of guanine and sugar oxidation by para-substituted derivatives of oxoruthenium(IV). Inorg Chem 39 44-49 Fasman GD (1975) Handbook of biochemistry and molecular biology. Nucleic acids. CRC Press, Cleveland... 

The complex Ru(tpy)(bpy)02 [tpy = 2,2,2"-terpyridine, bpy = 2,2 -bypyridine] oxidizes organic substrates by hydride abstraction or oxo transfer. This complex, and its derivatives, cleave DNA by oxidation of the sugar at the V position and oxidation of guanine. Oxidation at the V position leads to the release of free bases and a furanone product. The kinetic parameters for the oxidation of D-ribose, 2-deoxy-D-ribose, and nucleotides by Ru(tpy)(bpy)02 were determined in phosphate buffer (pH 7). The increased reactivity of DNA as compared to RNA was rationalized on the basis of deactivation of the sugar oxidation product by the polar effect of the 2 -hydroxyl group.160... 

The oxidant can be formulated either as a hydroxy radical bound to Cu(II) or as a hydroxide ligand on Cu(III). In either case, the activated complex is capable of strand scission, and the cleavage pattern suggests that the oxidant is nondiffusible and therefore bound to the metal (17). Cleavage by this reagent involves sugar oxidation, as discussed in subsequent paragraphs. 

The ability to incorporate deuterium or tritium selectively into appropriate positions on nucleotides has had a tremendous impact on mechanistic studies on sugar oxidation. In particular, Stubbe and coworkers have shown that when thymidine deuterated at the 4 position is incorporated into restriction fragments, sequence-selective isotope effects are observed for cleavage by Fe-BLM (12). These isotope effects are essentially equal for the radical and carbocation pathways (Scheme... 

Kline and Acree studied the hypoiodite oxidation extensively. The alkali and iodine were both added in small portions throughout the reaction. In this manner the concentration of sugar relative to the sodium hypoiodite was kept at a level favorable to the sugar oxidation (reaction 14). At the end of the reaction, the formation of iodate increased rapidly (reaction 15), taking precedence over the oxidation of ketoses and non-reducing sugars. 

Sugar oxidation measurements equilibrium solutions at O.S°C. crystalline sugars ... 

The 3rields of aldonic and oxalic acids are shown in Table XI. They are based on the amount of sugar oxidized (determined by reducing value) and not on the total amount of starting material. The formation of L-arabonic acid occurs with the highest percentage yield, but even this is low compared with other methods of preparation. As the lactobionic acid was isolated as the calcium lactobionate-calcium bromide salt, the actual amount of product, expressed in millimoles, is very low. 

The conversion of a-hydroxy acids into aldehydes with one less carbon has great importance in the chemistry of sugars. Oxidation with bromine water transforms aldoses into the corresponding aldonic acids, which, in the form of their calcium salts, are treated with aqueous hydrogen peroxide in the presence of ferrous or ferric sulfate (Fenton reagent) and are degraded to aldoses with one less carbon (Ruff degradation) (equation 479) [57]. 

Sugar oxidizing enzyme Surface Mediator Cell conditions Potential (V) Current density (mAcrn ) (approx.) Ref. 

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