Of 4-oxoacid

Esters of 4-oxoacids, such as ethyl levulinate, can also be cyclized in the cold by treatment with hydrogen sulfide under acid conditions. An early report (39JCS1116) described the conversion of diethyl 2-acetylsuccinate (168) to ethyl 2-methyl-5-ethoxythiophene-3-carboxylate (169), by treatment with hydrogen sulfide in alcoholic HC1 at 0 °C. The reaction was reviewed in 1977 <77PS(3)377) a large number of 4-oxoesters (170) were subjected to the hydrogen sulfide treatment, and the products were carefully isolated and characterized. 

The Mn(n)-catalysed BrOj" oxidation of 4-oxoacid in the presence of H2SO4 and Hg(II) ion as a Br ion scavenger has fractional order in both 4-oxoacid and Mn(II). The rates decrease with increasing dielectric constant of the medium. The solvent isotope... 

With concentrated nitric acid, selenium and tellurium form only their +4 oxoacids, H2Se03 and H2Te03 respectively, indicating a tendency for the higher oxidation states to become less stable as the atomic number of the element is increased (cf. Group V, Chapter 9). 

Figure 8.13 The central role of transdeamination in metabolism of amino adds and further metabolism of the oxoacids in the liver. The box contains the reactions for conversion of the amino acids to their respective oxoacids. Processes are as follows (1) digestion of protein in the intestine and absorption of resultant amino acids, (2) degradation of endogenous protein to amino acids (primarily but not exclusively muscle protein), (3) protein synthesis, (4) conversion of amino acid to other nitrogen-containing compounds (see Table 8.4), (5) oxidation to CO2, (6) conversion to glucose via gluconeogenesis, (7) conversion to fat.

Thioamides of 3-oxoacids 118 are transformed into 1,2,4-dithiazolidines 29 by treatment with cerium ammonium nitrate (CAN) in MeOH or with CF3SC1 in CH2CI2 (Equation 16) <1996SC4165, 2001SC189>. The thermal conversion of 6/7-1,3,5-oxathiazine A-oxides 119 in refluxing benzene results in 1,2,4-oxathiazolines 20 with extrusion of R CHO. This reaction involves the heterodiene intermediate 120, which can be independently trapped by the reaction with EtOH (Scheme 32) <2003TL2517, 2004HAC175>. 

It was very difficult to obtain the new compound of P d or P d as a solid salt, because a very small amount of P d or P d was present in very dilute aqueous solution. However, the preparation of a small volume of P d solution of relatively high concentration was successfully achieved by the following procedure the enrichment of phosphorus oxoacid species into a certain amount of an anion-exchange resin and the subsequent elution with a calculated volume of potassium chloride solution of a proper concentration. By adding small volumes of magnesium chloride solution and methyl alcohol to the resulting P d solution, 4 mg of magnesium salt of Pgd was obtained. 

Examples of Szilard-Chalmers reactions are given in Table 9.4. Radionuclides of the halides may be obtained in high specific activities by neutron irradiation of alkyl or aryl halides or of the salts of the oxoacids. Radionuclides of other elements may also be produced in high specific activities by neutron irradiation of covalent compounds. 

The presence of the second enzyme in the pathway in higher plants can be inferred from results obtained by Saytanrayana and Radhakrishnan (1965). NADPH-dependent conversion of the acetohydroxyacids to the oxo-analogues of isoleucine and valine indicated that partially purified extracts of Phaseolis radiatus contained the enzymes required to catalyze both the second and third reactions illustrated in Fig. 4. Reductoisomerase activity would require NADPH for synthesis of the dihydroxyacids which would, in turn, be dehydrated for synthesis of the oxoacids. The rates of NADPH oxidation differed when 2-acetolactate and 2-acetohydroxybutyrate were tested as alternate substrates, but it was not established whether more than one reductoisomerase was present in the preparations. 

Assay Methods. 2-Oxoacid ferredoxin oxidoreductase activity is determined by following the absorbance at 550 nm, due to the ferredoxin-dependent reduction of horse heart cytochrome c (Sigma Chemicals, St. Louis, MO) in the presence of 2-oxoacid substrates, essentially as described by Kerscher et al. The assay is conducted at 50°, in 10 mAf potassium phosphate buffer, pH 6.8, in the presence of 2-4 mAf 2-oxoacids (2-oxoglutarate purchased from Nacalai Tesque, Japan, was mainly used), 50-100 p,Af coenzyme A (Kohjin, Japan), 17 pg of the Sulfolobus zinc-containing ferredoxin (purified as described above), 50 pAf horse heart cytochrome c (Sigma Chemicals), and an appropriate amount of enzyme, in a total volume of 1 ml. The reaction is initiated by addition of the enzyme, and nonenzymatic reduction of cytochrome c by coenzyme A at this temperature is... 

Metal cations in molten halides form halide complexes. The reaction [10.4.20] for chloride melts (N. =1) suggests that the distribution of Me between different complexes MeCl remains unchanged (similarly to eq. [10.4.10]-[10.4.12] for the oxide ion distribution). It is clear that the solubility data may be used for estimations of the oxoacidity indices only in melts with the same anion composition. The anion changes cause errors since Me " in eq. [10.4.21] is referred to essentially different acids, e.g., halide complexes MeCL, and... 

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