Ketobutyrate

L-threonine deaminase [9024-34 ] 4.2.1.16 L-threonine — 2-ketobutyric acid + NH3 antineoplastic... 

The only tetrasubstituted furans that have been prepared using the Feist-Benary reaction are substituted tetrahydrobenzofurans and octahydrodibenzofurans. This strategy was pioneered by Stetter and Chatterjea and applied in a series of total syntheses by Magnus. Stetter demonstrated that 1,3-cyclohexanedione (30) can act as the P-dicarbonyl component and readily combines with either 3-bromo-2-ketobutyric (29) acid or ethyl 2-chloroacetoacetate (32) in the presence of potassium hydroxide to yield tetrahydrobenzofuran derivatives 31 and 33, respectively. ... 

Co(kbtsc)(Hkbtsc) has the 2-ketobutyric acid thiosemicarbazone (H2kbtsc) bound as both a mono-and di-anion, with small differences between the two forms found in the crystal structure.1058... 

In the synthesis of propionyl-CoA, the PDC competes with the enzyme of the isoleucine biosynthetic pathway for 2-ketobutyrate (Fig. 3). Since the PDC has a... 

The wild type ilvA gene was modified to target the protein to the plastid and expressed in A. thaliana. Transgenic plants showed a 20-fold increase in levels of 2-ketobutyrate as well as a large increase in 2-aminobutyrate, the transaminated product of 2-ketobutyrate [27, 41]. The levels of threonine remained stable whereas isoleucine concentration increased. Constitutive expression of the ilvA protein along with bktB, phaA, and phaC proteins in the plastids of A. thaliana led to the synthesis of poly(3HB-co-3HV) in the range of 0.2 - 0.8 % dry weight, with a HV level between 4-17 mol % [27,41]. Co-expression of the iso-... 

Fig. 3. Generation of propionyl-CoA from the isoleucine biosynthetic pathway. The intermediate 2-ketobutyrate can be decarboxylated by either the 2-oxoacid dehydrogenase complex or at low efficiency by the pyruvate dehydrogenase complex. Inhibition of the threonine deaminase by isoleucine and of the acetolactate synthase by herbicides are indicated with dashed arrows...

Selectively deuterated 1-aminocyclopropanecarboxylic acid ACC 71 was prepared to investigate the biosynthesis of ethylene in plants [105 a] and of ammonia and 2-ketobutyrate in Pseudomonas [105bj. 

EC 1.11.1.7) (68) and diphenol oxidase (EC 1.10.3.1) (69) have been identified. The potential role of pyruvic decarboxylase (EC 4.1.1.1) catalyzed reaction as a source of acetaldehyde and other aldehydes in juice was discussed (70). Raymond et al. (71) isolated the decarboxylase from orange juice sections and demonstrated that only 10 to 15% of the enzyme was in an active form. Since the purified enzyme was only active with pyruvic acid and 2-ketobutyric acid of the series of 2-ketoacids examined, they (71) concluded that the direct contribution of orange pyruvic decarboxylase to the orange volatile profile was limited to acetaldehyde and possibly propionaldehyde. 

Methionine 7-lyase, in contrast, has been purified from Aeromonas sp., Pseudomonas putida and Clostridium sporogenes (361. This enzyme effects a a,y-elimination of methanethiol and ammonia from L-methionine with the direct formation of 2-ketobutyrate ... 

In addition to the identification of the appropriate biosynthetic enzyme, the feasibility of all biotransformation processes depends heavily on other criteria, such as the availability of inexpensive starting materials, the reaction yield, and the complexity of product recovery, hi the case of transaminase processes, the reversible nature of the reaction (Scheme 3.1) and the presence of a keto acid by-product is a concern that limits the overall yield and purity of product and has led to efforts to increase the conversion beyond the typical 50% yield of product.99 100 Additionally, there are cost considerations in the large-scale preparation of keto acid substrates such as 2-ketobutyrate, which are not commodity chemicals. 

Threonine dehydratase catalyzes the formation of 2-ketobutyrate from threonine, and pyruvate from serine. This assay can be used to examine the reaction in the presence of both substrates. 

The quinoxalone derivatives of pyruvate and 2-ketobutyrate were separated on a /iBondapak Qg reversed-phase column (3.9 mm x 300 mm). The mobile phase was a mixture of acetonitrile, methanol, and 40 mM phosphate buffer (pH 7) (5 8 12, v/v/v) run at a flow rate of 1 mL/min. Detection could be carried out spectrophotometrically at 254 nm, or fluorometrically with excitation and emission wavelengths of 340 and 389 nm, respectively. 

First, the enzyme has at least two and probably three active-site basic groups involved in proton transfers to and from substrates, intermediates, and nascent products and all three bases are located on the si face of the substrate-PLP aldimine system as are the protons to be shuffled about, so all the proton transfers are likely to be economically suprafacial. Several pieces of stereochemical evidence suggest that the j5,y-olefinic PLP-p-quinoidal-a-anion (141) can rotate around its C(P)-C(ol) bond and also implicate that the cisoid isomer of this n complex and then the Z-isomer of the nascent aminocrotonate carry 80 % of the reaction flux. Furthermore, a 15% internal retention of the from the Pro-R methylene of ACPC (9) on B2H (85 % exchange with solvent, 15 % internal return) in the active site and the overall 22/78 H /H5 distribution at C(3) of the mono- and dideutero 2-ketobutyrate (138) products at C(3) are also noted. 

Aminocyclopropane carboxylic acid deaminase, obtained from Pseudomonas bacteria, decomposes 6 to ammonia and 2-ketobutyrate (647)3 i43.733-735 gy using R- and S-2,2-dideuterio-(6) it was shown that the methyl group in 647 has its specific origin in the pro-S methylene moiety of 63 ... 

Threonine can be broken down by tw o separate pathways. Serine dehydratase catalyzes the conv ersion of threonine to 2-ketobutyrate plus an ammonium ion 2-ketobutyrate is then converted by branched-chaln keto acid (BCKA) dehydrogenase to propionyl-CoA plus carbon dioxide. Propionyl-CoA catabolism is described later in this chapter. Threonine can also be broken down by a complex that has been suggested to be composed of threonine dehydrogerraseand acetoacetone synthase (Tressel ef al., 1986). Here, threonine catabolism results in the production of acetyl CoA plus glycure. 

Propan-1-ol is directly originated by the loss of the 2-ketobutyric acid carboxyl group and subsequent reduction of propionic aldehyde formed. 

Acetoacetic Acid. 3-Oxobutanoic acid diaceiic add acetylacetic add acetonecarboxylic acid 3-fcetobutyric acid 2-ketobutyric acid. C4H6Oj mol wt 102.09. C 47.06%, H 5.92%. O 47.02%. CH,COCH2COOH. Prepd by hydrolysis of ethyl acetoacetate Krueger, J. Am. Chem. Soc. 74, 5536 (1952),... 

Fig. 3.22. GC separation of keto and hydroxy acids from the urine of a patient with maple syrup urine disease. Top chromatogram, the patient before dietary treatment middle chromatogram, the same patient after two days on a diet bottom chromatogram, a mixture of reference compounds. Peaks 1, lactic acid 2, 2-hydroxyisobutyric acid 3, 2-hydroxybutyric acid 4, pyruvic acid 5, 3-hydroxyisobutyric acid 6, 3-hydroxybutyric acid 7, 2-hydroxyisovaleric acid 8, 2-ketobutyric acid 9, malonic acid (internal standard) 10, 2-methyl-3-hydroxybutyric acid 11, 2-hydroxy-n-valeric acid 12. methylmalonic acid 13, 3-hydroxyisovaleric acid 14a and b, 2-ketoisovaleric acid IS, acetoacetic add 16, 2-hydroxyisocaproic acid 17, 2-hydroxy-3-methylvaleric acid 18a, L-2-keto-3-methylvaleric add 18b, D-2-keto-3-methyl-valeric acid 19, 2-ketoisocaproic acid. Reproduced from [386],...

Loss of tritium originally present at C-2 of methionine can be accounted for if 4-amino-2-ketobutyric acid is an intermediate derivable from 2,4-diaminobutyric acid. Ring closure of the amino-ketone would give azetine-2-carboxylic acid... 

The presence of Sotolon in foodstuffs has been reported to be the result of an aldol condensation between 2-ketobutyric acid and pyruvic acid 10), similar to the mechanism proposed for the 5-ethyl-3-hydrox> -4-methyl-2(5H)-furanone formation in protein hydrolysates (77). The aldol condensation between acetaldehyde and 2-ketobutyric acid has also been suggested (77) to explain the presence of Sotolon in fortified type wines. 

Otlier mechanisms, which exclude 2-ketobutyric acid as a reactant have also been reported, such as Sotolon formation from chemical or enzymatic conversion of 4-hydroxyisoleucine (78,79) as a product of reaction from hexoses and pentoses in the presence of cysteine (20) and from the aldol... 

Other analytical measurements Redox potential, free SO2 concentration and chromatic index were performed (27). Acetaldehyde, higher alcohols (28), acetals (7), 2-ketobutyric acid (9) and furanic aldehydes (29) were determined. The concentration of dissolved oxygen was measured using a WTW 340 Oxygen Probe . 

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