Ketoisovaleric acid

Capsaicin.—It is known that phenylalanine acts as the source of the vanillylamine moiety of capsaicin (132) in Capsicum annuum and that valine (136) is used for the construction of the acyl part.2 It has been noted107 that whilst radioactive valine (136) was incorporated into capsaicin (132) and its dihydro-derivative (133), L-[U-14C]leucine [as (137)] labelled the capsaicin analogues (134) and (135) in Capsicum fruits both amino-acid precursors were very considerably better incorporated into capsaicinoid metabolites by using spheroplasts prepared from the placentas of Capsicum fruits. or-Ketoisovaleric acid (138) and cr-ketoisocaproic acid... 

The 2,4-dinitrophenylhydrazone derivatives of a-ketoisovaleric acid and a-keto-jS-methylvaleric acid are separated from 2,4-dinitrophenylhydrazine by chromatography at room temperature on a Zorbax Cjg column (4.6 mm x 250 mm). Solvent A was 25% acetonitrile in water containing 0.1% triethyla-mine (v/v) and adjusted to pH 4.5 with acetic acid. Solvent B was acetonitrile. A linear gradient from 20 to 50% B was made within 20 minutes. The effluent was monitored at 254 nm. 

This vitamin is synthe.sized by most green plants and microorganisms. The precursors are y-ketoisovaleric acid and /S-alanine. The latter originates from the decarboxylation of aspartic acid. y-KetoLsovalcric acid is converted to keto-pantoic acid by Ar.W" -methyIenetetrahydrofolic acid then, on reduction, pantoic acid is formed. Finally, pantoic acid and alanine react by amide formation to form pantothenic acid. 

Figure 13.2 Analysis of a-keto acids in plasma [afterT. Hayashi, H. Tsuchiya and H. Naruse, J. Chromatogr., 273,245 (1983)]. Conditions sample, extract from 50 pi of human plasma, derivatized with o-phenylenediamine column, 25cm x 4mm i.d. stationary phase, LiChrosorb RP-8, Spm mobile phase, 1 ml min of 1 mM tetrapropylammonium bromide in 50 mM phosphate buffer-acetonitrile, gradient from 5 to 60% acetonitrile temperature, 50 C fluorescence detector, 350/ 410 nm. Peaks 1 = a ketoglutaric acid 2 = pyruvic acid (a-ketopropionic acid) 3 = a-ketoisovaleric acid 4 —a-ketoisocaproic acid 5 —a-keto-/3-methylvaleric acid IS = a-ketocaprylic acid (internal standard).

De Schepper et al. (D15) found also a-keto-P-methylvaleric acid in normal whole blood in contradiction to the previous results (H19) they detected also a-ketoisovaleric acid, the keto acid corresponding to valine. The concentration of this keto acid in normal whole blood of children is 0.13 0.02 mg% (Kl). Traces occur also in urine (Kl, VI). 

A reduction in the blood levels of a-ketoisocaproic, a-keto-P-methyl-valeric, and a-ketoisovaleric acids has been reported in patients with hepatic cirrhosis, whereas no significant variation was found during acute hepatitis (D4). 

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],...

L-Leucine is derived from L-valine by the x-keto acid elongation system, i.e., via x-ketoisovaleric acid and -carboxy-j8-hydroxyisocaproic acid as outlined in Fig. 199. The transformation of ot-ketoisovaleric acid to (X-ketoisocaproic acid closely resembles the conversion of oxaloacetic acid to (X-ketoglutaric acid in the tricarboxylic acid cycle (D 5). x-Ketbacid elongation systems also participate in the formation of L-lysine via the x-aminoadipic acid pathway (D 18) and in the biosynthesis of a number of secondary amino acids which are precursors of gluco-sinolates (D 9.4). 

Ketoisovaleric Acid Dimethylpyruvic acid, isoibulyrylformic acid, isopropylglyoxylic acid)... 

Updated Entry replacing M-02849 2-Oxoisopentanoic acid. cn-Ketoisovaleric acid. Dimethylpyruvic acid [759-05-7]... 

As with most other amino acids, the catabolism of valine is initiated by removal of its amino group, in this case to yield a-ketoisovaleric acid. L-Valine is readily susceptible to transamination, and it is slowly attacked by L-amino acid oxidase. The n-valine is readily deaminated by D-amino acid oxidase. ... 

Valine is glycogenic and antiketogenic. From the observation that a-ketoisovaleric acid and isobutyric acid, as well as valine, each con-... 

The sum total of facts indicates that a>ketoisovaleric acid yields leucine by decarboxylation and condensation with a C2 fragment. 

Valine is glycogenic and antiketogenic (78, 79). From the observation that a-ketoisovaleric acid and isobutyric acid, as well as valine, each contributed three of their carbons to the formation of glucose. Rose and coworkers (80) postulated the steps 1 and 2 shown in Fig. 5 in the catabolism of valine. Subsequently Atchley (81) was able to show that isobutyric acid is converted to propionic acid by the action of the fatty acid-oxidizing systems of liver and kidney. 

The ketol condensation scheme has received firm support and must be substantially correct. The evidence is reviewed below. Lewis and Wein-house 159) showed that extracts of yeast and E. cdi were capable of converting pyruvate to a-acetolactate. The latter was isolated as the osazone and shown to contain radioactivity derived from C -pyruvate. Strassman et al. 160) determined that yeast was able to convert aceto-lactate to a-ketoisovaleric acid. 

The final steps in the formation of valine and isoleucine is the transamination of a-ketoisovaleric acid and of a-keto-jS-methylvaleric acid to the corresponding amino acids. 

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