Hydroxyisocaproate

Enzyme-catalyzed syntheses of enantiomeric pure hydroxy acids use lactate dehydrogenases (LDH E.C. 1.1.1.27) or hydroxyisocaproate dehydrogenases (HicDH). Both kinds of enzymes are available as D- or L-specific catalysts. L-specific [5, 6] LDHs as well as D-specific [7-10] LDHs favorably catalyze the reduction of pyruvate, HicDHs (and mandelate dehydrogenase, too) convert keto acids with longer aliphatic or aromatic side chains. These enzymes can be isolated from Lactobacillus strains [11-14]. 

There are two lactate dehydrogenases (LdHs) with different stereospecificities that have been very useful for the preparation of chiral 2-hydroxy acids.33 4 L-LdH (E.C. 1.1.1.27) and D-LdH (E.C. 1.1.1.28) are obtained from various microbial sources (Table 19.1). Along with hydroxyisocaproate... 

Selected Substrates and Stereochemical Product Configuration with Lactate (L) and Hydroxyisocaproate (Hie) Dehydrogenases (dH) from Various Sources that Catalyze the Reaction Shown in Scheme 19.2... 

Commercially available C. boidinii-FDH was used to recycle the NADH cofactor in stereospecific reductions by (/ )-2-hydroxyisocaproate dehydrogenase from L. casei [174]. Enantiomerically pure (R)-2-hydroxy-4-methylpentanoic acid was obtained with 88% yield. The broad substrate specificity of this enzyme enables the synthesis of a broad range of enantiomerically pure ot-hydroxy acids with aliphatic or aromatic side chains. 

Mandelic acid Benzoylformic acid Hydroxyisocaproate dehydrogenase... 

Fig. 3-84. Separation of various monocarboxylic acids at an anion exchanger IonPac AS6 (CarboPac). - Eluent 0.0017 mol/L NaHCOj + 0.0018 mol/L Na2C03 flow rate 1 mL/min detection suppressed conductivity injection 50 pL solute concentrations 3 ppm fluoride (1), 40 ppm acetic acid (2), 20 ppm glycolic acid (3), 10 ppm a-hydroxyisocaproic acid (4), 20 ppm formic acid (5), oxamic acid (6), methanesulfonic acid (7), amidosulfonic acid (8), and a-ketoisocaproic acid (9).

Asymmetric protonations of prochiral ketenes, metal enolates or enamines are performed with chiral alcohols, amines or amine salts [552], Recently, good enantiomeric excesses ( 80%) have been obtained in ketene protonations with the following a-hydroxyesters methyl (R)- or ([Pg.88]

The reaction is catalyzed by D-hydroxyisocaproate dehydrogenase (D-HicDH). The essential cofactor PEG-NADH is regenerated from PEG-NAD+ by a second enzyme, formate dehydrogenase (FDH). By coupling to water-soluble polyethyleneglycol with a molar mass of 20 000 g mol-1, the cofactor can be retained, together with the enzymes, by an ultrafiltration membrane, and the whole process may be performed continuously in an enzyme membrane reactor. 

Fukuda and coworkers have described one of the first applications of the enantioselective hydrolysis of nitriles (Scheme 12.1-6). Using a whole cell biocatalyst optically pure a-hydroxy acids (L-a-hydroxyisovaleric acid and L-a-hydroxyisocaproic acid) have been prepared from the racemates of the corresponding a-hydroxyni-... 

Little is known about the metabolism of branched-chain amino acids in parasites. Addition of leucine to Trichomonas vaginalis results in the production and release of a-hydroxyisocaproate synthesized via the corresponding keto acid, a-ketoisocaproate... 

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],...

FDH, Formate dehydrogenase L-HicDH, L-Hydroxyisocaproate dehydrogenase LeuDH, Leucine dehydrogenase PheDH, Phenylalanine dehydrogenase. 

DL-phenyllactic acid + NH D- and L-hydroxyisocaproate dehydrogenase + Phe dehydrogenase Eactobacillus casei ... 

Schustolla D, Deckwer WD, Schiigerl K et al. (1992) Enzyme purification by immobilized metal ion affinity partitioning — application to D-hydroxyisocaproate dehydrogenase. Bioseparation 3(2-3) 167-175... 

Hummel W, Schiitte H, Kula MR (1985) D-2-Hydroxyisocaproate dehydrogenase from Lactobacillus casei. A new enzyme suitable for stereospedfic reduction of 2-ketocarboxylic acids. Appl Microbiol Biotechnol 21 7-15... 

Amino-acid analogs DL-a-Amino-n-octanoate, D-a-aminophenylacetate, p-amino-DL-phenylalanine, M-benzoyl-DL-leucine, L-a-hydroxyisocaproate, a-ketoisocaproate, N-methyl-DL-leucine [747]... 

The sequence of reactions leading to the synthesis of leucine originates with the condensation of 2-oxoisovalerate and acetyl-CoA to form 3-carboxy-3-hydroxyisocaproate (a-isopropylmalate) (Fig. 5). An isomerization which entails dehydration and rehydration results in formation of a... 

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