D-2-hydroxy acid dehydrogenase

ACID-BASE RELATIONSHIPS OXYGEN, OXIDES 0X0 ANIONS d-2-HYDROXY-ACID DEHYDROGENASE (S)-2-HYDROXY-ACID OXIDASE 3-HYDROXYACYL-CoA DEHYDROGENASE /3-HYDROXYACYL THIOESTER (or, ACP) DE-HYDRASE... 

A limited quantity of D-lactate is converted to pyruvate by a mitochondrial flavoprotein enzyme D-2-hydroxy acid dehydrogenase. Thus, the development of D-lactate acidosis requires excessive production of D-lactate and an impairment in its metabolism. The clinical manifestations of D-lactic acidosis are characterized by episodes of encephalopathy after ingestion of foods containing carbohydrates. 

Transfer of a hydride between substrate and coenzyme and proton relay in active site of an NADH-dependent D-2-hydroxy acid dehydrogenase. 

Adam, W., Lazarus, M., Saha-Moller, C.R. and Schreier, P. (1998) Quantitative transformation of racemic 2-hydroxy acids into (R)-2-hydroxy acids by enantioselective oxidation with glycolate oxidase and subsequent reduction of 2-keto acids with D-lactate dehydrogenase. Tetrahedron Asymmetry, 9 (2), 351-355. 

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... 

Stereospecific reductions of a-keto acids are well documented. l- and D-lactate dehydrogenases from common mammalian or bacterial sources are available for this purpose. By using a preselected l- or d-LDH, the preparation of a (2S)- or (2/ )-hydroxy acid of >99% ee can be virtually assured. The structural range of a-keto acids (29) that has been subjected to preparative-scale reductions to hydroxy acids... 

Table 16.2-8. Conversion of racemic 2-hydroxy acids into (R)-2-hydroxy acids by the combined action of glycolate oxidase and D-lactate dehydrogenase[,8).

Kinetic resolutions have a maximum yield of only 50%. Therefore, a second enzymatic process was added after completion of the glycolate oxidase-catalyzed kinetic resolution[131). By addition of D-lactate dehydrogenase (E.C. 1.1.1.28) together with formate dehydrogenase for NADH regeneration, enantiospecific reduction of the 2-keto acid was achieved. Overall, a quantitative transformation (deracemization) of the racemic 2-hydroxy acid into the corresponding (R)-2-hydroxy acid was achieved (Fig. 16.2-29). 

R)-2-Hydroxy-4-phenylbutyric acid was produced continuously in an enzyme membrane reactor by enzymatic reductive animation of the a-keto acid with d-lactate dehydrogenase coupled with formate dehydrogenase (FDH) for regeneration of NADH. Reactor performance data matched a kinetic reactor model (Schmidt, 1992). 

The following abbreviations will be used ADH—alcohol dehydrogenase DPN — diphosphopyridine nucleotide DPNH—reduced diphosphopyridine nucleotide OP—1,10-phenanthroline 8-OHQ—8-hydroxyquinoline a,a -D—a,a -dipyridyl 8-OHQ5SA—8-hydroxyquinoline-5-sulfonie acid TU—thiourea EDTA—ethylene-diamine tetraacetic acid zincon —2-carboxy-2 -hydroxy-5-sulformazylbenzene diamox — sodium 2 - acetylamino -1,3,4- thiodiazole - 5 - sulf onamide NaDDC — so -dium-diethyldithiocarbamate CGP—carbobenzoxyglycyl-L-phenylalanine. 

A more recent EMR-process for the enantioselective reduction of 2-oxo-4-phenylbutyric acid (OPBA) to (R)-2-hydroxy-4-phenylbutyric acid (HPBA, e.e.>99.9%) with NADH-de-pendent D-lactate dehydrogenase (D-LDH) from Staphylococcus epidermidis and FDH/for-mate for co-factor recycling uses free NADH instead of PEG-NADH [100, 101] (Fig. 3). Within the selected residence time of 4.6 h, a cycle number for the co-factor of 1000 can easily be achieved. Instead of NADH, the less expensive NAD+ is used. A second reason for the application of the native co-enzyme is the fact that the activity of D-LDH is reduced to one tenth when PEG-enlarged co-enzyme is used instead of the native co-enzyme. HPBA produced by this method with a space-time yield of 165 g 1 d-1 is of considerably higher enantiomeric purity and the process shows competitive economy in comparison with chemical... 

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