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Mandelic acid racemase

In our laboratory we have been investigating the mechanism of action of mandelic acid racemase from Pseudomonas putida (101), which catalyzes the racemization of either D or L-mandelic acid, 47. Evidence from kinetic and isotopic exchange studies indicates that the racemization proceeds via an... [Pg.405]

On the basis of presently available information, mandelic acid racemase might display the simplest enzymatic proton transfer mechanism. The enzyme, isolated from Pseudomonas putida, catalyses the epimerization reaction [49] ... [Pg.402]

Faber and coworkers have reported a DKR of mandelic acid by using a lipase-catalyzed O-acylation followed by a racemization catalyzed by mandelate racemase. However, these two transformations do not take place simultaneously in the same pot. When the sequence was repeated four times, (S)-O-acetylmandelic acid was obtained in 80% isolated yield and >98% ee [57]. [Pg.107]

Faber et al. have reported a novel process for the overall deracemization of racemic mandelic acid derivatives using a combination of an enantioselective lipase and a mandelate racemase activity from Lactobacillus paracasei (Figure 5.19) [32]. [Pg.125]

The degradation of mandelic acid by the bacterium Pseudomonas putida (Chapter 25) is initiated by mandalate racemase, another (a/(3)8-barrel protein.101 X-ray structures of bound inhibitors together with modeling suggest that the side chain of Lys 264 is the catalytic base that abstracts the a-H from S-mandelate (Fig. 13-5) and that the catalytic pair of His 297 and Asp 270 acts as proton donor, or, in the reverse direction, as catalytic... [Pg.691]

Enolases mandelate racemase (MR), muconate-lactonizing enzyme (MLE), N-acetylamino acid racemase (NAAR) Hasson, 1998 Palmer, 1999... [Pg.464]

If Ke signifies the concentrations of enol and keto tautomers in a carboxylic acid, then pfCE is the difference between the pKa values of the a-protons of the keto tautomer and the hydroxyl group of the enol tautomer. pfCE, however, is also the difference in pfCa values between the a-protons and the proton of the carbonyl group of the carbonyl-protonated acid, that is deemed to be decisive (Gerlt, 1991) for the kinetics of abstraction of a proton, rather than the pfQ value of the substrate in solution. The pki of mandelic acid (15.4) links the pka of the a-proton of the keto tautomer (22.0) with the pK.d value of the enol tautomer (6.6). The pk, value also links the pka value of the a-proton with that of the carbonyl-bound proton of the protonated mandelic acid. If the pka value of the carbonyl-bound proton of the protonated mandelic acid is assumed to be about -8.0 then the pfQ value of the a-proton is about 7.4. This value matches well with the pka -values of Lys and His residues which have been assigned recently in the active center of mandelate race-mase, so electrophilic catalysis alone is able to explain the catalytic power of mandelate racemase. [Pg.481]

The first example of the use of a two-enzyme system in ionic liquids was reported by Kaftzik et al. [75], who investigated the deracemization of ( )-mandelic acid using a lipase-mandelate racemase two-enzyme system in ionic hquids (Fig. 7.9). They used a combination of the mandelate racemase-catalysed racemisation of (R)-mandelic acid and the lipase-catalysed kinetic resolution of (5)-mandelic acid to... [Pg.182]

The reaction to be catalyzed poses problems for the enzyme [34]. The abstraction of a proton from an aliphatic carbon atom is generally difficult and slow. The plf of the carbon-bound a-proton of mandelic acid is 22.0 [55], while the p/f the a-proton of the mandelate anion (as for the phenylacetate anion) is approximately 29 [36, 37]. In spite of this, mandelate racemase increases the rate of the racemiza-tion reaction by a factor of 1.7 x 10 to approximately 1000 per second at 25 °C at pH 7 [57, 55]. Interactions of mandelate with enzyme, analogous to those with inhibitor (5)-atrolactate in which one carboxylate oxygen atom is coordinated to the magnesium ion and also hydrogen-bonded to the e-ammonium group of Lysi 64,... [Pg.237]

A DKR process was used for the synthesis of (R)-mandelic acid ester from racemic mandelic acid using an aqueous/organic two-phase system with two enzymes. KR first took place with a lipase in the organic solvent and there was an in situ racemization in the aqueous medium by recombinant mandelate racemase. The procedure employed a hollow-fibre membrane bioreactor and gave (R)-mandehc acid ethyl ester in 98% ee and 65% yield (Scheme 4.36) [88]. [Pg.147]

The synthesis of optically pure L-phenylglycine via the deracemization of mandelic acid was reported via three steps (racemization, enantioselective oxidation and stereoselective reductive amination). Racemization by mandelate racemase combined with simultaneous oxidation and reduction reactions with cofactor recycling gave the amino acid in 97% ee and 94% yield (Scheme 4.43) [96]. [Pg.150]

More recently, the focus has been put on formal nucleophilic substitution of —OH or —NH2 groups. To perform this biocatalytic variant of the Mitsunobu reaction, an oxidation-nucleophilic addition-reduction sequence is necessary, for which linked NAD-dependent oxidoreductases are ideally suited. The early contributions from the Forschungszentrum Jiilich [79] have been recently rediscovered by Kroutil and coworkers [80]. By combining a mandelate racemase (MR) with a mandelate dehydrogenase and an L-amino acid dehydrogenase, the authors could completely transform racemic mandelic acid into enantiopure (S)-phenyl-glycine (Scheme 8.16). [Pg.226]

Complete conversion ofthe racemic starting material was achieved by in situ racemization of the nonconverted mandelic acid enantiomer by a mandelate racemase (MR). [Pg.227]

Mandelate racemase, another pertinent example, catalyzes the kinetically and thermodynamically unfavorable a-carbon proton abstraction. Bearne and Wolfenden measured deuterium incorporation rates into the a-posi-tion of mandelate and the rate of (i )-mandelate racemi-zation upon incubation at elevated temperatures. From an Arrhenius plot, they obtained a for racemization and deuterium exchange rate was estimated to be around 35 kcal/mol at 25°C under neutral conditions. The magnitude of the latter indicated mandelate racemase achieves the remarkable rate enhancement of 1.7 X 10, and a level of transition state affinity (K x = 2 X 10 M). These investigators also estimated the effective concentrations of the catalytic side chains in the native protein for Lys-166, the effective concentration was 622 M for His-297, they obtained a value 3 X 10 M and for Glu-317, the value was 3 X 10 M. The authors state that their observations are consistent with the idea that general acid-general base catalysis is efficient mode of catalysis when enzyme s structure is optimally complementary with their substrates in the transition-state. See Reference Reaction Catalytic Enhancement... [Pg.118]

Figure 13-5 An S-mandelate ion in the active site of mandelate racemase. Only some of the polar groups surrounding the active site are shown. The enzyme has two catalytic acid-base groups. Lysine 166 is thought to deprotonate S-mandelate to form the aci anion, while His 297 deprotonates R-mandelate to form the same anion.106... Figure 13-5 An S-mandelate ion in the active site of mandelate racemase. Only some of the polar groups surrounding the active site are shown. The enzyme has two catalytic acid-base groups. Lysine 166 is thought to deprotonate S-mandelate to form the aci anion, while His 297 deprotonates R-mandelate to form the same anion.106...
The plant acid S-mandelate must undergo conversion to R-mandelate by action of a racemase (Fig. 13-5) dehydrogenation, and side-chain cleavage as shown in Eq. 25-8 to form benzoate before it can be metabolized further.165... [Pg.1437]

Deracemization of mandelic add with the combined action of two enzymes has been reported. rac-MandeUc acid is acylated by a Pseudomonas sp. lipase in diisopropyl ether. After solvent removal the mfacture of mandeUc acid enriched in the R-form and the 0-acetyl derivative of the S-configuration are subjected to the mandelate racemase-catalyzed racemization in aqueous buffer. In these conditions only the non-acetylated hydroxy acid is racemized. In order to obtain (S)-0-acetylmandelic acid in an 80% isolated yield and a >98% e.e. the process must be repeated four times [9]. [Pg.198]


See other pages where Mandelic acid racemase is mentioned: [Pg.327]    [Pg.327]    [Pg.480]    [Pg.182]    [Pg.956]    [Pg.1152]    [Pg.236]    [Pg.237]    [Pg.1167]    [Pg.287]    [Pg.88]    [Pg.89]    [Pg.255]    [Pg.54]    [Pg.298]    [Pg.692]    [Pg.923]    [Pg.292]    [Pg.96]    [Pg.8]    [Pg.692]   
See also in sourсe #XX -- [ Pg.405 ]

See also in sourсe #XX -- [ Pg.402 ]




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Mandelate

Mandelate racemase

Mandelates

Mandelic acid

Mandell

Racemase

Racemases mandelate racemase

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