Biocatalytic acid reduction

Scheme 8.5 A biocatalytic (whole-cell) acid reduction scheme. AOR aldehyde oxidoreductase, ADH alcohol dehydrogenase.

Diacids. The microbial generation of mahc, fumaric, and succinic acid essentially imphes Krebs cycle pathway engineering of biocatalytic organisms to overproduce oxaloacetate as the primary four-carbon diacid that subsequently undergoes reduction and dehydration processes (Scheme 2.9). The use of these four-carbon diacids as intermediate chemicals and the state of their desirable microbial production is briefly outlined. 

The biocatalytic reduction of carboxylic acids to their respective aldehydes or alcohols is a relatively new biocatalytic process with the potential to replace conventional chemical processes that use toxic metal catalysts and noxious reagents. An enzyme known as carboxylic acid reductase (Car) from Nocardia sp. NRRL 5646 was cloned into Escherichia coli BL21(DE3). This E. coli based biocatalyst grows faster, expresses Car, and produces fewer side products than Nocardia. Although the enzyme itself can be used in small-scale reactions, whole E. coli cells containing Car and the natural cofactors ATP and NADPH, are easily used to reduce a wide range of carboxylic acids, conceivably at any scale. The biocatalytic reduction of vanillic acid to the commercially valuable product vanillin is used to illustrate the ease and efficiency of the recombinant Car E. coli reduction system." A comprehensive overview is given in Reference 6, and experimental details below are taken primarily from Reference 7. 

Venkitasubramanian, P., Daniels, L. and Rosazza, J.P.N., Biocatalytic reduction of carboxylic acids mechanism and application. In Biocatalysis in the Pharmaceutical and Biotechnology Industries, Patel, R. (ed). CRC Press LLC Boca Raton, FL, 2006, pp. 425-440. 

The significance of chiral unnatural amino acids to drug and natural product synthesis is shown in the example of the antihypertensive dmg omapatrilat (Vanlev ), which is composed of no less than three amino acid derived intermediates [144-147]. Diverse biocatalytical approaches to L-6-oxonorleucine were made (Fig. 21). Two different enzymes were applied in reductive amination reactions to produce derivatives of the desired intermediate. 

Two biocatalytic routes were also developed to the pilot stage by Ciba-Geigy, namely the enantioselective reduction of the corresponding a-keto acid with immobihzed Proteus vulgaris (route A in Scheme 12.10) and with D-LDH in a membrane reactor (route B), respechvely. It was therefore of interest to compare the four approaches. The EATOS (Environmental Assessment Tool for Organic Syntheses) program was used to compare the mass consumption (kg input of raw materials for 1 kg of product) as well as other parameters [28]. 

In summary, a broad range of large-scale applicable biocatalytic methodologies have been developed for the production of L-amino acids in technical quantities. Among these industrially feasible routes, enzymatic resolutions play an important role. In particular, L-aminoacylases, L-amidases, L-hydantoinases in combination with L-carbamoylases, and /l-lactam hydrolases are efficient and technically suitable biocatalysts. In addition, attractive manufacturing processes for L-amino acids by means of asymmetric (bio-)catalytic routes has been realized. Successful examples are reductive amination, transamination, and addition of ammonia to rx,/fun-saturated carbonyl compounds, respectively. 

R)-3-(4-fluorophenyl)-2-hydroxy propionic acid 1 is a building block for the synthesis of Rupintrivir, a rhinovirus protease inhibitor currently in human clinical trials to treat the common cold (Fig. 1) [1, 2], Retrosynthetically, Rupintrivir was prepared from four fragments the lactam derivative Pi, the chiral 2-hydroxy acid P2 (compound 1), the valine derivative P3, and an isoxazole acid chloride P4 (Fig. 1). In this chapter the preparation of 1 using a biocatalytic reduction performed in a membrane reactor will be discussed in detail. 

In a further example, phenyl boronic add-functionalized CdSe/ZnS QDs were used to bind NADor NADH via the boronic acid ligand to form boronate esters. The quenching of the QDs luminescence by the NAD + cofactor, via an ET quenching route, was substantially more efficient than was the quenching of QDs by NADH. This difference in quenching between NAD and NADH enabled QDs to be used for the luminescence analysis of NAD -dependent enzymes and their substrates, such as the AlcDH/ethanol system [141] (Figure 6.31a). The biocatalytic reduction of the... 

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