Carbonyl reductases enzymes

Prior to the widespread awdlabdity of recombiant carbonyl reductases enzymes, the use of microbial reductions using either actively growing or dormant cells was commonplace Bakers yeast in particular, was a readily available source of stereoselective carbonyl reductases enzymes. Even with the widespread knowledge of the power of recombinant CRED biocatalysts, the literature is still rife with wild-type whole-cell microbial reductions. The reductions presented have advanced well beyond the early Bakers yeast reduction and have an apphcation even today. When the whole-cell fermentation is developed and finely tuned, high titers of product alcohol are possible and Scheme 6.4 shows m example of a keto-amide 12 bioreduction performing at 100 g/L with more than 98% ee with multi-kg isolation [12]. The bioprocess was performed over 8 days at pH 7 using the yeast Candida sorbophila. 

Coexpression of Genes for Carbonyl Reductase and Cofactor-Regenerating Enzymes... 

Figure 8.15 Coexpression of genes for carbonyl reductase and cofactor-regenerating enzymes [llc,dj.

Baker s yeast has been widely used for the reduction of ketones. The substrate specificity and enantioselectivity of the carbonyl reductase from baker s yeast, which is known to catalyze the reduction of P-keto ester to L-hydroxyester (L2-enzyme) [15], was investigated, and the enzyme was found to reduce chloro-, acetoxy ketones with high enantioselectivity (Figure 8.32) [24aj. 

The usefulness of the carbonyl reductase from Candida magnoliae as an enzyme catalyst in the synthesis of chiral alcohol intermediates has been demonstrated by carrying out the reduction of several ketones on a preparative scale [56]. The isolated yields and enantiomeric excess of the product alcohols are summarized in Table 7.1, from which it can be seen that these chiral alcohols were obtained in essentially optically pure forms in excellent yields. These chiral alcohols are important intermediates in the synthesis of pharmaceuticals and agrichemicals. For example, optically active 2-hydroxy-3-methylbutyrate is an important chiral synthon... 

Zhu, D., Yang, Y., Buynak, J.D. and Hua, L. (2006) Stereoselective ketone reduction by a carbonyl reductase from Sporobolomyces salmonicolor. Substrate specificity, enantioselectivity and enzyme—substrate docking studies. Organic and Biomolecular Chemistry, 4 (14), 2690-2695. 

The carbonyl reductases catalyze reduction of aldehydes and ketones by reduced pyridine nucleotides (NADH and/or NADPH). As mentioned earlier, alcohol dehydrogenase can perform this function in the presence of a high ratio of NADH to NAD+. Other enzymes capable of carbonyl reduction include the aldehyde and ketone reductases. The aldehyde and ketone reductases have a ubiquitous species distribution, with the enzymes present in organisms ranging from bacteria to vertebrates. The mammalian carbonyl reductases have been extensively reviewed (101). 

There are a number of findings suggesting that agents that facilitate elimination of protein carbonyls (by either proteolytic elimination or by enzymically mediated chemical reduction) may suppress neurodegenerative conditions in model systems (Botella et al., 2004). Consequently, as carnosine may also react with protein carbonyls, it is theoretically possible that it could suppress formation and /the reactivity of protein carbonyls in the brain. Whether carnosine participates in carbonyl reductase activity has not been investigated but it is also a reasonable speculation. 

In a photometric assay NADP(H)-dependent LBADH (see above) [9] and NAD(H) -dependent Candida parapsilosis carbonyl reductase (CPCR) [40] were identified as suitable catalysts accepting a broad range of ynones as substrates. Both enzymes catalyze the reduction of various aryl alkynones 21 with high enantioselectivity and efficiency (Scheme 2.2.7.13) [41]. 

Carbonyl Reductase Inhibition (Aldo-Keto-Reductase Family of Enzymes)... 

The enzyme catalyzing the reduction of ketopantolactone to D-pantolactone was isolated in a crystalline form from the cells of Candida parapsilosis and characterized in some detail [106] (see Tables 4 and 5). It is a novel NADPH-dependent carbonyl reductase with a molecular mass of about 40,000. In addition to the reduction of ketopantolactone, the enzyme catalyzes those of a variety of cyclic diketones, including derivatives of ketopantolactone, isatin, camphorquinone and so on, to give the corresponding (R)-alcohols [106, 107], The enzyme was termed conjugated polyketone reductase , since the enzyme catalyzes only the reduction of conjugated polyketones as follows. 

Carbonyl reductases and alcohol and aldehyde dehydrogenases are cytosolic enzymes being involved in the oxidation of alcohols and aldehydes and in the reduction of aldehydes and ketones (Lang and Kalgutkar 2003). 

This bioreduction system is applicable to the production of many other useful chiral alcohols by replacing the carbonyl reductase gene with that of another appropriate enzyme for carbonyl reduction (Fig. 19.6). A good library of microbial carbonyl reductases with different substrate and stereospecifici-... 

Synthetic statins are important lipid regulating drugs for the treatment of atherosclerosis and other diseases related to hyperlipidaemia, especially coronary heart disease. As the pharmacophore, all synthetic statins contain a saturated or partially unsaturated syn-3,5-dihydroxy C7-carboxylate. An important building block for the synthesis of the side chain is represented by 4-chloro-3-hydroxybutanoate esters (CHBE). Both enantiomers can be obtained by enzyme-catalyzed reduction of the (1-keto ester. The group of Kataoka and Shimizu found that an aldehyde reductase of Sporobolomyces salmonicolor [161] and a carbonyl reductase of Candida... 

Haloperidol is a butyrophenone neuroleptic drug. The enzymes involved in its biotransformation include oxidative cytochrome P450 isozymes, carbonyl reductase, and uridine diphosphoglucose glucuronosyltransferase (1). It is mainly cleared by glucuronidation. 

In addition to this, that an interesting novel emulsion membrane reactor concept overcomes the difficulties of the large solvent volume otherwise required for the reduction of poorly soluble ketones [30]. 2-Octanone was reduced by a carbonyl reductase from Candida parapsilosis to (S)-2-octanol with > 99.5 % ee and total turnover number of 124 - the 9-fold value of that obtained in a classical enzyme reactor. 

Lactate dehydrogenases represent another important subgroup of carbonyl reductases. They reduce a-oxo acids enantiospecifically to a-hydroxy acids. Both the D- and the L-selective enzymes are available, giving access to both enantiomers of various a-hydroxy acids [39]. 

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