Candida parapsilosis carbonyl reductase

For reduction of acetylenic ketones, two oxidoreductases were used [25]. Lactobacillus brevis alcohol dehydrogenase (LBADH) gave the (R)-alcohols and Candida parapsilosis carbonyl reductase (CPCR) afforded the (S)-isomer, both in good yield and excellent enantioselectivity. By changing the steric demand of the substituents, the enantiomeric excess values can be adjusted and even the configurations of the products can be altered (Figure 8.34). 

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]. 

R. erythropolis Rhodococcus erythropolis CPCR Candida parapsilosis carbonyl reductase ... 

In a direct comparison of the reduction of acetophenone to highly enantio-en-riched (R)-phenylethanol (94% e.e.) by heterogenized (S)-diphenyloxazaborolidine (Corey-Itsuno catalyst) or to enantiomerically pure (S)-phenylethanol (> 99% e.e.) by Candida parapsilosis carbonyl reductase (CPCR), the superior solubility of acetophenone in THF (0.25 m) versus water (0.04 m) leads to a vastly superior space-time yield of 290 g (L d) 1 in THF with the Corey-Itsuno catalyst in comparison with 27 g (L d) 1 in water with CPCR (Rissom, 1999). Conversely, the turnover frequencies (tofs) of 0.3 min-1 (Corey-Itsuno catalyst) versus 2.3 x 104 min-1 (CPCR) portend the difference in total turnover number (TTNs) of 2.4 x 108 versus 560. 

R.Z. Zhang, Y. Xu, Y. Sun, W.C. Zhang, R. Xiao, Ser67Asp and His68Asp substitutions in Candida parapsilosis carbonyl reductase alter the coenzyme specificity and enantioselectivity of ketone reduction, Appl. Environ. Microbiol. 75 (2009) 2176-2183. 

Figure 13 Reaction schemes for the synthesis of (5)-l-phenyl-2-propanol and (5)-2-octanol (ADH, alcohol dehydrogenase CPCR, Candida parapsilosis carbonyl reductase FDH, formate dehydrogenase).

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. 

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. 

As a new option, for the bioconversion of poorly soluble substrates the classical EMR-concept can be extended to an Emulsion Membrane Reactor , comprising a separate chamber for emulsification (with a hydrophilic ultrafiltration membrane), an EMR-Ioop with a normal ultrafiltration module, and a circulation pump. This approach has been successfully demonstrated for the enzymatic reduction of poorly soluble ketones [107]. Using this device, e.g., for the enantioselective reduction of 2-octanone to (S)-2-octanol (e.e. >99.5%) with a carbonyl reductase from Candida parapsilosis under NADH-regeneration with FDH/for-mate, the total turnover number was increased by a factor 9 as compared with the classical EMR. 

D-Pantoyl lactone Carbonyl reductase (Candida parapsilosis) 350 (100)... 

Fig. 11 Biotechnological approaches for the production of y-valerolactone (y-VL) from levulrnic acid. The key step is the bioreduction of levulinic acid 4-hydroxyvalerate (4-VL), which subsequently can lactonize to y-VL. (a) Biotransformation using Pseudomonas putida whole-cell overexpression of thioesterase tesB and paraoxonase I PONl (Martin et al. 2010). (b) A new variant of 3-hydroxybutyrate dehydrogenase 3HBDH from Alcaligenes faecalis catalyzes the bioreduction of levulinic acid to 4-hydroxyvalerate (4-HV) (Yeon et al. 2013). (c) Chemoenzymatic route using carbonyl reductase from Candida parapsilosis CPCR2 and lipase B CAL-B from Candida antarctica (Gotz et al. 2013)...

Until now, several oxidoreductases or microorganisms have been used in the preparation of chiral alcohols including NAD -dependent alcohol dehydrogenases (ADHs) from yeast and horse liver [11] (EC 1.1.1.1), Candida parapsilosis [12] and Pseudomonas sp. [13], and NADP -dependent ADHs from yeast [14], Thermoanaer-obium brockii [15] and Lactobacillus kefir [16], aldehyde reductases from Sporobolo-myces salmonicolor (EC 1.1.1.2) [17] and Penicillium citrinum (EC 1.1.1.21) [18], and carbonyl reductase (EC 1.1.1.184) from Candida magnoliae [19]. Our research group has reported an efficient method for producing both enantiomers of chiral alcohols... 

A novel NADH-dependent carbonyl reductase with an extremely broad substrate range from Candida parapsilosis purification and characterization. Enzyme Microbiol. Technol, 15, 950-958. 

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