Candida parapsilosis carbonyl reductase CPCR

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]. 

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

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).

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