Influence of the ethanol and glucose supply rate on the rate and enantioselectivity of 3‐oxo ester reduction by baker's yeast

Abstract

Baker's-yeast-mediated reductions of ketones hold great potential for the industrial production of enantiopure alcohols. In this article we describe the stoichiometry and kinetics of asymmetric ketone reduction by cell suspensions of bakers' yeast (Saccharomyces cerevisiae). A system for quantitative analysis of 3-oxo ester reduction was developed and allowed construction of full mass and redox balances as well as determination of the influence of different process parameters on aerobic ketone reduction. The nature of the electron donor (ethanol or glucose) and its specific consumption rate by the biomass (0-1 mol.kg dw(-1).h(-1)) affected the overall stoichiometry and rate of the process and the final enantiomeric excess of the product. Excess glucose as the electron donor, i.e. a very high consumption rate of glucose, resulted in a high rate of alcoholic fermentation, oxygen consumption, and biomass formation and therefore causing low efficiency of glucose utilization. Controlled supply of the electron donor at the highest rates applied prevented alcoholic fermentation but still resulted in biomass formation and a high oxygen requirement, while low rates resulted in a more efficient use of the electron donor. Low supply rates of ethanol resulted in biomass decrease while low supply rates of glucose provided the most efficient strategy for electron donor provision and yielded a high enantiomeric excess of ethyl (S)-3-hydroxybutanoate. In contrast to batchwise conversions with excess glucose as the electron donor, this strategy prevented by-product formation and biomass increase, and resulted in a low oxygen requirement.

Strain engineering for stereoselective bioreduction of dicarbonyl compounds by yeast reductases

“…A different strategy to lower the co‐substrate utilisation rate has consisted of controlling the supply of co‐substrate via the fed‐batch technique. The fraction of co‐substrate used for co‐factor regeneration has been increased from 2% on glucose batch to 25% and 38% on ethanol and glucose fed‐batch, respectively, during the aerobic reduction of β‐keto ester 3b [67]. The fed‐batch process, however, requires higher investment costs for more elaborate reactors, feed pumps and process monitoring.…”

A complex process of the asymmetric reduction of prochiral aromatic ketone by yeast cell with the introduction of an organic solvent as the separation medium

“…Second, it provides an electronic donator for the asymmetric reduction. [24] The effect of ACP concentration on the asymmetric reduction in a biphasic system Figure 4 is the result of the effect of the initial ACP concentration on the asymmetric reduction reaction in the biphasic system. The experiments were carried out with 1 : 4 of φ o/w and the initial ACP concentrations increasing from 10 to 60 mmol/l.…”

Oxidation of a mixture of 2-(R) and 2-(S)-heptanol to 2-heptanone bySaccharomyces cerevisiaein a biphasic system

“…Baker's yeast, Saccharomyces cerevisiae, is generally used to prepare enantiomerically pure chiral compounds (Bertau and Burli, 2000;Chin-Joe et al , 2001;Novak et al , 2001;Orlich and Schomaecker, 1999). These reactions mainly correspond to reduction processes.…”