Archive | 2021
Enzymatic Dynamic Reductive Kinetic Resolution Towards 115 g/L (S)-2-Phenylpropanol
Abstract
\n BackgroundPublished biocatalytic routes towards chiral 2-phenylpropanol by oxidoreductases showed product concentrations of maximally 80 mM. Enzyme deactivation turned out as one major limitation and was attributed to adduct formation of the aldehyde substrate with the catalytic reductase.ResultsA Candida tenuis xylose reductase single-point mutant (CtXR D51A) with very high catalytic efficiency (43ยท103 s-1M-1) for (S)-2-phenylpropanal was identified. The enzyme showed high enantioselectivity for the (S)-enantiomer but was deactivated by 0.5 mM substrate within 2 h. A whole-cell biocatalyst based on the engineered reductase and a yeast formate dehydrogenase for NADH-recycling provided substantial stabilization of the reductase. The relatively slow in situ racemization of 2-phenylpropanal and the still limited biocatalyst stability required a subtle adjustment of the substrate-to-catalyst ratio. A value of 3.4 gsubstrate/gcell-dry-weight turned out as compromise between product enantiopurity and conversion. A catalyst loading of 40 gcell-dry-weight was used to convert 1 M racemic 2-phenylpropanal to (S)-phenylpropanol in 93.1 % e.e. ConclusionMainly hydrolases have been exploited for the production of profenols at industrial scale so far. The herein established bioreduction presents an alternative route towards profenols that is competitive to hydrolase-catalyzed kinetic resolutions.