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Enantioselective, continuous (R)- and (S)-2-butanol synthesis: Achieving high space-time yields with recombinant E. coli cells in a micro-aqueous, solvent-free reaction system

Paper ID Volume ID Publish Year Pages File Format Full-Text
23005 43409 2014 7 PDF Available
Title
Enantioselective, continuous (R)- and (S)-2-butanol synthesis: Achieving high space-time yields with recombinant E. coli cells in a micro-aqueous, solvent-free reaction system
Abstract

•Biocatalytic, stereoselective 2-butanone reduction in continuous micro-aqueous system.•High conversions (>95%) and ee (>96%) achieved for (R)-2-butanol.•Extremely high space-time yields were obtained.•System was successfully transferred to a (S)-selective catalyst.

The stereoselective production of (R)- or (S)-2-butanol is highly challenging. A potent synthesis strategy is the biocatalytic asymmetric reduction of 2-butanone applying alcohol dehydrogenases. However, due to a time-dependent racemisation process, high stereoselectivity is only obtained at incomplete conversion after short reaction times. Here, we present a solution to this problem: by using a continuous process, high biocatalytic selectivity can be achieved while racemisation is suppressed successfully.Furthermore, high conversion was achieved by applying recombinant, lyophilised E. coli cells hosting Lactobacillus brevis alcohol dehydrogenase in a micro-aqueous solvent-free continuous reaction system. The optimisation of residence time (τ) and 2-butanone concentration boosted both conversion (>99%) and enantiomeric excess (ee) of (R)-2-butanol (>96%). When a residence time of only τ = 3.1 min was applied, productivity was extraordinary with a space-time yield of 2278 ± 29 g/(L × d), thus exceeding the highest values reported to date by a factor of more than eight. The use of E. coli cells overexpressing an ADH of complementary stereoselectivity yielded a synthesis strategy for (S)-2-butanol with an excellent ee (>98%). Although conversion was only moderate (up to 46%), excellent space-time yields of up to 461 g/(L × d) were achieved. The investigated concept represents a synthesis strategy that can also be applied to other biocatalytic processes where racemisation poses a challenge.

Keywords
τ, residence time; % (v/v), percent (volume per volume); ADH, alcohol dehydrogenase; c, concentration; CMR, continuous membrane reactor; CPCR, carbonyl reductase from Candida parapsilosis; E. coli, Escherichia coli; ee, enantiomeric excess; GC, gas chroma
First Page Preview
Enantioselective, continuous (R)- and (S)-2-butanol synthesis: Achieving high space-time yields with recombinant E. coli cells in a micro-aqueous, solvent-free reaction system
Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Biotechnology - Volume 191, 10 December 2014, Pages 106–112
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering