Asymmetric reduction of ketones using recombinant E. coli cells that produce a versatile carbonyl reductase with high enantioselectivity and broad substrate specificity

Chemoenzymatic Conversion of Biomass-Derived D-Xylose to Furfuryl Alcohol with Corn Stalk-Based Solid Acid Catalyst and Reductase Biocatalyst in a Deep Eutectic Solvent–Water System

In this work, the feasibility of chemoenzymatically transforming biomass-derived D-xylose to furfuryl alcohol was demonstrated in a tandem reaction with SO42−/SnO2-CS chemocatalyst and reductase biocatalyst in the deep eutectic solvent (DES)–water media. The high furfural yield (44.6%) was obtained by catalyzing biomass-derived D-xylose (75.0 g/L) in 20 min at 185 °C with SO42−/SnO2-CS (1.2 wt%) in DES ChCl:EG–water (5:95, v/v). Subsequently, recombinant E.coli CF cells harboring reductases transformed D-xylose-derived furfural (200.0 mM) to furfuryl alcohol in the yield of 35.7% (based on D-xylose) at 35 °C and pH 7.5 using HCOONa as cosubstrate in ChCl:EG–water. This chemoenzymatic cascade catalysis strategy could be employed for the sustainable production of value-added furan-based chemical from renewable bioresource.

One-pot chemo-enzymatic conversion of D-xylose to furfuralcohol by sequential dehydration with oxalic acid plus tin-based solid acid and bioreduction with whole-cells

In this study, organic acid could be used as co-catalyst for assisting solid acid SO₄^2-/SnO₂-argil to convert hemicellulose-derived D-xylose into furfural. The relationship between pKa of organic acid and turnover frequency (TOF) of co-catalysis with organic acid plus SO₄^2-/SnO₂-argil was explored on the conversion of D-xylose to furfural. Oxalic acid (pKa = 1.25) (0.35 wt%) was found to be the optimum co-catalyst for assisting SO₄^2-/SnO₂-argil (3.6 wt%) to synthesize furfural from D-xylose (20 g/L) at 180 °C for 20 min, and the furfural yield and TOF could be obtained at 57.07% and 6.26 h^-1, respectively. Finally, the obtained furfural (107.6 mM) could be completely biotransformed to furfuralcohol by recombinant Escherichia coli CCZU-K14 whole-cells at 30 °C and pH 6.5 in the presence of 1.5 mol glucose/mol furfural and 400 mM D-xylose. Clearly, this strategy shows high potential application for the effective synthesis of furfuralcohol from biomass-derived D-xylose.

Enhanced bioreduction synthesis of ethyl (R)-4-chloro-3-hydroybutanoate by alkalic salt pretreatment

In this study, biomass-hydrolysate was used for enhancing the bioreduction of ethyl 4-chloro-3-oxobutanoate (COBE). Firstly, dilute alkalic salt pretreatment was attempted to pretreat bamboo shoot shell (BSS). It was found that enzymatic in situ hydrolysis of 20-50 g/L BSS pretreated with dilute alkalic salts (0.4% Na₂CO₃, 0.032% Na₂S) at 7.5% sulfidity by autoclaving at 110 °C for 40 min gave sugar yields at 59.9%-73.5%. Moreover, linear relationships were corrected on solid recovery-total delignification-sugar yield. In BSS-hydrolysates, xylose and glucose could promote the reductase activity of recombinant E. coli CCZU-A13. Compared with glucose, hydrolysate could increase the reductase activity by 1.35-folds. Furthermore, the cyclohexane-hydrolysate (10:90, v/v) biphasic media containing ethylene diamine tetraacetic acid (EDTA, 40 mM) and l-glutamine (150 mM) was built for the effective biosynthesis of ethyl (R)-4-chloro-3-hydroxybutanoate [(R)-CHBE] (94.6% yield) from 500 mM COBE. In conclusion, this strategy has high potential for the effective biosynthesis of (R)-CHBE (>99% e.e.).

Highly Efficient Deracemization of Racemic 2-Hydroxy Acids in a Three-Enzyme Co-Expression System Using a Novel Ketoacid Reductase

Enantiopure 2-hydroxy acids (2-HAs) are important intermediates for the synthesis of pharmaceuticals and fine chemicals. Deracemization of racemic 2-HAs into the corresponding single enantiomers represents an economical and highly efficient approach for synthesizing chiral 2-HAs in industry. In this work, a novel ketoacid reductase from Leuconostoc lactis (LlKAR) with higher activity and substrate tolerance towards aromatic α-ketoacids was discovered by genome mining, and then its enzymatic properties were characterized. Accordingly, an engineered Escherichia coli (HADH-LlKAR-GDH) co-expressing 2-hydroxyacid dehydrogenase, LlKAR, and glucose dehydrogenase was constructed for efficient deracemization of racemic 2-HAs. Most of the racemic 2-HAs were deracemized to their (R)-isomers at high yields and enantiomeric purity. In the case of racemic 2-chloromandelic acid, as much as 300 mM of substrate was completely transformed into the optically pure (R)-2-chloromandelic acid (> 99% enantiomeric excess) with a high productivity of 83.8 g L^-1 day^-1 without addition of exogenous cofactor, which make this novel whole-cell biocatalyst more promising and competitive in practical application.

Efficient biocatalytic stereoselective reduction of methyl acetoacetate catalyzed by whole cells of engineered E. coli

Asymmetric synthesis of chiral β-hydroxy esters, the key building blocks for many functional materials, is currently of great interest. In this study, the biocatalytic anti-Prelog reduction of methyl acetoacetate (MAA) to methyl-(R)-3-hydroxybutyrate ((R)-HBME) was successfully carried out with high enantioselectivity using the whole cell of engineered E. coli, which harbored an AcCR (carbonyl reductase) gene from Acetobacter sp. CCTCC M209061 and a GDH (glucose dehydrogenase) gene from Bacillus subtilis 168 for the in situ regeneration of the coenzyme. Compared with the corresponding wild strain, the engineered E. coli cells were proved to be more effective for the bio-reduction of MAA, and afforded much higher productivity. Under the optimized conditions, the product e.e. was >99.9% and the maximum yield was 85.3% after a reaction time of 10 h, which were much higher than those reported previously. In addition, the production of (R)-HBME increased significantly by using a fed-batch strategy of tuning pH, with a space-time yield of approximately 265 g L-1 d-1, thus the issue in previous research of relatively low substrate concentrations appears to be solved. Besides, the established bio-catalytic system was proved to be feasible up to a 150 mL scale with a large-scale relatively high substrate concentration and selectivity. For further industrial application, these results open a way to use of whole cells of engineered E. coli for challenging higher substrate concentrations of β-ketone esters enantioselective reduction reactions.

Chemical-enzymatic conversion of corncob-derived xylose to furfuralcohol by the tandem catalysis with SO42-/SnO2-kaoline and E. coli CCZU-T15 cells in toluene-water media

One-pot synthesis of furfuralcohol from corncob-derived xylose was attempted by the tandem catalysis with solid acid SO₄^2-/SnO₂-kaoline and recombination Escherichia coli CCZU-T15 whole-cells in the toluene-water media. Using SO₄^2-/SnO₂-kaoline (3.5wt%) as catalyst, the furfural yield of 74.3% was obtained from corncob-derived xylose in the toluene-water (1:2, v:v) containing 10mM OP-10 at 170°C for 30min. After furfural liquor was mixed with corncob-hydrolysate from the enzymatic hydrolysis of oxalic acid-pretreated corncob residue, furfural (50.5mM) could be completely biotransformed to furfuralcohol with Escherichia coli CCZU-T15 whole-cells harboring an NADH-dependent reductase (ClCR) in the toluene-water (1:3, v:v) containing 12.5mM OP-10 and 1.6mM glucose/mM furfural at 30°C and pH 6.5. Furfuralcohol was obtained at 13.0% yield based on starting material corncob (100% furfuralcohol yield for bioreduction of furfural step). Clearly, this one-pot synthesis of furfuralcohol strategy shows high potential application for the effective utilization of corncob.

One-pot chemo-enzymatic synthesis of furfuralcohol from xylose

Furfuralcohol (FOL) is an important intermediate for the production of lysine, ascorbic acid, and lubricants. It can be used as a hypergolic fuel in rocketry. In this study, it was attempted to synthesize FOL from xylose by tandem catalysis with solid acid SO₄^2-/SnO₂-Montmorillonite and recombination Escherichia coli CCZU-K14 whole cells. Using SO₄^2-/SnO₂-Montmorillonite (3.0wt% dosage) as catalyst, a highest furfural yield of 41.9% was achieved from xylose at 170°C for 20min. Furthermore, Escherichia coli CCZU-K14 whole cells were used for bioconverting furfural to FOL. The optimum biocatalytic reaction temperature, reaction pH, cosubstrate concentration, and substrate concentration were 30°C, 6.5, 1.5mol glucose/mol furfural, and 200mM, respectively. Finally, the yield of FOL from 200mM furfural was achieved to 100% by Escherichia coli CCZU-K14 whole cells after 24h. In conclusion, this strategy show high potential application for the effective synthesis of FOL.

Effective pretreatment of sugarcane bagasse with combination pretreatment and its hydrolyzates as reaction media for the biosynthesis of ethyl (S)-4-chloro-3-hydroxybutanoate by whole cells of E. coli CCZU-K14

In this study, sugarcane bagasse (SB) was pretreated with combination pretreatment (e.g., sequential KOH extraction and ionic liquid soaking, sequential KOH extraction and Fenton soaking, or sequential KOH extraction and glycerol soaking). After the enzymatic hydrolysis of pretreated SBs, it was found that all these three concentrated hydrolyzates could be used for the asymmetric bioreduction of ethyl 4-chloro-3-oxobutanoate (COBE) into ethyl (S)-4-chloro-3-hydroxybutanoate [(S)-CHBE]. Compared with glucose, arabinose and cellobiose couldn't promote the initial reaction rate, and xylose could increase the intracellular NADH content. Moreover, it was the first report that hydrolyzates could be used for the effective biosynthesis of (S)-CHBE (∼500g/L; 98.0% yield) from 3000 COBE by whole cells of Escherichia coli CCZU-K14 in the presence of β-CD (0.4mol β-CD/mol COBE), l-glutamine (200mM) and glycine (500mM). In conclusion, it is a new alternative to utilize bioresource for the synthesis of key chiral intermediate (S)-CHBE.

Chiral surfactant-type catalyst: enantioselective reduction of long-chain aliphatic ketoesters in water

A series of amphiphilic ligands were designed and synthesized. The rhodium complexes with the ligands were applied to the asymmetric transfer hydrogenation of broad range of long-chained aliphatic ketoesters in neat water. Quantitative conversion and excellent enantioselectivity (up to 99% ee) was observed for α-, β-, γ-, δ- and ε-ketoesters as well as for α- and β-acyloxyketone using chiral surfactant-type catalyst 2. The CH/π interaction and the strong hydrophobic interaction of long aliphatic chains between the catalyst and the substrate in the metallomicelle core played a key role in the catalytic transition state. Synergistic effects between the metal-catalyzed site and the hydrophobic microenvironment of the core in the micelle contributed to high stereoselectivity.

Improved biosynthesis of ethyl (S)-4-chloro-3-hydroxybutanoate by adding L-glutamine plus glycine instead of NAD+ in β-cyclodextrin-water system

To reduce dependence on the expensive cofactor and effectively biotransform ethyl 4-chloro-3-oxobutanoate, L-glutamine and glycine were found to enhance the content of intracellular NADH and the reductase activity. Adding the mixture of 200 mM of L-glutamine and 500 mM of glycine to the reaction media, a 1.67-fold of reductase activity was increased over the control without the addition of the two compounds. Moreover, β-cyclodextrin (0.4 mol β-cyclodextrin/mol ethyl 4-chloro-3-oxobutanoate) was also added into this reaction media, and the biocatalytic activity of the whole-cell biocatalyst of Escherichia coli CCZU-K14 was increased by 1.34-fold than that without β-cyclodextrin. In this β-cyclodextrin-water media containing L-glutamine (200 mM) plus glycine (500 mM), ethyl (S)-4-chloro-3-hydroxybutanoate (>99% ee) could be obtained from 3000 mM ethyl 4-chloro-3-oxobutanoate in the yield of 98.0% after 8h. All the positive features demonstrate the potential applicability of the bioprocess for the large-scale production of ethyl (S)-4-chloro-3-hydroxybutanoate.

Discovery of a reductase-producing strain recombinant E. coli CCZU-A13 using colorimetric screening and its whole cell-catalyzed biosynthesis of ethyl (R)-4-chloro-3-hydroxybutanoate

An NADH-dependent reductase (SsCR) was discovered by genome data mining. After SsCR was overexpressed in E. coli BL21, recombinant E. coli CCZU-A13 with high reductase activity and excellent stereoselectivity for the reduction of ethyl 4-chloro-3-oxobutanoate (COBE) into ethyl (R)-4-chloro-3-hydroxybutanoate ((R)-CHBE) was screened using one high-throughput colorimetric screening strategy. After the reaction optimization, a highly stereoselective bioreduction of COBE into (R)-CHBE (>99% ee) with the resting cells of E. coli CCZU-A13 was successfully demonstrated in n-butyl acetate-water (10:90, v/v) biphasic system. Biotransformation of 600mM COBE for 8h in the biphasic system, (R)-CHBE (>99% ee) could be obtained in the high yield of 100%. Moreover, the broad substrate specificity in the reduction of aliphatic and aromatic carbonyl compounds was also found. Significantly, E. coli CCZU-A13 shows high potential in the industrial production of (R)-CHBE (>99% ee) and its derivatives.

Biosynthesis of ethyl (S)-4-chloro-3-hydroxybutanoate by NADH-dependent reductase from E. coli CCZU-Y10 discovered by genome data mining using mannitol as cosubstrate

The reductase (PgCR) from recombinant Escherichia coli CCZU-Y10 displayed high reductase activity and excellent stereoselectivity for the reduction of ethyl 4-chloro-3-oxobutanoate (COBE) into ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE). To efficiently synthesize (S)-CHBE (>99 % enantiomeric excess (ee)), the highly stereoselective bioreduction of COBE into (S)-CHBE with the whole cells of E. coli CCZU-Y10 was successfully demonstrated in a dibutyl phthalate-water biphasic system. The appropriate ratio of the organic phase to water phase was 1:1 (v/v). The optimum reaction temperature, reaction pH, cosubstrate, NAD(+), and cell dosage of the biotransformation of 100 mM COBE in this biphasic system were 30 °C, 7.0, mannitol (2.5 mmol/mmol COBE), 0.1 μmol/(mmol COBE), and 0.1 g (wet weight)/mL, respectively. Moreover, COBE at a high concentration of (1,000 mM) could be asymmetrically reduced to (S)-CHBE in a high yield (99.0 %) and high enantiometric excess value (>99 % ee). Significantly, E. coli CCZU-Y10 shows high potential in the industrial production of (S)-CHBE (>99 % ee).

Development of a whole-cell biocatalyst with NADPH regeneration system for biosulfoxidation

A formate dehydrogenase gene (fdh) originated from Candida boidinii was co-expressed in E. coli BL21 (DE3) with the cyclohexanone monooxygenase gene (chmo) cloned from Acinetobacter calcoaceticus NCIMB 9871. The co-expression system was then used as a whole-cell biocatalyst to synthesize chiral phenyl methyl sulfoxide (PMSO) from thioanisole (PMS) and the reaction conditions were investigated. When the initial concentration of PMS was 20 mM, the specific productivity of PMSO in this system was 2.07 μmol g(-1) cw min(-1) (cw: wet cell weight) and the ee value for the R-sulfoxide was 99 %. In contrast, when chmo was the only gene expressed in E. coli, the specific productivity of PMSO was 0.053 μmol g(-1) cw min(-1) with no exact enantioselectivity. Further determination of NADPH concentration in the whole-cell catalysts suggested that co-expression of fdh with chmo significantly improved NADPH supply. Thus, this whole-cell biocatalyst system is highly advantageous for the synthesis of optically pure R-sulfoxide.

Purification and characterization of a novel NADH-dependent carbonyl reductase from Pichia stipitis involved in biosynthesis of optically pure ethyl (S)-4-chloro-3-hydroxybutanoate

A novel NADH-dependent dehydrogenases/reductases (SDRs) superfamily reductase (PsCRII) was isolated from Pichia stipitis. It produced ethyl (S)-4-chloro-3-hydroxybutanoate [(S)-CHBE] in greater than 99% enantiomeric excess. This enzyme was purified to homogeneity by ammonium sulfate precipitation followed by Q-Sepharose chromatography. Compared to similar known reductases producing (S)-CHBE, PsCR II was more suitable for production since the purified PsCRII preferred the inexpensive cofactor NADH to NADPH as the electron donor. Furthermore, the Km of PsCRII for ethyl 4-chloro-3-oxobutanoate (COBE) was 3.3 mM, and the corresponding Vmax was 224 μmol/mg protein/min. The catalytic efficiency is the highest value ever reported for NADH-dependent reductases from yeasts that produce CHBE with high enantioselectivity. In addition, this enzyme exhibited broad substrate specificity for several β-keto esters using NADH as the coenzyme. The properties of PsCRII with those of other carbonyl reductases from yeasts were also compared in this study.

Asymmetric synthesis of (S)-ethyl-4-chloro-3-hydroxy butanoate using a Saccharomyces cerevisiae reductase: enantioselectivity and enzyme-substrate docking studies

Ethyl (S)-4-chloro-3-hydroxy butanoate (ECHB) is a building block for the synthesis of hypercholesterolemia drugs. In this study, various microbial reductases have been cloned and expressed in Escherichia coli. Their reductase activities toward ethyl-4-chloro oxobutanoate (ECOB) have been assayed. Amidst them, Baker's yeast YDL124W, YOR120W, and YOL151W reductases showed high activities. YDL124W produced (S)-ECHB exclusively, whereas YOR120W and YOL151W made (R)-form alcohol. The homology models and docking models with ECOB and NADPH elucidated their substrate specificities and enantioselectivities. A glucose dehydrogenase-coupling reaction was used as NADPH recycling system to perform continuously the reduction reaction. Recombinant E. coli cell co-expressing YDL124W and Bacillus subtilis glucose dehydrogenase produced (S)-ECHB exclusively.

Engineering cofactor preference of ketone reducing biocatalysts: A mutagenesis study on a γ-diketone reductase from the yeast Saccharomyces cerevisiae serving as an example

The synthesis of pharmaceuticals and catalysts more and more relies on enantiopure chiral building blocks. These can be produced in an environmentally benign and efficient way via bioreduction of prochiral ketones catalyzed by dehydrogenases. A productive source of these biocatalysts is the yeast Saccharomyces cerevisiae, whose genome also encodes a reductase catalyzing the sequential reduction of the γ-diketone 2,5-hexanedione furnishing the diol (2S,5S)-hexanediol and the γ-hydroxyketone (5S)-hydroxy-2-hexanone in high enantio- as well as diastereoselectivity (ee and de >99.5%). This enzyme prefers NADPH as the hydrogen donating cofactor. As NADH is more stable and cheaper than NADPH it would be more effective if NADH could be used in cell-free bioreduction systems. To achieve this, the cofactor binding site of the dehydrogenase was altered by site-directed mutagenesis. The results show that the rational approach based on a homology model of the enzyme allowed us to generate a mutant enzyme having a relaxed cofactor preference and thus is able to use both NADPH and NADH. Results obtained from other mutants are discussed and point towards the limits of rationally designed mutants.

Asymmetric synthesis of (S)-3-chloro-1-phenyl-1-propanol using Saccharomyces cerevisiae reductase with high enantioselectivity

3-Chloro-1-phenyl-1-propanol is used as a chiral intermediate in the synthesis of antidepressant drugs. Various microbial reductases were expressed in Escherichia coli, and their activities toward 3-chloro-1-phenyl-1-propanone were evaluated. The yeast reductase YOL151W (GenBank locus tag) exhibited the highest level of activity and exclusively generated the (S)-alcohol. Recombinant YOL151W was purified by Ni-nitrilotriacetic acid (Ni-NTA) and desalting column chromatography. It displayed an optimal temperature and pH of 40 degrees C and 7.5-8.0, respectively. The glucose dehydrogenase coupling reaction was introduced as an NADPH regeneration system. NaOH solution was occasionally added to maintain the reaction solution pH within the range of 7.0-7.5. By using this reaction system, the substrate (30 mM) could be completely converted to the (S)-alcohol product with an enantiomeric excess value of 100%. A homology model of YOL151W was constructed based on the structure of Sporobolomyces salmonicolor carbonyl reductase (Protein Data Bank ID: 1Y1P). A docking model of YOL151W with NADPH and 3-chloro-1-phenyl-1-propanone was then constructed, which showed that the cofactor and substrate bound tightly to the active site of the enzyme in the lowest free energy state and explained how the (S)-alcohol was produced exclusively in the reduction process.