Effective asymmetric bioreduction of ethyl 4-chloro-3-oxobutanoate to ethyl (R)-4-chloro-3-hydroxybutanoate by recombinant E. coli CCZU-A13 in [Bmim]PF6-hydrolyzate media

Efficient Synthesis of Chiral Aryl Alcohol with a Novel Kosakonia radicincitans Isolate in Tween 20/L-carnitine: Lysine-Containing Synergistic Reaction System

Chiral trifluoromethyl alcohols as vital intermediates are of great interest in fine chemicals and especially in pharmaceutical synthesis. In this work, a novel isolate Kosakonia radicincitans ZJPH202011 was firstly employed as biocatalyst for the synthesis of (R)-1-(4-bromophenyl)-2,2,2-trifluoroethanol ((R)-BPFL) with good enantioselectivity. By optimizing fermentation conditions and bioreduction parameters in aqueous buffer system, the substrate concentration of 1-(4-bromophenyl)-2,2,2-trifluoroethanone (BPFO) was doubled from 10 to 20 mM, and the enantiomeric excess (ee) value for (R)-BPFL increased from 88.8 to 96.4%. To improve biocatalytic efficiency by strengthening the mass-transfer rate, natural deep-eutectic solvents, surfactants and cyclodextrins (CDs) were introduced separately in the reaction system as cosolvent. Among them, L-carnitine: lysine (C: Lys, molar ratio 1:2), Tween 20 and γ-CD manifested higher (R)-BPFL yield compared with other same kind of cosolvents. Furthermore, based on the excellent performance of both Tween 20 and C: Lys (1:2) in enhancing BPFO solubility and ameliorating cell permeability, a Tween 20/C: Lys (1:2)-containing integrated reaction system was then established for efficient bioproduction of (R)-BPFL. After optimizing the critical factors involved in BPFO bioreduction in this synergistic reaction system, BPFO loading increased up to 45 mM and the yield reached 90.0% within 9 h, comparatively only 37.6% yield was acquired in neat aqueous buffer. This is the first report on K. radicincitans cells as new biocatalyst applied in (R)-BPFL preparation, and the developed Tween 20/C: Lys-containing synergistic reaction system has great potential for the synthesis of various chiral alcohols.

Improved biotransformation of lignin-valorized vanillin into vanillylamine in a sustainable bioreaction medium

Lignin is a critical biopolymer for creating a large number of highly valuable biobased compounds. Vanillin, one of lignin-derived aromatics, can be used to synthesize vanillylamine that is a key fine chemical and pharmaceutical intermediate. To produce vanillylamine, a productive whole-cell-catalyzed biotransformation of vanillin was developed in deep eutectic solvent - surfactant - H2O media. One newly created recombinant E. coli 30CA cells expressing ω-transaminase and L-alanine dehydrogenase was employed to transform 50 mM and 60 mM vanillin into vanillylamine in the yield of 82.2% and 8.5% under 40 °C, respectively. The biotransamination efficiency was enhanced by introducing surfactant PEG-2000 (40 mM) and deep eutectic solvent ChCl:LA (5.0 wt%, pH 8.0), and the highest vanillylamine yield reached 90.0% from 60 mM vanillin. Building an effective bioprocess was utilized for transamination of lignin-derived vanillin to vanillylamine with newly created bacteria in an eco-friendly medium, which had potential application for valorization of lignin to value-added compounds.

Pushing the limits: Cyclodextrin-based intensification of bioreductions

The asymmetric reduction of ketones is a frequently used synthesis route towards chiral alcohols. Amongst available chemo- and biocatalysts the latter stand out in terms of product enantiopurity. Their application is, however, restricted by low reaction output, often rooted in limited enzyme stability under operational conditions. Here, addition of 2-hydroxypropyl-β-cyclodextrin to bioreductions of o-chloroacetophenone enabled product concentrations of up to 29 % w/v at full conversion and 99.97 % e.e. The catalyst was an E. coli strain co-expressing NADH-dependent Candida tenuis xylose reductase and a yeast formate dehydrogenase for coenzyme recycling. Analysis of the lyophilized biocatalyst showed that E. coli cells were leaky with catalytic activity found as free-floating enzymes and associated with the biomass. The biocatalyst was stabilized and activated in the reaction mixture by 2-hydroxypropyl-β-cyclodextrin. Substitution of the wild-type xylose reductase by a D51A mutant further improved bioreductions. In previous optimization strategies, hexane was added as second phase to protect the labile catalyst from adverse effects of hydrophobic substrate and product. The addition of 2-hydroxypropyl-β-cyclodextrin (11 % w/v) instead of hexane (20 % v/v) increased the yield on biocatalyst 6.3-fold. A literature survey suggests that bioreduction enhancement by addition of cyclodextrins is not restricted to specific enzyme classes, catalyst forms or substrates.

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.).

Biosynthesis of tert-butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate by carbonyl reductase from Rhodosporidium toruloides in mono and biphasic media

tert-Butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate ((3R,5S)-CDHH) is the key intermediate for synthesis of atorvastatin and rosuvastatin. Carbonyl reductase exhibits excellent activity toward tert-butyl (S)-6-chloro-5-hydroxy-3-oxohexanoate ((S)-CHOH) to synthesize (3R,5S)-CDHH. In this study, a whole cell biosynthesis reaction system to produce (3R,5S)-CDHH was constructed in organic solvents. A solution of 10% (v/v) Tween-80 was introduced to the reaction system as a co-solvent, which greatly enhanced biotransformation process, giving 98.9% yield, >99% ee and 1.8-fold higher space time yield in 5 h bioconversion of 1 M (S)-CHOH, compared with 98.7% yield and >99% ee in 9 h bioconversion of a purely aqueous reaction system. Moreover, a water-octanol biphasic reaction system was built and 20% of octanol was added as reservoir of substrate resulting in 98% yield, >99% ee and 4.08 mmol L^-1 h^-1 g^-1 (wet cell weight) space time yield. This study paved a way for the whole cell biosynthesis of (3R,5S)-CDHH in mono and biphasic media.

Efficient synthesis of a (S)-fluoxetine intermediate using carbonyl reductase coupled with glucose dehydrogenase

(S)-3-chloro-1-phenyl-1-propanol ((S)-CPPO) is an important chiral intermediate predominantly used in the synthesis of the chiral side chain of (S)-fluoxetine. In this study, carbonyl reductase (CBR) from Novosphingobium aromaticivorans was successfully expressed in recombinant E. coli. The enzymatic activity of the recombinant CBR was significantly increased to 1875 U/mL in the fed-batch fermentation in a 10 L fermenter and recombinant CBR was then purified and characterized. By regenerating NADH with glucose dehydrogenase, 100 g/L 3-chloro-1-phenyl-1-propanone (3-CPP) was successfully converted to (S)-CPPO with a conversion of 100% and ee value of 99.6% after 12 h at 30 °C in PBS buffer (pH 7.0), which are the highest reported to date for the bio-production of (S)-CPPO and presented great potential for green production of (S)-CPPO at industrial scale.

Biological synthesis of 2,5-bis(hydroxymethyl)furan from biomass-derived 5-hydroxymethylfurfural by E. coli CCZU-K14 whole cells

Biocatalytic upgrading of bio-based platform chemical 5-hydroxymethylfurfural (5-HMF) to 2,5-bis(hydroxymethyl)furan (BHMF) is currently of great interest due to the product specificity, mild reaction and high efficiency. In this work, 200mM 5-HMF could be effectively biotransformed to BHMF at 90.6% with highly 5-HMF-tolerant recombinant E. coli CCZU-K14 whole cells at pH 6.5 and 30°C under the optimum reaction conditions (cosubstrate glucose 1.0mol glucose/(mol 5-HMF), D-xylose 400mM, l-glutamic acid 250mM, Mg²⁺ 1.5mM, 0.2mol β-cyclodextrin/(mol 5-HMF), CTAB (cetyltrimethyl ammonium bromide) 12.5mM, and 0.1g wet cells/mL). It was found that E. coli CCZU-K14 was highly tolerant to 5-HMF (up to 400mM). Effective bioreduction of biomass-derived 5-HMF (≤200) to BHMF was successfully demonstrated in this study. In conclusion, this strategy showed high potential application for the synthesis of BHMF.

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.

Enzymatic synthesis of an ezetimibe intermediate using carbonyl reductase coupled with glucose dehydrogenase in an aqueous-organic solvent system

(4S)-3-[(5S)-5-(4-Fluorophenyl)-5-hydroxypentanoyl]-4-phenyl-1,3-oxazolidin-2-one ((S)-ET-5) is an important chiral intermediate in the synthesis of chiral side chain of ezetimibe. Recombinant Escherichia coli expressing carbonyl reductase (CBR) was successfully constructed in this study. The total E. coli biomass and the specific activity of recombinant CBR in 5L fermenter culture were 10.9gDCWL^-1 and 14900.3Ug^-1DCW, respectively. The dual-enzyme coupled biocatalytic process in an aqueous-organic biphasic solvent system was first constructed using p-xylene as the optimal organic phase under optimized reaction conditions, and 150gL^-1 (4S)-3-[5-(4-fluorophenyl)-1,5-dioxophentyl]-4-phenyl-1,3-oxazolidin-2-one (ET-4) was successfully converted to (S)-ET-5 with a conversion of 99.1% and diastereomeric excess of 99% after 24-h, which are the highest values reported to date for the production of (S)-ET-5.