Enantioselective enzymatic hydrolysis of racemic glycidyl butyrate by lipase from Bacillus subtilis with improved catalytic properties

The lipase from Bacillus subtillus (BSL2), a highly active lipase expressed from newly constructed strain of Bacillus subtilis BSL2, is used in the kinetic resolution of glycidyl butyrate. A high enantiomeric ratio (E = 108) was obtained by using 1,4-dioxane as co-solvent (18%, v/v) and decreasing the reaction temperature to 5 °C. The ratio is about 16-fold more than that (E = 6.52) obtained in pure buffer solutions (25 °C, pH 7.8). Under the optimum conditions, the remained (R)-glycidyl butyrate with high enantiopure (ee > 98%) was obtained when the conversion was above 52%.     

Improvements of enzyme activity and enantioselectivity in lipase-catalyzed alcoholysis of (R,S)-azolides

With Candida antarctica lipase B (CALB)-catalyzed alcoholysis of (R,S)-naproxenyl 1,2,4-triazolide at the optimal conditions (i.e. anhydrous MTBE as the solvent, and methanol as the acyl acceptor at 45 °C) as the model system, the enzyme enantioselectivity in terms of V_R/V_S = 105.8 and specific activity for the fast-reacting (R)-azolide V_R/(E_t) = 0.979 mmol/(h g) were greatly improved in comparison with V_R/V_S = 8.0 and V_R/(E_t) = 0.113 mmol/(h g) of using (R,S)-naproxenyl 2,2,2-trifluoroethyl ester as the substrate. The resolution strategy was successfully extended to other (R,S)-profenyl 1,2,4-triazolides and lipases from Candida rugosa (Lipase MY) and Carica papaya (CPL) having opposite enantioselectivity to CALB. Moreover, the kinetic constants were estimated, compared with those obtained via hydrolysis, and employed for modeling time-course conversions of (R,S)-naproxenyl 1,2,4-triazolide in anhydrous MTBE. The advantages of easy substrate preparation, high enzyme reactivity and enantioselectivity, as well as easy product separation from the remaining substrate via reactive extraction demonstrate merits of using (R,S)-azolides but not the corresponding esters for the alcoholytic resolution.     

Enantioselective synthesis of (S)-phenylephrine by whole cells of recombinant Escherichia coli expressing the amino alcohol dehydrogenase gene from Rhodococcus erythropolis BCRC 10909

(R)-phenylephrine [(R)-PE] is an α₁-adrenergic receptor agonist that is widely used in over-the-counter drugs to treat the common cold. We found that Rhodococcus erythropolis BCRC 10909 can convert detectable level of 1-(3-hydroxyphenyl)-2-(methylamino) ethanone (HPMAE) to (S)-PE by high performance liquid chromatography tandem mass spectrometry analysis. An amino alcohol dehydrogenase gene (RE_AADH) which possesses the ability to convert HPMAE to (S)-PE was then isolated from R. erythropolis BCRC 10909 and expressed in Escherichia coli NovaBlue. The purified RE_AADH, tagged with 6×His, had a molecular mass of approximately 30 kDa and exhibited a specific activity of 0.19 μU/mg to HPMAE in the presence of NADPH, indicating this enzyme could be categorized as NADP⁺-dependent short-chain dehydrogenase reductase. E. coli NovaBlue cell expressing the RE_AADH gene was able to convert HPMAE to (S)-PE with more than 99% enantiomeric excess (ee), 78% yield and a productivity of 3.9 mmol (S)-PE/L h in 12 h at 30 °C and pH 7. The (S)-PE, recovered from reaction mixture by precipitation at pH 11.3, could be converted to (R)-PE (ee > 99%) by Walden inversion reaction. This is the first reported biocatalytic process for the production of (S)-PE from HPMAE.     

Gynostemosides A–E,megastigmane glycosides from Gynostemma pentaphyllum

Megastigmane glycosides (1–5) together with seven (6–12) related known compounds were isolated from the whole plants of Gynostemma pentaphyllum. The structures were elucidated by means of spectroscopic methods, including 2D NMR, HR-ESIMS, and circular dichroism (CD), as well as chemical transformations to be (3R, 4R, 5S, 6S, 7E)-3,4,6-trihydroxymegastigmane-7-en-9-one-3-O-β-d-glucopyranoside (gynostemoside A, 1), (3S, 4S, 5R, 6R, 7E, 9R)-3,4,6,9-tetrahydroxymegastigmane-7-en-3-O-β-d-glucopyranoside (gynostemoside B, 2), (3S, 4S, 5S, 6S, 7E, 9R)-3,4,9-trihydroxymegastigmane-7-en-9-O-β-d-glucopyranoside (gynostemoside C, 3), (3S, 4S, 5S, 6S, 7E, 9R)-3,4,9-trihydroxymegastigmane-7-en-3-O-β-d-glucopyranoside (gynostemoside D, 4), and (3S, 4S, 5S, 6S, 7E, 9R)-3,4,9-trihydroxymegastigmane-7-en-4-O-β-d-glucopyranoside (gynostemoside E, 5), respectively.     

Bacillus alcalophilus MTCC10234 catalyzed enantioselective kinetic resolution of aryl glycidyl ethers

The phenyl glycidyl ether derivatives have been kinetically resolved with the growing cells of Bacillus alcalophilus MTCC10234 yielding (S)-epoxides with up to >99% ee and (R)-diols with up to 89% ee. The enantiomeric ratio (E) of up to 67 has been obtained for biohydrolysis process. The effect of different substituents of phenyl glycidyl ether on the biocatalytic efficiency of B. alcalophilus MTCC10234 showed preference for methyl- and chloro-substituted aryl glycidyl ether derivatives whereas nitro-derivatives were transformed at a slower rate. 2,6-Dimethylphenyl glycidyl ether which contains a bulky aryl group having methyl group on both the ortho positions was resolved with an E = 39.     

Biocatalytic synthesis of ethyl (R)-2-hydroxy-4-phenylbutyrate with Candida krusei SW2026: A practical process for high enantiopurity and product titer

Ethyl (R)-2-hydroxy-4-phenylbutyrate ((R)-HPBE), a key intermediate in the production of angiotensin-converting enzyme (ACE) inhibitors, was prepared by the microbial reduction of ethyl 2-oxo-4-phenylbutyrate (OPBE). Among 63 microorganisms tested, Candida krusei SW2026, for the first time, was proven to be a highly effective biocatalyst in this reduction process, leading to the (R)-enantiomer in 99.7% ee and 95.1% yield at 2.5 g/L of OPBE (under optimal conditions of 30 °C, pH 6.6, and in the presence of 5% glucose as co-substrate). In order to achieve higher product concentration with desired enantiopurity and yield for application in large-scale production, strategies such as substrate fed-batch and aqueous/organic biphasic system were successfully conducted in the biotransformation reaction. At 20 g/L of OPBE, the enantiomeric excess (ee), yield, and product concentration were enhanced to 97.4%, 82.0%, and 16.6 g/L, respectively, in water/dibutyl phthalate biphasic system, compared with 87.5%, 45.8%, and 9.2 g/L in aqueous medium. This study provides an attractive process of (R)-HPBE production for potential green chemistry applications.     

Synthesis and antioxidant evaluation of (S,S)- and (R,R)-secoisolariciresinol diglucosides (SDGs)

Secoisolariciresinol diglucosides (SDGs) (S,S)-SDG-1 (major isomer in flaxseed) and (R,R)-SDG-2 (minor isomer in flaxseed) were synthesized from vanillin via secoisolariciresinol (6) and glucosyl donor 7 through a concise route that involved chromatographic separation of diastereomeric diglucoside derivatives (S,S)-8 and (R,R)-9. Synthetic (S,S)-SDG-1 and (R,R)-SDG-2 exhibited potent antioxidant properties (EC₅₀ = 292.17 ± 27.71 μM and 331.94 ± 21.21 μM, respectively), which compared well with that of natural (S,S)-SDG-1 (EC₅₀ = 275.24 ± 13.15 μM). These values are significantly lower than those of ascorbic acid (EC₅₀ = 1129.32 ± 88.79 μM) and α-tocopherol (EC₅₀ = 944.62 ± 148.00 μM). Compounds (S,S)-SDG-1 and (R,R)-SDG-2 also demonstrated powerful scavenging activities against hydroxyl [natural (S,S)-SDG-1: 3.68 ± 0.27; synthetic (S,S)-SDG-1: 2.09 ± 0.16; synthetic (R,R)-SDG-2: 1.96 ± 0.27], peroxyl [natural (S,S)-SDG-1: 2.55 ± 0.11; synthetic (S,S)-SDG-1: 2.20 ± 0.10; synthetic (R,R)-SDG-2: 3.03 ± 0.04] and DPPH [natural (S,S)-SDG-1: EC₅₀ = 83.94 ± 2.80 μM; synthetic (S,S)-SDG-1: EC₅₀ = 157.54 ± 21.30 μM; synthetic (R,R)-SDG-2: EC₅₀ = 123.63 ± 8.67 μM] radicals. These results confirm previous studies with naturally occurring (S,S)-SDG-1 and establish both (S,S)-SDG-1 and (R,R)-SDG-2 as potent antioxidants and free radical scavengers for potential in vivo use.     

Microbial alcohol dehydrogenase screening for enantiopure lactone synthesis: Down-stream process from microtiter plate to bench bioreactor

One-pot conversion with whole cells of bacteria was performed for biooxidation of meso monocyclic (3a–b) and bicyclic diols (3c–e) into corresponding chiral lactones of bicyclo[4.3.0]nonane structure (2a–b) as well as exo- and endo-bridged lactones with the structure of [2.2.1] (3c–d) and [2.2.2] (3e). Micrococcus sp. DSM 30771 was selected as biocatalyst with significant alcohol dehydrogenase activity. Among tested strains, microbial oxidation of meso diols 3a–e catalyzed by Micrococcus sp. afforded enantiomerically pure ((+)-(2S,3R)-2c (ee = 99%), (+)-(2S,3R)-2e (ee = 99%)) or enriched ((+)-(1S,5R)-2a (ee = 90%), (−)-(1S,5R)-2b (ee = 86%), (+)-(2S,3R)-2d (ee = 80%)) lactone moieties. Comparative study with respect to microbial cultivation as well as biooxidation was undertaken to verify agreement of secondary metabolite biosynthesis in different scales: from MTP (4 mL), across shake flask (100 mL) till bioreactor (4 L). The results from biotransformations showed quite similar dependence in oxidation of all substrates 3a–e in MTP and flasks as well, thereby confirmed the validity and reasonable approach of using MTP for preliminary studies.     

Enantioselective hydrolysis of rasemic naproxen methyl ester with sol–gel encapsulated lipase in the presence of sporopollenin

Sporopollenin is a natural polymer obtained from Lycopodium clavatum, which is highly stable with constant chemical structure and has high resistant capacity to chemical attack. In this study, the Candida rugosa lipase (CRL) was encapsulated within a chemically inert sol–gel support prepared by polycondensation with tetraethoxysilane (TEOS) and octyltriethoxysilane (OTES) in the presence and absence of sporopollenin and activated sporopollenin as additive. The catalytic properties of the immobilized lipases were evaluated into model reactions, i.e. the hydrolysis of p-nitrophenylpalmitate (p-NPP), and the enantioselective hydrolysis of rasemic Naproxen methyl ester that was studied in aqueous buffer solution/isooctane reaction system. The results indicated that the sporopollenin based encapsulated lipase particularly had higher conversion and enantioselectivity compared to the sol–gel free lipase. In this study, excellent enantioselectivity (E > 400) has been noticed for most lipase preparations (E = 166 for the free enzyme) with an ee value ～98% for S-Naproxen. Moreover, (S)-Naproxen was recovered from the reaction mixture with 98% optical purity.     

Bio-resolution of a chiral epoxide using whole cells of Bacillus megaterium ECU1001 in a biphasic system

Optically active epoxides can be prepared by kinetic resolution of racemic mixtures using stereospecific epoxide hydrolases. To increase the bio-resolution efficiency of a sparingly water-soluble epoxide (glycidyl phenyl ether, GPE), we investigated the use of organic/aqueous two-phase system. Various conditions were systematically examined and optimized in shake flasks. Isooctane was found to be the most suitable solvent as the organic phase. The phase volume ratio (ϕ_o/w) and biocatalyst concentration were shown to be sensitive parameters affecting both the reaction rate and the enzyme enantiospecificity in the biphase system. An isooctane/aqueous system was developed to overcome the low solubility and instability of GPE in the aqueous phase, resulting in a significant improvement of enatiomeric ratio (E-value) from 39.5 to 94.0 and an average productivity of 18.8 mg GPE/(h g) biocatalyst to 48.9 mg GPE/(h g) biocatalyst, respectively. Resolution of a 90.1 g/l solution of racemic glycidyl phenyl ether in isooctane phase was successfully carried out in a mechanically stirred reactor (120 ml), affording (S)-glycidyl phenyl ether in high (100%) enantiomeric excess with a yield of 44.5%.     

Structure–cytotoxic activity relationship of sesquilignan,morinol A

The cytotoxic activities of sesquilignans, (7S,8S,7′R,8′R)- and (7R,8R,7′S,8′S)-morinol A and (7S,8S,7′S,8′S)- and (7R,8R,7′R,8′R)-morinol B were compared, showing no significant difference between stereoisomers (IC₅₀ = 24–35 μM). As a next stage, the effect of substituents at 7, 7′, and 7″-aromatic ring on the activity was evaluated to find out the higher activity of (7S,8S,7′R,8′R)-7,7′,7″-phenyl derivative 18 (IC₅₀ = 6–7 μM). In the research on the structure–activity relationship of 7″-position of (7S,8S,7′R,8′R)-7,7′,7″-phenyl derivative 18, the most potent compounds were 7,7′,7″-phenyl derivative 18 (IC₅₀ = 6 μM) against HeLa cells. Against HL-60 cells, 7″-(4-nitrophenyl)-7,7′-phenyl derivative 33 and 7″-hexyl-7,7′-phenyl derivative 37 (IC₅₀ = 5 μM) showed highest activity. We discovered the compounds showed four to sevenfold potent activity than that of natural (7S,8S,7′R,8′R)-morinol A. It was also confirmed that the 7′-benzylic hydroxy group have an important role for exhibiting activity, on the other hand, the resonance system of cinnamyl structure is not crucial for the potent activity.     

Nitrite correlates with 3-nitrotyrosine but not with the F2-isoprostane 15(S)-8-iso-PGF2α in urine of rheumatic patients

In vitro studies suggested that nitrite may play a cytoprotective role in inflammation. The aim of the present clinical study was to investigate the relationship between the NO metabolites nitrite and nitrate and the biomarkers of oxidative stress 3-nitrotyrosine (3-NT) and 15(S)-iso-PGF_2α in patients suffering from chronic inflammatory rheumatic diseases. In morning urine from 28 patients with different chronic inflammatory rheumatic diseases (23–82 years of age) and from 41 healthy persons of both genders, nitrite and nitrate were quantitated by GC-MS, and 3-NT and 15(S)-iso-PGF_2α by GC-MS/MS. Mean creatinine-corrected urinary excretion rates of nitrite (1.1 versus 0.19 μmol/mmol, P = 0.00012) and 3-NT (1.2 versus 0.39 nmol/mmol, P = 0.01629), but not of nitrate (105 versus 106 μmol/mmol), were significantly elevated in rheumatism as compared to health. Urinary excretion rate of 15(S)-iso-PGF_2α did not differ between patients and healthy subjects (65 versus 69 pmol/mmol creatinine, P = 0.48). In rheumatism, urinary 3-NT correlated closely with nitrite (R = 0.788, P < 0.0001) and moderately with nitrate (R = 0.45, P < 0.016), but did not correlate with 15(S)-iso-PGF_2α (R = ?0.083, P = 0.68). In healthy persons there was no correlation between urinary 3-NT and nitrite or nitrate. Our study suggests that urinary nitrite may represent a novel specific biomarker of nitrative stress in chronic inflammatory rheumatic disease. In another eight patients with chronic inflammatory rheumatic diseases we found higher nitrite concentrations in synovial fluid as compared to serum (1.30 versus 0.35 μM). We hypothesize that in chronic inflammatory rheumatic diseases nitrite concentration is elevated in the inflamed joint and contributes to the inactivation of myeloperoxidase-catalyzed production of hypochloric acid by forming nitryl chloride which eventually nitrates tyrosine to form 3-NT.     

Asymmetric reduction of (4S)-(+)-carvone catalyzed by baker's yeast: A green method for monitoring the conversion based on liquid–liquid–liquid microextraction with polypropylene hollow fiber membranes

The α,β-unsaturated carbonyl compound (4S)-(+)-carvone was selectively reduced to (1R,2R,4S)-iso-dihydrocarveol using baker's yeasts. The conversion of the bioreduction reaction was monitored using a green hollow-fiber liquid–liquid–liquid microextraction (HF-LLLME) technique. Several parameters which may affect the bioreduction of (4S)-(+)-carvone, such as temperature, time, substrate/enzyme ratio, pH and buffer concentration, were evaluated. The effect of some additives, such as trehalose, DMSO and the ionic liquid [BMIm][PF₆], was also studied. The (1R,2R,4S)-iso-dihydrocarveol was recovered with 52.7% conversion and diastereoisomeric excess >99% after 48 h of reaction at 40 °C in an aqueous monophasic system, with 0.1 mol L^?1 buffer concentration (pH 7.5) and a substrate/yeast cell mass ratio of 8.0 mg g^?1. The HF-LLLME microextraction technique allowed the optimization of the reaction with a reduction of over 99.5% in relation to the use of organic solvents.     

Enantioselective synthesis of (S)-phenylephrine by recombinant Escherichia coli cells expressing the short-chain dehydrogenase/reductase gene from Serratia quinivorans BCRC 14811

BackgroundAn amino alcohol dehydrogenase gene (RE_AADH) from Rhodococcus erythropolis BCRC 10909 has been used for the conversion of 1-(3-hydroxyphenyl)-2-(methylamino) ethanone (HPMAE) to (S)-phenylephrine [(S)-PE]. However RE_AADH uses NADPH as cofactor, and only limited production of (S)-PE from HPMAE is achieved.MethodsA short-chain dehydrogenase/reductase gene (SQ_SDR) from Serratia quinivorans BCRC 14811 was expressed in Escherichia coli BL21 (DE3) for the conversion of HPMAE to (S)-PE.ResultsThe SQ_SDR enzyme was capable of converting HPMAE to (S)-PE in the presence of NADH and NADPH, with specific activities of 26.5 ± 2.3 U/mg protein and 0.24 ± 0.01 U/mg protein, respectively, at 30 °C and at a pH of 7.0. The E. coli BL21 (DE3), expressing NADH-preferring SQ_SDR, converted HPMAE to (S)-PE with more than 99% enantiomeric excess, a conversion yield of 86.6% and a productivity of 20.2 mmol/l h, which was much higher than our previous report using E. coli NovaBlue expressing NADPH-dependent RE_AADH as the biocatalyst.ConclusionThe SQ_SDR enzyme with its high catalytic activity and strong preference for NADH as a cofactor provided a significant advantage in bioreduction.     

An enzymatic approach to the synthesis of optically pure (3R)- and (3S)-enantiomers of green tea flavor compound 3-hydroxy-3-methylnonane-2,4-dione

Both (3R)- and (3S)-enantiomers of the chiral green tea flavor compound 3-hydroxy-3-methylnonane-2,4-dione were synthesized by the combined use of acetylacetoin synthase and acetylacetoin reductase from Bacillus licheniformis. The first enzyme was utilized to catalyze the homo-coupling of 2,3-octanedione and obtain the enantioenriched (3R)-3-hydroxy-3-methylnonane-2,4-dione (ee 44%). The NADH-dependent acetylacetoin reductase was then employed for the diastereoselective (de > 95%) C2 carbonyl reduction of the sole (3R)-enantiomer of the above 2,4-dione, thus affording the syn diol (2S,3R)-2,3-dihydroxy-3-methylnonan-4-one in enantiomerically pure form. While this step allowed for the recovery of unreacted, optically pure (3S)-3-hydroxy-3-methylnonae-2,4-dione, the corresponding (3R)-enantiomer was obtained by subsequent TEMPO-mediated oxidation of the syn diol intermediate. Moreover, using the title compounds as analytical standards, predominance of the (3R) enantiomer in the natural flavor compound was finally demonstrated by chiral GC–MS analysis.     

Production of (R)-mandelic acid by immobilized cells of Saccharomyces cerevisiae on chitosan carrier

The asymmetric microbial reduction of phenylglyoxylic acid (PGA) to (R)-mandelic acid ((R)-MA) with immobilized Saccharomyces cerevisiae cells on globular chitosan was studied. The immobilization conditions and characterization of the immobilized cells were carried out. Chitosan–acetic acid solution was injected into a mixture of 20% NaOH and 30% CH₃OH aqueous solution to obtain globular chitosan, and then the globular chitosan was treated with 1% solution of glutaraldehyde to immobilize yeast cells, which were used to synthesize (R)-MA. The optimum conditions were identified as the substrate concentration of 10 mmol L⁻¹, pH of 6.5 and reaction temperature of 30 °C with the yield of 62% for (R)-MA and the enantiomeric excess (e.e.) of 98% for (R)-MA. The immobilized cells showed good operation and storage stability.     

Biosynthesis of glycyrrhetic acid 3-O-mono-β-d-glucuronide catalyzed by β-d-glucuronidase with enhanced bond selectivity in an ionic liquid/buffer biphasic system

The bond selective hydrolysis of glycyrrhizin (GL) to glycyrrhetic acid 3-O-mono-β-d-glucuronide (GAMG) catalyzed by recombinant β-d-glucuronidase from Escherichia coli BL21 (PGUS-E) was successfully performed in an ionic liquid (IL)/buffer biphasic system. Five ILs were analyzed, however, a hydrophobic IL 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆) showed the best biocompatibility with PGUS-E. An obvious enhancement in the initial reaction rate, substrate conversion, GAMG yield and chemical bond selectivity (S_cb) was observed using 40% (v/v) [BMIM]PF₆/buffer as the reaction medium when compared to the acetate buffer medium. Under the optimized conditions (pH 6.0, temperature 50 °C, substrate concentration 6 mM and shaking speed 200 rpm), the initial reaction rate, the GAMG yield and the S_cb reached 3.15 mM h⁻¹, 74.36% and 98.12%, respectively. The recyclability of [BMIM]PF₆ was also studied and found to be reusable for five batches with high recovery percentage (≥92%). Furthermore, the desired product and byproduct were easily separated since they were distributed in different phases. Additionally, higher V_max (3.14 versus 2.24 mM h⁻¹), lower apparent K_m (1.21 versus 1.80 mM) and E_a (25.97 versus 32.60 kJ mol⁻¹) were achieved in [BMIM]PF₆/buffer biphasic system than that in monophasic buffer system.     

Chemical constituents from Saussurea cordifolia

Thirty-six naturally occurring compounds, including four C₁₀-acetylenic glycosides and a lignan, were isolated from the whole plants of Saussurea cordifolia. Their structures were elucidated by means of spectroscopic and chemical methods to be 4,6-decadiyne-1-O-β-d-apiofuranosyl-(1 → 6)-β-d-glucopyranoside (1), 4,6-decadiyne-1-O-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside (2), (8E)-decaene-4, 6-diyn-1-O-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside (3), (8Z)-decaene-4,6-diyn-1-O-β-d-apiofuranosyl-(1 → 6)-β-d-glucopyranoside (4), and (2R, 3S, 4S)-4-(4-hydroxy-3-methoxybenzyl)-2-(5-hydroxy-3-methoxyphenyl)-3-(hydroxymethyl)-tetrahydrofuran-3-ol (5).     

Production of a key chiral intermediate of Betahistine with a newly isolated Kluyveromyces sp. in an aqueous two-phase system

(S)-(4-Chlorophenyl)-(pyridin-2-yl)methanol [(S)-CPMA] is an important chiral intermediate of anti-allergic drug Betahistine. Carbonyl reductase-producing microorganisms were isolated from soil samples for the stereoselective reduction of (4-chlorophenyl)-(pyridin-2-yl)methanone (CPMK) to (S)-CPMA. Among over 400 microorganisms isolated, one strain exhibiting the highest activity was selected and identified as Kluyveromyces sp. After optimization, the biotransformation reaction catalyzed by Kluyveromyces sp. CCTCC M2011385 whole-cell gave product (S)-CPMA in 81.5% ee and 87.8% yield at substrate concentration of 2 g/L in aqueous phase. Using an aqueous two-phase system (ATPs) consisted of PEG4000 (20%, w/w) and Na₂HPO₄ (14%, w/w), the product reached 86.7% ee and 92.1% yield at a higher substrate concentration of 6 g/L. The substrate tolerance and biocompatibility of microbial cells are greatly improved in ATPs by accumulating substrate/product in the upper PEG solution. This study, for the first time, reports the production of (S)-CPMA catalyzed by microbial cells.     

A novel enantioselective epoxide hydrolase from Agromyces mediolanus ZJB120203: Cloning,characterization and application

A new strain Agromyces mediolanus ZJB120203, capable of enantioselective epoxide hydrolase (EH) activity was isolated employing a newly established colorimetric screening and chiral GC analysis method. The partial nucleotide sequence of an epoxide hydrolase (AmEH) gene from A. mediolanus ZJB120203 was obtained by PCR using degenerate primers designed based on the conserved domains of EHs. Subsequently, an open reading frame containing 1167 bp and encoding 388 amino acids polypeptide were identified. Expression of AmEH was carried out in Escherichia coli and purification was performed by Nickel-affinity chromatography. The purified AmEH had a molecular weight of 43 kDa and showed its optimum pH and temperature at 8.0 and 35 °C, respectively. Moreover, this AmEH showed broad substrates specificity toward epoxides. In this study, it is demonstrated that the AmEH could unusually catalyze the hydrolysis of (R)-ECH to produce enantiopure (S)-ECH. Enantiopure (S)-ECH could be obtained with enantiomeric excess (ee) of >99% and yield of 21.5% from 64 mM (R,S)-ECH. It is indicated that AmEH from A. mediolanus is an attractive biocatalyst for the efficient preparation of optically active ECH.