Dual production of highly pure methyl (R)-4-chloro-3-hydroxybutyrate and (S)-3-hydroxy-γ-butyrolactone with Enterobacter sp

Production of Optically Pure (S)-3-Hydroxy-γ-butyrolactone from d-Xylose Using Engineered Escherichia coli

Biocatalysis has advantages in asymmetric synthesis due to the excellent stereoselectivity of enzymes. The present study established an efficient biosynthesis pathway for optically pure (S)-3-hydroxy-γ-butyrolactone [(S)-3HγBL] production using engineered Escherichia coli. We mimicked the 1,2,4-butanetriol biosynthesis route and constructed a five-step pathway consisting of d-xylose dehydrogenase, d-xylonolactonase, d-xylonate dehydratase, 2-keto acid decarboxylase, and aldehyde dehydrogenase. The engineered strain harboring the five enzymes could convert d-xylose to 3HγBL with glycerol as the carbon source. Stereochemical analysis by chiral GC proved that the microbially synthesized product was a single isomer, and the enantiomeric excess (ee) value reached 99.3%. (S)-3HγBL production was further enhanced by disrupting the branched pathways responsible for d-xylose uptake and intermediate reduction. Fed-batch fermentation of the best engineered strain showed the highest (S)-3HγBL titer of 3.5 g/L. The volumetric productivity and molar yield of (S)-3HγBL on d-xylose reached 50.6 mg/(L·h) and 52.1%, respectively. The final fermentation product was extracted, purified, and confirmed by NMR. This process utilized renewable d-xylose as the feedstock and offered an alternative approach for the production of the valuable chemical.

Selective continuous flow synthesis of hydroxy lactones from alkenoic acids

The first in-flow selenium-mediated catalysis has been realized under eco-friendly conditions to convert alkenoic acids into hydroxy lactones with a high regio- and diastereo-selectivity ratio.

Biorefineries for the production of top building block chemicals and their derivatives

Due to the growing concerns on the climate change and sustainability on petrochemical resources, DOE selected and announced the bio-based top 12 building blocks and discussed the needs for developing biorefinery technologies to replace the current petroleum based industry in 2004. Over the last 10 years after its announcement, many studies have been performed for the development of efficient technologies for the bio-based production of these chemicals and derivatives. Now, ten chemicals among these top 12 chemicals, excluding the l-aspartic acid and 3-hydroxybutyrolactone, have already been commercialized or are close to commercialization. In this paper, we review the current status of biorefinery development for the production of these platform chemicals and their derivatives. In addition, current technological advances on industrial strain development for the production of platform chemicals using micro-organisms will be covered in detail with case studies on succinic acid and 3-hydroxypropionic acid as examples.

Uses and production of chiral 3-hydroxy-gamma-butyrolactones and structurally related chemicals

Enantiopure (S)-3-hydroxy-gamma-butyrolactone (HGB) and its structurally related C3-C4 chemicals are an important target for chiral building blocks in synthetic organic chemistry. For the production of these compounds, more economical and practical synthetic routes are required. To date, chiral HGBs have been produced from petrochemicals and biomass, especially malic acids and carbohydrates. This report provides a short review on the production and application of enantiopure HGBs and their related compounds. Emphasis is focused mainly on synthetic routes using biocatalysis (microbial and chemoenzymatic) and application of these compounds. Biological methods have concentrated on devising different kinds of enzymes for the synthesis of the same compound as shown in the case of hydroxynitrile, a key intermediate of synthetic statins, and integrating unit processes for the optically active HGBs and 4-chloro-3-hydroxybutyrate with recombinant microorganisms expressing multiple enzymes. Chemical methods involve selective hydrogenation of carbohydrate-based starting materials. Both types of pathways will require further improvement to serve as a basis for a scalable route to HGBs and related compounds. Several of their synthetic applications are also introduced.

Asymmetric reduction of (S)-3-chloro-1-phenylpropanol from 3-chloropropiophenone by preheated immobilized Candida utilis

An efficient method for asymmetric reduction of (S)-3-chloro-1-phenylpropanol from 3-chloropropiophenone was developed using preheated Candida utilis cells immobilized in calcium alginate gel beads. Heating the immobilized cells (bead diameter 1.5 mm) at 45 degrees C for 50 min allowed the reaction to proceed with 99.5% enantiomeric excess (ee) and an 85% yield with 1 g substrate l(-1) (batch addition in three aliquots) in 48 h. The immobilized cells retained approximately 50% of their original catalytic activity after being reused three times.

Production of (S)-4-chloro-3-hydroxybutyrate by microbial resolution using hydrolase from Rhizobium sp. DS-S-51

(S)-4-Chloro-3-hydroxybutyrate (CHB) is essential for the synthesis of biologically and pharmacologically important compounds. Rhizobium sp. DS-S-51 isolated from soil samples showed hydrolytic activity toward (R)-CHB in the racemate to (R)-3-hydroxy-gamma-butyrolactone (HL) under a simple composition of the reaction. Residual (S)-CHB was obtained with high optical purity. The gene encoding the enzyme concerned, designated CHB hydrolase, was isolated from DS-S-51, and the gene was highly expressed in Escherichia coli JM109. When the resolution of racemic methyl CHB (CHBM) as a substrate was performed using this recombinant cell, JM109 (pKK-R1), the hydrolytic activity was found to be 40-fold greater than that of DS-S-51, and the maximum concentration of the substrate added increased 2-fold. Moreover, (R)-HL was also obtained without decreasing the optical purity compared with that when (R)-CHBM was used as a substrate.

A chemoenzymatic approach to the synthesis of enantiomerically pure (S)-3-hydroxy-gamma-butyrolactone

Optically pure (S)-3-hydroxy-gamma-butyrolactone, an important chiral building block in the pharmaceutical industry, was synthesized from L: -malic acid by combining a selective hydrogenation and a lipase-catalyzed hydrolysis. Lipase from Candida rugosa was found to be the most efficient enzyme for the hydrolysis of (S)-beta-benzoyloxy-gamma-butyrolactone. The use of organic solvent-aqueous two-phase system was employed to extract benzoic acid generated from enzymatic hydrolysis of the substrate. Tert-butyl methyl ether as an organic solvent was effective to extract the reaction product, benzoic acid, and stably maintained the enzyme activity of Lipase OF immobilized on polymeric supports Amberlite XAD-7. The immobilization made the recovery of the product simpler and prevented the formation of the emulsion. The pH adjustment was unnecessary with the immobilized Lipase OF. The scale-up of the enzymatic hydrolysis of S-BBL at 1,850-kg scale was carried out without problems to give 728.5 kg of S-HGB at 80% isolated yield. The scale-up results are similar to those of bench scale reactions. Racemic (R,S)-beta-benzoyloxy-gamma-butyrolactone was prepared from D-, L: -malic acid and was found to be hydrolyzed nonselectively by the enzyme.

Isolation and properties of a levo-lactonase from Fusarium proliferatum ECU2002: a robust biocatalyst for production of chiral lactones

A fungus strain ECU2002, capable of enantioselectively hydrolyzing chiral lactones to optically pure hydroxy acids, was newly isolated from soil samples through two steps of screening and identified as Fusarium proliferatum (Matsushima) Nirenberg. From the crude extract of F. proliferatum ECU2002, a novel levo-lactonase was purified to homogeneity, with a purification factor of 460-folds and an overall yield of 9.7%, by ultrafiltration, acetone precipitation, and chromatographic separation through DEAE-Toyopearl, Butyl-Toyopearl, Hydroxyapatite, Toyoscreen-Super Q, and TSK-gel columns. The purified enzyme is a monomer; with a molecular mass of ca 68 kDa and a pI of 5.7 as determined by two-dimensional electrophoresis. The catalytic performance of the partially purified levo-lactonase was investigated, giving temperature and pH optima at 50 degrees C and 7.5, respectively, for gamma-butyrolactone hydrolysis. The substrate specificity of the partially purified lactonase was also examined using several useful lactones, among which alpha-hydroxy-gamma-butyrolactone was the best substrate, with 448-fold higher lactonase activity as compared to gamma-butyrolactone. The F. proliferatum lactonase preferentially hydrolyzed the levo enantiomer of butyrolactones, including beta-butyrolactone, alpha-hydroxy-gamma-butyrolactone, alpha-hydroxy-beta,beta-dimethyl-gamma-butyrolactone (pantolactone), and beta-hydroxy-gamma-butyrolactone, affording (+)-hydroxy acids in high (94.8 approximately 98.2%) enantiomeric excesses (ee) and good conversions (38.2 approximately 44.2%). A simple immobilization of the crude lactonase with glutaraldehyde cross-linking led to a stable and easy-to-handle biocatalyst for catalytic resolution of chiral lactones. The immobilized lactonase also performed quite well in repeated batch resolution of dl-pantolactone at a concentration of 35% (w/v), retaining 67% of initial activity after ten cycles of reaction (corresponding to a half life of 20 cycles) and affording the product in 94 approximately 97% ee, which can be easily enhanced to >99% ee after the d-hydroxy acid was chemically converted into l-lactone and crystallized.

Improvement on production of (R)-4-Chloro-3-hydroxybutyrate and (S)-3-hydroxy-γ-butyrolactone with recombinant Escherichia coli cells

(R)-4-Chloro-3-hydroxybutyrate (CHB) and (S)-3-hydroxy-gamma-butyrolactone (HL) are used for the synthesis of biologically and pharmacologically important compounds. Enterobacter sp. DS-S-75 was found to have the unique activity to convert (S)-CHB in the racemate to (S)-HL through asymmetric dechlorination, hydrolysis, and lactonization. As a result, the remaining (R)-CHB and formed (S)-HL could be obtained in a one-pot reaction. We purified the CHB degrading enzyme which catalyzing these reactions and isolated the coding gene from the strain DS-S-75 in order to improve the productivity of these compounds using the transformant. Interestingly, the purified enzyme showed not only dechlorinating, but also hydrolyzing activities on CHB and the similar carboxylic esters, it was then designated CHB hydrolase, and appears to be a novel enzyme. The gene had 1101 bp encoding 367 amino acids including a signal peptide composed of 25 residues. The deduced amino acid sequence contained a conserved region generally found in esterases and lipases, but did not have significant similarity. When asymmetric degradation of racemic methyl CHB (CHBM) was performed using a culture broth of Escherichia coli DH5alpha transformed with the isolated gene, the reaction time was shortened 20-fold over that of the strain DS-S-75, and the maximum concentration of the substrate could be increased from 8% to 15% (w/v). Moreover, both of the obtained residual (R)-CHBM and the formed (S)-HL had high optical purities (>99% e.e.).

Thiol-tolerant assay for quantitative colorimetric determination of chloride released from whole-cell biodehalogenations

Determination of inorganic chloride released from a chloro-organic compound by whole-cell or enzymatic dehalogenation can be affected by free thiols, phosphate, sugars, pH, the chloro-organic substrate, and its dehalogenation product. For these reasons a highly sensitive, colorimetric chloride assay on the basis of [FeCl]2+ (lambda(max) = 340 nm) formed in highly acidic medium which is insensitive to composition of culture medium, free thiols, substrate, and dehalogenation product was developed. It is applicable to both fungal and bacterial high-cell-density cultures. The [FeCl]2+ method provides reliable data and is convenient for the rapid and facile determination of dehalogenation kinetics.