Aqueous-organic Biphasic System Research Articles

Target-oriented discovery of a new esterase-producing strain Enterobacter sp. ECU1107 for whole cell-catalyzed production of (2S,3R)-3-phenylglycidate as a chiral synthon of Taxol

A new strain, Enterobacter sp. ECU1107, was identified among over 200 soil isolates using a two-step screening strategy for the enantioselective synthesis of (2S,3R)-3-phenylglycidate methyl ester (PGM), a key intermediate for production of a potent anticancer drug Taxol®. An organic-aqueous biphasic system was employed to reduce spontaneous hydrolysis of the substrate PGM and isooctane was found to be the most suitable organic solvent. The temperature and pH optima of the whole cell-mediated bioreaction were 40 °C and 6.0, respectively. Under these reaction conditions, the enantiomeric excess (ee(s)) of (2S,3R)-PGM recovered was greater than 99 % at approximately 50 % conversion. The total substrate loading in batch reaction could reach 600 mM. By using whole cells of Enterobacter sp. ECU1107, (2S,3R)-PGM was successfully prepared in decagram scale in a 1.0-l mechanically stirred reactor, affording the chiral epoxy ester in >99 % ee s and 43.5 % molar yield based on the initial load of racemic substrate.

The dual role of cis-[RuCl2(dmso)4] in the synthesis of new water-soluble Ru(II)–phosphane complexes and in the catalysis of redox isomerization of allylic alcohols in aqueous–organic biphasic systems

New air-stable, water-soluble Ru(II)–phosphane complexes were synthesized in high purity by the reaction of cis-[RuCl2(dmso)4] with 2 equivalents of 1,3,5-triaza-7-phosphaadamantane (pta) and its N-methyl and N-benzyl derivatives (pta-Me and pta-Bn, respectively). All new complexes were characterized by elementary analysis and spectroscopic methods (NMR, ESI-MS) and the molecular structures of cis-cis-trans-[RuCl2(dmso)2(pta)2], cis-cis-trans-[RuCl2(dmso)2(pta-H)2]Cl2 (obtained in acidic solutions) and that of cis-cis-trans-[RuCl2(dmso)2(pta-Me)2](CF3SO3)2 were determined by single crystal X-ray diffraction.Under mild conditions, cis-[RuCl2(dmso)4] actively catalyzed the transformation of allylic alcohols into the corresponding ketones with 100% selectivity while in the same reaction the new Ru(II)–pta complexes showed moderate activity and selectivity.

Enzymatic Synthesis of Galacto-oligosaccharides in an Organic–Aqueous Biphasic System by a Novel β-Galactosidase from a Metagenomic Library

Prebiotic galacto-oligosaccharides (GOS) were effectively synthesized from lactose in organic-aqueous biphasic media by a novel metagenome-derived β-galactosidase BgaP412. A maximum GOS yield of 46.6% (w/w) was achieved with 75.4% lactose conversion rate in the cyclohexane/buffer system [95:5 (v/v) cyclohexane/buffer] under the optimum reaction conditions (initial lactose concentration = 30% (w/v), T = 50 °C, pH 7.0, and t = 8 h). The corresponding productivity of GOS was approximately 17.5 g L(-1) h(-1). The GOS mixture consisted of tri-, tetra-, and pentasaccharides. Trisaccharides were the chief component of reaction products. These experimental results showed that a low water content, a high initial lactose concentration, and an elevated reaction temperature could significantly promote the transgalactosylation activity of β-galactosidase BgaP412; at the same time, the enhanced GOS yield in an organic-aqueous biphasic system is because of the fact that thermodynamic equilibrium can be shifted to the synthetic direction by reversing the normal hydrolysis.

Amphiphilic tannin-stabilized Rh nanopartciles: A highly active and reusable catalyst in biphasic aqueous–organic system

Abstract A series of Rh nanoparticles were prepared by using plant tannins as stabilizers. The as-prepared plant tannin-stabilized Rh nanoparticles were subsequently characterized by TEM, DES, FTIR and XPS. Due to the amphiphilic nature of plant tannins, the plant tannin-stabilized Rh nanoparticles were highly active in aqueous–organic biphasic hydrogenation of styrene. Furthermore, the as-prepared Rh catalyst can be reused 5 times without significant loss of catalytic activity, thus exhibiting a remarkable reusability.

α-Rhamnosyl-β-glucosidase-Catalyzed Reactions for Analysis and Biotransformations of Plant-Based Foods

Most aroma compounds exist in vegetal tissues as disaccharide conjugates, rutinose being an abundant sugar moiety in grapes. The availability of aroma precursors would facilitate analytical analysis of plant-based foods. The diglycosidase α-rhamnosyl-β-glucosidase from Acremonium sp. DSM 24697 efficiently transglycosylated the rutinose moiety from hesperidin to 2-phenylethanol, geraniol, and nerol in an aqueous-organic biphasic system. 2-Phenethyl rutinoside was synthesized up to millimolar level with an 80% conversion regarding the donor hesperidin. The hydrolysis of the synthesized aroma precursors was not detected in an aqueous medium. However, in the presence of ethanol as a sugar acceptor, the enzyme was able to transfer the disaccharide residue forming the alkyl-rutinoside. The aroma precursors were significantly hydrolyzed (up to 3-4% in 2 h at 30 °C), which indicated the potential use of the enzyme for biotechnological applications, for example, in aroma modulation of fermented foods.

Enhanced whole-cell biodehydrogenation of 11β-hydroxyl medroxyprogesterone in a biphasic system containing ionic liquid

A hydrophilic ionic liquid, 1-butyl-3-methylimidazolium (L)-lactate ([bmim][lactate]), was successfully employed as a co-solvent to improve the biodehydrogenation of steroid 11β-hydroxyl medroxyprogesterone (HMP) to pregna-1,4-diene-6α-methyl-3,20-dione-11β,17α-dihydroxy (PDMDD) in an aqueous-organic biphasic system using Arthrobacter simplex UR106 cells. First, a suitable biphasic system was constituted, composed of toluene and Tris-HCl buffer (0.05 mol/L, pH 7.6) at a 0.4 (Vorg/Vaq) volumetric phase ratio. Investigation of biodehydrogenation with the addition of [bmim][lactate] to the aqueous phase was then performed. The results demonstrate that biodehydrogenation is more efficient in a biphasic system containing 2% [bmim][lactate] as a co-solvent compared to an aqueous-toluene two-phase system. Higher bioconversion (83.2% versus 56.4%) was observed after 16 h at a substrate concentration of 80 mg HMP in 8 mL of toluene.

Aqueous–Organic Biphasic Hydrogenation of trans‐Cinnamaldehyde Catalyzed by Rhodium and Ruthenium Phosphane‐Free Porphyrin Complexes

AbstractThe synthesis and spectroscopic characterization of new rhodium and ruthenium complexes with a porphyrin, possessing carboxylic groups in the arms of the porphyrin ring, is described. The complexes are completely soluble in water in the presence of a base (KOH or triethylamine). These phosphane‐free and air‐stable complexes were evaluated as catalysts in the aqueous hydrogenation of trans‐cinnamaldehyde. Catalysis was more efficient with the ammonium salts of the complexes rather than the corresponding potassium carboxylate salts, preferably in water/toluene rather than in neat water. The effect of catalyst concentration, reaction temperature, hydrogen pressure and methanol addition on the catalytic activity of the complexes in the presence of triethylamine in an aqueous–organic biphasic system was investigated. The catalysts were presumably homogeneous, and could be recycled and reused without any significant difference in activity and selectivity. This is the first time that porphyrin–metal complexes have been used as catalysts for hydrogenation of α,β‐unsaturated aldehydes.

Effects of biphasic aqueous–organic systems on equilibrium constant and percentage yield of a reverse reaction. A Review

Effects of biphasic aqueous–organic systems on equilibrium constant and percentage yield of a reverse reaction. A Review

Enzyme activity evaluation of organic solvent-treated phenylalanine ammonia lyase

The direct one-step synthesis of L-phenylalanine methyl ester in an organic-aqueous biphasic system using phenylalanine ammonia lyase (E.C.4.3.1.5, PAL) containing Rhodotorula glutinis yeast whole cells was reported earlier. We report here further optimization of this biotransformation using isolated PAL, when the lyophilized enzyme is treated with different water miscible and water immiscible organic solvents. Use of isolated PAL enzyme is advantageous in overcoming diffusion barriers encountered when using PAL containing R.glutinis whole cells, and resulted in increased product yield due to better interaction of enzyme with the substrate. Among the water miscible solvents, ethanol treated and methanol-treated enzymes supported maximum PAL forward and reverse activities; respectively. In the water immiscible solvents category, heptane-treated enzyme exhibited maximal activity for both PAL forward and reverse reactions. PAL activity obtained with enzyme specimens treated with methanol, ethanol, and heptane varied in the range of 91–99% of that observed in aqueous buffer medium for the forward reaction; and 89–95% for the reverse reaction. n-butanol,acetone, and benzene were found to have a inhibitory effect on PAL enzyme, in that, it resulted in only 31–33% activity of that obtained with aqueous solution. Raman spectroscopy was used to monitor amide I and II bands which are sensitive to changes in the secondary structure of proteins. No changes in structure could be detected from the analyses of AI and AII bands of PAL spectra. This data obtained for PAL, a tetramer, could be significant in predicting how solvent interactions affect the structure and function of multimeric proteins and enzymes in nonaqueous media.

Synthesis of ( R)-β-nitro alcohols catalyzed by R-selective hydroxynitrile lyase from Arabidopsis thaliana in the aqueous–organic biphasic system

Both enantiomers of β-nitro alcohols are versatile chiral building blocks. However, their synthesis using enzymes as catalysts has received little attention, with the exception of ( S)-β-nitro alcohols produced in a reaction catalyzed by an S-selective hydroxynitrile lyase (HNL) from Hevea brasiliensis ( HbHNL). An R-selective HNL containing an α/β-hydrolase fold from the noncyanogenic plant Arabidopsis thaliana ( AtHNL) accepts nitromethane (MeNO 2) as a donor in a reaction with aromatic aldehydes to yield ( R)-β-nitro alcohols (Henry reaction; nitro aldol reaction). This reaction proceeded in an aqueous–organic biphasic system. The organic solvent giving the highest enantioselectivity was n-butyl acetate (AcOBu) with an optimum aqueous phase content of 50% (v/v). This is the first example of the R-HNL-catalyzed synthesis of ( R)-β-nitro alcohols.

Efficient chemo-enzymatic synthesis of endomorphin-1 using organic solvent stable proteases to green the synthesis of the peptide

Endomorphin-1 (Tyr-Pro-Trp-Phe-NH2, EM-1), an effective analgesic, was efficiently synthesized by a combination of enzymatic and chemical methods. Peptide Boc-Trp-Phe-NH2 was synthesized with a high yield of 97.1% by the solvent-stable protease WQ9-2 in a 20% methanol medium. The maximum concentration (141 g L−1) of Boc-Trp-Phe-NH2 was obtained with an economical molar ratio of the substrate of 1 : 1. The products crystallized and separated from the substrates without purification, followed by the removal of the Boc group with trifluoroacetic acid to generate Trp-Phe-NH2. Using the efficient mixed carbonic anhydride method, Boc-Tyr-Pro-OH was synthesized chemically. The tetrapeptide Boc-Tyr-Pro-Trp-Phe-NH2 was synthesized with a yield of 84.5% by another organic solvent-tolerant protease, PT121, from Boc-Tyr-Pro-OH and Trp-Phe-NH2 in an organic–aqueous biphasic system and was extracted with ethyl acetate, shifting the equilibrium of the synthesis. EM-1 was obtained by removal of the Boc group from Boc-Tyr-Pro-Trp-Phe-NH2 in a high yield of 91% due to the free protection of the side-chain of the Tyr phenolic hydroxy group. After a one-step purification in the final step by using high speed countercurrent chromatography (HSCCC), EM-1 was obtained with a purity greater than 99.8%. The chemo-enzymatic synthesis of EM-1 proved to be efficient, productive, with minimal side-chain protection and simple purification, thus greening the synthesis of the peptide.

Preparation of ethyl 3R,5S-6-(benzyloxy)-3,5-dihydroxy-hexanoate by recombinant diketoreductase in a biphasic system

Diketoreductase from Acinetobacter baylyi ATCC 33305 is a unique carbonyl reductase, which can stereoselectively reduce ethyl-6-(benzyloxy)-3,5-dioxohexanoate to ethyl 3R,5S-6-(benzyloxy)-3,5-dihydroxy-hexanoate, an advanced intermediate for statin drugs. In the present study, we explored an aqueous-organic biphasic reaction system to make this biocatalyst more practical and valuable. Different from most oxidoreductases, diketoreductase displayed an excellent tolerance to certain organic solvents without any changes on the catalytic properties. After optimizing reaction conditions, an aqueous-hexane (1:1) biphasic system was established for the preparation of 3R,5S-dihydroxy product by diketoreductase. This system was further scaled up to 0.5 l at a substrate concentration of 105 g/l (378 mM), and the 3R,5S-hydroxy product was obtained with a yield of 83.5% and excellent stereoselectivity (de>99.5%, ee>99.5%).

Significantly improved asymmetric oxidation of sulfide with resting cells of Rhodococcus sp. in a biphasic system

Enantiopure sulfoxides can be prepared via the asymmetric oxidation of sulfides using sulfide monooxygenases. Five different organic–aqueous biphasic systems were investigated for their abilities to increase the bio-oxidation efficiency of a water-insoluble sulfide (phenyl methyl sulfide, PMS). Isooctane was found to be the most suitable organic phase solvent. In this isooctane–aqueous system, the oxidation reaction was not sensitive to pH, giving high yields over the entire range of the tested pH values (5.0–11.0). In contrast, cell concentration significantly affected the reaction rate. (S)-Phenyl methyl sulfoxide ((S)-PMSO) was formed at a higher concentration and a greater enantiomeric excess (18.3mM and >99.0% ee(S)) in this isooctane–aqueous biphasic system than in an aqueous single-phase system (2.17mM and 59.9% ee(S)). The asymmetric oxidation of 150mM PMS in the isooctane phase was successfully carried out in a mechanically stirred bioreactor (2.4L) and resulted in a 49.0% yield of (S)-PMSO with enantiomeric excess greater than 99.0%.

Systematic assessment of the stability of benzaldehyde lyase in aqueous–organic biphasic systems and its stabilization by modification with methoxy-poly(ethylene) glycol

Abstract Benzaldehyde lyase from Pseudomonas fluorescens Biovar I [BAL; E.C.4.1.2.38] catalyzes the stereoselective formation of C–C bonds coupling aldehydes to generate alpha-hydroxy ketones. A broad range of poorly water-soluble substrates are accepted in forward and reverse reactions. In this study, the stability of BAL in aqueous–organic biphasic systems as promising reaction media was systematically investigated using methyl-tert-butylether, 2-octanone, and toluene as the organic phase. Surprisingly, a strong individual molecular toxicity of these water-immiscible solvents was observed along with the interfacial toxicity exerted by the aqueous–organic interfaces. They could be considerably reduced by covalent attachment of methoxy-poly(ethylene) glycol (mPEG750 and mPEG2000) to the enzyme surface increasing the half-life by a factor of up to 18. However, under reactive conditions solvent effects were strongly superimposed by an additional deactivating effect, possibly caused by the aldehyde substrate, and no differences between unmodified and modified BAL were detectable. For technical application of the enzyme in aqueous–organic biphasic media additional strategies for stabilization will therefore be desirable.

ChemInform Abstract: TEMPO‐Mediated Oxidation of Primary Alcohols to Carboxylic Acids by Exploitation of Ethers in an Aqueous—Organic Biphase System.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis, characterization and hydroformylation activity of 7‐azaindolate‐bridged dinuclear rhodium(I)phosphines with pendant polar‐groups

AbstractNew dinuclear Rh(I)–Phosphines of the types [Rh(µ‐azi)(CO)(L)]2 (1,3–7) and [Rh(µ‐azi)(L)]2 (8) with pendant polar groups, and a chealated mononuclear compound [Rh(azi‐H)(CO)(L)] (2) (where azi = 7‐azaindolate, L = polar phosphine) were isolated from the reaction of [Rh(µ‐Cl)(CO)2]2 with 7‐azaindolate followed by some polar mono‐ and bis‐phosphines (L1–L8). A relationship between Δδ31P‐NMR and ν(CO) values was considered to define the impact of polar‐groups on σ‐donor properties of the phosphines. These compounds were evaluated as catalyst precursors in the hydroformylation of 1‐hexene and 1‐dodecene both in mono‐ and biphasic aqueous organic systems. While the biphasic hydroformylations (water + toluene) gave exclusively the aldehydes, the monophasic one (aqueous ethanol) showed propensity to form both aldehydes and alcohols. The influence of bimetallic cooperative effects, and σ‐donor and hydrophilic properties of the phosphines with pendant polar‐groups in enhancing the yields and selectivity of hydroformylation products was emphasized. In addition, when strong σ‐donor phosphine was used, the π‐acceptor nature of pyridine ring of 7‐azaindolate spacer was found to be a considerable factor in facilitating the facile cleavage of CO group during hydroformylation and in supplementing the cooperative effects. Copyright © 2009 John Wiley & Sons, Ltd.

TEMPO-Mediated Oxidation of Primary Alcohols to Carboxylic Acids by Exploitation of Ethers in an Aqueous–Organic Biphase System

Abstract Expeditious and benign methods for primary alcohol–carboxylic acid conversions with TEMPO were developed in a biphasic system composed of a slightly miscible ether (THP) and aqueous layer. Easily available co-oxidants such as Py·HBr3, Bu4NBr3, and electrooxidation were successfully applied to generate N-oxoammonium species as a recyclable catalyst.

Radical Polymerization of n-BMA Using a Di-Site Phase Transfer Catalyst

The di-site phase transfer catalyzed radical polymerization of butyl methacrylate with the phase transfer catalyst N,N′-diheptyl-N,N,N′,N′-tetramethyl-1,2-ethanediammonium dibromide (DHTMEDADB) was carried out in an aqueous-organic biphase system at 60 ± 1°C under nitrogeneous atmosphere at fixed pH and ionic strength. A suitable kinetic scheme has been proposed and its significance was discussed. The polymers obtained were investigated and characterized (FTIR, 1H-NMR and XRD studies).

Free Radical Polymerization of Acrylonitrile Using Potassium Peroxy Disulphate Initiator and a Phase Transfer Catalyst

Free radical polymerization of acrylonitrile with the di-site phase transfer catalyst 1,4-bis(tetramethylhexyl)ethylenediammonium bromide (TMHEDAB) was investigated using the water-soluble initiator PDS (potassium peroxydisulphate) and water-insoluble solvent ethylacetate in an aqueous-organic biphase system at 60±1°C under nitrogen atmosphere at fixed pH and ionic strength. Rp increased with the increase in concentration of the monomer, initiator and catalyst. The order of Rp, with respect to monomer and catalyst concentration was found to be unity and with respect to initiator was found to be 0.5. A suitable mechanism has been proposed and its significance was discussed. The polymers obtained were characterized by spectral studies such as FTIR, 1H-NMR, XRD, DSC, and TGA.

Solvent-dependent reactivity in porcine pancreatic lipase (PPL)-catalyzed hydrolysis

The solvent-dependent enzyme reactivity of porcine pancreatic lipase (PPL)-catalyzed hydrolysis was investigated using trans- 3 and cis-(3-(benzyloxymethyl)oxiran-2-yl)methyl acetate 4 as substrates. The conversion efficiency and enantioselectivity of the hydrolysis of these compounds were measured in three different types of enzymatic media: neat organic solvents, organic–aqueous mixture solvent systems, and an aqueous buffer solution. Comparison of the catalytic hydrolysis that occurred in 12 different organic solvents with log P values in the range of −1.10 to 3.50 revealed that the reactivity and selectivity of PPL-catalyzed hydrolysis toward (+)- and (−)-isomers were strongly affected by the solvent system. In neat organic solvents and organic–aqueous biphasic systems, (+)- cis oxirane acetate (+)- 4 was selectively hydrolyzed by PPL over the (−)- cis isomer. In contrast, hydrolysis of the (+)- trans substrate (+)- 3 was preferred in monophasic organic–aqueous systems and buffer solutions. The addition of water to the organic solvent increased the overall hydrolysis rate. However, hydrolysis in the aqueous buffer solution was considerably retarded since the organic substrates were insoluble in water. Therefore, control of the solvent system can result in the successful kinetic resolution of oxirane esters and their corresponding alcohols.