Biocatalytic Reduction Of Ketones Research Articles

New Anti-Prelog Stereospecific Whole-Cell Biocatalyst for Asymmetric Reduction of Prochiral Ketones.

The biocatalytic asymmetric reduction of prochiral ketones for the production of enantiopure alcohols is highly desirable due to its inherent advantages over chemical methods. In this study, a new bacterial strain capable of transforming ketones to corresponding alcohols with high activity and excellent enantioselectivity was discovered in a soil sample. The strain was subsequently identified as Bacillus cereus TQ-2 based on its physiological characteristics and 16S rDNA sequence analysis. Under optimized reaction conditions, the resting cells of B. cereus TQ-2 converted acetophenone to enantioenriched (R)-1-phenylethanol with 99% enantiometric excess following anti-Prelog's rule, which is scarce in biocatalytic ketone reduction. The optimum temperature for the cells was 30 °C, and considerable catalytic activity was observed over a broad pH range from 5.0 to 9.0. The cells showed enhanced catalytic activity in the presence of 15% (v/v) glycerol as a co-substrate. The catalytic activity can also be substantially improved by adding Ca2+ or K+ ions. Moreover, the B. cereus TQ-2 cell was highly active in reducing several structurally diverse ketones and aldehydes to form corresponding alcohols with good to excellent conversion. Our study provides a versatile whole-cell biocatalyst that can be used in the asymmetric reduction of ketones for the production of chiral alcohol, thereby expanding the biocatalytic toolbox for potential practical applications.

Biocatalytic asymmetric synthesis of (S)-1-indanol using Lactobacillus paracasei BD71

Enantiopure benzo-fused cyclic alcohols have been used as a building block of a drug for Parkinson’s disease. Biocatalytic reduction of ketones is one of the most promising and significant routes to prepare optically active alcohols. In this study, the reductive capacity of seven lactic acid bacteria (LAB) strains were investigated as whole-cell biocatalyst in the enantioselective reduction of 1-indanone (1). Lactobacillus paracasei BD71 was found to have the best reductive capacity. Effects of different parameters such as pH, incubation time, agitation speed and temperature, on enantiomeric excess (ee) and conversion were investigated in a bioconversion. (S)-1-indanol ((S)-2) could be used as precursor for the synthesis of rasagiline mesylate TVP1012 for the therapy of Parkinson’s illness. It was produced in gram-scale (5.24 g), high yield (93%) and enantiomerically pure form using L. paracasei BD71 whole-cell biocatalysts. Also, to our knowledge, this is the first report on production of (S)-2 using whole-cell catalyst in enantiopure form, excellent yield, conversion and gram scale. This is a cheap, clean and eco-friendly process for production of (S)-2 compared to chemical processes.

Biocatalytic asymmetric synthesis of (R)-1-tetralol using Lactobacillus paracasei BD101.

Asymmetric bioreduction of ketones is a fundamental process in the production of organic molecules. Compounds containing tetralone rings are found in the structure of many biologically active and pharmaceutical molecules. Biocatalytic reduction of ketones is one of the most promising and significant routes to prepare optically active alcohols. In this study, the reductive capacity of Lactobacillus paracasei BD101 was investigated as whole-cell biocatalyst in the enantioselective reduction of 1-tetralone (1). In biocatalytic reduction reactions, the conversion of the substrate and the enantiomeric excess (ee) of the product are significantly affected by optimization parameters such as temperature, agitation rate, pH, and incubation time. Effects of these parameters on ee and conversion were investigated comprehensively. (R)-1-tetralol ((R)-2), which can be used to treat disorder such as obsessive compulsive, post-traumatic stress, premenstrual dysphoric, and social anxiety, was manufactured in enantiopure form, high yield and gram-scale, using whole-cell biocatalysts of L.paracasei BD101. The 7.04 g of (R)-2 was obtained in optically pure form with 95% yield. Also, to our knowledge, this is the first report on production of (R)-2 using whole-cell biocatalyst in excellent yield, conversion, enantiopure form and gram scale. This is a clean, eco-friendly and cheap method for the synthesis of (R)-2 compared with chemical catalyst.

Biocatalytic ketone reductions using Biobeads for miniaturized high throughput experimentation

Miniaturized reactions conducted in parallel can lead to increased productivity in laboratories without depleting high value reagents.

Biocatalytic reduction of ketones in a secondary school laboratory

AbstractBiocatalysis is one of the most important industrial methods which has been increasingly attracting attention of scientists as a new and environmentally acceptable method. It is used in the preparation of chiral alcohols - important building blocks for the synthesis of fine chemicals, pharmaceuticals, agrochemicals and analogues of natural substances. In biocatalysis the use of traditional chiral agents based on heavy metals has been replaced by the use of enzymes. In many cases, the number of reaction steps has been limited, the selectivity of the desired products has been increased while the negative impact on the environment has been reduced. The principles of biocatalysis have been applied by us to design a simple chemical experiment for the students of higher secondary education. The modified assignment of a lab task consisted of bioreduction of 4-nitroacetophenone using the enzymes present in plant tissues of carrot, parsley and white radish. Within our pedagogical research, the adequacy of the chemical experiment for secondary school students was examined and the extent of understanding of the green chemistry experiment was analysed by the method of a semi-structured interview.

Asymmetric Synthesis of Akt Kinase Inhibitor Ipatasertib.

A highly efficient asymmetric synthesis of the Akt kinase inhibitor ipatasertib (1) is reported. The bicyclic pyrimidine 2 starting material was prepared via a nitrilase biocatalytic resolution, halogen-metal exchange/anionic cyclization, and a highly diastereoselective biocatalytic ketone reduction as key steps. The route also features a halide activated, Ru-catalyzed asymmetric hydrogenation of a vinylogous carbamic acid to produce α-aryl-β-amino acid 3 in high yield and enantioselectivity. The API was assembled in a convergent manner through a late-stage amidation/deprotection/monohydrochloride salt formation sequence.

Asymmetric reduction of ketones by biocatalysis using medlar (Mespilus germanica L) fruit grown in Algeria

The biocatalytic reduction of ketones was performed using medlar fruit (Mespilus germanica L), which is grown in large amounts in Algeria. Experiments were performed using aqueous medium with fresh medlar. Prochiral heteroaryl ketones containing furan, thiophene, chroman, and thiochroman moieties were reduced with enantiomeric excess (ee) of up to 98%. High enantioselectivities have been observed especially for the bioreduction of tetralone 4 and thiochromanone 5 with ee of 89% and 98%, respectively. Bioreduction using different parts of medlar indicate that chromanone 6 was reduced with good asymmetric inductions 77% < ee < 85% whichever part of fruit was employed (whole, flesh, or juice) and medlar juice exhibited the best activity.

ChemInform Abstract: Chemoenzymatic Synthesis of Enantiomerically Pure syn‐Configured 1‐Aryl‐3‐methylisochroman Derivatives.

A two-step synthesis of various enantiomerically pure 1-aryl3-methylisochroman derivatives was accomplished through asymmetric biocatalytic ketone reduction followed by an oxa-Pictet–Spengler reaction. The compounds were obtained in good to excellent yield (47–92%) in favor of the syn diastereomers [dr (syn/anti) up to 99:1]. Enantiopure arylpro

Biocatalytic Ketone Reduction - A Study on Screening and Effect of Culture Conditions on the Reduction of Selected Ketones

Microbial conversions are gaining importance in the synthesis of important drug metabolites and their intermediates as they are good alternative to chemical synthesis since they are enantio-selective and regio-selective and even can be carried out at ambient temperature and atmospheric pressure. Till date, biocatalytic reduction of acetophenone and its derivatives has been widely reported. In the present study, we have made an attempt to carry out the microbial bioreduction of o-hydroxyacetophenone by screening some of the selected microorganisms which were obtained from culture collection centre as well as those which are isolated in our Microbiology lab. The selected microorganisms include Aspergillus ochraceous, Aspergillus flavus, Aspergillus tubingenesis, Aspergillus niger, Rhizopus stolanifer MTCC 162, Rhizopus stolanifer MTCC 2591 and Baker’s yeast.Among the seven microorganisms screened for the bioreduction of o-hydroxyacetophenone, Baker’s yeast and Aspergillus tubingenesis showed significant bioconversion where as Aspergillus ochraceous exhibited the least bioconversion.In our earlier study it was found that Aspergillus flavus has the required bioreductase enzyme, which showed the maximum conversion of p-chloroacetophenone to p-chlorophenylethanol. Hence optimization of culture conditions to get maximum enzyme expression and hence maximum conversion was thought off. The parameters considered for the study include effect of various Carbon sources, Nitrogen source, Metal ions, incubation Temperature and media pH on enzyme expression. The optimized culture a condition at which maximum bioconversion was achieved was maltose among various carbon sources. Tryptone was found to have maximum effect among the nitrogen sources. Media pH 7.6 and incubation temperature of 35 °C was found to be favourable for maximum enzyme activity. Among various divalent metal salts, addition of magnesium sulphate to the media significantly increased the enzyme activity.

Chemoenzymatic Synthesis of Enantiomerically Pure syn‐Configured 1‐Aryl‐3‐methylisochroman Derivatives

AbstractA two‐step synthesis of various enantiomerically pure 1‐aryl‐3‐methylisochroman derivatives was accomplished through asymmetric biocatalytic ketone reduction followed by an oxa‐Pictet–Spengler reaction. The compounds were obtained in good to excellent yield (47–92 %) in favor of the syn diastereomers [dr (syn/anti) up to 99:1]. Enantiopure arylpropanols serving as pronucleophiles for the C–C bond‐formation step were obtained by biocatalytic reduction by employing enantiocomplementary alcohol dehydrogenases, which gave access to the (S) and (R) enantiomer with up to &gt;99 % conversion and up to &gt;99 % ee.

Biocatalytic Ketone Reduction - A Study on Screening and Effect of Culture Conditions on the Reduction of Selected Ketones

Microbial conversions are gaining importance in the synthesis of important drug metabolites and their intermediates as they are good alternative to chemical synthesis since they are enantio-selective and regio-selective and even can be carried out at ambient temperature and atmospheric pressure. Till date, biocatalytic reduction of acetophenone and its derivatives has been widely reported. In the present study, we have made an attempt to carry out the microbial bioreduction of o-hydroxyacetophenone by screening some of the selected microorganisms which were obtained from culture collection centre as well as those which are isolated in our Microbiology lab. The selected microorganisms include Aspergillus ochraceous, Aspergillus flavus, Aspergillus tubingenesis, Aspergillus niger, Rhizopus stolanifer MTCC 162, Rhizopus stolanifer MTCC 2591 and Baker’s yeast.Among the seven microorganisms screened for the bioreduction of o-hydroxyacetophenone, Baker’s yeast and Aspergillus tubingenesis showed significant bioconversion where as Aspergillus ochraceous exhibited the least bioconversion.In our earlier study it was found that Aspergillus flavus has the required bioreductase enzyme, which showed the maximum conversion of p-chloroacetophenone to p-chlorophenylethanol. Hence optimization of culture conditions to get maximum enzyme expression and hence maximum conversion was thought off. The parameters considered for the study include effect of various Carbon sources, Nitrogen source, Metal ions, incubation Temperature and media pH on enzyme expression. The optimized culture a condition at which maximum bioconversion was achieved was maltose among various carbon sources. Tryptone was found to have maximum effect among the nitrogen sources. Media pH 7.6 and incubation temperature of 35 °C was found to be favourable for maximum enzyme activity. Among various divalent metal salts, addition of magnesium sulphate to the media significantly increased the enzyme activity.

Immobilization of marine fungi on silica gel, silica xerogel and chitosan for biocatalytic reduction of ketones

Abstract The scanning electron microscopy (SEM) analysis showed that whole living hyphal of marine fungi Aspergillus sclerotiorum CBMAI 849 and Penicillium citrinum CBMAI 1186 were immobilized on support matrices of silica gel, silica xerogel and/or chitosan. P. citrinum immobilized on chitosan catalyzed the quantitative reduction of 1-(4-methoxyphenyl)-ethanone ( 1 ) to the enantiomer (S)-1-(4-methoxyphenyl)-ethanol ( 3b ), with excellent enantioselectivity ( ee > 99%, yield = 95%). Interestingly, ketone 1 was reduced with moderate selectivity and conversion to alcohol 3b ( ee = 69%, c 40%) by the free mycelium of P. citrinum . This free mycelium of P. citrinum catalyzed the production of the ( R )-alcohol 3a , the antipode of the alcohol produced by the immobilized cells. P. citrinum immobilized on chitosan also catalyzed the bioreduction of 2-chloro-1-phenylethanone ( 2 ) to 2-chloro-1-phenylethanol ( 4a,b ), but in this case without optical selectivity. These results showed that biocatalytic reduction of ketones by immobilization hyphal of marine fungi depends on the xenobiotic substrate and the support matrix used.

Principles into Practice Setting the Bar for Green Chemistry

Recent years have seen a disheartening string of revelations in which everyday items once considered safe—food packaging, toys, clothes, furniture, electronic components, and many more products—are found to contain carcinogens, endocrine disruptors, and other harmful chemicals.1 Growing demand for healthier alternatives, already seen in food production and housing construction,2 is also happening at the building-block level of manufacturing, where so-called green chemistry represents a revolutionary change in preventing pollution and health problems starting at the chemical design stage. Many industry and government entities are beginning to espouse the principles of green chemistry on their websites and in public statements. Now comes the task of crafting policy to put those principles into action. The U.S. Environmental Protection Agency (EPA) defines green chemistry as “the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances. Green chemistry applies across the life cycle of a chemical product, including its design, manufacture, and use.”3 Green chemistry also aims to mitigate the type of uncertainty Alan Gold-berg, a professor of toxicology at the Johns Hopkins Bloomberg School of Public Health, recently described to The New York Times: “I can get [toxicity] information on only 20 percent of chemicals we interact with on a daily basis.”4 Of that 20%, he now says, he may be able to find information on overt toxicity for about half, but for details on specific effects such as developmental neurotoxicity, the figure shrinks toward zero. So what does green chemistry look like? Consider the example of pregabalin, the active ingredient in the neuropathic pain drug Lyrica®. Pfizer developed an alternative green-chemistry process that converted several steps of pregabalin synthesis from use of organic solvents to water. That reduced both health hazards and production heating requirements. With the new synthesis, waste from the process dropped from 86 kg of waste per kg product to 17 kg, and energy use dropped by 82%.5 Proponents say that’s how the field can offer a win–win–win solution: good performance, lower cost, and less environmental impact—what Richard Engler, program manager of the EPA Green Chemistry Program, calls the “triple bottom line.” For many, a standard is a logical next step. “At some point you have to go beyond a definition and principles,” says Engler. “I think that’s something the standard will enable.”

A Continuously Operated Bimembrane Reactor Process for the Biocatalytic Production of (2R,5R)-Hexanediol

Alcohol dehydrogenase-catalyzed reductions of prochiral ketones to chiral alcohols require the regeneration of consumed cofactors such as NADH or NADPH. In the substrate-coupled cofactor regeneration approach, where 2-propanol is oxidized to acetone, complete conversion is inhibited by a thermodynamic limitation. This can be overcome by applying methods of in situ product removal techniques such as pervaporation. Here we present a new reactor concept which enables a continuous biocatalytic ketone reduction process with concurrent in situ removal of the byproduct acetone. In such a bimembrane reactor system recombinant Escherichia coli cells expressing alcohol dehydrogenase from Lactobacillus brevis were applied for the continuous reduction of 2,5-hexanedione. The product (2R,5R)-hexanediol could be synthesized with exceedingly high space-time yield of >170 g/(L·d) and catalyst usage (17.9 gP/gwetcellweight).

Advances in the Enzymatic Reduction of Ketones

Historically, biocatalytic ketone reductions involved the use of Baker's yeast. Within the last five years, a significant and growing number of isolated ketoreductases have become available that have rendered yeast-based reductions obsolete. The broad substrate range and exquisite selectivities of these enzymes repeatedly outperform other ketone reduction chemistries, making biocatalysis the general method of choice for ketone reductions. Presented here is a summary of our understanding of the capabilities and limitations of these enzymes.

Asymmetric biocatalytic reduction of ketones using hydroxy-functionalised water-miscible ionic liquids as solvents

Bi- and monophasic ionic liquid (IL)/buffer systems were successfully employed for the biocatalytic reduction of ketones catalysed by the alcohol dehydrogenase ADH-‘A’ from Rhodococcus ruber via hydrogen transfer. Two different catalyst preparations were employed, namely recombinant ADH-‘A’ ‘immobilised’ in Escherichia coli and partially purified ADH-‘A’. For biphasic systems conversions were acceptable until 20% v v −1 of IL. In contrast, hydroxy-functionalised ‘Tris-like’-ILs were successfully employed in monophasic systems up to 90% v v −1 IL. The use of these solvents allowed highly stereoselective enzymatic carbonyl reductions at substrate concentrations from 1.2 to 1.5 M.

Biocatalytic ketone reduction—a powerful tool for the production of chiral alcohols—part I: processes with isolated enzymes

Enzymes are able to perform reactions under mild conditions, e.g., pH and temperature, with remarkable chemo-, regio-, and stereoselectivity. Because of this feature, the number of biocatalysts used in organic synthesis has rapidly increased during the last decades, especially for the production of chiral compounds. The present review highlights biotechnological processes for the production of chiral alcohols by reducing prochiral ketones. These reactions can be catalyzed by either isolated enzymes or whole cells that exhibit ketone-reducing activity. The use of isolated enzymes is often preferred because of a higher volumetric productivity and the absence of side reactions. Both types of catalysts have also deficiencies limiting their use in synthesis of chiral alcohols. Because reductase-catalyzed reactions are dependent on cofactors, one major task in process development is to provide an effective method for regeneration of the consumed cofactors. In this paper, strategies for cofactor regeneration in biocatalytic ketone reduction are reviewed. Furthermore, different processes carried out on laboratory and industrial scales using isolated enzymes are presented. Attention is turned to process parameters, e.g., conversion, yield, enantiomeric excess, and process strategies, e.g., the application of biphasic systems or methods of in situ (co)product recovery. The biocatalytic production of chiral alcohols utilizing whole cells is presented in part II of this review.

Biocatalytic ketone reduction—a powerful tool for the production of chiral alcohols—part II: whole-cell reductions

Enzymes are able to perform reactions under mild conditions, e.g., pH and temperature, with remarkable chemo-, regio-, and stereoselectivity. Due to this feature the number of biocatalysts used in organic synthesis has rapidly increased during the last decades, especially for the production of chiral compounds. The present review highlights biotechnological processes for the production of chiral alcohols by reducing prochiral ketones with whole cells. Microbial transformations feature different characteristics in comparison to isolated enzymes. Enzymes that are used in whole-cell biotransformations are often more stable due to the presence of their natural environment inside the cell. Because reductase-catalyzed reactions are dependent on cofactors, one major task in process development is to provide an effective method for regeneration of the consumed cofactors. Many whole-cell biocatalysts offer their internal cofactor regeneration that can be used by adding cosubstrates, glucose or, in the case of cyanobacteria, simply light. In this paper, various processes carried out on laboratory and industrial scales are presented. Thereby, attention is turned to process parameters, e.g., conversion, yield, enantiomeric excess, and process strategies, e.g., the application of biphasic systems. The biocatalytic production of chiral alcohols utilizing isolated enzymes is presented in part I of this review.

Enzymatic Reduction of Ketones in “Micro-aqueous” Media Catalyzed by ADH-A fromRhodococcusruber

Mono- and biphasic aqueous-organic solvent systems (50% v v-1) as well as micro-aqueous organic systems (99% v v-1) were successfully employed for the biocatalytic reduction of ketones catalyzed by alcohol dehydrogenase ADH-A from Rhodococcus ruber via hydrogen transfer. A clear correlation between the log P of the organic solvent and the enzyme activity--the higher, the better--was found. The use of organic solvents allowed highly stereoselective enzymatic carbonyl reductions at substrate concentrations close to 2.0 M.

Biocatalytic Deuterium- and Hydrogen-Transfer using Over-Expressed ADH-‘A’

A highly enantioselective, biocatalytic reduction of ketones via hydrogen transfer in the presence of 2-propanol as hydrogen source and lyophilized E. coli cells containing over-expressed alcohol dehydrogenase ADH-‘A’ from Rhodococcus rubber DSM 44541 is reported. Using this single enzyme, enantiopure, versatile building blocks, which were not accessible employing the wild-type catalyst, could be prepared in an efficient way. By replacing 2-propanol with d 8-2-propanol, the biocatalytic synthesis of enantiopure deuterium-labelled sec-alcohols on a preparative scale and using a single enzyme has been achieved for the first time.