Applied Biotransformations in Green Solvents

Discovery and mechanism explanation of a novel green biocatalyst esterase Bur01 from Burkholderia ambifaria for ester synthesis under aqueous phase

Biocatalyst catalyzing the synthesis of esters under aqueous phase is an alternative with green and sustainable characteristics. Here, a biocatalyst esterase Bur01 was identified through genome sequencing and gene library construction from a Burkholderia ambifaria BJQ0010 with efficient ester synthesis property under aqueous phase for the first time. Bur01 was soluble expressed and the purified enzyme showed the highest activity at pH 4.0 and 40 °C. It had a broad substrate spectrum, especially for ethyl esters. The structure of Bur01 was categorized as a member of α/β fold hydrolase superfamily. The easier opening of lid under aqueous phase and the hydrophobicity of substrate channel contribute to easier access to the active center for substrate. Molecular docking and site-directed mutation demonstrated that the oxyanion hole Ala22, Met112 and π-bond stacking between His24 and Phe217 played essential roles in catalytic function. The mutants V149A, V149I, L159I and F137I enhanced enzyme activity to 1.42, 1.14, 1.32 and 2.19 folds due to reduced spatial resistance and increased hydrophobicity of channel and ethyl octanoate with the highest conversion ratio of 68.28 % was obtained for F137I. These results provided new ideas for developing green catalysts and catalytic basis of mechanistic studies for ester synthetase under aqueous phase.

Lipase-Catalyzed Strategies for the Preparation of Enantiomeric THIQ and THβC Derivatives: Green Aspects

This report reviews the most important lipase-catalyzed strategies for the preparation of pharmaceutically and chemically important tetrahydroisoquinoline and tetrahydro-β-carboline enantiomers through O-acylation of the primary hydroxy group, N-acylation of the secondary amino group, and COOEt hydrolysis of the corresponding racemic compounds with simple molecular structure, which have been reported during the last decade. A brief introduction describes the importance and synthesis of tetrahydroisoquinoline and tetrahydro-β-carboline derivatives, and it formulates the objectives of this compilation. The strategies are presented in chronological order, classified according to function of the reaction type, as kinetic and dynamic kinetic resolutions, in the main text. These reactions result in the desired products with excellent ee values. The pharmacological importance of the products together with their synthesis is given in the main text. The enzymatic hydrolysis of the hydrochloride salts as racemates of the starting amino carboxylic esters furnished the desired enantiomeric amino carboxylic acids quantitatively. The enzymatic reactions, performed in tBuOMe or H2O as usable solvents, and the transformations carried out in a continuous-flow system, indicate clear advantages, including atom economy, reproducibility, safer solvents, short reaction time, rapid heating and compression vs. shaker reactions. These features are highlighted in the main text.

YfeX - A New Platform for Carbene Transferase Development with High Intrinsic Reactivity

Carbene transfer biocatalysis has evolved from basic science to an area with vast potential for the development of new industrial processes. In this study, we show that YfeX, naturally a peroxidase, has great potential for the development of new carbene transferases, due to its high intrinsic reactivity, especially for the N-H insertion reaction of aromatic and aliphatic primary and secondary amines. YfeX shows high stability against organic solvents (methanol and DMSO), greatly improving turnover of hydrophobic substrates. Interestingly, in styrene cyclopropanation, WT YfeX naturally shows high enantioselectivity, generating the trans product with 87 % selectivity for the (R,R) enantiomer. WT YfeX also catalyzes the Si-H insertion efficiently. Steric effects in the active site were further explored using the R232A variant. Quantum Mechanics/Molecular Mechanics (QM/MM) calculations reveal details on the mechanism of Si-H insertion. YfeX, and potentially other peroxidases, are exciting new targets for the development of improved carbene transferases.

Application of Biobased Solvents in Asymmetric Catalysis

The necessity of more sustainable conditions that follow the twelve principles of Green Chemistry have pushed researchers to the development of novel reagents, catalysts and solvents for greener asymmetric methodologies. Solvents are in general a fundamental part for developing organic processes, as well as for the separation and purification of the reaction products. By this reason, in the last years, the application of the so-called green solvents has emerged as a useful alternative to the classical organic solvents. These solvents must present some properties, such as a low vapor pressure and toxicity, high boiling point and biodegradability, and must be obtained from renewable sources. In the present revision, the recent application of these biobased solvents in the synthesis of optically active compounds employing different catalytic methodologies, including biocatalysis, organocatalysis and metal catalysis, will be analyzed to provide a novel tool for carrying out more ecofriendly organic processes.

Biocatalysis for the asymmetric synthesis of Active Pharmaceutical Ingredients (APIs): this time is for real

INTRODUCTION

Biocatalysis has emerged as a powerful and useful strategy for the synthesis of active pharmaceutical ingredients (APIs). The outstanding developments in molecular biology techniques allow nowadays the screening, large-scale production, and designing of biocatalysts, adapting them to desired reactions. Many enzymes can perform reactions both in aqueous and non-aqueous media, broadening even further the opportunities to integrate them in complex pharmaceutical multi-step syntheses.

AREAS COVERED

This paper showcases several examples of biocatalysis in the pharmaceutical industry, covering examples of different enzymes, such as lipases, oxidoreductases, and transaminases, to deliver active drugs through complex synthetic routes. Examples are critically discussed in terms of reaction conditions, motivation for using an enzyme, and how biocatalysts can be integrated in multi-step syntheses. When possible, biocatalytic routes are benchmarked with chemical reactions.

EXPERT OPINION

The reported enzymatic examples are performed with high substrate loadings (>100 g L^-1) and with excellent selectivity, making them inspiring strategies for present and future industrial applications. The combination of powerful molecular biology techniques with the needs of the pharmaceutical industry can be aligned, creating promising platforms for synthesis under more sustainable conditions.

Recent developments in the biology and biotechnological applications of halotolerant yeasts

Natural hypersaline environments are inhabited by an abundance of prokaryotic and eukaryotic microorganisms capable of thriving under extreme saline conditions. Yeasts represent a substantial fraction of halotolerant eukaryotic microbiomes and are frequently isolated as food contaminants and from solar salterns. During the last years, a handful of new species has been discovered in moderate saline environments, including estuarine and deep-sea waters. Although Saccharomyces cerevisiae is considered the primary osmoadaptation model system for studies of hyperosmotic stress conditions, our increasing understanding of the physiology and molecular biology of halotolerant yeasts provides new insights into their distinct metabolic traits and provides novel and innovative opportunities for genome mining of biotechnologically relevant genes. Yeast species such as Debaryomyces hansenii, Zygosaccharomyces rouxii, Hortaea werneckii and Wallemia ichthyophaga show unique properties, which make them attractive for biotechnological applications. Select halotolerant yeasts are used in food processing and contribute to aromas and taste, while certain gene clusters are used in second generation biofuel production. Finally, both pharmaceutical and chemical industries benefit from applications of halotolerant yeasts as biocatalysts. This comprehensive review summarizes the most recent findings related to the biology of industrially-important halotolerant yeasts and provides a detailed and up-to-date description of modern halotolerant yeast-based biotechnological applications.

Enzymatic synthesis of novel fructosylated compounds by Ffase from Schwanniomyces occidentalis in green solvents

The β-fructofuranosidase from the yeast Schwanniomyces occidentalis (Ffase) produces potential prebiotic fructooligosaccharides (FOS) by self-transfructosylation of sucrose, being one of the highest known producers of 6-kestose. The use of Green Solvents (GS) in biocatalysis has emerged as a sustainable alternative to conventional organic media for improving product yields and generating new molecules. In this work, the Ffase hydrolytic and transfructosylating activity was analysed using different GS, including biosolvents and ionic liquids. Among them, 11 were compatible for the net synthesis of FOS. Besides, two glycerol derivatives improved the yield of total FOS. Interestingly, polyols ethylene glycol and glycerol were found to be efficient alternative fructosyl-acceptors, both substantially decreasing the sucrose fructosylation. The main transfer product of the reaction with glycerol was a 62 g L-1 isomeric mixture of 1-O and 2-O-β-d-fructofuranosylglycerol, representing 95% of all chemicals generated by transfructosylation. Unexpectedly, the non-terminal 2-O fructo-conjugate was the major molecule catalysed during the process, while the 1-O isomer was the minor one. This fact made Ffase the first known enzyme from yeast showing this catalytic ability. Thus, novel fructosylated compounds with potential applications in food, cosmetics, and pharmaceutical fields have been obtained in this work, increasing the biotechnological interest of Ffase with innocuous GS.

Applied biocatalysis beyond just buffers - from aqueous to unconventional media. Options and guidelines

In nature, enzymes conventionally operate under aqueous conditions. Because of this, aqueous buffers are often the choice for reaction media when enzymes are applied in chemical synthesis. However, to meet the demands of an industrial application, due to the poor water solubility of many industrially relevant compounds, an aqueous reaction system will often not be able to provide sufficient substrate loadings. A switch to a non-aqueous solvent system can provide a solution, which is already common for lipases, but more challenging for biocatalysts from other enzyme classes. The choices in solvent types and systems, however, can be overwhelming. Furthermore, some engineering of the protein structure of biocatalyst formulation is required. In this review, a guide for those working with biocatalysts, who look for a way to increase their reaction productivity, is presented. Examples reported clearly show that bulk water is not necessarily required for biocatalytic reactions and that clever solvent systems design can support increased product concentrations thereby decreasing waste formation. Additionally, under these conditions, enzymes can also be combined in cascades with other, water-sensitive, chemical catalysts. Finally, we show that the application of non-aqueous solvents in biocatalysis can actually lead to more sustainable processes. At the hand of flowcharts, following simple questions, one can quickly find what solvent systems are viable.

Biocatalyzed Redox Processes Employing Green Reaction Media

The application of biocatalysts to perform reductive/oxidative chemical processes has attracted great interest in recent years, due to their environmentally friendly conditions combined with high selectivities. In some circumstances, the aqueous buffer medium normally employed in biocatalytic procedures is not the best option to develop these processes, due to solubility and/or inhibition issues, requiring biocatalyzed redox procedures to circumvent these drawbacks, by developing novel green non-conventional media, including the use of biobased solvents, reactions conducted in neat conditions and the application of neoteric solvents such as deep eutectic solvents.

Highly efficient asymmetric reduction of ketopantolactone to d-(−)-pantolactone by Escherichia coli cells expressing recombinant conjugated polyketone reductase and glucose dehydrogenase in a fed-batch biphasic reaction system

Enantiopure d-(−)-pantolactone was efficiently synthesized by Escherichia coli cells expressing recombinant CduCPR and BsuGDH in a fed-batch biphasic reaction system.

Biocatalysis as Useful Tool in Asymmetric Synthesis: An Assessment of Recently Granted Patents (2014–2019)

The broad interdisciplinary nature of biocatalysis fosters innovation, as different technical fields are interconnected and synergized. A way to depict that innovation is by conducting a survey on patent activities. This paper analyses the intellectual property activities of the last five years (2014–2019) with a specific focus on biocatalysis applied to asymmetric synthesis. Furthermore, to reflect the inventive and innovative steps, only patents that were granted during that period are considered. Patent searches using several keywords (e.g., enzyme names) have been conducted by using several patent engine servers (e.g., Espacenet, SciFinder, Google Patents), with focus on granted patents during the period 2014–2019. Around 200 granted patents have been identified, covering all enzyme types. The inventive pattern focuses on the protection of novel protein sequences, as well as on new substrates. In some other cases, combined processes, multi-step enzymatic reactions, as well as process conditions are the innovative basis. Both industries and academic groups are active in patenting. As a conclusion of this survey, we can assert that biocatalysis is increasingly recognized as a useful tool for asymmetric synthesis and being considered as an innovative option to build IP and protect synthetic routes.

Biocatalytic potential of Streptomyces spp. isolates from rhizosphere of plants and mycorrhizosphere of fungi

Biocatalytic potential of Streptomyces strains isolated from the rhizosphere of plants and from mycorrhizosphere of fungi has been investigated. A total of 118 Streptomyces isolates were selected and functionally screened for 10 different biotechnologically important enzymatic activities: hydrolase (cellulase, cutinase, gelatinase, lipase, protease, polyhydroxyalkanoate (PHA) depolymerase), phenol oxidase and peroxidase (laccase, tyrosinase, and lignin peroxidase), and aminotransferase. Out of 118 tested Streptomyces spp., 90% showed at least one enzymatic activity. The most abundant were enzymes involved in the biomass degradation, as the production of cutinase, cellulase, and lignin peroxidase were detected in 31%, 40%, and 48% of the isolates, respectively. The improved specific activities of lipase (isolates BV315 and BV100) and tyrosinase (isolates BV87 and BV88) were shown in comparison with the industrially relevant activities of Pseudomonas strains. Plant rhizosphere soils were more prolific source of Streptomyces strains with biocatalytic potential in comparison with mycorrhizosphere soils. Overall, 284 enzyme activities among 118 Streptomyces isolates have been detected. This is the first comprehensive screening of Streptomyces isolates from rhizosphere and mycorrhizosphere soils for novel biocatalysts, showing that specific environmental habitats, such as rhizosphere soils, are "treasure troves" of Streptomyces with biocatalytic potential.

Biotransformation using halotolerant yeast in seawater: a sustainable strategy to produce R-(-)-phenylacetylcarbinol

Acyloin condensation between benzaldehyde and decarboxylated pyruvate results in the production of R-(-)-phenylacetylcarbinol, a chiral precursor of the drug ephedrine. Huge research efforts have been made to improve the conditions of this reaction and to avoid the generation of by-products. Recently, we reported the advantages of using whole cells of the yeast Debaryomyces etchellsii as biocatalysts for this purpose. In this work, a new strategy, which fulfills green chemistry principles, is proposed and is based on using seawater as a gentle solvent. We demonstrate that, under these conditions, several improvements can be made compared to employing freshwater: (1) the conversion of the starting material in (R)-PAC is higher and with a minimum production of by-products; (2) it is possible to increase at least twofold the benzaldehyde load in the reaction medium; (3) cells can maintain their activity after several recycling rounds, which makes (R)-PAC production an easy and economical process.

Chiral protic imidazolium salts with a (-)-menthol fragment in the cation: synthesis, properties and use in the Diels-Alder reaction

New chiral protic imidazolium salts containing a (1R,2S,5R)-(-)-menthol substituent in the cation and four different anions (chloride, hexafluorophosphate, trifluoromethanesulfonate and bis(trifluoromethylsulfonyl)imide) were efficiently prepared and extensively characterized. Detailed NMR analysis was performed, and a comparison of the chemical shifts of the protons and carbons of the imidazolium cation as a function of the combined anion was discussed. The specific rotation, solubility in commonly used solvents, thermal properties including phase transition temperatures, and thermal stability were also determined. Three of the synthesized tertiary salts (Cl, PF6 or OTf anion) were crystalline solids; 1-H-3-[(1R,2S,5R)-(-)-menthoxymethyl]-imidazolium bis(trifluoromethylsulfonyl)imide, (-)[H-Ment-Im][NTf2] was a liquid at room temperature. The chiral protic salts were used in a Diels-Alder reaction as a test reaction, and the results were compared with those from aprotic chiral ionic liquids having the same chiral substituent in the cation (1R,2S,5R)-(-)-menthol with a bis(trifluoromethylsulfonyl)imide anion. Both protic and aprotic chiral salts, used in a Diels-Alder reaction, were pure (-)-enantiomers, which was determined by NMR with Δ-TRISPHAT tetrabutylammonium salt as a chiral shift reagent. Protic salts offered distinctly higher endo/exo ratios than aprotic ones, but an enantiomeric excess was not obtained. The stereoselectivity reached the same high level even after the fourth recycle of (-)[H-Ment-Im][NTf2] in the reaction of ethyl-vinyl ketone with cyclopentadiene at temperature of -35 °C.

Physical stability of N,N-dimethyldecanamide/α-pinene-in-water emulsions as influenced by surfactant concentration

In recent years, interest in submicron emulsions has increased due to their high stability and potential applications in the encapsulation and release of active ingredients in many industrial fields, such as the food industry, pharmaceuticals or agrochemicals. Furthermore, the social demand for eco-friendly solutions to replace hazardous solvents in many dispersion formulations has steadily risen. In this study, the influence of surfactant concentration on the formation and physical stability of submicron oil-in-water emulsions using a high-pressure dual-channel homogenizer (microfluidizer) has been investigated. The formulation involved the use of a blend of two green solvents (N,N-dimethyldecanamide and α-pinene) as dispersed phase and a nonionic polyoxyethylene glycerol ester derived from coconut oil as emulsifier (Levenol^® C-201), which enjoys a European eco-label. Therefore, these emulsions may find applications as matrices for agrochemicals. Physical stability and rheological properties of the emulsions studied showed an important dependence on the eco-friendly surfactant concentration. The lowest surfactant concentration (1wt%) yielded the onset of a creaming process after a short aging time and was not enough to avoid recoalescence during emulsification. On the other hand, the higher surfactant concentrations (4-5wt%) resulted in depletion flocculation, which in turn triggered emulsion destabilization by coalescence. The optimum physical stability was exhibited by emulsions containing intermediate surfactant concentrations (2-3wt%) since coalescence was hardly significant and the onset of a weak creaming destabilization process was substantially delayed.

Beyond the outer limits of nature by directed evolution

For more than thirty years, biotechnology has borne witness to the power of directed evolution in designing molecules of industrial relevance. While scientists all over the world discuss the future of molecular evolution, dozens of laboratory-designed products are being released with improved characteristics in terms of turnover rates, substrate scope, catalytic promiscuity or stability. In this review we aim to present the most recent advances in this fascinating research field that are allowing us to surpass the limits of nature and apply newly gained attributes to a range of applications, from gene therapy to novel green processes. The use of directed evolution in non-natural environments, the generation of catalytic promiscuity for non-natural reactions, the insertion of unnatural amino acids into proteins or the creation of unnatural DNA, is described comprehensively, together with the potential applications in bioremediation, biomedicine and in the generation of new bionanomaterials. These successful case studies show us that the limits of directed evolution will be defined by our own imagination, and in some cases, stretching beyond that.

Bio-based solvents for the Baylis–Hillman reaction of HMF

The Baylis–Hillman reaction of HMF was investigated in various bio-based solvent systems and in water.

Redesigning the synthesis of vidarabine via a multienzymatic reaction catalyzed by immobilized nucleoside phosphorylases

The comparison between the biocatalyzed synthesis of araA here described and the chemical synthesis of this nucleoside showed that the enzymatic route is superior (less steps, milder conditions and reagents, easier downstream, lower E-factor).

Sustainable synthesis of N-acetyllactosamine using an immobilized β-galactosidase on a tailor made porous polymer

An efficient enzymatic synthesis of N-acetyllactosamine has been developed in biosolvents, mediated by the action of an immobilized β-galactosidase on a tailor made porous polymer.

Glycerol as an efficient medium for the petasis borono-mannich reaction

The multicomponent Petasis borono–Mannich (PBM) reaction is a useful tool for the preparation of complex molecules in a single step from boronic acids, aldehydes/ketones, and amines. Here, we describe the use of glycerol in the PBM reaction of salicylaldehydes or 2-pyridinecarbaldehyde with several boronic acids and secondary amines. From these readily available starting materials, alkylaminophenols, 2-substituted pyridines, and 2H-chromenes were prepared in reasonable to good yields. Glycerol was compared with other solvents, and in some cases, it provided the reaction product in higher yield. Crude glycerol, as generated by the biodiesel industry, was evaluated and found to be a suitable solvent for the PBM reaction, successfully expanding the potential use of this industry by-product. Based on density functional theory (DFT) calculations and the obtained experimental results, the involvement of glycerol-derived boronic esters in the reaction mechanism is suggested to be competitive with the free boronic acid pathway. Similar Gibbs free energies for the aryl migration from the boronate species to the iminium were determined for both mechanisms.

Efficient asymmetric synthesis of 1-cyano-tetrahydroisoquinolines from lipase dual activity and opposite enantioselectivities in α-Aminonitrile resolution

Dual promiscuous racemization/amidation activities of lipases leading to efficient dynamic kinetic resolution protocols of racemic α-aminonitrile compounds are described. α-Amidonitrile products of high enantiomeric purity could be formed in high yields. Several lipases from different sources were shown to exhibit the dual catalytic activities, where opposite enantioselectivities could be recorded for certain substrates.

Application of supercritical fluid carbon dioxide to the extraction and analysis of lipids

Supercritical carbon dioxide (SCCO2) is an ecofriendly supercritical fluid that is chemically inert, nontoxic, noninflammable and nonpolluting. As a green material, SCCO2 has desirable properties such as high density, low viscosity and high diffusivity that make it suitable for use as a solvent in supercritical fluid extraction, an effective and environment-friendly analytical method, and as a mobile phase for supercritical fluid chromatography, which facilitates high-throughput, high-resolution analysis. Furthermore, the low polarity of SCCO2 is suitable for the extraction and analysis of hydrophobic compounds. The growing concern surrounding environmental pollution has triggered the development of green analysis methods based on the use of SCCO2 in various laboratories and industries. SCCO2 is becoming an effective alternative to conventional organic solvents. In this review, the usefulness of SCCO2 in supercritical fluid extraction and supercritical fluid chromatography for the extraction and analysis of lipids is described.

2-Methyltetrahydrofuran (2-MeTHF): a biomass-derived solvent with broad application in organic chemistry

2-Methyl-tetrahydrofuran (2-MeTHF) can be derived from renewable resources (e.g., furfural or levulinic acid) and is a promising alternative solvent in the search for environmentally benign synthesis strategies. Its physical and chemical properties, such as its low miscibility with water, boiling point, remarkable stability compared to other cyclic-based solvents such as THF, and others make it appealing for applications in syntheses involving organometallics, organocatalysis, and biotransformations or for processing lignocellulosic materials. Interestingly, a significant number of industries have also started to assess 2-MeTHF in several synthetic procedures, often with excellent results and prospects. Likewise, preliminary toxicology assessments suggest that the use of 2-MeTHF might even be extended to more processes in pharmaceutical chemistry. This Minireview describes the properties of 2-MeTHF, the state-of-the-art of its use in synthesis, and covers several outstanding examples of its application from both industry and academia.