Choose Your Own Adventure: A Comprehensive Database of Reactions Catalyzed by Cytochrome P450 BM3 Variants

Cytochrome P450 BM3 monooxygenase is the topic of extensive research as many researchers have evolved this enzyme to generate a variety of products. However, the abundance of information on increasingly diversified variants of P450 BM3 that catalyze a broad array of chemistry is not in a format that enables easy extraction and interpretation. We present a database that categorizes variants by their catalyzed reactions and includes details about substrates to provide reaction context. This database of >1500 P450 BM3 variants is downloadable and machine-readable and includes instructions to maximize ease of gathering information. The database allows rapid identification of commonly reported substitutions, aiding researchers who are unfamiliar with the enzyme in identifying starting points for enzyme engineering. For those actively engaged in engineering P450 BM3, the database, along with this review, provides a powerful and user-friendly platform to understand, predict, and identify the attributes of P450 BM3 variants, encouraging the further engineering of this enzyme.

Strategies for the biological synthesis of D-glucuronic acid and its derivatives

D-glucuronic acid is a kind of glucose derivative, which has excellent properties such as anti-oxidation, treatment of liver disease and hyperlipidemia, and has been widely used in medicine, cosmetics, food and other fields. The traditional production methods of D-glucuronic acid mainly include natural extraction and chemical synthesis, which can no longer meet the growing market demand. The production of D-glucuronic acid by biocatalysis has become a promising alternative method because of its high efficiency and environmental friendliness. This review describes different production methods of D-glucuronic acid, including single enzyme catalysis, multi-enzyme cascade, whole cell catalysis and co-culture, as well as the intervention of some special catalysts. In addition, some feasible enzyme engineering strategies are provided, including the application of enzyme immobilized scaffold, enzyme mutation and high-throughput screening, which provide good ideas for the research of D-glucuronic acid biocatalysis.

Distinct chemical factors in hydrolytic reactions catalyzed by metalloenzymes and metal complexes

The selective hydrolysis of the extremely stable phosphoester, peptide and ester bonds of molecules by bio-inspired metal-based catalysts (metallohydrolases) is required in a wide range of biological, biotechnological and industrial applications. Despite the impressive advances made in the field, the ultimate goal of designing efficient enzyme mimics for these reactions is still elusive. Its realization will require a deeper understanding of the diverse chemical factors that influence the activities of both natural and synthetic catalysts. They include catalyst-substrate complexation, non-covalent interactions and the electronic nature of the metal ion, ligand environment and nucleophile. Based on our computational studies, their roles are discussed for several mono- and binuclear metallohydrolases and their synthetic analogues. Hydrolysis by natural metallohydrolases is found to be promoted by a ligand environment with low basicity, a metal bound water and a heterobinuclear metal center (in binuclear enzymes). Additionally, peptide and phosphoester hydrolysis is dominated by two competing effects, i.e. nucleophilicity and Lewis acid activation, respectively. In synthetic analogues, hydrolysis is facilitated by the inclusion of a second metal center, hydrophobic effects, a biological metal (Zn, Cu and Co) and a terminal hydroxyl nucleophile. Due to the absence of the protein environment, hydrolysis by these small molecules is exclusively influenced by nucleophile activation. The results gleaned from these studies will enhance the understanding of fundamental principles of multiple hydrolytic reactions. They will also advance the development of computational methods as a predictive tool to design more efficient catalysts for hydrolysis, Diels-Alder reaction, Michael addition, epoxide opening and aldol condensation.

Machine Learning for Prediction, Classification, and Identification of Immobilized Enzymes for Biocatalysis

BACKGROUND

Enzyme immobilization is a beneficial component involved in biocatalytic strategies. Understanding and evaluating the enzyme immobilization system plays an important role in the successful development and implementation of the biocatalysis route. Ensuring the implementation of a successful enzyme immobilization process is vital for realizing a highly functioning and well suited biocatalytic process within pharmaceutical development.

AIM

To develop a method which can accurately and objectively identify and classify differences within enzyme immobilization systems, sample preparation methods, and data collection parameters.

METHODS

Raman hyperspectral imaging was used to obtain a total of eight spectral data sets from enzyme immobilization samples. Partial least squares discriminant analysis (PLS-DA) was used to classify and identify the samples based on their differences.

RESULTS

Several two-class, four-class, and eight-class PLS-DA models were built to classify the different sample data sets. All models reached between 92-100% accuracy after cross-validation and external validation, illustrating great success of the models for identifying differences between the samples.

CONCLUSION

Raman hyperspectral imaging with machine learning can be used to investigate, interpret, and classify different data collection parameters, sample preparation methods, and enzyme immobilization supports, providing crucial insight into enzyme immobilization process development.

Application of Emerging Techniques in Reduction of the Sugar Content of Fruit Juice: Current Challenges and Future Perspectives

In light of the growing interest in products with reduced sugar content, there is a need to consider reducing the natural sugar concentration in juices while preserving the initial concentration of nutritional compounds. This paper reviewed the current state of knowledge related to mixing juices, membrane processes, and enzymatic processes in producing fruit juices with reduced concentrations of sugars. The limitations and challenges of these methods are also reviewed, including the losses of nutritional ingredients in membrane processes and the emergence of side products in enzymatic processes. As the existing methods have limitations, the review also identifies areas that require further improvements and technological innovations.

Turning thermostability of Aspergillus terreus (R)-selective transaminase At-ATA by synthetic shuffling

As versatile and green biocatalysts for the asymmetric amination of ketones, the insufficient thermostability of transaminases always limits its broad application in the pharmaceutical and fine chemical industries. Here, synthetic shuffling technology was used to enhance stability of (R)-selective transaminase from Aspergillus terreus. The results showed that 30 out of 5000 mutants had improved thermostability by color-based screening method, among which mutants with residual enzyme activity higher than 50% at 45 °C for 10 min were selected for further analysis. Especially, the half-inactivation temperature (T₅₀¹⁰), half-life (t_1/2), and melting temperature (T_m) of the best mutant M14 (M280C-H210N-M150C-F115L) were 13.7 °C, 165.8 min, and 13.9 °C higher than that of the wild type (WT), respectively. M14 also exhibited a significant biocatalytic efficiency toward acetophenone and 1-acetylnaphthalene, the yield of which were 265.6% and 117.5% higher than WT, respectively. Based on molecular dynamics simulation, improved catalytic efficiency of M14 could be attributed to its increased hydrogen bonds interaction around the mutation sites. Additionally, the introduction of disulfide bond combined with above mutations has a synergistic effect on the improved protein thermostability.

Resolution of Racemic Aryloxy-Propan-2-yl Acetates via Lipase-Catalyzed Hydrolysis: Preparation of Enantiomerically Pure/Enantioenriched Mexiletine Intermediates and Analogs

The lipase kinetic resolution (KR) of aryloxy-propan-2-yl acetates, via hydrolysis, produced enantiomerically pure/enantioenriched mexiletine intermediates and analogs. Racemic acetates rac-1-(2,6-dimethylphenoxy)propan-2-yl acetate (rac-5a), rac-1-(2,4-dimethylphenoxy)propan-2-yl acetate (rac-5b), rac-1-(o-tolyloxy)propan-2-yl acetate (rac-5c) and rac-1-(naphthalen-1-yloxy)propan-2-yl acetate (rac-5d) were used as substrates. A preliminary screening (24 h, phosphate buffer pH 7.0 with 20% acetonitrile as co-solvent, 30 °C and enzyme:substrate ratio of 2:1, m:m) was carried out with twelve lipases using acetate 5a as substrate. Two enzymes stood out in the KR of 5a, the Amano AK lipase from Pseudomonas fluorescens and lipase from Thermomyces lanuginosus (TLL) immobilized on Immobead 150. Under these conditions, both the (R)-1-(2,6-dimethylphenoxy)propan-2-ol [(R)-4a] and the remaining (S)-1-(2,6-dimethylphenoxy)propan-2-yl acetate [(S)-5a] were obtained with enantiomeric excess (ee) > 99%, 50% conversion and enantiomeric ratio (E) > 200. The KR study was expanded to racemic acetates 5b-d, leading to the corresponding chiral remaining acetates with ≥95% ee, and the alcohols 4b-d with ≥98% ee, and conversion values close to 50%. The best conditions for KRs of rac-5b-d involved the use of lipase from P. fluorescens or TLL immobilized on Immobead 150, 24 or 48 h and 30 °C. These intermediates had their absolute configurations determined using 1H NMR spectroscopy (Mosher’s method), showing that the KRs of these acetates obeyed the Kazlauskas’ rule. Molecular docking studies corroborated the experimental results, indicating a preference for the hydrolysis of (R)-5a-d.

Immobilized Lipase in Resolution of Ketoprofen Enantiomers: Examination of Biocatalysts Properties and Process Characterization

In this study, lipase from Aspergillus niger immobilized by physical immobilization by the adsorption interactions and partially interfacial activation and mixed physical immobilization via interfacial activation and ion exchange was used in the kinetic resolution of the ketoprofen racemic mixture. The FTIR spectra of samples after immobilization of enzyme-characteristic signals can be seen, and an increase in particle size diameters upon immobilization is observed, indicating efficient immobilization. The immobilization yield was on the level of 93% and 86% for immobilization unmodified and modified support, respectively, whereas activity recovery reached around 90% for both systems. The highest activity of immobilized biocatalysts was observed at pH 7 and temperature 40 °C and pH 8 and 20 °C for lipase immobilized by physical immobilization by the adsorption interactions and partially interfacial activation and mixed physical immobilization via interfacial activation and ion exchange, respectively. It was also shown that over a wide range of pH (from 7 to 10) and temperature (from 20 to 60 °C) both immobilized lipases retained over 80% of their relative activity, indicating improvement of enzyme stability. The best solvent during kinetic resolution of enantiomers was found to be phosphate buffer at pH 7, which obtained the highest efficiency of racemic ketoprofen methyl ester resolution at the level of over 51%, followed by enantiomeric excess 99.85% in the presence of biocatalyst obtained by physical immobilization by the adsorption interactions and partially interfacial activation.

Potential of the Signal Peptide Derived from the PAS_chr3_0030 Gene Product for Secretory Expression of Valuable Enzymes in Pichia pastoris

Pichia pastoris is widely used for the production of valuable recombinant proteins. An advantage of P. pastoris over other expression systems is that it secretes low levels of endogenous proteins, which facilitates the purification processes if the desired recombinant proteins are efficiently secreted into the culture medium. However, not all recombinant proteins can be successfully secreted by P. pastoris, especially enzymes that are located in intracellular compartments in their native hosts. Few studies have reported strategies for releasing recombinant proteins which cannot be secreted by standard protocols. Here, we investigated whether this challenge can be addressed using novel secretion leaders. Analysis of the secretome and transcriptome of P. pastoris indicated that the four genes with the highest protein-to-transcript ratios were EPX1, PAS_chr3_0030, SCW10, and UTH1, suggesting that their gene products contain efficient secretion leaders. Our data revealed that the signal peptide derived from the PAS_chr3_0030 gene product conferred secretion competence to certain industrial enzymes, e.g., a nitrilase of Alcaligenes faecalis ZJUTB10, a ribosylnicotinamide kinase of P. pastoris, and a glucose dehydrogenase of Exiguobacterium sibiricum. Therefore, the signal peptide derived from the PAS_chr3_0030 gene product represents a novel secretion sequence for the secretory expression of recombinant enzymes in P. pastoris. IMPORTANCE Although P. pastoris is widely used for the secretory production of pharmaceutical proteins, its successful applications in the secretory production of industrial enzymes are limited. The α-mating factor pre-pro leader is the most widely used secretion signal in P. pastoris, but numerous industrial enzymes cannot be secreted using it. The importance of this study is that we identified a signal peptide derived from the PAS_chr3_0030 gene product which conferred secretion competence to three-quarters of the enzymes tested. This signal peptide derived from the PAS_chr3_0030 gene product may facilitate the application of P. pastoris in industrial biocatalysis.

High-Yield Synthesis of Enantiopure 1,2-Amino Alcohols from l-Phenylalanine via Linear and Divergent Enzymatic Cascades

Enantiomerically pure 1,2-amino alcohols are important compounds due to their biological activities and wide applications in chemical synthesis. In this work, we present two multienzyme pathways for the conversion of l-phenylalanine into either 2-phenylglycinol or phenylethanolamine in the enantiomerically pure form. Both pathways start with the two-pot sequential four-step conversion of l-phenylalanine into styrene via subsequent deamination, decarboxylation, enantioselective epoxidation, and enantioselective hydrolysis. For instance, after optimization, the multienzyme process could convert 507 mg of l-phenylalanine into (R)-1-phenyl-1,2-diol in an overall isolated yield of 75% and >99% ee. The opposite enantiomer, (S)-1-phenyl-1,2-diol, was also obtained in a 70% yield and 98–99% ee following the same approach. At this stage, two divergent routes were developed to convert the chiral diols into either 2-phenylglycinol or phenylethanolamine. The former route consisted of a one-pot concurrent interconnected two-step cascade in which the diol intermediate was oxidized to 2-hydroxy-acetophenone by an alcohol dehydrogenase and then aminated by a transaminase to give enantiomerically pure 2-phenylglycinol. Notably, the addition of an alanine dehydrogenase enabled the connection of the two steps and made the overall process redox-self-sufficient. Thus, (S)-phenylglycinol was isolated in an 81% yield and >99.4% ee starting from ca. 100 mg of the diol intermediate. The second route consisted of a one-pot concurrent two-step cascade in which the oxidative and reductive steps were not interconnected. In this case, the diol intermediate was oxidized to either (S)- or (R)-2-hydroxy-2-phenylacetaldehyde by an alcohol oxidase and then aminated by an amine dehydrogenase to give the enantiomerically pure phenylethanolamine. The addition of a formate dehydrogenase and sodium formate was required to provide the reducing equivalents for the reductive amination step. Thus, (R)-phenylethanolamine was isolated in a 92% yield and >99.9% ee starting from ca. 100 mg of the diol intermediate. In summary, l-phenylalanine was converted into enantiomerically pure 2-phenylglycinol and phenylethanolamine in overall yields of 61% and 69%, respectively. This work exemplifies how linear and divergent enzyme cascades can enable the synthesis of high-value chiral molecules such as amino alcohols from a renewable material such as l-phenylalanine with high atom economy and improved sustainability.

Enabling biocatalysis in high-concentration organic cosolvent by enzyme gate engineering

Biocatalysis in high-concentration organic solvents (OSs) offers many advantages, but realizing this process remains a huge challenge. An R-selective ω-amine transaminase variant (AcATA_M2 ) exhibited high activity toward 50 g/L pro-sitagliptin ketone 1-[1-piperidinyl]-4-[2,4,5-trifluorophenyl]-1,3-butanedione (PTfpB). However, AcATA_M2 displayed unsatisfactory organic-cosolvent resistance against high-concentration dimethyl sulfoxide (DMSO), which is required to enhance the solubility of the hydrophobic substrate PTfpB. Located in the substrate-binding tunnel, enzyme gates are structural elements that undergo reversible conformational transitions, thus affecting the accessibility of the binding pocket to solvent molecules. Depending on the conformation of the enzyme gates, one can define an open or closed conformation on which the enzyme activity in OSs may depend. To enhance the DMSO resistance of AcATA_M2 , we identified the beneficial residues at the "enzyme gate" region via computational analysis, alanine scanning, and site-saturation mutagenesis. Two beneficial variants, namely, AcATA_M2 ^F56D and AcATA_M2 ^F56V , not only displayed improved enzyme activity but also exhibited enhanced DMSO resistance (the half-life value increased from 25.71 to 42.49 h under 60% DMSO). Molecular dynamic simulations revealed that the increase in DMSO resistance was mainly caused by the decrease in the number of DMSO molecules in the substrate-binding pocket. Moreover, in the kilogram-scale experiment, the conversion of 80 g/L substrate was increased from 50% (AcATA_M2 ) to 85% (M2^F56D in 40% DMSO) with a high e.e. of >99% within 24 h.

In situ H2O2 generation methods in the context of enzyme biocatalysis

Hydrogen peroxide is a versatile oxidant that has use in medical and biotechnology industries. Many enzymes require this oxidant as a reaction mediator in order to undergo their oxygenation chemistries. While there is a reliable method for generating hydrogen peroxide via an anthraquinone cycle, there are several advantages for generating hydrogen in situ. As highlighted in this review, this is particularly beneficial in the case of biocatalysts that require hydrogen peroxide as a reaction mediator because the exogenous addition of hydrogen peroxide can damage their reactive heme centers and render them inactive. In addition, generation of hydrogen peroxide in situ does not dilute the reaction mixture and cause solution parameters to change. The environment would also benefit from a hydrogen peroxide synthesis cycle that does not rely on nonrenewable chemicals obtained from fossil fuels. Generation of hydrogen peroxide in situ for biocatalysis using enzymes, bioelectrocatalyis, photocatalysis, and cold temperature plasmas are addressed. Particular emphasis is given to reaction processes that support high total turnover numbers (TTNs) of the hydrogen peroxide-requiring enzymes. Discussion of innovations in the use of hydrogen peroxide-producing enzyme cascades for antimicrobial activity, wastewater effluent treatment, and biosensors are also included.

Scope and limitations of biocatalytic carbonyl reduction with white-rot fungi

The reductive activity of various basidiomycetous fungi towards carbonyl compounds was screened on an analytical level. Some strains displayed high reductive activities toward aromatic carbonyls and aliphatic ketones. Utilizing growing whole-cell cultures of Dichomitus albidofuscus, the reactions were up-scaled to a preparative level in an aqueous system. The reactions showed excellent selectivities and gave the respective alcohols in high yields. Carboxylic acids were also reduced to aldehydes and alcohols under the same conditions. In particular, benzoic, vanillic, ferulic, and p-coumaric acid were reduced to benzyl alcohol, vanillin, dihydroconiferyl alcohol and 1-hydroxy-3-(4-hydroxyphenyl)propan, respectively.

A Glimpse into Green Chemistry Practices in the Pharmaceutical Industry

In this Minireview, the importance and implementation of green chemistry practices in the pharmaceutical industry are illustrated. With notable examples, some of the most important industrial organic transformations are discussed along with their applications in the synthesis of drug molecules. A brief comparison between traditional unsustainable methods and modern green methods is made to shed light on the economic and environmental benefits of greener methods. Finally, green chemistry practices in the pharmaceutical industries of India and China are also discussed.

Development of a simple high-throughput assay for directed evolution of enantioselective sulfoxide reductases

We report on the development of high-throughput fluorogenic assay that can streamline directed evolution of enantioselective sulfoxide reductases. As a model, methionine sulfoxide reductase A (MsrA) has been evolved to expand its limited substrate scope. The resulting mutant MsrA can resolve a range of new challenging racemic sulfoxides with high efficiency including the pharmaceutically relevant albendazole sulfoxide. The simplicity and the level of throughput make this method also suitable for the screening of metagenomic libraries in future for the discovery of new enzymes with similar reactivities.

Continuous Flow Bioamination of Ketones in Organic Solvents at Controlled Water Activity using Immobilized ω-Transaminases

Compared with biocatalysis in aqueous media, the use of enzymes in neat organic solvents enables increased solubility of hydrophobic substrates and can lead to more favorable thermodynamic equilibria, avoidance of possible hydrolytic side reactions and easier product recovery. ω-Transaminases from Arthrobacter sp. (AsR-ωTA) and Chromobacterium violaceum (Cv-ωTA) were immobilized on controlled porosity glass metal-ion affinity beads (EziG) and applied in neat organic solvents for the amination of 1-phenoxypropan-2-one with 2-propylamine. The reaction system was investigated in terms of type of carrier material, organic solvents and reaction temperature. Optimal conditions were found with more hydrophobic carrier materials and toluene as reaction solvent. The system's water activity (aw) was controlled via salt hydrate pairs during both the biocatalyst immobilization step and the progress of the reaction in different non-polar solvents. Notably, the two immobilized ωTAs displayed different optimal values of aw, namely 0.7 for EziG3-AsR-ωTA and 0.2 for EziG3-Cv-ωTA. In general, high catalytic activity was observed in various organic solvents even when a high substrate concentration (450-550 mM) and only one equivalent of 2-propylamine were applied. Under batch conditions, a chemical turnover (TTN) above 13000 was obtained over four subsequent reaction cycles with the same batch of EziG-immobilized ωTA. Finally, the applicability of the immobilized biocatalyst in neat organic solvents was further demonstrated in a continuous flow packed-bed reactor. The flow reactor showed excellent performance without observable loss of enzymatic catalytic activity over several days of operation. In general, ca. 70% conversion was obtained in 72 hours using a 1.82 mL flow reactor and toluene as flow solvent, thus affording a space-time yield of 1.99 g L-1 h-1. Conversion reached above 90% when the reaction was run up to 120 hours.

Chitin/Chitosan and Its Derivatives: Fundamental Problems and Practical Approaches

In this review, we present the data on the natural occurrence of chitin and its partially or fully deacetylated derivative chitosan, as well as their properties, methods of modification, and potential applications of derivatives with bactericidal, fungicidal, and antioxidant activities. The structure and physicochemical characteristics of the polymers, their functions, and features of chitin microbial synthesis and degradation, including the processes occurring in nature, are described. New data on the hydrolytic microorganisms capable of chitin degradation under extreme conditions are presented. Special attention is focused on the effect of physicochemical characteristics of chitosan, including molecular weight, degree of deacetylation, polydispersity index, and number of amino group derivatives (quaternized, succinyl, etc.) on the antimicrobial and antioxidant properties of modified polymers that can be of particular interest for biotechnology, medicine, and agriculture. Analysis of the available literature data confirms the importance of fundamental research to broaden our knowledge on the occurrence of chitin and chitosan in nature, their role in global biosphere cycles, and prospects of applied research aimed at using chitin, chitosan, and their derivatives in various aspects of human activity.

Zinc(ii)-mediated diastereoselective Passerini reactions of biocatalytically desymmetrised renewable inputs

A chiral aldehyde, obtained in both enantiomeric forms from renewable 2,5-Bis(hydroxymethyl)tetrahydrofuran by a chemoenzymatic procedure, was submitted to a modified diastereoselective Passerini reaction employing zinc dicarboxylates.

Biocatalysis and Pharmaceuticals: A Smart Tool for Sustainable Development

Biocatalysis is the term used to describe the application of any type of biocatalyst (enzymes, as isolated preparations of wild-type or genetically modified variants, or whole cells, either as native cells or as recombinant expressed proteins inside host cells) in a given synthetic schedule [...]

Whole Cell Actinobacteria as Biocatalysts

Production of fuels, therapeutic drugs, chemicals, and biomaterials using sustainable biological processes have received renewed attention due to increasing environmental concerns. Despite having high industrial output, most of the current chemical processes are associated with environmentally undesirable by-products which escalate the cost of downstream processing. Compared to chemical processes, whole cell biocatalysts offer several advantages including high selectivity, catalytic efficiency, milder operational conditions and low impact on the environment, making this approach the current choice for synthesis and manufacturing of different industrial products. In this review, we present the application of whole cell actinobacteria for the synthesis of biologically active compounds, biofuel production and conversion of harmful compounds to less toxic by-products. Actinobacteria alone are responsible for the production of nearly half of the documented biologically active metabolites and many enzymes; with the involvement of various species of whole cell actinobacteria such as Rhodococcus, Streptomyces, Nocardia and Corynebacterium for the production of useful industrial commodities.

Enzymatic kinetic resolution of chiral sulfoxides – an enantiocomplementary approach

A new enzymatic assay for the preparation of chiral sulfoxides that is enantiocomplementary to the known (S)-enantiomer-reducing activity of methionine sulfoxide reductase A (MsrA) is described.

Integrating biocatalysis and multicomponent reactions

While often multicomponent reactions (MCR) are used for the diversity-oriented synthesis of racemic (or achiral) molecular entities, this short review describes two alternative approaches for accessing enantiopure products exploiting the power of biocatalysis. Enzymes or microorganisms may be used for preparing enantiopure MCR inputs or for resolving racemic (or achiral) MCR adducts.

Whole Cells as Biocatalysts in Organic Transformations

Currently, the power and usefulness of biocatalysis in organic synthesis is undeniable, mainly due to the very high enantiomeric excess reached using enzymes, in an attempt to emulate natural processes. However, the use of isolated enzymes has some significant drawbacks, the most important of which is cost. The use of whole cells has emerged as a useful strategy with several advantages over isolated enzymes; for this reason, modern research in this field is increasing, and various reports have been published recently. This review surveys the most recent developments in the enantioselective reduction of carbon-carbon double bonds and prochiral ketones and the oxidation of prochiral sulfides using whole cells as biocatalytic systems.

Selective catalytic amination of halogenated aldehydes with calcined palladium catalysts

This work focuses on understanding the influence of the conditions used in the calcination step of palladium catalysts on the performance of this catalyst in the reductive amination of halogen-containing substrates. The results show that increasing the calcination temperatures (from 100 °C to 400 °C) has a detrimental effect on catalytic activity but a strong positive effect on the selectivity (from 45 to 96%), avoiding the undesired dehalogenation reaction. TEM investigation showed that the reason for the different selectivity can be addressed to different Pd mean particles size and particle size distribution. In particular, larger Pd particles obtained at the highest calcination temperature (400 °C) showed the best selectivity to halogenated benzylamines (96%), with a good stability in terms of both activity and selectivity as confirmed by performing recycling tests.

This work focuses on understanding the influence of the conditions used in the calcination step of palladium catalysts on the performance of this catalyst in the reductive amination of halogen-containing substrates.

Application of ω-Transaminases in the Pharmaceutical Industry

Chiral amines are valuable building blocks for the pharmaceutical industry. ω-TAms have emerged as an exciting option for their synthesis, offering a potential "green alternative" to overcome the drawbacks associated with conventional chemical methods. In this review, we explore the application of ω-TAms for pharmaceutical production. We discuss the diverse array of reactions available involving ω-TAms and process considerations of their use in both kinetic resolution and asymmetric synthesis. With the aid of specific drug intermediates and APIs, we chart the development of ω-TAms using protein engineering and their contribution to elegant one-pot cascades with other enzymes, including carbonyl reductases (CREDs), hydrolases and monoamine oxidases (MAOs), providing a comprehensive overview of their uses, beginning with initial applications through to the present day.

A Biocatalytic Route to Highly Enantioenriched β-Hydroxydioxinones

A novel biocatalytic system to access a wide variety of β-hydroxydioxinones from β-ketodioxinones employing commercial engineered ketoreductases has been developed. This practical system provides a remarkably straightforward solution to limitations in accessing certain chemical scaffolds common in β-hydroxydioxinones that are of great interest due to their diversification capabilities. A few highlights of this system are that it is high yielding, highly enantioselective, and chromatography-free. We have demonstrated both a wide substrate scope and a high degree of scalability.

Enzymatic site-selectivity enabled by structure-guided directed evolution

This review covers recent advances in the directed evolution of enzymes for controlling site-selectivity of hydroxylation, amination and chlorination.