Enzyme‐Catalysed Synthesis of Secondary and Tertiary Amides

Efficient Enzymatic Synthesis of Carbamates in Water Using Promiscuous Esterases/Acyltransferases

Biocatalysis provides an attractive approach to facilitate synthetic reactions in aqueous media. Motivated by the discovery of promiscuous aminolysis activity of esterases, we exploited the esterase from Pyrobaculum calidifontis VA1 (PestE) for the synthesis of carbamates from different aliphatic, aromatic, and arylaliphatic amines and a set of carbonates such as dimethyl-, dibenzyl-, or diallyl carbonate. Thus, aniline and benzylamine derivatives, aliphatic and even secondary amines could be efficiently converted into the corresponding benzyloxycarbonyl (Cbz)- or allyloxycarbonyl (Alloc)-protected products in bulk water, with (isolated) yields of up to 99 %.

Biocatalytic Heteroaromatic Amide Formation in Water Enabled by a Catalytic Tetrad and Two Access Tunnels

The amide moiety belongs to the most common motives in pharmaceutical chemistry, present in many prescribed small-molecule pharmaceuticals. Methods for its manufacture are still in high demand, especially using water/buffer as a solvent and avoiding stoichiometric amounts of activation reagents. Herein, we identified from a library of lipases/esterases/acyltransferases and variants thereof a lipase originating from Sphingomonas sp. HXN-200 (SpL) able to form amides in aqueous solution starting from a broad scope of sterically demanding heteroaromatic ethyl esters as well as aliphatic amines, reaching isolated yields up to 99% on preparative scale and space time yields of up to 864 g L-1 d-1; thus, in selected cases, the amide was formed within minutes. The enzyme features an aspartate next to the canonical serine of the catalytic triad, which was essential for amide formation. Furthermore, the enzyme structure revealed two tunnels to the active site, presumably one for the ester and one for the amine, which permit the bringing together of the sterically demanding heteroaromatic esters and the amine in the active site. This work shows that biocatalytic amide formation starting from various five- and six-membered heteroaromatic ethyl esters in the buffer can serve as a platform for preparative amide synthesis.

Discovery and Mechanistic Understanding of a Lipase from Rhizorhabdus dicambivorans for Efficient Ester Aminolysis in Aromatic Amines

The formation of amide bonds via aminolysis of esters by lipases generates a diverse range of amide frameworks in biosynthetic chemistry. Few lipases have satisfactory activity towards bulky aromatic amines despite numerous attempts to improve the efficiency of this transformation. Here, we report the discovery of a new intracellular lipase (Ndbn) with a broad substrate scope. Ndbn turns over a range of esters and aromatic amines in the presence of water (2 %; v/v), producing a high yield of multiple valuable amides. Remarkably, a higher conversion rate was observed for the synthesis of amides from substrates with aromatic amine rather than aliphatic amines. Molecular dynamics (MD) and quantum mechanical/molecular mechanical (QM/MM) studies showcase the mechanism for the preference for aromatic amines, including a more suitable orientation, shorter catalytic distances in the active site pocket and a lower reaction barrier for aromatic than for aliphatic amines. This unique lipase is thus a promising biocatalyst for the efficient synthesis of aromatic amides.

Recent advances in biocatalytic C-N bond-forming reactions

Molecules containing C-N bonds are of paramount importance in a diverse array of organic-based materials, natural products, pharmaceutical compounds, and agricultural chemicals. Biocatalytic C-N bond-forming reactions represent powerful strategies for producing these valuable targets, and their significance in the field of synthetic chemistry has steadily increased over the past decade. In this review, we provide a concise overview of recent advancements in the development of C-N bond-forming enzymes, with a particular emphasis on the inherent chemistry involved in these enzymatic processes. Overall, these enzymatic systems have proven their potential in addressing long-standing challenges in traditional small-molecule catalysis.

Achieving cinnamic acid amides in water by a variant of acyltransferase from Mycobacterium smegmatis and its immobilized form using Ni-NTA modified aspen powder as a carrier

An aqueous N-acylation reaction for preparing cinnamic acid amides was realized by using a variant of acyltransferase from Mycobacterium smegmatis (MsAcT-L12A), whereas the wild-type MsAcT showed no activity. MsAcT-L12A exhibited broad substrate adaptability, and preferred the substrates with electron-donating group. When the vinyl cinnamate (1a, 40 mM) and p-methoxyaniline (2a, 4 mM) were involved in the reaction, the excellent yield reached to 86.7 % ± 2.1 % within 3 h by MsAcT-L12A (1 mgpro./mL) in a PBS buffer (100 mM, pH 8.0) at 25 °C. The aqueous N-acylation reaction could be further improved by using an immobilized MsAcT-L12A. The biomass aspen powder (AP) as a carrier provided a low-cost, green, and environmental-friendly immobilization strategy. After it was modified by Ni-NTA, the obtained Ni-NAP could realize one-step purification and immobilization of MsAcT-L12A. The accomplished MsAcT-L12A-Ni-NAP exhibited excellent stability and recyclability, and retained its relative yield as 83.3 % ± 2.2 % even after the 7th cycle of reuse. Using only PBS buffer as a reaction medium, the operation for MsAcT-L12A-catalyzed acyl transfer was greatly simplified, and the improved stabilities of MsAcT-L12A-Ni-NAP could enhance its application potential.

Experimental and computational investigation of the α-amylase catalyzed Friedel-Crafts reaction of isatin to access symmetrical and unsymmetrical 3,3',3''-trisindoles

Trisindoles are of tremendous interest due to their wide range of biological activities. In this context, a number of methods have been reported in the past to synthesize 3,3',3''-trisindoles. However, most of the methods are only able to produce symmetrical 3,3',3''-trisindoles. Herein, we develop a sustainable and efficient approach to synthesize symmetrical as well as unsymmetrical 3,3',3''-trisindoles in a very selective manner using the α-amylase enzyme as a catalyst. Furthermore, various differently substituted isatin and indoles were used to prove the generality of the protocol and symmetrical or unsymmetrical 3,3',3''-trisindoles were obtained in 43-97% isolated yields. Next, a probable mechanism is proposed and investigated using molecular dynamics (MD) investigation to gain more insight into the role of residues available in the active site of the α-amylase enzyme. These studies revealed that Glu230, Lys209, and Asp206 in the active site of α-amylase play an important role in this catalysis. Moreover, the DFT studies suggested the formation of bisindole and alkylideneindolenine intermediates during the transformation. We synthesized four different biologically important 3,3',3''-trisindoles on a gram scale, which proved the robustness and scalability of this protocol.

Broad Spectrum Enantioselective Amide Bond Synthetase from Streptoalloteichus hindustanus

The synthesis of amide bonds is one of the most frequently performed reactions in pharmaceutical synthesis, but the requirement for stoichiometric quantities of coupling agents and activated substrates in established methods has prompted interest in biocatalytic alternatives. Amide Bond Synthetases (ABSs) actively catalyze both the ATP-dependent adenylation of carboxylic acid substrates and their subsequent amidation using an amine nucleophile, both within the active site of the enzyme, enabling the use of only a small excess of the amine partner. We have assessed the ability of an ABS from Streptoalloteichus hindustanus (ShABS) to couple a range of carboxylic acid substrates and amines to form amine products. ShABS displayed superior activity to a previously studied ABS, McbA, and a remarkable complementary substrate specificity that included the enantioselective formation of a library of amides from racemic acid and amine coupling partners. The X-ray crystallographic structure of ShABS has permitted mutational mapping of the carboxylic acid and amine binding sites, revealing key roles for L207 and F246 in determining the enantioselectivity of the enzyme with respect to chiral acid and amine substrates. ShABS was applied to the synthesis of pharmaceutical amides, including ilepcimide, lazabemide, trimethobenzamide, and cinepazide, the last with 99% conversion and 95% isolated yield. These findings provide a blueprint for enabling a contemporary pharmaceutical synthesis of one of the most significant classes of small molecule drugs using biocatalysis.

Development of a green, concise synthesis of nicotinamide derivatives catalysed by Novozym® 435 from Candida antarctica in sustainable continuous-flow microreactors

An increasing number of studies have shown that many nicotinamide derivatives exhibited extensive biological activities, such as anti-inflammatory and antitumor activity. In this paper, a green, concise synthesis of nicotinamide derivatives in sustainable continuous-flow microreactors catalysed by Novozym® 435 from Candida antarctica has been developed. Application of an easily obtainable and reusable lipase in the synthesis of nicotinamide derivatives from methyl nicotinate and amines/benzylamines reacted for 35 min at 50 °C led to high product yields (81.6-88.5%). Environmentally friendly tert-amyl alcohol was applied as a reaction medium. Substantially shorter reaction times as well as a significant increase in the product yield were obtained as compared to the batch process. This innovative approach provides a promising green, efficient and rapid synthesis strategy for pharmaceutical synthesis and further activity research of novel nicotinamide derivatives.

Substrate Positioning Dynamics Involves a Non-Electrostatic Component to Mediate Catalysis

Substrate positioning dynamics (SPD) orients the substrate in the active site, thereby influencing catalytic efficiency. However, it remains unknown whether SPD effects originate primarily from electrostatic perturbation inside the enzyme or can independently mediate catalysis with a significant non-electrostatic component. In this work, we investigated how the non-electrostatic component of SPD affects transition state (TS) stabilization. Using high-throughput enzyme modeling, we selected Kemp eliminase variants with similar electrostatics inside the enzyme but significantly different SPD. The kinetic parameters of these mutants were experimentally characterized. We observed a valley-shaped, two-segment linear correlation between the TS stabilization free energy (converted from kinetic parameters) and substrate positioning index (a metric to quantify SPD). The energy varies by approximately 2 kcal/mol. Favorable SPD was observed for the distal mutant R154W, increasing the proportion of reactive conformations and leading to the lowest activation free energy. These results indicate the substantial contribution of the non-electrostatic component of SPD to enzyme catalytic efficiency.

Reductive coupling of nitroarenes with carboxylic acids - a direct route to amide synthesis

A straightforward and selective way for the preparation of amides from nitroarenes and carboxylic acids using carbon monoxide as a reductant was developed. This protocol does not require any non-gaseous additives, thus simplifying product isolation. Aliphatic carboxylic acid was modified in the presence of aromatic ones, and reducible functional groups such as CC, Ar-Br, and R-NO2 were saved.

Realizing the Continuous Chemoenzymatic Synthesis of Anilines Using an Immobilized Nitroreductase

The use of biocatalysis for classically synthetic transformations has seen an increase in recent years, driven by the sustainability credentials bio-based approaches can offer the chemical industry. Despite this, the biocatalytic reduction of aromatic nitro compounds using nitroreductase biocatalysts has not received significant attention in the context of synthetic chemistry. Herein, a nitroreductase (NR-55) is demonstrated to complete aromatic nitro reduction in a continuous packed-bed reactor for the first time. Immobilization on an amino-functionalized resin with a glucose dehydrogenase (GDH-101) permits extended reuse of the immobilized system, all operating at room temperature and pressure in aqueous buffer. By transferring into flow, a continuous extraction module is incorporated, allowing the reaction and workup to be continuously undertaken in a single operation. This is extended to showcase a closed-loop aqueous phase, permitting reuse of the contained cofactors, with a productivity of >10 g_product g_NR-55^-1 and milligram isolated yields >50% for the product anilines. This facile method removes the need for high-pressure hydrogen gas and precious-metal catalysts and proceeds with high chemoselectivity in the presence of hydrogenation-labile halides. Application of this continuous biocatalytic methodology to panels of aryl nitro compounds could offer a sustainable approach to its energy and resource-intensive precious-metal-catalyzed counterpart.

N-Amidation of Nitrogen-Containing Heterocyclic Compounds: Can We Apply Enzymatic Tools?

Amide bond is often seen in value-added nitrogen-containing heterocyclic compounds, which can present promising chemical, biological, and pharmaceutical significance. However, current synthesis methods in the preparation of amide-containing N-heterocyclic compounds have low specificity (large amount of by-products) and efficiency. In this study, we focused on reviewing the feasible enzymes (nitrogen acetyltransferase, carboxylic acid reductase, lipase, and cutinase) for the amidation of N-heterocyclic compounds; summarizing their advantages and weakness in the specific applications; and further predicting candidate enzymes through in silico structure-functional analysis. For future prospects, current enzymes demand further engineering and improving for practical industrial applications and more enzymatic tools need to be explored and developed for a broader range of N-heterocyclic substrates.

Data-driven enzyme engineering to identify function-enhancing enzymes

Identifying function-enhancing enzyme variants is a 'holy grail' challenge in protein science because it will allow researchers to expand the biocatalytic toolbox for late-stage functionalization of drug-like molecules, environmental degradation of plastics and other pollutants, and medical treatment of food allergies. Data-driven strategies, including statistical modeling, machine learning, and deep learning, have largely advanced the understanding of the sequence-structure-function relationships for enzymes. They have also enhanced the capability of predicting and designing new enzymes and enzyme variants for catalyzing the transformation of new-to-nature reactions. Here, we reviewed the recent progresses of data-driven models that were applied in identifying efficiency-enhancing mutants for catalytic reactions. We also discussed existing challenges and obstacles faced by the community. Although the review is by no means comprehensive, we hope that the discussion can inform the readers about the state-of-the-art in data-driven enzyme engineering, inspiring more joint experimental-computational efforts to develop and apply data-driven modeling to innovate biocatalysts for synthetic and pharmaceutical applications.

Convergence in determining enzyme functional descriptors across Kemp eliminase variants

Molecular simulations have been extensively employed to accelerate biocatalytic discoveries. Enzyme functional descriptors derived from molecular simulations have been leveraged to guide the search for beneficial enzyme mutants. However, the ideal active-site region size for computing the descriptors over multiple enzyme variants remains untested. Here, we conducted convergence tests for dynamics-derived and electrostatic descriptors on 18 Kemp eliminase variants across six active-site regions with various boundary distances to the substrate. The tested descriptors include the root-mean-square deviation of the active-site region, the solvent accessible surface area ratio between the substrate and active site, and the projection of the electric field (EF) on the breaking C-H bond. All descriptors were evaluated using molecular mechanics methods. To understand the effects of electronic structure, the EF was also evaluated using quantum mechanics/molecular mechanics methods. The descriptor values were computed for 18 Kemp eliminase variants. Spearman correlation matrices were used to determine the region size condition under which further expansion of the region boundary does not substantially change the ranking of descriptor values. We observed that protein dynamics-derived descriptors, including RMSD_{active_site} and SASA_ratio, converge at a distance cutoff of 5 Å from the substrate. The electrostatic descriptor, EF_C-H, converges at 6 Å using molecular mechanics methods with truncated enzyme models and 4 Å using quantum mechanics/molecular mechanics methods with whole enzyme model. This study serves as a future reference to determine descriptors for predictive modeling of enzyme engineering.

Highly Efficient Synthesis of Cinnamamides from Methyl Cinnamates and Phenylethylamines Catalyzed by Lipozyme® TL IM under Continuous-Flow Microreactors

While a few derivatives of cinnamamides exhibited anti-inflammatory and/ or analgesic activity, in this study, we developed a highly efficient method for the synthesis of cinnamamides from methyl cinnamates and phenylethylamines catalyzed by Lipozyme® TL IM in continuous-flow microreactors. The reaction parameters and broad substrate range of the new method was studied. Maximum conversion (91.3%) was obtained under the optimal condition of substrate molar ratio of 1:2 (methyl 4-chlorocinnamate: phenylethylamine) at 45 °C for about 40 min. The remarkable features of this work include short residence time, mild reaction conditions, easy control of the reaction process, and that the catalyst can be recycled or reused, which provide a rapid and economical strategy for the synthesis and design of cinnamamide derivatives for further research on drug activity.

Efficient catalyst-free direct amidation of non-activated carboxylic acids from carbodiimides

A novel and efficient catalyst- and activating agent-free amidation method via direct amidation of carboxylic acids where carbodiimides act as a reagent instead of an activating agent is reported. The reaction is conducted under non-traditional coupling conditions where a higher temperature is employed. Besides not using stoichiometric ratios of activating agent or catalyst, this approach is made even more attractive by occurring in the presence of the environmentally friendly and recyclable non-toxic solvent of DMSO. A wide variety of benzylic, aliphatic, α,β-unsaturated and aromatic carboxylic acids provide related amides in up to 95% yield. The excellent yield from a gram-scale reaction shows that this application is particularly convenient for larger-scale synthesis applications.

One‐Step Biocatalytic Synthesis of Sustainable Surfactants by Selective Amide Bond Formation**

N‐alkanoyl‐N‐methylglucamides (MEGAs) are non‐toxic surfactants widely used as commercial ingredients, but more sustainable syntheses towards these compounds are highly desirable. Here, we present a biocatalytic route towards MEGAs and analogues using a truncated carboxylic acid reductase construct tailored for amide bond formation (CARmm‐A). CARmm‐A is capable of selective amide bond formation without the competing esterification reaction observed in lipase catalysed reactions. A kinase was implemented to regenerate ATP from polyphosphate and by thorough reaction optimisation using design of experiments, the amine concentration needed for amidation was significantly reduced. The wide substrate scope of CARmm‐A was exemplified by the synthesis of 24 commercially relevant amides, including selected examples on a preparative scale. This work establishes acyl‐phosphate mediated chemistry as a highly selective strategy for biocatalytic amide bond formation in the presence of multiple competing alcohol functionalities.

Merging enzymes with chemocatalysis for amide bond synthesis

Amides are one of the most fundamental chemical bonds in nature. In addition to proteins and other metabolites, many valuable synthetic products comprise amide bonds. Despite this, there is a need for more sustainable amide synthesis. Herein, we report an integrated next generation multi-catalytic system, merging nitrile hydratase enzymes with a Cu-catalysed N-arylation reaction in a single reaction vessel, for the construction of ubiquitous amide bonds. This synergistic one-pot combination of chemo- and biocatalysis provides an amide bond disconnection to precursors, that are orthogonal to those in classical amide synthesis, obviating the need for protecting groups and delivering amides in a manner unachievable using existing catalytic regimes. Our integrated approach also affords broad scope, very high (molar) substrate loading, and has excellent functional group tolerance, telescoping routes to natural product derivatives, drug molecules, and challenging chiral amides under environmentally friendly conditions at scale.

Proteins, other metabolites and many valuable synthetic products contain amide bonds and there is a need for more sustainable amide synthesis routes. Here the authors show an integrated next generation multi-catalytic system, merging nitrile hydratase enzymes with a Cu-catalysed N-arylation reaction in a single reaction vessel, for the construction of ubiquitous amide bonds.

A CO2-Catalyzed Transamidation Reaction

Transamidation reactions are often mediated by reactive substrates in the presence of overstoichiometric activating reagents and/or transition metal catalysts. Here we report the use of CO₂ as a traceless catalyst: in the presence of catalytic amounts of CO₂, transamidation reactions were accelerated with primary, secondary, and tertiary amide donors. Various amine nucleophiles including amino acid derivatives were tolerated, showcasing the utility of transamidation in peptide modification and polymer degradation (e.g., Nylon-6,6). In particular, N,O-dimethylhydroxyl amides (Weinreb amides) displayed a distinct reactivity in the CO₂-catalyzed transamidation versus a N₂ atmosphere. Comparative Hammett studies and kinetic analysis were conducted to elucidate the catalytic activation mechanism of molecular CO₂, which was supported by DFT calculations. We attributed the positive effect of CO₂ in the transamidation reaction to the stabilization of tetrahedral intermediates by covalent binding to the electrophilic CO₂.

Mechanistic insights into lysine-targeting covalent inhibition through a theoretical study of ester aminolysis

Development of targeted covalent inhibitors in drug design has a broad and important interest and many efforts are currently being made in this direction. Targeted covalent inhibitors have special relevance in oncology due to the possibilities they offer to overcome the problems of acquired resistance. In recent experiments, lysine-targeting has been envisaged for the irreversible inhibition of the heterodimeric lipid kinase phosphoinositide 3-kinase delta (PI3Kδ). Activated esters have been evaluated and shown to be promising inhibitors of this enzyme, but the reaction mechanisms display specificities that are not yet fully understood. In the present work, we have carried out a theoretical study of the aminolysis reaction of model esters in aqueous solution to gain insights into the corresponding biological processes. We have found that phenolic esters bearing electron-withdrawing groups are particularly reactive. The predicted mechanism involves the formation of a tetrahedral zwitterionic intermediate, which dissociates into an alkoxide and a protonated amide, this charge separation being the driving force for the subsequent proton transfer and final product formation. Structure-reactivity relationships are reported and shown to be a useful tool for evaluating potential inhibitor candidates.

Enzymkatalysierte späte Modifizierungen: Besser spät als nie

Die Enzymkatalyse gewinnt zunehmend an Bedeutung in der Synthesechemie. Die durch Bioinformatik und Enzym‐Engineering stetig wachsende Zahl von Biokatalysatoren eröffnet eine große Vielfalt selektiver Reaktionen. Insbesondere für späte Funktionalisierungsreaktionen ist die Biokatalyse ein geeignetes Werkzeug, das oftmals der konventionellen De‐novo‐Synthese überlegen ist. Enzyme haben sich als nützlich erwiesen, um funktionelle Gruppen direkt in komplexe Molekülgerüste einzuführen sowie für die rasche Diversifizierung von Substanzbibliotheken. Biokatalytische Oxyfunktionalisierungen, Halogenierungen, Methylierungen, Reduktionen und Amidierungen sind von besonderem Interesse, da diese Strukturmotive häufig in Pharmazeutika vertreten sind. Dieser Aufsatz gibt einen Überblick über die Stärken und Schwächen der enzymkatalysierten späten Modifizierungen durch native und optimierte Enzyme in der Synthesechemie. Ebenso werden wichtige Beispiele in der Wirkstoffentwicklung hervorgehoben.

Enzymatic Late-Stage Modifications: Better Late Than Never

Enzyme catalysis is gaining increasing importance in synthetic chemistry. Nowadays, the growing number of biocatalysts accessible by means of bioinformatics and enzyme engineering opens up an immense variety of selective reactions. Biocatalysis especially provides excellent opportunities for late-stage modification often superior to conventional de novo synthesis. Enzymes have proven to be useful for direct introduction of functional groups into complex scaffolds, as well as for rapid diversification of compound libraries. Particularly important and highly topical are enzyme-catalysed oxyfunctionalisations, halogenations, methylations, reductions, and amide bond formations due to the high prevalence of these motifs in pharmaceuticals. This Review gives an overview of the strengths and limitations of enzymatic late-stage modifications using native and engineered enzymes in synthesis while focusing on important examples in drug development.

The broad amine scope of pantothenate synthetase enables the synthesis of pharmaceutically relevant amides

Pantothenate synthetase from Escherichia coli (PSE. coli) catalyzes the ATP-dependent condensation of (R)-pantoic acid and β-alanine to yield (R)-pantothenic acid (vitamin B5), the biosynthetic precursor to coenzyme A. Herein we show that besides the natural amine substrate β-alanine, the enzyme accepts a wide range of structurally diverse amines including 3-amino-2-fluoropropionic acid, 4-amino-2-hydroxybutyric acid, 4-amino-3-hydroxybutyric acid, and tryptamine for coupling to the native carboxylic acid substrate (R)-pantoic acid to give amide products with up to >99% conversion. The broad amine scope of PSE. coli enabled the efficient synthesis of pharmaceutically-relevant vitamin B5 antimetabolites with excellent isolated yield (up to 89%). This biocatalytic amide synthesis strategy may prove to be useful in the quest for new antimicrobials that target coenzyme A biosynthesis and utilisation.

Power of Biocatalysis for Organic Synthesis

Biocatalysis, using defined enzymes for organic transformations, has become a common tool in organic synthesis, which is also frequently applied in industry. The generally high activity and outstanding stereo-, regio-, and chemoselectivity observed in many biotransformations are the result of a precise control of the reaction in the active site of the biocatalyst. This control is achieved by exact positioning of the reagents relative to each other in a fine-tuned 3D environment, by specific activating interactions between reagents and the protein, and by subtle movements of the catalyst. Enzyme engineering enables one to adapt the catalyst to the desired reaction and process. A well-filled biocatalytic toolbox is ready to be used for various reactions. Providing nonnatural reagents and conditions and evolving biocatalysts enables one to play with the myriad of options for creating novel transformations and thereby opening new, short pathways to desired target molecules. Combining several biocatalysts in one pot to perform several reactions concurrently increases the efficiency of biocatalysis even further.

Biocatalysis: Enzymatic Synthesis for Industrial Applications

Biocatalysis has found numerous applications in various fields as an alternative to chemical catalysis. The use of enzymes in organic synthesis, especially to make chiral compounds for pharmaceuticals as well for the flavors and fragrance industry, are the most prominent examples. In addition, biocatalysts are used on a large scale to make specialty and even bulk chemicals. This review intends to give illustrative examples in this field with a special focus on scalable chemical production using enzymes. It also discusses the opportunities and limitations of enzymatic syntheses using distinct examples and provides an outlook on emerging enzyme classes.

Biocatalytic routes to anti-viral agents and their synthetic intermediates

An assessment of biocatalytic strategies for the synthesis of anti-viral agents, offering guidelines for the development of sustainable production methods for a future COVID-19 remedy.

Repurposing the 3-Isocyanobutanoic Acid Adenylation Enzyme SfaB for Versatile Amidation and Thioesterification

Genome mining of microbial natural products enables chemists not only to discover the bioactive molecules with novel skeletons, but also to identify the enzymes that catalyze diverse chemical reactions. Exploring the substrate promiscuity and catalytic mechanism of those biosynthetic enzymes facilitates the development of potential biocatalysts. SfaB is an acyl adenylate-forming enzyme that adenylates a unique building block, 3-isocyanobutanoic acid, in the biosynthetic pathway of the diisonitrile natural product SF2768 produced by Streptomyces thioluteus, and this AMP-ligase was demonstrated to accept a broad range of short-chain fatty acids (SCFAs). Herein, we repurpose SfaB to catalyze amidation or thioesterification between those SCFAs and various amine or thiol nucleophiles, thereby providing an alternative enzymatic approach to prepare the corresponding amides and thioesters in vitro.

Fast Amide Couplings in Water: Extraction, Column Chromatography, and Crystallization Not Required

In the micelle of PS-750-M, the presence of 3° amides from the surfactant proline linker mimics dimethylformamide, dimethylacetamide, and N-methyl-2-pyrrolidone. The resultant micellar properties enable extremely fast amide couplings mediated by 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide (without hydroxybenzotriazole), rather than expensive and specialized coupling agents. Conditions have been developed wherein products precipitate, and isolation by filtration completely avoids the use of organic solvent. This methodology is scalable and avoids product epimerization.