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Nor(pseudo)ephedrines [N(P)Es] are naturally occurring compounds showing sympathomimetic activity that have many applications especially in the chemical industry and in the pharmaceutical field. Recently a two‐step biocatalytic cascade for the preparation of (1S)‐N(P)E was designed, consisting of a benzoin‐type condensation catalyzed by the (S)‐selective acetoin:dichlorophenolindophenol oxidoreductase (Ao : DCPIP OR) followed by a transamination mediated by either a (S)‐ or (R)‐selective amine transaminase (ATA). In this study, we successfully immobilized both Ao : DCPIP OR and two ATAs of opposite enantioselectivity and used them in the biosynthetic cascade to N(P)Es. Immobilization yield, activity recovery, and stability of the immobilized enzymes, both after use (enzyme recycling) and storage (shelf‐life), were assessed. Ao : DCPIP OR immobilized on glyoxyl‐agarose exhibited remarkable stability under storage conditions throughout the 30‐days monitoring period. Moreover, it was successfully reused in the synthesis of (S)‐phenylacetylcarbinol [(S)‐PAC] yielding high conversion (>94 %) and enantiomeric excess (>99 %). The (R)‐selective At‐ATA from Aspergillus terreus, immobilized on Eupergit® C, demonstrated a slightly higher storage stability when compared to the (S)‐selective Sbv333‐ATA from Streptomyces sp. Bv333 immobilized on the same carrier. Remarkably, both enzymes were effectively reused for ten reaction cycles in the synthesis of N(P)Es, starting from the enzymatically synthesized (S)‐PAC, achieving complete conversions and excellent diastereoselectivity (>99 %). [ABSTRACT FROM AUTHOR]

The application of biocatalysis has become essential in both academic and industrial domains for the asymmetric synthesis of chiral amines, and it serves as an alternative tool to transition‐metal catalysis and complements traditional chemical methods. It relies on the swift expansion of available processes, primarily as a result of advanced tools for enzyme discovery, combined with high‐throughput laboratory evolution techniques for optimizing biocatalysts. This concept paper explores the utilization of non‐conventional media such as ether‐type solvents, deep eutectic solvents, and micellar catalysis to enhance biocatalytic reactions for chiral amine synthesis. Each section focuses on the unique properties of these media, including their ability to stabilize enzymes, alter substrate solubility, and modulate enzyme selectivity. The paper aims to provide insights into how these innovative media can overcome traditional limitations, offering new avenues for sustainable and efficient chiral amine production through biocatalytic processes. [ABSTRACT FROM AUTHOR]

Amine dehydrogenases (AmDHs) are NAD(P)H‐dependent oxidoreductases that catalyze the reductive amination between carbonyl compounds and ammonia as the amine donor yielding valuable amines, typically with excellent enantioselectivity. While nature has provided enzymes with inherent AmDH activities, protein engineering techniques allowed researchers to expand the toolbox of available AmDHs, extend their substrate scope, improve their catalytic activities and stability under synthetically relevant conditions and even enable new reactivity concepts. The biocatalytic synthesis of amines using AmDHs has matured to a point where hundreds of aldehydes or ketones, of varying steric demands and bearing diverse functional groups, can be efficiently transformed. This review offers an overview of the available AmDHs and their substrate spectrum, covering from structural and evolutionary analyses to diverse methods employing these enzymes. Depending on the catalytic activities of other enzymes as reaction partners, AmDHs were applied in kinetic resolution (KR) and deracemization processes, cascade reactions for the amination of alcohols and alkenes or for the synthesis of amines and amino alcohols featuring multiple stereogenic centers. Moreover, the synthetic potential of AmDHs in novel pathways, such as the synthesis of secondary amines or alcohols, presents exciting opportunities for expanding their catalytic repertoire. [ABSTRACT FROM AUTHOR]

In recent decades, the chiral allylation of imines emerged as a key methodology in the synthesis of alkaloids and natural products with 4-, 5- and 6-membered cyclic amine motifs. Initially reliant on stoichiometric reagents, synthetic chemists predominantly used N-substituted chiral imines, organometallic chiral reagents and achiral reagents with an equimolar chiral controller. However, recent years have witnessed the rise of asymmetric transition-metal catalysts and, importantly, organocatalytic allylation, reshaping the landscape of modern synthetic chemistry. This review explores the latest developments in the asymmetric allylation of imines, encompassing cutting-edge advances in hydrogen-bond catalysis and non-classical approaches. Furthermore, practical examples showcasing the application of these innovative methodologies in total synthesis are presented.

Sayali Shantaram Vikhrankar,1 Seema Satbhai,2 Priyanka Kulkarni,2 Ranjit Ranbhor,3 Vibin Ramakrishnan,4 Prashant Kodgire1 1Biosciences and Biomedical Engineering, Indian Institute of Technology Indore, Indore, MP, India; 2Sevit Healthcare Private Limited, Pune, MH, India; 3Pergament & Cepeda LLP, Florham Park, NJ, USA; 4Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, Assam, IndiaCorrespondence: Ranjit Ranbhor, Pergament & Cepeda LLP, 25A Hanover Road, Florham Park, NJ, 07932, USA, Tel +1 973 967 0490, Email ranjitranbhor@gmail.comAbstract: Chiral amines are essential motifs in pharmaceuticals, agrochemicals, and specialty chemicals. While traditional chemical routes to chiral amines often lack stereoselectivity and require harsh conditions, biocatalytic methods using engineered enzymes can offer high efficiency and selectivity under sustainable conditions. This review discusses recent advances in protein engineering of transaminases, oxidases, and other enzymes to improve catalytic performance. Strategies such as directed evolution, immobilization, and computational redesign have expanded substrate scope and enhanced efficiency. Furthermore, process optimization guided by techno-economic assessments has been crucial for establishing viable biomanufacturing routes. Combining state-of-the-art enzyme engineering with multifaceted process development will enable scalable, economical enzymatic synthesis of diverse chiral amine targets.Keywords: chiral amines, biocatalysis, protein engineering, ω-transaminases, sitagliptin, enzyme immobilization, co-factor regeneration

Nitrogen containing compounds like chiral amines have been widely used in synthetic medicines, biomass, and fine chemical products because of their particularly valuable motifs and exceedingly broad range of functionality. Enantioconvergent synthesis of chiral amines has high atomic economy and enantioselectivity with theoretically 100 % yield of enantioenriched products. In this concept article, we hope to provide a further understanding of chiral amines enantioconvergent synthesis methodology with an introduction of recent progresses in enantioconvergent amination reactions catalyzed by early transition metals and facilitate the development of enantioconvergent C(sp3)−N coupling for benign and efficient preparation of highly valuable chiral nitrogen‐containing units. [ABSTRACT FROM AUTHOR]

Chiral amines are valuable building blocks in the manufacture of agrochemicals, pharmaceuticals, natural products, fine chemicals, functional materials among others. Compared to asymmetric hydrogenation of imines/enamides and biocatalytic/organocatalytic asymmetric reductive amination, transition metal catalyzed direct asymmetric hydrogenative amination reactions (DAHA) using molecular dihydrogen as the reductant are highly economical, atom and/or step‐efficient and thus attractive for researchers from both industry and academia. In previous reviews, catalysts/methods development, applications in synthesis of pharmaceuticals and [N] source were summarized and discussed. In this review, we summarize and discuss the ketone substrates scope upon utilizing the state‐of‐the‐art transition metal catalysts. The substrate limitations, potential applications and key mechanisms are also critically concluded. [ABSTRACT FROM AUTHOR]

A combined computational and experimental approach allowed us to develop overall the most selective catalyst for the direct hydrogenation of N‐methyl, N‐alkyl and N‐aryl imines described to date. Iridium catalysts with a cyclometallated cyclic imide group provide selectivity of up to 99 % enantiomeric excess. Computational studies show that the selectivity results from the combined effect of H‐bonding of the imide C=O with the substrate iminium ion and a stabilizing π–π interaction with the cyclometallated ligand. The cyclometallated ligand thus exhibits a unique mode of action, serving as a template for the H‐bond directed approach of the substrate which results in enhanced selectivity. The catalyst (2) has been synthesized and isolated as a crystalline air‐stable solid. X‐ray analysis of 2 confirmed the structure of the catalyst and the correct position of the imide C=O groups to engage in an H‐bond with the substrate. 19F NMR real‐time monitoring showed the hydrogenation of N‐methyl imines catalyzed by 2 is very fast, with a TOF of approx. 3500 h−1. [ABSTRACT FROM AUTHOR]

Purified SpyCatcher-ATA117 (5 µM) and SpyTag-ADH (5 µM) were covalently combined to form self-assembled dual-enzyme clusters (DENCs) at 4 °C for 3 h. The successful assembly of DENCs was verified using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and dynamic light scattering (DLS). DENCs improved the storage stability by 36.2% and pH stability by 11.2% compared with those of free double enzymes. 56.89 g/L (R)− 1-[3,5-bis(trifluoromethyl)phenyl]ethanamine (R -BPA) was synthesized using DENCs with high yield (99.9%) and high enantiomeric excess (99.9%) at 45 °C and pH 9 for 24 h. Moreover, DENCs retained more than 78% of the initial activity after being reused in the preparation of R -BPA for five cycles. Thus, DENCs were successfully formed, and efficient amination was achieved, providing a new biocatalyst for efficient biosynthesis of chiral amines via asymmetric transamination cascade reaction. [Display omitted] • Self-assembled dual-enzyme clusters (DENCs) were effectively prepared. • DENCs were prepared by the SpyTag/SpyCatcher conjugation strategy. • Evaluated the effects of self-assembly conditions on relative enzyme activity of DENCs. • DENCs improved storage stability and pH stability than free double enzymes. • DENCs exhibited high reusability after five cycles. [ABSTRACT FROM AUTHOR]

This review summarizes the recent progress of organocatalytic and biocatalytic asymmetric reductive amination (ARA), a challenging but important topic for drug discovery and the pharmaceutical industry. At present, ARA can be divided into three categories: metal catalysis, organic catalysis, and biocatalysis. In the past decade, transition metal‐catalysed ARA has been well established. Organocatalytic ARA has emerged as a powerful alternative to metal‐catalysed ARA, the hydrogen sources used in organocatalytic ARA are usually Hantzsch esters, benzothiazolines, boranes, and hydrosilanes, which require Lewis base or phosphoric acid catalysts to activate them to give secondary chiral amines. It is worth mentioning that biocatalytic ARA has made remarkable progress in the last decade, amino acid dehydrogenases, amine dehydrogenases, opine dehydrogenases and imine reductases have been successfully used in ARA. [ABSTRACT FROM AUTHOR]

An efficient three‐step synthesis of (1R)‐1‐(4‐bromophenyl)‐2,2,2‐trifluoroethan‐1‐amine hydrochloride (1) starting from inexpensive and readily available starting materials was developed. The sequence features a highly diastereoselective trifluoromethylation of a chiral sulfinimine using the Rupert–Prakash reagent TMSCF3 in combination with K3PO4 as an initiator. The diastereomeric purity of the resulting sulfinamide was further improved by direct precipitation of the desired diastereomer from the reaction mixture upon addition of water. The chiral auxiliary was then removed under acidic conditions, resulting in the isolation of chiral benzylamine 1 as its hydrochloride salt in 71 % overall yield and excellent purity (LC/MS: >99 % a/a; e.r.=99 : 1). [ABSTRACT FROM AUTHOR]

A novel and sustainable tandem‐catalysis system for asymmetric synthesis is disclosed, which is fabricated by bio‐inspired self‐assembly of artificial arthropod exoskeletons (AAEs) or artificial fungi cell walls (AFCWs) containing two different types of catalysts (enzyme and metal nanoparticles). The heterogeneous integrated enzyme/metal nanoparticle AAE/AFCW systems, which contain chitosan as the main structural component, co‐catalyze dynamic kinetic resolution of primary amines via a tandem racemization/enantioselective amidation reaction process to give the corresponding amides in high yields and excellent ee. The heterogeneous AAE/AFCW systems display successful heterogeneous synergistic catalysis at the surfaces since they can catalyze multiple reaction cycles without metal leaching. The use of natural‐based and biocompatible structural components makes the AAE/AFCW systems fully biodegradable and renewable, thus fulfilling important green chemistry requirements. [ABSTRACT FROM AUTHOR]

We report the synthesis and chiroptical properties of novel chiral carbon nanorings Sp‐/Rp‐[12]PCPP containing a planar chiral [2.2]PCP unit, and demonstrate that Sp‐/Rp‐[12]PCPP can not only host crown ether 18‐Crown‐6 to form ring‐in‐ring complexes with a binding constant 3.35×103 M−1, but also accommodate the complexes of 18‐Crown‐6 and S/R‐protonated amines to form homochiral S@Sp‐/R@Rp‐ and heterochiral S@Rp‐/R@Sp‐ ternary complexes, displaying significantly larger binding constants of up to 3.31×105 M−1 depending on the chiral guests. Importantly, homochiral S@Sp‐/R@Rp‐ ternary complexes exhibit an enhanced CD signal, while the heterochiral S@Rp‐/R@Sp‐ ones have a constant CD signal compared with the chiral carbon nanorings, respectively, which suggests that homochiral S@Sp‐/R@Rp‐ ternary complexes display a highly narcissistic chiral self‐recognition for S/R‐protonated chiral amines, respectively. Finally, the chiral ternary complexes can be further applied to determine the ee values of chiral guests. The findings highlight a new application of carbon nanorings in supramolecular sensors, beyond the common recognition of π‐conjugated molecules. [ABSTRACT FROM AUTHOR]

In lipase-catalyzed kinetic resolutions (KRs), the choice of immobilization support and acylating agents (AAs) is crucial. Lipase B from Candida antarctica immobilized onto magnetic nanoparticles (CaLB-MNPs) has been successfully used for diverse KRs of racemic compounds, but there is a lack of studies of the utilization of this potent biocatalyst in the KR of chiral amines, important pharmaceutical building blocks. Therefore, in this work, several racemic amines (heptane-2-amine, 1-methoxypropan-2-amine, 1-phenylethan-1-amine, and 4-phenylbutan-2-amine, (±)-1a–d, respectively) were studied in batch and continuous-flow mode utilizing different AAs, such as diisopropyl malonate 2A, isopropyl 2-cyanoacetate 2B, and isopropyl 2-ethoxyacetate 2C. The reactions performed with CaLB-MNPs were compared with Novozym 435 (N435) and the results in the literature. CaLB-MNPs were less active than N435, leading to lower conversion, but demonstrated a higher enantiomer selectivity, proving to be a good alternative to the commercial form. Compound 2C resulted in the best balance between conversion and enantiomer selectivity among the acylating agents. CaLB-MNPs proved to be efficient in the KR of chiral amines, having comparable or superior properties to other CaLB forms utilizing porous matrices for immobilization. An additional advantage of using CaLB-MNPs is that the purification and reuse processes are facilitated via magnetic retention/separation. In the continuous-flow mode, the usability and operational stability of CaLB-MNPs were reaffirmed, corroborating with previous studies, and the results overall improve our understanding of this potent biocatalyst and the convenient U-shape reactor used. [ABSTRACT FROM AUTHOR]

An aqueous solution of the reaction product R-(+)-1-(1-naphthyl)ethylamine hydrochloride, having high enantiomeric excess, was spontaneously resolved into the two enantiomers by simple crystallization to afford the product in nearly 100% ee. [ABSTRACT FROM AUTHOR]

Using the diphosphine‐cobalt‐zinc catalytic system, an efficient asymmetric hydrogenation of internal simple enamides has been realized. In particular, the Ph‐BPE ligand can achieve convergent asymmetric hydrogenation of E/Z‐substrates. High yields and excellent enantioselectivities were obtained for both acyclic and cyclic enamides bearing α‐alkyl‐β‐aryl, α‐aryl‐β‐aryl, and α‐aryl‐β‐alkyl substituents. Hydrogenated products can be applied for the synthesis of useful chiral drugs such as Arfromoterol, Rotigotine, and Norsertraline. In addition, reasonable catalytic mechanism and stereocontrol mode are proposed based on DFT calculations. [ABSTRACT FROM AUTHOR]

Reductive aminases (RedAms) have recently emerged as promising biocatalysts for the synthesis of chiral secondary amines by coupling primary amines with aldehydes/ketones. However, access to tertiary amines remains more problematic, particularly when coupling ketones with secondary amines. Here we show that the scope of these enzymes can be extended to allow selective reductive aminations of cyclic secondary amines, such as piperidines and morpholines, with both aldehydes and ketones. These biotransformations provide access to important motifs found in active pharmaceutical ingredients and other bioactive molecules. RedAm‐361, discovered from a metagenomic library, was engineered via directed evolution to allow efficient coupling of cyclic amines with carbonyl partners, including dynamic kinetic resolutions of α‐functionalized aldehydes and enantioselective amination of ketones. These RedAms now serve as valuable scaffolds for the engineering of industrial biocatalysts to produce key pharmaceutical intermediates. [ABSTRACT FROM AUTHOR]

The synthesis of enantiopure chiral cyclic amines is of critical importance but highly challenging. In this study, a metal‐enzyme hybrid catalyst was fabricated by the co‐immobilization of palladium nanoparticles and monoamine oxidases on dendritic organosilica nanoparticles (DONs) for chemoenzymatic deracemization, furnishing a panel of chiral cyclic amines in high enantioselectivities (96–98 % ee). Catalyst optimization revealed that the ultra‐high specific surface area, mesoporous channels and hydrophobic microenvironment of the DONs are responsible for the improved catalyst stability, activity and catalytic efficiency. [ABSTRACT FROM AUTHOR]

α‐Chiral amines represent a frequently observed functional group in pharmaceuticals. Here, the synthesis of such motifs (up to 91% ee) is described by asymmetric hydrogenation of imines catalyzed by NHC,P‐iridium complexes. The hydrogenation proceeded smoothly, even under balloon pressure of hydrogen atmosphere. Mechanistic experiments indicated that the reduction most likely advances by a combination of direct hydrogenation and a hydrogen transfer process using either H2 or iPrOH as the reductant, respectively. [ABSTRACT FROM AUTHOR]

ω-Transaminase (ω-TA) serves as an attractive biocatalyst for the asymmetric synthesis of chiral amines from prochiral ketones. However, the ω-TA reactions suffer from exceedingly unfavorable equilibrium and severe product inhibitions. Most reaction engineering strategies to overcome such limitations have focused on coproduct removal, which fails to mitigate enzyme inhibition by the desired amine product. Herein, we demonstrated in situ removal of both inhibitory products using ion exchange resin (IER). L-Alanine was chosen as a cosubstrate for S-selective ω-TA by considering a zwitterionic character, affording selective adsorption of the resulting products, i.e. (S)-amine and pyruvate on cation and anion exchange resin, respectively. The addition of both IERs to the reaction mixture containing 10 mM acetophenone and 200 mM L-alanine led to a 65 % yield of (S)-α-methylbenzylamine, whereas the same reaction without IER permitted only 3 % yield close to a thermodynamic limit. Computational prediction of the reaction yield was carried out using a Langmuir analysis, showing good agreements with the experimental results. The in situ product removal (ISPR) enabled amination of 2-octanone to reach even 84 % reaction yield. Preparative-scale synthesis of (S)-2-aminohexane was carried out using a batch recirculation reactor implemented with consecutive IER columns. The ISPR strategy could afford virtually inhibition-free reaction conditions and facile recovery of both valuable products.

ω-Transaminases (ω-TAs) have gained growing attention owing to their capability for asymmetric synthesis of chiral amines from ketones. Reliable high-throughput activity assay of ω-TAs is essential in carrying out extensive substrate profiling and establishing a robust screening platform. Here we report spectrophotometric and colorimetric methods enabling rapid quantitation of ω-TA activities toward ketones in a 96-well microplate format. The assay methods employ benzylamine, a reactive amino donor for ω-TAs, as a cosubstrate and exploit aldehyde dehydrogenase (ALDH) as a reporter enzyme, leading to formation of benzaldehyde detectable by ALDH owing to concomitant NADH generation. Spectrophotometric substrate profiling of two wild-type ω-TAs of opposite stereoselectivity was carried out at 340 nm with 22 ketones, revealing subtle differences in substrate specificities that were consistent with docking simulation results obtained with cognate amines. Colorimetric readout for naked eye detection of the ω-TA activity was also demonstrated by supplementing the assay mixture with color-developing reagents whose color reaction could be quantified at 580 nm. The colorimetric assay was applied to substrate profiling of an engineered ω-TA for 24 ketones, leading to rapid identification of reactive ketones. The ALDH-based assay is expected to be promising for high-throughput screening of enzyme collections and mutant libraries to fish out the best ω-TA candidate as well as to tailor enzyme properties for efficient amination of a target ketone.

ω-Transaminase (ω-TA) is an important enzyme for asymmetric synthesis of chiral amines. Rapid creation of a desirable ω-TA variant, readily available for scalable process operation, is demanded and has attracted intense research efforts. In this study, we aimed to develop a quantitative mutational analysis (i. e., R-analysis) that enables prediction of combinatorial mutation outcomes and thereby provides reliable guidance of enzyme engineering through combination of already characterized mutations. To this end, we determined three mutatable active-site residues of ω-TA from Ochrobactrum anthropi (i. e., leucine 57, tryptophan 58 and valine 154) by examining activities of nine alanine-scanning mutants for seven substrate pairs. The R-analysis of the mutatable residues is based on assessment of changes in relative activities for a series of structurally analogous substrates. Using three sets of substrates (five α-keto acids, six arylalkylamines and three arylalkyl ketones), we found that combination of two point mutations display additive effects of each mutational outcome such as steric relaxation for bulky substrates or catalytic enhancement for amination of ketones. Consistent with the R-analysis-based prediction, the ω-TA variant harboring triple alanine mutations, i. e. L57A, W58A and V154A, showed high activity improvements for bulky substrates, e. g. a 3.2×104-fold activity increase for 1-phenylbutylamine. The triple mutant even enabled asymmetric amination of isobutyrophenone, carrying a branched-chain alkyl substituent to be accepted in a small binding pocket that normally shows a steric limit up to an ethyl group, with >99% ee of a resulting (S)-amine. (Figure presented.).

Herein we report the first method for highly enantioselective Brønsted acid catalyzed Heyns rearrangements. These reactions, catalyzed by a chiral spiro phosphoric acid, afforded synthetically valuable chiral α‐aryl‐α‐aminoketones which cannot be obtained by means of previously reported Heyns rearrangement methods. This method features low catalyst loadings, high yields and high enantioselectivities, making these reactions highly practical. We used the method to efficiently synthesize various chiral amines, including some biologically active molecules. We experimentally proved that these acid‐catalyzed Heyns rearrangements proceeded via a proton‐transfer process involving an enol intermediate and the stereocontrol was realized during the proton‐transfer step. [ABSTRACT FROM AUTHOR]

ω‐Transaminases (ω‐TAs) show considerable potential for the synthesis of chiral amines. However, their low catalytic efficiency towards bulky substrates limits their application, and complicated catalytic mechanisms prevent precise enzyme design. Herein, we address this challenge using a mechanism‐guided computational enzyme design strategy by reprograming the transition and ground states in key reaction steps. The common features among the three high‐energy‐barrier steps responsible for the low catalytic efficiency were revealed using quantum mechanics (QM). Five key residues were simultaneously tailored to stabilize the rate‐limiting transition state with the aid of the Rosetta design. The 14 top‐ranked variants showed 16.9–143‐fold improved catalytic activity. The catalytic efficiency of the best variant, M9 (Q25F/M60W/W64F/I266A), was significantly increased, with a 1660‐fold increase in kcat/Km and a 1.5–26.8‐fold increase in turnover number (TON) towards various indanone derivatives. [ABSTRACT FROM AUTHOR]

Transaminases (EC 2.6.1.X, TAs) are important biocatalysts in the synthesis of chiral amines, and have significant value in the field of medicine. However, TAs suffer from low enzyme activity and poor catalytic efficiency in the synthesis of chiral amines or non-natural amino acids, which hinders their industrial applications. In this study, a novel TA derived from Paracoccus pantotrophus (pp TA) that was investigated in our previous study was employed with a semi-rational design strategy to improve its enzyme activity to 2-ketobutyrate. By using homology modeling and molecular docking, four surrounding sites in the substrate-binding S pocket were selected as potential mutational sites. Through alanine scanning and saturation mutagenesis, the optimal mutant V153A with significantly improved enzyme activity was finally obtained, which was 578 % higher than that of the wild-type pp TA (WT). Furthermore, the mutant enzyme pp TA-V153A also exhibited slightly improved temperature and pH stability compared to WT. Subsequently, the mutant was used to convert 2-ketobutyrate for the preparation of L-2-aminobutyric acid (L-ABA). The mutant can tolerate 300 mM 2-ketobutyrate with a conversion rate of 74 %, which lays a solid foundation for the preparation of chiral amines. [Display omitted] • A semi-rational design strategy was proposed to enhance ω-transaminase activity. • The specific enzymatic activity of ω-aminotransferases has been significantly improved. • 300 mM sodium 2-ketobutyrate has been efficiently converted to L-2-aminobutyric acid. [ABSTRACT FROM AUTHOR]

The title compound C9H14N+·Cl−, (1), can be synthesized starting from (S)-N-methyl-1-phenylethan-1-amine (2). Compound 2 upon addition of HCl·Et2O leads to crystallization of compound 1 as colorless blocks. The configuration of compound 1 is stable as well as preserved in space group P212121. Ammonium chlorides, like the title compound, are often observed as undesirable by-products in aminosilylation of chlorosilanes. Additionally, these by-products are usually soluble in selected organic solvents, which require difficult separation steps. Therefore, detailed studies on structural features and intermolecular interactions performed by Hirshfeld atom refinement (HAR) using NoSpherA2 [Kleemiss et al. (2021). Chem. Sci. 12, 1675–1692] and Hirshfeld surface analysis were used to address structural issues on that separation problem.

The synthesis of chiral amines is significant in the pharmaceutical industry. Imine reductase (IRED), a promising biocatalyst that was previously known to only catalyze asymmetric imine reduction (IR), was revealed to achieve direct asymmetric reductive amination (RA) of ketones with excess amines, producing secondary and tertiary amines. Moreover, conjugate reduction (CR) and RA activity by a single IRED has been reported for the preparation of valuable amine diastereomers. IREDs catalyzing these different reactions share the same standard quaternary structure, but possess varying active sites, indicating correlations and differences between their catalytic mechanisms. In this review, we trace the catalytic mechanisms reported for IRED‐catalyzed IR, RA, and CR‐RA. Insights obtained from structural and protein engineering in understanding the IRED‐catalyzed asymmetric synthesis are also included. This review will help readers acquire comprehensive insights into the catalytic mechanism of IREDs and ultimately inspire the engineering of IREDs for industrial applications. [ABSTRACT FROM AUTHOR]

The compatibility between gold(I) catalysts and amine transaminases has been explored to transform racemic propargylic alcohols into enantioenriched allylic amines in a straightforward and selective manner. The synthetic approach consists of a gold(I)‐catalysed Meyer‐Schuster rearrangement of a series of 2‐arylpent‐3‐yn‐2‐ols and a subsequent stereoselective enzyme‐catalysed transamination of the resulting α,β‐unsaturated prochiral ketones. The design of cascade processes involving sequential or concurrent approaches has been studied in our search for ideal reaction conditions to produce the desired amines. Thus, the N‐heterocyclic carbene complex [1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene]‐[bis(trifluoromethanesulfonyl)‐imide]gold(I) ([Au(IPr)(NTf2)] (A) in aqueous medium was found to be an ideal catalyst, while selective, made‐in‐house and commercial amine transaminases permitted the asymmetric synthesis of both (E)‐4‐arylpent‐3‐en‐2‐amine enantiomers in good isolated yields (53–84%) and excellent stereoselectivities (97 to >99% enantiomeric excess). [ABSTRACT FROM AUTHOR]

Optically active amines represent critically important subunits in bioactive natural products and pharmaceuticals, as well as key scaffolds in chiral catalysts and ligands. Kinetic resolution of racemic amines and enantioselective desymmetrization of prochiral amines have proved to be efficient methods to access enantioenriched amines, especially when the racemic or prochiral amines were easy to prepare while the chiral ones are difficult to be accessed directly. In this Account, we systematically summarized the development of kinetic resolution and desymmetrization of amines through nonenzymatic asymmetric catalytic approaches in the last two decades. 1 Introduction 2 Kinetic Resolution of Amines 2.1 Kinetic Resolution of Amines via Asymmetric Transformations of the Amino Group 2.1.1 Asymmetric N-Acylations 2.1.2 Asymmetric N-Alkylation 2.1.3 Asymmetric N-Arylation 2.1.4 Other Asymmetric N-Functionalizations 2.1.5 Asymmetric Dehydrogenation of Amines 2.1.6 Selective C–N Bond Cleavage of Amines 2.2 Kinetic Resolution of Amines via Asymmetric Transformations without Amino Group Participating 3 Enantioselective Desymmetrization of Amines 3.1 Desymmetrization of Diamines 3.2 Desymmetrization of Prochiral Monoamines 4 Conclusion and Outlooks [ABSTRACT FROM AUTHOR]

(R)-1-[3,5-bis(trifluoromethyl)phenyl]ethanamine, a key chiral intermediate of selective tetrodotoxin-sensitive blockers, was efficiently synthesized by a bienzyme cascade system formed by with R-ω-transaminase (ATA117) and an alcohol dehydrogenase (ADH) co-expression system. Herein, we report that the use of ATA117 as the biocatalyst for the amination of 3,5-bistrifluoromethylacetophenone led to the highest efficiency in product performance (enantiomeric excess > 99.9%). Moreover, to further improve the product yield, ADH was introduced into the reaction system to promote an equilibrium shift. Additionally, bienzyme cascade system was constructed by five different expression systems, including two tandem expression recombinant plasmids (pETDuet-ATA117-ADH and pACYCDuet-ATA117-ADH) and three co-expressed dual-plasmids (pETDuet-ATA117/pET28a-ADH, pACYCDuet-ATA117/pET28a-ADH, and pACYCDuet-ATA117/pETDuet-ADH), utilizing recombinant engineered bacteria. Subsequent studies revealed that as compared with ATA117 single enzyme, the substrate handling capacity of BL21(DE3)/pETDuet-ATA117-ADH (0.25 g wet weight) developed for bienzyme cascade system was increased by 1.50 folds under the condition of 40 °C, 180 rpm, 0.1 M pH9 Tris-HCl for 24 h. To the best of our knowledge, ours is the first report demonstrating the production of (R)-1-[3,5-bis(trifluoromethyl)phenyl]ethanamine using a bienzyme cascade system, thus providing valuable insights into the biosynthesis of chiral amines. [ABSTRACT FROM AUTHOR]

Amine transaminases (ATAs) are biocatalysts for the synthesis of chiral amines and can be identified in sequence databases by specific sequence motifs. This study shows that the activity level towards the model substrate 1‐phenylethylamine can be predicted solely from the sequence. To demonstrate this, 15 putative ATAs with a different distribution of hydrophobic or hydrophilic amino acid side chains near the active site were characterized. Hydrophobic side chains were associated with a high activity level and were a better predictor of activity than global sequence identity to known ATAs with high or low activities. Enzyme stability investigations revealed that four out of the 15 ATAs showed a good operational stability. [ABSTRACT FROM AUTHOR]

ATAs engineered for having an enlarged small binding pocket were applied for the synthesis of enantiomerically pure (R)‐benzo[1,3]dioxol‐5‐yl‐butylamine, a chiral component of human leukocyte elastase inhibitor DMP 777 (L‐694,458). Kinetic resolution of the racemic amine was performed by using the L59A variant of the (S)‐selective ATA from Chromobacterium violaceum (Cv‐ATA), providing the residual (R)‐enantiomer in excellent yield and >99% ee. At moderate enzyme loading and absence of co‐solvent, high volumetric productivity of 0.22 mol L−1 h−1 (42.5 g L−1 h−1) was achieved. Complementarily, the (S)‐enantiomer was generated via kinetic resolution using the (R)‐selective ATA‐117‐Rd11 from Arthrobacter sp. with acetone as the amino acceptor. In an alternative approach, we employed ATA‐117‐Rd11 for the asymmetric amination of the prochiral ketone precursor, which at 86% conversion gave the (R)‐benzo[1,3]dioxol‐5‐yl‐butylamine with excellent >99% ee. We further evaluated the utility of Cv‐ATA L59A for the asymmetric synthesis of pharmaceutically relevant (S)‐1‐phenylbutan‐1‐amine, a chiral component of the deubiquitinase inhibitor degrasyn (WP1130). The enzyme showed good tolerance to high concentrations of isopropylamine, producing (S)‐1‐phenylbutan‐1‐amine in enantiomerically pure form (>99% ee). [ABSTRACT FROM AUTHOR]

Isatins are extensively researched compounds with diverse applications, particularly as synthetic precursors in pharmaceutical developments. However, their use as optical probes for enantioselective sensing of chiral amines has not been explored to date. Herein, we present a novel chiroptical assay with an optimized isatin that generates strong, red-shifted circular dichroism (CD) signals at approximately 380 nm upon ketimine formation with chiral amines. The intensity of the induced CD signal increases linearly with the enantiomeric excess of the analyte and thus allows quantitative chirality analysis. The general usefulness of this approach is demonstrated with a broad range of aliphatic and aromatic chiral amines, and by accurate determination of the enantiomeric composition of 10 samples., (© 2024 Wiley Periodicals LLC.)

In recent decades, the chiral allylation of imines emerged as a key methodology in the synthesis of alkaloids and natural products with 4-, 5- and 6-membered cyclic amine motifs. Initially reliant on stoichiometric reagents, synthetic chemists predominantly used N -substituted chiral imines, organometallic chiral reagents and achiral reagents with an equimolar chiral controller. However, recent years have witnessed the rise of asymmetric transition-metal catalysts and, importantly, organocatalytic allylation, reshaping the landscape of modern synthetic chemistry. This review explores the latest developments in the asymmetric allylation of imines, encompassing cutting-edge advances in hydrogen-bond catalysis and non-classical approaches. Furthermore, practical examples showcasing the application of these innovative methodologies in total synthesis are presented., (Copyright © 2024, Kondratyev and Malkov.)

Direct reductive amination of ketones by reductive aminases (RedAms) is a promising method for the synthesis of primary, secondary and tertiary amines. In this work, five naturally occurring RedAms possessing reductive amination activity were identified using a structure-guided genome mining (SGGM) approach, which was based on highly conserved substrate binding and catalysis motif alignment. This RedAm toolbox facilitated the reductive amination of cyclohexanone and 4-fluoropropiophenone with various amine nucleophiles. In a preparative biotransformation (100 ​mg) with low stoichiometric ammonia donor and low catalyst loading, and three types of N-alkylcyclohexylamine were efficiently synthesized with a space-time yield up to 64.2 ​g ​L−1 ​d−1, demonstrating the potential of the RedAm enzymes as a biocatalyst toolbox for the synthesis of primary and secondary amines. Additionally, through protein engineering, the W205F variant of KfRedAm from Kribbella flavida was obtained with a 2-fold increased catalytic efficiency (kcat/Km), and the general applicability of the variant was verified, providing useful guidance for further evolution of RedAms within this family.

In lipase-catalyzed kinetic resolutions (KRs), the choice of immobilization support and acylating agents (AAs) is crucial. Lipase B from Candida antarctica immobilized onto magnetic nanoparticles (CaLB-MNPs) has been successfully used for diverse KRs of racemic compounds, but there is a lack of studies of the utilization of this potent biocatalyst in the KR of chiral amines, important pharmaceutical building blocks. Therefore, in this work, several racemic amines (heptane-2-amine, 1-methoxypropan-2-amine, 1-phenylethan-1-amine, and 4-phenylbutan-2-amine, (±)-1a–d, respectively) were studied in batch and continuous-flow mode utilizing different AAs, such as diisopropyl malonate 2A, isopropyl 2-cyanoacetate 2B, and isopropyl 2-ethoxyacetate 2C. The reactions performed with CaLB-MNPs were compared with Novozym 435 (N435) and the results in the literature. CaLB-MNPs were less active than N435, leading to lower conversion, but demonstrated a higher enantiomer selectivity, proving to be a good alternative to the commercial form. Compound 2C resulted in the best balance between conversion and enantiomer selectivity among the acylating agents. CaLB-MNPs proved to be efficient in the KR of chiral amines, having comparable or superior properties to other CaLB forms utilizing porous matrices for immobilization. An additional advantage of using CaLB-MNPs is that the purification and reuse processes are facilitated via magnetic retention/separation. In the continuous-flow mode, the usability and operational stability of CaLB-MNPs were reaffirmed, corroborating with previous studies, and the results overall improve our understanding of this potent biocatalyst and the convenient U-shape reactor used.

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Although imine reductases (IREDs) are emerging as attractive reductive aminases (RedAms), their substrate scope is still narrow, and rational engineering is rare. Focusing on hydrogen bond reorganization and cavity expansion, a concise strategy combining rational cavity design, combinatorial active‐site saturation test (CAST), and thermostability engineering was designed, that transformed the weakly active IR‐G36 into a variant M5 with superior performance for the synthesis of (R)‐3‐benzylamino‐1‐Boc‐piperidine, with a 4193‐fold improvement in catalytic efficiency, a 16.2 °C improvement in Tm, and a significant increase in the e.e. value from 78 % (R) to >99 % (R). M5 exhibits broad substrate scope for the synthesis of diverse azacycloalkylamines, and the reaction was demonstrated on a hectogram‐scale under industrially relevant conditions. Our study provides a compelling example of the preparation of versatile and efficient IREDs, with exciting opportunities in medicinal and process chemistry as well as synthetic biology. [ABSTRACT FROM AUTHOR]

The direct asymmetric reductive amination of heteroaryl ketones has been a long‐standing synthetic challenge. Here we report the engineering of an amine dehydrogenase (AmDH) from Jeotgalicoccus aerolatus for the asymmetric synthesis of chiral α‐(hetero)aryl primary amines in excellent conversions (up to 99 %) and enantioselectivities (up to 99 % ee). The best AmDH variant (Ja‐AmDH‐M33) exhibited high activity and specificity toward alkyl (hetero)aryl ketones, even for those bearing a bulky alkyl chain. An efficient directed evolution approach based on molecular docking was implemented to enlarge the active pocket with a more hydrophobic entrance, which is responsible for the high activity. The Ja‐AmDH‐M33 was also used for preparative‐scale synthesis of pharmaceutically relevant amines and a key intermediate of chiral pincer ligands, which highlighted its practical application in synthetic chemistry. [ABSTRACT FROM AUTHOR]

Amino acid dehydrogenases (AADHs) are a group of enzymes that catalyze the reversible reductive amination of keto acids with ammonia to produce chiral amino acids using either nicotinamide adenine dinucleotide (NAD+) or nicotinamide adenine dinucleotide phosphate (NADP+) as cofactors. Among them, glutamate dehydrogenase, valine dehydrogenase, leucine dehydrogenase, phenylalanine dehydrogenase, and tryptophan dehydrogenase have been classified as a superfamily of amino acid dehydrogenases (s-AADHs) by previous researchers because of their conserved structures and catalytic mechanisms. Owing to their excellent stereoselectivity, high atom economy, and low environmental impact of the reaction pathway, these enzymes have been extensively engineered to break strict substrate specificities for the synthesis of high value-added chiral compounds (chiral amino acids, chiral amines, and chiral amino alcohols). Substrate specificity engineering of s-AADHs mainly focuses on recognition engineering of the substrate side chain R group and substrate backbone carboxyl group. This review summarizes the reported studies on substrate specificity engineering of s-AADHs and reports that this superfamily of enzymes shares substrate specificity engineering hotspots (the inside of the pocket, substrate backbone carboxyl anchor sites, substrate entrance tunnel, and hinge region), which sheds light on the substrate-specific tailoring of these enzymes. [ABSTRACT FROM AUTHOR]

This work proposes a new selective palladium catalyst supported on dolomite to synthesize enantiomerically enriched N-[(R)-(+)-1-phenylethyl] amide. 2.5 wt.% Pd catalyst demonstrated high activity for reactions performed under mild conditions reaching a total enantiomeric excess up to 99%. It could be reused up to 5 cycles after the regeneration step. [ABSTRACT FROM AUTHOR]

We report the enantiodivergent reaction of ketimines derived from α‐ketoesters with malononitriles using a single chiral source. The reactions using an 8‐quinolinesulfonyl cinchona alkaloid catalyst in the presence and absence of Et2Zn gave both enantiomers in high yields with high enantioselectivities (53∼99% yield, 99:1∼3:97 er). The obtained malononitrile‐derived α‐amino acids were converted into various optically active compounds. A reaction mechanism is proposed to explain the observed enantiodivergency. [ABSTRACT FROM AUTHOR]

The title compound C9H14N+·Cl-, (1), can be synthesized starting from (S)-N-methyl-1-phenylethan-1-amine (2). Compound 2 upon addition of HCl·Et2O leads to crystallization of compound 1 as colorless blocks. The configuration of compound 1 is stable as well as preserved in space group P212121. Ammonium chlorides, like the title compound, are often observed as undesirable by-products in aminosilylation of chlorosilanes. Additionally, these by-products are usually soluble in selected organic solvents, which require difficult separation steps. Therefore, detailed studies on structural features and intermolecular interactions performed by Hirshfeld atom refinement (HAR) using NoSpherA2 [Kleemiss et al. (2021). Chem. Sci. 12, 1675-1692] and Hirshfeld surface analysis were used to address structural issues on that separation problem. [ABSTRACT FROM AUTHOR]

Multi-enzyme cascade catalysis has become an important technique for chemical reactions used in manufacturing and scientific study. In this research, we designed a four-enzyme integrated catalyst and used it to catalyse the deracemization reaction of cyclic chiral amines, where monoamine oxidase (MAO) catalyses the enantioselective oxidation of 1-methyl-1,2,3,4-tetrahydroisoquinoline (MTQ), imine reductase (IRED) catalyses the stereo selective reduction of 1-methyl-3,4-dihydroisoquinoline (MDQ), formate dehydrogenase (FDH) is used for the cyclic regeneration of cofactors, and catalase (CAT) is used for decomposition of oxidative reactions. The four enzymes were immobilized via polydopamine (PDA)-encapsulated dendritic organosilica nanoparticles (DONs) as carriers, resulting in the amphiphilic core-shell catalysts. The hydrophilic PDA shell ensures the dispersion of the catalyst in water, and the hydrophobic DON core creates a microenvironment with the spatial confinement effect of the organic substrate and the preconcentration effect to enhance the stability of the enzymes and the catalytic efficiency. The core-shell structure improves the stability and reusability of the catalyst and rationally arranges the position of different enzymes according to the reaction sequence to improve the cascade catalytic performance and cofactor recovery efficiency., (© 2024 Wiley-VCH GmbH.)

Chiral indoline‐2‐carboxylic acid has been identified to enable a highly enantioselective Catellani‐type annulation of (hetero)aryl, alkenyl triflate and conjugated vinyl iodides with 4‐(bromomethyl)cyclohexanone, directly assembling a diverse range of chiral all‐carbon bridged ring systems. Control experiments and DFT calculations suggest that the coordinating orientation of the chiral amino acid to the arylpalladium(II) center allows for high levels of stereochemical control. [ABSTRACT FROM AUTHOR]

2‐Aminotetralin and 3‐aminochroman derivatives are key structural motifs present in a wide range of pharmaceutically important molecules. Herein, we report an effective biocatalytic approach towards these molecules through the enantioselective reductive coupling of 2‐tetralones and 3‐chromanones with a diverse range of primary amine partners. Metagenomic imine reductases (IREDs) were employed as the biocatalysts, obtaining high yields and enantiocomplementary selectivity for >15 examples at preparative scale, including the precursors to Ebalzotan, Robalzotan, Alnespirone and 5‐OH‐DPAT. We also present a convergent chemo‐enzymatic total synthesis of the Parkinson's disease therapy Rotigotine in 63 % overall yield and 92 % ee. [ABSTRACT FROM AUTHOR]