Chemoenzymatic dynamic kinetic resolution: a powerful tool for the preparation of enantiomerically pure alcohols and amines

Dynamic Kinetic Asymmetric Hydroacylation: Racemization by Soft Enolization

We report a dynamic kinetic asymmetric transformation (DyKAT) of racemic aldehydes by Rh-catalyzed hydroacylation of acrylamides. This intermolecular hydroacylation generates 1,4-ketoamides with high enantio- and diastereoselectivity. DFT and experimental studies provide mechanistic insights and reveal an unexpected Rh-catalyzed pathway for aldehyde racemization. Our study represents a pioneering kinetic resolution by intermolecular hydroacylation and contributes to the growing field of stereoconvergent catalysis featuring C-C bond construction.

Chemoenzymatic Dynamic Kinetic Resolution of Atropoisomeric 2-(Quinolin-8-yl)benzylalcohols

The chemoenzymatic dynamic kinetic resolution of 2-(quinolin-8-yl)benzylalcohols using a combination of lipases and ruthenium catalysts is described. While CalB lipase performs highly selective enzymatic kinetic resolution, the combination with Shvo's or Bäckvall's catalysts promotes atropisomerization of the substrate via the reversible formation of configurationally labile aldehydes, thereby enabling a dynamic kinetic resolution. This synergistic approach was applied to the synthesis of a variety of heterobiaryl acetates in excellent yields and enantioselectivities.

Changing the absolute configuration of atropisomeric bisnaphthols (BINOLs)

Bisnaphthol (BINOL) is a ubiquitous core skeleton in versatile chiral catalysts and ligands for transition metals, and this representative atropisomeric structure also serves as a building block in various optically active natural products. Due to the high rotational barrier (∼40 kcal mol-1) in the neutral form of BINOL, it displays stable atropisomerism. Asymmetric catalysis using racemic BINOL substrates generally exhibits a kinetic resolution process, with reaction yields having to be below 50%. Dynamic kinetic resolution (DKR) combines kinetic resolution with a racemization process to push the ideal yield to 100%. A changing of the absolute configuration of BINOL has been observed since Brussee et al. did so in 1985, but its mechanism remains unknown. Recently, racemization strategies and a mechanism based on single-electron oxidation, producing a released radical-anion species as the key intermediate, have been clearly disclosed. In particular, deracemization of BINOLs achieved by using stochiometric amounts of a chiral amine or ammonium salt, and dynamic kinetic resolution in cooperation with biocatalysis, have been well established for accessing enantioenriched BINOL derivatives, as summarized and discussed in this review.

Access to Chiral Dihydro-1,4-Benzoxazine-2-Carboxylates through NHC-Catalyzed Dynamic Kinetic Resolution

A chiral carbene-catalyzed dynamic kinetic resolution for the facile synthesis of enantioenriched dihydro-1,4-benzoxazine-2-carboxylates is disclosed. The reaction conditions are mild, and a diversity of substituents are well-tolerated in this transformation. In addition, our methodology also provides an efficient strategy for building chiral chromane-2-carboxylate and 2,3-dihydro-1,4-benzodioxane-2-carboxylate. The optically pure products generated from this protocol can be easily derived as the key intermediates of chiral drugs and bioactive molecules.

Copper-catalysed dynamic kinetic asymmetric C-O cross-coupling to access chiral aryl oxime ethers and diaryl ethers

Dynamic kinetic resolution (DKR) has emerged as an elegant and powerful tool for enantioselective synthesis, enabling the transformation of racemic compounds into enantiomerically enriched products with theoretically quantitative yields. Despite its widespread success, the dynamic kinetic asymmetric C-O cross-coupling has presented significant challenges and remains unexplored. In this study, we report a dynamic kinetic asymmetric C-O cross-coupling of oximes and phenols via copper/BOX-catalysed enantioselective O-arylation with diaryliodonium salts. This method efficiently produces a wide range of inherently chiral oxime ethers, as well as axially chiral styrenes, with high yields and excellent regio- and enantioselectivities. Through controlled experiments and Density Functional Theory (DFT) studies, we have elucidated the dynamic kinetic resolution process and gained insights into the origins of regio- and enantioselectivity.

Bienzymatic Dynamic Kinetic Resolution of Secondary Alcohols by Esterification/Racemization in Water

Dynamic kinetic resolution (DKR) is a key method used to prepare optically pure compounds in 100 % theoretical yield starting from racemic substrates by combining the interconversion of substrate enantiomers with an enantioselective transformation. Various chemoenzymatic DKR approaches have been developed to deracemize secondary alcohols, typically requiring an organic solvent to facilitate enantioselective acylation, primarily catalyzed by lipases, alongside racemization mediated by an achiral, non-enzymatic catalyst. Achieving both steps in an aqueous solution remained elusive. Herein, we report a DKR of racemic sec-alcohols in an aqueous solution requiring only two biocatalysts. The first key to success was to achieve fast racemization in a buffer employing a non-stereoselective variant of an alcohol dehydrogenase (Lk-ADH-Prince) via a hydrogen-borrowing oxidation-reduction sequence. Engineered variants of the acyltransferase from Mycobacterium smegmatis (MsAcT) enabled enantioselective acyl transfer in water. Besides the appropriate choice of the enzymes, identifying a suitable acyl donor was a second key to the success. The DKR was successfully demonstrated using (R)-selective MsAcT variants for a broad range of racemic (hetero)benzylic alcohols with 2,2,2-trifluoroethyl acetate as the acyl donor, yielding (R)-acetates with up to >99 % conv. and high-to-excellent optical purity (83-99.9 % ee). The (S)-acetates were accessible using a stereocomplementary (S)-selective MsAcT variant. Notably, substrate concentrations of up to 400 mM were tolerated in selected cases.

Topology of Gemini-shaped Hexagonal Heterojunction for Efficient Stereoconvergent Transformation via Dynamic Kinetic Resolution

Despite recent advances in the combination of kinetic resolution and racemization for efficient stereoconvergent transformation, the poor stability and limited reaction activities of the products restrict their wide application in industrial production. To overcome these problems, Gemini-shaped hexagons with para-heterojunctions for one-dimensional and two-dimensional supramolecular polymers were designed via hydrogen-bonding adhesion by racemization catalyst 1 and kinetic resolution 2 in this work. The polymers from the assembly of Gemini-shaped hexagons exhibit rapid catalytic behaviour with efficient selectivity for the desired configuration in the synthesis of tertiary alcohols with contiguous stereocenters through dynamic kinetic resolution for the nanoscale heterojunctions of dissimilar catalysts. Among them, the developed 2D polymers gave outstanding enantioselectivities and diastereoselectivities (>99 % ee, 20 : 1 dr) through the cooperation of adjacent dissimilar catalysts. The heterojunctions varying dimensions and distances of dissimilar catalysts provide new insight for increasing the enantioselectivity of chiral organocatalysts.

Reaction Engineering for Asymmetric R-/S-PAC Synthesis With Ephedrine or Pseudoephedrine Dehydrogenase in Pickering Emulsion

The synthesis of enantiopure α-hydroxy ketones, particularly R- and S-phenylacetylcarbinol (PAC), represents an important process in the pharmaceutical industry, serving as a pivotal step in the production of drugs. Recently, two novel enzymes, ephedrine dehydrogenase (EDH) and pseudoephedrine dehydrogenase (PseDH), have been described. These enzymes enable the specific reduction of 1-phenyl-1,2-propanedione (PPD) to R-PAC and S-PAC, respectively. In this study, we transferred these enzymes into Pickering emulsions, which is an attractive reaction set-up for large-scale synthesis. The bioactive w/o Pickering emulsion (bioactive Pickering emulsion [BioPE]), in which methyl tert-butyl ether served as the continuous phase, was stabilized by silica nanoparticles. Formate dehydrogenase from Rhodococcus jostii was utilized for cofactor regeneration. Given the considerable complexity of the BioPE, this reaction system underwent a first-time application of design of experiment (DOE) for systematic engineering. A definitive screening design was employed to identify significant factors affecting space-time yield (STY) and conversion. Response surface methodology was used to optimize the conditions, resulting in the observation of a high STY of 4.2 g L⁻¹ h⁻¹ and a conversion of 83.2% for BioPE with EDH, and an STY of 4.4 g L⁻¹ h⁻¹ and a conversion of 64.5% for BioPE with PseDH.

Synthesis and catalytic testing of the first hydrophilic derivative of Shvo's catalyst

Although commonly applied in various reactions, Shvo's catalyst has not been modified towards solubility in highly polar solvents until now. Here, we report the straightforward synthesis of a disulfonate derivative of the complex, which allows to (transfer) (de-)hydrogenate aldehydes and ketones in aqueous solutions. A proof of principle for the recycling of the catalyst is also provided.

Protein Engineering of Lipase A from Candida Antarctica to Improve Esterification of Tertiary Alcohols

Chiral tertiary alcohols are important organic compounds in science as well as in industry. However, their preparation in enantiomerically pure form is still a challenge due to their complex structure and steric hindrances compared with primary and secondary alcohols, so kinetic resolution could be an attractive approach. Lipase A from Candida antarctica (CAL-A) has been shown to catalyze the enantioselective esterification of various tertiary alcohols with excellent enantioselectivity but low activity. Here we report a mutagenesis study by rational design to improve CAL-A activity against tertiary alcohols. Single mutants of CAL-A were selected, expressed, immobilized and screened for esterification of the tertiary alcohol 1,2,3,4-tetrahydronaphthalen-1-ol. A double mutant V278S+S429G showed a 1.5-fold higher reaction rate than that of the wild type CAL-A, while maintaining excellent enantioselectivity.

Overcoming the Limitations of Transition-Metal Catalysis in the Chemoenzymatic Dynamic Kinetic Resolution (DKR) of Atropisomeric Bisnaphthols

Chemoenzymatic dynamic kinetic resolution (DKR), combining a metal racemization catalyst with an enzyme, has emerged as an elegant solution to transform racemic substrates into enantiopure products, while compatibility of dual catalysis is the key issue. Conventional solutions have utilized presynthesized metal complexes with a fixed and bulky ligand to protect the metal from the enzyme system; however, this has been generally limited to anionic ligands. Herein, we report our strategy to solve the compatibility issue by employing a reliable ligand that firmly coordinates in situ to the metal. Such a reliable ligand offers π* orbitals, allowing additional metal-to-ligand d-π* back-donation, which can significantly enhance coordination effects between the ligand and metal. Therefore, we developed an efficient DKR method to access chiral BINOLs from racemic derivatives under dual copper and enzyme catalysis. In cooperation with lipase LPL-311-Celite, the DKR of BINOLs was successfully realized with a copper catalyst via in situ coordination of BCP (L8) to CuCl. A series of functionalized C 2- and C 1-symmetric chiral biaryls could be synthesized in high yields with good enantioselectivity. The racemization mechanism was proposed to involve a radical-anion intermediate, which allows the axial rotation with a dramatic decrease of the rotation barrier.

An Engineered Imine Reductase for Highly Diastereo- and Enantioselective Synthesis of β-Branched Amines with Contiguous Stereocenters

β-Branched chiral amines with contiguous stereocenters are valuable building blocks for preparing various biologically active molecules. However, their asymmetric synthesis remains challenging. Herein, we report a highly diastereo- and enantioselective biocatalytic approach for preparing a broad range of β-branched chiral amines starting from their corresponding racemic ketones. This involves a dynamic kinetic resolution-asymmetric reductive amination process catalyzed using only an imine reductase. Four rounds of protein engineering endowed wild-type PocIRED with higher reactivity, better stereoselectivity, and a broader substrate scope. Using the engineered enzyme, various chiral amine products were synthesized with up to >99.9 % ee, >99 : 1 dr, and >99 % conversion. The practicability of the developed biocatalytic method was confirmed by producing a key intermediate of tofacitinib in 74 % yield, >99.9 % ee, and 98 : 2 dr at a challenging substrate loading of 110 g L-1. Our study provides a highly capable imine reductase and a protocol for developing an efficient biocatalytic dynamic kinetic resolution-asymmetric reductive amination reaction system.

Candidaantarctica Lipase B mediated kinetic resolution: A sustainable method for chiral synthesis of antiproliferative β-lactams

Biocatalysis is a valuable industrial approach in active pharmaceutical ingredient (API) manufacturing for asymmetric induction and synthesis of chiral APIs. Herein, we investigated synthesis of a panel of microtubule-destabilising antiproliferative β-lactam enantiomers employing a commercially available immobilised Candida antarctica lipase B enzyme together with methanol and MTBE. The β-lactam ring remained intact during chiral kinetic resolution reactions, plausibly due to a bulky N-1 phenyl substituent on the β-lactam ring substrate. The predominant reaction mediated by CAL-B was methanol catalysed conversion of the β-lactam 3-acetoxy substituent to a 3-hydroxyl group, with preferential methanolysis of the 3S, 4S enantiomer. The unreacted substrate underwent progressive enantioenrichment to the 3R, 4R enantiomer. Substitution patterns on the B ring C3 meta position of the β-lactam scaffold greatly affected the rate of reaction. Halo substituents (fluoro-, chloro- and bromo-) reduced the rate of conversion compared to unsubstituted analogues, which in turn increased enantiomeric excess (ee). Ee values up to 86 % for the 3S, 4S 3-hydroxyl enantiomer were achieved. A double resolution approach for unreacted substrate yielded high ee values (>99 %) for the 3R, 4R 3-acetoxy enantiomer. CAL-B mediated methanolysis is a more sustainable method for resolution of racemic antiproliferative β-lactams compared to a previous technique of chiral diastereomeric resolution. Yields of β-lactams obtained using CAL-B are far superior than previously described, which will facilitate progression toward pre-clinical and clinical development. Biocatalysis is a useful tool in the toolbox of the medicinal chemist.

Isothiourea-Catalysed Acylative Dynamic Kinetic Resolution of Tetra-substituted Morpholinone and Benzoxazinone Lactols

The development of methods to allow the selective acylative dynamic kinetic resolution (DKR) of tetra-substituted lactols is a recognised synthetic challenge. In this manuscript, a highly enantioselective isothiourea-catalysed acylative DKR of tetra-substituted morpholinone and benzoxazinone-derived lactols is reported. The scope and limitations of this methodology have been developed, with high enantioselectivity and good to excellent yields (up to 89 %, 99 : 1 er) observed across a broad range of substrate derivatives incorporating substitution at N(4) and C(2), di- and spirocyclic substitution at C(5) and C(6), as well as benzannulation (>35 examples in total). The DKR process is amenable to scale-up on a 1 g laboratory scale. The factors leading to high selectivity in this DKR process have been probed through computation, with an N-C=O⋅⋅⋅isothiouronium interaction identified as key to producing ester products in highly enantioenriched form.

Multi-Catalytic Metal-Based Homogeneous-Heterogeneous Systems in Organic Chemistry

The combination of metal-based homogeneous and heterogeneous catalysts in the same reaction media is a powerful, yet relatively unexplored approach in organic chemistry. This strategy can address important limitations associated with purely homogeneous or heterogeneous catalysis such as the incompatibility of different catalytic species in solution, or the limited tunability of solid catalysts, respectively. Moreover, the facile reusability of the solid catalyst, contributes to increase the overall sustainability of the process. As a result, this semi-heterogeneous multi-catalytic approach has unlocked significant advances in organic chemistry, improving existing reactions and even enabling the discovery of novel transformations, exemplified by the formal alkane metathesis. This concept article aims to showcase the benefits of this strategy through the exploration of diverse relevant examples from the literature, hoping to spur research on new metal-based homogeneous-heterogeneous catalyst combinations that will result in reactivity challenging to achieve by conventional homogeneous or heterogeneous catalysis alone.

Construction of Multi-Enzyme Integrated Catalysts for Deracemization of Cyclic Chiral Amines

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.

One-pot chemo- and photo-enzymatic linear cascade processes

The combination of chemo- and photocatalyses with biocatalysis, which couples the flexible reactivity of the photo- and chemocatalysts with the highly selective and environmentally friendly nature of enzymes in one-pot linear cascades, represents a powerful tool in organic synthesis. However, the combination of photo-, chemo- and biocatalysts in one-pot is challenging because the optimal operating conditions of the involved catalyst types may be rather different, and the different stabilities of catalysts and their mutual deactivation are additional problems often encountered in one-pot cascade processes. This review explores a large number of transformations and approaches adopted for combining enzymes and chemo- and photocatalytic processes in a successful way to achieve valuable chemicals and valorisation of biomass. Moreover, the strategies for solving incompatibility issues in chemo-enzymatic reactions are analysed, introducing recent examples of the application of non-conventional solvents, enzyme-metal hybrid catalysts, and spatial compartmentalization strategies to implement chemo-enzymatic cascade processes.

Synthesis of N-N Axially Chiral Pyrrolyl-oxoisoindolin via Isothiourea-Catalyzed Acylative Dynamic Kinetic Resolution

The development of methods for the asymmetric synthesis of N-N axial chirality remains elusive and challenging. Here, we disclose a method for the construction of N-N axially chiral pyrrolyl-oxoisoindolins along with central chirality via the isothiourea (ITU)-catalyzed acylative dynamic kinetic resolution (DKR). Axial chirality was introduced into the acylative DKR of hemiaminals for the first time. This protocol features mild conditions with excellent yields and enantioselectivities.

Strategies to Design Chemocatalytic Racemization of Tertiary Alcohols: State of the Art & Utilization for Dynamic Kinetic Resolution

The synthesis of enantiomerically pure tertiary alcohols is an important issue in organic synthesis of a range of pharmaceuticals including molecules such as the anti-HIV drug Efavirenz. A conceptually elegant approach to such enantiomers is the dynamic kinetic resolution of racemic tertiary alcohols, which, however, requires efficient racemization strategies. The racemization of tertiary alcohols is particularly challenging due to various side reactions that can occur because of their high tendency for elimination reactions. In the last few years, several complementary catalytic concepts for racemization of tertiary alcohols have been developed, characterized by efficient racemization and suppression of unwanted side-reactions. Besides resins bearing sulfonic acid moieties and a combination of boronic acid and oxalic acid as heterogeneous and homogeneous Brønsted-acids, respectively, immobilized oxovanadium and piperidine turned out to be useful catalysts. The latter two catalysts, which have already been applied to different types of substrates, also have proven good compatibility with lipase, thus leading to the first two examples of chemoenzymatic dynamic kinetic resolution of tertiary alcohols. In this review, the difficulties in racemizing tertiary alcohols are specifically described, and the recently developed complementary concepts to overcome these hurdles are summarized.

Co-Immobilization of ADH and GDH on Metal-Organic-Framework: An Effective Biocatalyst for Asymmetric Reduction of Ketones

Chiral alcohols are not only important building blocks of various bioactive natural compounds and pharmaceuticals, but can serve as synthetic precursors for other valuable organic chemicals, thus the synthesis of these products is of great importance. Bio-catalysis represents one effective way to obtain these molecules, however, the weak stability and high cost of enzymes often hinder its broad application. In this work, we designed a biological nanoreactor by embedding alcohol dehydrogenase (ADH) and glucose dehydrogenase (GDH) in metal-organic-framework ZIF-8. The biocatalyst ADH&GDH@ZIF-8 could be applied to the asymmetric reduction of a series of ketones to give chiral alcohols in high yields (up to 99 %) and with excellent enantioselectivities (>99 %). In addition, the heterogeneous biocatalyst could be recycled and reused at least four times with slight activity decline. Moreover, E. coli containing ADH and GDH was immobilized by ZIF-8 to form biocatalyst E. coli@ZIF-8, which also exhibits good catalytic behaviours. Finally, the chiral alcohols are further converted to marketed drugs (R)-Fendiline, (S)-Rivastigmine and NPS R-568 respectively.

Chemoenzymatic Dynamic Kinetic Resolution Protocol with an Immobilized Oxovanadium as a Racemization Catalyst

An excellent compatible and cost-effective dynamic kinetic resolution (DKR) protocol has been developed by combining a novel immobilized oxovanadium racemization catalyst onto cheap diatomite (V-D) with an immobilized lipase LA resolution catalyst onto a macroporous resin (LA-MR). V-D was prepared via grinding immobilization, which may become a promising alternative for the immobilization of metals, especially precious metals due to its low cost, high efficiency, easy separation, and large reaction interface. The DKR afforded high yield (96.1%), e.e. (98.67%), and Sel (98.28%) under optimal conditions established using response surface methodology as follows: the amount of V-D 10.83 mg, reaction time 51.2 h, and temperature 48.1 °C, respectively, indicating that all the reactions in the DKR were coordinated very well. The DKR protocol was also found to have high stability up to six reuses. V-D exhibited excellent compatibility with LA-MR because the lipase immobilized onto MR did not physically contact with the vanadium species immobilized onto diatomite, thus avoiding inactivation. Considering that lipase, oxovanadium, diatomite, and MR used are relatively inexpensive, and the adsorption or grinding immobilization is simple, the LA-V-MD DKR by coupling LA-MR with V-D is a cost-effective and promising protocol for chiral secondary alcohols.

New methods for resolution of hydroxychloroquine by forming diastereomeric salt and adding chiral mobile phase agent on RP-HPLC

Hydroxychloroquine (HCQ), 2-([4-([7-Chloro-4-quinolyl]amino)pentyl]ethylamino)ethanol, exhibited significant biological activity, while its side effects cannot be overlooked. The RP-HPLC enantio-separation was investigated for cost-effective and convenient optical purity analysis of HCQ. The thermodynamic resolution of Rac-HCQ, driven by enthalpy and entropy, was achieved on the C18 column using Carboxymethyl-β-cyclodextrin (CM-β-CD) as the chiral mobile phase agent (CMPA). The effects of CCM-β-CD, pH, and triethylamine (TEA) V% on the enantio-separation process were explored. Under the optimum conditions at 24°C, the retention times for the two enantiomers weret R 1 = 29.39 min $$ {t}_{R1}=29.39\ \min $$ andt R 2 = 32.42 min $$ {t}_{R2}=32.42\ \min $$ , resulting inR s = 1.87 $$ {R}_s=1.87 $$ . The resolution via diastereomeric salt formation of Rac-HCQ was developed to obtain the active pharmaceutical ingredient of single enantiomer S-HCQ. Di-p-Anisoyl-L-Tartaric Acid (L-DATA) was proved effective as the resolution agent for Rac-HCQ. Surprisingly, it was found that refluxing time was a key fact affecting the resolution efficiency, which meant the kinetic dominate during the process of the resolution. Four factors-solvent volume, refluxing time, filtration temperature, and molar ratio-were optimized using the single-factor method and the response surface method. Two cubic models were established, and the reliability was subsequently verified. Under the optimal conditions, the less soluble salt of 2L-DATA:S-HCQ was obtained with a yield of 96.9% and optical purity of 63.0%. The optical purity of this less soluble salt increases to 99.0% with a yield of 74.2% after three rounds recrystallization.

Covalent Organic Frameworks Based Photoenzymatic Nano-reactor for Asymmetric Dynamic Kinetic Resolution of Secondary Amines

Bio-catalysis represents a highly efficient and stereoselective method for the synthesis of valuable chiral compounds, however, the poor stability and limited reaction types of free enzymes restrict their wide application in industrial production. In this work, to overcome these problems, a multifunctional photoenzymatic nanoreactor CALB@COF-Ir was developed through the encapsulation of Candida antarctica lipase B (CALB) in a photosensitive covalent organic framework COF-Ir. This bio-nanocluster serves as efficient catalysts in asymmetric dynamic kinetic resolution (DKR) of secondary amines to give a series of chiral amines in high yields (up to 99 %) and enantioselectivities (up to 99 % ee). The well-designed COF-Ir not only acts as safety cover to prevent CALB from deactivation but promotes racemization of secondary amines via photo-induced hydrogen atom transfer (HAT) process. Photoelectric characterization and TDDFT calculation revealed that (ppy)2Ir units in COF-Ir play crucial role in this photocatalytic system which enhance its photo-redox properties through facilitating the separation between photoelectrons (e-) and holes (h+). Furthermore, the heterogeneous photoenzymatic nanoreactor could be recycled for five rounds with slight decline of catalytic reactivity.

Near-infrared light-driven asymmetric photolytic reduction of ketone using inorganic-enzyme hybrid biocatalyst

Effective photolytic regeneration of the NAD(P)H cofactor in enzymatic reductions is an important and elusive goal in biocatalysis. It can, in principle, be achieved using a near-infrared light (NIR) driven artificial photosynthesis system employing H2O as the sacrificial reductant. To this end we utilized TiO2/reduced graphene quantum dots (r-GQDs), combined with a novel rhodium electron mediator, to continuously supply NADPH in situ for aldo-keto reductase (AKR) mediated asymmetric reductions under NIR irradiation. This upconversion system, in which the Ti-O-C bonds formed between r-GQDs and TiO2 enabled efficient interfacial charge transfer, was able to regenerate NADPH efficiently in 64 % yield in 105 min. Based on this, the pharmaceutical intermediate (R)-1-(3,5-bis(trifluoromethyl)phenyl)ethan-1-ol was obtained, in 84 % yield and 99.98 % ee, by reduction of the corresponding ketone. The photo-enzymatic system is recyclable with a polymeric electron mediator, which maintained 66 % of its original catalytic efficiency and excellent enantioselectivity (99.9 % ee) after 6 cycles.

Biocatalysis: landmark discoveries and applications in chemical synthesis

Biocatalysis has become an important tool in chemical synthesis, allowing access to complex molecules with high levels of activity and selectivity and with low environmental impact. Key discoveries in protein engineering, bioinformatics, recombinant technology and DNA sequencing have contributed towards the rapid acceleration of the field. This tutorial review explores enzyme engineering strategies and high-throughput screening approaches that have been applied for the discovery and development of enzymes for synthetic application. Landmark developments in the field are discussed and have been carefully selected to highlight the diverse synthetic applications of enzymes within the pharmaceutical, agricultural, food and chemical industries. The design and development of artificial biocatalytic cascades is also examined. This tutorial review will give readers an insight into the landmark discoveries and milestones that have helped shape and grow this branch of catalysis since the discovery of the first enzyme.

Stereodivergent Protein Engineering of Fatty Acid Photodecarboxylase for Light-Driven Kinetic Resolution of Sec-Alcohol Oxalates

Stereodivergent engineering of one enzyme to create stereocomplementary variants for synthesizing optically pure molecules with tailor-made (R) or (S) configurations on an optional basis is highly desirable and challenging. This study aimed to engineer fatty acid photodecarboxylase from Chlorella variabilis (CvFAP) using the focused rational iterative site-specific mutagenesis (FRISM) strategy to obtain two highly stereocomplementary variants with excellent selectivity (both giving products with up to 99 % e.e.). These variants were used for the CvFAP-catalyzed light-driven kinetic resolution of oxalates or oxamic acids prepared from the corresponding sec-alcohols or amines, providing a new biotransformation process for preparing chiral sec-alcohols and amines. Molecular dynamics simulation, kinetic data and transient spectra revealed the source of selectivity. This study represents the first example of the kinetic resolution of sec-alcohols or amines catalyzed by a pair of stereocomplementary CvFAPs.

Regio- and Enantioselective Construction of Tetrazole Hemiaminal Esters and Related Prodrugs via Biocatalytic Dynamic Kinetic Resolution

Enzyme-catalyzed dynamic kinetic resolution was applied to the one-pot regio- and enantioselective synthesis of 2,5-disubstituted tetrazole hemiaminal esters, among which 72% of the products were obtained in excellent enantiopurities (99% ees). Tunable stereoselectivity was achieved by using different types of enzymes during the synthesis of a key intermediate for a clinic drug candidate. Successful preparation of tetrazole ester prodrugs and high catalyst recyclability further demonstrated the potential practical application of this protocol.

Reprogramming biocatalytic futile cycles through computational engineering of stereochemical promiscuity to create an amine racemase

Repurposing the intrinsic properties of natural enzymes can offer a viable solution to current synthetic challenges through the development of novel biocatalytic processes. Although amino acid racemases are ubiquitous in living organisms, an amine racemase (AR) has not yet been discovered despite its synthetic potential for producing chiral amines. Here, we report the creation of an AR based on the serendipitous discovery that amine transaminases (ATAs) can perform stereoinversion of 2-aminobutane. Kinetic modeling revealed that the unexpected off-pathway activity results from stereochemically promiscuous futile cycles due to incomplete stereoselectivity for 2-aminobutane. This finding motivated us to engineer an S-selective ATA through in silico alanine scanning and empirical combinatorial mutations, creating an AR with broad substrate specificity. The resulting AR, carrying double point mutations, enables the racemization of both enantiomers of diverse chiral amines in the presence of a cognate ketone. This strategy may be generally applicable to a wide range of transaminases, paving the way for the development of new-to-nature racemases.

Enantioconvergent 6π Electrocyclization Enabled by Photoredox Racemization

This study presents a novel photoredox-enabled enantioconvergent catalytic strategy used to construct chiral 2H-1,3-benzoxazines via an unprecedented oxa-6π electrocyclization utilizing racemic α-substituted glycinates as substrates. The approach leverages a cobalt-based chiral Lewis acid catalyst, which promotes the transformation under thermal or photoredox conditions. While the thermal reaction selectively converts only the (S)-configured glycinates into enantioenriched 2H-1,3-benzoxazines (up to 96:4 e.r.), the addition of 0.5 mol % of a commercially available iridium photocatalyst under visible light irradiation transforms the reaction into an enantioconvergent process. Detailed mechanistic and time course studies of optically pure α-deuterated substrates revealed the presence of an enantiospecific kinetic isotope effect, which helped to clarify the role of both the photo- and chiral Lewis acid catalyst in the reaction sequence. In this dual catalytic system, the photocatalyst promotes a dynamic interconversion between the substrate enantiomers─a process not accessible via ground-state chemistry─while the chiral Lewis acid selectively transforms only the (S)-configured substrates. Further mechanistic evidence for the proposed mechanism is provided by linear free energy relationship analysis, which suggests that the stereodetermining step involves a 6π electrocyclization under both thermal and photoredox conditions.

Bottom-Up Synthesis of Multicompartmentalized Microreactors for Continuous Flow Catalysis

The bottom-up assembly of biomimetic multicompartmentalized microreactors for use in continuous flow catalysis remains a grand challenge because of the structural instability or the absence of liquid microenvironments to host biocatalysts in the existing systems. Here, we address this challenge using a strategy that combines stepwise Pickering emulsification with interface-confined cross-linking. Our strategy allows for the fabrication of robust multicompartmentalized liquid-containing microreactors (MLMs), whose interior architectures can be exquisitely tuned in a bottom-up fashion. With this strategy, enzymes and metal catalysts can be separately confined in distinct subcompartments of MLMs for processing biocatalysis or chemo-enzymatic cascade reactions. As exemplified by the enzyme-catalyzed kinetic resolution of racemic alcohols, our systems exhibit a durability of 2000 h with 99% enantioselectivity. Another Pd-enzyme-cocatalyzed dynamic kinetic resolution of amines further demonstrates the versatility and long-term operational stability of our MLMs in continuous flow cascade catalysis. This study opens up a new way to design efficient biomimetic multicompartmental microreactors for practical applications.

Nickel-Catalyzed Remote Asymmetric Hydroalkylation of Alkenyl Ethers to Access Ethers of Chiral Dialkyl Carbinols

Site- and enantio-selective alkyl-alkyl bond formation is privileged in the retrosynthetic analysis due to the universality of sp³-hybridized carbon atoms in organic molecules. Herein, we report a nickel-catalyzed remote asymmetric hydroalkylation of alkenyl ethers via synchronous implementation of alkene isomerization and enantioselective C(sp³)-C(sp³) bond formation. Regression analysis of catalyst structure-activity relationships accelerates the rational ligand modification through modular regulation. This reaction has several advantages for synthesizing chiral dialkyl carbinols and their ether derivatives, including the broad substrate scope, good functional group tolerance, excellent regioselectivity (>20:1 regioisomeric ratio), and high enantioselectivity (up to 95% enantiomeric excess).

Protein-supported transition metal catalysts: Preparation, catalytic applications, and prospects

The immobilization of transition metal catalysts onto supports enables their easier recycling and improves catalytic performance. Protein supports not only support and stabilize transition metal catalysts but also enable the incorporation of biocompatibility and enzymatic catalysis into these catalysts. Consequently, the engineering of protein-supported transition metal catalysts (PTMCs) has emerged as an effective approach to improving their catalytic performance and widening their catalytic applications. Here, we review the recent development of the preparation and applications of PTMCs. The preparation of PTMCs will be summarized and discussed in terms of the types of protein supports, including proteins, protein assemblies, protein-polymer conjugates, and cross-linked proteins. Then, their catalytic applications including organic synthesis, photocatalysis, polymerization, and biomedicine, will be surveyed and compared. Meanwhile, the established catalytic structures-function relationships will be summarized. Lastly, the remaining issues and prospects will be discussed. By surveying a wide range of PTMCs, we believe that this review will attract a broad readership and stimulate the development of PTMCs.

The Asymmetric Buchwald-Hartwig Amination Reaction

Over the past few decades, the Buchwald-Hartwig reaction has emerged as a powerful tool for forging C-N bonds, and has been vital to the pharmaceuticals, materials, and catalysis fields. However, asymmetric Buchwald-Hartwig amination reactions for constructing centered chirality, planar chirality, and axial chirality remain in their infancy owing to limited substrate scope and laggard ligand design. The recent surge in interest in the synthesis of C-N/N-N atropisomers, has witnessed a renaissance in asymmetric Buchwald-Hartwig amination chemistry as the first practical protocol for the preparation of C-N atropisomers. This review highlights reported asymmetric Buchwald-Hartwig amination protocols and provides a brief overview of their chemical practicality.

Preparation of Coupling Catalyst HamZIF-90@Pd@CALB with Tunable Hollow Structure for Efficient Dynamic Kinetic Resolution of 1-Phenylethylamine

Chiral amines are essential components for many pharmaceuticals and agrochemicals. However, the difficulty in obtaining enantiomerically pure amines limits their application. In this study, hollow amorphous ZIF-90 (HamZIF-90) materials were prepared by template engraving, and chemical-enzyme coupling catalysts (HamZIF-90@Pd@CALB) were constructed for the chiral resolution of 1-phenylethylamine. Different from conventional materials, HamZIF-90 had tunable hollow structures by altering its central node zinc ion concentrations, and the embedded hydrogel template gave it more pore structures, which facilitated the loading of enzyme molecules and Pd nanoparticles (NPs). The establishment of the coupling catalysts shortened the mass transfer distance of the reactant molecules between the metal nanoparticles and the enzyme catalyst in the dynamic kinetic resolution (DKR) reaction, resulting in 98% conversion of 1-phenylethylamine and 93% selectivity of Sel.R-amide. The proposal of this idea provided a good idea for future tailor-made MOFs loaded with chemical and enzyme coupled catalyst.

Expanding the Synthetic Toolbox through Metal-Enzyme Cascade Reactions

The combination of metal-, photo-, enzyme-, and/or organocatalysis provides multiple synthetic solutions, especially when the creation of chiral centers is involved. Historically, enzymes and transition metal species have been exploited simultaneously through dynamic kinetic resolutions of racemates. However, more recently, linear cascades have appeared as elegant solutions for the preparation of valuable organic molecules combining multiple bioprocesses and metal-catalyzed transformations. Many advantages are derived from this symbiosis, although there are still bottlenecks to be addressed including the successful coexistence of both catalyst types, the need for compatible reaction media and mild conditions, or the minimization of cross-reactivities. Therefore, solutions are here also provided by means of catalyst coimmobilization, compartmentalization strategies, flow chemistry, etc. A comprehensive review is presented focusing on the period 2015 to early 2022, which has been divided into two main sections that comprise first the use of metals and enzymes as independent catalysts but working in an orchestral or sequential manner, and later their application as bionanohybrid materials through their coimmobilization in adequate supports. Each part has been classified into different subheadings, the first part based on the reaction catalyzed by the metal catalyst, while the development of nonasymmetric or stereoselective processes was considered for the bionanohybrid section.

Chemoenzymatic Protocol for the Synthesis of Enantiopure β-Blocker (S)-Bisoprolol

The β-blocker (S)-bisoprolol hemifumarate has been synthesised in 96% enantiomeric excess with 19% total yield in a six-step synthesis. A transesterification reaction of the racemic chlorohydrin 1-chloro-3-(4-((2-isopropoxyethoxy)methyl)phenoxy)propan-2-ol catalysed by lipase B from Candida antarctica resulted in the R-chlorohydrin in high enantiomeric purity. Reaction of this building block with isopropylamine in methanol gave (S)-bisoprolol, and further reaction with fumaric acid gave (S)-bisoprolol fumarate in 96% ee. Specific rotation value confirmed the absolute configuration of the enantiopure drug.

One-Pot Biocatalytic Synthesis of Primary, Secondary, and Tertiary Amines with Two Stereocenters from α,β-Unsaturated Ketones Using Alkyl-Ammonium Formate

The efficient asymmetric catalytic synthesis of amines containing more than one stereogenic center is a current challenge. Here, we present a biocatalytic cascade that combines ene-reductases (EReds) with imine reductases/reductive aminases (IReds/RedAms) to enable the conversion of α,β-unsaturated ketones into primary, secondary, and tertiary amines containing two stereogenic centers in very high chemical purity (up to >99%), a diastereomeric ratio, and an enantiomeric ratio (up to >99.8:<0.2). Compared with previously reported strategies, our strategy could synthesize two, three, or even all four of the possible stereoisomers of the amine products while precluding the formation of side-products. Furthermore, ammonium or alkylammonium formate buffer could be used as the only additional reagent since it acted both as an amine donor and as a source of reducing equivalents. This was achieved through the implementation of an NADP-dependent formate dehydrogenase (FDH) for the in situ recycling of the NADPH coenzyme, thus leading to increased atom economy for this biocatalytic transformation. Finally, this dual-enzyme ERed/IRed cascade also exhibits a complementarity with the recently reported EneIRED enzymes for the synthesis of cyclic six-membered ring amines. The ERed/IRed method yielded trans-1,2 and cis-1,3 substituted cyclohexylamines in high optical purities, whereas the EneIRED method was reported to yield one cis-1,2 and one trans-1,3 enantiomer. As a proof of concept, when 3-methylcyclohex-2-en-1-one was converted into secondary and tertiary chiral amines with different amine donors, we could obtain all the four possible stereoisomer products. This result exemplifies the versatility of this method and its potential for future wider utilization in asymmetric synthesis by expanding the toolbox of currently available dehydrogenases via enzyme engineering and discovery.

Green Dynamic Kinetic Resolution—Stereoselective Acylation of Secondary Alcohols by Enzyme-Assisted Ruthenium Complexes

Dynamic kinetic resolution allows for the synthesis of enantiomerically pure asymmetric alcohols. Cyclopentadienyl-derived ruthenium catalysts were immobilized with an ionic liquid, [BMIM][NTf2], on multiwall carbon nanotubes and used for the racemization of chiral secondary alcohols. This successful approach was combined with the enantioselective enzymatic acylation of secondary alcohols (1-phenylethanol and 1-(1-naphthyl)ethanol) using Novozyme® 435. The resulting catalytic system of the ruthenium racemization catalysts and enzymatic acylation led to chiral esters being obtained by dynamic kinetic resolution. The immobilized catalytic system in the ionic liquid gave the same activity of >96% yield within 6 h and a selectivity of 99% enantiomeric excess as the homogeneous system, while allowing for the convenient separation of the desired products from the catalyst. Additionally, the process can be regarded as green, since the efficient reuse of the catalytic system was demonstrated.

Lipase-Catalysed Enzymatic Kinetic Resolution of Aromatic Morita-Baylis-Hillman Derivatives by Hydrolysis and Transesterification

Acylated Morita-Baylis-Hillman (MBH) adducts were synthesised and subjected to enzymatic kinetic resolution (EKR) by hydrolysis employing various lipase enzymes: from P. fluorescens, P. cepacia (PCL), C. antarctica A (CAL-A), C. antarctica B (CAL-B) and Novozyme 435. In a number of instances enantiopure Morita-Baylis-Hillman acetates or butyrates and their corresponding hydrolysed MBH adducts were obtained with ee values of >90 %, at ca. 50 % conversion, corresponding to enantiomeric ratio (E) values of >200. Enantioselective transesterification reactions on MBH adducts was achieved using acyl anhydrides in THF or the greener organic solvent 2-MeTHF in the presence of CAL-A. This is the first report of successful lipase-catalysed EKR of aromatic MBH adducts by transesterification in organic medium.

Deracemization of racemic alcohols combining photooxidation and biocatalytic reduction

We described a cascade reaction for deracemization of racemic alcohols combining photooxidation and enzymatic reduction under mild conditions without the isolation of intermediate ketones. Using different ketoreductases, a variety of racemic alcohols can be successfully converted into (R)- or (S)-enantiomers in high yields (up to 95%) and stereoselectivity (up to 99%).

Cooperative chemoenzymatic synthesis of N-heterocycles via synergizing bio- with organocatalysis

Inspired by Nature's ingenuity, considerable progress has been made in recent years to develop chemoenzymatic processes by the integration of environmentally friendly feature of biocatalysis with versatile reactivity of chemocatalysis. However, the current types of chemoenzymatic processes are relatively few and mostly rely on metal catalysts. Here, we report a previously unexplored cooperative chemoenzymatic system for the synthesis of N-heterocycles. Starting from alcohols and amines, benzimidazole, pyrazine, quinazoline, indole, and quinoline can be obtained in excellent yields in water with O₂ as the terminal oxidant. Synthetic bridged flavin analog is served as a bifunctional organocatalyst for the regeneration of cofactor nicotinamide adenine dinucleotide in the bioprocess and oxidative cyclodehydrogenation in the chemoprocess. Compared to the classical acceptorless dehydrogenative coupling strategy, being metal and base free, requiring only water as solvent, and not needing atmosphere protection were observed for the present method, exhibiting a favorable green and sustainable alternative.

Green Chemo-Enzymatic Protocols for the Synthesis of Enantiopure β-Blockers (S)-Esmolol and (S)-Penbutolol

The β-blocker (S)-esmolol, has been synthesized in 97% enantiomeric excess and 26% total yield in a four-step synthesis, with a transesterification step of the racemic chlorohydrin methyl 3-(4-(3-chloro-2-hydroxypropoxy)phenyl)propanoate, catalysed by lipase B from Candida antarctica from Syncozymes, Shanghai, China. The β-blocker (S)-penbutolol, has been synthesized in 99% enantiomeric excess and in 22% total yield. The transesterification step of the racemic chlorohydrin 1-chloro-3-(2-cyclopentylphenoxy)propan-2-ol was catalyzed by the same lipase as used for the esmolol building block. We have used different bases for the deprotonation step of the starting phenols, and vinyl butanoate as the acyl donor in the transesterification reactions. The reaction times for the kinetic resolution steps catalysed by the lipase varied from 23 to 48 h, and were run at 30–38 °C. Specific rotation values confirmed the absolute configuration of the enantiopure drugs, however, an earlier report of the specific rotation value of (S)-esmolol is not consistent with our measured specific rotation values, and we here claim that our data are correct. Compared to the previously reported syntheses of these two enantiopure drugs, we have replaced toluene or dichloromethane with acetonitrile, and replaced the flammable acetyl chloride with lithium chloride. We have also reduced the amount of epichlorohydrin and bases, and identified dimeric byproducts in order to obtain higher yields.

Cascade Catalysis Through Bifunctional Lipase Metal Biohybrids for the Synthesis of Enantioenriched O-Heterocycles from Allenes

Lipase/metal nanobiohybrids, generated by growth of silver or gold nanoparticles on protein matrixes are used as highly effective dual-activity heterogeneous catalysts for the production of enantiomerically enriched 2,5-dihydrofurans from allenic acetates in a one-pot cascade process combining a lipase-mediated hydrolytic kinetic resolution with a metal-catalyzed allene cycloisomerization. Incorporating a novel strategy based on enzyme-polymer bioconjugates in the nanobiohybrid preparation enables excellent conversions in the process. Candida antarctica lipase B (CALB) in combination with a dextran-based polymer modifier (DexAsp) proved to be most efficient when merged with silver nanoparticles. A range of hybrid materials were produced, combining Ag or Au metals with Thermomyces lanuginosus lipase (TLL) or CALB and its DexAsp or polyethyleneimine polymer bioconjugates. The wider applicability of the biohybrids is demonstrated by their use in allenic alcohol cyclizations, where a variety of dihydrofurans are obtained using a CALB/gold nanomaterial. These results underline the potential of the nanobiohybrid catalysis as promising approach to intricate one-pot synthetic strategies.

Tri-templating Synthesis of Multilevel Mesoporous Silica Microspheres with a Complex Interior Structure for Efficient CO2 Capture and Catalysis

Multilevel porous architectures with microscopic shape control and tailor-made complex structures offer great potential for various innovative applications, but their elaborate design and synthesis have remained a scientific and technological challenge. Herein, we report a simple and effective tri-templating method, in which microscale Pickering droplets, nanoscale polystyrene colloids (PS), and molecular cetyltrimethylammonium chloride micelles are synchronously employed, for the fabrication of such micro-nanohierarchical mesoporous silica microspheres. In this protocol, Pickering droplet-directed interfacial sol-gel growth and its spatially confined surfactant assembly-directed sol-gel coating on PS suspensions are coupled together, enabling the successful formation of structured mesoporous silica that consists of numerous nanocompartments enclosed by a permeable shell. By varying the quantity of PS colloidal templates, rational regulation of the complex interior structure is achieved. Also, ascribed to the multilevel arrangement, this peculiar architecture not only shows desirable fast mass transport of external molecules but also possesses easy handling ability. After loading with tetraethylenepentamine or enzyme species, the yielded microspherical CO₂ sorbents or immobilized biocatalysts, respectively, exhibit enhanced CO₂ capture capacity and enzymatic catalysis efficiency. Notably, taking advantage of their microscopic characteristics, the immobilized biocatalysts could be ideally packed in a fixed-bed reactor for long-term continuous-flow enzymatic reactions. This tri-templating strategy provides a new synthetic route to access other multilevel microscopic materials with fascinating complex structures and paves a way to promote their practical applications.

Chemoenzymatic conversion of glycerol to lactic acid and glycolic acid

Catalytic valorization of raw glycerol derived from biodiesel into high-value chemicals has attracted great attention. Here, we report chemoenzymatic cascade reactions that convert glycerol to lactic acid and glycolic acid. In the enzymatic step, a coenzyme recycling system was developed to convert glycerol into 1,3-dihydroxyacetone (DHA) with a yield of 92.3% in potassium phosphate buffer (300 mM, pH 7.1) containing 100 mM glycerol, 2 mM NAD+, 242 U/mL glycerol dehydrogenase-GldA and NADH oxidase-SpNoxK184R at 30 °C. Subsequently, NaOH or NaClO2 catalyzes the formation of lactic acid and glycolic acid from DHA. The high yield of lactic acid (72.3%) and glycolic acid (78.2%) verify the benefit of the chemoenzymatic approaches.

Ni-Catalyzed Enantioselective Dialkyl Carbinol Synthesis via Decarboxylative Cross-Coupling: Development, Scope, and Applications

The first enantioselective decarboxylative Negishi-type alkylations of α-oxy carboxylic acids are reported via the intermediacy of redox-active esters (RAEs). This transformation enables a radical-based retrosynthesis of seemingly trivial enantiopure dialkyl carbinols. This article includes a discussion of the history of such couplings, the retrosynthetic ramifications of such a coupling, the development of general conditions, and an extensive series of applications that vividly demonstrate how it can simplify synthesis.