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Enantioselective reduction of cyclobutenones to optically active cyclobutanones has been achieved by using whole‐cell overexpressing Seqenzym ene‐reductases (EREDs). By using these enzymes, trans‐cyclobutanones were isolated in good yields and with enantiomeric excesses up to 99%. [ABSTRACT FROM AUTHOR]

A series of functionalized α-chiral phosphonates was obtained by enzymatic reduction of the corresponding β-activated vinylphosphonate derivatives employing several ene-reductases of the Old Yellow Enzyme family as biocatalysts. The insufficient activation of the phosphonate group alone was compensated by introduction of an electron-withdrawing group at the β-position, which resulted in high levels of conversion (up to >99%). All active enzymes consistently furnished ( R)-configurated products with exquisite stereoselectivity, thereby providing a stereo-complementary approach to current asymmetric hydrogenation protocols on similar compounds. Preparative-scale syntheses performed in aqueous buffer using formate/formate dehydrogenase for recycling of the nicotinamide cofactor granted access to β-keto-, cyano- and ester phosphonates from the ( E)-isomers of α,β-unsaturated phosphonates in up to 72% isolated yield and >99% ee. [ABSTRACT FROM AUTHOR]

In contrast to the widely studied asymmetric bioreduction of α,β-unsaturated carboxylic acid esters catalyzed by ene-reductases, the reaction applied to lactones remains unexplored. A broad set of ene-reductases was found to reduce various α-, β- and γ-substituted α,β-unsaturated butyrolactones to yield the corresponding saturated non-racemic lactones. Substitution patterns greatly influenced activities and stereoselectivities and lactone products were obtained in moderate to excellent yields; importantly, enzyme-based stereocontrol allowed access to both enantiomers in up to >99% ee. Chiral recognition of a distant γ-center led to kinetic resolution with remarkable enantioselectivities (E values up to 49). An unprecedented case of dynamic kinetic resolution was observed with 3-methyl-5-phenylfuran-2(5 H)-one, whereby spontaneous racemization of the substrate furnished the product in up to 73% conversion and >99% ee and 96% de. [ABSTRACT FROM AUTHOR]

Ene reductases (ERs) are attractive biocatalysts in terms of their high enantioselectivity and expanded substrate scope. Recent works have proved that synthetic nicotinamide coenzyme biomimetics (NCBs) can be used as easily accessible alternatives to natural cofactors in ER‐catalyzed reactions. However, the structure‐reactivity relationships between NCBs and ERs and influence factors are still poorly understood. In this study, a series of C‐5 methyl modified NCBs were synthesized and tested in the PETNR‐catalyzed asymmetric reductions. The physicochemical properties of these NCBs including electrochemical properties, stability, and kinetic behavior were studied in detail. The results showed that hydrophobic interaction caused by the introduced methyl group contributed to the stabilization of binding conformation in enzyme active site, resulting in comparable catalytic activity with that of NADPH. Molecular dynamics and steered molecular dynamics simulations were further performed to explain the binding mechanism between PETNR and NCBs, which revealed that stable catalytic conformation, appropriate donor‐acceptor distance and angle, as well as free dissociation energy are important factors affecting the activity of NCBs. [ABSTRACT FROM AUTHOR]

γ‐Amino esters and γ‐lactams containing α,γ‐stereogenic centers are widely used as chiral intermediates in various bioactive compounds, while their efficient synthesis remains a challenge. Herein, an enzymatic cascade reaction involving an ene reductase (ERED) and an imine reductase (IRED) for accessing to α,γ‐stereospecific γ‐amino esters and γ‐lactams from α,β‐unsaturated γ‐ketoesters has been developed. 21 EREDs and 13 IREDs have been identified with high activity and stereoselectivity toward various α,β‐unsaturated γ‐ketoesters and the corresponding chiral γ‐ketoesters, respectively. By employing suitable ERED and IRED, (1S,3S), (1S,3R), (1R,3S), and (1R,3R) stereoisomers of methyl 3‐(cyclopropyl amino) cyclohexane‐1‐carboxylate were obtained as a single stereoisomer in 63–72% yield, and (3R,5R)‐ and (3R,5S)‐1‐cyclopropyl‐3,5‐dimethylpyrrolidin‐2‐one and 1‐cyclopropyl‐3,5‐dipropylpyrrolidin‐2‐one were also prepared as a single stereoisomer in 60–65% yields. This study establishes an environmentally friendly enzymatic route for the synthesis of γ‐amino esters and γ‐lactams containing α,γ‐stereogenic centers. [ABSTRACT FROM AUTHOR]

Ene reductases (EREDs) have great potential as oxidation biocatalysts, as demonstrated by their efficient conversion of a number of tetralones to the corresponding naphthols. Of 96 enzymes tested, 57 were able to produce 2-naphthol in this way. Further tests with substituted tetralones revealed typically high conversions up to >99%. The reactions were performed under mild conditions in aqueous buffer with only co-solvent, biocatalyst and oxidation substrate required for conversion. Production of a methoxy-substituted naphthol was also successfully performed on a gram scale, with 91% yield. This methodology provides a new avenue to produce substituted naphthols as valuable building blocks, with the possibility to extend the approach to the production of phenols also being demonstrated. [ABSTRACT FROM AUTHOR]

The chemoselective hydrogenation of alkenes in the presence of alkynes is a very challenging transformation to achieve with traditional chemical methods. The development of an effective procedure to perform this transformation would enrich the tool‐kit available to organic chemists for the development of useful synthetic routes, and the creation of novel structural motifs. The reduction of activated alkene bonds by ene‐reductases (ERs) is completely chemoselective, because of the mechanism of the reaction. Thus, we investigated the use of ERs belonging to the Old Yellow Enzyme family for the reduction of α,β‐unsaturated aldehydes with a conjugated C≡C triple bond at the γ position. This reaction was exploited as the key step for the development of an effective homologation route to convert aryl and alkyl substituted propynals and butynones into 4‐alkynals and 4‐alkynols, avoiding some troublesome or hazardous steps of known synthetic routes. [ABSTRACT FROM AUTHOR]

The asymmetric reduction of alkenes is a widely used transformation in industry. Ene reductases (ERs) are (βα)8‐barrel folded enzymes capable of catalyzing this hydrogenation reaction. At the expense of nicotinamide coenzymes, ERs can reduce a wide range of electron‐deficient alkenes in an anti‐specific manner and with high regio‐ and stereoselectivities. However, a cost‐effective industrial use of these enzymes is hampered, since most ERs prefer nicotinamide adenine dinucleotide phosphate (NADPH) to the more stable and less expensive non‐phosphorylated nicotinamide adenine dinucleotide (NADH) as coenzyme. Here, we demonstrate an approach to both modify the biocatalysts coenzyme selectivity and strongly increase the activity and affinity with NADH. By swapping loop regions of the cyanobacterial NostocER1 for the corresponding regions of two NADH‐favoring ERs, a strong alteration of the biocatalyst's coenzyme binding was achieved. This made possible a transfer of the respective donor‐ER kinetic parameters to NostocER1. Additionally, outperformance of both donors in terms of activity was achieved through combinatorial swapping of loops of both species. These findings demonstrate the high potential of loop swapping as protein engineering approach to selectively optimize the coenzyme binding of ERs. [ABSTRACT FROM AUTHOR]

Ene reductases from the Old Yellow Enzyme family are versatile biocatalysts useful for the synthesis of optically active compounds. One disadvantage of biocatalysts when compared to competing catalysts in chemical syntheses is that often only one stereoisomer of the product is available. Another drawback can be the lack of activity in certain enzyme-substrate combinations. We were able to approach both of these challenges rationally in the case of the enzymatic synthesis of methyl 3-hydroxy-2-methylpropanoate (commonly denoted as the Roche ester) and derivatives thereof using the ene reductase YqjM. By a highly efficient, concept-based approach of designing mutant variants of YqjM and engineering substrates we could alter both the rate constant and the enantioselectivity of the reaction. Preparative scale reactions have been performed with successful mutants. In addition, the iterative modification of the substrate gave experiment-based insights into the binding mode of the Roche ester precursor and its derivatives. [ABSTRACT FROM AUTHOR]

The ene-reductase-mediated reduction of the carbon-carbon double bond of some alkyl 2-substituted butenedioates was investigated. The stereochemical outcome of the reaction was found to be influenced by steric effects. Ethyl and butyl citraconates were converted into the corresponding alkyl ( R)-2-methylsuccinates with excellent enantioselectivity, whereas ethyl and butyl mesaconates were completely unreactive. Methyl 2-substituted fumarates were reduced to enantiomerically enriched methyl ( S)-2-substituted succinates, whereas the ( Z)-stereoisomers were left unreacted by ene-reductases. Labelling experiments were performed to investigate the mechanism of these bioreductions and explain their stereochemical outcome. [ABSTRACT FROM AUTHOR]

Ene‐reductase (ERED)‐catalyzed asymmetric reduction of α,β‐unsaturated ketones is an attractive method in organic synthesis. Through the discovery and further structure‐guided protein engineering of BsER, an ERED from Bacillus subtilis, the selective bio‐reduction of the well‐known building blocks Hajos‐Parrish ketone (HPK, 1 a) and Wieland‐Miescher ketone (WMK, 1 b) was achieved in this study. The optically pure (R)‐HPK ((R)‐1 a) and (R)‐WMK ((R)‐1 b) with corresponding >99% and 98% enantiomeric excess (ee) values were obtained by kinetic resolution of the racemic substrates. To the best of our knowledge, this is the first example of ERED mediated kinetic resolution of rac‐HPK and rac‐WMK. In addition, the reduction products cis‐7a‐methylhexahydro‐1H‐indene‐1,5(4H)‐dione (cis‐2 a) and cis‐8a‐methylhexahydronaphtha‐ lene‐1,6(2H,5H)‐dione (cis‐2 b) with high diastereomeric ratios (dr) were also obtained. We also developed four routes of biocatalytic cascade reduction involving BsER and ketoreductases (KREDs). Using optimized ERED‐KRED and KRED‐ERED cascades, (S)‐HPK ((S)‐1 a) and (S)‐WMK ((S)‐1 b) could be reduced stepwise, yielding the bioactive products all with >91% purity. This study presents a biocatalytic strategy for the kinetic resolution and cascade reduction of HPK and WMK (1 a and 1 b). [ABSTRACT FROM AUTHOR]

Enzyme discovery for use in the manufacture of chemicals, requiring high stereoselectivities, continues to be an important avenue of research. Here, a sequence directed metagenomics approach is described to identify short chain carbonyl reductases. PCR from a metagenomic template generated 37 enzymes, with an average 25% sequence identity, twelve of which showed interesting activities in initial screens. Six of the most productive enzymes were then tested against a panel of 21 substrates, including bulkier substrates that have been noted as challenging in biocatalytic reductions. Two enzymes were selected for further studies with the Wieland Miescher ketone. Notably, enzyme SDR‐17, when co‐expressed with a co‐factor recycling system produced the anti‐(4aR,5S) isomer in excellent isolated yields of 89% and 99% e.e. These results demonstrate the viability of a sequence directed metagenomics approach for the identification of multiple homologous sequences with low similarity, that can yield highly stereoselective enzymes with applicability in industrial biocatalysis. [ABSTRACT FROM AUTHOR]

No Abstract [ABSTRACT FROM AUTHOR]

Abstract: A chemo‐enzymatic catalytic system, comprised of Bobbitt's salt and laccase from Trametes versicolor, allowed the [1,3]‐oxidative rearrangement of endocyclic allylic tertiary alcohols into the corresponding enones under an Oxygen atmosphere in aqueous media. The yields were in most cases quantitative, especially for the cyclopent‐2‐en‐1‐ol or the cyclohex‐2‐en‐1‐ol substrates without an electron withdrawing group (EWG) on the side chain. Transpositions of macrocyclic alkenols or tertiary alcohols bearing an EWG on the side chain were instead carried out in acetonitrile by using an immobilized laccase preparation. Dehydro‐Jasmone®, dehydro‐Hedione®, dehydro‐Muscone and other fragrance precursors were directly prepared with this procedure, while a synthetic route was developed to easily transform a cyclopentenone derivative into trans‐Magnolione® and dehydro‐Magnolione®. The rearrangement of exocyclic allylic alcohols was tested as well, and a dynamic kinetic resolution was observed: α,β‐unsaturated ketones with (E)‐configuration and a high diastereomeric excess were synthesized. Finally, the 2,2,6,6‐tetramethyl‐1‐piperidinium tetrafluoroborate (TEMPO+BF4−)/laccase catalysed oxidative rearrangement was combined with the ene‐reductase/alcohol dehydrogenase cascade process in a one‐pot three‐step synthesis of cis or trans 3‐methylcyclohexan‐1‐ol, in both cases with a high optical purity. [ABSTRACT FROM AUTHOR]

Abstract: Over the last decades biocatalysis has emerged as an indispensable and versatile tool for the asymmetric synthesis of active pharmaceutical ingredients (APIs). In this context, especially transaminases (TAs) have been successfully used for the preparation of numerous α‐chiral, optically pure amines, serving as important building blocks for APIs. Here we elaborate on the development of transaminases recognizing the α‐chiral centre adjacent to an aldehyde moiety with aliphatic residues, opening up concepts for novel synthetic routes to the antiepileptic drugs Brivaracetam and Pregabalin. The transformation proceeded via dynamic kinetic resolution (DKR) based on the bio‐induced racemisation of the aldehyde enantiomers, enabling the amination of the racemic substrates with quantitative conversions. Medium, substrate as well as enzyme engineering gave access to both (R)‐ and (S)‐enantiomers of the amine precursors of the stereocomplementary drugs in high optical purity, representing a short route to mentioned APIs. [ABSTRACT FROM AUTHOR]

Multi-step processes catalysed by several catalysts working concurrently have been developed in nature, thus improving reaction efficiency. The quest for novel and improved catalytic systems has led to the development of biocatalytic and later to organocatalytic procedures as very valuable tools in asymmetric synthesis while using mild reaction conditions in the absence of metal catalysts. As a timeless challenge, chemists are facing the need for process designs in which different sorts of catalysts can operate successfully in a one-pot concurrent fashion. Likewise, such designs bring about the best of each catalyst and, in certain cases, enable us to improve problematic issues, such as reactivity, selectivity, solubility, inhibition, etc. Specifically, to combine these two types of catalysts in one-pot, achieving high yields and selectivity, is a fascinating aspect of catalysis. This review covers representative advances in this field, in particular those in which biocatalysts and organocatalysts are employed either in sequential reactions or in simultaneous processes. [ABSTRACT FROM AUTHOR]

The Trp 116 mutants of Old Yellow Enzyme 1 that catalyse the reduction of ( Z)-β-aryl-β-cyanoacrylates give the opposite enantioselectivity according to the nature of the amino acid in position 116. Small amino acids (e.g., alanine) make the substrate bind to the enzyme′s active site in a 'classical' orientation, affording the ( S)-enantiomer of the reduced product. When the size of the amino acid increases (e.g., leucine), a 'flipped' binding mode is adopted by the substrate, which is converted into the corresponding ( R)-derivative. With bulky amino acids (e.g., tryptophan in the wild-type) the reduction does not occur. The enantiomerically enriched cyanopropanoates thus prepared can be converted into the corresponding ( S)- and ( R)-β-aryl-γ-lactams, precursors of inhibitory neurotransmitters belonging to the class of γ-aminobutyric acids, by a simple functional group interconversion in a sequential one-pot procedure. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue including biocatalysis, imine reductases and dynamic kinetic resolutions.