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Chiral heterocyclic compounds are privileged structures in medicinal chemistry. Here, the authors report an in silico strategy for the enzymatic synthesis of pharmaceutically significant chiral N- and O-heterocycles via Baldwin cyclization of hydroxy- and amino-substituted epoxides and oxetanes using epoxide hydrolase mutants.

Connecting conformational dynamics and epistasis has so far been limited to a few proteins and a single fitness trait. Here, the authors provide evidence of positive epistasis on multiple catalytic traits in the evolution and dynamics of engineered cytochrome P450 monooxygenase, offering insights for in silico protein design.

Candida antarctica lipase B (CALB) is a serine lipase. Here, the authors use directed evolution to exchange serine with cysteine in the catalytic triad of the enzyme, thereby obtaining a highly active CALB variant that — unlike the wild type — accommodates bulky substrates.

An intriguing advance in the rational protein engineering of a newly identified glycosyltransferase from Siraitia grosvenorii (UGT74AC2) has been accomplished by Zhoutong Sun, Yuanxia Sun and coworkers for the targeted pharmaceutically significant glucosylation of the polyhydroxy substrate silybin. Using an advanced version of Focused Rational Iterative Site-specific Mutagenesis (FRISM), they were able to evolve mutants that allow the formation of the 3-OH, 7-OH and the 3,7-O-diglycoside products with 94%, > 99% and > 99% regioselectivity, respectively. This can be viewed as a breakthrough because the wildtype UGT74AC2 delivers a difficult to separate mixture of products in a ratio of 22%:39%:39%. Even N- and S-glucosylations were achieved, a likewise unusual accomplishment.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The majority of enzymatic Kemp elimination reactions proceed via a well-established acid-base mechanism. Here, the authors show that cytochrome P450 is able to metabolize the leflunomide drug via a redox Kemp elimination, offering new insights into enzyme catalysis.

Arbutin (also called β-arbutin) is a natural product occurring in the leaves of a variety of different plants, the bearberries of the Ericaceae and Saxifragaceae families being prominent examples. It is a β-glucoside derived from hydroquinone (HQ; 1,4-dihydroxybenzene). Arbutin has been identified in traditional Chinese folk medicines as having, inter alia, anti-microbial, anti-oxidant, and anti-inflammatory properties that useful in the treatment of different ailments including urinary diseases. Today, it is also used worldwide for the treatment of skin ailments by way of depigmenting, which means that arbutin is a component of many products in the cosmetics and healthcare industries. It is also relevant in the food industry. Hundreds of publications have appeared describing the isolation, structure determination, toxicology, synthesis, and biological properties of arbutin as well as the molecular mechanism of melanogenesis (tyrosinase inhibition). This review covers the most important aspects with special emphasis on the chemical and biocatalytic methods for the production of arbutin.

In the title compound, C16H14O, the cyclohexene ring has a half-chair conformation. The mean plane, calculated through all non-H atoms of the molecule, except for the central CH2 atoms of the cyclohexene ring, which deviate by 0.340 (3) and −0.369 (3) Å from this mean plane, has an r.m.s. deviation of 0.012 Å. In the crystal, there are C—H...π contacts present, resulting in the formation of zigzag chains propagating along the [010] direction.

The development of chiral catalysts for use in synthetic organic chemistry is traditionally associated with progress in asymmetric transition metal catalysis or organocatalysis. In addition to these options chemists have employed enzymes for a number of asymmetric transformations for a long time. However, limited substrate acceptance and insufficient enantioselectivity are the crucial factors which prevent the general exploitation of biocatalysis in organic chemistry. In order to solve this long-standing problem, we proposed some time ago the concept of directed evolution of enantioselective enzymes. This report constitutes a short overview of the principle involved, together with a description of the first examples and the illumination of the present and future challenges.

The electrocatalytic activity of Pt-nanoparticles used in fuel cells increases by 34% upon going from the usual Pt/Vulcan XC72 to support systems such as Pt/Printex XE2 which have a relatively rough surface structure.

A chiral phosphoric acid diester, specifically the BINOL-based derivative, has been used for the first time in Rh-, Ir-, and Pd-catalyzed hydrogenation of olefins and imines, giving ee-values of up to 85%.

The first step in applying the recently proposed concept concerning the application of directed evolution to the creation of selective hybrid catalysts is described, specifically the covalent attachment of Mn-salen moieties and of Cu-, Pd-, and Rh-complexes of dipyridine derivatives as well as the implantation of a diphosphine moiety in a protein, future steps being cycles of mutagenesis/screening.

The simultaneous use of a biocatalyst (lipase Candida antarctica) and a transition-metal catalyst (palladium) makes the dynamic kinetic resolution of racemic phenylethylamine possible, conversion to the enantiomerically pure N-acylated form being 75–77% (ee = 99%).

Borylated zirconocenes of the type (L2B–C5H4)2ZrCl2 and (L2B–C5H4)(C5H5)ZrCl2 are readily available in two steps. In the polymerization of ethylene and propylene in the presence of AlEt3 or methylalumoxan (MAO), these zirconocenes are more active than the unsubstituted reagent Cp2ZrCl2.

The lipase Candida antarctica catalyzes the enantioselective acetylation of chiral primary amines, kinetic resolution leading to an enantiomeric excess (ee) of 90–98%.

The [Ni(cod)2]/Ph2P(CH2)4PPh2-catalyzed reaction of hex-3-yne with CO2 under supercritical conditions affords tetraethylpyrone

The previously reported concept of using mixtures of monodentate ligands in a combinatorial manner in order to influence enantio- or regioselectivity of transition metal catalyzed processes has been extended to include diastereoselectivity. Accordingly, 1,2- and 1,3-asymmetric induction in the Rh-catalyzed hydrogenation of a chiral allylic alcohol and a chiral homo-allylic alcohol has been studied by using mixtures of monodentate P-ligands. It was found that appropriate 1:1 mixtures of two different P-ligands enhance the degree of diastereoselectivity relative to the use of the respective pure ligands themselves. Here, as in the previous cases regarding enantio- or regioselectivity, this type of combinatorial catalysis leads to improved catalytic profiles without the need to prepare new ligands.

Chiral heterocyclic compounds are needed for important medicinal applications. We report an in silico strategy for the biocatalytic synthesis of chiral N- and O-heterocycles via Baldwin cyclization modes of hydroxy- and amino-substituted epoxides and oxetanes using the limonene epoxide hydrolase from Rhodococcus erythropolis. This enzyme normally catalyzes hydrolysis with formation of vicinal diols. Firstly, the required shutdown of the undesired natural water-mediated ring-opening is achieved by rational mutagenesis of the active site. In silico enzyme design is then continued with generation of the improved mutants. These variants prove to be versatile catalysts for preparing chiral N- and O-heterocycles with up to 99% conversion, and enantiomeric ratios up to 99:1. Crystal structural data and computational modeling reveal that Baldwin-type cyclizations, catalyzed by the reprogrammed enzyme, are enabled by reshaping the active-site environment that directs the distal RHN and HO-substituents to be intramolecular nucleophiles. Chiral heterocyclic compounds are privileged structures in medicinal chemistry. Here, the authors report an in silico strategy for the enzymatic synthesis of pharmaceutically significant chiral N- and O-heterocycles via Baldwin cyclization of hydroxy- and amino-substituted epoxides and oxetanes using epoxide hydrolase mutants. [ABSTRACT FROM AUTHOR]

Alcohol dehydrogenases (ADHs) have become important catalysts for stereoselective oxidation and reduction reactions of alcohols, aldehydes and ketones. The aim of this contribution is to provide the reader with a timely update on the state-of-the-art of ADHcatalysis. Mechanistic basics are presented together with practical information about the use of ADHs. Current concepts of ADH engineering and ADH reactions are critically discussed. Finally, this contribution highlights some prominent examples and futurepointing concepts. [ABSTRACT FROM AUTHOR]

Engineering artificial enzymes with high activity and catalytic mechanism different from naturally occurring enzymes is a challenge in protein design. For example, many attempts have been made to obtain active hydrolases by introducing a Ser → Cys exchange at the respective catalytic triads, but this generally induced a breakdown of activity. We now report that this long-standing dogma no longer pertains, provided additional mutations are introduced by directed evolution. By employing Candida antarctica lipase B (CALB) as the model enzyme with the Ser-His-Asp catalytic triad, a highly active cysteine-lipase having a Cys-His-Asp catalytic triad and additional mutations W104V/A281Y/A282Y/V149G can be evolved, showing a 40-fold higher catalytic efficiency than wild-type CALB in the hydrolysis of 4-nitrophenyl benzoate, and tolerating bulky substrates. Crystal structures, kinetics, MD simulations and QM/MM calculations reveal dynamic features and explain all results, including the preference of a two-step mechanism involving the zwitterionic pair Cys105−/His224+ rather than a concerted process. Candida antarctica lipase B (CALB) is a serine lipase. Here, the authors use directed evolution to exchange serine with cysteine in the catalytic triad of the enzyme, thereby obtaining a highly active CALB variant that — unlike the wild type — accommodates bulky substrates. [ABSTRACT FROM AUTHOR]

In the title compound, C16H14O, the cyclohexene ring has a half-chair conformation. The mean plane, calculated through all non-H atoms of the molecule, except for the central CH2 atoms of the cyclohexene ring, which deviate by 0.340 (3) and -0.369 (3) Å from this mean plane, has an r.m.s. deviation of 0.012 Å. In the crystal, there are C--H⋯π contacts present, resulting in the formation of zigzag chains propagating along the [010] direction. [ABSTRACT FROM AUTHOR]

On Monday, November 6, 2006, the rector Prof. Dr. K. Osterwalder presented the Prelog Medal 2006 to Prof. Dr. Manfred T. Reetz, Max-Planck-Institut für Kohleforschung, Mülheim an der Ruhr, Germany. The title of the lecture that followed was 'Evolution in the Test-Tube as a Means to Create Selective Biocatalysts'.

Previously, Lipase A from Bacillus subtilis was subjected to in vitro directed evolution using iterative saturation mutagenesis, with randomization sites chosen on the basis of the highest B-factors available from the crystal structure of the wild-type (WT) enzyme. This provided mutants that, unlike WT enzyme, retained a large part of their activity after heating above 65°C and cooling down. Here, we subjected the three best mutants along with the WT enzyme to biophysical and biochemical characterization. Combining thermal inactivation profiles, circular dichroism, X-ray structure analyses and NMR experiments revealed that mutations of surface amino acid residues counteract the tendency of Lipase A to undergo precipitation under thermal stress. Reduced precipitation of the unfolding intermediates rather than increased conformational stability of the evolved mutants seems to be responsible for the activity retention. [ABSTRACT FROM AUTHOR]

Directed evolution has emerged as a powerful method for engineering essentially any catalytic parameter of enzymes for application in synthetic organic chemistry and biotechnology, including thermostability, substrate scope, and enantioselectivity. Enantioselectivity is especially crucial when applying biocatalysts to synthetic organic chemistry. This contribution focuses on recent methodology developments in laboratory evolution of stereoselective enzymes, hydrolases, and monooxygenases serving as the enzymes. Specifically, iterative saturation mutagenesis (ISM) has been developed as an unusually effective method to evolve enhanced or reversed enantioselectivity, broader substrate scope, and/or higher thermostability of enzymes. [ABSTRACT FROM AUTHOR]

Presents a table of contents of the "Canadian Journal of Chemistry."

A high-throughput method is described, where the enantioselectivity of approximately 10 000 catalysts or biocatalysts can be determined per day. The method is based on electrospray mass spectrometric techniques using an eight-channel multiplexed (MUX) sprayer system connected to a time-of-flight mass spectrometer. The inlet of the ion source is controlled by a stepping rotor that is continuously moving from one sprayer to the next with a recording time of 100 ms for each channel and a delay time of 50 ms, thus allowing a spectrum to be obtained from each channel every 1.2 s. One cycle, where eight samples are being sprayed in parallel, requires around 70 s, which allows a 96-well microtiter plate to be screened in 14 min. Integration of two pseudo-enantiomers (S)-glycidyl phenyl ether and (R)-D[sub 5] -glycidyl phenyl ether is necessary to quantify the enantiomeric excess (ee-value), where one enantiomer is isotopically labeled to allow easy identification of the mass spectrometric signals. Errors of ~2% for the ee-values indicate that in addition to the significant improvement in sample throughput this is also a precise method for high-throughput screening. This second-generation assay is useful for combinatorial enantioselective transition-metal catalysis and in the directed evolution of enantioselective enzymes.On décrit une méthode à grand débit à l'aide de laquelle on peut déterminer l'énantiosélectivité d'environ 10,000 catalyseurs ou biocatalyseurs par jour. La méthode est basée sur des techniques de spectrométrie de masse avec électronébulisation à l'aide d'un système de nébulisation multiplex à huit canaux relié à un spectromètre de masse à temps de vol. L'insertion dans la source ionique est contrôlée par un rotor variable qui se déplace continuellement d'un nébulisateur au suivant, avec un temps d'enregistrement de 100 ms pour chaque canal et un délai de 50 ms qui permet d'obtenir un spectre pour chaque canal toutes les 1,2 s. Un cycle, dans lequel on soumet huit échantillons à la nébulisation en parallèle, requiert 70 s; il est donc possible de traiter un bloc de 96 échantillons en 14 min. Quand un énantiomère est marqué d'un isotope, il est nécessaire d'introduire deux pseudo-énantiomères, l'oxyde de (S)-glycidyle et de phényle et l'oxyde de (R)-D[sub 5] -glycidyle et de phényle, pour identifier rapidement les signaux de spectrométrie de masse et pour quantifier les excès énantiomériques (valeur ee). Des erreurs d'environ 2% dans les valeurs ee indiquent que, en plus d'être une amélioration sensible au débit des échantillons, cette méthode s'avère aussi très précise pour une évaluation à grand débit. Cette méthode de deuxième génération est utile dans le domaine de la catalyse énantiosélective combinatoire par les métaux de transition et dans l'évolution orientée des enzymes énantiosélectifs.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The phenomenon of diastereotopic group recognition has been structurally documented for the first time. A diphenylphosphine-modified β-cyclodextrin having two diastereotopic phenyl groups in close vicinity to the inner cavity of this host was prepared. The crystal structure analysis reveals selective intramolecular complexation of one of the two diastereotopic phenyl groups.Key words: supramolecular chemistry, stereotopic group recognition, cyclodextrins, intramolecular complexation.Le phénomène de reconnaissance de groupement diastéréotopique a été structurellement demontré pour la première fois. Une β-cyclodextrine fonctionnalisée avec un groupement diphénylphosphine a été synthétisée. Les deux groupements phényle sont situés à proximité de la cavité de la cyclodextrine et la structure déterminée par rayons X fait apparaître une complexation sélective et intramoléculaire d'un des deux groupement phényle.Mots clés : chimie supramoléculaire, reconnaissance de groupement stéréotopique, cyclodextrines, complexation intramoléculaire. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

Nowadays, biocatalysts have received much more attention in chemistry regarding their potential to enable high efficiency, high yield, and eco-friendly processes for a myriad of applications. Nature's vast repository of catalysts has inspired synthetic chemists. Furthermore, the revolutionary technologies in bioengineering have provided the fast discovery and evolution of enzymes that empower chemical synthesis. This article attempts to deliver a comprehensive overview of the last two decades of investigation into enzymatic reactions and highlights the effective performance progress of bio-enzymes exploited in organic synthesis. Based on the types of enzymatic reactions and enzyme commission (E.C.) numbers, the enzymes discussed in the article are classified into oxidoreductases, transferases, hydrolases, and lyases. These applications should provide us with some insight into enzyme design strategies and molecular mechanisms. [ABSTRACT FROM AUTHOR]

Arbutin (also called β-arbutin) is a natural product occurring in the leaves of a variety of different plants, the bearberries of the Ericaceae and Saxifragaceae families being prominent examples. It is a β-glucoside derived from hydroquinone (HQ; 1,4-dihydroxybenzene). Arbutin has been identified in traditional Chinese folk medicines as having, inter alia, anti-microbial, anti-oxidant, and anti-inflammatory properties that useful in the treatment of different ailments including urinary diseases. Today, it is also used worldwide for the treatment of skin ailments by way of depigmenting, which means that arbutin is a component of many products in the cosmetics and healthcare industries. It is also relevant in the food industry. Hundreds of publications have appeared describing the isolation, structure determination, toxicology, synthesis, and biological properties of arbutin as well as the molecular mechanism of melanogenesis (tyrosinase inhibition). This review covers the most important aspects with special emphasis on the chemical and biocatalytic methods for the production of arbutin. [ABSTRACT FROM AUTHOR]

The title compound, C16H36N+·C6H7O3−, crystallizes with two independent anions and two independent cations in the asymmetric unit. Each anion adopts an s- trans conformation and forms O⋯H-C hydrogen bonds to the α-methyl­ene groups of four neighbouring tetra­butyl­ammonium cations, to create a three-dimensional hydrogen-bonded network. [ABSTRACT FROM AUTHOR]

Value-added utilization of biomass-derived 5-hydroxymethylfurfural (HMF) to produce useful derivatives is of great interest. In this work, extremely radiation resistant Deinococcus wulumuqiensis R12 was explored for the first time as a new robust biocatalyst for selective oxidation of HMF to 5-hydroxymethylfuroic acid (HMFCA). Its resting cells exhibited excellent catalytic performance in a broad range of pH and temperature values, and extremely high tolerance to HMF and the HMFCA product. An excellent yield of HMFCA (up to 90%) was achieved when the substrate concentration was set to 300 mM under the optimized reaction conditions. In addition, 511 mM of product was obtained within 20 h by employing a fed-batch strategy, affording a productivity of 44 g/L per day. Of significant synthetic interest was the finding that the D. wulumuqiensis R12 cells were able to catalyze the selective oxidation of other structurally diverse aldehydes to their corresponding acids with good yield and high selectivity, indicating broad substrate scope and potential widespread applications in biotechnology and organic chemistry. [ABSTRACT FROM AUTHOR]