Trends in lipase-catalyzed asymmetric access to enantiomerically pure/enriched compounds

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Production, purification, properties and current perspectives for modification and application of microbial lipases

With the industrialization and development of modern science, the application of enzymes as green and environmentally friendly biocatalysts in industry has been increased widely. Among them, lipase (EC. 3.1.1.3) is a very prominent biocatalyst, which has the ability to catalyze the hydrolysis and synthesis of ester compounds. Many lipases have been isolated from various sources, such as animals, plants and microorganisms, among which microbial lipase is the enzyme with the most diverse enzymatic properties and great industrial application potential. It therefore has promising applications in many industries, such as food and beverages, waste treatment, biofuels, leather, textiles, detergent formulations, ester synthesis, pharmaceuticals and medicine. Although many microbial lipases have been isolated and characterized, only some of them have been commercially exploited. In order to cope with the growing industrial demands and overcome these shortcomings to replace traditional chemical catalysts, the preparation of new lipases with thermal/acid-base stability, regioselectivity, organic solvent tolerance, high activity and yield, and reusability through excavation and modification has become a hot research topic.

An overview on the conversion of glycerol to value-added industrial products via chemical and biochemical routes

Glycerol is a common by-product of industrial biodiesel syntheses. Due to its properties, availability, and versatility, residual glycerol can be used as a raw material in the production of high value-added industrial inputs and outputs. In particular, products like hydrogen, propylene glycol, acrolein, epichlorohydrin, dioxalane and dioxane, glycerol carbonate, n-butanol, citric acid, ethanol, butanol, propionic acid, (mono-, di-, and triacylglycerols), cynamoil esters, glycerol acetate, benzoic acid, and other applications. In this context, the present study presents a critical evaluation of the innovative technologies based on the use of residual glycerol in different industries, including the pharmaceutical, textile, food, cosmetic, and energy sectors. Chemical and biochemical catalysts in the transformation of residual glycerol are explored, along with the factors to be considered regarding the choice of catalyst route used in the conversion process, aiming at improving the production of these industrial products.

The combination of covalent and ionic exchange immobilizations enables the coimmobilization on vinyl sulfone activated supports and the reuse of the most stable immobilized enzyme

The coimmobilization of lipases from Rhizomucor miehei (RML) and Candida antarctica (CALB) has been intended using agarose beads activated with divinyl sulfone. CALB could be immobilized on this support, while RML was not. However, RML was ionically exchanged on this support blocked with ethylendiamine. Therefore, both enzymes could be coimmobilized on the same particle, CALB covalently using the vinyl sulfone groups, and RML via anionic exchange on the aminated blocked support. However, immobilized RML was far less stable than immobilized CALB. To avoid the discarding of CALB (that maintained 90% of the initial activity after RML inactivation), a strategy was developed. Inactivated RML was desorbed from the support using ammonium sulfate and 1% Triton X-100 at pH 7.0. That way, 5 cycles of RML thermal inactivation, discharge of the inactivated enzyme and re-immobilization of a fresh sample of RML could be performed. In the last cycle, immobilized CALB activity was still over 90% of the initial one. Thus, the strategy permits that enzymes can be coimmobilized on vinyl sulfone supports even if one of them cannot be immobilized on it, and also permits the reuse of the most stable enzyme (if it is irreversibly attached to the support).

Microwave-induced biocatalytic reactions toward medicinally important compounds

Microwaves in the presence of enzymes are used to execute a number of reactions for the preparation of biologically active compounds. The success of microwave-induced enzymatic reactions depends on frequencies, field strength, waveform, duration, and modulation of the exposure. Enzymes under microwave irradiation become activated and this activation is sufficient to investigate simple to complex reactions that were not reported under these reaction conditions before. Enzymatic catalysis together with microwave technology and solvent-free chemical reaction is a nature-friendly procedure. The most interesting reactions that are performed by enzymes in the microwave are documented here with reference to examples that are related to medicinally active molecules.

Acylative Kinetic Resolution of Cyclic Hydroxamic Acids

Racemic cyclic hydroxamic acids bearing an aryl substituent adjacent to the hydroxyl group undergo effective acylative kinetic resolution promoted by benzotetramisole (BTM).

Activation and Stabilization of Lipase B from Candida antarctica by Immobilization on Polymer Brushes with Optimized Surface Structure

A reusable support system for the immobilization of lipases is developed using hybrid polymer-inorganic core shell nanoparticles. The biocatalyst core consists of a silica nanoparticle. PMMA is grafted from the nanoparticle as polymer brush via ARGET ATRP (activator regenerated by electron transfer atom transfer radical polymerization), which allows defining the surface properties by chemical synthesis conditions. Lipase B from Candida antarctica is immobilized on the hybrid particles. The activity and stability of the biocatalyst are analyzed by spectroscopic activity analysis. It is shown that the hydrophobic PMMA brushes provide an activating surface for the lipase giving a higher specific activity than the enzyme in solution. Varying the surface structure from disordered to ordered polymer brushes reveals that the reusability of the biocatalyst is more effectively optimized by the surface structure than by the introduction of crosslinking with glutaraldehyde (GDA). The developed immobilization system is highly suitable for biocatalysis in non-native media which is shown by a transesterification assay in isopropyl alcohol and an esterification reaction in n-heptane.

Combination of high throughput and structural screening to assess protein stability - a screening perspective

High throughput screening to measure the stability of industrially relevant proteins and their variants is necessary for quality assessment in the development process. Advances in automation, measurement time and sample consumption for many techniques allow rapid measurements with minimal amount of protein. However, many methods include automated data analysis, potentially neglecting important aspects of the proteińs behavior in certain conditions. In this study we implement small angle X-ray scattering (SAXS), typically not used to assess protein behavior in industrial screening, in a high throughput screening workflow to address problems of contradicting results and reproducibility among different high throughput methods. As a case study we use the lipases of Thermomyces lanuginosus and Rhizomucor miehei, widely used industrial biocatalysts. We show that even the initial analysis of the SAXS data without performing any time-consuming modelling provide valuable information on interparticle interactions. We conclude that recent advances in automation and data processing, have enabled SAXS to be used more widely as a tool to gain in-depth knowledge highly useful for protein formulation development. This is especially relevant in light of increasing accessibility to SAXS due to the commercial availability of benchtop instruments.

Stabilization of enzymes via immobilization: Multipoint covalent attachment and other stabilization strategies

The use of enzymes in industrial processes requires the improvement of their features in many instances. Enzyme immobilization, a requirement to facilitate the recovery and reuse of these water-soluble catalysts, is one of the tools that researchers may utilize to improve many of their properties. This review is focused on how enzyme immobilization may improve enzyme stability. Starting from the stabilization effects that an enzyme may experience by the mere fact of being inside a solid particle, we detail other possibilities to stabilize enzymes: generation of favorable enzyme environments, prevention of enzyme subunit dissociation in multimeric enzymes, generation of more stable enzyme conformations, or enzyme rigidification via multipoint covalent attachment. In this last point, we will discuss the features of an "ideal" immobilization protocol to maximize the intensity of the enzyme-support interactions. The most interesting active groups in the support (glutaraldehyde, epoxide, glyoxyl and vinyl sulfone) will be also presented, discussing their main properties and uses. Some instances in which the number of enzyme-support bonds is not directly related to a higher stabilization will be also presented. Finally, the possibility of coupling site-directed mutagenesis or chemical modification to get a more intense multipoint covalent immobilization will be discussed.

Hydrogen Bonds and n → π* Interactions in the Acetylation of Propranolol Catalyzed by Candida antarctica Lipase B: A QTAIM Study

Enzyme-substrate interactions play a crucial role in enzymatic catalysis. Quantum theory of atoms in molecules (QTAIM) calculations are extremely useful in computational studies of these interactions because they provide very detailed information about the strengths and types of molecular interactions. QTAIM also provides information about the intramolecular changes that occur in the catalytic reaction. Here, we analyze the enzyme-substrate interactions and the topological properties of the electron density in the enantioselective step of the acylation of (R,S)-propranolol, an aminoalcohol with therapeutic applications, catalyzed by Candida antarctica lipase B. Eight reaction paths (four for each enantiomer) are investigated and the energies, atomic charges, hydrogen bonds, and n → π* interactions of propranolol, the catalytic triad (composed of D187, H224, and S105), and the oxyanion hole are analyzed. It is found that D187 acts as an electron density reservoir for H224, and H224 acts as an electron density reservoir for the active site of the protein. It releases electron density when the tetrahedral intermediate is formed from the Michaelis complex and receives it when the enzyme-product complex is formed. Hydrogen bonds can be grouped into noncovalent and covalent hydrogen bonds. The latter are stronger and more important for the reaction than the former. We also found weak n → π* interactions, which are characterized by QTAIM and the natural bond orbital (NBO) analysis.

Finite-temperature effect in the O-acylation of (R,S)-propranolol catalyzed by Candida antarctica lipase B

CalB is a triacylglycerol hydrolase (E.C.3.1.1.3) used in the O-acylation of the beta-adrenergic blocking agent (R,S)-propranolol. The catalytic mechanism involves two steps: enzyme acylation and enzyme deacylation. The enantioselectivity of the O-acylation of (R,S)-propranolol originates from the second step, where the acyl-enzyme transfers the acyl group to the racemic substrate. This step occurs via an initial Michaelis complex (MCC) and a tetrahedral intermediate (TI-2). To gain more insight into the molecular basis of this reaction, we performed an exhaustive conformational sampling along the reaction coordinate of the enantioselective step of the reaction (MCC→TI-2→EPC) applying a QM/MM MD protocol (SCC-DFTB/CHARMM) in combination with umbrella sampling and the weighted histogram analysis method. To identify finite temperature effects we compare the PMF and the potential energy pathway. It is found that the effect of the finite temperature in this reaction is a destabilization of the tetrahedral intermediate and an increase of the barrier height of its formation. This increase is higher for the S-enantiomer.

Current perspectives for microbial lipases from extremophiles and metagenomics

Microbial lipases are most broadly used biocatalysts for environmental and industrial applications. Lipases catalyze the hydrolysis and synthesis of long acyl chain esters and have a characteristic folding pattern of α/β hydrolase with highly conserved catalytic triad (Serine, Aspartic/Glutamic acid and Histidine). Mesophilic lipases (optimal activity in neutral pH range, mesophilic temperature range, atmospheric pressure, normal salinity, non-radio-resistant, and instability in organic solvents) have been in use for many industrial biotransformation reactions. However, lipases from extremophiles can be used to design biotransformation reactions with higher yields, less byproducts or useful side products and have been predicted to catalyze those reactions also, which otherwise are not possible with the mesophilic lipases. The extremophile lipase perform activity at extremes of temperature, pH, salinity, and pressure which can be screened from metagenome and de novo lipase design using computational approaches. Despite structural similarity, they exhibit great diversity at the sequence level. This diversity is broader when lipases from the bacterial, archaeal, plant, and animal domains/kingdoms are compared. Furthermore, a great diversity of novel lipases exists and can be discovered from the analysis of the dark matter - the unexplored nucleotide/metagenomic databases. This review is an update on extremophilic microbial lipases, their diversity, structure, and classification. An overview on novel lipases which have been detected through analysis of the genomic dark matter (metagenome) has also been presented.

Asymmetric Catalysis Mediated by Synthetic Peptides, Version 2.0: Expansion of Scope and Mechanisms

Low molecular weight synthetic peptides have been demonstrated to be effective catalysts for an increasingly wide array of asymmetric transformations. In many cases, these peptide-based catalysts have enabled novel multifunctional substrate activation modes and unprecedented selectivity manifolds. These features, along with their ease of preparation, modular and tunable structures, and often biomimetic attributes make peptides well-suited as chiral catalysts and of broad interest. Many examples of peptide-catalyzed asymmetric reactions have appeared in the literature since the last survey of this broad field in Chemical Reviews (Chem. Rev. 2007, 107, 5759-5812). The overarching goal of this new Review is to provide a comprehensive account of the numerous advances in the field. As a corollary to this goal, we survey the many different types of catalytic reactions, ranging from acylation to C-C bond formation, in which peptides have been successfully employed. In so doing, we devote significant discussion to the structural and mechanistic aspects of these reactions that are perhaps specific to peptide-based catalysts and their interactions with substrates and/or reagents.

Multi-Combilipases: Co-Immobilizing Lipases with Very Different Stabilities Combining Immobilization via Interfacial Activation and Ion Exchange. The Reuse of the Most Stable Co-Immobilized Enzymes after Inactivation of the Least Stable Ones

The lipases A and B from Candida antarctica (CALA and CALB), Thermomyces lanuginosus (TLL) or Rhizomucor miehei (RML), and the commercial and artificial phospholipase Lecitase ultra (LEU) may be co-immobilized on octyl agarose beads. However, LEU and RML became almost fully inactivated under conditions where CALA, CALB and TLL retained full activity. This means that, to have a five components co-immobilized combi-lipase, we should discard 3 fully active and immobilized enzymes when the other two enzymes are inactivated. To solve this situation, CALA, CALB and TLL have been co-immobilized on octyl-vinyl sulfone agarose beads, coated with polyethylenimine (PEI) and the least stable enzymes, RML and LEU have been co-immobilized over these immobilized enzymes. The coating with PEI is even favorable for the activity of the immobilized enzymes. It was checked that RML and LEU could be released from the enzyme-PEI coated biocatalyst, although this also produced some release of the PEI. That way, a protocol was developed to co-immobilize the five enzymes, in a way that the most stable could be reused after the inactivation of the least stable ones. After RML and LEU inactivation, the combi-biocatalysts were incubated in 0.5 M of ammonium sulfate to release the inactivated enzymes, incubated again with PEI and a new RML and LEU batch could be immobilized, maintaining the activity of the three most stable enzymes for at least five cycles of incubation at pH 7.0 and 60 °C for 3 h, incubation on ammonium sulfate, incubation in PEI and co-immobilization of new enzymes. The effect of the order of co-immobilization of the different enzymes on the co-immobilized biocatalyst activity was also investigated using different substrates, finding that when the most active enzyme versus one substrate was immobilized first (nearer to the surface of the particle), the activity was higher than when this enzyme was co-immobilized last (nearer to the particle core).

Enzymatic Esterification as Potential Strategy to Enhance the Sorbic Acid Behavior as Food and Beverage Preservative

Sorbic acid is the most commonly used preservative in the food industry. The antimicrobial inhibition of sorbic acid could be influenced by its lipophilic nature, which reduces its use in hydrophilic food formulations. Reactions between sorbic acid and glycerol catalyzed by lipases were studied in order to develop a novel sorbic acid derivate with a promising hydrophilic profile. The esterification reaction between sorbic acid and glycerol in a solvent-free system were performed with an immobilized lipase B from Candida antarctica (CALB). The glycerol sorbate product has been tested against S. griseus bacterium and Saccharomyces cerevisiae yeast. Results indicate that the esterification of sorbic acid with glycerol does improve its antimicrobial properties against Saccharomyces cerevisie. The reported results demonstrate that esterification can be used as a strategy to improve the antimicrobial activity of sorbic acid.

The Use of Ion Liquids as a Trojan Horse Strategy in Enzyme-Catalyzed Biotransformation of (R,S)-Atenolol

The enzymatic method was used for the direct biotransformation of racemic atenolol. The catalytic activities of commercially available lipases from Candida rugosa were tested for the kinetic resolution of (R,S)-atenolol by enantioselective acetylation in various two-phase reaction media containing ionic liquids. The composed catalytic system gave the possibility to easy separate substrates and products of the conducted enantioselective reaction and after specific procedure to reuse utilized enzymes in another catalytic cycle.

Stereoselective Synthesis of Terpenoids through Lipase-Mediated Resolution Approaches

This review article focuses on the scientific developments concerning the lipase-mediated synthesis of terpenoids that have been reported in the literature during the last twenty years. More specifically, this review describes in depth the resolution approaches that allow the preparation of the chiral building blocks used for the stereoselective synthesis of bioactive terpenoids. The synthetic methods that have given new and innovative perspectives from a scientific standpoint, and the preparative approaches that possess industrial importance, are described thoroughly.

"Fishing and Hunting"-Selective Immobilization of a Recombinant Phenylalanine Ammonia-Lyase from Fermentation Media

This article overviews the numerous immobilization methods available for various biocatalysts such as whole-cells, cell fragments, lysates or enzymes which do not require preliminary enzyme purification and introduces an advanced approach avoiding the costly and time consuming downstream processes required by immobilization of purified enzyme-based biocatalysts (such as enzyme purification by chromatographic methods and dialysis). Our approach is based on silica shell coated magnetic nanoparticles as solid carriers decorated with mixed functions having either coordinative binding ability (a metal ion complexed by a chelator anchored to the surface) or covalent bond-forming ability (an epoxide attached to the surface via a proper linker) enabling a single operation enrichment and immobilization of a recombinant phenylalanine ammonia-lyase from parsley fused to a polyhistidine affinity tag.

Enhancing Activity by Supercritical CO2 Mediated Immobilization of Lipase on Mesocellular Foam in Preparation of Hexyl Laurate

Hexyl laurate is employed in several cosmetics having great demand. It could be synthesized catalytically like a "natural" perfume using a lipase. The use of mesocellular foam silica (MCF) for immobilization of lipases could be made using supercritical CO₂ as a medium to enhance its activity in comparison with the normal techniques. Three different catalysts were supported on MCF such as Candida antractica B (CALB), Amano AYS, and Porcine pancreas (PPL), and their activity was evaluated in the preparation of hexyl laurate from lauric acid and hexyl alcohol. CALB@ MCF was the best among all. A systematic study was conducted to assess the effects of different operating parameters. It was ternary complex mechanism with inhibition by hexyl alcohol. The enzyme was reusable and the process is green.

Double nucleophilic addition to iminomalonate, leading to the synthesis of quaternary α-amino diesters and desymmetrization of the products

Alkylation of iminomalonate with Grignard reagents followed by oxidation and allylation gave symmetrical quaternary α-amino diesters in good yields. Subsequent desymmetrization of a diol derivative from these products was conducted via asymmetric carbamylation catalyzed by Cu-Bnbox to give chiral quaternary aminodiol mono-carbamates.

Reuse of Lipase from Pseudomonas fluorescens via Its Step-by-Step Coimmobilization on Glyoxyl-Octyl Agarose Beads with Least Stable Lipases

Coimmobilization of lipases may be interesting in many uses, but this means that the stability of the least stable enzyme determines the stability of the full combilipase. Here, we propose a strategy that permits the reuse the most stable enzyme. Lecitase Ultra (LU) (a phospholipase) and the lipases from Rhizomucor miehei (RML) and from Pseudomonas fluorescens (PFL) were immobilized on octyl agarose, and their stabilities were studied under a broad range of conditions. Immobilized PFL was found to be the most stable enzyme under all condition ranges studied. Furthermore, in many cases it maintained full activity, while the other enzymes lost more than 50% of their initial activity. To coimmobilize these enzymes without discarding fully active PFL when LU or RML had been inactivated, PFL was covalently immobilized on glyoxyl-agarose beads. After biocatalysts reduction, the other enzyme was coimmobilized just by interfacial activation. After checking that glyoxyl-octyl-PFL was stable in 4% Triton X-100, the biocatalysts of PFL coimmobilized with LU or RML were submitted to inactivation under different conditions. Then, the inactivated least stable coimmobilized enzyme was desorbed (using 4% detergent) and a new enzyme reloading (using in some instances RML and in some others employing LU) was performed. The initial activity of immobilized PFL was maintained intact for several of these cycles. This shows the great potential of this lipase coimmobilization strategy.

Cyclopentyl Methyl Ether (CPME): A Versatile Eco-Friendly Solvent for Applications in Biotechnology and Biorefineries

The quest for sustainable solvents is currently a matter of intense research and development, as solvents significantly contribute heavily to the waste generated by chemical industries. Cyclopentyl methyl ether (CPME) is a promising eco-friendly solvent with valuable properties such as low peroxide formation rate, stability under basic and acidic conditions, and relatively high boiling point. This Review discusses the potential use of CPME for applications in biotechnology (e.g., biotransformations, as solvent or cosolvent), biorefineries, and bioeconomy (e.g., for furan synthesis or as an extractive agent in liquid-liquid separations), as well as for other purposes, such as chromatography or peptide synthesis. Although CPME is currently produced by petrochemical means with a remarkably high atom economy, its biogenic production can be envisaged from substrates such as cyclopentanol or cyclopentanone, which can be derived from furfural or from (bio-based) adipic acid, respectively. The combination of the promising properties of CPME as a (co)solvent with a future (economic) biogenic origin would be advantageous for setting strategies aligned with the sustainable chemistry principles.

Manipulating the stereoselectivity of a thermostable alcohol dehydrogenase by directed evolution for efficient asymmetric synthesis of arylpropanols

Chiral arylpropanols are valuable components in important pharmaceuticals and fragrances, which is the motivation for previous attempts to prepare these building blocks enantioselectively in asymmetric processes using either enzymes or transition metal catalysts. Thus far, enzymes used in kinetic resolution proved to be best, but several problems prevented ecologically and economically viable processes from being developed. In the present study, directed evolution was applied to the thermostable alcohol dehydrogenase TbSADH in the successful quest to obtain mutants that are effective in the dynamic reductive kinetic resolution (DYRKR) of racemic arylpropanals. Using rac-2-phenyl-1-propanal in a model reaction, (S)- and (R)-selective mutants were evolved which catalyzed DYRKR of this racemic substrate with formation of the respective (S)- and (R)-alcohols in essentially enantiomerically pure form. This was achieved on the basis of an unconventional form of iterative saturation mutagenesis (ISM) at randomization sites lining the binding pocket using a reduced amino acid alphabet. The best mutants were also effective in the DYRKR of several other structurally related racemic aldehydes.

Lipase Catalysed Kinetic Resolution of Racemic 1,2-Diols Containing a Chiral Quaternary Center

Optically active 1,2-diols are valuable buildings blocks in organic synthesis. In the present paper, a set of racemic 1,2-diols with an ester functional group are prepared, starting from α-ketoesters in a three-step procedure with moderate yields. The racemic 1,2-diols, containing a chiral quaternary center in their structure, are subjected to selective acylation in order to perform their kinetic resolution catalysed by a set of commercially available lipases. Under optimized reaction conditions, good conversions and enantioselectivities are achieved by using the lipase PSL-C from Pseudomonas cepacia in tert-butyl methyl ether. This biocatalyst could be reused up to five times without losing its properties.

Función de los confórmeros de ataque cercano en la acilación enantioselectiva del (R,S)-propranolol catalizada por lipasa B de Candida antarctica

La lipasa B de Candida antarctica (CalB) se ha utilizado en la acilación quimio- y enantioselectiva del racemato (R,S)-propranolol. CalB tiene enantioselectividad moderada (E=63) por el R-propranolol. La enantioselectividad, se origina en la reacción de transferencia del grupo acilo desde la serina catalítica, acilada, al propranolol. La fase inicial de esta reacción involucra la formación de complejos de Michaelis y posteriormente conformaciones de ataque cercano. El análisis de las conformaciones de ataque cercano ha permitido en varios casos explicar el origen de la catálisis o reproducir el efecto catalítico. En este trabajo se profundiza en la comprensión la función de las conformaciones de ataque cercano en la enantioselectividad de la acilación del (R,S)-propranolol catalizada por CalB. Para lo anterior se realizó un estudio detallado de los complejos de Michaelis y de las conformaciones de ataque cercano del paso enantioselectivo de la reacción de acilación del (R,S)-propranolol utilizando un protocolo de dinámica molecular QM/MM (SCCDFTB/CHARMM) utilizando 6 distribuciones de velocidades iniciales y simulaciones de 2,5 ns. Se estudiaron 7 complejos CalB-propranolol. Los enlaces de hidrógeno del sitio activo de CalB acilada relevantes para la actividad catalítica fueron estables en todas las simulaciones. Las poblaciones de los complejos de Michaelis y de las conformaciones de ataque cercano son dependientes de la distribución de las velocidades iniciales de la dinámica molecular. La enantioselectividad moderada de CalB acilada, encontrada experimentalmente, puede ser parcialmente atribuida a la alta población de conformaciones de ataque cercano observada para el S-propranolol.

CALB-Catalyzed Two-Step Alcoholytic Desymmetrization of 3-Methylglutaric Diazolides in MTBE

Optically pure 3-substituted glutarates can be prepared from the alcoholic ring-opening of cyclic anhydride derivatives, esterification of 3-substituted glutaric acid, and hydrolysis, alcoholysis, aminolysis, and ammonolysis of the diester derivatives via hydrolases or organocatalysts. Unfortunately, most of them mainly focus on the first-step desymmetrization, leading to the difficulty on producing optically pure enantiomers. As a general trend in lipase-catalyzed desymmetrization of 3-methylglutarates, poorer enantiomeric excesses with lower chemical yields were found, as the methyl substituent is relatively small to induce a high enzyme stereodiscrimination. The two-step desymmetrization for CALB-catalyzed alcoholysis of 3-methylglutaric di-1,2,4-triazolide 1a in anhydrous MTBE is first developed to increase the enzyme activity in each reaction step. The enantioselectivity for the second-step kinetic resolution is furthermore improved by using 3-methylglutaric dipyrazolide 1b as the substrate. The kinetic and thermodynamic analysis is, moreover, addressed for shedding insights into the desymmetrization process.

Kinetic resolution of (RS)-1-chloro-3-(4-(2-methoxyethyl)phenoxy)propan-2-ol: a metoprolol intermediate and its validation through homology model of Pseudomonas fluorescens lipase

Kinetic resolution of (±)-1-chloro-3-(4-(2-methoxyethyl)phenoxy)propan-2-ol: a metoprolol intermediate and its validation through homology model of Pseudomonas fluorescens lipase.

Optimization of oligomeric enzyme activity in ionic liquids using Rhodotorula glutinis yeast phenylalanine ammonia lyase

Phenylalanine ammonia lyase (E.C.4.3.1.24, PAL) activity of Rhodotorula glutinis yeast has been demonstrated in four commonly used ionic liquids. PAL forward reaction was carried out in 1-butyl-3-methylimidazolium methyl sulfate ([BMIM][MeSO₄]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) and 1-butyl-3-methylimidazolium lactate ([BMIM][lactate]). Our experiments have revealed that PAL is catalytically active in ionic liquids and the enzyme activity in ([BMIM][PF₆]) is comparable to that obtained in aqueous buffer medium. Different conditions were optimized for maximal PAL forward activity including time of incubation (30.0min)_L-phenylalanine substrate concentration (30.0mM), nature of buffer (50.0mM Tris-HCl), pH (9.0), temperature (37°C), and speed of agitation (100 rev min^-1). Under these optimized conditions, about 83% conversion of substrate to product was obtained for the PAL forward reaction that was determined using UV spectroscopy at 290nm. PAL reverse reaction in ([BMIM][PF₆]) was determined spectrophotometrically at 520nm; and about 59% substrate conversion was obtained. This data provides further knowledge in enzyme biocatalysis in non-aqueous media, and may be of importance when studying the function of other oligomeric/multimeric proteins and enzymes in ionic liquids.

Kinetic behaviour of recombinant Fusarium solani lipases using monomolecular films: Effect of the heterologous expression

Two lipases from Fusarium solani, FSL and FSL2, were efficiently expressed in Pichia pastoris. To check the influence of the expression on interfacial properties of FSL and to study kinetic properties of FSL2, interfacial parameters of FSL2, native FSL, untagged recombinant and tagged recombinant forms of FSL were compared using the monomolecular film technique. Kinetic study on the dependence of the stereoselectivity of these lipases on the surface pressure was performed using three dicaprin isomers spread in the form of monomolecular films at the air-water interface. The FSL2 seems to have an important penetration power with a preference for adjacent ester groups and the heterologous expression accompanied or not with the N-His-tag extension on the FSL were found to modify the pressure preference and increase the catalytic hydrolysis rate of three dicaprin isomers. The heterologous expression was found to preserve the FSL regioselectivity without affecting its stereospecificity at high and low surface pressure. The evaluation of the recombinant expression Effects on Catalysis (REC), the N-Tag Effects on Catalysis (TEC), and the N-Tag and Recombinant expression Effects on Catalysis (TREC) showed that the heterologous expression was more efficient than the presence of the N-terminal tag extension on the FSL.