Cascade enzymatic synthesis of a statin side chain precursor - the role of reaction engineering in process optimization.

Statins are an important class of drugs used to lower blood cholesterol levels and are often used to combat cardiovascular disease. In view of the importance of safe and reliable supply and production of statins in modern medicine and the global need for sustainable processes, various biocatalytic strategies for their synthesis have been investigated. In this work, a novel biocatalytic route to a statin side chain precursor was investigated in a one-pot cascade reaction starting from the protected alcohol N-(3-hydroxypropyl)-2-phenylacetamide, which is oxidized to the corresponding aldehyde in the first reaction step, and then reacts with two equivalents of acetaldehyde to form the final product N-(2-((2S,4S,6S)-4,6-dihydroxytetrahydro-2H-pyran-2-yl)ethyl)-2-phenylacetamide (phenylacetamide-lactol). To study this complex reaction, an enzyme reaction engineering approach was used, i.e. the kinetics of all reactions occurring in the cascade (including side reactions) were determined. The obtained kinetic model together with the simulations gave an insight into the system and indicated the best reactor mode for the studied reaction, which was fed-batch with acetaldehyde feed to minimize its negative effect on the enzyme activity during the reaction. The mathematical model of the process was developed and used to simulate different scenarios and to find the reaction conditions (enzyme and coenzyme concentration, substrate feed concentration and flow rate) at which the highest yield of phenylacetamide-lactol (75%) can be obtained. In the end, our goal was to show that this novel cascade route is an interesting alternative for the synthesis of the statin side chain precursor and that is why we also calculated an initial estimate of the potential value addition.

Biocatalytic Synthesis of Homochiral 2-Hydroxy-4-butyrolactone Derivatives by Tandem Aldol Addition and Carbonyl Reduction.

Chiral 2-hydroxy acids and 2-hydroxy-4-butyrolactone derivatives are structural motifs often found in fine and commodity chemicals. Here, we report a tandem biocatalytic stereodivergent route for the preparation of these compounds using three stereoselective aldolases and two stereocomplementary ketoreductases using simple and achiral starting materials. The strategy comprises (i) aldol addition reaction of 2-oxoacids to aldehydes using two aldolases from E. coli, 3-methyl-2-oxobutanoate hydroxymethyltransferase (KPHMT Ecoli ), 2-keto-3-deoxy-l-rhamnonate aldolase (YfaU Ecoli ), and trans-o-hydroxybenzylidene pyruvate hydratase-aldolase from Pseudomonas putida (HBPA Pputida ) and (ii) subsequent 2-oxogroup reduction of the aldol adduct by ketopantoate reductase from E. coli (KPR Ecoli ) and a Δ1-piperidine-2-carboxylate/Δ1-pyrroline-2-carboxylate reductase from Pseudomonas syringae pv. tomato DSM 50315 (DpkA Psyrin ) with uncovered promiscuous ketoreductase activity. A total of 29 structurally diverse compounds were prepared: both enantiomers of 2-hydroxy-4-butyrolactone (>99% ee), 21 2-hydroxy-3-substituted-4-butyrolactones with the (2R,3S), (2S,3S), (2R,3R), or (2S,3R) configuration (from 60:40 to 98:2 dr), and 6 2-hydroxy-4-substituted-4-butyrolactones with the (2S,4R) configuration (from 87:13 to 98:2 dr). Conversions of aldol adducts varied from 32 to 98%, while quantitative conversions were achieved by both ketoreductases, with global isolated yields between 20 and 45% for most of the examples. One-pot one-step cascade reactions were successfully conducted achieving isolated yields from 30 to 57%.

Unifying Scheme for the Biosynthesis of Acyl-Branched Sugars: Extended Substrate Scope of Thiamine-Dependent Enzymes.

Thiamine diphosphate (ThDP) dependent enzymes are useful catalysts for asymmetric C-C bond formation through benzoin-type condensation reactions that result in α-hydroxy ketones. A wide range of aldehydes and ketones can be used as acceptor substrates; however, the donor substrate range is mostly limited to achiral α-keto acids and simple aldehydes. By using a unifying retro-biosynthetic approach towards acyl-branched sugars, we identified a subclass of (myco)bacterial ThDP-dependent enzymes with a greatly extended donor substrate range, namely functionalized chiral α-keto acids with a chain length from C4 to C8 . Highly enantioenriched acyloin products were obtained in good to high yields and several reactions were performed on a preparative scale. The newly introduced functionalized α-keto acids, accessible by known aldolase-catalyzed transformations, substantially broaden the donor substrate range of ThDP-dependent enzymes, thus enabling a more general use of these already valuable catalysts.

Effect of light intensity on steviol glycosides production in leaves of Stevia rebaudiana plants.

Stevia rebaudiana leaf extracts contain stevioside and rebaudioside A, two steviol glycosides (SGs) used as natural sweeteners because of their non-toxic, thermally stable and non-caloric properties. Indeed, leaf extracts can be up to 300 times sweeter than sucrose. Stevioside and rebaudioside A have organoleptic differences, the first one having an undesirable bitterness and the second one a higher sweetener capacity. Selection of the S. rebaudiana varieties and the best environmental conditions that elicit higher SGs content and the appropriate composition is an important goal. In this study we quantified and compared the amount of stevioside and rebaudioside A in two of the most used S. rebaudiana cultivars, Morita II and Criolla. Our results show a strong differential ratio of stevioside and rebaudioside A accumulated in the leaf between these cultivars. The Criolla cultivar showed about 3 times more stevioside per mg of dry weight than Morita II, whereas the Morita II accumulated almost 10 times more rebaudioside A than that produced in Criolla. We observed an enhanced expression in Morita II of three genes (SrKA13H, SrUGT74G1 and SrUGT76G1) known to encode three enzymes that participate in SGs biosynthesis, likely contributing to the differences in the stevioside and rebaudioside A accumulation. Not only genetic variation can affect SGs composition, but also environmental factors and crop management. Numerous studies have shown that the light regime in which S. rebaudiana cultivars grow can affect SGs accumulation. However, the optimal light regime to increase total SGs content is currently controversial. By applying various light intensities, we detected an increase of expression of these three biosynthetic genes at higher light intensity, accompanied by higher levels of stevioside and rebaudioside A, demonstrating that light intensity influences the synthesis of SGs.

Synthesis of γ-Hydroxy-α-amino Acid Derivatives by Enzymatic Tandem Aldol Addition-Transamination Reactions.

Three enzymatic routes toward γ-hydroxy-α-amino acids by tandem aldol addition-transamination one-pot two-step reactions are reported. The approaches feature an enantioselective aldol addition of pyruvate to various nonaromatic aldehydes catalyzed by trans-o-hydroxybenzylidene pyruvate hydratase-aldolase (HBPA) from Pseudomonas putida. This affords chiral 4-hydroxy-2-oxo acids, which were subsequently enantioselectively aminated using S-selective transaminases. Three transamination processes were investigated involving different amine donors and transaminases: (i) l-Ala as an amine donor with pyruvate recycling, (ii) a benzylamine donor using benzaldehyde lyase from Pseudomonas fluorescens Biovar I (BAL) to transform the benzaldehyde formed into benzoin, minimizing equilibrium limitations, and (iii) l-Glu as an amine donor with a double cascade comprising branched-chain α-amino acid aminotransferase (BCAT) and aspartate amino transferase (AspAT), both from E. coli, using l-Asp as a substrate to regenerate l-Glu. The γ-hydroxy-α-amino acids thus obtained were transformed into chiral α-amino-γ-butyrolactones, structural motifs found in many biologically active compounds and valuable intermediates for the synthesis of pharmaceutical agents.

Thermostability Engineering of a Class II Pyruvate Aldolase from Escherichia coli by in Vivo Folding Interference.

The use of enzymes in industrial processes is often limited by the unavailability of biocatalysts with prolonged stability. Thermostable enzymes allow increased process temperature and thus higher substrate and product solubility, reuse of expensive biocatalysts, resistance against organic solvents, and better "evolvability" of enzymes. In this work, we have used an activity-independent method for the selection of thermostable variants of any protein in Thermus thermophilus through folding interference at high temperature of a thermostable antibiotic reporter protein at the C-terminus of a fusion protein. To generate a monomeric folding reporter, we have increased the thermostability of the moderately thermostable Hph5 variant of the hygromycin B phosphotransferase from Escherichia coli to meet the method requirements. The final Hph17 variant showed 1.5 °C higher melting temperature (T m) and 3-fold longer half-life at 65 °C compared to parental Hph5, with no changes in the steady-state kinetic parameters. Additionally, we demonstrate the validity of the reporter by stabilizing the 2-keto-3-deoxy-l-rhamnonate aldolase from E. coli (YfaU). The most thermostable multiple-mutated variants thus obtained, YfaU99 and YfaU103, showed increases of 2 and 2.9 °C in T m compared to the wild-type enzyme but severely lower retro-aldol activities (150- and 120-fold, respectively). After segregation of the mutations, the most thermostable single variant, Q107R, showed a T m 8.9 °C higher, a 16-fold improvement in half-life at 60 °C and higher operational stability than the wild-type, without substantial modification of the kinetic parameters.

Biocatalytic Construction of Quaternary Centers by Aldol Addition of 3,3-Disubstituted 2-Oxoacid Derivatives to Aldehydes.

The congested nature of quaternary carbons hinders their preparation, most notably when stereocontrol is required. Here we report a biocatalytic method for the creation of quaternary carbon centers with broad substrate scope, leading to different compound classes bearing this structural feature. The key step comprises the aldol addition of 3,3-disubstituted 2-oxoacids to aldehydes catalyzed by metal dependent 3-methyl-2-oxobutanoate hydroxymethyltransferase from E. coli (KPHMT) and variants thereof. The 3,3,3-trisubstituted 2-oxoacids thus produced were converted into 2-oxolactones and 3-hydroxy acids and directly to ulosonic acid derivatives, all bearing gem-dialkyl, gem-cycloalkyl, and spirocyclic quaternary centers. In addition, some of these reactions use a single enantiomer from racemic nucleophiles to afford stereopure quaternary carbons. The notable substrate tolerance and stereocontrol of these enzymes are indicative of their potential for the synthesis of structurally intricate molecules.

Aldolase-Catalyzed Asymmetric Synthesis of N-Heterocycles by Addition of Simple Aliphatic Nucleophiles to Aminoaldehydes.

Nitrogen heterocycles are structural motifs found in many bioactive natural products and of utmost importance in pharmaceutical drug development. In this work, a stereoselective synthesis of functionalized N-heterocycles was accomplished in two steps, comprising the biocatalytic aldol addition of ethanal and simple aliphatic ketones such as propanone, butanone, 3-pentanone, cyclobutanone, and cyclopentanone to N-Cbz-protected aminoaldehydes using engineered variants of d-fructose-6-phosphate aldolase from Escherichia coli (FSA) or 2-deoxy-d-ribose-5-phosphate aldolase from Thermotoga maritima (DERA Tma ) as catalysts. FSA catalyzed most of the additions of ketones while DERA Tma was restricted to ethanal and propanone. Subsequent treatment with hydrogen in the presence of palladium over charcoal, yielded low-level oxygenated N-heterocyclic derivatives of piperidine, pyrrolidine and N-bicyclic structures bearing fused cyclobutane and cyclopentane rings, with stereoselectivities of 96-98 ee and 97:3 dr in isolated yields ranging from 35 to 79%.

Accessing to the Nicotiana tabacum leaf antimicrobial activity: In-silico and in-vitro investigations.

In this research, in-silico and in-vitro approaches were adopted with the aim to investigate the relationship between the tobacco leaf structures (trichomes) and the production of secondary metabolites with antimicrobial activity. Machine learning techniques were used to know the correlation between phenotypic traits and the production of secondary metabolites in Nicotiana tabacum plants. Then, an in-vitro experimental study was carried out to corroborate the proposed model. The relationship between the morphology and distribution of the different types of trichomes in the upper and lower leaves with the contrasting profiles of the chemical composition (diterpenes and sugar esters) of the leaf exudates between different lines of tobacco were found. We determined the influence of each trichome type with secondary metabolites production and the necessary concentration to achieve antimicrobial and antioxidant activity.

Biocatalytic Aldol Addition of Simple Aliphatic Nucleophiles to Hydroxyaldehydes.

Asymmetric aldol addition of simple aldehydes and ketones to electrophiles is a cornerstone reaction for the synthesis of unusual sugars and chiral building blocks. We investigated d-fructose-6-phosphate aldolase from E. coli (FSA) D6X variants as catalysts for the aldol additions of ethanal and nonfunctionalized linear and cyclic aliphatic ketones as nucleophiles to nonphosphorylated hydroxyaldehydes. Thus, addition of propanone, cyclobutanone, cyclopentanone, or ethanal to 3-hydroxypropanal or (S)- or (R)-3-hydroxybutanal catalyzed by FSA D6H and D6Q variants furnished rare deoxysugars in 8-77% isolated yields with high stereoselectivity (97:3 dr and >95% ee).

Nucleophile Promiscuity of Natural and Engineered Aldolases.

The asymmetric aldol addition reaction mediated by aldolases is recognized as a green and sustainable method for carbon-carbon bond formation. Research in this area has unveiled their unprecedented synthetic potential toward diverse, new chemical structures; novel product families; and even as a technology for industrial manufacturing processes. Despite these advances, aldolases have long been regarded as strictly selective catalysts, particularly for nucleophilic substrates, which limits their broad applicability. In recent years, advances in screening technologies and metagenomics have uncovered novel C-C biocatalysts from superfamilies of widely known lyases. Moreover, protein engineering has revealed the extraordinary malleability of different carboligases to offer a toolbox of biocatalysts active towards a large structural diversity of nucleophile substrates. Herein, the nucleophile ambiguity of native and engineered aldolases is discussed with recent examples to prove this novel concept.

Nucleophile Promiscuity of Engineered Class†II Pyruvate Aldolase YfaU from E.†Coli.

Pyruvate-dependent aldolases exhibit a stringent selectivity for pyruvate, limiting application of their synthetic potential, which is a drawback shared with other existing aldolases. Structure-guided rational protein engineering rendered a 2-keto-3-deoxy-l-rhamnonate aldolase variant, fused with a maltose-binding protein (MBP-YfaU W23V/L216A), capable of efficiently converting larger pyruvate analogues, for example, those with linear and branched aliphatic chains, in aldol addition reactions. Combination of these nucleophiles with N-Cbz-alaninal (Cbz=benzyloxycarbonyl) and N-Cbz-prolinal electrophiles gave access to chiral building blocks, for example, derivatives of (2S,3S,4R)-4-amino-3-hydroxy-2-methylpentanoic acid (68 %, d.r. 90:10) and the enantiomer of dolaproine (33 %, d.r. 94:6) as well as a collection of unprecedented α-amino acid derivatives of the proline and pyrrolizidine type. Conversions varied between 6-93 % and diastereomeric ratios from 50:50 to 95:5 depending on the nucleophilic and electrophilic components.

Intramolecular Benzoin Reaction Catalyzed by Benzaldehyde Lyase from Pseudomonas Fluorescens Biovar I.

Intramolecular benzoin reactions catalyzed by benzaldehyde lyase from Pseudomonas fluorescens biovar I (BAL) are reported. The structure of the substrates envisaged for this reaction consists of two benzaldehyde derivatives linked by an alkyl chain. The structural requirements needed to achieve the intramolecular carbon-carbon bond reaction catalyzed by BAL were established. Thus, a linker consisting of a linear alkyl chain of three carbon atoms connected through ether-type bonds to the 2 and 2' positions of two benzaldehyde moieties, which could be substituted with either Cl, Br, or OCH3 at either the 3 and 3' or 5 and 5' positions, were suitable substrates for BAL. Reactions with 61-84 % yields of the intramolecular product and ee values between 64 and 98 %, were achieved.

Expedient synthesis of C-aryl carbohydrates by consecutive biocatalytic benzoin and aldol reactions.

The introduction of aromatic residues connected by a C-C bond into the non-reducing end of carbohydrates is highly significant for the development of innovative structures with improved binding affinity and selectivity (e.g., C-aril-sLex). In this work, an expedient asymmetric "de novo" synthetic route to new aryl carbohydrate derivatives based on two sequential stereoselectively biocatalytic carboligation reactions is presented. First, the benzoin reaction of aromatic aldehydes to dimethoxyacetaldehyde is conducted, catalyzed by benzaldehyde lyase from Pseudomonas fluorescens biovar I. Then, the α-hydroxyketones formed are reduced by using NaBH4 yielding the anti diol. After acetal hydrolysis, the aldol addition of dihydroxyacetone, hydroxyacetone, or glycolaldehyde catalyzed by the stereocomplementary D-fructose-6-phosphate aldolase and L-rhamnulose-1-phosphate aldolase is performed. Both aldolases accept unphosphorylated donor substrates, avoiding the need of handling the phosphate group that the dihydroxyacetone phosphate-dependent aldolases require. In this way, 6-C-aryl-L-sorbose, 6-C-aryl-L-fructose, 6-C-aryl-L-tagatose, and 5-C-aryl-L-xylose derivatives are prepared by using this methodology.

Engineered L-serine hydroxymethyltransferase from Streptococcus thermophilus for the synthesis of α,α-dialkyl-α-amino acids.

α,α-Disubstituted α-amino acids are central to biotechnological and biomedical chemical processes for their own sake and as substructures of biologically active molecules for diverse biomedical applications. Structurally, these compounds contain a quaternary stereocenter, which is particularly challenging for stereoselective synthesis. The pyridoxal-5'-phosphate (PLP)-dependent L-serine hydroxymethyltransferase from Streptococcus thermophilus (SHMT(Sth); EC 2.1.2.1) was engineered to achieve the stereoselective synthesis of a broad structural variety of α,α-dialkyl-α-amino acids. This was accomplished by the formation of quaternary stereocenters through aldol addition of the amino acids D-Ala and D-Ser to a wide acceptor scope catalyzed by the minimalist SHMT(Sth) Y55T variant overcoming the limitation of the native enzyme for Gly. The SHMT(Sth) Y55T variant tolerates aromatic and aliphatic aldehydes as well as hydroxy- and nitrogen-containing aldehydes as acceptors.

Evaluation of styrene-divinylbenzene beads as a support to immobilize lipases.

A commercial and very hydrophobic styrene-divinylbenzene matrix, MCI GEL® CHP20P, has been compared to octyl-Sepharose® beads as support to immobilize three different enzymes: lipases from Thermomyces lanuginosus (TLL) and from Rhizomucor miehie (RML) and Lecitase® Ultra, a commercial artificial phospholipase. The immobilization mechanism on both supports was similar: interfacial activation of the enzymes versus the hydrophobic surface of the supports. Immobilization rate and loading capacity is much higher using MCI GEL® CHP20P compared to octyl-Sepharose® (87.2 mg protein/g of support using TLL, 310 mg/g using RML and 180 mg/g using Lecitase® Ultra). The thermal stability of all new preparations is much lower than that of the standard octyl-Sepharose® immobilized preparations, while the opposite occurs when the inactivations were performed in the presence of organic co-solvents. Regarding the hydrolytic activities, the results were strongly dependent on the substrate and pH of measurement. Octyl-Sepharose® immobilized enzymes were more active versus p-NPB than the enzymes immobilized on MCI GEL® CHP20P, while RML became 700-fold less active versus methyl phenylacetate. Thus, the immobilization of a lipase on this matrix needs to be empirically evaluated, since it may present very positive effects in some cases while in other cases it may have very negative ones.

Simple and efficient immobilization of lipase B from Candida antarctica on porous styrene-divinylbenzene beads.

Two commercial porous styrene-divinylbenzene beads (Diaion HP20LX and MCI GEL CHP20P) have been evaluated as supports to immobilize lipase B from Candida antarctica (CALB). MCI GEL CHP20P rapidly immobilized the enzyme, permitting a very high loading capacity: around 110mgCALB/wetg of support compared to the 50mg obtained using decaoctyl Sepabeads. Although enzyme specificity of the enzyme immobilized on different supports was quite altered by the support used in the immobilization, specific activity of the enzyme immobilized on MCI GEL CHP20P was always higher than those found using decaoctyl Sepabeads for all assayed substrates. Thus, a CALB biocatalyst having 3-8 folds (depending on the substrate) higher activity/wet gram of support than the commercial Novozym 435 was obtained. Half-live of CAL-Diaion HP20LX at 60°C was 2-3 higher than the one of Novozym 435, it was 30-40 higher in the presence of 50% acetonitrile and it was around 100 folds greater in the presence of 10M hydrogen peroxide. Results indicate that styrene-divinylbenzene supports may be promising alternatives as supports to immobilize CALB.

Control of protein immobilization: coupling immobilization and site-directed mutagenesis to improve biocatalyst or biosensor performance.

Mutagenesis and immobilization are usually considered to be unrelated techniques with potential applications to improve protein properties. However, there are several reports showing that the use of site-directed mutagenesis to improve enzyme properties directly, but also how enzymes are immobilized on a support, can be a powerful tool to improve the properties of immobilized biomolecules for use as biosensors or biocatalysts. Standard immobilizations are not fully random processes, but the protein orientation may be difficult to alter. Initially, most efforts using this idea were addressed towards controlling the orientation of the enzyme on the immobilization support, in many cases to facilitate electron transfer from the support to the enzyme in redox biosensors. Usually, Cys residues are used to directly immobilize the protein on a support that contains disulfide groups or that is made from gold. There are also some examples using His in the target areas of the protein and using supports modified with immobilized metal chelates and other tags (e.g., using immobilized antibodies). Furthermore, site-directed mutagenesis to control immobilization is useful for improving the activity, the stability and even the selectivity of the immobilized protein, for example, via site-directed rigidification of selected areas of the protein. Initially, only Cys and disulfide supports were employed, but other supports with higher potential to give multipoint covalent attachment are being employed (e.g., glyoxyl or epoxy-disulfide supports). The advances in support design and the deeper knowledge of the mechanisms of enzyme-support interactions have permitted exploration of the possibilities of the coupled use of site-directed mutagenesis and immobilization in a new way. This paper intends to review some of the advances and possibilities that these coupled strategies permit.

Hydrolysis of triacetin catalyzed by immobilized lipases: effect of the immobilization protocol and experimental conditions on diacetin yield.

The effect of the immobilization protocol and some experimental conditions (pH value and presence of acetonitrile) on the regioselective hydrolysis of triacetin to diacetin catalyzed by lipases has been studied. Lipase B from Candida antarctica (CALB) and lipase from Rhizomucor miehei (RML) were immobilized on Sepabeads (commercial available macroporous acrylic supports) activated with glutaraldehyde (covalent immobilization) or octadecyl groups (adsorption via interfacial activation). All the biocatalysts accumulated diacetin. Covalently immobilized RML was more active towards rac-methyl mandelate than the adsorbed RML. However, this covalent RML preparation presented the lowest activity towards triacetin. For this reason, this preparation was discarded as biocatalyst for this reaction. At pH 7, acyl migration occurred giving a mixture of 1,2 and 1,3 diacetin, but at pH 5.5, only 1,2 diacetin was produced. Yields were improved at acidic pH values and in the presence of 20% acetonitrile (to over 95%). RML immobilized on octadecyl Sepabeads was proposed as optimal preparation, mainly due to its higher specific activity. Each enzyme preparation presented very different properties. Moreover, changes in the reaction conditions affected the various immobilized enzymes in a different way.

Historia de la cirugía de revascularización miocárdica / History of myocardial revascularization surgery

La cirugía de revascularización miocárdica es la más frecuente de las cirugías cardíacas y uno de los mayores logros obtenidos en la cirugía. Su historia puede dividirse en cuatro etapas. Las ideas relacionadas con ella surgen ya a finales del siglo XIX y tienen un desarrollo vertiginoso en el siglo XX. Como muchos de los descubrimientos de la humanidad y la medicina, la cirugía cardíaca y la revascularización miocárdica tienen paternidades discutidas y fechas controvertibles. Se hace una revisión bibliográfica de su desarrollo y avances, así como de algunos aspectos de la circulación extracorpórea, la protección miocárdica y la cirugía cardíaca en general, necesarios para su progreso(AU)

Myocaridal revascularization surgery is the most common of the heart surgeries and one of the greatest achievements attained in surgery. Its history may be divided into 4 stages. The ideas related to it appeared at the end of the XIX century and had a quick development in the XX century. As many of the discoveries of mankind and medicine, heart surgery and myocardial revascularization have disputed paternities and controvertible dates. A bibliographic review of their development and advances, as well as of some aspects of extracorporeal circulation, myocardial protection and heart surgery in general, which are necessary for their progress, was made(AU)