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Enzyme-Mediated Stereoselective Synthesis

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ISBN: 9783039219360 9783039219377 Year: Pages: 116 DOI: 10.3390/books978-3-03921-937-7 Language: English
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Science (General) --- Chemistry (General) --- Inorganic Chemistry
Added to DOAB on : 2020-01-07 09:08:26
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This book is a collection of studies focused on the exploitation of enzyme stereoselectivity for the synthesis of relevant chemicals, such as innovative materials, chiral building blocks, natural products, and flavor and fragrance compounds. Different catalytic approaches are reported. The first study describes a resolution-based process for the stereoselective synthesis of the enantiomeric forms of the flavor compound linaloyl oxide, whereas other enantiomeric enriched aroma compounds were obtained through a novel microbial approach based on solid-state fermentation. Two relevant works exploit the potential of the biocatalyzed reduction reactions. The first of these contributions describes the enantioselective synthesis of ?-nitroalcohols by enzyme-mediated reduction of ?-nitroketones, whereas a second contribution reports the preparation of chiral 1,4-diaryl-1,4-diols through ADH-catalyzed bioreduction of the corresponding diketones. Concerning enantioenriched alcohol derivatives, natural hydroxy fatty acids are prepared by means of the biocatalytic hydration reaction of natural fatty acids using the probiotic bacterium Lactobacillus rhamnosus as a whole-cell biocatalyst. Further studies describe the use of modified pullulan polysaccharide for lipase immobilization and the recent advances in synthetic applications of ?-transaminases for the production of chiral amines.

Asymmetric and Selective Biocatalysis

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ISBN: 9783038978466 9783038978473 Year: Pages: 154 DOI: 10.3390/books978-3-03897-847-3 Language: English
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Science (General) --- Chemistry (General)
Added to DOAB on : 2019-06-26 09:16:44
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This Issue contains one communication, six articles, and two reviews. The communication from Paola Vitale et al. represents a work where whole cells were used as biocatalysts for the reduction of optically active chloroalkyl arylketones followed by a chemical cyclization to give the desired heterocycles. Among the various whole cells screened (baker’s yeast, Kluyveromyces marxianus CBS 6556, Saccharomyces cerevisiae CBS 7336, Lactobacillus reuteri DSM 20016), baker’s yeast provided the best yields and the highest enantiomeric ratios (95:5) in the bioreduction of the above ketones. In this respect, valuable chiral non-racemic functionalized oxygen-containing heterocycles (e.g., (S)-styrene oxide, (S)-2-phenyloxetane, (S)-2-phenyltetrahydrofuran), amenable to be further elaborated on, can be smoothly and successfully generated from their prochiral precursors. Studies about pure biocatalysts with mechanistical studies, application in different reactions, and new immobilization methods for improving their stability were reported in five different articles. The article by Su-Yan Wang et al. describes the cloning, expression, purification, and characterization of an N-acetylglucosamine 2-epimerase from Pedobacter heparinus (PhGn2E). For this, several N-acylated glucosamine derivatives were chemically synthesized and used to test the substrate specificity of the enzyme. The mechanism of the enzyme was studied by hydrogen/deuterium NMR. The study at the anomeric hydroxyl group and C-2 position of the substrate in the reaction mixture confirmed the epimerization reaction via ring-opening/enolate formation. Site-directed mutagenesis was also used to confirm the proposed mechanism of this interesting enzyme. The article by Forest H. Andrews et al. studies two enzymes, benzoylformate decarboxylase (BFDC) and pyruvate decarboxylase (PDC), which catalyze the non-oxidative decarboxylation of 2-keto acids with different specificity. BFDC from Pseudomonas putida exhibited very limited activity with pyruvate, whereas the PDCs from S. cerevisiae or from Zymomonas mobilis showed virtually no activity with benzoylformate (phenylglyoxylate). After studies using saturation mutagenesis, the BFDC T377L/A460Y variant was obtained, with 10,000-fold increase in pyruvate/benzoylformate. The change was attributed to an improvement in the Km value for pyruvate and a decrease in the kcat value for benzoylformate. The characterization of the new catalyst was performed, providing context for the observed changes in the specificity. The article by Xin Wang et al. compares two types of biocatalysts to produce D-lysine L-lysine in a cascade process catalyzed by two enzymes: racemase from microorganisms that racemize L-lysine to give D,L-lysine and decarboxylase that can be in cells, permeabilized cells, and the isolated enzyme. The comparison between the different forms demonstrated that the isolated enzyme showed the higher decarboxylase activity. Under optimal conditions, 750.7 mmol/L D-lysine was finally obtained from 1710 mmol/L L-lysine after 1 h of racemization reaction and 0.5 h of decarboxylation reaction. D-lysine yield could reach 48.8% with enantiomeric excess (ee) of 99%. In the article by Rivero and Palomo, lipase from Candida rugosa (CRL) was highly stabilized at alkaline pH in the presence of PEG, which permitted its immobilization for the first time by multipoint covalent attachment on different aldehyde-activated matrices. Different covalent immobilized preparation of the enzyme was successfully obtained. The thermal and solvent stability was highly increased by this treatment, and the novel catalysts showed high regioselectivity in the deprotection of per-O-acetylated nucleosides. The article by Robson Carlos Alnoch et al. describes the protocol and use of a new generation of tailor-made bifunctional supports activated with alkyl groups that allow the immobilization of proteins through the most hydrophobic region of the protein surface and aldehyde groups that allows the covalent immobilization of the previously adsorbed proteins. These supports were especially used in the case of lipase immobilization. The immobilization of a new metagenomic lipase (LipC12) yielded a biocatalyst 3.5-fold more active and 5000-fold more stable than the soluble enzyme. The PEGylated immobilized lipase showed high regioselectivity, producing high yields of the C-3 monodeacetylated product at pH 5.0 and 4 °C. Hybrid catalysts composed of an enzyme and metallic complex are also treated in this Special Issue. The article by Christian Herrero et al. describes the development of the Mn(TpCPP)-Xln10A artificial metalloenzyme, obtained by non-covalent insertion of Mn(III)-meso-tetrakis(p-carboxyphenyl)porphyrin [Mn(TpCPP), 1-Mn] into xylanase 10A from Streptomyces lividans (Xln10A). The complex was found able to catalyze the selective photo-induced oxidation of organic substrates in the presence of [RuII(bpy)3]2+ as a photosensitizer and [CoIII(NH3)5Cl]2+ as a sacrificial electron acceptor, using water as oxygen atom source. The two published reviews describe different subjects with interest in the fields of biocatalysis and mix metallic-biocatalysis, respectively. The review by Anika Scholtissek et al. describes the state-of-the-art regarding ene-reductases from the old yellow enzyme family (OYEs) to catalyze the asymmetric hydrogenation of activated alkenes to produce chiral products with industrial interest. The dependence of OYEs on pyridine nucleotide coenzyme can be avoided by using nicotinamide coenzyme mimetics. In the review, three main classes of OYEs are described and characterized. The review by Yajie Wang and Huimin Zhao highlights some of the recent examples in the past three years that combine transition metal catalysis with enzymatic catalysis. With recent advances in protein engineering, catalyst synthesis, artificial metalloenzymes, and supramolecular assembly, there is great potential to develop more sophisticated tandem chemoenzymatic processes for the synthesis of structurally complex chemicals. In conclusion, these nine publications give an overview of the possibilities of different catalysts, both traditional biocatalysts and hybrids with metals or organometallic complexes to be used in different processes—particularly in synthetic reactions—under very mild reaction conditions.

Biocatalysis and Pharmaceuticals: A Smart Tool for Sustainable Development

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ISBN: 9783039217083 9783039217090 Year: Pages: 176 DOI: 10.3390/books978-3-03921-709-0 Language: English
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Technology (General) --- Biotechnology
Added to DOAB on : 2019-12-09 11:49:16
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Biocatalysis, that is, the use of biological catalysts (enzymes, cells, etc.) for the preparation of highly valuable compounds is undergoing a great development, being considered an extremely sustainable approach to undertaking environmental demands. In this scenario, this book illustrates the versatility of applied biocatalysis for the preparation of drugs and other bioactive compounds through the presentation of different research articles and reviews, in which several authors describe the most recent developments in this appealing scientific area. By reading the excellent contributions gathered in this book, it is possible to have an updated idea about new advances and possibilities for a new exciting future.

Synthetic and Biosynthetic Approaches to Marine Natural Products

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ISBN: 9783039284665 9783039284672 Year: Pages: 182 DOI: 10.3390/books978-3-03928-467-2 Language: English
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Medicine (General) --- Therapeutics
Added to DOAB on : 2020-04-07 23:07:09
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Marine natural products containing a heterocyclic moiety in their structure are present in a wide variety of sponges, corals, algae, and fungi. Many of them show important biological activities such as cytotoxic properties against several cancer cell lines. Their challenging chemical structures have attracted the attention of many researchers who have developed various synthetic approaches. This Special Issue presents some examples of new synthetic or biosynthetic methodologies to access this type of marine natural drug.

Possible Scenarios for Homochirality on Earth

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ISBN: 9783039217229 9783039217236 Year: Pages: 318 DOI: 10.3390/books978-3-03921-723-6 Language: English
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Science (General)
Added to DOAB on : 2019-12-09 11:49:16
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In 1978, Fred Hoyle proposed that interstellar comets carrying several viruses landed on Earth as part of the panspermia hypotheses. With respect to life, the origin of homochirality on Earth has been the greatest mystery because life cannot exist without molecular asymmetry. Many scientists have proposed several possible hypotheses to answer this long-standing L-D question. Previously, Martin Gardner raised the question about mirror symmetry and broken mirror symmetry in terms of the homochirality question in his monographs (1964 and 1990). Possible scenarios for the L-D issue can be categorized into (i) Earth and exoterrestrial origins, (ii) by-chance and necessity mechanisms, and (iii) mirror-symmetrical and non-mirror-symmetrical forces as physical and chemical origins. These scenarios should involve further great amplification mechanisms, enabling a pure L- or D-world.

Keywords

chirogenesis --- enantiomorphism --- nepheline --- magmatic flow --- etch figures --- origin of life --- biological homochirality --- deracemization --- super-high-velocity impact --- plasma reactor --- absolute asymmetric synthesis --- amino acids --- origin of life --- amino acid handedness --- nucleus–molecular coupling --- chirality --- circularly polarized luminescence --- circular dichroism --- symmetry breaking --- parity violation --- weak neutral current --- tunneling --- Z0 boson --- homochirality --- precision measurement --- homochirality --- circularly polarized light --- asymmetric reaction --- polymer --- ?-strand --- hidden chirality --- two-fold helix --- multi-point approximation --- tilt-chirality --- high dimensional chirality --- spin polarized electrons --- homochirality --- magnetism --- prebiotic --- environmental chirality --- C1- and C2-symmetric catalysts --- chiral field (memory) --- racemic field --- Viedma ripening effect --- Wallach’s rule --- heat capacity --- metal-organic framework --- triethylenediamine (DABCO) molecules --- racemate --- Salam hypothesis --- homochirality --- parity violation --- neutrinos --- gravitation --- enantiomer self-disproportionation --- SDE --- achiral stationary phase --- homochiral and heterochiral aggregates --- chiral separation --- chirality --- genesis of life chirality --- asymmetric autocatalysis --- homochirality --- chirality --- asymmetric synthesis --- Soai reaction --- biological homochirality --- enantioselective reaction --- autocatalysis --- origin of life --- replicators --- bioorganic homochirality --- circularly polarized photon --- spin-polarized lepton --- parity violation in the weak interaction --- symmetry breaking --- assemblies --- supramolecular chirality --- homochirality --- self-assembly --- vortex --- lipid --- supramolecular assembly --- symmetry breaking --- homochirality

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