Glycosidases in Carbohydrate Synthesis: When Organic Chemistry Falls Short

Thanks to the stability, good availability, stereoselectivity and broad substrate specificity, oligosaccharide synthesis catalyzed by glycosidases represents an elegant way to complex carbohydrate structures. Two approaches to glycosidase catalysis are presented: i) the use of structurally modified substrates that carry various functional moieties in the molecule, and ii) the design of mutant glycosidases void of hydrolytic activity. Products of glycosidase-catalyzed synthesis are applicable in a range of are as such as immunology, therapy of Alzheimer's or Parkinson's diseases and the synthesis of neoglycoproteins

Modified Substrates in β-N-Acetylhexosaminidase-Catalyzed Synthesis

4 Conclrrsion 4 CoNcrusroN This Ph. D. thesis is a systematic study of the substrate specificity and the synthetic potential of B-N-acetylhexosaminidases (EC 3.2.1.52) with structurally modified substrates. It comprises four publications in intemational journals, one review and 17 oral and poster contributions. The following parts of the substrate molecule were modified: 2-acetamido moiety, the C-6 hydroxyl (oxidations, introduction of a cyano group) and the aglycon part (glycosyl azides - C-N bond hydrolysis). Thirteen modified substrates were synthesized, seven of them were described for the first time. They were tested for hydrolysis and transglycosylation by over thirty fungal -N-acetylhexosaminidases (culture collections at Charles University and at the Institute of Microbiology, Academy of Sciences of the Czech Republic) and the results were discussed in relation to the conclusions of molecular modeling (B-N-acetylhexosaminidase from Aspergillus oryzae CCF 1066). Eight oligosaccharidic structures (six of them novel) were prepared by semi- preparative transglycosylation reactions (tens of miligrams), isolated (mostly 16_377a yields, even 787o yie\ď) and fully characterized. Noteworthy properties like immunoactivity (binding to natural killer cell activation receptors) and inhibitory potential were...4 Conclrrsion 4 CoNcrusroN This Ph. D. thesis is a systematic study of the substrate specificity and the synthetic potential of B-N-acetylhexosaminidases (EC 3.2.1.52) with structurally modified substrates. It comprises four publications in intemational journals, one review and 17 oral and poster contributions. The following parts of the substrate molecule were modified: 2-acetamido moiety, the C-6 hydroxyl (oxidations, introduction of a cyano group) and the aglycon part (glycosyl azides - C-N bond hydrolysis). Thirteen modified substrates were synthesized, seven of them were described for the first time. They were tested for hydrolysis and transglycosylation by over thirty fungal -N-acetylhexosaminidases (culture collections at Charles University and at the Institute of Microbiology, Academy of Sciences of the Czech Republic) and the results were discussed in relation to the conclusions of molecular modeling (B-N-acetylhexosaminidase from Aspergillus oryzae CCF 1066). Eight oligosaccharidic structures (six of them novel) were prepared by semi- preparative transglycosylation reactions (tens of miligrams), isolated (mostly 16_377a yields, even 787o yie\ď) and fully characterized. Noteworthy properties like immunoactivity (binding to natural killer cell activation receptors) and inhibitory potential were...Department of BiochemistryKatedra biochemieFaculty of SciencePřírodovědecká fakult

История и перспективы применения железобетона

Строительство из бетона и железобетона по праву можно назвать самым перспективным из существующих технологий возведения зданий. «Бетон – наилучший из материалов, изобретенных человечеством», – сказал знаменитый итальянский архитектор П.Л. Нерви. И он был прав. Сегодня большинство домов в современных городах сделано из бетона. Он применяется для строительства мостов, портов и плотин, дорог, подземных сооружений, атомных электростанций и стартовых площадок для ракет

Выбор параметров установок продольной и поперечной компенсаций дальних электропередач с промежуточными системами

Приведены аналитические выражения по определению компенсирующих устройств дальних электропередач в зависимости от места присоединения ПС (к вводу или выводу установок продольной емкостной компенсации) с учетом предельности режима

Comparison of experimental results from three dual fluidized bed test facilities capturing CO2 with CaO

10th International Conference on Greenhouse Gas Control Technologies[EN] Postcombustion CO2 capture technologies using CaO as a regenerable solid sorbent have emerged as a promising route to reduce the electricity penalty and the cost of CO2 capture from flue gases of both new and existing fossil fuelled power plants. Rapid progress is taking place in the understanding of these processes at different levels. However, experimental information, validating the concept under continuous operating conditions similar to those expected for large-scale application, remain scarce. We present here a comparative analysis of the results obtained in three laboratory-scale dual fluidized bed (DFB) test facilities in Spain, Germany and Canada. The test facilities range from 10 to 75 kWth with riser heights between 4.5 and 12.4 m. They have been operated to capture CO2 with CaO from simulated flue gases in the bubbling, turbulent and fast fluidization fluid-dynamic regimes. The carbonator reactors are interconnected with regenerators, where the CaCO3 decomposition has been conducted continuously and semi-continuously, operated in both air-combustion and oxy-combustion modes. Many stationary and non-stationary states have been achieved at different combinations of the key operating parameters (e.g. calcium looping ratio). All DFB test facilities showed a carbon balance closure of high quality in most tests. The trends of CO2 capture efficiency with respect to operating conditions and sorbent characteristics are compared and a discussion is made on the most appropriate methodology to conduct future tests under a joint new FP7 project (CaOling) that aims at the rapid scaling up of the calcium looping technology.This work is being funded by the European Commision 7th Framework Programme under the CaOling Project.Peer reviewe

Discovery of human hexosaminidase inhibitors by in situ screening of a library of mono- and divalent pyrrolidine iminosugars

Two libraries of mono- and dimeric pyrrolidine iminosugars were synthesized by CuAAC and (thio)urea-bond-forming reactions from the respective azido/aminohexylpyrrolidine iminosugar precursors. The resulting monomeric and dimeric compounds were screened for inhibition of β-N-acetylglucosaminidase from Jack beans, the plant ortholog of human lysosomal hexosaminidases. A selection of the best inhibitors of these libraries was then evaluated against human lysosomal β-N-acetylhexosaminidase B (hHexB) and human nucleocytoplasmic β-N-acetylglucosaminidase (hOGA). This evaluation identified a potent (nM) and selective monomeric inhibitor of hOGA (compound 7A) that showed a 6770-fold higher affinity for this enzyme than for hHexB. The corresponding dimeric derivative (compound 9D) further remarkably improved the selectivity in the inhibition of hOGA (2.7 × 104 times more selective for hOGA over hHexB) and the inhibition potency (by one order of magnitude). Docking studies were performed to explain the selectivity of inhibition observed in compound 7A.Ministerio de Ciencia e Innovación PID2020-116460RB-100Ministerio de Economía y Competitividad CTQ2016-77270-RConsejería de Economía y Conocimiento. Junta de Andalucía FQM-345Czech Science Foundation GA21-01948

Oxalyltransferase, a plant cell-wall acyltransferase activity, transfers oxalate groups from ascorbate metabolites to carbohydrates

In the plant apoplast, ascorbate is oxidised, via dehydroascorbic acid, to O-oxalyl esters [oxalyl-l-threonate (OxT) and cyclic oxalyl-l-threonate (cOxT)]. We tested whether OxT and cOxT can donate the oxalyl group in transacylation reactions to form oxalyl-polysaccharides, potentially modifying the cell wall. [oxalyl-14 C]OxT was incubated with living spinach (Spinacia oleracea) and Arabidopsis cell-suspension cultures in the presence or absence of proposed acceptor substrates (carbohydrates). In addition, [14 C]OxT and [14 C]cOxT were incubated in vitro with cell-wall enzyme preparations plus proposed acceptor substrates. Radioactive products were monitored electrophoretically. Oxalyltransferase activity was detected. Living cells incorporated oxalate groups from OxT into cell-wall polymers via ester bonds. When sugars were added, [14 C]oxalyl-sugars were formed, in competition with OxT hydrolysis. Preferred acceptor substrates were carbohydrates possessing primary alcohols e.g. glucose. A model transacylation product, [14 C]oxalyl-glucose, was relatively stable in vivo (half-life >24 h), whereas [14 C]OxT underwent rapid turnover (half-life ~6 h). Ionically wall-bound enzymes catalysed similar transacylation reactions in vitro with OxT or cOxT as oxalyl donor substrates and any of a range of sugars or hemicelluloses as acceptor substrates. Glucosamine was O-oxalylated, not N-oxalylated. We conclude that plants possess apoplastic acyltransferase (oxalyltransferase) activity that transfers oxalyl groups from ascorbate catabolites to carbohydrates, forming relatively long-lived O-oxalyl-carbohydrates. The findings increase the range of known metabolites whose accumulation in vivo indicates vitamin C catabolism. Possible signalling roles of the resulting oxalyl-sugars can now be investigated, as can the potential ability of polysaccharide oxalylation to modify the wall's physical properties

Phenylpropanoid Glycoside Analogues: Enzymatic Synthesis, Antioxidant Activity and Theoretical Study of Their Free Radical Scavenger Mechanism

Phenylpropanoid glycosides (PPGs) are natural compounds present in several medicinal plants that have high antioxidant power and diverse biological activities. Because of their low content in plants (less than 5% w/w), several chemical synthetic routes to produce PPGs have been developed, but their synthesis is a time consuming process and the achieved yields are often low. In this study, an alternative and efficient two-step biosynthetic route to obtain natural PPG analogues is reported for the first time. Two galactosides were initially synthesized from vanillyl alcohol and homovanillyl alcohol by a transgalactosylation reaction catalyzed by Kluyveromyces lactis β-galactosidase in saturated lactose solutions with a 30%–35% yield. To synthesize PPGs, the galactoconjugates were esterified with saturated and unsaturated hydroxycinnamic acid derivatives using Candida antarctica Lipase B (CaL-B) as a biocatalyst with 40%–60% yields. The scavenging ability of the phenolic raw materials, intermediates and PPGs was evaluated by the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH•) method. It was found that the biosynthesized PPGs had higher scavenging abilities when compared to ascorbic acid, the reference compound, while their antioxidant activities were found similar to that of natural PPGs. Moreover, density functional theory (DFT) calculations were used to determine that the PPGs antioxidant mechanism proceeds through a sequential proton loss single electron transfer (SPLET). The enzymatic process reported in this study is an efficient and versatile route to obtain PPGs from different phenylpropanoid acids, sugars and phenolic alcohols

Protection of spring barley with fungicides

The history of cultivating barley dates back to the beginning of conscious agriculture, accompanying humans together with wheat, as the second oldest grain. It is not possible to understand the current role barley plays in our economy only from the perspective of its use of malting, although we regard it as a priority, both in light of breeding and cultivating, and its research. With regard to the short growing season, the weaker root system and its biological character, barley reacts sensitive to stressful conditions of all kind, and thus also to any br1eeding mistake. Throughout its entire vegetation period, spring barley is exposed to the pressure of a number of fungal diseases. Especially in regard to the malting barley, it is necessary to fight against this danger effectively. High demands are put on the quality of malting barley and diseases can - to a large extent - decide on economic breeding results. It says: For successful breeding of malting barley, its outcome is the tax of the complex breeding proceedings. The fight against fungal diseases is a significant part of agricultural engineering. A series of preparations against fungal diseases exist and further registrations of preparations continue to occur. The laboratory Kluky s.r.o. is one of the companies that makes registered experiments of the preparations. Within this recognized laboratory, the experiment of monitoring diseases of the spring barley was carried out while applying chosen beneficent substances

Grammar school students criteria for university selection

The bachelor thesis investigates the issue of university selection made by Czech secondary grammar school students as well as the area of career counseling as such. The objective is to answer the question: What are the decision-making criteria of secondary grammar school students when choosing a university? The theoretical part explores professional literature focused on career counseling which deals with the choice of future profession and thus also with the university selection. The information related to various tertiary study motives is in compliance with the point of view of experts on individual criteria for university selection provided in the works mentioned in the theoretical part. The final part presents the results of the research aimed on finding the criteria for university selection of the Czech secondary grammar school students in the third year of their studies