753 research outputs found
Über Strukturen und Überstrukturen
No full textLindel T, Sewald N, Wittmann V. Über Strukturen und Überstrukturen. Nachrichten aus Chemie, Technik und Laboratorium. 1999;47(1):16-20
Synthetic Approaches to Study Multivalent Carbohydrate Lectin Interactions
No full textThe specific recognition of carbohydrate structures in biological systems by carbohydrate-binding proteins (lectins) is the basis of numerous intra- and intercellular events ranging from the control of protein folding to cell cell communication during development, inflammation, and cancer metastasis. Investigation of carbohydrate lectin interactions can be approached from two directions. One is characterization of the protein part by molecular biology and structure determination (X-ray crystallography, NMR spectroscopy). In the other approach, which relies on synthetic organic chemistry, the specificity and affinity of modified or artificial lectin ligands and their effect on lectin function is studied. High-affinity lectin ligands are, furthermore, of considerable medicinal interest in the diagnosis and inhibition of carbohydrate-mediated processes such as inflammation or microbial adhesion. The generation of high-affinity lectin ligands, however, is not trivial because most saccharide ligands bind to their protein receptors only weakly with dissociation constants typically in the milli- to micromolar range. Because many lectins have several binding sites or occur in oligomeric or clustered form on cell membranes, the creation of multivalent carbohydrate derivatives is a promising means of producing high-affinity ligands.publishe
Beck, Rose Marie & Frank Wittmann (eds.) 2004. African Media Cultures – Transdisciplinary Perspectives. Cultures de médias en Afrique. Perspectives transdisciplinaires - Topics in African Studies, Vol. 2, Köln: Köppe Verlag, 320 pages, 2 b/w photos, 17 tables, 15 graphs, €34,80
No full textBeck and Wittmann\u27s volume is a most welcome contribution about types and uses of traditional and modern media in Africa. Their volume is divided into fifteen chapters preceded by a comprehensive introduction and followed by some information about the author
Structure elucidation of selectin antagonists in solution and synthesis of sialyl Lewis x mimics pre-organized in their bioactive conformation
No full textSelectins are an extensively studied class of carbohydrate binding proteins. They mediate the first contact and rolling of leukocytes on endothelia cells, initiating leukocyte infiltration from blood circulation to the diseased or infected tissue. Many inflammatory diseases are associated with an excessive extravasation of leukocytes to the inflamed tissue, and several kinds of metastatic cancer adopt the selectin mediated pathways. Thus, blocking selectins with synthetic antagonists is a promising therapeutic approach.
The common carbohydrate epitope present in all physiological selectin ligands is the tetrasaccharide sialyl Lewisx (sLex). To overcome the problem of structural complexity, nature rigidifies the 3 dimensional Lex core conformation by several stabilizing elements and thus, pre-organizes the pharmacophores in their bioactive conformation. For the development of potent sLex mimics it is crucial to understand the principles of stabilization and to adopt and optimize these structural motives.
Schematically sLex can be divided into a rigid Lex trisaccharide core and a rather flexible neuraminic acid part. The first part of the thesis is focused on the core trisaccharide Lex, which bears five of six pharmacophores. Since there are contradictory reports about the conformation of Lewis antigens in solution, i.e. do they adopt a single conformation or are they flexible, the conformations of Lex and related oligosaccharides in solution were investigated.
• An universal approach to analyze conformations of small molecules at room temperature in solution was developed. By converting the small Lex trisaccharide in a high-molecular-weight glycoconjugate the tumbling time was drastically increased, which is essential to obtain sufficient structural information by NMR spectroscopy. Thus, we achieved a well-defined solution conformation of Lex, which disclosed a nonconventional CH···O hydrogen bond as a major stabilizing element (Chapter 3.1.1/Publication).
• It could be shown that nonconventional CH···O hydrogen bonds are a common structural element stabilizing the conformation of various branched oligosaccharides. A widespread database search revealed numerous fucosylated carbohydrate structures that fulfill the requirements of nonconventional CH···O hydrogen bonds. Furthermore, the structures of six representative fucosylated carbohydrates were elucidated in solution. All of them are stabilized by nonconventional CH···O hydrogen bonds (Chapter 3.1.2/Manuscript).
In the second part of this thesis, the effects of neuraminic acid replacements in sLex mimics on conformational flexibility were evaluated, and antagonists with an acid pharmacophore pre-organized in the bioactive conformation were synthesized.
• By solving the solution conformation of a potent selectin antagonist, it was shown that the acid pharmacophore is pre-organized prior to binding by intramolecular interactions of hydrophobic residues. This antagonist showed stronger binding affinities over mimics with a flexible acid moiety. Based on these results, a series of selectin antagonists was designed and synthesized, where the acid pharmacophore is incorporated in a ring system and therefore, locked in the bioactive conformation (Chapter 3.2.1/Manuscript). The synthesis of two additional cyclic selectin antagonist series was not successful. Possible reasons are discussed in chapter 3.2.1.2.
• In chapter 3.2.2, the potential for a bioisosteric replacement of the acid pharmacophore in cyclic selectin antagonists was evaluated by synthesis, biological assays and ab initio calculations (Manuscript)
Boreomysis bispinosa O. S. Tattersall 1955
No full text<i>Boreomysis bispinosa</i> O.S. Tattersall, 1955 <p> <b>Material examined</b> (non-types only) ANGOLA BASIN • 1 imm. (BL = 8.3 mm, eyes missing); 17°4.935′ S, 4°40.805′ E to 17°07.454′ S,</p> <p>4°42.276′ E; bottom depth 5460– 5460 m; 25 Jul. 2000; DIVA-1 exped., #344; epinet of epibenthic sledge; ZMH 58248 • 1 ♀ ad. (estimated BL = 12.6 mm, cephalothorax and exuvia); 16°16.989′ S, 5°27.279′ E to 16°19.280′ S, 5°27.205′ E; bottom depth 5430–5433 m; 28 Jul. 2000; DIVA-1 exped., #348; supranet of epibenthic sledge; ZMH 58249.</p> Type locality <p>Not stated by O.S. Tattersall (1955). On page 14 she indicated a “female type ” taken off Cape Town, depth 1350 – 1250 m, and a “male type ” NE of St. Helena, depth 1450 – 700 m. A rough estimate by the present author suggests that the stations are from 34° S, 17° E and 15° S, 5° W, respectively.</p> Distribution <p> Previously reported from the Atlantic Ocean and from the Atlantic sector of the Southern Ocean, 51° N– 54° S, 36° W– 17° E (O.S. Tattersall 1955; Mauchline & Murano 1977; Hargreaves 1997; Wittmann <i>et al.</i> 2004; Petryashov 2005 b; San Vicente 2011). The animals were sampled with benthic as well as pelagic gears. The here documented records in the SE-Atlantic at 16– 17° S, 5° E are within the already known geographical range, while the bathymetrical range of 700–4050 m is now extended down to 5430–5460 m (see also Discussion).</p>Published as part of <i>Wittmann, Karl J., 2020, Lophogastrida and Mysida (Crustacea) of the " DIVA- 1 " deep-sea expedition to the Angola Basin (SE-Atlantic), pp. 1-43 in European Journal of Taxonomy 628</i> on page 15, DOI: 10.5852/ejt.2020.628, <a href="http://zenodo.org/record/3756146">http://zenodo.org/record/3756146</a>
Tool for Disrupting and Monitoring Sialic Acid Biosynthesis
No full textSialinsäuren sind Teil der äußersten Komponente der Glykokalyx aller Wirbeltiere. Als solche sind sie grundlegende Marker in physiologischen und pathologischen Prozessen. Der „Hauptregulator“ der Sialinsäure-Biosynthese ist die bifunktionelle UDP-N-Acetylglucosamin-2-Epimerase/N-Acetylmannosamin-Kinase (GNE/MNK). Das Hauptziel dieser Dissertation war die Identifizierung neuer Inhibitoren der GNE-Subdomäne, die zur Hemmung der Sialinsäurebiosynthese in Zellen und zur Verringerung der Sialylierung der Zelloberfläche eingesetzt werden könnten. Zu diesem Zweck wurde GNE rekombinant exprimiert und eine Screening-Kampagne mit fast 70 000 Verbindungen gegen seine Aktivität durchgeführt. Die primären Treffer aus der Screening-Kampagne wurden anschließend in vitro und in cellulo charakterisiert. Die Inhibitoren haben nicht auf Zellen funktioniert, dafür haben sie in einem neu entwickelten NMR basierten Assay GNE Aktivität im Rattenleberzytosolextrakt inhibiert.Sialic acids are part of the outermost component of the glycocalyx of all vertebrates. As such, they are fundamental markers in physiological and pathological processes. The "main regulator" of sialic acid biosynthesis is the bifunctional UDP-N-Acetylglucosamine-2-Epimerase/N-Acetylmannosamin Kinase (GNE/MNK). The main objective of this dissertation was the identification of new inhibitors of the GNE subdomain, which could be used to inhibit sialic acid biosynthesis in cells and reduce the sialylation of the cell surface. For this purpose, GNE was recombinantly expressed and a screening campaign against its activity was conducted with nearly 70,000 compounds. The primary hits from the screening campaign were subsequently characterized in vitro and in cellulo. The inhibitors did not work on cells, but they inhibited GNE activity in a rat liver cytosol extract in a newly developed NMR-based assay
Neue Auxiliare für die Peptidfragmentverknüpfung
No full textIn dieser Dissertation wurden Verfahren für die konvergente Synthese von Peptide entwickelt. Für die erweiterte native chemische Ligation kamen bisher raumbeanspruchende Auxiliare zum Einsatz, die anspruchsvolle Ligationen behinderten. Zudem waren die drastischen säure-basierten Abspaltbedinungen mit vielen post-translationalen Modifikationen nicht vereinbar. In dieser Arbeit wurde ein neuartiges Auxiliargerüst mit geringerem Raumanspruch untersucht, dass eine erheblich mildere Abspaltung unter basischen Bedingungen ermöglichte. Dazu wurde ein kleiner Elektronenakzeptorsubsituent eingeführt, durch den nach der Ligation eine das Zielpeptid freisetzende Eliminierungsreaktion induziert werden konnte. Weiterhin konnte die Verwendung des kommerziell verfügbaren Penicillamins als Vorläufer in der Ligations-Entschwefelungs-Strategie demonstriert werden. Abschließend wurde die Ligation mit sequenz-internem Cystein untersucht. Hierbei zeigte sich, dass Peptide mit Cystein in einer bestimmten Position bevorzugt in thioester-basierten Kondensationen reagierten.In this thesis approaches for convergent synthesis of peptides have been developed. In the extended native chemical ligation so far space demanding auxiliaries encumbered challenging condensations. Furthermore the required drastic acidolytic cleavage conditions were furthermore incompatible with many post-translational modifications. In the thesis a nouvelle less space demanding scaffold was scrutinized which allowed a milder basic cleavage. Therefore a small electron-accepting substituent was introduced that enabled the induction of an elimination reaction liberating the target peptide after the peptide ligation had taken place. Furthermore the applicability of the commercially available penicillamine as precursor of valine in the ligation-desulfurization strategy could be demonstrated. Finally the ligation with sequence internal cysteines was scrutinized. Herein it could be shown that certain peptides with cysteine in a distinctive position of the sequence preferable reacted in thioester-based condensation reactions
Multivalente Kohlenhydrat-PNA∙DNA-Konjugate zur Charakterisierung von Hämagglutininen und Entwicklung hochpotenter Inhibitoren von Influenza-Viren
No full textDas Prinzip der Multivalenz ist in der Natur allgegenwärtig, welches auch von Influenza-Viren genutzt wird, um über ihre Oberflächenproteine an epitheliale Wirtszellen zu binden. Diese Interaktion bietet einen interessanten Ansatzpunkt für multivalente Inhibitoren, wenn es gelingt, die Bedingungen für eine effiziente Wechselwirkung mit dem Virus zu entschlüsseln. Hierzu wurde in dieser Arbeit eine Charakterisierung des Hämagglutinin-Trimers (HA) auf viralen Partikeln mittels Kohlenhydrat-Nukleinsäuregerüsten und Kohlenhydrat-Polyethylenglykol (PEG)-Gerüsten vorgenommen. Distanz-Affinitäts-Beziehungen für die Interaktion des trimeren HA mit den bivalenten Präsentationen des Sialyl-LacNAc zeigten, dass bivalente PEG-Konjugate nicht in der Lage sind, eine bivalente Verstärkung der Wechselwirkungen mit der löslichen HA-Ektodomäne oder mit HA auf der viralen Oberfläche herbeizuführen, wobei die räumliche Rasterung mit PNA∙DNA-Gerüsten eine bimodale Distanz-Affinitäts-Beziehung ergab. Ein Affinitätsmaximum in einem Abstand von 52 - 59 Å wurde einer simultanen Bindung an zwei kanonische Bindungsstellen eines HA-Trimers zugeordnet, wobei ein zweites Affinitätsmaximum bei 26 Å auf die Existenz einer sekundären Bindungsstelle hindeutet. In dieser Arbeit wurde erstmals die multivalente Präsentation von Glykoliganden auf langen repetitiven DNA-Templaten demonstriert. Es wurden Nukleinsäure-Komplexe erhalten die eine vollständige Inhibierung der Virus-induzierten Hämagglutination bei einer Konzentration von 10^(-9) M des Templats erzielten, was einer 10^7-fachen Verstärkung bezogen auf den monovalenten Zucker entspricht. Neben einer hochpotenten Inhibition offenbarten distanzoptimierte bivalente und multivalente Binder auf Nukleinsäuregerüsten auch subtypspezifische Inhibition.The principle of multivalency is omnipresent in nature, which is also used by influenza viruses to bind to epithelial host cells via their surface proteins. This interaction offers an interesting starting point for multivalent inhibitors if the conditions for an efficient interaction with the virus can be deciphered. For this purpose, the hemagglutinin trimer (HA) on viral particles was characterized using carbohydrate-nucleic acid scaffolds and carbohydrate-polyethylene glycol (PEG) scaffolds. Distance-affinity relationships for the interaction of the trimeric HA with the bivalent presentations of the sialyl-LacNAc showed that bivalent PEG conjugates are not capable of a bivalent enhancement of the interactions with the soluble HA ectodomain or with HA on the viral surface, whereby the spatial screening with PNA∙DNA scaffolds resulted in a bimodal distance-affinity relationship. An affinity maximum at a distance of 52 - 59 Å was assigned to simultaneous binding to two canonical binding sites of an HA trimer, with a second affinity maximum at 26 Å indicating the existence of a secondary binding site. In this work the multivalent presentation of carbohydrate ligands on long repetitive DNA templates was demonstrated for the first time. Nucleic acid complexes were obtained which achieved a full inhibition of the virus-induced hemagglutination at a concentration of 10^(-9) M of the template, which corresponds to a 10^7-fold increase in relation to the monovalent sugar. In addition to a highly potent inhibition, distance-optimized bivalent and multivalent binders on nucleic acid structures also revealed subtype-specific inhibition
Synthesis of Oligosaccharides on Solid Support Using Thioglycosides and Pentenyl Glycosides
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