49 research outputs found
Lewis acid-catalyzed Diels-Alder reaction of 2-cyclopentenones with Danishefsky’s diene: double bond isomerization of tetrahydro-1H-indene-1,5(7aH)-diones, and attempts on an asymmetric catalysis
No full textEnantioselective total synthesis of cylindramide
No full textKey steps in the convergent enantioselective synthesis of the cytotoxic natural product cylindramide are tandem Michael addn./electrophilic trapping reactions, Sonogashira coupling, Julia-Kocienski olefination, and macrocyclization. For example, the Sonogashira coupling of pentalene I with iodoacrylate II followed by Julia-Kocienski olefination with sulfone III gave an intermediate which underwent macrocyclization. Formation of the tetramic acid completed the synthesis.LCSACAPLUS AN 2005:104408(Journal
„Das Kind hat einen Fremdkörper verschluckt“ – was tun?
No full textZusammenfassungSowohl Ingestions- als auch Aspirationsunfälle sind häufige Ereignisse bei Kindern. Sie können unmittelbar lebensbedrohlich sein oder bei fehlender direkter Bedrohung dennoch erhebliche langfristige Beeinträchtigungen für die Kinder verursachen. Der Beitrag zeigt die diagnostischen und therapeutischen Möglichkeiten und Notwendigkeiten auf, durch die eine bestmögliche Sicherheit und möglichst geringe Folgeschäden zu gewährleisten sind.</jats:p
Toward controlling the formation, degradation behavior, and properties of hydrogels synthesized by Aza-Michael reactions
No full textS.1865-1873The aza-Michael reaction of amino-functionalized polymers with acrylate and acrylamide crosslinkers for the formation of hydrogels is investigated. It is studied how far the reaction conditions (pH value, chemical structures of the compounds involved) influence the crosslinking and degradation rate of the gels. When crosslinking the polymer poly(1-glycidylpiperazine), high pH values lead to fast crosslinking. Fast degradation of -aminoester crosslinks is observed when acrylate crosslinkers are used due to a neighboring group effect. With acrylamide crosslinkers, hydrolytically stable gels are formed, in which the shear moduli and swelling ratio can be adjusted and in which the extracts show no toxic effect on primary human fibroblasts, making them a promising material for biotechnological applications.214Nr.1
Toward Controlling the Formation, Degradation Behavior, and Properties of Hydrogels Synthesized by Aza-Michael Reactions
No full textThe aza-Michael reaction of amino-functionalized polymers with acrylate and acrylamide crosslinkers for the formation of hydrogels is investigated. It is studied how far the reaction conditions (pH value, chemical structures of the compounds involved) influence the crosslinking and degradation rate of the gels. When crosslinking the polymer poly(1-glycidylpiperazine), high pH values lead to fast crosslinking. Fast degradation of β-aminoester crosslinks is observed when acrylate crosslinkers are used due to a neighboring group effect. With acrylamide crosslinkers, hydrolytically stable gels are formed, in which the shear moduli and swelling ratio can be adjusted and in which the extracts show no toxic effect on primary human fibroblasts, making them a promising material for biotechnological applications
Charge-Controlled Synthetic Hyaluronan-Based Cell Matrices
No full textThe extracellular matrix (ECM) represents a highly charged and hydrated network in which different cells in vertebrate tissues are embedded. Hydrogels as minimal ECM mimetics with a controlled chemistry offer the opportunity to vary material properties by varying the negative network charge. In this paper, a synthetic biology model of the ECM based on natural and highly negatively charged polyelectrolyte hyaluronic acid (HA) is characterized with specific emphasis on its charge-related bioactivity. Therefore, the thiol-Michael addition click reaction is used to produce HA hydrogels with defined network structure and charge density. The presented hydrogels show enzymatic degradability and cell attachment. These properties depend on both covalent and electrostatic interactions within the hydrogel network. Furthermore, no unspecific or specific attachment of proteins to the presented hydrogels is observed. In addition, these fundamental insights into charge-related ECM behavior and the influence of electrostatic properties could also lead to innovations in existing biomedical products
Novel (imino-η6-arene)chromium-complexes and their diastereoselective intramolecular hetero-Diels-Alder reactions
No full textNovel (imino-η6-arene)chromium complexes 3 with nonactivated olefins tethered to the 2-azadiene system were prepared and further used in a new diastereoselective intramolecular Lewis-acid-catalyzed hetero-Diels-Alder reaction to give (η6-octahydroacridine)chromium complexes 4. The trans selectivity of the cyclization reaction is mainly controlled by the Cr- (CO)3 fragment and to a minor extent by the catalyst, solvent, and substituents. Complexes 4 also could be obtained by a one-pot reaction starting from aldehyde 1, (o-toluidine)Cr(CO)3 (2), and Lewis acid. The stereochemistry of 4a was established by single-crystal X-ray structure analysis
