Ein trifunktioneller Katalysator: In einem Flussreaktor wird Ethen an dem Wolframhydrid‐Trägerkatalysator W(H)3/Al2O3 selektiv in Propen umgewandelt. Da der Katalysator auch die Olefinmetathese vermittelt, erfüllt er in der Reaktion vermutlich drei Funktionen: Dimerisierung von Ethen, Isomerisierung von Buten und Kreuzmetathese von Ethen mit 2‐Butenen (siehe Schema).

A broad spectrum of physiological processes is mediated by highly specific noncovalent interactions of carbohydrates and proteins. In a recent communication we identified several cyclic hexapeptides in a dynamic combinatorial library that interact selectively with carbohydrates with high binding constants in water. Herein, we report a detailed investigation of the noncovalent interaction of two cyclic hexapeptides (Cys-His-Cys (which we call HisHis) and Cys-Tyr-Cys (which we call TyrTyr)) with a selection of monosaccharides and disaccharides in aqueous solution. The parallel and antiparallel isomers of HisHis or TyrTyr were synthesized separately, and their interaction with monosaccharides and disaccharides in aqueous solution was studied by isothermal titration calorimetry, NMR spectroscopic titrations, and circular dichroism spectroscopy. From these measurements, we identified particularly stable complexes (Ka> 1000 M(-1)) of the parallel isomer of HisHis with N-acetylneuraminic acid and with methyl-a-d-galactopyranoside as well as of both isomers of TyrTyr with trehalose. To gain further insight into the structure of the peptide–carbohydrate complexes, structure prediction was performed using quantum chemical methods. The calculations confirm the selectivity observed in the experiments and indicate the formation of multiple intermolecular hydrogen bonds in the most stable complexes.

Die Nadel im Heuhaufen: Eine dynamische kombinatorische Bibliothek (DCL) aus Peptiden wurde durch die Disulfidaustauschreaktion von Cysteinen erhalten. Drei cyclische Peptide sind selektive Rezeptoren für Kohlenhydrate in Wasser; eines davon ist HisHis, das in einer DCL aus drei Tripeptiden in Gegenwart des Neurotransmitters NANA bevorzugt entsteht.

SummaryThe molecular recognition of carbohydrates and proteins mediates a wide range of physiological processes and the development of synthetic carbohydrate receptors (“synthetic lectins”) constitutes a key advance in biomedical technology. In this article we report a synthetic lectin that selectively binds to carbohydrates immobilized in a molecular monolayer. Inspired by our previous work, we prepared a fluorescently labeled synthetic lectin consisting of a cyclic dimer of the tripeptide Cys-His-Cys, which forms spontaneously by air oxidation of the monomer. Amine-tethered derivatives of N-acetylneuraminic acid (NANA), β-D-galactose, β-D-glucose and α-D-mannose were microcontact printed on epoxide-terminated self-assembled monolayers. Successive prints resulted in simple microarrays of two carbohydrates. The selectivity of the synthetic lectin was investigated by incubation on the immobilized carbohydrates. Selective binding of the synthetic lectin to immobilized NANA and β-D-galactose was observed by fluorescence microscopy. The selectivity and affinity of the synthetic lectin was screened in competition experiments. In addition, the carbohydrate binding of the synthetic lectin was compared with the carbohydrate binding of the lectins concanavalin A and peanut agglutinin. It was found that the printed carbohydrates retain their characteristic selectivity towards the synthetic and natural lectins and that the recognition of synthetic and natural lectins is strictly orthogonal.

The genes coding for quinaldine catabolism in Arthrobacter sp. strain Rue61a are clustered on the linear plasmid pAL1 in two upper pathway operons (meqABC and meqDEF) coding for quinaldine conversion to anthranilate and a lower pathway operon encoding anthranilate degradation via coenzyme A (CoA) thioester intermediates. The meqR2 gene, located immediately downstream of the catabolic genes, codes for a PaaX-type transcriptional repressor. MeqR2, purified as recombinant fusion protein, forms a dimer in solution and shows specific and cooperative binding to promoter DNA in vitro. DNA fragments recognized by MeqR2 contained a highly conserved palindromic motif, 5=-TGACGNNCGTcA-3=, which is located at positions ؊35 to ؊24 of the two promoters that control the upper pathway operons, at positions ؉4 to ؉15 of the promoter of the lower pathway genes and at positions ؉53 to ؉64 of the meqR2 promoter. Disruption of the palindrome abolished MeqR2 binding. The dissociation constants (K D ) of MeqR2-DNA complexes as deduced from electrophoretic mobility shift assays were very similar for the four promoters tested (23 nM to 28 nM). Anthraniloyl-CoA was identified as the specific effector of MeqR2, which impairs MeqR2-DNA complex formation in vitro. A binding stoichiometry of one effector molecule per MeqR2 monomer and a K D of 22 nM were determined for the effector-protein complex by isothermal titration calorimetry (ITC). Quantitative reverse transcriptase PCR analyses suggested that MeqR2 is a potent regulator of the meqDEF operon; however, additional regulatory systems have a major impact on transcriptional control of the catabolic operons and of meqR2.A rthrobacter sp. strain Rue61a, an isolate from sludge of the wastewater treatment plant of a coal tar refinery, is able to utilize quinaldine (2-methylquinoline) as a source of carbon and energy (1, 2). Methylquinolines and related N-heteroaromatic compounds are constituents of coal tar and shale oil. Quinolines are more water soluble than their homocyclic naphthalene analogs, and hence they are more readily transported to subsoil and groundwater if entering the environment, e.g., from abandoned coal processing facilities or from wood-creosoting activities. Many quinoline derivatives are considered toxic and/or mutagenic and thus are of environmental concern. However, quinaldine is used in aquaculture for anesthesia of fish (3). Interestingly, quinaldine is also a possible chemical signal in the urine of the male red fox (4) and the male ferret (5) and a component of the anal sac secretion of skunks (6). Quinoline derivatives of natural origin moreover include a plethora of alkaloids from microbial, animal, and plant sources, especially from the Rutaceae (7). A number of bacterial isolates, mainly aerobes from soil, with the ability to degrade quinoline derivatives have been described in the literature (reviewed in reference 8).Quinaldine degradation by Arthrobacter sp. Rue61a is initiated by two hydroxylation steps, catalyzed by the molybdenum enzyme quinaldine 4-oxidase...