Die Bildung von Semibenzolen bei der Dimerisierung von Benzyl-Radikalen

Bei der Dimerisierung von Benzyl-Radikalen bilden sich neben dem -Kopplungsprodukt Bibenzyl (9) auch instabile Semibenzole durch o- und p-Kopplung, die im Verlauf der Reaktion zu Bibenzyl umlagern. Sie werden anhand ihrer 1H-CIDNP-NMR-Spektren nachgewiesen. Mit Säure lassen sie sich als o- und p-Benzyltoluole abfangen. Aus der Ausbeute der Benzyltoluole wird geschlossen, daß die Dimerisierung bei 30°C zu 19% über Semibenzole verläuft. Die Produktverteilung und ihre Temperaturabhängigkeit weisen auf intermediäre energetisch verschiedene bimolekulare Benzyl-Komplexe als produktkontrollierende Zwischenstufen hin

Model studies of lantibiotic biogenesis

A six residue polypeptide has been synthesized to study the proposed biosynthesis of lanthionine. It is shown that this peptide spontaneously cyclizes in a biomimetic fashion via a completely stereoselective intramolecular Michael addition to form (2s, 6R)-lanthionine, as found in naturally occurring lantibiotics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30395/1/0000014.pd

Towards novel difluorinated sugar mimetrics; syntheses and conformational analyses of highly-functionalised difluorinated cyclooctenones

Highly-functionalised difluorinated cyclooctenones were synthesised from trifluoroethanol using either metallated difluoroenol acetal or carbamate chemistry, followed by a [2,3]-Wittig rearrangement or aldol reaction. Efficient RCM reactions afforded the title compounds which showed rather restricted fluxional behaviour by VT 19F NMR. Topological characterisation by molecular modelling and NOESY/ROESY experiments offered a number of challenges, but allowed the identification of two favoured boat-chair conformers which interconverted by pseudorotation with relatively large activation barriers

The synthesis and characterization of some new difluorophosphine derivatives

The heretofore unknown chelating fluorophosphine ligands, F2PCH2PF2 and F2PCH2CH=CH2 have been prepared and characterized. The reagent F2PCH2I has been prepared and used in the synthesis of F2PCH2PF2. NMR data are given.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21864/1/0000268.pd

Probing degeneracy in antigen-antibody recognition at the immunodominant site of foot-and-mouth disease virus

Antigen-antibody binding is regarded as one of the most representative examples of specific molecular recognition in nature. The simplistic view of antigenic recognition in terms of a lock-and-key mechanism is obsolete, as it is evident that both antigens and antibodies are flexible and can undergo substantial mutual adaptation. This flexibility is the source of complexities such as degeneracy and nonadditivity in antigenic recognition. We have used surface plasmon resonance to study the effects of combining multiple amino acid replacements within the sequence of the antigenic GH loop of foot-and-mouth disease virus, Our aim was 2-fold: to explore the extent to which antigenic degeneracy can be extended in this particular case, and to search for potential nonadditive effects in introducing multiple amino acid replacements. Combined Spain analysis of one such multiply substituted peptide by SPR, solution NMR and X-ray diffraction shows that antigenic degeneracy can be expected as long as residues directly interacting with the paratope are conserved and the peptide bioactive folding is unaltered

An α-Helical Signal in the Cytosolic Domain of the Interleukin 2 Receptor β Chain Mediates Sorting Towards Degradation after Endocytosis

High-affinity IL2 receptors consist of three components, the α, β, and γ chains that are associated in a noncovalent manner. Both the β and γ chains belong to the cytokine receptor superfamily. Interleukin 2 (IL2) binds to high-affinity receptors on the cell surface and IL2-receptor complexes are internalized. After endocytosis, the components of this multimolecular receptor have different intracellular fates: one of the chains, α, recycles to the plasma membrane, while the others, β and γ, are routed towards late endocytic compartments and are degraded. We show here that the cytosolic domain of the β chain contains a 10–amino acid sequence which codes for a sorting signal. When transferred to a normally recycling receptor, this sequence diverts it from recycling. The structure of a 17–amino acid segment of the β chain including this sequence has been studied by nuclear magnetic resonance and circular dichroism spectroscopy, which revealed that the 10 amino acids corresponding to the sorting signal form an amphipathic α helix. This work thus describes a novel, highly structured signal, which is sufficient for sorting towards degradation compartments after endocytosis

Review NMR studies of RNA dynamics and structural plasticity using NMR residual dipolar couplings

An increasing number of RNAs are being discovered that perform their functions by undergoing large changes in conformation in response to a variety of cellular signals, including recognition of proteins and small molecular targets, changes in temperature, and RNA synthesis itself. The measurement of NMR residual dipolar couplings (RDCs) in partially aligned systems is providing new insights into the structural plasticity of RNA through combined characterization of large-amplitude collective helix motions and local flexibility in noncanonical regions over a wide window of biologically relevant timescales (<milliseconds). Here, we review RDC methodology for studying RNA structural dynamics and survey what has been learnt thus far from application of these methods. Future methodological challenges are also identified. © 2007 Wiley Periodicals, Inc. Biopolymers 86: 384–402, 2007. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at [email protected] Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/56044/1/20765_ftp.pd