1,3-Oxazoline- and 1,3-oxazolidine-2-thiones as substrates in direct modified Stille and Suzuki cross-coupling

1,3-Oxazoline- (OXT) and 1,3-oxazolidine-2-thiones (OZT) can undergo direct Stille and Suzuki cross-coupling reactions under microwave activation to produce 2-aryloxazoles and 2-aryloxazolines in reasonable to good yields.     

Electrochemical Nickel-Catalyzed Selective Inter- and Intramolecular Arylations of Cysteine-Containing Peptides**

Here we report a simple electrochemical route towards the synthesis of S-arylated peptides by a site selective coupling of peptides with aryl halides under base free conditions. This approach demonstrates the power of electrochemistry to access both highly complex peptide conjugates and cyclic peptides.     

A surfactant-assisted preparation of well dispersed rhodium nanoparticles within the mesopores of AlSBA-15: characterization and use in catalysis

Well dispersed and efficient Rh(0) hydrogenation catalysts were obtained by the reduction of Rh(III)-exchanged mesoporous aluminosilicates by sodium borohydride in the presence of N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl) ammonium chloride.     

Propensity for local folding induced by the urea fragment in short-chain oligomers

Examination of local folding and H-bonding patterns in model compounds can be extremely informative to gain insight into the propensity of longer-chain oligomers to adopt specific folding patterns (i.e. foldamers) based on remote interactions. Using a combination of experimental techniques (i.e. X-ray diffraction, FT-IR absorption and NMR spectroscopy) and theoretical calculations at the density functional theory (DFT) level, we have examined the local folding patterns induced by the urea fragment in short-chain aza analogues of beta- and gamma-amino acid derivatives. We found that the urea-turn, a robust C(8) conformation based on 1<--3 H-bond interaction, is largely populated in model ureidopeptides (I-IV) obtained by replacing the alpha-carbon of a beta-amino acid by a nitrogen. This H-bonding scheme is likely to compete with remote H-bond interactions, thus preventing the formation of secondary structures based on remote intrastrand interactions in longer oligomers. In related oligomers obtained by the addition of a methylene in the main chain (V-VIII), nearest-neighbour H-bonded interactions are unfavourable i.e. the corresponding C9 folding pattern is hardly populated. In this series, folding based on remote intrastrand interactions becomes possible for longer oligomers. We present spectroscopic evidence that tetraurea VIII is likely to be the smallest unit capable of reproducing the H-bonded motif found in 2.5-helical N,N'-linked oligoureas.     

Docking, synthesis, and NMR studies of mannosyl trisaccharide ligands for DC-SIGN lectin

DC-SIGN, a lectin, which presents at the surface of immature dendritic cells, constitutes nowadays a promising target for the design of new antiviral drugs. This lectin recognizes highly glycosylated proteins present at the surface of several pathogens such as HIV, Ebola virus, Candida albicans, Mycobacterium tuberculosis, etc. Understanding the binding mode of this lectin is a topic of tremendous interest and will permit a rational design of new and more selective ligands. Here, we present computational and experimental tools to study the interaction of di- and trisaccharides with DC-SIGN. Docking analysis of complexes involving mannosyl di- and trisaccharides and the carbohydrate recognition domain (CRD) of DC-SIGN have been performed. Trisaccharides Manalpha1,2[Manalpha1,6]Man 1 and Manalpha1,3[Manalpha1,6]Man 2 were synthesized from an orthogonally protected mannose as a common intermediate. Using these ligands and the soluble extracellular domain (ECD) of DC-SIGN, NMR experiments based on STD and transfer-NOE were performed providing additional information. Conformational analysis of the mannosyl ligands in the free and bound states was done. These studies have demonstrated that terminal mannoses at positions 2 or 3 in the trisaccharides are the most important moiety and present the strongest contact with the binding site of the lectin. Multiple binding modes could be proposed and therefore should be considered in the design of new ligands.     

Automated image-based method for laboratory screening of coating libraries for adhesion of algae and bacterial biofilms

Assessment and down-selection of non-biocidal coatings that prevent the adhesion of fouling organisms in the marine environment requires a hierarchy of laboratory methods to reduce the number of experimental coatings for field testing. Automated image-based methods are described that facilitate rapid, quantitative biological screening of coatings generated through combinatorial polymer chemistry. Algorithms are described that measure the coverage of bacterial and algal biofilms on coatings prepared in 24-well plates and on array panels, respectively. The data are used to calculate adhesion strength of organisms on experimental coatings. The results complement a number of physical and mechanical methods developed to screen large numbers of samples.     

Bacterial base excision repair enzyme Fpg recognizes bulky N7-substituted-FapydG lesion via unproductive binding mode

Fpg is a bacterial base excision repair enzyme that removes oxidized purines from DNA. This work shows that Fpg and its eukaryote homolog Ogg1 recognize with high affinity FapydG and bulky N7-benzyl-FapydG (Bz-FapydG). The comparative crystal structure analysis of stable complexes between Fpg and carbocyclic cFapydG or Bz-cFapydG nucleoside-containing DNA provides the molecular basis of the ability of Fpg to bind both lesions with the same affinity and to differently process them. To accommodate the steric hindrance of the benzyl group, Fpg selects the adequate rotamer of the extrahelical Bz-cFapydG formamido group, forcing the bulky group to go outside the binding pocket. Contrary to the binding mode of cFapydG, the particular recognition of Bz-cFapydG leads the BER enzymes to unproductive complexes which would hide the lesion and slow down its repair by the NER machinery.     

Reduction of the Gibbs phenomenon for smooth functions with jumps by the -algorithm

Recently, Brezinski has proposed to use Wynn's ε-algorithm in order to reduce the Gibbs phenomenon for partial Fourier sums of smooth functions with jumps, by displaying very convincing numerical experiments. In the present paper we derive analytic estimates for the error corresponding to a particular class of hypergeometric functions, and obtain the rate of column convergence for such functions, possibly perturbed by another sufficiently differentiable function. We also analyze the connection to Padé–Fourier and Padé–Chebyshev approximants, including those recently studied by Kaber and Maday.