Helvetica Chimica Acta最新文献

A protocol for the isolation of the antibiotic fidaxomicin (Fdx) from Actinoplanes deccanensis and the isolation of shunt metabolites from A. deccanensis fdxG2⁻ is reported. We constructed the mutant strain A. deccanensis fdxG2⁻ by genetic manipulation which enabled the isolation of shunt metabolites as useful starting points for semisynthetic analogues of Fdx. Furthermore, a synthetic protocol for the conversion of complex A. deccanensis fdxG2⁻ extracts into the single compound FdxG2-OH via methanolysis is presented. This synthetic procedure is complemented by images and practical notes. Full structure assignment is given in the SI and the characterization data files are published to aid experimentalists. The protocol is also suitable as an undergraduate laboratory project. We hope to facilitate research into new Fdx derivatives through the availability of this procedure.

In metal coordination compounds of the divergent ligands 4,2′:6′,4“-terpyridine and 3,2′:6′,3”-terpyridine and their 4′-functionalized derivatives, the central pyridine ring of the 4,2′:6′,4“-terpyridine and 3,2′:6′,3”-terpyridine domains is non-coordinated. We present an overview of data from the Cambridge Structural Database to assess whether there are structural similarities between the coordination compounds of 4,2′:6′,4“-tpy and 1,3-di(pyridin-4-yl)benzene, and between 3,2′:6′,3”-tpy and 1,3-di(pyridin-3-yl)benzene. Based upon structurally characterized compounds, it emerges that the coordination chemistry of ligands including one or more 4,2′:6′,4“-terpyridine or 3,2′:6′,3”-terpyridine metal-binding domains is more abundantly exemplified than that of corresponding ligands based upon 1,3-di(pyridin-4-yl)benzene and 1,3-di(pyridin-3-yl)benzene. We provide an overview of metallamacrocycles and cages, 1D-coordination polymers and 2D- and 3D-networks.

Herein we report that the submonomer method for peptoid synthesis enables access to pure i-PAMAM dendrimers up to 16 amino termini by a divergent solid-phase synthesis using the inexpensive bis(3-trifluoroacetamidopropyl)amine as branching unit. We exemplify this new and efficient approach by a structure-activity relationship study of antibacterial dendrimers obtained by appending the polycationic i-PAMAM dendrimer to a hydrophobic core consisting of either an oligoleucine peptide or an oligo-N-isobutylglycine peptoid. These non-hemolytic dendrimers kill Gram-negative bacteria such as Pseudomonas aeruginosa, Acinetobacter baumannii and Escherichia coli as well as the Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) by a non-membrane disruptive mechanism involving aggregation of intracellular content as reported for antimicrobial peptoids.

We report on a protocol for the hydroxyalkenylation of alkenes using an acridinium photoredox catalyst in combination with 1,2-bis(phenylsulfonyl)ethylene and water. Using the protocol, alkenes could be converted into the corresponding 1-phenylsulfonyl-4-hydroxyalkenes in good yields. The hydroxyalkenylation involves the nucleophilic hydroxylation of alkene-derived radical cations to give β-hydroxyalkyl radicals, which then undergo a radical addition/β-elimination sequence. The catalytic cycle is likely sustained by electron transfer from the acridine radical to the benzenesulfonyl radical, which is formed via a radical addition/elimination sequence.

Biofilms of pathogenic bacteria are responsible for persistent infections in humans, therefore investigations of biofilm formation and treatment strategies are required. The gram-negative enterobacterium Escherichia (E.) coli is the most common pathogen causing chronic or recurring urinary tract infections. Metabolomics approaches targeted the bacterium to investigate specific metabolic patterns of biofilms and regulatory influences on biofilm formation. In this study, we aimed to investigate the metabolome of biofilms formed by the multidrug-resistant extended-spectrum beta-lactamase-producing (ESBL) E. coli PBIO729. For this purpose, a protocol for fast sampling of the macrocolony biofilms and efficient extraction of metabolites was optimized. Validation of an LC-MS/MS method confirmed its usability for the analysis of nucleotides and other phosphorylated metabolites. A GC-MS approach was used to monitor nutrient uptake from the medium in addition to the analysis of amino acid content and metabolites of glycolysis and TCA cycle in E. coli biofilms.

In this communication, a straighforward asymmetric synthesis of spiro-indoline-pyrazolone compounds is described. This methodology consists in a formal [4+1] cycloaddition reaction of 4-bromopyrazolones and aza-ortho-quinone methides generated in situ catalyzed by a bisquinine-derived squaramide in CHCl₃ under basic conditions. A variety of chiral spirocyclic compounds bearing a pyrazolone and an indoline moieties were obtained in moderate to good yields (up to 68 %) and moderate to excellent enantioselectivities (up to 93 % ee).

It is often said that pnictogen-bonding catalysis, and σ-hole catalysis in general, would not work in aqueous systems because the solvent would interfere as an overcompetitive pnictogen-bond acceptor. In this study, we show that the transfer of pnictogen-bonding catalysis from hydrophobic solvents to aqueous systems is possible by replacing only hydrophobic with hydrophilic substrates, without changing catalyst or reaction. This differs from conventional covalent Lewis acid catalysts, which are instantaneously destroyed by ligand exchange. With their water-proof substituents in place of exchangeable ligands, pnictogen-bonding catalysts, the supramolecular counterpart of Lewis acid catalysts, are evinced to catalyze transfer hydrogenation of quinolines in neutral aqueous systems. To secure these results, we introduce a water-soluble fluorogenic substrate that releases a coumarin upon the reduction of quinolines instead of activated quinolidiniums, and stiborane catalysts with deepened σ holes. They demonstrate that pnictogen-bonding catalysts can operate in higher-order architectures for supramolecular systems catalysis under biologically relevant conditions, and provide an operational assay for high-throughput catalyst screening by fluorescence imaging, in situ under relevant aqueous conditions.

Alkylation of N-substituted imidazoles ImR’ (R’=2,4,6-trimethylphenyl, 2,6-diisopropylphenyl, 1-adamantyl) with Mn(I) methylenephosphonium complexes [Cp(CO)₂Mn(η²-P,C-R₂P=C(H)Ph)](BF₄) (PR₂=PPh₂, PCy₂, trans-PC(H)PhCH₂CH₂C (H)Ph) followed by photochemical demetallation afforded a series of bidentate NHC-phosphine ligand precursors [R₂PC(H)PhImR’](BF₄) in moderate to good yield. The same strategy was successfully applied to N-functionalized imidazoles ImL (L=2-pyridyl, CH₂SMe, CH₂ImMe) to afford selectively NHC core pincer pre-ligands featuring phosphine/thioether, phosphine/NHC and phosphine/pyridine side arms. For PCy₂ derivatives, free NHCs in both bidentate and pincer series generated by deprotonation of the corresponding cationic precursors were shown to be persistent at room temperature.