Search results for "heterocyclic"

Rearrangements of 1,2,4-Oxadiazole: “One Ring to Rule Them All”

2017

[Figure not available: see fulltext.] 1,2,4-Oxadiazoles are heterocycles characterized by low aromaticity and the presence of a weak O–N bond and are widely studied due to their tendency to rearrange into more stable heterocyclic compounds. This review covers literature from the last fifteen years, highlighting the general features of 1,2,4-oxadiazoles and their applications. Regarding the reactivity, the development of classical reactions (thermal and photochemical rearrangements) is presented in terms of synthetic utility and mechanistic insight. Among the relevant rearrangement reactions, the Boulton–Katritzky Rearrangement (BKR), Migration – Nucleophilic Attack – Cyclization (MN…

The Role of 1,3-Dipolar Cycloaddition Reactions in the Design and Synthesis of Complex Heterocyclic Scaffolds with Anti-tumor/Anti-infective Activity

2009

A three-coordinate iron–silylene complex stabilized by ligand–ligand dispersion forces

2016

The structural and bonding properties of a three-coordinate N-heterocyclic silyene (NHSi) complex of the iron(II) amide [Fe{N(SiMe3)2}2] are reported. Computational studies reveal that dispersion forces between the amido SiMe3 substituents and the isopropyl substituents on the NHSi ligand significantly enhance the stability of the complex, along with Fe-to-Si π-backbonding. peerReviewed

Side‐on Coordination in Isostructural Nitrous Oxide and Carbon Dioxide Complexes of Nickel

2021

Abstract A nickel complex incorporating an N2O ligand with a rare η2‐N,N′‐coordination mode was isolated and characterized by X‐ray crystallography, as well as by IR and solid‐state NMR spectroscopy augmented by 15N‐labeling experiments. The isoelectronic nickel CO2 complex reported for comparison features a very similar solid‐state structure. Computational studies revealed that η2‐N2O binds to nickel slightly stronger than η2‐CO2 in this case, and comparably to or slightly stronger than η2‐CO2 to transition metals in general. Comparable transition‐state energies for the formation of isomeric η2‐N,N′‐ and η2‐N,O‐complexes, and a negligible activation barrier for the decomposition of the lat…

Acidic Co-Catalysts in Cationic Gold Catalysis.

2016

A systematic study on the effects of Lewis or Bronsted acid co-catalysts in gold-catalyzed reactions was undertaken using representative reactions (O-, N-, and C-nucleophilic additions to alkynes). Through these reactions, it was demonstrated that an acidic co-catalyst can increase the catalyst turnover significantly, enabling practical reaction rates at competitive catalyst loadings (<1 mol %). Further investigation is currently underway to improve the understanding of the subtle principles underlying these experimental observations.

Self-Assembled Molecular Rafts at Liquid|Liquid Interfaces for Four-Electron Oxygen Reduction

2011

The self-assembly of the oppositely charged water-soluble porphyrins, cobalt tetramethylpyridinium porphyrin (CoTMPyP(4+)) and cobalt tetrasulphonatophenyl porphyrin (CoTPPS(4-)), at the interface with an organic solvent to form molecular "rafts", provides an excellent catalyst to perform the interfacial four-electron reduction of oxygen by lipophilic electron donors such as tetrathiafulvalene (TTF). The catalytic activity and selectivity of the self-assembled catalyst toward the four-electron pathway was found to be as good as that of the Pacman type cofacial cobalt porphyrins. The assembly has been characterized by UV-visible spectroscopy, Surface Second Harmonic Generation, and Scanning …

A non-canonical chemical feedback self-limits nitric oxide-cyclic GMP signaling in health and disease

2018

Endothelial nitric oxide (NO) stimulates the heme protein, soluble guanylyl cyclase (sGC) to form vasoprotective cyclic GMP (cGMP). In different disease states such as pulmonary hypertension, NO-cGMP signaling is pharmacologically augmented, yet the pathomechanisms leading to its dysregulation are incompletely understood. Here we show in pulmonary artery endothelial cells that endogenous NO or NO donor compounds acutely stimulate sGC activity, but chronically down-regulate both sGC protein and cGMP formation. Surprisingly, this endogenous feedback mechanism was independent of canonical cGMP signaling via cGMP-dependent protein kinase. It did not involve thiol-dependent modulation, a process…

Comparative effectiveness of helicopter emergency medical services compared to ground emergency medical services

2013

Physician-staffed helicopter emergency medical services (HEMS) are a well-established component of prehospital trauma care in Germany. Reduced rescue times and increased catchment area represent presumable specific advantages of HEMS. In contrast, the availability of HEMS is connected to a high financial burden and depends on the weather, day time and controlled visual flight rules. To date, clear evidence regarding the beneficial effects of HEMS in terms of improved clinical outcome has remained elusive.Traumatized patients (Injury Severity Score; ISS≥9) primarily treated by HEMS or ground emergency medical services (GEMS) between 2007 and 2009 were analyzed using the TraumaRegister DGU® o…

Cytochrome-P450 phosphorylation as a functional switch

2002

Xenobiotic metabolizing cytochromes P450 (CYP) were shown to be phosphorylated in vitro (using purified protein kinases together with purified CYPs), in intact cells (in V79 cells after transfection of cDNAs coding for individual CYPs, in diagnostic mutants, in hepatocytes), and in whole organisms (rats). CYP phosphorylation is highly isoenzyme selective in that only some CYPs are phosphorylated. Protein kinase A (PKA) was identified as a major catalyst for the phosphorylation of CYPs. The PKA recognition motif Arg-Arg-X-Ser is present in several members of the CYP2 family, but is used by only some of them, most notably by CYP2B1/2B2 and CYP2E1. For CYP2B1 it was shown that a substantial po…

A solvent-free regioselective iodination route of ortho-carboranes.

2006

Tetraiodo-ortho-carborane based X-ray contrast agents can be readily prepared in a high yield, fast, clean, regioselective fashion by a solvent-free reaction of ortho-carboranes with iodine in sealed tubes.