Novel michael addition networks containing urethane hydrogen bonding

Covalently crosslinked networks based on poly(propylene glycol) bis(acetoacetate) with either neopentyl glycol diacrylate or hydroxyethyl acrylate derivatized bis(4‐isocyanatocyclohexyl)methane (HMDI) were prepared utilizing the Michael addition reaction in the presence of catalytic quantities of diazabicyclo[5.4.0]undec‐7‐ene (DBU). These networks were prepared in the absence of solvent at 23 °C without the formation of byproducts. Mechanical and thermal analyses of the networks were performed utilizing DMA, tensile testing, and TGA. Tensile analysis revealed that the introduction of hydrogen‐bonding urethane linkages in the diacrylate segment resulted in higher tensile strengths and elongation to break compared with nonhydrogen‐bonding analogs. All crosslinked products exhibited high gel fractions and excellent thermomechanical properties. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4118–4128, 2007     

Lewis and Brönsted acid catalyzed Friedel-Crafts hydroxyalkylation of mucohalic acids: a facile synthesis of functionalized γ-aryl γ-butenolides

A catalytic, green and practical method for Friedel-Crafts hydroxyalkylation of mucohalic acid has been accomplished. Reaction of mucohalic acids with various electron-rich aromatic compounds in the presence of catalytic (1 mol % to 10 mol %) In(OTf)₃ or Brönsted acid, such as H₂SO₄ in acetic acid provides γ-aryl γ-butenolides in moderate to excellent yield.     

19F NMR Monitoring of Reversible Protein Post-Translational Modifications: Class D β-Lactamase Carbamylation and Inhibition

Bacterial production of β-lactamases with carbapenemase activity is a global health threat. The active sites of class D carbapenemases such as OXA-48, which is of major clinical importance, uniquely contain a carbamylated lysine residue which is essential for catalysis. Although there is significant interest in characterizing this post-translational modification, and it is a promising inhibition target, protein carbamylation is challenging to monitor in solution. We report the use of ¹⁹F NMR spectroscopy to monitor the carbamylation state of ¹⁹F-labelled OXA-48. This method was used to investigate the interactions of OXA-48 with clinically used serine β-lactamase inhibitors, including avibactam and vaborbactam. Crystallographic studies on ¹⁹F-labelled OXA-48 provide a structural rationale for the sensitivity of the ¹⁹F label to active site interactions. The overall results demonstrate the use of ¹⁹F NMR to monitor reversible covalent post-translational modifications.     

Synthesis of the seco-Limonoid BCD Ring System Identifies a Hsp90 Chaperon Machinery (p23) Inhibitor

D-Ring-seco-limonoids (tetranortriterpenoids), such as gedunin and xylogranin B display anti-cancer activity, acting via inhibition of Hsp90 and/or associated chaperon machinery (e.g., p23). Despite this, these natural products have received relatively little attention, both in terms of an enabling synthetic approach (which would allow access to derivatives), and as a consequence their structure–activity relationship (SAR). Disclosed herein is a generally applicable synthetic route to the BCD ring system of the seco-D-ring double bond containing limonoids. Furthermore, cell based assays revealed the first skeletal fragment that exhibited inhibition of the p23 enzyme at a level which was equipotent to that of gedunin, despite being much less structurally complex.     

Biological Applications of Electron Paramagnetic Resonance Viscometry Using a 13C-Labeled Trityl Spin Probe

Alterations in viscosity of biological fluids and tissues play an important role in health and diseases. It has been demonstrated that the electron paramagnetic resonance (EPR) spectrum of a ¹³C-labeled trityl spin probe (¹³C-dFT) is highly sensitive to the local viscosity of its microenvironment. In the present study, we demonstrate that X-band (9.5 GHz) EPR viscometry using ¹³C-dFT provides a simple tool to accurately measure the microviscosity of human blood in microliter volumes obtained from healthy volunteers. An application of low-field L-band (1.2 GHz) EPR with a penetration depth of 1–2 cm allowed for microviscosity measurements using ¹³C-dFT in the living tissues from isolated organs and in vivo in anesthetized mice. In summary, this study demonstrates that EPR viscometry using a ¹³C-dFT probe can be used to noninvasively and rapidly measure the microviscosity of blood and interstitial fluids in living tissues and potentially to evaluate this biophysical marker of microenvironment under various physiological and pathological conditions in preclinical and clinical settings.     

Rheo-NMR in food science—Recent opportunities

For over 25 years, nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques have been used to study materials under mechanical deformation. Collectively, these methods are referred to as Rheo-NMR. In many cases, it provides spatially and temporally resolved maps of NMR spectra, intrinsic NMR parameters (such as relaxation times), or motion (such as diffusion or flow). Therefore, Rheo-NMR is complementary to conventional rheological measurements. This review will briefly summarize current capabilities and limitations of Rheo-NMR in the context of material science and food science in particular. It will report on recent advances such as the incorporation of torque sensors or the implementation of large amplitude oscillatory shear and point out future opportunities for Rheo-NMR in food science.     

Direct carbamation of cellulose fiber sheets

The paper is on introducing carbamate groups in sheets of cellulose fiber assemblies by pad-dry-cure treatments with aqueous solutions of polyethylene glycol, amide and salt. The effects of process variables—on carbamation levels and on mechanical properties of the substrate—are reported. Depending on treatment conditions, the nitrogen contents in substrates are in the range 0.668–2.252 wt%, corresponding to nominal degrees of carbamate group substitution of 0.08–0.28. The carbamation is initiated at 140 °C curing, and the levels rise with temperature up to 220 °C, but decrease at higher temperatures. The duration of curing also exerts an influence. There is a catalytic effect of sodium acetate on the carbamation, but the salt also induces a brown coloration in samples, which is likely a result of Maillard-type reactions. The treatments cause hydrolytic degradation in substrates, but there are options to adjust treatment conditions and minimize damage. Pad-dry-cure treatments are a common operation in the textile and paper industries, and the process may be adopted in commercial-scale operations to create derivatized paper or fabrics (woven, knitted or non-woven) for utilization in applications such as adsorbents for heavy metals from waste water, in hygiene products, in the creation of flame retardant products, or in creating all-cellulose composites by further treatment with alkali.     

Photochemical Alkene Isomerization for the Synthesis of Polysubstituted Furans and Pyrroles under Neutral Conditions

A photochemical approach to polysubstituted heterocycles using UV-induced alkene isomerization is described. The method allows for the synthesis of disubstituted furans and pyrroles under mild and neutral conditions and also provides access to a class of trisubstituted furans pertinent to natural-product synthesis. The method has broad functional-group tolerance and many richly decorated heterocycles have been prepared incorporating functional groups that are unstable under Brønsted and Lewis acidic conditions.     

Iron-Catalyzed Cross-Coupling of Alkynyl and Styrenyl Chlorides with Alkyl Grignard Reagents in Batch and Flow

Transition-metal-catalyzed cross-coupling chemistry can be regarded as one of the most powerful protocols to construct carbon–carbon bonds. While the field is still dominated by palladium catalysis, there is an increasing interest to develop protocols that utilize cheaper and more sustainable metal sources. Herein, we report a selective, practical, and fast iron-based cross-coupling reaction that enables the formation of Csp−Csp³ and Csp²−Csp³ bonds. In a telescoped flow process, the reaction can be combined with the Grignard reagent synthesis. Moreover, flow allows the use of a supporting ligand to be avoided without eroding the reaction selectivity.