Pd-catalysed intramolecular regioselective arylation of 2-pyrones,pyridones, coumarins and quinolones by C–H bond functionalization

The intramolecular arylation of 2-pyrones, 2-pyridones, coumarins and quinolones is reported using Pd^II precatalyst sources without added phosphine ligands. The excellent yields and convenient reagents enables the formation of various analogues containing these moieties, and access to potential biologically active candidates. Stoichiometric studies were carried out to provide an insight into the oxidation addition step. A switch in regioselectivity, together with a hydrodebromination process, was observed in the case of a 3-bromo-2-pyrone.     

Halogen‐ and Hydrogen‐Bonded Salts and Co‐crystals Formed from 4‐Halo‐2,3,5,6‐tetrafluorophenol and Cyclic Secondary and Tertiary Amines: Orthogonal and Non‐orthogonal Halogen and Hydrogen Bonding,and Synthetic Analogues of Halogen‐Bonded Biological Systems

Co‐crystallisation of, in particular, 4‐iodotetrafluorophenol with a series of secondary and tertiary cyclic amines results in deprotonation of the phenol and formation of the corresponding ammonium phenate. Careful examination of the X‐ray single‐crystal structures shows that the phenate anion develops a C?O double bond and that the C?C bond lengths in the ring suggest a Meissenheimer‐like delocalisation. This delocalisation is supported by the geometry of the phenate anion optimised at the MP2(Full) level of theory within the aug‐cc‐pVDZ basis (aug‐cc‐pVDZ‐PP on I) and by natural bond orbital (NBO) analyses. With sp² hybridisation at the phenate oxygen atom, there is strong preference for the formation of two non‐covalent interactions with the oxygen sp² lone pairs and, in the case of secondary amines, this occurs through hydrogen bonding to the ammonium hydrogen atoms. However, where tertiary amines are concerned, there are insufficient hydrogen atoms available and so an electrophilic iodine atom from a neighbouring 4‐iodotetrafluorophenate group forms an I???O halogen bond to give the second interaction. However, in some co‐crystals with secondary amines, it is also found that in addition to the two hydrogen bonds forming with the phenate oxygen sp² lone pairs, there is an additional intermolecular I???O halogen bond in which the electrophilic iodine atom interacts with the C?O π‐system. All attempts to reproduce this behaviour with 4‐bromotetrafluorophenol were unsuccessful. These structural motifs are significant as they reproduce extremely well, in low‐molar‐mass synthetic systems, motifs found by Ho and co‐workers when examining halogen‐bonding interactions in biological systems. The analogy is cemented through the structures of co‐crystals of 1,4‐diiodotetrafluorobenzene with acetamide and with N‐methylbenzamide, which, as designed models, demonstrate the orthogonality of hydrogen and halogen bonding proposed in Ho’s biological study.     

Mechanically Modulating the Photophysical Properties of Fluorescent Protein Biocomposites for Ratio‐ and Intensiometric Sensors

Mechanically sensitive biocomposites comprised of fluorescent proteins report stress through distinct pathways. Whereas a composite containing an enhanced yellow fluorescent protein (eYFP) exhibited hypsochromic shifts in its fluorescence emission maxima following compression, a composite containing a modified green fluorescent protein (GFPuv) exhibited fluorescence quenching under the action of mechanical force. These ratio‐ and intensiometric sensors demonstrate that insights garnered from disparate fields (that is, polymer mechanochemistry and biophysics) can be harnessed to guide the rational design of new classes of biomechanophore‐containing materials.     

Improvement of derivatized amino acid detection sensitivity in micellar electrokinetic capillary chromatography by means of acid-induced pH-mediated stacking technique

Derivatization is a frequently used sample preparation procedure applicable to the enhancement of analyte detection sensitivity. Amino acids mostly require derivatization prior to electrophoretic or chromatographic analysis, especially if spectrophotometric detection is used. This study presents an on-line preconcentration technique for derivatized amino acids. The sensitivity of the method was improved by the utilization of the proposed acid-induced pH-mediated stacking mechanism. The method is demonstrated by preconcentration of amino acids labeled with 2,4-dinitrofluorobenzene. Use of optimized conditions for a large sample volume injection (40 s, 13.8 kPa) followed by electrokinetic injection of 0.1 M HCl (20 s, 10 kV) gave a 20- to 30-fold enhancement of sensitivity. The significance of the sweeping mechanism and pseudo-isotachophoresis for the on-line sample focusing and the influence of parameters on the preconcentration process were discussed. The applicability of the elaborated method was demonstrated using human urine samples.     

LC-MS/MS determination of potential endocrine disruptors of cortico signalling in rivers and wastewaters

A targeted analytical method was established to determine a large number of chemicals known to interfere with the gluco- and mineralocorticoid signalling pathway. The analytes comprise 30 glucocorticoids and 9 mineralocorticoids. Ten out of these corticosteroids were primary metabolites. Additionally, 14 nonsteroids were included. These analytes represent a broader range of possible adverse modes of action than previously reported. For the simultaneous determination of these structurally diverse compounds, a single-step multimode solid-phase extraction and pre-concentration was applied. Extracts were separated by a short linear HPLC gradient (20 min) on a core shell RP column (2.7 μm particle size) and compounds identified and quantified by LC-MS/MS. The method provided excellent retention time reproducibility and detection limits in the low nanograms per litre range. Untreated hospital wastewater, wastewater treatment plant influent, treated effluent and river waters were analysed to demonstrate the applicability of the method. The results show that not all compounds were sufficiently eliminated by the wastewater treatment, resulting in the presence of several steroids (～20 ng/L) and nonsteroids in the final effluent, some of them at high concentrations up to 200 ng/L. Most of the detected mono-hydroxylated steroidal transformation products were found at significantly higher concentrations than their parent compounds. We therefore recommend to include these potentially bioactive metabolites in environmental toxicity assessment.     

Development of a broad spectrum method for measuring flame retardants - Overcoming the challenges of non-invasive human biomonitoring studies

Flame retardants (FRs), such as polybrominated diphenyl ethers (PBDEs) and phosphate flame retardants (PFRs), are a diverse group of compounds that are used to improve fire safety in many consumer products, such as furniture, textiles, electronics, etc. As these compounds are potentially harmful for human health, there is a need to better understand human exposure. Exposure to environmental contaminants can be monitored by the measurement of external sources of exposures and also by the determination of contaminant levels in human samples. For ethical and practical reasons, noninvasive matrices, such as hair, are preferred but, unfortunately, not widely used due to methodological limitations. A major challenge is sample availability: only small amounts can be sampled per individual. Multi-residue methods are therefore essential in order to determine multiple compounds in low sample amounts. In the framework of the FP7 project (INFLAME), an analytical method for the simultaneous determination of PBDEs and PFRs in human hair has been optimized and validated. Before extraction, hair samples (200 mg) were denaturated in nitric acid (HNO₃) for 25 min at 25 °C. Consecutively, the samples were extracted using a mixture of hexane:dichloromethane, and extracts were further fractionated on Florisil. Fraction A which contained PBDEs was additionally cleaned on acidified silica gel and measured by gas chromatography coupled with electron capture negative ionization mass spectrometry (GC-ECNI-MS), while fraction B containing PFRs was directly analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS). This approach resulted in recoveries between 81–120 % for PBDEs and 75–113 % for PFRs (relative standard deviation (RSD)?n?=?9). The optimized multi-residue method has been applied to 20 human hair samples. The obtained results indicated that the levels of PBDEs in hair samples were very low (0.2–12 ng/g) in relation to PBDE levels in human hair samples from other studies and most of the time below the method limit of quantification (LOQ_m). On the contrary, the PFR levels were relatively high as they were in the range of the levels previously found in dust samples (2–5,032 ng/g hair). We would like to highlight that the contribution of air and dust cannot be neglected (especially in the case of PFRs); therefore, we suggest that hair might be a good indicator of retrospective and integral exposure (which includes atmospheric deposition as well as endogenous mechanisms). Moreover, the aim of our study is focused on exposure assessment and levels detected in hair (independently of whether they come from internal or external exposure) and will significantly contribute to the exposure assessment. Graphical abstract

Hair - an efficient way for sampling of personal cloud of exposure. Copyright ©2014 iStockphoto LP     

Generic positivity and foliations in positive characteristic

We prove generic semipositivity of the tangent bundle of a non-uniruled Calabi–Yau variety in positive characteristic. We also construct an example of a nef line bundle in characteristic zero, whose each reduction to positive characteristic is not nef.     

A Short Synthesis of Fusaric Acid and Analogues

Fusaric acid (5-n-butyl-pyridine-2-carboxylic acid) and other substituted picolinic acid derivatives are synthesized in two steps from readily available α,β-unsaturated hydrazones and 2-chloroacrylonitrile in high yield.     

Crystallographic evidence for unintended benzisothiazolinone 1‐oxide formation from benzothiazinones through oxidation

1,3‐Benzothiazin‐4‐ones (BTZs) are a promising new class of drugs with activity against Mycobacterium tuberculosis, which have already reached clinical trials. A product obtained in low yield upon treatment of 8‐nitro‐2‐(piperidin‐1‐yl)‐6‐(trifluoromethyl)‐4H‐benzothiazin‐4‐one with 3‐chloroperbenzoic acid, in analogy to a literature report describing the formation of sulfoxide and sulfone derived from BTZ043 [Tiwari et al. (2015). ACS Med. Chem. Lett. 6 , 128–133], is a ring‐contracted benzisothiazolinone (BIT) 1‐oxide, namely, 7‐nitro‐2‐(piperidine‐1‐carbonyl)‐5‐(trifluoromethyl)benzo[d]isothiazol‐3(2H)‐one 1‐oxide, C₁₄H₁₂F₃N₃O₅S, as revealed by X‐ray crystallography. Single‐crystal X‐ray analysis of the oxidation product originally assigned as BTZ043 sulfone provides clear evidence that the structure of the purported BTZ043 sulfone is likewise the corresponding BIT 1‐oxide, namely, 2‐[(S)‐2‐methyl‐1,4‐dioxa‐8‐azaspiro[4.5]decane‐8‐carbonyl]‐7‐nitro‐5‐(trifluoromethyl)benzo[d]isothiazol‐3(2H)‐one 1‐oxide, C₁₇H₁₆F₃N₃O₇S. A possible mechanism for the ring contraction affording the BIT 1‐oxides instead of the anticipated constitutionally isomeric BTZ sulfones and antimycobacterial activities thereof are discussed.