Electron Paramagnetic Resonance for the Detection of Electrochemically Generated Hydroxyl Radicals: Issues Associated with Electrochemical Oxidation of the Spin Trap.

For the detection of electrochemically produced hydroxyl radicals (HO·) from the oxidation of water on a boron-doped diamond (BDD) electrode, electron paramagnetic resonance spectroscopy (EPR) in combination with spin trap labels is a popular technique. Here, we show that quantification of the concentration of HO· from water oxidation via spin trap electrochemical (EC)-EPR is problematic. This is primarily due to the spin trap oxidizing at potentials less positive than water, resulting in the same spin trap-OH· adduct as formed from the solution reaction of OH· with the spin trap. We illustrate this through consideration of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap for OH·. DMPO oxidation on a BDD electrode in an acidic aqueous solution occurs at a peak current potential of +1.90 V vs SCE; the current for water oxidation starts to rise rapidly at ca. +2.3 V vs SCE. EC-EPR spectra show signatures due to the spin trap adduct (DMPO-OH·) at potentials lower than that predicted thermodynamically (for water/HO·) and in the region for DMPO oxidation. Increasing the potential into the water oxidation region, surprisingly, shows a lower DMPO-OH· concentration than when the potential is in the DMPO oxidation region. This behavior is attributed to further oxidation of DMPO-OH·, production of fouling products on the electrode surface, and bubble formation. Radical scavengers (ethanol) and other spin traps, here N-tert-butyl-α-phenylnitrone, α-(4-pyridyl N-oxide)-N-tert-butylnitrone, and 2-methyl-2-nitrosopropane dimer, also show electrochemical oxidation signals less positive than that of water on a BDD electrode. Such behavior also complicates their use for the intended application.

Electrocardiographic characteristics in patients with heart failure and normal ejection fraction: A systematic review and meta-analysis.

BACKGROUND: Little is known about ECG abnormalities in patients with heart failure and normal ejection fraction (HeFNEF) and how they relate to different etiologies or outcomes. METHODS AND RESULTS: We searched the literature for peer-reviewed studies describing ECG abnormalities in HeFNEF other than heart rhythm alone. Thirty five studies were identified and 32,006 participants. ECG abnormalities reported in patients with HeFNEF include atrial fibrillation (prevalence 12%-46%), long PR interval (11%-20%), left ventricular hypertrophy (LVH, 10%-30%), pathological Q waves (11%-18%), RBBB (6%-16%), LBBB (0%-8%), and long JTc (3%-4%). Atrial fibrillation is more common in patients with HeFNEF compared to those with heart failure and reduced ejection fraction (HeFREF). In contrast, long PR interval, LVH, Q waves, LBBB, and long JTc are more common in patients with HeFREF. A pooled effect estimate analysis showed that QRS duration ≥120 ms, although uncommon (13%-19%), is associated with worse outcomes in patients with HeFNEF. CONCLUSIONS: There is high variability in the prevalence of ECG abnormalities in patients with HeFNEF. Atrial fibrillation is more common in patients with HeFNEF compared to those with HeFREF. QRS duration ≥120 ms is associated with worse outcomes in patients with HeFNEF. Further studies are needed to address whether ECG abnormalities correlate with different phenotypes in HeFNEF.

Metallohelices that kill Gram-negative pathogens using intracellular antimicrobial peptide pathways.

A range of new water-compatible optically pure metallohelices - made by self-assembly of simple non-peptidic organic components around Fe ions - exhibit similar architecture to some natural cationic antimicrobial peptides (CAMPs) and are found to have high, structure-dependent activity against bacteria, including clinically problematic Gram-negative pathogens. A key compound is shown to freely enter rapidly dividing E. coli cells without significant membrane disruption, and localise in distinct foci near the poles. Several related observations of CAMP-like mechanisms are made via biophysical measurements, whole genome sequencing of tolerance mutants and transcriptomic analysis. These include: high selectivity for binding of G-quadruplex DNA over double stranded DNA; inhibition of both DNA gyrase and topoisomerase I in vitro; curing of a plasmid that contributes to the very high virulence of the E. coli strain used; activation of various two-component sensor/regulator and acid response pathways; and subsequent attempts by the cell to lower the net negative charge of the surface. This impact of the compound on multiple structures and pathways corresponds with our inability to isolate fully resistant mutant strains, and supports the idea that CAMP-inspired chemical scaffolds are a realistic approach for antimicrobial drug discovery, without the practical barriers to development that are associated with natural CAMPS.

NMR-based assignment of isoleucine vs. allo-isoleucine stereochemistry.

A simple 1H and 13C NMR spectrometric analysis is demonstrated that permits differentiation of isoleucine and allo-isoleucine residues by inspection of the chemical shift and coupling constants of the signals associated with the proton and carbon at the α-stereocentre. This is applied to the estimation of epimerisation during metal-free N-arylation and peptide coupling reactions.

Antifreeze Protein Mimetic Metallohelices with Potent Ice Recrystallization Inhibition Activity.

Antifreeze proteins are produced by extremophile species to control ice formation and growth, and they have potential applications in many fields. There are few examples of synthetic materials which can reproduce their potent ice recrystallization inhibition property. We report that self-assembled enantiomerically pure, amphipathic metallohelicies inhibited ice growth at just 20 µM. Structure-property relationships and calculations support the hypothesis that amphipathicity is the key motif for activity. This opens up a new field of metallo-organic antifreeze protein mimetics and provides insight into the origins of ice-growth inhibition.

Chronic total occlusion in an infarct-related coronary artery and the risk of appropriate ICD therapies.

INTRODUCTION: Risk stratification for ventricular arrhythmias in patients with ischemic cardiomyopathy needs to be improved. Coronary chronic total occlusions in an infarct-related artery (IRA-CTOs) have been associated with an increased arrhythmic risk. This study aimed to evaluate the association between IRA-CTOs and appropriate implantable cardioverter-defibrillator (ICD) therapies. METHODS AND RESULTS: Observational cohort study that included 342 patients with ischemic cardiomyopathy, an ICD implanted for primary or secondary prevention, and a coronary angiography performed shortly before ICD implantation. The ICD was implanted for primary prevention in 163 patients (48%). IRA-CTO was found in 161 patients (47%). During a median follow-up of 33 months, 41% of patients experienced at least one appropriate ICD therapy. Patients with IRA-CTO had higher proportions of appropriate ICD therapies (57% vs. 26%, P < 0.001) and appropriate ICD shocks (40% vs. 17%, P < 0.001). At multivariate Cox regression, IRA-CTO was the only variable that consistently resulted as independent predictor of appropriate ICD therapies and shocks both in the global population of the study (HR 2.3, P < 0.001 and HR 3, P < 0.001, respectively) and when analyzing separately patients with primary or secondary prevention ICD. CONCLUSIONS: IRA-CTO is an independent predictor of appropriate ICD therapies, including appropriate ICD shocks. This association is consistent across all the subgroups analyzed. Patients with IRA-CTO have a very high risk of appropriate ICD therapies. These findings may help improving risk stratification as well as the management of ventricular arrhythmias in patients with ischemic cardiomyopathy.

Synthesis and characterization of triangulene.

Triangulene, the smallest triplet-ground-state polybenzenoid (also known as Clar's hydrocarbon), has been an enigmatic molecule ever since its existence was first hypothesized. Despite containing an even number of carbons (22, in six fused benzene rings), it is not possible to draw Kekulé-style resonant structures for the whole molecule: any attempt results in two unpaired valence electrons. Synthesis and characterization of unsubstituted triangulene has not been achieved because of its extreme reactivity, although the addition of substituents has allowed the stabilization and synthesis of the triangulene core and verification of the triplet ground state via electron paramagnetic resonance measurements. Here we show the on-surface generation of unsubstituted triangulene that consists of six fused benzene rings. The tip of a combined scanning tunnelling and atomic force microscope (STM/AFM) was used to dehydrogenate precursor molecules. STM measurements in combination with density functional theory (DFT) calculations confirmed that triangulene keeps its free-molecule properties on the surface, whereas AFM measurements resolved its planar, threefold symmetric molecular structure. The unique topology of such non-Kekulé hydrocarbons results in open-shell π-conjugated graphene fragments that give rise to high-spin ground states, potentially useful in organic spintronic devices. Our generation method renders manifold experiments possible to investigate triangulene and related open-shell fragments at the single-molecule level.

Axially Chiral Enamides: Substituent Effects, Rotation Barriers, and Implications for their Cyclization Reactions.

The barrier to rotation around the N-alkenyl bond of 38 N-alkenyl-N-alkylacetamide derivatives was measured (ΔG(⧧) rotation varied between <8.0 and 31.0 kcal mol(-1)). The most important factor in controlling the rate of rotation was the level of alkene substitution, followed by the size of the nitrogen substituent and, finally, the size of the acyl substituent. Tertiary enamides with four alkenyl substituents exhibited half-lives for rotation between 5.5 days and 99 years at 298 K, sufficient to isolate enantiomerically enriched atropisomers. The radical cyclizations of a subset of N-alkenyl-N-benzyl-α-haloacetamides exhibiting relatively high barriers to rotation round the N-alkenyl bond (ΔG(⧧) rotation >20 kcal mol(-1)) were studied to determine the regiochemistry of cyclization. Those with high barriers (>27 kcal mol(-1)) did not lead to cyclization, but those with lower values produced highly functionalized γ-lactams via a 5-endo-trig radical-polar crossover process that was terminated by reduction, an unusual cyclopropanation sequence, or trapping with H2O, depending upon the reaction conditions. Because elevated temperatures were necessary for cyclization, this precluded study of the asymmetric transfer in the reaction of individual atropisomers. However, enantiomerically enriched atropsiomeric enamides should be regarded as potential asymmetric building blocks for reactions that can be accomplished at room temperature.

Are Some Anticoagulants More Equal Than Others? - Evaluating the Role of Novel Oral Anticoagulants in AF Ablation.

Left atrial ablation strategies are being increasingly performed as a Class 1 therapeutic indication for drug refractory paroxysmal atrial fibrillation (AF). Traditionally AF ablation has been performed with patients on uninterrupted warfarin therapy, however over the last few years, novel oral anticoagulants (NOACs) have emerged as attractive alternatives to warfarin in order to reduce stroke risk due to AF. NOACs are therefore increasingly being used instead of warfarin in the management of AF. There is also mounting evidence mainly in the form of small randomised studies and meta-analysis that have demonstrated that the use of NOACs for AF ablation is efficacious, safe and convenient. However the peri-procedural dosing protocols used in various studies especially in terms of whether NOAC use is interrupted or uninterrupted during AF ablation, have significant inter-operator and inter-institution variability. Currently there is also a lack of randomised controlled trials to validate the data obtained from meta-analyses. There is also evidence that use of NOACs may increase the requirement of unfractionated heparin during the procedure. This review article shall examine the currently available evidence-base, appraise the gaps in the current evidence and also underscore the need for larger randomised clinical trials in this rapidly developing field.

Correction: Unique post-translational oxime formation in the biosynthesis of the azolemycin complex of novel ribosomal peptides from Streptomyces sp. FXJ1.264.

[This corrects the article DOI: 10.1039/C5SC03021H.].

Total synthesis of the azolemycins.

The first total syntheses of newly isolated polyazole natural products azolemycins A-D, along with the synthesis of the tetra-oxazole non-natural analogue, are described.

Unique post-translational oxime formation in the biosynthesis of the azolemycin complex of novel ribosomal peptides from Streptomyces sp. FXJ1.264.

Streptomycetes are a rich source of bioactive specialized metabolites, including several examples of the rapidly growing class of ribosomally-biosynthesized and post-translationally-modified peptide (RiPP) natural products. Here we report the discovery from Streptomyces sp. FXJ1.264 of azolemycins A-D, a complex of novel linear azole-containing peptides incorporating a unique oxime functional group. Bioinformatics analysis of the Streptomyces sp. FXJ1.264 draft genome sequence identified a cluster of genes that was hypothesized to be responsible for elaboration of the azolemycins from a ribosomally-biosynthesized precursor. Inactivation of genes within this cluster abolished azolemycin production, consistent with this hypothesis. Moreover, mutants lacking the azmE and azmF genes accumulated azolemycin derivatives lacking the O-methyl groups and an amino group in place of the N-terminal oxime (as well as proteolysed derivatives), respectively. Thus AzmE, a putative S-adenosyl methionine-dependent methyl transferase, is responsible for late-stage O-methylation reactions in azolemycin biosynthesis and AzmF, a putative flavin-dependent monooxygenase, catalyzes oxidation of the N-terminal amino group in an azolemycin precursor to the corresponding oxime. To the best of our knowledge, oxime formation is a hitherto unknown posttranslational modification in RiPP biosynthesis.

Stereo- and Chemodivergent NHC-Promoted Functionalisation of Arylalkylketenes with Chloral.

Stereo- and chemodivergent enantioselective reaction pathways are observed upon treatment of alkylarylketenes and trichloroacetaldehyde (chloral) with N-heterocyclic carbenes, giving selectively either ß-lactones (up to 88:12 dr, up to 94 % ee) or α-chloroesters (up to 94 % ee). Either 2-arylsubstitution or an α-branched iPr alkyl substituent within the ketene favours the chlorination pathway, allowing chloral to be used as an electrophilic chlorinating reagent in asymmetric catalysis.

Ring closing metathesis reactions of α-methylene-ß-lactams: application to the synthesis of a simplified phyllostictine analogue with herbicidal activity.

Ring closing metathesis (RCM) reactions of α-methylene-ß-lactams are used to construct strained 11- and 12-membered macrocycles that mimic key structural elements of phyllostictine A. The highest yield and stereoselectivity was achieved making 12-membered macrocycle Z-19 with use of a p-methoxyphenyl group on the lactam nitrogen. Interestingly, substrate concentration had an important influence on the stereochemical course of the reaction. A simplified analogue produced using this approach displays phytotoxic activity against Chlamydomonas reinhardtii suggesting that the α-methylene-ß-lactam subunit is responsible, at least in part, for the herbicidal activity of phyllostictine A.

Photo-induced living radical polymerization of acrylates utilizing a discrete copper(II)-formate complex.

A photo-polymerization protocol, utilizing a pre-formed and well-characterized Cu(II) formate complex, [Cu(Me6-Tren)(O2CH)](ClO4), mediated by UV light is described. In the absence of additional reducing agents and/or photosensitizers, ppm concentrations of the oxidatively stable [Cu(Me6-Tren)(O2CH)](ClO4), furnish near-quantitative conversions within 2 h, yielding poly(acrylates) with low dispersities (∼1.10) and exceptional end-group fidelity, capable of undergoing in situ chain extension and block copolymerization.

Synthesis of 1- and 4-substituted piperazin-2-ones via Jocic-type reactions with N-substituted diamines.

Enantiomerically-enriched trichloromethyl-containing alcohols, obtained by asymmetric reduction, can be transformed regioselectively into 1-substituted piperazinones by modified Jocic reactions with little or no loss of stereochemical integrity. This methodology can be easily used to synthesise important pharmaceutical compounds such as the fluorobenzyl intermediate of a known PGGTase-I inhibitor.

How does Chronic Atrial Fibrillation Influence Mortality in the Modern Treatment Era?

Atrial fibrillation (AF) continues to impose a significant burden upon healthcare resources. A sustained increase in the ageing population and better survival from conditions such as ischaemic heart disease have ensured that both the incidence and prevalence of AF continue to increase significantly. AF can lead to complications such as embolism and heart failure and these acting in concert with its associated co-morbidities portend increased mortality risk. Whilst some studies suggest that the mortality risk from AF is due to the "bad company it keeps" i.e. the associated co-morbidities rather than AF itself; undoubtedly some of the mortality is also due to the side-effects of various therapeutic strategies (anti-arrhythmic drugs, bleeding side-effects due to anti-coagulants or invasive procedures). Despite several treatment advances including newer anti-arrhythmic drugs and developments in catheter ablation, anti-coagulation remains the only effective means to reduce the mortality due to AF. Warfarin has been used as the oral anticoagulant in the treatment of AF for many years but suffers from disadvantages such as unpredictable INR levels, bleeding risks and need for haematological monitoring. This has therefore spurred a renewed interest in research and clinical studies directed towards developing safer and more efficacious anti-coagulants. We shall review in this article the epidemiological features of AF-related mortality from several studies as well as the cardiovascular and non-cardiac mortality mechanisms. We shall also elucidate why a rhythm control strategy has appeared to be counter-productive and attempt to predict the likely future impact of novel anti-coagulants upon mortality reduction in AF.

The synthesis and STM/AFM imaging of 'olympicene' benzo[cd]pyrenes.

H-Benzo[cd]pyrene ('Olympicene') is a polyaromatic hydrocarbon and non-Kekulé fragment of graphene. A new synthetic method has been developed for the formation of 6H-benzo[cd]pyrene and related ketones including the first time isolation of the unstable alcohol 6H-benzo[cd]pyren-6-ol. Molecular imaging of the reaction products with scanning tunnelling microscopy (STM) and non-contact atomic force microscopy (NC-AFM) characterised the 6H-benzo[cd]pyrene as well as the previously intangible and significantly less stable 5H-benzo[cd]pyrene, the fully conjugated benzo[cd]pyrenyl radical and the ketones as oxidation products.

Asymmetric triplex metallohelices with high and selective activity against cancer cells.

Small cationic amphiphilic α-helical peptides are emerging as agents for the treatment of cancer and infection, but they are costly and display unfavourable pharmacokinetics. Helical coordination complexes may offer a three-dimensional scaffold for the synthesis of mimetic architectures. However, the high symmetry and modest functionality of current systems offer little scope to tailor the structure to interact with specific biomolecular targets, or to create libraries for phenotypic screens. Here, we report the highly stereoselective asymmetric self-assembly of very stable, functionalized metallohelices. Their anti-parallel head-to-head-to-tail 'triplex' strand arrangement creates an amphipathic functional topology akin to that of the active sub-units of, for example, host-defence peptides and p53. The metallohelices display high, structure-dependent toxicity to the human colon carcinoma cell-line HCT116 p53(++), causing dramatic changes in the cell cycle without DNA damage. They have lower toxicity to human breast adenocarcinoma cells (MDA-MB-468) and, most remarkably, they show no significant toxicity to the bacteria methicillin-resistant Staphylococcus aureus and Escherichia coli.