Regiodivergent synthesis of pyrazino-indolines vs. triazocines via α-imino carbenes addition to imidazolidines

Hexahydropyrazinoindoles were prepared in a single step from N-sulfonyl triazoles and imidazolidines. Under dirhodium catalysis, α-imino carbenes were generated and formed nitrogen ylide intermediates that, after subsequent aminal opening, afforded the pyrazinoindoles predominantly via formal [1,2]-Stevens and tandem Friedel–Crafts cyclizations. Of mechanistic importance, a regiodivergent reactivity was engineered through the use of a specific unsymmetrically substituted imidazolidine that promoted the exclusive formation of 8-membered ring 1,3,6-triazocines. Based on DFT calculations, an original Curtin–Hammett-like situation was demonstrated for the mechanism. Further derivatizations led to functionalized tetrahydropyrazinoindoles in high yields.

Hexahydropyrazinoindoles are prepared in a single step from N-sulfonyl triazoles and imidazolidines. Of mechanistic importance, a regiodivergent reactivity can be engineered towards the exclusive formation of 8-membered ring 1,3,6-triazocines.     

First asymmetric synthesis of an acyclic β,β-dialkylated-γ-aminobutyric acid

Enantiomerically pure (R)-γ-amino-β-benzyl-β-methylbutyric acid, an acyclic β,β-dialkyl GABA derivative, is efficiently synthesised from (1S,2R,4R)-10-dicyclohexylsulfamoylisobornyl 2-cyanopropanoate by a sequence based on benzylation, Arndt-Eistert homologation and nitrile reduction. Benzylation of (1S,2R,4R)-10-dicyclohexylsulfamoylisobornyl 2-cyanopropanoate using potassium carbonate under not strictly anhydrous conditions occurs diastereoselectively to afford (1S,2R,4R)-10-dicyclohexylsulfamoylisobornyl (S)-2-cyano-2-methyl-3-phenylpropanoate, the key chiral intermediate from which the desired γ-amino acid is obtained in five steps in 65% overall yield.     

Reaction of 1,2-diarylethylamides with ethyl polyphosphate (Epp): Correlation of the von braun,ritter and bischler-napieralski reactions

The Bischler-Napieralski cyclization of the 1,2-diaryiethylamides in a “one-pot” process using ethyl poly-phosphate as the reagent only yields the dihydroisoquinolines in certain cases. The trans-stilbenes and in-danes are obtained as neutral products and sometimes as sole products. Results clearly indicate the effect of aryl group substitution on the course of the reaction and the relationship between the Bischler-Napieralski and Ritter reactions.     

Gaudin subalgebras and wonderful models

Gaudin Hamiltonians form families of r-dimensional abelian Lie subalgebras of the holonomy Lie algebra of the arrangement of reflection hyperplanes of a Coxeter group of rank r. We consider the set of principal Gaudin subalgebras, which is the closure in the appropriate Grassmannian of the set of spans of Gaudin Hamiltonians. We show that principal Gaudin subalgebras form a smooth projective variety isomorphic to the De Concini–Procesi compactification of the projectivized complement of the arrangement of reflection hyperplanes.     

Fast and Simple Preparation of a Sensor Based on Electrochemically Reduced Graphene Oxide (rGO) for the Determination of Zopiclone in Pharmaceutical Dosage by Square Wave Adsorptive Stripping Voltammetry (SWAdSV)

The interactions of zopiclone with electrochemically reduced graphene oxide (rGO) modified electrode were examined. A comparison of GC/rGO and glassy carbon electrode (GC) by electrochemical impedance spectroscopy and scanning electrochemical microscopy (SECM) shows that the modified surface is much less conductive than GC. The role of rGO is to act as a site of specific adsorption of the analyte. Molecular dynamics showed that the monoanionic form of zopiclone presents more interactions with defects of rGO. The analytical methodology allowed obtaining a linearity of 10–130 μg L⁻¹, with a limit of detection of 2.14 μg L⁻¹ using SWAdSV at pH 10.0.     

To smooth or not to smooth? ROC analysis of perfusion fMRI data

Blood oxygenation level dependent (BOLD) contrast has been widely used for visualizing regional neural activation. Temporal filtering and parameter estimation algorithms are generally used to account for the intrinsic temporal autocorrelation present in BOLD data. Arterial spin labeling perfusion imaging is an emerging methodology for visualizing regional brain function both at rest and during activation. Perfusion contrast manifests different noise properties compared with BOLD contrast, represented by the even distribution of noise power and spatial coherence across the frequency spectrum. Consequently, different strategies are expected to be employed in the statistical analysis of functional magnetic resonance imaging (fMRI) data based on perfusion contrast. In this study, the effect of different analysis methods upon signal detection efficacy, as assessed by receiver operator characteristic (ROC) measures, was examined for perfusion fMRI data. Simulated foci of neural activity of varying amplitude and spatial extent were added to resting perfusion data, and the accuracy of each analysis was evaluated by comparing the results with the known distribution of pseudo-activation. In contrast to the BOLD fMRI, temporal smoothing or filtering reduces the power of perfusion fMRI data analyses whereas spatial smoothing is beneficial to the efficacy of analyses.     

Optimization of yield in kinetically controlled synthesis of ampicillin with immobilized penicillin acylase in organic media

Immobilized penicillin acylase is a moderately priced versatile enzyme, that is able to catalyze the synthesis of derived penicillins and cephalosporins from the corresponding β-lactam nuclei and proper side-chain precursors. Kinetically controlled synthesis is a better strategy when product yield is a key issue. Yield should increase at reduced water activity by depressing the competing hydrolytic reactions in favor of synthesis; therefore, organic cosolvents can be a suitable reaction media for synthesis. Using response surface methodology and product yield as objective function, temperature and pH were optimized in the kinetically controlled synthesis of ampicillin using previously screened cosolvents and reaction conditions. Optimum pH was 6.0 for ethylene glycol (EG) and glycerol (GL) and 6.6 for 1–2 propanediol (PD); optimum temperature was 30°C for GL and for EG and PD was in the lower extreme of the range studied, optimum lying below 26°C. Maximum molar yields predicted by the model were 58,51, and 46% for EG, GL, and PD, respectively, which were experimentally validated. Highest yield in aqueous buffer was always <40%. Molar yields about 60% compare favorably with values reported for the kinetically and thermodynamically controlled synthesis of ampicillin and other derived penicillins.     

Coexistence of Three Ferroic Orders in the Multiferroic Compound [(CH3)4N][Mn(N3)3] with Perovskite‐Like Structure

The perovskite azido compound [(CH₃)₄N][Mn(N₃)₃], which undergoes a first‐order phase change at T_t=310 K with an associated magnetic bistability, was revisited in the search for additional ferroic orders. The driving force for such structural transition is multifold and involves a peculiar cooperative rotation of the [MnN₆] octahedral as well as order/disorder and off‐center shifts of the [(CH₃)₄N]⁺ cations and bridging azide ligands, which also bend and change their coordination mode. According to DFT calculations the latter two give rise to the appearance of electric dipoles in the low‐temperature (LT) polymorph, the polarization of which nevertheless cancels out due to their antiparallel alignment in the crystal. The conversion of this antiferroelectric phase to the paraelectric phase could be responsible for the experimental dielectric anomaly detected at 310 K. Additionally, the structural change involves a ferroelastic phase transition, whereby the LT polymorph exhibits an unusual and anisotropic thermal behavior. Hence, [(CH₃)₄N][Mn(N₃)₃] is a singular material in which three ferroic orders coexist even above room temperature.     

Electrochemical Properties of a Conducting Film Derived from Iron(II) Tris(diaminopolypyridyl) Complex in the S(IV) Oxoanions Reduction

A new conducting film derived from the complex [Fe (diaphen)₃]²⁺, (diaphen=5,6‐diamino‐1,10‐phenanthroline) was electropolymerized by cyclic voltammetry onto a glassy carbon electrode. Poly‐[Fe^II (diaphen)₃] was studied by cyclic voltammetry, SEM, UV‐vis and micro‐Raman spectroscopy. Poly‐[Fe^II (diaphen)₃] shows electrocatalytic activity in HSO₃^? reduction in an ethanol/water solution. Electrocatalysis is centered at the π ring of phenanthroline. Rotating disk electrode studies showed a 0.117 V/dec Tafel slope, suggesting an EC process where the electrochemical process is the determining step. The chemical step was studied by UV‐vis spectroelectrochemistry. Amperometric behavior showed a linear range between 47.5 µM to 417 µM and the LOD was 19.5 µM.     

Determination of S(IV) Oxoanions at Poly[Ru(5‐NO2‐Phen)2Cl] Tetrapyridylporphyrin Glassy Carbon Modified Electrode

Glassy carbon electrodes modified with conducting polymers of Ni(II), Zn(II) and metal free tetraruthenated porphyrin were evaluated for reduction and oxidation processes of S(IV) oxoanions in Na₂SO₃/water‐ethanol at pH 1.0 and 3.5, showing electrocatalytic activity. A Ni(II) film was able to reduce the S(IV) oxoanions selectively in presence of high concentration of gallic acid. The Ni(II) film was also used as an amperometric sensor toward S(IV) oxoanions reduction in white wine samples showing a detection and quantification limit of 1.40 mg L^?1 and 4.68 mg L^?1, respectively. These results are promising for the electrochemical determination of S(IV) using conducting polymers from these macrocycles.