α-Methoxymethyl ketones via aldol reaction

Paraformaldehyde in a methanolic solution of KOH converts ketones into α-methoxymethylated and α- hydroxymethylated products. The method was tested on nine steroidal ketones. On prolonged treatment the ketones formed are reduced to alcohols.     

Development and validation of a new RP-HPLC method for determination of quercetin in green tea

Green tea (Camellia sinensis) contains quercetin as a bioactive compound. Quercetin has anti-inflammatory and anticancer effects. The aim of this paper was to develop and validate an RP-HPLC method for determination of quercetin in green tea simpler and faster than other available methods. RP-HPLC analysis was performed by isocratic elution with a flow rate of 1.0 mL/min. Pure methanol was used as a mobile phase, while the quantification was effected at 370 nm. The separation was performed at 35°C using a C₁₈ column (4.6 × 250 mm, 5 μm). The results showed that the peak area response is linear within the concentration range of 10–70 μg/mL (r = 0.9986). The values of LOD and LOQ were 1.2 and 4 μg/mL, respectively. For the intra-day and intra-instrument reproducibility, RSD were in the range of 0.05–0.84% and 0.89–1.55%, respectively. The results of accuracy for the different concentrations of quercetin (40, 50 and 60 μg/mL) were 101.3, 98.4, and 98.2%. The developed and validated method was successfully applied to the determination of quercetin in green tea extract.     

Detection of Protein S‐Sulfhydration by a Tag‐Switch Technique

Protein S‐sulfhydration (forming ‐S‐SH adducts from cysteine residues) is a newly defined oxidative posttranslational modification and plays an important role in H₂S‐mediated signaling pathways. In this study we report the first selective, “tag‐switch” method which can directly label protein S‐sulfhydrated residues by forming stable thioether conjugates. Furthermore we demonstrate that H₂S alone cannot lead to S‐sulfhydration and that the two possible physiological mechanisms include reaction with protein sulfenic acids (P‐SOH) or the involvement of metal centers which would facilitate the oxidation of H₂S to HS^..     

Inhibition of cyclin-dependent kinases, GSK-3beta and CK1 by hymenialdisine, a marine sponge constituent

BACKGROUND: Over 2000 protein kinases regulate cellular functions. Screening for inhibitors of some of these kinases has already yielded some potent and selective compounds with promising potential for the treatment of human diseases. RESULTS: The marine sponge constituent hymenialdisine is a potent inhibitor of cyclin-dependent kinases, glycogen synthase kinase-3beta and casein kinase 1. Hymenialdisine competes with ATP for binding to these kinases. A CDK2-hymenialdisine complex crystal structure shows that three hydrogen bonds link hymenialdisine to the Glu81 and Leu83 residues of CDK2, as observed with other inhibitors. Hymenialdisine inhibits CDK5/p35 in vivo as demonstrated by the lack of phosphorylation/down-regulation of Pak1 kinase in E18 rat cortical neurons, and also inhibits GSK-3 in vivo as shown by the inhibition of MAP-1B phosphorylation. Hymenialdisine also blocks the in vivo phosphorylation of the microtubule-binding protein tau at sites that are hyperphosphorylated by GSK-3 and CDK5/p35 in Alzheimer's disease (cross-reacting with Alzheimer's-specific AT100 antibodies). CONCLUSIONS: The natural product hymenialdisine is a new kinase inhibitor with promising potential applications for treating neurodegenerative disorders.     

Kinetics and mechanism of ring transformation of S-[1-(4-methoxyphenyl)pyrrolidin-2-on-3-yl]isothiuronium bromide to 2-methylimino-5-[2-(4-methoxyphenylamino)ethyl]thiazolidin-4-one

The kinetics and mechanism of transformation reaction of S-[1-(4- methoxyphenyl)pyrrolidin-2-one-3-yl]-N-methyl-isothiuronium bromide into 2-methylimino-5-[2-(4-methoxyphenylamino) ethyl)]thiazolidin-4-one have been studied in aqueous solutions of amine buffers (pH 8.1-11.5) and sodium hydroxide solutions (0.005-0.5 mol l-1) at 25 degrees C and at I = 1 mol l-1 at pseudo-first-order reaction conditions. The kinetics observed shows that the transformation reaction is subject to general base, general acid, and hydroxide-ion catalyses. The rate-limiting step of transformation is the splitting-off a proton from the tetrahedral intermediate In. The value of pKa for S-[1-(4-methoxyphenyl)- pyrrolidin-2-one-3-yl]-N-methylisothiuronium bromide has been determined from the kinetic data (pKa = 8.75 +/- 0.10) and by potentiometric titration (pKa = 8.90 +/- 0.05). With increasing pKa value of the acid buffer component, the value of Br?nsted coefficient beta gradually decreases from about 0.7 to almost zero. The value of pKa approximately 10 for the intermediate to base-catalysed transformation has been found from this dependence. In the N-methylpyrrolidine and triethylamine buffers, the rate-limiting step of transformation is changed into ring opening of In-, and the general-base-catalysed reaction changes into a specific-base-catalysed one.     

Spin-trapping of oxygen free radicals in chemical and biological systems: new traps, radicals and possibilities

The choice of the spin-trap that is to be applied in any EPR study represents the crossroad between a comprehensive investigation and an "ordinary" quantification of production of radicals. So, the scope of our study was to compare the performance of different spin-traps for qualitative analysis of radical-generating systems, and their ability to recognize previously unnoticed radicals. In addition, we present a brief account of the difficulties involved in the detection of oxygen-centered radicals in chemical and biological systems accompanied by the rationale for using the EPR spin-trapping technique in quantitative studies of such reactive species. Certain technical aspects of EPR experiments related to efficient trapping of free radicals in biochemical systems are also discussed. As an example we present here results obtained using EPR spectroscopy and the spin-trap DEPMPO, which show that the Fenton reaction, as well as various biological systems generate a previously unappreciated hydrogen (*H) atom.     

Are chelate rings aromatic? Calculations of magnetic properties of acetylacetonato and o-benzoquinonediimine chelate rings

The aromaticity of the chelate rings of acetylacetonato (acac) and o-benzoquinonediimine (bqdi) ligands was investigated theoretically by calculating nucleus-independent chemical shifts (NICS). The calculations were done for the complexes with various metals and various other ligands. The results show that acac chelate rings in none of the complexes satisfy this magnetic criterion for aromaticity. According to the results for bqdi chelate rings, there is only the Ru2+-bqdi chelate ring with large negative NICS values, indicating possible aromaticity by magnetic criterion.     

Synthesis and Characterization of a Helicene‐Based Imidazolium Salt and Its Application in Organic Molecular Electronics

Herein we demonstrate the synthesis of a helicene‐based imidazolium salt. The salt was prepared by starting from racemic 2‐methyl[6]helicene, which undergoes radical bromination to yield 2‐(bromomethyl)[6]helicene. Subsequent treatment with 1‐butylimidazole leads to the corresponding salt 1‐butyl‐3‐(2‐methyl[6]helicenyl)‐imidazolium bromide. The prepared salt was subsequently characterized by using NMR spectroscopy and X‐ray analysis, various optical spectrometric techniques, and computational chemistry tools. Finally, the imidazolium salt was immobilized onto a SiO₂ substrate as a crystalline or amorphous deposit. The deposited layers were used for the development of organic molecular semiconductor devices and the construction of a fully reversible humidity sensor.     

Continuity of Halfspace Depth Contours and Maximum Depth Estimators: Diagnostics of Depth-Related Methods

Continuity of procedures based on the halfspace (Tukey) depth (location and regression setting) is investigated in the framework of continuity concepts from set-valued analysis. Investigated procedures are depth contours (upper level sets) and maximum depth estimators. Continuity is studied both as the pointwise continuity of data-analytic functions, and the weak continuity of statistical functionals—the latter having relevance for qualitative robustness. After a real-data example, some general criteria and counterexamples are given, as well as positive results holding for “typical” data. Finally, some consequences for diagnostics and practical use of the depth-based techniques are drawn.