Oxidation of Oxazolines and Thiazolines to Oxazoles and Thiazoles. Application of the Kharasch-Sosnovsky Reaction

Using a modification of the Kharasch-Sosnovsky reaction, the oxidation of oxazolines and thiazolines bearing a variety of 2-alkyl substituents (chiral and achiral) were smoothly oxidized to their corresponding oxazoles and thiazoles, respectively. The key feature involved in the successful implementation of this important oxidation was the use of a mixture of Cu(I) and Cu(II) salts to enhance the oxidation of the intermediate captodative radical, 24. The main limitation of this method was shown when the oxidation failed with oxazolines/thiazolines lacking the carboalkoxy group at C-4.     

Nano-LC: An updated review

Low-flow chromatography has a rich history of innovation but has yet to reach widespread implementation in bioanalytical applications. Improvements in pump technology, microfluidic connections, and nano-electrospray sources for MS have laid the groundwork for broader application, and innovation in this space has accelerated in recent years. This article reviews the instrumentation used for nano-flow LC, the types of columns employed, and strategies for multidimensionality of separations, which are key to the future state of the technique to the high-throughput needs of modern bioanalysis. An update of the current applications where nano-LC is widely used, such as proteomics and metabolomics, is discussed. But the trend toward biopharmaceutical development of increasingly complex, targeted, and potent therapeutics for the safe treatment of disease drives the need for ultimate selectivity and sensitivity of our analytical platforms for targeted quantitation in a regulated space. The selectivity needs are best addressed by mass spectrometric detection, especially at high resolutions, and exquisite sensitivity is provided by nano-electrospray ionization as the technology continues to evolve into an accessible, robust, and easy-to-use platform.     

Carcinogenic Chromium(VI) Compounds Formed by Intracellular Oxidation of Chromium(III) Dietary Supplements by Adipocytes

Chromium(III) nutritional supplements are widely consumed for their purported antidiabetic activities. X‐ray fluorescence microscopy (XFM) and X‐ray absorption near‐edge structure (XANES) studies have now shown that non‐toxic doses of [Cr₃O(OCOEt)₆(OH₂)₃]⁺ ( A ), a prospective antidiabetic drug that undergoes similar H₂O₂ induced oxidation reactions in the blood as other Cr supplements, was also oxidized to carcinogenic Cr^VI and Cr^V in living cells. Single adipocytes treated with A had approximately 1 μm large Cr hotspots containing Cr^III, Cr^V, and Cr^VI (primarily Cr^VI thiolates) species. These results strongly support the hypothesis that the antidiabetic activity of Cr^III and the carcinogenicity of Cr^VI compounds arise from similar mechanisms involving highly reactive Cr^VI and Cr^V intermediates, and highlight concerns over the safety of Cr^III nutritional supplements.     

Determination of the intraparticle electroosmotic volumetric flow-rate, velocity and Peclet number in capillary electrochromatography from pore network theory

The results obtained from the pore network model employed in this work, clearly show that the magnitudes of the intraparticle electroosmotic volumetric flow-rate, Qintrap, and velocity, (v(intrap,x)), in the pores of the charged porous silica particles considered in this study are greater than zero. The intraparticle Peclet number, Pe(intra, of a solute in these charged porous silica particles would be greater than zero, and, in fact, the magnitude of the intraparticle Peclet number, Pe(intrap), of lysozyme is greater than unity for all the values of the pore connectivity, nT, of the intraparticle pores and of the applied electric potential difference per unit length, Ex, along the axis of the capillary column considered in this work. Furthermore, the values of the intraparticle electroosmotic volumetric flow-rate, Qintrap, and velocity, (v(intrap,x)), as well as the magnitude of the pore diffusion coefficient, Dp, of the solute increase as the value of the pore connectivity, nT, of the intraparticle pores increases. The intraparticle electroosmotic flow can contribute significantly, if the appropriate chemistry is employed in the mobile liquid phase and in the charged porous particles, in (i) decreasing the intraparticle mass transfer resistance, (ii) decreasing the dispersive mass transfer effects, and (iii) increasing the intraparticle mass transfer rates so that high column efficiency and resolution can be obtained.     

Synthesis,Characterisation, and in vitro Cytotoxic Activity of Dithiocarbamato Glycoconjugate Half-Sandwich Ruthenium and Osmium Complexes

The synthesis by transmetallation and in-depth characterisation by IR spectroscopy of five half-sandwich ruthenium and osmium dithiocarbamato isonipecotamide glycoconjugate complexes are presented herein. The evaluation of their in vitro cytotoxicity and of the zinc precursors’ in vitro cytotoxicity towards ovarian cancer (A2780 and A2780cisR) and normal prostate (PNT2) cells is reported. While the cytotoxicity of the compounds is rather limited, some selectivity is observed.     

Palladium-catalyzed asymmetric allylic alkylation of meso- and dl-1,2-divinylethylene carbonate

The palladium-catalyzed asymmetric allylic alkylation of a 1:1 mixture of dl- and meso-1,2-divinylethylene carbonate is reported. For the first time, both the ionization and nucleophilic addition steps of the catalytic cycle act as enantiodiscriminating steps to give a single product in high enantiomeric excess. The reactions proceed in >98% ee to efficiently generate useful chiral building blocks from acrolein. The absolute and relative configurations of iso-cladospolide B and 11-epi-iso-cladospolide B were verified by total synthesis, solving an apparent discrepancy in the literature.     

PHOTOREACTIVATION OF ULTRAVIOLET IRRADIATED NON-DIVIDING POPULATIONS OF ICR 2A FROG CELLS

Abstract— Ultraviolet (UV) irradiation of non-dividing populations of ICR 2A frog cells led to their detachment from the surface of the culture dish and eventual lysis. Exposure of the cells to photoreactivating light after UV irradiation prevented cell killing and was accompanied by a loss of endonuclease sensitive sites from DNA. This photoreversal did not take place when the cells were exposed at 4°C to photoreactivating light indicating that the reversal was the result of photoenzymatic repair. As the action of photoreactivating enzyme is specific for the repair of pyrimidine dimers in DNA, these results suggest that pyrimidine dimers in DNA are the critical lesions leading to the death of non-dividing populations of UV irradiated cells.     

Duplex-promoted platination of adenine-N3 in the minor groove of DNA: challenging a longstanding bioinorganic paradigm

The interactions of [Pt(en)Cl(ACRAMTU-S)](NO3)2 (PT-ACRAMTU, en = ethane-1,2-diamine, ACRAMTU = 1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea) with adenine in DNA have been studied using a combination of analytical and high-resolution structural methods. For the first time, a cytotoxic platinum(II) complex has been demonstrated to form adducts in the minor groove of DNA through platination of the adenine-N3 endocyclic nitrogen. An acidic depurination assay was developed that allowed the controlled and selective (pH 2, 60 degrees C, 12 h) release of platinum-modified adenine from drug-treated nucleic acid samples. From the digested mixtures, three adducts were isolated by semipreparative reverse phase high-performance liquid chromatography and studied by electrospray ionization mass spectrometry (in-line LC-MS), variable-pH 1H NMR spectroscopy, and, where applicable, X-ray crystallography. The three species were identified as the N7 (A-I), N3 (A-II), and N1 (A-III) linkage isomers of [Pt(en)(ACRAMTU-S)(adenine)]3+ (A). Incubations carried out with the single- and double-stranded model sequences, d(TA)5 and d(TA)15, as well as native DNA indicate that the adduct profiles (A-I:A-II:A-IIIratios) are sensitive to the nature of the nucleic acid template. A-II was found to be a double-strand specific adduct. The crystal structure of this adduct has been determined, providing ultimate evidence for the N3 connectivity of platinum. A-II crystallizes in the triclinic space group P in the form of centrosymmetric dimers, {[Pt(en)(ACRAMTU-S)(adenine-N3)]2}6+. The cations are stabilized by a combination of adenine-adenine base pairing (N6...N1 2.945(5) A) and mutual acridine-adenine base stacking. Tandem mass spectra and 1H chemical shift anomalies indicate that this type of self-association is not merely a crystal packing effect but persists in solution. The monofunctional platination of adenine at its N7, N3, and N1 positions in a significant fraction of adducts breaks a longstanding paradigm in platinum-DNA chemistry, the requirement for nucleophilic attack of guanine-N7 as the principal step in cross-link formation. The biological consequences and potential therapeutic applications of the unique base and groove recognition of PT-ACRAMTU are discussed.