Complete 1H and 13C NMR assignments of sesquiterpene glucosides from Ixeris sonchifolia

Four sesquiterpene glucosides were isolated from Ixeris sonchifolia Hance. The structure of a new compound (1) was assigned as 9beta-monohydroxy-2,12-dioxo-guaia-3,11(13)-dien-1alpha,5alpha,6beta,7alpha,9beta,10alphaH-12,6-olide-9-O-beta-D- glucopyranoside (ixerinoside). In addition, unambiguous and complete assignments of (1)H NMR chemical shifts for crepidiaside A (2), ixerin Z (3), and 11,13alpha-dihydroixerin Z (4) are presented. The assignments were achieved by two-dimensional NMR (gCOSY, gHSQC, gHMBC, NOESY) and one-dimensional nuclear Overhauser effect (NOE) experiments.     

Temperature-dependent coordination of phosphine to five-coordinate alkenylruthenium complexes

The red, five-coordinate complexes Ru(CO)Cl(PPh(3))2(CH=CHPh) and [Ru(CO)Cl(PPh(3))2]2(mu-CH=CHC(6)H(4)CH=CH) undergo reversible coordination of PPh(3) at low temperature to produce the pale yellow, six-coordinate complexes Ru(CO)Cl(PPh(3))3(CH=CHPh) and [Ru(CO)Cl(PPh(3))3]2(mu-CH=CHC(6)H(4)CH=CH). X-ray crystal structures of the latter complex and of the hydride complex RuH(CO)Cl(PPh(3))3 were obtained. 1H and 31P NMR spectra between 20 and -70 degrees C exhibit large changes in both equilibrium constants and dynamic effects. Thermodynamic parameters, DeltaH = -17.5 +/- 2.0 kcal/mol and DeltaS = -57.5 +/- 7.6 eu, were obtained for PPh(3) coordination to the monoruthenium complex, and activation parameters, DeltaH = 20.6 +/- 0.7 kcal/mol and DeltaS = 41.6 +/- 2.0 eu, were obtained for the reverse decoordination. Coordination of PPh(3) was not observed upon cooling of the shorter bridged complex, [Ru(CO)Cl(PPh(3))2]2(mu-CH=CHCH=CH).     

Determination of ochratoxin A at parts-per-trillion levels in cereal products by immunoaffinity column cleanup and high-performance liquid chromatography/mass spectrometry

Ochratoxin A (OTA) is a toxic and potentially carcinogenic fungal toxin found in a variety of food commodities. A new sensitive method has been developed to quantify OTA in cereal products by reversed-phase liquid chromatography (LC) with mass spectrometric (MS) detection. Ochratoxin B was used as the internal standard. OTA was extracted from cereal products with acetonitrile-water, and the extract was diluted with a buffer; the diluted extract was cleaned up on an immunoaffinity column before LC/MS analysis. Two multiple-reaction monitoring transitions were used, one for quantification of OTA and one for confirmation of identity. The method was shown to be highly sensitive, with a low decision limit (CCalpha) of 0.012 microg/kg and a detection capability (CCbeta) of 0.021 microg/kg. Within-laboratory repeatability coefficient of variation values were 7.1, 3.7, and 3.1%, and the corresponding recoveries were 104, 106, and 103% for rice samples fortified with OTA at 0.05, 0.10, and 0.15 microg/kg, respectively. Method validation was performed according to the criteria of European Commission Decision 2002/657/EC. All criteria as presented in the Commission Decision were fulfilled. This method is the first fully validated method using immunoaffinity chromatography for cleanup and MS for detection in the analysis of cereals for OTA. The method was also successfully applied to cereal-derived products. The analytical results for determination of the OTA content of cereal products commercially available in Hong Kong are also reported.     

Thermally Induced Denitrogenative Annulation for the Synthesis of Dihydroquinolinimines and Chroman‐4‐imines

A rapid growth in synthetic methods for the preparation of diverse organic molecules using N‐sulfonyl‐1,2,3‐triazoles is of great interest in organic synthesis. Transition metals are generally used to activate the α‐imino diazo intermediates. Metal‐free methods have not been studied in detail, but can be a good complement to transition metal catalysis in the mild reaction conditions. We herein report a novel method for the preparation of 2,3‐dihydroquinolin‐4‐imine and chroman‐4‐imine analogs from their corresponding N‐sulfonyl‐1,2,3‐triazoles in the absence of metal catalysts. To achieve intramolecular annulation, the introduction of an electron‐donating group is required at the meta position of N‐sulfonyl‐1,2,3‐triazole methyl anilines. The inclusion of tailored substituents on the aniline moieties and nitrogen atoms enhances the nucleophilicity of the phenyl π‐electrons, thus allowing them to undergo a Friedel–Crafts‐type reaction with the highly electrophilic ketenimines. This metal‐free method was carefully optimized to generate a variety of dihydroquinolin‐4‐imines and chroman‐4‐imines in moderate‐to‐good yields.     

Synthesis of Complex Druglike Molecules by the Use of Highly Functionalized Bench‐Stable Organozinc Reagents

The reactivity of a representative set of 17 organozinc pivalates with 18 polyfunctional druglike electrophiles (informers) in Negishi cross‐coupling reactions was evaluated by high‐throughput experimentation protocols. The high‐fidelity scaleup of successful reactions in parallel enabled the isolation of sufficient material for biological testing, thus demonstrating the high value of these new solid zinc reagents in a drug‐discovery setting and potentially for many other applications in chemistry. Principal component analysis (PCA) clearly defined the independent roles of the zincates and the informers toward druggable‐space coverage.     

Stereoselective Halogenation in Natural Product Synthesis

At last count, nearly 5000 halogenated natural products have been discovered. In approximately half of these compounds, the carbon atom to which the halogen is bound is sp³‐hybridized; therefore, there are an enormous number of natural products for which stereocontrolled halogenation must be a critical component of any synthesis strategy. In this Review, we critically discuss the methods and strategies used for stereoselective introduction of halogen atoms in the context of natural product synthesis. Using the successes of the past, we also attempt to identify gaps in our synthesis technology that would aid the synthesis of halogenated natural products, as well as existing methods that have not yet seen application in complex molecule synthesis. The chemistry described herein demonstrates yet again how natural products continue to provide the inspiration for critical advances in chemical synthesis.     

Enhanced Pseudocapacitance in Multicomponent Transition‐Metal Oxides by Local Distortion of Oxygen Octahedra

Anomalously high pseudocapacitance of a metal oxide was observed when Ni, Co, and Mn were mixed in a solid solution. Analysis by X‐ray absorption near‐edge spectroscopy (XANES) identified a wider redox swing of Ni as the origin of the enlarged pseudocapacitance. Ab initio DFT calculations revealed that aliovalent species resulting from the copresence of multiple transition metals can generate permanent local distortions of [NiO₆] octahedra. As this type of distortion breaks the degenerate e_g level of Ni²⁺, the Jahn–Teller lattice instability necessary for the Ni^2+/3+ redox flip can be effectively diminished during charge–discharge, thus resulting in the significantly increased capacitance. Our findings highlight the importance of understanding structure–property correlation related to local structural distortions in improving the performance of pseudocapacitors.     

Ultraviolet-B radiation upregulates expression of dectin-2 on epidermal Langerhans cells by activating the gene promoter

Epidermal Langerhans cells (LC) belong to the antigen-presenting cell (APC) family of dendritic cells that can initiate antigen-specific immunogenic or tolerogenic responses. In mice, we have shown ultraviolet-B (UV-B) irradiation to induce long-lasting suppression (tolerance) of contact hypersensitivity responses by converting LC from immunogenic to tolerogenic APC. The C-type lectin receptor, dectin-2, expressed preferentially by LC and dendritic cells, has also been shown to be involved in inducing this form of UV-B-induced immunosuppression. These observations led us to question whether UV-B can modulate dectin-2 expression by LC. In ICR mice engineered to express the dectin-2 gene promoter linked to a luciferase reporter gene, we found broadband UV-B treatment in vivo to activate the promoter in LC. In wild-type C3H/HeN mice, we found such treatment in vivo to yield LC with increased dectin-2 expression at both mRNA and protein levels. Broadband UV-B treatment in vitro of bone marrow-derived dendritic cells from these mice also showed upregulated expression of dectin-2 mRNA. These findings lead us to conclude that broadband UV-B upregulates dectin-2 expression in LC by activating the dectin-2 gene promoter. Such amplification suggests that UV-B-induced immunosuppression may be due (at least in part) to augmented dectin-2 expression in LC.     

X-ray diffraction and Raman studies of the CuGeO3(III)-(IV) transformation under high pressures

Both X-ray diffraction and Raman spectroscopy measurement were carried out on the same powder sample of CuGeO(3)(III) in a diamond anvil cell to high pressures at room temperature. The phase transformation of (III)-(IV) phase was observed at about 7GPa with both methods and the results were also in accord with previous powder diffraction and Raman measurements, respectively. However, the powder diffraction data were strikingly different from those reported in a recent single-crystal study on the phase (III). It is, therefore, evident that the phase transformations in CuGeO(3)(III) would be as complicated as those in CuGeO(3)(I) and that the monoclinic phase obtained from single-crystal phase (III) at approximately 7GPa is not the phase (IV) previously observed but rather a new phase (IVa) in CuGeO(3).     

Determination of toxic and trace elements in algae by instrumental neutron activation analysis

Instrumental neutron activation analysis has been applied in the determination of toxic and other trace elements in a set of three algae materials provided by the International Atomic Energy Agency, with the aim of environmental preservation through enhanced applications of nuclear analytical techniques. The quality of the analysis method has been evaluated by analyzing a number of biological standard reference materials. By adding mineral nutrients, the cultivation of algae for metals is enhanced, in particular, selected toxic heavy metals such as As, Cd, Cr, Hg, Ni and Pb. It is believed that the level of elemental concentration in algae samples are dependent on environmental conditions due to its biochemical properties. Therefore, algae materials may be useful as an indicator or controller of environmental water pollution.