Synthesis of All Stereoisomers of Monomeric Spectomycin A1/A2 and Evaluation of Their Protein SUMOylation-Inhibitory Activity

A synthetic methodology to access all possible stereoisomers of spectomycin A1 (SMA1) and A2 (SMA2) has been established through late-stage diversification. The key reaction for the construction of all four diastereomers is an intramolecular cyclization based on the umpolung of π-allyl palladium species with bis(pinacolato)diborane (B₂(pin)₂). Silyl group assisted direct benzylic oxidation of each isomer enabled construction of the fragile β-hydroxytetralone skeleton to provide the SMAs. The relative and absolute stereochemistry of SMA2 was also determined, and the absolute stereochemistry of SMA1 was extrapolated based on the optical rotation of SMA2. The axial chirality of SMAs is discussed based on circular dichroism spectra and DFT calculations, and it is concluded that the M isomer is predominant in solution. Biochemical assessment of all isomers in vitro revealed that the C9 hydroxyl group and dimeric structure were both important for protein SUMOylation-inhibitory activity.     

Simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by slurry-sampling graphite furnace AAS.

A fast and accurate analytical method was established for the simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by graphite furnace atomic absorption spectrometry using a slurry sampling technique and a Hitachi Model Z-9000 atomic absorption spectrometer. The slurry samples were prepared by the ultrasonication of silicon carbide or silicon nitride powders with 0.1 M nitric acid. Calibration curves were prepared by using a mixed standard solution containing aluminum, calcium, iron and 0.1 M nitric acid. The analytical results of the proposed method for aluminum, calcium and iron in silicon carbide and silicon nitride reference materials were in good agreement with the reference values. The detection limits for aluminum, calcium and iron were 0.6 microg/g, 0.15 microg/g and 2.5 microg/g, respectively, in solid samples, when 200 mg of powdered samples were suspended in 20 ml of 0.1 M nitric acid and a 10 microl portion of the slurry sample was then measured. The relative standard deviation of the determination of aluminum, calcium and iron was 5 - 33%.     

One‐pot Annulation for Biaryl‐fused Monocarba‐closo‐dodecaborate through Aromatic B−H Bond Disconnection

We have developed a one‐pot annulation reaction of monocarba‐closo‐dodecaborate with cyclic diaryliodonium salts to afford biaryl‐fused derivatives. Aryl functionalities are introduced at both the 1‐carbon and unreactive ortho‐boron vertices of the “σ‐aromatic” carborane cage without the need for pre‐functionalization. DFT calculations revealed that the palladium‐catalyzed C?B bond‐formation step in this process proceeds through a concerted metalation–deprotonation (CMD)‐type pathway for the B?H bond disconnection on the aromatic cage, though such bonds are generally regarded as hydridic.     

Helical structures of N-alkylated poly(p-benzamide)s

Poly(p-benzamide)s 1 bearing a chiral side chain on the nitrogen atom were synthesized by chain-growth polycondensation methodology. The polyamides exhibited well-defined molecular weights with narrow polydispersities. Solutions of the polyamides in several organic solvents (CH(3)CN, CHCl(3), and CH(3)OH) showed dispersion type CD signals characteristic of coupled-oscillator and much larger as compared with the corresponding monomer. The CD signals were dependent on the temperature and molecular weight of the polyamides but independent of the solvent, as far as examined. An exciton model analysis of the absorption and CD spectra provided a clear-cut picture for the secondary structure of these polyamides in solution that the N-alkylated poly(p-benzamide)s possess a right-handed helical conformation ((P)-helix). In the solid states, the results of X-ray crystallographic analysis of 4-(methylamino)benzoic acid oligomers substantiated that they have a helical conformation with three monomer units per turn.     

Pre-ashing of biological samples — a sample preparation technique for solid sampling ZAAS

Summary A pre-ashing method by a conventional electrothermal furnace was used as a concentration technique for powdered biological samples in the solid sampling technique with GF-ZAAS. A relationship equation between the concentration factors and the concentrations of main inorganic components in biological samples has been established, and it has become possible to calculate the concentration factors, if the total concentration of K, Na, Mg and Ca, or total concentration of K and Mg, or the concentration of K only are known. The proposed method has been successfully applied to the direct determination of Co, Ni, Mn and Pb at the g/kg levels in biological samples.Presented at the 5th International Colloquium on Solid Sampling, with Atomic Spectroscopy, May 18–20, 1992; Geel, Belgium. Papers edited by R.F.M. Herber, Amsterdam     

Preconcentration by coprecipitation of arsenic and tin in natural waters with a Ni–pyrrolidine dithiocarbamate complex and their direct determination by solid-sampling atomic-absorption spectrometry

A method for the determination of trace amounts of arsenic and tin in natural waters is described. Trace amounts of arsenic and tin were preconcentrated by coprecipitation with a Ni–ammonium pyrrolidine dithiocarbamate (APDC) complex. The coprecipitates obtained were directly analyzed by graphite-furnace atomic-absorption spectrometry (GFAAS) using the Ni–APDC complex solid-sampling technique. The coprecipitation conditions used for the trace amounts of arsenic and tin in natural water were investigated in detail. It was found that arsenic and tin at sub-ng mL^–1 levels were both coprecipitated quantitatively by Ni(PDC)₂ in the pH range 2–3. The concentration factors by coprecipitation reached approximately 40,000 when 2 mg nickel was added as a carrier element to 500 mL of the water sample. The proposed method has been applied to the determination of trace amounts of arsenic and tin in river water and seawater reference materials, and the detection limits for arsenic and tin, which were calculated from three times of the standard deviation of the procedural blanks, are 0.02 ng mL^–1 and 0.04 ng mL^–1, respectively, for 500-mL volumes of water sample.     

Destabilization and enhanced dehydriding reaction of LiNH<Subscript>2</Subscript>: an electronic structure viewpoint

First-principles calculations have been applied to lithium amide, LiNH₂, to characterize its electronic structure. Based on the theoretical study, we predict that an effective method for destabilizing LiNH₂ is to partially substitute Li by other elements with larger electronegativity, such as Mg. Experimental results on dehydriding reactions of LiNH₂ with/without the partial Mg substitutions suggest the destabilization of the samples with increasing Mg concentrations, which is in good agreement with our prediction. The dehydriding reactions of LiNH₂ with partial Mg substitutions are useful as hydrogen-storage materials for fuel-cell applications. PACS 81.05.Zx; 71.20.Ps; 82.30.-b     

Destabilization of LiBH4 by mixing with LiNH2

It was revealed that LiBH₄ is destabilized by mixing with LiNH₂ and the mixture desorbs a large amount of hydrogen. First-principles calculations predicted that the enthalpies of dehydrogenation for LiBH₄ alone and the mixture of LiBH₄+2LiNH₂ are 75 kJ/molH₂ and 23 kJ/molH₂, respectively. Motivated by this prediction, we experimentally examined the dehydrogenation properties for LiBH₄ and the mixture under hydrogen pressure. The amounts of desorbed hydrogen from LiBH₄ and the mixture at 703 K and 522 K were 10.6 mass% and 7.8 mass%, respectively. The dehydrogenation pressure of the mixture was much higher than that of LiBH₄ alone, although the mixture was measured at approximately 180 K lower temperature. This result suggests that the mixture is much unstable as compared with LiBH₄ alone.PACS 81.05.Zx; 71.20.Ps; 82.30.-b