Asymmetric synthesis of 4,8-dihydroxyisochroman-1-one polyketide metabolites using chiral hypervalent iodine(III)

Stereoselective oxylactonization of ortho-alkenylbenzoate with chiral hypervalent iodine is applied to the asymmetric synthesis of 4-oxyisochroman-1-one polyketide metabolites including 4-hydroxymellein (1), a derivative of fusarentin 2, monocerin (3), and an epimer of monocerin epi-3.     

Crystal Growth,Structure, and Magnetic Properties of a Two‐dimensional Triangular Lattice Magnet,Cu2(OH)3HCO2

We prepared single crystals of basic copper formate Cu₂(OH)₃HCO₂ ( 1) by hydrolysis of formate anions in an aqueous solution of copper formate. X‐ray structure analysis showed that this material has a two‐dimensional triangular lattice network with S=1/2. The temperature dependence of magnetic susceptibility revealed antiferromagnetic ordering at 5.4 K. A spin‐flop transition was observed at about 20 kOe at 2 K, thereby indicating metamagnetic‐like behavior. The saturation magnetization was almost one‐half of the theoretical value at 2 K under 70 kOe. The magnetic behaviors of 1 were also discussed with regard to its crystal structure. The preparation method presented herein is convenient and available for single crystal growth of metal hydroxide derivatives with various anions.     

Engineering strain-sensitive yellow fluorescent protein

Various biological events including muscle contraction and vesicle transport can be described as a mechanical process. Many of the corresponding proteins are thus required to generate or sense a force. Here we describe a strain-sensitive yellow fluorescent protein (YFP) recombinant that can detect the intramolecular strains these proteins experience.     

Fusion using fast heating of a compactly imploded CD core

A compact fast core heating experiment is described. A 4-J 0.4-ns output of a laser-diode-pumped high-repetition laser HAMA is divided into four beams, two of which counterilluminate double-deuterated polystyrene foils separated by 100 μm for implosion. The remaining two beams, compressed to 110 fs for fast heating, illuminate the same paths. Hot electrons produced by the heating pulses heat the imploded core, emitting x-ray radiations >20 eV and yielding some 10(3) thermal neutrons.     

Interpretations of National Curricula: the case of geometry in textbooks from England and Japan

This paper reports on how the geometry component of the National Curricula for mathematics in Japan and in one selected country of the UK, specifically England, is interpreted in school mathematics textbooks from major publishers sampled from each country. The findings we report identify features of geometry, and approaches to geometry teaching and learning, that are found in a sample of textbooks aimed at students in Grade 8 (aged 13–14). Our analysis raises two issues which are widely recognised as very important in mathematics education: the teaching of mathematical reasoning and proof, and the teaching of problem-solving. In terms of the teaching of mathematical reasoning and proof, our evidence indicates that this is dispersed in the textbook in England while it is concentrated in geometry in the textbook in Japan. In terms of the teaching of mathematical problem-solving and modeling, our analysis shows that it is more concentrated in the textbook from England, and rather more dispersed in the textbook from Japan. These findings indicate how important it is to consider ways in which these issues can be carefully designed in the geometry sections of future textbooks.     

Product and pulse radiolysis studies on radical-ion splitting of N(1)-C(5')-linked dimer hydrates of 5-substituted uracils by one-electron reduction in anoxic aqueous solution

Steady-state gamma-radiolysis, pulse radiolysis, and cyclic voltammetry have been performed to identify the mechanism by which N(1)-C(5')-linked homodimer hydrates [1-(6'-hydroxy-5',6'-dihydrothymin-5'-yl)thymine (2a) and [1-(5'-fluoro-6'-hydroxy-5',6'-dihydrouracil-5'-yl)-5-fluorouracil (2b)], N(1)-C(6')-linked dimer hydrate [1-(5'-hydroxy-5',6'-dihydrothymin-6'-yl)thymine (3a)], and N(1)-C(5')-linked heterodimer hydrate [1-(6'-hydroxy-5',6'-dihydrothymin-5'-yl)-5-fluorouracil (2ba)] undergo radiolytic reductive splitting to regenerate the parent monomers in anoxic aqueous solution. Radiolytic reductions of the thymine homodimer hydrates 2a and 3a by hydrated electrons (e(aq)-) regenerated the parent thymine (1a) almost quantitatively, while the 5-fluorouracil homodimer hydrates cis-2b and trans-2b afforded 1-(uracil-5'-yl)-5-fluorouracil efficiently along with a small amount of the parent 5-fluorouracil (1b). In contrast to 2b, the heterodimer hydrate analogue 2ba with noneliminating 5'-methyl substituent releases 5-fluorouracil 1b almost quantitatively in the radiolytic reduction. The pulse radiolysis studies suggested that the electron adducts are produced primarily at the thymine and 5-fluorouracil structural unit in the dimer hydrates 2a,b, respectively, in which the resulting dimer hydrate radical anion of 2b (2b*-) was more stable than that of 2a (2a*-). As characterized by pulse radiolysis and cyclic voltammetry, the 5-fluorouracil homodimer hydrate 2b bearing F-substituent at C(5') undergoes one-electron reduction to eliminate exclusively fluoride ion along with the formation of dimer hydrate C(5') radical (2b(-F)*) with oxidizing property. The formation of a possible dimer hydrate radical intermediate 2b(-F)* was also supported by the effect of amines as the reducing additives on the yields of 1b and 4b in the radiolytic reduction of 2b.     

Solvent-dependent regioselectivity of hydrogen chloride-mediated ring opening of alkylidenecyclopropanone acetal

Ring opening reactions of 2-cyclohexylidene-3,3-dimethylcyclopropanone acetal (1) are readily induced by treatment of hydrogen chloride in various solvents. Bond cleavage takes place at the C1-C2 or C2-C3 bond, and the ratio of C1-C2/C2-C3 cleavages changes from >99/1 to <1/99 depending on the solvent. The two modes of bond cleavage must be initiated by protonations at the carbon-carbon double bond and the acetal oxygen, respectively. The regioselectivity can be rationalized by the rate-determining protonation at carbon and the equilibrium protonation at oxygen.     

2D hydrogen-bonded square-grid coordination networks with a substitution-active metal site

Reported here is the preparation and property of 2D coordination networks composed of rodlike ligands with ethylene glycol side chains (1). Two 2D coordination networks, [[Co(1)2(H2O)2](NO3)2.1.5H2O]n and [[Ni(1)2(H(2)O)2](NO3)2.1.5H2O]n, have been synthesized and characterized by single-crystal X-ray diffraction, TG, DSC, UV-vis spectroscopy, and magnetic measurements. The structural analyses clarified that infinite 1D hydrogen-bond arrays composed of ethylene glycol chains contribute to the stabilization of 2D coordination frameworks, keeping the environment of substitution-active metal sites unchanged. They are more stable than a similar square-grid coordination network that does not possess an ethylene glycol chain on the ligand. We also succeeded in the direct observation of a reversible apical-ligand-exchange reaction at the cobalt(II) and nickel(II) ions in a single-crystal-to-single-crystal fashion because of the considerable stability as well as moderate flexibility of the framework. The cobalt-containing coordination network crystal showed chromic behavior depending on temperatures. Crystallographic and spectroscopic studies revealed that the color change of the crystal was attributed to the ligand-exchange process between H2O and a NO3 anion on the cobalt metal. Magnetic measurements indicated weak antiferromagnetic nearest-neighbor spin coupling between cobalt(II) ions.     

Synthesis and optical resolution of aminophosphines with axially chiral C(aryl)-N(amine) bonds for use as ligands in asymmetric catalysis

N-Aryl indoline-type aminophosphines 1a-c were obtained in good yields by a nucleophilic aromatic substitution (S(N)Ar) reaction followed by silane reduction. Aminophosphine 1d was also prepared from 2,3-difluorobenzaldehyde (4) via dimethylhydrazone. Optical resolution of C(aryl)-N(amine) bond atropisomers was achieved using (S)-(+)-di-mu-chlorobis[2-[(dimethylamino)ethyl]phenyl-C(2),N]dipalladium(II) ((S)-10). The determination of absolute configuration and the investigation of the rotation barrier for C(aryl)-N(amine) bond axial stability of an aminophosphine 1 are described. Finally, the ability of the chiral phosphine ligand 1 is demonstrated in a catalytic asymmetric reaction, such as a palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate (up to 95% ee).