New and efficient catalysts for enantioselective borohydride reduction of ketones and imines

Optically active aldiminato cobalt(II) complexes have been found to catalyze the enantioselective reduction of ketones with sodium borohydride affording the corresponding optically active secondary alcohols in high chemical yields with high enantioselectivities. The enantioselective borohydride reduction is also applicable to not only C=O bonds in aromatic ketones but also to C=N bonds in aromatic imines.     

Electroreductive intramolecular coupling of chiral alpha-imino esters: stereoselective synthesis of mixed ketals of cis-2,4-disubstituted azetidine-3-ones

The electroreduction of chiral aromatic alpha-imino esters prepared from (S)-alpha-amino acids, such as (S)-valine, (S)-leucine, and (S)-phenylalanine, in the presence of chlorotrimethylsilane and triethylamine afforded four-membered cyclized products, mixed ketals of cis-2,4-disubstituted azetidine-3-ones, stereospecifically (>99% de, 85-99% ee). The best result of the electroreductive cyclization was obtained using Bu(4)NClO(4) as a supporting electrolyte and a Pt cathode. The absolute stereochemistry of the obtained single stereoisomers was confirmed to be 2R,3R,4S by X-ray crystallography. Calculations for the transition states of the cyclization support the stereospecific formation of the (2R,3R,4S)-isomers.     

Non-destructive neutron activation analysis studies on a withering disease of lowland rice occurring near an iodine plant

The withering disease of lowland rice that seems to be an injury from exess iodine was recognized in the paddy fields near an iodine isolation plant. To investigate the cause of this disease a pot experiment of lowland rice was performed and iodine contents of soils and rice plants were determined by non-destructive neutron activation analysis. The soils of the disease-produced paddy fields were remarkably polluted by iodine, its contents in roots of diseased rice plants were more than the reported limiting values for the disease.     

Preconcentration of phthalic acid esters in water samples by Saccharomyces cerevisiae immobilized on silica gel

A sensitive and selective column adsorption method is proposed for the off-line preconcentration and determination of phthalic acid esters (PAEs), namely benzyl-butyl phthalate (BBP), di-n-butyl phthalate (DBP) and di-cyclohexyl phthalate (DCHP). The PAEs was preconcentrated on Saccharomyces cerevisiae immobilized on silica gel and then determined by high performance liquid chromatography (HPLC). Several parameters on the recovery of the analytes were investigated. Recoveries of BBP, DBP and DCHP were 100±2, 98±2 and 98±3%, respectively, at 95% confidence level under optimum conditions. The detection limits (3S/N) of BBP, DBP and DCHP were 3.2, 6.3 and 3.1 μg l⁻¹, respectively. The capacity of the adsorbent was also examined and found to be 1.4 mg g⁻¹ for BBP and DBP, and 3.6 mg g⁻¹ for DCHP. S. cerevisiae immobilized on silica gel is suitable for repeated use without decreasing recovery up to about 25 adsorption-elution cycles. The proposed method was successfully applied to the determination of PAEs in river water with high precision and accuracy.     

Acid-base equilibria of various oxidation states of aqua-ruthenium complexes with 1,10-phenanthroline-5,6-dione in aqueous media

Syntheses and pH dependent electrochemical properties of aqua-ruthenium(II) complexes, [Ru(trpy)(PDA-N,N')(OH2)](ClO4)2 ([1](ClO4)2) and [Ru(trpy)(PD-N,N')(OH2)](ClO4)2 ([2](ClO4)2) (trpy = 2,2':6',2'-terpyridine, PDA = 6-acetonyl-6-hydroxy-1,10-phenanthroline-5-one, PD = 1,10-phenanthroline-5,6-dione) are presented. Treatment of [Ru(trpy)(PD-N,N')Cl](PF6) with AgClO4 in a mixed solvent of acetone and H2O selectively produced the acetonyl-PD complex [1](ClO4)2, and the similar treatment in a mixed solvent of 2-methoxyethanol and H2O gave the PD complex [2](ClO4)2. The molecular structures of both complexes were determined by X-ray structural analysis. The proton dissociation constants of various oxidations state of [1]2+ and [2]2+ were evaluated by simulation of E(1/2) values of those redox potentials depending on pH. The simulation revealed that the acetonyl-PD complex [1]2+ underwent successive Ru(II)/Ru(III) and Ru(III)/Ru(IV) redox couples though the two redox reactions were not separated in the cyclic voltammograms. The redox behavior of [2]2+ in H2O is reasonably explained by not only the similar successive metal-centered redox reactions but also simultaneous two-electron quinone/catechol redox couple of the PD ligand including the contribution of hydration on a carbonyl carbon.     

Effects of Moderately Low Temperature (20°C) on Phytochrome Responses During Preirradiation: Anthocyanin Synthesis in Sorghum bicolor at High- and Low-Pfr/Ptot Ratios

Abstract— Effects on phytochrome-mediated anthocyanin synthesis of moderately low temperature (MLT) given during the preirradiation culture period were studied with seedlings of broom sorghum ( Sorghum bicolor Moench, cvs. Acme Broomcorn and Sekishokuzairai-Fukuyama). Seedlings were grown in the dark at 20°C (MLT) and 24°C (control). The MLT treatment strikingly enhanced the action induced by a red light (R) pulse above ca 200 μmol m⁻² and suppressed the action induced by an R pulse below ca 30 μmol m⁻² and by a far-red light (FR) pulse alone. We refer to these MLT-affected distinct responses as "high-Pfr/Ptot response" and "low-Pfr/Ptot response," as they have features different from the high-irradiance and very-low-fluence responses, respectively. The destruction rate of spectroscopically detectable phytochrome (phyA) and the time course of escape of anthocyanin synthesis from FR reversibility did not match, and hence the possibility of phyA being involved in high-Pfr/Ptot response was rejected, although it might be involved in low-Pfr/Ptot response. Possible mechanisms for the two distinct phytochrome responses are discussed.     

Enantioselective 1,3-dipolar cycloaddition of nitrones catalyzed by optically active cationic cobalt(III) complexes

[reaction: see text] The optically active beta-ketoiminato cationic cobalt(III) complexes were employed as efficient Lewis acid catalysts for the enantioselective 1,3-dipolar cycloaddition reaction of alpha,beta-unsaturated aldehydes with nitrones. Excellent endo selectivities and high enantioselectivities were achieved in the cycloaddition reaction of 1-cyclopentene-1-carbaldehyde and the nitrones derived from 2-halobenzaldehyde.     

Enantioselective total synthesis of aspidophytine

[structure: see text] An enantioselective total synthesis of aspidophytine is described. The indole fragment bearing a cis-alkene substituent was efficiently prepared through radical cyclization of a 2-alkenylphenylisocyanide followed by Sonogashira coupling of the generated 2-iodoindole derivative with a functionalized acetylene unit. After formation of the 11-membered cyclic amine, the aspidosperma skeleton and lactone ring were constructed to complete the total synthesis.     

Preparation and structural determination of methyl 3-C-p-tolylsulfonyl-2-C-p-tolylthio-β-d-glucopyanoside derivatives and their 5a-carba-dl-analogs having non-chair conformation in solutions

Methyl 4,6-O-benzylidene-2,3-dideoxy-3-C-p-tolylsulfonyl-2-C-p-tolylthio-β-d-glucopyranoside and its 5a-carba-dl-analog exit mainly in a non-chair conformation in solutions, but the latter occupies a chair conformation in a solid state.     

Synthesis of 8-methylpyrido[2,3-d:6,5-d'x]dipyrimidine-2,4,6(3H,10H,7H)-triones and their use in the oxidation of alcohols

A new-type pyridodipyrimide, 8-methylpyrido[2,3-d:6,5-d']dipyrimidine-2,4,6(3H,10H,7H)-triones were prepared by the condensation of 6-alkyl- or 6-aryl-amino-2-methylpyrimidin-4(3H)-ones with 2,4,6-trichloropyrimidine-5-carbaldehyde or 3-alkyl-6-chloro-5-formyluracils. The pyridodipyrimidines thus obtained oxidized alcohols under neutral conditions to yield the corresponding carbonyl compounds and a significant autorecycling in the oxidation was observed.