Stereoselective synthesis of azasugars by electrochemical oxidation

A new method using electrochemical oxidation has been exploited for the stereoselective synthesis of 2,3,6-trihydroxylated 5S-piperidine derivatives. The electrochemical method was successively used for the conversion of N-protected piperidines to N-protected 1-methoxypiperidines and for the conversion of 1-methoxy-2,3-didehydropiperidine derivatives to 1,2,3-triacetoxypiperidine derivatives. The method provided a new synthetic route to 2S,3S,6-triacetoxy-5S-methylpiperidine and 2R,3R,6-triacetoxy-5S-methylpiperidine.     

Efficient oxidation of cycloalkanols by sodium nitrite with molecular oxygen in trifluoroacetic acid

Oxidation of aliphatic cycloalkanols by sodium nitrite in trifluoroacetic acid gave α,ω-dicarboxylic acids in good yields. Adipic acid was obtained in a quantitative yield from cyclohexanol using 1 equiv of sodium nitrite under oxygen atmosphere but the oxidation required more than 3 equiv of sodium nitrite under nitrogen atmosphere. The oxidation method was applicable to the conversion of 1-alkanols to the corresponding carboxylic acids.     

A novel parallel algorithm for large-scale Fock matrix construction with small locally distributed memory architectures: RT parallel algorithm

We developed a novel parallel algorithm for large-scale Fock matrix calculation with small locally distributed memory architectures, and named it the "RT parallel algorithm." The RT parallel algorithm actively involves the concept of integral screening, which is indispensable for reduction of computing times with large-scale biological molecules. The primary characteristic of this algorithm is parallel efficiency, which is achieved by well-balanced reduction of both communicating and computing volume. Only the density matrix data necessary for Fock matrix calculations are communicated, and the data once communicated are reutilized for calculations as many times as possible. The RT parallel algorithm is a scalable method because required memory volume does not depend on the number of basis functions. This algorithm automatically includes a partial summing technique that is indispensable for maintaining computing accuracy, and can also include some conventional methods to reduce calculation times. In our analysis, the RT parallel algorithm had better performance than other methods for massively parallel processors. The RT parallel algorithm is most suitable for massively parallel and distributed Fock matrix calculations for large-scale biological molecules with more than thousands of basis functions.     

Structural determination of metallofullerene Sc3C82 revisited: a surprising finding

We report here the structural determination of the Sc3C82 molecule by 13C NMR spectroscopy and X-ray single-crystal structure analysis. From the present study, it is obvious that the structure of Sc3C82 is not Sc3@C82 but Sc3C2@C80.     

A novel synthesis, including asymmetric synthesis, of α-quaternary α-amino acid methyl esters from ketones via sulfinyloxiranes

Sulfinyloxiranes were synthesized from ketones and chloromethyl p-tolyl sulfoxide in two steps in almost quantitative yields. The sulfinyloxiranes were treated with NaN₃ in the presence of NH₄Cl to afford α-azido aldehydes, which were oxidized with iodine in the presence of KOH in methanol to give α-azido methyl esters in good overall yields. Catalytic hydrogenation of the α-azido esters afforded α-quaternary α-amino acid methyl esters in quantitative yields. Starting from β-tetralone and optically pure (R)-chloromethyl p-tolyl sulfoxide, an asymmetric synthesis of optically pure (R)-(+)-methyl 2-aminotetraline-2-carboxylate was realized in good overall yields.     

Analysis of the herbicides paraquat,diquat and difenzoquat in drinking water by micellar electrokinetic chromatography using sweeping and cation selective exhaustive injection

Optimum conditions for the determination of the herbicides paraquat, diquat and difenzoquat by micellar electrokinetic chromatography (MEKC) using sweeping and cation-selective exhaustive injection (CSEI) as on-line concentration methods were developed. Sodium dodecyl sulfate (80 mM) in 50 mM phosphate buffer (pH 2.5) with 20% acetonitrile was used as a background electrolyte for the methods studied. The limits of detection, based on a signal-to-noise ratio of 3:1, were about 2.6-5.1 mg 1(-1) in purified water when MEKC was applied for the standards. By using an on-line preconcentration method known as sweeping-MEKC, up to a 500-fold increase in detection sensitivity was obtained whereas up to a 50 000-fold increase for CSEI-sweeping-MEKC was achieved. The limits of detection using optimum CSEI-sweeping-MEKC were lower than 1 microg 1(-1) and the method was validated obtaining good reproducibility (relative standard deviation lower than 22%) and linearity. CSEI-sweeping-MEKC was successfully applied to the determination of the three herbicides in spiked tap water below the levels established by the US Environmental Protection Agency.     

Configuration-Interaction study of lower excited states of O2: Valence and rydberg characters of the two lowest 3Σu − states

Configuration-interaction calculations, with an extended basis, are carried out on the ground and lower excited states of O₂ and O₂⁺ at and near the equilibrium internuclear distance (R = 2.3 a.u.) of the ground state of O₂. Particular attention has been paid to the two lowest ³Σ_u^? states, and the mixing of the valence and Rydberg characters in these states are studied. The lowest ³Σ_u^? state is a Rydberg-type state for R < 2.3 a.u., but becomes valence-type for R ? 2.3 a.u. The second ³Σ_u^? state, which is 1.6 eV above the lowest ³Σ_u^? at R = 2.3 a.u., changes its character from Rydberg to valence, valence to Rydberg, and then to valence again when R increases from 1.9 to 3.1 a.u. Satisfactory agreement between the calculated and experimental vertical excitation energies is obtained.     

Optimum heat treatment conditions for masking the bitterness of the clarithromycin wax matrix

The effects of the contents of aminoalkyl methacrylate copolymer E (AMCE) in a wax matrix on the mechanism of polymorphic transformation of glyceryl monostearate (GM) were clarified by evaluating the enthalpy change defined as 1.51 (DeltaH(1)-DeltaH(2))/DeltaH(2), where DeltaH(1) and DeltaH(2) denote the enthalpies in the first and second thermal analyses, respectively. Using this value, K(1), the rate constant of transformation from alpha-form to beta'-form, and K(2), the rate constant of transformation from beta'-form to beta-form, could be obtained. As the ratio of AMCE increased, K(2) increased, but a minimum point existed for K(1). K(1) was always larger than K(2), but gradually approached K(2) as the ratio of AMCE increased. The optimum temperature for the transformation of GM was 50 degrees C, at which the enthalpy change was maximum. To prepare the wax matrix preparation of clarithromycin (CAM), we considered 40 degrees C the optimum treatment temperature for the transformation of GM in a CAM wax matrix compounded from CAM, GM and AMCE, since the matrices were mutually welded at above 45 degrees C during the spray congealing process. Although K(1) and K(2) were almost the same at 40 degrees C, the rate of transformation was accelerated by tumbling. By applying the tumbling that accelerated the transformation of GM in a CAM wax matrix, almost all of the alpha-form disappeared, and the release of CAM from the wax matrix diminished when the enthalpy change was more than 0.8.     

Preparation and properties of solvent-soluble bridged polybiphenylenes and related copolymers

A solvent-soluble polybiphenylene with a single hetero atom in the chain (a bridged polybiphenylene) was prepared according to the synthetic procedure for a solvent-soluble poly(4,4′-biphenylene). In addition, a related copolymer was similarly prepared by the addition of the MMA monomer in the reaction system. The thermal properties and viscosity behavior of each product were influenced by the hetero atom, especially by the introduction of MMA component in the chain. Each viscosity curve (η_sp/c vs. c) shows an anomalous peak at a specific concentration (0.3–0.002 g/100 ml DMF), depending upon the atomic group. The η_sp/c value for each homopolymer was not over 0.1 except in the neighborhood of the anomalous peak, while those for copolymers became 3–4 times larger than values for corresponding homopolymers. It is obvious that the viscosity of each copolymer increases due to an increase in flexibility due to introduction of the MMA units in the chain, since little difference in molecular weights is found between homopolymers (16,000–15,000) and copolymers (10,000–12,000).     

Preparation of nitrogen-containing pi-deficient heteroaromatic Grignard reagents: oxidative magnesiation of nitrogen-containing pi-deficient halogenoheteroaromatics using active magnesium

The oxidative magnesiation of nitrogen-containing pi-deficient halogenoheteroaromatics using active magnesium was accomplished. Both magnesiation followed by addition of a carbonyl compound (Grignard reaction) and magnesiation in the presence of a carbonyl compound (Barbier reaction) were carried out to afford the corresponding product. Especially, the latter method enabled fused halogenodiazines such as 4-chloro-1-phenyl-1H-pyrazolo[3,4-d]pyrimidine or 2-chloroquinoxaline to magnesiate at a mild temperature (-20 to 30 degrees C).