Total synthesis of sorbistin A1 and a positional isomer

Total synthesis of sorbistin A₁ (1) and a positional isomer (7) is described for the first time in a regio- and stereo-controlled manner.     

Analysis of fractionation of ethylene–propylene copolymers

Analysis of the solution fractionation of ethylene–propylene copolymers was carried out by assuming a bivariate normal distribution function for the distribution of molecular weight and chemical composition. It was found that the variation of the molecular weight and composition distributions in fractions was complicated, because two distribution characteristics of the original copolymer affect fractionation to differing extents. The hypothetical cumulative weight distribution curves thus obtained agreed essentially with those obtained experimentally.     

Organic sulfur compounds containing heterocycles. II: Methyl 2-pyridyl sulfoxide as phase transfer catalyst.

Methyl 2-pyridyl sulfoxide was found to be an excellent phase transfer catalyst which promotes simple S_N2 type displacement reactions of alkyl halides with some nucleophiles.     

Structure-activity correlation of flavonoids for inhibition of bovine lens aldose reductase

To clarify the structure-activity correlation of flavonoids for inhibition of aldose reductase, about fifty flavonoid compounds were screened. The presence of hydrophobic substituents on the A ring and hydrophilic substituents on the B ring of the flavonoid skeleton was suggested to improve the potency of inhibitory activity. The activities of extracts of Scutellaria baicalensis, Andrographis paniculata and Gutierrezia microcephala are also described.     

Level crossing mechanism in new coherence resonance

The mechanism of level crossing in the new coherence resonance for the case that a spin-$\text{1}\text{2}$ atom interacts with an oscillating rf field in optical pumping is theoretically analyzed considering the higher-order effects of a strong rf field.     

Polyaromatic ether–ketones and ether–keto–sulfones having various hydrophilic groups

Polyaromatic ether–ketones and polyaromatic ether–keto–sulfones were sulfonated by suspending the polymer powders in dichloroethane containing liquid sulfur tiroxide and trialkyl phosphate at room temperature. It was found that more than one sulfonic group can be introduced per each repeating unit of the polymers without degradation. The sulfonated polymers were soluble in various organic solvents, and solubility and mechanical properties depended on the initial molecular weight of polymers as well as the degrees of sulfonation. Strong films can be cast from their dimethylformamide solutions.     

(+)‐3‐{(4S,5S)‐5‐[1,1‐Di­methyl‐2‐(phenyl­thio)­ethyl]‐2,2‐di­methyl‐1,3‐dioxolan‐4‐yl}prop‐2‐yn‐1‐ol

The absolute configuration was determined for the title compound, (+)‐C₁₈H₂₄O₃S, (I), which was prepared in a synthetic study on the natural products, bryostatins.     

Maltopentaose-Forming Amylase-Mediated p-Nitrophenyl α-Maltohexaoside formation in an Aqueous-Organic Solvent System :A Substrate for Human Amylase in Serum

ABSTRACT

A maltopentaose-forming amylase [EC 3.2.1.1] from Bacillus licheniformis effectively produced p-nitrophenyl α-maltohexaoside (3) through a transglycosylation reaction from maltohexaose as a donor and p-nitrophenyl α-glucoside (1) as an acceptor in an aqueous solution containing hydrophilic organic solvents. The enzyme specifically transferred from maltohexaose to the 4-position of 1. The yield of 3 depended on the kind of donor, concentration of solvent, pH, and temperature. By the addition of solvents such as dimethyl sulfoxide and 1-butanol, respectively, effects of acceleration on transferase activity of the enzyme and improvement of acceptor solubility were achieved, and resulted in a great increase in the formation of 3.     

Nature of magnetic impurity induced superparamagnetism and anomalous Hall effect in β-FeSi2 single crystals

The magnetic properties of β-FeSi₂ single crystals were investigated using magnetization and anomalous Hall effect measurements. These measurements clearly show the appearance of superparamagnetism, the origin of which is attributed to defect-induced magnetic aggregates. Unlike previous reports, based on our combined analysis using magnetization and the anomalous Hall effect, we found that two kinds of aggregates, which are magnetically distinct, exist in our samples. Among the two types found, one gives an anomalous Hall term, which follows a side-jump mechanism while the other is a completely new kind, suggesting that magnetic properties of β-FeSi₂ are very unconventional. The sizes of the aggregates were estimated from our experimental data.