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.     

Non-resonant microwave absorption studies of superconducting MgB2 and MgB2 + MgO

Non-resonant microwave absorption (NRMA) studies of superconducting MgB₂ and a sample containing ∼10% by weight of MgO in MgB₂ are reported. The NRMA results indicate near absence of intergranular weak links in the pure MgB₂ sample. A linear temperature dependence of the lower critical field H _c1 is observed indicating a non-s wave superconductivity. However, the phase reversal of the NRMA signal which could suggest d wave symmetry is also not observed. In the MgB₂ + MgO sample, much larger low field dependent absorption is observed indicating the presence of intergranular weak links. The hysteretic behavior of NRMA is compared and contrasted in the two samples. In the pure MgB₂ sample, a large hysteresis is observed between the forward and the reverse scans of the magnetic field indicating strong pinning of flux lines. This hysteresis saturates a few degrees below T _c while in the MgB₂ + MgO sample, a much slower increase of hysteresis with decreasing temperature is observed, a signature of weaker pinning.     

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.