Studies toward the total synthesis of armatol F: stereoselective construction of the C6 and C7 stereocenters and formation of the A-ring skeleton

Armatol F, isolated from the red alga Chondria armata as a polyether triterpene, has a solitary oxepane (A-ring) and a fused tricyclic ether moiety (BCD-ring). The A-ring features a rare cis-relationship between the hydroxy group at the quaternary carbon C6 and the carbon chain at C7. As part of our program toward the total synthesis of armatol F, a new stereoselective method for the construction of the C6 and C7 stereocenters has been developed based on chirality-transferring Ireland-Claisen rearrangement. The A-ring skeleton has also been synthesized from the rearrangement product by a process including ring-closing olefin metathesis.     

Asymptotic linear expansion of profile likelihood in the Cox mode

By introducing a new parameterization, Hirose [12] improved on the seminal work of Murphy and van der Vaart [16]: the improvement establishes the efficiency of the estimator through direct quadratic expansion of the profile likelihood, which requires fewer assumptions. This paper aims to demonstrate that the approach in [12] is fully applicable to the Cox proportional hazard model.     

Theory for electron hopping through nanometer-scale contacts: From tunneling regime to ballistic regime

Using the recursion-transfer-matrix (RTM) method combined with nonequilibrium Green's function (NEGF) method, we study the electronic states and current–voltage (I–V) characteristics of junction systems with atomic-scale nanocontacts as a function of the distance between electrodes. We observe a strong nonlinear behavior in the I–V characteristics and correspondingly a gap structure appears in conductance. We find that such a nonlinear behavior emerges when the transport properties change from tunneling to ballistic regimes.     

Sorption and partial molar volume of gases in poly (dimethyl siloxane)

Sorption of N₂, O₂, Ar, CH₄, CO₂, C₂H₄, and C₂H₆ in poly (dimethyl siloxane) liquid and rubber and the dilation of the polymers due to sorption of the gases are studied at 25°C under pressures up to 50 atm. In the liquid, the sorption isotherms for low-solubility and high-solubility gases are described by Henry's law and the Flory–Huggins equation, respectively. Gas sorption in the rubber, which contains a 29 wt % silica filler, follows the dual-mode sorption model, though marked hysteresis is observed in the sorption of O₂ and CH₄. The dilation isotherms increase linearly or exponentially in both polymers with increasing pressure. Considering that gas molecules adsorbed into micropores of the filler particles do not participate in the dilation, partial molar volumes of the dissolved gases in the rubber are determined from data of sorption and dilation. The values are nearly equal to the partial molar volumes in the liquid (48–60 cm³/mol).     

Separation and some characteristics of two factors from rat liver particulate fraction which stimulate and inhibit the low-Km adenosine 3',5' cyclic monophosphate (cAMP) phosphodiesterase of rat fat cells.

Two factors were separated from rat liver particulate fraction treated with insulin, one of them having a stimulating effect on low-Km adenosine 3',5' cyclic monophosphate (cAMP) phosphodiesterase activity of crude microsomal fraction (P-2 fraction) and the other having an inhibiting effect on the activity of low-Km cAMP phosphodiesterase solubilized with 0.3% Brij 58 from P-2 fraction. Trypsin and heat treatments had essentially no effect on these two factors. The stimulating factor did not significantly change the apparent Km value of enzyme in P-2 fraction but increased the maximal velocity of the reaction. The inhibiting factor raised the Km value of solubilized enzyme without affecting the maximal velocity of the reaction. The stimulating factor level in diabetic rat was larger than that in normal rat while the inhibiting factor level in diabetic rat was smaller than that in normal rat. Possible participation of both factors in insulin action is discussed.     

Chemical synthesis and application of C-terminally 5-carboxyfluorescein-labelled thymopentin as a fluorescent probe for thymopoietin receptor.

Thymopentin (TP5) is a synthetic pentapeptide fragment, which corresponds to position 32 - 36 of thymic polypeptide thymopoietin. Thymopoietin and TP5 display a variety of biological functions, including phenotypic differentiation of T cells and the regulation of immune systems. Previous chemical modification experiments suggested that there was an absolute requirement for N-terminal amino acids to maintain the biological activity of TP5. On the basis of this structure-activity relationship, we designed and synthesized the C-terminally 5-carboxyfluorescein-coupled TP5 (TP5-FAM) as a fluorescent probe for thymopoietin receptor. TP5-FAM could bind to the membrane of human lymphoid cell lines, MOLT-4 cells, in which the thymopoietin receptor is expressed. The binding is specific and saturable (K(d) = 33 microM). TP5 and human splenopentin are nearly equipotent inhibitors of TP5-FAM binding to the thymopoietin receptor, but porcine secretin did not show any significant inhibition of TP5-FAM binding to MOLT-4 cells. Thus, TP5-FAM is suggested to be a potent and biologically active ligand that would be useful for studying the binding and functional characteristics of the human thymopoietin receptor.     

Synthetic studies on oligomycins. Enantiospecific synthesis of the oligomycin B spiroketal portion and establishment of the absolute stereochemistry of oligomycin B

The enantiospecific synthesis of the oligomycin B degradation product 2, corresponding to the C19–C34 spiroketal portion, has been achieved by sequential coupling of the C19–C21, C22–C27, and C28–C34 subunits, establishing the absolute stereochemistry of oligomycin B.     

Phase transition in dilute solution of poly(γ-benzyl-L-glutamate) in dichloromethane at a low temperature

The dielectric constant of solutions of poly(γ-benzyl-L -glutamate) (PBLG) in dichloromethane shows a jump near 195°K, irrespective of frequency. Therefore, the discontinuity is not a dispersion phenomenon but a phase transition in the thermodynamic sense. The transition temperature is independent of the concentration in the range from 0.01 to 10% by weight, but it increases linearly with the logarithm of the molecular weight of PBLG. The height of the jump depends strongly on frequency, concentration, and molecular weight. The viscosity also changes abruptly at 195°K. These results suggest that the PBLG molecule forms a cluster like a liquid crystal or is in a random coil state below the transition point.     

Recent trends of industrial catalysts for resid hydroprocessing in Japan

To meet the gradual changes in petroleum demand, in particular a reduced demand for heavy fuel oil, advanced technology for resid hydroprocessing is now extremely necessary. The catalyst technology for resid hydroprocessing in Japan, especially fixed bed type of hydrodesulfurization and hydroconversion, is reviewed in this article.