A new entry to Amaryllidaceae alkaloids from carbohydrates: total synthesis of (+)-vittatine

The stereoselective and chiral synthesis of the Amaryllidaceae alkaloid, (+)-vittatine 1, is described; the quaternary carbon in 1 was generated by Claisen rearrangement of a cyclohexenol derived from D-glucose by way of a Ferrier's carbocyclisation reaction and a hexahydroindole skeleton was effectively constructed by intramolecular aminomercuration-demercuration, followed by Chugaev reaction.     

Acceleration effect of an allylic hydroxy group on ring-closing enyne metathesis of terminal alkynes: scope, application, and mechanistic insights

An interesting acceleration effect of an allylic hydroxy group on ring-closing enyne metathesis has been found. Ring-closing enyne metathesis of terminal alkynes possessing an allylic hydroxy group proceeded smoothly without the ethylene atmosphere generally necessary to promote the reaction. The synthesis of (+)-isofagomine with the aid of this efficient reaction has been demonstrated. Mechanistic studies of the acceleration effect were also carried out. Results of NMR studies suggested that the reaction proceeded via an "ene-then-yne" pathway. Kinetic studies indicated switching of the rate-determining step as a consequence of the presence of an allylic hydroxy group. These results suggest acceleration of the reentry step of Ru-carbene species by the allylic hydroxy group.     

Melt spinning of syndiotactic 1, 2-polybutadiene for preparation of carbon fibers

The thermal crosslinking and loss of vinyl unsaturation of syndiotactic 1, 2-polybutadiene(_s-PB) at 180–230°C were prevented by stabilizers with 3, 5-di-t-butyl-4-hydroxybenzyloxy group. The _s-PB samples (mp 140–198°C and MW 20,000–70,000) that contained the stabilizers could be melt-spun at a temperature below 220°C into 1-denier fibers to be used for the preparation of carbon fibers. The _s-PB fibers with higher mp and/or higher MW could be obtained by the addition of a high boiling solvent such as tetralin. The relationship between the molecular structures of _s-PB and the properties of resulting _s-PB fibers, including the degree of molecular orientation measured by birefringence and x-ray diffraction, is presented. Spun fibers showed small swellings here and there along the fiber axis, which would have resulted from the inhomogeneity of the melt of _s-PB spun at a temperature slightly above the melting point. The gelation was unlikely to occur.     

Convergent and rapid assembly of substituted 2-pyridones through formation of N-alkenyl alkynylamides followed by gold-catalyzed cycloisomerization

A new method for the convergent and rapid assembly of substituted 2-pyridones was developed through the formation of N-alkenyl alkynylamides (amide-linked 1,5-enynes) by N-acylation of imines with alkynoyl chlorides and the subsequent cationic Au(I)/PPh 3-catalyzed cycloisomerization.     

Experimental investigation of the closest parallel pulses in holographic femtosecond laser processing

In holographic femtosecond laser processing, diffractive parallel pulses are distorted by phase discontinuities and mutual interference between the neighborhoods in the reconstructed image of a Fourier computer-generated hologram when the interval is smaller than the beam diameter. We investigated holographic fabrication on a glass surface using parallel pulses with different intervals. We found the closest parallel pulses with sufficient separation to avoid mutual interference in holographic femtosecond laser processing. The minimum interval was 2.8 times larger than the diffracted beam diameter. The experimental results were also supported by a computer simulation. Our findings will be very useful in the design of holographic laser processing systems.     

Unconventional pairing originating from the disconnected Fermi surfaces of superconducting LaFeAsO1-xFx

For a newly discovered iron-based high T_{c} superconductor LaFeAsO1-xFx, we have constructed a minimal model, where inclusion of all five Fe d bands is found to be necessary. The random-phase approximation is applied to the model to investigate the origin of superconductivity. We conclude that the multiple spin-fluctuation modes arising from the nesting across the disconnected Fermi surfaces realize an extended s-wave pairing, while d-wave pairing can also be another candidate.     

Electrorheological Response and Structure Growth of Colloidal Silica Suspensions

The electrorheological response and structure growth of colloidal silica suspension was studied with in situ measurements of the shear stress, electric conductivity, and dielectric permittivity of the suspension. The measurements were carried out under steady and sweep shears after the application of an electric field of alternative current (100 Hz) using silica particles with a diameter of 630 nm and a water content of 4.5 wt%. The measurements of the conductivity enabled the detection of structure growth formed by particle aggregation and clarified that the development of the particle aggregation enlarged the dielectric permittivity and the shear stress. Hysteretic behavior observed in the electrorheological response was explained by considering structure growth of the particle aggregation. The correlation equation for the shear stress and the dielectric permittivity obtained in our previous work (1) was found to be applicable to the present results. Copyright 2001 Academic Press.     

Enhanced Cytotoxic Effects of Arenite in Combination with Active Bufadienolide Compounds against Human Glioblastoma Cell Line U-87

The cytotoxicity of a trivalent arsenic derivative (arsenite, As^III) combined with arenobufagin or gamabufotalin was evaluated in human U-87 glioblastoma cells. Synergistic cytotoxicity with upregulated intracellular arsenic levels was observed, when treated with As^III combined with arenobufagin instead of gamabufotalin. Apoptosis and the activation of caspase-9/-8/-3 were induced by As^III and further strengthened by arenobufagin. The magnitude of increase in the activities of caspase-9/-3 was much greater than that of caspase-8, suggesting that the intrinsic pathway played a much more important role in the apoptosis. An increase in the number of necrotic cells, enhanced LDH leakage, and intensified G₂/M phase arrest were observed. A remarkable increase in the expression level of γH2AX, a DNA damage marker, was induced by As^III+arenobufagin. Concomitantly, the activation of autophagy was observed, suggesting that autophagic cell death associated with DNA damage was partially attributed to the cytotoxicity of As^III+arenobufagin. Suppression of Notch signaling was confirmed in the combined regimen-treated cells, suggesting that inactivation of Jagged1/Notch signaling would probably contribute to the synergistic cytotoxic effect of As^III+arenobufagin. Given that both As^III and arenobufagin are capable of penetrating into the blood–brain barrier, our findings may provide fundamental insight into the clinical application of the combined regimen for glioblastoma.     

Synthesis and properties of polyurethanes derived from bis-N-hydroxyimides and diisocyanates

Polyurethanes were synthesized by polyaddition reaction of bis-N-hydroxyimides and diisocyanates. The reactions were carried out in an aprotic polar solvent such as dimethylacetamide or N-methyl-2-pyrrolidone, and the polymers with inherent viscosities of up to 1.32 dl/g were obtained. These polyurethanes were found to exhibit high reactivity toward nucleophiles such as water and amines, which brought about rapid reduction of viscosity. The stabilities against heat and exposure to sunlight were also studied.