LDA-catalyzed cycloisomerization of 2-(2-propynyloxy)ethyl iodides leading to 3-(iodomethylene)tetrahydrofurans

LDA catalyzes cycloisomerization of 2-(2-propynyloxy)ethyl iodides to give 3-(iodomethylene)tetrahydrofurans. The reaction is proposed to proceed through a mechanism involving exo-cyclization of an alkynyllithium intermediate and protonation of the resulting alkylidene carbenoid by the starting iodide. [reaction: see text]     

High-pressure synthesis and transport properties of a new binary germanide, SrGe6-delta (delta congruent with 0.5), with a cagelike structure

A new germanide, SrGe6-delta (delta congruent with 0.5), was synthesized by the reaction of Sr and Ge mixtures under a pressure of 5 GPa at 1200 degrees C. It crystallized in the orthorhombic space group Cmcm (No. 63) with a = 4.0981(6) A, b = 11.159(1) A, c = 12.6825(8) A, V = 580.0(1) A3, and Z = 4. SrGe6-delta is composed of a Ge covalent network having a cagelike structure and Sr atoms situated in the cages. Each Ge atom is coordinated by four neighboring Ge atoms. The coordination polyhedra are fairly distorted from an ideal tetrahedron, and the Ge network contains vacancies and disordering. The resistivity shows metallic behavior down to 2 K, and the positive thermoelectric power indicates the dominant carriers to be holes.     

The network structure of amorphous silicon-carbon alloy

The network structure of amorphous silicon-carbon alloy (a-Si_1−xC_x) has been studied over a wide range of x. The a-Si_1−xC_x thin films were prepared by sputtering silicon and carbon target with argon in radio-frequency magnetron sputtering equipment. The films were characterized by X-ray photoelectron spectroscopy, optical absorption, infrared absorption, and mechanical measurements. The results showed that the network structure could be classified neither as the random covalent network nor as the chemically ordered covalent network. The structure as a whole was close to the random covalent network, but the Si-Si combination at x>0.5 showed a feature of the chemically ordered covalent network. The film at 0.6<x<0.8 was hard and showed a high energy gap, due to the sp³ configuration in Si-C combinations.     

Assay of α-glucosidase inhibitory activity using flow-biosensor system

A convenient and continuous method for the assay of α-glucosidase (AGH) inhibitory activity was developed using a continuous-flow/stopped-flow system combined with biosensors. The amount of glucose liberated from maltose by the action of AGH was quantified by an immobilized glucose oxidase (GOD) reactor with a Clark oxygen sensor in the downstream. The immobilized AGH reactor was set in the flow-line. When an inhibitor containing 10 mM maltose substrate was injected and as it reaches the center of the immobilized AGH reactor, the working solution (synthetic intestinal fluid) was stopped for a certain period. After the reaction of inhibitor and/or substrate with AGH, the working solution was propelled again, and the glucose liberated was passed through the immobilized GOD reactor. The inhibition ratios (%) were calculated as the percent inhibition, which were the glucose concentrations in the presence of maltose and inhibitor divided by those in the presence of maltose alone. The multi-channel stopped-flow (MCSF) system was also developed, in which a seven-port, six-positioned rotary valve was inserted and six immobilized AGH reactors were set in a parallel configuration. The IC₅₀ values of acarbose and 1-deoxynojirimycin, a medicinal inhibitor for diabetes, were 0.46±0.062 and 0.23±0.031 μM, respectively, and coincided well with those by our pseudo-in vivo method [Biol. Pharm. Bull. 232 (2000) 1084]. The time to assay the inhibitory activity of one unknown sample was estimated to be 11 min by the 6-channel modified-MCFS system. The proposed MCFS system offers a useful method to evaluate the inhibitory activity for AGH.     

Convolution equivalence and distributions of random sums

A serious gap in the Proof of Pakes’s paper on the convolution equivalence of infinitely divisible distributions on the line is completely closed. It completes the real analytic approach to Sgibnev’s theorem. Then the convolution equivalence of random sums of IID random variables is discussed. Some of the results are applied to random walks and Lévy processes. In particular, results of Bertoin and Doney and of Korshunov on the distribution tail of the supremum of a random walk are improved. Finally, an extension of Rogozin’s theorem is proved.     

Polymer combination increased both physical stability and oral absorption of solid dispersions containing a low glass transition temperature drug: physicochemical characterization and in vivo study

The purpose of this study was establishing a solid dispersion formulation containing a low glass transition temperature (T(g)) and poorly water-soluble drug. Drug/polymer blends with differing physicochemical stabilities and oral absorption were prepared from copolyvidone (PVP-VA), polyvinylpyrrolidone (PVP) or hydroxypropylmethylcellulose (HPMC) by a hot melt extrusion. HPMC drastically increased the drug oral absorption property, while PVP-VA or PVP stabilized solid dispersions during storage by increasing the T(g) in proportion to polymer concentration. Experimental T(g) values corresponded closely with theoretical T(g) values; indeed, the T(g) values of solid dispersion with HPMC did not increase significantly compared to the T(g) value for the drug alone. A solid dispersion formulation incorporating two different polymers-HPMC and either PVP-VA or PVP-maintained increased T(g), physicochemical stability, solubility, and bioavailability of the solid dispresions owing to each polymer. These findings suggested that both oral absorption and physicochemical stability of low-T(g) drug will be improved using less amount of solid dispersion of combined two polymers than polymer alone.