Studies on antiulcer drugs. III. Synthesis and antiulcer activities of imidazo[1,2-a]pyridinylethylbenzoxazoles and related compounds. A novel class of histamine H2-receptor antagonists.

A series of imidazo[1,2-a]pyridinylalkylbenzoxazole derivatives was synthesized and tested for histamine H2-receptor antagonist, gastric antisecretory and antiulcer activities. Some of 2-amino-6-[2-(imidazo[1,2-a]pyridin-2-yl)ethyl]benzoxazole derivatives were found to have good pharmacological activities. Among them, 2-amino-6-[2-(7-methoxy-3-methylimidazo[1,2-a]pyridin-2-yl)ethyl] benzoxazole (II-11) and 2-acetamido-6-[2-(7-methylimidazo[1,2-a]pyridin-2-yl)ethyl] benzoxazole (II-38) showed potent antisecretory and cytoprotective activity. The structure-activity relationships of these compounds are discussed.     

Potassium and sodium chloride ion pairs are presumed to constitute a complex during elution from a Sephadex G-15 column with sodium phosphate buffer

When a mixed solution of 0.72 M potassium and sodium chloride was eluted from a Sephadex G-15 column with 0.025 M sodium phosphate buffer (pH 7.0), the elution profiles of ions showed that the potassium and chloride ion pair from the sample and the sodium and chloride ion pair produced by ion-exchange reaction, were eluted in the same fractions as if they constituted a complex. When a mixed solution of different concentrations of potassium and sodium chloride was eluted with the same buffer, the excess amount of one ion pair over the other was eluted freely from the presumed complex.     

Energy transfer reaction of cationic porphyrin complexes on the clay surface: effect of sample preparation method

Photochemical energy transfer of non-aggregated cationic porphyrins on an anionic-type clay (Smecton SA) surface was investigated. The efficiency of energy transfer and excited-state quenching in the absence of energy transfer were evaluated at various loading levels of porphyrin on the clay surface and were found to be significantly affected by the loading level. As the latter increased, both energy transfer efficiency and excited-state quenching increased. Judging from the dependency of energy-transfer efficiency on the porphyrin loading level, a partially clustered structure, but without aggregation, of porphyrins on the clay surface is proposed.     

Catalytic specificity exhibited by p-sulfonatocalix[n]arenes in the methanolysis of N-acetyl-l-amino acids

Specific acid catalysis of p-sulfonatocalix[n]arenes (n = 4, Calix-S4; n = 6, Calix-S6; n = 8, Calix-S8) was observed in the alcoholysis of N-acetyl-l-amino acids in methanol. The methanolysis rates of basic amino acid substrates (His, Lys, and Arg) were markedly enhanced in the presence of Calix-Sn, as compared with rates observed with p-hydroxybenzenesulfonic acid (pHBS), which is a noncyclic analogue of Calix-Sn. This catalytic effect of Calix-Sn was not observed for the methanolysis of Phe, Tyr, and Trp substrates. On the other hand, (1)H NMR experiments following the effect of Calix-Sn on N-acetyl-l-amino acid substrates in CD(3)OD showed that the spectrum of a mixture of the His substrate with Calix-Sn was significantly different from the combined spectra of the respective compounds. These changes in spectra support the formation of an inclusion complex of Calix-Sn with basic amino acids. Furthermore, it was obvious that methanolysis of the His substrate catalyzed by Calix-S4 and Calix-S6 obeyed Michaelis-Menten kinetics. These results indicate that the catalytic activity of Calix-Sn originates from its forming a complex with specific substrates (basic amino acids), similar to enzymatic reactions.     

Laser-induced fluorescence of the SiH2 radical

The laser-induced fluorescence of the SiH₂ radical was observed in the photolysis of phenylsilane by an ArF excimer laser in the 550–650 nm range. The apparent fluorescence lifetime is 60 ± 5 ns at 580.1 nm. The bending vibrational spacing in the ground state was found to be 990 ± 20 cm^?1 from the dispersed fluorescence spectrum.     

Enantiodifferentiating photoaddition of alcohols to 1,1-diphenylpropene in supercritical carbon dioxide: sudden jump of optical yield at the critical density

In the enantiodifferentiating photoaddition of ROH (R = Me, Et, i-Pr) to 1,1-diphenylpropene sensitized by fructosyl 1,4-naphthalenedicarboxylate in supercritical carbon dioxide, the enantiomeric excess of photoadduct increased with increasing bulkiness of the alcohol at all pressures used, with an accompanying sudden jump at the critical density, for which the enhanced clustering of alcohol, particularly in the subcritical pressure region, was revealed to be responsible from the fluorescence spectral examinations.     

Supramolecular chirogenesis in zinc porphyrins: interaction with bidentate ligands,formation of tweezer structures,and the origin of enhanced optical activity

The complexation behavior, binding properties, and spectral parameters of supramolecular chirality induction in the achiral host molecule, syn (face-to-face conformation) ethane-bridged bis(zinc porphyrin), upon interaction with chiral bidentate guests (diamines and amino alcohols) have been studied by means of UV-vis, CD, fluorescence, (1)H NMR, and ESI MS techniques. It was found that the guest structure plays a decisive role in the chirogenesis pathway. The majority of bidentate ligands (except those geometrically unsuitable) exhibit two major equilibria steps: the first guest ligation leading to formation of the 1:1 host-guest tweezer structure (K(1)) and the second guest molecule ligation (K(2)) forming the anti bis-ligated species (1:2). The second ligation is much weaker (K(1) > K(2)) due to the optimal geometry and stability of the 1:1 tweezer complex. The enhanced conformational stability of the tweezer complex ensures an efficient chirality transfer from the chiral guest to the achiral host, consequently inducing a remarkably high optical activity in the bis-porphyrin.     

Change in dislocation distribution of KCl single crystals during thermal cyclic annealing

The change in dislocation distribution of KCl single crystals during thermal cyclic annealing was studied by etch pit method. The results obtained are summarized as follows. (1) In contrast to the case in Cu (KITAJIMA et al.; HASEGAWA et al.), the dislocation distribution in KCl crystals became non-uniform with an increase in the cyclic annealing time, i.e., in the region near the surface, many sub-boundaries were formed, but in the interior, the density of dislocations and sub-boundaries decreased. The cyclic annealing is more effective in reducing the dislocation density than the isothermal annealing. (2) The longer the period of thermal cycle, the more effective in reducing the dislocation density. (3) The larger the temperature difference between the maximum and minimum during one cycle, the more effective in reducing the dislocation density. (4) In the Sr-doped crystals, the thermal cyclic annealing was also effective in reducing the dislocation density within subgrains but sub-boundary length per unit area slightly increased by the cyclic annealing. (5) When the samples were annealed under the atmosphere of Cl₂, the dislocation density remarkably increased against our expectation, although the scattering centres had disappeared by this treatment.