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71.
Kiyoshi Tanaka Hideki Takahashi Kozo Takimoto Masahiko Sugita Keiryo Mitsuhashi 《Journal of heterocyclic chemistry》1992,29(4):771-777
Synthesis of pyrido[1′,2′:1,2]imidazo[4,5-b]quinoxalines by the facile cyclizations of 2,3-dichloroquinoxalines with 2-aminopyridines and of 2-amino-3-chloroquinoxalines with various substituted pyridines is described. 相似文献
72.
Motokawa R Annaka M Nakahira T Koizumi S 《Colloids and surfaces. B, Biointerfaces》2004,38(3-4):213-219
By employing small-angle neutron scattering (SANS), we investigated the microstructures of, poly(N-isopropylacrylamide) (PNIPA)-block-poly(ethylene glycol) (PEG) (NE) in deuterated water D2O, as related to macroscopic behaviors of fluidity, turbidity and synerisis. SANS revealed following results: (i) microphase separation occurs at around above 17 °C in a temperature range of transparent sol below 30 °C. In the microdomain appeared in the transparent sol state, both block chains of PNIPA and PEG are swollen by water; (ii) for the NE solution of polymer concentration Wp > 3.5% (w/v), corresponding to opaque gel above 30 °C, a percolated structure, i.e., network-like domain is formed by NE as a result of macrophase separation due to dehydration of the PNIPA chains. As the temperature increases toward 40 °C, the network domain is squeezed along a direction parallel to the NE interface, which leads to increase of the interfacial thickness given by swollen PEG chains and to the macroscopic synerisis behavior. 相似文献
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74.
The development of solid strong base catalysts utilizable in green but acidic medium of scCO2 is reviewed. The strong base sites on mesoporous alumina and sulfated mesoporous alumina that had been generated by severe treatment at 773 K under vacuum (10?4 Torr) were not neutralized by the compressed Lewis acidic molecules of CO2, promoting a representative strong base-catalyzed reaction of the Tishchenko reaction as well as a typical base-catalyzed reaction of the Knoevenagel reaction in scCO2. Infrared spectroscopy of the adsorbed pyrrole, temperature-programmed desorption of CO2, and the poisoning by a very weak Brönsted acid of methanol have revealed that the average strengths of the base sites on mesoporous alumina and sulfated mesoporous alumina are weaker than that on conventional γ-alumina like JRC-ALO-4, but that they have a small number of strong base sites which function even in scCO2 medium. It was found that the addition of a slight amount of THF cosolvent into scCO2 remarkably accelerates the Tishchenko reaction over sulfated mesoporous alumina; the reaction rate in the scCO2–THF medium was 1.5-fold and 2-fold faster than those in ordinary organic solvents such as benzene and THF and that in pure scCO2, respectively. The unique structures of mesoporous alumina and sulfated mesoporous alumina have been fully characterized by N2 adsorption–desorption measurements and XRD analyses. 相似文献
75.
T Kawaguchi T Hasegawa T Seki K Juni Y Morimoto A Miyakawa M Saneyoshi 《Chemical & pharmaceutical bulletin》1992,40(5):1338-1340
Five ester prodrugs of 2'3'-dideoxyinosine (DDI) were synthesized for the purpose of improving oral bioavailability. The prodrugs, acetate (C2-DDI), octanoate (C8-DDI), stearate (C18-DDI), benzoate (Bz-DDI), and hemisuccinate (Suc-DDI) were proved to quantitatively regenerate their parent drug by enzymatic hydrolysis. Though the chemical stability of the prodrugs under acidic conditions was not improved, their solubility in water was significantly decreased by esterification, except for Suc-DDI. Bioavailability was evaluated by oral administration to rats. Two hydrophobic prodrugs (C8-DDI and Bz-DDI) showed higher absolute bioavailability (23.5% and 31.0%, respectively) than did DDI (15.2%), though that of C2-DDI (11.5%) and Suc-DDI (4.5%) was poor. 相似文献
76.
77.
Y Watanabe Y Matsumoto M Seki M Takase M Matsumoto 《Chemical & pharmaceutical bulletin》1992,40(11):3042-3047
The absorption of insulin (from porcine pancreas) from the rectum of rabbits after the administration of hollow-type suppositories containing insulin and five kinds of cyclodextrins (CyDs) was investigated. Three types of suppositories were employed: suppository I containing insulin (approximately 26 IU/mg) and various amounts of each CyD in citric buffer solution at pH 3.0 or powder in its cavity, suppository II containing CyD without insulin, and suppository III containing insulin without CyD. Without CyD, the insulin and glucose levels in plasma were unchanged, whereas a significant increase in the plasma insulin concentration and a marked decrease in the glucose levels were found following simultaneous administration of insulin and CyDs by suppository I. The enhancing effect of CyD on rectal insulin absorption (absorption-enhancing effect) by chemically modified CyDs (heptakis(2,6-di-O-methyl)-beta-CyD (DM-beta-CyD) and 2-hydroxypropyl-beta-CyD (HP-beta-CyD)) was higher than those by natural CyDs (alpha-, beta-, and gamma-CyD). The area under the plasma concentration-time curve (AUC) and Cmax of insulin significantly decreased with the preadministration (administration of CyD 6, 24 and 48 h before rectal insulin administration) of DM-beta-CyD. The absorption-enhancing effect disappeared 24 h after preadministration. These results suggest that CyDs enhance insulin absorption from the rectum, and that attenuation of the membrane transport barrier function in the rectum recovers at a maximum of 24 h after administration of CyDs. 相似文献
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