Enantioselective enol lactone synthesis under double catalytic conditions

[reaction: see text] The reaction of dimedone with 1-(2-alkenoyl)-4-bromo-3,5-dimethylpyrazoles in THF, catalyzed by catalytic amounts of both DBFOX/Ph-nickel(II) perchlorate trihydrate and 2,2,6,6-tetramethylpiperidine, in the presence of acetic anhydride in THF produces the corresponding enol lactones in high enantioselectivities through enantioselective Michael additions followed by cyclization with removal of the pyrazole auxiliary. Other related nucleophile precursors can be successfully applied in the enantioselective enol lactone synthesis under the double catalytic conditions.     

Solution-phase automated synthesis of tripeptide derivatives

An improved general method for automated synthesis of tripeptides was developed, in which methanesulfonic acid (MSA) was used in place of trifluoroacetic acid (TFA), thus making it possible to avoid, 1) corrosion of the apparatus by strong acid vapor, 2) formation of emulsions, and 3) use of the restricted solvent, dichloromethane. As an application of the automated synthesis apparatus, 216 fragment tripeptide derivatives were synthesized systematically using the MSA method, in excellent yield and with increased efficiency.     

Molecular hydrogen-originated protonic acid site as active site on solid acid catalyst

The protonic acid sites are formed from hydrogen molecules on Pt/SO₄ ^2--ZrO2 , and the resulting protonic acid sites act as active sites for acid-catalyzed reactions. Promotion of molecular hydrogen on the activities is observed not only for the Pt/SO₄ ^2--ZrO2, but also for the other catalysts such as a physical mixture of Pt/SiO2 and H-ZSM5, and Co.Mo/SiO2-/Al2O3 . A molecular hydrogen-originated protonic acid site is proposed as a widely applicable concept for an active site on solid acid catalysts.     

Thermometric titration of the dodecyl sulphate ion with metal-phenanthroline complexes

Docecyl sulphate forms precipitates with certain metal-1,10-phenanthroline complexes. This is the basis of a simple and direct thermometric titration of dodecyl sulphate with Cd(phen)(2+)(3).     

Structural requirements of flavonoids and related compounds for aldose reductase inhibitory activity

The methanolic extracts of several natural medicines and medicinal foodstuffs were found to show an inhibitory effect on rat lens aldose reductase. In most cases, flavonoids were isolated as the active constituents by bioassay-guided separation, and among them, quercitrin (IC(50)=0.15 microM), guaijaverin (0.18 microM), and desmanthin-1 (0.082 microM) exhibited potent inhibitory activity. Desmanthin-1 showed the most potent activity, which was equivalent to that of a commercial synthetic aldose reductase inhibitor, epalrestat (0.072 microM). In order to clarify the structural requirements of flavonoids for aldose reductase inhibitory activity, various flavonoids and related compounds were examined. The results suggested the following structural requirements of flavonoid: 1) the flavones and flavonols having the 7-hydroxyl and/or catechol moiety at the B ring (the 3',4'-dihydroxyl moiety) exhibit the strong activity; 2) the 5-hydroxyl moiety does not affect the activity; 3) the 3-hydroxyl and 7-O-glucosyl moieties reduce the activity; 4) the 2-3 double bond enhances the activity; 5) the flavones and flavonols having the catechol moiety at the B ring exhibit stronger activity than those having the pyrogallol moiety (the 3',4',5'-trihydroxyl moiety).     

Stereoselective dialkylation of the proximal hydroxy groups of calix- and thiacalix[4]arenes

Treatment of p-tert-butylcalix[4]arene (C1) and its sulfur-bridged analog T1 with 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane in the presence of imidazole gives proximally O,O'-disiloxane-1,3-diyl-bridged calixarenes C2 and T2 in excellent yields, respectively. Subsequent base-catalyzed etherification of the remaining hydroxy groups with alkyl halides gives syn- and anti-O',O'-dialkylated products, the stereoselectivity of which varies depending on the nature of the macrocycle, as well as the metal cation of the base employed. Thus, conventional calixarene C2 preferentially affords syn compounds of 1,2-alternate conformation (C3) with the aid of tert-BuOK and K(2)CO(3) and anti counterparts of partial-cone conformation (C4) with Cs(2)CO(3). On the other hand, thiacalixarene T2 affords syn compounds of 1,2-alternate conformation (T3) with any of the bases. The disiloxanediyl bridge of the resulting products can readily be removed by treatment with tetrabutylammonium fluoride. Thus, the net process provides an efficient method for the regio- and stereoselective synthesis of proximally dialkylated calix[4]arenes.     

Preparation of 2- and 4-(2-alkylcarbamoyl-1-methylvinyl)-7-alkyloxybenzo[b]furans having potent antagonistic activity against human leukotriene B4 BLT1 and/or BLT2 receptors

(E)-2-Acetyl-4-(2-diethylcarbamoyl-1-methylvinyl)-7-(1-phenylethoxy)benzo[b]furan (4b) with a characteristic conformation and (E)-2-(2-morpholinocarbo-1-methylvinyl)-7-ethoxycarbopropoxybenzo[b]furan ((E)-3b) were prepared and evaluated for their leukotriene B4(LTB4) antagonistic activity. Compound 4b showed potent antagonistic activity against human BLT1 and BLT2 receptors. Compound (E)-3b displayed selective BLT2 receptor antagonistic activity. Both compounds were inactive to cysteinyl LT receptors.     

Silicon hydrides and nickel complexes : I. Phosphine-nickel(II) complexes as hydrosilylation catalysts

A variety of dihalodiphosphinenickel(II) complexes have been found to be effective catalysts for hydrosilylation of olefins and acetylenes. Reactions with nickel(II) catalysts, at least those containing a bidentate phosphine ligand, scarcely proceed below 90°. At 120° the reaction proceeds smoothly to form, in many cases, an unexpected (“abnormal”) adduct which has arisen from an interchange of hydrogen and chlorine on silicon in addition to the expected (“normal”) one. Both total yields, and the ratios of the “abnormal” to the “normal” adduct increase, in general, with increasing electron-donating ability of both the phosphine ligands and the substituents on the olefins. Isomerization of olefins occurs during the course of hydrosilylation. cis-Addition occurs preferentially. The reactivity of the silicon hydrides decreases in the order HSiCl₃ ? HSiMeCl₂ ? HSiMe₂Cl ? HSiMe₃.     

Microwave-assisted palladium-catalyzed allylation of aryl halides with homoallyl alcohols via retro-allylation

The palladium-catalyzed allylation of aryl halides with homoallyl alcohols via retro-allylation proceeds at 200-250 °C in a toluene-DMF mixed solvent using microwave heating. Even at such high temperatures, the regio- and stereospecificity of the allyl transfer reaction is still satisfactory. The amount of the palladium catalyst can be reduced to 0.5 or 0.05 mol %.     

Hairpin conformation of amphidinols possibly accounting for potent membrane permeabilizing activities

Amphidinols are a unique dinoflagellate metabolite with potent antifungal activity. We examined membrane permeabilizing action by amphidinol analogues with structural variations in polyhydroxy and polyene moieties. Consequently, the polyene and polyhydroxy moieties turned out to play important roles in binding to lipid bilayer membrane and in forming ion-permeable pore/lesion across membrane, respectively. NMR-constrained modeling experiments have revealed for the fist time that amphidinols in membrane generally take a hairpin configuration, which plausibly accounts for their potent antifungal and other membrane permeabilizing activities.