A facile synthesis of (±)-sesbanine via γ-addition of ketene silyl acetal with quaternized methyl nicotinate

Total synthesis of (±)-sesbanine ($\text{1}$) was carried out using γ-addition of ketene silyl acetal of methyl 3-cyclopentenecarboxylate to quaternized methyl nicotinate. The resulting 1,4-dihydropyridine ($\text{7}$) was oxidized with DDQ to give 4-substituted nicotinate ($\text{2}$) and $\text{2}$ was converted to alcohol ($\text{8}$) by stereoselective oxymercuration followed by treatment with ammonia to give $\text{1}$.     

Novel bifunctional probe for radioisotope-free photoaffinity labeling: compact structure comprised of photospecific ligand ligation and detectable tag anchoring units

A novel method for radioisotope-free photoaffinity labeling was developed, in which a bifunctional ligand is connected to a target protein by activation of a photoreactive group, such as an aromatic azido or 3-trifluoromethyl-3H-diazirin-3-yl group, and identification of the ligated product is achieved by anchoring of a detectable tag through the Staudinger-Bertozzi reaction with an alkyl azido moiety that survives photolysis. The chemical ground of this method was confirmed using model compounds with the bifunctional group under photoirradiation in the presence of trapping agents for reactive intermediates. The utility of the method has been demonstrated by specific labeling of the catalytic portion of human HMG-CoA reductase.     

Formation of an η-allyl and a cyclic γ-hydroxyalkyl complex of molybdenum from reaction of MoH2(η-cyclopentadienyl)2 with homoallyl alcohol

The reaction of Cp₂MoH₂ (Cp=η⁵-C₅H₅) with homoallyl alcohol in the presence of a protonic acid afforded a cationic η³-crotyl molybdenum complex and a cyclic α-methyl-γ-hydroxypropyl molybdenum complex. This reaction proceeds via the stepwise formation of the cyclic complex, followed by formation of the η³-crotyl complex.     

Functionalization of cyclodextrins via reactions of 2,3-anhydrocyclodextrins

Three types of reactions of 2,3-anhydro-beta-cyclodextrins, namely nucleophilic ring-opening, reduction to 2-enopyranose, and reduction to 3-deoxypyranose, have been investigated to regio- and stereoselectively functionalize the secondary face of beta-cyclodextrin. Upon treatment with various nucleophiles, both 2,3-mannoepoxy and 2,3-alloepoxy-beta-cyclodextrins are found to undergo nucleophilic ring-opening reaction generating 3- and 2-modified cyclodextrin derivatives. In each case, the 3-position is more easily accessible than the 2-position. By using these ring-opening reactions, imidazolyl, iodo, azido, and benzylmercapto groups are selectively introduced to the secondary face of beta-cyclodextrin in place of the 2- or 3-hydroxyl groups. The functionalized cyclodextrins have either modified glucosidic subunits or modified altrosidic subunits that make the hydrophobic cavity slightly distorted from that of native beta-cyclodextrin. Thiourea also reacts with the cyclodextrin epoxides. In this case, thiirane and olefin species are generated instead of any ring-opening products. By ameliorating the reaction condition, cyclodextrin olefin, diene, and triene derivatives are prepared in moderate to good yields. Reduction of per[6-(tert-butyldimethyl)silyl]-beta-cyclodextrin permannoepoxide with lithium aluminum hydride produces the per(3-deoxy)-beta-cyclomannin. All these chemically modified cyclodextrins are structurally well characterized and most of them are expected to serve as versatile scaffolds for diverse purposes such as the construction of catalysts and development of synthetic receptors and molecular containers.     

Thermal conductivity of vitreous sodium phosphates

Summary The thermal conductivity was measured for vitreous sodium phosphates of a variety of compositions in the temperature range from 50° to 160°. The temperature coefficient of the thermal conductivity decreases with the increase ofR (Na₂O/P₂O₅ mole ratio), and changes its sign from positive to negative at the value ofR near unity. In the composition range fromR=0.7 toR=1.4, where the thermal conductivity increases with the increase ofR, the composition dependence of thermal conductivity can be explained by the composition dependences of density and of compressibility. The residual water in the phosphates on the ultraphosphate side of composition seems to have some large effect on the thermal conductivity.

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Zusammenfassung Die thermische Leitfähigkeit für glasige Natriumphosphate verschiedener Zusammensetzung wurde im Temperaturbereich von 50 bis 160° gemessen. Der Temperaturkoeffizient thermischer Leitfähigkeit nimmt mit dem Anteil anR (Na₂O/P₂O₅ molares Verhältnis) zu und ändert sein Vorzeichen von positiven zum negativen Werten vonR in der Nähe von eins. Im Bereich der Zusammensetzung vonR=0,7 bisR=1,4, indem die thermische Leitfähigkeit mit Zunahme vonR zunimmt, läßt sich die Abhängigkeit von der Zusammensetzung für die thermische Leitfähigkeit durch die Abhängigkeit von Dichte und Kompressibilität von der Zusammensetzung erklären. Das restliche Wasser in den Phosphaten auf der Ultraphosphat-Seite der Zusammensetzung scheint einen großen Einfluß auf die thermische Leitfähigkeit zu haben.

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With 7 figures and 1 table     

Application of a chiral copper-1,1-bis{2-[(4S)-tert-butyloxazolinyl]}cyclopropane catalyst for asymmetric cyclopropanation of styrene

The structural effects of the bridge moiety and 5-position on bisoxazoline ligands were studied for the copper-catalyzed asymmetric cyclopropanation of styrene with ethyl diazoacetate. The 1,1-bis{2-[(4S)-tert-butyloxazolinyl]}cyclopropane ligand showed a remarkable enhancement in the stereoselectivities (trans/cis = 84/16, >99.9% ee for the trans product) compared with the previously reported best ligand, 2,2-bis{2-[(4S)-tert-butyloxazolinyl]}propane (trans/cis = 75/25, 99.0% ee for the trans product).     

Interfacial tension and wetting behavior of air/oil/ionic liquid systems

We measured the interfacial tension and the density of air/n-hexane, n-decane, 1-perfluorohexane/1-hexyl-3-methyl-imidazolium hexafluorophosphate systems as a function of temperature. From the air/ionic liquid surface tension values, it was suggested that Coulombic interaction between imidazolium cations and counter anions are not so much different between the surface and bulk. The density values indicated that the decrease of surface tension by saturating organics was closely correlated to the mutual solubility between ionic liquid and organics. Interfacial tension at the oil/ionic liquid interfaces suggested that ionic liquid molecules were more ordered at the oil/ionic liquid interfaces compared to the air/ionic liquid interfaces, but the decrease of the entropy due to the interfacial orientation of ionic liquid was compensated by the increase of the entropy due to the contact of different chemical species. The initial spreading coefficients and the Hamaker constants indicated that all the oil phases spread at the air/ionic liquid interfaces spontaneously, and form the complete wetting films.     

Experimental and theoretical studies of small-angle electron scattering by the water molecule

The total (elastic plus inelastic) intensities of 51 keV electrons scattered by water molecules have been measured over a range of 1 ≦ K = (4π/λ) sin(θ/2) ≦ 12 Å^?1. A computer program, ELIC, has been written for calculating the total intensities of electrons scattered by free molecules. The intensities can be calculated with self-consistent field and configuration interaction wavefunctions. The theoretical intensities based on a CI wavefunction are in good agreement with the observed intensities.     

High-performance liquid chromatographic assay of N(G)-monomethyl-L-arginine, N(G),N(G)-dimethyl-L-arginine, and N(G),N(G)'-dimethyl-L-arginine using 4-fluoro-7-nitro-2, 1,3-benzoxadiazole as a fluorescent reagent

N(G)-Monomethyl-L-arginine (L-NMMA), N(G),N(G)-dimethyl-L-arginine (ADMA), and N(G),N(G)'-dimethyl-L-arginine (SDMA) are emerging cardiovascular risk factors. A high-performance liquid chromatographic method with fluorescence detection for the simultaneous determination of L-NMMA, ADMA and SDMA is described. The assay employed 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) as a fluorescent derivatization reagent. After solid phase extraction with cation-exchange column, the methylated arginines were converted to fluorescent derivatives with NBD-F, and the derivatives were separated within 32 min on a reversed-phase column. Nomega-Propyl-L-arginine was Used as an internal standard. Extrapolated detection limits were 12 nM (12 fmol per injection) for L-NMMA and 20 nM (20 fmol per injection) for ADMA and SDMA, respectively, with a signal-to-noise ratio of 3. The calibration curves for L-NMMA, ADMA and SDMA were linear within the range of 50-5000 fmol. The method was applied to the quantitative determination of L-NMMA, ADMA and SDMA in 200 microl of rat plasma. The concentrations of L-NMMA, ADMA and SDMA in rat plasma were 0.16 +/- 0.03, 0.80 +/- 0.25 and 0.40 +/- 0.21 microM, respectively (n = 5).