Resveratrol derivatives from Upuna borneensis

Four new resveratrol derivatives, upunaphenols B (1), C (4), D (5) (resveratrol tetramer) and E (6, resveratrol dimer with a C6-C1 unit), together with nine known resveratrol oligomers and resveratrol were isolated from an acetone soluble part of stem of Upuna borneensis (Dipterocarpaceae). The structures of new compounds were determined by spectral analysis including 1D and 2D NMR experiments.     

Characterizations of hyperbolically convex regions

Let X be a simply connected and hyperbolic subregion of the complex plane C. A proper subregion Ω of X is called hyperbolically convex in X if for any two points A and B in Ω, the hyperbolic geodesic arc joining A and B in X is always contained in Ω. We establish a number of characterizations of hyperbolically convex regions Ω in X in terms of the relative hyperbolic density ρΩ(w) of the hyperbolic metric of Ω to X, that is the ratio of the hyperbolic metric of Ω to the hyperbolic metric of X. Introduction of hyperbolic differential operators on X makes calculations much simpler and gives analogous results to some known characterizations for euclidean or spherical convex regions. The notion of hyperbolic concavity relative to X for real-valued functions on Ω is also given to describe some sufficient conditions for hyperbolic convexity.     

Non-destructive observation of electrically detected magnetic resonance in bulk material using AC bias

DC bias is normally found in conventional measurements of electrically detected magnetic resonance (EDMR). Usually, electrodes are formed on the sample surface to make ohmic contacts for detecting changes in the electrical characteristics of the sample material. Thus, destructive procedures are required to detect the EDMR signal of bulk material with such methods. An AC bias detection technique was developed to allow the non-destructive EDMR measurement of bulk materials. An AC bridge circuit was constructed to detect the change in impedance of the sample, which when changed by ESR, an unbalanced AC voltage can be detected. By detecting this AC bias, it is possible to cancel the effects, such as Shottky barriers, that disturb the ohmic contact between the electrodes and a sample material. Further, the AC bias current penetrates the thin surface layer of a sample such as silicon oxide, which normally obstructs a DC current. This method was utilized using conductive rubber contacts for non-destructive EDMR measurements of part of a silicon wafer. EDMR spectra observed were the same as those obtained by the conventional method of using DC bias detection.     

Solution structure of Vanabin2, a vanadium(IV)-binding protein from the vanadium-rich ascidian Ascidia sydneiensis samea

Ascidians belonging to the suborder Phlebobranchia are known to accumulate high levels of a transition metal, vanadium, in their blood cells, called vanadocytes, although the mechanism for this biological phenomenon remains unclear. Recently, we identified vanadium(IV)-binding proteins, designated as Vanabins, from vanadium-accumulating ascidians. Here, we report the first 3D structure of Vanabin2 from an ascidian, Ascidia sydneiensis samea, in an aqueous solution. The structure revealed a novel bow-shaped conformation, with four alpha-helices connected by nine disulfide bonds. There are no structural homologues reported so far. The 15N heteronuclear single-quantum coherence (HSQC) perturbation experiments of Vanabin2 indicated that vanadyl cations, which are exclusively localized on the same face of the molecule, are coordinated by amine nitrogens derived from amino acid residues such as lysines, arginines, and histidines, as suggested by the electron paramagnetic resonance (EPR) results. The present NMR studies provide information that will contribute toward elucidating the mechanism of vanadium accumulation in ascidians.     

A practical procedure for the large-scale preparation of methyl (2R,3S)-3-(4-methoxyphenyl)glycidate,a key intermediate for diltiazem

A practical synthesis of methyl (2R,3S)-3-(4-methoxyphenyl)glycidate (-)-2, a key intermediate for diltiazem (1), was developed. Treatment of methyl (E)-4-methoxycinnamate 3 with chiral dioxirane, generated from chiral ketone 4, provided (-)-2 in 77% ee and 89% yield. The crude mixture of (-)-2 and 4 was efficiently separated by the use of novel and simple equipment performing a lipase-catalyzed transesterification and a continuous dissolution and crystallization to furnish the optically pure (-)-2 and recovery of 4 in 74% and 91% yield, respectively.     

A facile synthesis of novel types of cyclodextrin derivatives by insertion of an aromatic dicarbonyl spacer into a permethylated alpha-cyclodextrin skeleton

Novel types of cyclodextrin derivatives are easily synthesized by the insertion of an aromatic dicarbonyl spacer into the skeleton of permethylated alpha-cyclodextrin, and the isophthaloyl-inserted one shows almost the same complexing ability toward p-nitrophenol as permethylated beta-cyclodextrin.     

Stereochemical anomaly in the thermal conversion of 7,8-dioxy-7-alkenylbenzocyclobutenes to dihydronaphthalenes

[reaction: see text] The stereochemistry of the thermal conversion of alkenylbenzocyclobutenol into dihydronaphthalene was studied. Experiments on the substrates IV, in which two oxy functions are cis, often resulted in the formation of abnormal products in view of the orbital consideration.     

Coexistence of superconductivity and itinerant-antiferromagnetism in CrRe alloys

Zero field Re NMR of CrRe alloy with more than 18%Re in superconducting state has been observed. The nuclear spin-lattice relaxation time (T₁) of Re in the vortex state increases exponentially with decreasing temperature as in the case of BCS superconductor. The result shows a coexistence of superconductivity and itinerant-electron antiferromagnetism.     

Die Rolle der Halogen-Liganden in der Oberfl?che von Ti-Metall-stellan bei der stereospezifischin Polymerisation mit ziegler-Natta-Katalysatoren

Ohne Zusammenfassung     

The mass spectra of 2,4,7-trihydroxypteridines and their trimethylsilyl derivatives

The mass spectra of a series of 2,4,7-trihydroxypteridines and their trimethylsilyl derivatives have been determined. Fragmentation mechanisms are supported by high resolution, deuterium labeling and metastables.