Cycloartane glycosides from the rhizomes of Cimicifuga racemosa and their cytotoxic activities

Phytochemical analysis of the rhizomes of Cimicifuga racemosa (Ranunculaceae) resulted in the isolation of twelve cycloartane glycosides (1--12), including four new ones (4--6, 12). The structures of the new compounds were determined by spectroscopic analysis, including two-dimensional (2D) NMR data, and chemical methods. The isolated compounds were evaluated for their cytotoxic activities against human oral squamous cell carcinoma (HSC-2) cells and normal human gingival fibroblasts (HGF).     

Ligand-controlled highly stereoselective syntheses of e- and z-allylsilanes from dienes and aldehydes using nickel complex

Synthetic methods of highly stereocontrolled E- and Z-allylsilanes were developed. When a toluene solution of diene having a silicon moiety and aldehyde was refluxed in the presence of silane using a catalytic amount of Ni(cod)(2) bearing PPh(3), E-allylsilane was obtained in high yield. On the other hand, when the reaction was carried out in THF upon heating in the presence of Ni(cod)(2), imidazolium salt, Cs(2)CO(3), and PPh(3), Z-allylsilane was formed as a sole product.     

Highly enhanced enantioselectivity in the memory of chirality via acyliminium ions

[reaction: see text] Electrochemical oxidation of N-acylated serine derivative 1b in methanol gave optically active methoxylated compound 2b with an enantiomeric excess of up to 80%. The bulky o-phenyl benzoyl N-protecting group was found to be the main contributing factor for the enhanced enantioselectivity. The mechanistic aspect of this methoxylation reaction was investigated and found to proceed via a retention mechanism.     

Studies on the constituents of bocconia cordata. III Structure elucidation of bocconine by means of nuclear magnetic resonance spectroscopic studies

The nmr spectroscopic studies on methoxybocconine are described. The spectral data indicate bocconine to be 2,3,7,8-bis(methylenedioxy)-10-methoxy-5-methylbenzo[c]phenanthridine.     

Flourescence quenching in aqueous solution of Amphiphilic copolymers: a kinetic model for downward curvature in a stern—volmer-type plot

A kinetic model is presented for downward curvature in a Stern—Volmer-type plot for flourescence quenching of flourophores in hydrophobic microdomains of amphiphilic copolymers in aqueous media. In the extreme case where quenchers were rigorously associated with the microdomains, the association constant and the aggregation number of the chromophores in the microdomains could be estimated.     

Elastic response of single DNA molecules exhibits a reentrant collapsing transition

We measured the elastic response of single DNA molecules at various concentrations of the trivalent cation, spermidine. When added spermidine caused the DNA to collapse, the force-extension curves showed either plateaus or stick-release patterns depending on the concentration. The periodic stick-release response determines a characteristic length, which may reflect toroidal supercoiling. At high concentrations of spermidine, we observed the reelongation of single molecules of collapsed DNA. Thus condensation occurs between lower and upper critical concentrations, verifying that the transition is reentrant as theoretically predicted.     

Room-temperature grating-based morphological hole burning in Sm2+-doped glass powders

We have observed grating-based morphological hole burning in Sm2+-doped glass powders at room temperature. When photobleaching on the 4f(6)-4f(5)5d transition of Sm2+ is combined with multiple light scattering, holes are produced in frequency and wave-vector domains. The hole profile depends on the amount of light absorption of Sm2+; it sharpens as the absorption decreases. The variation of the hole shape is explained theoretically based on a diffusion approximation.     

Strain-induced regioselectivities in reactions of benzyne possessing a fused four-membered ring

[reaction: see text] A fused four-membered ring has a powerful directing ability in effecting the regioselective reactions of benzyne with ketene silyl acetal, nucleophile, and alpha-alkoxyfuran.