Diastereoselective reductive N-alkylation of (R,R)-trans-1,2-diaminocyclohexane with prochiral ketones using the Ti(OiPr)4/NaBH4 system

A simple and convenient one-pot method for the reductive N-alkylation of (R,R)-trans-1,2-diaminocyclohexane by prochiral ketones using a Ti(OⁱPr)₄/NaBH₄ system to obtain the corresponding alkyl amine derivatives in 76–95% yields with good diastereoselectivity (dr = up to 23:1:1) is reported.     

Chemoselective Protection of Hydroxyl Groups and Deprotection of Silyl Ethers

Summary.  Trimethylsilylation of alcohols and phenols is carried out using hexamethyldisilazane and LiClO₄ under microwave irradiation and neutral conditions. The deprotection of silyl ethers is carried out similarly using natural kaolinitic clay and a few drops of water. Received March 1, 2001. Accepted (revised) April 17, 2001     

Effect of ethanolic extract of Rubia peregrina L. (Rubiaceae) on monoamine-mediated behaviour

In the traditional system of medicine in Sardinia, Rubia peregrina (RP) is reported as an aphrodisiac herb. Since aphrodisiacs may also have dopaminergic activity, and there can be a reciprocal relationship between dopaminergic and serotonergic functions in the central nervous system, the aim here was to study the effect of the ethanolic extract of the aerial parts of R. peregrina on monoamine-mediated behaviour. The RP (100 and 200?mg?kg(-1) intraperitoneally) significantly inhibited haloperidol (1?mg?kg(-1) i.p.) induced catalepsy in mice (p?相似文献   

Comparison theorems for nonlinear elliptic systems of second order with applications

In this paper comparison theorems concerning Dirichlet problem for a class of weakly coupled nonlinear second order elliptic systems have been developed. Some applications of these results to deflection or vibration of membranes and plates are also given.     

Positive integer solutions of certain diophantine equations

In this study, the diophantine equations \(x^2 -32B_nxy-32y^2 =\pm 32^{r}\), \(x^4 -32B_nxy-32y^2 =\pm 32^{r}\) and \(x^2 -32B_nxy-32y^4 =\pm 32^{r}\) are considered and determined when these equations have positive integer solutions. Moreover, all positive integer solutions of these diophantine equations in terms of balancing and Lucas-balancing numbers are also found out.     

Recent advances in Garratt-Braverman cyclization: Mechanistic and synthetic explorations

Garratt-Braverman cyclization has emerged as one of the simplest synthetic tool to construct two consecutive CC bonds leading to the formation of various important structural scaffolds having significance in the field of therapeutics and material science. The strategic design of suitable precursor for this cycloaromatization reaction involves the deep understanding of reaction pathways involving diradicals and ions. On the other hand, the reaction offers an unprecedented mechanistic paradox for the chemists to solve. This report aims at outlining the recent mechanistic and synthetic developments with special emphasis on the research outcomes from our laboratory.     

Long-term exposure to CdTe quantum dots causes functional impairments in live cells

Several studies suggested that the cytotoxic effects of quantum dots (QDs) may be mediated by cadmium ions (Cd2+) released from the QDs cores. The objective of this work was to assess the intracellular Cd2+ concentration in human breast cancer MCF-7 cells treated with cadmium telluride (CdTe) and core/shell cadmium selenide/zinc sulfide (CdSe/ZnS) nanoparticles capped with mercaptopropionic acid (MPA), cysteamine (Cys), or N-acetylcysteine (NAC) conjugated to cysteamine. The Cd2+ concentration determined by a Cd2+-specific cellular assay was below the assay detection limit (<5 nM) in cells treated with CdSe/ZnS QDs, while in cells incubated with CdTe QDs, it ranged from approximately 30 to 150 nM, depending on the capping molecule. A cell viability assay revealed that CdSe/ZnS QDs were nontoxic, whereas the CdTe QDs were cytotoxic. However, for the various CdTe QD samples, there was no dose-dependent correlation between cell viability and intracellular [Cd2+], implying that their cytotoxicity cannot be attributed solely to the toxic effect of free Cd2+. Confocal laser scanning microscopy of CdTe QDs-treated cells imaged with organelle-specific dyes revealed significant lysosomal damage attributable to the presence of Cd2+ and of reactive oxygen species (ROS), which can be formed via Cd2+-specific cellular pathways and/or via CdTe-triggered photoxidative processes involving singlet oxygen or electron transfer from excited QDs to oxygen. In summary, CdTe QDs induce cell death via mechanisms involving both Cd2+ and ROS accompanied by lysosomal enlargement and intracellular redistribution.