Incubation of ginseng sapogenins with microsomes from rat liver resulted in formation of their 20,24-epoxides as major metabolites. Identification of the metabolites was performed by HPLC, FAB-MS and EI-MS. 相似文献
The carcinogenic process is usually multifactor in its causation and multistep in its evolution. It is likely that entirely different molecular mechanisms underlie the many steps in this process. In contrast to initiating carcinogens, the action of the tumor-promoting phorbol esters does not appear to involve covalent binding to cellular DNA and they are not mutagenic. Recent studies in cell culture have revealed two interesting biologic effects of the phorbol esters and related macrocyclic plant diterpenes. The first is that at nanomolar concentrations they induce several changes that resemble those seen in cells transformed by chemical carcinogens or tumor viruses. These include altered morphology and increased saturation density, altered cell surface fucose-glycopeptides, decrease in the LETS protein, increased transport of deoxyglucose, and increased levels of plasminogen activator and ornithine decarboxylase. In transformed cells exposed to phorbol esters the expression of these features is further accentuated. Phorbol esters do not induce normal cells to grow in agar but they do enhance the growth in agar of certain transformed cells. The second effect of the phorbol esters is inhibition of terminal differentiation. This effect extends to a variety of programs of differentiation and is reversible when the agent is removed. With certain cell culture systems induction of differentiation, rather than inhibition, is observed. Both the transformation mimetic and the differentiation effects are exerted by plant diterpenes that have tumor-promoting activity but not by congeners that lack such activity. The primary target of phorbol esters appears to be the cell membrane. Early membrane-related effects include enhanced uptake of 2-deoxyglucose and other nutrients, altered cell adhesion, induction of arachidonic acid release and prostaglandin synthesis, inhibition of the binding of epidermal growth factor to cell surface receptors, altered lipid metabolism, and modifications in the activities of other cell surface receptors. A model of "two stage" carcinogenesis encompassing the known molecular and cellular effects of initiating carcinogens and tumor promoters is presented. According to this model, initiating carcinogens induce stable alterations in the cellular genome but these are not manifested until tumor promoters modulate programs of gene expression and induce the clonal outgrowth of the initiated cell. 相似文献
The effect of Ce doping and pretreatment of Pt/Al2O3 on its catalysis of propane oxidation was investigated after aging the catalysts. The Ce amount and pretreatment conditions were varied, and the propane oxidation activity was measured. The properties of the catalysts were investigated by means of XRD, STEM-EDX, FT-IR, and H2-TPR. The size of the Pt nanoparticles (PtNPs) decreased for water-treated catalysts doped with a small amount of Ce, suggesting that water treatment of Ce-doped catalysts inhibits Pt sintering. The minimum PtNP size was obtained with ca. 3.6 wt% of Ce. The Ce species with less than 3.6 wt% existed in a dispersed state, whereas above this value, CeO2 particulates co-existed. The propane oxidation temperature of the water-treated catalysts was lowered to an extent that depended on the Ce content. This tendency is consistent with the PtNP size in the catalysts. It is considered that highly dispersed Ce species take a primary role in promoting propane oxidation on PtNPs. The reduction temperature of Ce species on water-treated catalysts was lower than that of untreated catalysts, probably owing to a stronger interaction between Pt and Ce, demonstrated by FT-IR measurements. The increased reducibility of Ce species may be the reason for the improved oxidation activity of the catalysts.
A general and mild catalytic allylation of carbonyl compounds, applicable to aldehydes, ketones, and imines is developed using allyltrimethoxysilane as the allylating reagent. The reaction proceeds smoothly with 1-10 mol % of CuCl and TBAT in THF at ambient temperature. Mechanism studies indicated that the copper alkoxide, allylfluorodimethoxysilane, and allyltrimethoxysilane are essential to promote the reaction efficiently. Preliminary extension of the reaction to the first catalytic enantioselective allylation of ketones using an allylsilane produced the product with 61% ee from acetophenone, using a CuCl-p-tol-BINAP-TBAT catalyst (15 mol %). 相似文献
The 13C-NMR spectra of hydrogenated polyisoprenes were investigated. Polyisoprenes containing various ratios of 1,4 and 3,4 units were prepared with n-BuLi/Et2O and were hydrogenated by using p-toluenesulfonylhydrazide. 13C-NMR signals of the hydrogenated polymers were assigned for the triad sequences arising respectively from the 1, 4 and 3, 4 units of polyisoprenes. On the basis of these assignments it was confirmed that 1,4 and 3,4 units were randomly distributed in the polyisoprenes prepared with n-BuLi and that these polymers did not contain appreciable amounts of head-to-head or tail-to-tail 1,4 linkages. 相似文献
The present study aims to investigate an odd–even effect of the number of ethylene imine units in the side-groups of totally abiotic synthetic polymers on their efficiency in DNA transfection. A library of fifteen polymers was fabricated. Two star homopolymers and one linear homopolymer based on glycidyl methacrylate were synthesized and used as precursors to which five linear oligo(ethylene imine)s (OEI) were grafted. The number of ethylene imine groups of the OEIs was varied. Specifically, ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, and pentaethylene hexamine were used. Each of these fifteen OEI-grafted polymers was evaluated in terms of their efficiency to transfer plasmid DNA encoding firefly luciferase in C2C12 mouse myoblast cells. The transfection efficiency displayed an odd-even pattern, with all OEI-grafted polymers with an odd number of ethylene imine repeating units exhibiting higher transfection efficiency compared with those possessing an even number of ethylene imine repeating units. The odd–even effect was more pronounced for the star polymers with longer arms (degree of polymerization, DP = 100), while in case of the linear polymers, the odd–even effect was only observed for the lowest polymer loading. The cytotoxicity of the OEI-grafted polymers also followed an odd–even pattern, with the OEI-grafted star polymers with an arm DP of 100 and the linear polymers clearly presenting an odd-even effect, while the cytotoxicity of the OEI-grafted star polymers with an arm DP of 20 slightly increased with the number of ethylene imine repeating units. 相似文献
Spin-trapping technique was employed to detect and identify free radical intermediates produced in aqueous solutions of nucleic acid constituents (pyrimidine bases and pyrimidine nucleosides) after irradiation by monochromatic 160 nm vacuum-UV light from the electron storage ring. Short-lived free radicals produced in the molecules were converted into relatively long-lived free radicals (spin-adducts) by the reaction with MNP used as a spin trap. The resulting nitroxide radicals were subsequently analysed by esr. The esr measurements were made after irradiating H2O solution containing sample and the spin trap and once freeze-drying it and re-dissolving the residual powder in D2O to get the spectrum with a well-resolved hyperfine structure. Thus, clear evidence that most of the radicals were not formed by H-addition but formed by OH-addition at the C5 position of the 5, 6 double bond were obtained for pyrimidine bases. For pyrimidine nucleosides, although the effect of H2O-D2O exchange was not recognized on resolution improvement of the hyperfine structure of the esr spectra, careful analysis of the hyperfine structure made it possible to identify the radical structures; OH-addition radicals at the C6 of the double bond of the base moiety in addition to the OH-addition radicals at the C5 position for all except for 2-deoxycytidine. Evidence for the formation of free radicals at the sugar moiety was not clear. 相似文献