The X-ray structure of a vinyl cation.
Explore the source record for details and available documents.
Boron Compounds↗
SEARCH · Search PubMed
Results for “Organosilicon Compounds”
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Antitumor effect of novel silatranes on renal cell carcinoma in mice.
The effect of several novel silatrane derivatives on the growth of syngeneic renal cell carcinoma (RENCA) in BALB/c mice and the survival rate of the animals were evaluated. The RENCA-bearing animals were treated subcutaneously and weekly with either a water-insoluble or a water-soluble derivative. The silatrane-treated animals were either free of palpable tumors or developed tumors much more slowly in comparison with the control animals without silatranes. The treated animals as a whole also died of tumor at much slower rates. Attempts to use higher silatrane dosages to achieve better curative effects were hampered by the toxicity of these compounds.
Animals↗
[An analysis of the possible mechanism of the ulcerostatic action of 1-ethoxysilatrane].
Stimulating effect of 1-ethoxysilatrane on healing processes of experimental stomach ulcers was studied in rats. 1-ethoxysilatrane inhibited lipid peroxidation in blood and stomach wall tissues, interacted with artificial membranes, and affected the rate of mitochondrial respiration in liver. A hypothesis is put forward on the membranotropic effect of 1-ethoxysilatrane which underlies its ulcerostatic effect.
Acetates↗
Synthesis of 2'-O-substituted ribonucleosides.
An efficient synthesis of 2'-O-substituted ribonucleosides, including 2'-O-TBDMS and 2'-O-TOM protected as well as 2'-O-Me and 2'-O-allyl derivatives is presented. Di-t-butylsilylene group was employed for simultaneous protection of 3'- and 5'- hydroxyl functions of nucleoside on the first step. Subsequent silylation or alkylation of free 2'-OH followed by introduction of suitable protection on the base moiety and removal of cyclic silyl protection gave target compounds in a high yield.
Alkylation↗
The tert-butyl dimethyl silyl group as an enhancer of drug cytotoxicity against human tumor cells.
In this study, we synthesized a series of enantiomerically pure (2R,3S)-disubstituted tetrahydropyranes with diverse functional groups using known methodologies. In addition to the tert-butyl dimethyl silyl group, other common protecting groups for hydroxyl groups such as allyl, acetate, and benzoate were used to obtain appropriate derivatives. Pure compounds were evaluated in vitro against HL60 human leukemia cells and MCF7 human breast cancer cells. From the growth inhibition data a structure-activity relationship was obtained. Overall the results point to the relevant role of the tert-butyl dimethyl silyl group in the modulation of cytotoxic activity.
Acetates↗
Gas-liquid chromatography-mass spectrometry of mono- and dithiols as their tert.-butyldimethylsilyl derivatives.
The use of gas-liquid chromatography and mass spectrometry with derivatizing agents that give stable derivatives and consistent fragmentation patterns allows for accurate identification of a variety of compounds. In this study either N-methyl-N-tert.-butyldimethylsilyltrifluoroacetamide or N-tert.-butyldimethylsilylimidazole were employed to derivatize a range of mono- and dithiols: from ethanethiol to 1-hexadecanethiol and 1,2-ethanedithiol to 1,9-nonanedithiol. When analyzed in this way, the resulting tert.-butyldimethylsilyl derivatives of the 24 thiols tested were readily distinguishable. Complete baseline separation of each derivative by capillary gas-liquid chromatography was achieved, and each produced a prominent mass minus 57 [M+. - 57] fragment ion. The tert.-butyldimethylsilyl-thioethers were colorless and were stable at room temperature for over 3 months. This method may provide a convenient approach to the analysis of thiol compounds from a wide variety of sources.
Gas Chromatography-Mass Spectrometry↗
Preparation of a soluble 58 kDa-3-hydroxy-3-methylglutaryl CoA reductase from liver microsomes and its inhibition by ethoxysilatrane, a hypocholesterolemic compound.
On repeated thawing at room temperature of frozen preparations of heavy microsomes from rat livers, HMGCoA reductase activity was solubilized due to limited proteolysis. This soluble enzyme was partially purified by fractionation with ammonium sulfate and filtration on Sephacryl S-200 column. The active enzyme was coeluted with a major 92 kDa-protein and was identified as a 58 kDa-protein after separation by SDS-PAGE and immunoblotting. Ethoxysilatrane, a hypocholesterolemic compound, which decreased the liver-microsomal activity of HMGCoA reductase on intra-peritonial treatment of animals, showed little effect on the enzyme activity with isolated microsomes or the 50 kDa-soluble enzyme when added in the assay. But it was able to inhibit the activity of the soluble 58 kDa-enzyme in a concentration-dependent, reversible manner. Cholesterol and an oxycholesterol were without effect whereas chlorophenoxyisobutyrate and ubiquinone showed small inhibition under these conditions. The extra region that links the active site domain (50 kDa protein) to the membrane, present in the 58 kDa-protein appears to be involved in mediating the inhibition by silatrane.
Animals↗
Biological activity of silatranes.
Explore the source record for details and available documents.
Adjuvants, Immunologic↗
Gas chromatography-mass spectrometry of monohydroxyeicosatetraenoic acids as their methyl esters trimethylsilyl, allyldimethylsilyl and tert.-butyldimethylsilyl ethers.
The gas chromatographic and mass spectrometric properties of the monohydroxy acids 5-hydroxyeicosatetraenoic acid (5-HETE), 12-hydroxyeicosatetraenoic acid (12-HETE) and 15-hydroxyeicosatetraenoic acid (15-HETE) as their methyl ester trimethylsilyl, methyl ester allyldimethylsilyl and methyl ester tert.-butyldimethylsilyl ethers were investigated. The gas chromatographic properties of the trimethylsilyl and tert.-butyldimethylsilyl derivatives were found to be excellent while the allyldimethylsilyl derivative required a well deactivated column. The mass spectra of these silyl derivatives with the exception for 12-HETE did not exhibit particularly intense ions in the upper mass region. A quantitative analysis by selected-ion monitoring of the most intense ion in the upper mass region of respective mass spectrum demonstrated that a detection limit in the low picogram range could only be obtained for 12-HETE. Since the mass spectra indicated that the double bonds exerted a strong influence on the fragmentation pattern, the trimethylsilyl, allyldimethylsilyl and tert.-butyldimethylsilyl ethers of the methyl esters of the reduced analogues of the monohydroxy acids were prepared. The saturation of the double bonds completely altered the fragmentation patterns and very intense ions carrying a high percentage of the total ion abundance were found in all of the mass spectra. The developed technique was utilized for measurements of 5-HETE in lung tissue samples from patients with lung cancer.
12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
Conformational transmission in condensed lipid model compounds. Chain packing modification by head-group-induced conformational changes in the glyceryl backbone.
On changing the phosphorus coordination from four to five via a trigonal bipyramidal geometry in phospholipid model systems, a conformational change is initiated around the C2-C3 linkage caused by enhanced electrostatic repulsion between the atoms O3 and O2, situated in the axis of the trigonal bipyramid. This is supported by the absence of conformational change upon substitution of O2 by methylene. With solid-state cross-polarization and magic-angle spinning 13C-NMR it is shown that such a conformational transmission leads to an increased packing density of the lipid chains. It seems to us that changes in lipid packing caused by conformational transmission may also occur when pentacoordination is present transiently, as under biological conditions, thereby inducing an activation of the transport proteins that are embedded in the membrane.
Bridged Bicyclo Compounds↗
Silsesquioxane models for silica surface silanol sites with adjacent siloxide functionalites and olefin polymerization catalysts thereof.
Incompletely condensed silsesquioxanes of the type R7Si7O9(O[SiR'2O]n)OH (R = c-C5H9, c-C6H11; R' = Me, Ph; n = 1-4), containing a siloxane ring of variable size and rigidity and a remaining silanol, are described. Compared with a truly isolated silanol [R7Si8O12(OH)], solution and solid state FT-IR spectra of these compounds show a nu(OH) shift of approximately 150 cm(-1) to lower frequency, which suggests hydrogen bonding of the silanol with the internal siloxane ring. In agreement with this, the relative ion pair acidities of the silanols in THF, determined by UV/Vis, were lowered by 0.8-1.2 compared with a truly isolated silanol. Density functional theory (DFT) calculations on these systems confirm the presence of intramolecular hydrogen bonding. Possible interaction of the silyl ether functionalities with Lewis acidic metal sites was studied for the neutral gallium-substituted systems and cationic titanium silsesquioxane complexes, models for an immobilized titanium olefin polymerization catalyst. The electron donating capability of the siloxide functionalities in 1, 6, and 7 is not sufficient to satisfy the electron deficiency of the corresponding gallium silsesquioxane species, which form dimeric structures with a bridging siloxide unit rather than Lewis base adducts with coordinated siloxide functionalities. Metallation of 1 and 4 with [Cp"Ti(CH2Ph)3] (Cp" = eta5-1,3-C5H3(SiMe3)2) in a 1:1 ratio afforded monomeric titanasilsesquioxanes. To probe the effect of the neighboring siloxane ring on the highly Lewis acidic titanium center, the catalytic activities of the corresponding cationic half-sandwich complexes were tested in 1-hexene polymerization. Compared with the catalyst system based on the isolated silanol [(c-C5H9)7Si8O12OH], the presence of a neighboring siloxane ring causes considerable retardation of the polymerization process but also improves the stability of the catalyst.
Alkenes↗
Influence of 1-(alkylamino)silatranes and isoniazid on the antitumor activity of cyclophosphamide in mice bearing Sa 180 tumors.
It was the aim of our investigations to increase the antitumor activity of cyclophosphamide. Therefore we applied a combined treatment with silatranes and isoniazid in relation 1:20:1. The effects were directed against a transplantable sarcoma 180. The parablastomatous invasive zone and the regional lymph nodes draining an implanted tumor were taken for the histochemical and morphological studies. The doses ranged from 50 to 175 mg of body mass. The combined derivatives inhibited tumor growth by 70% in relation to the control. The authors connect the limitation of tumor progression in the applied experimental model in mice with the active response of T dependent zone of the regional lymph nodes, the rebuilding of stroma within the borderline invasive zone and the changes within the composition of cellular immune response of the peritumor tissue.
Animals↗
X-ray structure of a trimeric 5,5'-biaryl/erythro-beta-O-4-ether lignin model: evidence for through-space weak interactions.
The crystal structure of a trimeric lignin model 1 presenting the characteristic pattern of biphenyl (5,5') and aryl-alkyl-ether (beta-O-4) linkages has been determined. The crystal system is triclinic and the crystallographic unit cell consists of two monomeric molecules. These results are compared with crystal data from the literature of simple models of the 5,5' and beta-O-4 structure type. The availability of a terminal aldehyde function on the model affords some interesting intermolecular interactions by weak hydrogen bonding which controls the conformation of the molecule and the aromatic ring orientation in particular; an unexpected cisoïd conformation of the biaryl unit is observed based on the 64.4 degrees value found for the torsion angle between the two 5,5' aromatic rings.
Alcohols↗
[Synthesis of long-chain 2-(dimethylalkylsilyl)ethylsaccharides].
Research has shown that acetyl protected sugars bond over silicon-oxygen are quiet hard to handle in order to remove the protected group with methods described in literature. However free OH-groups are essential for instance for the processes of biochemical identification. Through the fitting of an ethylen-spacer-group between the silicon atom and the oxygen atom, it is possible to get sugar compounds without the protected acetyl group. The target compounds 14, 16, 18 and 20 were received through reaction of 11 or 12 with 5 or 7 with a mixture of HgO and HgBr2 as a catalyst and following reaction with KOCH3. Compounds 21 and 22, prepared analogeously to 10 and 5 or 7, were isolated as a product mixture, which contained the target compounds relatively in low yield. All synthesized compounds were identified by 1H-, 13C- and 29Si-NMR spectroscopy.
Glucosides↗
Inhibition of invasion activity in vitro by a novel class of antitumor agents: silatrane derivatives.
The effect of several silatranes on in vitro invasion of the human amnion basement membrane (BM) by A549 human lung carcinoma cells was examined. Cells treated for two days with the derivatives were examined for invasive activity in the absence of the compounds. From silatrane dose-invasion response curves, an 80% inhibition of invasiveness compared to untreated cells was obtained with 40 micrograms/mg of 1-vinyl silatrane, 50 micrograms/ml of 1-(p-aminophenyl) silatrane, 80 micrograms/mg of 1-(3-phenylthiocarbamidopropyl) silatrane, 66 micrograms/ml of parent silatrane or 171 micrograms/ml of 1-bromosilatrane. Treatment with these doses had no effect on viability, growth or BM attachment of A549 cells.
Antineoplastic Agents↗
N-methyl-N-alkylsilyltrifluoroacetamide-I2 as a new derivatization reagent for anabolic steroid control.
Analytical methods for the control of growth promoters have to be specific and sensitive. At low concentration levels, it is difficult to identify some molecules unambiguously even with the improved performance of analytical methods. GC-MS analysis of 17 beta-trenbolone and its major metabolite, 17 alpha-trenbolone, is a good example. A new derivatization agent has been developed which is based on silylation of the 3- and 17-oxygenated functions and nucleophilic substitution in the 4-position. The structure of the derivatized products was demonstrated using a simple model, cyclohex-2-en-1-one, by NMR and MS spectrometry. In contrast to data found in the literature, this derivative permitted specific mass spectra for trenbolone, sensitive signals for high mass ions and reproducible gas chromatograms to be obtained. The addition of an N(CH3)COCF3 radical to the steroid nucles allowed highly specific detection in GC-high resolution MS even following extraction from complex matrices; sensitive responses were also observed in the negative chemical ionization mode. Moreover, there are significant differences in the electron ionization mass spectra of the two stereoisomers, 17 alpha- and 17 beta-trenbolone. These preliminary results and those obtained for androsta-1,4-dien-3-one and pregna-4,6-dien-3-one indicate useful advances for the determination of steroids and potential applications for metabolism studies on such compounds.
Anabolic Agents↗
Antibody catalyzed cationic cyclization.
Two major goals for the design of new catalysts are the facilitation of chemical transformations and control of product outcome. An antibody has been induced that efficiently catalyzes a cationic cyclization in which an acyclic olefinic sulfonate ester substrate is converted almost exclusively (98 percent) to a cyclic alcohol. The key to the catalysis of the reaction and the restriction of the product complexity is the use of antibody binding energy to rigidly enforce a concerted mechanism in accord with the design of the hapten. Thus, the ability to direct binding energy allows the experimenter to dictate a reaction mechanism which is an otherwise difficult task in chemistry. New catalysts for cationic cyclization may be of general use in the formation of carbon-carbon and carbon-heteroatom bonds leading to multi-ring molecules including steroids and heterocyclic compounds.
Animals↗
Palladium-catalyzed alpha-arylation of esters.
A new and simple one-pot procedure for the palladium-catalyzed intermolecular alpha-arylation of esters is described. A number of esters can be functionalized with a wide range of aryl bromides using Pd(OAc)(2) or Pd(2)(dba)(3) and bulky electron-rich o-biphenyl phosphines 1-3. Under the reaction conditions, using LiHMDS as base, alpha-arylation proceeds at room temperature or at 80 degrees C with very good yields and high selectivities for monoarylation. Important nonsteroidal antiinflammatory drug derivatives such as (+/-)-naproxen tert-butyl ester and (+/-)-flurbiprofen tert-butyl ester can be prepared in 79% and 86% yield, respectively. The catalyst system based on the di-tert-butylphosphine (2) is also active for the alpha-arylation of esters using aryl chlorides. Furthermore, using (3) the alpha-arylation of trisubstituted ester enolates can be accomplished to provide compounds that have quaternary centers.
Acetates↗