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At least 73 records · Page 4Linked to original sources
PubMed2005

Separation of microorganisms using electromigration techniques.

Like other colloidal particles bacteria have a surface charge that originates from the ionization of surface molecules and of the adsorption of ions from solution. Bacterial cell wall and membranes containing numerous proteins, lipid molecules, teichoic acids, lipopolisaccharides which give them characteristic charge. Therefore, bacterial cells undergo electrophoresis in a free solution with their own mobility depending on ionic strength and pH of buffer solution. Various electromigration techniques can be used to separate and determine the intact cells. Successful separation of five species of bacteria was obtained using a trimethylchlorosilane-modified capillary and a divinylbenzene-modified with suppressed EOF over a short distance (8.5 cm). The utilization of coated capillaries prevents adsorption of bacteria to the capillary wall. Another approach is utilization of a dilute dissolved polymer, polyethylene oxide (PEO) in the running buffer as a non-bonded coating for the purpose of altering the EOE These experiment have proved the possibility of diagnosing a variety of diseases and the ability to separate and identify viable cells.

Bacteria↗
PubMedDate not supplied

Leishmania tropica: cysteine proteases are essential for growth and pathogenicity.

Leishmania parasites are responsible for a diverse collection of diseases of humans and other animals. Cysteine proteases are putative virulence factors of leishmania parasites. There are differences in the susceptibility of specific stages in different Leishmania species to cysteine protease inhibitors. Here, we establish a key role of cysteine proteases in growth, viability, and pathogenicity of Leishmania tropica by using a specific cysteine protease inhibitor (N-Pip-F-hF-VS Phenyl). Reduction or arrest of promastigote growth occurred at inhibitor concentration of 5 and 100 microM, respectively. This shows an essential role for cysteine proteases in viability and growth of L. tropica promastigotes. It confirms that the promastigote stage of L. tropica more closely resembles that of Leishmania major than that of Leishmania mexicana, which is refractory to this inhibitor. Pathogenicity of L. tropica amastigotes in mice, as assessed by footpad swelling, was also reduced by treatment with the cysteine protease inhibitor. This suggests that cysteine proteases are essential for pathogenicity of L. tropica amastigote in mammalian host, similar to both L. major and L. mexicana.

Animals↗
PubMed2002

A novel chiral sulfonium yilde: highly enantioselective synthesis of vinylcyclopropanes.

A newly designed chiral sulfonium allylide, generated in situ from the corresponding sulfonium salt in the presence of KOBu(t), reacted with alpha,beta-unsaturated esters, ketones, amides, and nitriles to afford trans-2-silylvinyl-trans-3-substituted cyclopropyl esters, ketones, amides, and nitriles with outstanding diastereoselectivity and excellent enantioselectivity in good to high yields. A mechanistic rationale is proposed.

Cyclopropanes↗
PubMed2002

Stereoselective synthesis of trifluoromethylated vicinal ethylenediamines with alpha-amino N-tert-butanesulfinimines and TMSCF3.

Isolable alpha-amino N-tert-butanesulfinimines were prepared through the condensation of Reetz's alpha-amino aldehydes (prepared from alpha-amino acids) with Ellman's (R)-N-tert-butanesufinamide without any racemization, and these were trifluoromethylated with TMSCF3 and TMAF (tetramethylammonium fluoride) to the corresponding vicinal ethylenediamines derivatives. Imines derived from l-amino acids gave exclusively one diastereomer with a very high yield.

Ethylenediamines↗
PubMed2003

A second-generation synthesis of the C1-C28 portion of the altohyrtins (spongistatins).

A practical second-generation synthesis of an advanced intermediate in our total synthesis of altohyrtin C (spongistatin 2) has been developed. A new approach to the C1-C15 (AB) portion features a vinyllithium addition to an aldehyde followed by a palladium-catalyzed allylic reduction to install the troublesome C13-C15 segment. Our general approach to the C16-C28 (CD) spiroketal has been retained, but some improvements have been made. Most notably, the kinetically controlled CD-spiroketalization reaction now proceeds in high yield with excellent diastereoselection. This new strategy uses the anti-aldol coupling used in our first-generation synthesis to join AB and CD fragments. A total of 9.6 g of intermediate 57 has been produced using this improved route.

Antineoplastic Agents↗
PubMed2003

Chemistry, biochemistry, and safety of acrylamide. A review.

Acrylamide (CH2=CH-CONH2), an industrially produced alpha,beta-unsaturated (conjugated) reactive molecule, is used worldwide to synthesize polyacrylamide. Polyacrylamide has found numerous applications as a soil conditioner, in wastewater treatment, in the cosmetic, paper, and textile industries, and in the laboratory as a solid support for the separation of proteins by electrophoresis. Because of the potential of exposure to acrylamide, effects of acrylamide in cells, tissues, animals, and humans have been extensively studied. Reports that acrylamide is present in foods formed during their processing under conditions that also induce the formation of Maillard browning products heightened interest in the chemistry, biochemistry, and safety of this vinyl compound. Because exposure of humans to acrylamide can come from both external sources and the diet, a need exists to develop a better understanding of its formation and distribution in food and its role in human health. To contribute to this effort, this integrated review presents data on the chemistry, analysis, metabolism, pharmacology, and toxicology of acrylamide. Specifically covered are the following aspects: nonfood and food sources; exposure from the environment and the diet; mechanism of formation in food from asparagine and glucose; asparagine-asparaginase relationships; Maillard browning-acrylamide relationships; quenching of protein fluorescence; biological alkylation of amino acids, peptides, proteins, and DNA by acrylamide and its epoxide metabolite glycidamide; risk assessment; neurotoxicity, reproductive toxicity, and carcinogenicity; protection against adverse effects; and possible approaches to reducing levels in food. Further research needs in each of these areas are suggested. Neurotoxicity appears to be the only documented effect of acrylamide in human epidemiological studies; reproductive toxicity, genotoxicity/clastogenicity, and carcinogenicity are potential human health risks on the basis of only animal studies. A better understanding of the chemistry and biology of pure acrylamide in general and its impact in a food matrix in particular can lead to the development of improved food processes to decrease the acrylamide content of the diet.

Acrylamide↗
PubMed2002

Approach toward the total synthesis of griseoviridin: formation of thioethynyl and thiovinyl ether-containing nine-membered lactones through a thioalkynylation-macrolactonization-hydrostannylation sequence.

Synthesis of the lactone core 17 of 8-epi-griseoviridin is reported. Thioethynyl derivative 11 was easily prepared via an anionic coupling reaction between acetylenic compound 9 and sulfone 10. After desilylation of 11, saponification of the resulting hydroxy ester 12 followed by a Mitsunobu macrolactonization furnished the unusual triple-bond-containing nine-membered lactone 13 in 50% yield for the last two steps (39% after recrystallization). Stannylation under Magriotis conditions led to the pure regio- and stereocontrolled vinyltin 14 (80% yield). After a Sn/I exchange, palladium-catalyzed carbonylation delivered either the ester lactone 16 in 67% yield or the propargyl amide 17 in 65% yield. Synthesis of propargyl amide 17 of the lactone core of 8-epi-griseoviridin was achieved in 11.9% overall yield from commercial L-cystin dimethyl ester (nine steps).

Anti-Bacterial Agents↗
PubMed2005

Quantum theory of atoms in molecules analysis on the conformational preferences of vinyl alcohol and related ethers.

Vinyl alcohol, methyl vinyl ether, and tert-butyl vinyl ether were studied within the framework of the quantum theory of atoms in molecules at the B3LYP/6-311++G(2d,2p) level. Local and integrated properties of the charge density indicate that the anti conformational preference of the tert-butyl derivative is not due to a differing resonance contribution with regard to the less bulky vinyl ethers but to steric effects. There is a small delocalization of charge density, either total or pi, between oxygen and the terminal vinyl carbon, which does not support the resonance picture of vinyl compounds.

Journal Article↗
PubMed2000

Synthetic studies on the trans-chlorocyclopropane dienyne side chain of callipeltoside A.

[structure] Enantiomerically enriched trans-chlorocyclopropanemethanol was obtained by lipase kinetic resolution of dichlorocyclopropanemethanol 3, followed by reduction. The sp-sp(2) bond of the trans-chlorocyclopropane dienyne side chain of callipeltoside A was constructed via a Stille coupling reaction of 1, 1-dibromo-1-alkene 7 and a vinylstannane in a highly dipolar solvent capable of promoting HBr elimination to give internal alkynes.

Animals↗
PubMed2005

Highly regioselective Diels-Alder reactions toward oroidin alkaloids: use of a tosylvinyl moiety as a nitrogen masking group with adjustable electronics.

[reaction: see text] The use of the p-toluenesulfonyl (Ts) and tosylvinyl (Tsv) groups as nitrogen masking groups imparted high regioselectivity in Diels-Alder reactions directed toward members of the oroidin-derived marine alkaloid family. The electron-withdrawing Tsv group was utilized as an electronically adjustable nitrogen-protecting group as subsequent hydrogenation provided the more electron-rich tosylethyl (Tse) group. This electronic adjustment strategy avoided a protecting group exchange and provided the required electronics for the key chlorination/ring-contraction sequence.

Alkaloids↗
PubMedDate not supplied

Synthesis of [4,5,6,8-(13)C4]guanine, a reagent for the production of internal standards of guanyl DNA adducts.

Using readily available labeled compounds, [4,5,6,8-(13)C4]guanine was synthesized in high overall yield. Intermediates as well as the final product were characterized by 1H NMR, 13C NMR, and high resolution mass spectrometry. The labeled guanine was used to generate [13C4]-labeled analogs of the guanine adducts, N2,3-ethenoguanine and 7-(2-hydroxyethyl)guanine. The application of such adducts in isotope dilution mass spectrometry was illustrated with DNA samples from rats exposed to two different mutagenic compounds, vinyl chloride and ethylene oxide.

Animals↗
PubMed1992

The anomalous hydrolytic behavior of 1-phenylvinyl phosphate.

The kinetics of hydrolysis of 1-phenylvinyl phosphate, 1, were studied over a pH range of 1 to 8.3 and over a pD range of 1 to 5.6 at 25 degrees C and mu = 0.5 M with sodium chloride. The hydrolytic behavior of 1 was found to differ, in many respects, from that of alkyl and aryl phosphomonoesters. First, the rates of hydrolysis of 1 were extremely rapid and, in the hydronium ion-catalyzed region, gave a solvent deuterium isotope effect (kH/kD) of 3.20. Also, the 1H-NMR spectrum of acetophenone formed upon complete hydrolysis of 1 in D2O (pD 1.2) revealed that only one deuterium atom was incorporated into the methyl group. Hence, the evidence was consistent with a rate-limiting and nonreversible proton transfer from the solvent to 1. In addition, using an H2 18O labeling study in conjunction with 31P-NMR analysis, the hydrolytic mechanism appeared to involve nucleophilic attack by water at both the alpha-carbon and the phosphorus atom with concurrent C-O and P-O bond fission. Second, in the pH region where the monoanionic species of 1 predominated, buffers had a pronounced catalytic effect on the hydrolysis rate; there appeared to be a normal solvent deuterium isotope effect; and the rate constant, k' o, showed a positive deviation from the established Brønsted relationship. The dissimilarities between 1 and alkyl and aryl phosphomonoesters supported the involvement of an alternate dephosphorylation pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed2005

Generation of alpha-phosphonovinyl radicals and development of a new route to highly functionalized vinylphosphonates and vinylphosphonate-incorporated carbocyclic or heterocyclic compounds via a radical trapping sequence.

The first direct generation of synthetically useful alpha-phosphonovinyl radicals was achieved by treatment of alpha-phosphonovinyl halides with a tributyltin radical. The alpha-phosphonovinyl radicals 2a-d were trapped with electron-rich olefins and an electron-deficient olefin to produce alpha-functionalized vinylphosphonates 3a-f in 16-55% yields. The alpha-phosphonovinyl radicals 7e-g containing the YCH2CH=CH2 (Y = O, CH2, S) substituent at the beta-position afforded mixtures of 5-exo and 6-endo cyclization products, 5e-g and 6e-g, in good yields. The 5-exo/6-endo product ratios increase in the following order of the beta-substituent: OCH2CH=CH2 > CH2CH2CH=CH2 > SCH2CH=CH2. The effects of the beta-substituents upon the cyclization reaction were discussed. Radical cyclization of alpha-phosphonovinyl radicals bearing functional groups such as geranyloxy, geranylthio, and (2-cyclohexen-1-yl)thio groups at the beta-position afforded 5-exo, 5-exo and 6-endo, and cis-fused-5,6-ring cyclization products incorporating an alpha,beta-unsaturated phosphonate unit within the ring, respectively, in good yields. The alpha-phosphonovinyl radical 20 underwent tandem radical cyclization-radical cyclization to produce a mixture of two isomeric bicyclo[4.3.0]nonenes including a vinylphosphonate moiety in high yield.

Alkenes↗