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At least 1,495 records · Page 83Linked to original sources
PubMed2001

Modular synthesis of pi-acceptor cyclophanes derived from 1,4,5,8-naphthalenetetracarboxylic diimide and 1,5-dinitronaphthalene.

Three neutral cyclophanes were synthesized, and their association with indole, an aromatic pi-donor, was studied. The cyclophanes were designed to contain a rigid, hydrophobic binding cavity with 1,4,5,8-naphthalenetetracarboxylic diimide or 1,5-dinitronaphthalene as the pi-acceptor. Two of the cyclophanes also contain a (S)-(valine-leucine-alanine) tripeptide unit to provide chiral hydrogen bonding interactions with guest molecules. Despite the fact that these cyclophanes contain a hydrophobic binding cavity of appropriate dimensions, their association with indole is very weak. In the case of cyclophanes derived from 1,5-dinitronaphthalene, steric interactions force the nitro groups out of the plane of the naphthalene ring, diminishing their effectiveness as pi-acceptors. A simple UV--visible titrimetric method, using N,N,N',N'-tetramethyl-1,4-phenylenediamine (TMPD) as a pi-donor, was used to rank the pi-acceptor strength of these and other aromatic units. These titrations show that 1,4,5,8-naphthalenetetracarboxylic diimide and 1,5-dinitronaphthalene derivatives are weaker pi-acceptors than viologens, which make good pi-acceptor cyclophanes. Methyl viologen is in turn a weaker pi-acceptor than anthaquinone disulfonate, suggesting that the latter may serve as a useful building block for pi-accepting cyclophane hosts.

Ethers, Cyclic↗
PubMedDate not supplied

Assessment of a modular transfection system based upon cellular localization of DNA.

Delivery of plasmid DNA for protein production in mammalian cells is not an efficient process. In this study, the theory that cellular localization of plasmid DNA increases transfection efficiency is examined with an emphasis on the understanding of the cellular association of the components of a ternary transfection complex. Mammalian cells take up transfection reagent-DNA complexes primarily from their local environment. Via formation of a ternary complex consisting of the DNA-transfection reagent complex and a heavy particle, such as silica, the efficiency of transfection is substantially increased. We have analyzed cells transfected with the ternary complexes to determine if sedimentation alone affects the percentage of cells that contain the complexes or specific components of the complex. A significant fraction of cells associate with the ternary complexes, including silica nanoparticles. The percentage of cells that associate with DNA was not significantly influenced by the use of the ternary complex. This result suggests that the silica nanoparticles are more than just a sedimentation agent, being also a secondary transfection reagent. These data also confirm that cells may contain transfection reagent-DNA complex but do not express the protein of interest. This knowledge will be used in further research to better design transfection reagents that will increase the efficiency of protein production.

Animals↗
PubMed2000

A modular approach to marine macrolide construction. 3. Enantioselective synthesis of the C1-C28 sector of spongistatin 1 (altohyrtin A).

[structure: see text] A completely stereocontrolled approach to assembly of the major C1-C28 subunit of spongistatin 1 (altohyrtin A) is described. Key steps included the control of two asymmetric aldols by means of Fujita-Nagao (chiral N-acyl-1,3-thiazolidine-2-thione auxiliary) and Mukaiyama (BF3 x OEt2-promoted enolsilane coupling) protocols in complex settings.

Animals↗
PubMed2000

A straightforward modular approach to NLO-active beta-amino vinyl nitrothiophenes

Secondary amines add very efficiently to 2-ethynyl-5-nitrothiophene to give beta-amino vinyl nitrothiophenes, a novel class of push-pull chromophores. According to first HRS measurements these highly solvochromic compounds with relatively short dipole axes display remarkably high static first hyperpolarizabilities = 29-31 x 10(-)(30) esu.

Journal Article↗
PubMed2002

Modular synthesis of amine-functionalized oxazolines.

Substituted oxazoline amines have been prepared in high yield from beta-amino alcohols and Fmoc-protected alpha-amino acids using CCl(4), PPh(3), and Hünig's base in a one-pot procedure followed by base-mediated deprotection. [reaction: see text]

Journal Article↗
PubMed2003

Modular, parallel synthesis of an illudinoid combinatorial library.

[structure: see text] A library of 49 illudinoids was prepared via a three-step synthesis using a parallel synthesizer and solid-phase extractive purification. Products could be rapidly prepared for initial biological testing against three cancer cell lines, which revealed library members that inhibit nonsmall cell lung cancer. The activities of the library members are not easily correlated with structure, meaning the empirical approach used here is essential for such nonintuitive discoveries.

Agaricales↗
PubMed2004

Modular synthesis of pantetheine and phosphopantetheine.

[structure: see text] D-Pantetheine and D-phosphopantetheine, precursors to coenzyme A, have been synthesized though a linear sequence from three modules (M1-M3) in 9 and 10 steps, respectively. These routes provide access to analogues of coenzyme A containing modified cystamines, beta-alanines, and pantoic acid residues. All three modules were joined using conventional methods of peptide synthesis. The chiral component, M3, was derived from D-pantolactone.

Molecular Structure↗
PubMed2005

A modular approach to polyketide building blocks: cycloadditions of nitrile oxides and homoallylic alcohols.

A general approach to the diastereoselective synthesis of Delta(2)-isoxazolines via magnesium-mediated, hydroxyl-directed diastereoselective nitrile oxide cycloadditions of homoallylic alcohols and monoprotected homoallylic diols is disclosed. A broad spectrum of aliphatic and aromatic nitrile oxides and a variety of homoallylic alcohols participate in the cycloaddition, thus expanding the scope of polyketide building blocks that can be accessed using this strategy.

Alcohols↗
PubMed2005

Proline-based N-oxides as readily available and modular chiral catalysts. Enantioselective reactions of allyltrichlorosilane with aldehydes.

[reaction: see text]. A proline-based N-oxide is identified that serves as an effective catalyst for the reaction of allyltrichlorosilane with aryl and alpha,beta-unsaturated aldehydes at room temperature to afford the desired homoallylic alcohols in up to 92% ee. The chiral catalyst can be easily prepared from optically pure proline in three simple steps and 60% overall yield.

Alcohols↗
PubMed2005

Pd-catalyzed tandem C-N/C-C coupling of gem-dihalovinyl systems: a modular synthesis of 2-substituted indoles.

2-substituted indoles were synthesized via a Pd-catalyzed tandem C-N/Suzuki-Miyaura coupling from readily prepared ortho-gem-dihalovinylanilines. Optimal conditions used a Pd(OAc)(2)/S-Phos catalyst in the presence of K(3)PO(4).H(2)O and an organoboron reagent, which included boronic acids, esters, alkyl 9-BBN derivatives, and trialkylboranes. Yields of the desired indoles were good to excellent using low catalyst loadings (typically 1 mol %). [reaction: see text]

Journal Article↗
PubMed2005

Structurally simple, modular amino alcohols for the recognition of carboxylic acids. Application to the development of a new chiral solvating agent.

[structure: see text] Two flexible receptors for carboxylic acids, based on 1-amino-3-fluoro-2-alcohol functional arrays and built on aminomethylpyridine platforms, are described. The C(2)-symmetric one [from 2,6-bis(aminomethyl)pyridine] has been shown to be an efficient CSA due to its ability to form geometrically different diastereomeric complexes enabling the discrimination between the enantiomers of a series of carboxylic acid in the (1)H NMR spectra.

Journal Article↗
PubMed2006

Synthesis of bisbenzannulated spiroketals-model studies for a modular approach to rubromycins.

[reaction: see text] A highly flexible synthesis of bisbenzannulated spiroketals is described with additions of lithiated methoxyallene to aryl aldehydes and Heck reactions as key steps. Subsequent hydrogenations and ketalizations afforded the desired spiroketals in good yields and with predominating trans-configuration. With model compound 30, already bearing the fully substituted naphthyl core of rubromycins, the ketalization proceeded efficiently providing the expected product 31 and the isopropoxy compound 32. Both products are advanced model compounds of heliquinomycin.

Benzoquinones↗
PubMed1999

Modular nucleic acid surrogates. Solid phase synthesis of alpha-helical peptide nucleic acids (alpha PNAs).

[formula: see text] The synthesis and characterization of prototype alpha-helical peptide nucleic acid (alpha PNA) modules 1-3 as well as disulfide dimers 4 and 5 are reported. These molecules combine an alpha-helical peptidyl scaffold with well-defined nucleobase molecular recognition patterns and could serve as a basis for novel antisense and/or antigene agents. Structure assignments for these alpha PNAs were supported by MALDI-TOF mass spectrometry, and the alpha-helical nature of 4 in water was confirmed by circular dichroism (CD) spectroscopy.

Circular Dichroism↗
PubMed2006

Modular stop and go extraction tips with stacked disks for parallel and multidimensional Peptide fractionation in proteomics.

Proteome complexity necessitates protein or peptide separation prior to analysis. We previously described a pipet-tip based peptide micropurification system named StageTips (STop and Go Extraction Tips), which consists of a very small disk of membrane-embedded separation material. Here, we extend this approach in several dimensions by stacking disks containing reversed phase (C(18)) and strong cation exchange (SCX) materials. Multidimensional fractionation as well as desalting, filtration, and concentration prior to mass spectrometry in single or tandem columns is described. C(18)-SCX-C(18) stacked disks significantly improved protein identification by LC-MS/MS for an E. coli protein digest and by MALDI-MS for a 12 standard protein digest. Sequential fractionation based on C(18)- followed by SCX material was also developed. This multidimensional fractionation approach was expanded to parallel sample preparation by incorporating C(18)-SCX-StageTips into a 96-well plate (StagePlate). Fractions were collected into other C(18)-StagePlates and desalted and eluted in parallel to sample well plates or MALDI targets. This approach is suitable for high throughput protein identification for moderately complex, low abundance samples using automated nanoelectrospray-MS/MS or MALDI-MS.

Bacterial Proteins↗