bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two Contrasting Asymmetric Approaches to Muscarine Based on 5‐endo‐trig Cyclisations
Authors: Knight David W. , Shaw Duncan E. , Staples Emily R. 
Published: April 2004

Abstract5‐endo‐trig cyclisation of the (Z)‐hydroxyalkenoate 17 using iodine as the electrophile gave a good yield of the β‐hydroxytetrahydrofuran 18, probably via the corresponding iodohydrin. A variety of one‐carbon degradation methods were then used to generate precursors to (−)‐muscarine (25d). An alternative strategy featured control of a 5‐endo‐trig iodocyclisation by an allylic hydroxyl group, which can be used for the highly stereocontrolled synthesis of hydroxy‐iodotetrahydrofurans 28. Application of this strategy to the (Z)‐alkenediol derivative 38 led to an excellent yield of the tetrahydrofuran 39 when iodine monobromide was used as the electrophile. Two simple and efficient transformations then gave the (+)‐muscarine precursor 40b. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Amphiphilic [5:1]‐ and [3:3]‐Hexakisadducts of C60
Authors: Braun Martin , Hartnagel Uwe , Ravanelli Elena , Schade Boris , Böttcher Christoph , Vostrowsky Otto , Hirsch Andreas 
Published: April 2004

AbstractWe have synthesized and characterized a variety of new amphiphilic hexakisadducts of C60 involving mixed octahedral [5:1]‐ and [3:3]‐addition patterns. The [5:1]‐adducts 3 and 13 contain five pairs of didodecyl or diethyl malonates as non‐polar addends and, as their polar part, an extended bis(malonate) involving C14 and ethylene glycol chains and two biotin termini. For the first time, amphiphilic [3:3]‐hexakisadducts have been prepared using the e,e,e‐trisadduct 18, which contains a cyclo‐[3]‐octyl malonate addend, as the precursor. As polar groups, we used malonates featuring carboxy, amino, or peptide termini. The charge on the termini, which can range from zero up to sixfold positive or sixfold negative, can be built up by protonation or deprotonation. All the amphiphilic [3:3]‐hexakisadducts are very soluble in water in their completely charged forms. Initial investigations on the aggregation properties of the amphiphilic [3:3]‐hexakisadducts, conducted using transmission electron microscopy (TEM) and pulse‐gradient spin echo (PGSE) NMR spectroscopy, reveal the pH‐dependent formation of aggregates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Competition between Non‐Classical Single and Double Epimerizations in Cyclitol Chemistry
Authors: Miethchen Ralf , Neitzel Katharina , Weise Kathrin , Michalik Manfred , Reinke Helmut , Faltin Franziska 
Published: April 2004

AbstractTwo competitive regio‐ and stereoselective epimerization reactions were investigated in four cyclitols characterized by four contiguous OH groups with a cis‐trans‐trans sequence and by varied substituents (OMe, OBz, F, H) adjacent to this tetrol unit. The starting materials were synthesized from L‐quebrachitol (compounds 5−7) and myo‐inositol (compound 8). Their acetalization with the chloral/DCC reagent system gave cyclic acetals with one epimerized chiral ring atom and also with two epimerized chiral centres. The single epimerization takes place exclusively at the middle C‐atom of the cis‐trans triol unit in the tetrol sequence (products 15, 17, 19/20 and 24−27), whereas the double epimerization occurs at both of the "centrally located" C‐atoms in the cis‐trans‐trans tetrol unit (products 16, 18, 21 and 28). The product ratios of singly to doubly inverted compounds change as follows: the lower the electron‐withdrawing effect of the substituents adjacent to the tetrol unit, the higher the percentage of the corresponding doubly inverted product. However, the singly inverted products remain the major products in all cases. X‐ray analyses are given for the starting material 1‐fluoro‐2‐O‐(methyl)cyclohexane‐2,3,4,5,6‐pentol (5) and for the products 1‐O‐cyclohexylcarbamoyl‐2,3‐O‐(2,2,2‐trichloroethylidene)5‐O‐(methyl)cyclohexane‐1,2,3,4,5‐pentol (17), 3‐O‐acetyl‐1‐O‐benzoyl‐6‐O‐cyclohexylcarbamoyl‐2‐O‐methyl‐4,5‐O‐(2,2,2‐trichloroethylidene)‐muco‐inositol (22) and 2,3‐di‐O‐ethylidene)‐(+/‐)‐chiro‐inositol (24). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
9‐Fluoro‐18‐hydroxy‐[3.3]metacyclophane: Synthesis and Estimation of a C−F···H−O Hydrogen Bond
Authors: Takemura Hiroyuki , Kotoku Masayuki , Yasutake Mikio , Shinmyozu Teruo 
Published: April 2004

AbstractA cyclophane composed of fluorobenzene and phenol units was synthesized in order to observe the C−F···H−O hydrogen bond. In the crystal structure, 20% of the molecule clearly shows the intramolecular hydrogen bond and the other 80% is free from hydrogen bonding. On the other hand, a distinct low‐field shift of the phenolic OH proton was observed in the 1H NMR spectrum compared to that of the F‐free analog. Furthermore, O−H···F through‐space coupling was observed. From the results of the crystallographic analysis, IR, and NMR spectra, the C−F···H−O hydrogen bond energy of this system was estimated to be 0.84−3.7 kJ·mol−1. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Ketonic Decarboxylation Catalysed by Weak Bases and Its Application to an Optically Pure Substrate
Authors: Renz Michael , Corma Avelino 
Published: April 2004

AbstractKetonic decarboxylation is a very old reaction that transforms two carboxylic acids into a ketone or a dicarboxylic acid into a cyclic ketone, in particular adipic acid into cyclopentanone. Herein it is reported that catalytic amounts of weak bases such as sodium carbonate can carry out this reaction selectively. This is in accordance with a mechanism involving decarboxylation and nucleophilic attack at a second carboxyl group. The reaction can be employed in asymmetric syntheses since the stereogenic centres in the β‐positions retain their stereochemistry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Peptide Bond Formation Using Polymer‐Bound BOP
Authors: Filip Sorin V. , Lejeune Valérie , Vors Jean‐Pierre , Martinez Jean , Cavelier Florine 
Published: April 2004

AbstractA new polymer‐supported BOP (P‐BOP) has been prepared starting from the commercially available polystyrene‐bound 1‐hydroxybenzotriazole (P‐HOBt) and successfully used as a solid‐supported reagent for peptide‐coupling reactions. Compared to BOP, less epimerization was observed. P‐BOP is also a suitable activating reagent for difficult peptide coupling reactions involving α,α‐dialkyl amino acids. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis and Stereochemistry of the Four Himachalene‐Type Sesquiterpenes Isolated from the Flea Beetle (Aphthona flava) as Pheromone Candidates
Authors: Muto Shin‐etsu , Bando Masahiko , Mori Kenji 
Published: April 2004

AbstractBoth the (1S,2R) and (1R,2S) isomers of 2,6,6‐trimethylbicyclo[5.4.0]undec‐7‐en‐9‐one (1) were synthesized by starting from (S)‐ and (R)‐citronellal (5), respectively. The stereochemistry of (1R,2S)‐(−)‐1 was established by an X‐ray analysis; it exhibits a CD spectrum similar to that of cholest‐4‐en‐3‐one, in agreement with its absolute configuration. The ketones (1S,2R)‐ and (1R,2S)‐1 were converted into the enantiomers of three other himachalene hydrocarbons, 2,2,6‐trimethyl‐10‐methylenebicyclo[5.4.0]undec‐1(11)‐ene (2), 1,1,5,8‐tetramethyl‐1,2,3,4,5,6,5a‐heptahydrobenzo[1,2‐a][7]annulene (3), and 1,1,5,8‐tetramethyl‐1,2,3,4,5‐pentahydrobenzo[a][7]annulene (ar‐himachalene, 4). The stereochemistry of these himachalene‐type sesquiterpenes isolated from flea beetles such as Aphthona flava and Phyllotreta cruciferae as their male‐pheromone components was revised to (1S,2R)‐1, (6R,7S)‐2, (5R,5aS)‐3, and (R)‐4. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Cycloaddition of Benzonitrile Oxide to Acetonitrile, Propyne and Propene − A Comparative Theoretical Study of the Reaction Mechanism and Regioselectivity
Authors: Vullo Vincenzo , Danks Timothy N. , Wagner Gabriele 
Published: April 2004

AbstractQuantum chemical calculations (MP2/6‐31G* and B3LYP/6‐31G*) were used to compare the reactivity, regioselectivity and orbital involvement of the reaction of benzonitrile oxide with the dipolarophiles acetonitrile, propyne and propene. All reactions are thermodynamically favoured. The product stability decreases in an order propyne > acetonitrile > propene, and reflects the degree of aromatic stabilisation of the product. The activation barriers depend strongly on the computational method used and decrease in the expected order of increasing reactivity (acetonitrile > propyne > propene) in the MP2 calculations, but are similar to each other when B3LYP is applied. The regiochemistry is correctly predicted for all reactions and the experimentally observed regioisomer is both thermodynamically and kinetically favoured. The transition state geometries indicate that, in some of the reactions, the benzonitrile oxide does not interact through its frontier orbitals, as traditionally assumed. Instead, the FMO±2 are involved in the reaction, indicating that the classical FMO concept should be applied with care as it might lead to wrong conclusions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Cover Picture: Enantioselective Routes to Sulfoxides Based Upon the Use of Carbanionic Leaving Groups (Eur. J. Org. Chem. 9/2004)
Authors: Capozzi Maria Annunziata M. , Cardellicchio Cosimo , Naso Francesco 
Published: April 2004

AbstractThe cover picture shows a typical street with “trulli”, characteristic Apulian houses with a conical roof, which are rather common in Alberobello, a town located near Bari (Italy), where part of the research reported in the Microreview by F. Naso et al. on p. 1855 ff. was performed. The view acts as a background for the scheme demonstrating the use of carbanionic leaving groups in enantioselective routes to sulfoxides.
Application of cycling gradient capillary electrophoresis to detection of APC, K‐ras, and DCC point mutations in patients with sporadic colorectal tumors
Authors: Minarik Marek , Minarikova Lucie , Hrabikova Michala , Minarikova Petra , Hrabal Petr , Zavoral Miroslav 
Published: April 2004

AbstractA previously introduced technique of cycling gradient capillary electrophoresis (CGCE) was applied to monitoring of molecular changes during adenoma‐carcinoma transition in progression of sporadic colorectal cancer. The purpose of this work was optimization of separation parameters for selected mutation regions in tumor suppressor genes involved in the early stages of colorectal carcinogenesis, followed by scanning for these mutations in clinical tissue samples from patients with adenomatous polyps and early carcinomas. A total of 47 colorectal tumors in various stages of progression were examined. Main emphasis was given to evaluation of mutation detection sensitivity and specificity required for effective early disease detection. A total of 7 different somatic mutations was identified among 32 K‐ras mutant samples, 1 inherited mutation and 5 somatic mutations were identified among 15 adenomatous polyposis coli (APC) mutated samples. None of the two previously reported “deleted in colorectal carcinomas” (DCC) mutations was found in any of the clinical samples. In addition to simple optimization of running conditions, CGCE has demonstrated sensitivity and selectivity allowing detecting small mutant fractions as well as combination of multiple mutants within a single target sequence.
Fast visible dye staining of proteins in one‐ and two‐dimensional sodium dodecyl sulfate‐polyacrylamide gels compatible with matrix assisted laser desorption/ionization‐mass spectrometry
Authors: Choi Jung‐Kap , Chae Ho‐Zoon , Hwang Sun‐Young , Choi Hoon‐In , Jin Li‐Tai , Yoo Gyurng‐Soo 
Published: April 2004

AbstractA fast and matrix assisted laser desorption/ionization‐mass spectrometry (MALDI‐MS) compatible protein staining method in one‐ and two‐dimensional sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (1‐ and 2‐D SDS‐PAGE) is described. It is based on the counterion dye staining method that employs oppositely charged two dyes, zincon (ZC) and ethyl violet (EV) to form an ion‐pair complex. The protocol, including fixing, staining and quick washing steps, can be completed in 1–1.5 h depending upon gel thickness. It has a sensitivity of 4–8 ng, comparable to that of colloidal Coomassie Brilliant Blue G (CBBG) staining with phosphoric acid in the staining solution. The counterion dye stain does not induce protein modifications that complicate interpretation of peptide mapping data from MS. Considering the speed, sensitivity and compatibility with MS, the counterion dye stain may be more practical than any other dye‐based protein stains for routine proteomic researches.
Application of in‐gel protease assay in a biological sample: Characterization and identification of urokinase‐type plasminogen activator (uPA) in secreted proteins from a prostate cancer cell line PC‐3
Authors: Zhao Zhenjun , Raftery Mark J. , Niu Xiao Mei , Daja Merilla M. , Russell Pamela J. 
Published: April 2004

AbstractA considerable problem in proteomics is to separate and identify functional proteins that participate in specific biological processes. To expedite the analysis of active proteases, we have developed a substrate‐specific, sensitive in‐gel trypsin activity assay after two‐dimensional (2‐D) separation in a sodium dodecyl sulphate (SDS)‐polyacrylamide gel [22]. Using this method, we detected and characterized Arg‐specific protease activity in the secreted protein sample of a prostate cancer cell line, PC‐3, in 1‐D and 2‐D gels. Mass spectrometry (MS) identified the protease as urokinase‐type plasminogen activator (uPA). Western blotting using anti‐uPA antibody and protease inhibition tests confirmed the identification. Since no antibody was involved in the procedure, the result clearly demonstrates the feasibility of this method for identifying novel proteases in biological samples.
Optimum sample medium for single‐nucleotide polymorphism and mutation detection by capillary electrophoresis
Authors: Kozlowski Piotr , Krzyzosiak Wlodzimierz J. 
Published: April 2004

AbstractCapillary electrophoresis (CE) is a versatile analytical platform widely used for nucleic acids analysis. Its applications in research and diagnostics include scanning and screening for mutations and polymorphisms by such reliable methods as single‐strand conformation polymorphism (SSCP), heteroduplex analysis (HA), and combined SSCP/HA. This study, aimed at the further development of these methods, is focused on detailed sample‐media characteristics. Factors affecting single‐strand conformer stability and DNA intake efficiency were analyzed. The sample media optimal for efficient mutation or SNP detection were determined, and complex SSCP‐CE patterns arising from unpurified PCR products were explained. It turns out, that the nondenaturing aqueous media assure both efficient DNA intake, and single‐strand conformers stability required for the SSCP and combined SSCP/HA. The results of this study are applicable to all these areas of biomedical research, in which capillary electrophoresis is used for the characterization of nucleic acids.
Determination of dissociation constants by competitive binding in partial filling capillary electrophoresis
Authors: Nilsson Mikael , Johansson Gunnar , Isaksson Roland 
Published: April 2004

AbstractThe determination of dissociation constands (Kd) by competitive ligand binding in partial filling capillary electrophoresis is demonstrated. Two different strategies were applied, one of which only uses a single reporter ligand and a more elaborated one which suppresses systemic disturbances by using a racemic mixture as reporter. The dissociation constants obtained by both alternatives were virtually identical and in good agreement with those previously reported.
An efficient protocol for the identification of protein phosphorylation in a seedless plant, sensitive enough to detect members of signalling cascades
Authors: Heintz Dimitri , Wurtz Virginie , High Anthony A. , Van Dorsselaer Alain , Reski Ralf , Sarnighausen Eric 
Published: April 2004

AbstractWe describe a reproducible protocol to explore for the first time the phosphoproteome of a seedless plant, the moss Physcomitrella patens. Following tryptic digestion of a total protein extract, phosphorylated peptides were isolated using the combination of C18 reverse‐phase chromatography (RP‐C18), immobilized Fe3+ metal affinity chromatography (IMAC), capillary zone electrophoresis (CZE), liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) and matrix assisted laser desorption/ionization‐time of flight‐mass spectrometry (MALDI‐TOF‐MS) analysis. The total protein extracts were first prepared as usually made for plant two‐dimensional gel electrophoresis, the tryptic digest was desalted and concentrated by reverse phase chromatography, and from this mixture the phosphorylated peptides were captured by IMAC. Subsequently, the complex phosphopeptide mixture was separated into ten fractions by RP‐C18‐HPLC and each analyzed by CZE. This permitted the detection of 253 distinct phosphopeptides. These were identified by nano‐LC‐MS/MS and MALDI‐TOF‐MS analysis in conjunction with alkaline phosphatase treatment to remove covalently bound phosphate to specifically identify the phosphopeptides. Among others, several kinases and a transcription factor were identified. This protocol will be taken as a basis to unravel early events in plant signal transduction known to occur via rapid phosphorylation/dephosphorylation of proteins.
Moving boundaries in sodium dodecyl sulfate‐polyacrylamide gel electrophoresis
Authors: Buzás Zsuzsanna , Chrambach Andreas 
Published: April 2004

AbstractIn sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE), moving boundaries I–IV (Table 1) form. They migrate isotachophoretically at displacement rates that increase in the order of I to II to III. Moving boundaries IV and V comprising Pyronin‐SDS as a leading constituent are retarded at high gel concentrations in comparison with the isotachophoretically migrating species. Since analytes depending on their net mobilities stack within any of those moving boundaries, previous Rf values and Ferguson plots may have to be revised.
Prevention of artifactual protein oxidation generated during sodium dodecyl sulfate‐gel electrophoresis
Authors: Sun Gang , Anderson Vernon E. 
Published: April 2004

AbstractPrevention of artifactual protein oxidation occurring during sodium dodecyl sulfate (SDS) acrylamide gel electrophoresis is critical for identifying physiological protein oxidation implicated in human diseases due to the routine use of gel electrophoresis to separate the multiple proteins in proteomic studies. To develop a methodology that completely prevents artifactual protein oxidation in SDS acrylamide gel electrophoresis, cytochrome c was electrophoresed on polyacrylamide gels and subjected to trypsin in‐gel digestion followed by tryptic peptide analysis by mass spectrometry. It was found that degassing the acrylamide solution to remove molecular oxygen prior to gel polymerization is a crucial process to protect the electrophoresed protein from reactive oxygen species generated during electrophoresis. However, significant artifactual protein oxidation remains that can only be eliminated entirely, if proteins are electrophoresed on an SDS gel photopolymerized with flavin as the photoinitiator and thioglycolate included in the cathode buffer as a reactive oxygen species scavenger. Using this combination of methodologies, cytochrome c isolated from adult rat heart mitochondria was purified and digested followed by mass spectrometric analysis, demonstrating the requisite high resolution of the polyacrylamide gel and the entire elimination of artifactual oxidation.
Electrophoretically mediated microanalysis with partial filling technique and indirect or direct detection as a tool for inhibition studies of enzymatic reaction
Authors: Telnarová Magdaléna , Vytisková Soňa , Monincová Marta , Glatz Zdeněk 
Published: April 2004

AbstractThe inhibition of the model enzyme, haloalkane dehalogenase from Sphingomonas paucimobilis, was investigated by a combination of electrophoretically mediated microanalysis with a partial filling technique, followed by indirect or direct detection. In this setup, part of the capillary is filled with a buffer suitable for the enzymatic reaction (20 mM glycine buffer, pH 8.6) whereas the rest of the capillary is filled with the background electrolyte optimal for separation of substrates and products. Two different background electrolytes and corresponding detection approaches were used to show the versatility of the developed method. The inhibition effect of 1,2‐dichloroethane on the dehalogenation of brominated substrate 1‐bromobutane was studied by means of 10 mM chromate − 0.1 mM cetyltrimethylammonium bromide (pH 9.2) in combination with indirect detection or 20 mM β‐alanine – hydrochloric acid (pH 3.5) in combination with direct detection. The method was used to estimate the inhibition constant KI (0.44 mM by indirect detection and 0.63 mM by of direct detection) and to determine the inhibition type. Compared to spectrophotometric and other discontinuous assays, the method is rapid, can be automated, and requires only small amount of reagents that is especially important in the case of enzymes and inhibitors.
Proteomic profiling of human hippocampus
Authors: Yang Jae‐Won , Czech Thomas , Lubec Gert 
Published: April 2004

AbstractThe hippocampus is an important brain region playing a central role in short‐term memory formation. Information on protein expression in human hippocampus is limited and we therefore decided to generate a protein map of this pivotal brain structure thus providing protein building blocks and an analytical tool. Two‐dimensional electrophoresis with in‐gel digestion of protein spots followed by mass spectrometrical identification coupled to the Mascot search program was applied. Matrix‐assisted laser desorption/ionization‐time of flight (MALDI‐TOF) or in special cases MALDI‐TOF/TOF was used in order to warrant unambiguous identification. 266 protein spots representing 165 different proteins and 101 probable isoforms or post‐translational modifications were identified. The identified proteins were categorized into several protein groups as metabolic, cytoskeleton, antioxidant, chaperone, signaling, transcriptional, proteolytic, synaptosomal and neuronal, hypothetical and miscellaneous structures. This human hippocampus protein map provides an analytical tool for hydrophilic and even relatively small‐molecular‐weight proteins and contributes to the knowledge on protein building blocks thus forming the basis for protein‐chemical work in this brain area in health and disease.
Impulsive Dirac‐delta forces in the rocking motion
Authors: Prieto F. , Lourenço P. B. , Oliveira C. S. 
Published: April 2004

AbstractIn this work the classical theory of one block rocking motion is revisited. A Dirac‐delta type interaction as impact mechanism is found to be an alternative for the traditional model. Numerical computations with this new formulation have shown that the agreement with the classical theory is excellent for the case of slender blocks and small displacements. Good agreement with experimental data has also been found for the case of arbitrary angles and slenderness.The approach presented in this paper opens new lines for further theoretical developments and computational applications. Copyright © 2004 John Wiley & Sons, Ltd.