bluuebunny/crossref_metadata_2025_split huggingface dataset:
Template Effects of Metal Cations for Controlling the Regioisomer Distribution on the Photodimerization of N,N′‐Linked Bis(anthracenecarboxamides)
Authors: Hiraga Hisafumi , Morozumi Tatsuya , Nakamura Hiroshi 
Published: November 2004

AbstractTwo bis(fluorophore) compounds linked by an oxyethylene chain, N,N′‐(4,7,10‐trioxatridecane‐1,13‐diyl)bis(1‐anthracenecarboxamide) (1) and N,N′‐(4,7,10‐trioxatridecane‐1,13‐diyl)bis(2‐anthracenecarboxamide) (2), were synthesized, and the intramolecular photodimerization of the anthracene units was carried out in acetonitrile solution. The photoproduct ratios of the regioisomers derived from 1 and 2 were quantified in the absence and presence of metal cations. Upon photo‐irradiation of 1, three intramolecular photodimers, trans head‐to‐head dimer D1, cis head‐to‐head D2 and cis head‐to‐tail D3, were formed. In the photodimerization of 1, the presence of Ba2+ enhanced the formation of D1, whereas Mg2+ suppressed it. These isomer distributions strongly depended on the structure of the complex induced by the metal cations in the ground state. On the other hand, upon photo‐irradiation of 2, only two photodimers, cis head‐to‐tail dimer D5 and cis head‐to‐head D6, were formed in both the absence and presence of metal cations, and their ratio changed only slightly suggesting that no conformational changes were induced by the complexation with metal cations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Mutual Influence of (Dimethylhydrazono)methyl Groups and α‐Hydroxy Ketone Moieties in Hetaryl Analogues of Unsymmetric Benzoins
Authors: Ivonin Sergey P. , Lapandin Andrey V. , Anishchenko Andrey A. , Shtamburg Vasilii G. 
Published: November 2004

AbstractReactions between phenylglyoxal hydrate and the N,N‐dimethylhydrazones of furfural and pyrrole‐2‐carbaldehyde run regioselectively at the 5‐position of the heterocycle. The resulting hetaryl analogues of α‐benzoins quantitatively isomerize to β‐compounds, the (dimethylhydrazono)methyl group activating the hetaryl residue and thus affording faster isomerization than in their unfunctionalized counterparts. The (dimethylhydrazono)methyl group is easily convertible into the aldehyde or nitrile group and can also be involved in rehydrazonation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of Substituted Azepino[3,4‐b]indole‐1,5‐diones
Authors: Perron Julien , Joseph Benoît , Mérour Jean‐Yves 
Published: November 2004

AbstractCyclic β‐amino esters 4, obtained from lactams, were condensed with indole‐2‐carbonyl chloride to afford the corresponding amides. Similarly, unusual conditions led to cyclisation at the 3‐position of the indole moiety in the presence of pTSA and ethylene glycol to afford previously unknown pentacyclic derivatives 12 and 15. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Simple Synthetic Transformations of Highly Enantio‐Enriched 4‐Alkyl‐2,5,7‐cyclooctatrienols into Functionalized Bicyclo[4.2.0]octa‐2,4‐dienes and 2,6‐Cyclooctadienones
Authors: Pineschi Mauro , Del Moro Federica , Crotti Paolo , Macchia Franco 
Published: November 2004

Abstract4‐Alkyl‐2,5,7‐cyclooctatrienols with high enantiomeric purities (93−96% ee), obtained by an improved copper‐phosphoramidite‐catalyzed addition of dialkylzinc reagents to cyclooctatetraene monoepoxide, have been subjected to simple and practical manipulations. Simple esterification reactions are able to deliver new functionalized isomeric 8‐alkyl‐7‐acyloxybicyclo[4.2.0]octa‐2,4‐dienes through a domino sequence of rearrangement reactions, in good yields. Moreover, new 4‐alkyl‐substituted‐2,6‐cyclooctadienones with high optical purity can be efficiently obtained from gram‐scale reactions by simple thermal treatment. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Solvent‐Dependent Conformational Behaviour of Model Tetrapeptides Containing a Bicyclic Proline Mimetic
Authors: Trabocchi Andrea , Potenza Donatella , Guarna Antonio 
Published: November 2004

AbstractTwo model tetrapeptides containing bicyclic analogues of either D‐ or L‐proline were synthesised and their conformational properties were studied by NMR in different solvent systems and by molecular modelling techniques. Compound 1, with the bicyclic D‐proline mimetic in the i+1 position, generated a unique trans isomer, and the peptide showed a well organised structure, in accordance with the tendency of D‐proline to act as a good turn inducer with respect to its enantiomer. Peptide 2 displayed structures equilibrating from type I,II to type VI β‐turns, thus confirming the hypothesised relationship between the chirality of BGS/Bgs and proline enantiomers on nucleating compact turns. Moreover, such behaviour suggested a tool for peptidomimetic design of reverse turn peptides containing BGS/Bgs bicyclic proline mimetics, as the choice of chirality might influence the generation either of compact γ‐ and β‐turns or of flexible equilibrating reverse turn structures. The effect of solvent on conformational behaviour was also studied. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of Novel Functionalized Polymers for the Diastereoselective Protonation of Chiral Enolates
Authors: Mackenstedt Marc , Krause Norbert 
Published: November 2004

AbstractThe polymeric, chelating proton donors 7 and 8 were synthesized by radical polymerization of the monomers 5/6 with different amounts of styrene. Protonation of chiral lithium enolates derived from silyl enol ethers 9 gave cis/trans ratios of up to 94:6 (10a) and 99:1 (10b), respectively. The polymers can be recycled and used repeatedly without appreciable loss of selectivity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of Pyrazolyl‐2‐pyrazolines by Treatment of 3‐(3‐Aryl‐3‐oxopropenyl)chromen‐4‐ones with Hydrazine and Their Oxidation to Bis(pyrazoles)
Authors: Lévai Albert , Silva Artur M. S. , Pinto Diana C. G. A. , Cavaleiro José A. S. , Alkorta Ibon , Elguero José , Jekö József 
Published: November 2004

AbstractThe synthesis of several 1‐acetyl‐3‐aryl‐5‐[3‐(2‐hydroxyphenyl)pyrazol‐4‐yl]‐2‐pyrazolines 3a−3h has been accomplished by treatment of the 3‐(3‐aryl‐3‐oxopropenyl)chromen‐4‐ones 1a−h with hydrazine hydrate in hot acetic acid. The 1‐acetyl‐3‐aryl‐5‐(3‐chromonyl)‐2‐pyrazolines 2a−2f were also obtained as by‐products. Oxidation of the 1‐acetyl‐4‐pyrazolyl‐2‐pyrazolines 3a−3f with DDQ gave the 3(5)‐aryl‐5(3)‐[3‐(2‐hydroxyphenyl)pyrazol‐4‐yl]pyrazoles 5a−5f. The oxidation of the 2‐pyrazoline rings was accompanied by N‐deacylation. The reaction mechanisms of both transformations are discussed, the first one being supported by experimental results. The structures of all new derivatives were established by NMR and the evidence of prototropic tautomerism is carefully discussed. Theoretical calculations of energies and of the 1H and 13C NMR chemical shifts of the possible tautomeric forms of 5(3)‐[3‐(2‐hydroxyphenyl)pyrazol‐4‐yl]‐3(5)‐(4‐methoxyphenyl)pyrazole (5c), by B3LYP and GIAO, showed that compounds of this type probably exist as mixtures of two tautomers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Lanthanide(III) Nitrobenzenesulfonates as New Nitration Catalysts: The Role of the Metal and of the Counterion in the Catalytic Efficiency
Authors: Parac‐Vogt Tatjana N. , Pachini Sophia , Nockemann Peter , Van Hecke Kristof , Van Meervelt Luc , Binnemans Koen 
Published: November 2004

AbstractLanthanide(III) complexes of p‐nitrobenzenesulfonic acid, Ln(p‐NBSA)3, m‐nitrobenzenesulfonic acid, Ln(m‐NBSA)3, and 2,4‐nitrobenzenesulfonic acid, Ln(2,4‐NBSA)3, were prepared, characterized and examined as catalyst for the nitration of benzene, toluene, xylenes, naphthalene, bromobenzene and chlorobenzene. The initial screening of the catalysts showed that lanthanum(III) complexes were more effective than the corresponding ytterbium(III) complexes, and that catalysts containing the bulky 2,4‐NBSA ligand were less effective than the catalyst containing p‐NBSA (nosylate) or m‐NBSA ligands. Examination of a series of Ln(p‐NBSA)3 and Ln(m‐NBSA)3 catalysts revealed that there is a clear correlation between the ionic radii of the lanthanide(III) ions and the yields of nitration, with the lighter lanthanides being more effective. The X‐ray single crystal structure of Yb(m‐NBSA)3·6H2O shows that two m‐NBSA ligands are directly bound to the metal centre while the third ligand is not located in the first coordination sphere, but it is hydrogen bonded to one of the water molecules which is coordinated to ytterbium(III). NMR studies suggest that this structure is preserved under the conditions used in the nitration reaction. The structure of Yb(m‐NBSA)3 is markedly different from the structure of the well‐known ytterbium(III) triflate catalyst. The coordination of the nitrobenzenesulfonate counterion to the lanthanide(III) ion suggests that steric effects might play an important role in determining the efficiency of these novel nitration catalysts. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthetic Circularized Analogues of Bovine Pancreatic Trypsin Inhibitor
Authors: Tulla‐Puche Judit , Getun Irina V. , Alsina Jordi , Albericio Fernando , Barany George 
Published: November 2004

AbstractTwo cyclic analogues of the protein bovine pancreatic trypsin inhibitor (BPTI), c‐[R]Smc and c‐Cys5[R]Abu, have been synthesized. For the first target, a semisynthetic approach featured a cyclization that took advantage of the constraint imposed by the three disulfides of the native protein. For the second target, an entirely unstructured 58‐residue thiolester, prepared by total synthesis with mild Fmoc chemistry and a side‐chain anchoring strategy, was cyclized by native chemical ligation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Inter‐ and Intramolecular [2+2]‐Photocycloaddition of Tetronates − Stereoselectivity, Mechanism, Scope and Synthetic Applications
Authors: Kemmler Michael , Herdtweck Eberhardt , Bach Thorsten 
Published: November 2004

Abstract[2+2]‐photocycloaddition reactions of various tetronates (3−8, 12, 16, 20, 37) have been examined. The tetronates were prepared from the corresponding tetronic acid by O‐alkylation with an alkyl bromide or with an alcohol (Mitsunobu protocol). If the photocycloaddition reaction (λ = 254 nm, solvent: diethyl ether or tert‐butyl alcohol) was carried out in an intramolecular fashion the tri‐ and tetracyclic products 21−23, 27−36 were obtained in good yields (52−75%) and with excellent simple diastereoselectivity. The reaction tolerates a high degree of substitution at both the tetronate and at the alkene double bond. High facial diastereoselectivities were observed if stereogenic centers were present in the alkene tether (e.g. 7a → 33) or if the alkenyl substituent was attached to the stereogenic C5 carbon atom of the tetronate irradiation precursor (e.g. 20 → 32). The reaction was also conducted in an intermolecular fashion. The methoxyethoxymethoxy (MEM) protecting group was suitable to protect the free tetronate hydroxy group. The photocycloaddition of tetronate 8 to cyclopentene was highly selective delivering the tricyclic products 39 in an 8:1 exo/endo ratio (59% yield). The products obtained from the intermolecular reaction underwent a de Mayo‐like ring expansion delivering oxepane‐diones 45−47 in good yields (74−84%). In mechanistic studies it was found that the formation of the photoproduct was supressed upon addition of piperylene. Furthermore, in the presence of acetone as a sensitizer the reaction could be conducted at λ = 300 nm. At this wavelength no conversion occurred under direct irradiation. These observations suggest the involvement of triplet intermediates in the reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Sulfonic Acid Libraries Attained Through Opening of 2‐Sulfobenzoic Acid Anhydride
Authors: Robinson Richard I. , Stephens John C. , Worden Steve M. , Blake Alexander J. , Wilson Claire , Woodward Simon 
Published: November 2004

Abstract2‐Sulfobenzoic acid anhydride opens cleanly with N‐Boc‐protected α‐amino alcohols to afford zwitterionic esters 1,2‐C6H4(SO3−)(CO2CH2CHR1NH3+) (R1 = H, alkyl), the species R1 = iPr is crystallographically characterised. Dehydration of these species affords zwitterionic oxazoline sulfonic acid derivatives 1,2‐C6H4(SO3−)(CA=NH+CHR1CH2OA) (CA and OA are bonded C−O) for R1 = iPr (X‐ray), iBu, tBu, CH2Ph. Reaction with water regenerates the zwitterionic esters while exposure to M(OAc)2 (M = Cu, Pd) leads to the formation of the crystallographically characterised complexes MIIL2 (L = anion of the iPr‐oxazolinesulfonic acid). Heating either the zwitterionic esters or oxazolines with R2NH2 [R2 = CH2Ph, CH2(1‐C10H7), R‐CH(Me)Ph] leads to SN2 attack at the oxazoline methylene group leading to the amido sulfonic acids 1,2‐C6H4(CONHCHRCH2NHR2)(SO3H) based on crystallographic studies on R1 = iPr, R2 = CH2(1‐C10H7). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
FLOX® Steam Reforming for PEM Fuel Cell Systems
Authors: Schmid H.‐P. , Wünning J. A. 
Published: November 2004

AbstractPrimary energy savings and CO2 reduction is one of the key motivations for the use of fuel cell systems in the energy sector. A benchmark of domestic cogeneration by PEMFC with existing large scale power production systems such as combined steam‐gas turbine cycle, clearly reveals that only fuel cell systems optimising overall energy efficiency (> 85%) and electrical efficiencies (> 35%) show significant primary energy savings, about 10%, compared with the best competing technology.In this context, fuel processing technology plays a dominant role. A comparison of autothermal and steam reforming concepts in a PEMFC system shows inherent advantages in terms of efficiency at low complexity for the latter. The main reason for this is that steam reforming allows for the straightforward and effective use of the anode‐off gas energy in the reformer burner. Consequently, practical electrical system efficiencies over 40% seem to be achievable, most likely by steam reformers.FLOX®‐steam reforming technology has reached a high state of maturity, offering diverse advantages including: compact design, stable anode off‐gas usage, high efficiency, as well as simple control behaviour. Scaling of the concept is straightforward and offers an opportunity for efficient adaptation to smaller (1 kW) and larger (50 kW) units.
PEM – Fuel Cell System for Residential Applications
Authors: Britz P. , Zartenar N. 
Published: November 2004

AbstractViessmann is developing a PEM fuel cell system for residential applications. The uncharged PEM fuel cell system has a 2 kW electrical and 3 kW thermal power output. The Viessmann Fuel Processor is characterized by a steam‐reformer/burner combination in which the burner supplies the required heat to the steam reformer unit and the burner exhaust gas is used to heat water. Natural gas is used as fuel, which is fed into the reforming reactor after passing an integrated desulphurisation unit. The low temperature (600 °C) fuel processor is designed on the basis of steam reforming technology. For carbon monoxide removal, a single shift reactor and selective methanisation is used with noble metal catalysts on monoliths. In the shift reactor, carbon monoxide is converted into hydrogen by the water gas shift reaction. The low level of carbon monoxide at the outlet of the shift reactor is further reduced, to approximately 20 ppm, downstream in the methanisation reactor, to meet PEM fuel cell requirements. Since both catalysts work at the same temperature (240 °C), there is no requirement for an additional heat exchanger in the fuel processor. Start up time is less than 30 min.In addition, Viessmann has developed a 2 kW class PEFC stack, without humidification. Reformate and dry air are fed straight to the stack. Due to the dry operation, water produced by the cell reaction rapidly diffuses through the electrolyte membrane. This was achieved by optimising the MEA, the gas flow pattern and the operating conditions. The cathode is operated by an air blower.
Selective reduction of fibrotic markers in repairing corneas of mice deficient in Smad3
Authors: Stramer Brian M. , Austin Jeffrey S. , Roberts Anita B. , Elizabeth Fini M. 
Published: November 2004

AbstractThe cytokine transforming growth factor‐β (TGF‐β) is a key mediator of fibrosis in all organs. Expression of fibrotic markers in repairing cutaneous wounds is reduced in mice lacking Smad3, a downstream cytoplasmic mediator of TGF‐β signaling (Ashcroft et al., 1999, Nat Cell Biol 1(5):260–266). This is correlated with a reduction in inflammation, and thus in the blood elements thought to be a significant source of TGF‐β at the wound site, the principle form being TGF‐β1. Since the major cellular source of TGF‐β in corneal wounds is the epithelium, and the principal isoform is TGF‐β2, we investigated whether Smad3 deficiency has similar anti‐fibrotic effects on corneal repair. In contrast to the situation of cutaneous repair, expression of the fibrotic marker, fibronectin, was equivalent in corneal repair tissue of Smad3−/− mice as compared to their +/− littermates, even though expression of a second fibrotic marker not previously examined in cutaneous wounds, α‐smooth muscle (sm) actin, was reduced. Also unlike in cutaneous wounds, the inflammatory response was unaffected. These differences between corneal and cutaneous repair correlated with the lack of apparent change in the levels of corneal TGF‐β2. There was a significant reduction of α‐sm actin expression in stromal cell cultures established from Smad3−/− mice as compared to their +/− littermates, but the rate of cell proliferation stimulated by TGF‐β, as well as expression of fibronectin, was unaffected. Therefore, a deficiency in Smad3 has different effects on corneal and cutaneous repair, probably due to the difference in cellular source and principal isoform of the TGF‐β involved. © 2004 Wiley‐Liss, Inc.
The role of caldesmon in the regulation of endothelial cytoskeleton and migration
Authors: Mirzapoiazova Tamara , Kolosova Irina A. , Romer Lew , Garcia Joe G.N. , Verin Alexander D. 
Published: November 2004

AbstractThe actin‐ and myosin‐binding protein, caldesmon (CaD) is an essential component of the cytoskeleton in smooth muscle and non‐muscle cells and is involved in the regulation of cell contractility, division, and assembly of actin filaments. CaD is abundantly present in endothelial cells (EC); however, the contribution of CaD in endothelial cytoskeletal arrangement is unclear. To examine this contribution, we generated expression constructs of l‐CaD cloned from bovine endothelium. Wild‐type CaD (WT‐CaD) and truncated mutants lacking either the N‐terminal myosin‐binding site or the C‐terminal domain 4b (containing actin‐ and calmodulin‐binding sites) were transfected into human pulmonary artery EC. Cell fractionation experiments and an actin overlay assay demonstrated that deleting domain 4b, but not the N‐terminal myosin‐binding site, resulted in decreased affinity to both the detergent‐insoluble cytoskeleton and soluble actin. Recombinant WT‐CaD co‐localized with acto‐myosin filaments in vivo, but neither of CaD mutants did. Thus both domain 4b and the myosin‐binding site are essential for proper localization of CaD in EC. Overexpression of WT‐CaD led to cell rounding and formation of a thick peripheral subcortical actin rim in quiescent EC, which correlated with decreased cellular migration. Pharmacological inhibition of p38 MAPK, but not ERK MAPK, caused disassembly of this peripheral actin rim in CaD‐transfected cells and decreased CaD phosphorylation at Ser531 (Ser789 in human h‐CaD). These results suggest that CaD is critically involved in the regulation of the actin cytoskeleton and migration in EC, and that p38 MAPK‐mediated CaD phosphorylation may be involved in endothelial cytoskeletal remodeling. © 2004 Wiley‐Liss, Inc.
HSG cells differentiated by culture on extracellular matrix involves induction of S‐adenosylmethione decarboxylase and ornithine decarboxylase
Authors: Lam Kirby , Zhang Lianfeng , Bewick Mary , Lafrenie Robert M. 
Published: November 2004

AbstractThe human salivary gland (HSG) epithelial cell line can differentiate when cultured on extracellular matrix preparations. We previously identified >30 genes upregulated by adhesion of HSG cells to extracellular matrix. In the current studies, we examined the role of one of these genes, the polyamine pathway biosynthetic enzyme S‐adenosylmethionine decarboxylase (SAM‐DC) and the related enzyme, ornithine decarboxylase (ODC), on HSG cell differentiation during culture on extracellular matrix. HSG cells cultured on fibronectin‐, collagen I gel‐, and Matrigel‐coated substrates for 12–24 h upregulated SAM‐DC and ODC mRNA expression and enzyme activity compared to cells cultured on non‐precoated substrates. After 3–5 days, HSG cells grown on Matrigel‐ or collagen I gel‐coated substrates acquired a differentiated phenotype: the cells showed changes in culture morphology and increased expression of salivary gland differentiation markers (vimentin, SN‐cystatin, and α‐amylase). Further, culturing the cells on substrates precoated with an anti‐β1‐integrin‐antibody promoted differentiation‐like changes. HSG cells cultured on collagen I‐ or Matrigel‐coated substrates rapidly entered the cell cycle but showed decreased cell proliferation at longer times. In contrast, cell proliferation was enhanced on fibronectin‐coated substrates compared to cells on non‐precoated substrates. Treatment with the polyamine synthesis inhibitors, difluoromethylornithine (DFMO), and methylglyoxal bis‐(guanylhydrazone) (MGBG), inhibited cell proliferation and delayed 3H‐thymidine incorporation in HSG cells cultured on all of the substrates. Further, inclusion of DFMO and MGBG inhibited or delayed acquisition of the differentiated phenotype in HSG cells cultured on Matrigel‐ or collagen I gel‐coated substrates. This suggests that the adhesion‐dependent expression of SAM‐DC and ODC contributes to extracellular matrix‐dependent HSG cell differentiation. © 2004 Wiley‐Liss, Inc.