bluuebunny/crossref_metadata_2025_split huggingface dataset:
Total Synthesis of Myxovirescin A1
Authors: Fürstner Alois , Bonnekessel Melanie , Blank Jarred T. , Radkowski Karin , Seidel Günter , Lacombe Fabrice , Gabor Barbara , Mynott Richard 
Published: September 2007

AbstractA convergent total synthesis of the antibiotic macrolide myxovirescin A1 (1) is described that is largely based on reagent‐ and catalyst‐controlled transformations. This includes a highly regioselective Negishi reaction of dibromo‐alkene 48 with an alkynylzinc reagent, and a palladium catalyzed alkyl‐Suzuki coupling of the resulting enyne derivative 12 with the 9‐BBN‐adduct derived from alkene 61. The latter was obtained via an asymmetric hydrogenation of the chlorinated β‐ketoester 49 and an anti‐selective oxyallylation of the functionalized aldehyde 53 as the key steps. The preparation of the bis‐borylated allyl‐donor 57 used in the oxyallylation step, however, required careful optimization and led to important insights into the nature of the classical hydroborating agent “di(isopinocampheyl)borane (Ipc2BH)”. It was unambiguously shown by X‐ray crystallography that in the solid state this compound is dimeric, but it is prone to undergo an essentially quantitative mono‐deborylation when dissolved in CH2Cl2 or benzene; its composition in ethereal solvents is even more complex as evident from 11B NMR data. Product 71 derived from 12 and 61 was elaborated into the enyne–yne derivative 75, which served as the substrate for an exquisitely selective ring closing alkyne metathesis reaction (RCAM) catalyzed by the molybdenum tris‐amido complex 20 activated in situ with CH2Cl2. The resulting cyclic enyne 76 was subjected to a ruthenium catalyzed trans‐hydrosilylation/proto‐desilylation tandem. Although [Cp*Ru(MeCN)3]PF6 had previously been recommended as catalyst of choice for trans‐hydrosilylation reactions of internal alkynes, this complex failed to afford the desired product, whereas its sterically less hindered congener [CpRu(MeCN)3]PF6 permitted the reaction to be performed in appreciable yield, but at the expense of a lower stereoselectivity. AgF‐mediated proto‐desilylation of the isomeric silanes 79 and 80 followed by cleavage of the remaining acetal protecting groups afforded myxovirescin A1 and its hitherto unknown 14Z‐isomer 81, respectively.
Steric Modulation of Coordination Number and Reactivity in the Synthesis of Lanthanoid(III) Formamidinates
Authors: Cole Marcus L. , Deacon Glen B. , Forsyth Craig M. , Junk Peter C. , Konstas Kristina , Wang Jun 
Published: September 2007

AbstractReactions of a range of the readily prepared and sterically tunable N,N′‐bis(aryl)formamidines with lanthanoid metals and bis(pentafluorophenyl)mercury (Hg(C6F5)2) in THF have given an extensive series of tris(formamidinato)lanthanoid(III) complexes, [Ln(Form)3(thf)n], namely [La(o‐TolForm)3(thf)2], [Er(o‐TolForm)3(thf)], [La(XylForm)3(thf)], [Sm(XylForm)3], [Ln(MesForm)3] (Ln=La, Nd, Sm and Yb), [Ln(EtForm)3] (Ln=La, Nd, Sm, Ho and Yb), and [Ln(o‐PhPhForm)3] (Ln=La, Nd, Sm and Er). [For an explanation of the N,N′‐bis(aryl)formamidinate abbreviations used see Scheme 1.] Analogous attempts to prepare [Yb(o‐TolForm)3] by this method invariably yielded [{Yb(o‐TolForm)2(μ‐OH)(thf)}2], but [Yb(o‐TolForm)3] was isolated from a metathesis synthesis. X‐ray crystal structures show exclusively N,N′‐chelation of the Form ligands and a gradation in coordination number with Ln3+ size and with Form ligand bulk. The largest ligands, MesForm, EtForm and o‐PhPhForm give solely homoleptic complexes, the first two being six‐coordinate, the last having an η1‐π‐ArLn interaction. Reaction of lanthanoid elements and Hg(C6F5)2 with the still bulkier DippFormH in THF resulted in CF activation and formation of [Ln(DippForm)2F(thf)] (Ln=La, Ce, Nd, Sm and Tm) complexes, and o‐HC6F4O(CH2)4DippForm in which the formamidine is functionalised by a ring‐opened THF that has trapped tetrafluorobenzyne. Analogous reactions between Ln metals, Hg(o‐HC6F4)2 and DippFormH yielded [Ln(DippForm)2F(thf)] (Ln=La, Sm and Nd) and 3,4,5‐F3C6H2O(CH2)4DippForm. X‐ray crystal structures of the heteroleptic fluorides show six‐coordinate monomers with two chelating DippForm ligands and cisoid fluoride and THF ligands in a trigonal prismatic array. The organometallic species [Ln(DippForm)2(CCPh)(thf)] (Ln=Nd or Sm) are obtained from reaction of Nd metal, bis(phenylethynyl)mercury (Hg(CCPh)2) and DippFormH, and the oxidation of [Sm(DippForm)2(thf)2] with Hg(CCPh)2, respectively. The monomeric, six‐coordinate, cisoid [Ln(DippForm)2(CCPh)(thf)] complexes have trigonal prismatic geometries and rare (for Ln) terminal CCPh groups with contrasting LnCC angles (Ln=Nd, 170.9(4)°; Ln=Sm, 142.9(7)°). Their formation lends support to the view that [Ln(DippForm)2F(thf)] complexes arise from oxidative formation and CF activation of [Ln(DippForm)2(C6F5)] intermediates.
Demonstration of spontaneous chiral symmetry breaking in asymmetric Mannich and Aldol reactions
Authors: Mauksch Michael , Tsogoeva Svetlana B. , Wei Shengwei , Martynova Irina M. 
Published: September 2007

AbstractSpontaneous symmetry breaking in reactive systems, known as a rare physical phenomenon and for the Soai autocatalytic irreversible reaction, might in principle also occur in other, more common asymmetric reactions when the chiral product is capable to promote its formation and an element of “nonlinearity” is involved in the reaction scheme. Such phenomena are long sought after in chemistry as a possible explanation for the biological homochirality of biomolecules. We have investigated homogeneous organic stereoselective Mannich and Aldol reactions, in which the product is capable to form H‐bridged complexes with the prochiral educt, and found by applying NMR spectroscopy, HPLC analysis, and optical rotation measurements 0.3–50.8% of random product enantiomeric excess under essentially achiral reaction conditions. These findings imply a hitherto overlooked mechanism for spontaneous symmetry breaking and, hence, a novel approach to the problem of absolute asymmetric synthesis and could have also potential significance for the conundrum of homochirality. Chirality, 2007. © 2007 Wiley‐Liss, Inc.
Emission detected circular dichroism from long‐lived excited states: Application to chiral Eu(III) systems
Authors: Muller Françoise C. , Muller Gilles , Riehl James P. 
Published: September 2007

AbstractThe measurement of the difference in intensity of luminescence following excitation with left and right circularly polarized light for racemic terdentate Eu(III) complexes with 2,6‐pyridine dicarboxylic acids perturbed by the addition of (+)‐dimethyltartrate and for tris chiral complexes of Eu(III) with (R,R)‐N,N′‐bis(1‐phenylethyl)‐2,6‐pyridine‐dicarboxamide are presented. The experimental technique used for these measurements is identical in design to fluorescence detected circular dichroism spectroscopy, but is referred to in this manuscript as emission detected circular dichroism (EDCD) because of the long lifetime of the Eu(III) excited state requiring specialized instrumentation. These measurements required relatively slow modulation of the incident circular polarization, which was accomplished with a liquid crystal polarizer. The results are compared with conventional CD measurements, and additional characteristics and potential applications of EDCD are presented. Chirality, 2007. © 2007 Wiley‐Liss, Inc.
The Fe2+‐Mediated Decomposition, PfATP6 Binding, and Antimalarial Activities of Artemisone and Other Artemisinins: The Unlikelihood of C‐Centered Radicals as Bioactive Intermediates
Authors: Haynes Richard K. , Chan Wing Chi , Lung Chung‐Man , Uhlemann Anne‐Catrin , Eckstein Ursula , Taramelli Donatella , Parapini Silvia , Monti Diego , Krishna Sanjeev 
Published: September 2007

AbstractThe results of Fe2+‐induced decomposition of the clinically used artemisinins, artemisone, other aminoartemisinins, 10‐deoxoartemisinin, and the 4‐fluorophenyl derivative have been compared with their antimalarial activities and their ability to inhibit the parasite SERCA PfATP6. The clinical artemisinins and artemisone decompose under aqueous conditions to give mixtures of C radical marker products, carbonyl compounds, and reduction products. The 4‐fluorophenyl derivative and aminoartemisinins tend to be inert to aqueous iron(II) sulfate and anhydrous iron(II) acetate. Anhydrous iron(II) bromide enhances formation of the carbonyl compounds and provides a deoxyglycal from DHA and enamines from the aminoartemisinins. Ascorbic acid (AA) accelerates the aqueous Fe2+‐mediated decompositions, but does not alter product distribution. 4‐Oxo‐TEMPO intercepts C radicals from a mixture of an antimalaria‐active trioxolane, 10‐deoxoartemisinin, and anhydrous iron(II) acetate to give trapped products in 73 % yield from the trioxolane, and 3 % from the artemisinin. Artemisone provides a trapped product in 10 % yield. Thus, in line with its structural rigidity, only the trioxolane provides a C radical eminently suited for intermolecular trapping. In contrast, the structural flexibility of the C radicals from the artemisinins allows facile extrusion of Fe2+ and collapse to benign isomerization products. The propensity towards the formation of radical marker products and intermolecular radical trapping have no relationship with the in vitro antimalarial activities of the artemisinins and trioxolane. Desferrioxamine (DFO) attenuates inhibition of PfATP6 by, and antagonizes antimalarial activity of, the aqueous Fe2+‐susceptible artemisinins, but has no overt effect on the aqueous Fe2+‐inert artemisinins. It is concluded that the C radicals cannot be responsible for antimalarial activity and that the Fe2+‐susceptible artemisinins may be competitively decomposed in aqueous extra‐ and intracellular compartments by labile Fe2+, resulting in some attenuation of their antimalarial activities. Interpretations of the roles of DFO and AA in modulating antimalarial activities of the artemisinins, and a comparison with antimalarial properties of simple hydroperoxides and their behavior towards thapsigargin‐sensitive SERCA ATPases are presented. The general basis for the exceptional antimalarial activities of artemisinins in relation to the intrinsic activity of the peroxide within the uniquely stressed environment of the malaria parasite is thereby adumbrated.
Amelioration of Hyperglycemia and Metabolic Syndromes in Type 2 Diabetic KKAy Mice by Poly(γ‐glutamic acid)oxovanadium(IV) Complex
Authors: Karmaker Subarna , Saha Tapan K. , Yoshikawa Yutaka , Sakurai Hiromu 
Published: September 2007

AbstractRecently, we found that poly(γ‐glutamic acid)oxovanadium(IV) complex (VO(γ‐pga)) exhibits a potent antidiabetic activity in streptozotocin (STZ)‐induced type 1 diabetic mice. This result prompted us to examine its ability to treat the type 2 diabetic model KKAy mice with insulin resistance. We studied the in vivo antidiabetic activity of VO(γ‐pga), compared with that of vanadium(IV) oxide sulfate (VS) as control. Both compounds were orally administered at doses of 5–10 mg (0.1–0.2 mmol) V kg−1 body mass to the KKAy mice for 30 days. VO(γ‐pga) normalized the hyperglycemia within 21 days, whereas VS lowered the blood glucose concentration only by a small degree. In addition, the glucose intolerance, HbA1c level, hyperinsulinemia, hypercholesterolemia, and hyperleptinemia were significantly improved in VO(γ‐pga)‐treated KKAy mice compared with those treated with VS. Based on these observations, VO(γ‐pga) is proposed to be the first orally active oxovanadium(IV)‐polymer complex for the efficacious treatment of not only type 2 diabetes but also metabolic syndrome in animals.
Nuclear magnetic moments from NMR spectra—Experimental gas phase studies and nuclear shielding calculations
Authors: Jackowski Karol , Jaszuński Michał 
Published: September 2007

AbstractNMR spectra of gaseous compounds and quantum chemical calculations are combined to determine new accurate values of magnetic dipole moments for a series of nuclei. We have analyzed shielding constants, resonance frequencies, and nuclear magnetic moments for a group of simple molecules. The chemical shifts and resonance frequencies are measured at 300 K and extrapolated to the zero‐density limit in order to remove all the intermolecular effects from the experimental parameters. The absolute shielding constants in the studied molecules are obtained from ab initio calculations. Assuming the proton magnetic moment as the reference, we determine the nuclear magnetic moments of 13C, 14N, 15N, 17O, 19F, 29Si, 31P, 33S, and 73Ge. The new nuclear magnetic moments are consistent with the experimental NMR parameters, and using these new values one can for the first time predict successfully the shielding constant of a nucleus in a molecule when the corresponding resonance frequency is known. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 246–260, 2007.
Using PGSE NMR for chemical mixture analysis: Quantitative aspects
Authors: Antalek Brian 
Published: September 2007

AbstractPulsed gradient spin echo NMR coupled with a data processing approach such as direct exponential curve resolution algorithm may be used to resolve individual components in a mixture. Differences in the diffusivities of the components lead to differences in their signal decay behavior in the experiment and allow for pure component spectra to be resolved. Because the experiment is echo‐based, differences in the relaxation behavior of the nuclei within the various components lead to nonquantitative spectra. As a consequence it is rarely used to directly determine the levels of the components quantitatively. This article explores the effects of signal loss in the PGSE NMR experiment because of relaxation and describes an extrapolation method to ultimately obtain quantitative pure component spectra from mixtures. Examples of surface‐modified nanoparticles are presented. © 2007 Wiley Periodicals, Inc.Concepts Magn Reson Part A 30A: 219–235, 2007.
Treatment outcomes of small cell carcinoma of the prostate
Authors: Spiess Philippe E. , Pettaway Curtis A. , Vakar‐Lopez Funda , Kassouf Wassim , Wang Xuemei , Busby Joseph E. , Do Kim‐Anh , Davuluri Rajayogesh , Tannir Nizar M. 
Published: September 2007

AbstractBACKGROUND.The current study was conducted to determine the clinical characteristics and prognostic features associated with prostatic small cell carcinoma (SCC).METHODS.Between January 1985 and May 2005, 83 patients with SCC of the prostate were identified. Univariate and multivariate Cox proportional hazards modeling were used to assess the prognostic significance of the clinical parameters associated with disease‐specific outcomes.RESULTS.Twenty‐one patients had no evidence of distant metastasis at the time of the diagnosis of SCC, with the remaining patients demonstrating radiologic or biopsy‐proven evidence of metastatic disease. Compared with patients with metastases, patients without metastases at the time of diagnosis were older (P = .001) and had a lower serum lactate dehydrogenase (LDH) level at the time of diagnosis (P = .002). On multivariate analysis, an elevated serum LDH level and low serum albumin at the time of SCC diagnosis was found to be predictive of inferior progression‐free survival (P = .02 and P = .008, respectively) and inferior disease‐specific survival (DSS) (P = .02 and P = .01, respectively). At the time of last follow‐up, 72 patients (87%) had died of disease, with a median DSS duration of 13.1 months (range, 10.7–17.1 months). There was a statistically significant difference noted with regard to the median DSS of patients with nonmetastatic versus those with metastatic SCC (17.7 months [95% confidence interval (95% CI), 12.1–39.2 months] vs 12.5 months [95% CI, 8.1–16.1 months], respectively; P = .03).CONCLUSIONS.SCC of the prostate is a highly aggressive tumor, with serum LDH and albumin levels at the time of diagnosis believed to be predictive of disease‐related outcomes. Although palliative, current systemic therapy does not result in cure and does not provide long‐term survival for patients with metastases. For patients with nonmetastatic disease, a strategy utilizing systemic and local therapies should be evaluated further. Cancer 2007. © 2007 American Cancer Society.
Trends in childhood leukemia mortality in Brazil and correlation with social inequalities
Authors: Ribeiro Karina B. , Lopes Luiz F. , de Camargo Beatriz 
Published: September 2007

AbstractBACKGROUND.Mortality from childhood leukemia has declined substantially in developed countries but less markedly in the developing world. This study was designed to describe mortality trends in childhood leukemia and the impact of social inequalities on these trends in Brazil from 1980 to 2002.METHODS.Cancer mortality data by cause and estimates of resident population stratified by age and sex were obtained from the Brazilian Mortality Information System (SIM) for the years 1980 to 2002. Age‐standardized (ages 0‐19 years) mortality rates were calculated by the direct method using the 1960 world standard population. Trends were modeled using linear regression with 3‐year moving average rates as the dependent variable and with the midpoint of the calendar year interval (1991) as the independent variable. The Index of Social Exclusion was used to classify the 27 Brazilian states. Pearson correlation was used to describe the correlation between social exclusion and variations in mortality in each state.RESULTS.Age‐standardized mortality rates for boys decreased from 2.05 per 100,000 habitants in 1984 to 1.44 100,000 habitants in 1995, whereas the observed corresponding decline among girls was from 1.60 per 100,000 habitants in 1986 to 1.14 per 100,000 habitants in 1995. Statistically significant declining trends in mortality rates were observed for boys (adjusted correlation coefficient [r2] = 0.68; P < .001) and girls (adjusted r2 = 0.62; P < .001). Significant negative correlations between social inequality and changes in mortality were noted for boys (r = −0.66; P = .001) and for girls (r = −0.78; P < .001).CONCLUSIONS.A consistent decrease in mortality rates from childhood leukemia was noted in Brazil. Higher decreases in mortality were observed in more developed states, possibly reflecting better health care. Cancer 2007. © 2007 American Cancer Society.
Application of high‐order Higdon non‐reflecting boundary conditions to linear shallow water models
Authors: Neta Beny , van Joolen Vince , Dea John R. , Givoli Dan 
Published: September 2007

AbstractA shallow water model with linear time‐dependent dispersive waves in an unbounded domain is considered. The domain is truncated with artificial boundaries ℬ︁ where a sequence of high‐order non‐reflecting boundary conditions (NRBCs) proposed by Higdon are applied. Methods devised by Givoli and Neta that afford easy implementation of Higdon NRBCs are refined in order to reduce computational expenses. The new refinement makes the
computational effort associated with the boundary treatment quadratic rather than exponential (as in the original scheme) with the order. This allows for implementation of NRBCs of higher orders than previously. A numerical example for a semi‐infinite channel truncated on one side is presented. Finite difference schemes are used throughout. Copyright © 2007 John Wiley & Sons, Ltd.
Global exponential stability for uncertain bidirectional associative memory neural networks with multiple time‐varying delaysviaLMI approach
Authors: Gau Ruey‐Shyan , Hsieh Jer‐Guang , Lien Chang‐Hua 
Published: September 2007

AbstractThe global exponential stability for uncertain delayed bidirectional associative memory neural networks (DBAMNN) with multiple time‐varying delays is considered in this paper. Delay‐dependent criteria are proposed to guarantee the robust stability of DBAMNNvialinear matrix inequality approach. Two classes of system uncertainties are investigated in this paper. Some numerical examples are given to illustrate the effectiveness of our results. From the numerical simulations, significant improvement over the recent results can be observed. Copyright © 2007 John Wiley & Sons, Ltd.
Baukonstruktionen mit Mauerwerk – Überblick zu aktuellen technischen Entwicklungen
Authors: Fehling Ekkehard , Stürz Jochen 
Published: September 2007

AbstractDie ständig wachsenden Anforderungen an den Baustoff Mauerwerk erfordern eine stetige Weiterentwicklung seiner Eigenschaften. So soll Mauerwerk heute zuverlässig und dauerhaft Wärme‐ und Schallschutz bieten, das Errichten der Wände auf der Baustelle soll möglichst rationell durchzuführen sein und die Standsicherheit muss auch für die durch neue Normen erhöhten Wind‐ und Erdbebenbeanspruchungen gewährleistet werden können. Hierfür ist ein umfangreiches und grundlegendes Verständnis des Tragverhaltens von Mauerwerk unter Schubbeanspruchung notwendig, welches in dem europäischen Forschungsvorhaben ESECMaSE umfangreich untersucht werden soll.
Praxistipps zur Ausführung von Mauerwerk
Authors: Schubert Peter 
Published: September 2007

AbstractEine wesentliche Voraussetzung für die normgerechte Standsicherheit und Gebrauchsfähigkeit von Mauerwerk ist deren regel‐ und sachgerechte Ausführung. Wichtige Ausführungsregeln betreffen vor allem das Überbindemaß, die Ausführung von Lager‐ und Stoßfugen sowie die Maßtoleranzen der Bauteile, besonders die Ebenheitsanforderungen an die Rohbauoberflächen. Im Beitrag werden der Einfluss dieser Ausführungsparameter auf die Mauerwerkeigenschaften, die entsprechenden Bestimmungen in den Technischen Regelwerken sowie die Frage nach hinzunehmenden Abweichungen von den Anforderungen behandelt.
Chancen für Nachhaltigkeit und Energieeffizienz in Deutschland
Authors: Hegner Hans‐Dieter 
Published: September 2007

AbstractDie Bewertung des Beitrages von Einzelbauwerken zu einer nachhaltigen Entwicklung führen zur Forderung der Entwicklung eines Gesamtsystems zur Beschreibung und Beurteilung von Gebäuden einschließlich des Grundstücks. Ansätze für ein solches System gibt es, selbst Normungsbemühungen, aber eine standardisierte Regel lässt auf sich warten. Ungeachtet dessen bieten sich international Zertifizierungssysteme an, um die Nachhaltigkeit von Gebäuden festzustellen. Vielfach wird unter nachhaltigem Bauen insbesondere energieeffizientes Bauen verstanden. Dies ist nicht generell falsch. Aber Energieeffizienz ist nur ein Teil der Nachhaltigkeit. Dieser Teil ist jedoch mittlerweile gut geregelt. Mit der Umsetzung der EG‐Richtlinie 2002/91/EG über die Gesamtenergieeffizienz von Gebäuden in nationales Recht wurde in Deutschland das Energieeinsparrecht (Energieeinspargesetz, Energieeinsparverordnung) umfassend novelliert. Das Zweite Gesetz zur Änderung des Energieeinspargesetzes ist am 08.09.2005 in Kraft getreten. Auf dieser Grundlage hat die Bundesregierung die Energieeinsparverordnung 2007 (EnEV 2007) am 24.07.2007 endgültig beschlossen. Sie wird voraussichtlich im Oktober 2007 in Kraft treten. Der folgende Beitrag gibt eine Übersicht zu den vorgesehenen neuen Anforderungen beim energiesparenden Bauen und zu den geplanten Anforderungen und Instrumenten des Bundes beim nachhaltigen Bauen.