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  • General Chemistry  (77,717)
  • Chemical Engineering  (17,982)
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  • 1
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    transcript Verlag | transcript Verlag
    Publication Date: 2024-03-28
    Description: Land Grabbing, die Industrialisierung der Landwirtschaft und damit einhergehende Konflikte um Land nehmen seit Mitte der 2000er Jahre stetig zu. Landarbeiter*innen sind zentrale Akteure in diesem Kontext, finden in der wissenschaftlichen und entwicklungspolitischen Debatte jedoch kaum Beachtung. Jan Brunner nimmt sich dieser Leerstelle an und erforscht in seiner Studie des Zuckerrohrsektors die Auswirkungen agrarindustrieller Transformationen auf Landarbeiter*innen im Bundesstaat São Paulo (Brasilien). Aus arbeitssoziologischer und klassentheoretischer Perspektive analysiert er, wie sich Arbeitsverhältnisse sowie Arbeitskämpfe verändern und welche Herausforderungen, aber auch Chancen sich dadurch für die Organisierung und Kämpfe von Landarbeiter*innen ergeben.
    Keywords: Arbeit ; Arbeitskampf ; Klassenkampf ; Land Grabbing ; Transformation ; Konflikt ; Landwirtschaft ; Agrarindustrie ; Brasilien ; Gewerkschaft ; Landarbeit ; Zuckerrohr ; Wirtschaft ; Globalisierung ; Konfliktforschung ; Arbeits- und Industriesoziologie ; Arbeitsökonomie ; Lateinamerika ; Politikwissenschaft ; Work ; Labour Struggle ; Class War ; Conflict ; Agriculture ; Agricultural Industry ; Brazil ; Labour Union ; Land Work ; Sugar Cane ; Economy ; Globalization ; Conflict Studies ; Sociology of Work and Industry ; Labour Economics ; Latin America ; Political Science ; thema EDItEUR::G Reference, Information and Interdisciplinary subjects::GT Interdisciplinary studies::GTU Peace studies and conflict resolution ; thema EDItEUR::J Society and Social Sciences::JH Sociology and anthropology::JHB Sociology::JHBL Sociology: work and labour ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCF Labour / income economics
    Language: German
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  • 2
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    MDPI - Multidisciplinary Digital Publishing Institute
    Publication Date: 2023-06-23
    Description: The aim of this second Eng Special Issue is to collect experimental and theoretical re-search relating to engineering science and technology. The general topics of Eng are as follows: electrical, electronic and information engineering; chemical and materials engineering; energy engineering; mechanical and automotive engineering; industrial and manufacturing engineering; civil and structural engineering; aerospace engineering; biomedical engineering; geotechnical engineering and engineering geology; and ocean and environmental engineering. Therefore, the following editorial is a selection of representative works of these topics.
    Keywords: &nbsp ; Environment Management ; Environmental Engineering ; Chemical Engineering ; Materials Engineering&nbsp ; bic Book Industry Communication::T Technology, engineering, agriculture::TB Technology: general issues ; bic Book Industry Communication::T Technology, engineering, agriculture::TB Technology: general issues::TBX History of engineering & technology
    Language: English
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  • 3
    Publication Date: 2024-02-26
    Description: Identifcation of ontogenetic age classes plays an important role in the felds of zoology, palaeontology and archaeology, where accurate age classifcations of (sub)fossil remains are a crucial component for the reconstruction \nof past life. Textural ageing\xe2\x80\x94the identifcation of age-related bone surface textures\xe2\x80\x94provides a size-independent \nmethod for age assessment of vertebrate material. However, most of the work so far is limited to qualitative results. \nWhile qualitative approaches provide helpful insights on textural ageing patterns, they are heavily subject to observer \nbias and fall short of quantitative data relevant for detailed statistical analyses and cross-comparisons. Here, we present a pilot study on the application of 3D surface digital microscopy to quantify bone surface textures on the long \nbones of the grey heron (Ardea cinerea) and the Canada goose (Branta canadensis) using internationally verifed \nroughness parameters. Using a standardised measuring protocol, computed roughness values show a strong correlation with qualitative descriptions of textural patterns. Overall, higher roughness values correspond to increased numbers of grooves and pits and vice versa. Most of the roughness parameters allowed distinguishing between diferent \nontogenetic classes and closely followed the typical sigmoidal animal growth curve. Our results show that bone \ntexture quantifcation is a feasible approach to identifying ontogenetic age classes.
    Keywords: General Physics and Astronomy ; General Environmental Science ; General Biochemistry ; Genetics and Molecular Biology ; General Materials Science ; General Chemistry ; Roughness ; Surfaces ; Taphonomy ; Topography ; Bone ; Ontogeny ; Digital microscopy
    Repository Name: National Museum of Natural History, Netherlands
    Type: info:eu-repo/semantics/article
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  • 4
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    De Gruyter | De Gruyter
    Publication Date: 2024-04-05
    Description: The essential principles of green chemistry are the use of renewable raw materials, highly efficient catalysts and green solvents linked with energy efficiency and process optimization in real-time. Experts from different fields show, how to examine all levels from the molecular elementary steps up to the design and operation of an entire plant for developing novel and efficient production processes.
    Keywords: Process Engineering ; Chemical Engineering ; Technical Chemistry ; thema EDItEUR::P Mathematics and Science::PN Chemistry ; thema EDItEUR::R Earth Sciences, Geography, Environment, Planning::RN The environment ; thema EDItEUR::R Earth Sciences, Geography, Environment, Planning::RN The environment::RNU Sustainability ; thema EDItEUR::T Technology, Engineering, Agriculture, Industrial processes::TD Industrial chemistry and manufacturing technologies::TDC Industrial chemistry and chemical engineering ; thema EDItEUR::T Technology, Engineering, Agriculture, Industrial processes::TG Mechanical engineering and materials::TGM Materials science ; thema EDItEUR::T Technology, Engineering, Agriculture, Industrial processes::TQ Environmental science, engineering and technology
    Language: English
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  • 5
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    Böhlau
    Publication Date: 2024-04-09
    Description: Taking the province of Niederdonau as an example, this pioneer study highlights everyday fields-of-force between National Socialism and agrarian society in which rural actors competed for resources among themselves and with official functionaries. The megaproject of ‘volkish productivism’ – the creation of an efficient peasantry in ‘racial’ and economic terms – got stuck with regard to technical development. However, with regard to institutional development, there emerged a pathway towards an alternative modernity beyond Liberalism and Communism.
    Description: Diese Pionierstudie beleuchtet am Beispiel des Reichsgaues Niederdonau alltägliche Kräftefelder zwischen Nationalsozialismus und Agrargesellschaft, in denen ländliche Akteure untereinander und mit Funktionsträgern um Ressourcen rangen. Das Entwicklungsprojekt des ‚völkischen Produktivismus‘ – die Erzeugung eines „rassisch“ und wirtschaftlich leistungsfähigen „Bauerntums“ – blieb zwar in technischer Hinsicht stecken. Jedoch stellte es in institutioneller Hinsicht die Weichen der Agrarentwicklung in Richtung einer alternativen Moderne jenseits von Liberalismus und Kommunismus.
    Keywords: agrarian society ; agriculture ; everyday life ; productivism ; National Socialism ; Second World War ; Austria ; Agrargesellschaft ; Landwirtschaft ; Alltagsleben ; Produktivismus ; Nationalsozialismus ; Zweiter Weltkrieg ; Österreich ; Hektar ; Reichsmark ; thema EDItEUR::R Earth Sciences, Geography, Environment, Planning
    Language: German
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  • 6
    Publication Date: 2021-03-29
    Description: Die entwässerungsbasierte Nutzung von Moorstandorten führt einerseits zu einer erheblichen Emission von Treibhausgasen und andererseits zum Verlust der Ökosystemdienstleistungen und Lebensraumfunktionen eines naturnahen Moores. Zur Wiederherstellung von landwirtschaftlich vorgenutzten Hochmoorbiotopen fehlen bisher strukturierte, wissenschaftliche Erkenntnisse. Anders als ehemalige Torfabbau- oder Ödlandflächen waren intensiv genutzte landwirtschaftliche Flächen bisher nicht Ziel von großflächigen und wissenschaftlich begleiteten Wiederherrichtungsmaßnahmen. Vorrangiges Ziel des Projekts „OptiMoor – Erprobung und Entwicklung der Sanierung von landwirtschaftlich vorgenutzten Hochmooren zur Erhöhung der Biodiversität und Kohlenstoffspeicherung“ ist die Entwicklung eines Leitfadens für die Wiederherstellung von Hochmoorbiotopen nach intensiver landwirtschaftlicher Nutzung. Darin werden Maßnahmen beschrieben, die sich als erfolgsversprechend für die Umwandlung von Hochmoorgrünland zurück in ein naturnahes Hochmoorökosystem erwiesen haben. Das Projekt wird gefördert im Rahmen eines „Erprobungs- und Entwicklungsvorhabens“ des Bundesamts für Naturschutz sowie im durch das EFRE Förderprogramms „Klimaschutz durch Moorentwicklung“ des Landes Niedersachsens.
    Description: DFG, SUB Göttingen, DGMT
    Description: conference
    Keywords: 553.21 ; conference report ; Tagungsbericht ; Landwirtschaft ; land-use ; Moor ; Torf ; peat ; peatland ; FID-GEO-DE-7
    Language: German
    Type: article , publishedVersion
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  • 7
    Publication Date: 2021-03-29
    Description: Apart from the traditional contribution of geographers to the study of population, this particular thesis attempts to divert the emphasis of geographical enquiry towards the examination of how particular innovations affect the population distribution and the organization of human society. It deals specifically with questions concerning the demographic, social and economic impact of population mobility on both sending in receiving areas. It attempts to shed light on the different variables that work to produce a selective type of population mobility within a particular socio—economic set-up. Although various aspects of population mobility have been studied in some detail during the present decade, no attempt has been made, however, towards a concrete presentation of its multiple causes and its socio-economic impact on the areas and people that are left behind. Far from assuming complete coverage of all interrelated fields of study we attempt here to draw attention t0 the expected socio-economic repercussions of population mobility as induced by a particular factor, namely agricultural mechanization. Certain limitations‚ however, have made it difficult to deal with every aspect of population mobility in the Sudan.
    Description: thesis
    Description: DFG, SUB Göttingen
    Keywords: 910 ; Wanderungen {Entwicklungsländerforschung} ; Wirtschaft {Entwicklungsländerforschung} ; Sudan {Geographie} ; Mechanisierung ; Landwirtschaft ; Mobilität ; Landwirtschaft ; Mechanisierung ; Mobilität ; FID-GEO-DE-7
    Language: English
    Type: monograph_digi
    Format: V, 287 Seiten, 2 Karten
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  • 8
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    Reimer Verlag Berlin
    In:  Herausgeberexemplar | QA = 4 Z GEOGR 107:51
    Publication Date: 2021-03-29
    Description: Die vorliegende Arbeit stellt ein Konzept zur Bestimmung der Tragfähigkeit in nomadisch genutzten Weidegebieten vor, das es erlaubt, Weide-Öko-Nutzungs-Systeme zu beschreiben, zu evaluieren und ihre Leistungsfähigkeit weitgehend zu quantifizieren. Am Fallbeispiel einer Untersuchungsregion in Zentralsomalia werden die Charakteristika und Potentiale des Natur- sowie des Wirtschaftsraumes analysiert und in einen synthetischen Zusammenhang gestellt. Die Erfassung des Naturraumes beinhaltet neben der quantitativen Bemessung der Weideressourcen auch die qualitative Bewertung des Weidezustandes. Daneben sind die vielschichtigen ökonomischen und ökologischen Implikationen, die das tatsächliche Weidenutzungspotential bestimmen, aufgezeigt. Lösungsansätze zur Erhaltung der bestehenden Weideressourcen werden angeboten, die auf der Basis der nomadischen Perzeption der Umweltproblematik erarbeitet wurden. Das vorgeschlagene Konzept zeichnet sich dadurch aus, dass die Erhebungen mit relativ geringem Aufwand bewerkstelligt werden können und dennoch eine sehr detaillierte Datenbasis erzielen.
    Description: thesis
    Description: DFG, SUB Göttingen
    Keywords: 910 ; Somalia {Geographie} ; Nomadismus ; Weidewirtschaft ; Landwirtschaft ; FID-GEO-DE-7
    Language: German
    Type: monograph_digi
    Format: 344
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  • 9
    Publication Date: 2021-03-29
    Description: Summary: Most of the Emsland moorlands finally vanished with the „Emsland plan“. The foundation of settlements in the 17th and 18th century which stagnated in poor development, picked up again under the aegis of the Prussian government. Wasteland cultivation, internal colonisation and economic exploitation of peat became guiding principles in the „conquest“ of the moors, not only of the Emsland district or northwest Germany. This development was interrupted by the Second World War. Acting as a consequence of the necessity to create living space for refugees in the post-war period, the moor cultivation grew into a space reform of an unimaginable degree, especially in the districts of the Emsland and Grafschaft Bentheim. The present essay investigates the different stages of this development and shows the research desiderata according to the latest state of research.
    Description: Zusammenfassung: Mit dem Emslandplan verschwand der größte Teil der emsländischen Moore als Naturraum endgültig. Was mit Siedlungsgründungen im 17. und 18. Jahrhundert begann und lange Jahre in ärmlicher Entwicklung stagnierte, nahm unter der Ägide der preußischen Regierung Fahrt auf. Ödlandkultivierung, Binnenkolonisation und wirtschaftliche Nut zung der Torfe wurden zu Leitmotiven der „Eroberung“ der Moore, nicht nur des Emslandes oder Nordwestdeutschlands. Diese Entwicklung wurde durch den Zweiten Welt krieg unterbrochen. In der Nachkriegszeit, aus der Not heraus forciert Lebensraum für Flüchtlinge zu schaffen, erwuchs die Moorkultivierung in der Zeit des Wirtschaftswunders vor allem in den Landkreisen Emsland und Grafschaft Bentheim zu einer Raumneuordnung unvorstellbaren Ausmaßes. Der vorliegende Aufsatz folgt diesen Entwicklungsschritten und zeigt anhand des aktuellen Forschungsstandes die Forschungsdeside rata auf.
    Description: DFG, SUB Göttingen, DGMT
    Description: research
    Keywords: 553.21 ; Moor ; Torf ; Torfabbau ; Landwirtschaft ; land-use ; Emsland ; peatland ; peat ; peatmining ; FID-GEO-DE-7
    Language: German
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  • 10
    Publication Date: 2021-03-29
    Description: Abstract: The effects of different grassland management on vegetation pattern and yield potential were investigated in a long-term study on a low peat site typical for the county of Mecklenburg (Northeast-Germany). For this purpose we varied nutrient supply and the utilisation regime (cutting and grazing). Recordings of weathering data and soil water table were additional used to explain water-supply effects on grassland yields. Utilisation and K-supply were identified as the strongest predictors of vegetation patterns, whereas above ground biomass depends mainly from water supply during mid and late summer despite of significant management effects. We concluded that distinguishing between combined effects of vegetation utilisation and site condition water supply had necessarily to taken into account to got reliable information about grassland yield on drained low peat soils.
    Description: Zusammenfassung: In einer langjährigen Studie auf einem für Mecklenburg typischen Niedermoorstandort sind die Auswirkungen verschiedener Bewirtschaftungen auf den Pflanzenbestand und dessen Ertragsfähigkeit untersucht worden. Variiert wurden die Nährstoffversorgung und die Nutzung. Die Aufzeichnung von Witterung und Grundwasserflurabständen dienten der Abschätzung der Einflüsse des Wasserdargebotes auf den Ertrag. Der markanteste Einfluss auf die botanische Zusammensetzung des Grünlandes ging von der Nutzungsart und der Kalium-Düngung aus. Der Ertrag (bei Schnitt ohne Düngung 69 dt TM ha-1, mit NPK-Düngung 100 dt TM ha-1 und bei Weide ohne Düngung 59 dt TM ha-1, mit NPK-Düngung 74 dt TM ha-1) wurde hingegen ungeachtet signifikanter Bewirtschaftungseffekte am stärksten vom Wasserdargebot während der Sommermonate beeinflusst. Es wird gefolgert, dass für die Beurteilung der Ertragsfähigkeit von dränierten Niedermoorstandorten sowohl Nutzung als auch Witterung zu berücksichtigen sind, um zu realitätsnahen Richtwerten zu gelangen.
    Description: DFG, SUB Göttingen, DGMT
    Description: research
    Keywords: 553.21 ; Moor ; Niedermoor ; land-use ; vegetation ; Landwirtschaft ; fen ; peatland ; FID-GEO-DE-7
    Language: German
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  • 11
    Publication Date: 2021-03-29
    Description: Summary: In some fen areas in Brandenburg, the landscape element is marked by narrow grassland areas which are separated from each other at regular intervals by ditches accompanied by trees and bushes. These structures, which characterise the landscape, are often the Rimpau bog sand-cover cultivation structured in the eighties of the 19th century. Rimpau bog sand-cover cultivation is an amelioration of fens for agriculture. Due to the high returns bog sand-cover cultivation spread very quickly in Germany at the time. Through subsequent ameliorative measures, most of the former 10,000 ha of bog sand-cover cultivation were modified or disappeared. Today there are only a few examples of this cultivation in its original condition. They are worth to be preserved as monuments of rural engineering and species-rich biotopes.
    Description: Zusammenfassung: In einigen Niedermoorgebieten Brandenburgs ist das Landschaftsbild von schmalen Grünlandflächen gekennzeichnet, die durch gehölzbestandene Gräben in regelmäßigem Abstand voneinander getrennt sind. Diese landschaftsprägenden Strukturen sind meist die in den 80er Jahren des 19. Jahrhunderts angelegten Rimpau’schen Moordammkulturen. Die Rimpau’sche Moordammkultur ist ein kulturtechnisches Verfahren, mit dem durch Besandung Niedermoorstandorte für eine ackerbauliche Nutzung erschlossen wurden. Wegen der damit erzielten höheren Erträge, verbreitete sich die Moordammkultur damals sehr schnell in Deutschland. Durch spätere Meliorationen sind von den ehemals etwa 10.000 ha Moordammkulturen die meisten verändert worden bzw. verschwunden. Heute gibt es nur noch wenige Beispiele dieser Kulturen im Originalzustand. Sie sind als Denkmale der Kulturtechnik und artenreiche Biotope als „Kulturhistorische Landschaftselemente“ erhaltenswert.
    Description: DFG, SUB Göttingen, DGMT
    Description: research
    Keywords: 553.21 ; Brandenburg ; land-use ; Landwirtschaft ; Moor ; peatland ; Geschichte ; history ; FID-GEO-DE-7
    Language: German
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  • 12
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    Centre for Development Studies (ZELF), Institute of Geographical Sciences, Freie Universität Berlin
    Publication Date: 2021-03-29
    Description: The mechanism of granting Economic Land Concessions (ELCs) to (inter-)national investors for agro-industrial exploitation was the starting point of a wave of large-scale land acquisitions in Cambodia since the Royal Government of Cambodia (RGC) issued a respective directive in 2005. While ELCs are supposed to combine overall economic benefits on the one hand with poverty reduction and the compliance with environmental standards on the other hand, it turned out that there is a wide gap between the legal framework, which is supposed to govern the granting of ELCs, and its actual implementation on the ground. Eventually, the granting of ELCs led to severe human rights violations and several land conflicts, involving the local population, investor companies, political and economic elites as well as authorities. This situation is especially difficult for the Indigenous Peoples of Cambodia, who not just struggle to claim rights to their lands, but for whom land is also an essential component of livelihood. Drawing on a literature review and the results of a two-month field study, this thesis aims at shedding light at the relationship between different actors of society and land as a resource in the context of asymmetrical power constellations within the land conflict of Samot Leu Village in Seda Commune, Lumphat District, Ratanakiri Province.
    Description: Stiftung der Deutschen Wirtschaft (sdw)
    Description: research
    Keywords: 910 ; Kambodscha ; Landwirtschaft ; FID-GEO-DE-7
    Language: English
    Type: monograph , publishedVersion
    Format: 60
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  • 13
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    Selbstverlag des 2. Geographischen Instituts der Freien Universität Berlin
    In:  Herausgeberexemplar (FU Berlin) | ZB 20559:11
    Publication Date: 2021-03-29
    Description: research
    Description: DFG, SUB Göttingen, FU Berlin
    Keywords: 554 ; 910 ; 910.02 ; Frankreich ; Agrargeografie ; Landwirtschaft ; FID-GEO-DE-7
    Language: German
    Type: monograph_digi
    Format: 102
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  • 14
    Publication Date: 2021-03-29
    Description: Abstract: The RIMPAU bog sand-cover cultivation was created in 1862 in the usually very shallow fens of the Drömling area. The objective had been to use these areas for agriculture. The shallowness of the fen made it possible to take the cover sand from the underground spreading it then on the dikes. For deep fen areas it became necessary to modify the process bringing in the sand from the mineral rim. However, difficulties arose from subsidence due to drainage and the sand load, the characteristics of the bog substrate and the grain size composition of the cover sand. Economic reasons, however, the agriculture bog sand-cover cultivation area was transformed into grassland. Today there are only a few examples of cultivated areas of this type left in their original shape. The bog sand-cover cultivations of SCHREYER in Wendemark may be considered an exception. The moderately deep to deep, highly degraded and nutrient-rich bog had been the deciding factor for creating the bog sand-cover cultivation. In the wake of collectivization of agriculture the bog sand-cover cultivations were filled in and large harvesting units were created. The location remained in fields und a transformation into grass land is not yet planned.
    Description: Zusammenfassung: Die RIMPAU‘sche Moordammkultur wurde im Jahre 1862 im überwiegend sehr flachgründigen Niedermoor des Drömling entwickelt. Ziel war es, hier Ackerbau betreiben zu können. Die Flachgründigkeit des Moores gestattete es, den Decksand aus dem Untergrund zu entnehmen und auf den Moordämmen zu verkarren. Für die tiefgründigen Moorstandorte war es erforderlich, das Verfahren dahingehend zu modifizieren, dass der Decksand aus dem Mineralrand herangeholt wurde. Probleme bereiteten hier bald die Moorsackung durch Entwässerung und Sandauflast, die Beschaffenheit der Moorsubstrate und die Korngrößenzusammensetzung des Decksandes. Ökonomische Gründe bewirkten jedoch, dass die Acker-Moordammkulturen in Grünland umgewandelt wurden. Es gibt heute nur noch wenige Beispiele, wo ein Originalzustand dieser Kulturen vorhanden ist. Eine Ausnahme sind die Moordammkulturen SCHREYER‘s in Wendemark. Das mitteltiefgründige, hochzersetzte und nährstoffreiche Moor war entscheidend für die Anlage der Acker-Moordammkulturen. Nach der Kollektivierung der Landwirtschaft wurden die Moordammgräben verfüllt und große Schlageinheiten eingerichtet. Die Standorte verblieben weiterhin in Ackernutzung und eine Umwandlung in Grünland war nicht vorgesehen.
    Description: DFG, SUB Göttingen, DGMT
    Description: research
    Keywords: 553.21 ; Moor ; peatland ; history ; Geschichte ; land-use ; Landwirtschaft ; FID-GEO-DE-7
    Language: German
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  • 15
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    Selbstverlag des 2. Geographischen Instituts der Freien Universität Berlin
    In:  SUB Göttingen, Überlassung des Instituts für Geographische Wissenschatfen der Freien Universität Berlin
    Publication Date: 2021-03-29
    Description: Das Ziel der vorliegenden Arbeit war, das jahreszeitlich wechselnde Bild ausgewählter britischer Agrarlandschaften an Hand von sieben Repräsentativbetrieben zu untersuchen. Unter Berücksichtigung der statischen Komponenten wurde die jahreszeitliche Rhythmik der Agrarlandschaft durch ihre dynamische Komponente, die Arbeit in der Landwirtschaft, erfaßt. Die Untersuchung erfolgte mit Hilfe der Arbeitsmethode von G. JENSCH (1957) bei einer Weiterentwicklung derselben; die von Jensch benutzten „Arbeitsdiagramme“ wurden in der Weise differenziert, daß sowohl Arbeitsart wie Arbeit an bestimmten Feldfrüchten und Tieren auf ihnen abzulesen ist. Danach wurde versucht, den räumlichen Bezug von diesen Arbeitsdiagrammen zur Agrarlandschaft zu finden. Zu diesem Zweck wurden Flurkarten der einzelnen Betriebe entworfen, die in 15 Darstellungen für jedes Feld das jeweilige Erscheinungsbild im Verlaufe eines Jahres darstellen. Ein Vergleich der beiden Darstellungen zeigt für jedes Flurstück durch die Art der Arbeit und die damit verbundene, für jede Frucht typische Veränderung des Feldes das Ausmaß und «den Zeitpunkt der Veränderung der Flur an. Damit konnte eine direkte Aussage über den Zustand und die Zustandsänderung der gesamten Flur, die mit Hilfe der Diagramme allein nur indirekt möglich war, gemacht werden. Für jeden der sieben Betriebe, die etwa auf einer SE-NW-Achse von Kent bis Sutherland zu suchen sind, wurde sein Arbeitsrhythmus mit Hilfe des für ihn entworfenen Arbeitsdiagrammes erklärt, danach die hierdurch hervorgerufene Veränderung in der Flur erläutert und ein regionaler Vergleich der einzelnen Arbeitsarten, ihrer Einsatztermine und Arbeitsandauer gegeben. Nach einer vergleichenden Beschreibung des Arbeitsaufwandes und Arbeitsrhythmus im Verlaufe des Jahres wurde schließlich im Vergleich aller sieben Repräsentativbetriebe versucht, unter Zuhilfenahme der Ergebnisse aus Arbeitsdiagrammen und Flurkarten die für jeden Betrieb geltende Rhythmik seines Landschaftsbildes darzustellen und mit denen der anderen Betriebe zu vergleichen. Hierdurch wurde erstmalig auf dem durch G. JENSCH angeregten Wege die mit Hilfe der Arbeit in der Landwirtschaft exakt meßbare jahresrhythmische Zustandsänderung der Flur für einige Agrarlandschaften einzeln und vergleichend dargestellt.
    Description: research
    Description: DFG, SUB Göttingen, FU Berlin
    Keywords: 554 ; 910.02 ; Agrarlandschaft ; Landwirtschaft ; Britannien ; FID-GEO-DE-7
    Language: German
    Type: monograph_digi
    Format: 62
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  • 16
    Publication Date: 2021-03-29
    Description: Die meisten Moore in Nordwestdeutschland werden seit mehreren Jahrhunderten landwirtschaftlich genutzt. Die Kultivierungsverfahren der Moore entscheiden, welche Nutzungen möglich sind. Tiefumbruchböden lassen sich vielfältig, überwiegend als Acker nutzen. Auf den Schwarzkulturen dominiert heute die standortgerechte Grünlandnutzung, wobei die nicht standortgerechte, ackerbauliche Nutzung in jüngster Zeit zugenommen hat. Mit zunehmender Intensität der Flächenbewirtschaftung verschlechtern sich die Torfeigenschaften und durch Mineralisierung der Torfe treten Höhenverluste auf. Die Grenzen der Befahrbarkeit bzw. Trittfestigkeit werden häufig erreicht. In der Nährstoffdynamik unterscheiden sich Hoch- und Niedermoore. Bei der extensiven Grünlandnutzung, verbunden mit reduzierter Entwässerungsintensität, bereiten häufig Flatterbinse (Juncus effusus) und Rasenschmiele (Deschampsia caespitosa) Probleme. Neue Nutzungsverfahren der Paludikultur befinden sich noch in der Entwicklung und Erprobung. Eine dauerhafte Sicherung der Produktionsstandorte für landwirtschaftliche Nutzungen ist auf Tiefumbruchböden möglich.
    Description: report
    Keywords: 553.21 ; Moor ; land-use ; Landwirtschaft ; peatland ; FID-GEO-DE-7
    Language: German
    Type: article , publishedVersion
    Format: 19
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  • 17
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    Institut für Geographie und Geologie der Universität Greifswald
    Publication Date: 2022-01-11
    Description: Trotz relativ guter physiogeographischer Rahmenbedingungen fällt die Landwirtschaft Mecklenburg-Vorpommerns nach Wertschöpfung, Flächenproduktivität, Subventionseffektivität weit hinter die der westlichen Bundesländer zurück. Ursachen sind unter anderem die Inflexibilität und Unproduktivität übergroßer Unternehmen, die Dominanz billiger Massenproduktion und der Verzicht der Großbetriebe auf die Bedienung nachfragestarker Marktsegmente im ökologischen und hochqualitativen Bereich. Die Subventionierung und Privilegierung der großbetrieblich strukturierten Agrarindustrie muss abgebaut, die Förderung innovativer kleiner und mittlerer bäuerlicher Betriebe intensiviert werden. Die Infrastruktur in Ländlichen Räumen muss wachstumsorientiert für Landwirtschaft, Tourismus, hochwertiges Wohnen und seniorenbezogene Dienstleistungen ausgebaut werden.
    Description: In spite of relatively good general conditions and good soils, agriculture in Mecklenburg-Vorpom-mern is the only economic sector in the state whose gross value added has not seen a positive development in the last 20 years. Mecklenburg-Vorpommern’s agricultural sector stagnates at a low level and with a productivity of only 613 euros per hectare at 31.7 per cent below the German average. One of the most significant causes for this are the large farming businesses which are specialised in cheap mass production. Low area productivity is a result of inadequate flexibility of the large farming companies when it comes to reacting to market signals. Whilst smaller farms, which dominate agriculture in West Germany, can adjust their productive alignment relatively quickly or diversify to mix their income, large farming businesses try to avoid changes or put them off for as long as possible. The form of production, which is dominated by industrial farming, and the marginalisation of small and medium-sized farms as a result of land speculation and price dumping, cause the federal state of Mecklenburg-Vorpommern regional economic damages of at least € 250 million annually. The subsidisation and privileged treatment of industrial farming has to be cut down on as quickly as possible. We propose a new model of cooperation in rural areas called “Garden of metropolises”. It combines small and medium sized farms, preferably family farms, with tourism, leisure, high quality service, medium and high standard of living.
    Description: Fraktion Bündnis 90/Die Grünen im Landtag von Mecklenburg-Vorpommern
    Description: Unternehmerverband MiLaN, Wietzow
    Description: research
    Description: research
    Keywords: 910 ; QGB 570 ; QER 250 ; Mecklenburg-Vorpommern {Geographie} ; Agrar- und Forstgeographie {Wirtschaftsgeographie} ; Landwirtschaft ; Ländliche Räume ; Mecklenburg-Vorpommern
    Language: German
    Type: map , publishedVersion
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  • 18
    Publication Date: 2016-03-19
    Description: Exploiting binding affinities between molecules is an established practice in many fields, including biochemical separations, diagnostics, and drug development; however, using these affinities to control biomolecule release is a more recent strategy. Affinity-controlled release takes advantage of the reversible nature of noncovalent interactions between a therapeutic protein and a binding partner to slow the diffusive release of the protein from a vehicle. This process, in contrast to degradation-controlled sustained-release formulations such as poly(lactic-co-glycolic acid) microspheres, is controlled through the strength of the binding interaction, the binding kinetics, and the concentration of binding partners. In the context of affinity-controlled release--and specifically the discovery or design of binding partners--we review advances in in vitro selection and directed evolution of proteins, peptides, and oligonucleotides (aptamers), aided by computational design.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pakulska, Malgosia M -- Miersch, Shane -- Shoichet, Molly S -- Canadian Institutes of Health Research/Canada -- New York, N.Y. -- Science. 2016 Mar 18;351(6279):aac4750. doi: 10.1126/science.aac4750.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemical Engineering and Applied Chemistry, Institute of Biomaterials and Biomedical Engineering, and Donnelly Centre, University of Toronto, Toronto, Ontario, Canada. ; Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada. ; Department of Chemical Engineering and Applied Chemistry, Institute of Biomaterials and Biomedical Engineering, and Donnelly Centre, University of Toronto, Toronto, Ontario, Canada. Department of Chemistry, University of Toronto, Toronto, Ontario, Canada.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26989257" target="_blank"〉PubMed〈/a〉
    Keywords: Chemical Engineering ; Combinatorial Chemistry Techniques ; Delayed-Action Preparations/*chemistry ; Directed Molecular Evolution ; *Drug Design ; Humans ; Lactic Acid/*chemistry ; Microspheres ; Polyglycolic Acid/*chemistry ; Proteins/*administration & dosage
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 19
    Publication Date: 2024-02-28
    Description: Abstract: In Germany, more than 70% of peat soils are used for agriculture. Due to drainage and utilization, these peat soils have considerable environmental impact. Drainage-based use also leads to continuous peat mineralization and subsidence and over time to a loss of productive land. In an expert meeting (16 - 18 June 2016), organized by the MoorDialog project (Greifswald Mire Centre) and the DGMT, representatives from agriculture, water management, research, and nature conservation discussed the ‘good professional practice’ of agricultural use of peat soils in Germany. The overarching goal should be to secure the availability of productive land. As the management of peat soils also affects the provision of other ecosystem services such as climate and water protection, a good professional practice must consider and balance all these benefits. The expert meeting explored criteria for water management and land management to define good professional practice in societal consensus. Finally, the necessary changes of legal and economic frameworks were discussed. This paper can be the basis for a broad discussion in the political arena.
    Description: Zusammenfassung: In Deutschland werden mehr als 70% der Moorböden landwirtschaftlich genutzt. Von der mit der Bewirtschaftung verbundenen Entwässerung gehen meist erhebliche Umweltbelastungen aus, die im Widerspruch zu internationalen Vorgaben und nationalen Vorschriften stehen. Die entwässerungsbasierte Nutzung von Moorböden führt zur kontinuierlichen Abnahme des Höhenniveaus und damit über die Zeit zu einem Verlust an Kulturland. Auf einem vom Projekt MoorDialog (Greifswald Moor Centrum) und der DGMT organisierten Fachgespräch vom 16. bis 18. Juni 2016 haben Vertreter aus Land- und Wasserwirtschaft, Wissenschaft sowie Natur- und Umweltschutz diskutiert, was eine gute fachliche Praxis der Nutzung von landwirtschaftlich genutzten Moorböden in Deutschland beinhalten sollte. Als übergeordnetes Ziel wurde definiert, heutiges Kulturland dauerhaft als nutzbares Land zu erhalten. Die Bewirtschaftung von Moorstandorten beeinflusst neben der Produktionsfunktion die Bereitstellung von anderen gesellschaftsrelevanten Ökosystemleistungen wie den Klima- und Gewässerschutz und die Lebensraumfunktion für einheimische Organismen. Im Rahmen einer guten fachlichen Praxis sollten diese Leistungen berücksichtigt und integral abgewogen werden. Als Ergebnis des Fachgesprächs wurden Kriterien für die Steuerung des Wasserhaushalts und das Flächenmanagement sondiert, anhand derer eine gute fachliche Praxis definiert und im gesellschaftlichen Konsens vereinbart werden kann. Abschließend werden die dafür notwendigen Änderungen der rechtlichen und ökonomischen Rahmenbedingungen diskutiert. Der vorliegende Entwurf soll als Grundlage für eine breite Diskussion im politischen Raum dienen.
    Description: DFG, SUB Göttingen, DGMT
    Description: research
    Keywords: ddc:553.21 ; ddc:630.914 ; Moor ; peatland ; land-use ; Landwirtschaft ; peat ; Torf ; soil ; Boden
    Language: German
    Type: doc-type:article , publishedVersion
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  • 20
    Publication Date: 2014-10-04
    Description: Ethanol toxicity in the yeast Saccharomyces cerevisiae limits titer and productivity in the industrial production of transportation bioethanol. We show that strengthening the opposing potassium and proton electrochemical membrane gradients is a mechanism that enhances general resistance to multiple alcohols. The elevation of extracellular potassium and pH physically bolsters these gradients, increasing tolerance to higher alcohols and ethanol fermentation in commercial and laboratory strains (including a xylose-fermenting strain) under industrial-like conditions. Production per cell remains largely unchanged, with improvements deriving from heightened population viability. Likewise, up-regulation of the potassium and proton pumps in the laboratory strain enhances performance to levels exceeding those of industrial strains. Although genetically complex, alcohol tolerance can thus be dominated by a single cellular process, one controlled by a major physicochemical component but amenable to biological augmentation.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4401034/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4401034/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lam, Felix H -- Ghaderi, Adel -- Fink, Gerald R -- Stephanopoulos, Gregory -- R01 GM035010/GM/NIGMS NIH HHS/ -- R01-GM035010/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 2014 Oct 3;346(6205):71-5. doi: 10.1126/science.1257859. Epub 2014 Oct 2.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemical Engineering, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA. Whitehead Institute for Biomedical Research, Cambridge, MA, USA. ; Department of Chemical Engineering, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA. ; Whitehead Institute for Biomedical Research, Cambridge, MA, USA. gfink@wi.mit.edu gregstep@mit.edu. ; Department of Chemical Engineering, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA. gfink@wi.mit.edu gregstep@mit.edu.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25278607" target="_blank"〉PubMed〈/a〉
    Keywords: *Biofuels ; Cation Transport Proteins/genetics ; Cell Culture Techniques ; Cell Membrane/metabolism ; Chemical Engineering ; *Drug Resistance, Fungal/genetics ; Ethanol/*metabolism/pharmacology ; Fermentation ; Genetic Engineering ; Glucose/metabolism ; Hydrogen-Ion Concentration ; Phosphates/*metabolism ; Potassium Compounds/*metabolism ; Proton Pumps/genetics ; Proton-Translocating ATPases/genetics ; Saccharomyces cerevisiae/drug effects/genetics/*metabolism ; Saccharomyces cerevisiae Proteins/genetics ; Up-Regulation ; Xylose/metabolism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 21
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2014-11-29
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Langer, Robert S -- Gura, Trisha -- New York, N.Y. -- Science. 2014 Nov 28;346(6213):1146. doi: 10.1126/science.346.6213.1146.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Trisha Gura is a freelance writer who lives in Boston. For more on life and careers visit www.sciencecareers.org.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25430772" target="_blank"〉PubMed〈/a〉
    Keywords: Biotechnology ; *Career Choice ; Chemical Engineering ; *Entrepreneurship ; *Science
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 22
    Monograph available for loan
    Monograph available for loan
    London : Portobello Books
    Keywords: Lebensmittelproduktion ; Lebensmittelversorgung ; Ernährungssicherung ; Hunger ; Fehlernährung ; Mangelernährung ; Armut ; Unterprivilegierung ; Lebensmittelproduktion ; Lebensmittelindustrie ; Globalisierung ; Agrarpolitik ; Wirtschaftspolitik ; Welternährung ; Landwirtschaft ; Bevölkerungswachstum ; Ernährungssicherung
    Type of Medium: Monograph available for loan
    Pages: IX, 418 S. , Ill., graph. Darst. , 20 cm
    Edition: Revised 2. edition
    ISBN: 1846274796 ((pbk)) , 9781846274794 ((pbk))
    Language: English
    Branch Library: PIK Library
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  • 23
    Publication Date: 2012
    Description: Analysen zum Auftreten des Kohlschotenrüßlers in Raps der Vergangenheit und Abschätzungen zum Befall in der Zukunft mit Ensembleläufen verschiedener Klimamodelle KATASTER-BESCHREIBUNG: Beschreibung der Biologie (Überwinterungsdauer, Erstauftreten und Aktivität) der Kohlschotenrüßlers (Ceutorhynchus pallidactylus (Mrsh.)) in Raps in Luxemburg, Auswertung historischer Daten für 1961-90 und Vergleich mit Szenarienzeiträumen (2021-50 bzw. 2069-2098), Bandbreite der Simulationen aus 5 Globalen Klimamodellen (GCM) mit A1B und weiter regionalisiert (25x25km) mit 6 regionalen Klimamodellen KATASTER-DETAIL: Für die Zeit 2090-2099 im Vergleich zu 1980-1999 prognostizieren die GCM bei dem Szenario A1B eine Temperaturzunahme um 2.8 °C (Bandbreite 1.7 bis 4.4 °C) Delta T, dann Auftreten des Kohlschotenrüsslers um 3.3 Tage pro Dekade eher
    Keywords: Großherzogtum Luxemburg ; 1961-90 ; Szenarien ; Klima ; Landwirtschaft ; Pflanzenschädling ; Raps
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  • 24
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2012-11-28
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Savage, Phillip E -- New York, N.Y. -- Science. 2012 Nov 23;338(6110):1039-40. doi: 10.1126/science.1224310.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Chemical Engineering Department, University of Michigan, Ann Arbor, MI 48109, USA. psavage@umich.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23180853" target="_blank"〉PubMed〈/a〉
    Keywords: *Biofuels ; Cell Culture Techniques ; Chemical Engineering ; Chlorophyta/*chemistry/growth & development ; *Hot Temperature ; *Hydrostatic Pressure ; *Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 25
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    Geozon Science Media
    Publication Date: 2021-03-29
    Description: Es ist das Bemühen des Naturparks, seiner Mitarbeiter und des Fördervereins, das ihnen anvertraute Gebiet und sein Umfeld in seiner Entstehungsgeschichte darzustellen. Durch Tun und Lassen wandelte sich die einst waldreiche Naturlandschaft schrittweise zu einer immer stärker vom Menschen geprägten Kulturlandschaft (Ellenberg 1990). Anfangs waren es die Steinzeit-, Bronze- und Eisenzeitmenschen und dann die Slawen, die ihre heute noch erkennbaren Spuren in unserem Raum hinterließen, z.B. Grabanlagen, alte Burgwälle, Dorfnamen. Mit der Besiedlung des Slawenlandes durch deutsche Bauern ab dem 13. Jh. kam es zur Gründung neuer Dörfer unterschiedlichen Typs, wodurch auch die Naturlandschaft stark verändert wurde. Die sich ständig zahlreicher, umfangreicher und vielfältiger gestaltenden menschlichen Ansiedlungen wurden immer mehr zu einem wesentlichen Bestandteil unseres Gebietes.
    Description: research
    Keywords: 910 ; QGB 570 ; Kulturgeographie {Norddeutschland} ; Siedlungsgeografie ; Kulturgeschichte ; Ländlicher Raum ; Landwirtschaft ; Landesgeschichte ; Naturpark Nossentiner/Schwinzer Heide ; Mecklenburg-Vorpommern
    Language: German
    Type: anthology , publishedVersion
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  • 26
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    In:  Münster: proPlant GmbH. http://www.proplant.de/data/2010/ 2010_12_Volk-Richthofen-Johnen_Abschlussbericht- Klimawandel-und-Pflanzenschutz_proPlant.pdf
    Publication Date: 2010
    Description: Infektionsrisiko für pilzliche, bakterielle und tierische Schädlinge bei Weizen, Winterraps, Kartoffeln, Zuckerrüben und Mais werden für das Szenario A1B abgeschätzt KATASTER-BESCHREIBUNG: Schwerpunkt auf den 8 bedeutensten Krankheiten bei Weizen, Halmbruch, Mehltau, Septoria-Blattdürre, Gelbrost, Braunrost, DTR-Blattdürre, Septoria nodorum und Fusarium, Simulationen mit proPlant.expert und Einteilung in Trendklassen (1-5) von linearer Trend ansteigend (=1) bis abnehmend (=5) KATASTER-DETAIL: Tmit+ (Wettreg 2006, A1B), dann ansteigendes Risiko für Septoria tritici, Braunrost, Mehltau, Fusarium, für Halmbruch und DTR kein ansteigendes Risiko ermittelt Detaillierte Trendübersicht und Beurteilung für einzelne Kulturen und Regionen in NRW siehe Dokument, Anhang
    Keywords: Nordrhein-Westfalen ; 2001-2050 ; Insekten ; Zuckerrüben ; Kartoffeln ; Infektionskrankheiten ; Landwirtschaft ; Mais ; Niederschlag ; Pflanzenkrankheit ; Pflanzenschädling ; Temperatur ; Weizen ; Raps ; Modell
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  • 27
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    In:  Global Change Biology (2007) 13, 1550–1564, doi: 10.1111/j.1365-2486.2007.01394.x
    Publication Date: 2007
    Description: Biologie zum Auftreten und der Ausbreitung verschiedener Läusearten (Blatt, Baumlaus etc) durch Auswertung europaweiter Fallen, Ableitungen eines statistischen Ansatzes durch Verschneiden geografischer, klimatischer und Landnutzngsindikatoren mit dem Auftreten bestimmter Aphis-Aten, Hochrechnungen für die Zukunft KATASTER-BESCHREIBUNG: Zusammenhang zwischen den Läuseflug und der Umwelt wurde anhand von Fallenfunden über die am EXAMINE-Projekt beteiligten Länder, bzw. Partner geschätzt, Verschneiden geografischer, klimatischer und Landnutzngsindikatoren mit dem Flugverhalten, Herleiten eines stat. Models KATASTER-DETAIL: Delta T+, dann erwarteter Läuseflug in den nächsten 50 Jahren etwa 8 Tage eher Regressionsmodel: Julian Day=137.976+0.000023574*ARABLE + 0.0000390578xGRASS + 0.0000287559xSEA + 0.000102947xWATER -3.36069xC30DAY - 6.44658xC30P60DAY +0.0524365xDECPRN +0.108988xFEBRN + 0.0590551xNOVPRN ARABLE=Arable land (area in ha in a circle of R575 km), GRASS=Grassland (area in ha in a circle of R575 km), SEA=Sea (area in ha in a circle of R575 km), WATER=Inland waters (area in ha in a circle of R575 km), C30DAY=Mean temperature of the mean coldest 30 days, P60DAY=Mean temperature of the 60 days immediately after the mean coldest 30, DECPRN=Mean rainfall during the previous December, FEBRN=Mean rainfall during February, NOVPRN=Mean rainfall during the previous November
    Keywords: Europa ; 1970-2006, Szenarien ; Insekten ; Landwirtschaft ; Parasit ; Modell
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  • 28
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    In:  2 -NAP 02-231 Bericht IV Interreg IIIA Literaturstudie alpine Kulturpflanzen Vs. 3.0 070425.
    Publication Date: 2007
    Description: Sammlung historischer Informationen und Dokumentation des bäuerlichen Erfahrungswissens Kulturpflanzen von der Prähistorie - 20. Jahrhundert KATASTER-BESCHREIBUNG: KATASTER-DETAIL:
    Keywords: Südtirol, Nordtirol und GraubündenSüdtirol, Nordtirol und Graubünden ; Kartoffeln ; Anbautermine ; Boden ; Ertrag ; Getreide ; Hafer ; Klima ; Landwirtschaft ; Mais ; Niederschlag ; Pflanzenkrankheit ; Pflanzenschädling ; Roggen ; Temperatur ; Trockenheit ; Vegetationsperiode ; Weizen ; Wetterbeobachtung ; Witterung ; Düngung ; Hackfrüchte
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  • 29
    Publication Date: 2007-11-17
    Description: Artificial biochemical circuits are likely to play as large a role in biological engineering as electrical circuits have played in the engineering of electromechanical devices. Toward that end, nucleic acids provide a designable substrate for the regulation of biochemical reactions. However, it has been difficult to incorporate signal amplification components. We introduce a design strategy that allows a specified input oligonucleotide to catalyze the release of a specified output oligonucleotide, which in turn can serve as a catalyst for other reactions. This reaction, which is driven forward by the configurational entropy of the released molecule, provides an amplifying circuit element that is simple, fast, modular, composable, and robust. We have constructed and characterized several circuits that amplify nucleic acid signals, including a feedforward cascade with quadratic kinetics and a positive feedback circuit with exponential growth kinetics.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zhang, David Yu -- Turberfield, Andrew J -- Yurke, Bernard -- Winfree, Erik -- New York, N.Y. -- Science. 2007 Nov 16;318(5853):1121-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Computation and Neural Systems, California Institute of Technology, MC 136-93, 1200 East California Boulevard, Pasadena, CA91125, USA. dzhang@dna.caltech.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18006742" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Catalysis ; Chemical Engineering ; *Computers, Molecular ; DNA/*chemistry ; Entropy ; Equipment Design ; Feedback, Physiological ; Mice ; Nanotechnology ; Nucleic Acid Hybridization ; Rabbits
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 30
    Keywords: Biomass conversion ; Biotechnology ; Chemical Engineering ; Chemistry industry ; Industrial Chemistry ; Kent ; Riegel ; biochemical engineering
    Description / Table of Contents: Substantially revising and updating the classic reference in the field, this handbook offers a valuable overview and myriad details on current chemical processes, products, and practices. No other source offers as much data on the chemistry, engineering, economics, and infrastructure of the industry. The Handbook serves a spectrum of individuals, from those who are directly involved in the chemical industry to others in related industries and activities. It provides not only the underlying science and technology for important industry sectors, but also broad coverage of critical supporting topics. Industrial processes and products can be much enhanced through observing the tenets and applying the methodologies found in chapters on Green Engineering and Chemistry (specifically, biomass conversion), Practical Catalysis, and Environmental Measurements; as well as expanded treatment of Safety, chemistry plant security, and Emergency Preparedness. Understanding these factors allows them to be part of the total process and helps achieve optimum results in, for example, process development, review, and modification. Important topics in the energy field, namely nuclear, coal, natural gas, and petroleum, are covered in individual chapters. Other new chapters include energy conversion, energy storage, emerging nanoscience and technology. Updated sections include more material on biomass conversion, as well as three chapters covering biotechnology topics, namely, Industrial Biotechnology, Industrial Enzymes, and Industrial Production of Therapeutic Proteins.
    Pages: Online-Ressource (XIV, 1562 pages)
    ISBN: 9780387278438
    Language: English
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  • 31
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    In:  Diss., Sozialwissenschaftliche Schriften zur Landnutzung und ländlichen Entwicklung, no. 62. Margraf Verlag. , Kapitel 4
    Publication Date: 2005
    Description: Beschreibung der Entstehung des landwirtschaftlichen Wissens und der Entwicklung der Wissensvermittlung KATASTER-BESCHREIBUNG: - KATASTER-DETAIL: -
    Keywords: Baden-Württemberg ; 800 v. Chr. bis 1945 ; Ertrag ; Getreide ; Landwirtschaft
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  • 32
    ISSN: 1434-193X
    Keywords: Triplet recombination ; Electron transfer ; Radical ions ; Photochemistry ; Terpenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The triphenypyrylium tetrafluoroborate (TPT)-sensitized reactions of several terpene donor molecules, including sabinene (1), α-phellandrene (4), α-terpinene (5) and γ-terpinene (6) give rise to significantly different products than reactions induced by other electron-transfer sensitizers, such as 1,4-dicyanobenzene (DCB). The divergent reactions require decidedly different key intermediates; the products obtained with TPT can be explained by dissociative recombination of the intermediate radical-radical cation pair in the triplet state, generating donor-derived biradicals.
    Type of Medium: Electronic Resource
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  • 33
    ISSN: 1434-193X
    Keywords: Azides ; Cleavage reactions ; Cycloadditions ; Nitrogen heterocycles ; Polycycles ; Ring expansion ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---2-Alkyl-1-methylquinazolinium hexafluorophosphates 9 are deprotonated by sodium or potassium hydride to afford solutions of 2-alkylidenedihydroquinazolines 10, which were investigated by NMR spectroscopy. Trapping with methanesulfonyl azide (5a) of 10 in situ or subsequent treatment with trifluoromethanesulfonyl azide (5b) gives mixtures of colourless (15) and intensely yellow N-sulfonylimino-1,4-benzodiazepines 16 along with products due to cleavage of the exocyclic double bond of 10, viz. 11 and 13. The ethylidene compound 10b yields the bicyclic products 18 and 19, apparently by complex sequences of reactions that are triggered by removal of the acidic proton at C-2 of 16b and 16f. The structures of the products are based on spectroscopic evidence and X-ray diffraction analyses performed on 15b, 16d, 16e, and 19.
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  • 34
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1589-1593 
    ISSN: 1434-193X
    Keywords: Azaallenium ions ; Azaallylium ions ; Iminium ion ; Kinetics ; Linear Free Energy Relationships ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The rate constants for the reactions of the 2-azaallenium ion 1b+, the 2-azaallylium ion 2a+ and the iminium ion 3+ with different nucleophiles were determined by 1H NMR spectroscopy. By correlation with the Linear Free Enthalpy Relationship (LFER) lg k20°C = s (E + N), developed by Mayr and Patz, the electrophilicity parameters E(1b+) = -3.7, E(2a+) ≍ -16 and E(3+) = -10.43 were obtained. They show that the relative reactivities of these ions are approximately 1012:1:106. Quantum chemical calculations (ab initio, DFT) of the methyl anion affinities for the ions 1b+,2a+ and3+ are in agreement with the experimental E values. The X-ray structure of 3+·CF3SO3- is reported for the first time; it shows no strong interaction between the cation and the anion.
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  • 35
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1595-1601 
    ISSN: 1434-193X
    Keywords: Oxazoline N-oxide ; Cycloadditions ; Cycloadditions ; Lactams ; Thienamycin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---[3+2] Cycloaddition between a camphor-derived oxazoline N-oxide 9 and the γ,δ-unsaturated enamino ester 11 afforded the single adduct 6. A stereoselective reduction of the enamino ester side chain allowed the control of the absolute configuration of the two additional asymmetric centres. Nitrogen protection and oxidative hydrolysis of the resulting product 13, followed by further functional group manipulations, led to the β-lactam derivative 1, a known precursor of the β-methylthienamycin derivative2a.
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  • 36
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    Liebigs Annalen 2000 (2000), S. 1603-1607 
    ISSN: 1434-193X
    Keywords: Boron ; Cyclotrimerizations ; Nitrogen heterocycles ; Macrocycles ; Subphthalocyanines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The regioselective preparation of ortho-substituted subphthalocyanides was achieved employing 3-substituted phthalonitrile derivatives as starting materials. A mechanistic proposal has been outlined.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99525_s.pdf or from the author.
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  • 37
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    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1609-1615 
    ISSN: 1434-193X
    Keywords: Terpenoids ; Natural products ; Total synthesis ; Cyclizations ; Rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new route for the synthesis of 2,7- and 7-functionalized labdanes starts from (R)-carvone (1). 11-Nordrim-7-en-9-one (15) is an appropriate starting material for the total synthesis of hispanone (21), a biologically active furolabdane isolated from the Mediterranean medicinal plant Ballota saxatilis.
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  • 38
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    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1623-1626 
    ISSN: 1434-193X
    Keywords: Iridoid glucoside ; (8S)-Kingiside ; (8S)-Loganin ; (8S)-7-Ketologanin ; Asymmetric synthesis ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The tetraacetyl derivative 8 of the naturally occurring kingiside (8a) was prepared from aucubin (1). Intermediates in the synthesis were (8S)-tetraacetyl loganin (6) and (8S)-tetraacetyl-7-ketologanin (7), whose free (8R)-epimers occur in many different plants (Caprifoliaceae, Loganiaceae). The 13C NMR spectrum allows the structure to be unequivocally identified.
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  • 39
    ISSN: 1434-193X
    Keywords: Tetrakis(dimethylamino)naphthalenes ; Basicity ; Hydrogen bonds ; Cyclicvoltammetry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---For comparison to the recently described 2,3,6,7-tetrakis(dimethylamino)naphthalene (1) the three isomers 2,3, and 4 were synthesized. The basicities of this group of isomers are strongly dependent upon the different mutual orientations of the pairs of dimethylamino substituents: only the isomers 3 and, partially, 4, both with dimethylamino groups in adjacent peri-positions of the naphthalene, are strong “proton sponges”. For the isomers 1 and 2 with the same number and kind of twofold dimethylamino substituents in neighbouring ortho-positions, however, no significant basicity increase is observed. To explain this difference between the two groups of isomers it is suggested that in the ortho-pairs of 1 and 2 the C-N bonds diverge considerably, leading to an increased N···N distance and consequently to less stable [N···H···N]+ hydrogen bonds in contrast to the parallel C-N bonds in the peri-substituted isomers 3 and 4. X-ray crystal structure analyses of the bases and of some of the salts derived therefrom were solved and are discussed. Cyclic voltammetry indicates that 1 to 4 are strong electron donors, reacting easily to radical cations or dications which with suitable acids have been obtained as salts.
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  • 40
    Electronic Resource
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    Liebigs Annalen 2000 (2000), S. 1677-1683 
    ISSN: 1434-193X
    Keywords: Radicals ; Cyclizations ; Pyridinethione ; Tetrahydrofurans ; Asymmetric synthesis ; Thiazolethione ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The trisubstituted functionalized tetrahydrofurans 10, 11, 16, 18, and 19 were photochemically prepared from 2,3-syn- and 2,3-anti-configuredN-(3-benzoyloxy-5-hexen-2-oxy)thiazole-2(3H)-thione anti-6, pyridinethiones 7, anti-8, and BrCCl3. The formation of tetrahydrofurans was achieved by an efficient and highly regioselective alkoxyl radical cyclization (5-exo-trig). The 2,3-anti substituted intermediates 9 and 12 cyclize stereoselectively whereas a 2,3-syn-configured O-radical affords both possible diastereomeric addition products in equal amounts. The cyclized tetrahydrofuryl methyl radicals were trapped with the bromine atom donor BrCCl3 to afford the bromomethyl-substituted cyclic ethers 10, 11, 18, and 19 in excellent yields. The utility of this reaction was stressed by conversion of one of the newly prepared tetrahydrofurans in a two-step synthesis into (+)-allo-muscarine (+)-20.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99590_s.pdf or from the author.
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  • 41
    ISSN: 1434-193X
    Keywords: Thioketones ; Thiocarbonyl ylides ; Cycloadditions ; Cycloreversions ; Sulfur heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Reactions of diaryl thioketones with diazomethane at room temperature afford 4,4,5,5-tetraaryl-1,3-dithiolanes; the scope of this surprising 2:1 interaction has been studied for decades (Schönberg Reaction). The clue to the mechanism was our observation that the stoichiometry is 1:1 at -78 °C, and 2,5-dihydro-2,2-diaryl-1,3,4-thiadiazoles are formed as primary [2+3] cycloadducts. They lose N2 at -45 °C in first-order reactions generating diaryl thioketone S-methylides which can be intercepted by thioketones (→1,3-dithiolanes), multiple CC bonds, or acids HX. In the absence of trapping reagents, the elusive intermediates either dimerize furnishing 2,2,3,3-tetraaryl-1,4-dithianes or give rise to 2,2-diarylthiiranes by electrocyclization. Beyond thiobenzophenone and diazomethane, our main model reaction, the studies involve fluorene-9-thione, 4,4-dimethoxy- and 4,4-dichlorothiobenzophenone. The ring of 2,5-dihydro-2,2-diphenyl-1,3,4-thiadiazole (8) is opened by LDA at -78 °C and derivatives of anion 12 are obtained. - In summa: The Schönberg reaction consists of two 1,3-dipolar cycloadditions, linked by a 1,3-dipolar cycloreversion.
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  • 42
    ISSN: 1434-193X
    Keywords: Conjugation ; Boron ; Sensors ; Cyclic voltammetry ; Polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---New electropolymerizable aromatic compounds (i.e. pyrrole, thiophene, aniline) bearing boronic acid and ester substituents have been synthesized and their electrochemical behavior has been investigated. Functionalized polythiophene and polypyrrole films could be anodically generated in acetonitrile, whereas the polyaniline derivative was electroformed in an acidic aqueous solution. The electrochemical responses of some of these materials were changed when fluoride ions were added to the electrolytic solutions. The strongest modifications, caused by binding of fluoride by the immobilized boron, were observed for the polypyrrole derivative in hydroorganic media.
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  • 43
    ISSN: 1434-193X
    Keywords: Heterocycles ; Zinc ; Palladium ; Catalysts ; Sulfur ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Organozinc halides derived from Grignard reagents behave differently in their reaction with ethyl (±±)-(2RS,3SR)-tetrahydro-4-methylene-2-phenyl-3-(phenylsulfonyl)furan-3-carboxylate (3) according to the hybridisation of the carbon ligand. During the development of short multi-component reactions for the synthesis of diverse functionalized ethyl 2,5-dihydrofuran-3-carboxylates it was discovered that aryl and vinyl zinc halides undergo clean reaction with 3 in the presence of Pd(PPh3)4. In contrast, when alkyl zinc halides are reacted with 3 in the presence of Pd(PPh3)4, reductive desulfonation of 3 is observed. Remarkably, in the absence of a transition metal catalyst, the allylic substitution of 3 with alkyl zinc halides proceeds cleanly and in moderate to good yield.
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  • 44
    ISSN: 1434-193X
    Keywords: Self-assembly ; Vapor-pressure osmometry ; Resorcin[4]arenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Resorcin[4]arene tetracarboxylic acids 5,6 (A) and resorcin[4]arene tetrapyridines 2,3 (P) self-assemble in chloroform solution to form stable heterotopic AP dimers. Data from NMR titration and dilution experiments, as well as from vapor-pressure osmometry (VPO), indicate that the AP dimer is formed with an association constant greater than 107 M-1. Solid-solution extraction experiments are indicative of the formation of a 2:1 trimer (A2P), while self-associated homotopic species (A2 and A3) can be detected by NMR and VPO. Analysis of the heterotopic noncovalent assembly process over a range of compositions shows that these other species are much less stable than the AP heterodimer, which is the exclusive species at an A/P concentration ratio of 1:1 (〉 99.7% of the total at 10 mM).
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  • 45
    ISSN: 1434-193X
    Keywords: Sulfoxides ; β-Amino sulfones ; Mannich type reaction ; Lithium perchlorate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The LiClO4-mediated one-pot reaction of aldehydes with (trimethylsilyl)dialkyl amines and the lithium salt of sulfoxides or sulfones, affords the corresponding β-(dialkylamino) sulfoxides and β-(dialkylamino) sulfones in high yields. The aminosulfoxidation reaction of aliphatic or aromatic aldehydes lacks diastereoselectivity, but the diastereomeric sulfoxides can be separated by HPLC or column chromatography for further use.
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  • 46
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    Liebigs Annalen 2000 (2000), S. 1741-1744 
    ISSN: 1434-193X
    Keywords: Bridged pyranose derivatives ; Ring enlargement ; Carbenes ; Glycosides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Addition of dichlorocarbene to the glycal (±±)-2 followed by cyclopropyl-allyl rearrangement leads to the chloro-2H-pyran (±±)-4. Oxidation of (±±)-4 and reduction of the obtained hydroxypyranone (±±)-5 gave the methyl pyranoside (±±)-6. The relative configuration of (±±)-6 was established by X-ray structural analysis of the corresponding acetate (±±)-7. The synthesis of the optically active starting materials (+)-2 and (-)-2 is also reported.
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  • 47
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    Liebigs Annalen 2000 (2000), S. 1745-1758 
    ISSN: 1434-193X
    Keywords: CMP-Neu5Ac analogues ; Enzyme inhibitors ; Substrate analogues ; Transition state analogues ; Transferases ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Quinic acid was transformed into phosphitamides 16, 25, and 36, which could be readily linked to 5′-O-unprotected cytidine derivative 17. Ensuing oxidation of the obtained phosphite triesters with tBuO2H and hydrogenolytic de-O-benzylation furnished the corresponding phosphate diesters 18, 26, and 38. Base catalyzed removal of acetyl protecting groups, and methyl ester hydrolysis furnished CMP-Neu5Ac analogues 1d, 1e, and 2. Quinic acid was also transformed into 1,2-unsaturated diallyl α-hydroxymethyl-phosphate derivatives (R)- and (S)-46, which on reaction with cytidine phosphitamide 47 afforded the phosphite triesters. Subsequent oxidation with tBuO2H and then treatment with NEt3 gave phosphate diester derivatives (R)- and (S)-48. Deallylation, acetyl group removal, and methyl ester hydrolysis furnished (R)- and (S)-3, respectively. Treatment of (R)- and (S)-48 with DBU as a base led to acetic acid elimination, thus yielding, after de-O-allylation, acetyl group cleavage, and ester hydrolysis, diene derivative (E)-4. Donor substrate analogues 1d and 1e exhibited good α(2-6)-sialyltransferase inhibition (Ki: 2.0·10-4 and 2.0·10-5 M). However, transition state analogues (R)-, and particularly (S)-3 showed excellent inhibition properties (Ki: 1.6·10-6 and 2.7·10-7 M).
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  • 48
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    Liebigs Annalen 2000 (2000), S. 1759-1765 
    ISSN: 1434-193X
    Keywords: Cyclitols ; Aminocyclitols ; Glycosidase inhibitors ; α-Mannosidase inhibitors ; Deoxygenation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Three deoxy derivatives 2-4 of the α-mannosidase inhibitor mannostatin A (1) were synthesized, and their inhibition of Jack bean α-mannosidase was evaluated in order to elucidate the roles of each of the three hydroxyl groups of the inhibitor. The 1- and 2-deoxy derivatives 2 and 3 retained some inhibitory activity, although reduced by a factor of about 100 relative to the parent, whereas it was completely lost with the 3-deoxy derivative 4. Structure and activity relationships are discussed in the light of these findings.
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  • 49
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    Liebigs Annalen 2000 (2000), S. 1767-1772 
    ISSN: 1434-193X
    Keywords: Circular dichroism ; Conformation analysis ; s-Triazines ; Chiral auxiliaries ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---CD data of the optically pure 2-[(R)-1-(9-anthryl)ethylamino]-4-chloro-6-[(R)-1-(1-naphthyl)ethylamino]-1,3,5-triazine, 2[(R)-1-(9-anthryl)ethylamino]-4,6-bis[(R)-1-(1-naphthyl)ethylamino]-1,3,5-triazine, 2,4-bis[(R)-1-(9-anthryl)ethylamino]-6-chloro-1,3,5-triazine are presented. The analysis of the CD spectra by means of the nonempirical DeVoe approach has afforded the complete conformational characterisation of the three s-triazine derivatives, allowing us to establish how the conformation of these derivatives depends on the nature of the substituent 1-arylethylamino groups.
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  • 50
    ISSN: 1434-193X
    Keywords: Cycloadditions ; Carbenes ; Nitrones ; Nitrilimines ; Pyrazolines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The reaction of tert-butylalkynyl chromium Fischer carbene complex 1 with nitrones 2 affords β-enamino-ketoaldehydes 4 by the light-promoted rearrangement of the corresponding [3+2] cycloadduct carbene complexes 3. On the other hand, [3+2] cycloaddition of chiral nonracemic Fischer alkenyl carbene complexes 19 with nitrilimines 10 yields enantiomerically pure Δ2-pyrazolines with high regio- and diastereoselectivity.
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  • 51
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Zinc ; Transition structures ; QM/MM computations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Trimethylsilyl substitutions of the fenchyl alcohols [(1R,2R,4S)-exo-(2-Ar)-1,3,3-trimethylbicyclo[2.2.1]heptan-2-ol, Ar = 2-methoxyphenyl (1) and Ar = 2-(dimethylaminomethyl)phenyl (2)] yield the chiral ligands 3 [Ar = 2-methoxy-3-(trimethylsilyl)phenyl] and 4 [Ar = 2-(dimethylaminomethyl)3-(trimethylsilyl)phenyl]. Increased reactivities and enantioselectivities in diethylzinc additions to benzaldehyde are obtained from 3 (63% ee R) and 4 (93% ee S), relative to 1 (26% ee S) and 2 (73% ee S). X-ray crystal structures of 3 and of its methylzinc complex 3-Zn reveal out-of-plane bending of the methoxy groups as major geometrical consequences of the trimethylsilyl substitutions. Analyses of QM/MM ONIOM μ-O transition-structure models for 1, 2, 3, and 4 show that trimethylsilyl-induced distortions of methoxy and of dimethylaminomethyl groups explain the observed increased enantioselectivities.
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  • 52
    ISSN: 1434-193X
    Keywords: Palladium ; exo-π-Allylpalladium complexes ; Allylic alkylation ; Spiro compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The palladium(0)-catalyzed alkylation of 2,3-bis(acetoxymethyl)bicyclo[2.2.1]hepta-2,5-diene 1 with malonate-type enolates as nucleophiles is investigated. A monoalkylated product is formed first, and undergoes (depending on the nucleophile used) a second intramolecular reaction leading to spirocyclopropane-annulated bicyclo[2.2.1]heptene derivatives 5. The formation of endo spirobicyclic cyclopropanes adducts as major isomer is rationalized by assuming formation of an intermediate exo-(π-allyl)palladium complex.
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  • 53
    ISSN: 1434-193X
    Keywords: Ketones ; Reductions ; Micelles ; Cobalt ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Operationally simple and environmentally benign procedures have been developed to selectively reduce different α,β-unsaturated ketones, 4,4-dimethylcyclohex-2-ene-1-one (1), isophorone (2), benzylideneacetone (3), chalcone (4) by NaBH4 or by the system NaBH4 + CoCl2. Alternative reaction media to the extensively used MeOH have been explored, and new procedures take advantage of the acceleration and chemoselectivity induced by water or by aqueous micellar solutions. It was possible to selectively and quantitatively afford pure products of 1,2 and of 1,4 reduction as well as the totally reduced compounds (yield and selectivity 〉 90%) by simple changes in the experimental conditions.
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  • 54
    ISSN: 1434-193X
    Keywords: C-Glycosides ; Conformation analysis ; Molecular dynamics ; Selectins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The conformational behavior of the C-glycosyl analogue of sialyl-α-(2→3)-galactose, synthesized as a glycosidase inhibitor, has been studied using a combination of NMR spectroscopy (J and NOE data) and molecular dynamics calculations. The obtained results show that the population distribution of conformers with respect to the orientation about the pseudo-glycosidic linkages is mainly controlled by steric interactions. This is in contrast to findings made for O-glycosides. In these natural compounds, the conformational behavior about the glycosidic linkage Φ is mainly governed by the exo-anomeric effect.
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  • 55
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    Liebigs Annalen 2000 (2000), S. 1815-1820 
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Palladium-catalysed couplings ; Palladacycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Chiral C2-symmetric N-benzylazetidines have been conveniently prepared from optically pure anti-1,3-diols without loss of enantiomeric purity. N-Debenzylation led to the corresponding N-unsubstituted azetidines, which were then subjected to palladium-catalysed coupling reactions with aryl bromides to afford chiral N-arylazetidines. (R,R)-N-Benzyl-2,4-dimethylazetidine has been employed in the synthesis of a new cyclopalladated complex, which can be used, for instance, as a chiral recognition agent for phosphorus ligands.
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  • 56
    ISSN: 1434-193X
    Keywords: Cyclizations ; Spiro compounds ; Nucleosides ; Isomerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Syntheses of the spiro nucleosides 2′-deoxyhydantocidin 3a and its 1′-epimer 3b are described. The newly developed route involves a Horner-Wadsworth-Emmons condensation of the phosphonate 16 with the erythrose derivative 15 affording a mixture of six isomers which was fully assigned by NMR spectroscopy. The mixture was directly converted into the final compounds in an efficient base-catalyzed cyclization reaction. A base-catalyzed interconversion between the two isomers was observed.
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  • 57
    ISSN: 1434-193X
    Keywords: Benzodiazepines ; Heterocycles ; Azeto[1,2-a]-1,5-benzodiazepines ; Cyclizations ; Cycloadditions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The reaction of o-phenylenediamine (4) with one, two or three equivalents of p-substituted 3-dimethylaminopropiophenone hydrochlorides 5a-e was studied. 4-Aryl-2,3-dihydro-1H-1,5-benzodiazepine derivatives 6a-e were obtained in good yields, along with the 1:2-adducts 7c-e and the unexpected 1:3-adducts rac-8c-e. The type of adduct formed is determined by the molar ratio of the reactants 4 and 5 and by the nature of the substituent in the para position of the propiophenone 5.
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  • 58
    ISSN: 1434-193X
    Keywords: Cup-shaped PAHs ; Host-guest compounds ; Host-guest chemistry ; Cyclizations ; Semiempirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Cyclotrimerisation of benzo-polycyclic bromostannylalkenes 8a-d with Cu(NO3)2·3H2O in THF affords benzotri(benzonorbornadienes) 3a-d as a mixture of the syn and anti isomers. The ratio of syn to anti is close to the 1:3 statistical value in most cases (i.e. in cyclotrimers 3a,b,d), but highly in favour of the anti isomer in 3c, where steric hindrance by the methoxy groups plays an important role in the stereochemistry of the cyclotrimerisation. The substrates for the cyclotrimerisation, i.e. the bromostannyl alkenes 8a-d, were prepared from bromoalkenes 7a-d by treatment with base (LDA) and quenching with trimethyltin chloride. In turn, bromoalkenes 7a-d were prepared from alkenes 5a-d by radical bromination-elimination. The reaction conditions used were designed to minimise Wagner-Meerwein rearrangements that would lead to unwanted bromo isomers. The cup-shaped syn cyclotrimers 3a-d exhibit high electron density within the cavity as determined by AM1 semiempirical calculations of their electrostatic potential surfaces and are valuable substrates for supramolecular chemistry. As an example, it is shown that fullerene C60 is drawn into solution in acetonitrile by complexation with both the syn and anti trimer of benzonorbornadiene 3a.
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  • 59
    ISSN: 1434-193X
    Keywords: Carbene complexes ; Enamines ; Metallatrienes ; Cyclopentadienes ; Dihydropyrroles ; spiro-Tetrahydropyrroles ; Iminium carbonylmetalates ; Dimetallapolyenes ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Reactions of the [(1-alkynyl)carbene]tungsten complex (CO)5W=C(OEt)C≡CPh (1) with 1-aminocyclohexenes 2a-c and 7a-c afford different types of products depending on the amino substituents and the reaction conditions. (4-Aminocyclobutenyl)carbene complexes B have been shown to be generated in the first reaction step through a [2+2] cycloaddition. These are key intermediates and afford cross-conjugated tungstatrienes E, (conjugated) 1-tungsta-1,3,5-hexatrienes G, or (non-conjugated) 1-tungsta-1,3,6-heptatrienes F by following competing reaction pathways. Cross-conjugated 1-tungstatrienes 3 have been isolated in 52-74% yield by performing the reactions of 1-aminobenzocyclohexenes 2a-c with compound 1 in pentane. In dichloromethane instead of pentane, (conjugated) 1-tungsta-1,3,5-hexatrienes 4 are obtained, which subse-quently undergo fragmentation to give cyclopentadienes 6 (by π-cyclization) and dihydropyrroles (by α-cyclization) in a molar ratio dependent on the nature of the amino substituents. (Non-conjugated) 1-tungsta-1,3,6-heptatrienes 10 are generated upon reaction of 1-aminocyclohexenes 7a-c with compounds 1, which are transformed into cyclopentadienes 12 via conjugated 1-tungsta-1,3,5-hexatrienes 9 as intermediates. Reactions of 1-tungsta-1,3,6-heptatrienes 10 with the (1-alkynyl)carbene complex 1 afford dinuclear compounds 14, which subsequently yield indenes 15 (by two successive π-cyclization steps) and spiro-tetrahydropyrroles 16 (by both a π-cyclization and an α-cyclization step), depending on the steric bulk of the amino substituent.
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  • 60
    ISSN: 1434-193X
    Keywords: Allyl alcohols ; Organocerium reagents ; Alkenes ; Addition reactions ; Cerium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Alkylcerium reagents add to the multiple bonds of allyl and propargyl alcohols in good yields and under mild conditions. The double bond can be reduced with lithium aluminum hydride in the presence of cerium trichloride. The regiochemistry of the attack depends on electronic factors.
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  • 61
    ISSN: 1434-193X
    Keywords: Amidines ; Chiral bases ; N-Acyliminium ions ; Enantioselective catalysis ; Chiral pool ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The synthesis of four enantiopure hydroxyamidines is described. One amidine was obtained from (S)-pyroglutamic acid. Its key step involved the addition of phenylmagnesium bromide to the corresponding ester, affording the tertiary alcohol without detectable racemization. The second amidine was obtained by coupling of an (S)-malic acid derived N-acyliminium ion with β-naphthol. The other amidines were obtained from an (S)-serine-derived imide which was reduced to two diastereomeric lactams that were eventually transformed into the corresponding amidines.
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  • 62
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    Liebigs Annalen 2000 (2000), S. 155-163 
    ISSN: 1434-193X
    Keywords: Macrocycles ; Cyclizations ; Strained compounds ; Ketophosphonate ; Iodoalkyne ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Two strategies have been explored to build the highly strained eleven-membered ring 2, a potential precursor for the biosynthetic key intermediate of the protoilludane family: an intramolecular Horner-Wadsworth-Emmons olefination and an intramolecular Nozaki-Hiyama-Kishi type-ring closure.
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  • 63
    ISSN: 1434-193X
    Keywords: Neutral anion receptor ; Hydrogen bonds ; Urea moieties ; Donor-acceptor systems ; Macrocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The synthesis of macrocyclic and acyclic cleft-like anion receptors in which four hydrogen bond donating urea moieties are present in a preorganized fashion is described. NMR spectroscopy shows the complex formation with H2PO4- and Cl -. Cleft-like receptors bind H2PO4- in a 2:1 guest-host stoichiometry (Ka = 107M-2) in DMSO, whereas Cl - is bound in a 1:1 stoichiometry (Ka = 103M-1). The macrocyclic receptors form a 1:1 complex with H2PO4- (Ka = 103M-1 in DMSO) with a 100-fold selectivity for H2PO4- over Cl -.
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  • 64
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    Liebigs Annalen 2000 (2000), S. 193-198 
    ISSN: 1434-193X
    Keywords: Nucleophilic substitutions ; Azulenes ; Hydroxylation ; Amination ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Hydroxylation of azulenes with tert-butylhydroperoxide proceeds efficiently at the 6-position when the former contain electron-withdrawing substituents in the five-membered ring. Similarly, VNS amination of azulenes proceeds with 4-amino-1,2,4-triazole; its anion, being an active nucleophile, also reacts with unsubstituted azulene. A variety of transformations of 6-hydroxyazulenes, such as substitution of the corresponding sulfonates with nitrogen, oxygen, sulfur, carbon nucleophiles and halogens, and the Claisen rearrangement of allylic ethers, is reported.
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  • 65
    ISSN: 1434-193X
    Keywords: Heterocycles ; Carbohydrates ; Imidazolidines ; Oxazolidines ; Spiro compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Prochiral 1,3-dihydroxyacetone forms racemic oxazolidine- and oxazoline-type spiro[4.4]nonanes upon reactions with potassium (thio)cyanate and cyanamide. In contrast, 1,3-diaminoacetone yields only the corresponding spiro-bisimidazolidinethione under similar conditions together with monocyclic by-products, but the spiro-bisimidazolidinone is accessible by reaction of 1,3-dichloroacetone with urea. The resolution of the racemic spiro-bisoxazolidinethione 2a was achieved by using brucine as the resolving agent.
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  • 66
    ISSN: 1434-193X
    Keywords: Homogeneous catalysis ; Palladium ; Acetoxylation ; Acryloxylation ; Addition reactions ; Cyclooctadiene ; Cyclooct-4-enone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Palladium-catalyzed acryloxylation of several cycloalkenes in the presence of the Pd(OAc)2/p-benzoquinone/MnO2 catalytic system is reported. This oxidation reaction yields allylic acrylates as the sole products through the intermediacy of an η3-allyl complex. However, with 1,5-cyclooctadiene (3), cyclooct-4-enone (4) is the major reaction product. Its formation results from oxidation, which is also observed in the palladium-catalyzed acetoxylation of 3. It has been shown that this is the result of a 1,2-trans addition (acryloxy-palladation), followed by a β-hydride elimination, which yields an enol acrylate or acetate. A second Markovnikov-oriented 1,2-trans-acryloxy-palladation on the latter yields a palladium complex, rearrangement of which gives 4.
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  • 67
    ISSN: 1434-193X
    Keywords: Amino acids ; coupling ; N-Substituted amide ; Cyclizations ; Cyclic dipeptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A short synthesis of new, functionalized seven-membered ring cyclic dipeptides is described. After the coupling of N-protected β-amino acids to N-substituted α-amino tert-butyl esters, the protective groups of the terminal functions were removed and the cyclization took place diastereoselectively in the presence of the coupling agent BOP. Amide substitution was found to be effective in promoting the cyclization of linear dipeptides.
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  • 68
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    Liebigs Annalen 2000 (2000), S. 275-280 
    ISSN: 1434-193X
    Keywords: Radical reactions ; Substituent effects ; Nitrogen heterocycles ; Dihydropyridines ; Pyrrolines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A set of allene-tethered benzoyloximes (5) has been treated with nBu3SnH. Depending on their substitution pattern, a wide range of compounds has been obtained. If the stannyl radical adds on the allene, the C-centred radical thus formed undergoes either a 5-exo ring closure to give the cyclopentene derivatives 7 or a 6-endo ring closure onto the N atom to give the dihydropyridines 8. If the stannyl radical adds on the benzoyl moiety, an iminyl radical is formed which leads to the 3H-pyrroles 9 and the alkylidene-pyrrolines 10. Steric effects as well as polar effects are the factors governing the reaction course.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99373_s.pdf or from the author.
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  • 69
    ISSN: 1434-193X
    Keywords: Antibiotics ; Configuration determination ; Heterocycles ; Hongoquercin A ; Terpenoids ; Total synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---(±)-Hongoquercin A (1), the racemate of an antibacterial fungal metabolite, has been synthesized starting from geranylacetone (2) and ethyl orsellinate (ethyl 2,4-dihydroxy-6-methylbenzoate, 5). The structure (±)-1 has been confirmed by X-ray analysis of its ethyl ester (±)-10. Synthesis of the naturally occurring (+)-hongoquercin A from (-)-sclareol (11) established its configuration as depicted in 1.
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  • 70
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Amino sugars ; Protecting groups ; Glycosylations ; Trichloroacetimidates ; Oligosaccharides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The N-DMM-Protected lactosamine derivative 2 was readily transformed into the corresponding glycosyl donor 4 and into acceptor 5. A TMSOTf-catalyzed glycosidation afforded the derived tetrasaccharide 6 which led to glycosyl donor 9. Reaction of 9 with lactose derivative 10 as acceptor gave the desired hexasaccharide 11. Cleavage of all protective groups and N-acetylation afforded the target molecule 1b (lacto-N-neohexaose). Glycosylation of acceptor 10 with donor 4 furnished tetrasaccharide 16 which, employing standard procedures, gave acceptor 18. Glycosylation of 18 with donor 9 furnished, under standard conditions, octasaccharide 19. Cleavage of all protective groups and N-acetylation afforded the target molecule 1c (lacto-N-neooctaose). Both 1b and 1c were obtained in good overall yields.
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  • 71
    ISSN: 1434-193X
    Keywords: Sharpless asymmetric dihydroxylation ; Asimilobin ; Tetrahydrofuran ring ; Wittig reactions ; Annonaceous acetogenins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The most efficient method for the synthesis of the trans/threo/trans-bis(tetrahydrofuran) (THF) ring unit was established, and the first total synthesis of (-)-asimilobin and its diastereomer was then accomplished in twelve and fourteen steps, respectively, from trans-1,5,9-decatriene, by a convergent route with a Wittig reaction as the key step. By virtue of these synthetic results, the absolute configuration of the bis(THF) unit in naturally occurring asimilobin should be corrected.
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  • 72
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    Liebigs Annalen 2000 (2000), S. 381-385 
    ISSN: 1434-193X
    Keywords: Enynes ; Macrocycles ; Coordination chemistry ; Crown compounds ; Radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The complex molecular structure and interesting activation mechanisms of naturally occurring enediynes have inspired the synthesis of a variety of simpler model systems to mimic their properties. While in most model compounds nucleophilic attack, isomerization or bioreduction are used to activate the unsaturated system for diradical cyclization, some attempts have been made to employ metal-ion coordination for this purpose. Significant enhancement of the thermal reactivity has been achieved by metal-ion induced conformational and electronic changes of suitably substituted enediynes, such as 1, 5, 6, 17 and 18. Enediyne activation by stoichiometric or catalytic formation of vinylidene complexes, such as 22, from terminal alkynes has also been investigated. This paper summarizes recent results pursuing the activation of enediyne diradical cyclization by metal ions.
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  • 73
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    Liebigs Annalen 2000 (2000), S. 419-423 
    ISSN: 1434-193X
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The first enantioselective synthesis of enantiomerically pure (-)-wine lactone, (-)-1a, a fragrance constituent of various white wines, and its epimer (+)-1b, was carried out. The key steps are allylic substitution of (±)-2-cyclohexen-1-yl acetate (2) with dimethylmalonate using palladium complexes of phosphanyldihydrooxazol L1 or of the phosphanylcarboxylic acid L2 as catalyst, subsequent decarboxylation, iodolactonization and elimination, furnishing enantiomerically pure bicyclic lactone (+)-7 in 47% overall yield. The diastereoselective introduction of methyl groups by SN2′-type substitution with an organocopper compound and by enolate alkylation gave lactone (-)-1a in 43% overall yield from (+)-7.
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  • 74
    ISSN: 1434-193X
    Keywords: Aplykurodins ; Marine steroids ; C-C coupling ; Cyclic peroxides ; Lactonization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---An approach to the synthesis of aplykurodins, ichthyotoxic marine lactones, is presented. The carbon framework was derived from vitamin D3 by conversion of the readily accessible allyl alcohol 13 to the protected Grundmann's hydroxy ketone 22 and subsequent introduction of the C2 side chain through a Pd0-promoted coupling. Highly stereoselective hetero Diels-Alder reaction with O21 produced the key intermediate peroxide 25. Functional group transformations, coupled with a series of chemo- and stereoselective reactions, finally resulted in the synthesis of the unnatural analogue 17,18-dihydro-3,9-di-epi-aplykurodinone B (6).
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  • 75
    ISSN: 1434-193X
    Keywords: Zeolites ; Radical ions ; Ring opening ; Electron transfer ; Oxidations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Incorporation of trans-1,2-diphenylcyclopropane (1) and its 3,3-D2-isotopomer into the channels of a redox-active pentasil zeolite (Na-ZSM-5) resulted in the formation of exo,exo-1,3-diphenylallyl radical (2•) and its 2-D1 isotopomer, respectively. This conversion requires oxidation, ring opening, and deprotonation, in an unspecified sequence. The allyl radical 2• is also formed upon incorporation of trans-1,3-diphenylpropene (3). A comparison with the solution photochemistry, in the presence or absence of added base, shows the conversion of 1 into 2• to be a zeolite-specific reaction. Incorporation of arylcyclopropanes 9 (R = H, OCH3) into ZSM-5 generated trans-propenylbenzene radical cations 10•+ (R = H, OCH3); the 2,2-D2 isotopomer of 9 (R = OCH3) gave rise to three different isotopomers of 10•+ (R = OCH3).
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  • 76
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    Liebigs Annalen 2000 (2000), S. 485-490 
    ISSN: 1434-193X
    Keywords: Calixarenes ; Tripodal cryptand ; Extraction abilities ; Cations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The tripodal calixcryptands have been one of the scarcely explored fields in calixarene chemistry due to the difficulties in their preparation. The strategy presented in this paper shows that novel tripodal calixcryptands can be conveniently prepared by directly treacing p-tert-butylcalix[n]arenes (n = 4, 6) with a multi-functional polypode reagent, e.g. 1,1,1-tris(tosyloxyethoxyethoxymethyl)propane or tetrakis(tosyloxyethoxyethoxymethyl)methane, under selected conditions. The first example of 1,2,4-tripodal calix[6]cryptands has been prepared. Novel calix[6]crown and doublecalix[4]arenes were co-prepared. The extraction abilities of these novel calixcryptands toward several alkali metal ions, ammonium and alkylammonium ions are presented.
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  • 77
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    Liebigs Annalen 2000 (2000), S. 521-525 
    ISSN: 1434-193X
    Keywords: Allyl aryl sulfones ; Nitroarenes ; Condensation reaction ; Lewis acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Allyl aryl sulfones 2 react with aryl nitrocompounds 1 in a DBU/MgCl2 system giving the 4-arylsulfonyl quinolines 3. Some mechanistic aspects of the reaction are discussed. Application of this reaction to the formal total synthesis of the natural product (-)Eupolauramine is described.
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  • 78
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    Liebigs Annalen 2000 (2000), S. 527-538 
    ISSN: 1434-193X
    Keywords: Furans ; Pyrans ; Dihydropyran-2-ylidenes ; Ring closure ; Addition reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---On treatment with base the pentynones 8a-f undergo anionic addition reactions of the resulting enolate species to the alkyne moiety and afford the 2,5-disubstituted furans 10a-f in yields ranging from 10-91%. The proposed mechanism involves the 2-methylene-dihydrofurans 11 as intermediates which tautomerize to yield the observed products. In the case of the α-picolyl derivative 8g both possible enolates 12 and 13 are formed which are subsequently transformed to the products 10g and 14g, respectively. Starting with the hexynones 9a-e an analogous reaction takes place with the formation of the pyran derivatives 15 and 16 in comparable yields. Under the same reaction conditions the n-butyl ketone 9f gives rise to two isomeric compounds, namely the 4H-pyran 16f and the cyclohexenone 17. This result is explained by assuming initial formation of two isomeric enolates which react either by O- or C-attack on the carbon-carbon triple bond.
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  • 79
    ISSN: 1434-193X
    Keywords: Alkylations ; Deaminated AdoHcy ; Decarboxylated AdoHcy ; Mitsunobu reaction ; Nucleosides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---5′-Acetylthio-5′-deoxy-2′,3′-O-isopropylideneadenosine (8) was directly prepared from commercially available 2′,3′-O-isopropylideneadenosine (7) and thioacetic acid under Mitsunobu conditions in almost quantitative yield. In situ cleavage of the acetylthio function of 8 followed by coupling with different alkyl bromides proceeded with high yields. Deprotection of the obtained 5′-thionucleosides yielded the S-adenosyl-L-homocysteine analogues decarboxylated AdoHcy (11), deaminated AdoHcy (14) and 5′-[3-(cyano)propylthio]-5′-deoxyadenosine (16) in good overall yields. Direct deprotection of the thionucleoside 8 delivered 5′-thio-5′-deoxyadenosine (18) in excellent yield. In addition, binding constants of these AdoHcy analogues and the DNA methyltransferase M·HhaI were determined in a fluorescence assay.
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  • 80
    ISSN: 1434-193X
    Keywords: Amino ketones ; Homogeneous catalysis ; Aziridination ; Copper ; Enols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A series of acyclic and cyclic enol derivatives 1 has been transformed into the corresponding α-amino-functionalized ketones 2 by means of enantioselective catalytic aziridination with chiral Cu complexes, prepared in situ from [Cu(MeCN)4]PF6 and the optically active ligands 3, by using (N-tosylimino)iodobenzene (PhINTs) as a nitrogen source. The best enantioselectivities (ee values of up to 52%) have been achieved for the electronically deactivated enol acetate 1aδ, but the incorporation of steric bulk and the substitution pattern at the enol double bond do not improve the ee values. The cyclic substrates react considerably less readily (only up to 45% conversion) compared to their acyclic counterparts (complete consumption). A transition structure is suggested for the asymmetric Cu-catalyzed aziridination of the enol acetate 1aδ in the presence of the chiral ligand 3b that could account for the sense of the (R)-configured product 2a.
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  • 81
    ISSN: 1434-193X
    Keywords: Porphyrins ; Chiral auxiliaries ; Macrocycles ; Pyrethroids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Esters, N,N-disubstituted amides, and a N-acylurea derived from the enantiopure industrial intermediate (1R)-cis-hemicaronaldehydic acid (or biocartol) are convenient synthons for the preparation of a series of chiroporphyrins by condensation with pyrrole. These chiral meso-tetracyclopropylporphyrins are obtained exclusively as the D2-symmetric α,β,α,β atropisomer, generally in low to moderate yields (2-20%), and in the urea case in excellent yield (60%). Hydrolysis of the urea substituents affords a chiroporphyrin with mono-N-substituted amide groups. 1H-NMR spectroscopy indicates that the ester, amide, and urea stereogenic groups sit on the porphyrin close to the metal binding site and restrict substrate or ligand access along a C2-symmetric groove. This structural feature of chiroporphyrins and of their metal complexes is of high potential interest in asymmetric catalysis and chiral recognition.
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  • 82
    ISSN: 1434-193X
    Keywords: Cyclophanes ; Molecular recognition ; Molecular shuttles ; Rotaxanes ; Template-directed synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Two dumbbell-shaped compounds (8 and 11), each composed of two polyether chains intercepted by a 1,4-dioxybenzene recognition site, terminated by tetraarylmethane-based stoppers, and emanating from a central 9,10- or a 2,6-dioxyanthracene unit, have been synthesized. Two [2]rotaxanes (9 · 4 PF6 and 12 · 4 PF6) have been prepared by interlocking these dumbbell-shaped compounds (8 and 11) with a bipyridinium-based tetracationic cyclophane (15 · 4 PF6) - namely, cyclobis(paraquat-p-phenylene). A [3]rotaxane (10 · 8 PF6) incorporating two cyclophane components (15 · 4 PF6) was also obtained when the 9,10-dioxyanthracene-containing dumbbell-shaped compound (8) incorporating two 1,4-dioxybenzene recognition sites was employed. The 1H-NMR spectroscopic investigation of the [2]rotaxanes (9 · 4 PF6 and 12 · 4PF6) revealed that the cyclophane component encircles one of the two 1,4-dioxybenzene recognition sites in the 9,10-dioxyanthracene-containing [2]rotaxane (9 · 4 PF6) and the 2,6-dioxyanthracene unit in the other [2]rotaxane (12 · 4 PF6). These structures have been confirmed by UV/Vis and electrochemical experiments. Comparison with the spectroscopic properties of simple model compounds shows the presence of electronic interactions which lead to (i) the occurrence of very efficient energy transfer processes in the dumbbell-shaped components and (ii) perturbations in the absorption spectra with appearance of two charge-transfer absorption bands and complete luminescence quenching in the [2]rotaxanes. For the 2,6-dioxyanthracene-containing [2]rotaxane (12 · 4 PF6), it has been demonstrated that the cyclophane can be displaced from the dioxyanthracene to the 1,4-dioxybenzene station upon electrochemical oxidation.
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  • 83
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    Liebigs Annalen 2000 (2000), S. 627-631 
    ISSN: 1434-193X
    Keywords: Complex nucleoside ; Antibiotics ; Radicals ; Zn-Cu couple ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Homosinefungin 5, which can be considered as an analogue of S-adenosylmethionine (SAM) and of S-adenosylhomocysteine (SAH), has been synthesized by means of a sequence in which the key step was the addition of a radical, produced by the simple treatment of an iodide precursor with a zinc-copper couple, to suitably activated olefins.
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  • 84
    ISSN: 1434-193X
    Keywords: Amide linkage ; Phosphodiester ; Hammerhead ribozyme ; Oligonucleotides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A nucleoside dimer in which the natural phosphodiester bond is replaced by an isosteric amide linkage has been prepared. This dimer analogue was subsequently incorporated chemically at the cleavage position of a hammerhead ribozyme substrate. Although the resulting substrate analogue exhibited a high affinity for the ribozyme as shown by gel retardation assays, the amide bond proved to be fully resistant to cleavage under standard conditions of ribozyme cleavage activity.
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  • 85
    ISSN: 1434-193X
    Keywords: Solid-phase synthesis ; Wang resin ; Hetero Diels-Alder reactions ; Dihydropyrans ; Reductive reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The OH groups of Wang resin were esterified with benzylidenepyruvic acid (1) to give the immobilized 1-oxabutadiene 2. The latter reacted with vinyl ethers 3a-h (dienophiles) in the presence of Eu(fod)3, and the resulting adducts 4a-h underwent reductive cleavage with LiAlH4 to afford the dihydropyrans 5a-h in high (62 to 100%) overall yields. A similar sequence carried out under conventional homogeneous liquid phase conditions led to significantly lower yields. The endo/exo selectivity of the cycloaddition reaction was the same in both cases.
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  • 86
    ISSN: 1434-193X
    Keywords: Cationic amphiphiles ; Transfection ; Pyridinium salts ; Vesicles ; Lipoplex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Pyridinium amphiphiles have found practical use for the delivery of DNA into cells. Starting from 4-methylpyridine, a general synthesis has been devised for the production of pyridinium amphiphiles which allows variation in both the hydrophobic part and in the headgroup area of the compounds. By means of differential scanning microcalorimetry, zeta potential, particle size measurements and cryo electron microscopy, some characteristics of the pyridinium amphiphile/DNA complexes have been determined.
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  • 87
    ISSN: 1434-193X
    Keywords: Pauson-Khand reaction ; Cyclopentenones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---1-Methyl-norbornene ester 9 and 1-methyl-2,3-diazabicyclo[2.2.1]heptene ester 10 were employed in intermolecular Pauson-Khand reactions with various terminal alkynes 11a-f to give the dimethyl 1-methyltricyclo[5.2.1.05,9]dec-7-en-6-one 2,3-dicarboxylates 12 and 13, and diethyl 2,3-diaza-1-methyltricyclo[5.2.1.05,9]dec-7-en-6-one 2,3-dicarboxylates 14 and 15, respectively. Whereas the co-cyclization of norbornene 9 with alkynes 11 bearing small substituents R resulted in the preferred formation of 12 (12:13 ≤ 85:15), regioisomer 13 was obtained as the major product when sterically bulky alkynes were employed (12:13 ≥ 6:94). For 2-methyl-3-butyn-2-ol 11e a strong temperature dependency of the regioselectivity was found. The ratio of regioisomers (12e:13e) changed from 95:5 at -25 °C to 12:88 at 120 °C in toluene. In contrast, reactions with 2,3-diazanorbornene 10 showed only moderate regioselectivities in favour of 14 (14:15 ≤ 69:31), regardless of the temperature and the size of R. The observed regioselectivities support a mechanism for the Pauson-Khand reaction in which the apical rather than the basal anti oriented carbon monoxide ligand of cobalt alkyne complex 1 is replaced by the alkene.
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  • 88
    ISSN: 1434-193X
    Keywords: Reverse-turn mimics ; γ-Turns ; β-Turns ; β-Hairpins ; Peptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Conformational analysis of N-acetylated hexapeptide mimics incorporating a bicyclic lactam (1-4) was carried out by a combination of 1H-NMR spectroscopy, IR spectroscopy, and computer modeling. The nature of the bicyclic lactam determines the turn motifs and the folding patterns of these constrained peptides. The (5,6)-bicyclic lactam derivatives 1 and 2, characterized by a type-II' β-turn (C=O3···H6-N), are very compact intramolecularly H-bonded structures. The (5,7)-bicyclic lactam derivative 3, characterized by an inverse γ-turn (C=O4···H6-N), is a quite flexible “tweezer-like” structure.
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  • 89
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 707-711 
    ISSN: 1434-193X
    Keywords: Radical reactions ; Photolysis ; X-ray scattering ; Rearrangements ; Semiempirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The previously reported tandem cyclisation of N-aryl α-(2-cyanophenyl)sulfanyl imidoyl radicals affords one quinoxaline derivative arising from exclusive 1,6-cyclisation of the final iminyl radical onto the N-aryl ring. When the imidoyl radicals are generated by addition of photolytically generated (2-cyanophenyl)sulfanyl radicals to isocyanides, the reaction also gives small amounts of a by-product that is formed by an analogous route and whose X-ray crystallographic data are reported here. The formation of this product entails a rare ortho-selective photo-Fries rearrangement of the starting disulfide, followed by addition to the isocyanide and regioselective 1,5-cyclisation of the resulting imidoyl onto only one of the two available radical acceptors, i.e. the cyano group and the sulfide moiety. Semiempirical MNDO-d calculations were performed in order to throw some light on the factors affecting these competitive cyclisations.
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  • 90
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 713-721 
    ISSN: 1434-193X
    Keywords: Reductive alkylation ; Acenaphthylenes ; Carbanions ; Polycycles ; Single-electron transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Reaction of the 5-hydroacenaphthylene anion with benzyl halides proceeds at carbon atom 1 as well as at carbon atom 2a, in the latter case creating a quaternary centre. The hardness-softness of the electrophiles was shown to play only a minor role in determining the regioselectivity of the reaction of the hydroanion with several benzyl and alkyl halides: the leaving group hardly affects the ratio of 1- and 2a-substituted products. This indicates that the alkylation might proceed by an electron transfer (SET) instead of an SN2 mechanism. Further evidence for SET was obtained by the use of free radical and electron scavengers. The substitution products 1-benzylacenaphthene and 2a-benzyl-2a,5-dihydroacenaphthylene could be isolated and purified.
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  • 91
    ISSN: 1434-193X
    Keywords: Isotopic labeling ; Isotopic labeling ; Isotopic labeling ; Deuterium ; Carbon-13 ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Three selectively labeled propynes were prepared either with deuterium or carbon-13 at position 3 and doubly labeled with carbon-13 at positions 1 and 2 by an alkylation reaction from the corresponding labeled or unlabeled monolithio acetylides and dimethylsulfates. Their lithiation with nBuLi gave the corresponding propynyllithium derivatives which reacted with dimethyl squarate to afford the corresponding propargylic alcohols. These were thermolysed in p-xylene to furnish [5-D3-methyl]-, [5-13C-methyl]-, and [5,6-13C2-2,5-cyclohexadienyl]ubiquinone. The farnesyl side chain was introduced onto the labeled quinones with farnesyl trimethyltin under BF3 catalysis to provide [5-D3-methyl]-, [5-13C-methyl]-, and [5,6-13C2-2,5-cyclohexadienyl]ubiquinone 3 (6c, 6b, 6a, respectively).
    Additional Material: 1 Ill.
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  • 92
    ISSN: 1434-193X
    Keywords: Tetrathiafulvalenes ; Charge transfer ; UV/Vis spectroscopy ; Cyclic voltammetry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---4-[2-tetrathiafulvalenyl-ethenyl]pyridine (1) has been prepared from a Wittig reaction between formyltetrathiafulvalene and 4-picolyltriphenylphosphonium chloride hydrochloride. Conversion of the pyridine moiety of 1 by reaction with methyl iodide leads to 4-[2-tetrathiafulvalenyl-ethenyl]-1-methylpyridinium iodide (2a). Neutralization of 1 with a large excess of L-tartaric acid affords 4-[2-tetrathiafulvalenyl-ethenyl]-1-methylpyridinium hydrogen tartrate (3). These TTF-π-spacer-acceptor compounds have been characterized by elemental analysis, and IR and 1H NMR spectroscopy. The crystal structure of 2a has been determined by X-ray diffraction. The cation is essentially planar. Examination of the bond lengths in 2a, UV/Vis spectra and CV data, and calculations indicate that an intramolecular charge transfer occurs in the studied compounds, although it is rather limited, and larger in 2a and 3 than in 1.
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  • 93
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 807-811 
    ISSN: 1434-193X
    Keywords: Proline analogues ; Asymmetric synthesis ; Schöllkopf's method ; Silicon ; Amino acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The asymmetric synthesis of a new proline surrogate, incorporating the dimethylsilyl group at position 4 of proline using Schöllkopf's bis-lactim ether method, is described.
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  • 94
    ISSN: 1434-193X
    Keywords: Bisdiazenes ; Homoconjugation ; Photochemistry ; Heterocycles ; Diazenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Rigid N=N/N=N (diazene/diazene) systems (F) consisting of more or less alkylated DBH and DBO chromophoric units (1, 2, X-ray structures), with very short π,π distances [d = 2.849 (1a, av.), 2.822 Å (2)] and almost perfect syn-periplanar π,π alignments [ω = 168.6 (1a), 174.2° (2)] as well as the more flexible, less “proximate” metathesis isomers (3a,c, 27a,c, d 〉4.6 Å, ω = 90-100°) have been synthesized. Homoconjugate π,π interaction (in 1, 2, not in 3, 27) is deduced from UV spectroscopic measurements [π → π* maxima at 239 (234) nm (sh, 260)], while PE analyses furnished only small interaction parameters (1a: 〈0.3 eV). The potential of the novel syn-periplanar N=N/N=N motif in 1 and 2 for the synthesis of somewhat exotic polyheterocycles has been explored by calculation (B3LYP) as well as experimentally: i.a. kinetically stabilized, all-cis-peralkylated tetrazolidines (38, 44) and perhydro-1,2,4,5-tetrazines (41, 47) have become accessible (i.a. via novel azomethine/diazene and azomethine/azomethine cycloadditions). In 1a with its unreactive DBO chromophoric subunits, in the “buttressed” derivatives 1b-d, as well as in the DBH/DBO combination 2, and likewise in more ‘distant’ 27 (differently from the analogous C=C/C=C and N=N/C=C systems), irrespective of the excitation conditions employed (light of λ ≥≥ 280, 254 nm, low temperature matrix irradiation, acetone sensitization) no [2+2]photocycloaddition was observed. Instead exclusively N2-elimination took place. It is argued that unproductive N=N/N=N photocycloaddition would have become observable through metathesis isomerization of the respective tetrazetidines.
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  • 95
    ISSN: 1434-193X
    Keywords: Photochemistry ; Heterocycles ; Diazenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Of two very proximate syn-periplanar bisdiazenes (1,2) mono-, di-, tri- and tetra-N-oxides were prepared, representing six combinations of the individual N=N/N=NO/ON=NO chromophores. According to DFT calculations (B3LYP/6-31G*), [2+2]photocycloaddition to the respective oxidized tetrazetidines is significantly to moderately endothermic. The metathesis isomerization of the oxidized tetrazetidines is generally highly exothermic and kinetically increasingly favorable with increasing oxidation state. In practice, four out of the six bichromophoric combinations undergo selectively, in competition with N2 elimination from a DBH unit (13) still partially, metathesis isomerization upon π → π* excitation (monochromatic 254 nm light). In the case of the syn-N=NO/N=NO combinations (5/6, 14), the photoaddition is thermally reversed. For a ON=NO/N=N combination (30), internal electron transfer is responsible for a complex reaction pattern. The preparative value of the metathesis reactions, though, is limited: The metathesis-derived bis[diazene mono(di)oxides] undergo relatively fast secondary photoreactions, while the tri(tetra)oxides undergo rapid thermal transformations. For the N=N/N=NO systems (12), of three potential pathways for its metathesis isomerization, the one that takes place via σ-symmetric intermediates (63, 64) is excluded by virtue of the retention of optical purity in the photometathesis of a highly enriched enantiomer [(-)-12]. Matrix irradiation experiments (12 K, IR control) with 12 result in the appearance of a kinetically highly labile transient. Supported by DFT calculations it is concluded that in the metathesis reactions, the respective tetrazetidine oxides (increasingly destabilized by interactions between oxygen lone pairs and NNσ* orbitals) function as vibrationally excited transients. That thermal reversion of these transients might be a general, nonproductive competition, is suggested by the experimental verification of a “reversed photometathesis” (51 → 15) and by the generally low rates in product formation upon irradiation. The question remains to be answered why in structurally analogous molecular skeletons, [2+2]photocycloaddition occurs in the C=C/N=N and variously oxidized N=N/N=N, and not, however, in the parent N=N/N=N combinations.
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  • 96
    ISSN: 1434-193X
    Keywords: Amphiphiles ; Ketone ; Glycosides ; Electron transfer ; Chiral resolution ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Electroreducible amphiphilic aromatic ketones derived from D-glucose and D-glucofuranurono-6,3-lactone (D-glucurone) have been synthesized by Schmidt condensation and reaction of the unprotected lactone with the appropriate substrates, respectively. The macroscale electrolyses of the glucose derivatives, performed in an aprotic solvent (DMF), yield the pinacols possessing two glycosidic side chains. Under the same conditions of electrolysis with the D-glucurone derivative, the glyosidic carbon-oxygen bond is cleaved. The use of a redox mediator (couple anthracene-•/anthracene) has demonstrated that a glucosidic bond can be reduced by a homogeneous electron transfer. In the presence of a proton donor the expected D-glucuronic pinacol is obtained. The radical-radical coupling involves the formation of two chiral centers. The diastereo- and the enantioselectivity of the reaction have been studied by 1H- and 2H-NMR spectroscopy, respectively.
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  • 97
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 837-840 
    ISSN: 1434-193X
    Keywords: Chiral auxiliaries ; Analytical methods ; Through-space interactions ; Lactic acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The enantiomeric purity of a chiral compound is determined by NMR spectroscopic analysis of the diastereomers formed with a chiral derivatizing agent. Fluorinated O-aryllactic acids (FAC) 1 are efficient chiral reporters, whose spectacular remote anisotropic effects allow an easy identification and measurement of diastereomers. The remote effects are attributed to the particular design of FAC esters relative to other CDAs.
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  • 98
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 849-855 
    ISSN: 1434-193X
    Keywords: Marine alkaloids ; Heterocycles ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Ascididemine (9H-quino[4,3,2-de][1,10]phenanthrolin-9-one) (1) and an isomer (9H-quino[4,3,2-de][1,7]phenanthrolin-9-one) (4) have been synthesized starting from 1,4-dimethoxyacridone (7). The acridone was converted into 1,4-dimethoxy-9-ethynylacridine (11) by a triflate coupling. The ethynylacridine was converted in one-pot into 3H-6-methoxypyrido[2,3,4-kl]acridine (15) by reaction with sodium diformylamide; the mechanism of this key transformation is discussed. Conversion into 6H-4-bromopyrido[2,3,4-kl]acridin-6-one (19) and 6H-pyrido[2,3,4-kl]acridin-6-one (17), followed by reaction of each of these under high pressure conditions with acrolein N,N-dimethylhydrazone, gave ascididemine and its isomer, respectively.
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  • 99
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 861-866 
    ISSN: 1434-193X
    Keywords: DNA ; Dihydroxyacetone monophosphate ; Aldolase ; Carbon-13 ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A synthesis of [3′,4′-13C2]thymidine (1) is described in which [13C2]acetic acid (2) is converted into the nucleoside in twelve steps with 9% overall yield. D-2-Deoxyribose-5-phosphate aldolase (DERA, EC 4.1.2.4) and triosephosphate isomerase (TPI, EC 5.3.1.1) are used for the stereocontrolled formation of D-[3,4-13C2]-2-deoxyribose-5-phosphate (8) from [2,3-13C2]dihydroxyacetone monophosphate (DHAP, 7) and acetaldehyde in 80% yield. The route permits the introduction of isotopically enriched carbon atoms at any position or combination of positions in the furanose ring and the product can be coupled with any of the four naturally occurring base moieties.
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  • 100
    ISSN: 1434-193X
    Keywords: Benzothiazole carbene ; Palladium complex ; Homogeneous catalysis ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The first diiodo palladium complex with nucleophilic benzothiazole carbenes as ligands has been synthesized and characterized. The complex, which is extraordinarily stable towards heat, oxygen, and moisture, has been found to show good catalytic activity in the Heck coupling reaction.
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