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  • 1995-1999  (7,736)
  • 1935-1939  (2,943)
  • General Chemistry  (9,793)
  • Magnetic resonance imaging  (885)
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  • 101
    Electronic Resource
    Electronic Resource
    Clinical outcome and magnetic resonance imaging of carbon monoxide intoxication. A long-term follow-up study (1999)
    Springer
    Italian journal of neurological sciences 20 (1999), S. 171-178 
    Details
    ISSN: 1126-5442
    Keywords: Key words Carbon monoxide poisoning ; Delayed neurologic sequelae ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The clinical and neuroradiological outcome of carbon monoxide (CO) intoxication was evaluated prospectively in 30 patients over a follow-up period of 3 years. Among the patients studied, 22 had been acutely exposed to CO while 8 were chronically exposed. One month after CO poisoning, 12 of the 22 patients with acute intoxication showed magnetic resonance imaging (MRI) abnormalities: 6 also had neurological sequelae and 6 were asymptomatic. The remaining 10 patients showed neither MRI abnormalities nor neurological sequelae. During the 3-year follow-up, 4 of the patients with both MRI abnormalities and neurological sequelae improved in both clinical features and MRI findings. One of the 6 asymptomatic patients with MRI abnormalities developed a progressive cognitive impairment 2 months after acute intoxication, with a concomitant severe worsening of the MRI lesions. Among the 10 patients with neither MRI abnormalities nor neurological sequelae, only 1 developed neurological sequelae after a clear period of 4 months. In the group of patients who experienced chronic CO intoxication, only 1 presented with a neuropsychiatric syndrome which improved at follow-up. Brain MRI showed white matter lesions which remained unchanged at control scan after 1 year. In conclusion, we observed that some patients with severe CO poisoning and neurological sequelae may fully regain normal functions after approximately 1 year. The presence of MRI lesions 1 month after CO poisoning did not accurately predict the subsequent outcome. The observation of a clear period longer than the usual 2–40 day interval in 2 patients should be considered for careful planning of follow-up and for prognosis in CO-poisoned patients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100720050028
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  • 102
    Electronic Resource
    Electronic Resource
    Optic neuropathy in Behçet's disease. Report of two cases (1999)
    Springer
    Italian journal of neurological sciences 20 (1999), S. 183-186 
    Details
    ISSN: 1126-5442
    Keywords: Key words Behçet's disease ; Optic neuropathy ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Orbital magnetic resonance imaging demonstrated increased signal of the optic nerve in short time inversion recovery (STIR) images of two young women with unilateral visual blurring. In both, recurrent oral and genital ulcerations and papulopustular lesions appeared within the next 14–15 months, respectively, allowing a diagnosis of Behçet's disease. Optic neuropathy may be an early manifestation of Behçt's disease and clinical follow-up is crucial for its diagnosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100720050030
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  • 103
    Electronic Resource
    Electronic Resource
    Radiation-induced rhombencephalopathy (1999)
    Springer
    Italian journal of neurological sciences 20 (1999), S. 55-58 
    Details
    ISSN: 1126-5442
    Keywords: Key words Rhombencephalopathy ; Radionecrosis ; Magnetic resonance imaging ; Hyperbaric oxygen ; Heparin ; Buspirone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We report the case of a patient who underwent radiotherapy of the neck because of an epidermoid carcinoma in Rosenmüller's fossa. Eleven months later, T1-weighted brain magnetic resonance imaging (MRI) revealed a bulbo-pontine lesion, and the clinical course and sequential MRI results led to a diagnosis of radionecrosis-induced rhombencephalopathy. At a distance of more than three years, the lesion is no longer visible on MRI images but the severe neurological deficits remain. The clinical picture has not been improved by treatment with prednisone, hyperbaric oxygen, symptomatic therapies or anticoagulants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100720050011
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  • 104
    Electronic Resource
    Electronic Resource
    Psychiatric symptoms as late onset of Wilson's disease: neuroradiological findings, clinical features and treatment (1999)
    Springer
    Italian journal of neurological sciences 20 (1999), S. 49-54 
    Details
    ISSN: 1126-5442
    Keywords: Key words Hepatolenticular degeneration ; Affective disorders ; Magnetic resonance imaging ; Antidepressive agents ; Interpersonal psychotherapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We describe a case of Wilson's disease with late psychiatric onset. Major depressive disorder was the first clinical manifestation at the age of 38 years. After pharmacotherapy with antidepressive agents, a manic episode was oberseved. Extrapyramidal hand tremor and micrography were the first neurological signs. Emotional lability occurred during worsening of extrapyramidal signs. Diagnosis was based on urinary and serum copper levels, ceruloplasmin serum level, Kayser-Fleischer ring, and liver biopsy that detected cirrhosis. Magnetic resonance imaging revealed basal ganglia hyperintensity on T1-weighted images, and hypodensity in the central part and hyperintensity in the peripheral part of the lentiform nucleus on 72-weighted images. Hyperintensity on T2-weighted images was also observed in the dorsal part of the midbrain. 123I-iodobenzamide single photon emission computed tomography (IBZM-SPECT) detected a normal distribution of the drug in the brain, with better signal in the right side and deficit of D2-dopaminergic receptors in the basal ganglia, Abnormal manganese erythrocyte level was observed. Treatment was based on penicillamine, zinc salts, low-copper diet, antidepressant agents, interpersonal psychotherapy and neurorehabilitation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100720050010
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  • 105
    Electronic Resource
    Electronic Resource
    Die spontane intrazerebrale Blutung aus klinisch- neuroradiologischer Sicht (1999)
    Springer
    Der Radiologe 39 (1999), S. 828-837 
    Details
    ISSN: 1432-2102
    Keywords: Schlüsselwörter Zerebrovaskuläre Erkrankungen ; Intrazerebrale Blutung ; Magnetresonanztomographie ; Computertomographie ; Key Words Cerebrovascular diseases ; Intracerebral hemorrhage ; Magnetic resonance imaging ; Computed tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Intracerebral hemorrhage is a common cause of acute neurological deterioration and a frequent indication for emergency neuroimaging. Stroke symptoms are caused in 10 to 15% by intracerebral hemorrhage. It is often not possible to differentiate intracerebral hemorrhage from cerebral ischemia by clinical examination. The therapeutic decision between thrombolysis or conservative therapy is comprised by the etiology. To exclude intracerebral hemorrhage as the cause of clinical symptoms, a CT is usually performed. Localisation and extension of the acute intracerebral hemorrhage are easy to detect. Subacute and chronic intracerebral hemorrhage are better delineated with magnetic resonance imaging. The different signal of the hemorrhage can be used for the age of the intracerebral hemorrhage. The cause of a non-traumatic intracerebral hemorrhage is in over 60% hypertony, less frequent alcoholism, malformation, or amyloid angiopathy. Uncommon causes of hemorrhage are head trauma, blood dyscrasia, tumor or venous thrombosis. Non-traumatic intracerebral hemorrhage are most common in patients between 50 and 70 years. In younger patients a malformation should be excluded with a cerebral angiography. Intracerebral hemorrhages are usually conservatively treated, in some cases an operative decompression is performed.
    Notes: Zusammenfassung Die intrazerebrale Blutung ist eine häufige Ursache akut auftretender neurologischer Symptome und führt oft zu einer notfallmäßigen neuroradiologischen Untersuchung. Etwa 15% der „Schlaganfälle” sind auf eine intrazerebrale Blutung zurückzuführen. Intrazerebrale Blutungen sind klinisch oft nicht von ischämischen Infarkten zu unterscheiden. Eine Computertomographie ist zur Zeit für die Diagnosesicherung – und damit auch zur weiterführenden Therapie – unerläßlich. Ausdehnung und Lokalisation der akuten intrazerebralen Blutung können damit schnell und sicher erfaßt werden. Subakute und chronische Blutungen sind dagegen verläßlicher mit der Magnetresonanztomographie nachweisbar. Aus der unterschiedlichen Signalgebung in den verschiedenen MR-Sequenzen kann auf das Alter der Blutung geschlossen werden. Die Ursache einer nicht-traumatischen intrazerebralen Blutung ist in über 60% der Fälle eine Hypertonie, weniger häufig die Folgen des Alkoholismus, Gefäßfehlbildungen oder die Amyloidangiopathie. Seltener sind Blutgerinnungsstörungen, Traumen, Tumoren, Venenthrombosen oder Intoxikationen die Ursachen einer intrazerebralen Blutung. Nicht-traumatische intrazerebrale Blutungen treten am häufigsten zwischen dem 5.–7. Lebensjahrzehnt auf. Bei jüngeren Patienten sind vor allem Gefäßfehlbildungen als Ursache zu berücksichtigen. Insbesondere bei jüngeren Patienten sollte zur ätiopathogentischen Klärung eine zerebrale Angiographie durchgeführt werden. Spontane intrazerebrale Blutungen werden in der Regel konservativ behandelt, außer man verspricht sich von der operativen Dekompression eine Verbesserung des klinischen Zustandes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001170050719
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  • 106
    Electronic Resource
    Electronic Resource
    Die intrazerebrale Blutung im Rahmen der Amyloidangiopathie (1999)
    Springer
    Der Radiologe 39 (1999), S. 847-854 
    Details
    ISSN: 1432-2102
    Keywords: Schlüsselwörter Zerebrale Amyloidangiopathie ; Intrazerebrale Blutung ; Computertomographie ; Kernspintomographie ; Key words Cerebral amyloid angiopathy ; Intracerebral hemorrhage ; Computed tomography ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary The purpose of our study was to evaluate the characteristic findings of acute hemorrhage due to amyloid angiopathy with computed tomography. 14 patients of intracranial hemorrhage with histologically confirmed cerebral amyloid angiopathy were observed over a period of 4 years. Characteristic findings were a lobar hemorrhage in superficial localisation, cortical involvment, subarachnoid hemorrhage, the multiplicity of hemorrhages and repeated episodes. Severe cerebral amyloid angiopathy is often accompanied by multiple petechial hemorrhages, restricted to a cortical-subcortical distribution, detectable by magnetic resonance imaging. These findings suggest that cerebral amyloid angiopathy is not a rare cause of atraumatic lobar hemorrhage. Amyloid angiopathy should be considered in any elderly patient with superficial intracerebral hemorrhage in an atypical location.
    Notes: Zusammenfassung In der Arbeit werden die computertomographischen Befunde der intrazerebralen Blutung im Rahmen der Amyloidangiopathie untersucht. 14 Patienten mit Massenblutung und histologisch bestätigter Amyloidangiopathie wurden in einem Zeitraum von 4 Jahren beobachtet. Charakteristische Befunde waren eine lobäre, oberflächlich gelegene Blutung, eine kortikale Beteiligung, eine begleitende Subarachnoidalblutung sowie ein mehrfaches und mehrzeitiges Auftreten der Blutungen. Eine schwere Amyloidangiopathie geht oft mit multiplen petechialen Blutungen in kortiko-subkortikaler Lokalisation einher, die sich kernspintomographisch nachweisen lassen. Die Befunde zeigen, daß die Amyloidangiopathie keine seltene Ursache einer nicht traumatischen lobären Blutung ist. Sie sollte daher bei jedem älteren Patienten mit einer intrazerebralen, oberflächlich gelegenen Blutung in atypischer Lokalisation in Betracht gezogen werden.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001170050721
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  • 107
    Electronic Resource
    Electronic Resource
    Radiologisches Staging von thorakalen und abdominalen Tumoren im Kindesalter (1999)
    Springer
    Der Radiologe 39 (1999), S. 538-545 
    Details
    ISSN: 1432-2102
    Keywords: Schlüsselwörter Staging thorakoabdominaler Tumoren ; Kinder ; Computertomographie (CT) ; Magnetresonanztomographie (MRT) ; Malignome ; Key words Staging of tumors ; Thoracoabdominal tumors ; Childhood ; Computed tomography ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Thoracoabdominal tumors in childhood can arise from all organs and affect children from the neonate to the adolescent. Better prognosis of childhood tumors, due to better biological understanding and improvement of chemotherapy, require sufficient radiological staging. Sufficiency in radiological staging needs modern cross-sectional techniques with high resolution, good availability and lower radiation dose. In general computed tomography (CT) is being used for radiological staging; increasingly MR imaging is being used because of multiplanar imaging techniques. Replacement of invasive techniques such as myelography and lymphography and modern cross-sectional techniques create painless staging conditions. Nevertheless, scintigraphy will always be a major examination technique, especially for evaluation of metastases and postoperative control examinations. The most common thoracoabdominal tumors in childhood and their staging are described.
    Notes: Zusammenfassung Thorakale und abdominale Tumoren im Kindesalter nehmen ihren Ausgang von allen Organsystemen und können vom Neugeborenen bis zum Adoleszenten auftreten. Verbesserte Prognose, bedingt durch das bessere biologische Verständnis der Tumorerkrankung, sowie der effiziente Einsatz von Chemotherapeutika machen ein radiologisches Staging unumgänglich. Üblicherweise wird zum Staging die Computertomographie (CT) eingesetzt. Durch die Möglichkeit der multiplanaren Schnittführung und die bessere Auflösung bei Tumoren mit Beteiligung des ZNS wird in zunehmendem Maße die Magnetresonanztomographie (MRT) eingesetzt. Diese modernsten Schnittbildverfahren haben invasive Methoden wie Lymphographie und Angiographie in den Hintergrund gedrängt. Im weiteren werden die häufigsten thorakalen und abdominalen Tumoren im Kindesalter besprochen und deren Stagingsysteme erläutert.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001170050548
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  • 108
    Electronic Resource
    Electronic Resource
    Präoperatives Staging des Kolorektalen Karzinoms (1999)
    Springer
    Der Radiologe 39 (1999), S. 562-567 
    Details
    ISSN: 1432-2102
    Keywords: Schlüsselwörter Kolorektales Karzinom ; Präoperatives Staging ; Endosonographie ; CT ; MRT ; Key words Colorectal cancer ; Preoperative staging ; Endosonography ; Computed tomography ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Carcinoma of the colorectum is one of the most frequent neoplasias, with an incidence of 40 in 100 000. For the effective use of new, differentiated, less invasive treatment options, exact preoperative staging of the tumor is essential. The introduction of endosonography in rectal tumor staging allows for exact differentiation of the rectal wall layers and thus of tumor stages 1–3 with median accuracy of 89%. Magnetic resonance imaging of the rectum, especially in double-contrast technique, can also be employed in high and stenosing tumors and leads to an average accuracy of 85% for the stages 1–4. Computed tomography is the method of choice in screening for metastases. In lymph node staging, all modalities show only moderate accuracy around 75%.
    Notes: Zusammenfassung Das kolorektale Karzinom stellt mit einer Inzidenz von 40 auf 100000 eine der häufigsten Neoplasien dar. Für den effektiven Einsatz neuer differenzierter Therapien mit geringerer Invasivität ist ein exaktes präoperatives Staging erforderlich. Die Einführung der Endosonographie im Tumorstaging erlaubt eine exakte Differenzierung der Wandschichten und damit der Tumorstadien 1–3 mit einer mittleren Genauigkeit von 89%, die Magnetresonanztomographie des Rektums, insbesondere in Doppelkontrasttechnik, kann auch bei hohen und stenosierenden Tumoren angewendet werden, bei einer Genauigkeit von durchschnittlich 85% für die Stadien 1–4. Die Computertomographie ist Methode der Wahl im Metastasenscreening. Im Lymphknotenstaging zeigen alle Modalitäten nur bescheidene Genauigkeiten um 75%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001170050551
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  • 109
    Electronic Resource
    Electronic Resource
    Das kernspintomographische Erscheinungsbild der spontanen intrazerebralen Blutung (1999)
    Springer
    Der Radiologe 39 (1999), S. 838-846 
    Details
    ISSN: 1432-2102
    Keywords: Schlüsselwörter Intrazerebrale Blutung ; Kernspintomographie ; MR-Angiographie ; Key words Intracerebral hematoma ; Magnetic resonance imaging ; Magnetic resonance angiography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary We review the signal characteristics of intracerebral hematomas (ICH) on magnetic resonance imaging (MRI), with special emphasis on the diagnosis of intracerebral hemorrhage within the first hours after stroke. The detection of peracute ICH was evaluated in 42 patients of a prospective, MR randomized stroke trial. These patients underwent a protocol of T1 and T2 weighted sequences, diffusion weigthed sequences and MR – angiography within 6 hours after onset of acute hemiparesis. The signal behaviour of ICH in any stage after bleeding was additionally reviewed in a retrospective series of 63 patients, who were submitted for MRI over a 12 months period because of known ICH. MRI correctly identified 4 hyperacute ICH in the prospective group and 4 hyperacute ICH in the retrospective group. These ICHs had high signal on T2 weighted images, were isointense in T1 weighted images and had signal voids on the diffusion weighted sequences. The signal intensities of acute, subacute and chronic ICHs correlated to previous experiences as reported in the literature. In conclusion, MRI reliably identified all hematomas even in the hyperacute stage. Diffusion weighted images were most sensitive to the presence of deoxyhemoglobine and helpful for the differentiation and characterization of acute ischemia. Therefore, MRI at 1.5 T can be employed as an alternative to CT for the emergency diagnosis of acute stroke.
    Notes: Zusammenfassung In dieser Übersicht wird das kernspintomographische (KST) Erscheinungsbild der intrazerebralen Blutung (IZB) anhand eigener Erfahrungen und der Literatur diskutiert. Besonderes Gewicht wurde auf den KST Nachweis der hyperakuten IZB innerhalb der ersten Stunden gelegt. Es wurden einerseits die Befunde von 42 Patienten einer prospektiven, KST randomisierten Schlaganfallstudie ausgewertet, bei denen die KST als Erstuntersuchung innerhalb von 6 Stunden durchgeführt worden war. Andererseits werteten wir retrospektiv jene KST Untersuchungen aus, die im Jahr 1998 unter der Fragestellung einer IZB (n=63) erfolgten. Die KST erwies sich als sensitiv im Nachweis auch der hyperakuten IZB. Es wurden weder falsch-negative noch falsch-positive Befunde erhoben. Die hyperakute IZB kommt in der T2-Gewichtung hyperintens und in der T1-Gewichtung isointens zur Darstellung. Auf den diffusionsgewichteten Sequenzen führen minimale Deoxyhämoglobinkonzentrationen bereits in dieser Phase zu Signalauslöschungen. Das Erscheinungsbild der akuten, subakuten und chronischen IZB entsprach dem, in der Literatur mitgeteilten, Signalverhalten. Zusammenfassend waren alle IZB, unabhängig vom Stadium in der KST nachweisbar. Die Diffusionsgewichtung war in der hyperakuten Blutungsdiagnose und deren Abgrenzung von der akuten Ischämie hilfreich. Zumindest bei 1,5T erscheint die KST somit für die Diagnostik des akuten Schlaganfalls geeignet und sollte, da Ischämien besser als mit der Computertomographie charakterisiert werden können, für die Akutdiagnostik verfügbar gemacht werden.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001170050720
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  • 110
    Electronic Resource
    Electronic Resource
    Vergleich der Wertigkeit der Computertomographie und der Magnetresonanztomographie in der Diagnostik der akuten intrazerebralen Blutung (1999)
    Springer
    Der Radiologe 39 (1999), S. 855-859 
    Details
    ISSN: 1432-2102
    Keywords: Schlüsselwörter Schlaganfall ; Intrazerebrale Blutung ; Magnetresonanztomographie ; Computertomographie ; Ratten ; Key words Cerebrovascular diseases ; Intracerebral hemorrhage ; Magnetic resonance imaging ; Rats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Background and Purpose: Stroke symptoms are caused in 10 to 15% by intracerebral hemorrhage. From the clinical examination it is often impossible to differentiate intracerebral hemorrhage from cerebral ischemia. To exclude intracerebral hemorrhage as the cause of clinical symptoms a CT is usually performed. The aim of our study was a direct comparison of the sensitivity of Computed Tomography and MRI using different MR sequences for the detection of acute intracerebral hemorrhage. Methods: In 8 male Wistar rats intracerebral hemorrhage was induced by infusion of collagenase into the caudate nucleus. After 1hour the brains were subsequently imaged with CT and MRI using T2- and T1-weighted Spin Echo sequences, diffusion-weighted sequences, T2*-weighted gradient echo sequences and FLAIR-sequences. Visibility of the intracerebral hemorrhage was examined using a scoring system from 1=not visible to 5=excellent visible. Finally, the intracerebral hemorrhage was verified by histological staining. Results: In all animals, intracerebral hemorrhage was visible in T2*-weighted gradient echo and diffusion weighted MR images 1 h after infusion of collagenase. T2- and PD-weighted SE images were positive in 7/8 rats. T1-weighted images revealed signal changes in 5/8 rats, and FLAIR sequence was positive in 8/8 rats. In CT intracerebral hemorrhage was only visible in 3/8 rats. When measuring the increase of Hounsfield units within the suspected hemisphere we saw a mean increase of 7% compared to the normal hemisphere in 3/8 rats. Conclusions: In this animal model, T2*-weighted magnetic resonance imaging proved to be the most sensitive imaging modality in the detection of acute intracerebral hemorrhage and is by far more sensitive than CT.
    Notes: Zusammenfassung Hintergrund und Ziel: Die Symptome eines Schlaganfalls sind in 10 bis 15% durch eine intrazerebrale Blutung verursacht. Oft ist es in der klinischen Untersuchung nicht möglich, zwischen einer intrazerebralen Blutung und einer zerebralen Ischämie zu differenzieren. Um eine intrazerebrale Blutung bei Schlaganfallsymptomatik auszuschließen, wird in der Regel zuerst eine Computertomographie (CT) durchgeführt. Ziel der vorliegenden Studie ist ein direkter Vergleich der Sensitivität der CT mit verschiedenen magnetresonanztomographischen (MR) Sequenzen in der Diagnostik der akuten intrazerebralen Blutung. Material und Methoden: Durch intrazerebrale Applikation von Kollagenase wurde bei 8 männlichen Wistar-Ratten eine intrazerebrale Blutung im linken Nucleus caudatus induziert. Nach einer Stunde wurden die Gehirne zunächst im CT und direkt anschließend in einem klinischen MR-Tomographen unter Verwendung von Protonendiche-, T2- und T1-gewichteten Spinechosequenzen, T2*-gewichten Gradientenechosequenzen, FLAIR-Sequenzen sowie diffusions- und perfusionsgewichteten Gradientenechosequenzen untersucht. Die Visibilität der Blutung wurde anhand einer Skala von 1 (=nicht sichtbar) bis 5 (=klar sichtbar) bewertet. Die Größe der Blutungsherde wurde für jede Untersuchungstechnik bestimmt und mit der Histologie verglichen. Ergebnisse: Bei allen Tieren konnte die Blutung in den T2*-gewichteten Gradientenecho-, FLAIR- sowie diffusionsgewichteten MRT-Bildern 1 h nach Kollagenaseinfusion erkannt werden. Auch in den T2- und Protonendichte-gewichteten Bildern konnte die Blutung bei 8/8 Ratten erkannt werden, wohingegen sie in den T1-gewichteten Aufnahmen nur bei 5/8 Ratten zu erkennen war. In der CT war die intrazerebrale Blutung nur bei 3/8 Ratten sichtbar, wobei bei diesen Tieren eine Zunahme der Dichte in Hounsfield-Einheiten (HE) in der Läsion um 15% auftrat. Schlußfolgerung: In dem verwendeten Tiermodell erwiesen sich T2*-und diffusionsgewichtete Aufnahmen sowie FLAIR-Sequenzen als sehr sensitive Methode in der Diagnostik der akuten intrazerebralen Blutung. Sie waren hierbei sensitiver als die CT. Deshalb sollte ein MR-tomographisches Untersuchungsprotokoll zur Diagnostik des akuten Schlaganfalls T2*- und diffusionsgewichtete Sequenzen beinhalten. Hierdurch gelingt eine rasche Unterscheidung zwischen der akuten intrazerebralen Blutung und der Frühphase der zerebralen Ischämie.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001170050722
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  • 111
    Electronic Resource
    Electronic Resource
    Use of vector volume manometry and endoanal magnetic resonance imaging in the adult female for assessment of anal sphincter dysfunction (1999)
    Springer
    Diseases of the colon & rectum 42 (1999), S. 1411-1418 
    Details
    ISSN: 1530-0358
    Keywords: Endoanal ; Magnetic resonance imaging ; Vector volume ; Manometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract PURPOSE: This study compared conventional water-perfused and vector volume anal manometry in female patients with neurogenic fecal incontinence and chronic anal fissure and in healthy female volunteers. We used endoanal magnetic resonance (MR) imaging to measure internal and external sphincter lengths and thicknesses and contrasted these with the manometric findings in the different anorectal conditions. METHODS: One hundred thirty-three female subjects were studied over an eight-month period, including 33 control volunteers, 83 patients with neurogenic fecal incontinence, and 17 patients with chronic anal fissure. Conventional manometry was contrasted with automated vector volume-derived parameters. Endoanal magnetic resonance images were obtained using a previously described internal coil with a 0.5 T Asset™ scanner measuring quadrantal internal sphincter thickness and averaged coronal internal and external sphincter lengths. RESULTS: There was a statistically significant relationship between parameters measured by conventional manometry and those variables derived from vector volume manometry at rest and squeeze. There was no difference in sectorial vector-derived pressures within any anorectal condition and no correlation between quadrantal internal sphincter thickness measurements and sectorial pressures at rest. Patients with chronic anal fissure and neurogenic fecal incontinence had constitutionally shorter superficial and subcutaneous external sphincters than healthy control subjects (P〈0.001). CONCLUSIONS: There is no association between manometric findings and morphologic sphincter measurement; however, the shorter distal external sphincter in patients with fissure might render the lower anal canal relatively unsupported after internal sphincterotomy in the female patient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02235038
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  • 112
    Electronic Resource
    Electronic Resource
    Soft-tissue signs of the upper extremity revisited: radiologic and magnetic resonance imaging correlation (1999)
    Springer
    Emergency radiology 6 (1999), S. 282-289 
    Details
    ISSN: 1438-1435
    Keywords: Key words Radiology ; Computed tomography ; Magnetic resonance imaging ; Soft-tissue sign ; Arm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract More modern imaging techniques allow us to supplement the information available on soft-tissue signs seen on radiographs. This improves our diagnostic capability, as demonstrated here in the upper extremity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s101400050069
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  • 113
    Electronic Resource
    Electronic Resource
    MR imaging of a severe cervical fracture-dislocation after traumatic delivery (1999)
    Springer
    Emergency radiology 6 (1999), S. 143-145 
    Details
    ISSN: 1438-1435
    Keywords: Key words Spinal cord ; Birth injury ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We present the acute MR findings in an infant with a complicated traumatic delivery, asphyxia, spinal cord injury, and a radiographically apparent cervical spine fracture-dislocation. MRI including diffusion-weighted imaging allowed early characterization and localization of the extent of spinal cord injury.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s101400050040
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  • 114
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    Comparative study of transrectal ultrasonography, pelvic computerized tomography, and magnetic resonance imaging in preoperative staging of rectal cancer (1999)
    Springer
    Diseases of the colon & rectum 42 (1999), S. 770-775 
    Details
    ISSN: 1530-0358
    Keywords: Rectal cancer ; Transrectal ultrasonography ; Computerized tomography ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract PURPOSE: The preoperative assessment of rectal cancer wall invasion and regional lymph node metastasis is essential for the planning of optimal therapy. This study was done to determine the accuracy and clinical usefulness of transrectal ultrasonography, pelvic computed tomography, and magnetic resonance imaging in preoperative staging. METHODS: A total of 89 patients with rectal cancer were examined with transrectal ultrasonography (n=89), pelvic computed tomography (n=69), and magnetic resonance imaging with endorectal coil (n=73). The results obtained by these diagnostic modalities were compared with the histopathologic staging of specimens. RESULTS: In staging depth of invasion, the overall accuracy was 81.1 percent (72/89) by transrectal ultrasonography, 65.2 percent (45/69) by computed tomography, and 81 percent (59/73) by magnetic resonance imaging. Overstaging was 10 percent (9/89) by transrectal ultrasonography, 17.4 percent (12/69) by computed tomography, and 11 percent (8/73) by magnetic resonance imaging; and understaging was 8 of 89 (8.9 percent) by transrectal ultrasonography, 12 of 69 (17.4 percent) by computed tomography, and 6 of 73 (8 percent) by magnetic resonance imaging. In staging lymph node metastasis, the overall accuracy rate was 54 of 85 (63.5 percent) in transrectal ultrasonography, 39 of 69 (56.5 percent) in computed tomography, and 46 of 73 (63 percent) in magnetic resonance imaging. The sensitivity was 24 of 45 (53.3 percent) in transrectal ultrasonography, 14 of 25 (56 percent) in computed tomography, and 33 of 42 (78.5 percent) in magnetic resonance imaging; and specificity was 30 of 40 (75.0 percent) in transrectal ultrasonography, 25 of 44 (56.8 percent) in computed tomography, and 13 of 31 (41.9 percent) in magnetic resonance imaging. The accuracy in detection of positive lateral pelvic lymph nodes under magnetic resonance imaging (n=8) was 12.5 percent. The accuracy in detection of posterior vaginal wall invasion was 100 percent in transrectal ultrasonography (n=7) and 100 percent in magnetic resonance imaging (n=3), but 28.5 percent in computed tomography (n=7). CONCLUSIONS: Both transrectal ultrasonography and magnetic resonance imaging with endorectal coil exhibited similar accuracy and were superior to conventional computed tomography in preoperative assessment of depth of invasion and adjacent organ invasion. Because transrectal ultrasonography is a safer and more cost-effective modality than magnetic resonance imaging, transrectal ultrasonography is an appropriate method for preoperative staging of rectal cancer. Further efforts will be needed to provide a better staging of lymph node involvement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02236933
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  • 115
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    Bifocal temporal ganglioglioma (1999)
    Springer
    Neurosurgical review 22 (1999), S. 112-116 
    Details
    ISSN: 1437-2320
    Keywords: Key words Ganglioma ; Brain tumor ; Magnetic resonance imaging ; Epilepsy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The authors present the case of a 33-year-old patient with a bifocal ganglioglioma located in the right superior temporal gyrus. He had a history of tonic–clonic seizures and developed intermittent nausea and vertigo later on. Magnetic resonance imaging showed two distinct, small lesions in the right temporal lobe. Both tumors were removed microsurgically with ultrasound guidance. Intraoperatively, two distinct tumors were found. Histological diagnosis of both tumors was of ganglioglioma WHO II. Postoperatively, the patient was free of symptoms. Bifocal occurrence or the coincidence of two distinct gangliogliomas is a very uncommon finding. So far, it has not yet been reported in benign gangliogliomas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s101430050042
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  • 116
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    Combining steady-state constructive interference and diffusion-weighted magnetic resonance imaging in the surgical treatment of epidermoid tumors (1999)
    Springer
    Neurosurgical review 22 (1999), S. 159-162 
    Details
    ISSN: 1437-2320
    Keywords: Key words Cerebellopontine angle ; Constructive interference in steady-state imaging ; Diffusion-weighted imaging ; Epidermoid tumor ; Magnetic resonance imaging ; Surgical treatment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We describe the usefulness of three-dimen-sional Fourier transformation-constructive interference in steady-state (CISS) imaging and diffusion-weighted imaging (DWI) in the pre- and postoperative magnetic resonance imaging evaluation of intracranial epidermoid tumors. Two surgically proven epidermoid tumors in the cerebellopontine (CP) angle were not identified in conventional T1- and T2-weighted images because of a signal intensity similar to that of cerebrospinal fluid (CSF). CISS images clearly demonstrated displacement of the cranial nerves and a shift caused by a lesion in the cistern, but the signal intensity of the tumor by CISS was not sufficiently different from that of CSF to demonstrate the tumor directly. Using DWI, the tumor in the cistern was shown clearly by its increased signal intensity. Together, CISS and DWI compensated for each other's disadvantages, and this combination was useful in guiding surgical treatment of epidermoid tumors in the CP cistern.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s101430050055
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  • 117
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    Synthesis and physicochemical characterization of a novel precursor for covalently bound macromolecular MRI contrast agents (1999)
    Springer
    JBIC 4 (1999), S. 341-347 
    Details
    ISSN: 1432-1327
    Keywords: Key words Contrast agents ; Gadolinium complexes ; Magnetic resonance imaging ; Relaxivity ; Tetraazamacrocycles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The ligand DOTASA was designed and synthesized in the aim of obtaining a kinetically and thermodynamically stable Gd(III) chelate which, through its uncoordinated carboxylate function, will provide an efficient pathway to couple the complex to bio- or macromolecules without affecting the coordination pattern of DOTA. Furthermore, it allows us to study the influence of an extra carboxylate arm on the parameters determining proton relaxivity in comparison to the commercial agent [Gd(DOTA)(H2O)]–. A combined variable-temperature 17O NMR, EPR and nuclear magnetic relaxation dispersion study on the Gd(III) chelate resulted in k 298 ex=(6.3±0.2)×106 s–1 for the water exchange rate and τ298 R=125±2 ps for the rotational correlation time. The slight increase in both k 298 ex and τ298 R, as compared to those for [Gd(DOTA)(H2O)]–, is attributed to the presence of the extra negative charge. The longer rotational correlation time results in a proton relaxivity of 5.03 mM–1 s–1 for [Gd(DOTASA)(H2O)]2–, which is approximately 30% higher than that for [Gd(DOTA)(H2O)]–. The increased water exchange rate of [Gd(DOTASA)(H2O)]2– has no consequence for proton relaxivity since this latter is exclusively limited by fast rotation for both complexes. However, for slowly rotating macromolecular agents, which contain a covalently coupled DOTASA unit instead of a coupled DOTA, this increased exchange rate will have a significant positive effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050320
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  • 118
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    Contrast agents for magnetic resonance angiographic applications: 1H and 17O NMR relaxometric investigations on two gadolinium(III) DTPA-like chelates endowed with high binding affinity to human serum albumin (1999)
    Springer
    JBIC 4 (1999), S. 766-774 
    Details
    ISSN: 1432-1327
    Keywords: Gadolinium(III) complexes ; Contrast agents ; Magnetic resonance imaging ; Human serum albumin ; Proton relaxation enhancement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: N,N′,N″,N‴ -pentaacetic acid) bearing different substituents for binding to human serum albumin (HSA) are compared. In spite of the structural differences of the recognition synthon and of the residual electric charge, the two chelates display an analogous binding affinity for the serum protein. Upon formation of the adducts with HSA, the exchange rates of the coordinated water appear slowed down by an amount corresponding to ca. 50% of the rates found for the free complexes. The relaxivity of [Gd(BOM)3DTPA (H2O)]2 −  is significantly higher than that of MS-325 either in the free complex or in the macromolecular adduct. Finally, the effect of pH on the stability of the HSA adducts and on the values of their relaxivities has been investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050349
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  • 119
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    Multiple sclerosis: interobserver agreement in reporting active lesions on serial brain MRI using conventional spin echo, fast spin echo, fast fluid-attenuated inversion recovery and post-contrast T1-weighted images (1999)
    Springer
    Journal of neurology 246 (1999), S. 920-925 
    Details
    ISSN: 1432-1459
    Keywords: Key words Multiple sclerosis ; Magnetic resonance imaging ; Disease activity ; Fast spin echo ; Fast fluid-attenuated inversion ; recovery ; Reproducibility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Previous studies have addressed the question of the precision in assessing multiple sclerosis (MS) activity by counting enhancing lesions on gadolinium enhanced brain magnetic resonance imaging (MRI). However, counting the active lesions on serial unenhanced MRI obtained by various pulse sequences has not been yet considered. We compared the interobserver levels of agreement in reporting active MS lesions on serial enhanced and unenhanced MRI to assess whether the use of various unenhanced techniques may change the degree of interobserver measurement reproducibility. Dual-echo conventional spin echo (CSE), dual-echo fast spin echo (FSE), fast fluid-attenuated inversion recovery (FLAIR) and Gd-enhanced T1-weighted brain MRI were obtained from five MS patients at baseline and monthly for 2 months. Six experienced observers independently identified and counted active MS lesions on the two follow-up MRI scans. Active lesions were considered to be all the enhancing lesions and any new or enlarging lesion on enhanced and unenhanced scans. Interobserver levels of agreement were calculated by weighted κ values. Very good agreement was reached only for counting total and new Gd-enhancing lesions. Good agreement was achieved for counting new lesions on the three unenhanced techniques, whereas the agreement for counting enlarging lesions was poor with all the MRI techniques. The level of agreement was significantly heterogeneous for various MRI techniques but not for various lesion sites. These results confirm that counting enhancing lesions is the most reliable method for assessing MS activity, but the use of any of the available unenhanced MRI techniques did not result in different levels of interobserver agreement when reporting new and enlarging MS lesions on serial scans.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004150050483
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  • 120
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    Early diagnosis of dementia: neuroimaging (1999)
    Springer
    Journal of neurology 246 (1999), S. 16-20 
    Details
    ISSN: 1432-1459
    Keywords: Key words Dementia ; Alzheimer’s disease ; Neuroimaging ; Magnetic resonance imaging ; Single photon emission computed tomography ; Atrophy ; Hippocampus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The use of neuroimaging is reviewed in the diagnosis of dementia, especially Alzheimer’s disease (AD). Computed tomography (CT) may be used to exclude other causes of dementia than AD. The finding of cortical or subcortical atrophy on CT or magnetic resonance imaging (MRI) itself does not indicate AD. Hippocampal atrophy on CT/MRI provides a useful early marker, although further longitudinal and neuropathological study is required. CT- and MRI-based measurements of hippocampal atrophy show promise in providing useful diagnostic information for discriminating patients with probable AD from normal elderly individuals. Using a standardized imaging protocol, including some assessment of hippocampal atrophy, can save costs since patients with suspected AD must undergo a cross-sectional imaging study to exclude other (treatable) causes of dementia. Combining an assessment of hippocampal atrophy with cerebral blood flow measurements by single photon emission computed tomography is not warranted either from a clinical or from an economic point of view.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004150050300
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  • 121
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    Bilateral reductions of hippocampal volume, glucose metabolism, and Wada hemispheric memory performance are related to the duration of mesial temporal lobe epilepsy (1999)
    Springer
    Journal of neurology 246 (1999), S. 926-933 
    Details
    ISSN: 1432-1459
    Keywords: Key words Temporal lobe epilepsy ; Hippocampus ; Magnetic resonance imaging ; Fluoro-2-deoxy-d-glucose positron-emission tomography ; Wada test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In refractory temporal lobe epilepsy (TLE) temporal lobe structures and functions are continuously or intermittently affected by abnormal brain electrical events, noxious neurochemical agents, and metabolic disturbances. There is conflicting evidence regarding the relationship between the duration of refractory mesial TLE and quantitative measures of temporal lobe functions and volumes of the hippocampi. Twenty patients (aged 28 ± 7 years, 14 males) with an initial precipitating injury before the age of 5 years were subjected to high-resolution magnetic resonance imaging, fluoro-2-deoxy-d-glucose positron-emission tomography (PET), and the Wada test. We investigated whether the duration of unilateral refractory TLE (12 left, 8 right) affects hippocampal volume, glucose metabolism, or Wada hemispheric memory performance. Ipsilateral to the epileptogenic zone the hippocampal volume, metabolism, and Wada hemispheric memory performance were reduced compared to the corresponding contralateral measures. The duration of epilepsy controlled for age at investigation, side of seizure origin, underlying cause, and sex were negatively correlated with ipsi- and contralateral hippocampal volume, hippocampal metabolism, and Wada hemispheric memory performance. Moreover, ipsilateral Wada hemispheric memory performance and contralateral hippocampal glucose metabolism were correlated with the frequency of habitual seizures. Refractory TLE seems to be associated with a slow but ongoing bilateral temporal lobe damage. These cross-sectional results require verification by longitudinal studies carried out over a period of more than two decades.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004150050484
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  • 122
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    Detection of anterior horn lesions by MRI in central European tick-borne encephalomyelitis (1999)
    Springer
    Journal of neurology 246 (1999), S. 1169-1171 
    Details
    ISSN: 1432-1459
    Keywords: Key words European tick-borne encephalitis ; Magnetic resonance imaging ; Central nervous system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We report a case of central European tick-borne encephalitis with cervical myelitis presenting clinically as a lower motor neuron syndrome of the upper limbs with proximal asymmetrical pareses and atrophies. There were no sensory deficits nor signs of lesions of the spinal pathways or signs of encephalitis or meningitis. The affected motor fibers of the upper limbs were electrically inexcitable, but sensory findings were normal. Electromyography of the paralyzed muscles revealed pathological denervation activity without voluntary activation. The initial magnetic resonance imaging (MRI) showed a large hyperdense lesion in the anterior part of the cervical cord from C3 to T1. Despite the fact that MRI changes disappeared completely within 6 weeks the patient showed only little improvement in the paralyzed muscles after 6 months. To our knowledge, these MRI changes in patients with tick-borne encephalitis, consistent with an isolated anterior horn lesion, have never been reported previously. The course may have been aggravated by an initial antibiotic treatment with cephalosporins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004150050537
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  • 123
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    Depression in Parkinson’s disease: brainstem midline alteration on transcranial sonography and magnetic resonance imaging (1999)
    Springer
    Journal of neurology 246 (1999), S. 1186-1193 
    Details
    ISSN: 1432-1459
    Keywords: Key words Parkinson’s disease ; Depression ; Brainstem midline ; changes ; Transcranial sonography ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Recent studies using transcranial sonography (TCS) have provided evidence of alterations in the mesencephalic midline structures in patients with unipolar depression and depression in Parkinson’s disease (PD), suggesting an involvement of the basal limbic system in primary and secondary mood disorders. This study tested the hypothesis of brainstem midline abnormality in depression and investigated 31 PD patients by magnetic resonance imaging (MRI) and TCS. Signal intensity of the pontine and mesencephalic brainstem midline was rated on T2-weighted images and measured by relaxometry. In addition, two blinded investigators assessed the echogenicity of the brainstem midline by TCS. The severity of motor symptoms and depression were graded independently using standard research scales. Rating of signal intensity and T2 relaxometry of the pontomesencephalic midline structures revealed significant difference between depressed and nondepressed PD patients (P 〈 0.05). This corresponded to a significant reduction in mesencephalic midline echogenicity of depressed PD patients on TCS images. No correlation was found between raphe signal intensity, T2 relaxation times, or TCS echogenicity and the severity of motor symptoms or depression. This study is the first to show changes in signal intensity and T2 relaxation time of the pontomesencephalic midline structures on MRI in depressed PD patients confirming previous TCS findings. As these midline structures comprise fiber tracts and nuclei of the basal limbic system, the findings may support the hypothesis of an alteration in the basal limbic system in mood disorders.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004150050541
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  • 124
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    Supratentorial atrophy in spinocerebellar ataxia type 2: MRI study of 20 patients (1999)
    Springer
    Journal of neurology 246 (1999), S. 383-388 
    Details
    ISSN: 1432-1459
    Keywords: Key words Spinocerebellar ataxia type 2 ; Magnetic resonance imaging ; Cerebral atrophy ; Disease duration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract There have been only few studies of brain magnetic resonance imaging (MRI) in spinocerebellar ataxia (SCA) type 2. We investigated 20 SCA2 patients, from 11 Sicilian families, and 20 age-matched control subjects using MRI. Our data confirm that olivopontocerebellar atrophy (OPCA) is the typical pattern in SCA2. We found no significant correlation between infratentorial atrophy, disease duration, or the number of CAG repeats in our SCA2 patients, but there was supratentorial atrophy in 12 patients, with a significant correlation between supratentorial atrophy and disease duration. OPCA appears to represent the “core” of the SCA2: however, central nervous system involvement is not limited to pontocerebellar structures. We therefore consider central nervous system degeneration in SCA2 as a widespread atrophy. MRI is helpful in diagnosing SCA, but it is not diagnostic in the absence of clinical and molecular studies. We suggest that serial MRI may play a role in evaluating “in vivo” the progressive steps of neurodegeneration in SCA2, for a better comprehension of the pathophysiology of this disorder.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004150050368
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  • 125
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    Magnetic resonance imaging outcome of new enhancing lesions in relapsing-remitting multiple sclerosis patients treated with interferon β1a (1999)
    Springer
    Journal of neurology 246 (1999), S. 443-448 
    Details
    ISSN: 1432-1459
    Keywords: Key words Multiple sclerosis ; Magnetic resonance imaging ; Enhancing lesions ; Interferon-β1a
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. We investigated whether interferon-β1a modifies the course of new enhancing lesions in relapsing-remitting multiple sclerosis. Sixty-eight patients were studied by monthly magnetic resonance imaging (MRI) in a pretest-posttest design including 6 months of observation and 6 months of treatment. We examined the course of new Gd-enhancing lesions on two consecutive scans during observation and during treatment. Lesions detected during treatment were also analyzed by MRI 1 year later for persistence of enhancement, persistence of T2 hyperintensity, development of T1 hypointensity, or disappearance. Among the enhancing lesions detected by observation and treatment MRI, respectively, Gd-enhancement persisted at 2 months in 20% and 3% (P 〈 0.001), T2 hyperintensity persisted in 86% and 63% (P 〈 0.03), and T1 hypointensity developed in 49% and 15% (P 〈 0.01). Progression to T1 hypointensity was significantly more frequent in larger lesions during both the observation and treatment periods (P 〈 0.01). No reenhancement of plaques was present at 1-year follow-up; a further reduction in T2 hyperintensity (63% vs. 39%) was observed while T1 hypointensity remained unchanged. Both the duration of Gd enhancement and the short-term MRI course of new enhancing lesions benefited by treatment with recombinant interferon-β1a treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004150050380
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  • 126
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    Disease activity in multiple sclerosis studied by weekly triple-dose magnetic resonance imaging (1999)
    Springer
    Journal of neurology 246 (1999), S. 689-692 
    Details
    ISSN: 1432-1459
    Keywords: Key words Multiple sclerosis ; Magnetic resonance imaging ; Gadolinium-DTPA ; Triple dose ; Blood-brain barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This study assessed whether dysfunction of the blood-brain barrier is an obligatory early event in lesion formation in multiple sclerosis. Dual-echo and T1-weighted magnetic resonance imaging after the injection of a triple dose (0.3 mmol/kg) of gadolinium-DTPA were obtained from ten patients with relapsing-remitting multiple sclerosis every week for 2 months. Sixty-four newly active lesions were detected by the two techniques. All the 44 new lesions seen on dual-echo scans enhanced during the early phases of their formation: 33 at their first appearance, 10 1 week before their appearance on the dual-echo scans, and one the week thereafter. When the every fourth (monthly) scan was analyzed, a total of 55 newly active lesions were detected (i.e., 14% active lesions would have been missed compared to the number found on weekly scanning). Thirty-one of them were detected by both dual-echo and triple-dose scans, 15 only by enhanced scans, and nine only by dual-echo scans. This study confirms that with highly sensitive magnetic resonance imaging techniques dysfunction of the blood-brain barrier is an obligatory early event in new lesion formation in relapsing-remitting multiple sclerosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004150050433
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    Accuracy of Computational Hemodynamics in Complex Arterial Geometries Reconstructed from Magnetic Resonance Imaging (1999)
    Springer
    Annals of biomedical engineering 27 (1999), S. 32-41 
    Details
    ISSN: 1573-9686
    Keywords: Blood flow ; Magnetic resonance imaging ; Numerical flow modeling ; Carotid artery ; Three-dimensional ; Wall shear stress ; Atherosclerosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Purpose: Combining computational blood flow modeling with three-dimensional medical imaging provides a new approach for studying links between hemodynamic factors and arterial disease. Although this provides patient-specific hemodynamic information, it is subject to several potential errors. This study quantifies some of these errors and identifies optimal reconstruction methodologies. Methods: A carotid artery bifurcation phantom of known geometry was imaged using a commercial magnetic resonance (MR) imager. Three-dimensional models were reconstructed from the images using several reconstruction techniques, and steady and unsteady blood flow simulations were performed. The carotid bifurcation from a healthy, human volunteer was then imaged in vivo, and geometric models were reconstructed. Results: Reconstructed models of the phantom showed good agreement with the gold standard geometry, with a mean error of approximately 15% between the computed wall shear stress fields. Reconstructed models of the in vivo carotid bifurcation were unacceptably noisy, unless lumenal profile smoothing and approximating surface splines were used. Conclusions: All reconstruction methods gave acceptable results for the phantom model, but in vivo models appear to require smoothing. If proper attention is paid to smoothing and geometric fidelity issues, models reconstructed from MR images appear to be suitable for use in computational studies of in vivo hemodynamics. © 1999 Biomedical Engineering Society. PAC99: 8719Uv, 8761-c, 0705Pj, 8710+e
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.163
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  • 128
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    Estimation of Tendon Moment Arms from Three-Dimensional Magnetic Resonance Images (1999)
    Springer
    Annals of biomedical engineering 27 (1999), S. 247-256 
    Details
    ISSN: 1573-9686
    Keywords: Medical imaging ; Magnetic resonance imaging ; Biomechanics ; Tendon moment arm ; Functional neuromuscular stimulation ; Tendon transfer surgery ; Hand biomechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract New three-dimensional (3D) magnetic resonance imaging (MRI) methods for measuring the tendon moment arm were created and were evaluated on the tendon moment arm of the flexor digitorum profundus at the third metacarpophalangeal joint. Using an open magnet MRI system and a hand holder, a series of static images were acquired at four joint angles and analyzed using specially created computer programs. Three methods were evaluated: (1) a 3D tendon excursion method that extended the method of Landsmeer; (2) a 3D geometric method whereby the moment arm was the perpendicular distance between the joint axis of rotation and the tendon path, and (3) a two-dimensional (2D) geometric method whereby single image slices were analyzed. Repeating the imaging and measurement processes, the 3D tendon excursion method was more reproducible (6% variation) than the 3D geometric method (12%), and both were much more reproducible than the 2D geometric method (27%). By having three operators analyze a single set of image data, we found that the precision of the 3D tendon excursion method was much less affected by segmentation error than the 3D geometric method. With the 3D imaging methods, tendon bowstringing and a displacement of the joint center of rotation toward the dorsal side of the hand were evident, leading to as much as a 60% increase in moment arm with joint flexion. Because of the dependence on flexion and variation between subjects, we recommend patient-specific measurements for target applications in functional neuromuscular stimulation interventions and tendon transfer surgery. © 1999 Biomedical Engineering Society. PAC99: 8761Pk, 8719Rr, 0705Pj
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.180
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    Magnetic resonance imaging of meniscal degeneration in torn menisci: a comparison between anterior cruciate ligament deficient knees and stable knees (1999)
    Springer
    Knee surgery, sports traumatology, arthroscopy 7 (1999), S. 274-277 
    Details
    ISSN: 1433-7347
    Keywords: Key words Meniscus ; Degeneration ; Magnetic resonance imaging ; Histology ; Chronicity of the meniscal tear
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Sports Science
    Notes: Abstract Signal anomalies observed in magnetic resonance imaging of the intrameniscal tissue adjacent to the tear were compared between stable knees (group 1, 54 menisci) and anterior cruciate ligament (ACL) deficient knees (group 2, 98 menisci). The histological significance of these signal anomalies was also studied (n = 25). The frequency of intrameniscal signal anomalies adjacent to the tear was significantly lower in ACL-deficient knees than in ACL-stable knees (P = 0.0022). There was a close correlation between the imaging anomalies and the presence of histological lesions (fissures, degeneration) within meniscal tissues adjacent to the tear (sensitivity: 0.95, specificity: 0.60). Our results suggest that the severity of intrameniscal degenerative changes adjacent to the tear are lower in ACL-deficient knees than in ACL-stable knees.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001670050163
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    Serial magnetic resonance imaging of the donor site after harvesting the central third of the patellar tendon A prospective study of 37 patients after arthroscopic anterior cruciate ligament reconstruction (1999)
    Springer
    Knee surgery, sports traumatology, arthroscopy 7 (1999), S. 20-24 
    Details
    ISSN: 1433-7347
    Keywords: Key words Donor site morbidity ; Anterior cruciate ligament ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Sports Science
    Notes: Abstract The aim of this prospective study was to follow the development of repair tissue in the donor-site area using serial magnetic resonance imaging (MRI) evaluation and to assess whether the MRI findings were correlated with donor-site morbidity. Thirty-seven consecutive patients with unilateral anterior cruciate ligament injuries undergoing elective reconstruction of the ligament were included in the study. They were aged 27 (range 14–50) years. The graft was harvested through two 25-mm vertical incisions with the aim of protecting the infrapatellar nerve and sparing the paratenon. The tendon defect was left open. The patients underwent MRI evaluation at 6 weeks, 6 months and 27 months postoperatively. A final clinical follow-up was made 25 (range 23–29) months postoperatively. MRI demonstrated that the donor-site gap, i.e. the area corresponding to a pathological non-tendinous-like tissue signal, was 9 (range 4–18) mm at 6 weeks, 5 (range 2–14) mm at 6 months and 2 (range 0–5) mm at 27 months. The size of the donor-site gap had significantly decreased at 6 months compared with 6 weeks (P = 0.0001), as well as at 27 months compared with 6 months (P = 0.0001). We conclude that the patellar tendon at the donor site healed gradually, as expressed by a decrease in the area of non-tendinous-like tissue signal on the serial MRI evaluations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001670050115
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  • 131
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    Effect of head-down tilt on brain water distribution (1999)
    Springer
    European journal of applied physiology 79 (1999), S. 367-373 
    Details
    ISSN: 1439-6327
    Keywords: Key words Cerebral edema ; Cerebrospinal fluid ; Head-down tilt ; Intracranial pressure ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Vascular and tissue fluid dynamics in the microgravity of space environments is commonly simulated by head-down tilt (HDT). Previous reports have indicated that intracranial pressure and extracranial vascular pressures increase during acute HDT and may cause cerebral edema. Tissue water changes within the cranium are detectable by T 2 magnetic resonance imaging. We obtained T 2 images of sagittal slices from five subjects while they were supine and during −13° HDT using a 1.5-Tesla whole-body magnet. The analysis of difference images demonstrated that HDT leads to a 21% reduction of T 2 in the subarachnoid cerebrospinal fluid (CSF) compartment and a 11% reduction in the eyes, which implies a reduction of water content; no increase in T 2 was observed in other brain regions that have been associated with cerebral edema. These findings suggest that water leaves the CSF and ocular compartments by exudation as a result of increased transmural pressure causing water to leave the cranium via the spinal CSF compartment or the venous circulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004210050522
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  • 132
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    Hochauflösende Kernspintomographie bei traumatischen Veränderungen an Fingergelenken (1999)
    Springer
    European journal of trauma 25 (1999), S. 224-229 
    Details
    ISSN: 1615-3146
    Keywords: Kerspintomographie ; Kollateralbandruptur ; Knorpelläsion ; Hochauflösende Oberflächenspule ; Magnetic resonance imaging ; Collateral ligament rupture ; Cartilage lesion ; High-resolution coil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Abstract Aim of this study was the evaluation of a prototype of a new high-resolution MRI coil for the detection of finger trauma. The practicability of this new coil for the assessment of traumatic lesions of the finger joints and the diagnostic value of this new method in clinical practice was assessed. Twenty patients between 13 and 50 years of age (mean 28 years) were examined with a 1.5-T whole-body-imager Magnetom SP 63 scanner (Siemens, Erlangen, Germany). A prototype of a high-resolution MRI coil with a diameter of 2.5 cm was used. T1- and T2-weighted images with an in plane resolution of 0.I95 x 0.098 mm were acquired. Bone structures, joint cartilage and capsule, ligaments, tendons and soft tissue alterations were assessed. All 19 patients with pathological changes at the finger joints had a joint effusion. With MR imaging, fractures were detected in almost all patients, compared with the X-ray examinations. Cartilage contusion showed high signal intensity. The collateral ligaments could best be assessed in the transversal, and ligament ruptures in the coronal plane. Hemorrhage in the tendon showed an increased signal intensity in T1- and T2-weighted, edema only in T2-weighted images. Especially traumatic lesions of cartilage and of ligaments can be sufficiently assessed by the high-resolution MRI due to its high anatomic resolution compared to common methods like X-ray. High-resolution MRI is practicable in clinical routine.
    Notes: Zusammenfassung Ziel der vorliegenden prospektiven Untersuchung war es, die Wertigkeit der hochauflösenden Kernspintomographie mittels einer speziellen Oberflächenspule in der Beurteilung von traumatischen Veränderungen der Fingergelenke zu evaluieren. Ferner sollte die Praktikabilität der Methode in der klinischen Routine überprüft werden. Es wurden 20 Patienten im Alter zwischen 13 und 50 Jahren (im Mittel 28 Jahre) an einem 1,5-T-Ganzkörpertomographen (Magnetom SP 63, Firma Siemens, Erlangen) untersucht. Als Spule wurde ein Prototyp einer hochauflösenden Oberflächenspule mit einem Durchmesser von 2,5 cm benutzt. T1- und T2-gewichtete Sequenzen mit einer maximalen Auflbsung in der Bildebene von 0,195 x 0,098 mm wurden zur Beurteilung von Knochen, Gelenkknorpel und -kapsel, der Sehnen und des Weichteilgewebes akquiriert. Kernspintomographisch fand sich bei 19 Patienten ein pathologischer Befund. Bei all diesen Patienten konnte ein Gelenkerguß nachgewiesen werden. Knöcherne Absprengungen, die anhand konventioneller Röntgenaufnahmen diagnostiziert wurden, zeigten sich kernspintomographisch als dislozierte signalreiche Strukturen. Gelenkknorpelkontusionen stellten sich hyperintens dar. Zur Beurteilung der Kollateralbānder eignete sich vor allem die koronare Schichtebene, da in dieser die Kollateralbdnder per continuitatem darstellbar sind. Sehneneinblutungen wiesen eine Signalerhöhung in T1- und T2-Wichtung auf. Ödeme der Weichteile und Bandstrukturen imponierten in T2-gewichteten Aufnahmen als signalreiche Strukturveränderungen. Aufgrund der hohen anatomischen Detailerkennbarkeit eignet sich die hochauflbsende Kernspintomographie als ergänzendes diagnostisches Verfahren zur nichtinvasiven Diagnostik von traumatischen Knorpel- und Bandläsionen. Unter Berücksichtigung des Zeitaufwandes handelt es sich dabei um eine im klinischen Alltag praktikable Methode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00596731
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    Nucleophilic Aromatic Substitution of Hydrogen in the Reaction of tert-Alkylamines with Nitrosobenzenes - Synthesis and NMR Study of N-(tert-Alkyl)-ortho-nitrosoanilines (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 29-35 
    Details
    ISSN: 1434-193X
    Keywords: Nitrosobenzenes ; ortho-Nitrosoanilines ; 2-Nitroso-1,3-phenylenediamines ; Nucleophilic aromatic substitution ; Oxidative nucleophilic substitution of hydrogen ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reaction of primary amines bearing tertiary alkyl groups (e.g. R-NH2; R = tBu, 1-adamantyl) with nitrosobenzenes has been found to proceed by oxidative nucleophilic aromatic substitution of hydrogen, thereby affording N-(tert-alkyl)-ortho- and -para-nitrosoanilines. The replacement of hydrogen proceeds more rapidly than the replacement of ortho- or para-nitro or -bromo substituents. With p-nitronitrosobenzene, both ortho-hydrogen atoms are substituted to afford N,N′-di(tert-alkyl)-4-nitro-2-nitroso-1,3-phenylenediamines 8a,b. The addition of oxidizing agents (e.g. MnO2) increases the yield of products. 1H-, 13C-, 14N- and 15N-NMR studies have confirmed the structures of the compounds under investigation. In ortho-nitrosoanilines, the rotamer with the nitroso group syn to the amino group is favored.
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  • 134
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    Photochemistry of 9,10-Dicarbonyl-9,10-dihydroanthracene - A Source of 9,10-Dehydroanthracene? (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 57-60 
    Details
    ISSN: 1434-193X
    Keywords: Benzyne ; Dehydroanthracene ; Matrix isolation ; Photochemistry ; Bergman reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -9,10-Didehydroanthracene (1) is an interesting derivative of p-benzyne that has been subject of several studies. In contrast to an earlier report, the photochemical decarbonylation of 9,10-dicarbonyl-9,10-dihydroanthracene (2) does not lead to 1 but rather to the ring-opened ene-diyne 4. The key intermediate for this reaction is keto carbene 7 which is formed by monodecarbonylation of 2. Carbene 7 is labile towards visible-light irradiation and easily looses the second CO molecule to give 4. Carbene 7 and diyne 4 are characterized by IR and UV/Vis spectra, the IR spectra are compared to calculations at the B3LYP/6-31G(d,p) level of theory.
    Additional Material: 2 Ill.
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  • 135
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    Reversal Diastereofacial Selectivity in the n-Butyllithium Addition to O-Protected N-Trimethylsilylimines of (2S)-Lactal: Enthalpic versus Entropic Contributions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 61-65 
    Details
    ISSN: 1434-193X
    Keywords: Nucleophilic addition ; Solvent effect ; Reversal of diastereoselectivity ; Temperature effect ; Imines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Commonly observed, but rarely explored, is the possibility of modifying the diastereomeric excess (de%) by means of temperature. A complete reversal in the diastereofacial selectivity could be obtained whenever the diastereoisomers concerned are differentially favored by enthalpy and entropy. The enthalpic or entropic dominance of a diastereoisomer depends greatly on the reaction solvent used.
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  • 136
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    Syntheses of Donor-Acceptor-Substituted 2,6-Stellanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 73-81 
    Details
    ISSN: 1434-193X
    Keywords: Donor-acceptor systems ; Cage compounds ; Stelladione ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A number of condensations could be carried out using tricyclo[3.3.0.03,7]octane-2-one (stellanone, 4) and tricyclo[3.3.0.03,7]octane-2,6-dione (2,6-stelladione, 5) as starting materials. The components for condensations were 2-trimethylsilyl-1,3-dithiane (6), 1,1-bis(trimethylsilyl)-1H-cyclopropa[b]naphthalene (7), its 3,6-dimethoxy-substituted analogue 8, fluorene (12), xanthene (13), diethyl malonate (14), and malononitrile (15). The condensation reactions with 5 yielded mono- and disubstituted products, among them were the donor-acceptor-substituted 2,6-stellanes 33-35. The structures of 18 (prepared from stellanone and fluorene), 19, 24, 27, 31 and 32 (synthesized by condensation of 2,6-stelladione and 2-trimethylsilyl-1,3-dithiane and malononitrile, respectively) were determined by X-ray crystallography.
    Additional Material: 1 Ill.
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  • 137
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    Synthesis of ω-Nitro Acids and ω-Amino Acids by Ring Cleavage of α-Nitrocycloalkanones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 87-90 
    Details
    ISSN: 1434-193X
    Keywords: Water ; α-Nitrocycloalkanones ; ω-Nitro acids ; Surfactant ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reaction of various α-nitrocycloalkanones 1 with aqueous 0.05 M NaOH, at 80 °C, in the presence of cetyltrimethylammonium chloride (CTACl) as a cationic surfactant, produces ω-nitro acids 2 in good yields. Reduction of the latter with HCOONH4/Pd-C, in methanol, at 80 °C affords ω-amino acids 3. The synthesis of methyl 9-oxodecanoate (8) is also reported.
    Additional Material: 2 Tab.
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  • 138
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    On the Selective O-Alkylation of Ambident Nucleophiles - The Synthesis of Thiohydroxamic Acid O-Esters by Phase-Transfer Reactions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 97-106 
    Details
    ISSN: 1434-193X
    Keywords: O-Alkylation ; Ambident nucleophile ; Thiazolethione ; Thiohydroxamic acid ; Phase-transfer reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -O-Alkylation of cyclic thiohydroxamic acids 1 and 3-5 has been studied with a view to developing an efficient method for the synthesis of N-(alkoxy)pyridine-2(1H)-thiones and N-(alkoxy)thiazole-2(3H)-thiones. Four issues have been addressed and the following conclusions can be drawn: (i) Thiones 1 and 5 exist as O-H acids in the solid state. (ii) According to NMR investigations (1H, 13C), the thione structures should be largely retained in CDCl3, [D6]DMSO, and CD3OD solutions of acids 1, 3-5, as is also the case for pyridinethione salts 2a-h. (iii) O-Alkylation of pyridinethione salts occurs in competition with S-alkylation. Selective O-alkylation is however possible, if thiohydroxamate salts with large countercations, such as M = NBu4, are treated with hard alkylating reagents in polar aprotic media. (iv) As tetrabutylammonium thiohydroxamates, such as 2f, are highly useful in the synthesis of cyclic thiohydroxamic acid O-esters, we have developed an efficient protocol for the preparation of N-(alkoxy)pyridine-2(1H)-thiones directly from acid 1 using phase-transfer conditions (alkyl halide or sulfonic acid ester, CH3CN, K2CO3, Bu4NHSO4). This method has proved particularly successful for the synthesis of N-(alkoxy)thiazole-2(3H)-thiones 11, 20-28, which were obtained in yields of up to 87%.
    Additional Material: 2 Ill.
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  • 139
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    Stereoselective Synthesis of the Pheromone (R)-(-)-Sulcatol, and Its Enantiopure (R)- and (S)-1-Mono-, -1,1-Di-, and -1,1,1-Trifluoro Analogues[1] (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 117-127 
    Details
    ISSN: 1434-193X
    Keywords: Fluorine ; Pheromones ; Sulfoxides ; Sulcatol ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The pheromone (R)-(-)-sulcatol (10a) and three of its enantiomeric mono-, di-, and trifluoro analogues 10b-d have been synthesized, in six steps and with good overall yields, starting from chiral (R)-2-methyl-5-[(4-methylphenyl)sulfinyl]pent-2-ene (1) and commercially available fluorinated or non-fluorinated acetates.Supporting information for this article is available on the WWW under http://www.wileY-Vch.de/contents/jc_2046/1999/98375_s.pdf or from the author.
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  • 140
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    Stereoselective Synthesis of Enantiomerically Pure β-Fluoroalkyl γ-Butyrolactones by Sulfoxide-Directed Lactonization (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 111-115 
    Details
    ISSN: 1434-193X
    Keywords: Fluorine ; Lactones ; Annulation ; Ketene ; Sulfoxides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Enantiomerically pure α,α-dichloro β-fluoroalkyl γ-p-tolylthio γ-butyrolactones trans-6a-c have been obtained with excellent stereocontrol (〉 98:2) and enantiomeric purity (〉 98:2) by sulfoxide-directed lactonization (Marino's annu-lation reaction) of β-fluoroalkyl vinyl sulfoxides (R)-(E)-5a-c with dichloroketene. Highly chemoselective dechlorination and desulfurization reactions performed on trans-6c efficiently provided the β-chlorodifluoromethyl γ-butyrolactone (S)-8c, the absolute stereochemistry of which was determined by X-ray diffraction analysis of its γ-p-tolylthio precursor (2R,3S)-7c.
    Additional Material: 1 Ill.
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  • 141
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    Nickel- or Iron-Catalyzed Coupling of Lithiated Methylthiomethyl p-Tolyl Sulfone with Lithiated Alkyl Sulfones to Give Methylthioalkenes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 163-165 
    Details
    ISSN: 1434-193X
    Keywords: Alkenes ; Methylthiomethyl sulfone ; Carbenoids ; Hetero-substituted carbanions ; Vinyl sulfides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reaction of methylthiomethyl p-tolyl sulfone with alkyl sulfones when lithiated gives regioselectively vinyl sulfides in high yields in the presence of Ni(acac)2 or Fe(acac)3.
    Additional Material: 2 Ill.
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    Experimental Evidence for Intramolecular Attractive Nonbonded C-F…H-C Interactions in 2′,3′-Dideoxy-4′-(fluoromethyl)nucleosides - Through-Space JCF and JHF NMR Coupling Constants, Correlation with Empirical Parameters of Solvent Polarity and Single-Crystal X-ray Structures (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 187-196 
    Details
    ISSN: 1434-193X
    Keywords: Fluorinated dideoxynucleosides ; Through-space interactions ; Hydrogen bonds ; Long-range coupling constants ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A collection of 5′-O-benzyl-2′,3′-dideoxy-4′-(fluoromethyl)nucleosides carrying both purinic and pyrimidinic nucleobases (uracil, 5-Br-uracil, 5-O2N-uracil, 6-Cl-purine and inosine) were synthesized in both the α and the β form. Through-space-transmitted 6JCF NMR coupling constants between F and C-6 (pyrimidinic base) or C-8 (purinic base) were observed for all of the α anomers of the compounds examined, whilst the corresponding 7JHF coupling constants were resolved only for the 5-substituted uracil derivatives. The absolute values of all the through-space couplings were found to decrease monotonically with increasing solvent polarity (CDCl3, MeOD, [D6]acetone, [D6]DMSO). This trend suggests that the through-space interaction is mediated by an intramolecular (sp3)C-F…H-C(sp2) hydrogen bond. The possibility of any relevant solvent-induced conformational change influencing the F/base mutual spatial relationship in the molecules investigated was ruled out by heteronuclear steady-state 1H{19F}-NOE experiments. A linear correlation was observed between 6JCF and 7JHF coupling constants and the Kamlet-Taft's hydrogen bond basicity parameter β. The crystal structures of the α and β anomers of the 5-nitrouracil nucleoside show evidence that the H-6 of the nucleobase forms hydrogen-bond-like interactions involving the O-benzyl oxygen atom in the β anomer, and that in the case of the α anomer this is replaced by the F atom of the fluoromethyl group.
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  • 143
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    2,3-Dialkynyl-1,4-diazabuta-1,3-dienes as Novel π-Systems: Synthesis, Structure, and Electronic Properties (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 205-214 
    Details
    ISSN: 1434-193X
    Keywords: Alkynes ; Cyclic voltammetry ; Diazabutadienes ; Electronic structure ; UV/Vis spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The introduction of alkynyl groups into the 2,3-positions of the 1,4-diazabuta-1,3-diene (DAD) backbone succeeds along two complementary synthetic routes either by condensing triisopropylsilyl-terminated dialkynyl-1,2-diones with primary aromatic amines or by a palladium-mediated alkynylation of bis(imidoyl chlorides). X-ray crystallographic analyses of two dialkynyl DAD derivatives reveals their planar (E-s-trans-E) conformations in the solid state. However, the central CC bond of both DAD backbones investigated has a length of 1.491(2) Å, and is therefore too long to indicate efficient delocalization across the DAD core. The UV/Vis spectra of dialkynyl DADs demonstrate that their absorptions in comparison to those of non-alkynyl DADs are bathochromically shifted by more than 40 nm, thereby demonstrating the suitability of the title compounds for developing NIR chromophores. The electron absorption properties of differentially N,N′-disubstituted dialkynyl DADs gave no indication for a push-pull effect across the DAD skeleton and suggest the ynimine moiety as the active chromophore of dialkynyl DADs. The electrochemical properties of the title compounds were determined by cyclo- and steady state voltammetry and show that introducing alkynyl groups leads to more easily reducible DAD systems. Again, the perception of dialkynyl DADs as covalently linked, but electronically decoupled ynimine units is corroborated by the redox potential of a differentially N,N′-disubstituted dialkynyl DAD. Similar conclusions were drawn from semiempirical MO (PM3) calculations of dialkynyl DADs.
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    Synthesis and Biological Activity of Phosphonate Analogs of Mannose 6-Phosphate (M6P) (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 447-450 
    Details
    ISSN: 1434-193X
    Keywords: Phosphonate analogs ; Mannose 6-phosphate (M6P) ; M6P receptors ; Recognition markers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Two phosphonate analogs of mannose 6-phosphate (M6P) have been synthesized. The isosteric analog 1 was obtained by a Wittig-Horner reaction at position 6 of a sugar aldehyde. The non-isosteric analog 2 was obtained by a Michaelis-Arbuzov rearrangement of a 6-bromo derivative. In contrast to the non-isosteric analog 2, the isoster 1 was shown to bind to M6P receptors as effectively as does M6P itself, thus demonstrating the considerable potential of the system in drug design.
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  • 145
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    Isopulegol as a Model Compound: Metalation and Substitution of an Allylic Position in the Presence of an Unprotected Hydroxy Function (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 459-462 
    Details
    ISSN: 1434-193X
    Keywords: Electrophilic substitution ; Metalations ; Monoterpene ; Protective groups ; Superbase ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -When treated with butyllithium and potassium tert-butoxide for 2 h at 0 °C in hexanes, the unsaturated monoterpenic alcohol isopulegol is simultaneously deprotonated at the hydroxy function and the allylic methyl group. The metaloxy allylmetal species thus generated can be silylated, alkylated, carboxylated and oxidized to afford the expected products in good to excellent yields. Thus, a specific protection of hydroxy groups is not required, alcohols being instantaneously converted by superbases into alcoholates.
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  • 146
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    Isolation of Cross-Coupling Products in Model Studies on the Photochemical Modification of Proteins by Tiaprofenic Acid (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 497-502 
    Details
    ISSN: 1434-193X
    Keywords: Proteins ; Cross coupling ; Drug research ; Photochemistry ; Toxicology ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -To gain insight into the chemical nature of drug-induced photoallergy, model studies have been carried out on the photochemical modification of proteins by tiaprofenic acid. Irradiation of decarboxylated tiaprofenic acid (DTPA) in the presence of p-cresol leads to C-C- and C-O-connected p-cresol “dimers”, together with DTPA hydrodimers. The p-cresol-DTPA cross-coupling product was not detected in this reaction. However, a product of this type is formed using a more hindered phenol, such as 2,6-di-tert-butylphenol. Similar results are obtained when tiaprofenic acid (TPA) or its methyl ester are used as photosensitizers. The observed formation of “dimers” can be related to protein photo-crosslinking, through the coupling of two tyrosine units. On the other hand, phenol-(D)TPA cross-coupling may be relevant to the understanding of drug-protein photobinding.
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    Diastereoselective Addition of Chiral (2-Lithiophenyl)acetaldehyde Acetals to Various Imines as Key Step in the Asymmetric Synthesis of 1-Aryltetrahydroisoquinolines, Part 4 (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 503-517 
    Details
    ISSN: 1434-193X
    Keywords: Enantiomerically pure (2-bromophenyl)acetaldehyde acetals ; Halogen-metal exchange ; Diastereoselective addition to imines ; Asymmetric synthesis ; Tetrahydroisoquinolines ; NMDA antagonists ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A novel asymmetric synthesis of 1-aryl-1,2,3,4-tetrahydroisoquinolines has been developed. The key step in this synthesis is the diastereoselective addition of homochiral (2-lithiophenyl)acetaldehyde acetals to the sulfonylimine 25 and to the arylimines 28 and 31. The best diastereoselectivity is obtained by addition of the bis(2-methoxypropan-2-yl)-substituted 1,3-dioxolane 6e to benzylidene-p-anisidine (31) with an HPLC-determined diastereomeric ratio 32c/33c = 92.1:7.9. The N-tosyl and the N-(4-methoxyphenyl) groups of the addition products 26d, 27d, 32c, and 33c are cleaved with sodium in liquid ammonia and ammonium cerium(IV) nitrate, respectively, to yield the primary amines 35 and 36. The acid-catalysed cyclization of the sulfonamides 26d and 27d and the carbamates 37 and 38, prepared from 35 and 36, leads to the enantiomerically pure dihydroisoquinolines 40 and 41, respectively. During the cyclization of the sulfonamides 26d, 27d and the carbamates 37, 38 the chiral auxiliary - the diol 39 - is cleaved unchanged and can be recovered in good yields.
    Additional Material: 4 Tab.
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  • 148
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    Ligand Effects on the Diastereoselectivities of Samarium Diiodide Promoted Pinacol Coupling (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 565-572 
    Details
    ISSN: 1434-193X
    Keywords: Pinacol coupling ; Aldehydes ; Samarium diiodide ; 1,2-Diols ; Diastereoselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The samarium diiodide pinacol coupling of benzaldehyde and cyclohexanecarboxaldehyde in the presence of a variety of polyethylene glycols, including derivatives containing carbohydrates has been studied. Whereas such complexing agents allow for the formation of 1,2-diols, in the case of benzaldehyde the erythro-isomer predominates with diastereoselectivities of up to 7:1, while with cyclohexanecarboxaldehyde a stereoselectivity of up to 10:1 was observed but in favor of the threo-isomer. This divergence in the stereoselectivity of these two aldehydes suggests the presence of two different mechanisms occurring in these pinacol coupling reactions.
    Additional Material: 5 Ill.
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  • 149
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    Thermal Rearrangements of Di- and Triphenyl-Substituted Benzocyclobutenes and Corresponding o-Quinodimethanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 551-563 
    Details
    ISSN: 1434-193X
    Keywords: Benzocyclobutenes ; o-Quinodimethanes ; Pericyclic reactions ; Retrodisproportionation ; 9-Anthryl radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -7,8-Dimethoxy-7,8-diphenyl- (1c), 7,8-dimethyl-7,8-diphenyl- (1d), 7-methoxy-7,8,8-triphenyl- (1e), 7-methyl-7,8,8-triphenyl- (1f), 7-isocyano-7,8,8-triphenyl- (1g), and 7,7,8-triphenylbenzocyclobutene (1h) are amenable to a variety of thermal rearrangements following initial electrocyclic ring-opening to the corresponding 7,8-diphenyl- (2c,d) and 7,8,8-triphenyl-o-quinodimethanes (2e-h). meso-1c was found to undergo a facile meso/rac isomerization at room temperature, indicating that other processes such as a symmetry-forbidden disrotatory ring-opening or a stepwise reaction compete with the symmetry-allowed conrotatory process. An estimate of the energy profile of the 1c/2c reaction system was made by kinetic simulation in combination with oxygen trapping of the intermediate o-quinodimethanes (2c) and semiempirical PM3 calculations, and revealed that the barrier for the symmetry-forbidden pathway is merely about 4 kJ·mol-1 higher than that for the symmetry-allowed one. o-Quinodimethanes 2c, 2g, 2e, and 2h underwent further electrocyclic hexatriene-cyclohexadiene ring-closure to give 4a,10-dihydroanthracene derivatives at temperatures between 20 and 80 °C. The 4a,10-dihydroanthracenes were further transformed to 9,10-disubstituted anthracenes by elimination of methanol or HCN, as well as to 9,10-substituted 9,10-dihydroanthracene derivatives. ESR and ENDOR spectroscopic detection of related 9-anthryl radicals lends support to the view that 9,10-dihydroanthracene products are formed by a homolytic hydrogen-transfer reaction (retrodisproportionation). By way of contrast, the aforementioned transformations play only a minor role in the case of methyl-substituted benzocyclobutenes 1d, 1f as here they are overruled by faster 1,5-H shift reactions of the corresponding o-quinodimethanes 2d, 2f, leading to styrene derivatives.
    Additional Material: 11 Ill.
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  • 150
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    Synthesis of Pentathiepanes and Isolation of the Conformers Based on High Inversion Barrier of the Pentathiepane Ring (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 597-605 
    Details
    ISSN: 1434-193X
    Keywords: S Heterocycles ; Cyclic oligosulfides ; Pentathiepanes ; Conformational analysis ; Sulfuration ; Ring inversion ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Acenaphtho[1,2-a]acenaphthylene (1) was sulfurated with elemental sulfur to give a pentathiepane derivative (2). A dynamic NMR spectrum analysis revealed that the two naphthalene rings of 2 are chemically nonequivalent up to 100 °C. The pentathiepane ring of 2 was shown to adopt a chair conformation both in solution and crystals. In accordance with the NMR spectrum analysis, the sulfuration of 5-phenylacenaphtho[1,2-a]acenaphthylene (12) gave a pair of conformers (16a and 16b), which were isolated in pure form. The Friedel-Crafts acetylation of 2, followed by dithioacetalization with 1,2-ethanedithiol, also gave a pair of isolable conformers (18a and 18b). These two pairs of conformers isomerized, as a result of the ring inversion, to each other in solution at room temperature in the first-order kinetics. The activation parameters for this process, Ea, ΔH#, and ΔS#, were determined. Based on the experimental observations, a probable mechanism for the inversion process is proposed.
    Additional Material: 2 Ill.
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  • 151
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    Cerium(III) Chloride Catalyzed Michael Reaction of 1,3-Dicarbonyl Compounds and Enones in the Presence of Sodium Iodide Under Solvent-Free Conditions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 617-620 
    Details
    ISSN: 1434-193X
    Keywords: Cerium(III) chloride heptahydrate ; Catalysis ; 1,3-Dicarbonyl compounds ; Enones ; Michael reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Cerium(III) chloride heptahydrate in the presence of sodium iodide catalyses the Michael addition of 1,3-dicarbonyl compounds to α,β-unsaturated ketones and α,β-unsaturated aldehydes with extraordinary efficiency. The very mild conditions allow high chemoselectivity as shown by the absence of the typical side reactions, which can be observed in the conventional base-catalyzed processes. More interestingly, when at least one of the starting materials is liquid at room temperature, the reaction can also be performed without solvents. The CeCl3· 7 H2O/NaI catalyst system can be easily separated from the reaction mixture and it can be reused without an appreciable loss of activity. Advantages of the present procedure, which utilizes cheap and “friendly” reagents, over the previously reported ones, are discussed.
    Additional Material: 1 Ill.
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  • 152
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    Synthesis of γ-Amino- and δ-Amino-Functionalised Ethers, Amines, or Silanes by Hydroaminomethylation of Heterofunctionalised Allylic Compounds (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 653-660 
    Details
    ISSN: 1434-193X
    Keywords: Hydroaminomethylation ; Rhodium ; Catalysis ; Carbonylation ; Heterofunctionalised allylic compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Heterofunctionalised allylic ethers 1, silanes 5, and amines 9 are hydroformylated in the presence of primary or secondary amines 2 to form the corresponding γ-amino- and δ-amino-functionalised compounds. The rhodium(I)-catalysed reaction sequence proceeds by aldehyde formation and subsequent reductive amination to generate the corresponding functionalised secondary or tertiary amines. This selective one-pot hydroaminomethylation procedure establishes access to γ-amino- and δ-amino-functionalised ethers, amines or silanes with potential biological activity.
    Additional Material: 4 Tab.
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  • 153
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    Biomimetic Oxidation of Denaverine Hydrochloride (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 679-683 
    Details
    ISSN: 1434-193X
    Keywords: Biomimetic oxidations ; Cytochrome P450 ; Metalloporphyrins ; Denaverine ; Metabolism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The behavior of denaverine (1) in various chemical model systems based on metalloporphyrins as catalysts was investigated to determine the possible oxidative metabolism. The resulting derivatives were compared to a biological model system and in vivo metabolism in rat and human.
    Additional Material: 2 Tab.
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  • 154
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    A Comparison of Chemical and Photochemically Induced Reduction of Some 2(4),5-Dihydro-1,2,4-triazines and Aromatic 1,2,4-Triazines (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 685-689 
    Details
    ISSN: 1434-193X
    Keywords: Single-electron transfer ; Ring contractions ; 1,4-Dihydro-1,2,4-triazine ; Photochemical reduction ; Chemical reduction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Chemical reduction (Zn/AcOH) of the arene 1 and of 2(4),5-dihydro-1,2,4-triazine 7 has been reinvestigated, resulting in the amendment of literature data concerning this reaction. Chemical, electrochemical, and photochemically induced reductions and ring contractions of 1,2,4-triazine derivatives have been compared. The first example of a triaryl-1,4-dihydrotriazine has been prepared. Some further evidence is presented that supports the proposed mechanism of the photochemically induced reduction and ring contraction of 1,2,4-triazines.
    Additional Material: 2 Tab.
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  • 155
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    Preparation of 2,3,5-Tri-O-benzyl-4-thio-L-arabino-furanosides and the Corresponding 4′-Thionucleoside Analogues (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 691-696 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; 4-Thiofuranosides ; Nucleosides ; Reaction mechanisms ; NOE measurements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -1-O-Acetyl-2,3,5-tri-O-benzyl-4-thio-L-arabino-furanose (9) has been prepared from D-xylose via the 1,4-dithio-L-arabino-furanoside 8. The crucial step of the reaction, i.e. the intramolecular cyclization of the open-chain dithioacetal 5, has been achieved in a yield of 90% by applying tetrabutylammonium iodide as promoter. Reaction of 9 with bis(trimethylsilyl)uracil or -thymine led to the benzyl derivatives 12 and 13 from which the deprotected 4′-thionucleoside analogues 14 and 15 have been prepared by debenzylation with boron tribromide.
    Additional Material: 1 Ill.
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  • 156
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    Steric and Electronic Effects in the Diastereoselective Catalytic Epoxidation of Cyclic Allylic Alcohols with Methyltrioxorhenium (MTO) (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 785-790 
    Details
    ISSN: 1434-193X
    Keywords: Epoxidations ; Diastereoselectivity ; Allylic alcohols ; Homogeneous catalysis ; Methyltrioxorhenium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The steric effects of allylic substituents in the epoxidations with methyltrioxorhenium/urea/hydrogen peroxide adduct (MTO/UHP) have been assessed for a series of 3-alkyl-substituted cyclohexenes. The trans selectivity increases with the size of the substituent and the diastereoselectivities follow an excellent linear correlation with the steric substituent constants of Taft (Es) or Charton (ν). Good cis selectivity is observed in the epoxidation of the cyclic allylic alcohols 2-cyclopentenol and 2-cyclohexenol due to a hydroxy-directing effect through hydrogen bonding; however, for 2-cycloheptenol and 2-cyclooctenol hydrogen bonding is ineffective and steric interactions cause a higher trans selectivity. The conformationally fixed cis- and trans-5-tert-butyl-2-cyclohexenols serve as suitable substrates for gauging the dihedral angle of the transition states for the oxygen transfer in these epoxidations. Thus, the MTO/UHP oxidant favours a quasi-equatorial arrangement of the hydroxy group for effective hydrogen bonding (hydroxy-group directivity), in analogy to m-chloroperbenzoic acid (m-CPBA) and dimethyldioxirane (DMD), and a dihedral angle of ca. 130° is suggested.
    Additional Material: 2 Ill.
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  • 157
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    Catalytic Oxyselenenylation-Deselenenylation Reactions of Alkenes - Stereoselective One-Pot Conversion of 3-Alkenols into 2,5-Dihydrofurans (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 797-803 
    Details
    ISSN: 1434-193X
    Keywords: Phenylselenenyl sulfate ; Selenium-catalyzed reactions ; Stereoselective syntheses ; Dihydrofurans ; Tetrahydrofurans ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A stereoselective multi-step one-pot procedure for converting 2-methoxycarbonyl-3-alkenols into 3-methoxycarbonyl-2,5-dihydrofurans, using only catalytic amounts of diphenyl diselenide and an excess of ammonium persulfate, has been developed. The erythro alkenols give the trans dihydrofurans, while the threo stereoisomers give the corresponding cisproducts. The configurations of the starting alkenols were deduced from those of the intermediate phenylseleno tetrahydrofurans, which were independently obtained from reactions of the alkenols with stoichiometric amounts of phenylselenenyl sulfate.
    Additional Material: 3 Tab.
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  • 158
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    The Synthesis of Imidazol Sugars Which Mimic Cyclic Carboxonium Ions Formed During the Glycosidase-Catalysed Hydrolysis of Oligo and Polysaccharides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 893-898 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Amino sugars ; Imidazole ; Glycosidases ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Some naturally occurring carbohydrates, of which several hydroxy groups had been selectively protected, were condensed with formamidine to give the expected imidazole derivatives in the D-arabino (9), D-lyxo (12), L-xylo (17), D-threo (21), and in the L- and D-erythro (24) series. Introduction of a strong leaving group at the remaining free alcohol function of these products led at once to intramolecular SN2 cyclisation to the corresponding bicyclic aza sugar derivatives. This was followed by total deprotection to give the target aza sugars in the L-xylo (7), L-ribo (14), D-arabino (19), as well as in the D-threo (22) and the L- and D-erythro (26) series. Inhibitory assays with four glycosidases showed that the D-arabino aza sugar 19 is the only potent inhibitor (for an α-mannosidase of jack bean).
    Additional Material: 1 Tab.
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  • 159
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    Preparation and Characterization of Bridged Naphthoxazinium Salts (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 923-930 
    Details
    ISSN: 1434-193X
    Keywords: Bridged benzo[a]phenoxazinium salts ; Diazo compounds ; Cyclocondensation ; Absorption ; Fluorescence ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -By condensation of bridged 4-arylazo-substituted 3-hydroxyanilines 18 and bridged or unbridged 4-arylazo-substituted 1-naphthylamines 19-23 with bridged 1-naphthylamines 15-17 and 3-aminophenols 14, respectively, in the presence of perchloric acid, bridged naphthoxazinium perchlorates 24-30 have been prepared. The spectral properties of the products have been compared with those of the bridged phenoxazinium salt 31 as well as with data for some unbridged analogues.
    Additional Material: 1 Ill.
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  • 160
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    3-Trifloxy-3-trifluoromethylpropeniminium Triflate: Reaction with Aromatic Amines - An Efficient Synthesis of 2-Trifluoromethylquinolines (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 937-941 
    Details
    ISSN: 1434-193X
    Keywords: Iminium salts ; Triflic anhydride ; Arylamines ; 2-Trifluoromethyl quinolines ; 3-Trifluoromethyl-cinnamaldehydes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reaction of iminium triflates 2 and 7 with various aromatic amines were investigated. The 2-Rf-substituted quinolines 3 and 8 were prepared in excellent yields by the reaction of 2 and 7, respectively, with substituted anilines. The reactions of 2 and 7 with diarylamines proceeds, suprisingly, to afford the corresponding 3-Rf-substituted cinnamaldehydes 4 and 9.
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  • 161
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    Synthesis Mediated by Ring-Closing Metathesis - Applications in the Synthesis of Azasugars and Alkaloids (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 959-968 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Alkaloids ; Castanospermine ; Metathesis ; Azasugars ; Manzamine A ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The application of the ring-closing metathesis (RCM) reaction to the construction of a wide variety of nitrogen-containing ring systems is described. The examples include pyrrolizidine, indolizidine, and quinolizidine derivatives related to azasugars. A formal total synthesis of castanospermine (5) is presented. The utilisation of two RCM steps in the synthetic sequence leading to the multicyclic ABCDE nucleus 7 of the complex alkaloid manzamine A (6) is discussed.
    Additional Material: 3 Ill.
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  • 162
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    Hydrogen Transfer Hydrozirconation of Alkenes with iBuZrCp2Cl Catalyzed by Lewis-Acidic Metal Compounds Containing Al, Zn, Si, Ag, and Pd (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 969-971 
    Details
    ISSN: 1434-193X
    Keywords: Hydrogen transfer ; Zirconium ; Alkenes ; Isobutylzirconocene chloride ; Lewis acid catalysis ; Lewis acid catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The hydrozirconation reaction of monosubstituted alkenes with iBuZrCp2Cl can be significantly accelerated by catalytic amounts of various Lewis acidic metal compounds, most notably AlCl3, Me3SiI, and Pd complexes, such as Li2PdCl4 and Cl2Pd(PPh3)2.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/99042_s.pdf or from the author.
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  • 163
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    Synthesis of the Enantiomers of (Z)-21-Methyl-8-pentatriacontene, the Major Component of the Female-Produced Contact Sex Pheromone of the Yellow-Spotted Longicorn Beetle, Psacothea hilaris (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 981-984 
    Details
    ISSN: 1434-193X
    Keywords: Alkenes ; Chirality ; Longicorn beetle ; Pheromones ; Psacotheahilaris ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Both the enantiomers of (Z)-21-methyl-8-pentatriacontene (1), the major component of the female-produced contact sex pheromone of the yellow-spotted longicorn beetle (Psacotheahilaris), were synthesized by starting from the enantiomers of citronellol (2)
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  • 164
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    Pseudorotaxanes and Catenanes Containing a Redox-Active Unit Derived from Tetrathiafulvalene (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 985-994 
    Details
    ISSN: 1434-193X
    Keywords: Catenanes ; Molecular machines ; Pseudorotaxanes ; Template-directed synthesis ; Tetrathiafulvalenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Two bis(2-oxy-1,3-propylenedithio)tetrathiafulvalene-containing acyclic polyethers and two macrocyclic polyethers, each incorporating one bis(2-oxy-1,3-propylenedithio)tetrathiafulvalene unit and one p-phenylene ring, have been synthesized. The two acyclic polyethers are bound by cyclobis(paraquat-p-phenylene) with pseudorotaxane geometries in solution. The two macrocyclic polyethers have been mechanically interlocked with this tetracationic cyclophane to form [2]catenanes in a kinetically controlled self-assembly process. The X-ray crystallographic analysis of one of the two [2]catenanes and 1H-NMR-spectroscopic studies of both compounds showed that the p-phenylene ring of the macrocyclic polyether is located inside the cavity of the tetracationic cyclophane, while the bis(2-oxy-1,3-propylenedithio)tetrathiafulvalene unit resides alongside. The [2]pseudorotaxanes and [2]catenanes show broad bands around 780 nm, arising from the charge-transfer (CT) interaction between the electron-donor tetrathiafulvalene-(TTF-)type unit and the electron-acceptor units of the tetracationic cyclophane. 1H-NMR-spectroscopic studies have shown that the [2]pseudorotaxanes dissociate into their separate components upon oxidation of the TTF-type unit, as a result of disruption of the CT interaction and electrostatic repulsion between the tetracationic host and the newly formed monocationic guest. The subsequent reduction of the guest to its neutral state affords back the pseudorotaxane-type complex restoring the original equilibrium. The results obtained from electrochemical experiments are consistent with the reversible, redox-driven dethreading/rethreading process observed by 1H-NMR spectroscopy. Variable-temperature 1H-NMR-spectroscopic investigations have revealed two dynamic processes, both involving the relative movements of the mechanically interlocked components in the [2]catenanes. The two consecutive oxidation processes involving the TTF-type unit, observed electrochemically, are displaced toward more positive potentials compared with the free cyclic polyethers. The two reversible two-electron reduction processes, characteristic of free cyclobis(paraquat-p-phenylene), separate into four reversible one-electron processes because of the topological difference between the “inside” and “alongside” electron-acceptor units in the [2]catenane.
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  • 165
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    Totally Regio- and Stereoselective P-O-to-P-C Rearrangement in the Synthesis of Chiral P-(o-Hydroxyaryl)diazaphospholidine P-Oxides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1099-1105 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Chiral synthons ; P-(o-Hydroxyaryl)diazaphospholidine P-oxides ; Rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The totally regio- and stereoselective P-O-to-P-C rearrangement in the synthesis of various chiral P-(o-hydroxyaryl)diazaphospholidine P-oxides has been investigated. This reaction proceeds with excellent yields ranging from 72 to 92%, total retention of configuration at the phosphorus atom, and complete regioselectivity. An exception was found with naphthyl derivatives, which gave mixtures of two regioisomers. In all cases, the products generated have been unambiguously characterized by 1H-, 13C-, and 31P-NMR spectroscopy as well as by X-ray-diffraction analysis.
    Additional Material: 3 Ill.
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  • 166
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    Palladium-Catalyzed Cyclocarbonylation of o-Ethynylphenols and Vinyl Triflates To Form 3-Alkylidene-2-coumaranones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1137-1141 
    Details
    ISSN: 1434-193X
    Keywords: Cyclocarbonylation ; Alkynes ; Catalysis ; Palladium ; Vinyl triflates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -o-Ethynylphenols react with vinyl triflates, in the presence of tetrakis(triphenylphosphane)palladium(0) and under carbon monoxide, to form 3-alkylidene-2-coumaranones in good yield.
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    S-Linked Thiomimetics of Phytoalexin-Elicitor-Active, Branched Oligosaccharides, Their Synthesis, Protein-Binding Ability and Phytoalexin-Inducing Activity (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1143-1152 
    Details
    ISSN: 1434-193X
    Keywords: Sulfur-linked thiooligosaccharides ; Oligosaccharin thio analogs ; Phytoalexin elicitor thio analogs ; Soybean glucan-binding assays ; Structure-activity relationships ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The sulfur-linked pentathiohexasaccharide 3I,3IV-di-β-D-glucopyranosylthiogentiotetraose (12) has been prepared by a convergent approach involving the reaction of 1,2,4-tri-O-acetyl-6-deoxy-6-iodo-3-S-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-3-thio-β-D-glucopyranose (10) with the sodium salt of 2,3,4-tri-O-acetyl-6-S-[2,4-di-O-acetyl-3,6-di-S-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-3,6-dithio-β-D-glucopyranosyl]-1,6-dithio-β-D-glucopyranose (4). A further reaction, involving the sodium salt of the peracetylated β-1-thio derivative of 12 with 1,2,3,4-tetra-O-acetyl-6-deoxy-6-iodo-β-D-glucopyranose (26), afforded the homologous sulfur-linked hexathioheptasaccharide 3II,3V-di-β-D-glucopyranosylthiogentiopentaose (28). Related sulfur-linked positional isomers 3II,3IV-di-D-β-glucopyranosylthiogentiotetraose (34) and 3III,3V-di-β-D-glucopyranosylthiogentiopentaose (39) have been prepared using analogous synthetic strategies. Thus, SN2 displacement of the iodine atom in 10 by the sodium salt of 2,4-di-O-acetyl-3,6-di-S-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-1,3,6-trithio-β-D-glucopyranose afforded a tetrathiopentasaccharide, which resulted in the pentathiohexasaccharide 34 by a sequence of reactions involving the 1-thioglycose 32 in reaction with 26. The hexathioheptasaccharide 39 was obtained conveniently by the reaction of 26 with the acetylated 1-thio-6I, 3II, 6II, 3IV, 6IV-pentathio derivative 37, followed by deacylation. The four isomeric pentathiohexa- and hexathioheptasaccharides 12,34 and 28,39, respectively, were all found to be active in eliciting phytoalexin accumulation in soybean cotyledon tissue and in binding to a glucan-binding protein of soybean, although to a lesser extent than the corresponding O-oligosaccharides, the alternate thiohexa- and thioheptasaccharides 12,28 being more active as compared to the geminally branched isomers 34,39.
    Additional Material: 3 Tab.
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  • 168
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    Intramolecular Copper- and Rhodium-Mediated Carbenoid Reactions of α-(Propargyloxy)silyl-α-diazoacetates (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1213-1221 
    Details
    ISSN: 1434-193X
    Keywords: Diazo compounds ; Carbenes ; Carbenoids ; Silicon ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Copper(I) triflate catalyzes the transformation of α-[(2-alkynyl)oxy]silyl-α-diazoacetates 1a-g into 1,2-bis(2,5-dihydro-1,2-oxasilol-4-yl)ethenes 2 and/or 2H-1,2-oxasilines 3. With rhodium(II) perfluorobutyrate as catalyst, 1a-e furnish only 3 but no 2. Bicyclic 2-methoxyfurans 6 are formed when 1a,c,e (containing terminal alkyne functions) are treated with catalytic amounts of copper(I) chloride. The experimental observations are explained in terms of metal-mediated intramolecular cyclopropenation and subsequent metal-assisted ring-opening of the strained bicyclic cyclopropene leading to vinylcarbene-metal complexes. An unusual autoxidation of 2H-1,2-oxasilines 3a,c,e is also described.
    Additional Material: 1 Ill.
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  • 169
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    Syntheses of Cyclobutane Derivatives: Total Synthesis of (+) and (-) Enantiomers of the Oleander Scale Aspidiotus nerii Sex Pheromone (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1201-1211 
    Details
    ISSN: 1434-193X
    Keywords: Pheromones ; Aspidiotus nerii ; Sex attractant ; Cyclobutane ; Enantiomeric purity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Synthesis of both enantiomers of the Aspidiotus nerii sex pheromone and their diastereomers has been achieved using, as a key step, an intramolecular ester enolate alkylation reaction for the formation of the cyclobutane ring with a good control of the relative configurations of the asymmetric centers. Stereoselective synthesis of a number of other trisubstituted cyclobutane derivatives also proves the versatility of the methodology used for the synthesis of the Aspidiotus nerii sex pheromone.
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  • 170
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    Formation of Chiral N-Oxides from 2-Azabicyclo[3.3.0]octanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1249-1252 
    Details
    ISSN: 1434-193X
    Keywords: Amino alcohols ; Amine N-oxides ; Asymmetric synthesis ; Hydrogen bonds ; Structure determination ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Enantiopure 2-azabicyclo[3.3.0]octanes 1a-d and ent-1e were oxidized with mCPBA to provide either diastereomeric pairs of N-oxides (2a/3a and 2b/3b) or diastereomerically pure compounds (2c,d and ent-2e). The structure of compounds 2a and ent-2e was confirmed by an X-ray study. The factors that affect the oxidation process are discussed.
    Additional Material: 2 Ill.
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  • 171
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    Non-Classical Epimerisation of (1S,2S,3S,4R,5R)-1-O-Methylcyclohexane-1,2,3,4,5-pentol (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1259-1263 
    Details
    ISSN: 1434-193X
    Keywords: Inositols ; Epimerisation ; Acetals ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Methoxycyclitol 4 was acetalized in a non-classical one-pot procedure with chloral/dicyclohexylcarbodiimide forming the 4-epi derivative 6. The stepwise deprotection of compound 6 is also described. Thus, decarbamoylation to the acetal 7 was achieved by heating 6 with methanolic sodium methoxide, and cleavage of the acid-stable trichloroethylidene moiety was realised in two steps via the corresponding ethylidene acetals 8 and 9; the ethylidene function was removed with aqueous trifluoroacetic acid (compound 10 from 6 via 9). Finally, the carbamoyl derivative 10 was converted into the tetra-O-acetyl product 12 via the tetrol 11.
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  • 172
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    Reactions of Nepenthone with Chromium(II) Reagents in Neutral Aqueous Medium (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1265-1265 
    Details
    ISSN: 1434-193X
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -No abstract
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  • 173
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    Photoisomerization of Bicyclopropylidene and 1,2-Dimethylenecyclobutane in Rare-Gas Matrices: Towards the IR-Spectroscopic Identification of Tetramethyleneethane (2,3-Dimethylenebutane-1,4-diyl) (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1291-1294 
    Details
    ISSN: 1434-193X
    Keywords: Matrix isolation ; IR spectroscopy ; Photochemistry ; Diradicals ; Isomerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Bicyclopropylidene (3) and 1,2-dimethylenecyclobutane (7) have been irradiated in rare-gas matrices. If 1,2-dimethylenecyclobutane (7) is exposed to the light of a KrF excimer laser (λ = 248 nm), an isomeric species is produced, showing an absorption at 793.1 cm-1 (argon matrix) or 791.2 cm-1 (xenon matrix) in the IR spectrum. The back reaction can be induced with light of λ = 254 nm. This photochemical interconversion, together with the comparison between the experimental and calculated band positions, supports the assignment of the IR absorption near 790 cm-1 to tetramethyleneethane (5).
    Additional Material: 2 Ill.
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  • 174
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    A New Generation of Alkoxyl Radical Precursors - Preparation and Properties of N-(Alkoxy)-4-arylthiazole-2(3H)-thiones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1275-1290 
    Details
    ISSN: 1434-193X
    Keywords: Alkoxyl radical ; Cyclizations ; Radicals ; Tetrahydrofuran ; Thiazolethione ; Thiazolethione ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -N-(Hydroxy)thiazole-2(3H)-thiones 6-10 have been prepared in a short and efficient synthesis from p-substituted acetophenones. Alkylation of heterocycles 6-10 in the form of their potassium or tetraalkylammonium salts 11-15 affords N-alkoxy-4-arylthiazole-2(3H)-thiones 16-20 in good to satisfactory yields. The hitherto unknown thiones 16-20 have been subjected to a detailed structural investigation (NMR spectroscopy and X-ray crystallography) and furthermore to a mechanistic study in order to explore their utility as sources of oxygen-centered radicals in solution. From the results of these studies, the following conclusions can be drawn: (i) X-ray analyses of the p-chlorophenyl-substituted acid 9, of the O-alkyl derivatives 19c, 19f, and of the O-mixed anhydride 19k indicate short C-S bonds [C2-S2 = 1.637(5)-1.684(2) Å] and long N-O connectivities [N3-O1 = 1.369(3)-1.379(2) Å] in the thiohydroxamate functionalities. Furthermore, O-alkyl- or O-acyl substituents at O1 are twisted out of the thiazolethione plane by ca. 90°, which points to lone-pair repulsion between nitrogen and oxygen atom as the underlying structural motif of the cyclic thiohydroxamate derivatives. (ii) Alkylation of ambidentate thiohydroxamate anions (salts 11-15; oxygen and sulfur nucleophiles) affords almost exclusively O-esters 16-20 (alkylation at the oxygen atom). (iii) Based on the results of X-ray diffraction studies and on the 1H- and 13C-NMR spectra, guidelines for the characterization of N-(alkoxy)thiazolethiones 16-20 and 2-(alkylsulfanyl)thiazole N-oxides 21-25, i.e. the products of S-alkylation of thiohydroxamate salts 11-15, could be derived. (iv) Photolyses of substituted N-(4-pentenoxy)-4-arylthiazolethiones 16-20 in general and in particular of p-chloro derivatives 19 were carried out in the presence of the hydrogen donor Bu3SnH, and afforded substituted tetrahydrofurans 31 or tetrahydropyrans 32 as major products in good yields. The observed stereo- and regioselectivities of ethers 31 and 32 point to alkoxyl radicals 30 as reactive intermediates, which add intramolecularly by selective 5-exo-trig or 6-endo-trig pathways to the olefinic double bonds. In terms of synthetic access and ease of handling of the radical precursors, the p-chlorophenyl-substituted thiazolethiones 9 and 19 exhibit significant advantages over all the other thiones used in this study and are considered as excellent substitutes for the pyridinethiones as efficient sources of free alkoxyl radicals. Consequently, the present compounds may be of use in both mechanistic and synthetic studies.
    Additional Material: 3 Ill.
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  • 175
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    Studies on the Synthesis of Natural Products with Bicyclo[4.4.0]decene Skeleton: Synthesis and Uncatalysed Intramolecular Diels-Alder Reactions of the Decatrienone Substrates (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1377-1384 
    Details
    ISSN: 1434-193X
    Keywords: Natural products ; Intramolecular Diels-Alder reactions ; 2-Siloxycyclopropanecarboxylates ; 1,7,9-Decatrien-3-ones ; Octalones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Starting from enones 7 and 8 siloxydienes 9 and 12 were synthesized. Cyclopropanation and subsequent alkylation with sorbyl bromide provided tetrasubstituted siloxycyclopropanes 15 and 16 in good overall efficiency. Their ring cleavage with fluoride reagents gave 1,7,9-decatrienones 5 and 17; the latter was converted into the protected compound 6. The thermal intramolecular Diels-Alder reactions of 5 and 6 were compared with those of related trienones 3 and 4. Octalones 1, 2, 21, and 22 were formed as mixtures of three or four diastereomers. Thus, for the stereoselective construction of natural products such as α-eudesmol or dihydromevinolin alternative reaction conditions for the cycloaddition step have to be developed.
    Additional Material: 5 Tab.
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  • 176
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    A Stereoselective Synthesis of Nonracemic (+)-Desoxoprosophylline by a Tandem Wittig [2+3]-Cycloaddition Reaction (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1407-1414 
    Details
    ISSN: 1434-193X
    Keywords: L-Ascorbic acid ; (+)-Desoxoprosophylline ; Lactones ; Alkaloids ; Domino reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -L-Ascorbic acid serves as chiral starting material for the synthesis of (+)-desoxoprosophylline. The synthetic pathway includes the formation of an O-protected 5-azido-2,3-dideoxysugar which is subjected to a tandem Wittig [2+3]-cycloaddition reaction, leading to the heterocyclic core unit of (+)-prosophylline. Stereoselective hydrogenation and chain elongation yields the desired alkaloid.
    Additional Material: 1 Ill.
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  • 177
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    A New Access to Diarylmaleic Anhydrides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1421-1426 
    Details
    ISSN: 1434-193X
    Keywords: Anhydrides ; Coupling reaction ; Enols ; Palladium ; Tin ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A new three-step synthesis of diarylmaleic anhydrides 6, starting from 3-aryl-2-hydroxybut-2-enedioates 2, is reported.
    Additional Material: 1 Ill.
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  • 178
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    Synthesis, Reactions, and Properties of 2,8-Didehydronoradamantane Derivatives (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1401-1406 
    Details
    ISSN: 1434-193X
    Keywords: 2,8-Didehydronoradamantane derivatives ; Cyclopropylcarbinyl ; Rearrangements ; Ring-opening reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -2,8-Didehydronoradamantan-9-one (2) was readily prepared by oxa-di-π-methane photorearrangement of brend-4-en-2-one (1). Other new 9-substituted 2,8-didehydronoradamantanes have also been prepared from 2, [i.e. 2,8-didehydronoradamantan-9-ol (3) and tosylhydrazone 4] and the ring-opening reactions have been studied. In acidic media, 2,8-didehydronoradamantan-9-ol (3) rearranges to the corresponding 2-substituted brend-4-ene derivatives. Exclusive formation of exo-2-substituted brend-4-enes supports the formation of a bridged bicyclobutonium ion. However, treatment of ketone 2 with PCl5 proceeds through a concerted mechanism by cleavage of the C-1-C-2 bond in 2 to give exo-2,5-dichlorotricyclo[4.2.1.03,8]non-4-ene (6). The tricyclo[4.2.1.03,8]nonane skeleton was also obtained by photochemically induced electron transfer reduction of 2 and reduction of 2 with Li/NH3, as well as by reduction of tosylhydrazone 4 with both NaBH3CN and BH3 × THF. On the other hand, Wolff-Kishner reduction of 2 gave the non-rearranged product, 2,8-didehydronoradamantane (10).
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  • 179
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    1-Alkoxycarbonyl-3-bromoazetidin-2-ones as Potential Elastase Inhibitors (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1441-1447 
    Details
    ISSN: 1434-193X
    Keywords: Azetidinones ; Enzyme inhibitors ; Kinetics ; Molecular modelling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Three 1-alkoxycarbonyl-3-bromoazetidin-2-ones have been prepared by reaction of (3S)-3-(tert-butoxycarbonyl)aminoazetidin-2-one with benzyl, trichloroethyl, and trifluoroethyl chloroformates followed by tBoc deprotection, diazotation of the exocyclic amino function and its substitution with potassium bromide. The 3-bromoazetidin-2-ones were obtained as racemic mixtures. Their hydroxide-catalyzed hydrolysis exclusively affords ring-opening products. Porcine pancreatic elastase (PPE) catalyzes the same reaction stereospecifically. Model building suggests that it is the (R) isomer that is enzymatically hydrolysed. The PPE-catalyzed hydrolysis is characterised by low kcat and Km values. Accordingly, these compounds behave as transient inhibitors of the enzyme.
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  • 180
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    Electrosynthesis of Aromatic Aldehydes by Palladium-Catalyzed Carbonylation of Aryl Iodides in the Presence of Formic Acid (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1471-1473 
    Details
    ISSN: 1434-193X
    Keywords: Palladium ; Homogeneous catalysis ; Carbon monoxide ; Aromatic aldehyde ; Formic acid ; Carbonylation ; Electrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The palladium-catalyzed electrocarbonylation of aryl halides performed in the presence of formic acid under one atmosphere of carbon monoxide affords aromatic aldehydes in good to high yields.
    Additional Material: 2 Ill.
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  • 181
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    Novel Diamino and Diimino Thioethers - Chiral Tridentate Ligands for Asymmetric Michael Reactions? (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1475-1479 
    Details
    ISSN: 1434-193X
    Keywords: Amino alcohols ; Asymmetric catalysis ; Chirality ; Michael additions ; Tridentate ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Novel C2-symmetric enantiopure β,β′-diamino thioethers 1 and β,β′-diimino thioethers 2 have been prepared from chiral α-amino acids. Nine of these compounds have been screened as ligands, in combination with 13 metal salts, with a view to achieving the enantioselective catalysis of a Michael reaction of a β-oxo ester with methyl vinyl ketone resulting in an optimal ee of 17%.
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  • 182
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    Reaction of the Carbanions of 2-(Alkylthio)thiolane 1-Oxides with Oxiranes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1481-1488 
    Details
    ISSN: 1434-193X
    Keywords: Thiolane 1-oxides ; Carbanions ; Oxiranes ; Asymmetric synthesis ; X-ray structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Carbanions of the 2-(alkylthio)thiolane 1-oxides 1 and 2 are generated and subjected to reaction with the epoxides 3-5. The resulting carbinols 6-11 are formed with high α diastereoselectivity, which is explained by a stabilization of the trans configuration of the carbanions in the activated complex. A minor γ stereoselectivity is also observed in case of the reactions with 4 and 5. The pure enantiomers (1S,2S,2′S)-9a and (1R,2R,2′S)-11b were obtained from 2 and (S)-4 or (R)-5, respectively, and their configurations were proved by X-ray structural analyses.
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  • 183
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    A Convenient Preparation of Optically Active Diepoxyhenicosene (Leucomalure), Lymantrid Sex Pheromone, by Chiral HPLC (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1503-1506 
    Details
    ISSN: 1434-193X
    Keywords: Diepoxy sex pheromone ; Chiral HPLC ; Resolution ; Stereochemistry ; Diepoxyhenicosene ; Leucomalure ; Lymantrid satin moth ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From optically active (3Z,9Z)-cis-6,7-epoxy-3,9-henicosadiene (2), all stereoisomers of (3Z)-cis-6,7-cis-9,10-diepoxy-3-henicosene [leucomalure (1)], a sex pheromone component of the Satin moth, were prepared in addition to the cis-3,4-cis-6,7-diepoxy analog (3). Specifically, MCPBA oxidation of each enantiomer of this epoxydiene yielded a mixture of four compounds, namely two diastereomeric sets of leucomalure and the positional isomer, which were easily separable by chiral HPLC equipped with either a Chiralpak AD column or a Chiralcel OJ-R column. Their chemical structures were determined by 2D-NMR analyses, and it was further confirmed that the chiral HPLC columns also had a high capability of resolving the enantiomers of these diepoxides.
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  • 184
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    Synthesis of N,N′-Disubstituted (1R,2R)-1,2-Diaminocyclohex-4-enes by a Ruthenium-Catalyzed Ring-Closing Metathesis Reaction (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1523-1526 
    Details
    ISSN: 1434-193X
    Keywords: Ruthenium ; Ring-closing metathesis ; Metathesis ; EPC synthesis ; 1,2-Diaminocyclohex-4-ene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiopure (1R,2R)-1,2-diaminocyclohex-4-ene derivatives have been synthesized by the ruthenium-catalyzed ring-closing metathesis reaction of (4R,5R)-N,N′-bis[(S)-1-phenylethyl]-4,5-diamino-1,7-octadiene dihydrochloride.
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  • 185
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    An Efficient Procedure for Preparing γ-Hydroxy α,β-Unsaturated Sulfones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1545-1550 
    Details
    ISSN: 1434-193X
    Keywords: Takai-Hiyama-Nozaki-Kishi coupling ; Sulfones ; β-Ionone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chromium(II)-mediated Barbier condensation of β-iodovinyl p-tolylsulfone with aldehydes and β-ionone afforded the title hydroxysulfones in good to excellent yields.
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  • 186
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    Facile and General Synthesis of Polyphosphane Polyoxides with (O)PCP(O) Linkages (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1561-1569 
    Details
    ISSN: 1434-193X
    Keywords: Arbuzov reaction ; Phosphane oxide carbanion ; PCP linkage ; NMR spectroscopy ; Carbanions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polyphosphane polyoxides with (O)PCP(O) linkages are powerful chelating agents for extraction of actinides from nuclear wastes. They are obtained either by the Michaelis-Arbuzov reaction of chloromethylphosphane oxides and phosphorus(III) esters, or by the reaction of phosphane oxide carbanions with chlorophosphanes. With the latter method, the addition of a phosphane oxide carbanion in excess allowed us to overcome a transmetallation reaction and thereby obtain polyphosphane polyoxides in good yields. The 1H-NMR spectra of the PCH2P groups show the influence of the different R groups attached to the phosphorus atoms. We determined the coupling constants and the chemical shifts of these spin systems.
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    Synthesis, Fluorescence Properties, and Head-to-Tail Regioselectivity in the Photodimerization of a Donor-Acceptor-Substituted Anthracene (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1595-1600 
    Details
    ISSN: 1434-193X
    Keywords: Photochemistry ; Anthracenes ; Fluorescence spectroscopy ; Cycloaddition reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The novel 2,6-donor-acceptor-substituted anthracene, namely 6-methoxy-2-anthracene carboxylic acid (7), was synthesized. The emission of this compound exhibits significant solvatochromism. The fluorescence band position and intensity are also remarkably sensitive to H+. Irradiation of the anthracene 7 in solution yields the syn and anti head-to-tail dimers exclusively. A synergistic electronic effect between the donor and acceptor substituents is proposed to operate on the photophysical and photochemical properties of anthracene 7.
    Additional Material: 2 Ill.
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  • 188
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    Spectroscopic and Theoretical Investigations of Monocyclic Dioximes and Dimethoximes with Six-, Eight-, and Ten-Membered Rings (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1601-1609 
    Details
    ISSN: 1434-193X
    Keywords: Photoelectron spectroscopy ; Conformation analysis ; Ab initio calculations ; Through-space interactions ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dioximes 4-6 and the dimethoximes 7-9, which contain the functional groups in opposite positions of a six-, eight-, or ten-membered ring, were synthesized. Their conformational properties and transannular interactions were investigated by spectroscopic (PE, 13C NMR) and theoretical (MMX, AM1, ab initio HF, and B3LYP) methods. While the cyclooctane derivatives 5 and 8 have conformations favourable for through-space interactions of the π(C=N) orbitals, in the other compounds no such interactions can be ascertained. Through-space orbital interactions in the molecules with an eight-membered ring lead to a splitting of the π(C=N) MOs of 0.4 eV.
    Additional Material: 7 Ill.
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  • 189
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    Spectroscopic and Theoretical Investigations of Bicyclic Dioximes and Dimethoximes with Eight-Membered Rings (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1611-1617 
    Details
    ISSN: 1434-193X
    Keywords: Photoelectron spectroscopy ; Conformation analysis ; Ab initio calculations ; Through-space interactions ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bicyclic dioximes 4-6 and dimethoximes 7-9, which contain the functional groups in opposite positions of bridged eight-membered rings, were synthesized. Their conformational properties and transannular interactions were investigated by spectroscopic (PE, 13C NMR) and theoretical (MMX, AM1, ab initio HF, and B3LYP) methods. While in the 3,7-disubstituted bicyclo[3.3.1]nonane derivatives 5 and 8 the eight-membered ring has a CC conformation favourable for through-space interactions of the π(C=N) orbitals, in the bicyclo[3.3.0]octane derivatives 4 and 7 as well as the 2,6-disubstituted bicyclo[3.3.1]nonanes 6 and 9 the functional groups are in geometric orientations that are unfavourable for such interactions. Through-space orbital interactions in the molecules with favourable conformations lead to a splitting of the π(C=N) MOs of 0.4-0.6 eV.
    Additional Material: 7 Ill.
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  • 190
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    New Syntheses of Flavones from Diels-Alder Reactions of 2-Styrylchromones with ortho-Benzoquinodimethanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 135-139 
    Details
    ISSN: 1434-193X
    Keywords: Flavones ; Chromones ; ortho-Benzoquinodimethanes ; Diels-Alder reactions ; NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The first reported cycloaddition reactions of 2-styrylchromones with ortho-benzoquinodimethane afforded 2-[2-(3-aryl-1,2,3,4-tetrahydronaphthyl)]chromones. These cycloadducts were converted into the corresponding 2-[2-(3-arylnaphthyl)]chromones (benzoflavone derivatives) by bromination/dehydrobromination processes. These benzoflavone derivatives were also obtained in one-pot cycloaddition reactions of 2-styrylchromones with ortho-benzoquinodibromomethane.
    Additional Material: 1 Ill.
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  • 191
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    Reactions of Nepenthone with Chromium(II) Reagents in Neutral Aqueous Medium (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 149-153 
    Details
    ISSN: 1434-193X
    Keywords: Morphine alkaloids ; 6,14-Ethenomorphinans ; Chromium(II) complex reagents ; Organochromium(III) complex intermediates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A synthetic method for the selective transformations of a selected morphine alkaloid in neutral aqueous medium is introduced. Full diastereoselectivity was achieved by the transformation of nepenthone (1) with [Cr(ida)(H2O)3] into 2a (20R) showing a complementary method as compared to the reactions with classical reagents to result in 2b (20S). A new unexpected morphine derivative 3 was prepared by a ligand-induced modification of the reaction which involves an unprecedented rearrangement.
    Additional Material: 2 Ill.
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  • 192
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    Synthesis, Characterization, and Some Reactions of the Tricarbonylchromium Complexes of 1,3-Indandione and Ninhydrin (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 167-179 
    Details
    ISSN: 1434-193X
    Keywords: 1,3-Indandione ; Ninhydrin ; Chromium complexes ; Acetals ; Oxidation ; Hetero Diels-Alder reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The syntheses and characterization of the tricarbonylchromium complexes of 1,3-indandione and ninhydrin are described. As the direct complexation proved unsuccessful, the acetal route was tried. Although some complexes were obtained, complex deacetalization did not work in the case of ninhydrin. Finally, the oxidation of tricarbonyl(η6-1,3-indandione)chromium(0) with dimethyldioxirane gave the ninhydrin complex in 75% yield in equilibrium with the indantrione complex. The latter reacts in hetero Diels-Alder reactions with dienes with diastereoselective formation of spiro anellated pyran derivatives.
    Additional Material: 3 Ill.
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  • 193
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    Chiral Peptide Nucleic Acids (PNAs): Helix Handedness and DNA Recognition (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 197-204 
    Details
    ISSN: 1434-193X
    Keywords: DNA recognition ; Helical structures ; Induced chirality ; Peptide nucleic acid ; Thermal stability ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Peptide Nucleic Acids (PNAs) are DNA mimics in which the deoxyribose phosphate backbone has been replaced by a pseudo-peptide skeleton composed of N-(2-aminoethyl)glycine units; they bind to complementary DNA strands with high affinity and selectivity. In order to study the effect of stereogenic centers within the backbone on PNA preorganization and DNA binding properties, chiral PNA decamers were synthesized which contained thymine monomers derived from L-Leu and D- or L-Lys inserted either at C-terminus and/or in the middle of an achiral PNA strand. PNAs containing three chiral thymine monomers derived from L-Leu, D- or L-Lys, L-Asp, or D-Glu were also synthesized. CD spectral analyses showed that a charged chiral monomer inserted in the middle of the strand is able to induce a strong preference in the helix handedness of a PNA-PNA duplex. The effect is increased by the presence of three chiral charged monomers. The L-Lys- and L-Asp-PNAs induced a preference for the left-handed and the D-Lys and D-Glu-PNAs for the right-handed conformation. As expected, the PNA-DNA duplexes are dominated by the DNA strand and thus are right-handed with both D- and L-PNAs. However, the D-PNAs, being inherently right-handed, lead to more stable PNA-DNA duplexes than the L-PNAs. The lysine-based PNAs form more stable complexes with the DNA at low ionic strength, due to the electrostatic interactions between the charged lysine side chain and DNA.
    Additional Material: 10 Ill.
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  • 194
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    A New Cytotoxic Diterpene with the Dolabellane Skeleton from the Marine Sponge Sigmosceptrella quadrilobata (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 227-230 
    Details
    ISSN: 1434-193X
    Keywords: Diterpene ; Dolabellane ; Sigmosceptrella quadrilobata ; Sponge ; Antitumor agents ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A new diterpene with the dolabellane skeleton 1 has been isolated from the sponge of the Indian Ocean, Sigmosceptrellaquadrilobata. Its structure elucidation, including absolute stereochemistry, was performed with the aid of MS, NMR, and CD data and by molecular modeling. Compound 1 is moderately cytotoxic against four tumor cell lines.
    Additional Material: 2 Ill.
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  • 195
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    Ectyoplasides A-B - Unique Triterpene Oligoglycosides from the Caribbean Sponge Ectyoplasia ferox (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 231-238 
    Details
    ISSN: 1434-193X
    Keywords: Saponins ; Terpenoids ; Sponges ; Ectyoplasiaferox ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Two novel norlanostane triglycosides, ectyoplasides A (1) and B (2), have been isolated from the methanolic extracts of the Caribbean sponge Ectyoplasiaferox (Raspaliidae, Axinellida). Their structures have been established by extensive application of high-resolution FABMS and two-dimensional NMR techniques, supported by chemical and enzymatic degradation methods. Ectyoplasides A and B have been shown to possess identical sugar chains (composed of two β-galactose units and one α-arabinose unit), but to differ in their aglycone moieties, which possess nortriterpene skeletons with an unprecedented substitution pattern on ring A. Ectyoplasides A and B show moderate cytotoxic activity when tested in vitro towards various cell lines
    Additional Material: 1 Ill.
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  • 196
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    Reaction of Stabilised Phosphorus Ylides with Nitrogen Dioxide (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 251-254 
    Details
    ISSN: 1434-193X
    Keywords: Phosphonium ylides ; Nitrogen dioxide ; Oxidation ; Nitriles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reaction of the stabilised ylides 14-23 with an excess of NO2 in CH2Cl2 at room temperature gives different results depending on the structure of the starting ylide. The monacyl ylides 14-16 give the corresponding α-oxo nitriles 4 together with Ph3PO · HNO3 (24) which has been fully characterised for the first time. Under the same conditions, the ylide 18 gives 2,4-dinitrobenzonitrile (26), Ph3PO, and benzoic acid. The other ylides examined all give 24 together with a variety of other products.
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  • 197
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    Reactions of Diphenyl Ether with Chlorine and Bromine Atoms Around 750 K - Relevance for Gas-Phase “Dioxin” Formation (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 261-265 
    Details
    ISSN: 1434-193X
    Keywords: Dioxins ; Gas-phase reactions ; Diphenyl ether ; Hydrogen abstraction ; ipso Substitution ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The title reactions have been studied to scrutinize rate data recently inferred for the two reverse steps - reaction of phenoxy radicals with chlorobenzene and bromobenzene - which were at variance with commonly accepted model values. Both with chlorine and bromine atoms, splitting to halobenzene and phenoxy radical was found to occur in competition with abstraction of o-, m-, p-hydrogen atoms. On this basis, the displacements of Cl and Br from the benzene ring by phenoxy radicals must have activation energies above 20 kcal/mol, and are therefore slow. As a consequence, formation of “dioxins” from halogenated phenols, in (slow) combustion, should proceed by combination of two (halo)phenoxy radicals rather than by displacement of (ortho-)halogen in a halophenol molecule.
    Additional Material: 2 Ill.
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  • 198
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    Deprotonation of Amides and Polyfunctional Imides Probed by Heteronuclear NMR and Quantum Chemical Calculations (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 287-295 
    Details
    ISSN: 1434-193X
    Keywords: Ab initio calculations ; Amides ; Imides ; Acidity ; NMR spectroscopy ; Deprotonation site ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The site of deprotonation of several types of amide acids (carboxylic amides and imides, sulfonamides, cyanamide, N-hydroxyurea) has been investigated by quantum chemical calculations and heteronuclear NMR measurements. Relative energies of tautomeric ions deriving from protonation at the various sites were determined both in the gas phase and in water (by the IPCM continuum solvation method). NMR properties (nuclear shielding and electric field gradient) of the involved heteronuclei were calculated and compared with experimental 14N, 17O and 33S chemical shifts and relaxation rates. It is shown that the combination of theoretical and experimental tools allows a reliable prediction of spectral parameters and ultimately of the deprotonation site of polyfunctional acids.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98401_s.pdf or from the author.
    Additional Material: 3 Tab.
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  • 199
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    Silicon-Controlled Intramolecular Thermal H-Ene Reaction - A New Access to a Key Intermediate of (±)-cis-γ-Irone (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1825-1829 
    Details
    ISSN: 1434-193X
    Keywords: Ene reaction ; Allylsilane ; Annulation ; cis-γ-Irone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The primordial influence of the silyl group in an intramolecular thermal H-ene reaction is reported. The silyl group lowered the energy of the transition state and allowed the reaction to proceed at a lower temperature than that of the simple all-carbon analog, thereby excluding the formation of undesirable by-products. This sequence has been applied for new access to a key intermediate in the diastereoselective synthesis of (±)-cis-γ-irone with high chemocontrol and significantly improved overall yield.
    Additional Material: 1 Ill.
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  • 200
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    On the Unexpected Stereochemical Outcome of the Magnesium in Methanol - Conjugate Reduction of an Exocyclic α,β-Unsaturated Ester (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1803-1809 
    Details
    ISSN: 1434-193X
    Keywords: Magnesium-methanol reduction ; Reductions ; α,β-Unsaturated esters ; Stereoselectivity ; (R)-(-)-Carvone ; Analogs of 1α,25-(OH)2-vitamin D3 ; Steroids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conjugate reduction of the exocyclic α,β-unsaturated ester 9 with magnesium in methanol gives a mixture of diastereoisomers containing predominantly the less stable 10a. Eventual structural identification rests on the X-ray diffraction analysis of tosylate 18.
    Additional Material: 3 Ill.
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