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A new concept of a stereoselective synthesis of axially chiral biaryls, formed in the course of the dehydro-Diels-Alder (DDA) reaction, has been disclosed. It is based on asymmetric induction of the newly formed chirality axis by a chirality center, which is present in the two synthesized DDA reactants. Depending on the different length of the linkers joining the alkyne moieties the DDA reaction may be triggered photochemically or thermally, where only the thermal variant was stereoselective.
Five alkynyl pyridines were prepared and cyclized to naphthylpyridines as the main products in the course of a Photo-Dehydro-Diels-Alder reaction. Four of the final products are axially chiral and the determination of the rotational barrier by DFT calculations, dynamic NMR and H PLC experiments is demonstrated. (C) 2011 Elsevier B.V. All rights reserved.
The photo-dehydro-Diels-Alder (PDDA) reaction is a valuable extension of the classical Diels-Alder (DA) reaction. The PDDA reaction differs from the DA reaction by the replacement of one of the C-C-double bonds of the diene moiety by a C-C triple bond and by the photochemical triggering of the reaction. This entails that, in contrast to the DA reaction, the PDDA reaction proceeds according to a multistage mechanism with biradicals and cycloallenes as intermediates. The PDDA reaction provides access to a considerable variety of compound classes. For example, 1-phenylnaphthlenes, 1,1'-binaphthyls, N-heterocyclic biaryls, and naphthalenophanes could be obtained by this reaction.
Preparation of Strained Axially Chiral (1,5)Naphthalenophanes by Photo-dehydro-Diels-Alder Reaction
(2011)
The preparation of 10 (1,5)naphthalenophanes (10a-j) by photo-dehydro-Diels-Alder (PDDA) reaction is described. Owing to hindered rotation around the biaryl axis, compounds 10 are axially chiral and the separation of enantiomers by chiral HPLC was demonstrated in three cases (10a,b,e). The absolute configuration of the isolated enantiomers could be unambiguously determined by comparison of calculated and measured circular dichroism (CD) spectra. Furthermore, we analyzed ring strain phenomena of (1,5)naphthalenophanes 10. Depending on the length of the linker units, one can distinguish three classes of naphthalenophanes. Compounds 10a-c are highly strained (E-STR = 7-31 kcal/mol), and the strain is caused by small bond angles in the linker unit and deformation of the naphthalene moiety. Another type of strain is observed if the linker unit becomes relatively long (10g,h) originating from transannular interactions and is comparable with the well-known strain of medium sized rings. The naphthalenophanes 10d-f with a linker length of 10-14 atoms are only marginally strained. To clearly discriminate the different sources of strain, we defined two geometrical parameters (average central dihedral angle delta(C) and naphthalene thickness D-N) and demonstrated that they are well-suited to indicate naphthalene deformation of our naphthalenophanes 10 as well as of ten model naphthalenophanes (I-X) with different linker lengths and linking positions.
This article deals with the claim that the MAGNITUDE ESTIMATION (ME) method of gathering acceptability judgments produces data that are more informative for linguists than binary or n-point scale judgments. We performed three acceptability-rating experiments that directly compared ME data to binary and seven-point scale data. The results clearly falsify the hypothesis that data gathered by the ME method carry a larger amount of information about the acceptability of a given linguistic phenomenon. The three measures are largely equivalent with respect to informativity. Moreover, ME judgments are shown to be more liable to producing spurious variance under certain circumstances.*
In der vorliegenden Arbeit analysiert Yann Wernert die Rolle der Afrikanischen Union im Rahmen von Regionalkonflikten in Afrika. Dabei wird insbesondere Wert auf die konkrete Vorgehensweise der Afrikanischen Union in den jeweiligen Konflikten gelegt. Untersucht wird der Bürgerkrieg in Somalia sowie die Versuche seitens der internationalen Gemeinschaft, eine stabile politische Ordnung wieder aufzubauen. Ebenfalls analysiert wird der Darfur-Konflikt im Sudan und die Möglichkeiten, den regelmäßig stattfindenden Massakern Einhalt zu gebieten. Der Untersuchungszeitraum erstreckt sich von 2003 bis 2007.
Objectives: Stroke, frequently a consequence of hypertension, is one of the leading causes of death and neurological disabilities worldwide. In the ischemic brain, levels of endothelin-1, one of the most potent vasoconstrictors, are raised. Anti-inflammatory and neuroprotective effects of endothelin antagonists after stroke have been described in literature. Based on these findings, we investigated the protective effect of the endothelin converting enzyme/neutral endopeptidase blocker, SLV 338, in salt-loaded, stroke-prone, spontaneously hypertensive rats.
Methods: Male, 8-week-old spontaneously hypertensive stroke-prone rats were put on a high salt diet and treated with either 30 mg/kg or 100 mg/kg SLV 338 or vehicle for 27 weeks. Blood pressure, neurological outcome, body weight, and mortality were investigated throughout treatment. In weeks 1 and 9, animals were housed in metabolic cages for collection of urinary and blood samples and assessment of salt water and food intake. In weeks 22 and 27, additional blood samples were taken. At the end of the study, all brains were analyzed using magnetic resonance imaging.
Results: SLV 338 was well tolerated in all animals. Neurological outcome and infarct size were similar in all groups. Albuminuria was considerably delayed and the incidence of stroke significantly lowered in treated animals. In spontaneously hypertensive stroke-prone rats, treatment with SLV 338 significantly (P=0.01) improved survival in comparison to the vehicle treated group in a blood pressure-independent manner.
Discussion: Our data in spontaneously hypertensive stroke-prone rats demonstrate that combined endothelin converting enzyme/neutral endopeptidase inhibition could offer a new therapeutic approach for primary stroke prevention and improvement of mortality. The mechanism seems to be blood pressure-independent.
Die Arbeit beschreibt die humanistische Reform des 'Triviums', also der grammatischen, dialektischen (logisch-argumentativen) und rhetorischen Ausbildung, wie sie sich in dem Zeitraum von 1480 bis 1540 an Schulen und Universitäten durchsetzte. Die Arbeit ist dabei sowohl historisch wie systematisch angelegt, indem sie die Lehrinhalte der jeweiligen Kunst an ausgewählten Lehrbüchern darstellt, gleichzeitig aber unter ständigem Rückbezug auf die scholastisch-mittelalterliche Tradition die humanistischen Neuerungen davon abgrenzt. Im Zentrum stehen Werke von Lorenzo Valla, Rudolf Agricola, Erasmus, Juan Luis Vives und Philipp Melanchthon. Es stellt sich dabei heraus, daß die humanistischen Neuerungen in erster Linie die Praxisbezogenheit des Triviums betreffen, erst aus dieser ergeben sich dann die inhaltlichen Neuerungen. Unter Praxisbezogenheit ist dabei sowohl die Ableitung von Grammatik, Dialektik und Rhetorik aus der Beobachtung ihrer immer schon vorgängigen Anwendung zu verstehen, als auch ihre Anwendung zum Zweck der sprachlichen, argumentativ-logischen und rhetorischen Analyse. D.h. das grammatische, dialektische und rhetorische Regelwerk wird auf deskriptivem Wege gewonnen, um wiederum in der Analyse auf die Praxis zurückgewendet zu werden. Dieser Analyse werden dabei von alltäglichen Äußerungen, politischen, religiösen oder sonstigen sachlichen Texten bis hin zu literarischen Werken alles unterzogen. In einem letzten Teil stellt die Arbeit drei solcher Analysen vor und versucht sich schließlich selbst an einer dialektisch-rhetorischen Analyse dreier dramatischer Bearbeitungen der Parabel vom verlorenen Sohn.