Chiroptische Methoden in der Stereochemie II

Snatzke, G�nther

doi:10.1002/ciuz.19820160505

Cited by 17 publications

(2 citation statements)

References 3 publications

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“…Furthermore, CD spectroscopy was used to verify the absolute configuration. [184][185][186][187] It is known that CD spectroscopy is a suitable empirical method for the determination of the absolute stereochemistry of ellagitannins, without the need for chemical degradation reactions of the compound. 39,188 The Cotton effects near 220 and 250 nm can be correlated with the absolute configuration of the HHDP unit, using the sign of the Cotton effect between 220 and 235 nm as a diagnostic criterion.…”

Section: Scheme 22 Phase-transfer-catalyzed Monobenzylationmentioning

confidence: 99%

Strategies for the Synthesis of Ellagitannins

Khanbabaee¹,

Ree²

2001

Synthesis

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As a result of recent insights in the molecular structures and medicinal uses of the tannins, this class of natural products has enjoyed renewed scientific interest. This is reflected on the one hand in the enormously increased number of publications reporting on the isolation, characterization and biological activity of the tannins, and on the other hand in the steadily growing number of papers reporting tannin syntheses. In this review the most recent advances in the total synthesis of ellagitannins are discussed. In nature the ellagitannins occur usually only as the R-or only as the S-configured atropisomer, while the corresponding opposite atropisomers are seldom found. The configuration of the hexahydroxydiphenoyl units (HHDP's) found in ellagitannins is usually determined by the linkage position of the HHDP's with the polyol residues of the ellagitannins. Those ellagitannins of which the HHDP's are linked to the 2,3-or 4,6-positions of D-glucopyranose, have the S configuration; the corresponding 3,6-(HHDP)-ellagitannins are R-configured. Very few exceptions exist where both atropisomers are known. With one atropisomer showing the "normal" configuration, the other atropisomer is usually indicated in the literature as "unusual ellagitannin". This observed strict atropodiastereoselectivity in the biosynthesis of normally configured and unusual ellagitannins has led to the formulation of several hypotheses, which will be examined, in addition to the overview of effective concepts and strategies for the synthesis of ellagitannins.

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Section: Scheme 22 Phase-transfer-catalyzed Monobenzylationmentioning

confidence: 99%

Strategies for the Synthesis of Ellagitannins

Khanbabaee¹,

Ree²

2001

Synthesis

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“…Dabei wird der linear polarisierte Lichtstrahl in zwei aufeinander senkrecht stehende, linear polarisierte Komponenten gleicher Amplitude E 1 und E 2 aufgespalten (Snatzke, 1981).…”

Section: Theoretische Grundlagenunclassified

Hochohmige porenüberspannende Lipidmembranen: Elektrochemische Untersuchungen zur Aktivität von Gramicidin und Bacteriorhodpsin

Schmitt¹

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To study transmembrane proteins they need to be integrated in a lipid environment to preserve their functionality. For this purpose, model membranes have been developed which allow the investigation of ion channels and transporters in a defined environment. In recent years, a new artificial membrane system based on porous substrates has been developed, which exhibits on the one hand robustness and long-term stability and on the other hand allows for monitoring ion channel activity down to the single channel level. The drawback of this system is that transmembrane proteins can only be inserted from aqueous solution by dilution of a detergent solution. Furthermore, high protein densities, that are required for the investigation of membrane transporters with low turn over rates, cannot be obtained. Thus, the aim of this work was to develop a method to prepare lipid membranes on porous substrates, which allows the insertion of transmembrane proteins with high density. For this purpose, liposomes were used to generate lipid bilayers on gold coated porous alumina substrates, which were functionalised with the spacer lipid (cholesterylpolyethylenoxy)thiol CPEO3. Highly insulating and long-term stable pore-spanning membranes were obtained. By means of electrical impedance spectroscopy the membrane capacitance and resistance were elucidated. The obtained specific capacitance of (0,5 ± 0,1) µF cm -2 is in agreement with the expected value for lipid bilayer membranes. The membrane resistance was in the range of 10 6 -10 8 Ω. Partially ruptured membranes can be re-established by the fusion of vesicles. The pore-suspending membranes are very susceptible to the insertion of the detergent octyl-polyoxyetylene (o-POE), the membrane soluble proton carrier carbonyl-cyanide-m-chloro-phenylhydrazone (CCCP) and the bacterial outer membrane protein OmpF. The suitability of the established method for the transfer of integral membrane proteins from proteoliposomes into pore-spanning membranes was demonstrated by employing the well-investigated model ion channel gramicidin D and the light-driven proton transporter bacteriorhodopsin. The distinct ion channel activity of gramicidin D was investigated by electrical impedance spectroscopy. Gramicidin D-doped pore spanning membranes allowed for the read out of distinct ion channel properties such as the well-known selectivity for monovalent cations and the ion channel block by Ca 2+ in an integral manner. Furthermore, the mass transport -a result of the concentration gradient towards the Gramicidin D-doped membrane -was clearly discriminated. As an example for a transporter molecule the light driven proton pump Bacteriorhodopsin was integrated into pore-spanning membranes. Its specific activity was investigated by means of light induced photocurrent measurements.

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