1,720,976 research outputs found
SYNTHETIC AMATOXIN ANALOG - A TWO-DIMENSIONAL PROTON NMR-STUDY OF "S-DEOXY-(ILE3)-(D-ALA7)-AMANINAMIDE
No full textThe effect of substitution of l and d amino acids in amatoxin analogues is discussed in this paper. The structure of the analog where d-alanine substitutes for glycine in position 7 has been worked out in solution by two-dimensional NMR methods using a 500 MHz instrument. The combined use of COSY and NOESY two-dimensional spectra allows a clear assignment of the resonances. The use of the coupling constants permits the calculation of the φ angles of the backbone. The NOE effects reveal the through-space contacts between protons of different peptide units, thus determining the rigidity of the amatoxin structure. On these grounds it has been possible to elucidate the conformation of the amatoxin analogue that resembles very closely that of β-amanitin, thus explaining the high inhibitory activity toward RNA polymerase B
SYNTHETIC AMATOXIN ANALOGS .2. A PROTON NMR-STUDY OF S-DEOXO-ILE3-(L)ALA5 AND S-DEOXO-ILE3-(D)ALA5-AMANINAMIDE
No full textAmatoxin analogues with d and l-Ala substitutions in position 5 have been studied by means of 1- and 2-dimensional n.m.r. spectroscopy at 500 MHz. The assignment of all resonances for both analogues has been carried out mostly with the use of COSY and NOESY type experiments. Temperature coefficients for the amide NH protons have been measured and the data compared to known amatoxin structures. The results obtained demonstrate that the rigidity of the bicyclic amatoxin framework is preserved in the d and l-Ala5 analogues, although the temperature coefficients point to intramolecular hydrogen bonds stronger in the case of the l-Ala analogue. The 10-fold decrease of biological activity is discussed in terms of structural features involving also the Trp4 indole accessibility
Application of Two-Dimensional Shift Correlated NMR Techniques to the Structure Determination of an Unusual Marine Alkaloid, Isosraine-2
No full textAn extensive application of two-dimensional proton–proton and proton–carbon shift correlated spectroscopy allowed the structural elucidation of isosaraine-2, a minor component of an unique family of alkaloids from the sponge Reniera sarai
S-DEOXO-ABU1, ILE3-AMANINAMIDE, AN INACTIVE AMATOXIN ANALOG
No full textThe title compound 3, an amatoxin analogue containing l--aminobutyric acid instead of l-asparagine in position 1, as in natural toad stool peptides, has been synthesized. It does not inhibit the eukaryotic DNA-dependent RNA polymerase form II (or B) in concentrations up to 10-4M, whereas 50% inhibition is exerted in M solution by the corresponding Asn-analogue S-deoxo-Ile3-amaninamide 2. The striking difference seems to be due to a relatively small variation of the conformation recognized by sensitive NMR spectroscopic methods
1H-NMR Study of Cholesterol Autooxidation in Egg Powder and Cookies Exposed to Adverse Storage
No full textThe level of cholesterol oxides depends on the production and storage conditions for food. We studied the effect of prolonged storage, heat, and diffuse daylight on spray-dried egg powder and cookies containing large amounts of cholesterol. The cholesterol oxides were isolated by chromatographic procedures, and were identified by recording 1H-NMR spectra of selected HPLC fractions. Autooxidation was quite slow when the sample was stored in a freezer at — 20°C. Diffuse daylight increased the amounts of β-epoxide of cholesterol, whereas heating caused a sharp increase in C-7 oxidized cholesterol derivatives. Extent of cholesterol oxidation depended on storage conditions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
BICYCLIC PEPTIDES - SOLUTION CONFORMATION AND CA-2+ BINDING OF THE HETERODETIC BICYCLIC DECAPEPTIDE CYCLO(GLU1-LEU2-PRO3-GLY4-SER5-ILE6-PRO7-ALA8)-CYCLO(1-GAMMA- 5-BETA) PHE9-GLY10
No full textThe conformational behavior of a heterodetic bicyclic decapeptide (BCPLT) in the absence and in the presence of calcium ions has been studied by means of mono and two-dimensional nmr techniques. Free BCPLT possesses a quite compact structure stabilized by intramolecular bonds and turns. In the structure a cluster of carbonyls is located in a cavity that is supposed to be the cation binding site
Further Chemical Studies of Mediterranean and Atlantic Hypselodoris Nudibranchs: a New Furanosesquiterpenoid from Hypselodoris webbi
No full textChemical studies of three HypJelhis species from distinct geographical areas
are reported. A new furanosesquiterpenoid, (+)-(6R,1 lR)-9,1O-dehydrofurodysinin 161, was
isolated from H. wbbi from Spanish coasts and its structure was elucidated by spectroscopic data
and confirmed by chemical reduction to (-)-(6R,l lR)-furodysini
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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