1,721,024 research outputs found
SYNTHESIS OF C-GLYCOSYL AMINO ACIDS AS STABLE BUILDING BLOCKS FOR MODIFIED GLYCOPEPTIDE SYNTHESIS
No full textIn this thesis, we have studied and synthesized new class of C-glycosly amino acids whose structure features a
hetrocycle ring holding the carbohydrate and the amino acid fragments. Pyridine and tetrazole rings were used as
hetrocycle linkers in this project. This class of C-glycosyl amino acids is of interest as new chealtors and as building
building blocks for cotranslational glycopeptides synthesis. In the first part, C-Glycosylmethyl pyridylalanines were
synthesized via thermally induced Hantzsch-type cyclocondensation using an aldehyde-ketoester-enamino ester system.
To one of these reagents was attached a C-glycosyl residue, while to another was bound an amino acid fragment. In a
one-pot optimized methodology, the dihydropyridine was not isolated while its purification was carried out by removal
of unreacted material and side products using polymer-supported scavengers. Then the dihydropyridine (mixture of
diastereoisomers) was oxidized by a polymer-bound oxidant to give the target pyridine bearing the two bioactive
residues. In this way, a range of eight compounds (58-68% yield) was prepared in which the elements of diversity were
(i) the gluco and galacto configurations of the pyranose ring, (ii) the α- and β-configurations at the anomeric center, and
(iii) the positions of the carbohydrate and amino acid sectors in the pyridine ring. The orthogonal functional group
protection in these amino acids allowed their easy incorporation into oligopeptides via sequential amino and carboxylic
group coupling.
In the second part, tetrazole moiety was constructed via Huisgen 1,3-dipolar cycloaddition between nitriles and organic
azides. Two sets of compounds have been prepared, one being constituted of C-galactosyl and C-ribosyl O-tetrazolyl
serines, while the other contains S-tetrazolyl cysteine derivatives. In both cases, the synthetic scheme involved a twostep
route: the first one being the thermal cycloaddition of a sugar azide with p-toluensulfonyl cyanide (TsCN) to give a
1-substituted 5-sulfonyl tetrazole and the second the replacement of the tosyl group with a serine or cysteine residue.
For the high efficiency and operational simplicity, the azide-TsCN cycloaddition appears to be a true click process.
Finally, one of the amino acids prepared was incorporated into a tripeptid
Hantzsch-type three-component approach to a new family of carbon-linked glycosyl amino acids. Synthesis of C-glycosylmethyl pyridylalanines
No full text(Chemical Equation Presented) C-Glycosylmethyl pyridylalanines reported in this paper constitute a novel family of glycosyl amino acids that contain a pyridine ring linking the carbohydrate and amino acid residues. These amino acids may serve to prepare nonnatural glycopeptides displaying firmly bound carbohydrate fragments through a rigid and highly stable tether. A viable route to these new hybrid molecules has been opened via thermally induced Hantzsch-type cyclocondensation using an aldehyde-ketoester-enamino ester system. To one of these reagents was attached a C-glycosyl residue, while to another was bound an amino acid fragment. In a one-pot optimized methodology, the dihydropyridine was not isolated while its purification was carried out by removal of unreacted material and side products using polymer-supported scavengers. Then the dihydropyridine (mixture of diastereoisomers) was oxidized by a polymer-bound oxidant to give the target pyridine bearing the two bioactive residues. In this way a range of eight compounds (58-68% yield) was prepared in which the elements of diversity were (i) the gluco and galacto configurations of the pyranose ring, (ii) the α- and β-configurations at the anomeric center, and (iii) the positions of the carbohydrate and amino acid sectors in the pyridine ring. The orthogonal functional group protection in these amino acids allowed their easy incorporation into oligopeptides via sequential amino and carboxylic group coupling. © 2007 American Chemical Society
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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