1,720,982 research outputs found
Three-Component, One-Pot Sequential Synthesis of Glyco-Hydantoin Conjugates
No full textThe development of new methods for linking sugars to heterocycles and peptides is an attractive area of research because glyco-conjugates play important roles in biology and medicine and are indispensable tools for probing several processes. Herein we report a one-pot, three-component sequential procedure for the synthesis of a novel class of glyco-conjugates, i.e. glyco-hydantoin conjugates, in high yields and very mild conditions, using readily accessible starting materials. We also demonstrated that some of the glyco-hydantoin conjugates obtained are synthons for the preparation of a novel class of glyco-pseudopeptides in which the amino acid is tethered to the sugar through the hydantoin ring
Carbodiimides-Mediated Multi Component Synthesis of Biologically Relevant Structures
Full text linkMulti-component reactions are very popular because they offer a wealth of products, while requiring only a minimum effort
combining many elements of an ideal synthesis, such as operational simplicity, atom economy, bond-forming efficiency, and the access
to molecular complexity from simple starting materials. As such, multi-component reactions have become the cornerstones of both
combinatorial chemistry and diversity-oriented synthesis and thus playing a central role in the development of modern synthetic methodology
for pharmaceutical and drug discovery research. In this Insight we will highlight the development of novel multi-component
reactions based on the reactivity of carbodiimides, paying particular attention on their mechanistic features. We will address our attention
on the process developed by us and others groups, in these last years, for the synthesis of biologically relevant structures such as,
for example, heterocycles and glyco-conjugates
Multicomponent synthesis of peptide-sugar conjugates incorporating hexafluorovaline
No full textThe development of new methods for linking sugars to peptides or proteins is an active area of research because natural glycopeptides or neoglycoconjugates play important roles in biology and medicine and are indispensable tools for probing several biological processes. Herein we report a
novel one-pot, three-component process for the synthesis of peptide-urea conjugates incorporating a hexafluorovaline residue under very mild conditions and high yields using commercially available starting materials such as carbodiimides, a-amino acid derivatives and 4,4,4-trifluoro-3-trifluoromethylcrotonic acid. The reaction has been exploited for the synthesis of a library of structurally diverse peptidesugar conjugates incorporating hexafluorovaline through a four-component, one-pot sequential process by generating the carbodiimides in situ from
easily accessible sugar containing azides and commercial available isocyanates through the Staudinger (aza-Wittig) reaction
Psi[CH(CF3)NH]Gly-peptides: Synthesis and Conformation Analysis
No full textPsi[CH(CF3)NH]Gly peptides, a conceptually new class of peptidomimetics having a stereogenic
trifluoroethylamine group as a natural peptide-bond surrogate, have been synthesized by stereoselective
addition of a-amino acid esters to trans-3,3,3-trifluoro-1-nitropropene. Long range nuclear Overhauser
effects, detected via ROESY experiments, provided evidence that model Psi[CH(CF3)NH]Glytetrapeptides
incorporating a trifluoroethylamine mimic of the dipeptide loop Pro-Gly can be
represented by an ensemble of unfolded and folded conformations. The latter are driven by the
formation of a hydrogen bond between a carbonyl group and the aminic proton of the
trifluoroethylamine unit. MD calculations indicate a population of conformers which adopt folded b
turn structures for all the L-peptides; on the other hand, a D-stereochemistry at the Pro residue induces
a natural folding towards a b hairpin conformation driven by the formation of a second hydrogen bond,
regardless of the stereochemistry of the stereogenic peptide bond surrogate
Three-component sequential synthesis of N,N'-disubstituted 5-arylidenedihydropyrimidine-2,4-dione
No full textA three-component sequential process consisting in (1) in situ formation of carbodiimides by Staudinger
reaction, (2) reaction with 2-(bromomethyl)-3-aryl-2-propenoic acids, and (3) final cyclization of the
resulting N-acylurea intermediates in order to obtain the synthesis of an array of N,N0-disubstituted 5-
arylidenedihydropyrimidine-2,4-dione under mild conditions is presented
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
- …
