1,720,987 research outputs found
Synthesis of orthogonally protected labionin
No full textWe report the first synthesis of the complex amino acid labionin in a fully orthogonally protected and stereopure form. The structure-which incorporates five orthogonal protecting groups and three stereogenic centers-was assembled using two key synthetic steps: (1) a thia-Michael addition for installing the thioether bridge; (2) an electrophilic azidation for creating the central quaternary α-amino acid carbon in a stereochemically pure form. This work is expected to enable the solid phase synthesis of both natural and synthetic analogues labyrinthopeptins
Facile and stereoselective synthesis of non-racemic 3,3,3-trifluoroalanine
No full textA highly stereoselective enantiodivergent synthesis of non-racemic 3,3,3-
trifluoroalanine 7 is reported. The methodology is based on the reduction, by 9-BBN or
DIBAH, of the chiral sulfinimine 3 derived from ethyl trifluoropyruvate, followed by acidic
hydrolysis of the resulting diastereomeric sulfinamides 4 and 5
Highly stereoselective tandem Pummerer reaction alpha-hydroxy imine rearrangement of EP beta-sulfinylenamines
No full textThe highly stereoselective tandem Pummerer reaction/alpha-hydroxy imine rearrangement of E.P. alpha-fluoroalkyl-beta-sulfinylenamines affording chiral non-racemic fluoropyruvaldehydes N,S-ketals is described
Multicomponent Approach to Libraries of Substituted Dihydroorotic Acid Amides
No full textA process featuring a sequential multicomponent reaction followed by a regioselective postcyclization strategy was implemented for the facile synthesis of N,N'-disubstituted dihydroorotic acid amides under mild conditions. We obtained, for the first time, a library of 29 derivatives, encompassing 19 Nα-substituted-N4-dihydroorotyl-4-aminophenylalanine derivatives, a key residue of gonadotropin-releasing hormone antagonist Degarelix. The corresponding products were prepared from easily accessible starting materials in good to excellent yields with broad substrate scope
Multi-Component Sequential Synthesis of Dihydroorotic Acid-Based Amphiphilic Molecules
Full text linkAn efficient multicomponent sequential process, which occurs
in mild condition has been exploited for the synthesis of systematically
modified amphiphilic molecules where the cationic head is tethered
to a lipophilic tail through a dihydroorotic acid linker. The process
is operatively simple, high yielding, and flexible. Such a strategy could
impact combinatorial synthesis of wide libraries of amphiphilic molecules
to be tested as transfection agents and/or as antimicrobials
Separation of enantiomers of chiral sulfoxides in high-performance liquid chromatography with cellulose-based chiral selectors using acetonitrile and acetonitrile-water mixtures as mobile phases
No full textThe separation of 14 chiral sulfoxides was systematically studied on 12 cellulose-based chiral columns in acetonitrile and acetonitrile-water mobile phases. Out of all monosubstituted methylphenylcarbamates of cellulose the one having a methyl moiety in position 3 showed more universal chiral resolving ability compared to 2- and 4-substituted derivatives. Out of disubstituted phenylcarbamates of cellulose the ones with methyl substituents showed higher enantiomer resolving ability compared to chloro-substituted ones and substitution in positions 3 of the phenyl moiety was clearly advantageous. From disubstituted derivatives those possessing a combination of methyl- and chloro-substituents were advantageous compared to the ones having dimethyl- or dichloro-substituents. Chiral recognition ability of most chiral selectors towards studied sulfoxides was higher in pure acetonitrile compared to previously studied methanol. The effect of water addition to the mobile phase on analyte retention and enantioseparation was also quite different from that observed with methanol. In particular, with aqueous methanol by increasing the water content in the mobile phase retention increased in most cases and the separation factor improved. In contrast, with aqueous acetonitrile retention and separation factors decreased up to a certain water content in the mobile phase and then started to recover again for most of the studied analytes
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
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