1,721,025 research outputs found
Rapid microwave-assisted deprotection of N-Cbz and N-Bn derivatives
No full textCatalytic-transfer hydrogenation in ifo-propanol under microwave irradiation has been performed to rapidly deprotect N-Cbz and N-Bn derivatives. The method is particularly suitable for the synthesis of short peptides and can also be carried out on supported molecules. The rapid cleavage of chiral molecules derived from (S)-1-phenylethylamine can be very useful for asymmetric synthesis of nitrogen containing compounds. (C) 2001 Elsevier Science Ltd. All rights reserved
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
New chiral allylaminosilanes and their use in asymmetric Sakurai reactions
No full textThe new allylaminosilanes 2a-c, derived from chiral amines, react with benzaldehyde and pivalaldehyde in the presence of SnCl4 to give homoallylic alcohols 4a-b with enantiomeric excesses of up to 30%
A convenient conversion of α-aminoacids into NH-Boc protected α-aminoketones via imidazolides
No full textImidazolides obtained from natural α-aminoacids react with a twofold excess of Grignard reagents to afford in satisfactory to good yields the corresponding NH-Boc protected α-aminoketones. Under optimized conditions the reaction with phenyl- and n-pentylmagnesium bromide required the addition of catalytic amounts of Cu(I)-salt which turned out to be unnecessary in the case of Buchi's Grignard
Synthesis of enantiopure β- and γ-amino alcohols from homochiral α- and β-aminoacylsilanes as stable synthetic equivalents of α- and β-amino aldehydes
No full textA practical route is described for the synthesis of enantiopure β- and γ-amino alcohols with two stereocenters, starting from homochiral α- (1 and 5) and β- (13 and 16) -aminoacylsilanes, and involving stereoselective addition of allylmetal compounds and subsequent stereospecific protiodesilylation of the adducts. The degree of diastereoselectivity achieved in the nucleophilic addition step depends on both the nitrogen- protecting group and the reagents used. Diastereomeric excess (de) values equal to or higher than 98% were obtained in the TiCl4-promoted allylation of the N-Pht aminoacylsilanes 1 and 13 and of the N-Ts-aminoacylsilane 5 with allyltrimethylsilane. Lower de values were obtained in the Sc(OTf)3- catalyzed anylation of 5 with tetraallyltin and in the additions of both allyltrimethylsilane and tetraallyltin to the N-Ts-β-aminoacylsilane 16. Protiodesilylation of the adducts, leading to the β- and γ-amino alcohols, was accomplished with TBAF, except in the case of the adducts obtained from 5. For these, a preliminary removal of the tosyl group was necessary, which was accomplished with simultaneous desilylation by treatment with Na in liquid ammonia
Synthesis and reactivity of achiral and of a novel planar chiral thioferrocenoylsilanes
No full textThe reactions of thioferrocenoylsilanes with organolithium reagents, dienes and reducing agents which afford α-silyl sulphides, dihydrothiopyranes and α-silyl ferrocenyl thiols, respectively, have been investigated. α-Silyl sulphides were further functionalised through carbodesilylation with aldehydes. We also report the synthesis of a new planar chiral thioferrocenoylsilane that gave good diastereomeric excess in the reaction with t-butyllithium, lithium lutidine and 2,3-dimethylbuta-1,3-diene. The 1,1′-bis-thioferrocenoylsilane, too unstable to be isolated, was trapped in situ with dienes. © 2001 Elsevier Science B.V
Effect of new androgen receptor antagonists (SARMs) in the treatment of human prostate cancer.
No full textNew androgen receptor antagonists have been synthesize and analyzed for their activity in various PCa-derived cell lines
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
- …
