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Tunable stereoselectivity in the addition of 2-lithiothiazole to L-serinal derived N-benzyl nitroe. Synthesis of C-2 epimer 2,3-diamino-4-hydroxybutanals
No full textA Complete reversal of distereoselectivity (ds [gt-or-equal] 95%) in the addiition of 2-lithiothiazole to L-serinal derived N-benzylnitrone has been achieved by the change of the hydroxy and amino protective gruops in the aldehyde moiety; the resultant epimeric 2-thiazolyl N-benzyl hydroxylamines were converted to C-2 epimer 2,3-diaminio-4-hydroxybutanals via reductive dehydroxylation and thiazolyl-to-formaly conversion
Total synthesis of (+)-polyoxin J
No full textThe antifungal antibiotic, polyoxin J 1, has been obtained (46.4%) by the coupling of a protected derivative of 5-O-carbamoylpolyoxamic acid 2 with thymine polyoxin C 3 which were prepared by a stereoselective aminohomologation strategy of sugar aldehydes (L-threose and dialdo-D-ribofuranose) employing nitrones 4 and 5 as their iminium derivatives and furan as a carboxylate group equivalent
Alkylation of camphor and pinanone imines of 2-(aminomethyl)thiazole. Enantioselective synthesis of 2-(1-amino alkyl)thiazoles
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Determination of the absolute configuration of α-amino-2-alkylthiazoles by circular dichroism
No full textCorrelation between absolute configuration at the α-centre of the thiazole ring in the title compounds and the sign of their Cotton effect (CE) in the range 217-230 nm is reported. © 1995
Enantioselective addition of Grignard reagents to a 2-thiazolyl nitrone
No full textThe addition of organomagnesium compounds to the N-benzyl 2-thiazolyl nitrone 1 in the presence of various chiral additives and Lewis acids leads to hydroxylamines 2 in moderate to good enantiomeric excess (up to 74%); the reductive dehydroxylation of these compounds affords enantioenriched α-amino 2-alkylthiazoles 3 in good yields (76-66%)
Applications of sugar nitrones in synthesis: The total synthesis of (+)-polyoxin J
No full textA convergent synthesis of the peptidyl nucleoside antibiotic (inhibitor of chitin biosynthesis) polyoxin J (2) by coupling of 5-O-carbamoyl polyoxamic acid (3) and thymine polyoxin C (4) is described. These compounds were prepared by chain elongation and amination of sugar-derived aldehydes employing their nitrones as iminium derivatives and the furan ring as a masked carboxyl. Thus, the stereoselective addition of 2-lithiofuran to the L-threose derived N-benzyl nitrone 5 followed by reduction of the resulting hydroxylamine to amine, carbamoylation of the free hydroxy group, and oxidative cleavage of the furan ring to the carboxylate group gave a protected derivative of 3 (30%). The same method was followed for the synthesis of the ribofuranosyl α-amino acid nucleoside 4 (12.6%) starting from the D-ribose derived nitrone 6. The final coupling was performed by the N-hydroxysuccinimide active ester method in DMSO with the Hünig base (i-Pr2EtNH) using a derivative of 3 and unprotected 4
Stereoselective addition of 2-furyllithium and 2-thiazolyllithium to sugar nitrones. Synthesis of carbon-linked glycoglycines
No full textA route to epimeric carbon-linked glycoglycines that exploits the stereoselective addition of 2-lithiofuran and 2-lithiothiazole to sugar nitrones has been described. The reaction occurs with opposite diastereofacial selectivity depending on whether the free nitrone or the diethyl aluminum chloride precomplexed derivative is employed. The resulting furyl or thiazolyl hydroxylamines are dehydroxylated to amines by the action of titanium(III) chloride. From these compounds the amino acids are revealed by the oxidative cleavage of the furan ring or by the conversion of the thiazole into the formyl group and oxidation to carboxylic acid. Compounds have been prepared wherein the α-amino acid moiety is installed at C-4 and C-1 of furanoses (ribo, manno, xylo, and lyxo) and at C-5 and C-1 of a pyranose (galacto)
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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