1,720,962 research outputs found
Improved process for preparation of lysophosphatidylcholines by selective monoacylation of glycerophosphatidylcholine in the presence of diorganotin oxides.
No full textDiol-tin ketal as effective catalyst in the tin mediated benzoylation of polyols
No full textThe monobenzoylation of 1-phenyl-1,2-ethanediol in the presence of different tin reagent has been studied. The stannylene ketal of 1-phenyl-1,2-ethanediol has been prepared and used as a catalyst or generated in situ by exchange with other mixed tin ketals. In either case, the acylation occurs rapidly with 2 mol% of the catalyst with the known selectivity. These experiments clearly establish the catalytic nature of the acylation reaction. (c) 2005 Elsevier B.V. All rights reserved
Chemo-enzymatic approach to D-allo-isoleucine
No full textA mixture of D-alloisoleucine and L-isoleucine derivatives are selectively hydrolysed by enzymatic catalysis (alcalase) allowing the recovery of the D-allo stereoisomer in excellent d.e. and yields. Thus, N-formyl-D-allo-isoleucine benzylester is obtained after enzymatic hydrolysis of the diastereoisomeric mixture or by a crystallisation procedure. (C) 2003 Elsevier Ltd. All rights reserved
A pratical, selective synthesis of mixed short/long chain glycerophosphocholines
No full textGlycerophosphorylcholine (GPC) is transformed into the cyclic stannylene derivatives, which are selectively acylated to 1-acyl-2-lyso-glycerophosphocholines. The reaction is effective using C-2 to C-16 acid chlorides in 2-propanol. After solvent replacement the lyso-phospholipid (lyso-PL) is subjected to a second acylation using acid anhydrides in methylene chloride. A series of 1(2)short-2(1)-long-diacyl-glycerophosphocholines are obtained in high yields and selectivity. No diacylation product was detected. In order to detect mixed-chain lipids with inverted disposition of acyl chains, the long chain was introduced first and the thus resulting isomeric compounds compared by NMR. An NMR method was developed in order to determine the positional purity of the isomeric compounds. (c) 2007 Elsevier Ireland Ltd. All rights reserved
Phospholipase D catalysed synthesis of phosphadyl serine in a Hollow-fiber membrane reactor
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Synthesis and antiproliferative activity of alkylphosphocholines
No full textAlkylphosphocholines (APC) with one or more methylene groups in the alkyl chain replaced by oxygen atoms or carbonyl groups, or both have been assembled modularly using w-diols as central building blocks. Out of 25 new compounds of this kind, I I were evaluated for their antiproliferative activity on four cell lines and compared with miltefosine to evaluate their hemolytic activity (HA); and cytotoxicity on non-tumoral cells (MT2), used as markers of adverse effects. Compound 13 was more active on cancer cell lines than on non-tumoral cells and the data were similar for MTT and thymidine incorporation assays. It had less HA than miltefosine, Compound 13 could therefore be a candidate for the preparation of compounds with higher cytotoxicity on cancer cells and lower general toxicity. (C) 2003 Elsevier Ireland 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
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
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