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Sökning: LAR1:miun > Hedenström Erik

  • Resultat 11-20 av 151
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11.
  • Andersson, Fredrik, et al. (författare)
  • Highly stereoselective alkylation of (S)-proline-based chiral auxiliaries
  • 2004
  • Ingår i: Tetrahedron. - : Elsevier BV. - 0957-4166 .- 1362-511X. ; 15:16, s. 2539-2545
  • Tidskriftsartikel (refereegranskat)abstract
    • Alkylation of the enolates of the propanoylamides of two chiral auxiliaries (S)-(-)-2-(pyrrolidin-2-yl)propan-2-ol 1a and (S)-(-)-2-(2-methoxypropan-2-yl)pyrrolidine 1b, derived from (S)-proline, with benzyl bromide and n-butyl iodide has been studied. The auxiliaries 1a and 1b induced opposite selectivity that is (R)- and (S)-configuration, respectively, at the newly created stereogenic centre. The diastereoselectivities and conversion yields in these alkylations were moderate to excellent. When Cp2ZrCl2 was used as an enolate coordinating agent, benzylation of propanoylated 1b gave an excellent diastereomeric ratio of 99:1. The benzylated diastereomeric products from either propanoylated 1a or 1b were easily separated by liquid chromatography.
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12.
  • Andersson, Fredrik, et al. (författare)
  • Synthesis of two (S)-indoline-based chiral auxiliaries and their use in diastereoselective alkylation reactions
  • 2006
  • Ingår i: Tetrahedron. - : Elsevier BV. - 0957-4166 .- 1362-511X. ; 17:13, s. 1952-1957
  • Tidskriftsartikel (refereegranskat)abstract
    • Two chiral auxiliaries, 2-[(S)-indolin-2-yl]propan-2-ol 1a and (S)-2-(2-methoxypropan-2-yl)indoline 1b, were synthesised from enantiomerically pure (S)-indoline-2-carboxylic acid 3. High diastereoselectivities in alkylations of enolates of the propanoylamides derived from the two auxiliaries are presented. Surprisingly, both auxiliaries induced the same selectivity at the newly created stereogenic centre. The benzyl bromide and n-butyl iodide alkylation reactions showed diastereomeric ratios that were moderate (81:19) to very good (96:4) and with very good yields (86-98%). When LiCl was used as an enolate coordinating agent, in the benzylation of the enolate from propanoylated auxiliary 1a, a very high crude diastereomeric ratio was obtained (99.7:0.3).
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13.
  • Andersson, K., et al. (författare)
  • High-accuracy sampling of saproxylic diversity indicators at regional scales with pheromones : The case of Elater ferrugineus (Coleoptera, Elateridae)
  • 2014
  • Ingår i: Biological Conservation. - : Elsevier BV. - 0006-3207 .- 1873-2917. ; 171, s. 156-166
  • Tidskriftsartikel (refereegranskat)abstract
    • The rare beetle Elater ferrugineus was sampled at 47 sites in the county of Östergötland, Sweden by means of pheromone-baited traps to assess its value as an indicator species for hollow oak stands rich in rare saproxylic beetle species. In addition, Osmoderma eremita was also sampled with pheromone baits. These data were then compared against species survey data collected at the same sites by pitfall and window traps. Both species co-occur with many Red Listed saproxylic beetles, with E. ferrugineus being a somewhat better indicator for the rarest species. The conservation value of a site (measured as Red List points or number of Red Listed species) increased with the number of specimens of E. ferrugineus and O. eremita caught. Accuracy of sampling by means of pheromone trapping turned out to be radically different for the two model species. E. ferrugineus traps put out during July obtained full accuracy after only 6. days, whereas O. eremita traps needed to be out from early July to mid-August in order to obtain full accuracy with one trap per site. By using E. ferrugineus, or preferably both species, as indicator species, accuracy would increase and costs decrease for saproxylic biodiversity sampling, monitoring and identification of hotspots. © 2014 Elsevier Ltd.
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14.
  • Becher, Paul, et al. (författare)
  • The Scent of the Fly
  • 2018
  • Ingår i: Journal of Chemical Ecology. - : Springer Science and Business Media LLC. - 0098-0331 .- 1573-1561. ; 44:5, s. 431-435
  • Tidskriftsartikel (refereegranskat)abstract
    • (Z)-4-undecenal (Z4-11Al) is the volatile pheromone produced by females of the vinegar fly Drosophila melanogaster. Female flies emit Z4-11Al for species-specific communication and mate-finding. A sensory panel finds that synthetic Z4-11Al has a characteristic flavour, which can be perceived even at the small amounts produced by a single female fly. Since only females produce Z4-11Al, and not males, we can reliably distinguish between single D. melanogaster males and females, according to their scent. Females release Z4-11Al at 2.4 ng/h and we readily sense 1 ng synthetic Z4-11Al in a glass of wine (0.03 nmol/L), while a tenfold concentration is perceived as a loud off-flavour. This corroborates the observation that a glass of wine is spoilt by a single D. melanogaster fly falling into it, which we here show is caused by Z4-11Al. The biological role of Z4-11Al or structurally related aldehydes in humans and the basis for this semiochemical convergence remains yet unclear. 
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17.
  • Berglund, Per, et al. (författare)
  • Enantiorecognition of Chiral Acids by Candida rugosa Lipase : Two Substrate Binding Modes Evidenced in an Organic Medium
  • 2001
  • Ingår i: Applied Biocatalysis in Speciality Chemicals and Pharmaceuticals. - : American Chemical Society (ACS). - 0841236798 ; 776, s. 263-273
  • Konferensbidrag (refereegranskat)abstract
    • We have identified the existence of different modes of binding the enantiomers of 2-methyl-branched carboxylic acids to a lipase active site by rational substrate engineering. Similar to hydrolysis, previously investigated, we have now evidence for differential binding modes in the Candida rugosa lipase-catalyzed esterifications in cyclohexane. The relevance of considering two different binding modes to understand lipase enantiorecognition is demonstrated by introducing bulky substituents on a chiral carboxylic acid which impose a different orientation of the substrate acyl chain in the active site of Candida rugosa lipase. With this substrate engineering approach based on molecular modeling it is thus possible to markedly alter the enantioselectivity of the lipase. Examples from hydrolysis and new results from esterifications in an organic solvent are presented and discussed.
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