- Novel sol-gel lipases by designed bioimprinting for continuous-flow kinetic resolutions
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The bioimprinting effect in sol-gel immobilization of lipases was studied to develop efficient novel immobilized biocatalysts with significantly improved properties for biotransformations in continuous-flow systems. The bioimprinting candidates were selected systematically among the substrate mimics already found in the active site of experimental lipase structures. Four lipases (Lipase AK, Lipase PS, CaLB and CrL) were immobilized by a sol-gel process with nine bioimprinting candidates using various combinations of tetraethoxysilane (TEOS), phenyltriethoxysilane (PhTEOS), octyltriethoxysilane (OcTEOS) and dimethyldiethylsilane (DMDEOS) as silica precursors. The biocatalytic properties of the immobilized lipases were characterized by enantiomer selective acylation of various racemic secondary alcohols in two different multisubstrate systems (mixture A: a series of alkan-2-ols rac-1a-e and mixture B: heptan-2-ol rac-1f and 1-phenylethanol rac-1g). Except with Lipase AK, the most significant activity enhancement was found with the imprinting molecules already found as substrate mimics in X-ray structures of various lipases. The synthetic usefulness of the best biocatalysts was demonstrated by the kinetic resolution of racemic 1-(thiophen-2-yl)ethanol (rac-1h) in batch and continuous-flow systems. Copyright
- Hellner, Gabriella,Boros, Zoltan,Tomin, Anna,Poppe, Laszlo
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supporting information; experimental part
p. 2481 - 2491
(2011/11/06)
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- Enantioselective analysis of secondary alcohols and their esters in purple and yellow passion fruits
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The enantiomeric compositions of the acetates, butanoates, hexanoates, and octanoates of the secondary alcohols 2-pentanol, 2-heptanol, and 2-nonanol were determined in yellow (Passiflora edulis f. flavicarpa) and purple (Passiflora edulis Sims) passion fruits. The compounds were isolated by means of simultaneous distillation-extraction. Enantiodifferentiation was performed via multidimensional gas chromatography using heptakis(2,3-di-O-methyl-6-O-tert- butyldimethylsilyl)-β-cyclodextrin as chiral stationary phase. The series of homologous 2-alkyl esters, which are typical constituents of purple passion fruits, were shown to be present as nearly optically pure (R)-enantiomers. The proportions of the (S)-enantiomers varied in different batches and were dependent on the alcohol moieties of the esters. For minor amounts of esters detected in yellow fruits, the (R)-enantiomers were also dominating. However, the enantiomeric excesses were significantly lower than in the purple variety. Enantioselective analysis of the free alcohols revealed that 2-heptanol exhibited opposite configurations in purple and yellow passion fruits. A similar phenomenon was observed for 2-pentanol, which was present in the yellow fruits as a nearly racemic mixture. Data determined in extracts obtained by other techniques (liquid-liquid extraction, vacuum headspace technique) showed that the isolation procedure had no significant impact on the enantiomeric ratios.
- Strohalm, Hedwig,Dregus, Marta,Wahl, Astrid,Engel, Karl-Heinz
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experimental part
p. 10339 - 10344
(2009/09/25)
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- Mg(ClO4)2 as a powerful catalyst for the acylation of alcohols under solvent-free conditions
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A trace amount of magnesium perchlorate (from 0.1 mol% to 1 mol%) is able to promote quantitative acylation, with anhydrides, of a large variety of functionalized alcohols in short times, at room temperature and under solvent-free conditions.
- Bartoli, Giuseppe,Bosco, Marcella,Dalpozzo, Renato,Marcantoni, Enrico,Massaccesi, Massimo,Rinaldi, Samuele,Sambri, Letizia
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- Process for the production of chiral unsaturated alcohols in high optical purity
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The catalytic asymmetric hydrogenation of enol esters with a vinyllic or acetylenic substituent proceeds with extremely high enantioselectivity using a Rhodium-chiral bisphosphine catalyst. This is at variance with the hydrogenation of enol esters bearing a saturated substituent, which are hydrogenated with only marginal enantioselectivity under the same conditions.
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