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| 2. |
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| 3. |
- Andersson, Fredrik, et al.
(författare)
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Highly stereoselective alkylation of (S)-proline-based chiral auxiliaries
- 2004
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Ingår i: Tetrahedron. - : Elsevier BV. - 0957-4166 .- 1362-511X. ; 15:16, s. 2539-2545
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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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| 4. |
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| 5. |
- Berglund, Per, et al.
(författare)
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Enantiorecognition of Chiral Acids by Candida rugosa Lipase : Two Substrate Binding Modes Evidenced in an Organic Medium
- 2001
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Ingår i: Applied Biocatalysis in Speciality Chemicals and Pharmaceuticals. - : American Chemical Society (ACS). - 0841236798 ; 776, s. 263-273
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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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| 6. |
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| 7. |
- Bydén Sjöbom, Malin, et al.
(författare)
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Binary Phase Equilibria of Three alfa-Methylsubstituted Sodium Alkanoate Surfactant Systems.
- 2003
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797. ; 257:2, s. 333-336
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we continue our study of methyl -substituted surfactants and present the aqueous binary phase diagrams of racemic sodium 2-methyloctanoate, -nonanoate, and -dodecanoate, respectively. All systems have very low Krafft temperatures within the solution phase, between 1 and 4 degreesC. The phase sequences of the two shorter surfactants are very similar to those of the unsubstituted sodium octanoate, although with somewhat different range of existence for the phases formed. The sodium 2-methyldodecanoate system is different from the unsubstituted sodium dodecanoate system, as the former seems to lack a hexagonal phase. The surfactant systems were delineated using H-2 NMR splittings and crossed polarizers, and combined with SAXS for determination of phase structure.
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| 8. |
- Hedenström, Erik, et al.
(författare)
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Do enzymes recognise remotely located stereocentres? : Highly enantioselective Candida rugosa lipase-catalysed esterification of the 2- to 8-methyldecanoic acids
- 2002
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Ingår i: Tetrahedron. - 0957-4166 .- 1362-511X. ; 13:8, s. 835-844
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Tidskriftsartikel (refereegranskat)abstract
- Several racemic methyl decanoic acids have been synthesised and successfully resolved in esterification with 1-hexadecanol at aw=0.8 in cyclohexane using immobilised Candida rugosa lipase (CRL) as the catalyst. The enantiomeric ratios (E=2.8-68) obtained were surprisingly high even when the methyl group was as remotely located as in 8-methyldecanoic acid (E=25). Interestingly, the lipase shows enantiopreference for the S-enantiomer when the methyl group is located on even numbered carbons i.e. for the 2-,4-,6- and 8-methyldecanoic acids and to the R-enantiomer when the methyl group is located on uneven numbered carbons i.e. for the 3-,5- and 7-methyldecanoic acids.
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| 9. |
- Hedenström, Erik, et al.
(författare)
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Stereoselective esterification of 2,6-dimethyl-1,7-heptanedioic acid, catalysed by Candida rugosa lipase
- 2003
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Ingår i: Journal of Molecular Catalysis B. - 1381-1177 .- 1873-3158. ; 23:1, s. 53-59
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Tidskriftsartikel (refereegranskat)abstract
- The immobilised Candida rugosa lipase (CRL) displayed S-preference for both stereogenic centres in this sequential esterification of 2,6-dimethyl-1,7-heptanedioic acid (1) (pure meso and meso: (+/-) mixture, 53/47) with n-butanol in cyclohexane at a(w) = 0.8. The reaction was faster when short-chain primary n-alcohols was used and very slow, or even none reactive, when a Ion-chain alcohol was used.
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| 10. |
- Hedenström, Erik, et al.
(författare)
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Syntheses of female sex pheromone precursors of pine sawflies species and of some structurally related methyl-branched long-chain 2-alkanols
- 2002
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Ingår i: Journal of Chemical Ecology. - 0098-0331 .- 1573-1561. ; 28:6, s. 1237-1254
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Tidskriftsartikel (refereegranskat)abstract
- 3,7-Dimethyl-2-undecanol, 3,7,9-trimethyl-2-tridecanol, and 3,7, 11-trimethyl-2-tridecanol were synthesized as racemic mixtures in moderate yields. The alcohols are known precursors of the female sex pheromones of the pine sawfly species Diprion nipponica, Macrodiprion nemoralis, and Microdiprion pallipes, respectively. Stereoisomeric mixtures of 3,8,12-trimethyl-2-tridecanol, erythro-(2R,3R,11R/S)-3,11-dimethyl-2-tetradecanol, 3,5-dimethyl-2-tetradecanol, and 5,7-dimethyl-2-tetradecanol, structurally related to sex pheromone alcohol precursors of pine sawfly species, were also synthesized in moderate yields. The key reaction in the syntheses was the ring opening of γ-butyrolactones by using different alkyl lithiums as nucleophiles.
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