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- Berglund, Per, et al.
(författare)
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2-Methylalkanoic acids resolved by esterification catalysed by lipase from Candida rugosa : Alcohol chain length and enantioselectivity
- 1993
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Ingår i: Tetrahedron Asymmetry. - 0957-4166. ; 4:8, s. 1869-1878
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Tidskriftsartikel (refereegranskat)abstract
- Enantiomerically pure (R)-2-methyldecanoic acid and (S)-2-methyl-1-decanol were prepared in a multi gram scale by esterification reactions catalysed by lipase from Candida rugosa. The enantiomeric ratios (E-values) were determined as a function of the chain length of the alcohol used as the complementary substrate in cyclohexane. In the resolution of 2-methyldecanoic acid the highest value (E = 37 ± 5) was obtained, when either 2-hexanol, 1-heptanol or 1-octanol were used. In contrast, when resolving 2-methyloctanoic acid, the E-values increased continually with increasing chain length of the alcohol used. 1-Hexadecanol gave the highest value: E > 100. The E-values were determined from the enantiomeric excess (ee) of the product at a conversion below 0.4. After two consecutive esterification reactions enantiomerically pure (R)-2-methyldecanoic acid, >99.8% ee, and after subsequent reduction of the ester produced, (S)-2-methyl-1-decanol, 96.7% ee, were obtained.
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- Berglund, Per, et al.
(författare)
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Switched enantiopreference of Humicola lipase for 2-phenoxyalkanoic acid ester homologs can be rationalized by different substrate binding modes
- 1999
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Ingår i: Tetrahedron. - 0957-4166 .- 1362-511X. ; 10:21, s. 4191-4202
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Tidskriftsartikel (refereegranskat)abstract
- Humicola lanuginosa lipase was used for enantioselective hydrolyses of a series of homologous 2-phenoxyalkanoic acid ethyl esters. The enantioselectivity (E-value) of the enzyme changed from an (R)-enantiomer preference for the smallest substrate, 2-phenoxypropanoic acid ester, to an (S)-enantiomer preference for the homologous esters with longer acyl moieties. The E-values span the range from E=13 (R) to E=56 (S). A molecular modeling study identified two different substrate-binding modes for each enantiomer. We found that the enantiomers favored different modes. This discovery provided a model that offered a rational explanation for the observed switch in enantioselectivity. (C) 1999 Elsevier Science Ltd. All rights reserved.
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- Hallman, K., et al.
(författare)
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Polymer-bound bis(oxazoline) as a chiral catalyst
- 2001
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Ingår i: Tetrahedron. - 0957-4166 .- 1362-511X. ; 12:10, s. 1475-1478
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Tidskriftsartikel (refereegranskat)abstract
- A chiral bis(oxazoline) was grafted on ArgoGel and used in the palladium-catalysed substitution of (+/-)-1,3-diphenyl-2-propenyl acetate with dimethyl malonate. The enantioselectivity was the same as that observed when the analogous monomeric catalyst was used (94-95% e.e.), despite the fact that the C-2 symmetry of the ligand was affected when coupled to the polymer. The polymer-supported catalyst could be recycled several times after removal of precipitated Pd(0). The polymer-bound bis(oxazoline) was also applied in a zinc-catalysed Diels-Alder reaction but lower selectivity and reactivity than the monomer was observed.
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- 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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- Holmén, Anders, et al.
(författare)
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Direct determination of the absolute configuration of a cyclic thiolsulfinate by VCD spectroscopy
- 2003
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Ingår i: Tetrahedron. - : Pergamon Press. - 0957-4166 .- 1362-511X. ; 14:15, s. 2267-2269
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Tidskriftsartikel (refereegranskat)abstract
- Experimental and calculated vibrational circular dichroism (VCD) spectra of the enantiomers of the conformationally rigid thiolsulfinate, naphtho[1,8-cd]-1,2-dithiole 1-oxide 1, obtained by chromatographic resolution of the racemate, were in excellent agreement, showing a (+)-(S)-1/(-)-(R)-1 relationship.
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