| Popis: |
A simple approach to the resolution of chiral alcohols through a lipase-catalyzed transesterification of one enantiomer of the corresponding trifluoroethyl carbonate by a low molecular weight poly(ethylene glycol), PEG, is described. The method was demonstrated through resolution of (RS)-sec-phenethyl alcohol. The alcohol was converted to its 2,2,2-trifluoroethyl carbonate, 2, and the (R)-enantiomer was selectively transesterified with PEG in warm diisopropyl ether using porcine pancreas lipase, PPL, as the catalyst. The two carbonate enantiomers were easily separated by cooling and filtering off the solid PEG having the (R)-alcohol covalently attached. Hydrolysis of the unchanged (S)-carbonate was achieved in dilute aqueous base, and the enantiomeric excess of the (S)-alcohol was found to be 80% by NMR in the presence of the chiral shift reagent Eu(hfc)3. Methanolysis of the modified (R)-PEG carbonate yielded (R)-sec-phenethyl alcohol having enantiomeric excess=96% by NMR with Eu(hfc)3. |
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