One of the most difficult and challenging problems in the field of specialty chemicals is the production and separation of optically active compounds. In the case of ibuprofen [2-(4-Isobutylphenyl)propionic acid], only the (S)-enantiomer is known to be biologically active. A supported liquid membrane (SLM) has been widely studied as a selective separation technique, however, application of this technique has been limited mainly to the separation of metal ions. Employing ionic liquids as a liquid membrane phase resulted in the stabilization of the SLM, because ionic liquids have negligible vapor pressure and are water-immiscible. In the present study, we have succeeded in the enantioselective transport of the (S)-enantiomer from racemic ibuprofen through a lipase-facilitated SLM based on ionic liquids.

Lipase from Candida rugosa (CRL) is good at catalyzing esterification in the feed phase (at Interface 1), and another lipase from porcine pancreas (PPL) is an ester hydrolysis catalyst in the receiving phase (at Interface 2). (S)-Ibuprofen is selectively esterified by CRL in the feed phase, and the resulting ester dissolves into the ionic liquid phase of the SLM and diffuses across the SLM. At Interface 2 in the receiving phase, PPL catalyses the ester hydrolysis to produce the initial ibuprofen and ethanol, which are water soluble. Finally, the (S)-ibuprofen is selectively transported through the SLM, based on the enantioselectivity of lipases. A control experiment performed without the lipases resulted in no ibuprofen transport through the SLM. This is the first report that successfully demonstrates that enzyme-facilitated SLM based on ionic liquids can be utilized for the optical resolution of racemic ibuprofen.