Influence of water activity on the enantioselective esterification of (R,S)-ibuprofen byCandida antarctica lipase B in solventless media

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Abstract
The lipase‐catalyzed enantioselective esterification of ibuprofen has been studied in a media, composed only of substrates. When racemic ibuprofen is used, the alcohol‐chain length affects the esterification rates of individual enantiomers, but it does not affect the enantioselectivity. Water activity affects the esterification rates of (R)‐ and (S)‐ibuprofen differently, leading to higher enantioselectivity at lower water activities. Experiments were also conducted at various (R)‐ to (S)‐ibuprofen ratios. It appears that the esterification rate of (R)‐ibuprofen is always proportional to its concentration, whereas at low water activity the esterification rate of (S)‐ibuprofen shows a saturation at higher concentrations. Other 2‐phenyl carboxylic acids were studied, and the increase in apparent enantioselectivity at low‐water activity was not observed for the molecules tested. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 63: 502–505, 1999.