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This review is a journey concerning the investigations of the kinetic resolution of racemic ibuprofen for the last 20 years. The relevancy of the pharmacological uses of the S( + ) enantiomer along with its higher cost compared with racemic profen are the driving forces of a variety of scientific research studies addressing the enzymatic resolution of ibuprofen through enantiomeric esterification using lipases as biocatalysts. Lipases of fungal sources such as Candida rugosa, Rhizomucor miehei and the lipase B of Candida antarctica have been extensively studied both in homogeneous and heterogeneous (immobilized on solid supports) processes. In this context, the various alcohols and organic co-solvents frequently used in the esterification of racemic ibuprofen are summarized and discussed in this review. Moreover, recent investigations using membranes as reactors coupled with the separation of the desired product and microfluidic devices are presented. Finally, some guidelines about future perspectives regarding the technology of the kinetic resolution of profens and research niches are given.

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The stability of Novozym Ò 435 in the esterification of ibuprofen using ethanol as reactant and solvent was investigated. Additionally, the surface interaction of the isomers of ibuprofen and ethanol with the biocatalyst was screened through conventional adsorption isotherms and temperature programmed surface reaction (TPSR). These investigations evidenced strong alcohol adsorption and dissolution of the biocatalyst, which explains its deactivation upon reuses in the esterification reaction.

The stability of papain was studied in aqueous-organic mixtures by means of residual proteolytic activity along with various spectroscopic analyses (fluorescence and ATR-FTIR combined with isotopic exchange with D 2 O). The investigated systems contained 1 or 10% (v/v) of an aqueous buffered solution (pH 8.0) in acetonitrile (ACN), methanol (MeOH) or dimethyl formamide (DMF). The results evidenced that papain retained almost all its catalytic activity after 24 h of incubation in the presence of ACN, and a more compact conformation of the enzyme was detected. Papain suffered an important loss of enzymatic activity (ca. 80%) after 24 h incubation in MeOH although, no global conformational change and minor secondary structure rearrangements were detected. This observation suggests that somehow the active site region was altered. On the other hand, papain suffered a complete inactivation when exposed to those media containing DMF. Fluorescence analyses revealed that an irreversible conformational change took place after 24 h incubation, and a moderate increase in b-sheet and b-turn structures was the most relevant finding when secondary structure was analyzed. The evidences demonstrated that the organic solvents induce a more rigid and compact structure of papain regardless of the organic:buffer ratio investigated. In turn, these modifications affect the active catalytic site in the particular case of MeOH and DMF. These findings were in agreement with the thermo-stability of the enzyme performed after heating at 353 K in all the studied media, that is the presence of ACN did not substantially affect the secondary structure of papain. Nevertheless, the a-helix domain demonstrated to be less thermally stable than the b-sheet domain, turning into aggregated structures after heating, especially in the presence of MeOH and DMF.

CALB immobilized on hydrophobic supports exhibits higher conversion of ibuprofen and enantiomeric excess towards the S-enantiomer.