Enantioselective Esterification Of Ibuprofen Catalyzed By Enzyme Under Microwave Irradiation

Ibuprofen is a widely used non-steroidal anti-inflammatory drug with anasymmetric carbon in the second position. Although it has been reported that(S)-ibuprofen is28-fold more active than it’s (R)-enantiomer, currently it is mainlymarketed as a racemate. Some classical methods have been used to obtain its opticallypure (S)-enantiomer, for example, enantioselective crystallization, chemicalasymmetric synthesis, or chromatographic separation of the racemate. However,almost all classical methods are expensive and/or laborious. Compared with theabove-mentioned method, enzymatic resolution has many advantages, such as themild reaction conditions, low pollution, and high stereoselectivity.The enantioselective esterification of ibuprofen catalyzed by a novel thermophilicesterase (APE1547) from the archaeon Aeropyrum pernix K1was successfullyconducted in organic solvents. The effects of acyl acceptor, substrate ratio, organicsolvent, temperature, and water activity were investigated. Under optimum conditions,the highest enantioselectivity (E=38.1) was obtained with a higher enzyme activity(216.5μmol/g/h). Celites were added into the reaction mixture to remove the waterproduced in the esterification. The reaction achieved its equilibrium in approximately96h with a conversion of57and99%(ee) of the un-reacted (S)-ibuprofen obtained.However, its enantioselectivity and activity were not satisfactory even under theoptimum conditions. The techniques of microwave irradiation has been adopted toimprove the enzyme performance in this study.Microwave irradiation (MW) has been proved to be a clean, fast, and convenientenergy source and widely used in organic chemistry. It’s gen-erally believed thatmicrowave irradiation can produce efficient internal heating by direct coupling ofmicrowave energy with the molecules (solvents, re-agents, catalysts) in the reactionmixture and then accelerate the reaction.Enantioselective esterification of ibuprofen has been successfully carried out inorganic solvent catalyzed by APE1547(a thermophilic esterase expressed in arecombinant E. coli BL21harboring the APE1547gene from the archaeon Aeropyrumpernix K1). Microwave irradiation (MW) as heating mode has been used to improvethe enzyme performance. Under the optimum conditions, the enzyme activity of APE1547was4.16μmol/mg/h and the enantioselectivity (E value) was52.9. Comparedwith conventional shaking, the enzyme activity and the enantioselectivity increased about21.9-fold and1.4-fold, respectively. The results also indicated that APE1547could maintain95%of its initial activity even after reusing it five times, suggestingthat the enzyme is stable under low power MW conditions.