A Simple Molecular Model to Study the Substrate Diffusion into the Active Site of a Lipase-Catalyzed Esterification of Ibuprofen and Ketoprofen with Glycerol

Lipases are enzymes widely applied in the kinetic resolution of racemic non-steroidal anti-inflammatory drugs (NSAIDs). The esterification of racemic ibuprofen and ketoprofen with glycerol catalyzed by the lipase B of Candida antarctica (CALB) was performed by some of us, achieving very different results for both NSAIDs in terms of enzymatic activity, enantio- and regioselectivity. A molecular modelling investigation allowed to establish the steric energies and the enthalpy variations along the diffusion of glycerol through the enzymatic tunnel towards the active catalytic triad of the lipase along with the interaction with the acyl enzyme species. In this context, it was possible to demonstrate that glycerol approaching the acyl enzyme of the R-ibuprofen possesses lower steric hindrance than the S-ibuprofen acyl enzyme (- 185.3 vs - 188.6 kcal mol(-1) for S and R-enantiomers, in average). Although, the steric energy is somehow similar when the acyl enzyme of the R/S-ketoprofen is considered (- 201 kcal mol(-1)) the proximity of glycerol to the aminoacid residues of the enzymatic tunnel towards the active site plays a key role. In fact, the closer distance of glycerol to the tunnel walls when the acyl enzyme of ketoprofen is present than ibuprofen (2.1 angstrom vs 2.9 angstrom) allows multiple H-bonding interactions between the polyol and the aminoacids and also increases the enthalpy of formation of glycerol-acyl enzyme species.

Automated summary

Lipases play an important role in the kinetic resolution of anti-inflammatory drugs, but the results of esterification reactions can vary greatly depending on the enzyme's selectivity and active site. Molecular modeling investigation reveals that steric energies and interactions between glycerol and enzyme species are crucial factors in determining the outcome of the reactions.