Catalytic and molecular insights of the esterification of ibuprofen and ketoprofen with glycerol

Expanding Access to Optically Active Non-Steroidal Anti-Inflammatory Drugs via Lipase-Catalyzed KR of Racemic Acids Using Trialkyl Orthoesters as Irreversible Alkoxy Group Donors

Studies into the enzymatic kinetic resolution (EKR) of 2-arylpropanoic acids (‘profens’), as the active pharmaceutical ingredients (APIs) of blockbuster non-steroidal anti-inflammatory drugs (NSAIDs), by using various trialkyl orthoesters as irreversible alkoxy group donors in organic media, were performed. The enzymatic reactions of target substrates were optimized using several different immobilized preparations of lipase type B from the yeast Candida antarctica (CAL-B). The influence of crucial parameters, including the type of enzyme and alkoxy agent, as well as the nature of the organic co-solvent and time of the process on the conversion and enantioselectivity of the enzymatic kinetic resolution, is described. The optimal EKR procedure for the racemic profens consisted of a Novozym 435-STREM lipase preparation suspended in a mixture of 3 equiv of trimethyl or triethyl orthoacetate as alkoxy donor and toluene or n-hexane as co-solvent, depending on the employed racemic NSAIDs. The reported biocatalytic system provided optically active products with moderate-to-good enantioselectivity upon esterification lasting for 7–48 h, with most promising results in terms of enantiomeric purity of the pharmacologically active enantiomers of title APIs obtained on the analytical scale for: (S)-flurbiprofen (97% ee), (S)-ibuprofen (91% ee), (S)-ketoprofen (69% ee), and (S)-naproxen (63% ee), respectively. In turn, the employment of optimal conditions on a preparative-scale enabled us to obtain the (S)-enantiomers of: flurbiprofen in 28% yield and 97% ee, ibuprofen in 45% yield and 56% ee, (S)-ketoprofen in 23% yield and 69% ee, and naproxen in 42% yield and 57% ee, respectively. The devised method turned out to be inefficient toward racemic etodolac regardless of the lipase and alkoxy group donor used, proving that it is unsuitable for carboxylic acids possessing tertiary chiral centers.

Short-chain alcohols inactivate an immobilized industrial lipase through two different mechanisms

Broadly used in biocatalysis as acyl acceptors or (co)-solvents, short-chain alcohols often cause irreversible loss of enzyme activity. Understanding the mechanisms of inactivation is a necessary step toward the optimization of biocatalytic reactions and the design of enzyme-based sustainable processes. In this work, we explored the functional and structural response of an immobilized enzyme, Novozym 435, exposed to methanol, ethanol, and tert-butanol. N-435 consists of Candida antarctica lipase B (CALB) adsorbed on polymethacrylate beads and finds application in a variety of processes involving the presence of short-chain alcohols. The nature of the N-435 material required the development of an ad hoc method of structural analysis, based on Fourier transform infrared microspectroscopy, which was complemented by catalytic activity assays and by morphological observation by transmission electron microscopy. We found that the inactivation of N-435 is highly dependent on alcohol concentration and occurs through two different mechanisms. Short-chain alcohols induce conformational changes leading to CALB aggregation, which is only partially prevented by immobilization. Moreover, alcohol modifies the texture of the solid support promoting the enzyme release. Overall, knowledge of the molecular mechanisms underlying Novozym 435 inactivation induced by short-chain alcohols promises to overcome the limitations that usually occur during industrial processes. This article is protected by copyright. All rights reserved.