Chiral Inversion of 2-Arylpropionic Acid Enantiomers under Anaerobic Conditions

Abstract

This work examined the chiral inversion of 2-arylpropionic acids (2-APAs) under anaerobic conditions and the associated microbial community. The anaerobic condition was simulated by two identical anaerobic digesters. Each digester was fed with the substrate containing 11 either pure (R)- or pure (S)-2-APA enantiomers. Chiral inversion was evidenced by the concentration increase of the other enantiomer in the digestate and the changes in the enantiomeric fraction between the two enantiomers. Both digesters showed similar and poor removal of 2-APAs (≤30%, except for naproxen) and diverse chiral inversion behaviors under anaerobic conditions. Four compounds exhibited (S → R) unidirectional inversion [flurbiprofen, ketoprofen, naproxen, and 2-(4-tert-butylphenyl)­propionic acid], and the remaining seven compounds showed bidirectional inversion. Several aerobic and facultative anaerobic bacterial genera (Candidatus Microthrix, Rhodococcus, Mycobacterium, Gordonia, and Sphingobium) were identified in both digesters and predicted to harbor the 2-arylpropionyl-CoA epimerase (enzyme involved in chiral inversion) encoding gene. These genera presented at low abundances, <0.5% in the digester dosed with (R)-2-APAs and <0.2% in the digester dosed with (S)-2-APAs. The low abundances of these genera explain the limited extent of chiral inversion observed in this study.

Designing Powerful Biindole‐Based Inherently Chiral Selectors: Enhancing Enantiodiscrimination by Core Functionalization with Additional Coordination Elements

“…in the presence of the barely active/inactive ( R ) enantiomer [30] . The two enantiomers also have different impact on the environment (for instance, they have different antibacterial effects) and can undergo configuration inversion from ( R )‐ to ( S) ‐ in anaerobic conditions [31] . Even more importantly, the same inversion has been found to occur in vivo by an enzymatic mechanism both in animals and humans, although with differences among various profens [32] .…”

“…[30] The two enantiomers also have different impact on the environment (for instance, they have different antibacterial effects) and can undergo configuration inversion from (R)to (S)-in anaerobic conditions. [31] Even more importantly, the same inversion has been found to occur in vivo by an enzymatic mechanism both in animals and humans, although with differences among various profens. [32] Thus analytical protocols enabling to discriminate among profen enantiomers can be important in various contexts, from quality/process control to biomedicine studies, to forensic and environmental impact investigations.…”