It is well documented that (R)-enantiomers of profens in the presence of coenzyme A (CoA), adenosine triphosphate (ATP) and Mg are converted to active (S)-forms. The pathways of chiral inversion is illustrated taking ibuprofen as the prototype, in the scheme below.
The pathway consists mainly of three steps:
# Stereoselective activation: Stereoselective activation of (R)-profen by the formation of the thioester, in the presence of CoA, ATP and Mg. (S)-profen does not form the thioester.
# Epimerization (Racemization): The enzyme epimerase 2-arylpropionic-CoA changes the (R)-thioester to the (S)-thioester. This process is called "racemization" or "epimerization."
# Hydrolysis: With the help of hydrolase/thioesterase, thioesters are broken down into their (R)- and (S)-forms
Because the acyl-CoA thioester (profenyl-CoA) changes the structure of triglycerides and phospholipids, metabolic chiral inversion may cause toxic effects.