Biotransformation of flobufen enantiomers in ruminant hepatocytes and subcellular fractions

Flobufen ( F ), a new antiinflammatory drug, has one chiral and one prochiral center in its structure. Reduction of rac ‐ F , the principal biotransformation pathway, leads to the formation of four diastereoisomers of 4‐dihydroflobufen ( DHF ). F was chosen as a model substrate for interspecies comparison of activity, stereospecificity, and stereoselectivity of biotransformation enzymes in fallow bucks, red deer stags, and roe bucks in vitro. Formation of F metabolites was examined in hepatocyte suspension and in subcellular fractions of liver homogenate. (+)‐R ‐F , (−)‐S ‐F and rac ‐ F were used as substrates. After incubation of substrates, the amounts and ratios of DHF diastereoisomers and F enantiomers were assessed by HPLC, with (R,R)‐ULMO and terguride‐bonded columns. Considerable interspecies differences in stereoselectivity and stereospecificity of F reductases were found at the cellular and subcellular levels, although these ruminants are closely related. Chiral inversion of F enantiomers to their antipodes was detected in vitro in all ruminants tested, but individual species also differed in the direction and rate of this inversion. Chirality 13:760–764, 2001. © 2001 Wiley‐Liss, Inc.