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 biotransformati on pathway,. leads to the formation of four diastereoisomers of 4-dihydrofl obufen (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. Formatio n 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 sub strates. After incubation of substrates, the amounts and ratios of DHF dias tereoisomers and F enantiomers were assessed by HPLC, with (RR)-ULMO and te rguride-bonded columns. Considerable interspecies differences in stereosele ctivity and stereospecificity of F reductases were found at the cellular an d 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 an d rate of this inversion. (C) 2001 Wiley-Liss, Inc.