CHIRAL ASSAY-METHODS FOR LIFIBROL AND METABOLITES IN PLASMA AND THE OBSERVATION OF UNIDIRECTIONAL CHIRAL INVERSION FOLLOWING ADMINISTRATIONOF THE ENANTIOMERS TO DOGS

Lifibrol, a new drug for the treatment of hypercholesterolemia, contai ns a stereogenic center bearing a secondary alcohol group. A normal-ph ase achiral-chiral HPLC separation of the enantiomers of lifibrol and two of its metabolites was developed and validated for quantitation in dog plasma. A silica and a Chiralcel OD-H column were operated in ser ies and all six enantiomeric components and internal standard were dir ectly separated. An initial solid-phase extraction (phenyl) clean-up s tep and a column-switching step to eliminate late-eluting compounds we re also utilized. The solid-phase extraction step was automated using a robotic system. Assay development, validation, and application of th e method to a bioavailability study of the racemate and enantiomers of lifibrol in dogs are described. The lower limit of quantitation was 0 .0125 mu g/ml for each enantiomer of lifibrol using 200 mu l of dog pl asma with W detection (255 nm). In dog plasma following oral or intrav enous administration of the racemate, the (R)I(S) ratio of the enantio mers of lifibrol was greater than one and increased with time. Followi ng administration of the individual enantiomers, chiral inversion of t he (S)-enantiomer but not the (R)-enantiomer was observed. (C) 1994 Wi ley-Liss, Inc.