Study of the enantioselective binding between BOF-4272 and serum albumins by means of high-performance frontal analysis.

High-performance frontal analysis (HPFA) was incorporated in an on-line HPLC system for the study of the enantioselective binding of BOF-4272, a new xanthine oxidase inhibitor, with human, bovine and rat serum albumins. This HPLC system consists of a HPFA column (diol-silica column), an extraction column (C4 column) and a chiral separation column (beta-cyclodextrin immobilized silica column), which were connected in series via two column switching valves. After the direct injection of a solution of 0.5-400 microM racemic BOF-4272 and 550 microM serum albumin onto the HPFA column, BOF-4272 was eluted, under a mild mobile phase condition (phosphate buffer, pH 7.4, ionic strength 0.17), as a zonal peak containing a plateau region. The drug concentration in the plateau region is the same as that for the unbound drug concentration in the sample solution. A given volume of this plateau region was transferred into the extraction column, and subsequently the extracted BOF-4272 was transferred into the chiral separation column to determine the unbound concentration of each enantiomer. The binding between BOF-4272 and the serum albumins was enantioselective and species dependent. The unbound concentration of the (+)-isomer in rat serum albumin solution was 1.04-1.14 times larger than that of the antipode, while the unbound concentration of the (-)-isomer in bovine serum albumin solution was 1.04-1.16 times larger than that of the antipode. The enantioselectivity of the binding between BOF-4272 and human serum albumin was concentration dependent.(ABSTRACT TRUNCATED AT 250 WORDS)