Binding study of semotiadil and levosemotiadil with alpha(1)-acid glycoprotein using high-performance frontal analysis

High-performance frontal analysis (HPFA) was used to investigate the bindin g properties of human alpha(1)-acid glycoprotein (AGP) with semotiadil ((R) -isomer, Ca-channel blocker) and its antipode levosemotiadil ((S)-isomer, C a- and Na-channel blockers). An on-line HPLC system consisting of a HPFA co lumn, an extraction column, and an analytical HPLC column was used to deter mine the unbound concentrations of these enantiomers, and the experimental data were subsequently subjected to the Scatchard analyses to estimate thei r binding parameters. The binding affinity of the (R)-isomer (K = 3.17 x 10 (7) M, n = 0.74) is approximately 1.2 times stronger than that of (S)-isome r (K = 2.59 x 10(7) M, n = 0.74), An enantioselective competitive binding s tudy indicated that both enantiomers are bound at the same site on AGP mole cules. (C) 1999 Academic Press.