Analytical Sciences

Abstract − Analytical Sciences, 15(3), 217 (1999).

Binding Study of Semotiadil and Levosemotiadil withHuman Serum Albumin Using High-Performance Frontal Analysis
Maria Esther Rodriguez ROSAS, Akimasa SHIBUKAWA*, YukiYOSHIKAWA, Yoshihiro KURODA and Terumichi NAKAGAWA
Graduate School ofPharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501,Japan
High-performance frontal analysis (HPFA) wasapplied to investigate the binding properties of semotiadil(R-isomer, Ca-channel blocker) and levosemotiadil (S-isomer,Ca- and Na-channel blocker), an enantiomeric pair of drugs underdevelopment, to human serum albumin (HSA). An on-line HPLC systemconsisting of a HPFA column, an extraction column and an analytical HPLCcolumn was used to determine the unbound concentrations of theseenantiomers. The experimental data were subjected to Scatchard analyses toestimate the binding parameters. The binding affinity of levosemotiadil(K=6.59x105 M-1, n=0.97) is aboutthree-times stronger than that of semotiadil (K=2.15x105M-1, n=0.99). These results did not change in thepresence of warfarin, but were significantly decreased by the addition ofdiazepam, indicating that both enantiomers are bound at the diazepam siteon HSA molecule. (Keywords: Semotiadil, levosemotiadil, protein binding, albumin, highperformance frontal analysis, high-performance liquid chromatography)