Kinetic Analysis of Molecular Interconversion of Immunosuppressant FK506 by High-Performance Liquid Chromatography

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Abstract
High-performance liquid chromatography of FK506, a macrolide immunosuppressant, was performed on a reversed-phase column. The peak was broad with the column kept at room temperature, which was accounted for by slow interconversion between the two forms of FK506. With the use of a heated column, a sharp peak was observed because of the rapid interconversion at high temperature. When the column was cooled to 0°C, two sharp peaks were observed because essentially no interconversion occurred at 0°C during elution. Analysis of the chromatograms obtained at various eluant flow rates indicated that the conversion of the two forms follows first-order kinetics, and the apparent activation energies for the conversions were calculated. The interconvertibility between two molecular forms may be related to the immunosuppressive activity.