A sulfate conjugate of cyclosporin.

A metabolite of cyclosporin A was isolated from human bile and plasma. The material was identified as a sulfate conjugate by plasma desorption time-of-flight mass spectrometry and by in vitro technique using human liver preparations and radiolabeled substrates. A sulfate ester at the beta-carbon on the amino acid no. 1, the methylbutenyl-threonine amino acid, of cyclosporin was synthesized as a reference, and found to have the same plasma desorption time-of-flight and direct chemical ionization mass spectrum as the isolated metabolite. It also had the same chromatographic properties on both an ion-pair reversed phase system and an ion-exchanger. Hydrolysis with sulfuric acid on the purified and synthetic metabolite gave free cyclosporin. The amino acids in the metabolite, analyzed by gas chromatography/mass spectrometry, were the same as those in cyclosporin. Free cyclosporin was not found upon hydrolysis with commercial sulfatases.