Preparative chromatographic purification of cyclosporine metabolites

Polar and primary metabolites of cyclosporin A (CsA) have successfully been isolated by a novel separation protocol. An efficient, easy-to-scale-up chromatographic adsorption/desorption operation recovers polar and primary CsA metabolite pools from large volumes of urine; purified CsA metabolites are subsequently obtained by high-resolution preparative elution chromatography of the semipurified metabolite pools. Separations performed on a semipreparative scale [with a 250 x 9.4 mm (i.d.) reversed-phase HPLC column] yielded microgram quantities of CsA metabolites at > 97% purity, as determined by fast atom bombardment mass spectrometry. These separations also yielded two previously unreported CsA metabolites, similar to AM1A but with an additional hydroxylation. The yield of metabolites was increased to several milligrams by performing the separations with a preparative-scale [250 x 21.2 mm (i.d.)] reversed-phase column. The production rate of purified primary CsA metabolites was greatly increased by performing the separation with the preparative-scale column under conditions of severe mass overloading. In a single chromatographic run, we successfully isolated 11.0 and 5.0 mg of AM1 and AM1c, respectively, at a purity of > 97%. As expected, this increase in the yield of purified metabolites was accompanied by a decrease in the overall recovery. This separation scheme enables the rapid processing of large volumes of urine for isolation of the milligram quantities of CsA metabolites necessary to assess their biological activity. The procedure is applicable to small- or large-scale metabolite isolation and provides a ready source of purified metabolites for in vitro and whole-animal studies.