An available strategy for preparation of the major impurities in tacrolimus by silver ion complexation and preparative liquid chromatography technology.

Tacrolimus, a highly potent immunosuppressive agent produced by Streptomyces actinomycetes, is accompanied by structurally analogous impurities during its biosynthesis. In this study, a separation strategy combining silver ion complexation and preparative liquid chromatography technology was developed for isolating the major impurities in tacrolimus. Structural characterization was performed using liquid chromatography-mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. The results demonstrated that this integrated strategy effectively separates the impurities, which were identified as ascomycin, dihydrotacrolimus, and desmethylascomycin. To the best of our knowledge, this is the first report on the presence of desmethylascomycin, an unknown impurity, in tacrolimus. In conclusion, this study established a reliable and efficient method for separating and identifying tacrolimus impurities, providing a valuable contribution to the field of pharmaceutical analysis and quality control.