Isolation, identification and characterization of potential impurities of anidulafungin

Eight impurities ranging from 0.03 to 0.97% in anidulafungin bulk drug were detected by HPLC. Four impurities (Imp-I, Imp-II, Imp-III and Imp-VIII) among impurities were isolated from the self-prepared or marketed samples of anidulafungin bulk drug by means of preparative HPLC. A thorough study was undertaken to characterize these impurities and based on 1D (¹H, ¹³C, H-D, DEPT 90 and 135) and 2D (COSY, TOCSY, HSQC, HMBC) NMR and ESI-MS spectral data. Based on the characterization data, Imp-I was found to be known open-chain hydrolysis product formed during the synthesis and degradation. Imp-II and Imp-III was lacked a methyl group at the C-4 and C-8 in anidulafungin, respectively, whereas Imp-VIII contained a methoxy group at the C-23. The latter three new impurities were identified as process-related substances.