Isolation, identification, and characterization of potential impurities of doramectin and evaluation of their insecticidal activity

Abstract Seven impurities were detected in doramectin bulk drug by HPLC analysis. These impurities were named as Imp-I, Imp-II, Imp-III, Imp-IV, Imp-V, Imp-VI, and Imp-VII. All impurities were isolated from doramectin bulk drug by means of preparative HPLC. Among impurities, Imp-IV and Imp-V were unknown and have not been reported previously. Based on the complete spectral analysis, including 1D (1H, 13C, H-D, DEPT 90 and 135), 2D (COSY, HSQC, HMBC, and NOESY) NMR, IR, and ESI-HRMS, the structure of Imp-IV and Imp-V were elucidated. Imp-IV was found to be a furan ring-opening product, while Imp-V lacked a methyl group at the C-14 in doramectin. Identification, isolation, structural characterization, probable formation mechanism, and insecticidal activity of impurities of doramectin were also discussed.