Milbemycin derivatives: epoxidation of milbemycins

Structural elucidation of major degradation products of milbemycin oxime drug substance using LC-MS and NMR

Milbemycin oxime (MO) drug substance is a 16-membered macrocyclic lactone that exhibits a broad spectrum of biological activity and high potency towards parasites. In this study, a comprehensive forced degradation study was carried out on MO drug substance to identify and characterize its major degradation products (DPs). MO drug substance was subjected to acid, base, oxidation (H₂O₂), heat (solid and solution state), and photolytic (solid and solution state) stress degradation as per the ICH guidelines. Chromatographic separation of the drug substance (MO A₃ and MO A₄) and its DPs was achieved using a gradient elution on a HALO C18 column (100 × 4.6 mm, 2.7 µm). Mobile phase A consisted of water/acetonitrile (60/40, v/v) and mobile phase B consisted of ethanol/isopropanol (50/50, v/v). A total of twelve major DPs were observed for MO drug substance under various stress conditions. These DPs were further identified and characterized using liquid chromatography-high resolution mass spectrometry and comparison of their fragmentation profile with MO A₄ and MO A₃ using tandem mass spectrometry. Of these, H₂O₂ induced oxidative degradation product (3,4-dihydroperoxide MO A₄) was isolated using semi-preparative HPLC and characterized by comparison of its nuclear magnetic resonance spectroscopy data with MO A_4. The proposed structures of the DPs have been rationalized by appropriate degradation pathways for MO A₄ and MO A₃.

meta-Chloroperbenzoic acid (mCPBA): a versatile reagent in organic synthesis

This review aims to collect and discuss the synthetic applications of meta-chloroperbenzoic acid (mCPBA) over the past few decades.