Structural annotation of electro- and photochemically generated transformation products of moxidectin using high-resolution mass spectrometry

Identification and Characterization of Acidic Degradation Products of Moxidectin Drug Substance Including Degradation Pathways Using LC, HRMS, and NMR

BACKGROUND

Moxidectin is an active pharmaceutical ingredient (API) extensively used in various drug products within the pharmaceutical and animal health sectors. Despite its widespread use, the analytical methods prescribed by the United States Pharmacopeia (USP) and European Pharmacopoeia (EP, Ph. Eur.) exhibit significant limitations. These methods fail to adequately separate key impurities of (23Z)-moxidectin (EP impurity L) and 3,4-epoxy-moxidectin, potentially affecting the quality control, purity assessment, and safety of moxidectin-containing products.

OBJECTIVE

The objective was to develop and validate an alternative, improved stability-indicating high-performance liquid chromatography (HPLC) method for the identification, assay, and quantification of related substances in the moxidectin drug substance, along with the analysis of its degradation pathways.

METHODS

High-resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR) were employed to comprehensively examine moxidectin and its two degradation products under specified acidic conditions. The degradation products were isolated and identified using a range of analytical techniques, including HRMS, NMR, and other relevant methods.

RESULTS

The epoxy derivative of moxidectin (relative retention time [RRT] = 1.2) was not identified under the studied acidic degradation conditions. HRMS data indicated that the degradant at RRT = 1.2 is an isomer of moxidectin, as it exhibited an identical molecular ion. Detailed NMR studies on moxidectin and its impurity at RRT-1.2 revealed differences in carbon and proton chemical shifts at positions C-22 and C-24, strongly supporting the identification of the structure as an oxime geometric isomer of moxidectin, i.e. (23Z)-moxidectin.

CONCLUSIONS

The findings revealed specific degradation products formed under acidic conditions, offering valuable insights into the chemical transformations of moxidectin. This information is crucial for assessing the drug's stability profile and ensuring the quality and safety of moxidectin-containing products.

HIGHLIGHTS

The HPLC method developed in this study significantly improves on existing USP/EP methods with regard to a separation of key impurities of (23Z)-moxidectin and 3,4-epoxy-moxidectin, offering robust performance for routine analysis of bulk moxidectin API batches and stability samples in quality control (QC) laboratories.

Solar photodegradation of irinotecan in water: optimization and robustness studies by experimental design

Irinotecan, a widely prescribed anticancer drug, is an emerging contaminant of concern that has been detected in various aquatic environments due to ineffective removal by traditional wastewater treatment systems. Solar photodegradation is a viable approach that can effectively eradicate the drug from aqueous systems. In this study, we used the design of experiment (DOE) approach to explore the robustness of irinotecan photodegradation under simulated solar irradiation. A full factorial design, including a star design, was applied to study the effects of three parameters: initial concentration of irinotecan (1.0-9.0 mg/L), pH (5.0-9.0), and irradiance (450-750 W/m²). A high-performance liquid chromatography coupled with a high-resolution mass spectrometry (HPLC-HRMS) system was used to determine irinotecan and identify transformation products. The photodegradation of irinotecan followed a pseudo-first order kinetics. In the best-fitted linear model determined by the stepwise model fitting approach, pH was found to have about 100-fold greater effect than either irinotecan concentration or solar irradiance. Under optimal conditions (irradiance of 750 W/m², 1.0 mg/L irinotecan concentration, and pH 9.0), more than 98% of irinotecan was degraded in 60 min. With respect to irradiance and irinotecan concentration, the degradation process was robust in the studied range, implying that it may be effectively applied in locations and/or seasons with solar irradiance as low as 450 W/m². However, pH needs to be strictly controlled and kept between 7.0 and 9.0 to maintain the degradation process robust. Considerations about the behavior of degradation products were also drawn.

Elucidation of the photoinduced transformations of Aliskiren in river water using liquid chromatography high-resolution mass spectrometry

Aliskiren was selected as a compound of potential concern among a suspect screening list of more than 40,000 substances on a basis of high occurrence, potential risk and the absence of information about its environmental fate. This study investigated the photoinduced degradation of aliskiren in river water samples spiked at trace levels exposed to simulated sunlight. A half-life time of 24 h was observed with both direct and indirect photolysis playing a role on pollutant degradation. Its photo-induced transformation involved the formation of six transformation products (TPs), elucidated by LC-HRMS - resulted from the drug hydroxylation, oxidation and moieties loss with subsequent cyclization structurally. The retrospective suspected analysis performed on a total of 754 environmental matrices evidenced the environmental occurrence of aliskiren and two TPs in surface waters (river and seawater), fresh water, sediments and biota. In silico bioassays suggested that aliskiren degradation undergoes thought the formation of TPs with distinct toxicity comparing with the parent compound.