Tools and workflow for structure elucidation of drug degradation products

Differential role of potential stressors, underlying degradation mechanism, characterization of degradants using LC-MS/MS, and establishment of a stability-indicating analytical method for duvelisib

Duvelisib (DUV) was first approved globally in 2018. An extensive literature search revealed that the differential role of a potential degradation medium in altering the shelf-life of DUV due to its exposure during storage has not been identified till date. Moreover, its degradation impurities and degradation mechanism are not known. In addition, no analytical method has been reported for the quantification of DUV in the presence of its degradation impurities. Therefore, the aim of this study was to identify the impact of different potential degradation media on the stability of DUV, establish the degradation mechanism, and identify its major degradation impurities. The aim was also to establish a stability-indicating analytical method for the quantification of DUV in the presence of its degradation impurities. This study is the first to report the structure of degradation impurities and the step-by-step degradation mechanism of DUV. This information will be useful for the scientific community and manufacturers in optimizing the formulation parameters and/or storage conditions. The validated method can be employed for analysis of stability study and routine quality control samples of newer DUV formulations in pharmaceutical industries. The identified impurities may serve as impurity standards for specifying their limits in the drug after required qualification studies.

A critical assessment on stability behaviour of Vorinostat using LC-MS-QTOF with H/D exchange and NMR

Vorinostat is the first USFDA-approved HDAC inhibitor for the treatment of cutaneous t-cell lymphoma. Vorinostat was exposed to ICH-recommended hydrolytic (acid, base, and neutral), oxidative, thermal, and photolytic stress conditions to understand the degradation behaviour. A Stability indicating LC method was developed and validated for separating and identifying forced degradation products. Under different stress conditions, six degradants were identified and characterized by LC-HRMS, MS/MS, and hydrogen-deuterium exchange mass studies. Vorinostat was found to be highly susceptible to the acidic and basic environment. In contrast, the drug substance was stable in the solid state under thermal and photolytic conditions whereas, it was found moderately stable when photolytic stress was provided to dissolved state of Vorinostat in acetonitrile-water. The degradants were identified as 7-amino-N-phenylheptanamide, 8-hydrazineyl-8-oxo-N-phenyloctanamide, 8-oxo-8-(phenylamino)octanoic acid, 8-oxo-8-(2-(7-oxo-7-(phenylamino)heptyl)hydrazineyl)-N-phenyloctanamide, 8,8'-(1-hydroxyhydrazine-1,2-diyl)bis(8-oxo-N-phenyloctanamide), and N1-((8-oxo-8-(phenylamino)octanoyl)oxy)-N8-phenyloctanediamide. The mechanistic explanation for the formation of each degradant in stability conditions has also been derived. The major degradants were also isolated/synthesized and characterized through 1H NMR for preparing impurity standards. Additionally, in-silico toxicity of the degradants was predicted in comparison to the drug, to identify whether any degradant has any specific type of toxicity and requires special focus to set specification limits during formulation development. The predicted toxicity indicated that the degradants have similar safety profile as that of the drug and specification can be set as per general impurity guideline.

The degradation map process - a tool for obtaining a lean stability strategy in drug development

Stability is fundamental when exploring a drug candidate's potential as a drug product. During the pharmaceutical industry drug development process information regarding stability and degradation are captured in different departments, e.g. from discovery to operations, and will be included in the overall control strategy. With a profound understanding of a drug candidate's degradation chemistry, a science and risk based approach in progressing a lean stability strategy is possible. This case study present a clear and visible concept to facilitate a lean stability strategy by the use of degradation maps and describes a process for how these can be used during drug development. The understanding of possible and/or observed degradation pathways will guide the design of the drug product and stability studies in development. A degradation map displays degradation pathways with short comments on the reaction/mechanism involved. The degradation map process starts with a theoretical degradation map. The map is updated as the drug project progresses, preferably after forced degradation experiments, after compatibility studies and finally when the late stage formulation is set. The degradation map should be used to capture information of intrinsic chemical properties of the active pharmaceutical ingredient (API) and can thereby be used to mitigate stability issues. The map is foremost a cross-functionally available tool collecting and visualizing stability information throughout the development process, and as such a valuable tool to efficiently develop a lean stability strategy.

Kinetic Modeling of API Oxidation: (1) The AIBN/H2O/CH3OH Radical "Soup"

Stress testing of active pharmaceutical ingredients (API) is an important tool used to gauge chemical stability and identify potential degradation products. While different flavors of API stress testing systems have been used in experimental investigations for decades, the detailed kinetics of such systems as well as the chemical composition of prominent reactive species, specifically reactive oxygen species, are unknown. As a first step toward understanding and modeling API oxidation in stress testing, we investigated a typical radical "soup" solution an API is subject to during stress testing. Here we applied ab initio electronic structure calculations to automatically generate and refine a detailed chemical kinetics model, taking a fresh look at API oxidation. We generated a detailed kinetic model for a representative azobis(isobutyronitrile) (AIBN)/H₂O/CH₃OH stress-testing system with a varied cosolvent ratio (50%/50%-99.5%/0.5% vol water/methanol) for 5.0 mM AIBN and representative pH values of 4-10 at 40 °C that was stirred and open to the atmosphere. At acidic conditions, hydroxymethyl alkoxyl is the dominant alkoxyl radical, and at basic conditions, for most studied initial methanol concentrations, cyanoisopropyl alkoxyl becomes the dominant alkoxyl radical, albeit at an overall lower concentration. At acidic conditions, the levels of cyanoisopropyl peroxyl, hydroxymethyl peroxyl, and hydroperoxyl radicals are relatively high and comparable, while, at both neutral and basic pH conditions, superoxide becomes the prominent radical in the system. The present work reveals the prominent species in a common model API stress testing system at various cosolvent and pH conditions, sets the stage for an in-depth quantitative API kinetic study, and demonstrates the usage of novel software tools for automated chemical kinetic model generation and ab initio refinement.

Efficient and Straightforward Syntheses of Two United States Pharmacopeia Sitagliptin Impurities: 3-Desamino-2,3-dehydrositagliptin and 3-Desamino-3,4-dehydrositagliptin

Various organic impurities (starting materials, reagents, intermediates, degradation products, by-products, and side products) could be present in active pharmaceutical ingredients affecting their qualities, safeties, and efficacies. Herein, we present the efficient syntheses of two United States Pharmacopeia impurities of an antidiabetic drug sitagliptin, a potent and orally active dipeptidyl peptidase IV inhibitor: 3-desamino-2,3-dehydrositagliptin and 3-desamino-3,4-dehydrositagliptin. Our three-step synthetic approach is based on the efficient cobalt-catalyzed cross-coupling reaction of 1-bromo-2,4,5-trifluorobenzene and methyl 4-bromocrotonate in the first step, followed by hydrolysis of corresponding ester with 3 M HCl to (E)-(2,4,5-trifluorophenyl)but-2-enoic acid in high overall yield, whereas the reaction with 3 M NaOH resulted in the carbon-carbon double bond regio-isomerization and hydrolysis to give the (E)-(2,4,5-trifluorophenyl)but-3-enoic acid in 92% yield. Both acid derivatives were converted to title compounds via the amide bond formation with 3-(trifluoromethyl)-5,6,7,8-tetrahydro-[1,2,4]triazolo[4,3-a]pyrazine. Extensive screening of coupling/activation reagents, bases, and solvents reviled that the amide bond is formed the most efficiently using the (COCl)2/Et3N in THF or alternatively EDC/NMM/(DMAP or HOBt) in DMF obtaining the title compounds in 68-76% yields and providing the overall yields for the three-step process in the range of 57-64% on a gram scale. The presented study also demonstrates the importance of a proper selection of solvent, base, and coupling/activating reagent for amide bond formation using Michael acceptor-type allylbenzene derivatives as coupling partners to minimize the carbon-carbon double bond regio-isomerization.

Application of (LC/)MS/MS precursor ion scan for evaluating the occurrence, formation and control of polar halogenated DBPs in disinfected waters: A review

Water disinfection can result in the unintended formation of halogenated disinfection byproducts (DBPs), which have been the subject of intensive investigation over the past 40 years. Robust methods for evaluating and characterizing the formation of halogenated DBPs are prerequisites for ultimately controlling the formation of DBPs and ensuring quality and safe disinfected water. Only a fraction of the total organic halogen (TOX) formed during disinfection has been chemically identified or even well characterized by the classical (derivatization-)gas chromatography/mass spectrometry (GC/MS) method. Such a method may not be amenable to the detection of polar halogenated DBPs, which constitute a major portion of the TOX that is still unaccounted for. Accordingly, a novel precursor ion scan (PIS) method using (liquid chromatography/) electrospray ionization-triple quadrupole mass spectrometry was developed for the rapid selective detection of all polar halogenated DBPs-no matter whether the DBPs are known or unknown-in water. This article reviews recent literature on the application of the PIS method for evaluating the occurrence, formation and control of polar halogenated DBPs in disinfected waters. The challenges in developing the PIS method were briefly summarized. Application of the powerful method pinpointed >150 previously unknown DBPs and revealed the formation, speciation and transformation of halogenated DBPs in disinfected drinking water, wastewater effluents, and swimming pool water. For the same source water, positive correlations were found between the total ion intensity (TII) levels in the PIS spectra of m/z 35/79/126.9 and the total organic chlorine/bromine/iodine levels in the disinfected water sample, and a disinfected sample with a higher TII level generally showed a higher toxic potency. Accordingly, the TII value can be used as a surrogate to comparatively reflect the water quality and assess the efficiency of a DBP control approach. To achieve a more comprehensive and systematic understanding of the DBP compositions in different waters and thus better control the DBP formation and reduce their overall toxicity, topics for future work were discussed.

Exploring the chemistry of complex samples by tentative identification and semiquantification: A food contact material case

In fields such as food safety and environmental chemistry, ensuring safety is greatly challenged by large numbers of unknown substances occurring. Even with current state-of-the-art mass spectrometers, dealing with nonidentified substances is a very laborious process as it includes structure elucidation of a vast number of unknowns, of which only a fraction may be relevant. Here, we present an exploration and prioritization approach based on high-resolution mass spectrometry. The method uses algorithm-based precursor/product-ion correlations on quadrupole time-of-flight tandem mass spectrometry data to retrieve the most likely chemical match from a structure database. In addition, time-of-flight-only data are used to estimate analyte concentration via semiquantification. The method is demonstrated in recycled paper food contact material. Here, 585 chromatographic peaks were discovered, of which 117 were unique to the sample and could be tentatively elucidated via accurate mass, isotopic pattern, and precursor/product-ion correlations. Nearly 85% of these 117 peaks were matched with database entries, which provided varying certainty of information about the analyte structure. Semiquantitative concentration ranges of investigated compounds were between 0.7 and 1600 μg dm^-2 . With these data, a subgroup of chemicals was risk-categorized and prioritized by using the most likely candidate structure(s) obtained. Prioritization based on expected health impact was possible by using the tentatively assigned data. Overall, the described method not only is a valuable chemical exploration tool for nonidentified substances but may also be used as a preliminary prioritization tool for substances expected to have the highest health impact, for example, in food contact materials.

Levothyroxine sodium revisited: A wholistic structural elucidation approach of new impurities via HPLC-HRMS/MS, on-line H/D exchange, NMR spectroscopy and chemical synthesis

The structural elucidation of unknown pharmaceutical impurities plays an important role in the quality control of newly developed and well-established active pharmaceutical ingredients (APIs). The United States Pharmacopeia (USP) monograph for the API Levothyroxine Sodium, a synthetic thyroid hormone, features two high pressure liquid chromatography (HPLC) methods using UV-VIS absorption detection to determine organic impurities in the drug substance. The impurity profile of the first USP method ("Procedure 1") has already been extensively studied, however for the second method ("Procedure 2"), which exhibits a significantly different impurity profile, no wholistic structural elucidation of impurities has been performed yet. Applying minor modifications to the chromatographic parameters of USP "Procedure 2" and using various comprehensive structural elucidation methods such as high resolution tandem mass spectrometry with on-line hydrogen-deuterium (H/D) exchange or two-dimensional nuclear magnetic resonance spectroscopy (NMR) we gained new insights about the complex impurity profile of the synthetic thyroid hormone. This resulted in the characterization of 24 compounds previously unknown to literature and the introduction of two new classes of Levothyroxine Sodium impurities. Five novel compounds were unambiguously identified via isolation or synthesis of reference substances and subsequent NMR spectroscopic investigation. Additionally, Collision-Induced Dissociation (CID)-type fragmentation of identified major impurities as well as neutral loss fragmentation patterns of many characterized impurities were discussed.

NIR hyperspectral imaging to evaluate degradation in captopril commercial tablets

Pharmaceutical quality control is important for improving the effectiveness, purity and safety of drugs, as well as for the prevention or control of drug degradation. In the present work, near infrared hyperspectral images (HSI-NIR) of tablets with different expiration dates were employed to evaluate the degradation of captopril into captopril disulfide in different layers, on the top and on the bottom surfaces of the tablets. Multivariate curve resolution (MCR) models were used to extract the concentration distribution maps from the hyperspectral images. Afterward, multivariate image techniques were applied to the concentration distribution maps (CDMs), to extract features and build models relating the main characteristics of the images to their corresponding manufacturing dates. Resolution methods followed by extracting features were able to estimate the tablet manufacture date with a prediction error of 120days. The model developed could be useful to evaluate whether a sample shows a degradation pattern consistent with the date of manufacturing or to detect abnormal behaviors in the natural degradation process of the sample. The information provided by the HIS-NIR is important for the development of the process (QbD), looking inside the formulation, revealing the behavior of the active pharmaceutical ingredient (API) during the product's shelf life.

Pharmaceutical impurities and degradation products: uses and applications of NMR techniques

Current standards and regulations demand the pharmaceutical industry not only to produce highly pure drug substances, but to achieve a thorough understanding of the impurities accompanying their manufactured drug substances and products. These challenges have become important goals of process chemistry and have steadily stimulated the search of impurities after accelerated or forced degradation procedures. As a result, impurity profiling is one of the most attractive, active and relevant fields of modern pharmaceutical analysis. This activity includes the identification, structural elucidation and quantitative determination of impurities and degradation products in bulk drugs and their pharmaceutical formulations. Nuclear magnetic resonance (NMR) spectroscopy has evolved into an irreplaceable approach for pharmaceutical quality assessment, currently playing a critical role in unequivocal structure identification as well as structural confirmation (qualitative detection), enabling the understanding of the underlying mechanisms of the formation of process and/or degradation impurities. NMR is able to provide qualitative information without the need of standards of the unknown compounds and multiple components can be quantified in a complex sample without previous separation. When coupled to separative techniques, the resulting hyphenated methodologies enhance the analytical power of this spectroscopy to previously unknown levels. As a result, and by enabling the implementation of rational decisions regarding the identity and level of impurities, NMR contributes to the goal of making better and safer medicines. Herein are discussed the applications of NMR spectroscopy and its hyphenated derivate techniques to the study of a wide range pharmaceutical impurities. Details on the advantages and disadvantages of the methodology and well as specific challenges with regards to the different analytical problems are also presented.