An artifactual solution degradant of pregabalin due to adduct formation with acetonitrile catalyzed by alkaline impurities during HPLC sample preparation

Investigation of nirmatrelvir epimerization occurred in analytical sample solution by using high resolution LC-MSn, NMR, and hydrogen/deuterium exchange study

During the related substances testing of nirmatrelvir, an unknown peak was observed and the level of the peak increased over time during the storage of the sample solution. By using a strategy including LC-PDA/UV-MSⁿ analysis, the degradant was rapidly identified as an epimer of nirmatrelvir, a solution degradation product that is caused by the trace amount of alkaline impurities leaching from the glass HPLC vials. In addition, by using hydrogen/deuterium exchange NMR spectroscopy analysis, the epimerization position was determined to be the carbon α to the adjacent cyano group. Further investigation indicated that the occurrence of the solution degradation can be suppressed when the glass HPLC vials were replaced by plastic HPLC or mass spectrometric grade vials.

Forced degradation studies of elagolix sodium with the implementation of high resolution LC-UV-PDA-MSn (n = 1,2,3…) and NMR structural elucidation

Elagolix sodium (ELS) is a marketed product using to release moderate to severe endometriosis-associated pain. It contains functional groups such as carboxyl group, secondary amino group, 2,4-dioxo pyrimidinyl and several benzyl or benzyl-like position hydrogen atom that are susceptive to occur stress degradation. Forced degradation studies of ELS reveal different degradation profiles of the drug substance which are conducted under photo, thermal, acidic, neutral, alkaline and hydrogen peroxide oxidative conditions in the direction of the ICH guidances. With structural elucidation of LC-PDA/UV-MSⁿ and NMR, the degradants were identified, and seven new degradants are reported in this study. It is confirmed that most of the degradation behaviors of ELS are related to the carboxyl group and secondary amino group in the 3-carboxyl propylamine side chain. Under the oxidative condition using hydrogen peroxide as the oxidant, the secondary amine was oxidized to form an N-hydrogen amine degradant and two further degradants of amine and carbonyl analogs were generated. Under the alkaline degradation condition, the ELS is proven to be stable and no obvious degradants are produced. On the other hand, under the acidic and neutral degradation condition, the 2,4-dioxo pyrimidinyl core of elagolix sodium is stable but the carboxyl group and secondary amine will occur ring cyclization to form the δ-lactam analogs of elagolix sodium. The plausible mechanisms for the degradation of acidic, thermal, photo-degradative and hydrogen peroxide mediated oxidative of elagolix sodium are proposed. It is worth to note that DP-3-4 are the potential degradants which are only found in the solution degradation and are not the real impurities of elagolix sodium.

Quantitative Method for Liquid Chromatography–Mass Spectrometry Based on Multi-Sliding Window and Noise Estimation

LC-MS/MS uses information on the mass peaks and peak areas of samples to conduct quantitative analysis. However, in the detection of clinical samples, the spectrograms of the compounds are interfered with for different reasons, which makes the identification of chromatographic peaks more difficult. Therefore, to improve the chromatographic interference problem, this paper first proposes a multi-window-based signal-to-noise ratio estimation algorithm, which contains the steps of raw data denoising, peak identification, peak area calculation and curve fitting to obtain accurate quantitative analysis results of the samples. Through the chromatographic peak identification of an extracted ion chromatogram of VD2 in an 80 ng/mL standard and the spectral peak identification of data from an open-source database, the identification results show that the algorithm has a better peak detection performance. The accuracy of the quantitative analysis was verified using the LC-HTQ-2020 triple quadrupole mass spectrometer produced by our group for the application of steroid detection in human serum. The results show that the algorithm proposed in this paper can accurately identify the peak information of LC-MS/MS chromatographic peaks, which can effectively improve the accuracy and reproducibility of steroid detection results and meet the requirements of clinical testing applications such as human steroid hormone detection.

Investigation of an artificial solution degradant of linagliptin: An undesired linagliptin urea derivative generates in sample preparation of linagliptin tablet treated by sonication in acetonitrile containing diluent

During the related substances testing method development for linagliptin tablet, an unknown peak was observed in HPLC chromatograms with a level exceeding the identification threshold. By using a strategy that combines LC-PDA/UV-MSⁿ with mechanism-based stress studies, the unknown peak was rapidly identified as linagliptin urea, a solution degradant that is caused by the reaction between the API and hydrocyanic acid with sonication treatment to accelerate dissolution of the drug substance in sample preparation of linagliptin tablets, and hydrocyanic acid is a known impurity in HPLC grade acetonitrile and acetonitrile is used as part of diluent. The mechanism of the solution degradation chemistry was verified by stressing linagliptin API with trimethylsilyl cyanide (TMSCN, which can give off HCN slowly in the presence of water) treated with sonication in the sample preparation. Further investigation found that when the sonication treatment was replaced by vortex vibration in the process of the sample preparation, the RRT 1.28 species was decreased to below the level of the detection limit (0.02%). The structure of this impurity was further confirmed through the synthesis of the impurity and subsequent structure characterization by 1D and 2D NMR. Due to the presence of trace amount of HCN in HPLC grade acetonitrile, these types of solution degradation would likely occur in analysis of pharmaceutical finished products containing APIs with primary and secondary amine moieties drug product during sample preparations, particularly when sonication treatment is used to accelerate dissolution of drug substance from the finished drug product. In the GMP quality control laboratories, such events may trigger undesirable out-of-specification (OOS) events. Hence, the results of this paper can help to prevent these events from happening in the first place or resolve these OOS events in GMP laboratories.

Study of the isomeric Maillard degradants, glycosylamine and Amadori rearrangement products, and their differentiation via MS2 fingerprinting from collision-induced decomposition of protonated ions

RATIONALE

The focus of this work was to study glycosylamine and Amadori rearrangement products (ARPs), the two major degradants in the Maillard reactions of pharmaceutical interest, and utilize their MS² fingerprints by liquid chromatography/high-resolution tandem mass spectrometry (LC/HRMS² ) to quickly distinguish the two isomeric degradants. These two types of degradants are frequently encountered in the compatibility and stability studies of drug products containing primary or secondary amine active pharmaceutical ingredients (APIs), which are formulated with excipients consisting of reducing sugar functionalities.

METHODS

Vortioxetine was employed as the primary model compound to react with lactose to obtain the glycosylamine and ARP degradants of the Maillard reaction, and their MS² spectra (MS² fingerprints) were obtained by LC/MS² . Subsequently, the two degradants were isolated via preparative HPLC and their structures were confirmed by one- and two-dimensional (1D and 2D) nuclear magnetic resonance (NMR) determination.

RESULTS

The MS² fingerprints of the two degradants display significantly different profiles, despite the fact that many common fragments are observed. Specifically, protonated glycosylamine shows a prominent characteristic fragment of [M_vort  + C₂ H₃ O]⁺ at m/z 341 (M_vort is the vortioxetine core), while protonated ARP shows a prominent characteristic fragment of [M_vort  + CH]⁺ at m/z 311. Further study of the Maillard reactions between several other structurally diverse primary/secondary amines and lactose produced similar patterns.

CONCLUSIONS

The study suggests that the characteristic MS² fragment peaks and their ratios may be used to differentiate the glycosylamine and ARP degradants, the two isomeric degradants of the Maillard reaction, which are commonly encountered in finished dosage forms of pharmaceutical products containing primary and secondary amine APIs.

Structure elucidation and formation mechanistic study of a methylene-bridged pregabalin dimeric degradant in pregabalin extended-release tablets

During the pharmaceutical development of pregabalin extended-release tablets, an unknown degradant at a relative retention time (RRT) of 11.7 was observed and its nominal amount exceeded the ICH identification threshold in an accelerated stability study. The aim of this study is to identify the structure and investigate the formation mechanism of this impurity for the purpose of developing a chemically stable pharmaceutical product. By utilizing multi-stage LC-MS analysis in conjunction with mechanism-based stress study, the structure of the RRT 11.7 impurity was rapidly identified as a dimeric degradant that is caused by dimerization of two pregabalin molecules with a methylene bridging the two pregabalin moieties. The structure of the dimer was confirmed by 1D and 2D NMR measurement. The formation pathway of the dimeric degradant was also inferred from the mechanism-based stress study, which implicated that the bridging methylene could originate from formaldehyde which might be the culprit that triggers the dimerization in the first place. The subsequent API-excipients compatibility study indicated that the degradant was indeed formed in the compatibility experiments between pregabalin API and two polymeric excipients (PEO and PVPP) that are known to contain residual formaldehyde, but only in the co-presence of another excipient, colloidal silicon dioxide (SiO₂). The kinetic behavior of the degradant formation was also investigated and two kinetic models were utilized based on the Arrhenius and Eyring equations, respectively, to calculate the activation energy (E_a) as well as the enthalpy of activation (△H^‡), entropy of activation (△S^‡), and Gibbs free energy (△G^‡) of the degradation reaction. The results of this study would be useful for the understanding of similar dimeric degradant formation in finished products of drug substances containing primary or secondary amine moieties.