Structural Elucidation of Unknown Impurities in the Kinase Inhibitor Imatinib Using UHPLC and High-Resolution Mass Spectrometry

Importance of the Topic

Pharmaceutical impurities and degradation products can critically impact drug safety and performance. Characterizing trace-level contaminants in active pharmaceutical ingredients is essential to mitigate risk and streamline product development.

Objectives and Study Overview

This study aimed to identify and structurally elucidate four previously unknown impurities observed during the synthesis of the kinase inhibitor imatinib. The work combined high-resolution UHPLC separation, HDMSE data acquisition, informatics-driven library matching, expert interpretation, and chemical synthesis for final confirmation.

Methodology and Instrumentation

• UHPLC Separation: ACQUITY UPLC I-Class with Premier CSH Phenyl-Hexyl 1.7 µm column at 35 °C, gradient from 0.5 % to 100 % acetonitrile over 10 min.
• Mass Spectrometry: Vion IMS QTof platform operated in ESI positive and negative modes; HDMSE acquisition with low/high energy ramps.
• Data Analysis: UNIFI 1.9.4 software for formula generation, fragment assignment, in silico library searching, and custom structure import.

Main Results and Discussion

• Optimized UHPLC conditions achieved baseline separation of imatinib, nine known impurities, and four unknown peaks.
• Elucidation Tool assigned high-confidence structures to Unknowns 1 and 2; expert-driven fragmentation and custom library searches resolved Unknowns 3 and 4.
• Case Study (Unknown 3): identification of adduct patterns, calculation of molecular formula and double bond equivalents, detailed fragmentation pathway proposals in positive and negative modes, followed by custom synthesis of the benzoic acid derivative.
• Confirmation: matching retention times, UV spectra at 267 nm, HDMSE and MS/MS profiles, and spiking experiments validated the proposed structures.

Benefits and Practical Applications

• High-resolution chromatography and HR-MS/MS enable rapid impurity profiling without the need for time-consuming fraction collection.
• Integrated informatics tools streamline formula generation, fragment matching, and library searches.
• Custom synthesis of candidates provides unambiguous structural confirmation.
• The workflow is readily transferable to other pharmaceutical impurities and degradation studies.

Future Trends and Applications

Advances in ion mobility separation, expanded spectral libraries, and machine-learning–driven fragmentation prediction will further accelerate impurity identification. Integration with automated workflows and cloud-based databases promises even greater throughput and confidence in structure assignments.

Conclusion

The combination of UHPLC, HDMSE, informatics tools, expert interpretation, and targeted synthesis offers a comprehensive strategy for uncovering and confirming unknown pharmaceutical impurities. This modern LC-MS workflow enhances drug safety assessments and supports efficient product development.

References

1. Liu Y. et al. Mass spectrometry-based structure elucidation of small molecule impurities and degradation products in pharmaceutical development. Trends Anal. Chem. 121, 115686 (2019).
2. Pan C. et al. Identification of Pharmaceutical Impurities in Formulated Dosage Forms. J. Pharm. Sci. 100, 1228–1259 (2011).
3. Li M. et al. Application of LC–MSn in conjunction with mechanism-based stress studies in the elucidation of drug impurity structure. J. Pharm. Biomed. Anal. 48, 1451–1456 (2008).
4. Tian Z. et al. Strategies for structure elucidation of small molecules based on LC–MS/MS data from complex biological samples. Comput. Struct. Biotechnol. J. 20, 5085–5097 (2022).
5. Kind T. et al. Advances in structure elucidation of small molecules using mass spectrometry. Bioanal. Rev. 2, 23–60 (2010).
6. Stein S. Chemical Substructure Identification by Mass Spectral Library Searching. J. Am. Soc. Mass Spectrom. 6, 644–655 (1995).
7. Chen P. et al. Modernized Impurity Analysis of the Kinase Inhibitor Imatinib by High-Resolution LC with MS-Compatible Mobile Phases. Waters App. Note 720007340 (2021).
8. European Pharmacopeia 10.0, 2926–2928.