Supercritical Fluid Chromatography for Separating Chemotherapy Anti-Nausea Medication

In a recent study led by scientists from the Institute of Medicinal Biotechnology, Peking Union Medical College and Chinese Academy of Medical Sciences in Beijing, China, scientists developed a new supercritical fluid chromatography (SFC)-based method of separating palonosetron hydrochloride and its impurities. Their findings were published in the Journal of Chromatography A (1).

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Palonosetron hydrochloride is a highly selective 5-hydroxytryptamine 3 receptor antagonist that was recently approved by the U.S. Food and Drug Administration (FDA) for preventing acute or delayed nausea and vomiting caused by chemotherapy. This compound is injected intravenously and works by blocking the action of serotonin, a natural substance that may cause nausea and vomiting (2). Separating palonosetron hydrochloride and its impurities can present significant challenges, especially regarding distinguishing the compound with multiple chiral centers and its isomers, as well as discerning between achiral compounds with closely resembling structures. Primarily, two chiral centers existing in the structure of palonosetron hydrochloride escalates how many isomers are needed for separation, thus demanding heightened resolution for baseline separation, the research team wrote in the study (1).

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In this study, the scientists developed a novel supercritical fluid chromatography (SFC) method with reduced organic solvent consumption and robust separation capabilities to address these challenges. This method was applied to simultaneously achieve enantioselective, diastereoselective, and achiral separation of palonosetron hydrochloride and its six impurities. Further, the effects of the polysaccharide-based chiral stationary phase (CSP), modifier, additive, and column temperature on retention and separation were comprehensively evaluated. Overall, it was found that due to high structural similarity, one could not achieve complete separation with a combination of a polysaccharide-based CSP and a single modifier or a mixture of protonic modifiers. However, when the scientists used an ADH column and a ternary solvent mixture containing acetonitrile, satisfying separation was provided, notably for the enantiomer and diastereomers of palonosetron.

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The experimental findings highlighted acetonitrile, an aprotic solvent, as having a critical role in the modifier for efficient analyte separation, especially for the four isomers. Through both thermodynamic and molecular docking studies, a plausible separation mechanism was proposed, emphasizing the significance of hydrogen bonds and π-π interactions in recognition processes. Isomer separation mainly relies on differences in hydrogen bond interactions, while achiral separation mainly relies on the differences in hydrogen bond and π-π interactions, the scientists wrote. With this optimized method, the enantioselective, diastereoselective, and achiral separation of palonosetron hydrochloride and its six impurities could be accomplished in 18 min under gradient elution. Thermodynamic results also showed the separation process to be entropy-driven.

According to the scientists, this is the first report of simultaneous SFC separation of enantiomers, diastereoisomers, and highly structurally similar compounds. These findings demonstrate SFC’s ability to simultaneously separate above compounds while offering insights for developing quality control methods for palonosetron hydrochloride. Further, by matching the mass flow and mass composition of a mobile phase together with column outlet pressure and column average temperature, corresponding preparative SFC approaches are expected to be developed for palonosetron hydrochloride according to the analytical methods proposed in this study.

References

(1) Qiu, X.; Liu, Y.; Zhao, X.; Lian, X.; et al. Economical and Rapid Enantioselective, Diastereoselective and Achiral Separation of Palonosetron Hydrochloride and its Impurities Using Supercritical Fluid Chromatography. J. Chromatogr. A 2024, 1736, 465342. DOI: 10.1016/j.chroma.2024.465342

(2) Palonosetron Injection. MedlinePlus 2024. https://medlineplus.gov/druginfo/meds/a610002.html (accessed 2024-10-30)