Quantitative ³¹P-NMR for the purity determination of the organophosphorus compound brigatinib and its method validation

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The spectrum of ³¹P-NMR is fundamentally simpler than that of ¹H-NMR; consequently identifying the target signal(s) for quantitation is simpler using quantitative ³¹P-NMR (³¹P-qNMR) than using quantitative ¹H-NMR (¹H-qNMR), which has been already established as an absolute determination method. We have previously reported a ³¹P-qNMR method for the absolute determination of cyclophosphamide hydrate and sofosbuvir as water-soluble and water-insoluble organophosphorus compounds, respectively. This study introduces the purity determination of brigatinib (BR), an organophosphorus compound with limited water solubility, using ³¹P-qNMR at multiple laboratories.

Phosphonoacetic acid (PAA) and 1,4-BTMSB-d₄ were selected as the reference standards (RSs) for ³¹P-qNMR and ¹H-qNMR, respectively. The qNMR solvents were chosen based on the solubilities of BR and the RSs for qNMR. CD₃OH was selected as the solvent for ³¹P-qNMR measurements to prevent the influence of deuterium exchange caused by the presence of exchangeable intramolecular protons of BR and PAA on the quantitative values, while CD₃OD was the solvent of choice for the ¹H-qNMR measurements to prevent the influence of water signals and the exchangeable intramolecular protons of BR and PAA. The mean purity of BR determined by ³¹P-qNMR was 97.94 ± 0.69%, which was in agreement with that determined by ¹H-qNMR (97.26 ± 0.71%), thus indicating the feasibility of purity determination of BR by ³¹P-qNMR. Therefore, the findings of this study may provide an effective method that is simpler than conventional ¹H-qNMR for the determination of organophosphorus compounds.