Quantitative 31P-NMR for the Purity Determination of the Organophosphorus Compound Brigatinib and Its Method Validation

The spectrum of P-31-NMR is fundamentally simpler than that of H-1-NMR; consequently identifying the target signal(s) for quantitation is simpler using quantitative P-31-NMR (P-31-qNMR) than using quantitative H-1-NMR (H-1-qNMR), which has been already established as an absolute determination method. We have previously reported a P-31-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 P-31-qNMR at multiple laboratories. Phosphonoacetic acid (PAA) and 1,4-BTMSB-d(4) were selected as the reference standards (RSs) for P-31-qNMR and H-1-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 P-31-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 H-1-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 (3)1P-qNMR was 97.94 +/- 0.69%, which was in agreement with that determined by H-1-qNMR (97.26 +/- 0.71%), thus indicating the feasibility of purity determination of BR by P-31-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.