Quantitative ³¹P-NMR for Purity Determination of Sofosbuvir and Method Validation.

Area of Science:

• Analytical Chemistry
• Nuclear Magnetic Resonance Spectroscopy
• Pharmaceutical Analysis

Background:

• Quantitative 1H-NMR (1H-qNMR) is a standard method for determining the absolute purity of organic molecules.
• Signal overlap and complexity in 1H-qNMR can hinder accurate quantitation.
• Phosphorus-31 NMR (31P-NMR) offers simpler signal patterns, making it a potential alternative for purity assessment.

Purpose of the Study:

• To investigate the utility of 31P-qNMR for determining the purity of the organophosphorus compound sofosbuvir (SOF).
• To compare the accuracy and reliability of 31P-qNMR with traditional 1H-qNMR for SOF purity analysis.
• To evaluate the impact of different solvent systems (protic vs. aprotic) on 31P-qNMR measurements.

Main Methods:

• 31P-qNMR and 1H-qNMR were performed on sofosbuvir samples using methanol-d4 and DMSO-d6 as solvents.
• Phosphonoacetic acid (PAA) and 1,4-bis(trimethylsilyl)benzene-d4 (1,4-BTMSB-d4) were used as reference standards in methanol-d4.
• PAA and sodium 4,4-dimethyl-4-silapentanesulfonate-d6 (DSS-d6) served as reference standards in DMSO-d6.

Main Results:

• In methanol-d4, 31P-qNMR yielded a purity of 100.63 ± 0.95% for SOF, while 1H-qNMR gave 99.07 ± 0.50%.
• Instability in the 31P signal of PAA in methanol-d4 was observed, attributed to deuterium exchange, affecting quantitation.
• In DMSO-d6, 31P-qNMR determined SOF purity as 99.10 ± 0.30%, closely agreeing with the 1H-qNMR value of 99.44 ± 0.29%.

Conclusions:

• 31P-qNMR is a viable and accurate method for determining the purity of organophosphorus compounds like sofosbuvir.
• Aprotic solvents are preferable for 31P-qNMR of sofosbuvir to avoid deuterium exchange issues associated with protic solvents.
• 31P-qNMR provides results comparable to 1H-qNMR, offering a potentially simpler alternative for purity assessment.