Validation of an NMR-Spectroscopic Method for Authenticity Confirmation of Buserelin Acetate Pharmaceutical Substance

The specificity of different variants of an NMR spectroscopic method for authenticity confirmation of buserelin acetate drug substance was estimated by comparing PMR and 13C NMR spectra of buserelin acetate and [5-D-tyrosine]buserelin acetate in various solvents. Spectra of these diastereomers differed most if deuterated water was used as the solvent. Solvent and intramolecular non-bonded interactions influenced proton- exchange tautomerism in the L-histidine residue of the analyzed oligomers. The widths of 13C NMR resonances of this amino acid depended on the proton-exchange rate. The method based on 13C NMR spectroscopy (D2O solvent) was recommended for pharmacopoeial analysis.