Characterization by LC–MS/MS of oxidized products identified in synthetic peptide somatostatin and cetrorelix submitted to forced oxidative stress by hydrogen peroxide: Two case studies

Abstract In a broader scenario, the forced degradation studies provided by the ICH guidelines for Q1A, Q1B, and Q2B degradation studies allow to know the CQA of the molecule used as a drug product, to determine the appropriate analytical methods, excipients, and storage conditions ensuring the quality of the drug, its efficacy, and patient safety. In this study, we focused our attention on understanding how oxidative stress is performed by H 2 O 2 ‐impacted small synthetic peptides that do not contain residues susceptible to oxidation such as methionine. Among the amino acids susceptible to oxidation, methionine is the most reactive and depending on the structure of the protein where it is exposed, it tends to oxidize by converting into methionine sulfone or methionine sulfoxide by oxidation of its sulfur atom. Scouting experiments obtained by forced oxidative stress conditions are presented on two small synthetic peptides that do not contain any methionine residues spiked with different amounts of H 2 O 2 , and they are analyzed by LC–MS/MS. Less frequent oxidation products than those commonly observed on proteins/peptides‐containing methionine have been characterized on both peptides. The study demonstrated that somatostatin, by means of one residue of tryptophan on the molecule, can generate traces of several oxidized products detected by UPLC–MS. Furthermore, even at a negligible level, oxidation on tyrosine and proline in cetrorelix that does not contain methionine nor tryptophan has been detected by UHPLC–MS/MS. Identification and quantification of oxidized species were achieved by high‐resolution MS and MS/MS experiments. Thus, FDSs undoubtedly aid the evaluation of the CQAs as an important component of the characterization package as recommended by HAs and ICH, facilitating the understanding of unforeseen features of the studied molecule used as drugs.