A targeted partial reduction cyanylation strategy coupled with HRMS for accurate disulfide bridge mapping in...

Determining disulfide bridge connectivity in disulfide rich peptides presents significant analytical challenges, primarily due to the presence of isobaric species that cannot be distinguished by intact mass analysis alone. This study describes a targeted approach based on controlled partial reduction followed by cyanylation for the reliable assignment of disulfide linkages. The method was evaluated using representative approved cyclic peptide therapeutics, specifically Linaclotide, Plecanatide, and Ziconotide. These peptides were selected as model due to their clinical relevance, well-defined and diverse disulfide bond architectures, and their status as benchmark examples of disulfide-rich therapeutics. Partial reduction was optimized to generate mono-reduced intermediates, which were subsequently derivatized through cyanylation. This modification enabled selective cleavage at cysteine residues, producing structurally informative fragments after final reduction. These fragments were characterized using high-resolution mass spectrometry (HRMS), facilitating clear identification of disulfide connectivity. The proposed workflow demonstrates high reproducibility and analytical consistency, with excellent mass accuracy and enhanced structural resolution relative to conventional methodologies. Notably, it enables reliable differentiation of disulfide isomers that are otherwise indistinguishable using routine analytical techniques. Overall, this study establishes a practical and robust method for disulfide bond mapping in cyclic peptides, with broad applicability for structural characterization and quality assessment and don't require enzymatic digestion or specialized instrumentation.The methodology was successfully validated using Linaclotide, Plecanatide, and Ziconotide, which contain three, two, and three disulfide bridges, respectively.