Targeted partial reduction cyanylation strategy accurately maps disulfide bridges in cyclic peptides like Linaclotide

Accurate determination of disulfide bridge connectivity in disulfide-rich peptides presents significant analytical challenges, primarily due to the presence of isobaric species that cannot be differentiated by intact mass analysis alone. This ambiguity hinders robust structural characterization and quality assessment for peptide therapeutics. Current methods often fall short in resolving these complex structures, necessitating advanced techniques to ensure the integrity and efficacy of clinically relevant cyclic peptides. A reliable method for disulfide bond mapping is crucial for both drug development and quality control.

Researchers developed a targeted approach for disulfide linkage assignment using controlled partial reduction followed by cyanylation. The method was evaluated with approved cyclic peptide therapeutics: Linaclotide, Plecanatide, and Ziconotide, selected for their clinical relevance and diverse disulfide architectures. Partial reduction was optimized to generate mono-reduced intermediates. These intermediates were then derivatized via cyanylation, enabling selective cleavage at cysteine residues. The resulting structurally informative fragments were characterized using high-resolution mass spectrometry (HRMS) to identify disulfide connectivity.

The proposed workflow demonstrated high reproducibility and analytical consistency, achieving excellent mass accuracy and enhanced structural resolution compared to conventional methodologies. It successfully enabled reliable differentiation of disulfide isomers, which are otherwise indistinguishable by routine analytical techniques. The methodology was validated using Linaclotide, containing three disulfide bridges; Plecanatide, with two disulfide bridges; and Ziconotide, also with three disulfide bridges. This approach produced clear identification of disulfide connectivity for all model peptides. > The method achieved excellent mass accuracy and enhanced structural resolution, reliably differentiating disulfide isomers in complex cyclic peptides.