Snap-Trapping Strategy for Amine-Specific Bioconjugation with Pyridotriazole Carbaldehydes

While thiol-targeting methods have long defined the gold standard in bioconjugation, selective and clean modification of more abundant but intrinsically less nucleophilic amine groups remains a challenge. Methods that match the reactivity and precision of thiol chemistry, while maintaining strict thiol orthogonality, would greatly expand the scope of biomolecular labeling. Here, we report the development of pyridotriazole carbaldehyde (PTAC) reagents that enable efficient, selective, and highly clean labeling of primary alkyl amines in both small molecules and complex biomolecules under mild, biocompatible conditions. PTACs operate via a unique "snap-trapping" mechanism: Imine formation with the carbaldehyde bait triggers a tautomerization-mediated triazole ring swing that irreversibly captures the amine, releasing water as the sole byproduct. Fusion of a pyridine ring into the triazole core destabilizes the N-N bond, priming the system for selective activation by amines while ensuring excellent stability and thiol orthogonality. PTACs are broadly compatible with native functional groups and enable amine labeling with unmatched cleanliness. By combining high reactivity, chemoselectivity, and functional group tolerance, PTACs deliver thiol-level performance in amine-specific bioconjugation, providing both a compelling alternative and a valuable complement to established thiol-based approaches.