Used in bioorthogonal chemistry for rapid and selective labeling of biomolecules in live cells. Its tetrazine group undergoes fast inverse electron-demand Diels-Alder reactions with strained alkenes or alkynes, enabling efficient conjugation without interfering with biological processes. The PEG4 spacer enhances water solubility and reduces non-specific binding, improving performance in complex biological environments. Commonly employed in protein labeling, antibody-drug conjugate development, and live-cell imaging. The terminal amine group allows further functionalization with dyes, biotin, or other probes, making it valuable in drug discovery, diagnostics, and chemical biology research.