OH-CH2CH2-Tetrazine-CH2-PO(OEt)2

 1,2,4,5 - four oxazine with large tensile ring olefins, such as the small size of the ring propylene and trans cyclooctene (TCO) for biological orthogonal with the fastest reaction rate without catalyst, has been successfully applied to the antibody tag and a variety of applications such as protein modification.