Fig. 1. Chemical structures of Tyr³-octreotide (TOC), tetrazines 1 and 2, TCO-linkers attached to the TOC peptide (3, 4) and the IEDDA conjugates attached to the Tyr³-octreotide (TOC) derivatives (5, 6 and 7) after conjugation with 1 and 2 presented as the aromatized (oxidized) cycloaddition products. Structures 1 and 3–6 have been reported by us previously.¹⁹.