Figure 2.

Synthesis of PSMA PLT-TM. The (tBu protected) PSMA-binding motif and a PEG linker were coupled to either side of the Fe-protected HBED-CC double TFP ester (1) to give (2). The synthesis of the C-terminally modified E5B9 peptide (SKPLPEVTDEY-Propargylglycine) (3) was performed manually on a 2CT-Resin under application of standard Fmoc-protocols and cleaved from it with a mixture of TFA/TIPS/H₂O (95/2.5/2.5, v/v/v). Then, (2) and (3) reacted via the Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC), the final product was isolated and the tBu groups were deprotected with TFA. Then, Fe was removed from the complex by applying 1 M HCl on a C-18 SEP-PAK cartridge. The final product was eluted from the cartridge with a mixture of CH₃CN/water (7/3, v/v, 20 mL).