Marking precursor with squaric acid coupling

A labeling precursor for a radiopharmaceutical of the structure (A), (B), (E) or (F) with

• (A)=Ch-L1-QS-TV1,
• (B)=Ch-L1-QS-S-TV1,
• (E)=TV2-QS-L2-Ch-L1-QS-TV1,
• (F)=TV2-S3-QS-L2-Ch-Li-QS-S-TV1,
• comprising
• a chelator Ch, selected from the group consisting of DOTA (dodeca-1,4,7,10-tetraamine-tetraacetate), DOTAGA (2-(1,4,7,10-tetraazacyclododecane-4,7,10)-pentanedioic acid),
• one or two linkers L1 and L2, which are selected independently of one another from the group consisting of —(CH2)m, —(CH2CH2O)m— and —(CH2) mNH— with m=1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, residues of amide, carboxamide, alkyl, triazole, thiourea and ethylene;
• one or more squaric acid residues QS
• optionally one or two spacers S1 and S3 respectively, which are selected independently of one another from the group consisting of —(CH2)n—,
• —(CH2)—CH(COOH)—NH—, —(CH2CH2O)n and —(CH2)nNH— with n=1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, residues of amide, carboxamide, alkyl, triazole, thiourea and ethylene;
• and
• one or two targeting vectors, TV1 and TV2 respectively, which are selected independently of one another from the group comprising residues of compounds of the structures [5] and [6] with
• where the dashed bond of the targeting vectors [5] and [6] denotes a coupling site with a leaving group.