After the target mass was detected by LC-MS, the solvents were evaporated, and the crude product was purified by preparative HPLC on a C18 column (10-100% H2O/ACN with 0.1% formic acid over 30 min). Neutralisation of the collected product fractions with 1 M NaOH and subsequent evaporation of the solvents gave K222-PSMA as a white powder (3.5 mg, 2.5 µmol, 5% from K222-NH2). In a typical experiment, [ 201 Tl]TlCl (~1 MBq, 50 μL) was added to an Eppendorf vial together with 50 µL of the organic chelator (0.5 -2 mM). Na2CO3 (25 µL of 1 M) and water (75 µL) were added to the vial and the reaction was shaken at room temperature for 15 min.