Preparation of [61Cu]Pyruvaldehyde-bis (N4-methylthiosemicarbazone) complex as a possible PET radiopharmaceutical

Copper-61 (T1/2 = 3.33 h) produced via the natZn (p, x)61Cu nuclear reaction using natural zinc target, was separated from the irradiated target material by a two-step method developed in our laboratory and was used for the preparation of [61Cu]-pyruvaldehyde-bis(N 4-methylthiosemicarbazone) ([61Cu]-PTSM) using an in house-made PTSM ligand. An electroplated natural zinc layer on a gold-coated copper backing (zinc and gold layer thicknesses were 80 and 50 μm respectively) was irradiated with 22 MeV protons (22-12 MeV on the target). 61Cu was separated by a two-step chromatography method using a cation and an anion exchange column which gave satisfactory results. After 180 μA irradiation of the target for 3.2 hours, about 6.006 Ci of 61Cu 2+ was obtained with a radiochemical separation yield of more than 95% and a radionuclidic purity of more than 99% (60Cu as impurity). Colorimetric methods showed that traces of chemical impurities in the product were below the accepted limits. The solution of [61Cu]-PTSM was prepared with a radiochemical yield of higher than 80%, radiochemical purity of better than 98% and specific activity of about 246 Ci/mmol.