A convenient solution-phase method for the preparation of meta-iodobenzylguanidine in high effective specific activity

INTRODUCTION: There is a need for new methods of producing receptor-targeted molecular radioimaging and radiotherapy agents in high effective specific activity. This is particularly true for targets that are expressed in relatively low concentrations. METHODS: A highly fluorinated (fluorous) tin precursor of meta-iodobenzylguanidine (MIBG) was prepared, such that upon labeling, the desired product was formed with concomitant release of the fluorous group. The desired product was then readily separated from the starting material and fluorous by-products by chemoselective filtration using a fluorous solid-phase extraction cartridge. RESULTS: High purity [(125)I]- and [(123)I]MIBG were produced in 81+/-3% and 80% radiochemical yield respectively in less than 20 min without high-performance liquid chromatography (HPLC) purification. The purified product contained less than 1 ppm tin as determined by inductively coupled plasma-mass spectrometry (ICP-MS). CONCLUSIONS: A convenient, solution-phase method to produce radioiodinated MIBG in high effective specific activity without employing preparative HPLC was developed. Using the reported approach, a kit for the production of (123)I- and (125)I-MIBG is feasible and is currently being developed.