The present invention relates to compositions and methods for preparing radiopharmaceutical compounds in high chemical-purity and isotopic-purity. The present invention provides polymer-bound precursors to radiopharmaceutical compounds that can be converted to radiopharmaceutical compounds in one step. In a preferred embodiment, a radiopharmaceutical precursor is bound to a polymeric support via a prosthetic group comprising an alkenyl-tin bond. The radiopharmaceutical precursor is converted to a radiopharmaceutical compound in one step involving cleavage of the alkenyl-tin bond and incorporation of a radioisotope to form the radiopharmaceutical compound. Importantly, the polymeric support containing the toxic tin by-product can be easily removed from the radiopharmaceutical compound by filtration. The present invention can be used to install a large number of different radioisotopes. In a preferred embodiment, the radioisotope is 211At, 123I or 131I.