Iodination and radiolabeling of α-allocryptopine with iodine-125

A procedure for labeling of α-allocryptopine with 125I is reported in this article. α-allocryptopine is first iodinated with largely excessive iodine monochloride, and then radiolabeled by isotopic exchange with Na125I in a dichloromethane–water two-phase system. The radiochemical purity and yield of the labeled product are typically as high as 94% and 72%, respectively. Further chromatographic purification gives a highly pure product (radiochemical purity >99%). The distribution of 125I-labeled α-allocryptopine in mice at 2 h after injection shows that the uptake of radioiodine in thyroid is negligibly low.