Radioiodination and biodistribution of analogs of a calichemicin constituent.

Analogs of the aromatic constituent of calichemicins were labeled with 131I by exchange reactions. Radiochemical yield for methyl-4-hydroxy-5-iodo-2,3-dimethoxy-6-methylbenzoate was approx. 90%. For methyl-4-benzyloxy-2-hydroxy-3-iodo-6-methylbenzoate the yield was about 30%. Biodistribution studies were carried out in mice following intravenous administration of tracer doses. Average brain uptake of the first compound at 3 min was 0.28%, and that of the second 1.96%. Tissue distribution of the two compounds elsewhere was similar in nature. High uptake was observed initially in the liver; this reduced with time, while radioactivity in the GI-tract increased. The benzylated compound appeared potentially useful for designing a brain imaging radiopharmaceutical.