Synthesis and body distribution of several iodine-131 labeled centrally acting drugs.

1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane (3B), 4-iodo-2,5-dimethoxyphenylethylamine (3A), and 1-(4-iodo-2,5, dimethoxyhenyl)-2-aminobutane (3C) have been synthesized with 131I. Labeled iodine monochloride reacts with the appropriately substituted phthalimide at the aromatic 4 position, and the phthalic acid group is removed with hydrazine. Body distribution was measured in rats; the most prominent difference between the three compounds was a much greater concentration in the lung with 3b than with 3a or 3c. gamma-Ray scintigraphs of 3a-c in rats and of 3b in a dog indicate an uptake by the brain similar to that of the bromine analogue of 3b (DOB) in humans. [82Br]-DOB has been suggested as a potential brain scanning agent for nuclear medicine; 3b would have the advantage over DOB of providing the superior gamma-ray imaging properties of 131I or 123I.