Four 1251-labelled nicotine analogs were synthesized: 3-(methylpropylaminomethyl)-, 3-(diethylaminomethyl)-, 3-(isopropylaminomethy1)-, and 3-(diisopropylaminomethy1)-5-[ 1251]-iodopyridines. 5-Bromonicotinic acid was acylated with thionyl chloride and then reacted with the appropriate primary and secondary amines to give the corresponding amides which were reduced with diborane to the desirable amines. Radioiodination was done by halogen exchange. Biodistribution studies in rats, showed that all four labelled compounds were rapidly taken up by the brain and the adrenal gland. washout of the compounds from these or ans. The most promising of these compounds, 3-( diisopropylaminomethyl)-.5-[f~~I]-iodopyridine, showed a brain-toblood ratio of 6.0:l and an adrenal-to-blood ratio of 35.9:l at 2 minutes post administration. compounds depends on both protein binding and lipophilicity, whereas adrenal uptake depends only on lipophilicity. Keywords:This was followed by rapidIn vitro correlation studies showed that brain uptake of these Imaging, [125 I]-Nicotine analogs, Brain, Adrenal medulla.

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5-Bromonicotine, synthesized from nicotinic acid, was autoclaved with NalZ5I in the presence of copper sulfate and glacial acetic acid toThe radiochemical yield was 25.3%. The specific activity of the product was approximately 61 mCi/mmole. Biodistribution studies of 5-[1251]iodonicotine, performed in rats, showed that the labelled compound accummulated rapidly in the brain and the adrenal gland. The highest uptake of radioactivity in these organs occurred at 5 minutes after administration. The brain-to-blood and the adrenal-to-blood ratios at this time interval were 2.6:l and 3.3:l respectively.

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