[6-CHLORO-3-PYRIDYLMETHYL-H-3]NEONICOTINOIDS AS HIGH-AFFINITY RADIOLIGANDS FOR THE NICOTINIC ACETYLCHOLINE-RECEPTOR - PREPARATION USING (NABH4)-H-3 AND (LIBH4)-H-3

(NaBH4)-H-3 and (LiBH4)-H-3 at 78% and 97% isotopic enrichments, respe ctively, were used in the synthesis of H-3-labeled oro-3-pyridyl)methy l-2-nitromethyleneimidazolidine (CH-IMI) and -3-pyridyl)methyl]-N-''-c yano-N'-methylacetamidine (acetamiprid) (two very potent insecticides) and of 1-(6-chloro-3-pyridyl)methyl-2-iminoimidazolidine (desnitro-IM I) (a metabolite of the commercial insecticide imidacloprid). 6-Chloro nicotinoyl chloride was treated with either (NaBH4)-H-3 in methanol or (LiBH4)-H-3 in tetrahydrofuran and the resulting alcohol transformed to 2-chloro-5-chloromethylpyridine, which was then coupled to N-cyano- N'-methylacetamidine to give [H-3]acetamiprid (45 Ci/mmol). 2-Chloro-5 -chloro[H-3]methylpyridine was also reacted with ethylenediamine and t he product was either refluxed in absolute ethanol with 1,1-bis(methyl thio)-2-nitroethylene to provide [H-3]CH-IMI or reacted in toluene wit h a solution of cyanogen bromide to produce [H-3]desnitro-IMI (each 55 Ci/mmol).