The radiosynthesis of imidazole ring labeled [14c]metiamide, [1k]cimetidine and ["k]impromidine are described involving the reaction of the key common intexmediate 2-dimethyldithiocyanoiminocarbonate/methylamine and the novel dihydroknidazdiazepine 0, res ectively. The ring labeled precursor @ was prepared in five steps from potassium mCi/mmol. [ 1 B Clcyanide in an overall radiochemical yield of 63%, and having a specific activity of 9.3 14C]imidazol-5-yl)-methyl]thio]ethanamine. histamine H2-receptor antagonist, histamine H2receptor agonist, [14C]imidazole ring labeled.

Two complementary radiosynthetic routes to the potent PNMT inhibitor 7,8-dichloro-1 ,2,3,4-tetrahydroisoquinol i ne-l -l 4C(1) from 2,3-dichl orobenzal dehydeformyl-C(Q) are described. In the Pomeranz-Fritsch sequence isoquinoline 6 was prepared from Schiff's base 2.furnished 1 in 28% radiochemical yield from 4. sequence, 4 was converted via amino alcohol 7 to chloro amine 6. the latter with aluminum chloride/ammonium chloride (fusion, 190 "C) yielded labeled Jin 31% radiochemical yield from 2. 14 -Catalytic hydrogenation of fi (H2/Pt02) In the aluminum chloride fusion Treatment of m. i s 7.8-dichloro-l,2,3,4-tetrahydroisoquinol ine hydrochloride (1. S K f F 64139-A).(4) studies, we explored two complementary synthetic approaches both of which posi-One of the most potent of these agents. J I J In order to prepare carbon-14 tagged material for metabolite tioncd the carbon label in the 1-posltion of the tetrahydroisoquinoline. (5) The cmcn intermediate for the herein described methods was 2,3-dichlorobenzal-dehy~!e-formyl-'~C, readfly prepared from K CN. 14 RESULTSThe classical approach i s illustrated in SCHEHE 1. This method, which utilized the Pmeranz-Fritsch reaction(6a) for cyclization, produced 1 in 26-28 radiochemical yield from aldehyde 2. Commercial 2,3-dichloroiodobenzene SCHEME 1 CI CI DIBAL/

The H -antagonists, metiamide and cimetidine were labelled 2 with deuterium and tritium in the 2-position of the imidazole ring by the uncatalyzed exchange reaction with deuterium and tritium oxide at 100°C. The sulfur-35 labelled metiamide was prepared by an exchange reaction with elemental sulfur-35 in refluxing pyridine and by the reaction of 2[(4-methyl-S-imidazolyl) methylthio]ethylamine with m e t h y l i s~t h i o c y a n a t e -~~S in refluxing ethanol.

Phenoqbenzwnine ethylmine hydrochloride] has been labelled with Nitrogen-15 by a direct synthesis from "N-oniwn chloride. enrichment was 92.8%.The isotopic