Synthesis of 1-(2-ethoxyethyl)-2-(4-methyl-1-homopiperazinyl)-[2-14C]benzimidazole difumarate([14C]KB-2413)

1-(2-Ethoxyethyl)-2-(4-methyl-1-homopiperazinyl)-[2-14C]-benzimidazole difumarate ([14C]KB-2413), a new antihistaminic agent, was prepared from labelled urea. The synthetic intermediate, 1-(2-ethoxyethyl)benzimidazol-one, obtained in good yield by the condensation of N-(2-ethoxy-ethyl)-o-phenylenediamine with [14C]urea, was chlorinated with phosphorus oxychloride and followed by the reaction with N-methylhomopiperazine to give the base of [14C]KB-2413. It was then converted to the difumarate, which was obtained in an overall radiochemical yield of 74 % starting from [14C]urea. The specific activity was 54.4 mCi/mmol and its radiochemical purity was 98.0 % in reverse isotope dilution analysis. (author)