The synthesis of a tritiated analogue of CP-93,318 is as follows: Treatment of the phenacyl bromide (V) with N-bromosuccinimide in methanol affords selectively bromo derivative (VI). Subsequent condensation of (VI) and thioamide (IV) (Scheme 1) provides tritiation precursor (VII). Exposure of (VII) to tritium in the presence of palladium on carbon (triethylamine/tetrahydrofuran) followed by purification using high-performance liquid chromatography provides [3H]-CP-93,318 (specific activity: 16.2 Ci/mmol, radiochemical purity greater than or equal to 98%).
The synthesis of CP-93,318 is summarized: Treatment of 4-methyl-5-imidazolemethanol (I) with thionyl chloride affords chloromethylimidazole (II). Exposure of (II) to potassium cyanide provides nitrile (III), and subsequent reaction of (III) with diethyldithiophosphate in the presence of hydrochloric acid gives thioamide (IV), as its hydrochloride salt. Condensation of this hygroscopic salt with 2-bromo-2'-methoxyacetophenone (V) provides thiazole CP-93,318. Analogues of CP-93,318, modified at the methoxyphenyl moiety, were prepared similarly by condensation of convergent intermediate (IV) and the appropriate alpha-haloketone.