-(P-TRIMETHYLSILYLPHENYL)TROPANE-2-BETA-CARBOXYLIC ACID METHYL-ESTER - A NEW PRECURSOR FOR THE PREPARATION OF [I-123] RTI-55

Here we report the synthesis of 3 beta-(p-trimethylsilylphenyl)tropane -2 beta-carboxylic acid methyl ester, a new, easily prepared precursor for the synthesis of radioiodinated versions of RTI-55. In contrast t o the 3 beta-(p-trimethylstannylated) precursor for radioiodination, t he aryl silane is prepared directly by the 1,4 addition of p-trimethyl silylphenylmagnesium iodide to anhydroecgonine methyl ester in 49% yie ld (Scheme 1). Radioiododesilylation proceeded smoothly (approx. 85% r adioincorporation after 15 min at room temperature) using 1 mu g of th e novel precursor in trifluoroacetic acid and chloramine-T as oxidant. Isolated radiochemical yields for I-125 and I-123 radiolabelings were 72 and 48%, respectively, with a calculated specific activity for [I- 123]RTI-55 of >2000 mCi/mu mol.