Radical-mediated carboxylation of alkyl iodides with [11C]carbon monoxide in solvent mixtures

[carboxyl-C-11]Carboxylic acids were prepared from alkyl iodides via photoinitiated radical reactions using 10(-8) mol of [C-11] carbon monoxide in binary and ternary homogeneous solvent mixtures. Short-(isobutyric), medium-, and long-chain saturated fatty acids (heptadecanoic) were labeled with isolated decay-corrected radiochemical yields ranging from 55% to 70% in 5-7-min reactions. The conversion of [C-11]carbon monoxide to products reached 80-90%. To obtain good yields in the reactions performed in water-acetonitrile and water-THF mixtures, the addition of tetrabutylammonium hydroxide or potassium hydroxide was essential. The carboxylation was efficient for primary and secondary alkyl iodides. The carboxylation of tertiary iodides was feasible for 1-iodoadamantane but not for tert-butyl iodide. The dependence of the radiochemical yields on reaction time, photoirradiation conditions, and organic and inorganic additives was studied. The method provides a one-step route to [carboxyl-C-11]carboxylic acids; traditional methods, in contrast, would require several steps. For example, using the devised reaction conditions, 3.19 GBq of purified [1-C-11]1,10-decanedicarboxylic acid (specific radioactivity 188 GBq/mu mol) was obtained within 35 min of the end of 10 mu Ah bombardment. (1-C-13)4-Phenylbutyric acid was synthesized using(C-13)- carbon monoxide for identifying the labeling position with H-1 and 13C NMR.