Radical-Mediated Carboxylation of Alkyl Iodides with [~(11)C]Carbon Monoxide in Solvent Mixtures

摘要

[carboxyl-~(11)C]Carboxylic acids were prepared from alkyl iodides via photoinitiated radical reactions using 10~(-8) mol of [~(11)C]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-rnin reactions.The conversion of [~(11)C]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 tetrabut-ylammonium 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-~(11)C]carboxylic acids;traditional methods,in contrast,would require several steps.For example,using the devised reaction conditions.3.19 GBq of purified |l-~(11)C]l,10-decanedicarboxylic acid (specific radioactivity 188 GB_q/mumol) was obtained within 35 min of the end of 10 muAh bombardment.(1-~(13)C)4-Phenylbutyric acid was synthesized using (~(13)C)-carbon monoxide for identifying the labeling position with ~1H and ~(13)C NMR.