Caffeine, ephedrine and methylephedrine were labeled with carbon-11 by the action of methyliodide-11C on theophylline, norephedrine and ephedrine, respectively. Caffeine-11C was prepared in 44 min with a radiochemical yield of 40%, ephedrine-11C in 45 min with a 11% radiochemical yield and methylephedrine-11C in 36 min with a 43% radiochemical yield. When injected in mice intravenously, these products show a high uptake in the liver, the kidney and the blood for caffeine-11C and in the liver and the kidney for ephedrine-11C and methylephedrine-11C. The brain uptake for these products was found to be 2.4 to 3.9% of the injected dose per gram at 5 min after injection. These studies in mice have demonstrated that these products are potentially useful agents for the dynamic studies of the brain.
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