Labelling of some amino acids with radioiodine

Some radioiodine labelled compounds which have application in nuclear medicine have been prepared. Two common techniques were employed. A comparative study on the radioiodination of the amino acids, L - tyrosine, L - a - methyl tyrosine and L-tyrosine methyl ester has been carried out by the electrophilic radioiodination technique. The blood flow reagent, antipyrine, also has been prepared by this technique using chloramine - T, iodogen and H2 O2 as oxidizing agents to generate electrophilic iodine. Radio chromatograms revealed side product impurities at long reaction times and high oxidizing agent concentrations. Comparison between the different oxidizing agents was done. Optimization of the radioiodination conditions, such as Ph of the medium, reaction time, oxidizing agent and substrate concentrations and carrier KI concentration was performed resulting in high radiochemical yields of 97% L - 3 -(131) iodotyrosine, 95% L -3-(131) iodo-a-methyl tyrosine, 88% L-3-(131) iodotyrosine methyl ester and 96% 4-(131) iodoantipyrine within short reaction times at room temperature when chloramine - T was used as oxidizing agent. Purification by high pressure liquid chromatography resulted in high radiochemically pure products suitable for medical application. Radioiodinated 3- iodotyrosine and 4- iodophenyl alanine have been prepared by the isotopic exchange technique using cuprous chloride as catalyst for the exchange reaction. The effect of solvents and the different parameters affecting the labelling yield were investigated to optimize the conditions for labelling of these compounds. Kinetic study indicated a second order reaction with an activation energy of 9.6 and 12.20 Kcal/mole for 3- iodotyrosine and 4-iodophenyl alanine respectively. Reducing agents were added to the Cu CI catalyzed reactions to improve the yield and decrease side products formation. Applying the results obtained to the radioiodination of the phenyl fatty acid 15(p-iodophenyl) pentadecanoic acid, used for myocardial imaging, a labelling yield of 80% was obtained. 6 tabs., 48 figs., 135 refs