COPPER-CATALYZED RADIOIODINATION OF 3-IODOTYROSINE AND 4-IODOPHENYL ALANINE

The factors affecting the yield of the copper catalyzed labelling of 3 -iodotyrosine and 4-iodophenyl alanine such as pH of the medium, catal yst and substrate concentrations and solvent effects are described. Th e reaction is assumed to take place via an intermediate organo-copper complex which favours the exchange between radioiodine and the inactiv e iodine in the iodocompound. The reducing agents ascorbic acid, stann ous chloride or sodium metabisulphite are added to the cuprous chlorid e catalyzed reaction to prevent the oxidation of Cu (I) to Cu (II) in order to decrease side products formation and improve the labelling yi eld. Kinetics indicated a second order reaction with an activation ene rgy of 9.6 Kcal/mole for 3-iodotyrosine and 12.2 Kcal/mole for 4-iodop henyl alanine. The stronger 4-iodophenyl C-l bond favours para-iodinat ion in the preparation of radioiodinated monoclonal antibodies.